•Three main technologies:–Resist technology–Mask technology–Exposure tools•All need to be addressed to optimize the resolution•RET was relatively expensive•Short wavelength was selected•Recent much progress in RETResolution enhancement technology (RET)
•Challenges of conventional resists:–Low quantum yield -> fundamental limit on photosensitivity of these resists–+resist 0.2-0.3–-resist: 0.5-1–Worse for shorter light wavelength due to unbleachable absorption for +resist–Hard to be used for thicker resist•Methods for improvement–Chemical amplifier resists–Image reversal–Antireflective coating-thin film interference–Thin film imagingImproved resist performance
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•Chemical amplification:–A single photon initiates a cascade of chemical reaction of sort that characterize a silver halide photographic emulsion system–The amplification is based on the photogeneration of a catalytic photoproduct–The catalytic photoproduct is often an acidic species, that catalyze scission or cross-linking–The catalytic scission or cross linking depends on the post-exposure baking temperature, time and method Improved resist performance