Optical Profiler Papers
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Akiko Harasaki, Joanna Schmit, and James C.
Wyant
APPLIED OPTICS, Vol. 40, page
2102, May 2001
Different materials with different phase changes on reflection affect the
surface-height measurement when interferometric
techniques are employed for testing objects constructed of different
materials that are adjacent to one another. We
test the influence of this phase change on reflection when vertical
scanning interferometry with a broadband source is used. We show
theoretically and experimentally that the strong
linear dependence of the dispersion of the phase change on reflection
preserves the shape of the coherence envelope of
the fringes but shifts it along the optical axis by approximately 10–40 nm
for metallic surfaces. URL:
http://www.opticsinfobase.org/abstract.cfm?URI=ao-40-13-2102 |
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Akiko Harasaki and James C. Wyant
APPLIED OPTICS, Vol. 39, page
2101, May 2000
An interference fringe modulation skewing effect in white-light vertical
scanning interferometry that can produce a
batwings artifact in a step height measurement is described. The skewing
occurs at a position on or close to the edge of a
step in the sample under measurement when the step height is less than the
coherence length of the light source used. A diffraction model is
used to explain the effect. URL:
http://www.opticsinfobase.org/abstract.cfm?URI=ao-40-13-2102 |
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Akiko Harasaki, Joanna Schmit, and James C.
Wyant
APPLIED OPTICS, Vol. 39, page
2107, May 2000
We describe a method that combines phase-shifting and
coherence-peak-sensing techniques to permit
measurements with the height resolution of phase-shifting interferometry
without the interval-slope limitation of l/4
per data sample of phase-shifting interferometry. A five-frame algorithm is
used to determine both the best-focus frame
position and the fractional phase from the best-focus frame of the
correlogram acquired through vertical scanning. The two surface
profiles retrieved from the phase and the
modulation contrast of the correlograms are compared in the phase-unwrapping
process to remove fringe-order ambiguity.
URL:
http://www.opticsinfobase.org/abstract.cfm?URI=ao-39-13-2107 |
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James C.
Wyant and Joanna Schmit
Int. J. Mach Tools Manufact., Vol 38,
691-698, (1998)
It is difficult in interferometric metrology to
maintain high spatial resolution over a large field of view.
Interferometric microscope measurements yield high resolution, but only over
a small area. Other conventional interferometric systems can measure
large areas, but they fail to provide the necessary spatial resolution.
High spatial resolution over a large field-of-view (FOV) can be obtained by
stitching together multiple high spatial resolution measurements of adjacent
areas of a measured surface. The measurements can be fit together in a
global sense, or by matching the piston and tilt over the overlap region.
Care must be taken in the stitching process to make sure the measurements
are precisely overlapped to minimize errors. The larger the overlap
the easier it is to match data sets, but of course more data sets are
required to get a given field of view. This paper shows that a 20
percent overlap gives a good trade off between having good repeatability and
obtaining a large field of view with a minimum number of data sets.
Typical measurement results are shown for stitching as many as 285
sub-regions. |
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James C.
Wyant and Joanna Schmit
Proceedings of SPIE Vol. 2782 (SPIE, Bellingham, WA), pages
26-37, 1996
The addition of modern electronics, computers, and
software to an interference microscope greatly increases the surface height
measurement capability of the interference microscope. The RMS
repeatability of surface microstructure measured using a computerized
phase-shifting interference microscope can be less than 0.1 nanometer.
While phase-shifting interferometry having sub-nanometer height precision
has limited dynamic range, the dynamic range of an interference microscope
can be extended to hundreds, or even thousands, of microns by using vertical
scanning coherence peak sensing techniques. This paper describes the
measurement capabilities of an interference microscope employing both
phase-shifting phase measurement capability and coherence peak sensing.
Typical measurements obtained using phase-shifting and coherence peak
sensing are illustrated. Techniques for extending the measurement
capability of computerized interference microscopes are discussed. |
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James C.
Wyant
Proceedings of SPIE Vol. 2576 (SPIE, Bellingham, WA), pages
122-130, 1995
Nearly all modern high-quality measuring instruments
now use micro computers for the collection and analysis of data. This paper
describes a computerized interferometric microscope system for the
measurement of surface microstructure. For the instrument described in this
paper the surface microstructure can be measured at data array sizes as
large as 739 x 484 points for measurement fields ranging from 30 x 25
microns to 8.2 x 6. 1 mm. A repeatability of the surface height measurements
of less than 0. 1 nm can be obtained for smooth surfaces. Surfaces having
height variations as large as 500 microns can be measured to within an
accuracy of a few nanometers.
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James C.
Wyant and Katherine Creath
Int. J. Mach Tools Manufact., Vol 32,
5-10, (1992)
This paper discusses some advances in
non-contact, interferometric optical profilers. Topics discussed include:
(i) The advantages of using a white light source,
rather than a laser source, (ii) The tradeoff between the use of Michelson,
Mirau, and Linnik interferometers for different fields of view and different
lateral resolutions, and (iii) Techniques for
removing errors in the reference surface enabling a person to measure
sub-Angstrom surface microstructure in the presence of a much rougher
reference surface. |
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Jay Jahanmir and James C.
Wyant
Proceedings of SPIE Vol. 1720 (SPIE, Bellingham, WA), pages
111-118, 1992
The surface topography of various samples has been
measured using an optical profiler and a scanning probe microscope (SPM).
Optical profilers offer fast and accurate measurements of surface topography
but are limited in their lateral resolution by the wavelength of light used.
