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Dr. Juliette van der Meer
X-ray Metrology: Challenges and Solutions in the 3D era
Bruker Semiconductor Division
Head X-ray Application Development BSEMI Germany
Overview
• IntroductionWhat X-rays offer in the 3D era
• X-ray techniques, recent developments and applicationsHigh Resolution XRD for composition/strain analysis of epitaxial layers
µXRF for thickness and composition
TXRF for metal contamination monitoring
XRDI for inspection of crystalline defects in high-value substrates
• Summary
2
Bruker’s increased focus on semiconductor customers
Bruker Advanced X-ray Solutions Division
(BAXS)
Bruker Nano Surfaces Division
(BNS)
Bruker Nano Analytical Division
(BNA)
Formed January 2015 to meet the advanced
metrology needs of Semiconductor customers
Dedicated R&D, operations, sales and service
The leader in X-ray and AFM for
Semiconductor metrology - 2015 acquisition
of Jordan Valley Semiconductor
Increased focus on new product development
with new X-ray, AFM and 3D WLI Optical
products introduced in 2016 and 2017
Bruker Semiconductor Division
Bruker Semiconductor Division
(BSEMI)
Bruker Nano Group
11/20/2017 3Bruker Confidential 3
Challenges in the semiconductor industry
• Increased use of epi for 2D and 3D logic structures
How to determine strain, composition, stress, defectivity?
• Ultrathin layer analysis in 2D and 3D structures
Conformal layer thickness
• Advanced wafer level packaging
Composition of single bumps?
• Spatially resolved metal contamination control
Multiple embedded metal interconnects in 3D structures
New metals and non-Si substrates
• Wafer breakage
Monitoring and root cause analysis
4
What information do X-rays provide?
High-resolution X-ray diffraction (HRXRD) X-ray reflectivity (XRR)
• Thickness (first principle, 5-10 nm and above)• Composition and/or strain (first principle)• Relaxation and crystal quality• Single or multiple layers of epitaxial, single crystal
films, e.g. SiGe, SiC, III-V, GaN
• Thickness (first principle, 2-1000 nm)=• Density (<1%)• Roughness• Single layer or film stacks of any material
X-ray diffraction imaging (XRDI) X-ray fluorescence (XRF)
• Imaging of bulk and surface crystalline defects• Single crystal wafers, e.g. Si, SiC
• Thickness (calibrated, nm to several µm)• Composition (calibrated)• Single metal films and film stacks
Small angle X-ray scattering (SAXS) Total Reflection X-ray fluorescence (TXRF)
• CDs and shape profiling• Pores and holes distribution
• Metal contamination• Ultra-thin film analysis
5
Challenges in the semiconductor industry
• Increased use of epi for 2D and 3D logic structures
How to determine strain, composition, stress, defectivity?
• Ultrathin layer analysis in 2D and 3D structures
Conformal layer thickness
• Advanced wafer level packaging
Composition of single bumps?
• Spatially resolved metal contamination control
Multiple embedded metal interconnects in 3D structures
New metals and non-Si substrates
• Wafer breakage
Monitoring and root cause analysis
6
Metrology challenges with advanced epitaxy
• Metrology of SiGe channels on Si fins Strain, composition, stress,
defectivity
• Multilayer Si/SiGe for Gate- All-Around FETs Strain, composition, stress,
defectivity, thickness
• Measurement is done on representative structures, e.g. OCD pads
Source: IMEC
7
HRXRD principle and geometry
• Incident angle (ω) is between the X-ray source and the sample
• The diffracted angle (2q) is between the incident beam and the detector.
