We investigate indium nitrate hydrate films as a potential extreme ultraviolet (EUV) resist using electron beam (e-beam) exposure. Indium has an EUV absorption cross-section comparable to tin, the metal element in the state-of-the-art inorganic EUV resists. We choose indium nitrate salts as the metal precursor to minimize residual carbon in the resist. With a calibrated e-beam flood gun, we test the solubility switch in indium nitrate hydrate films as a function of e-beam energy. The resist becomes insoluble upon exposure to the e-beam, exhibiting a negative tone characteristic. The solubility switch occurs for e-beam energy from 500eV down to 92eV, the energy of the EUV photons. Furthermore, to determine the mechanism behind the solubility switch, we study the chemical changes upon e-beam exposure using operando Fourier transform infrared spectroscopy and residual gas analysis. The resists show similar optical contrast and nitric oxide release for three post-application bake (PAB) conditions. The sensitivity and contrast of indium nitrate hydrate are determined from the dose curves obtained using electron beam lithography (EBL) and e-beam flood gun. We obtained an average sensitivity of 226±46μC/cm2 from four EBL experiments and a contrast of γ=1.3±0.3. The results from the e-beam flood gun have a sensitivity of 295μC/cm2 and γ=1.0. A benchmarking experiment was also performed using an e-beam flood gun on organotin (SnOxo) resist, which has a sensitivity of 165μC/cm2 and γ=1.6. The similar characteristics between these two resists indicate that indium nitrate hydrate films hold high promise to be a sensitive EUV resist.
Indium nitrate hydrate films are evaluated as potential extreme ultraviolet (EUV) resists. To study the feasibility of these indium nitrate-based sol–gel precursor films as an EUV resist, the uniformity and stability of these films are examined as a function of metal composition, precursor concentration, chemical sources, precursor dissolution time, solvent drying time, post-application bake conditions, and relative humidity during the deposition. A 0.1 M indium nitrate hydrate solution forms a 20-nm thick resist, which is 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 during spin coating, dissolution time, and water content in the solvent. Hence, they are likely due to undissolved or re-crystallized indium nitrate hydrate crystals. The spin-coated indium nitrate hydrate films show great stability with no changes in defect density for up to 3 weeks. Using a 92-eV electron beam as a proxy for the EUV source, exposed regions of the film become insoluble upon exposure, acting as a negative-tone resist. Results of operando Fourier-transform 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. These results demonstrate the potential of indium nitrate hydrate films as an effective inorganic EUV resist.
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.
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