Slider Optical Constant Distribution, $n$ and $k$ Correlation, and FH Measurement Accuracy

The slider material is a composition of alumina (Al₂O₃) and titanium carbide (TiC) with a big difference in the optical constants. The random grain size, shape, and composition of TiC make the effective optical constant of slider air bearing surface (ABS) in the size of test spot vary largely. The spot-by-spot scanning of optical constant over slider ABS by ellipsometer indicates that the n and k correlate each other linearly. As the commercia flying height (FH) testers use the averaged n and k value to calculate FH, there is a concern of FH testing error if the n and k value at the testing spot derivates from the average value. This work discovered that the FH testing error is mainly determined by the n and k correlation rather than the absolute value of n and k dispersion. The laser phase detection method improves the repeatability of FH testing significantly, but the n and k correlation is the key to estimate the accuracy of FH measurement.