Development of a 3-Axis Displacement Measuring Heterodyne Interferometer System Usable with a He-Ne Laser of Either 3.76 MHz or 20 MHz Split Frequency

Abstract

We present a 3-axis displacement measuring heterodyne interferometer system developed for use with a He-Ne laser at the wavelength of 633 nm having a split frequency of either 3.76 MHz or 20 MHz. The system consists of an optical interferometer, a signal processing board, and a software.

The interferometer can simultaneously measure the displacements of three axes, from which the distance, tilt angles of a moving object can be determined in real time. A digital logic circuit which calculates the displacement values from electric signals converted from 3 optical interference signals, was developed. To demonstrate the measured results graphically, we developed a graphical-user-interface software. In addition, a feedback function through a high speed communication bus was added to the system so that it can be applied for motion control of a moving stage requiring scanning and alignment of a thin film coated substrate such as a silicon wafer. The performance of the interferometer was checked by comparing the measurement values of the displacement of a moving stage obtained simultaneously by a commercial laser interferometer and the developed interferometer.