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3D Metrology by MBIR
Jonny Höglund, Semilab USA
July 2012
www.semilab.com
Contents
• MBIR Technique Introduction
• TSV Applications
• HAR Contact Hole and Trench Applications
• Summary
3D Metrology by MBIR
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MBIR Technique Introduction
3D Metrology by MBIR
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Model-Based Infrared Reflectometry
Layers of Interest
Reflectance Spectrum
Interference
fringes
Absorption
bandsExp. Data
Model Fit
Re
flecta
nce
Wavenumber (cm-1)
Infrared Light
1 – 20 microns
wavelength
Detector
Infrared light is reflected off the sample and the reflectance intensity
versus wavelength is analyzed with a model of the sample structure.
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MBIR Measurement Principle
• Reflections & absorptions from
trenches and films determine
shape of reflectance spectrum
• Analysis of reflectance spectrum
yields thickness, depth, CD, and
composition
Re
fle
cta
nce
Frequency
Out-of-
phase In-phase
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TSV Applications
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ITRS 3D Interconnect TSV Roadmap
• Traditionally use x-section SEM in a PFA lab, or by white light interferometry for larger vias.
• Dimensions in ITRS specifying TSV pitch shrinking to < 6 μm, making it more challenging
to get collimated light reflected back from the bottom of the TSV’s for visible light
interferometry.
• Shrinking pitch means MBIR can be used with effective medium approximation with good
accuracy and high calculation speed.
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Structure and MBIR Model
Silicon Substrate
Hardmask
Trench
Bottom
Optical ModelPhysical Structure Model
(Not to Scale)
Silicon Substrate
Graded Layer
Hardmask
Voided Silicon
Silicon Substrate
Hardmask
Trench
Bottom
Optical ModelPhysical Structure Model
(Not to Scale)
Silicon Substrate
Graded Layer
Hardmask
Voided Silicon
• A mixture of silicon and air can be used to describe the optical
properties of the etched structure, as shown in the sketch above.
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3D Metrology by MBIR
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• The MBIR measurement
capability was evaluated
on TSV arrays such as the
one shown to the right in
the tilted SEM view.
Figure – Tilted SEM view of TSV array
TSV Overview
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• Excellent correlation was achieved for depth, top CD
and bottom CD, as shown in the plots above.
TSV Overview
22 23 24 25 2622
23
24
25
26
x-SEM TSV Depth [µm]
MB
IR T
SV
De
pth
[µ
m]
2 3 4 51.5
2
2.5
3
3.5
4
4.5
5
x-SEM TSV CD [µm]
MB
IR T
SV
CD
[µ
m]
Top CD
Bottom CD
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• Wafer maps measured on 6 µm pitch / 4 µm CD TSV array are showing
a concentric etch depth pattern.
• The etch profile it tapered with smaller CD towards the bottom of the
vias.
TSV Wafer Maps
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Contact Hole and Trench Applications
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SEMATECH HAR Hole and Trench Wafer
Expected Fingerprint
Exposure increasing along X.
Etch rate lower near edges.
150 μm Square Arrays
Both contact hole and linear trench
arrays available with variation in pitch
and CD
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Simulation Example: Structure Description
• Simulations are performed on the structure
with trenches etched in an oxide layer on top
of a silicon substrate.
• Nominal dimensions:
• Etch depth = 1.2um
• Top CD = 50nm
• Bottom CD = 30nm
• Pitch = 100nm
Structure Sketch
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Simulation Example: Spectra Etch Depth Top CD
-5nm
Nominal
+ 5 nm
-5nm
Nominal
+ 5 nm
-15nm
Nominal
+ 15 nm
Bottom CD
• The plots above are showing the simulated spectra and we can see that the 3
parameters affect the spectra differently.
• The simulations are indicating measurement capability for:
Etch Depth
Top CD
Bottom CD
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Model Fit Spectra
Measured
Calculated
• The plot to the right is showing an
example measured spectrum and
calculated spectrum from the model
fit.
• As we can see the model spectrum
is in good agreement with the
measured spectrum.
