Process development of high-k metal gate aluminum CMP at 28 nm technology node

The replacement metal gate (RMG) height range and defectivity (fall on particle, Al residue, corrosion and micro-scratch) performance controls are very challenging for high-k metal gate (HKMG) RMG chemical mechanical polishing (CMP) processes. In this study, a robust aluminum metal CMP (Al-CMP) process development was investigated to meet the criteria of RMG at 28 nm technology node. The Al metal gate height loss post-Al-CMP was found to increase with increasing the total area and pattern density of metal gates. Adding at least one extra ghost metal gate dummy structure on both sides of each metal gate and optimizing the metal gate dummy structure can effectively eliminate the metal gate height loss. Furthermore, implementing a real-time profile control (RTPC) end-point detecting system with lower down force polishing condition can further reduce the Al metal gate height loss and range levels. The defectivity issues of the microscratches and fall on particles can be fixed by using a soft pad with chemical wafer buff process on the final Al-CMP polishing step.

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