x-ray metrology: challenges and solutions in the 3d era · overview •introduction what x-rays...

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



(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

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• Wafer breakage


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

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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











• Wafer breakage


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

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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











• Wafer breakage


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

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• Wafer breakage


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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











• Wafer breakage


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)

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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)

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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

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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

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https://www.bruker.com/

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x-ray metrology: challenges and solutions in the 3d era · overview •introduction what x-rays...

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