UBC Theses and Dissertations
Reactions of the (100) face of gallium arsenide with atomic and molecular chlorine Ha, Jae Hee
Reactions of the (100) face of a gallium arsenide single crystal with atomic and molecular chlorine were studied in the temperature range from 25 to 160°C. Small chips cut from 3 inch undoped gallium arsenide wafers were mounted on a silicon heat sink and etched in a Pyrex reaction tube. The etch rate was monitored by laser interferometry, surface profilometry, and mass spectrometry which was also used to detect the etch product. For atom etching, chlorine atoms were produced by a 2450 MHz microwave discharge in Cl₂. The chlorine atom pressure was measured by titration with nitrosyl chloride. The etching by molecular chlorine was found to be first order in Cl₂ at low pressures. An activation enthalpy of 24.0( ± 2.8) kcal and a pre-exponential factor of 5.8x10[sup(13±1)] μm min⁻¹ Torr⁻¹, were measured for this low pressure reaction. At pressures above 15.0 Torr the reaction was found to reach a limiting rate with an activation enthalpy of 13.7 ( ± 1.6) kcal and a pre-exponential factor of 7.9x10[sup(7 ± 0.5) (μm min⁻¹. A mechanism is proposed in which the first step is dissociative adsorption of Cl₂ on the GaAs surface and this is followed by a reaction of the adsorbed atoms to form volatile products. The reaction with chlorine atoms showed a first order dependence on the partial pressure of Cl atoms and an activation enthalpy and pre-exponential factor of 9.0 ( ± 1.2) kcal and 8.7x10[sup(6 ± 0.70)] μm min⁻¹ Torr⁻¹, respectively. The etching of GaAs(100) both in atomic and molecular chlorine displayed crystallographic effects under the experimental conditions studied. A mesa with inward sloping planes and a mesa with outward sloping planes were obtained for both the atomic and molecular processes.
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