Potential cause of inhomogencous acid distribution

As feature sizes get smaller, the control of acid distribution and diffusion becomes more essential for the development of high performance chemically amplified resists. Below 45 nm node, chain length of acid catalytic reactions should be suppressed within several nanometers. An average distance between acids generated with the exposure dose of, for example, 2 μC/cm² is also several nanometers.[1] Under such circumstances, the initial distribution of acids is critical to the formation of ultra fine patterns. Up to now, two main channels leading to acid generation have been reported. One starts with the excitation of acid generator (excitation channel). The other starts with the ionization of base polymer (ionization channel). In photolithography such as KrF excimer lithography, the excitation channel dominates the acid generation process. On the other hand, in electron beam (EB) and X-ray lithography, the ionization process does. Also, in EUV lithography, the ionization process is likely to prevail in the acid generation processes because the energy of EUV is about 100 eV, As for the ionization channel, protons of acids are generated through deprotonation of base polymers. Therefore, the acid generation efficiency highly depends on polymer structure.[2] It was also reported that the protection of hydroxyl groups has considerable effects OR the acid generation ef???iciency.[3] In this paper, the details of protection effects were investigated.