Somewhat in analogy with the well-established applications of focused electron beams, carefully focused UV and visible lasers have been applied recently to the fabrication, by direct writing, of microstructures for electronics.1,2 In comparison with electron beams, largely useful for resist exposure, a much broader range of material processing is possible because of the qualitatively greater selectivity and versatility of optical photons in the excitation of local chemical reactions. Over the last several years, one-step etching, deposition, and semiconductor doping techniques have been demonstrated for a variety of electronic materials. By the use of surface processes, such as nucleation and catalysis, and the nonreciprocal response these localization processes imply for direct writing, it has been possible to controllably generate linewidths of ~0.2 μm, i.e., below the Rayleigh diffraction limit for the (visible) light used. Both thermal and photochemical methods have been applied to the fabrication of integrated circuit structures at increasing levels of complexity3–5 (Fig. 1).
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