Indium nitrate hydrate resist characteristics evaluated by low-energy electron beam exposure

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.