Accurate Roughness Measurement Using a Method for Evaluation and Interpolation of the Validity of Height Data from a Scanning White-light Interferometer

An effective and precise method using a scanning white-light interferometer (SWLI) for three-dimensionalsurface measurements, in particular for roughness measurements, has been proposed. The measurement ofa microscopically sloped area using an interferometer has limitations, due to the numerical aperture ofthe lens. In particular, for roughness measurements, it is challenging to obtain accurate height data fora sloped area using the interferometer, due to diffraction of the light. Owing to these optical limitationsof the interferometer for roughness measurements, the Ra measurements performed using an interferometercontain errors. To overcome the limitations, we propose a method consisting of the following two steps. First, we evaluate the height data and set the invalid height area to be blank, using the characteristicsof the modulus peak, which has a low peak value for signals that have low reliability in the interferogram. Next, we interpolate the blank area using the adjacent reliable area. Rubert roughness standards are usedto verify the proposed method. The results obtained by the proposed method are compared to those obtainedwith a stylus profilometer. For the considered sinusoidal samples, Ra ranges from 0.053 μm to 6.303 μm,and we show that the interpolation method is effective. In addition, the method can be applied to a randomsurface where Ra ranges from 0.011 μm to 0.164 μm. We show that the roughness results obtained usingthe proposed method agree well with profilometer results. The R2 values for both sinusoidal and randomsamples are greater than 0.995. KCI Citation Count: 3