Lithography projection lens system is a typical extremely small aberration system. In order to meet the requirement of exposure resolution, the wavefront aberration of system should be less than 10 nm ( immersion system even requires the system wavefront aberration to be less than 1 nm). The precondition to achieve the above-mentioned wavefront aberration is that the surface of the objective lens can get to sub-nanometer accuracy at low frequency ( affecting various aberrations ), mid- to- high frequency ( affecting contrast ) and ultra high frequency ( affecting transmittance ).
The manufacturing of ultra-precision optical elements is a step-by-step and iteratively convergent process between metrology and manufacturing. The team adopts high-precision Fizeau type interferometer, white light interferometer, atomic force microscope(AFM) and other high-performance metrology devices, so as to break through several critical technical difficulties such as deep sub-nanometer precision reproducibility and absolute testing, realizing full-band optical surface metrology with deep sub-nanometer precision. Supported by the above ultra-precision metrology technology, the team has self-developed some special processing machines such as robot pre-polishing machine and jet ultra-smoothing machine for the ultra-high precision optical elements surfaces (plano/ sphere/ asphere) processing. The processing technology combined by grinding, pre-polishing, corrective polishing, ultra-smoothing and ion beam figuring to finally realize the full-band manufacturing with deep sub-nanometer precision. At present, the accuracy of typical plano/ spherical elements is better than 0.3nmRMS and the surface roughness than 0.2nmRMS; The processing accuracy of typical rotationally sysmetrical aspheric surface and off-axis aspheric surface (departure less than 2mm) is better than 0.5 nm RMS and surface roughness than 0.3nmRMS.
The team has built a state of the art research and development platform for ultra-precision manufacturing technology supported by National Science and Technology Major Project. And it has more than 20 sets of high-precision CNC processing equipment, more than 20 sets of high-precision interferometers and workstations, as well as white light interferometers, and some high-precision metrology instruments used for testing mid-and-high frequency errors such as white light interferometer and atomic force microscope (AFM). The company has a special ultra-precision environmental control laboratory with an area of nearly 5,000m2 for the requirements of high-precision manufacturing, metrology and other related processing technology developments. The above-mentioned platform will be able to extend high-quality optical manufacturing and metrology services to more customers while supporting the research and development of projection lithography.