Method and system of using offset gage for CMP polishing pad alignment and adjustment

A method of establishing an alignment of a polishing pad on a turntable prior to using the polishing pad to polish a semiconductor wafer, comprising:

• a. bonding the polishing pad to a top surface of the turntable;
• b. detecting along a common radius a maximum difference in radial dimension between an outer peripheral edge of the polishing pad and an outer peripheral edge of the turntable;
• c. applying use criteria to the maximum difference, so that
• i. when the maximum difference is less than a first selected value, the polishing pad is acceptable for using;
• ii. when the maximum difference in radial dimension is greater than the first selected value and less than a second selected higher value, trimming, prior to using, peripheral edge material of the polishing pad extending beyond the outer peripheral edge of the turntable;
• and
• iii. when the maximum difference in radial dimension exceeds the second selected higher value, removing the polishing pad and repeating steps a-c.