Investigation of the Surface Morphology of a-Si:H by Atomic Force Microscopy and In-Situ Ellipsometry

Abstract

Combining real-time ellipsometry and atomic force microscopy (AFM) the growth of hydrogenated amorphous silicon (a-Si:H), deposited on crystalline silicon wafers with a native oxide layer on top and on fused silica from a dc glow discharge, has been studied from initial nucleation to the final morphology. By in-situ ellipsometry we detected the evolution of morphology changes. The surface structure has been determined by AFM in the nucleation phase and in the subsequent growth stage. During nucleation on crystalline silicon only few (about 40 per 1μm) flat islands of a-Si:H (up to 4 nm high and up to 50 nm in diameter) grow with a strongly enhanced rate compared to bulk deposition. Once the crystalline surface has completely been covered by a-Si:H, the fast deposition of these islands stops and further surface structures, comparable with the initial ones, start to grow gradually until a homogeneous final roughness up to 5nm high is formed. Nucleation of a-Si:H on fused silica yields densely distributed nuclei (up to 1.5 nm high and up to 25 nm in diameter), indicating a shorter surface diffusion length on this substrate compared to the growth on silicon wafers. The ongoing film deposition, however, finally results in a morphology comparable to the one of a-Si:H grown on crystalline silicon. Using hydrogen dilution we found that the final roughness is affected by the dilution ratio; furthermore infrared spectroscopy reveals the surface structure to be correlated with the hydrogen content of the a-Si:H films.

Explanation of the limiting thickness observed in low-temperature silicon epitaxy

“…These transitions have been studied by a variety of authors. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Aspects of our more detailed analysis 15 apply to many of these phase transitions. In this letter, we explain the temperature and growthrate dependence of the limiting-thickness observed in lowtemperature epitaxial Si growth 1,2,[8][9][10][11][12]14 based on the supersaturation of the growing layer with diffusing hydrogen.…”

High silicon etch rates by hot filament generated atomic hydrogen

“…In order to get a deeper insight into the details of the etch processes, we performed in situ ellipsometry studies in conjunction with atomic force microscopy (AFM), which serves to fix the morphology parameters that enter the ellipsometry data interpretation [18]. Hot wire etching of a-Si:H at standard conditions causes a blue shift of the spectroscopic ellipsometry data during the first 5 s (figure 2).…”