Physics and chemistry in the process of hot-wire deposition of thin film silicon

Hotwire Chemical Vapor Deposition (CVD) has been used in preparing high quality low hydrogen content hydrogenated amorphous or polycrystalline silicon thin film in recent years. Comparing to the most commonly used glow discharge method, Hotwire CVD has the potential of high speed deposition avoiding the damage caused by ion bombardment associated with plasma. Although device quality thin films have been prepared by this method, and some empirical optimized deposition conditions have been established, the mechanisms controlling this technique are not clear.; A homebuild threshold ionization mass spectrometer was constructed in this lab, allowing the radicals to be observed with high sensitivity.; Hydrogen dissociation on the hot metal surface was studied first both by the direct detection of hydrogen atoms from the hot surface and the temperature change due to the hydrogen dissociation, it was confirmed that the activation energy of this process is around 2.25eV, the same as the dissociation in the gas phase. Further, we observed a first order dependence of hydrogen dissociation probability on the hydrogen pressure. This observation contradicts previously reported models of second order desorption.; The monosilicon radicals Si and SiH3 were observed. It was observed that the silane decomposition on the hot surface is mainly a function of filament temperature, but the species released from that surface also depend on the surface condition, and thus on the silane exposure history of that piece of filament. Si is believed to deteriorate the film quality, by comparing the depleted silane and the Si flux, it is observed that Si experienced a lot of gas phase reactions before reaching the substrate, which leads to less reactive precursors. This observation is consistence with Molenbroek's study on the optimization of deposition condition. The dominant disilicon radical is identified as Si2H2, which in the form of lowest energy isomer, is suppose to be much less reactive than Si, and thus contributes to good quality thin film deposition. The corresponding Si insert reaction Si + SiH4 was also studied and an effective reaction coefficient of KSeff = 5 x 10-12( cm3/s was established.