• In plane rotation angle (Φ/Phi)
• Symmetric Bragg geometry is sensitive to lattice parameter perpendicular to the surface
• Asymmetric geometries are also sensitive to the lattice parameters both parallel and perpendicular to the surface
• Use of advanced high brightness sources allows HRXRD measurements on a 50x50µm pad
8
φ
χ2θ
ω
Strain/Stress analysis in fins
• Strain engineering is a critical aspect of high
performance CMOS devices
• Reciprocal space maps (RSMs) are used to plot in-
plane and out of plane lattice parameters
Made possible in manufacturing with the recent
development of high-performance 1D and 2D detectors
• Strain/composition of epi-layers on fins can be
measured
• Strain components can be converted to stress
components in all three directions along the fins
• Additional pitch/pitch-walk information is possible
x1
x2
x3
Si fins SiGe fins
Thin-film Planar
(a) (b)
(c) (d)
x1
x2
x3
Si fins SiGe fins
Thin-film Planar
(a) (b)
(c) (d)
Si
SiGe
dH = lattice parameter in Y
compared to substrate which
correlates to strain
dH = lattice parameter in X
compared to substrate which
correlates to strain
dL = lattice
parameter in Z
compared to
substrate
9
x1
x2
x3
Si fins SiGe fins
Thin-film Planar
(a) (b)
(c) (d)
x1
x2
x3
Si fins SiGe fins
Thin-film Planar
(a) (b)
(c) (d)
Si
SiGe
• Composition and thickness determined from fitting
x = 25%, t = 39.4 nm
• Sharp peaks are from high quality material
• Broad peak is due to defectivity, mainly
dislocations or stacking faults in the fins
• Ratio of these can be used to monitor
defectivity
Analysis of crystalline defects in fins
10
Strain analysis in nanowires
• RSMs are used to obtain critical parameters on fin and gate patterned structures Strain in Si and SiGe fins, parallel and
orthogonal to the fin direction; translated to stress
Thickness and composition on individual layers in multilayer stacks
• Application development on nanowire structures is done in consortia
Andreas Schultze et al, IMEC
Thickness and composition of
each Si / SiGe layer in the
nanowire stack is obtained by
µHRXRD
11
Challenges in the semiconductor industry
• Increased use of epi for 2D and 3D logic structures
How to determine strain, composition, stress, defectivity?
• Ultrathin layer analysis in 2D and 3D structures
Conformal layer thickness
• Advanced wafer level packaging
Composition of single bumps?
• Spatially resolved metal contamination control
Multiple embedded metal interconnects in 3D structures
New metals and non-Si substrates
• Wafer breakage
Monitoring and root cause analysis
12
Ultrathin layer challenge
• Ultrathin layers conformal to fins 3D shape challenge
Small volumes challenge the sensitivity of the technique
• Other metrology techniques have difficulties XPS is only top surface sensitive
Detection of very thin metal layers is difficult for optical techniques
Optical needs complicated models, esp. for 3D structures
13
X-ray fluorescence principle
• High energy X-rays excite an atom, which causes it to emit fluorescent X-rays
• Each element has a unique series of lines and the intensity is proportional to the number of atoms
• The analysis is qualitative or quantitative –after calibration Thickness
Concentrations
• Multilayer capability
Example of an XRF spectrum.
The peak position (energy) indicates the element.
The intensity is proportional to the number of atoms.
Si
W
Ti
Zr
14
Recent developments of µXRF at FEOL: Ultra-thin layer analysis
• Current µXRF technique lower limit of
detection for metal films is ~1nm
• Next generation µXRF lower limit of detection
for metal films is below one monolayer
Sensitivity and repeatability significantly improved
by enhancing signal to noise
• Measuring metal ALD films over 3D structures
increases volume (effective thickness) and
improves repeatability
Sidewall sensitive rather than top surface (XPS)
15
Significant signal enhancement between planar
and structured samples
Next generation XRF gives improved signal/noise, leading to increased sensitivity for ultra-thin films
CoKα
= 1°Excitation – Cu
Challenges in the semiconductor industry
• Increased use of epi for 2D and 3D logic structures
How to determine strain, composition, stress, defectivity?
• Ultrathin layer analysis in 2D and 3D structures
Conformal layer thickness
• Advanced wafer level packaging
Composition of single bumps?
• Spatially resolved metal contamination control
Multiple embedded metal interconnects in 3D structures
New metals and non-Si substrates
• Wafer breakage
Monitoring and root cause analysis
16
Recent developments of µXRF in advanced wafer level packaging:SnAg bump analysis
• µXRF analyzes composition and thickness of
single SnAg micro-bumps
Full stack of bump, UBM and Cu pillar
• Use of 3D-FP (= fundamental parameters) software to enable accurate and precise composition and thickness analysis on 3D features Calibration for finite features and to cover a wider
process window with fewer standardsCu pillar
NiSn-Ag solder
17
Challenges in the semiconductor industry
• Increased use of epi for 2D and 3D logic structures
How to determine strain, composition, stress, defectivity?
• Ultrathin layer analysis in 2D and 3D structures
Conformal layer thickness
• Advanced wafer level packaging
Composition of single bumps?
