Compatibility of chemically amplified photoresists with bottom anti-reflective coatings

The effects of acid structures and blocking groups in chemically amplified resists on compatibility with bottom antireflective coatings (BARCs), were investigated. The resists consisted of tert-butoxy carbonyl (t-BOC) or acetal blocked polyhydroxystyrene with three types of photoacid generators (PAGs) which generate trifluoromethanesulfonic acid (acid 1), 2,4-dimethyl benzensulfonic acid (acid 2) and cyclohexanesulfonic acid (acid 3). Three types of commercially available BARCs, Brewer Science CD9, DUV11 and DUV18 were used for this study. CD9 was decomposed by exposure and generated an acid substance, which induced the necking at the bottom of the resist films. In the case of DUV11, the generated acid from the FAG was neutralized, and footing was observed in t-BOC type resists. Acetal type resists had no footing on DUV11 because the deblocking reaction progressed without post-exposure baking. DUV18 had good compatibility with most of the resist materials because of its neutral acidity. From the viewpoint of resist materials, it was found that the acetal type resists tended to have necking, because the deblocking reaction occurred at lower acid concentration compared with t-BOC type resists. Moreover, the tendency to have a necking profile, in increasing order, was acid 3 > acid 2 > acid 1. This order corresponded with the reverse order of the efficiency of the deblocking reaction. A weak acid might be greatly affected by some substance diffused from a BARC. The acetal type resist with acid 1 had excellent compatibility with various BARCs. However, the resolution capability of the acetal type resist with acid 1 was lower than that of the acetal type resist with acid 3, because the acid diffusion length of acid 1 was larger than that of acid 3. It was concluded that good compatibility of the resist with the BARC is achieved by the high deblocking reaction efficiency and moderate diffusion length of acid in acetal type resists.