Generation of 193-nm femtosecond light pulses and their application to photomask repair

Femtosecond laser pulses at 193 nm were generated from visible Ti amplified pulses by using an Ar filled capillary tube as four-wave mixing medium. We could identify the dominant generation mechanism by experimenting with 3 different femtosecond pump pulses, the 772-nm fundamental and its second and third harmonics. To take advantage of the improved resolution at a shorter wavelength, we used the 193-nm output for photomask repair. Clean ablation of Cr on glass photomasks was demonstrated. Clean ablated lines as narrow as 175-nm could be obtained. The threshold pulse energy for ablation was less than 2 nJ, which is much smaller than the generated pulse energy, making it possible to extend the ablation wavelength to even deeper vacuum ultraviolet (VUV) wavelengths. The damage to the quartz substrate was found to be minimal. Our results show that high resolution VUV femtosecond photomask repair can play an important role in highly scaled semiconductor fabrication.