UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Sputtering and characterizations of titanium oxide films Burbidge, Douglas S. 1985

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1986_A6_7 B85.pdf [ 2.6MB ]
Metadata
JSON: 831-1.0085283.json
JSON-LD: 831-1.0085283-ld.json
RDF/XML (Pretty): 831-1.0085283-rdf.xml
RDF/JSON: 831-1.0085283-rdf.json
Turtle: 831-1.0085283-turtle.txt
N-Triples: 831-1.0085283-rdf-ntriples.txt
Original Record: 831-1.0085283-source.json
Full Text
831-1.0085283-fulltext.txt
Citation
831-1.0085283.ris

Full Text

SPUTTERING AND CHARACTERIZATION OF TITANIUM OXIDE FILMS by DOUGLAS S. BURBIDGE B . S c , McMaster U n i v e r s i t y , 1983 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE ' i n / THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF PHYSICS We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA NOVEMBER 1985 © Douglas S. B u r b i d g e , 1985 7 8 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the re q u i r e m e n t s f o r an advanced degree a t the The U n i v e r s i t y of B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g of t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head of my Department or by h i s or her r e p r e s e n t a t i v e s . I t i s under s t o o d t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . DEPARTMENT OF PHYSICS The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date: NOVEMBER 1985 A b s t r a c t R e a c t i v e magnetron s p u t t e r i n g of t i t a n i u m o x i d e s has been i n v e s t i g a t e d w i t h emphasis on the t e c h n i q u e of u s i n g a r e a c t i v e gas b a f f l e t o enhance f i l m o x i d a t i o n . T h i s method c o n s i s t s of p l a c i n g a p a r t i a l b a r r i e r between the s p u t t e r i n g t a r g e t and the s u b s t r a t e . For the f i r s t time the dependence of the e f f e c t i v e n e s s of t h i s t e c h n i q u e on the m a t e r i a l b e i n g s p u t t e r e d has been c o n s i d e r e d and the e f f e c t s of v a r i o u s b a f f l e s were compared f o r the same m a t e r i a l (TiO ,0<x<2). D e c r e a s i n g the t r a n s p a r e n c y of the b a f f l e t o s p u t t e r e d f l u x r e s u l t e d i n an i n c r e a s e i n the maximum a t t a i n a b l e oxygen p a r t i a l p r e s s u r e f o r the m e t a l l i c t a r g e t c o n d i t i o n . However, e l e c t r i c a l r e s i s t i v i t y d a t a f o r the s p u t t e r e d f i l m s r e v e a l e d t h a t f i l m o x i d a t i o n was not c o r r e s p o n d i n g l y enhanced. The s t r u c t u r a l , e l e c t r i c a l and o p t i c a l p r o p e r t i e s of the s p u t t e r e d t i t a n i u m o x i d e f i l m s were measured.The f i l m s were found t o be amorphous w i t h o u t d i s c e r n i b l e m i c r o s t r u c t u r e . The v i s i b l e a b s o r p t i o n band i n s u b s t o i c h i o m e t r i c f i l m s was found t o have i t s maximum a t 880 nm (1.41 eV) and the UV a b s o r p t i o n edge was a t 335 nm (3.70 e V ) . Based on r e p o r t e d p h o t o l u m i n e s c e n c e i n p o l y c r y s t a l l i n e f i l m s of T i 0 2 [39] an attempt was made t o observe p h o t o l u m i n e s c e n c e i n amorphous f i l m s w i t h n e g a t i v e r e s u l t s . i i T a b l e of C o n t e n t s A b s t r a c t i i Table of C o n t e n t s i i i L i s t of F i g u r e s i.v Acknowledgements v i I . INTRODUCTION 1 A. S p u t t e r i n g 1 B. Tar g e t O x i d a t i o n 2 C. The R e a c t i v e Gas B a f f l e 3 D. T h e s i s O b j e c t i v e s 4 E. C h o i c e of T i t a n i u m Oxide 5 I I . EXPERIMENTAL APPARATUS 6 A. The S p u t t e r i n g System 6 B. The R e a c t i v e Gas B a f f l e 10 C. D e p o s i t i o n Procedure 12 I I I . RESULTS AND DISCUSSION 15 A. S p u t t e r i n g C h a r a c t e r i s t i c s 15 B. E f f e c t i v e n e s s of the R e a c t i v e Gas B a f f l e 23 C. F i l m C h a r a c t e r i z a t i o n 33 1 . S t r u c t u r e 33 2. O p t i c a l P r o p e r t i e s 35 3. E l e c t r i c a l R e s i s t i v i t y 41 4. Ph o t o l u m i n e s c e n c e 43 IV. CONCLUSIONS 53 V. APPENDIX: C a l c u l a t i o n of B a f f l e A p e r t u r e 55 REFERENCES 64 i i i L i s t of F i g u r e s F i g u r e Page 2.1 Schematic of the s p u t t e r i n g chamber 7 2.2 E l e c t r o n t r a j e c t o r y a t the s p u t t e r i n g cathode 11 2.3 Mounting geometry of the r e a c t i v e gas b a f f l e 11 2.4 R e a c t i v e gas b a f f l e h o l e p a t t e r n s 13 2.5 A n g u l a r a c c e p t a n c e of the b a f f l e 14 3.1 V a r i a t i o n of s p u t t e r i n g parameters w i t h 0 2 f l o w r a t e . 1 6 3.2 C u r r e n t v s . p r e s s u r e a t c o n s t a n t d i s c h a r g e power 19 3.3 I-V c h a r a c t e r i s t i c s f o r the o x i d e - t o - m e t a l t a r g e t t r a n s i t i o n 22 3.4 C u r r e n t v s . p r e s s u r e a t v a r i o u s c o n s t a n t f l o w r a t e s . . 2 4 3.5 C a l c u l a t e d b a f f l e a p e r t u r e as a f u n c t i o n of b a f f l e h o l e r a d i u s 25 3.6 E f f e c t of b a f f l e a p e r t u r e on 0 2 p a r t i a l p r e s s u r e 27 3.7 E f f e c t of b a f f l e a p e r t u r e on d e p o s i t i o n r a t e 30 3.8 E f f e c t of b a f f l e a p e r t u r e on f i l m r e s i s t i v i t y 32 3.9 X-ray d i f f r a c t o g r a m of a p o l y c r y s t a l l i n e T i 0 2 f i l m . . . 3 4 3.10 SEM p h o t o m i c r o g r a p h of a t y p i c a l f i l m 36 3.11 R e f l e c t a n c e and t r a n s m i t t a n c e f o r s e v e r a l T i O x f i l m s . 3 8 3.12 O p t i c a l d e n s i t y of s e v e r a l TiO f i l m s 40 3.13 Schematic of p h o t o l u m i n e s c e n c e a p p a r a t u s 45 3.14 Schematic of p h o t o l u m i n e s c e n c e c o n t r o l e l e c t r o n i c s . . . 46 3.15 P r e v i o u s l y o b s e r v e d t h i n f i l m p h o t o l u m i n e s c e n c e i n T i 0 2 48 i v 3.16 E b e r t g r a t i n g mount c o n f i g u r a t i o n 49 3.17 C a l c u l a t e d g r a t i n g e f f i c i e n c y 50 3.18 D e m o n s t r a t i o n of lu m i n e s c e n c e i n C o r n i n g 7059 g l a s s a t 535 nm 52 5.1 D i s t r i b u t i o n of t a r g e t e t c h d e p t h . . . . 56 5.2 Geometry of b a f f l e a p e r t u r e c a l c u l a t i o n . . . . . 58 5.3 I l l u s t r a t i o n of the dependence of f l u x d e n s i t y on a n g l e of i n c i d e n c e 59 5.4 I l l u s t r a t i o n of the dependence of apparent a r e a of b a f f l e h o l e s on a n g l e of i n c i d e n c e 61 5.5 Dependence of s p u t t e r e d f l u x d i s t r i b u t i o n on w i d t h of d i s c h a r g e r i n g and a n g u l a r a c c e p t a n c e 63 v Acknowledgements I would l i k e t o thank Dr. Robert Parsons f o r s u g g e s t i n g t h i s p r o j e c t and f o r h i s e x p e r t guidance b o t h i n the e x p e r i m e n t a l work and i n w r i t i n g the t h e s i s . I am a l s o i n d e b t e d t o Dr. Mike B r e t t , Normand F o r t i e r and Dr. John A f f i n i t o f o r many i l l u m i n a t i n g d i s c u s s i o n s on the s u b j e c t of s p u t t e r i n g and t h i n f i l m a n a l y s i s . An i n v a l u a b l e c o n t r i b u t i o n t o my r e s e a r c h and my s a n i t y was made by B r i a n T. S u l l i v a n , whose p a t i e n t a s s i s t a n c e w i t h the p h o t o l u m i n e s c e n c e a p p a r a t u s and the computing was g r e a t l y a p p r e c i a t e d . Thanks a l s o t o Joe F o r d f o r h i s t h o u g h t f u l c r i t i c i s m s of the t h e s i s , and t o Dr. J i m C a r o l a n f o r h i s c a r e f u l r e a d i n g of the f i n a l m a n u s c r i p t . I a p p r e c i a t i v e l y acknowledge the f i n a n c i a l s u p p o r t of the N a t i o n a l S c i e n c e s and E n g i n e e r i n g R esearch C o u n c i l of Canada. L a s t but not l e a s t I would l i k e t o thank my f a m i l y f o r t h e i r c o n t i n u e d e n t h u s i a s t i c s u p p o r t and u n d e r s t a n d i n g . v i I . INTRODUCTION A. SPUTTERING " S p u t t e r i n g " i s a v e r y u s e f u l t e c h n i q u e f o r the f a b r i c a t i o n of t h i n s o l i d f i l m s . In t h i s p r o c e s s a t a r g e t m a t e r i a l i s bombarded by e n e r g e t i c i o n s , which causes the e j e c t i o n of t a r g e t atoms from the t a r g e t s u r f a c e and subsequent t h i n f i l m d e p o s i t i o n on a s u b s t r a t e . S p u t t e r i n g has advantages i n many a r e a s over o t h e r d e p o s i t i o n t e c h n o l o g i e s . The l a r g e s u r f a c e a r e a of the source ( i . e . the t a r g e t ) a l l o w s f i l m s t o be produced which have u n i f o r m t h i c k n e s s over a l a r g e a r e a . The l a r g e k i n e t i c energy of the s p u t t e r e d atoms r e s u l t s i n good a d h e s i o n of the f i l m t o the s u b s t r a t e . Low o p e r a t i n g t e m p e r a t u r e s e n a b l e d e p o s i t i o n onto p l a s t i c s u b s t r a t e s and a l s o , i n some c a s e s , the p r o d u c t i o n of amorphous f i l m s w i t h o u t s u b s t r a t e c o o l i n g a p p a r a t u s . In a d d i t i o n s p u t t e r i n g may be used t o produce multicomponent f i l m s of v i r t u a l l y any atomic r a t i o . These f e a t u r e s have made s p u t t e r i n g an i m p o r t a n t t o o l not o n l y f o r i n d u s t r i a l t h i n f i l m a p p l i c a t i o n s [1] but a l s o f o r p r o d u c t i o n of un u s u a l m a t e r i a l s f o r b a s i c r e s e a r c h [ 2 , 3 ] . D e s p i t e the g e n e r a l a p p l i c a b i l i t y of s p u t t e r i n g t o f a b r i c a t i o n of multicomponent f i l m s i t i s not always s t r a i g h t f o r w a r d t o produce even b i n a r y f i l m s over a complete range of s t o i c h i o m e t r i e s . A g i v e n compound may be d e p o s i t e d by s p u t t e r i n g from a t a r g e t of the same c o m p o s i t i o n but u n l e s s the t a r g e t i s m e t a l l i c the d e p o s i t i o n r a t e i s u s u a l l y 1 t 2 low. W i t h the use of " r e a c t i v e s p u t t e r i n g " which i n v o l v e s the a d m i s s i o n of a r e a c t i v e gas t o the s p u t t e r i n g chamber one can d e p o s i t n o n - m e t a l l i c compounds such as o x i d e s u s i n g a m e tal t a r g e t . Furthermore a range of s t o i c h i o m e t r i e s can be o b t a i n e d from the same t a r g e t . For example by s p u t t e r i n g t i t a n i u m i n argon and oxygen one can produce TiO where 0<x<2 by a l l o w i n g s u f f i c i e n t oxygen i n t o the chamber t o o b t a i n the n e c e s s a r y r e l a t i v e a r r i v a l r a t e s of m e t a l and oxygen a t the s u b s t r a t e [ 4 , 5 ] . B. TARGET OXIDATION An u n a v o i d a b l e consequence of making oxygen a v a i l a b l e t o the growing f i l m i s t h a t i t i s a l s o made a v a i l a b l e t o the s p u t t e r i n g t a r g e t . As the oxygen p a r t i a l p r e s s u r e i s i n c r e a s e d the b e h a v i o u r of the s p u t t e r i n g system i s as f o l l o w s . At low oxygen p a r t i a l p