Photolithography illumination needs

Abstract

Industrial photolithographic exposures are now performed almost entirely with the high pressure mercury arc, using one or more of the spectral lines at 365, 408 and 436 nm. It would be difficult for the free electron laser to replace the entrenched and reliable arc unless it could offer a significant improvement, for instance, in brightness. Lithography is currently being extended to shorter wavelengths, as far as the X-ray regime. At present, the excimer laser is the principal source in the UV. Since the excimer is comparatively new, the FEL might find a niche more easily in this domain. To compete with current sources in the near and far UV, the FEL should provide at least 4 W of useable power. Since lithographic illumination must be uniform, the coherence of the FEL output must be sufficiently low to avoid "noise" due to interference. In addition, a light source for industrial use must be reliable and maintainable by plant personnel. © 1985.