Photomask cleaning is getting important factor in whole mask process as device density is going to higher and introducing of P.S.M. Not only hard defect but contamination defects both on Qz and the Cr areas of photomask reticle can make problems on wafer. Especially contamination defect on the Cr of embedded type P.S.M. can cause the undesirable phase shift effect. Current method of photomask cleaning is not so improved compared to other areas of mask manufacturing. New technology of cleaning will be developed in near future but we try to figure out the limit of current cleaning method and maximize the current cleaning performance.
Ki Jong Kim,
"Photomask cleaning for high-density and embedded PSM", Proc. SPIE 2512, Photomask and X-Ray Mask Technology II, (3 July 1995); doi: 10.1117/12.212811; https://doi.org/10.1117/12.212811