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11 March 2002 Endpoint solution for photomask chrome loads down to 0.25%
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Abstract
Endpoint measurement sensitivity requirements in photomask can make or break an etch. The exposed chrome on today's photomask can vary between 0.25 percent and approximately 50 percent. Although excessive overetch does not deleteriously impact the underlying quartz, accurate endpoint detection is essential for preserving the critical dimension (CD) and CD uniformity across the mask. In order to provide a strong endpoint solution for photomask etch, a systematic investigation of etches with varying chrome loads was conducted. Passive monitoring of the optical emission spectra does not impact or interfere with the etch process. Also this method does not need specified endpoint sites on the mask as interferometric methods and provides an integrated endpoint signal over the whole mask area independent of the chrome clearing pattern. Two strong candidate wavelengths for calling endpoint in chrome etch were identified. However, optical emission spectroscopy endpoint detection has two drawbacks, which have historically limited its applicability. Firstly, the exposed area may be too low and/or secondly, the etch rate may be too slow for detection. Both of these concerns have been addressed in this paper by varying the exposed area on the photomasks from 0.25 percent to 99 percent. Endpoint was easily detected even for the slowest possible etch rate and for low exposed area.
© (2002) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Melisa J. Buie, Brigitte C. Stoehr, Alex H. Buxbaum, and Guenther G. Ruhl "Endpoint solution for photomask chrome loads down to 0.25%", Proc. SPIE 4562, 21st Annual BACUS Symposium on Photomask Technology, (11 March 2002); https://doi.org/10.1117/12.458342
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