r e s s u r e s the impingement r a t e of oxygen a t the t a r g e t i s s u f f i c i e n t l y low t h a t any oxygen which adsorbs on the t a r g e t s u r f a c e i s i m m e d i a t e l y r e s p u t t e r e d and t h e r e f o r e the t a r g e t s u r f a c e remains m e t a l l i c . At the same time s p u t t e r e d m e t a l atoms getter-pump oxygen from the chamber atmosphere so t h a t as the f l o w of oxygen i n t o the chamber i s i n c r e a s e d the oxygen p a r t i a l p r e s s u r e remains low. However, as the f l o w r a t e c o n t i n u e s t o i n c r e a s e a p o i n t i s reached a t which the. i o n s bombarding the t a r g e t can no l o n g e r c o m p l e t e l y remove the oxygen which d e p o s i t s t h e r e and a permanent o x i d e l a y e r c o v e r s the t a r g e t s u r f a c e . W i t h o x i d e exposed t o the d i s c h a r g e , g e t t e r - p u m p i n g 3 i s e s s e n t i a l l y stopped and c o n s e q u e n t l y the oxygen p a r t i a l p r e s s u r e i n c r e a s e s t o the s t e a d y - s t a t e v a l u e d e t e r m i n e d by the gas f l o w r a t e and the pumping speed of the e x t e r n a l pumping system. F i l m c o m p o s i t i o n i s d e t e r m i n e d by the r e l a t i v e a r r i v a l r a t e s of m e tal and oxygen atoms a t the s u b s t r a t e . Because of the i n s t a b i l i t y of the o p e r a t i n g c o n d i t i o n s i n the t r a n s i t i o n r e g i o n between a m e t a l l i c and o x i d i z e d t a r g e t , the oxygen p a r t i a l p r e s s u r e i s d i s c o n t i n u o u s as the flow r a t e i s i n c r e a s e d . T h i s e f f e c t c r e a t e s some d i f f i c u l t y i n p r o d u c i n g s u b s t o i c h i o m e t r i c f i l m s of h i g h oxygen c o n t e n t . A l t h o u g h s t o i c h i o m e t r i c f i l m s can be o b t a i n e d by s p u t t e r i n g from an o x i d i z e d t a r g e t the low s p u t t e r y i e l d of an o x i d i z e d m e t a l s u r f a c e r e l a t i v e t o a bare m e t a l s u r f a c e g i v e s low d e p o s i t i o n r a t e s f o r t h i s type of s p u t t e r i n g . C. THE REACTIVE GAS BAFFLE One s o l u t i o n t o the problem of t a r g e t o x i d a t i o n i s the r e a c t i v e gas b a f f l e . T h i s i s s i m p l y a m e t a l box s u r r o u n d i n g the t a r g e t , w i t h a p e r f o r a t e d p l a t e between the t a r g e t and the s u b s t r a t e . By t r a p p i n g some of the m e t a l f l u x the b a f f l e 1) d e c r e a s e s the r a t i o of m e tal t o oxygen a r r i v i n g a t the s u b s t r a t e and t h e r e f o r e promotes more complete o x i d a t i o n of the m e t a l d e p o s i t , and 2) p r o v i d e s a g e t t e r s u r f a c e c l o s e t o the t a r g e t which reduces the oxygen p a r t i a l p r e s s u r e i n t h a t v i c i n i t y and c o n s e q u e n t l y i n h i b i t s t a r g e t c o v e r a g e . The t o t a l e f f e c t of the b a f f l e i s t o i n c r e a s e the maximum 4 a t t a i n a b l e oxygen p a r t i a l p r e s s u r e i n the v i c i n i t y of the s u b s t r a t e w h i l e m a i n t a i n i n g a m e t a l l i c t a r g e t s u r f a c e [7]., The r e a c t i v e gas b a f f l e was f i r s t used by S c h i l l e r e t a l . [5] f o r s p u t t e r i n g t i t a n i u m and t a n t a l u m o x i d e s . I t has a l s o been used by Maniv e t a l . [6] f o r C d 2 S n 0 4 , and r e c e n t l y i n t h i s l a b o r a t o r y by B r e t t e t a l . [7] f o r . s p u t t e r i n g ZnO. These a u t h o r s r e p o r t e d r e s u l t s f o r t h e i r p a r t i c u l a r systems w i t h and w i t h o u t the b a f f l e . So f a r no study has been made to compare d i f f e r e n t b a f f l e s on the same system. In t h i s work i t was p o s s i b l e t o compare the r e s u l t s o b t a i n e d by B r e t t f o r ZnO w i t h r e s u l t s f o r T i 0 2 on the same system and w i t h the same b a f f l e . A l s o a number of d i f f e r e n t b a f f l e s were made i n o r d e r t o compare the e f f e c t s of d i f f e r e n t b a f f l e s on the s p u t t e r i n g b e h a v i o u r of a p a r t i c u l a r m a t e r i a l : T i 0 2 . D. THESIS OBJECTIVES The purpose of t h i s t h e s i s i s t o examine the a p p l i c a b i l i t y of r e a c t i v e s p u t t e r i n g t o the d e p o s i t i o n of t i t a n i u m o x i d e s . A l t h o u g h i t was n e c e s s a r y t o foc u s on a p a r t i c u l a r m a t e r i a l f o r t h i s i n v e s t i g a t i o n i t i s e x p e c t e d t h a t the r e s u l t s w i l l be a p p l i c a b l e t o r e a c t i v e s p u t t e r i n g of o t h e r compounds as w e l l , p a r t i c u l a r l y o x i d e s . More s p e c i f i c a l l y the o b j e c t i v e s of t h i s work a r e : 1. To i n v e s t i g a t e the u s e f u l n e s s of the r e a c t i v e gas b a f f l e as a g e n e r a l method of enhancing c o n t r o l of f i l m c o m p o s i t i o n i n r e a c t i v e s p u t t e r i n g . 5 2. To d e p o s i t f i l m s of t i t a n i u m o x i d e over a complete range of o x y g e n / t i t a n i u m r a t i o s . 3. To examine the p r o p e r t i e s of the f i l m s so produced. E. CHOICE OF TITANIUM OXIDE T i t a n i u m o x i d e was chosen f o r t h i s s t u d y f o r a v a r i e t y of r e a s o n s : 1. There i s c u r r e n t i n t e r e s t i n T i 0 2 f o r p r a c t i c a l a p p l i c a t i o n s , p a r t i c u l a r l y as an o p t i c a l c o a t i n g [3] and as a t h i n f i l m d i e l e c t r i c [ 8 , 9 ] . 2. The l i t e r a t u r e c o n t a i n s a g r e a t d e a l of i n f o r m a t i o n about the c r y s t a l l i n e forms of compounds i n the t i t a n i u m - o x y g e n b i n a r y system. S i n c e i t was found t h a t t i t a n i u m o x i d e s s p u t t e r e d onto room temperature s u b s t r a t e s were g e n e r a l l y amorphous i t was thought t h a t a comparison of the f i l m p r o p e r t i e s t o those of c r y s t a l l i n e samples would be i n t e r e s t i n g . 3. T i 0 2 i s an e l e c t r i c a l i n s u l a t o r , w h i l e TiO- i s an ' . - 2-x n-type semiconductor [ 1 0 ] , Some a t t e m p t s have been made t o s p u t t e r h e t e r o s t r u c t u r e s of t i t a n i u m and i t s o x i d e s f o r gas s e n s o r s [11] and as c a t a l y t i c e l e c t r o d e s f o r the p h o t o l y s i s of water [ 1 2 ] , I I . EXPERIMENTAL APPARATUS A. THE SPUTTERING SYSTEM F i g . 2.1 shows a c r o s s s e c t i o n of the s p u t t e r i n g chamber used i n t h i s s t u d y . I t i s a h o r i z o n t a l l y mounted c y l i n d r i c a l chamber eva c u a t e d t h r o u g h a p o r t on i t s u n d e r s i d e . The vacuum system c o n s i s t s of a 10 cm diameter o i l d i f f u s i o n pump used i n c o n j u n c t i o n w i t h a f r e o n c o o l e d c h e v r o n - t y p e c o l d t r a p . W ith t h i s system an u l t i m a t e chamber p r e s s u r e of 1 0 - 5 Pa can be a c h i e v e d . The pumping speed i s a d j u s t e d by means of a v a r i a b l e o r i f i c e . E l e c t r i c a l l y the system i s a d i o d e . The cathode assembly i s shown at the r i g h t of t h e diagram and the chamber i t s e l f a c t s as the anode. When the chamber i s f i l l e d w i t h gas ( i n my case a m i x t u r e of argon and oxygen) and an e l e c t r i c p o t e n t i a l i s a p p l i e d t o the cathode, any f r e e e l e c t r o n s i n the gas a r e a c c e l e r a t e d by the e l e c t r i c f i e l d . These undergo i o n i z i n g c o l l i s i o n s w i t h the n e u t r a l gas atoms and under a p p r o p r i a t e gas p r e s s u r e c o n d i t i o n s a plasma forms. A plasma i s a p a r t i a l l y i o n i z e d gas i n which the t o t a l c harge e q u a l s z e r o . The plasma i s s u s t a i n e d by c o n s t a n t i o n i z a t i o n of n e u t r a l s by secondary e l e c t r o n s e m i t t e d d u r i n g i o n bombardment of the t a r g e t . The i o n bombardment g i v e s the t a r g e t atoms, s u f f i c i e n t energy t o escape the t a r g e t and make t h e i r way t o the s u b s t r a t e . The cathode assembly c o n s i s t s of a water c o o l e d p l a t e , the s p u t t e r i n g t a r g e t , and a c i r c u l a r e l e c t r o m a g n e t . The 6 copocitonce monometer t o d i f fus ion pump gure 2.1 A schematic of the s p u t t e r i n g chamber, 8 purpose of the e l e c t r o m a g n e t i s t o i n c r e a s e the s p u t t e r i n g e f f i c i e n c y of the system f o r a g i v e n power and chamber p r e s s u r e . I t does t h i s by d i v e r t i n g the paths of the e n e r g e t i c e l e c t r o n s from the cathode so t h a t they take l o n g e r t o r e a c h the anode. As a r e s u l t they have more i o n i z i n g c o l l i s i o n s and the i o n d e n s i t y of the plasma i s i n c r e a s e d , which i n c r e a s e s the t a r g e t bombardment. When a magnetic f i e l d i s employed i n t h i s way the s p u t t e r i n g p r o c e s s i s r e f e r r e d t o as "magnetron s p u t t e r i n g " . The magnetic f i e l d l i n e s a r e as i n d i c a t e d i n F i g . 2.2. I t i s the magnetic f i e l d component p a r a l l e l t o the t a r g e t which i s most e f f e c t i v e i n r e t a r d i n g the p r o g r e s s of e l e c t r o n s toward the anode. T h i s component f o r c e s the e l e c t r o n s t o r e t u r n t o the t a r g e t , w h i l e the e l e c t r i c f i e l d f o r c e s them away from i t . The r e s u l t i s t h a t the e l e c t r o n s f o l l o w c y c l o i d a l t r a j e c t o r i e s as i n d i c a t e d i n F i g . 2.2. The magnetic f i e l d components which a r e p e r p e n d i c u l a r t o the t a r g e t s u r f a c e c o n s t r a i n the e l e c t r o n s t o t r a v e l around a c i r c u l a r p a t h so t h a t the d i s c h a r g e i s c o n f i n e d i n the form of a t o r u s . Thus the t a r g e t i s e t c h e d i n a r a d i a l l y symmetric p a t t e r n c o r r e s p o n d i n g t o the e l e c t r o n d e n s i t y i n the d i s c h a r g e " r i n g " . I n c r e a s e d i o n d e n s i t y may a l s o be a c h i e v e d by i n c r e a s i n g the chamber p r e s s u r e but a t the expense of d e c r e a s i n g the mean f r e e p a t h of the s p u t t e r e d p a r t i c l e s . The t a r g e t i s a c i r c u l a r p l a t e of 99.9% pure t i t a n i u m , 0.64 cm t h i c k and 15 cm i n d i a m e t e r . The o u t e r edge of the 9 t a r g e t i s machined t h i n n e r as shown i n the F i g . 