EXSITU AND INSITU ELLIPSOMETRIC STUDIES OF THE THERMAL OXIDE ON INP

The thermally grown InP oxide as etched by an aqueous dilute HF solution has been studied by ellipsometric techniques. The ex situ measurement reveals a two-layer structure for the oxide grown at 440-degrees-C. The refractive indexes for both oxide layers have been determined using a two-layer optical model. The etching process has also been monitored ellipsometrically in the actual etching environment, in situ. A fused silica cell, which enables the windows to be aligned properly, has been specifically designed for the in situ solution measurement. A liquid layer at the solution-oxide interface has been identified, and the layer is shown to contain P and In species resulting from the etching reactions. A theory based on the Lorentz-Lorenz relation results in a reasonable qualitative description of the liquid layer. During the etching of the oxide the liquid layer shrinks at a linear rate, and after removal of the outer oxide layer the liquid layer forms a dense electric double layer.