EUV resist curing technique for LWR reduction and etch selectivity enhancement

Abstract

This paper introduces a new technique utilizing a direct current superimposed (DCS) capacitively-coupled plasma (CCP) to enhance the etch selectivity to EUV resist with decreasing line width roughness (LWR). This new technique includes chemical and e-beam curing effects. DCS CCP generates ballistic electrons, which reform the chemical structure of photoresist. This surface modification hardens the photoresist (PR), and enhances the etch selectivity. The PR-hardening technique also improves the tolerance towards stress by polymer. Hence, a polymer becomes applicable to protect photoresist, and the etch selectivity increases even more. As a result, this cure can be processed without consuming the thickness of EUV resist. The mechanism of EUV resist cure is discussed based on the surface analysis. In addition to the basic physics of PR-hardening, this paper shows the benchmark results between DCS CCP and the conventional curing techniques by RIE, such as HBr cure and H₂ cure. Several new chemistries were applied to DCS CCP. In consequence, the PR-hardening by DCS CCP achieved a 33% reduction in LWR at pre-etch treatment, and a 30% reduction during under layer etch simultaneously maintaining enough thickness of EUV resist.