• Spatially resolved metal contamination control
Multiple embedded metal interconnects in 3D structures
New metals and non-Si substrates
• Wafer breakage
Monitoring and root cause analysis
18
Contamination Control: TXRF principle
TXRF analyzes metal contamination from Na to U
Silicon Drift
Detector
contaminatedwafer surface
X-Ray Fluorescence
incidentX-ray beam
~1 cm diameter spot size
reflectedX-rays
• A monochromatized X-ray beam hits the wafer surface
below the critical angle, in order to maximally excite metal
contamination on the surface
• Contaminants fluoresce into the detector with intensity
proportional to contamination level
• Non-destructive EDX technology keeping spatial
information
11/20/2017 1919
TXRF Applications
• Contamination control on Si substrates for logic and memory
SiC for power transistors
III-V substrates RF and opto
• Future developments: GIXRF capability Static mode for ultra thin-film measurements
Evaluation of scanning capability for doping profiles, performed with partners in consortia
Wafer map showing locations with
hot spots of metal contamination
JV-TXRF for robust spectrum analysis
20
Challenges in the semiconductor industry
• Increased use of epi for 2D and 3D logic structures
How to determine strain, composition, stress, defectivity?
• Ultrathin layer analysis in 2D and 3D structures
Conformal layer thickness
• Advanced wafer level packaging
Composition of single bumps?
• Spatially resolved metal contamination control
Multiple embedded metal interconnects in 3D structures
New metals and non-Si substrates
• Wafer breakage
Monitoring and root cause analysis
21
Wafer Breakage Challenge
• Fabs typically have low wafer breakage
(WB) rates but crisis periods of very high
breakage rates can occur and may last for
weeks
• Current optical tools
cannot reliably detect the onset of increase in
wafer break rate
have limited bevel edge capability
are possibly blind to critical damage if buried
or obscured by surface patterning or backside
films
• Fixing the issue can take several weeks
Waf
er
Bre
ak R
ate
Background WB Rate
Time
High WB
22
X-ray diffraction imaging (XRDI) principle
• Detects non-visual crystalline defects (cNVD) through
the wafer bulk and identifies wafers at risk of breakage
• Monitor crystalline defects from
mechanical damage (CMP, wafer handling)
high stress thermal treatment (slip bands, CVD chucks
misalignment, RTA support pins issues, laser anneal)
• Measure both blanket and patterned wafer (even
metallized) with no edge exclusion
• Strain effect in the lattice of even single dislocations
can extend tens of micronsSample showing single
dislocations, courtesy of
Dr Lee, LG Siltron
Wafer
Mo X-ray tube
Area (2D)detectorBeam-stop
Slits (sectiontopographs)
23
Wafer Breakage ROI
• XRDI tools routinely monitor product
wafers to give early indication of crisis
periods approaching in the fab
• XRDI can give the location of suspect
defects to identify the faulty process tool
and aid in root cause analysis
• By fixing the issue quickly vs weeks’ time
frame the ROI becomes very high
$4k wafers with 0.5% breakage rate and 300k
wafer start/year is $6M loss of product
High WB Rate
Background WB Rate
Defe
ct
Index
Typical defect type
which can cause wafer
breakage
Time
24
Defect inspection on non-Si substrates
• XRDI technique is applicable for many non-traditional and high value substrate types Crystalline only, but includes InP, GaAs, GaN (on Si),
CdTe, SiC
• GaN on Si example shows defects which may cause cracking and wafer breakage
• InP example shows many slip lines, which can cause yield issues if used for optical applications
XRDI data from GaN on Si (top)
and InP substrate (bottom)
25
Physical and chemical information at FEOL and BEOL through X-rays
Cu CMP
Si:C
Non Visual
Crystalline defects
BOX
(FD)SOI
SOI/SiGe/Si:C
uBump Ag%/Sn & Voids
UBM thickness
SiGe
SiGe
SiGe, Si:C
STI
HfO
SiGe
Cu
Cu Pillar & uBump Ag%
CD and shape profiling of
nanostructures
Metal contamination
• HRXRD: strain and composition in epi
• µXRF: layer thickness; bump composition
• TXRF: metal contamination monitoring
• XRDI: crystalline defect detection
26
Summary
• More-Moore and Moore-than-Moore applications are innovation drivers in the silicon and compound semiconductor industry, challenging the metrology
• X-ray techniques provide many unique capabilites for both in-line metrology and off-line materials characterization
• Bruker Semiconductor is the leading supplier of in-line X-ray metrology tools for the semiconductor industryOnly a selection of our applications was presented here For more information https://www.bruker.com/ Thank you for your attention
27
Thank You