Oscillation-Speed-Control-Type Polishing with a Small Tool (3rd Report)

Abstract

As ULSI feature dimensions continue to shrink, wafer flatness of less than 0.1μm has become essential, and any flaws in surface topography cause serious problems in device patterning. CMP has become a standard technology to planarize surface topography. We have developed an oscillation-speed-control-type sequential grinding and polishing machine and have simulated the polishing process. A previous paper showed that experimental profiles polished with normal and reverse rotations agreed well with the simulated result calculated with a modified equation of relative velocity. However, the simulation broke down when the tool overhung the wafer by a significant amount. This paper presents measured pressure distributions for various tool overhangs, and a method to compensate for the difference between theoretical and experimental distributions, and polishing amounts produced using the compensation. The pressure distribution from air pressure in an air-bag is significantly different than that from a weight, and its characteristics depend on the machine. The profile of the pressure distribution for large overhangs becomes concave rather than linear. The simulated results with concave pressure distributions agreed well with experimental results.