Initial Nucleation of Photo-CVD Amorphous Silicon by Photodecomposition of Disilane

Abstract

Nucleation of photo-CVD amorphous silicon (a-Si) from disilane on Si0₂ substrate was studied by using an Xe pulse tube as the light source. Detection of small Si nuclei was done rthrough chemical pre-amplification to colloidal silver, followed by examination with TEM. Clearly definite saturation was found in the relationships between Si necleus density and total number of light pulses, suggestive of island type growth and the contribution of surface diffusion of active radical species. The initial nucleation rate was found to increase with substrate temperature at least between 150 and 250°C, which may reflect the characteristic of the photo-CVD nucleation. When the pulse interruption period was varied from 20 ms to the order of seconds for a total of 2000 pulses, the Si nucleus density remained constant till a certain critical period which depended on substrate temperature and then decreased rapidly. This unique phenomenon was discussed from a kinetic point of view.