ABSTRACT
This chapter discusses the new classes of polymers along with new systems that have been created as topcoat or protective layer materials for immersion lithography. Photoresist systems have been classified as positive-tone or negative-tone. Positive-tone photoresist systems are those, where the relief image formed at the wafer level is the same as the one in the mask or reticle. Positive-tone, novolac-based photoresists with a diazonaphthoquinone sensitizer began replacing rubber-based photoresists in the mid 1970s as greater resolution was needed. A large change in the dissolution rate of the exposed vs. the unexposed resist is the fundamental principle that makes all novolac photoresists work. However, high-molecular-weight components can enhance other required photoresist properties, like thermal stability, because their glass transition temperature is higher. Molecular simulations of resist dissolution based on the Critical-Ionization Model were used to probe the mechanism of surface inhibition and the evolution of edge roughness and surface roughness in photoresist profiles.
