Gas Phase Chemistry Study During Deposition of a-Si:H and μc-Si:H Films by HWCVD using Quadrupole Mass Spectrometry

Amorphous and microcrystalline silicon films were deposited by HWCVD under different deposition conditions and the gas phase chemistry was studied by in situ Quadrupole Mass Spectrometry. Attempt is made to correlate the properties of the films with the gas phase chemistry during deposition. Interestingly, unlike in PECVD, partial pressure of H2 is higher than any other species during deposition of a-Si:H as well as μc-Si:H. Effect of hydrogen dilution on film properties and on concentration of various chemical species in the gas phase is studied. For low hydrogen dilution [H2]/ [SiH4] from 0 to 1 (where [SiH4] is 10 sccm), all films deposited are amorphous with photoconductivity gain of ∼ 106. During deposition of these amorphous films SiH2 was dominant in gas phase next to [H2]. Interestingly [Si]/[SiH2] ratio increases from 0.4 to 0.5 as dilution increased from 0 to 1, and further to more than 1 for higher hydrogen dilution leading to [Si] dominance. At hydrogen dilution ratio 20, consequently films deposited were microcrystalline.