###### Abstract  
A random copolymer (PTBM), utilized as deep ultra-violet (DUV) photoresist, was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization with tert-butyl methacrylate (tBMA), methyl methacrylate (MMA), triphenylsulfonium \(p\)-styrenesulfonate (TPS-SS), and functional poly (sesquierbonylisoloxanes) (POSS-MA) as the monomer components, and 4-cyano-4-[(dodecylsulfanylithocarbonyl) sulfanyl]lpentanoic acid (CDSPA) as the RAFT reagent. Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (\({}^{1}\)H NMR) proved successful synthesis. Ultraviolet absorption spectroscopy (UV) analysis verified the transparency of the polymer in the DUV band. RAFT polymerization kinetics showed that the polymerization rate conformed to the first-order kinetic relationship, and the polymerization process exhibited a typical controlled free radical polymerization behavior. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and static thermo-mechanical analysis (TMA) showed that the incorporation of POSS groups improved the thermal properties of the copolymer. According to scanning electron microscopy (SEM) images, the copolymerization of photoacid monomers (TPS-SS) resulted in photoresist copolymers exhibiting good resistance to acid diffusion and low roughness. DUV photoresists; RDRP; photoacid generators; POSS +
Footnote †: journal: Applied Sciences  
diffusion occurring within the photoresist during chemical amplification [13; 14]. This diffusion arises from the erratic movement of excess protons formed after the chain reactions. Historically, most commercially available photoresists have been developed by physically combining small molecular photoacid generators [15]. The elevated temperature during post-exposure bake (PEB) exacerbates the erratic movement of these small molecular photoacid, leading to increased acid diffusion. Addressing acid diffusion has become a critical concern in chemical amplification photoresists with high resolution. Meanwhile, variations in the composition of photoresist resin have notable impacts on LER, primarily due to the uneven distribution of chain lengths, resulting from the conventional free radical polymerization used in synthesis of photoresist resins. In addition, the conventional free radical polymerization contributes to drawbacks of the photoresist, such as uncontrollable molecular weight and poor batch-to-batch reproducibility, which negatively affect photolithography processes [16; 17; 18]. Currently, by regulating the equilibrium between dormant and active free radicals [19], various Reversible Deactivation Radical Polymerization (RDRP) methods [20; 21] were developed, including Atom Transfer Radical Polymerization (ATRP) [22; 23; 24], Nitroide-Mediated Polymerization (NMP) [25], and Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization [26; 27]. These techniques have rapidly evolved into potent tools for synthesizing macromolecules with precise structures, low polydispersity, and controlled average molecular weight [28; 29]. Preparation of photoresist resins by controlled free radical polymerization has become a new research direction. Thermal performance of photoresist significantly influences the quality and resolution of photoresist. The increased temperatures, even as high as 100-120 \({}^{\circ}\)C during pre-baking and post-exposure bake steps in photolithography, may cause deformation or collapse of photoresist patterns. [PERSON]\({}^{3}\) improved thermal performance of photoresist through the introduce of adamantlyl groups to reach 120 \({}^{\circ}\)C for T\({}_{\text{g}}\) and 190 \({}^{\circ}\)C for T\({}_{\text{d}}\), while [PERSON] [30] enhanced the heat resistance of photoresist by introducing cedryl alcohol ester groups to reach 128 \({}^{\circ}\)C for T\({}_{\text{g}}\) and 200 \({}^{\circ}\)C for T\({}_{\text{d}}\). Presently, cage-type polyhedral oligomeric silsesquioxane (POSS) is a novel organic-inorganic hybrid material.