SIMULATION ANALYSIS OF A CHEMICALLY AMPLIFIED POSITIVE RESIST FOR KRF LITHOGRAPHY

The reactions of a chemically amplified positive resist, CAMP6, which is composed of poly tert-butoxy carbonyl (t-BOC)-styrene copolymer as a base resin and 2,6-dinitrobenzyl tosylate as a photoacid generator, were analyzed. The acid generation and t-BOC deprotection reactions were analyzed by FTIR spectrometer and modeled successfully. The dissolution rates were measured by a Development Rate Monitor (DRM). A new and simple dissolution rate model is presented, since the dissolution rate behavior of chemically amplified positive resists cannot be explained by the conventional models that are designed primarily for novolac/dissolution inhibition systems. Furthermore, this new model can also explain the surface inhibition effect by considering acid loss (deactivation) due to airborne contaminant diffusion from the resist surface. Simulation software, Prolith/2, was modified to incorporate the model, and profile simulations were carried out successfully. Based on this accurate resist profile simulation, a new process window concept will be presented. This process window is defined on an exposure-defocus plane as the areas that are determined by linewidth error and sidewall angle at the resist thicknesses corresponding to maximum and minimum linewidths on a swing curve. This window concept can give a practical process margin, since the standing wave effects are incorporated. This method is applied to the process window analysis for KrF excimer laser lithography.