Interface-layer formation in microcrystalline Si:H growth on ZnO substrates studied by real-time spectroscopic ellipsometry and infrared spectroscopy

By applying real-time spectroscopic ellipsometry and infrared attenuated total reflection spectroscopy (ATR), we have characterized interface-layer formation in microcrystalline silicon (muc-Si:H) growth on ZnO substrates in a conventional rf plasma-enhanced chemical vapor deposition. With an increase in the hydrogen dilution ratio (R=[H-2]/[SiH4]), we find a significant increase in the interface-layer thickness from 0(R=0) to 48 Angstrom(R=100). In contrast, no interface-layer formation was observed in muc-Si:H growth on SiO2 substrates. Detailed analyses show that the interface layer formed on ZnO is porous amorphous Si:H with a large amount of SiH2 bonds (16 at. %). During the early stage of interface-layer formation, we observed almost no film deposition and a dramatic increase in free-carrier concentration within the ZnO substrate due to a chemical reduction of ZnO by H-containing plasma. Real-time ATR spectra revealed the predominant formation of SiHnO4-n (n=1-2) species on the ZnO surface prior to interface-layer formation.. These SiHnO4-n species are chemically inactive and remain at the muc-Si:H/ZnO interface. Based on these findings, we propose that the SiHnO4-n formation that results from ZnO reduction reaction by H suppresses chemical reactivity on the ZnO surface and induces porous interface-layer formation during the initial deposition process. (C) 2003 American Institute Of Physics.