After the preceding bulk Cu CMP step removes the thick copper overburden, the underlying Ta-based liner (typically a Ta/TaN stack) remains exposed on the field dielectric P1.This Ta-based liner CMP step is required to selectively remove this residual conductive barrier, thereby electrically isolating the adjacent MET6 copper lines and preventing short circuits P2.As part of the MET6 module in a 40nm BSI CMOS Image Sensor flow, this step is distinct from the earlier liner CMP steps (such as those