Catalytic and Autocatalytic Mechanisms of Acid Amplifiers for Use in EUV Photoresists

Abstract

Twelve fluorinated acid amplifiers (AAs) were synthesized and studied for use in photoresists exposed to 13.5 nm, extreme ultraviolet (EUV) light. Acid amplifiers are compounds that decompose in the presence of acid to generate more acid via catalytic or autocatalytic mechanisms. These AAs are composed of a body, trigger, and an acid precursor. Thermal decomposition rates of solutions of the AAs in C6D6/m-ethylphenol (50/50 wt %) at 100 °C were monitored by 19F NMR with and without 1.2 equiv. of 2,4,6-tri-t-butylpyridine. All of the AAs in the presence of base decompose according to first-order kinetics with rate constants kBase. The rate constants, kBase, at various temperatures yielded the activation parameters ΔH‡, ΔS‡, and ΔG‡. The enthalpy of activation, ΔH,‡, was in a narrow range of 16.6−19.1 (kcal/mol), whereas the entropy of activation, ΔS‡, spanned from 0 to −12 (cal/(mol K)). When acid is allowed to build up in solution (in the absence of base), six of the AAs with tertiary triggers (Body-3) decompose autocatalytically, but the six with secondary triggers (Body-2) are unaffected. Although Body-2 AAs do not decompose autocatalytically, nonaflate acid does catalyze their decomposition. Lithographic evaluation showed that some AAs are capable of simultaneously improving the resolution, line-edge-roughness, and sensitivity of a control EUV photoresist. This simultaneous improvement was quantified using the Z-Parameter. The AAs investigated here were found to improve the Z-Parameter by as much as a factor of 3.