Surface Metrology

Presented for CMA Analytical Workshop 2012
Neal Leddy

surface metrology
Applications
Roughness
Lay
Waviness
Form
Flatness
3D analysis
Step Height
Film thickness
Feature measurement
Radius of curvature

techniques
Tactile
Stylus
Atomic force microscopy
Optical
White light/Laser interferometry
Confocal microscopy
Ellipsometry
Focus variation

probe
cantilever
Diamond stylus
white light (filtered light)
laser
electron beam

piezo electric actuators
the linear electromechanical interaction
between mechanical and electrical state
in crystalline material.
reversible
examples - lead zirconium titinate,
quartz

detector
laser & photodiode
ccd camera

stylus
Diamond probe contacts sample surface
Tip size: >20nm ~ 25um
Direct measurement
Disadvantages – contact method, generally
single line,
Advantages – fast, widely accepted,
reasonable z resolution

afm
Cantilever tip
Contact mode
Non-contact mode
Tapping mode
Force modulation
Phase imaging
○
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○
○
○
○
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Local friction imaging
Surface potential imaging
Electrical conductivity imaging
Magnetic and electric field imaging
Thermal conductivity mapping
Temperature mapping
Modulus mapping

Disadvantages – limited sampling area, limited z
range, slow scan speed.
Advantages – high resolution, 3 dimensional, large
sample area and vertical range (>10mm)

Cantilever –
silicon/silicon nitride
Piezoelectric actuator
Laser –
Detector – photodiode

wli
White light source
Resolutiuon – 0.01 nm
Scanning mode
Phase shift mode
Disadvantages – requires reflective surface,
lateral resolution (diffraction limit) ~500nm
Advantages – high resolution, 3 dimensional,
large sample area and vertical range (>10mm)

wli
white light source
Beam-splitter
reference mirror
interference objective
piezo electric stage
ccd camera

confocal
Typical Scan area: 200 mm X 200 mm
X Resolution: 30 nm to 3 um
Z Range: 300 um to 30 mm
Disadvantages – limited z resolution.
Advantages – High vertical scan depth, fast
measurement speed.

ellipsometry
Change in polarisation of light reflected/transmitted from a
sample structure. response is dependent on optical properties
and thickness of each material.
film thickness
optical constants
characterise composition,
crystallinity,
roughness,
doping concentration,
Disadvantages – limited sample applicability
Advantages – transparent films (resolution 1nm ~ 10-15mm)

Light source
Polarizer
(Optional compensator)
Surface reflection
(Optional compensator)
Analyzer (2 nd polariszer)
Detector (voltage)

focus variation
Using optics with very little depth of field. Realised using
microscopy like optics and a microscope objective.
These objectives have a high numerical aperture which gives
a small depth of field.
sample or optics moved in relation to each other.
at each position the focus over each plane is calculated
the plane with the best focus gives the depth at that position
Disadvantages – resolution (30nm), flat surfaces
(requires form)
Advantages – Large scan range, Good for very
rough surfaces

summary of optical
techniques

other techniques
3D stereoscopic reconstruction
Stereo pair Scanning Electron Microscope
tilted with eucentric stage.
Algorhitm reconstructs 3d image.
Disadvantages – relies on good stereo pairs,
limited z resolution, requires structured surface
Advantages – high magnifications

Isotropic vs. anisotropic
Isotropy
Surface presents the same characteristics regardless of the
measurement direction, i.e. surfaces with a random texture
without any distinction or direction
anisotropy
Surfaces encountered with machined or formed features will
have a direction or periodic structure

Isotropic
anisotropic

oughness
Describes the texture of a surface. It is
measure of the vertical deviations of a
real surface from its ideal form.
Roughness: high frequency and short
wavelength
Largely related to surface interactions.

