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# Measuring the Refractive Index and Thickness of Thin Reflective Layers

IP.com Disclosure Number: IPCOM000093312D
Original Publication Date: 1967-Aug-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 28K

IBM

## Related People

Statz, HF: AUTHOR

## Abstract

For determining the refractive index of thin reflective layers deposited on reflective substrates, a wedge is cut through the layer and the substrate, the bevel angle being about 1 degree. The bevel, if inspected with a microscope in monochromatic light, exhibits an interference pattern of equally spaced lines. The distance between the lines is a function of the wavelength lambda of the light, of the refractive index n of the layer material, and of the bevel angle a. For the reflective layer part of the bevel this is Dl = lambda/2n tan a. For the substrate part it is Ds=lambda/2 tan a, if the bevel is inspected under a normal interference microscope. The refractive index then is n = Ds/Dl.

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Measuring the Refractive Index and Thickness of Thin Reflective Layers

For determining the refractive index of thin reflective layers deposited on reflective substrates, a wedge is cut through the layer and the substrate, the bevel angle being about 1 degree. The bevel, if inspected with a microscope in monochromatic light, exhibits an interference pattern of equally spaced lines. The distance between the lines is a function of the wavelength lambda of the light, of the refractive index n of the layer material, and of the bevel angle a. For the reflective layer part of the bevel this is Dl = lambda/2n tan a. For the substrate part it is Ds=lambda/2 tan a, if the bevel is inspected under a normal interference microscope. The refractive index then is n = Ds/Dl. With the refractive index being known, the thickness of any reflective layer can be determined by counting the fringes on a bevel under a conventional microscope. Dark stripes occur at zones where the layer thickness is d = (2N-1) lambda/4n where N=1, 2, 3,....

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