US 5,604,592 A · Laser ultrasonics-based material analysis system and method using matched filter processing

Abstract

Disclosed herein is an interferometric-based materials analysis system (10) that employs a novel combination of laser beam shaping and pointing techniques, the use of a low cost, rugged, and compact diode laser (22) as a detection laser, and the use of signal processing techniques that compensate for inherent instabilities and short-term drift in the diode laser. A matched filter processing technique is disclosed for processing interferometrically-obtained data points from a target being analyzed. The matched filter technique is shown to be especially useful for detecting and analyzing Lamb modes within thin targets, such as a silicon wafer undergoing a rapid thermal processing cycle. Also disclosed is a method and apparatus for interferometrically monitoring a target to determine, in accordance with predetermined criteria, an occurrence of a period of time that is optimum for obtaining a data point. In response to detecting such a period an impulse source, such as an impulse laser (14), is triggered to launch an elastic wave within the target so that a data point can be obtained. A plurality of data points so obtained are subsequently processed, such as by the matched filter technique, to determine a property of interest of the target. The property of interest may be, by example, the temperature of the target or the metallurgical status of the target.

Claims2

Dependent claims

A system for determining a characteristic of a target, comprising:

means for launching an elastic wave within the target;
an interferometer for detecting a displacement of a surface of the target in response to said launched elastic wave;
means, responsive to said detected displacement, for determining a time of flight of said elastic wave within the target;
and
means for correlating the determined time of flight with a characteristic of the target, wherein
said interferometer includes at least one photodetector, and wherein said correlating means is comprised of:
means for detecting a waveshape of a signal output from said photodetector;
and
matched filter processing means comprising means for storing a plurality of predetermined waveshapes, each of said plurality of predetermined waveshapes corresponding to a different target thickness;
means for comparing said detected waveshape to said stored plurality of predetermined waveshapes;
and means for correlating a thickness of the target with a predetermined thickness that is associated with a selected one of said stored plurality of waveshapes that best matches said detected waveshape.

8 more elements

Dependencies are inferred from the claim text.

Laser ultrasonics-based material analysis system and method using matched filter processing

Life of this patent

Laser ultrasonics-based material analysis system and method using matched filter processing

Life of this patent

Abstract

Claims2