IN-SITU N-PHASE AND K-PHASE COMPENSATION IN AN INTERFEROMETRIC FLYINGHEIGHT TESTER

Conventional multiwavelength flying height testers rely upon an extern al ellipsometer for measurement of the slider's n and k as in [1]. The se values are used to correct the phase offset of the interferometric signal [2]. Typically n and k measurements obtained from a sampling of 20 to 30 sliders are averaged and the results are used indefinitely i n production testing. This approach to n and k phase correction may be adequate for high flying heights but it becomes less attractive as fl ying heights decrease and the correction becomes a large fraction of t he nominal. In the new method described here phase offset is measured when a standard retract or rpm calibration is performed. Using the cal ibration data, an estimate is obtained of the absolute reflectivity of the slider. Next the value of the real part n of the complex index of the slider is inferred from an independent correlation of n to the sl ider reflectivity. Given these two numbers - the slider reflectivity R and the real part n of the index - the phase correction for flying he ight is calculated using a well-known relationship giving phase shift on reflection as a function of n and R.