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The pre-clean prior to tunnel oxidation is a key unit process for flash memory performance and reliability．This paper studies pre-clean quality by looking at the tunnel oxidation film quality.We compare tunnel oxides grown after a single wafer udHF and gas-phase ozone cleaning technology to a conventional RCA batch cleaning.The ozonated process shows improvements in thetunnel oxide resistivity，density of interface traps，and the total oxide charge.The electrical oxidethickness of the oxide increases even though theoptical thickness is not significantly different.The pre-clean improves the intrinsic breakdown voltage of the tunnel oxide while preserving the tunneling field.When applied to product wafers，the process demonstrates superior in-line defect densities after floating gate deposition.