Refractive projection lens for 90 nm resolution lithography

Lithographic exposure is the key processing in the manufacture of integrated circuit. 193 nm wavelength lithography is one of the promising technologies for the fabrication of critical dimension of 100~32 nm. The optical performance of projection lens is one of the most important factors to realize the fabrication of high resolution pattern. This paper presents the design process for lithography projection lens by optical software code V. 28 spheric lenses were used in this system. Numerical aperture can reach 0.75. With the assistance of resolution enhancement technology, image resolution reaches 90 nm. Exposure area is 26 mm × 10.5 mm and the reduction ratio is 0.25. The optical evaluation of optics was completed at full exposure area. The maximum distortion of 0.005 nm and the maximum wavefront aberration of 0.015λ (root mean square) can be reached. This projection lens can basically meet the requirements for lithographic equipments nowadays.