Oxidation and etching of hydrogenated amorphous silicon; An in situ ellipsometry study

Abstract

The effect of several oxidation and etching cycles on the surface structure of high quality a-Si : H is explored. Single wavelength ellipsometry measurements are used as a probe to monitor the HNO 3-forced oxidation and HF etching cycles. Spectroscopic ellipsometry experiments are performed on the films both before and after several such cycles to determine the overall microstructural changes. The results show that, for a-Si : H of low density (number of Si-Si bonds per volume), cycling causes a significant decrease in the density of sub-surface material. As demonstrated in previous work, this indicates preferential oxidation and etching along microstructural columns which may be present and extend into the bulk of the material. In contrast, however, high density a-Si : H exhibits much better cycling reversability, indicating that oxidation and etching proceed nearly uniformly, consuming Si atoms layer by layer. This, in turn, suggests a uniform microstructure for these samples to very small scales.