Selective low-pressure chemical vapor deposition of Si1−xGex alloys in a rapid thermal processor using dichlorosilane and germane

Abstract

Low‐pressure chemical vapor deposition of Si_1−xGe_x alloys in a cold wall, lamp‐heated rapid thermal processor was studied. Alloys were deposited using the reactive gases GeH₄ and SiH₂Cl₂ in a hydrogen carrier gas. The depositions were performed at a total pressure of 2.5 Torr and at temperatures between 500 and 800 °C using GeH₄:SiH₂Cl₂ ratios ranging from 0.025 to 1.00. Results showed that Si_1−xGe_x alloys can be deposited selectively on silicon in SiO₂. The selectivity is enhanced significantly by the addition of GeH₄ in the gas stream. In this work, selective depositions were obtained when the GeH₄:SiH₂Cl₂ gas flow ratio was greater than 0.2 regardless of the deposition temperature, corresponding to a Ge content of 20% or higher in the films as determined by Auger electron spectroscopy. An enhancement in the deposition rate was observed in agreement with earlier reports due to the addition of GeH₄. The activation energy for deposition in the surface reaction limited regime varied from 20 to 30 kcal/mole with the gas flow ratios used in this study.