18 December 1998 High-resolution near-field mask repair with femtosecond laser
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Abstract
Nanonics Lithography has demonstrated in the past a mask repair system based on near field optical technology. The basic system consisted of: (1) Near Field sub system -- Including a Near Field Head and the Near Field Optical Aperture (micro-pipette). (2) An X-Y stage with nanometer level accuracy, resolution and repeatability. (3) A doubled Nd:YAG laser for high resolution Near Field Optical Imaging, beyond the diffraction limits of the YAG laser. (4) A Nano- Second (NS) pulse width Arf Excimer laser for ablation of the Cr defect. The repairs performed with the system based on the above configuration suffered from inherent quality problems of Cr removal homogeneity and quartz substrate penetration. This is due to the relatively long duration of the NS pulse, in which the Cr is ablated by melting and evaporating the film accompanied by significant heat diffusion to the surrounding material. In order to improve the repair quality, we have introduced a Femto Second (FS) laser as the ablation source. In the FS regime the metal is evaporated within a time frame that does not allow heat diffusion to the surrounding material. The resultant cut in the metal is clean, without deposition on the edges and with a very limited effect on the substrate. In this paper, we will discuss the interaction of FS pulses with thin metal films and the integration issues of such a laser with Near Field optics. Cr and CrO ablation results of a programmed defect on masks will be presented. Clean homogeneous repairs of Cr. opaque defects with sharp edges and with minimal (less than 10 - 20 nm) Quartz penetration are also shown. Molten material at the line edge, which was common with the NS laser ablation, is also avoided with the FS laser ablation. The resulting mask repair system provides enhanced Cr. and CrO removal without deposition on the edge and with minimal Quartz effect.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Yosi Shani, Ian Melnik, Sasha Yoffe, Yuval Sharon, Klony S. Lieberman, Hanan Terkel, "High-resolution near-field mask repair with femtosecond laser", Proc. SPIE 3546, 18th Annual BACUS Symposium on Photomask Technology and Management, (18 December 1998); doi: 10.1117/12.332815; https://doi.org/10.1117/12.332815
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