The Influence of Photoacid Structure on the Design and Performance of 193-nm Resists

The impact of photoacid generator (PAG) structure has been largely ignored for 193nm single layer resists. Most published work to date has involved the use of triflic or metallic (antimonate or arsenate) photoacids. The importance of the PAG structure on the performance of 193nm resists is magnified in comparison to 248nm positve resists in use today, due to the absence of the electron-transfer sensitization pathway in the non-phenolic polymers in use in 193nm resists. Additionally, with the realtively low reactivity (high-bake) protecting groups that we (and others) employ in our resist design, greater control of photoacid evaporation and diffusion ar required. In this paper, we document the negative consequences of triflic acid on 193nm resist performance, including data on acid volatility and the impact of apparent diffusion. Model resists based on relatively hydrophobic polymers amplify the impact of triflic acid volatility on the degredation of performance in 193nm resists. Acid generators which combine high reactivity, low photoacid volatility, and improved resolution will be described. The basic chemical skeleton of these improved 193nm photoacid generators is shown in Figure 1. These iodonium sulfonates combine excellent thermal stability, dissolution inhibition, clean synthesis and readily tailorable photoacid size and strength. Most importantly, iodonium sulfonates based on haloalkyl and activated aromatic sulfonic acids efficiently deprotect t-butyl esters and other high activation protecting groups when formulated in 193nm resist materials and exposed to 193nm light.