| CPC B24B 37/32 (2013.01) [B24B 49/12 (2013.01); H01L 21/3212 (2013.01)] | 20 Claims |

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1. A method, comprising:
performing, using a chemical mechanical polishing (CMP) system, a CMP process on a wafer;
after performing the CMP process, capturing an image of a gap between an inner retaining ring and an outer retaining ring of a polish head of the CMP system using an image capture device, wherein the image capturing device is moved along a circular rail between the inner retaining ring and the outer retaining ring during capturing the image; and
observing a surface roughness of an inner sidewall of the inner retaining ring and a surface roughness of an inner sidewall of the outer retaining ring based on the captured image.
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