Single-layer photoresist develops at 193 nm
Photoresists are a critical element of the 193-nm lithography development effort. Aromatic molecules are highly absorptive at this wavelength, limiting the use of conventional matrix resins used in lithography, such as novolacs and polyvinylphenols. Chemists at Lucent Technologies, Bell Labs (Murray Hill, NJ), have developed new matrix resins for single-layer 193-nm photoresists that offer adequate photosensitivity and adhesion while remaining robust under etch conditions. Based on cyclo-olefin-maleic anhydride alternating copolymers, rather than the conventional methacrylates, the copolymers offer the advantages of synthesis by standard radical polymerization techniques, a potentially large pool of cyclo-olefin feedstocks, and a generic structural motif incorporating alicyclic structures directly into the polymer backbone.
The experimental resist consists of norbornene copolymerized with maleic anhydride and formulated with an appropriate dissolution inhibitor and photoacid generator in typical spinning solvents. Thin films of the material spin-cast on a quart¥substrate were transparent to both 193- and 248-nm illumination. In lithographic experiments using the resist, the grou¥was able to produce 0.19- and 0.17-µm line/space images. According to researcher Elsa Reichmanis, the resist is compatible with the production of 0.15-µm feature sizes and, with further development, will be capable of printing 0.13-µm features.