Measurement of Si Epitaxial Thickness Using a Michelson Interferometer

Abstract

A system has been designed to measure the thickness of silicon epitaxial material using a scanning Michelson interferometer rather than a conventional dispersive IR spectrometer. The sampling capacity of this system with a 5–6 sec sampling time exceeds that of several dispersive instruments. The long‐term precision on a single machine (3σ) is , where is the film thickness. Computer processing of the reflection interferogram from an epitaxial wafer provides film thickness data by a Fourier transform method. This method is shown to be mathematically equivalent to the method used for dispersion spectrometers as given by ASTM procedure F95‐68T. The two measurements are in agreement within the published interlaboratory precision of the ASTM method: for P‐type material and for N‐type. The lack of moving mechanical parts in the interferometer system contributes to making this type of instrument very reliable. Down time due to system failure has been minimal, and two systems have been in operation a total of over 4 machine years.