Presently available nanosecond laser based tools for removing Cr defects from photomasks have proven inadequate to the task due to the thermal nature of the ablation process which produces metal splatter, haze, reduced transmission, and pitting of the quartz substrate. These problems are virtually nonexistent when employing femtosecond pulses of light to ablate Cr defects in a nonthermal process. Photomasks repaired with ultrashort light pulses exhibit transmission approaching 100%, no observable glass damage, and exceptional spatial resolution. We have built a femtosecond pulsed laser mask repair system which is presently operating successfully in a manufacturing environment.

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Photomask pellicles play an important role in determining final photomask flatness, which is important to photomask optical performance. This study explores the impact of the pellicle frame flatness and pellicle-to-mask adhesive on photomask flatness. In addition, the change in mask flatness as a function of time after pellicle mounting is studied. Implications of these results on photomask manufacture and photolithography are discussed.

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