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Adrien DANEL, UCPSS 2006 1
20062006
UCPSS 2006 Tutorial
Metrology for contamination
Adrien DANEL – LETI
© CEA 2006. Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans l’autorisation écrite préalable du CEAAll rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA
CEA-LETI, MINATEC, 17 rue des Martyrs, 38054 Grenob le, France adrien.danel@cea.fr +33 438 782 069
Adrien DANEL, UCPSS 2006 2
2006 Agenda
� 1) Contamination in microelectronics
� 2) Metrology: focus on metallic contamination
� 1) Challenges� 2) What is named contamination ?� 3) Main sources of contamination� 4) Impact on devices� 5) Management issues� 6) Metrology: general information
� 1) Spectroscopic and quantitative methods• TXRF
• Collection of contamination • ICPMS
• AAS
� 2) Indirect methods• Lifetime
Adrien DANEL, UCPSS 2006 3
2006 1.1 Contamination: challenges
Yield
A big part of yield losses is due to contamination
Manufacturer notoriety
Contaminants affect devices reliability
A "scientific" production monitoring
IC manufacturing uses numerous expert methods to monitor and qualify the production
Adrien DANEL, UCPSS 2006 4
2006 1.2 What is named contamination ?Anything undesirable and potentially dangerous for the production
Depending on :Type of damageDetection method
Chemical nature of contaminants
• Particles• Metals• Organics• Bases• Acids• Dopants
International TechnologyRoadmap for Semiconductorshttp://public.itrs.net
Classification proposed by ITRS
Very low levels: "ultra traces"
ppb (10-9) 1 for 1 milliard
ppt (10-12) 1 pour 1000 milliardsVolume contamination:
1cm3 water = 3.3E22 molecules1cm3 Si = 5E22 atoms
Surface contamination: < 1011 at/cm2 1cm2 Si (100) = 6.8E14 atoms (metals)
Adrien DANEL, UCPSS 2006 5
2006
� Processes • Contact with solids (robots, chuck, boats, …)
• Equipments
• Process fluids (liquids and gas)• Material on devices
� Environment• Clean room air• FOUP, boxes, mini environments
• Human activity
Particles Metals Acids / Bases / Dopants Organics
Organics Acids / Bases / Dopants Particles Metals
1.3 Main sources of contamination
Adrien DANEL, UCPSS 2006 6
2006
80%60%40%20%Processes
10%30%40%30%Equipments
5%5%10%20%Clean room
<5%5%10%30%Human
2000199519901985
Ref.: Texas Instrument Don Lutz Pentagon Technologies
1.3 Sources of contamination
Particles
5.10-12 g/m3
5.10-5 g/m3
ParticlesClass 1
(0.5µm)
VOC
Σ = 50 ppbv
CH3-CH2-
CH2OH
NH3
HClBF3
DOP
Organics
Adrien DANEL, UCPSS 2006 7
2006 1.3 Sources of contamination
Metals = from processes mainly
Wet bench • As a paradox, cleaning equipments might be a huge source of contaminants in caseof malfunction
• Metals from hardware and chemicals grade SLSI (≤ 1ppb) or S2LSI (≤ 100ppt)
Na, Al, Ca, Fe, Zn, Cu
Chamber (furnaces, RTP, etch, epi, CVD, …) • Mainly stainless steel particles
Fe, Cr, Ni, Mn, MoRobots, chucks, boats • Particles and possible cross contamination
Chuck footprint
Diffusion of Cu from a contaminated quartz boat
Adrien DANEL, UCPSS 2006 8
2006 1.4 Impact on devices
Main effects
• Junction leakage• Dielectric breakdown• Interface segregation• Surface and interface roughness• Carriers lifetime degradation• Defect decoration• Electrical shortcut• Doping modification• Resist poisoning• Interconnects corrosion• Haze• Degradation of molecular bonding• Degradation of stepper optics • Modification of etch and dep parameters
MetalsParticles
Volatil contamination
Post etch panic !
Bug during litho ?
