Fabrication of Nanometer Scale Patterns with Polymer Langmuir-Blodgett Films

The continuing trend toward higher circuit density in microelectronic devices has motivated research efforts in varieties of high-resolution lithography techniques, including electron beam (EB), X-ray, and deep UV irradiation. Use of ultra-thin films and new materials have been proposed as approaches to improve resolution in lithography. The Langmuir-Blodgett (LB) technique is very effective method used to prepare well-defined ultra-thin film with controlled thickness and orientation at a molecular level. Therefore, LB films are expected to realize ultra-high resolution photolithography [1-4].

In previous studies, [5-7] we have found that N-octadecylacrylamide forms a uniform LB film with a highly ordered structure, and yielded a fine negative pattern by photopolymerization. Furthermore, we have also succeeded in the preparation of preformed polymer LB film that has a cross-linking group [8]. By the cross-linking reaction with deep UV and electron beam irradiation we obtained a fine negative pattern consisting of two-dimensional network. All of these polymer LB films resulted in negative-tone photopatterns. On the other hand, we also obtained positive type photopatterns using poly(N-tetradecylmethacrylamide)(p(TDMA)) LB films without any development process (self-development) [9, 10]. It was found that the higher sensitivity could be obtained by changing the alkyl side chain to the short-branched type [11]. In addition, the deprotection reaction of t-butoxycarbonyloxy group has also been used in positive patterning of polymer LB films [12-14]. Combining these interesting properties, the improvement of not only the sensitivity but also the imaging quality can be expected. In this work, we prepared the copolymers of photodegradable N-tetradecylmethacrylamide (TDMA) with t-butyl 4-vinylphenyl carbonate (tBVPC) (Figure 1) aiming at the fabrication of a new type of positive resist taking place both main chain scission and polarity change caused by t-butoxycarbonyloxy group deprotection.