Local/global planarization of polysilicon micropatterns by selectivity controlled CMP

The planarization CMP, which is considered as one of the most important ULSI chip, is introduced to make flat surface in patterned areas for multilevel MEMS devices. However, the conventional CMP is limited in its application to MEMS structures, due to their wide patterns of μm to mm order thick film layer of several μm. A new CMP process has been developed for application to MEMS structures by the control of selectivity between polysilicon and silicon oxide. A 30nm thick protective oxide layer is deposited to protect the recessed areas, and then polished with low selectivity slurry to partially remove the protruded area while suppressing the removal rate of the recessed area. During the second step of the new CMP process, high selectivity slurry is used to minimize the dishing amount and the variation in the step height according to pattern size and density. Experimental results showed that dishing amount was less than 30nm at the largest pattern of 1250 μm in width and showed no variation of entire pattern, which meant local and global planarization. This result suggests that the newly developed selectivity controlled CMP process can be successfully applied for fabrication the multilevel MEMS devices.