waviness
Describes the surface form.
Waviness: low frequency and usually
long wavelength
Generally a result of manufacture

oughness standards
ASME B46
ISO 4287 – profile
ISO 12085
ISO 13565
ISO 25178 – aeral surface
Geometrical Product Specifications and
Verification

surface amplitude
Symbol Name 2D Unit 3D
Sa Roughness Average DIN 4768 ASME B46.1 [nm] ISO/DIS 25178-2
Sq
Root Mean Square
(RMS)
Ssk Surface Skewness ISO 4287/1
ASME B46.1
Sku Surface Kurtosis ANSI B.46.1
ASME B46.1
ASME B46.1
ISO 4287/1 ASME B46.1 [nm] ISO/DIS 25178-2
ASME B46.1
ISO/DIS 25178-2
ASME B46.1
ISO/DIS 25178-2
ASME B46.1
Sz Peak-Peak ISO 4287/1 [nm] ISO/DIS 25178-2
St Peak-Peak ASME B46.1 [nm] ASME B46.1
Sy Peak-Peak [nm]
S10z Ten Point Height ANSI B.46.1 [nm] ISO/DIS 25178-2
ASME B46.1
Sv Max Valley Depth ASME B46.1 ISO/DIS 25178-2
ASME
Sp Max Peak Height ASME B46.1 ISO/DIS 25178-2
ASME B46.1

surface hybrid
Symbol Name 2D Unit 3D
Ssc Mean Summit Curvature [1/nm]
Sti
Texture Index
Sdq
Sdq6
Root Mean Square
Gradient
Area Root Mean Square
Slope
ISO/DIS 25178-2
ASME B46.1
Sdr Surface Area Ratio ISO/DIS 25178-2
S2A Projected Area nm^2
S3A Surface Area nm^2

Functional parameters
Symbol Name 2D Unit 3D
Sbi
Surface Bearing Index
Sci
Svi
Core Fluid Retention
Index
Valley Fluid Retention
Index
Spk Reduced Summit Height DIN 4776 [nm]
Sk Core Roughness Depth DIN 4776 [nm]
Svk Reduced Valley Depth DIN 4776 [nm]
Sδcl-h
l-h% height intervals of
Bearing Curve
ISO 4287
[nm]

Spatial parameters
Symbol Name 2D Unit 3D
Sds Density of Summits ASME B46.1
Std Texture Direction [deg] [6]
[6]
Stdi Texture Direction Index [7]
Srw
Dominant Radial Wave
Length
[nm] [7]
Srwi Radial Wave Index [7]
dShw Mean Half Wavelength [nm]
Sfd
Fractal Dimension
Scl20
Scl37
Str20
Str37
Correlation Length at
20%
Correlation Length at
37%
Texture Aspect Ratio at
20%
Texture Aspect Ratio at
37%
Symbol Name 2D Unit 3D

earing ratio
Mathematically it is the cumulative
probability density function of the
surface profile height
calculated by integrating the profile trace

White light interferometry

omniscan microXam

Scanning wli

Surface roughness
Shot Peened Steel:
Surface map
3D Surface

Profile through origin
Profile roughness (2d)
Rq/Ra = 1.22
Surface roughness (3d)
Rq/Ra = 1.25

Rq is more sensitive to peaks and
valleys than Ra, as amplitudes are
squared.
Typically for classic surface
Rq = 1.1(Ra)

surface filtering
Primary surface waviness roughness

Primary surface profile waviness profile roughness profile
primary surface waviness surface roughness surface
primary profile waviness profile roughness profile

step height

Step height standard:
•Nominal : 8.18 um
•Actual : 8.181um

film thickness

advanced feature analysis
Vickers indent:

vickers indent profile
vickers indent calculated hardness

phase mode
Phase mode utilizes narrowly filtered light to perform a
phase shifting of light fringes for acquisition
Achieved by phase shifting one of the interfering beams
along the optical axis.
Reduces system noise and gives best results for very flat
samples.

phase mode

3D Stereoscopic reconstruction

2d sem image of shot peened steel
• ± 5°tilt
• @ working distance
~10mm

mex vs wli
3d SEM reconstruction
White light interferometry

Nettle leaf
Nettle leaf – reconstructed tilt series

Flower detail
Flower detail – reconstructed tilt series