Structural effects on the performance of epoxide-based negative-tone molecular resists

Abstract

Several 0.26N tetramethylammonium hydroxide (TMAH)-soluble epoxide molecular resists have been synthesized and are reported here. Previously, the patterning performance of 1,1,2,2-tetrakis(p-hydroxyphenyl)ethane-3 epoxide (TPOE-3Ep) was reported and resolved 26 nm lines using extreme ultraviolet lithography. Here, a deeper study is performed to determine the effects of various structural features on the lithographic performance of 0.26N TMAH-soluble molecular resists. Increasing the number of phenols resulted in a notable increase in the glass transition temperature (Tg) of these materials, which required high postexposure bake (PEB) temperatures to achieve normalized remaining thickness (NRT) values of 1 in methyl isobutyl ketone development. Such high PEB temperatures resulted in insoluble material (high NRT values) in unexposed regions in the 248 nm contrast curves. Methyl groups were introduced adjacent to the hydroxyl group of phenol in an attempt to lower the Tg of the resists to allow the use of lower PEB temperatures. The methyl groups only slightly lowered the Tg of the resists, while detrimentally reducing the final NRT. Thus, instead of using the TPOE core or its methylated analog, a smaller core was used, and the resist trihydroxyphenyl ethane (THPE)-2Ep was designed and synthesized to be a low-Tg base-soluble resist. THPE-2Ep has a Tg of 41 °C and showed promising early performance using e-beam lithography and resolves 30 nm lines in 0.26N TMAH developer at a dose of 72 μC/cm2 at a PEB of 50 °C.