Deposition of Pure Hydrogenated Amorphous Silicon by Plasma-Enhanced Chemical Vapor Deposition for Polycrystalline Silicon Thin Film Transistors

摘要

A high-purity hydrogenated amorphous silicon film has been successfully deposited using an advanced plasma-enhanced chemical vapor deposition system that is available for mass-production use. Oxygen and carbon concentrations in the film were as low as 1.3 x 10~(17) and 2.6 x 10~(16) atoms/cm~3, respectively, i.e., about hundredth part of the typical values achieved using a recent large-area deposition system and as low as those in CZ-Si wafers. The film was characterized as a function of SiH_4 gas flow rate and outgas rate from the reaction chamber, and the results suggest that oxygen and carbon in the film comes predominantly from H_2O and CO_2 out-gassing from the chamber wall, respectively.