Catadioptric Lens for Excimer Laser Lithography

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Optical lithography is widely used in the manufacture of integrated circuits. The current systems utilize conventional I- line (356nm wavelength) lamps or to illuminate the lenses that print the IC patterns onto wafers. Future systems will use laser. All of the lithography optics used to date have been the refractive type. At the short ultraviolet (UV) laser wavelengths required for next generation device manufacturing, several limitations exist for this type of lens. These limitations include light scattering because of shot wavelengths, heat absorption due to high photon energies in the UV, and optical transmission losses (poor efficiency) from high absorption of the light. The PI propose to develop a catadioptric optical system that has high optical transmission, high resolution, is laser-resistant, and relatively easy to manufacture. Because the optics are mirror-based, optical distortion is greatly reduced and very high power levels can be used without damaging the optics. We have made preliminary experiments in our lab with this type of optics, and achieved 0.4um resolution. The development of this type of lens would lead to significant improvements in the high resolution imaging systems for VLSI microlithography, a critical step in manufacturing integrate circuits.