DEPOSITION MECHANISM OF SILICON-NITRIDE IN DIRECT PHOTOASSISTED CHEMICAL-VAPOR-DEPOSITION USING A LOW-PRESSURE HG LAMP

Silicon nitride (SiNx) films applicable to microelectronics are deposi ted by photoassisted chemical vapor deposition (CVD) with a low-pressu re Hg lamp (185 nm). We describe the deposition mechanism of SiNx in t he photo-CVD based on analyses of film structures and transient mass s pectroscopy. NH3 is decomposed into NH2 and H by UV-light irradiation. SiH4 is decomposed through the reaction with NH2 or H. SiNx films are formed through an intermediate species formed in gas phase. The forma tion of the intermediate species is controlled by the decomposition of NH3. At a substrate temperature of 350 degrees C, the deposition rate is controlled by the amount of the intermediate species with higher m ass (amu 77, Si2NH7), acid the films are pdlymeric solids. At 500 degr ees C, chemical species are deposited on the surface before they grow into the intermediate species with the high mass (amu 77), and the fil m structure becomes stoichiometric SiNx.