Thermal Deprotection Process in an E-Beam Exposed, Phenolic-Based Polymer.

摘要

An alkali soluble latent image can be generated in pure PBOCST (poly(tert-butoxycarbonoxystyrene)) by e-beam exposure followed by a post-exposure bake (PEB) at relatively high temperatures (140 - 150 C). Pattern wet development operates on the same basis as a PBOCST/acid generator two component system. Deprotection (heating), accelerated by the exposure, yields alkali soluble areas while unexposed areas remain insoluble. Sensitivities of 5-10 micro/cu cm and contrasts of 6-10 have been measured. Complete TBOC deprotection results in a film thickness loss of 35-40% as CO2 and isobutene are evolved. A laser interferometer/hotplate setup was used to track film thickness with time during the thermal deprotection process. Infrared analysis confirmed the correlation between conversion and thickness. It was found that a slow initial conversion rate was followed by an exponentially steep rise in rate after the 50% conversion point. Activation energies were on the order of 30 kcal/mol. It is apparent that thermolysis in both exposed and unexposed resist occurs during the PEB but that the difference in extent of conversion on exposure is sufficient to generate a pattern.