Surface Texture Analysis

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Surface Texture Analysis Standards

• Bala Muralikrishnan1 Jay Raja2
• Dept of MEES
• University of North Carolina at Charlotte
• 1 balam_at_nist.gov, bmuralik_at_uncc.edu, 301-975-3789
• 2 jraja_at_uncc.edu, 704-687-4390
• ASPE Tutorial 2004

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Outline

• Introduction- Measurement Techniques
• Session 1 Preprocessing Filtering
• Session 2 2D Surface Texture Parameters
• Session 3 PSD and ACF
• Session 4 New and Emerging Filters
• Session 5 Advanced Filtering
• Session 6 Morphological Filters
• Session 7 Applications
• Parameter Selection, Challenges in 3D,
  Uncertainty Issues, Resources

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Introduction

• Measurement Techniques

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Classification of Surface Texture Measurement
Methods

• Contacting Stylus
• Phase Shifting Interferometry
• Vertical Scanning (White Light) Interferometry
• Focus Sensing Confocal Microscopy
• Chromatic Length Aberration Confocal Microscopy
• Structured Light and Triangulation
• SEM Stereoscopy
• Scanning Tunneling Microscopy
• Atomic Force Microscopy
• Optical Difference Profiling
• Angle Resolved SEM

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Contacting Stylus Method(2D)

• Principle
• It is a surface topography measurement method
  where the probe is a contacting stylus whose
  vertical motion is converted into an electrical
  signal as a function of lateral position.

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Contacting Stylus Method(3D)

• Principle
• It is a surface topography measurement method
  where the probe is a contacting stylus whose
  vertical motion is converted into an electrical
  signal as a function of lateral position.

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Phase Shifting Interferometry

• Principle
• An optical microscope with illumination of a
  known wavelength integrated with an
  interferometry attachment produces multiple
  optical images with interferometric fringes from
  which the profile or topography image is obtained

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Vertical Scanning Interferometry (Scanning white
light interferometry)

• Principle
• An optical microscope with broad band
  illumination integrated with an interferometry
  attachment is scanned in Z-direction w.r.t the
  surface to produce an equal interferometric path
  condition for each point in the image, from which
  the surface topography is calculated.

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Focus Sensing Confocal Microscopy

• Principle
• The surface height at each point is
  determined by sensing its vertical position w.r.t
  optimum focus in an optical microscope and an
  areal topography image is then obtained by
  imaging multiple points.

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Chromatic Length Aberration (CLA) Confocal
Microscopy

• Principle
• The height at a point is determined by
  integrating a spectrometer into an optical
  microscope and sensing the chromatic dispersion
  of white light reflected from the surface.

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Structured Light and Triangulation Methods

• Principle
• A light image of known structure or pattern
  is cast on a surface and the pattern of reflected
  light together with knowledge of the incident
  structured light allows one to determine the
  surface topography.

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Angle Resolved Scanning Electron Microscopy (SEM)

• Principle
• Local gradients of a surface are determined
  by angular distributions of secondary electron
  emission intensity and an areal topography image
  is obtained by integration of these local
  gradients.

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SEM Stereoscopy

• Principle
• Two SEM images are taken of a surface
  oriented at slightly different angles and the
  comparison of the two images yields a stereo
  effect from which surface topography can be
  determined.

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Scanning Tunneling Microscopy (STM)

• Principle
• The determination of surface arises from the
  height-related variations in electrical tunneling
  current produced between a conducting surface and
  a conducting tip placed very close to it, with a
  constant voltage maintained between them.

Working principle of STM
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Atomic Force Microscope (AFM), Scanning Force
Microscope (SFM)

• Principle
• The surface height is sensed from the
  mechanical force of attraction or repulsion
  between a probe tip and a surface.

Working principle of AFM
http//stm2.nrl.navy.mil/how-afm/how-afm.html
http//www.triple-o.de/pages/application_spm.html
http//www.uni-leipzig.de/pwm/kas/afm/AFM.html
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Area-Integrating Method

• Surface measurement method that measures a
  representative area of a surface and produces
  numerical results that depends on area-integrated
  properties of the surface texture.

