Surface evolution during crystalline silicon film growth by low-temperature hot-wire chemical vapor deposition on silicon substrates

Abstract

We investigate the low-temperature growth of crystalline thin silicon films: epitaxial, twinned, and polycrystalline, by hot-wire chemical vapor deposition ͑HWCVD͒. Using Raman spectroscopy, spectroscopic ellipsometry, and atomic force microscopy, we find the relationship between surface roughness evolution and ͑i͒ the substrate temperature ͑230-350°C͒ and ͑ii͒ the hydrogen dilution ratio ͑H 2 / SiH 4 =0-480͒. The absolute silicon film thickness for fully crystalline films is found to be the most important parameter in determining surface roughness, hydrogen being the second most important. Higher hydrogen dilution increases the surface roughness as expected. However, surface roughness increases with increasing substrate-temperature, in contrast to previous studies of crystalline Si growth. We suggest that the temperature-dependent roughness evolution is due to the role of hydrogen during the HWCVD process, which in this high hydrogen dilution regime allows for epitaxial growth on the rms roughest films through a kinetic growth regime of shadow-dominated etch and desorption and redeposition of growth species.

The comparisons of growth mechanisms for Si thin films with different deposition rates in CVD process by the description of the roughness evolution

“…Hydrogen plays a critical role in crystallization of Si films by breaking the weak bonds and removing unstable adatoms. The above behaviors were suggested to be the shadow effect by Richardson et al [6], i.e. those atoms with lower bond energy on the mountains will be preferentially etched by hydrogen than those in the valleys.…”

“…Previously, some results on the evolution roughness of amorphous Si (a-Si) film with substrate temperature [1,5] and thickness etc. [2,6] of a-Si film can be well described by the KPZ model. For the lc-Si:H films, the growth process is more complicated than that of a-Si and is strongly dependent on the deposition process and substrate types.…”

Kinetic roughening and mound surface growth in microcrystalline silicon thin films

“…Many publications discussed the columnar growth and micro-voids in μc-Si:H films [12,13], which are correlated with the mounded surface growth. The simulation results from Yu and Amar [14] indicate that for the film deposited with a cosine distribution incident flux, the surface of film becomes ''rougher'' and more ''open'' in structure, in particular, presences of many ''valleys'' and ''fjords'' with different sizes which is explained by the shadowing effect.…”

Surface Evolution During Low Temperature Epitaxial Silicon Growth by Hot-Wire Chemical Vapor Deposition: Structural and Electronic Properties

“…This hydrogen etching effect increases the roughness of the films, but allows for the evolution of an epitaxial film to remain. [17] …”