Effect of Filament Material on the Decomposition of SiH4 in Hot Wire CVD of Si-Based Films

Abstract

AbstractThe choice of filament material has an effect on the decomposition of silane during the hot wire chemical vapor deposition (HW-CVD) of amorphous and microcrystalline silicon films. The Si radicals produced from W, Re, Mo and Ta filament materials have been probed by laserbased single photon ionization (SPI) as a function of hot wire temperature. The Si radical profiles are shown to demonstrate two distinct regimes: a regime below 1600°C-1800°C (depending on filament material) limited by surface reaction at the filament in which Si concentration increases monotonically; and a mass transfer limited regime above 1600°C-1800°C where Si intensity saturates. The apparent activation energy of Si radical production in the surface reaction regime from Ta (140-170 kcal/mol) is found to be close to the corresponding Si thermal desorption energy from a Ta surface, 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 (30-60 kcal/mol) are lower than the related desorption energies, suggesting that other rate limiting reactions play a role for these materials. The apparent activation energy for the Mo surface (60-90 kcal/mol) is intermediate between the other metal values. In addition to the Si radical study, corresponding film deposition is detected in situ by multiple internal reflection infrared (MIR-IR) spectroscopy. The IR measurements have been used to estimate the growth rate of a-Si:H deposited on a Ge substrate. The results show similar activation energies for both the growth rate and the Si formation from a W filament, implying that Si radical production and subsequent film growth may be dominated by the same elementary reactions within the decomposition and film growth processes at low pressure.