Advanced simulation techniques for thick photoresist lithography

A method has been developed that allows accurate simulation of pattern profiles in photoresist in excess of 10 micrometer thick. The method uses the DEPICTR photolithography simulator to model i-line exposure, bake and development of Shipley SJRR5740 thick film photoresists with an Ultratech 2244i Wafer StepperR. Kim model inputs were estimated from a family of development rate curves obtained by processing wafers with a range of expose energies for logarithmically increasing develop times and measuring thickness change as the develop process occurred. These results were compared with dissolution results obtained using a laser-based dissolution rate monitor. Uncertainties in the measured photoresist absorbence, photosensitivity and refractive index coefficients were estimated and their influence on the simulated results were considered. An optimization procedure and algorithm that allows quantitative comparison of experimental and simulated photoresist profiles is presented. Simulated photoresist profiles were compared with patterns obtained from processed wafers. As a further test of the models, pattern profiles were simulated for 2 micrometer spaces in 10 micrometer thick photoresist through focus. Experimental and simulated pattern profiles from a range of exposure doses were also compared.