2.1 so t h a t the t a r g e t can be clamped t o the c o o l e d cathode by means of a copper r i n g . C o o l i n g of the t a r g e t i s n e c e s s a r y t o d i s s i p a t e the l a r g e amount of t h e r m a l energy imparted t o i t by the bombarding i o n s . But i n the i n t e r e s t s of system f l e x i b i l i t y the t a r g e t i s c o o l e d i n d i r e c t l y by c o n t a c t w i t h the cathode p l a t e so t h a t t a r g e t s may be e a s i l y f a b r i c a t e d and i n t e r c h a n g e d . The f l a t shape of the t a r g e t i s r e f e r r e d t o by the term " p l a n a r " . Hence t h i s system i s a "dc p l a n a r magnetron s p u t t e r i n g system". As shown i n the diagram o n l y the t a r g e t p o r t i o n of the cathode i s exposed t o the chamber. The remainder i s s h i e l d e d by a p a r t of the chamber w a l l c a l l e d the "ground s h i e l d " . The reason f o r t h i s i s t o a v o i d s p u t t e r e t c h i n g of the cathode p l a t e i t s e l f , which would c o n t a m i n a t e the f i l m s and e v e n t u a l l y d e s t r o y the c a t h o d e . E l e c t r o n s t r a v e l l i n g from the edge of the cathode r e a c h the ground s h i e l d b e f o r e they become r e s p o n s i b l e f o r any s i g n i f i c a n t i o n i z a t i o n and t h e r e f o r e a d i s c h a r g e cannot be s u s t a i n e d i n between. The ground s h i e l d l e a v e s exposed a c i r c u l a r r e g i o n of the t a r g e t 9 cm i n d i a m e t e r . A l l gases e n t e r the chamber v i a the same p o r t , which i s l o c a t e d on t o p of the chamber near the end o p p o s i t e the c a t h o d e . The gas f l o w s a r e c o n t r o l l e d i n d i v i d u a l l y by means of s e r v o - d r i v e n v a l v e s ( G r a n v i l l e - P h i l l i p s model 203) and m o n i t o r e d u s i n g l i n e a r mass flowm e t e r s (Teledyne H a s t i n g s - R a y d i s t H-5 model A L L - 5 ) . Gas f l o w r a t e s a r e 10 measured i n s t a n d a r d c u b i c c e n t i m e t e r s per minute (SCCM). I n i t i a l chamber p r e s s u r e i s measured by an i o n gauge ( P e r k i n Elmer U l t e k DGC I I ) and o p e r a t i n g p r e s s u r e by a temperature s t a b i l i z e d c a p a c i t i v e manometer (MKS B a r a t r o n ) . The s p u t t e r i n g system i s equiped w i t h a mass sp e c t r o m e t e r as w e l l as an r f g e n e r a t o r f o r a p p l i c a t i o n of an r f d i s c h a r g e on t h e ' s u b s t r a t e ; however the s e f e a t u r e s were not used i n t h i s work. The gas f l o w s and d i s c h a r g e c u r r e n t were under computer c o n t r o l , u s i n g a s o f t w a r e package which has been d e s c r i b e d i n d e t a i l by McMahon [ 1 3 ] , The user may d i r e c t the computer t o s l o w l y move any one of the c o n t r o l parameters from one v a l u e t o another w h i l e s e v e r a l system parameters a r e s i m u l t a n e o u s l y m o n i t o r e d . T h i s i s r e f e r r e d t o as " w a l k i n g " the parameter. D u r i n g w a l k i n g , the s p e c i f i e d system parameters a r e m o n i t o r e d a t r e g u l a r i n t e r v a l s s p e c i f i e d by the u s e r . The v a l u e s of system parameters b e i n g m o n i t o r e d a r e i n t e g r a t e d over some o p e r a t o r - s p e c i f i e d p e r i o d p r i o r t o r e c o r d i n g . B. THE REACTIVE GAS BAFFLE The r e a c t i v e gas b a f f l e i s a t t a c h e d t o the ground s h i e l d as i n d i c a t e d i n F i g . 2.1. Some e x p e r i m e n t s were done u s i n g the b a f f l e which B r e t t et a l . [7] employed f o r s p u t t e r i n g ZnO. F i g . 2.3 shows a diagram of B r e t t ' s b a f f l e . I t i s s i m p l y an aluminum p l a t e p e r f o r a t e d w i t h a number of h o l e s and h e l d 4.5 cm away from the t a r g e t by a c y l i n d r i c a l ci??uLr 2pLnar:a1n reLcrfpuUe 9^n1%a r fL% l d S "$ t h * " t h o d e of a e l e c t r o n t r a j e c t o r y . s p u t t e r i n g target and the consequent Figure 2.3 The mounting geometry of the r e a c t i v e gas b a f f l e . 1 2 s p a c e r . The spacer was i n c l u d e d i n o r d e r t o keep the b a f f l e from i n t e r f e r i n g w i t h the glow d i s c h a r g e , s i n c e when i n p l a c e the b a f f l e a c t s as the system anode. The p a t t e r n of h o l e s i n B r e t t ' s b a f f l e i s d e t a i l e d i n F i g . 2.4A. S e v e r a l new b a f f l e s were a l s o c o n s t r u c t e d . These had a d i f f e r e n t p a t t e r n of h o l e s as shown i n F i g . 2.4B. A l l the new b a f f l e s had the same p a t t e r n but d i f f e r e d i n the d i a m e t e r of the h o l e s . The r a t i o of the p l a t e t h i c k n e s s t o h o l e d i a m e t e r was the same (1:2) f o r a l l the new b a f f l e s . T h i s was t o ensure t h a t the d i f f e r e n c e between the b a f f l e s would not depend on the a n g u l a r d i s t r i b u t i o n of s p u t t e r e d f l u x i n c i d e n t on them. As shown i n F i g . 2.5 t h i s r a t i o c o r r e s p o n d s t o an a n g u l a r a c c e p t a n c e of 60 d e g r e e s . The new b a f f l e p l a t e s were a l l mounted i n the same way as B r e t t ' s b a f f l e . C. DEPOSITION PROCEDURE The f i l m s made f o r t h i s work were a l l d e p o s i t e d a t a d i s c h a r g e power of 350 W. The oxygen c o n t e n t of the f i l m s was c o n t r o l l e d by a d j u s t i n g the f l o w r a t e of oxygen i n t o the chamber. The argon f l o w r a t e was always s e t t o 3.0 SCCM and the t h r o t t l e v a l v e was a d j u s t e d so t h a t t h i s c o r r e s p o n d e d t o an argon p a r t i a l p r e s s u r e of about 0.7 Pa. 13 Pattern 1 B. ..:<••• ft ft • .ft • A ? V • • • • ft. • ft..'• • • • ^ _ « _ A — ^ » A - A ^ • \ •••••••••••••••••• • • • • • • • / * * • • • • •••••••<?••••••• • ••••• • • • • • ft^ • • • • • • • ft • • • • • • • • • Aft ft ft•••ftft ft ft•••••• _\ • ft ft ft • ft ft • ft ft ft • • • • •\ftftftftftftftftft ft ft•• • ••••••••••••ft • - ft ft ft ft ft'ft 9 J Pattern 2 F i g u r e 2.4 Hole p a t t e r n s of the b a f f l e of B r e t t et a l r71 (P a t t e r n 1) and the new b a f f l e s ( P a t t e r n 2)? F i g u r e 2.5 A c r o s s s e c t i o n of a b a f f l e hole showing the d e f i n i t i o n of the angular acceptance a as the inverse tangent of the r a t i o of hole diameter to p l a t e t h i c k n e s s . I I I . RESULTS AND DISCUSSION A. SPUTTERING CHARACTERISTICS F i g . 3.1 shows how the v o l t a g e , c u r r e n t and p r e s s u r e depend on the r a t e of f l o w of oxygen i n t o the chamber a t a c o n s t a n t t a r g e t power of 350 W. The arrows i n d i c a t e the o r d e r of the d a t a f o r i n c r e a s i n g t i m e . S t a r t i n g from a m e t a l l i c t a r g e t i n pure argon the oxygen fl o w r a t e was s l o w l y i n c r e a s e d u n t i l the t a r g e t became c o m p l e t e l y o x i d i z e d and then d e c r e a s e d a g a i n u n t i l the o x i d e l a y e r was c o m p l e t e l y s p u t t e r e d o f f . The t a r g e t t r a n s i t i o n from metal t o o x i d e - c o v e r e d i s m a n i f e s t e d i n the d a t a by a s h a r p v o l t a g e i n c r e a s e c o i n c i d i n g w i t h a p r e s s u r e i n c r e a s e a t about 5 SCCM of oxygen. The p r e s s u r e i n c r e a s e i s due t o the c e s s a t i o n of g e t t e r pumping when the t a r g e t i s c o v e r e d . But the cause of the v o l t a g e i n c r e a s e i s not g e n e r a l l y agreed upon. The f o l l o w i n g mechanisms have been s u g g e s t e d . 1. As the oxygen f l o w r a t e i s i n c r e a s e d the w i d t h of the c i r c u l a r m e t a l l i c r e g i o n of the t a r g e t s u r f a c e d e c r e a s e s . A c c o r d i n g t o S c h i l l e r e t a l . [5] t h i s r e s u l t s i n a d e c r e a s e i n c u r r e n t and i s t h e r e f o r e r e s p o n s i b l e f o r the v o l t a g e i n c r e a s e a t c o n s t a n t power. O p e r a t i n g a t c o n s t a n t power and c o n s t a n t p r e s s u r e they f o u n d ' t h a t the maximum v o l t a g e c o r r e s p o n d e d t o the minimum w i d t h of the d i s c h a r g e r i n g . 2. The secondary e l e c t r o n y i e l d of t i t a n i u m o x i d e may be 15 16 Oxygen Flow Rote (SCCM) oxygen i n t o the s p u t t e r i n g chamber. 17 lower than t h a t of t i t a n i u m [ 1 4 ] . T h i s would r e s u l t i n d e c r e a s e d c u r r e n t s i n c e on average fewer e l e c t r o n s would be e j e c t e d from the t a r g e t f o r each bombarding p a r t i c l e . 3. More n e g a t i v e i o n s a r e s p u t t e r e d from an o x i d i z e d t a r g e t than from a m e t a l l i c t a r g e t [ 1 5 ] . H o l l a n d [16] has proposed t h a t the n e g a t i v e i o n s may p a r t i a l l y n e u t r a l i z e the space charge l a y e r a d j a c e n t t o the t a r g e t , thus d e c r e a s i n g the bombardment and t h e r e f o r e the c u r r e n t . 4. T i t a n i u m d i o x i d e i s an e l e c t r i c a l i n s u l a t o r so t h a t some of the a p p l i e d v o l t a g e might be dropped a c r o s s the o x i d e l a y e r on the t a r g e t [ 1 6 ] . Such a d i s c o n t i n u i t y i n the v o l t a g e i s c h a r a c t e r i s t i c of the r e a c t i v e s p u t t e r i n g of many m e t a l s w i t h oxygen. Some show a v o l t a g e i n c r e a s e on t a r g e t o x i d a t i o n ( e . g . molybdenum [ 1 7 ] , t a n t a l u m [18]) w h i l e o t h e r s show a v o l t a g e d e c r e a s e (e.g. aluminum [ 1 6 ] , z i n c [ 7 ] ) . In e i t h e r case the a r e a of the m e t a l l i c r e g i o n of the t a r g e t can be e x p e c t e d t o d e c r e a s e as the oxygen f l o w i s i n c r e a s e d . T h e r e f o r e I suggest t h a t a d e c r e a s e i n the a r e a of the t a r g e t which i s m e t a l l i c i s o n l y accompanied by c o n s t r i c t i o n of the d i s c h a r g e i n c a s e s where the secondary e l e c t r o n c o e f f i c i e n t of the o x i d e i s lower than t h a t of the m e t a l . A l t h o u g h the secondary e l e c t r o n c o e f f i c i e n t of t i t a n i u m o x i d e has not been measured t h e r e i s e v i d e n c e t h a t i t i s lower than t h a t of t i t a n i u m . F e r r o n e t a l . [19] have measured the work f u n c t i o n and secondary e l e c t r o n y i e l d from t a r g e t s of aluminum and molybdenum as f u n c t i o n s of oxygen 18 e x p osure. They found t h a t the secondary e l e c t r o n c o e f f i c i e n t of molybdenum d e c r e a s e d on exposure w h i l e t h a t of aluminum i n c r e a s e d . T h i s i s c o n s i s t e n t w i t h the b e h a v i o u r of the s p u t t e r i n g c h a r a c t e r i s t i c s of t h e s e m a t e r i a l s . They a l s o found a d i r e c t c o r r e l a t i o n between the secondary e l e c t r o n y i e l d and the work f u n c t i o n : an i n c r e a s e i n work f u n c t i o n c o r r e s p o n d s t o a d e c r e a s e i n the secondary e l e c t r o n y i e l d . Kandasamy and S u r p l i c e [20] measured the work f u n c t i o n of t i t a n i u m f i l m s as a f u n c t i o n of oxygen exposure and found t h a t i t i n c r e a s e d w i t h i n c r e a s i n g " oxygen dose. Based on t h e s e p r e v i o u s works, t h e r e f o r e , i t would appear t h a t the secondary e l e c t r o n y i e l d i s p r o b a b l y lower f o r t i t a n i u m o x i d e than f o r t i t a n i u m . The v o l t a g e peaks which a r e e v i d e n t a t the m e t a l - t o - o x i d e and o x i d e - t o - m e t a l t r a n s i t i o n s i n F i g . 