God save our copper …
Adrien DANEL, UCPSS 2006 9
2006
� Metals on gate oxide integrity
Detrimental impact depends on the nature of the contaminant
0
2
4
6
8
10
12
0 5 10 15 20 25 30 35Mea
n B
reak
dow
n F
ield
(M
V/c
m)
Contamination (x1E12 at/cm2)
Ca
Fe
Al
7 nm dry oxides
17 mm2 capacitors
Ca highly detrimental : roughness !
1.4 Impact on devices: examples
Detrimental impact depends on the technology
10-1
100
101
102
103
104
105
1010 1011 1012 1013 1014 1015
Densité de défauts (cm
-2)
Concentration du Fer (at/cm3)
20 nm16 nm13 nm10 nm
Critère :
claquage à
8MV/cm
Epaisseurs d'oxyde :
After B. Henley : thin oxides are more sensitive to contaminants
Iron concentration
Def
ect d
ensi
ty
Gate oxide thickness
Breakdown criteria: 8MV/cm
Adrien DANEL, UCPSS 2006 10
2006
Ionic species• Corrosion of interconnects by acids • Resist poisoning by bases (amines)
• Growth of post etch residues
� Volatil contamination
1.4 Impact on devices: examples
after M. Yamachika, 1999
Adrien DANEL, UCPSS 2006 11
2006 1.5 Management issues
Yield
Management of contamination
Clean ability ?
Monitoring capabilities ?
What do we face ?
Detrimental impact ?
Cross contamination ?
Different fab areas
Adrien DANEL, UCPSS 2006 12
2006
� Efficient management of contamination is mandatory
Fab competitiveness • Fast and safe introduction of new materials• Small volume production = shared equipments • High value production
� Ultra-cleanliness costs a lot
Define "just enough" levels and rules
1.5 Rationale
Measurement of new species ("exotic metals", Hf as a n example)
Detection of "standard" species on/in new layers (C u in HfO 2 gate oxide)
� New knowledge and metrology required
Understanding of detrimental impact
Understanding of dissemination
Adrien DANEL, UCPSS 2006 13
2006 1.5 Recommendations Generalities
Specification of critical particles simply follows the technology: size = ½ dimension of minimal size of the device
Requirement for metals : a threshold independent of the technology
Yield vs Contamination: very complex , case to case study
ITRS 2005 : 1E10 and 5E9 at/cm 2 for critical metals
To know the baseline of the processes and to keep i t
To clean !! Realistic and simple management rules
referring to ITRS, http://public.itrs.net
Requirements for volatile species : lack of knowledge and precaution suggest an overstatement of ultra cleanliness based on the extrapolation of present data
Adrien DANEL, UCPSS 2006 14
2006 1.5 What do we face ?trends in advanced IC manufacturing
• New substrates• High K dielectrics at gate• Salicides, metals, alloys for contact
• Cu + barriers
FEOL
BEOL
Many new metals and precursors introduced into production lines
That's all ?
• Non volatile memories • Above IC
New electrical, magnetic, optical, mechanical … or even biologic properties push the fast introduction of new materials.
Adrien DANEL, UCPSS 2006 15
2006 1.5 What do we face ?
