Acid Generation Efficiency of EUV PAGs via Low Energy Electron Exposure

Abstract

Optimizing the photochemistry of extreme ultraviolet (EUV) photoresists can lead to faster, more efficient resists needed for implementation of EUV lithography into high volume manufacturing. EUV photoresists must simultaneously meet three requirements: improved resolution, low line edge roughness (LER), and high sensitivity. Common EUV photoresists utilize photoacid generators (PAGs) to improve sensitivity, which is affected by many variables, such as developer choice, developer concentration, PAG quantum yield, etc. Isolating one of these parameters will aid in the optimization of sensitivity. Prior work using alternate methods shows it is possible for resists to generate 5-6 acids per absorbed photon. However, the energy of the weakest bond in a typical PAG molecule is on the order of a few electron volts, it should be possible to reach much higher quantum yields with EUV (92 eV) photons. The photochemistry in EUV lithography is believed to be dominated by the energetic electrons generated from ionization. Investigating the acid generation efficiency for a variety of PAGs and concentrations upon electron exposure may lead to the development of resists with higher quantum yield, improving current EUV photoresist platforms. In this study, the reactions between PAG molecules and electrons were measured by using a mass spectrometer to monitor the levels of small molecules produced by PAG decomposition that outgassed from the film.

Reactivity of metal-oxalate EUV resists as a function of the central metal

“…For reactions in EUV resists (or other systems) where there is a volatile byproduct, mass spectrometry can be used for quantitative measurement of reactions (Sec. 3) [29][30][31][32] . For the three metal-oxalate complexes, the proposed photomechanism suggests the first step in the photochemical process is the oxidation of the oxalate ligand with the accompanied reduction of the metal from M(III) to M(II) ultimately leading to a change in solubility when the coordination complex is formed 10 .…”

“…The oxalate ligand will decompose readily when detached from the metal center and produce carbon dioxide in the process. The rate of CO2 production can be monitored using in situ mass spectrometry measurements [29][30][31][32] . [24][25][26][27][28] .…”

“…Consequently, an 80 eV electron exposure is used as a model for EUV exposure mechanisms. Electron outgassing experiments are completed in our electron-resist interaction chamber (ERIC) [29][30][31][32] .…”

Isotopic Labeling Studies of EUV Photoresists Containing Antimony

“…Our recent work has focused on investigating the photomechanism of our antimony-carboxylate platform, by studying the volatile photoproducts following exposure to EUV (Fig. 1) [21][22][23].…”

EUV Mechanistic Studies of Antimony Resists

“…To better understand the chemistry occurring during exposure, we identified outgassed reaction products generated during photolysis via mass spectrometry [13][14][15]. In our initial experiment, we exposed a film of JP-18 to EUV and collected the positive-ion mass spectral data (Fig.…”