Study on Variable Rotation Polishing Method in Chemical Mechanical Polishing Process
Variable rotation polishing method has been studied to improve performance for the next generation wafer size of 450 mm in Chemical Mechanical Polishing (CMP) technology. This method adds the backward rotation of a polishing platen against the only forward rotation, i.e. the conventional polishing. Polishing slurry could be more efficiently supplied into the center area of the larger wafer due to the backward rotation of the platen. Material removal rate at the condition the backward rotation experimentally became 38% higher in comparison with only forward rotation. In this case, slurry film thickness of the Variable Rotation Polishing (VRP) method was slightly thinner than that of conventional rotation. Next, the asperities of polishing pad surfaces were evaluated by confocal laser scanning microscope. The higher material removal rates would also be achieved by the movement of the asperity bending back and forth direction on the polishing pad surface during the forward and backward rotation of the platen. These observed polishing pad surfaces indicated that the asperity preservation on the polishing pad is one of dominant parameters to improve the material removal rate of wafer surface in CMP process.
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