Process development of replacement metal gate Tungsten chemical mechanical polishing on 14nm technology node and beyond

Abstract

The control of gate height uniformity, especially within-die gate height uniformity, and metal gate surface properties of 14nm technology node replacement metal gate (RMG) chemical mechanical polishing is important for 14nm high-k metal gate (HKMG) process. Good within-die uniformity would benefit for the following Tungsten etching back process(WEB) to have a uniform within-die etching depth, and proper post CMP Tungsten gate surface properties would generate a thinner Tungsten oxide surface to reduce WEB process loading. This study demonstrated the possibility of Tungsten gate CMP(WGCMP) to obtain good within-die gate height uniformity by selection of slurry and proper Tungsten gate surface by post buffing step CMP treatment. Due to high hardness of Tungsten, hardness of polishing pad and abrasive of slurry selection should be not a gap for micro scratch improvement, what the performance focus would put on within-die uniformity and post CMP Tungsten surface properties. In this study, the first result showed the control of erosion was important for within-die gate height uniformity. The criteria of slurry selection for WGCMP were higher Tungsten removal rate and lower oxide removal rate which especially resulted in lower pattern density area of erosion. And the second result showed Chemical-A polish time of post-Tungsten buffing CMP would dominate the Tungsten surface properties and influence WEB behavior.