3.1 have not been r e p o r t e d e l s e w h e r e . The m e t a l - t o - o x i d e peak does not c o n s i s t of s t e a d y - s t a t e o p e r a t i n g p o i n t s . In o t h e r words i f the oxygen f l o w r a t e were h e l d c o n s t a n t a t 5.0 SCCM the v o l t a g e would not remain h i g h . T h i s i s because the v o l t a g e peak i s due t o an i n t e r m e d i a t e t a r g e t s t a t e which cannot be m a i n t a i n e d . Such b e h a v i o u r might be a t t r i b u t e d t o the p r e s s u r e i n c r e a s e i m m e d i a t e l y f o l l o w i n g the t r a n s i t i o n , s i n c e c u r r e n t i s known t o v a r y l i n e a r l y w i t h p r e s s u r e [ 2 1 ] . F i g . 3.2 shows t h e c u r r e n t as a f u n c t i o n of p r e s s u r e . The dependence i s a p p r o x i m a t e l y l i n e a r i n the p r e s s u r e r e g i o n " c o r r e s p o n d i n g t o an o x i d i z e d t a r g e t , but not a t the t r a n s i t i o n . E v i d e n t l y the the e f f e c t s of p r e s s u r e a l o n e are 19 0.5 0.7 0.9 1.1 13 1.5 Pressure (Pa) 1.7 1.9 F i g u r e 3.2 R e l a t i o n of c u r r e n t w i t h t o t a l pressure f o r constant d i s c h a r g e power and changing oxygen flow r a t e . The data i n t h i s f i g u r e correspond t o the data i n F i g . 3.1. 20 i n s u f f i c i e n t t o e x p l a i n the d a t a . The proposed e x p l a n a t i o n f o r the v o l t a g e peaks i s as f o l l o w s . As the t a r g e t i s suddenly exposed t o a l a r g e dose of oxygen i t f i r s t a d s o r b s and then chemisorbs the oxygen. The work of Kandasamy and S u r p l i c e [20] showed t h a t the work f u n c t i o n of . t i t a n i u m o x i d e was lower than t h a t of oxygen-covered m e t a l . They observed s i m i l a r peaks i n the work f u n c t i o n of t i t a n i u m f i l m s as a f u n c t i o n of time a f t e r the i n t r o d u c t i o n of oxygen t o the f i l m s . As d i s c u s s e d above an i n c r e a s e i n work f u n c t i o n can be e x p e c t e d t o c o r r e s p o n d t o an i n c r e a s e i n the s p u t t e r i n g v o l t a g e a t c o n s t a n t . power. As the oxygen f l o w r a t e i s d e c r e a s e d the o x i d e l a y e r becomes t h i n n e r . J u s t b e f o r e the o x i d e - t o - m e t a l t r a n s i t i o n the o x i d e l a y e r d i s a p p e a r s because the oxygen p r e s s u r e i s such t h a t oxygen which i s p h y s i s o r b e d on the t a r g e t i s r e s p u t t e r e d b e f o r e i t has time t o be chemisorbed. As a r e s u l t the work f u n c t i o n i n c r e a s e s and w i t h i t the v o l t a g e . The reason why the m e t a l - t o - o x i d e peak i s h i g h e r than the o x i d e - t o - m e t a l peak i s t h a t the sudden l a r g e dose of oxygen p r e s e n t e d t o the t a r g e t a t the m e t a l - t o - o x i d e t r a n s i t i o n r e s u l t s i n a much t h i c k e r a d l a y e r than i s the case f o r the o x i d e - t o - m e t a l t r a n s i t i o n . To summarize, s t a r t i n g w i t h a m e t a l l i c t a r g e t the a d d i t i o n of oxygen causes c o n s t r i c t i o n of the d i s c h a r g e so t h a t the v o l t a g e r i s e s g r a d u a l l y . When the e n t i r e t a r g e t c o v e r s over the v o l t a g e r i s e s d i s c o n t i n u o u s l y due t o a change i n the secondary e l e c t r o n c o e f f i c i e n t caused by the 21 p h y s i s o r p t i o n of oxygen. Other mechanisms, as mentioned above, may a l s o c o n t r i b u t e t o the v o l t a g e i n c r e a s e . As the oxygen p e n e t r a t e s i n t o the metal the secondary e l e c t r o n c o e f f i c i e n t . i n c r e a s e s r e s u l t i n g i n a lower v o l t a g e i m m e d i a t e l y a f t e r the t r a n s i t i o n . Once the t a r g e t i s o x i d i z e d the v o l t a g e depends l i n e a r l y on the t o t a l p r e s s u r e . As the p r e s s u r e i s d e c r e a s e d the v o l t a g e i n c r e a s e s and the o x i d e l a y e r becomes t h i n n e r . As the p r e s s u r e i s de c r e a s e d below about 1.3 SCCM the secondary e l e c t r o n c o e f f i c i e n t d e c r e a s e s as the t h i c k n e s s of the o x i d e l a y e r becomes n e g l i g i b l e . F i n a l l y the l a y e r of oxygen i s c o m p l e t e l y removed and the v o l t a g e d e c r e a s e s t o i t s o r i g i n a l v a l u e . Another more common way of d i s p l a y i n g the s p u t t e r i n g c h a r a c t e r i s t i c s i s t o show the r e l a t i o n s h i p between c u r r e n t and v o l t a g e . F i g . 3.3 d i s p l a y s t h i s r e l a t i o n s h i p f o r c o n s t a n t oxygen f l o w r a t e s of 1.0, 2.0, 3.0, and 4.0 SCCM and f o r s p u t t e r i n g t i t a n i u m i n pure argon. A l s o shown are the d a t a of F i g . 3.1 which i n d i c a t e the r e l a t i o n of these d a t a t o c o n s t a n t power o p e r a t i o n . The da t a was o b t a i n e d by f i r s t s e t t i n g the oxygen f l o w r a t e (the argon f l o w r a t e was always 3.0 SCCM) and then w a l k i n g the c u r r e n t up from 0 A. T h e r e f o r e t h e s e c u r v e s p e r t a i n o n l y t o the o x i d e - t o - m e t a l t a r g e t t r a n s i t i o n . I t can be seen i n F i g . 3.3 t h a t the t h r e s h o l d c u r r e n t f o r t a r g e t d e o x i d a t i o n i n c r e a s e s w i t h i n c r e a s i n g f l o w r a t e . However the change i n t h r e s h o l d c u r r e n t becomes s m a l l e r as the f l o w r a t e i s i n c r e a s e d . T h i s i s a t t r i b u t e d t o h e a t i n g of 22 280 320 360 400 440 480 520 560 Voltage (V) Figure 3.3 I-V c h a r a c t e r i s t i c s of t i t a n i u m i n argon/oxygen for inc r e a s i n g current (oxide-to-metal target t r a n s i t i o n ) . 23 the t a r g e t . I t was observed t h a t a f t e r o p e r a t i o n a t 600 W the t a r g e t was i n c a n d e s c e n t . High t a r g e t t e m p e r a t u r e s cause enhanced d e s o r b t i o n of oxygen from the t a r g e t so t h a t the t h r e s h o l d c u r r e n t f o r t a r g e t d e o x i d a t i o n would be lower than would be the case f o r a c o o l e r t a r g e t . In c o n s i d e r i n g F i g . 3.3 i t must be kept i n mind t h a t the p r e s s u r e was not h e l d c o n s t a n t . F i g . 3.4 shows the c u r r e n t as a f u n c t i o n of p r e s s u r e f o r the same expe r i m e n t . The p r e s s u r e was c o n s t a n t o n l y f o r the data o b t a i n e d w i t h pure argon as the s p u t t e r i n g gas. With argon/oxygen and an o x i d i z e d t a r g e t the p r e s s u r e i n c r e a s e s w i t h i n c r e a s i n g oxygen f l o w r a t e . H i g h e r p r e s s u r e c o r r e s p o n d s t o a lower v o l t a g e f o r a g i v e n o p e r a t i n g c u r r e n t . B. EFFECTIVENESS OF THE REACTIVE GAS BAFFLE In or d e r t o compare the r e s u l t s o b t a i n e d u s i n g d i f f e r e n t b a f f l e s i t was n e c e s s a r y t o c h a r a c t e r i z e the b a f f l e s i n some way. I t was d e c i d e d t h a t a u s e f u l q u a n t i t y f o r t h i s purpose would be the r a t i o of the s p u t t e r e d f l u x t r a n s m i t t e d t o the t o t a l s p u t t e r e d f l u x . T h i s q u a n t i t y w i l l be r e f e r r e d t o as the " b a f f l e a p e r t u r e " . A c a l c u l a t i o n was undertaken t o e s t i m a t e the b a f f l e a p e r t u r e as a f u n c t i o n of the r a d i u s of the b a f f l e h o l e s . The d e t a i l s of the c a l c u l a t i o n a r e g i v e n i n the Appendix. The r e s u l t s a r e shown i n F i g . 3.5 f o r the two b a f f l e p a t t e r n s of F i g . 2.4. Based on t h i s c a l c u l a t i o n the b a f f l e used by B r e t t i s e s t i m a t e d t o pass 7.3% of the f l u x . 24 F i g u r e 3.4 R e l a t i o n of c u r r e n t w i t h t o t a l pressure f o r v a r i o u s constant flow r a t e s and changing power. The data i n t h i s f i g u r e correspond to the data i n F i g . 3.3. 25 Hole Radius (cm) f o r the 26 B r e t t was s u c c e s s f u l i n u s i n g t h i s b a f f l e t o make s t o i c h i o m e t r i c ZnO. But u s i n g the same b a f f l e and the same t a r g e t - t o - s u b s t r a t e d i s t a n c e (10 cm) i t was not p o s s i b l e t o d e p o s i t s t o i c h i o m e t r i c T i 0 2 . E v i d e n t l y the e f f e c t i v e n e s s of the b a f f l e i s d i f f e r e n t f o r d i f f e r e n t m a t e r i a l s . One measure of b a f f l e e f f e c t i v e n e s s i s the maximum a t t a i n a b l e oxygen p a r t i a l p r e s s u r e w i t h a m e t a l l i c t a r g e t . F i g . 3.6 shows the r a t i o of oxygen p a r t i a l p r e s s u r e t o t o t a l p r e s s u r e as a f u n c t i o n of oxygen f l o w r a t e f o r a v a r i e t y of b a f f l e s and f o r the case of no b a f f l e . T h i s r a t i o was used i n s t e a d of the a c t u a l p a r t i a l p r e s s u r e because the i n i t i a l argon p r e s s u r e was s l i g h t l y d i f f e r e n t f o r each e x p e r i m e n t . The oxygen p a r t i a l p r e s s u r e was o b t a i n e d by s u b t r a c t i n g the i n i t i a l ( i . e . no oxygen) argon p r e s s u r e from the t o t a l p r e s s u r e . The c o n s i d e r a b l e s c a t t e r i n the p o i n t s i s due t o s m a l l f l u c t u a t i o n s i n the argon f l o w r a t e about 3.0 SCCM. The l i n e s i n the f i g u r e a r e o n l y g u i d e s t o the eye and the arrows i n d i c a t e the d i r e c t i o n of t i m e . The f i g u r e shows t h a t the maximum oxygen p a r t i a l p r e s s u r e w i t h the 7.3% b a f f l e was about 0.007 Pa i n c o n t r a s t t o the v a l u e of 0.05 Pa found by B r e t t f o r z i n c . The r e s u l t s a l s o show t h a t the oxygen p a r t i a l p r e s s u r e a t a g i v e n oxygen f l o w r a t e i n c r e a s e s w i t h d e c r e a s i n g b a f f l e a p e r t u r e . I t appears t h a t the p r e s s u r e change per u n i t change i n the b a f f l e a p e r t u r e becomes more s i g n i f i c a n t as the b a f f l e a p e r t u r e d e c r e a s e s . For a b a f f l e a p e r t u r e of z e r o t h e r e would be no t i t a n i u m a v a i l a b l e i n the chamber f o r g e t t e r 27 n 2 3 < 5 Oxygen Flow Rate (SCCM) «.»» E £ f e c t o f b a £ ( l e a p e r t u r e ^ ^ p a r t u i 28 pumping and the system would behave as i f the t a r g e t were o x i d i z e d . From F i g . 