Combined interferometer/ellipsometer for measuring small spacings

Abstract

An apparatus and method for measuring the space between a transparent member such as a substrate, and reflective member such as a slider. The apparatus includes a first optical system which detects a first light beam that is reflected from the substrate and the slider. The reflected light is separated into four separate beams. The intensities of the beams are detected and utilized to determine a first stokes parameter, a second stokes parameter, a third stokes parameter and a fourth stokes parameter of the reflected light. The stokes parameters are used to compute the real index of refraction n, extinction coefficient k and the thickness of the space. The four stokes parameters account for any depolarized light that is reflected from the slider. The first optical system may have a photodetector which detects an image of the slider. The image provides multiple data points that can be used to calculate n, k and the thickness of the air gap without a retract routine. The apparatus may also have a second optical system which detects a second light beam reflected from the substrate and the slider. The second optical system can be used to dynamically measure a thickness of the space. In the combined system the first optical system may accurately measure the n and k of a slider area while the second optical system dynamically measures the thickness of the air gap.