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Evolution of surface texture in thermal chlorine etching and molecular beam epitaxy of gallium arsenide

University of British Columbia

Many fabrication processes for semiconductor nanostructures rely on the understanding of surface pattern evolution during crystal growth and etching. In this thesis, the morphological evolution of GaAs surfaces during thermal chlorine etching and molecular beam epitaxial growth is investigated by atomic force microscopy and light scattering. The experimental results are compared to numerical simulations based on continuum models. For both etching and growth, the evolution of flat surfaces and small amplitude (<30 nm) random surface patterns can be modeled with excellent accuracy with stochastic differential equations for the surface height as predicted by kinetic roughening theory. For MBE growth this equation is the Kardar- Parisi-Zhang (KPZ) equation while etching requires the extension of the KPZ model with a fourth-order linear term. Anisotropic etch rates with respect to crystal orientation are found to be a major consideration for surface pattern transfer by thermal chlorine etching. It is shown how pattern transfer of one-and two-dimensional gratings can be predicted and optimized by varying the orientation of the pattern and by the use of a directional molecular beam to supply the chlorine. To describe the complex shapes evolving from etching and growth on microfabricated gratings, models based on two coupled differential equations for the surface concentration of etchant or adatoms and the surface height are developed. Excellent fits to the experimental shapes observed over a wide range of etching and growth conditions can be obtained with these models and they emerge as a powerful tool to understand the pattern evolution in terms of the underlying microscopic physics such as surface diffusion, spatial flux inhomogeneity, sticking coefficients, step edge incorporation and diffusion bias.

Thesis/Dissertation

application/pdf

2009-12-02

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http://hdl.handle.net/2429/16138

Physics

University of British Columbia

UBCV

DSpace