Thermal atomic layer deposition of SiNx protective coatings for hydrogen plasma-resistant carbon nanotube pellicles

Abstract

Thermal atomic layer deposition of silicon nitride (SiNx) as a conformal protective coating was investigated to enhance the hydrogen-plasma resistance of carbon nanotube (CNT) pellicles for extreme ultraviolet (EUV) lithography. SiNx films were deposited on Si wafers and free-standing CNT membranes in a tube-type furnace using Si2Cl6 and NH3 precursors, and the growth behavior was systematically examined over 500–800 °C. An effective ALD window was identified at 650–700 °C, yielding a growth per cycle of ∼1.9 Å/cycle. The deposited films on both Si wafers and CNT membranes exhibited Si–N-dominant bonding with no significant compositional difference between the substrates, together with low oxygen incorporation and negligible chlorine residues. After ozone pretreatment, continuous and conformal SiNx coatings were formed over the CNT network. The optical impact of the coating was evaluated at 13.5 nm; SiNx-coated CNT pellicles exhibited 95.2 % EUV transmittance, corresponding to a 2.5 percentage-point reduction compared with bare CNT pellicles. Hydrogen plasma exposure tests showed severe degradation of uncoated CNT pellicles, whereas SiNx-coated CNTs retained their morphology. These results demonstrate that thermal deposition of SiNx is an effective protective coating strategy for improving the durability of CNT pellicles in EUV lithography environments.