Surface Planarization of Strain-Relaxed SiGe Buffer Layers by CMP and Post Cleaning

Surface planarization of strain-relaxed SiGe buffer layers by chemical mechanical polishing (CMP), particularly the influence of a post-CMP cleaning process which is indispensable after CMP, on the surface morphology of SiGe buffer layers was investigated. It was found that the cleaning tended to enhance the surface roughness due to the etching effect that increased with increasing cleaning temperature. The etching effect was suppressed by optimizing cleaning reagents, and the ultrasmooth surfaces of SiGe buffer layers with Ge contents of 30 to 70% were obtained, irrespective to growth methods. The root mean square roughness reached 0.4 to 0.6 nm, which was the lowest value that was ever obtained.