B, Na, Mg, Al , P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As , Br , Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Ba, La, Ce, Pr, Nd, Gd, Dy, Er, Yb, Hf , Ta, W, Re, Ir, Pt, Au, Hg, Tl, Pb
� Volatile species:• Condensable organics originated from plastic boxes and clean room
materials (phthalates as an example) and litho solvents • SO2, HF, HCl, HBr, NH3 from chemicals
Transparent, conductive (oxide)Piezoelectric (alloys, nitride)MetallizationOptoelectronics
• In, Sn, Sr, Ti• Al, Pb, Zr, Ti• Al, W, Mo, Pt, Cr, Au• Ga, As, In, P, Hg, Cd, Te
Above IC
FRAM: magnetic, anti-ferromagnetic (metals and alloys)MRAM: magnetic (metals and alloys)Flash: adjustable capacity ; high k
• Co, Fe, Ni, Ir, Mn, Pt, Ta, Cu, • Ge, Sb, Te• Ag, Ge, Se, Hf, Al, Ti
Non-volatile memories
High-K (oxide, silicates, laminates)Low resistivity metal gates (salicides, metallization)High mobility substrates (SiGe alloy)Interconnects, barriers (metallization)
• Hf, Zr, Al, Ti, La, Ta, Y, Ba, Sr, Pr, Gd, Dy, Nd• Ni, Co, Ti, Pt, Ru, Ir, W, Re, Rh, Nb, Yb, Er• Ge• Ti, Ta Ni, Mo, P, Co, W, B, Pd, Cu, Ru, Tl
Advanced IC
Targeted propertiesMetalsApplications
+ contaminants coming from human activities, fluids, gas and equipments:
� Metals:
Adrien DANEL, UCPSS 2006 16
2006 1.6 Metrology for contamination
adsorbent + GCMSbubbling + ICIMSchemi-luminescenceUV fluorescenceFTIRphoto-acoustic spectroscopy
Particles Organics Metals
wafer
OH OH OH O OH
Ions Surface
xx
xx
xxVolatile species
ATR-FTIRXPS
Contact AngleAFMHaze
LPE – ICXPS
ToF SIMSTXRF
xx
x
TXRFVPD/LPD – ICPMS/AAS
ToF SIMSSi lifetime
PLGOI
TD – GCMS ToF SIMSMIR-FTIR
Light ScatteringSEM – EDX ToF SIMS
x
after Chia and Edgell
NB: Characterization for defectivity of devices not considered here
Adrien DANEL, UCPSS 2006 17
2006 1.6 Metrology for contaminationAcronym Measurement method Application
TXRF Total reflection X-Ray Fluorescence In-LinePL Photo Luminescence In-LineSi Lifetime Minority carrier lifetime In-Line(µ-PCD, SPV) micro wave Photo Conductivity Decay
Surface Photo VoltageLight Scattering Light Point Defects In-LineHaze Light Scattering background In-LineIMS Ion Mobility Spectrometry monitoringPhoto acoustic spectroscopy monitoringFTIR Fourier Transform Infra Red spectroscopy monitoringUltra Violet Fluorescence monitoringChemiluminescence monitoringCA Contact Angle At-LineAFM Atomic Force Microscopy At-LineSEM – EDX Scanning Electron Microscopy – Energy Dispersive X-Ray spectroscopy At-LineToF SIMS Time of Flight Secondary Ion Mass Spectrometry At-LineMIR-FTIR Multiple Internal Reflection – FTIR At-LineATR-FTIR Attenuated Total Reflectance – FTIR At-LineVPD/LPD Vapor Phase Decomposition / Liquid Phase Decomposition At-Line / LabICPMS Inductively Coupled Plasma Mass Spectroscopy At-Line / LabAAS Atomic Absorption Spectroscopy At-Line / LabXPS X-ray Photoelectron Spectroscopy At-Line / LabTD-GCMS Thermal Desoprtion – Gas Chromatographie Mass Spectroscopy At-Line / LabLPE-IC Liquid Phase Extraction – Ionic Chromatography At-Line / Lab
Adrien DANEL, UCPSS 2006 18
2006 1.6 Metrology strategy
Measurements on products
Pertinent
Monitoring and / or diagnostic
Control of production environment (air, liquids, equipments, witness wafers)
Problem anticipation, alarm
Monitoring and / or diagnostic
Curative
Monitoring
Adrien DANEL, UCPSS 2006 19
2006 2 Metrology for contamination: focus on metals
� 2.1) Spectroscopic and quantitative methods• TXRF• Collection of contamination• ICPMS• AAS
� 2.2) Indirect methods• Lifetime
3 Conclusion • Summary• References
Adrien DANEL, UCPSS 2006 20
2006 Metrology requirements
LLD: E8 – E9 at/cm2 (for critical contaminants, impact seen at E10)
Any elements (50 worst case)
Local and average information, with 2mm edge exclusion
Industrial aspects: high throughput, high uptime, easiness of use
IC manufacturing needs:
Adrien DANEL, UCPSS 2006 21
2006 What can be a metallic contamination ?
• Rational: An analytical tool should give information as close to the truth as possible
• Pragmatism: The users would like to have an equal quantification of a samecontamination, whatever the method and mode used
Is it possible ?
