Charge-related deposition phenomena in silicon CVD

Abstract

This thesis consists of three major parts; ``the effect of gas phase reaction on the roughness of silicon films in HF-CVD``, ``morphological evolution of silicon films induced by charges in CVD``, and ``new approach to SSD and SENTAXY in CVD``. All of them are closely related to ``charge-related deposition phenomena in silicon CVD``. Chapter III dealt with ``the effect of gas phase reaction on the roughness of silicon films in HF-CVD``, where the charges were introduced by the thermoemission effect of the hot-filament. For the $SiH_4-HCl-H_2$ system, combinations of the amount of the electron emission and the supersaturation ratio affected the deposition rate, the current, and finally the roughness of silicon film in a different way. Currents of 0.2 ~ 5 μwere measured in the hot filament CVD chamber for deposition of silicon. In such a highly ionizing atmosphere with the appreciable supersaturation for precipitation of silicon, it is highly probable that the charged clusters should be formed in the gas phase by ion-induced or photo-induced nucleation. The predicted nanometer silicon clusters were observed by TEM on a carbon membrane, which was placed in the hot-filament CVD chamber. The clusters for the filament temperatures of 1800℃ and 1600℃ were ~ 2 nm and 5 ~ 7 nm, respectively. Moreover, there was a linear relationship between the cluster sizes and the RMS roughness. These results, which could be explained by classical nucleation theory and Coulomb repulsion effect, leads to the following conclusion: higher electron emission enhances the gas phase nucleation with the help of the ionization process, but it prevents the charged clusters from growing to the large size, so smoother film can be deposited. Furthermore, at the constant electron emission, the gas phase with higher supersaturation ratio has lower nucleation energy barrier, and makes many small charged clusters by the ion-induced heterogeneous nucleation, thus producing smoother surface. From the ...