Acid diffusion control in chemical amplification positive resists by exchange reaction of conjugate bases

摘要

Alkyl-substituted-onium halides (tetraalkylammonium and trialkylsulfonium halides) are investigated for possible application as an acid diffusion controller in a chemical amplification positive resist. The resist sensitivity became lower as their concentration increased because these additives can trap the catalytically active acid to produce a neutral onium salt and a catalytically inactive acid in the resist matrix. The contrast of the resist with tetramethylammonium iodide (TMNI) and trimethylsulfonium iodide (MESI), which can both produce hydrogen iodide was more than two times higher than without an additive, while the resists with other onium halides showed no evidence of contrast enhancement. An experiment on the acid diffusion range showed that the diffusion range of these iodides was much lower than with no additive, and MESI exhibited a smaller diffusion range than TMNI. This indicates that MESI is the most effective diffusion controller. Patterning of resists was carried out with an e- beam lithography system at 50 kV. The resist with MESI exhibited a remarkable resolution enhancement. It can produce high resolution patterns (90-nm contact holes) at a dose of 16.2 $mu@C/cm$+2$/.