Development of the line-focus-beam ultrasonic material characterization system.

Abstract

A line-focus-beam ultrasonic material characterization (LFB-UMC) system has been developed to evaluate large diameter crystals and wafers currently used in electronic devices. The system enables highly accurate detection of slight changes in the physical and chemical properties in and among specimens. Material characterization proceeds by measuring the propagation characteristics, viz., phase velocity and attenuation, of Rayleigh-type leaky surface acoustic waves (LSAWs) excited on the water-loaded specimen surface. The measurement accuracy depends mainly upon the translation accuracy of the mechanical stages used in the system and the stability of the temperature environment. New precision mechanical translation stages have been developed, and the mechanical system, including the ultrasonic device and the specimen, has been installed in a temperature-controlled chamber to reduce thermal convection and conduction at the specimen. A method for precisely measuring temperature and longitudinal velocity in the water couplant has been developed, and a measurement procedure for precisely measuring the LSAW velocities has been completed, achieving greater relative accuracy to better than +/- 0.002% at any single chosen point and +/- 0.004% for two-dimensional measurements over a scanning area of a 200-mm diameter silicon single-crystal substrate. The system was developed to address various problems arising in science and industry associated with the development of materials and device fabrication processes.