Andrea Kraetz

Amorphous zinc-imidazolate (aZnMIm) resists show potential to meet the demands for next generation high-numerical aperture (high-NA) metal-containing extreme ultraviolet (EUV) resist materials given their ease of deposition by atomic/molecular layer deposition (ALD/MLD) at thicknesses of 20 nm and below. This study demonstrates that aZnMIm thin films, previously identified as high-resolution electron beam resists, can also function as negative tone EUV photoresists. Water development achieves high sensitivity (5 mJ/cm²) but leaves significant residue, while acetic acid development results in poor contrast. A hybrid approach—water followed by acetic acid—enables residue-free development with a sensitivity of 181 mJ/cm². Dry development using 1,1,1,5,5,5-hexafluoroacetylacetone (hfacH) is also possible, but shows lower sensitivity (375 mJ/cm²) compared to wet development methods. EUV photoelectron spectroscopy (PES), reflectometry/EUV absorption, total electron yield (TEY), residual gas analysis (RGA), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) were used to investigate the effects of EUV irradiation on aZnMIm resists. Reflectometry experiments reveal an aZnMIm EUV absorption coefficient of 6.2 µm-1, while PES and TEY analyses show that, compared to poly(4-hydroxystyrene) (PHS), a polymer-based reference resist, aZnMIm emits more primary and secondary electrons but generates fewer slow electrons relative to its primary electron emission; its total electron yield is similar to that of poly(methyl methacrylate) (PMMA) resists. When exposed to EUV, aZnMIm predominantly outgasses H2, as determined by RGA. TOF-SIMS measurements demonstrate that high dose EUV exposure only partially fragments the 2-methylimidazole (2MIm) organic linkers, unlike high dose electron beam exposure, which is known to completely degrade them. Additionally, aZnMIm resists show promise for potential beyond-EUV lithography (BEUVL) due to the presence of Zn, which provides higher sensitivity at 6.7 nm compared to other metal ions, like Sn, that are currently used in the best-performing EUV metal-organic resists. TEY measurements demonstrate that aZnMIm emits nearly twice as many electrons as PHS at 6.7 nm. The BEUV TEY of aZnMIm also surpasses that of PMMA, poly(pentafluorostyrene), and poly(4-iodostyrene), with the latter two being known for their high EUV TEYs. This work provides new insights into zeolitic imidazolate framework (ZIF)-based EUV and BEUV resists and highlights their potential for both wet and dry development.

Motivated by the drawbacks of solution phase processing, an all-dry resist formation process is presented that utilizes amorphous zinc-imidazolate (aZnMIm) films deposited by atomic/molecular layer deposition (ALD/MLD), patterned with electron beam lithography (EBL), and developed by novel low temperature (120 °C) gas phase etching using 1,1,1,5,5,5-hexafluoroacetylacetone (hfacH) to achieve well-resolved 22 nm lines with a pitch of 30 nm. The effects of electron beam irradiation on the chemical structure and hfacH etch resistance of aZnMIm films are investigated, and it is found that electron irradiation degrades the 2-methylimidazolate ligands and transforms aZnMIm into a more dense material that is resistant to etching by hfacH and has a C:N:Zn ratio effectively identical to that of unmodified aZnMIm. These findings showcase the potential for aZnMIm films to function in a dry resist technology. Sensitivity, contrast, and critical dimensions of the patterns are determined to be 37 mC cm-2, 0.87, and 29 nm, respectively, for aZnMIm deposited on silicon substrates and patterned at 30 keV. This work introduces a new direction for solvent-free resist processing, offering the prospect of scalable, high-resolution patterning techniques for advanced semiconductor fabrication processes.