MASS-SPECTROMETRIC STUDIES OF SIO2 DEPOSITION IN AN INDIRECT PLASMA-ENHANCED LPCVD SYSTEM

Reaction pathways for the low temperature deposition of SiO2 from sila ne and indirect plasma-excited oxygen-nitrogen mixtures are proposed b ased on experimental evidence gained from mass spectrometry in an indi rect plasma enhanced chemical vapor deposition chamber. It was observe d that approximately 80-85% of the silane was oxidized to byproduct hy drogen and only about 15-20% to water. Such conversion levels have led us to interpret that silanol (SiH3OH) could be the precursor for SiO2 film deposition rather than siloxane [(SiH3)2O] which has generally b een cited in the literature. From mass spectrometry, we have also show n the effects of the plasma, and of mixing small amounts of N2 with th e oxygen flow, in increasing the deposition rate Of SiO2. Free radical reaction of nitric oxide, synthesized from the reaction of oxygen and nitrogen in the plasma chamber, and an increase in atomic oxygen conc entration, are believed to be the reasons for these SiO2 deposition ra te increases. Through mass spectrometry we have, in addition, been abl e to identify products, presumably originating from terminating reacti ons, among a sequence of chemical reactions proposed for the depositio n of SiO2.