Method and apparatus for detecting photoacoustic signal and meth

Details Method and apparatus for detecting photoacoustic signal and meth Method and apparatus for detecting photoacoustic signal and meth

1990-02-14

1991-11-05

McGraw, Vincent P.

Optics: measuring and testing

For light transmission or absorption

G01N 2125, G01N 2171

Patent

active

050627155

ABSTRACT:
A photoacoustic signal detecting method and apparatus for intensity-modulating light having a wavelength penetrating a sample such as a semiconductor device at a desired frequency, the light being emitted from a first light source, focusing the intensity-modulated light on the sample as a light spot, by changing the position of the sample and the optical constant of the means for focusing, scanning the light spot inside the sample in a depth direction thereof to detect the photoacoustic effect generated in the sample, and extracting information relative to the surface and inside of the sample and defect information therein. The photoacoustic effect is detected using an interferometer. Light incident on the sample surface for a second light source in order to obtain interference light and the interference light reflected from the sample surface are adjusted in response to a signal indicative of the depth of the light spot to detect optimum interference light. Light reflected from the sample surface when light emitted from a third light source is incident on the surface is detected through the focusing optical system to generate the signal indicative of the depth of the light spot.

REFERENCES:
patent: 4689491 (1987-08-01), Lindow et al.
patent: 4854710 (1989-08-01), Opsal et al.
M. Hangyo et al., "Photoacoustic Microscope", Hihakai Kensa, vol. 36, No. 10, Oct. 1987 (Showa 62), pp. 730-736.
P. Cielo et al., "Laser Generation of Convergent Acoustic Waves and Applications to Materials Evaluation", IEEE 1986 Ultrasonics Symposium, pp. 515-526.

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