Recent understanding of the growth process of amorphous silicon from a silane glow-discharge plasma

Abstract

The film growth process of hydrogenated amorphous silicon (a-Si:H) from a monosilane glow-discharge plasma as been investigated as a representative case of thin film growth from a glow-discharge plasma. On the basis of our understanding of the gas phase as well as surface-reaction processes obtained from the results of a variety of process diagnoses such as infrared laser-absorption spectroscopy and infrared reflection - absorption spectroscopy, a reaction model explaining the determination step of defect density in the resulting a-Si:H has been proposed. The defect (dangling bond) density of a-Si:H has been controlled through the surface-diffusion length of silyl radicals produced in the monosilane plasma. This allows us to obtain low defect density a-Si:H having a range of optical band gaps and to avoid the use of alloying with elements other than hydrogen. At high temperature, precursor assisted defect suppression (PADS) produces a low band gap and defect density. At low temperature, heating of precursors in the gas phase allows defect reduction by energized precursors (DREP) to attain lower defect density. Furthermore, the electron and hole mobilities in the resulting a-Si:H have been controlled by making use of the kinetic energy of ionic species impinging on the film-growing surface from the plasma.