Using Smart Dummy Fill and Selective Reverse Etchback for Pattern Density Equalization

The techniques of dummy fill and reverse etchback are often used prior to a chemical mechanical polishing (CMP) process to prevent film pattern density mismatches that lead to post-CMP film thickness variation. In this work, we present a methodology that utilizes both techniques in an intelligent fashion, and shows that both techniques can be used together to create a better balance of pattern densities than each technique can do separately. We introduce the idea of a selective reverse etchback method to lower the pattern density in high density regions, and smart dummy fill to raise pattern densities in low density regions. We then verify the methodology on the STI active area layer of a test mask.