As semiconductor design rules decrease in size, total overlay performance requires a higher standard of the stepper and the photomask which affords a smaller error budget to each. Currently, photomask overlay assessment is done prior to pellicle attachment. However, the physical act of attaching a pellicle to a photomask imparts mechanical stress that distorts the reticle plane and changes the actual pattern placement from the design intent. With the advent of metrology tools capable of through-pellicle registration measurement, we are now able to assess and better characterize the effect pellicalization has on reticle distortion. The focus of this experimental investigation has been to quantify the incremental reticle distortion attributed to attaching the pellicle. To assess pellicle-induced distortion, both pattern registration and reticle flatness were evaluated. Two pellicle gasket materials were evaluated and one of the two materials was found to produce less reticle distortion. Relaxation of pellicle-induced reticle distortion after the pellicle is attached is also discussed.
As semiconductor design rules decrease in size, total overlay performance requires a higher standard of the stepper and the photomask which affords a smaller error budget to each. Currently, photomask overlay assessment is done prior to pellicle attachment. However, the physical act of attaching a pellicle to a photomask imparts mechanical stress that distorts the reticle plane and changes the actual pattern placement from the design intent. With the advent of metrology tools capable of through-pellicle registration measurement, we are now able to assess and better characterize the effect pelliclization has on reticle distortion. The focus of this experimental investigation has been to quantify the incremental reticle distortion attributed to attaching the pellicle. To assess pellicle-induced distortion, both pattern registration and reticle flatness were evaluated. Two pellicle gasket materials were evaluated and one of the two materials was found to produce less reticle distortion. Relaxation of pellicle-induced reticle distortion after the pellicle is attached is also discussed.
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