CMP and self-shadowing effect of overlay mark in metal sputtering process

Overlay mismatch of pre/post etch on metal layer is caused by asymmetric metal deposition on overlay mark. The major components of the mismatch are known to be composed of wafer scale and rotation caused by self-shadowing effect and CMP process, respectively. The behavior of each component was observed according to the changes in overlay mark shapes, metal thickness and CMP process conditions in this study. The overlay difference according to metal overhang on overlay mark was also investigated. It was found that overlay mismatch was reduced when the metal overhang on overlay mark happens, and over-polishing overlay mark during W CMP prevents formation of the metal overhang and increases wafer scale mismatch.