• Local spikes of contamination• Distribution on large area
Mi+
Mi+
M+M+
Mi+
(M+,X-)
MXSiY
M0M
Solid particlesCations physisorbed Salts
Metals plated
Metals diffused into the bulkPrecipitates (salicides, others)
QM QM
Charges in oxyde
Si
SiO2
Adrien DANEL, UCPSS 2006 22
2006
Mi+
Mi+
M+M+
Mi+
(M+,X-)
MXSiY
M0M
Solid particles Cations physisorbed Salts
Metals plated
Metals diffused into the bulkPrecipitates (salicides, others)
QM QM
Charges in oxyde
Si
SiO2
Overview of main methodsC(V) tests
SPVµ-PCDPLsome C(V) tests
TXRF, ToF SIMS VPD
LPD
Adrien DANEL, UCPSS 2006 23
2006
Fab
com
patib
ility
Detection limit (at/cm 2)
106 107 108 109 1010 1011 1012
Target
VPD-SR-TXRF
SP-TXRF
D-TXRFVPD-TXRF
ToF-SIMS
VPD-ICPMS
VPD-AAS
Integrated
Overview of main methodsSpectroscopic and quantitative analysis
after D. Hellin
Adrien DANEL, UCPSS 2006 24
2006 2.1 TXRF: principle
incident angle < critical angle
Flat and smooth substrate (Si, SiO2, Ge, thin films …)
Total reflection of the incident beam
Depth: a few nm
X-ray Fluorescence
Detector
Analyzed surface: a few cm2
Multi channel analyzerX-ray source• rotating anode (W, Pt,…)• sealed tube (Cr, W, Mo,…)• Synchrotron radiation
and selective optics
SSD (Solid State Detector, SiLi diode)SDD (Silicon Drift Detector)
X-ray fluorescence is specific for each element
Non invasive, non contact method
Number of photons is proportional to element concen trationQuantitative analysis
The selected monochromatic X-ray source defines the measurement range: ZW Lβ @ 9.67keV = P to Zn on Si, Kα linesW Mα @ 1.77keV = F, Na, Mg, Al on SiW continuum @ 24keV = → Ru K lines, → U L lines
Contamination identification
Adrien DANEL, UCPSS 2006 25
2006 2.1 TXRF: principle
Spectrum background
time
I
I
C3LLD bkd
i,net
i=
Low Limit of Detection
2
1
2t
1t
t
t
LLD
LLD =
Practical Low limit of Quantification
LOQ ≈ 3LLDDefined at σ=40% of [mean]
Incident beam W-Lβ peakSubstrate Si-Kα peakUseful spectrum area
No excitation for energy < absorption edge
Global fluorescence efficiency decreases(absorption factor X fluorescence desexcitation factor X detection factor)
Adrien DANEL, UCPSS 2006 26
2006 2.1 TXRF: performances
after D. Hellin
Adrien DANEL, UCPSS 2006 27
2006
• mapping-TXRF: local information, 90% surface
• TXRF with multiple sources: Na U
• VPD-TXRF: ultra low Low Limits of Detection
What can TXRF –based method offer ?
2.1 TXRF: equipments
Issue of constant quantification whatever the contaminant shape!
