Actinic photoemission spectroscopy of litho materials using a table-top ultrafast EUV source

Abstract

Extreme ultraviolet (EUV) lithography (92 eV) has recently entered logic and memory high-volume manufacturing to ensure the continuation of Moore's Law into advanced technology nodes (sub 5 nm). In parallel to advancements in the lithographic system, the development of suitable photoresists plays an equally important role in pushing the boundaries of EUV lithography. Fundamental work on well-established chemically amplified resists (CAR) for EUV as well as the upcoming resists based on metal-organic materials have indicated that the lithographic mechanism is largely governed by electron mediated chemistry. In a simplified model, the electrons emitted upon ionization of the material generate further secondary electrons, which interact with the resist components and induce a solubility switch driven by electron and radiation chemistry. To develop a better performing resist, it is of utmost importance to understand the photoelectron kinetic energy spectrum, secondary electrons and their generation efficiency, and the electron mean free path in the photoemission process. In this work, we use photoemission spectroscopy with a table-top, coherent, 92 eV photon source to shed light on the chemistry driven by photon exposure. The valence band photoelectron spectrum (PES) of an environmentally stable chemically amplified photoresist (ESCAP), as well as a model material for an open-source metal oxide (OSMO) resist were measured using our tabletop EUV photoemission setup. We report the evolution of the PES as a function of exposure dose; capturing chemical changes.