Modeling and Experimental Study of SiH4/GeH4/H2 Gas Discharge for Hydrogenated Silicon Germanium Deposition by RF PECVD

摘要

A one-dimensional model has been developed for radio frequency (RF) glow discharge of SiH_4/GeH_4/H_2 3-gases mixture at a high pressure regime based on the fluid model. The behavior of electrons, neutrals, radicals and ions with corresponding rate constants is described by drift-diffusion equations that are coupled with the Poisson's equation and solved with an explicit central-difference discretization scheme. The germanium (Ge) content in the deposited film and germane (GeH-2) radical fraction in the gas phase are found to decrease as total gas pressure increases in contrast to the increased deposition rate, which are explained by the fact that GeH_x-group species are more thoroughly depleted and less promoted by the denser plasma at high pressure compared to SiH_x-group species. The multiplied population of electrons and hydrogen atoms in the quadratically denser plasma also boosts secondary reactions which are favorable for SiH_3 and GeH_3 and consume SiH_2 and GeH_2 for high order radicals.