Synchronous Multifunctional Combinatorial Chemistry on a Molecular Glass Backbone─a Strategy for Developing Photoresists with Improved Lithography Performances

Although molecular photoresists exhibit higher resolution than polymer-based resists, the latter play a dominant role in lithography applications. The pivotal reason lies in the fact that multiple function integration can be readily achieved in polymer resists through one-pot copolymerization with various monomers, which is critical to enhance the overall performances; but for molecular photoresists, the functional monotonicity remains a significant drawback that needs to be overcome. Herein, a strategy named as Synchronous Multifunctional Combinatorial Chemistry (SMCC), i.e., one-pot multiple and different decorations on a molecular glass backbone, which integrates the idea of combinatorial synthesis with the approach of parallel processes analogous to copolymerization, is proposed to develop multifunction-integrated molecular photoresists. The feasibility of the SMCC strategy is exemplified by high yield syntheses of a series of diversely grafted spiroxanthene molecules via synchronous Suzuki coupling of X4Br (four bromo to be modified) with distinct phenylboronic acid/ester derivatives. Then, by the same way, an all-in-one photoresist X4EpTPS was conveniently constructed, in which both photoacid generator (PAG) triphenylsulfonium (TPS) and epoxy group (Ep, acid-driven cross-linking) were bound to a spiroxanthene core in a specified ratio. The lithography performance of X4EpTPS was studied and compared with physically blending formulation of direct adding PAG TPS-TF in X4Ep. It is confirmed that molecular level integration of multiple functions into X4EpTPS ensures more homogeneous PAG distribution during the PAB process while effectively confining photoacid diffusion in the PEB process, significantly enhancing lithographic performance. Finally, X4EpTPS achieves dense 25 nm HP L/S patterns with critical dimension 23 nm and LER 2.7 nm. Therefore, we are confident that in the future development of molecular photoresists, the strategy of SMCC is broadly extensible and applicable for performance enhancement tailored to diverse requirements.