CHEMISTRY OF SIO2 PLASMA DEPOSITION

The chemistry of SiO2 deposition from undiluted and He-diluted N2O-SiH4 mixtures was studied by line-of-sight mass spectrometry of plasma species led with analysis of film IR absorption and dielectric properties. It was found that if RF power is sufficient to generate an 0 atom supply well in excess of that needed to convert all of the SiH4 to SiO2, then clean IR spectra and high dielectric strength are obtained independent of dilution. Under these plasma conditions, many gas-phase products of the form Si(m)H(n)(OH)p were detected. Their concentration increased steeply with the partial pressure of the reactants (SiH4 + N2O)p and they are the likely source of the downstream particles and deposition rate loss which were seen at 130 Pa of reactant pressure. Reduction of reactant partial pressure to 13 Pa either by He dilution or by undiluted total pressure reduction eliminated these problems. No other effects of He dilution could be detected either in the plasma chemistry or in the film properties. Both SiOH concentration and electron trapping rate in the films were much higher than in thermal oxide and were unaffected by He dilution. There is some evidence that He plasma treatment does improve Si interface quality