Elementary processes of surface reaction in amorphous silicon film growth

Abstract

Surface reactions contributing to a-Si:H film growth both in thermal and in plasma chemical vapor deposition (CVD) were investigated by ab initio molecular orbital calculations. The conclusions obtained are as follows: (i) The primary activation process of a-Si:H growing surface is the silylene structure formation by hydrogen elimination. (ii) At low temperature, the subsequent reaction on the growing surface is the hydrogen migration from the adjacent SiH 2 group to the silylene structure and then the disilene structure is produced. Silyl radicals prepared in plasma reactors stick themselves to the disilene structures and contribute to a-Si:H film growth. (iii) At high temperature, rows of silylene radicals are produced on the growing surface. The silylene structures in the rows have a life time long enough to react with silane molecules in the CVD reactor. This reaction contributes to a-Si:H film growth in the thermal CVD. (iv) The conclusions (ii) and (iii) are the reason that higher surface temperature is required for a-Si:H film growth in the thermal CVD than in the plasma CVD.