| 摘要 |
<p>The invention relates to optical fluoride crystals, and particularly to optical fluoride crystals (20) such as calcium fluoride, which have high transmission levels to below 200nm light, such as produced by excimer lasers. In particular the invention relates to making optical fluoride crystals with improved transmission surfaces (23). The invention relates to the elimination of mid-spatial frequency roughness 1-1000 um spatial wavelengths and high-spatial frequency < 1 um spatial wavelengths from optical fluoride crystal surfaces. The removal of the mid-spatial frequency 1-1000 um spatial wavelengths and high-spatial frequency < 1 um spatial wavelengths from the optical fluoride crystal surfaces provides improved transmission at below 200nm optical lithography wavelengths such as 193nm and 157nm. The invention includes final finished optical fluoride crystals (20) having final finish high optical transmission surfaces (22) free of mid-spatial frequency roughness 1-1000 um spatial wavelengths and high-spatial frequency roughness 1-1000 um spatial wavelengths and high-spatial frequency roughness < 1 um spatial wavelengths with high transmission at wavelengths < 200nm.</p> |
