The integration and assembly of ultra-precision optical system is one of the key technologies in the development of precision optical system. For IC lithography projection objective lens, the spacing error and eccentricity error of assembly of optical components should be controlled within 1 μm. On this basis, the image quality indexes such as wave aberration and distortion are finally achieved through computer-aided adjustment and assembly and system-level component refinement.
Based on the technological research on the integration and assembly technology of ultra-precision optical system of lithography projection objective lens, the team has established a complete process of assembly, measurement and image quality compensation for precision optical system to effectively reduces the manufacturing cost of the optical system by comprehensive optimization. The position tolerance of measurement and assembly with sub-micron precision can be realized using the assembly technology of existing ultra-precision optical system and the developed high-precision assembly equipment and tooling.
In terms of image quality compensation technology of ultra-precision optical system, for the development of first set of NA0.75-ArF lithography objective lens in China, the core indexes that the average wave aberration of full field of view of objective lens is better than 4nm and the average distortion of that better than 5.7nm on the basis of effective control of manufacturing difficulty and cost of ultra-high precision optical system by fully giving play to compensation method of optical system, relying on the accurate measurement technology of optical system.
At present, the team has a sound optical system test and assembly instruments and equipment which are mainly used to perform the transfer function test, stress birefringence test, laser spectrum test, lens thickness test, lens position test/assembly/adjustment, material uniformity test and wave aberration test of objective lens system. In respect of the clean room which should meet the requirements for ultra-precision assembly, its top cleanliness can reach to 100 level ( ISO CLASS 5 ), the temperature stability can be up to ±0.02℃ and the precision vibration isolation system can control the vibration level at VC-E level, so as to fully support the integration, assembly and test of ultra-precision optical system.