SPMs extend the lateral resolution down to atomic dimensions. Topography
measurements are used to obtain surface roughness data. We find that for a
scan size of 50x50 tm, the roughness data obtained from the optical profiler
agree with the SPM measurements. The roughness data do not vary
significantly when higher magnification images are taken with the SPM on
surfaces that lack high frequency components. But for surfaces that have
rough features that are smaller than the resolution of the optical profiler,
roughness data calculated from higher magnification images by SPM can vary
significantly. |
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Katherine Creath and James C. Wyant
APPLIED OPTICS, Vol. 29, page
3823, 10 September
1990
In an interferometer which uses a reference surface,
the measured surface heights correspond to the difference between the test
and reference surfaces. To accurately determine the rms roughness of
supersmooth surfaces, the effects of the reference surface roughness needs
to be removed. One technique for doing this involves averaging a
number of uncorrelated measurements of a mirror to generate a reference
surface profile which can then be subtracted from subsequent measurements so
that they do not contain errors due to the reference surface. The
other technique provides an accurate rms roughness of the surface by taking
two uncorrelated measurements of the surface. These two techniques for
measurement of supersmooth surfaces are described in detail, and results of
the measurement of a 0.7-Å rms surface roughness
mirror are presented. The expected error in the rms roughness
measurement of a supersmooth mirror due to instrument noise is 0.02 Å.
URL:
http://www.opticsinfobase.org/abstract.cfm?URI=ao-31-22-4350 |
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James C. Wyant and Katherine Creath
Proceedings of SPIE Vol. 1319 (SPIE, Bellingham, WA), pages
568-569, 1990
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Bharat Bhushan, James C.
Wyant, and John Meiling
Wear, Vol. 122, pages
301-312, 1988
New features of a three-dimensional non-contact
digital optical profiler are described. This instrument uses a Michelson
interferometer for 1.5X, 2.5X, and 5X objective magnifications, a Mirau
interferometer for 10X, 20X, and 40X magnifications, and a Linnik
objective for 100X, 150X, and 200X magnifications. The instrument
is capable of a lateral resolution of 0.4 um and a vertical resolution as
small as 0.1 nm. The software can calculate various statistical roughness
parameters for flat, cylindrical, and spherical surfaces. The radii of
cylindrical and spherical surfaces can be measured with high accuracy.
Flatness, crown, camber, twist, taper angle, pole-tip gap recession, and
edge quality of magnetic slider surfaces can also be measured. |
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J. C. Wyant, C. L. Koliopoulos, B. Bhushan, and D. Basila
Journal of Tribology, Vol. 108, page 1, January
1986
A noncontact three-dimensional
optical profiler for measuring surface roughness is described. The system consists of a
reflection microscope, Mirau interferometer with a reference surface mounted on a
piezoelectric transducer, CID detector array, frame grabber, and micro-computer.
Interferometric phase-shifting techniques are used to obtain surface height information.
The height measurements are processed by a computer to obtain topographical statistical
parameters, which are useful in predicting tribological and magnetic performances of the
head-media interface in magnetic storage systems. Sample data are presented for magnetic
media (tape, floppy disk, and rigid disk), a magnetic head, a silicon wafer, and a glass
slide. |
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E. L. Church, T. V. Vorburger, and J. C. Wyant
Optical Engineering, Vol.
24, page 388,
May/June 1985
This paper compares two methods of measuring the
finish of precision machined optical surfaces: the older,
well-established mechanical stylus
gauge and a recently developed optical gauge using interference
microscopy. Results are found to be in good
quantitative agreement for both random and
periodic surface features, provided that appropriate filtering procedures
are included in the data
analysis to account for the differing transfer functions and
bandwidths of the two measurement techniques. These results affirm
the use of these techniques for the
quantitative measurement and specification of
machined optical surfaces. |
Bharat Bhushan, James C. Wyant, and Chris Koliopoulos
APPLIED OPTICS, Vol. 24, page 1489, May 1985
Stylus-profiling techniques
cannot be used for surface characterization of polymeric surfaces, such as magnetic tapes,
because of their relatively low hardness An interferometric-optical-profiling microscope
system was used to obtain high-accuracy surface profiles of magnetic media, rapidly and
without physical contact with the sample. The profilometer consists of a conventional,
reflection-type optical microscope with a Mirau two-beam interferometer attachment. The
interference patterns of the surface can be observed through the eyepieces and can be
detected with a solid-state linear array of 1024 detector elements. By translating the
reference surface of the interferometer with a piezoelectric transducer while taking
consecutive measurements, accurate surface-height measurements can be obtained from each
detector element. The microscope system is controlled by a microcomputer, which
communicates with a desk-top computer for further analysis of the surface-profile data. A
computer-controlled specimen stage is added to increase the sample size. The reasons for
selecting the Mirau two-beam interferometry are also discussed. Sample data of magnetic
tapes are presented. Experimental data presented in the paper show that optimization of
surface roughness is necessary to obtain optimum magnetic amplitude. friction, and wear
properties.URL:
http://www.opticsinfobase.org/abstract.cfm?URI=ao-24-10-1489 |
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James C. Wyant, Chris Koliopoulos, Bharat Bhushan,
and Orrin E. George
ASLE Trans, Vol. 27, pages 101-113,
1984
Conventional surface-characterization techniques
either are not sophisticated enough to provide complete
surface-topographical data or cannot be employed because of the relatively
low hardness of magnetic media. An optical profilometer has been
developed which provides a noncontact method of obtaining surface
characteristics from a magnetic medium. The system consists of a
standard Leitz reflection microscope, a Mirau interferometer controlled by a
piezoelectric transducer, a linear array of photodiode detectors, and a
microcomputer. The combination yields a system that measures the
optical-height variations of surfaces to a high degree of precision.
This height variation is processed by a computer to provide
surface-topographical statistical parameters, which are useful to predict
tribological and magnetic performances of the head-media interface.
Sample data of magnetic media (tape, floppy disk, and rigid disk) are
presented. |
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