MASS-SPECTROMETRIC AND KINETIC-STUDY OF LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITION OF SI3N4 THIN-FILMS FROM SIH2CL2 AND NH3

The deposition mechanism of Si3N4 films from dichlorosilane (DCS) and ammonia, formed by a conventional low-pressure chemical vapor depositi on system, was studied, combining mass spectrometric analysis and the ''macrocavity method.'' The dominant neutral species in the gas phase are NH3 and aminochlorosilane (ACS), which was produced by the gas-pha se reaction of DCS, in a high NH3 (a large NH3/DCS ratio) condition, w hile DCS dominantly exists in a low NH3 condition. Contrary to the mas s spectrometric results, there is not a major dependence of the kineti c constants of the deposition precursors on the gas-mixture ratio. By fitting the growth-rate profiles to an optimal theoretical profile, bo th of the two kinds of precursor are estimated to have low activity. T he conformal step coverage quality agrees with the small sticking prob abilities estimated as 10(-4) and 10(-6). Those precursors can be assi gned to DCS and ACS, so that the mass spectrometric data would be cons istent with the growth profiles. The conversion to ACS is calculated b ased on an assumed simple kinetic form and leads to a qualitative inte rpretation for gas-mixture ratio-dependence of conversion. A kinetic m odel including precursor molecules is presented to correlate the mass spectrometric results, the growth-rate profiles, and the step coverage quality.