Simple theory of steam oxidation of AlAs

Kinetics of AlAs steam oxidation process is investigated theoretically in cylindrically symmetric mesa structures. Under the assumption of a steady-state process, compact analytical formulae are obtained for time evolution of the oxidation front and for the oxidation rate. Values of main oxidation process parameters are extracted from existing experimental data for T = 350 °C and the layer thickness d = 250 nm. The oxidation rate is found to first decrease from its initial value of B/A and remain almost constant for a large range of intermediate sizes of unoxidized region. When the unoxidized region becomes very small, a rapid increase in this rate up to the value of B/[A(1-β)] is predicted. This renders the process control of fabricating miniature oxide apertures with diameters < 2 μm extremely difficult. Comparison with 1D model of oxidation process in cartesian geometry reveals significant differences in time evolution of the oxidation front. Understanding these differences is important for achieving a good control of the oxidation process in cylindrical structures.

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