Minimizing line/space pattern defects and roughness of indium nitrate resists through environmental control

The processing environment has a significant effect on the performance of metal oxide resists (MORs). Here, we examine the effects of relative humidity (RH) and atmospheric oxygen on the morphology, chemical composition, and line/space (L/S) patterning results of indium(III) nitrate hydrate (In(NO3)3·xH2O) MORs. Previous work shows that processing In(NO3)3-based resists under ambient conditions at RH≥40% produces localized surface protrusions at the nanoscale, which disrupt L/S patterns by breaking the lines and increasing line-edge roughness (LER) and line-width roughness (LWR). We find that processing in a humidity-controlled glovebox at or below 35% RH eliminates the nanoscale protrusions. Independent variation of the spin-coating and post-application bake environments further shows that these defects form only when both processing steps are performed in humidities above 35% RH. Transmission Fourier transform infrared spectroscopy reveals no discernible compositional differences among films prepared in compressed air and nitrogen, whereas decreasing RH produces stronger spectral contributions from precursor components, including nitrate, ammonium, and water species. These results indicate that resist morphology and chemistry are more sensitive to moisture than to oxygen during processing. L/S patterns are subsequently fabricated using 100-eV electron beam lithography. Resists processed in the humidity-controlled glovebox at 25% and 35% RH exhibit defect-free lines with significantly lower LER/LWR values compared with those processed in the ambient laboratory environment at 40% RH. We have achieved a minimum LER of 3.7 nm±0.4 nm and an average line width of 18.9 nm±1.9 nm. We demonstrate that controlling the processing environment can suppress patterning defects caused by morphology and improve the performance of In(NO3)3-based resists, highlighting process control as an important consideration in the development of MORs for extreme-ultraviolet lithography.