A NEGATIVE, DEEP-UV RESIST FOR 248 NM LITHOGRAPHY

The negative tone deep ultraviolet resist described in this paper is based on a novolak resin. The chemistry of this negative resist is based on an acid-hardening resin system. A novolak resin combined with an acid activatable cross-linker and a photoacid generator (PAG) comprise the resist. Exposure to high energy photons (below 320 nm) converts some PAG to acidic species. These acids catalyze the formation of several covalent bonds between the novolak and the substituted melamine cross-linker. A postexposure bake accelerates the cross-linking reaction. High contrast is obtained because the appropriate exposure dose and postbake process render the resist nearly insoluble in the developer. Thus, the high ratio of the unexposed to exposed dissolution rates of the resist provides high contrast, high resolution resist images.