Precision Positioning of Wafer Scanners Segmented Iterative Learning Control for Nonrepetitive Disturbances [Applications of Control]

Photolithography is a step in semiconductor manufacturing that uses a laser beam to transfer a pattern from a mask to the surface of a silicon wafer. This process is implemented by an optomechanical device called a wafer scanner. Wafer scanners require ultra-high-precision repetitive positioning capabilities. When the disturbances are repetitive, ILC improves performance of wafer-stage positioning from scan to scan. However, in the presence of nonrepetitive disturbances, ILC must be able to extract repetitive information, which is consistent from cycle to cycle, while avoiding nonrepetitive information.