Fundamentals of the reaction-diffusion process in model EUV photoresists

More demanding requirements are being made of photoresist materials for fabrication of nanostructures as the feature critical dimensions (CD) decrease. For EUV resists, control of line width roughness (LWR) and high resist sensitivity are key requirements to their success. The observed LWR and CD values result from many factors in interdependent processing steps. One of these factors is the deprotection interface formed during the post-exposure bake (PEB) step. We use model EUV photoresist materials to systematically address the influence of exposure-dose on the resulting surface roughness. We report the spatial evolution of the deprotection reaction using a bilayer geometry to represent the line-edge as a function of dose for fixed PEB time using neutron reflectivity. Resulting deprotection profile is also compared with integrated deprotection level obtained from FTIR. The bilayer consists of an acid feeder layer containing photoacid generator (PAG), whereas the bottom layer is a model ESCAP photoresist, poly(hydroxystyrene-co-tert-butylacrylate)with perdeuterated t-butyl moieties. The deuterium labeling allows the protection profile to be measured with nanometer resolution. The evolution of the compositional profile with exposure dose will be discussed