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Film Thickness Measurement with Null Detection

IP.com Disclosure Number: IPCOM000076942D
Original Publication Date: 1972-May-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 19K

Publishing Venue

IBM

Related People

Brezoczky, B: AUTHOR

Abstract

A noncontact interferometric method for measurement is described. The technique utilizes a variable monochrometer and does not require an approximate knowledge of film thickness in the range ~15 mu - 120 mu in.

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Film Thickness Measurement with Null Detection

A noncontact interferometric method for measurement is described. The technique utilizes a variable monochrometer and does not require an approximate knowledge of film thickness in the range ~15 mu - 120 mu in.

The interferometer is based upon light interference between a reflective sample and a partially reflective reference beam splitter.

The beam splitter separates the illumination light into two coherent parts. One part travels to the specimen surface, and the other part to the reference mirror. After reflection, both interfere at the beam splitter. The interference pattern is observed.

By changing the monochrometer wavelength in the visible spectrum the interference lines upon the deposit and the substrate are made to match on each other, then move away from each other, then match again, etc. When the interference lines upon the deposit and the substrate match on each other, then t = n lambda(3) over 2 + phi t = (n + 1) lambda(2) over 2 + phi' where t = film thickness n = order of interference lambda(3) > lambda(2) = wavelength at "null".

phi, phi' = correction due to the variation of phase change at the substrate interface. The function of lambda above lambda = 5000 angstroms is linear. Then, n = lambda(2) over lambda(3)-lambda(2). Where n is a whole integer, 1, 2, 3 ....

The measurement may be made manually or by electronic assist, utilizing television monitors, oscilloscope and/or photodetector means.

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