SELECTIVE LOW-PRESSURE CHEMICAL VAPOR-DEPOSITION OF SI1-XGEX ALLOYS IN A RAPID THERMAL PROCESSOR USING DICHLOROSILANE AND GERMANE

Low-pressure chemical vapor deposition of Si1-xGex alloys in a cold wall, lamp-heated rapid thermal processor was studied. Alloys were deposited using the reactive gases GeH4 and SiH 2Cl2 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 Si1-xGex 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:SiH 2Cl2 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.