System for performing spectral analyses under computer control

Details System for performing spectral analyses under computer control System for performing spectral analyses under computer control

1975-07-31

1977-02-15

Dildine, Jr., R. Stephen

Registers

Transfer mechanism

Traveling pawl

2351513, 356107, 356161, 444 1, G01B 1106, G01B 902, G01B 1908

Patent

active

RE0291382

ABSTRACT:
Measurements of physical attributes such as dielectric film thickness that are susceptible to spectral analysis are accomplished rapidly and accurately by a spectrophotometric system in which a programmed digital computer operating concurrently with the optical scanning means automatically performs the calibrating, normalizing and data reducing functions that otherwise must be carried out as time-consuming human, mechanical or analog electronic operations. The control over the optical data handling operations exercised by the computer eliminates the need for mechanically or electronically adjusting the optical apparatus to meet changing system conditions, whether periodic or aperiodic. Source light is transmitted through a rotating variable-wavelength interference filter which acts during one-half of its cycle to transmit light of varying wave-length through a fiber-optic reference path directly to the optical data acquisition apparatus, while acting in the next half-cycle to transmit light of such varying wavelength indirectly to said data acquisition apparatus through a measurement path. In the present example, where film thickness is the attribute being measured, the measurement path comprises a bifurcated fiber-optic bundle, one branch of which is used to carry the light of variable wavelength to the sample, and the other branch of which carries light reflected from the sample to the aforesaid data acquisition apparatus. A computer program enables light passed through the reference path in one half-cycle to calibrate the system for measuring optical transmission or reflectance in the next half-cycle. Reduction of relative reflectance data to absolute reflectance data (needed for the accurate determination of film thickness) is accomplished by additional computer programs whose algorithms are based upon the discovery that all graphs of absolute reflectance versus wavelength for film samples of a given material having different thicknesses are bounded by a common pair of wave envelopes.

REFERENCES:
patent: 3482105 (1969-12-01), Hutzler
patent: 3622765 (1971-11-01), Anderson
patent: 3646331 (1972-02-01), Lord
Bey, P. P., Optical Film Thickness Monitoring, In Rev. Sci. Inst. 42(1): pp. 57-60, Jan., 1971.
Campbell, R. D., Measurement of Film Thickness, In Proc. I.R.E.E., Australia, pp. 102-104, Apr., 1967.

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