• From the fit we can extract: • Etch depth
• Top Void Fraction
• Bottom Void Fraction
• If desired the void fraction values can be
calibrated to x-SEM to report CD.
Possible hydrogen/moisture
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-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
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Contact Hole - Etch Depth
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
C100P200
C65P160 C80P160
C60P120
• The maps to the right
are showing the etch
depth for the contact
hole sites.
• As expected the
maps are almost
identical.
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-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.495
0.5
0.505
0.51
0.515
0.52
0.525
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.49
0.5
0.51
0.52
0.53
0.54
0.55
0.56
0.57
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.34
0.36
0.38
0.4
0.42
0.44
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.35
0.355
0.36
0.365
0.37
0.375
0.38
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Contact Hole – Top Void Fraction C100P200
C65P160 C80P160
C60P120
• The maps to the
right are showing
the top void
fraction for the
contact hole sites.
• The etch rate is
increasing along
the X-axis, as
expected from the
higher exposure.
• Wafers with larger
CD have more
pronounced
concentric pattern.
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-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.15
0.155
0.16
0.165
0.17
0.175
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.145
0.15
0.155
0.16
0.165
0.17
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.095
0.1
0.105
0.11
0.115
0.12
0.125
0.13
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.13
0.135
0.14
0.145
0.15
0.155
0.16
0.165
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Contact Hole – Bottom Void Fraction C100P200
C65P160 C80P160
C60P120
• The maps to the right are
showing the bottom void
fraction for the contact
hole sites.
• The etch rate is
increasing along the X-
axis, as expected from
the higher exposure.
• Wafers with larger CD
have more pronounced
concentric pattern.
• The etch profile is
narrowing towards the
bottom.
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Trench - Etch Depth
T65P195
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
• The maps above are showing the etch depth for the trench sites.
• As expected the maps are almost identical.
T65P227 T65P260
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-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.45
0.46
0.47
0.48
0.49
0.5
0.51
0.52
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.54
0.55
0.56
0.57
0.58
0.59
0.6
0.61
0.62
0.63
0.64
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Trench - Top Void Fraction
T65P195
• The maps above are showing the etch depth for the trench sites.
• The etch rate tends to be a little higher on the +X side, as expected.
T65P227 T65P260
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.43
0.44
0.45
0.46
0.47
0.48
0.49
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3D Metrology by MBIR
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Trench – Bottom Void Fraction
T65P195
• The maps above are showing the etch depth for the contact sites.
• The maps have similar within wafer variation, with an offset between the
sites due to the pitch variation.
T65P227 T65P260
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.25
0.255
0.26
0.265
0.27
0.275
0.28
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.2
0.205
0.21
0.215
0.22
0.225
-150 -100 -50 0 50 100 150-150
-100
-50
0
50
100
150
0.175
0.18
0.185
0.19
0.195
0.2
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3D Metrology by MBIR
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Trench Correlation
• Nominal information for the
measured trench sites:
• As we can see in the plot to the right there is good agreement between the
measured and nominal values.
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3D Metrology by MBIR
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Contact Hole Correlation
• As we can see in the plot to the right there is good agreement between the measured and
nominal values.
• The sites with smaller CD are deviating a little from the nominal CD.
• A possible explanation is that sites with smaller CD have different sensitivity to exposure dose.
X-Section SEM will be performed in the near future for confirmation.
• Nominal
information
for the
measured
contact
hole sites:
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3D Metrology by MBIR
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Dynamic Repeatability
• The dynamic repeatability was evaluated for a variety of structures by running 5
site recipes 30 times, with unload/load of the wafer between the measurements.
• The void fraction repeatability was converted to nm using nominal conversion
factors.
• As we can see from the chart above the all the results are good with sigma < 1nm.
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Summary
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Summary
• MBIR is an excellent technique for non-destructive process
monitoring of the 3D structures etched in either silicon or
dielectric films.
• HAR structure dimensions are shrinking as technology nodes
advance and measurement results have proven the MBIR
technique to be versatile and to be responding well to structure
scaling.
• The repeatability on the evaluated HAR structures is very good
with sigma < 1nm.
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