3.1 i t can be seen t h a t i n t h i s case the r a t i o of oxygen p a r t i a l p r e s s u r e t o t o t a l p r e s s u r e would be about 0.45 f o r an oxygen f l o w r a t e of 3.0 SCCM. The d a t a a l s o shows t h a t the c r i t i c a l f l o w r a t e f o r the m e t a l - t o - o x i d e t a r g e t t r a n s i t i o n i s lower w i t h the b a f f l e than w i t h o u t i t , B r e t t et a l . [7] have a t t r i b u t e d t h i s t o the f a c t t h a t the b a f f l e i n h i b i t s d i f f u s i o n pumping of the gas i n the t a r g e t v i c i n i t y . I t i s i n t e r e s t i n g t h a t the c r i t i c a l f l o w r a t e d i d not change w i t h b a f f l e a p e r t u r e over the range s t u d i e d . T h i s i n d i c a t e s t h a t e i t h e r the r a t e of gas d i f f u s i o n t h r o u g h the b a f f l e i s not v e r y s e n s i t i v e t o the b a f f l e a p e r t u r e or t h e r e i s a n o t h e r reason f o r the de c r e a s e d c r i t i c a l f l o w r a t e . One p o s s i b i l i t y i s t h a t the b a f f l e a c t u a l l y does i n t e r f e r e w i t h the n e g a t i v e glow r e g i o n of the d i s c h a r g e . A c c o r d i n g t o Dr u y v e s t e y n and Penning [22] most of the i o n s o r i g i n a t e i n the n e g a t i v e glow f o r the case of an abnormal d i s c h a r g e (always the case i n s p u t t e r i n g ) . I f the b a f f l e a b b r e v i a t e d the n e g a t i v e glow t h e r e might be l e s s i o n i z a t i o n which would r e s u l t i n t a r g e t coverage . a t a reduced f l o w r a t e . I t was found t h a t even w i t h the e l e v a t e d oxygen p a r t i a l p r e s s u r e s c r e a t e d u s i n g the 3.8% b a f f l e i t was not p o s s i b l e t o make s t o i c h i o m e t r i c T i 0 2 a t a t a r g e t - t o - s u b s t r a t e d i s t a n c e of 10 cm. However, a f u r t h e r d e c r e a s e i n b a f f l e a p e r t u r e would r e s u l t i n a d e p o s i t i o n r a t e comparable t o or lower than the d e p o s i t i o n r a t e from an o x i d i z e d t a r g e t . 29 F i g . 3.7 g i v e s the d e p o s i t i o n r a t e s f o r f i l m s made w i t h the 3.8% b a f f l e and the 7.3% b a f f l e . F i l m t h i c k n e s s e s were measured u s i n g a s u r f a c e p r o f i l e r on a f i l m edge produced by c o v e r i n g p a r t of the s u b s t r a t e w i t h tape d u r i n g s p u t t e r i n g . In the f i g u r e the p o i n t a t 4.0 SCCM of oxygen c o r r e s p o n d s t o a f i l m d e p o s i t e d over a p e r i o d of 9.5 hours from an o x i d i z e d t a r g e t w i t h the 7.3% b a f f l e i n p l a c e . The r a t e would be h i g h e r f o r an o x i d i z e d t a r g e t w i t h no b a f f l e . A p p a r e n t l y t h e r e f o r e i t i s not advantageous t o use the r e a c t i v e gas b a f f l e f o r s p u t t e r i n g s t o i c h i o m e t r i c T i 0 2 a t a s m a l l t a r g e t - t o - s u b s t r a t e d i s t a n c e . F i g . 3.7 a l s o r e v e a l s the u s e f u l r e s u l t t h a t the d e p o s i t i o n r a t e i s independent of the oxygen f l o w r a t e f o r f i l m s made w i t h a m e t a l l i c t a r g e t . T h i s a l l o w s a check of the v a l i d i t y of the b a f f l e a p e r t u r e c a l c u l a t i o n . The d e p o s i t i o n r a t e f o r pure t i t a n i u m would be p r o p o r t i o n a l t o the amount of t i t a n i u m p a s s i n g t h r ough the b a f f l e . From the f i g u r e the d e p o s i t i o n r a t e w i t h the 7.3% b a f f l e i s about 2.25 t i m e s t h a t w i t h the 3.8% b a f f l e . The p r e d i c t i o n based on the c a l c u l a t e d b a f f l e a p e r t u r e would be 1.92 which i s r e a s o n a b l y c l o s e c o n s i d e r i n g the number of a p p r o x i m a t i o n s made. I t remains t o be seen how the f i l m p r o p e r t i e s depend on the b a f f l e a p e r t u r e . For T i 0 2 the e l e c t r i c a l r e s i s t i v i t y i s a s e n s i t i v e f u n c t i o n of the s t o i c h i o m e t r y [ 2 3 ] . The s t o i c h i o m e t r i c o x i d e i s i n s u l a t i n g , w i t h a room-temperature r e s i s t i v i t y on the o r d e r of 10 7 fi-cm [24] w h i l e pure 30 F i 9 u r e 3.7 E f f e c t of b a f n , a p e r t u r e o n d e p o s i t i o „ ^ 31 t i t a n i u m has a room-temperature r e s i s t i v i t y of 42„0 uti-cm [ 2 5 ] , F i g . 3.8 shows the room-temperature r e s i s t i v i t y of f i l m s produced w i t h the 7.3% and 3.8% b a f f l e s as a f u n c t i o n of oxygen f l o w r a t e . The t a r g e t - t o - s u b s t r a t e d i s t a n c e was 10 cm. The f i l m s made w i t h the s m a l l e r b a f f l e a p e r t u r e (and t h e r e f o r e h i g h e r oxygen p a r t i a l p r e s s u r e ) have lower e l e c t r i c a l r e s i s t i v i t y , which i n d i c a t e s t h a t they have a lower O/Ti r a t i o . T h i s i s s u r p r i s i n g because i t i s g e n e r a l l y a c c e p t e d t h a t o x i d a t i o n o c c u r s a t the s u b s t r a t e so t h a t a h i g h e r oxygen p a r t i a l p r e s s u r e s h o u l d c o r r e s p o n d t o a h i g h e r O/Ti r a t i o i n the f i l m . A p o s s i b l e e x p l a n a t i o n f o r t h i s i s t h a t the c o n s t i t u e n t atoms a r e i n a l e s s - e x c i t e d s t a t e w i t h the 3.8% b a f f l e than w i t h the 7.3% b a f f l e . S i n c e the b a f f l e a c t s as the anode of the d i s c h a r g e the plasma does not extend as f a r i n t o the chamber when the b a f f l e i s i n p l a c e as w i t h no b a f f l e . Perhaps the s i z e of the b a f f l e h o l e s has an e f f e c t on the degree t o which the plasma p e n e t r a t e s the b a f f l e and hence the degree of e x c i t a t i o n of atoms i n the v i c i n i t y of the s u b s t r a t e . An a l t e r n a t i v e e x p l a n a t i o n might be t h a t a s i g n i f i c a n t amount of o x i d e i s s p u t t e r e d from the t a r g e t i n the p a r t i a l l y c o v e r e d mode. Then the b a f f l e w i t h lower a p e r t u r e would i n h i b i t f i l m o x i d a t i o n by s i m p l y s t o p p i n g more of the s p u t t e r e d o x i d e r a d i c a l s . In any case the d a t a i n d i c a t e t h a t f o r a t a r g e t - t o - s u b s t r a t e d i s t a n c e of 10 cm the r e a c t i v e gas b a f f l e does not enhance f i l m o x i d a t i o n d e s p i t e i t s augmentation of the oxygen p a r t i a l p r e s s u r e near the s u b s t r a t e . ft-At 1 1 1 1 1 I , 1 , 1 , 1 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Oxygen Flow Rate (SCCM) F i g u r e 3.8 E f f e c t of b a f f l e a p e r t u r e on f i l m r e s i s t i v i t y 33 C. FILM CHARACTERIZATION 1. STRUCTURE The m i c r o s t r u c t u r e of the f i l m s was examined u s i n g X-ray d i f f r a t o m e t r y (XRD) and s c a n n i n g e l e c t r o n m i c r o s c o p y (SEM). The XRD s p e c t r a r e v e a l e d no s t r u c t u r e (amorphous f i l m s ) f o r a l l but one of the f i l m s . T h i s f i l m was s p u t t e r e d from an o x i d e t a r g e t f o r 9.5 hours and was the t h i c k e s t f i l m made (2 m i c r o n s ) . F i g . 3.9 shows the XRD spectrum f o r t h i s f i l m . Shown f o r comparison a r e the p o s i t i o n s of the most prominent powder p a t t e r n peaks a s s o c i a t e d w i t h r u t i l e and a n a t a s e , which a r e the two c r y s t a l l i n e phases of T i 0 2 o b s e r v e d i n s p u t t e r e d f i l m s [ 2 6 , 2 7 ] , The numbers c o r r e s p o n d i n g t o the powder p a t t e r n peaks are the r e l a t i v e peak i n t e n s i t i e s . The phase p r e s e n t i s c l e a r l y a n a t a s e . The f a c t t h a t some of the peaks a r e absent and the non-correspondence of peak i n t e n s i t i e s w i t h the p o w d e r - p a t t e r n d a t a i n d i c a t e s a p r e f e r r e d o r i e n t a t i o n of the c r y s t a l l i t e s . The sharpness of the peaks i s i n d i c a t i v e of l a r g e c r y s t a l l i t e s but the low i n t e n s i t i e s may mean t h a t t h e r e a r e o n l y a few i s o l a t e d c r y t s t a l l i t e s . The s t r u c t u r e i n t h i s f i l m was p r o b a b l y the r e s u l t of a n n e a l i n g of the f i l m d u r i n g growth. Two f a c t o r s unique t o the d e p o s i t i o n of t h i s f i l m c o u l d have c o n t r i b u t e d t o a n n e a l i n g : 1. The d e p o s i t i o n time was u n u s u a l l y l o n g . A l l o t h e r f i l m s were d e p o s i t e d over a p e r i o d of 30 t o 90 m i n u t e s . 2. The f i l m was made w i t h the t a r g e t o x i d i z e d . As seen i n 34 1? *M? i > i i ! 35 A 25 » 70 W 50 R A A A R 100 K>0 1! A ' i i /\ 1 1 1 1 1 1 1 1 1 60 55 50 45 AO 35 30 25 ' 20 Diffraction Angle 26 (degrees) F i g u r e 3.9 X-ray d i f f r a c t o g r a m of a p o l y c r y s t a l l i n e f i l m of T i 0 2 . Anatase and r u t i l e p o w d e r - p a t t e r n peaks a r e shown w i t h t h e i r c o r r e s p o n d i n g r e l a t i v e i n t e n s i t i e s . F i g . 3.3 the o x i d i z e d t a r g e t s t a t e c o r r e s p o n d s t o much h i g h e r power d i s s i p a t i o n w h i c h might be e x p e c t e d t o i n c r e a s e the s u b s t r a t e t e m p e r a t u r e due t o i n d i r e c t h e a t i n g . T a k e uchi e t a l . [27] o b s e r v e d s i m i l a r r e s u l t s f o r f i l m s produced by means of r f s p u t t e r i n g from an o x i d e t a r g e t . They found no s t r u c t u r e i n f i l m s of t h i c k n e s s l e s s than one mi c r o n and f a i n t XRD peaks of r u t i l e and an a t a s e f o r f i l m s more than one mi c r o n t h i c k . The r e p o r t e d d e p o s i t i o n r a t e of 1.7 nm/min would c o r r e s p o n d t o 9.8 hours f o r a f i l m one mi c r o n t h i c k . And the s u b s t r a t e t e m p e r a t u r e was r e p o r t e d t o r i s e t o 200°C a f t e r a few minutes due t o i n d i r e c t h e a t i n g . S c h i l l e r e t a l . [26] o b s e r v e d c r y s t a l s t r u c t u r e i n f i l m s r e a c t i v e l y s p u t t e r e d onto s u b s t r a t e s a t t e m p e r a t u r e s 35 above 100°C. However a l l my f i l m s were d e p o s i t e d w i t h one of the r e a c t i v e gas b a f f l e s i n p l a c e . T h i s would i n c r e a s e the time r e q u i r e d f o r the s u b s t r a t e t o r e a c h i t s e q u i l i b r i u m t e mperature s i n c e the b a f f l e i s a b a r r i e r between the heat source (the t a r g e t ) and the s u b s t r a t e . The absense of the r u t i l e s t r u c t u r e i s c o n t r a r y t o the r e s u l t s of both Takeuchi e t a l . and S c h i l l e r et a l . who r e p o r t e d mixed phase f i l m s c o n t a i n i n g b oth r u t i l e and a n a t a s e . F i g . 3.10 i s an SEM ph o t o m i c r o g r a p h of the edge of a t y p i c a l non s t o i c h i o m e t r i c f i l m . The f i l m was a p p r o x i m a t e l y 400 nm t h i c k . The edge was produced by b r e a k i n g the s u b s t r a t e . The sample was then s p u t t e r - c o a t e d w i t h a ve r y t h i n l a y e r of g o l d . The ph o t o m i c r o g r a p h shows a smooth s u r f a c e w i t h o u t the columnar s t r u c t u r e t h a t i s o f t e n o b s e r v e d i n s p u t t e r e d f i l m s . 