A Benchmark of 300mm RP-CVD Chambers for the Low Temperature Epitaxy of Si and SiGe

Abstract

We have assessed, in 300mm Reduced Pressure – Chemical Vapour Deposition chambers from major suppliers, the advantages and drawbacks of disilane for the low temperature growth of Si and SiGe. Si growth rates are, for T < 575°C, approximately ten times higher with Si2H6 than with SiH4, which are in turn roughly ten times higher than with SiH2Cl2. For given GeH4 and Si precursor mass-flow ratios, lower Ge contents and much higher SiGe growth rates are obtained at 550°C, 20 Torr with Si2H6 than with SiH4 and especially SiH2Cl2. Growth rates (Ge concentrations) are with SiH4 and SiH2Cl2 lower (slightly lower) in Supplier A than in Supplier B chamber. The situation is the opposite with Si2H6. This is assigned to (i) a ~ 5°C offset between the two and(ii) effective precursor flows which are different, most likely due to chamber geometry differences. Growth rate activation energies and relationships linking Ge concentration to precursor mass-flow ratios are quite similar, however, making process transfer between the two rather easy. Finally, we have compared ex-situ “HF-Last” wet cleanings and in-situ surface preparation processes for Si surface conditioning prior to epitaxy. Surfaces are after the latter always under high purity N2. This results in a threshold H2 bake temperature (above which there is no O interfacial contamination anymore) which is shifted downwards by ~ 25°C (from 775°C down to 750°C). Below that threshold, O sheet concentrations are with in-situ processes typically one third those associated with “HF-Last” wet cleanings and epitaxial surfaces are smoother.