Adrien DANEL, UCPSS 2006 28
2006 2.1 Direct–TXRF: plus and minus
Hf-LααααHf-Ll
Hf-Lαααα Esc
Hf-Mαααα
Hf-Mζζζζ
Hf-Mγγγγ
HfO2 high-k gate film
Hf-LββββW-Lββββ
Mg Al Fe Co Ni Cu Zn
Hf-LααααHf-Ll
Hf-Lαααα Esc
Hf-Mαααα
Hf-Mζζζζ
Hf-Mγγγγ
HfO2 high-k gate film
Hf-LββββW-Lββββ
Mg Al Fe Co Ni Cu Zn
+ Multiple sources cover all elements of interest (except B, F, Li)
Small surface coverage, Throughput
≈ 0.6 W per h4.8%10.8%17 points
≈ 1.0 W per h2.5%5.7%9 points
≈ 1.6 W per h1.4%3.2%5 points
300sec. /point300mm wafer200mm wafer
one beam≈ 2cm 2 per point
Challenge: overlaps
Al (Kα 1.49 keV) Br (Lα)
Mg (Kα 1.25 keV) As (Lα)
K (Kα 3.31 keV) In (Lα)
Na (Kα 1.04 keV) Zn (Lα)
• Peak separation (detector and data processing)• Specific sources
+ Low Limits of Detection
W-Mα 1.77keV source:• LLD – Al = 1.3E11 at/cm2
W-Lβ 9.67keV source:• LLD – Ni = 6.5E8 at/cm2
W-HE 24keV source:• LLD – Mo = 5.0E9 at/cm2
time
I
I
C3LLD
Bgd
i
i=
@ 1000s
Data for a Rigaku FAB300 system
Adrien DANEL, UCPSS 2006 29
20062.1 Surface Profiling–TXRF: plus and minus
+ Low Limit of Detection
+ Local and average information with 90% surface coverage
Throughput 2.8 Wph(1 beam, 200mm wafer, 65 points map, 3sec./point)
Σ(Σ(Σ(Σ(N spectra) ≡ entire surface average spectrum
LLD ≈ LLD D-TXRF :LLD @ 1000s Al = 1.4E11
Ni = 7.0E8Mo = 1.2E10
≈ 7mm edge exclusion
5sec. individual spectrum, "local" LLD ≈ 15 x LLD1000s
after Y. Mori et al., Anal. Chem. (74), 2002
Adrien DANEL, UCPSS 2006 30
2006
0
20
40
60
80
100
120
140
160
0.1 1 10 100 1000
contamination level (N x LLD)
sigm
a (%
)
D-TXRF point to point
SP-TXRF point to point
SP-TXRF integration
2.1 TXRF: quantification
LOQ can be defined as 3 x LLD (W-Lβ excitation at 0.08°)
Adrien DANEL, UCPSS 2006 31
2006
VPD (Vapor Phase Decomposition)
To collect all metals on substrates
To concentrate surface contaminants in an analytecompatible with analyzers without extra contaminati on
VPD reactor sealed
cooling plate25% HF
HF vaporSiO2decomposition
Vapour Phase Decomposition Scanning (droplet collection) Analysis
Moisture+ metals
80 µL H2O, HNO3, HF, H2O2 –based chemistry
Collection droplet + additional DI water
ICPMSAAS
Teflon cup
Si wafer
SiO2 + 6HF H2SiF6 + H2O
LPD (Liquid Phase Decomposition)
Bulk decomposition with specific chemistry
Extraction by liquid
2.1 Collection of contaminants
Adrien DANEL, UCPSS 2006 32
2006 VPD collection efficiency• Table of results (uncertainty: 5%)• Decomposition + collection
performed 2 times
CE (%) = 100(1 – Q2/Q1)
HF 2% + H2O2 2% HNO3 0.1%
Na > 95% (98.4, 99.6) > 95% (98.3)
Al > 95% (98.8, 99.8) > 95% (95.5)
Ca > 95% (99.2, 98.7) > 95% (98.2)Ti > 95% (99.7) > 95% (98.8)
Cr 95% (94.9) 95% (94.2)
Fe > 95% (99.2, 99.7) > 95% (98.4)
Co > 95% (99.5, 99.7) > 95% (95.3)
Ni > 95% (98.9) > 95% (97.3)Cu 50 – 70% (54.5, 68.1, 60.6) 20 – 50 %Zn > 95% (98.8) > 95% (98.3)
Ge > 95% (98.8, 98.8) > 95% (98.7)
Sr > 95% (98.8) > 95% (99.2)
Mo 95% (95.6, 85.2, 98.2) 95% (97.2)Ru 75% (74.2) > 95% (96.7)
Ag < 5% < 5%In > 95% (99.5) > 95% (99.0)
Sn > 95% (99.5) > 95% (98.8)
Hf > 95% (98.3) > 95% (99.0)Ta > 95% (98.7) > 95% (99.7)
Ir > 95% (98.4) > 95% (98.2)
Au < 5% < 5%
• Key parameters:
� Type of contamination� Kinetic� Collection chemistry
� Level of contamination
Test wafers: intentional contamination by spin drye r (about E12 at/cm 2)Kinetic: 1s/surface unit for HF/H 2O2 and 0.1s/surface unit for HNO 3
Adrien DANEL, UCPSS 2006 33
2006 2.1 VPD–TXRF: plus and minus + Low Limit of Detection
Challenge: Ultra clean hardware to avoid any parasitic contamination during the decomposition, the collection, the drying and thehandling steps.
