Oligomerization and Polymerization Steps in Remote Plasma Chemical Vapor Deposition of Silicon−Carbon and Silica Films from Organosilicon Sources

Remote hydrogen and remote oxygen plasma chemical vapor depositions (RHP−CVD and ROP−CVD, respectively) of amorphous hydrogenated silicon−carbon (a-Si:C:H) and amorphous silica (a-SiO2) films, respectively, from organosilicon source compounds were selected as model processes for the mechanistic study. Hexamethyldisilane (HMDS) and trimethylsilane (TrMS) source compounds were used for RHP−CVD, whereas tetraethoxysilane (TEOS) was a source compound for ROP−CVD. The reactivity of HMDS and TrMS with atomic hydrogen and TEOS with atomic oxygen was characterized by determining the rate constants of RHP−CVD and ROP−CVD, respectively. On the basis of the values of the rate constants, the identified low-molecular-weight and oligomeric products collected from the gas phase, and the chemistry involved in their formation, the mechanisms of the precursors formation step are proposed. The results provide strong evidence for the gas-phase conversion of HMDS and TrMS to 1,1-dimethylsilene, Me2SiCH2, and TEOS to diethoxysilanone, (EtO)2SiO, transient intermediates as major precursors to the a-Si:C:H and a-SiO2 films, respectively. Owing to the high-reactivity π-bonds in the silene (>SiC<) and silanone (>SiO) units, the precursors may readily undergo polymerization. A hypothetical mechanism of the polymerization and cross-linking steps contributing to the growth of the a-Si:C:H and a-SiO2 films are discussed.