Selective Dissolution Resistance Control of EUV Photoresist Using Multiscale Simulation: Rational Design of Hybrid System

A photoresist (PR) that can be fabricated in sub-10 nm patterns with the introduction of extreme ultraviolet lithography (EUVL) is a key requirement for transistor downsizing. To produce such ultrafine patterns, assigning small molecular components on the edge surface is a fundamental approach; however, lightweight constituents (PR chain) trigger severe polymer loss in unexposed regions (dark loss) during the dissolution process, thus destroying the uniformity of the pattern. Using computational modeling, we designed a new hybrid-type PR that can eliminate the dark loss of the low-M-n polymer (<= 5 kg/mol) by integrating the positive-tone resist (deprotection) with the negative one (cross-linking). Through the selective cross-linking reaction on protection side groups, chemical linkages are generated exclusively for the unexposed chains and adequately endure the aqueous treatment. Moreover, the accurately controlled cross-link density enables suppression of resist swelling. Such improvements result in the smoothing of the line edge roughness (LER) for the hybrid pattern at the sub-10 nm scale. To set up the design rule of the proposed system, physical correlation among the chain size-dark loss-LER was thoroughly investigated, and the PR chain of 54-mers (10 kg/mol) was shown to exhibit the best LER quality with the mild condition of dark loss (<= 11 mol %) and the moderate chain dimension (R-g similar to 2 nm). The sequential multiscale simulation used in this computational approach allows a full description of the photochemistry in the EUVL process at the molecular level, which involves phototriggered acid activation/diffusion, deprotection, PR dissolution, and cross-linking reaction, and also provides reliable LER prediction, consistent with experimental observations.