Ultra-precision optical fabrication technology

In order to satisfy the precision in different frequency bands of the 193 nm projection lens, an ultra-precision optical fabrication technology was introduced, which includes ultra-smooth polishing and high-precision surface figuring. The mechanisms of micro fluid jet ultra-smooth surfaces polishing(MJP) and ion beam figuring (IBF) were introduced. To demonstrate the process, an 100 mm fused silica flat optical element was polished on the ultra-smooth polishing and IBF machine. Through two MJP and one IBF iteration, its surface figure accuracy root-mean-square (rms) is improved from initial 35.042 nm to final 3.393 nm, the intermediate frequency surface roughness root-mean-square (rms) is improved from initial 0.389 nm to final 0.303 nm, and the high frequency surface roughness root-mean-square (rms) is improved from initial 0.218 nm to final 0.0802 nm. At last, the surface quality of the lens before and after polishing was analyzed by power spectral density. The result shows that the surface figure accuracy and roughness of optical element could be all highly improved by MJP and IBF union, and the ultra-precision element of 193 nm projection lens will be realized through optimizing the technological parameters.