Chemical-mechanical polishing for polysilicon surface micromachining

This paper explores the use of chemical-mechanical polishing (CMP) in polysilicon surface micromachining for removing the inherent surface roughness of polysilicon to create a mirror surface finish and for globally planarizing the wafer surface to extend mechanical design capabilities in polysilicon surface micromachining processes. It is demonstrated that device fabrication with polished polysilicon films deposited over unpolished ones benefit from improved feature definition and delineation and better sidewall quality. Experiments were performed to determine the effect of CMP process parameters on the polysilicon removal rate and surface roughness reduction rate. Undoped and heavily phosphorus-doped 11 mu m thick polysilicon films were polished with roughness reduction rates of 47 and 71 Angstrom/min, respectively, removal rates of 167 and 513 Angstrom/min were achieved. The undoped and heavily phosphorous-doped films, which had initial average roughness values of 580 and 517 Angstrom, respectively were polished down to average roughness values of 17 and 19 Angstrom. A 15:1 polysilicon to oxide selectivity was achieved and utilized for global planarization to create polysilicon islands in oxide.