Interferometric measurement of disk/slider spacing: the effect of phase shift on reflection

In an interferometric system for measurement of spacing between a transparent disk and a slider, the effect of phase shift on reflection off the slider surface must be considered to obtain an accurate measurement. Here, a theoretical treatment of the problem is described and typical measurements are provided of phase shift on reflection for several types of slider materials in use today. The technique used to measure phase shift utilizes an ellipsometric measurement of the slider´s complex index of refraction from which the phase shift on reflection is calculated. Monochromatic interferometric theory is used to show that assuming the slider to behave as a dielectric with a phase shift on reflection of π can result in flying height measurement errors on the order of 12 nm. The magnitude of the phase-shift effect is investigated for different slider materials. In addition, the variation in phase shift as a function of the wavelength of light is investigated