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Elimination of bottom-pinching effect in environmentally stable chemically amplified resists

Chemically amplified deep UV photoresist is well known with its sensitivity towards base contaminants either from track and stepper ambience or from substrate. The former gives 'T- top' formation whereas the latter leads to 'footing' in line pattern. This sensitivity originates from the chemically amplification nature that uses photoacid to catalyze the deprotection of resin. To overcome environmental unstability, a variety of chemically stable resists have been formulated. However, during evaluation of some of these new deep UV photoresist, 'bottom pinching' (BP) effect was observed for photoresist on top of organic bottom anti-reflection coating (BARC). BP effect is the slimming of photoresist line immediately above the substrate, which shows the photoresist actually dissolutes at a higher rate near the substrate. This might be caused by higher concentration of acid in the photoresist near the substrate. It is believed that the excess amount of acid diffuses out from the BARC layer. Thus, the softbake of BARC and photoresist, the post-exposure bake of photoresist are to be optimized for the 'bottom pinching' effect.