Methods and apparatus for identifying the material of a particle

Details Methods and apparatus for identifying the material of a particle Methods and apparatus for identifying the material of a particle

1999-01-14

2000-09-19

Pham, Hoa Q.

Optics: measuring and testing

Inspection of flaws or impurities

Surface condition

3563274, 356338, G01N 2188

Patent

active

061220477

ABSTRACT:
The composition of a particle occurring on the surface of a smooth substrate is identified by impinging the surface with a light beam having a strong P-polarized component at an oblique angle of incidence to the surface, and collecting light scattered from the surface at forward, center, and back locations relative to the portion of the surface impinged by the incident beam. The intensities of the light collected at these locations are measured by detectors and converted into signals, and the magnitudes of the signals are compared to correlations of particle material as a function of the relative magnitudes of the forward-, center-, and back-scatter signals so as to identify the material whose correlation most nearly matches the measured detector signals. Preferably, a ratio of the back detector signal magnitude to forward detector signal magnitude is correlated with particle material and back detector signal magnitude. Alternatively or additionally, a ratio of back detector signal magnitude to center detector signal magnitude is correlated with particle material and back detector signal magnitude. Average particle diameter versus back detector signal magnitude is correlated with particle material.

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