Plasma‐Sequence‐Engineered Atomic Layer Deposition of Ultra‐Thin SiN _x for Enhanced Etching Resistance in Extreme Ultraviolet Pellicles

ABSTRACT The fabrication of protective layers on graphite faces a fundamental dilemma because high‐quality, dense films are required to withstand the harsh plasma environments of extreme ultraviolet lithography (EUVL) applications, yet forming such robust coatings without damaging the graphite remains highly challenging. In this study, uniform and dense SiN _x ultrathin films for the EUV pellicle are formed on graphite using mild, plasma‐sequence‐engineered atomic layer deposition, without any damage to graphite. Si ₂ Cl ₆ is used as the precursor, NH ₃ plasma as the prime reactant, and sequential N ₂ plasma as a promoting reactant. The SiN _x film fabricated using NH ₃ plasma, followed by N ₂ plasma, exhibits a mass density of 3.07 g/cm ³ , close to the bulk density, with low O and H concentrations. The film exhibits an improved wet‐etching resistance against 30 wt.% KOH for 16 h and 250 W H ₂ plasma for 5 min, mimicking the EUVL environment. Therefore, the optimized SiN _x ultrathin film (5 nm) formed on graphite effectively protects graphite against H ₂ plasma for high‐performance EUV pellicles. Furthermore, the mass spectra of the byproducts, such as HCl, reveal the reason for the densification by N ₂ plasma, while the correlation between film properties and etch resistances is statistically validated through a permutation test.