In Situ Measurement and Analysis of Plasma-Grown GaAs Oxides with Spectroscopic Ellipsometry

A versatile ellipsometer with variable energy (1.5-5.6 eV) and angle of incidence (60°-75°) has been constructed for in situ thin film diagnostics on a linear plasma reactor. This instrument has been used to study the plasma oxidation of GaAs (100) surfaces. During oxidation the ellipsometer is set at a fixed wavelength and a fixed angle of incidence for monitoring the thickness of the oxide. Such information as the rate of oxidation, transient effects, uniformity, and optical absorption of the oxide layer are obtained during plasma processing. The oxidation process can be interrupted at any moment for examining the sample as a function of energy and angle of incidence. A multilayer analysis is presented to determine (i) the dielectric function and the thickness of the oxide layer, and (ii) the composition and the thickness of the interface region between the oxide and the GaAs substrate. The effect of the rate of plasma oxidation on the oxide properties is also discussed.