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

摘要

The roughness evolutions of micro-crystalline silicon thin films (mu c-Si:H) with different growth rates prepared by chemical vapor depositions have been investigated by atomic force microscopy. The growth exponent beta was measured as 0.8 +/- 0.03, 1.1 +/- 0.07 and 0.75 +/- 0.02 for three sets of samples prepared by PECVD with and without hydrogen dilution ratio modulation and by HWCVD, respectively, and does not correlated with the deposition rate in a set. However, the root-mean-square roughness and lateral correlation length decrease with increasing the deposition rate for both PECVD and HWCVD process. We suggested that the nonstationary growth with large beta is correlated with the shadowing effect. The influence of the deposition rate on the surface roughness could be related to the diminishing of the shadowing effect by surface species diffusion with higher mobility on an H-covered surface. The initial surface and nucleation condition play an important role in the surface roughness evolution.