Run-to-run control of backside pressure for CMP radial uniformity optimization based on center-to-edge model

A method of planarizing wafers, the method comprising:

• measuring thickness of a layer of a first wafer already planarized by chemical mechanical polishing, the thickness being measured at a plurality of locations on the first wafer to yield a plurality of measurements;
• automatically determining a backside pressure to be used in chemical mechanical polishing in future, based at least on the plurality of measurements of the first wafer, by (i) keeping a current value of backside pressure unchanged if an indication of fit of the plurality of measurements to a line is less than or equal to the first limit, (ii) keeping the current value of backside pressure unchanged if the difference in thickness between the center and the edge of the wafer as determined from the line is within a predetermined range between the second limit and the third limit, (iii) decreasing the current value of backside pressure by a predetermined amount if the indication of fit of the plurality of measurements to the line is above the first limit and if the difference in thickness is below the second limit, wherein the second limit is smaller than the third limit, (iv) increasing the current value of backside pressure by a predetermined amount if the indication of fit of the plurality of measurements to the line is above the first limit and if the difference in thickness is above the third limit wherein the second limit is smaller than the third limit if the current value of the backside pressure is lower than a fourth limit, (v) keeping the current value of backside pressure unchanged if the current value of the backside pressure is greater than the fourth limit;
• and
• planarizing another wafer by chemical mechanical polishing at said backside pressure.

A system comprising:

• a chemical mechanical polishing tool;
• a metrology tool located adjacent to the chemical mechanical polishing tool;
• and
• a computer coupled directly or indirectly to each of the metrology tool and the chemical mechanical polishing tool, the computer being programmed to automatically supply to the chemical mechanical polishing tool a backside pressure determined based on the plurality of measurements from the metrology tool, wherein the computer is programmed to automatically fit the plurality of measurements to a model of center-to-edge profile of a wafer and automatically compute the backside pressure using at least one parameter from the model if an indication of fit satisfies a predetermined limit test.