Residual gas analysis for evaluating a metal-oxide photoresist

Details

Supervisors

Hackens, Benoît ; Holzmeier, Fabian

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux, à finalité spécialisée

Abstract

enExtreme ultraviolet (EUV) lithography has become a standard technique in the fabrication of semiconductor devices at advanced process nodes, as its short wavelength of 13.5 nm enables the patterning of features just a few nanometers in size. The relatively low photon flux of EUV exposure tools, the ionizing nature of EUV radiation, and the transition to thinner resist films for higher resolution have drawn attention to molecular photoresists containing metal atoms, which exhibit a high absorption cross section at 13.5 nm. However, the exposure chemistry of such metal-containing photoresists differs fundamentally from that of commonly employed chemically amplified resists. Therefore, a deeper understanding of their chemical behaviour is essential for optimizing lithographic performance. In this study, a zinc-based molecular resist from the class of metal oxide resists (MORs) was investigated using residual gas analysis (RGA) under EUV exposure. The resulting mass spectra were analysed to identify the volatile species released, providing validation for a previously proposed reaction mechanism. The main outgassed species include acetonitrile, carbon dioxide, methyl alcohol, and formaldehyde. The presence of formaldehyde is likely due to the dehydrogenation of methyl alcohol on the zinc oxide surface. Given that EUV irradiation induces a combination of photon-driven and electron-driven processes, the specific role of electrons was further examined by studying the outgassing behaviour under controlled electron irradiation at various kinetic energies. A clear difference in the outgassing response was observed between low-energy and high-energy electrons, indicating that a threshold energy is necessary to initiate the key chemical reactions. The thermal stability of the resist was also evaluated using temperature-programmed desorption (TPD). The results showed that the resist begins to degrade at approximately 100°C, releasing volatile products consistent with those observed under EUV exposure. Contrast curve measurements further demonstrated that processing the resist at elevated temperatures results in reduced lithographic performance, including lower contrast and higher required dose.