Flying height and topography measuring interferometer

Abstract

Apparatus is disclosed for the measurement of the distance between a test surface (55) and a plano reference surface (58) which are in close proximity to each other. The preferred way of accomplishing this is with a polarization phase modulated interferometer. The modulated interference pattern is photosensed with an array camera (52), and the signals are processed by a computer (80), which also controls the rotation speed of the rotating glass disk (54) which contains the plano reference surface (58), to provide not only the distance between the test surface (55) and the plano reference surface (58) but also the topography of the test surface (55) independent of the phase changes on reflection from the test surface (55). A method is also disclosed, using the instant invention, for determining the flying height (h) of a slider assembly used in magnetic storage systems. In this method, the computer (80) synchronizes the frame rate of the camera (52) such that the camera (52) integrates the intensity at each photosensitive element over one revolution of the disk (54) and collects four frames of such integrated intensity in order to determine the flying height (h). To eliminate the phase shift on reflection, a second set of data is taken with the glass disk (54) rotating at a different rotation rate.