Study On An Optimized Dummy Metal Insertion Method

With the development of technology node in the semiconductor manufacturing,CMP is becoming more and more important.However,CMP is a highly pattern-dependent process.Large amount of dummy metal are required to ensure the uniformity of the CMP process in the whole wafer.Traditional rule-based dummy metal insertion provides a fast,easy method to insert as much dummy metal in the chip as needed,to increase the pattern density as well as decrease the pattern gradient.However,more dummy metal will increase the coupled capacity in the chip and result in chip failure at high frequency.Another method called smart fill can significantly decrease the amount of inserted dummy metal and the pattern gradient as well.However,smart fill will decrease the consistency for repeated pattern.In this paper,an optimized dummy metal insertion method is introduced.Firstly,by using pattern search,the repeated pattern and hotspot are found in the chip and dummy metal is inserted separately by using rule-based fill or smart fill.After the insertion,we merge these patterns into chip and add block layer to avoid second insertion.Secondly,smart fill is utilized to insert dummy metal for the whole chip,to ensure the pattern density and pattern gradient conform to the specification.The result shows,the pattern density and the pattern gradient of this method is similar to those of the smart fill(max gradient 0.4).The maximum gradient is optimized from 0.9 to 0.4,significantly better than the rule-based insertion with the maximum gradient of 0.7.This method also overcomes the inconsistency for repeated pattern and the coupled capacitance is optimized as well.