2. OPTICAL PROPERTIES I t was found t h a t s u b s t o i c h i o m e t r i c f i l m s ( p a r t i a l l y t r a n s m i t t i n g f i l m s of TiO where x<2) were b l u e - g r e y i n c o l o u r , s t o i c h i o m e t r i c f i l m s ( T i 0 2 ) were c o l o u r l e s s and t r a n s p a r e n t , and f i l m s made w i t h l i t t l e oxygen ( i . e . oxygen f l o w r a t e < 1.0 SCCM) were s h i n y and m e t a l l i c i n appearance. The b l u e c o l o u r a s s o c i a t e d w i t h n o n s t o i c h i o m e t r y has been ob s e r v e d p r e v i o u s l y i n s p u t t e r e d f i l m s [28,29] and a l s o i n n o n s t o i c h i o m e t r i c r u t i l e c r y s t a l s i n which the d e p a r t u r e from s t o i c h i o m e t r y i s a c h i e v e d by r e d u c t i o n [10,23,30], 36 Figure 3.10 Side-on SEM photomicrograph of aTiO xf i lm. 37 There have been many s t u d i e s c o n c e r n i n g the n a t u r e of the broad a b s o r p t i o n which g i v e s r i s e t o t h i s b l u e c o l o u r i n reduced r u t i l e . However, t h i n f i l m o p t i c a l s t u d i e s have been c o n c e n t r a t e d on the u l t r a v i o l e t (UV) a b s o r p t i o n edge [24,28,31]. S c h i l l e r e t a l . [29] have measured the o p t i c a l p r o p e r t i e s of r e a c t i v e l y s p u t t e r e d s u b o x i d e s a t l o n g e r wavelengths ( t o lOOOnm) but the data i s somewhat ambiguous as t o the p o s i t i o n of the broad a b s o r p t i o n peak. In the p r e s e n t work o p t i c a l p r o p e r t i e s were measured from 300 nm t o 2500 nm u s i n g a Beckman UV5270 sp e c t r o p h o t o m e t e r f i t t e d w i t h an i n t e g r a t i n g sphere. F i g . 3.11 shows the r e f l e c t a n c e and t r a n s m i t t a n c e of s e v e r a l f i l m s made w i t h a m e t a l l i c t a r g e t a t v a r i o u s oxygen f l o w r a t e s . These f i l m s were d e p o s i t e d on C o r n i n g 7059 g l a s s s u b s t r a t e s so t h a t the d a t a i s o n l y v a l i d f o r wavelengths above 350 nm. For oxygen f l o w r a t e s between 0.0 SCCM and 0.5 SCCM the r e f l e c t a n c e d e c r e a s e s w i t h i n c r e a s e d f l o w r a t e . However as the f l o w r a t e i s f u r t h e r i n c r e a s e d the v i s i b l e r e f l e c t a n c e i n c r e a s e s w i t h f l o w r a t e w h i l e the near i n f r a r e d (NIR) r e f l e c t a n c e c o n t i n u e s t o d e c r e a s e . The t r a n s m i t t a n c e i n c r e a s e s w i t h oxygen f l o w r a t e over the e n t i r e wavelength range. The broad v i s i b l e a b s o r p t i o n i s e v i d e n t i n the t r a n s m i t t a n c e s p e c t r a of the f i l m s made a t oxygen f l o w r a t e s of 2.5 SCCM and 3.0 SCCM. The a b s o r p t i o n band i s narrower f o r the f i l m made w i t h a h i g h e r f l o w r a t e . The s t r u c t u r e i n the r e f l e c t a n c e s p e c t r a of th e s e f i m s i s due t o t h i n f i l m i n t e r f e r e n c e . I t i s b a r e l y d e t e c t a b l e i n the t r a n s m i t t a n c e 38 .5 fi .7 .8 .9 13 1.7 2.1 25 Wavelength ( p ) m a d ^ ^ ^ 1 v a r I O U c S m L t ^ 2 n e } ? d r e f l e c t ^ e f o r a number of f i l m s ~ d I c . K t h r o x y U g S e n ° H ^ n r a ^ 0 r n TcCM?' ^ °" ^ ™ 39 s p e c t r a because the f i l m s a r e too a b s o r b i n g t o a l l o w m u l t i p l e i n t e r n a l r e f l e c t i o n s . F i g . 3.12 shows the o p t i c a l d e n s i t y ( - l o g 1 0 T ) of s e v e r a l t r a n s m i t t i n g f i l m s made w i t h d i f f e r e n t oxygen f l o w r a t e s , and d e p o s i t e d on f u s e d q u a r t z s u b s t r a t e s . The v i s i b l e a b s o r p t i o n i s w e l l d e f i n e d a t 880 nm. T h i s i s c o n s i s t e n t w i t h the d a t a of S c h i l l e r et a l . [29] who r e p o r t e d an a b s o r p t i o n peak between 850 nm and 1100 nm. For flo w r a t e s from 1.0 SCCM t o 1.8 SCCM the peak p o s i t i o n does not change. For the two f i l m s made w i t h h i g h e r f l o w r a t e s i t would appear t h a t the peak has s h i f t e d t o a lower wavelength. T h i s c o u l d be due t o the i n c r e a s e d c o n t r i b u t i o n of i n t e r f e r e n c e f r i n g e s t o the t r a n s i t t a n c e s p e c t r a of f i l m s w i t h l i t t l e a b s o r p t i o n . In any case the r e s u l t s a r e i n c o n t r a s t t o the da t a f o r reduced r u t i l e and f o r "l o w e r " o x i d e s of t i t a n i u m ( i . e . T i 2 0 3 , T i 3 0 5 and the M a g n e l i phases T i n 0 2 n - 1 ^ * S a k a t a [30] r e p o r t e d t h a t the main peak f o r s l i g h t l y reduced r u t i l e i s a t 1968 nm w i t h a s h o u l d e r a t 1127 nm, and t h a t the peak s h i f t s w i t h i n c r e a s i n g r e d u c t i o n . P o r t e r e t a l . [32] found a s i m i l a r r e s u l t f o r the lower o x i d e s . They found t h a t the a b s o r p t i o n peak s h i f t e d t o h i g h e r wavelength w i t h i n c r e a s i n g O/Ti r a t i o , and r e p o r t e d a l i n e a r r e l a t i o n s h i p between the v a l u e of n i n T i 0~ . and the wavenumber. n 2n- 1 The h i g h e r energy (lower wavelength) a b s o r p t i o n maximum and l a c k of peak s h i f t i n g w i t h c o m p o s i t i o n a l changes i n amorphous f i l m s p o i n t t o a d i f f e r e n t a b s o r p t i o n mechanism. 40 'c 3 - O O c CL> Q o l_> Q. O VISIBLE 0 2 f low (SCCM): 1.0 07 0.8 1.2 Wavength (/ jm) 41 I t i s a l s o apparent from F i g . 3.12 t h a t the UV edge i s the same f o r a l l the f i l m s . The wavelength of the edge i s about 335 nm which c o r r e s p o n d s t o 3.70 eV. T h i s v a l u e i s i n good agreement w i t h o t h e r r e s e a r c h e r s [ 3 1 ] . A lower v a l u e (3.14 eV) has been found f o r p o l y c r y s t a l l i n e samples produced by s p u t t e r i n g onto heated s u b s t r a t e s [ 2 8 ] . The UV edge f o r r u t i l e s i n g l e c r y s t a l s i s a t a s t i l l lower energy of 3.05 eV [ 3 0 ] . 3. ELECTRICAL RESISTIVITY The e l e c t r i c a l r e s i s t i v i t y d a ta have a l r e a d y been p r e s e n t e d i n F i g . 3.8. I t was measured u s i n g a f o u r p o i n t probe. The major e r r o r i n the measurements was due t o u n c e r t a i n t y i n the f i l m t h i c k n e s s e s . The r e s i s t i v i t y i n c r e a s e s w i t h i n c r e a s i n g oxygen f l o w r a t e . A l s o , i t appears t h a t the r a t e of change of r e s i s t i v i t y w i t h oxygen f l o w r a t e d e c r e a s e s f o r f l o w r a t e s above about 1.0 SCCM. The measured r e s i s t i v i t y f o r a f i l m s p u t t e r e d i n pure argon was 165 nSl-cm, which i s comparable t o the l i t e r a t u r e v a l u e of 42 (ifi-cm [ 2 5 ] . The d i s c r e p a n c y c o u l d be due t o c o n t a m i n a t i o n of the f i l m by s u r f a c e a b s o r p t i o n of a i r a f t e r removal from the vacuum chamber. The maximum r e s i s t i v i t y f o r a f i l m s p u t t e r e d w i t h a m e t a l l i c t a r g e t was on the o r d e r of 1 Q-cm, which i s many o r d e r s of magnitude l e s s than the r e p o r t e d 10 7 O-cm r e p o r t e d f o r s t o i c h i o m e t r i c s p u t t e r e d T i 0 2 [ 2 4 ] . However, a study of s i n t e r e d ' s a m p l e s of v a r i o u s c o m p o s i t i o n s [33] has shown t h a t f o r O/Ti r a t i o s near 2.0 the r e s i s t i v i t y 42 changes d r a m a t i c a l l y w i t h the c o m p o s i t i o n . In t h a t study f o r example T i 0 1 > 9 9 6 was found t o have a room-temperature r e s i s t i v i t y of 0.464 fl-cm w h i l e the r e s i s t i v i t y of s i n t e r e d T i 0 2 was 1 0 1 3 O-cm. T i t a n i u m has s e v e r a l s t o i c h i o m e t r i c o x i d e s of lower O/Ti r a t i o than T i 0 2 . Thus i n s t u d i e s of s i n g l e - c r y s t a l and p o l y c r y s t a l l i n e samples the r e s i s t i v i t y does not i n c r e a s e m o n o t o n i c a l l y w i t h oxygen c o n t e n t [ 3 3 , 3 4 ] . For i n s t a n c e the r e s i s t i v i t y of c r y s t a l l i n e T i 3 0 5 i s two o r d e r s of magnitude h i g h e r than t h a t of TigO,, a t room temperature [ 3 4 ] , Gruber and K r a u t z [33] found t h a t the r e s i s t i v i t y of s i n t e r e d samples had extrema near s t o i c h i o m e t r i c c o m p o s i t i o n s . That such v a r i a t i o n s do not appear t o be e v i d e n t i n the d a t a of F i g . 3.8 i s a p p a r e n t l y a consequence of the l a c k of c r y s t a l s t r u c t u r e i n the f i l m s . F i n a l l y , the r e s i s t i v i t y d a t a a r e h e l p f u l i n e v a l u a t i n g the r e s u l t s of the o p t i c a l s t u d i e s . The o b s e r v a t i o n t h a t the v i s i b l e a b s o r p t i o n peak d i d not s h i f t w i t h oxygen f l o w r a t e might be i n t e r p r e t e d as i n d i c a t i n g t h a t the f i l m c o m p o s i t i o n was not a v e r y s e n s i t i v e f u n c t i o n of the oxygen f l o w r a t e . However, u s i n g the r e s u l t s of Gruber and K r a u t z as a f i r s t a p p r o x i m a t i o n t o the r e l a t i o n between f i l m c o m p o s i t i o n and r e s i s t i v i t y , a change i n r e s i s t i v i t y from 0.464 t o 0.046 O-crn would c o r r e s p o n d t o a change i n c o m p o s i t i o n from T i O i . 9 9 6 t o T i i o O i 9 « The r e s u l t s of P o r t e r e t a l . would then i n d i c a t e a c o r r e s p o n d i n g a b s o r p t i o n peak s h i f t of about 800 nm. Thus the r e s i s t i v i t y d a t a s u p p o r t the c o n t e n t i o n 43 t h a t the v i s i b l e a b s o r p t i o n peak p o s i t i o n does not change w i t h f i l m c o m p o s i t i o n . 4. PHOTOLUMINESCENCE Phot o l u m i n e s c e n c e (PL) i s an im p o r t a n t t o o l f o r the a n a l y s i s of s e m i c o n d u c t i n g m a t e r i a l s [ 3 5 ] . I t c o n s i s t s of d e t e c t i n g the l i g h t which i s e m i t t e d by a sample as a r e s u l t of e x c i t a t i o n by photons. The two ty p e s of photoluminescence s p e c t r o s c o p y a re e x c i t a t i o n s p e c t r o s c o p y , i n which the t o t a l i n t e n s i t y of lumines c e n c e i s measured as a f u n c t i o n of the e x c i t a t i o n w a v e l e n g t h , and e m i s s i o n s p e c t r o s c o p y , which d e t e r m i n e s the lu m i n e s c e n c e i n t e n s i t y as a f u n c t i o n of luminesc e n c e wavelength w i t h an unchanging e x c i t a t i o n spectrum. PL has been obse r v e d i n r u t i l e s i n g l e c r y s t a l s [36,37] and i n s i n g l e c r y s t a l s of reduced r u t i l e [ 3 8 ] . Deb [39] observ e d PL i n p o l y c r y s t a l l i n e f i l m s of T i 0 2 d e p o s i t e d by r f s p u t t e r i n g . I t was t h e r e f o r e d e c i d e d t o det e r m i n e whether amorphous s p u t t e r e d samples e x h i b i t e d l u m i n e s c e n c e . I t was thought t h a t PL might r e v e a l some d e t a i l s of the e l e c t r o n i c s t r u c t u r e not e v i d e n t from the o p t i c a l p r o p e r t i e s . The e x p e r i m e n t a l s e t u p was based on an e a r l i e r a p p a r a t u s used f o r e m i s s i o n s p e c t r o s c o p y of i n f r a r e d l u m i n e s c e n c e from doped s e m i c o n d u c t o r s . The b a s i c changes which were made c o n s i s t e d of u p d a t i n g the computer c o n t r o l system and add i n g a new e x c i t a t i o n s o u r c e . The o v e r a l l system i s shown i n F i g . 