Improving on-product overlay (OPO) by grouping wafers according to ingot

摘要

In the scanner the height of every wafer (wafer map) is measured using the level sensor which takes several seconds. The problem to solve is: is there a way to skip or shorten wafer map measurements and spend more time on wafer align measurements? Since overlay performance is typically more critical than focus performance, being able to spend more time on measuring wafer alignment marks could be beneficial for on-product overlay performance. Each wafer has an unique ID lasered on the backside, which is used to trace back the wafer to the ingot from which it was cut. This wafer ID is described by SEMF standard M12/M13 and it has the following meaning (for example: CH3ZR 226 SE G4): CH3ZR = Ingot ID, 226 = Position of a wafer within a ingot, SE = Wafer supplier and G4 = Checksum.