Photoemission spectroscopy on photoresist materials: A protocol for analysis of radiation sensitive materials

The continued downscaling, following the so-called Moore's law, has motivated the development and use of extreme ultraviolet (EUV) lithography scanners with specialized photoresists. Since the quality and precision of the transferred circuit pattern are determined by the EUV-induced chemical changes in the photoresist, having a deep understanding of these chemical changes is of pivotal importance. For this purpose, several spectroscopic and material characterization techniques have already been employed. Among them, photoemission can be essential as it not only allows direct probing of chemical bonds in a quantitative way but also provides useful information regarding the generation and distribution of primary and secondary electrons. However, since high energy photons are being employed for characterization of a photosensitive material, modification of the sample during the measurement is possible, and this must be considered when investigating the chemical changes in the photoresist before and after exposure to EUV light. In this paper, we investigate the chemical changes occurring during the photoemission measurements of an unexposed, model chemically amplified resist based on the well-known environmentally stable chemically amplified photoresist as a function of a number of measurement parameters, using both an x ray (AlK_α, 1486.6 eV) and a UV source (HeII, 40.8 eV). We will show that these chemical changes can be simulated through theoretical modeling of the photoemission spectra. Based on these results, we propose a measurement protocol allowing to minimize or eliminate this modification which will help to guide (or enable) photoemission measurements on radiation-sensitive materials (e.g., photoresists).