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

Abstract

Real-time spectroscopic ellipsometry (SE) has been applied to investigate the nucleation and grain growth processes in microcrystalline silicon $(\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H})$ thin films deposited by a conventional plasma-enhanced chemical vapor deposition using hydrogen dilution of silane source gas. Real-time SE results revealed the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ nucleation from hydrogenated amorphous silicon $(a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H})$ phase, followed by the coalescence of isolated $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grains exposed on growing surfaces. In the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grain growth process, the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ shows an enhanced surface roughening. The onset of the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grain growth and the coalescence of $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grains were readily characterized by monitoring surface roughness evolution. We found that a $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ nuclei density increases significantly as the hydrogen dilution ratio $R=([{\mathrm{H}}_{2}]/[{\mathrm{SiH}}_{4}])$ increases. In contrast, a film thickness at which most of the surface is covered with the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H},$ 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 $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}/\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ 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 $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ thin film are discussed.