Chemical Vapor Deposition of Organosilicon Thin Films from Methylmethoxysilanes

Plasma enhanced chemical vapor deposition was used to deposit organosilicate glass (OSG) thin films from trimethylmethoxysilane, dimethyldimethoxysilane, and methyltrimethoxysilane. Depositions were performed from the pure OSG precursor, as well as from mixtures where either oxygen or hydrogen was added to the gas feed. These films were analyzed via Fourier transform infrared spectroscopy (FTIR), variable angle spectroscopic ellipsometry (VASE), and electrical measurements. Reactions involved in the deposition of OSG thin films from methylmethoxysilanes with oxygen are not selective and lead to the undesirable loss of methyl functionality. Reducing chemistry achieved with hydrogen addition is selective, with hydrogen atoms reacting preferentially with the methoxy groups creating silanol or siloxyl radicals. This selectively forms bonds networking through condensation reactions without sacrificing the “built‐in” alkyl content of the precursor. Low‐k OSG thin films from methylmethoxysilanes and hydrogen were deposited via a low power, W/FM from 10.0 to 10.5 J/g dependent upon OSG precursor, PECVD process resulting in material dielectric constants ranging from 2.84 to 3.18. Dielectric constant as a function of increasing methyl substitution in the silicon precursor (n) shown for discharges the pure precursor, and for the cases of gas mixtures with H2 and O2 (OMe≡methoxy, Me≡methyl).