Patent ID: 7355680

Claim:
A method for adjusting the flatness of a lithographic mask, the method comprising: determining an initial mask flatness of the mask, the mask at an ambient temperature; determining an applied stress for bringing the mask to a desired mask flatness; determining a mounting temperature of a pellicle frame to be mounted to the mask, said mounting temperature corresponding to said applied stress, wherein at least a portion of said pellicle frame has a different coefficient of thermal expansion with respect to the mask; adjusting the actual temperature of said pellicle frame to said determined mounting temperature; and mounting said pellicle frame, being at said mounting temperature, to the mask, being at said ambient temperature; wherein the pellicle frame provides one of an expansive force or a contractive force to the mask as a result of a difference in pellicle frame mounting temperature and mask ambient temperature, and the difference in coefficient of thermal expansion between the pellicle frame and the mask.