What We Don’t Know About EUV Exposure Mechanisms

Abstract

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 ( = 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.

Universal direct patterning of colloidal quantum dots by (extreme) ultraviolet and electron beam lithography

“…26 Yet even electrons with energy much lower than this bond strength can induce chemical change in the material by means of dissociative electron attachment, where electrons are trapped by a molecule in an antibonding orbital. 24,27 This process results in bond cleavage and subsequently in the generation of reactive species like radicals which can react with double bonds and induce the formation of new bonds, leading to the carbon chains cross-linking. 28,29 As the absorption of one EUV photon can lead to a multiple of lower-energy photoelectrons, EUV radiation can have an inherent chemical amplification, possibly requiring lower exposure doses.…”

Role of low-energy electrons in the solubility switch of Zn-based oxocluster photoresist for extreme ultraviolet lithography

“…4,6 A detailed understanding of the chemistry that occurs upon EUV irradiation and leads to the solubility switch of the EUV resist material is needed to design efficient novel EUVL resists. [8][9][10] Compared to conventional DUV (193 nm) lithography, the chemical processes underlying EUVL are more complex. 1 At 193 nm (6.4 eV), the absorption of a DUV photon by the resist only leads to a neutral valence excited state that can then decay in a photochemical reaction to produce a desired solubility switch.…”

Mixed-ligand zinc-oxoclusters: efficient chemistry for high resolution nanolithography

“…[7][8][9] The understanding of this complex EUV-induced chemistry is currently rather limited. 10,11 Yet, without the proper EUVchemistry knowledge, it is a challenge to custom-design materials for EUVL that can meet the industrial targets of sensitivity (o20 mJ cm À2 ), low line width/line edge roughness (LWR/LER o 20%), and resolution (o20 nm). 4,[11][12][13] A prerequisite for EUV resist materials is high absorbance at 13.5 nm.…”