Surface radicals in silane/hydrogen discharges

Using threshold ionization mass spectrometry, radical densities have been measured at the substrate surface of a radio frequency discharge in silane plus hydrogen vapor. The conditions are 100-300 Pa pressure and a ratio (R) of hydrogen flow/silane flow typical of discharges used to produce large area amorphous (R=20) and microcrystalline (R=40) silicon. For comparison, we include measurements in pure-silane vapor. The neutral radicals observed in the mixed gases are H, SiH3, Si2H2, and Si2H5, with decreasing flux in that order. (Si2H4 is also seen in pure silane and SiH2 for R=20.) The H flux is sufficient for major film etching and restructuring, particularly for R=40. The ion-bombardment species were also measured, establishing that SiyHn+ (y=1-3) ion flux is much larger than the Hn+ (n=1-3) flux. The ion flux provides 15±4% of the total Si flux to the film for R=20 and 37±10% for R=40. This is larger than in pure-silane discharges, and it may be very important to film properties due to the impact energy