The influence of filament material on radical production in hot wire chemical vapor deposition of a-Si:H

The choice of filament material has an influence on the decomposition of silane during the hot wire chemical vapor deposition of amorphous and microcrystalline silicon films. In this paper, the Si radicals produced from W, Re, Mo and Ta filament materials are probed by laser-based single photon ionization as a function of hot wire temperature. The apparent activation energy of the Si radical production in the surface reaction regime from Ta (140-180 kcal/mol) and Mo (120-160 kcal/mol) are found to be close to the corresponding Si thermal desorption energies from these surfaces, suggesting that the Si production is controlled by the desorption process from the bare metal. On the other hand, the Si activation energies from W and Re (60 kcal/mol) are lower than the related desorption energies, suggesting silicon desorption from a silicon layer formed on the surfaces. Kinetic modeling supports this desorption mechanism. In addition to the Si radical study, the corresponding film deposition is detected in situ by multiple internal reflection infrared spectroscopy, from which growth rates are estimated. The results show similar activation energies for both the growth rate and Si formation from the various filaments, implying that Si radical production and subsequent film growth are dominated by the same elementary reactions at low pressure.