The design of a multi-point probe for a scanning low-coherence distance-measuring interferometer

Abstract

A highly efficient method for splitting the probe beam produced by a scanning low-coherence distance-measuring interferometer (SLCDI) is presented. The SLCDI is used to measure thicknesses of materials with thicknesses in the range of 12 microns-50 mm, with a repeatability of 0.1 microns. The measurements are made optically with a beam with a wavelength of 1.3 microns. The SLCDI is also capable of simultaneous measurement of a stack of multiple films. Splitting of the beam from the SLCDI probe to create a multi-point probe allows for multiple, simultaneous measurements to be made at a surface. An advantage of this capability is that it provides the ability of to measure the surface normal at each of the surfaces that are under test. The operation of the SLCDI will be described along with how the operation impacts the requirements for the multi-point probe system. The requirements are discussed from the standpoint of the coherence length of the SLCDI source and the operational usage of the probe. The splitting is achieved through the use of polarization components. The function and performance of the resulting probe is also discussed.