Photoacid generation and acid mobility: Mechanistic studies relevant to photolithography.

Abstract

Although highly varied, all of the work in this thesis involves studying acid in photolithographically relevant systems. The objectives of the individual projects never stray far from the central goal of acquiring mechanistic insight into both the photoacid generation process as well as acid mobility in polymer films. It is the ultimate goal of this work to gain a fundamental understanding of chemical processes and reaction mechanisms, in order to apply this knowledge to the evaluation and design of materials for use in photolithography. Techniques for quantifying and locating photogenerated acid in solution and in polymer films were both developed and extensively employed. These techniques are based on the protonation of acid-sensitive dyes and were used for the purposes of studying acid diffusion as well as evaluating photoacid generating efficiencies of photoacid generators (PAGs). A novel technique for monitoring acid desorption from polymer films was developed in order to study the behaviour of acid in polymer films under processing conditions similar to those employed industrially. The kinetics for acid desorption were measured and the factors which control acid mobility were identified. Much of the work presented in this thesis is focused on determining the mechanisms by which PAGs generate acid as well as designing and testing new molecules for use as PAGs. Among the molecules studied in these contexts were sulfones, N-heteroaromatic salts and sulfonium salts tethered to ketones. The key steps towards photoacid generation for these molecules include homolytic bond cleavage, photoinduced electron transfer and triplet energy transfer, respectively.