In situ studies of the amorphous to microcrystalline transition of hot-wire chemical vapor deposition Si:H films using real-time spectroscopic ellipsometry

Abstract

In situ real-time spectroscopic ellipsometry (RTSE) provides detailed information on the evolution of the structural and optical properties of Si:H films during growth [Collins et al., Appl. Surf. Sci. 154-155, 217 (2000)]. We have used in situ RTSE to characterize the morphology and crystallinity of hot-wire chemical vapor deposition (HWCVD) Si:H films grown on native-oxide covered crystal silicon substrates as a function of substrate temperature Ts, hydrogen dilution R=[H2/SiH4], and film thickness db. Transitions from one mode of film growth to another are correlated with abrupt changes in the magnitude of the surface roughness during film growth. The degree of crystallinity of the film can be determined from the shape of the dielectric spectrum. We have studied the growth parameter space consisting of R from 0 to 14, Ts of 250 and 500 °C, and db from 0 to 1 μm. We have mapped out the crystallinity versus R, Ts, and db based on our analysis of the RTSE data. The transition between a-Si:H and μc-Si:H for growth on crystalline silicon substrates is near the R=3 to R=4 dividing line and is also a strong function of film thickness. Initial coalescence of purely μc-Si:H material does not occur until R⩾10. These results have been corroborated using Raman scattering and atomic force microscopy to characterize the crystallinity and surface morphology of the films.