The silicon oxide film on a Si wafer with guaranteed traceability to NIST (Standard sample: VLSI Standard Inc. FTS4-1000) is measured. The figure shows the tanψ and cosΔ spectra. As a result of fitting, the film thickness obtained is 96.9nm. This value agrees with the reported thickness of this standard sample 96.7 ± 0.6nm within a guaranteed tolerance. The reference film thickness of the standard sample is measured with the NIST traceable ellipsometer