Development of a trench depth measurement system for VLSI dynamic random access memory vertical capacitor cells using an interferometric technique with a Michelson interferometer

Abstract

A practical trench depth measurement system for VLSI dynamic random access memory vertical capacitor cells has been developed with a Michelson interferometer. The system is composed of an optical head, a Michelson interferometer, and a host computer. A He-Ne laser is used to monitor a prism displacement in the interferometer and to perform the coherent averaging of interferograms. It is found that the accuracy of the measured values with the system is within +/-0.1microm in the 2-5-,microm depth range. Both trench depth and reflection coefficient distributions of test wafer trenches are demonstrated by the system.