Integrated circuits routinely produced by microlithography have feature sizes as small as 65 nm, well below the traditional diffraction limit for the exposure wavelength of 193 nm. Achieving this level of performance requires using a number of techniques to bypass the resolution limitations posed by the wave nature of light. It also means that the optical system always must perform to specification, with little tolerance for deviation. One problem in microlithography tools is uneven heating of the imaging lens elements by the excimer laser, which results in focus issues. This article explores the background and development of a CO2 laser-based system that controls lens heating and that has proved sufficiently robust for the demands of production semiconductor fabrication.

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