What We Don’t Know About EUV Exposure Mechanisms

The lithography community has studied EUV photoresists for nearly thirty years. Yet, some of the most basic details of the interaction of EUV photons with photoresists remain poorly understood. In a typical photochemical reaction using long-wavelength light (λ = 157-1000 nm), photons create excited states in photoactive compounds, thereby creating known quantities of intermediates and photoproducts at measurable rates. The photochemical reactions occurring during EUV exposure are much more complex and, as yet, not fully explored. The 92 eV EUV photons ionize molecules in the resist, creating holes and free electrons, however, the numbers of these electrons created, their reaction mechanisms, lifetimes and reaction cross-sections are not well known. Here, we will discuss experimental results and provide insight into these poorly understood aspects of EUV exposure mechanisms.