Wafer bending/orientation characterization and their effects on fluid lubrication during chemical mechanical polishing

• Distance sensors are used to monitor wafer status during 12-inch CMP.
• Wafer has about 10 μm slight convex bending during CMP.
• Wafer leading edge is lifted up and generates positive pitch angle.
• Wafer orientation and fluid pressure have the same trend with rotational speed.
• The convergent-dominated wedged gap causes the positive dominated-fluid pressure.

A novel in-situ wafer bending/orientation measurement system, cooperated with our previous developed fluid pressure mapping system, was developed for 12-inch chemical mechanical polishing (CMP) equipment. Wafer bending and wafer orientation are studied for copper wafer sliding against the IC1000 pad. The results reveal a micron level wafer bending, and a slight wafer pitch angle of 10−5 degree. Both the wafer pitch angle and interfacial fluid pressure increase with the speed till a critical speed and then decrease. The convergent-dominated wedged gap caused by the convexly bended, trailing edge pitched wafer gives a reasonable explanation to the positive-dominated fluid pressure.