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Roughness Measurement by Means of a Fabry-Perot Interferometer

IP.com Disclosure Number: IPCOM000036099D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Kempf, J: AUTHOR [+2]

Abstract

Optical methods of measuring the peak-to-valley height of technical surfaces with a sensitivity below light wavelength are a) scattered light methods, b) speckle contrast methods and c) white light coherence methods.

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Roughness Measurement by Means of a Fabry-Perot Interferometer

Optical methods of measuring the peak-to-valley height of technical surfaces with a sensitivity below light wavelength are a) scattered light methods,

b) speckle contrast methods and

c) white light coherence methods.

The peak-to-valley depths that may be measured by those methods are

a) 5 nm - 600 nm,

b) 60 nm - 10,000 nm,

c) 30 nm - 12,000 nm.

Future semiconductor products, mirrors for astronomical telescopes and X- lithography require extremely smooth surfaces which must be tested at high speeds without destruction. The method described below is suitable for peak-to- valley measurements of a few nanometers.

A Fabry-Perot interferometer (Fig. 1) is formed by the surface of the probe PR to be tested and a plane-parallel glass plate Q covered with a metal layer M on the resonator side, the thickness of which is

(Image Omitted)

such that the measuring light supplied by a laser L is reflected as frequently as possible between the glass plate and the probe surface, with a sufficient amount of light from the resonator reaching detector D. The distance d between the surface of probe PR and the glass plate Q is adjusted by a piezoelement PE such that the reflected measuring light is minimal. Fig. 2A shows the reflection signal R as a function of d. The minimum reflection Rmin is highly responsive to the roughness of the probe surface. Estimates show that Rmin increases considerably if the peak-to-valley dept...