Indium nitrate hydrate films as EUV resists by evaluating with 92-eV electron beam

Abstract

Indium nitrate hydrate films are evaluated as potential extreme ultraviolet (EUV) resists. The uniformity and stability of indium nitrate-based sol-gel precursor films are studied as a function of metal composition, concentration, chemical sources, precursor dissolution time, post-application bake (PAB) conditions, and relative humidity during the deposition. 0.1 M indium nitrate solution forms a 20-nm thick resist, ideal for EUV lithography. We find two types of defects: macroscale defects that are visible under an optical microscope and nanoscale defects that can only be detected using an atomic force microscope. Both types of defects are affected by humidity and dissolution time and are likely due to indium nitrate crystals. Once formed, indium nitrate hydrate films show great stability with no changes in defect density up to 3 weeks. Using a 92-eV electron beam as a proxy for the EUV source, preliminary studies show exposed films become insoluble after 10 min exposure (8 mC/cm2 dose), acting as a negative-tone resist. Results of in-situ Fourier-transformed infrared spectroscopy and residual gas analysis during the exposure show that the solubility switch is accompanied by the decomposition of nitrate species and the release of water.