Unraveling the role of secondary electrons upon their interaction with photoresist during EUV exposure

Abstract

The interaction of 91.6eV EUV photons with photoresist is very different to that of optical lithography at DUV wavelength. The latter is understood quite well and it is known that photons interact with the resist in a molecular way through the photoacid generator (PAG) of the chemically amplified resist (CAR). In EUV however, the high energy photons interact with the matter on atomic scale, resulting in the generation of secondary electrons. It is believed that these secondary electrons in their turn are responsible in chemical modification and lead to switching reactions that enable resist local dissolution. However, details of the interaction are still unclear, e.g. which reaction an electron with a given energy can initiate.In this work we have introduced a method to measure the chemical interaction of the secondary electrons with the EUV resist. The method is based on electron gun exposures of low energy electrons (range ~1eV to ~80eV) in the photoresist. The chemical interaction is then measured by Residual Gas Analysis (RGA), which can analyze out of the outgassing which and how much reaction products are generated. In this way a 'chemical yield' can be quantified as function of electron energy. This method has been successfully applied to understand the interaction of secondary electrons on the traditional CAR materials. The understanding was facilitated by testing different compositions of an advanced EUV CAR, where resp. polymer only, polymer+PAG, and polymer+PAG+quencher are tested with the electron gun. It was found that lowenergy electrons down to ~3-4eV can activate PAG dissociation, which can lead to polymer deprotection. However it was observed too that energy electrons of ~12eV and higher can do direct deprotection even in absence of the PAG. In addition, testing suggests that electrons can generate also other chemical changes on the polymer chain that could lead to cross-linking.

Extreme Ultraviolet-Printability and Mechanistic Studies of Engineered Hydrogen Silsesquioxane Photoresist Systems

“…RGA/QMS analyses of EUV and electron-induced desorption: EUV-and the electroninduced mechanism is studied by the Residual Gas Analyzer (RGA)/ quadrupole mass spectrometer (QMS) setup installed in Imec's outgas tool, on the 40 nm thick films. 37 Exposure to EUV-radiation and electron-beam causes chemical changes in the resist bulk and results in the desorption of certain volatile species. In the RGA, the desorbing species are ionized by electron impact and analyzed by a QMS to obtain a mass spectrum.…”

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

“…A few studies have addressed the electron-driven chemistry that is fundamental to the conversion of chemically amplified resists (CARs) during EUV exposure. [18][19][20][21][22] In these studies, direct insight in the chemical reactions was obtained by mass spectrometry (MS) that monitored volatile fragments desorbing from the resist layers during electron exposure. More recently, MS was also applied to investigate the electron-induced chemistry of Sn oxoclusters as an example of metal-containing molecular resist.…”

Key Role of Very Low Energy Electrons in Tin-Based Molecular Resists for Extreme Ultraviolet Nanolithography

“…When an EUV photon is absorbed by the resist, primary and secondary electrons (SEs) with energies in the 0–80 eV range are produced. , These electrons play a central role in the chemical transformations that photoresists undergo. Specifically, they can induce molecular bond scissions, , which change the photoresist structure and thus its solubility properties, thereby enabling pattern formation. ,− However, very few studies of the electron energy dependence of these processes have been performed up to date. ,,− …”