Contributions of Silicon-Hydride Radicals to Hydrogenated Amorphous Silicon Film Formation in Windowless Photochemical Vapor Deposition System

Abstract

Hydrogenated amorphous silicon (a-Si:H) films are prepared using a windowless photochemical vapor deposition system. Vacuum ultraviolet light of 121.6 nm from hydrogen-helium mixture plasma is thought to decompose silane molecules into mainly SiH and SiH2 radicals. Contributions of these radicals to film growth result in growth rate dependence upon substrate temperature (T s). The apparent sticking probability of both radicals is determined to be 0.84 at T s=100° C and 0.68 at T s=250° C, from the variation of step coverage as a function of T s. Adjusting the substrate position close to the light source brings about an increase of incident SiH and SiH2 radicals through primary photolysis by 121.6 nm light, as well as decrease of gas-phase reactions, which allows us to control the Si–H2 bond density in the film. The effect of the Si–H2 bond in the film is also shown.

Surface Reaction Probabilities of Silicon Hydride Radicals in SiH4/H2 Thermal Chemical Vapor Deposition

“…In the literature, the reactive sticking coefficients of radicals are estimated between 1.0 and 0.1. − Our correlated RSC rd values are near the sticking coefficients of SiH and SiH 2 , reported by Sawado et al, lower than that of SiH reported by Ho, Breiland, and Buss . Our result of extrapolated unity RSC rd at pristine Si surface is consistent with the simulation result of Ramalingam et al on SiH and SiH 3 interaction with bare Si atom.…”

“…Ho, Breiland, and Buss 16 estimated that 94% of SiH in a molecular beam was incorporated in colliding with an amorphous Si:H surface. Sawado et al 17 estimated the apparent sticking coefficients of SiH and SiH 2 radicals on hydrogenated amorphous Si surface to be 0.84 (373 K) and 0.68 (523 K). Tachibana 18 assumed the sticking coefficient of SiH 3 to be 0.2 and those of SiH 2 , SiH, and Si to be 1.0 while simulating the their concentrations in silane RF plasma.…”

Silylenes

“…SiH 2 is also believed to contribute to film growth when vacuum ultraviolet radiation is employed to decompose silane, thus avoiding both high temperatures and plasma damage 388 . These conditions produce SiH, SiH 2 and H atoms as primary dissociation products in unknown ratios 388 .…”

“…These conditions produce SiH, SiH 2 and H atoms as primary dissociation products in unknown ratios 388 .…”