0.01
0.1
1
10
100
1000
0.01 0.1 1 10 100 1000VPD-TXRF results (E10 at/cm 2)
VP
D-I
CP
MS
re
sults
(E
10
at/
cm2 )
Cr
Ti
Fe
Ni
Cu
LLD of manual VPD –based methodFe: 8.2E10 at/cm2
Cu: 0.8E10 at/cm2
0.01
0.1
1
10
100
1000
0.01 0.1 1 10 100 1000VPD-TXRF results (E10 at/cm 2)
VP
D-I
CP
MS
re
sults
(E
10
at/
cm2 )
Cr
Ti
Fe
Ni
Cu
LLD of manual VPD –based methodFe: 8.2E10 at/cm2
Cu: 0.8E10 at/cm2
Multiple VPD on ultra clean wafer show no contamination:LLD cab really be limited by TXRF measurement
LLD ≈ LLD D-TXRF/wafer surface :LLD @ 1000s Al = 6.0E8200mm wafer Ni = 6.6E6
Mo = 8.2E7
Throughput 2.2 Wph(200mm wafer, VPD preparation only)
Average value onlyLoss of local information
Good cleanliness of the VPD module
VP
D m
odul
e N
OT
cle
an
!Collection efficiency: challenge for noble metals and solid particles
Adrien DANEL, UCPSS 2006 34
2006 2.1 ICP- MS (Inductively Coupled Plasma - Mass Spectrometry)
Principle
1) Introductionof liquid analyte
Nebulization chamber :2) µ-droplet aerosol formationwith analyte + vector gas
Vector gas: Argon3) Aerosol ionisationby RF plasma
4) Extraction of ions fromplasma and acceleration
5) ion Filterby quadrupole (m/z)
6) DetectionIdentification and quantification (daily calibration using standard solutions)
Mass spectrum analysis: Elements detection and semi -quantification
Precise quantification of an element set
Adrien DANEL, UCPSS 2006 35
2006 ICP- MS: performancesMulti element method ultra sensitive (ppt range)
Limitation due to spectroscopic interferences with vector gas (Ar) and dominant elements (Si, H, O …)
• Example: "normal" plasma mode generates ArO+ (= Fe !), Ar+ (= K) and ArH+ (= Ca !)