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Angle Resolved Scatter

• Principle
• The light scattered from the surface is
  collected as a function of incident angle or
  scattered angle or both and the measured function
  may be used to calculate rms roughness, power
  spectral density and other roughness parameters.

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Lasercheck Tropel Metrology instruments
Lasercheck is a non-contact surface roughness
measuring instrument. Lasercheck illuminates the
surface with a shallow incident angle visible
laser (650nm). Specular, reflected and scattered
light from the surface is detected by a
photodiode array with 35 small closely packed
detectors inside the head. Software converts
these signals into Rs surface roughness and
alignment values to aid setup in automated
installations.
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• Amplitude Wavelength (A-W) Characteristics of a
  Surface and A-W Maps

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Why Measure Surface Texture

• Functionally Important
• Process Control
• Quality Control
• Research and Development
• Contractual Obligation

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Amplitude-Wavelength
Src ASME B46.1
Any measurement method finally produces a surface
map/profile from which we extract parameters that
describe its amplitude and/or wavelength
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A-W Maps

• A-W Map is a pictorial description of relevant
  amplitudes and wavelengths for
• A surface (think PSD)
• For an instrument (its work volume)
• For processes (in terms of tolerances)
• For function (think specification)

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A-W Maps for Instruments

• Vertical range (Rv) and resolution (rv)
• Horizontal range (Rh) and resolution (rh)
• Horizontal datum (maximum slope Smax)
• Probe geometry (minimum radius of curvature Rmin)
  

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Limits of surface measurement by stylus
instruments log AW space

• Vertical range (Rv) and resolution (rv)
• Rv and rv restrict amplitude. ie., Rv gt 2A gt
  rv
• Horizontal range (Rh) and resolution (rh)
• Rh and rh restrict wavelength. Ie., Rh gt W gt rh
• Horizontal datum
• Slope of flanks of the stylus (Ss) and maximum
• slope error of the datum (Sd) restrict
  surface slope
• that can be measured.
• ie., Ss gt Smax gt Sd
• Probe geometry
• Tip of radius of the stylus (Rs) and curvature
• error of the datum (Rd) restrict radius of
  curvature
• that can be measured.
• ie., Rd gt Rmin gt Rs

Log AW space
Src M Stedman K Lindsey, SPIE vol 1009
Surface Measurement Characterization, 1988
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AW maps for Stylus instruments
AW maps of stylus instruments Schmaltz (1936)
Widely spaced dots Talysurfs 1 2 closely
spaced dots Talysurfs 5 6 short dashes
Talystep solid line Form Talysurf - longdashes
Limits of traditional stylus , Profilomaters
vs. newer instruments traditional limits
shaded area STM/AFM - dashes Nanosurf-2 - solid
line
Src M Stedman K Lindsey, SPIE vol 1009
Surface Measurement Characterization, 1988
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Limits of surface measurement by optical probe
instruments

• Vertical range (Rv) and resolution (rv)
• Rv and rv restrict amplitude.
• Horizontal range (Rh) and resolution (rh)
• Rh and rh restrict wavelength. Wavelength is
  direct limiting factor in the case of optical
  probes.
• rh 0.61?/NA for focused beam.
• rh 1/e2 for unfocused beam.
• Horizontal datum
• Numerical aperture (NA) of an objective lens
  and maximum density of tilt fringes restricts
  maximum slope.
• ie., Smax lt NA/2
• Probe geometry

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AW maps for optical probe instruments
Optical probe instruments DD, Dew Fizeau
interferometer EV, Ennos-Virdee profilometer D,
Downs polarizing interferometer
M Stedman, SPIE Vol 1009 Surface Measurement
Characterization, 1988
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A-W maps
Mapping the process, the function and Instrument
capability as an A-W map
Process map
Amplitude
Function map
Instrument capability
Wavelength