Buried Tungsten Metal Gate Formation with Chemical Mechanical Polishing Technique and Involved Issues

Buried metal gate has been adopted to improve short channel effect and to reduce parasitic capacitance in semiconductor devices. During buried metal gate formation, metal CMP process is applied to isolate buried gate line, and this CMP process is very critical because physical dimension made by CMP has direct effects on several electrical properties and subsequent critical process parameters. This, so called, buried metal gate CMP, has some unique process features, and causes CMP related critical issues that have not been experienced, such as uneven Tungsten recess, scratches resulting in Si substrate damage, stopping layer erosion causing Si substrate attack, stopping layer thickness variation that is difficult to predict. This paper summarizes above issues and solutions to solve the problems. Keywords: Chemical Mechanical Polishing, Buried Metal Gate, Tungsten CMP, Uneven Recess, Unetch, Erosion