Fabrication of Polycrystalline Silicon Films from SiF 4 /H 2 /SiH 4 Gas Mixture Using Very High Frequency Plasma Enhanced Chemical Vapor Deposition with In Situ Plasma Diagnostics and Their Structural Properties

Polycrystalline silicon ( poly -Si) films were fabricated by very high frequency (VHF) plasma enhanced (PE) chemical vapor deposition (CVD) from SiF 4 and H 2 gas mixture with small amounts of SiH 4 . Reactions and growth of poly -Si in the SiF 4 /H 2 /SiH 4 system were discussed together with the results obtained from in situ plasma diagnostics, and compared with those obtained by microwave PECVD (MW CVD). As a result, similar relationships among growth temperature, SiF 4 /H 2 gas flow ratio and film structure to those obtained with MW CVD were obtained with VHF CVD. For example, growth temperature could be reduced to 100°C while keeping a high crystal fraction (>80%) when small SiF 4 /H 2 gas flow ratios were used. In contrast, under large SiF 4 /H 2 gas flow ratios, crystal fraction rapidly decreased with decreasing temperature. The role of fluorine-related species in the growth of poly -Si was examined in relation to film microstructure and the results obtained from plasma diagnostics. Finally, guiding principles to achieve high rate and/or low-temperature growth of poly -Si by VHF CVD using SiF 4 /H 2 gas mixtures were discussed.