Formation of aminosilanes in the hot-wire chemical vapor deposition process using SiH4 - NH3 gas mixtures

Vacuum ultraviolet laser single photon-ionization coupled with time-of-flight mass spectrometry has been used to detect the gas-phase reaction products from the HWCVD reactor with SiH4 - NH3 mixtures with various partial pressure ratios ranging from 1: 1 to 200 : 1 for NH3 : SiH4. The identity of the products depends strongly on the relative amounts of SiH4 and NH3 in the mixture. Low NH3 content favors the production of disilane and trisilane. When the NH3 content is high, the formation of aminosilanes becomes the primary pathway. The production of sufficient amount of NH2 (or ND2) radicals is found to play a key role in the competition between the two pathways. The formation of aminosilanes when using mixtures with an ammonia to silane pressure ratio greater than 49 : 1 is confirmed through the use of the isotopomer ND3 in place of NH3 in the gas mixtures. A stepwise amination reaction scheme, initiated by the reaction between the SiH3 and NH2 radicals, is responsible for the formation of aminosilanes. The effect of filament temperature on the formation of aminosilanes and di-/tri-silane has also been investigated.