Dae-Joung Kim

Wafer-induced reading error in metal sputtering process

For higher density devices electric performances have been focused more than the others. In the case of metal sputtering process some of machine makes local asymmetric deposition across the wafer. In this study, a couple of overlay reading errors which comes from asymmetric metal deposition has been studied in terms of photo process. As a result, scaling error could be reduced down to a certain amount with the optimization of overlay reading marks. However it will not be cleared no matter what kinds of mark are used as long as overlay marks are asymmetry. A symmetric sputtering should be the only way to figure out this problem. In order to make total product, related processes have to be concerned as well.

Is it possible to improve MEEF

As the design rule of device has shrunken, obtaining a feasible process window at low k1 factor in photolithography is the major concerning in order to shorten the total period from development to the mass production of devices. In this low k1 factor region, a tiny CD variation on mask might be increased abruptly on the wafer. In particular, such variation so called MEEF (Mask Error Enhancement Factor) is closely related with various types of process parameter. In this paper, we reviewed optimized process condition to minimize MEEF and defined uDoF (Usable Depth of Focus) considering a correlation between MEEF and DoF (Depth of Focus).