The viability of GeH4-based in situ clean for low temperature silicon epitaxial growth

Several groups have reported on the use of GeH4 for in situ cleaning of the silicon surface prior to the epitaxial growth of silicon. However, questions remain as to the extent to which the surface oxide can be removed from the silicon surface by GeH4. We report here our results from the study of an in. situ GeH4-based clean in the temperature range of 500 to 700 degrees C with 10 to 100 ppm GeH4 in H-2. For comparison, a H-2 bake in. situ clean was also examined in the temperature range of 600 to 950 degrees C. The results showed that surface oxide could not be removed by GeH, to an adequate level before excessive Ge deposits which causes epitaxial stacking fault. A 120 s H-2 bake at 850 degrees C of an HF dipped surface results in no detectable oxygen based on secondary ion mass spectroscopy. Also, we demonstrate that the quality of the epitaxial layer grown after the clean is not necessarily a good indication of the effectiveness of the clean when the surface oxygen coverage is below a certain value. We conclude that due to the competition between the surface oxide removal and the Ge deposition, GeH4-based clean is not suitable for high quality Si epitaxial growth by chemical vapor deposition techniques.