Functionalization of Polymer Surfaces for Organic Photoresist Materials

Photoresists are thin film materials designed to transform an optimal image into a mechanical mask. Diverse exposure techniques such as photolithography induce modifications in the exposed areas that result in solubility changes that can then be selectively removed with appropriate agents (developers). Photoresist materials need to keep pace with the increasingly demand for feature size reduction. Typically, photoresist materials are organic polymers that can present small cross sections to the incoming photons, resulting in poor trade-off between resolution, sensitivity, or line-edge roughness. Photoresists also require a high etch-resistance relative to the substrate material, in order to preserve patterned features after the mechanical mask has been created. The main strategy to improve polymer performance during such processes is functionalization with different elements that can deliver higher efficiencies while keeping the chemical reactivity of the original polymer design. Here we consider a photoresist polymer structure model with general characteristics and investigate the functionalization of the polymer surface using density-functional theory (DFT), with a focus on reactive halogen adsorption. Physical and chemical surface reactions and the corresponding byproducts are identified, obtaining self-limitation thresholds for each specific functionalizing agent. Moreover, spectral signals of the modified polymer surfaces are analyzed in detail, to allow experimental validation of the proposed surface modifications. Finally, using ab initio molecular dynamics (AIMD) and real time time-dependent DFT (rt-TDDFT), we study the interaction of energetic ions and electrons with the modified polymer surfaces, to validate the obtained functionalizations as effectively enhanced etch-resistance strategies. The computational results provide valuable insights on the complex physical, chemical, and dynamic ion and electron interactions with functionalized polymer photoresists, with the immediate consequence of allowing the extraction of definite strategies for improving photoresist polymer performance.