Measuring Deprotection Kinetics in Chemically Amplified Resists with In-Situ Infrared Spectroscopy
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Chemically amplified photoresists have been used in semiconductor lithography for over 40 years. These materials are based on an acid-sensitive polymer containing a low concentration of a strong acid catalyst. Patterns are formed in the polymer through a coupled reaction-diffusion process. The diffusion length of the acid catalyst may control the pattern dimensions, which is a significant challenge for future manufacturing processes that need to resolve features at the scale of 10 nm. The goal of this project is to develop predictive models of pattern formation using a model photoresist system. First, reaction kinetics was measured with in-situ infrared absorbance spectroscopy as a function of temperature (below the glass transition temperature), acid catalyst concentration, and acid-anion size. These data demonstrate that a smaller acid-anion pair leads to faster reactions. Second, conversion kinetics was analyzed with a simple model of reaction with slow catalyst loss. The model qualitatively captures the observed trends and suggests an activation energy on the order of 100 kJ/mol for each catalyst/polymer system, which is the magnitude expected for a diffusion-controlled reaction in a glassy polymer. Collectively, these outcomes demonstrate that pattern formation in chemically amplified photoresists is largely controlled by acid catalyst diffusion.