3.13. L i g h t from the e x c i t a t i o n 44 source E i s f o c u s s e d on the sample S which i s immersed i n a dewar of l i q u i d n i t r o g e n . E x c i t a t i o n l i g h t i s f i l t e r e d by f i l t e r s F1 t o remove l i g h t i n the wavelength range of the ex p e c t e d l u m i n e s c e n c e , and p o l a r i z e d by a c a l c i t e Glan-Thompson p r i s m p o l a r i z e r (P1) p r i o r t o s t r i k i n g the sample. Luminescence from the sample passes t h r o u g h a n o t h e r Glan-Thompson p o l a r i z e r (P2) which i s c r o s s e d w i t h r e s p e c t t o P1. In t h i s way most of the UV e x c i t a t i o n l i g h t i s p r e v e n t e d from e n t e r i n g the monochromator. A f t e r p a s s i n g t h r o u g h P2 the lumines c e n c e i s r e f l e c t e d and f o c u s s e d onto the monochromator e n t r a n c e s l i t by m i r r o r s M1 and M2. L i g h t of the wavelength s e l e c t e d by the monochromator emerges from the e x i t s l i t and i s f o c u s s e d onto the d e t e c t o r P. F i l t e r s F2 and F3 e l i m i n a t e any e x c i t a t i o n l i g h t which has passed t h r o u g h P2. The a u t o m a t i c s c a n n i n g system i s shown s c h e m a t i c a l l y i n F i g . 3.14. The method of photon c o u n t i n g was used. A p u l s e from t h e p h o t o m u l t i p l i e r i s a m p l i f i e d and sent t o the d i s c r i m i n a t o r . The d i s c r i m i n a t o r i s a d j u s t e d t o p r o v i d e the maximum s i g n a l - t o - n o i s e r a t i o . The s i g n a l s a r e p r e - c o u n t e d by a f a s t s c a l e r which sends one p u l s e f o r eve r y f o u r r e c e i v e d . T h i s i s done t o i n c r e a s e the maximum p u l s e r a t e which t h e system can h a n d l e . The photon c o u n t e r i s i n s t r u c t e d by s o f t w a r e t o count f o r a c e r t a i n p e r i o d of t i m e , a f t e r which i t s i g n a l s the i n t e r r u p t c o n t r o l l e r t h a t i t has f i n i s h e d : The i n t e r r u p t c o n t r o l l e r i n f o r m s the computer which reads the number of p u l s e s counted and 45 F i g u r e 3.13 A schematic of the apparatus used to search f o r v i s i b l e photoluminescence i n amorphous T i 0 2 . E i s the e x c i t a t i o n source, a mercury arc lamp; F1-F3 are o p t i c a l f i l t e r s ; M0-M5 are m i r r o r s ; P i and P2 are c a l c i t e Glan-Thompson prism p o l a r i z e r s ; and S i s the sample, immersed i n l i q u i d n i t r o g e n . 46 stepping motor controller monochromator NIM crate interrupt controller photon counter computer Figure 3.14 system. Computer c o n t r o l system for the photoluminescence 47 i n s t r u c t s the s t e p p i n g motor c o n t r o l l e r t o move the monochromator t o the next wavelength. When t h i s has been done the s t e p p i n g motor c o n t r o l l e r i n f o r m s the computer v i a the i n t e r r u p t c o n t r o l l e r , the computer s t a r t s the photon c o u n t e r and the p r o c e s s r e p e a t s u n t i l the scan i s f i n i s h e d . F i g . 3.15 shows the lum i n e s c e n c e s p e c t r a r e p o r t e d by Deb." They i n d i c a t e t h a t the e x c i t a t i o n was most e f f i c i e n t i n the u l t r a v i o l e t (UV) and the luminescence was v i s i b l e , c e n t e r e d a t 500 nm. The e x c i t a t i o n source used was a 100 W mercury a r c lamp. The lamp h o u s i n g (PEK 911) was f i t t e d w i t h c o l l i m a t i n g o p t i c s and a r e f l e c t o r t o maximize the l i g h t o u t p u t . Fused s i l i c a l e n s e s were used t o f o c u s the e x c i t a t i o n l i g h t t o a spot about 0.5 cm i n d i a m e t e r on the sample. C o r n i n g f i l t e r s 7-54 and 7-60 were used t o e l i m i n a t e v i s i b l e l i g h t from the e x c i t a t i o n l i g h t . The monochromator was a P e r k i n Elmer E-1 d o u b l e - p a s s monochromator. I t c o n t a i n e d a g r a t i n g b l a z e d a t 1.4 m i c r o n s w i t h a b l a z e a n g l e of 23.6°. The g r a t i n g was mounted i n the E b e r t c o n f i g u r a t i o n as shown i n F i g 3.16 w i t h the a n g l e <p e q u a l t o 6.25°. F i g . 3.17 g i v e s the c a l c u l a t e d e f f i c i e n c y of the g r a t i n g mounted i n t h i s way f o r a s i n g l e p a s s . Based on the c a l c u l a t e d g r a t i n g e f f i c i e n c y and Deb's r e s u l t s i t was n e c e s s a r y t o l o o k f o r the l u m i n e s c e n c e i n t h i r d o r d e r . Because the g r a t i n g was b l a z e d i n the i n f r a r e d (IR) i n s t e a d of .the v i s i b l e , g r e a t c a r e had t o be taken t o p r e v e n t unwanted f i r s t and second o r d e r l i g h t from r e a c h i n g 48 Wavelength ( u ) F i g u r e 3.15 E x c i t a t i o n and emission luminescence spe c t r a reported by Deb [39] f o r r f sp u t t e r e d p o l y c r y s t a l l i n e T i 0 2 . the p h o t o m u l t i p l i e r . IR l i g h t was not a problem because the p h o t o m u l t i p l i e r used (EMI 9659B with extended S-20 photocathode) was only s e n s i t i v e to a wavelength of 900 nm. Unfo r t u n a t e l y none of the Corning f i l t e r s which transmit w e l l i n the UV are completely opaque i n the near i n f r a r e d (NIR). Thus the luminescence f i l t e r s (F2 i n F i g . 3.13) had to e l i m i n a t e UV and NIR l i g h t w hile t r a n s m i t t i n g v i s i b l e l i g h t . For t h i s purpose 4-96 and 3-72 f i l t e r s were used. I t was found that the 3-72 f i l t e r luminesced at room temperature i n the v i s i b l e . Therefore i t was placed at the e x i t s l i t of the monochromator (F3 i n F i g . 3.13) instead of at the entrance s l i t . In t h i s way the i n t e r f e r e n c e due to f i l t e r luminescence would have a wavelength range corresponding to the narrow f o u r t h order Figure 3.16 The Ebert g r a t i n g c o n f i g u r a t i o n . 6 i s the g r a t i n g angle. The angle 0 i s a monochromator design parameter, which equals 6.25° for the Perkin-Elmer E-1. 50 0.0 0.5 1.0 1.5 2.0 2.5 Wavelength (nm) F i g u r e 3.17 The c a l c u l a t e d g r a t i n g e f f i c i e n c y f o r the g r a t i n g used i n the photoluminescence experiment. A plane g r a t i n g b l a z e d i n f i r s t order a t a wavelength of X i s a l s o b l a z e d i n n ^ order at X/n. The bandwidth of the response becomes narrower f o r i n c r e a s i n g o r d e r . 51 g r a t i n g e f f i c i e n c y r a t h e r than the wavelength range of the f i l t e r l u minescence i t s e l f . A l s o much of the UV l i g h t would be e l i m i n a t e d a t the e n t r a n c e s l i t by the n o n - l u m i n e s c i n g 4-96 f i l t e r . The e x c i t a t i o n s ource was surrounded by a b l a c k box t o e l i m i n a t e s t r a y v i s i b l e l i g h t and the p h o t o m u l t i p l i e r was c o o l e d t o -10°C t o e l i m i n a t e t h e r m a l n o i s e , u s i n g a h o u s i n g c o n t a i n i n g a t h e r m o e l e c t r i c r e f r i g e r a t o r ( P r o d u c t s f o r Research TE-104). The system was t e s t e d u s i n g o r d i n a r y g l a s s which l u m i n e s c e s i n the v i s i b l e w i t h UV e x c i t a t i o n . F i g . 3.18 shows the lum i n e s c e n c e i n t e n s i t y as a f u n c t i o n of time w h i l e l i q u i d n i t r o g e n was b e i n g added t o the sample dewar. The s e l e c t e d wavelength was 535 nm. As the n i t r o g e n began t o condense on the sample the i n t e n s i t y r o s e s h a r p l y . There can be no m i s t a k e t h a t t h i s s i g n a l was l u m i n e s c e n c e because the o n l y change was i n the sample t e m p e r a t u r e . Hence the system was s e n s i t i v e t o v i s i b l e l u m i n e s c e n c e . The r e s u l t s of e x p e r i m e n t s w i t h T i 0 2 samples showed no lum i n e s c e n c e i n zhe wavelength range r e p o r t e d by Deb f o r p o l y c r y s t a l l i n e samples. 2 3 Time (min.) IV. CONCLUSIONS T h i s i n v e s t i g a t i o n has shown the f i r s t e v i d e n c e t h a t the r e a c t i v e gas b a f f l e i s not a g e n e r a l l y a p p l i c a b l e s o l u t i o n t o the problem of t a r g e t o x i d a t i o n i n r e a c t i v e s p u t t e r i n g . A l t h o u g h the maximum a t t a i n a b l e oxygen p a r t i a l p r e s s u r e near the s u b s t r a t e i s i n c r e a s e d u s i n g t h i s t e c h n i q u e , the degree of f i l m o x i d a t i o n i s not c o r r e s p o n d i n g l y i n c r e a s e d . The reason f o r t h i s has not been det e r m i n e d and m e r i t s f u r t h e r s t u d y . B e s i d e s i n d i c a t i n g a l i m i t t o the a p p l i c a b i l i t y of the r e a c t i v e gas b a f f l e , t h i s r e s u l t a l s o s u g gests the importance of o t h e r f a c t o r s i n the s p u t t e r i n g environment b e s i d e s oxygen p a r t i a l p r e s s u r e which c o n t r i b u t e t o f i l m o x i d a t i o n . The f i l m s produced were amorphous and m i c r o s c o p i c a l l y smooth. The p o s i t i o n of the NIR a b s o r p t i o n which i s c h a r a c t e r i s t i c of the compounds w i t h O/Ti r a t i o s l e s s than two was found t o be a t 880 nm (1.41 eV) independent of the f i l m c o m p o s i t i o n , c o n t r a r y t o the r e s u l t s i n the l i t e r a t u r e f o r s i n g l e - c r y s t a l and p o l y c r y s t a l l i n e samples. The UV a b s o r p t i o n edge was a t 335 nm (3.70 eV), a h i g h e r energy than the r e p o r t e d edge f o r p o l y c r y s t a l l i n e or s i n g l e c r y s t a l t i t a n i u m o x i d e . The edge appeared t o be the same f o r a l l the f i l m s . E l e c t r i c a l r e s i s t i v i t y was found t o i n c r e a s e w i t h the oxygen f l o w r a t e . No l o c a l extrema i n the r e s i s t i v i t y were o b s e r v e d , as i s the case f o r s t o i c h i o m e t r i c c o m p o s i t i o n s w i t h p o l y c r y s t a l l i n e samples. 