APPLICATION OF HIGH-INTENSITY VACUUM-ULTRAVIOLET LIGHT FOR AMORPHOUS-SILICON FILM FABRICATION USING A WINDOWLESS PHOTOCHEMICAL VAPOR-DEPOSITION SYSTEM

Windowless photochemical vapor deposition (photo-CVD) system for hydrogenated amorphous silicon (a-Si:H) film fabrication has been established. Vacuum ultraviolet (VUV) light with a wavelength of 121.6 nm (a Rydberg transition of the hydrogen atom) was obtained using microwave discharge in active medium, i.e., a mixture of helium and hydrogen. The maximum intensity of 121.6 nm VUV light was achieved at a mixing ratio of helium to hydrogen of 25:1. A large amount of helium would consume wide distributed energy in the microwave discharge, and energy transfer would occur from the metastable helium to hydrogen molecules. Backward flowing of the source gas into the microwave discharge region was prevented with a large flow rate of the active medium, such as 100 sccm. Using the 121.6 nm VUV light for the direct dissociation of monosilane molecule, a-Si:H film with less silicon-dihydride bondings was deposited.