Real-time spectroscopic ellipsometry studies of the nucleation and grain growth processes in microcrystalline silicon thin films

Real-time spectroscopic ellipsometry (SE) has been applied to investigate the nucleation and grain growth processes in microcrystalline silicon (μc-Si:H) thin films deposited by a conventional plasma-enhanced chemical vapor deposition using hydrogen dilution of silane source gas. Real-time SE results revealed the μc-Si:H nucleation from hydrogenated amorphous silicon (a-Si:H) phase, followed by the coalescence of isolated μc-Si:H grains exposed on growing surfaces. In the μc-Si:H grain growth process, the μc-Si:H shows an enhanced surface roughening. The onset of the μc-Si:H grain growth and the coalescence of μc-Si:H grains were readily characterized by monitoring surface roughness evolution. We found that a μc-Si:H nuclei density increases significantly as the hydrogen dilution ratio R=([H₂]/[SiH₄]) increases. In contrast, a film thickness at which most of the surface is covered with the μc-Si:H, gradually reduces with increasing R. The real-time SE results described above showed remarkable agreement with those estimated by transmission electron microscopy and atomic force microscopy. For the a-Si:H/μc-Si:H mixed-phase surface formed during the phase transition, however, the SE results showed relatively large errors in the analyses. Such difficulties in the real-time SE analysis for the μc-Si:H thin film are discussed.