Low pressure silicon selective epitaxial growth and its thermodynamic considerations

Abstract
In a rapid thermal processing reactor QUPLAS II, full selective epitaxial growth of silicon has been obtained using DCS in H₂ without addition of HCl. This is mainly achieved by reducing total process pressure down to the millibar regime. Selectivity can also be controlled by reducing DCS gas flow rate ; however, the growth rate is greatly reduced. Process temperature has, on the other hand, a minor effect on selectivity control. The selective epitaxial growth (SEG) occurs under conditions of near thermodynamic equilibrium. Thus equilibrium partial pressures of the predominant species in the Si-H-Cl system have been calculated to give an insight into the experimental results. The availability of HCl species relative to silicon containing species in the gas phase, P_HCl/P_Si, has shown why no external HCl is required, for depositions in millibar regime or low DCS flow rate, to obtain full selectivity. While reaction system is near-equilibrium, the reposition of Cl, dissociated from Si containing species, into HCl species, plays an important role in determining the system etching function.