Method for adjusting lithographic mask flatness using thermally induced pellicle stress
View Patent ↗A method for adjusting the flatness of a lithographic mask includes determining an initial mask flatness of the mask, determining an applied stress for bringing the mask to a desired mask flatness, and determining a mounting temperature of a pellicle frame to be mounted to the mask, the mounting temperature corresponding to the applied stress. The actual temperature of the pellicle frame is adjusted to the determined mounting temperature, and the pellicle frame is mounted to the mask at the mounting temperature.
1. An apparatus for adjusting the flatness of a lithographic mask, comprising:
a pellicle frame configured for mounting to the mask;
said pellicle frame having a plurality of sides, at least a portion of which comprising a material having a different coefficient of thermal expansion with respect to the mask so as to provide one of an expansive force or a contractive force to the mask;
wherein said one of an expansive force or a contractive force provided by said pellicle frame causes an initially measured mask flatness to be adjusted to a desired mask flatness.
2. The apparatus of claim 1 , wherein said sides of said pellicle frame disposed in a first direction have a first thickness and said sides of said pellicle frame disposed in a second direction have a second thickness.
3. The apparatus of claim 1 , wherein said sides of said pellicle frame disposed in a first direction comprise first material and said sides of said pellicle frame disposed in a second direction comprise a second material having a different coefficient of thermal expansion than said first material.
4. The apparatus of claim 1 , wherein said first material is aluminum and said second material is quartz.
5. The apparatus of claim 1 , wherein said sides of said pellicle frame comprise an electrically conductive material and corners of said pellicle frame comprise a thermally insulating material.
6. The apparatus of claim 5 , wherein said sides of said pellicle frame are configured to be heated by passing an electrical current therethrough.
7. The apparatus of claim 6 , wherein said sides of said pellicle frame are electrically insulated from one another.