Printability of opaque repairs for DUV EPSM clear defects at sub-half-micrometer design rules

In this paper, the effect of opaque film deposition for 6% embedded phase shift mask (EPSM) clear defect repair in the wafer level via experiment and simulation are discussed. In the experiment, a 248 nm printing tool with 0.5 NA and 0.6 partial coherence were used. All the repairs were done with a laser repair tool. The original clear mask defects are placed on 0.26 micrometer and 0.44 micrometer mask dark lines (1x). The repaired areas as large as 0.26 micrometer multiplied by 0.7 micrometer were studied experimentally. We found in our study that the resist critical dimension (CD) of an opaque repaired region (line) tends to print narrower than that of a defect-free region in a DUV wafer process due to the transmission and phase mismatch. This result is consistent with our simulation prediction. This line narrowing effect could become an issue at 0.25 micrometer design rule since the process window at that design rule is usually very small as compared to that of larger design rules. In the experiment, we also observed resist CD asymmetrical response to the defocus due to laser damage to the quartz. This quartz damage is induced during a follow-up laser ablation process to trim off the excessive repair material near the line edge.