Silicon nitride and oxynitride deposition by RT-LPCVD

Abstract

Silicon nitride (Si-N) and oxynitride (Si-O-N) thin films are obtained by low pressure rapid thermal chemical vapor deposition (RT-LPCVD) by using the reaction of diluted silane (SiH 4/Ar = 10%) with ammonia (NH 3) or a mixture of ammonia and nitrous-oxide (N 2O) at various gas ratios ( R = NH 3/SiH 4 and R′ = [N 2O + N 2O]). Deposition kinetics of silicon nitride films have been studied in the medium to high temperature range (700–850°C) at fixed total pressure of 9.5 mbar and gas flow ratio ( R = 10). Oxynitride deposition rates have been also studied as a function of R′ at fixed temperature and total pressure parameters of 750 °C and 9.5 mbar respectively. Rutherford backscattering spectrometry results showed that the RT-LPCVD Si-N films are silicon-rich and that the composition stoichiometry is mainly controlled by the process parameters, particularly the gas flow ratios. Si 3N 4 silicon nitride stoichiometry can only be approached for R ≥ 10. Fourier transform spectrometry measurements revealed that the Si-O-N films have a particular structure formed by a mixture of Si-O and Si-N bonds with no apparent separated phases. In addition, in contrast to the few 10 at % usually reported for classical CVD processes, no significant traces of hydrogen bonds (Si-H or N-H) were detected for R ≥ 10. Furthermore, secondary ion mass spectrometry analysis always indicated that Si-N and Si-O-N RT-LPCVD deposited layers are homogeneous along the whole film thickness.