To transfer a photomask to a cleaning part with an appropriate timing so as to prevent a defect occurring in the photomask and having transferability to a wafer from reducing the yield.
The photomask is inspected every predetermined exposure frequency, and defects having transferability to the wafer are evaluated. When defects having transferability are detected, their size and the number of defects are stored with the exposure frequency, and it is predicted as a function f(Ex) of the exposure frequency Ex based on data of a plurality of times (4 times). The exposure frequency Ey is calculated at which the value of the function f(Ex) of the size Sn of the defects reaches a preset size Sy of the defect for reducing the yield of the wafer, after that, the photomask is not inspected, and the photomask is cleaned when the exposure frequency Ex reaches Ey. Thus, the photomask can be cleaned with the appropriate timing, and the cost can be reduced.
HARADA HISASHI
YAMAGUCHI SHINJI
NAKA MASATO
SHIBAYAMA KOICHIRO
IKEDA TAKAHIRO
