Improving a lapping process using robust parameter design and run-to-run control

Lapping is a critical step of wafer manufacture. Some wafer quality characteristics, such as total thickness variation (TTV) and thickness, are largely determined by lapping. A lapping process has a collection of factors. In practice, some factors are seldom changed once been fixed; while some others are tuned online continuously. We classify the factors into online factors, offline factors, uncontrollable factors, and noises. In this work, we analyze the physical mechanism of lapping factors then conduct experiments to study the lapping process. Offline factors are optimized via the robust parameter design (RPD); online factors are optimized via the double exponential weighted moving average Run-to-Run control. Verifying experiments proved that the RPD and RtR control can help to improve the TTV and the batch-to-batch thickness variation, respectively.