Impact of COF2 dry cleaning on the physicochemical properties of plasma enhanced chemical vapor deposited SiO2 thin films

Carbonyl fluoride (COF2) has attracted increasing attention as a low-global-warming-potential (low-GWP) cleaning gas for plasma-enhanced chemical vapor deposition (PECVD) chamber cleaning, offering a potential alternative to conventional nitrogen trifluoride (NF3). However, the influence of COF2 chamber cleaning on the properties of subsequently deposited thin films has not yet been sufficiently clarified. In this study, the physicochemical properties of PECVD SiO2 films deposited on 300 mm Si wafers after COF2-based dry cleaning with an O2 additive were investigated and compared with those obtained after conventional NF3 cleaning. Residual gas analysis during O2-remote plasma source conditioning suggested the possible presence of carbon-containing residual species in the chamber system with a COF2 processing history, supporting the need to evaluate the postcleaning chamber environment. X-ray photoelectron spectroscopy analysis showed near-surface compositional differences in the SiO2 films deposited after COF2 cleaning, including relative increases in C and N concentrations and a relative decrease in O concentration compared with those deposited after NF3 cleaning. Qualitative N 1s fitting suggested a possible relative increase in the N–Si–O-related spectral contribution under the COF2 cleaning condition. However, spectroscopic ellipsometry showed that the refractive index of the COF2-cleaned samples was slightly lower but remained comparable to that of the NF3 reference sample under the same Cauchy-based fitting procedure. Wet etch rate analysis also showed that the COF2-cleaned samples did not exhibit degraded etch resistance, with wet etch rates of 236 nm/min for the NF3 reference sample and 223±5 nm/min for the COF2 samples. These results indicate that COF2 cleaning can induce measurable near-surface compositional differences in subsequently deposited SiO2 films, while not significantly degrading their average optical and physical properties. Therefore, COF2 can be considered a promising low-GWP dry-cleaning gas candidate with potential wafer-level process compatibility for subsequent PECVD SiO2 deposition processes.