53 54 An attempt t o d e t e c t p h o t o l u m i n e s c e n c e i n amorphous T i 0 2 was u n s u c c e s s f u l , whereas s t r o n g l u m i n e s c e n c e had been r e p o r t e d f o r p o l y c r y s t a l l i n e T i 0 2 . These d i f f e r e n c e s between the p r o p e r t i e s of amorphous and c r y s t a l l i n e phases of the same m a t e r i a l a r e i l l u s t r a t i v e of the p o t e n t i a l f o r new and d i f f e r e n t m a t e r i a l s o b t a i n a b l e through c o n t r o l of s t r u c t u r e and s t o i c h i o m e t r y . R e a c t i v e s p u t t e r i n g i s a c o n v e n i e n t and r e l i a b l e method of e f f e c t i n g both t h e s e t y p e s of c o n t r o l . V. APPENDIX: CALCULATION OF BAFFLE APERTURE In o r d e r t o c a l c u l a t e the b a f f l e a p e r t u r e i t i s n e c e s s a r y f i r s t t o c a l c u l a t e the d i s t r i b u t i o n of s p u t t e r e d p a r t i c l e s i m p i n g i n g on the b a f f l e . To do t h i s c e r t a i n a ssumptions were made about the s o u r c e of the p a r t i c l e s . F i r s t , i t was assumed t h a t a l l i o n s s t r i k e the t a r g e t a t normal i n c i d e n c e , s i n c e f o r n o r m a l l y i n c i d e n t bombardment of a p o l y c r y s t a l l i n e t a r g e t i t i s w e l l known t h a t the a n g u l a r d i s t r i b u t i o n of s p u t t e r e d p a r t i c l e s i s a c o s i n e d i s t r i b u t i o n . Second, i t was n e c e s s a r y t o e s t i m a t e the r e l a t i v e s p u t t e r i n g y i e l d from the t a r g e t a t a g i v e n l o c a t i o n a t i t s s u r f a c e . The d i s t r i b u t i o n of y i e l d i s h i g h l y non-uniform f o r a magnetron s p u t t e r i n g system, s i n c e i t depends upon the d e t a i l s of the magnetic f i e l d . I t was f e l t t h a t a r e a s o n a b l e e s t i m a t e of the r e l a t i v e y i e l d was the e x p e r i m e n t a l l y observed d i s t r i b u t i o n e t c h d e pth on the t a r g e t a f t e r extended use. Because of the r a d i a l symmetry of the magnetic f i e l d , t h i s i s a f u n c t i o n of t a r g e t r a d i u s o n l y . The measured e t c h depth i s shown i n F i g . 5.1. For the purposes of t h i s c a l c u l a t i o n i t was c o n v e n i e n t t o f i t the data t o a c o n t i n u o u s f u n c t i o n . A s u i t a b l e f u n c t i o n p r o v e d t o be a m o d i f i c a t i o n of the P o i s s o n d i s t r i b u t i o n : ( a - r ) where the f i t parameters were a=4.9l4 cm; 0=1.830 cm; /u=2.150 cm; and r i s the t a r g e t r a d i u s . 55 Figure 5.1 Measured d i s t r i b u t i o n of etch depth on a t i t a n i u m t a r g e ^ a f t e r extended use. The f i t t e d curve i s o f ^ f o r ^ ^ v e T 57 F i g . 5.2 shows the geometry of the c a l c u l a t i o n . At an an g l e d from the normal t o r , the s p u t t e r e d f l u x i s p r o p o r t i o n a l t o 77 ( r f c )cos ( 6). Now c o n s i d e r t h a t the f l u x from r f c impinges on a s u r f a c e (the b a f f l e ) a d i s t a n c e d away, a t a p o i n t l o c a t e d by r g . The a n g l e & can now be s t a t e d i n terms of d, r , and r f c . To s i m p l i f y the n o t a t i o n , l e t us a l s o d e f i n e r as the d i s t a n c e from r. t o r . t s r=i/r* + r 2 - 2 r . r cosU)+d 2 Eq. 2 where <j> i s the a n g l e between r and r, . Then we have 3 s t c o s ( 0 ) = d/r - Eq. 3 We must t a k e i n t o account the f a c t t h a t the f l u x d e n s i t y d e c r e a s e s as r i n c r e a s e s , and a l s o depends on the a n g l e of i n c i d e n c e 6. As shown i n F i g . 5.3 the f l u x c o n t a i n e d i n a s o l i d a n g l e dfi w i l l be spread over an a r e a dA = dfi r 2 / c o s ( 0 ) Eq. 4 Thus the f l u x d e n s i t y a t r g due t o a p o i n t s o u r c e a t r i s p r o p o r t i o n a l to X ( \ I r, \ ^ cos (6) ' „ [ T ? ( r t ) c o s ( 0 ) J r 2 d f l Eq. 5 U s i n g eq. 2 and summing over the d i s c h a r g e r i n g , we o b t a i n the f l u x d e n s i t y d i s t r i b u t i o n 58 F i g u r e 5.2 C e 0 m e t r y c f the b a f f l e a p e r t u r e c a l c u l a t i o n (see 59 b a ? n e \ 5 A n 3 a?ea S mdA^r th^ba^?U tsubtenIr e m i ^ / l u x .towards the depends on the t a r g e t - t o - b a f f i f r^J* a S o 1 ^ a n 9 l e d R w h i^h i n c i d e n c e 6. t a r 9 e t to b a f f l e d i s t a n c e and the angle of 60 1 d 2 f ( r s ) = - / d r t / r t d 0 T j ( r f c ) Eq. 6 where C i s a c o n s t a n t . We may n o r m a l i z e t h i s by i n s i s t i n g t h a t £ / d r s f ( r s ) = 1 Eq. 7 from which we o b t a i n the n o r m a l i z a t i o n c o n s t a n t C. Now the p o r t i o n of the f l u x which passes t h r o u g h a h o l e i n the b a f f l e i s j u s t the f l u x d e n s i t y m u l t i p l i e d by the a r e a of the h o l e . However one must keep i n mind t h a t the apparent a r e a of a c i r c u l a r h o l e depends upon the a n g l e of i n c i d e n c e and the t h i c k n e s s of the b a f f l e p l a t e . As shown i n F i g . 5.4 t h i s a pparent a r e a i s the a r e a of o v e r l a p between two i d e n t i c a l e l l i p s e s . The semimajor of each e l l i p s e i s the h o l e r a d i u s R, w h i l e the semiminor i s R c o s ( 0 ) . The o v e r l a p d i s t a n c e i s d o = t s i n ( 0 ) where t i s the p l a t e t h i c k n e s s . The r a t i o of apparent a r e a t o a c t u a l a r e a i s c°l{9) [Tt-x(d,a)-sin(x(e,a)] e<a H{6,a)= <{ Eq. 8 D 0>a where x(^,a) = 2 s i n ~ 1 ( t a n ( 6 ) / t a n ( a ) ) , a b e i n g the a n g u l a r a c c e p t a n c e as d e f i n e d i n F i g . 2.5. Then the f l u x t h r o u g h a h o l e of u n i t a r e a nt a r a d i u s of r g i s 61 Rcos(0) a F i g u r e 5.4 A. Appearance of a hole at non-normal inc i d e n c e showing that the apparent area depends on the angle of i n c i d e n c e and the apparent p l a t e t h i c k n e s s d 0 . B. A c r o s s s e c t i o n of a b a f f l e hole showing the r e l a t i o n of apparent hole r a d i u s and apparent p l a t e t h i c k n e s s d 0 t o the angle of i n c i d e n c e 6. The t r u e p l a t e t h i c k n e s s i s t . 62 F ( r s ) = £ / d r t /r td0 ^„ TJ( r f c ) H ( r f c , r g , d , a) Eq. 9 and the b a f f l e a p e r t u r e i s s i m p l y B.A. = L F ( r s ) i r R 2 Eq. 10 h o l e s In o r d e r t o c a l c u l a t e F ( p g / t h e i n t e g r a t i o n was performed n u m e r i c a l l y . The a n g u l a r s t e p s i z e was one degree, and the r a d i a l s t e p s i z e was 1 mm. In n o r m a l i z i n g the f l u x d e n s i t y , the s t e p s i z e of r g was 2 mm, and the summation was c a r r i e d t o a 40 cm r a d i u s . Because of the importance of the f l u x d i s t r i b u t i o n a t the b a f f l e i n d e t e r m i n i n g the b a f f l e a p e r t u r e , i t was n e c e s s a r y t o d e t e r m i n e i f the d i s t r i b u t i o n would be s i g n i f i c a n t l y changed by 1) a change i n the a n g u l a r acceptance of the b a f f l e , or 2) a change i n the w i d t h of the d i s c h a r g e r i n g . F i g . 5.5 shows the s p u t t e r e d f l u x d i s t r i b u t i o n a t a b a f f l e d i s t a n c e of 4.5 cm w i t h changes i n these two p a r a m e t e r s . R e c a l c u l a t i o n of the b a f f l e a p e r t u r e showed t h a t the change i n the f l u x d i s t r i b u t i o n s shown i n the f i g u r e had an i n s i g n i f i c a n t e f f e c t on the c a l c u l a t e d v a l u e of the b a f f l e a p e r t u r e . 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Baf f le Radius ( c m ) Baf f le Radius ( c m ) F i g u r e 5.5 C a l c u l a t e d f l u x d e n s i t y d i s t r i b u t i o n s . A. Dependence on d i s c h a r g e r i n g w i d t h : Curve (a) i s f o r a d i s c h a r g e r i n g 1 mm wide c e n t e r e d a t a t a r g e t r a d i u s of 2.9 cm. Curve (b) i s f o r a d i s c h a r g e r i n g e x t e n d i n g from a r a d i u s of 1.0 cm t o a r a d i u s of 4.25 cm. B. Dependence on a n g l e of acc e p t a n c e a. REFERENCES 1. R. Rosenberg, Tung-Sheng Kuan, and H.J. H o v e l , P h y s i c s Today 33(5), 40 (1980) 2. H e l l m u t F r i t s c h e , P h y s i c s Today 37 2 (1984) 3. S.R. E l l i o t , P h y s i c s of Amorphous M a t e r i a l s (Longman, New York, 1984) p.9 4. J . A f f i n i t o , N. F o r t i e r , and R.R. P a r s o n s , J . Vac. S c i . T e c h n o l . A 2 ( 2 ) , 316 (1984) 5. S. S c h i l l e r , U. H e i s i g , K. S t e i n f e l d e r , J . S t r u m p f e l , and W. S i e b e r , Vak. Tech. 30, 3 (1981) 6. S. Maniv, C. M i n e r , and W.D. Westwood, J . Vac. S c i . T e c h n o l . j_8, 195 (1981 ) 7. M.J. B r e t t , R.W. McMahon, J . A f f i n i t o and R.R. P a r s o n s , J . Vac. S c i . T e c h n o l . A.1(2), 372 (1983) 8. B. B a b u j i , C. Balasubramanian, and M. R a d h a k r i s h n a n , J . Non- C r y s t . S o l i d s 55, 405 (1983) 9. M. T a k e u c h i , T. I t o h , and H. Nagasaka, T h i n S o l i d F i l m s 51, 83 (1977) 10. D.C. Cronemeyer, Phys. Rev. 8 7 ( 5 ) , 876 (1952) 11. L.A. H a r r i s , J . E l e c t r o c h e m . Soc. 127(12), 2657 (1980) 12. A.A. Soliman and H.J.J. S e g u i n , S o l . Energy. Mat. 5, 95 (1981) 13. R.W. McMahon, M a s t e r s T h e s i s , U n i v e r s i t y of B r i t i s h C o l umbia, (1982) 14. A.R. N y a i e s h and L. H o l l a n d , J . Vac. S c i . T e c h n o l . 2 0 ( 4 ) , 1389 (1982) 15. A. M u l l e r and A. Benninghoven, S u r f a c e S c i e n c e H , 493 (1974) 16. L. H o l l a n d , T h i n S o l i d F i l m s 86, 227 (1981) 17. John A f f i n i t o , PhD T h e s i s , U n i v e r s i t y of B r i t i s h C o l u m b i a , (1984) 18. S. S c h i l l e r , U. H e i s i g , K. S t e i n f e l d e r and J . S t r u m p f e l , T h i n S o l i d F i l m s 63, 369 (1979) 19. J . F e r r o n , E.V. A l o n s o , R.A. B a r a g i o l a and A. O l i v i a - F l o r i o , S u r f a c e S c i e n c e 120, 427 (1982) 64 65 2 0 . K. Kandasamy and N.A. S u r p l i c e , J . Phys C: S o l i d S t . Phys. 21, 6 8 9 ( 1 9 8 0 ) 2 1 . L. M a i s s e l i n Handbook of T h i n F i l m Technology e d i t e d by L. M a i s s e l and R. G l a n g , ( M c G r a w - H i l l , New York, 1 9 7 0 ) p. 4 - 1 S 2 2 . M.J. D r u y v e s t e y n and F.M. Pe n n i n g , Rev. Mod. Phys. 1 2 , 8 7 ( 1 9 4 0 ) 2 3 . R.G. B r e c k e n r i d g e and W.R. H o s i e r , Phys. Rev. 9 J _ ( 4 ) , 7 9 3 ( 1 9 5 3 ) 2 4 . M. T a k e u c h i , Phys. S t a t . S o l . ( a ) 5 5 , 6 5 3 ( 1 9 7 9 ) 2 5 . CRC Handbook of C h e m i s t r y and P h y s i c s e d i t e d by R.C. Weast, (CRC P r e s s , Boca Raton, 1 9 8 0 ) p. F-1 7 3 2 6 . S. S c h i l l e r , G. B e i s t e r , W. S e i b e r , G. S c h i r m e r and E. Hacker, T h i n S o l i d F i l m s 8 3 , 2 3 9 ( 1 9 8 1 ) 2 7 . M. T a k e u c h i , T. I t o h and H. Nagasaka, T h i n S o l i d F i l m s 5 1 . , 8 3 ( 1 9 7 7 ) 2 8 . A.A. Soliman and H.J.J. S e g u i n , T h i n S o l i d F i l m s 1 0 0 , 33 ( 1 9 8 3 ) 2 9 . S. S c h i l l e r , G. B e i s t e r , S. S c h n e i d e r and W. S e i b e r , T h i n S o l i d F i l m s 7 2 , 4 7 5 ( 1 9 8 0 ) 3 0 . K . S a k a t a , Phys. S t a t . S o l . ( b ) J J _ 6 , 1 4 5 ( 1 9 8 3 ) 3 1 . K.G. Geraghty and L.F. Donaghey, T h i n S o l i d F i l m s 4J3 3 7 5 ( 1 9 7 7 ) 3 2 . V.R. P o r t e r , W.B. White and R. Roy, J . S o l . S t . Chem. 4 , 2 5 0 ( 1 9 7 2 ) 3 3 . H. Gruber and E. K r a u t z , Phys. S t a t . S o l . ( a ) 69, 2 8 7 ( 1 9 8 2 ) 3 4 . R.F. Bartholomew and D.R. F r a n k l , Phys. Rev. 187(3), 8 2 8 ( 1 9 6 9 ) 3 5 . K.K. Sm i t h , T h i n S o l i d F i l m s 84, 1 7 1 ( 1 9 8 1 ) 3 6 . A.K. Ghosh, F.G. Wakiin and R.R. A d d i s s , J r . , Phys. Rev. 1 8 4 ( 3 ) , 9 7 9 ( 1 9 6 9 ) 3 7 . G.A. Royce and R.B. Kay, A p p l i e d O p t i c s 2 J 3 ( 1 2 ) , 1 9 7 5 ( 1 9 8 4 ) 3 8 . Y. Nakato, A. Tsumura and H. Tsubomura, Chem. Phys. L e t t . 8 5 ( 4 ) , 3 8 7 ( 1 9 8 2 ) 66 39. S.K. Deb, S o l i d S t . Comm. 11, 713 (1972) 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0085283/manifest

Comment

Related Items