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Measuring Ultra-Thin Air Films

IP.com Disclosure Number: IPCOM000041331D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Korth, HE: AUTHOR

Abstract

Air films in the 100 nm range are measured with an accuracy of 1 nm in a white light interferometric set-up, using sheared beams having a constant path difference of some 1000 nm. Interferometric thickness measurements in the sub-wavelength range do not yield periodic interference signals but require an absolute determination of the intensities, which is very difficult to realize in practice because of the great number of parameters involved. A periodic interference pattern can however be artificially generated by introducing a fixed path difference between the beams of a two-beam interferometric set-up. Figs. 1 and 2 are lateral elevational and top views of a shearing interferometric set-up for measuring the air film 16 between a glass disk 14 and a reflecting sample 15.

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Measuring Ultra-Thin Air Films

Air films in the 100 nm range are measured with an accuracy of 1 nm in a white light interferometric set-up, using sheared beams having a constant path difference of some 1000 nm. Interferometric thickness measurements in the sub- wavelength range do not yield periodic interference signals but require an absolute determination of the intensities, which is very difficult to realize in practice because of the great number of parameters involved. A periodic interference pattern can however be artificially generated by introducing a fixed path difference between the beams of a two-beam interferometric set-up. Figs. 1 and 2 are lateral elevational and top views of a shearing interferometric set-up for measuring the air film 16 between a glass disk 14 and a reflecting sample 15. The white light of a lamp 10 passes lens 11 and polarizer 12 (oriented at 45OE) to reach birefringent plate 13 at which two beams 24 and 25 with mutual orthogonal polarizations are generated. The beams impinge on the upper surface of plate 14 at the Brewster angle r; the directly reflected light is stopped by a shading plate 22. Beam 25, which is polarized parallel to the plane of incidence, is reflected only at sample 15 (Brewster's law), whereas beam 24 is partially reflected at the lower (inner) surface of disk 14. Sample 15 is oriented such that the part of beam 24 exiting from disk 14 is not reflected. Beam 25 and the reflected part of beam 24 are recombined...