# = "cold" plasma
Sensitivity depends on the ionization energy of each element (Agilent 4500 system)
• Example: LLD = 0.1ppt-w for Zr, coupled to VPD (1mL collection droplet) on 300mm wafer, the LLD corresponds to:
25
21
Avogadro13
cm/atE3.9cm707mol.g2.91
NgE1=
××
−
−
Interferences are minimized using "cold"
plasma mode or a collision chamber
Adrien DANEL, UCPSS 2006 36
2006 2.1 AAS (Atomic Absorption Spectrometry)
LCkLogAbs élémentI
I == 0
Single element method: one specific source per element to quantify
Quantification with Lamber – Beer law:
Na Al Ca Fe Ni Cu Zn Ag Au
50 200 50 200 200 200 50 200 200
LLD (ppt)
Multiple injection used to win a factor 10
Performances
GF-AAS
I0
Monochromator
Photomultiplicator
Signal treatment
Graphite furnaceEvaporation: 150°C, salt decomposition: 400 – 1800°CAtomization: 2000 – 2700°C
Optical source(hollow cathode lamp)
Coating with element to be quantified
Sample
Injection window: a few µL
I
L-+
λi λiAr+
Ar
Principle
Adrien DANEL, UCPSS 2006 37
2006
SIMS Direct method dedicated to bulk analysis LLD of about E16 at/cm 3 (Cu)
Applied to near surface (1µm), LLD is equivalent to E12 at/cm2
XPS Direct method dedicated to surface analysis LLD of about 0.1% to 1% Information on chemical bonds
TOF SIMS Direct method dedicated to surface Very good LLD (< E9 at/cm 2) Local analysis capabilities (on pattern, a few µm 2)Information on elements, molecules and fragments
Industrial aspects for IC manufacturing under validation
2.1 Others
Adrien DANEL, UCPSS 2006 38
2006
Principle All indirect methods detect contaminants via their impact on some electrical properties of the semiconductor, minority carrier lifetime in Si as an example
Measurements on bare wafers: characterization of a few processesWet clean, Thermal treatments, Epitaxy or witness wafers
2.2 Detection of a metallic contamination using indirect method
VsW (Qs, Nsc)
ττττsS
ττττvLdiff
• Surface chemistry• Surface contamination• Bulk contamination• Doping• Roughness, ….
Measurements Physico-chemical properties
Surface charges lifetime
surface bulk
!
Adrien DANEL, UCPSS 2006 39
2006
• Band bending, depletion capacitance: Vs, Wd
Vs, Wd = f(Qs, Nsc) : surface charge and space charge region doping
• Surface recombination: S (speed), τs (lifetime)
• Bulk recombination: Ldiffusion, τvolume
τvdiffL
D=
2
• Radiative recombination: photoluminescence
Surface and Bulk properties of Si: symbols
Surface
Nsc
Si bulk, neutral
P-type doping
Bore
-
-
-
-- - - - - - - - - - -+ + + + + + + +
Qs
Qsc
+
+
Ec
Ev
EF
+
-
+
+
B-
++
BH
X+
Y-
xWd
Vs
Optical
excitation
e-
h+
S
ττττs
Trap
e-
h+
Ldiff, ττττvhν>Eg
Silicon
h+
e-
hνννν
Non radiativerecombination
Radiativerecombination
Adrien DANEL, UCPSS 2006 40
2006 2.2 µ-PCD microwave Photo-Conductivity Decay
Proposed in 1959, introduced into production during the 80
Interaction µ-wave – Si: depends on wafer resistivity
Principle
Probehead
1) Carriers Photo-generation
Laser pulse
2) Homogenization
Probehead
Carriers homogenization across the wafer
3) Measurement ofµ-wave reflection
Probehead
Photo-conductivity decay due to recombination
Typical reflectivity curveLaser pulse Time (µs)
µ-wave reflected power
homogenization
Measurement of equilibrium returntime constant
Adrien DANEL, UCPSS 2006 41
2006
Measurement Time constant contains bulk and surfaces contributions
Wafer from RTP: hardware signature
Method popular thanks to a possible "selectivity" to Feand to fast and high resolution mapping (1000pts/min.)
1 1 1 1
1 2τ τ τ τµ−= + +
PCD S S v
Surface contribution usually neglected:• measurements on thick oxide • chemical passivation
Bulk contribution usually dominated by Fe: strong lifetime killer and very usual contaminant
2.2 µ-PCD
Adrien DANEL, UCPSS 2006 42
2006
Principle Change of surface potential under illumination
2.2 SPV Surface PhotoVoltage
Proposed in 1961, introduced into production during the 80
Equilibrium, Vs0
Surface
illumination
illumination
∆∆∆∆Vs
Si bulk neutral
α-1α-1
Light penetration depth
∆∆∆∆Vs depends on S, L diff , φφφφoptic and αααα-1
Adrien DANEL, UCPSS 2006 43
2006
Measurement
Good measurements for Ldiff <= wafer thickness
Measurement of ∆Vs versus α-1 using constant incident flux gives S and Ldiff
Classic systems with 5 or 7 λ: mapping 1000 points in 40 min.
New systems with 2 simultaneous λ: 1000 points in 5min.
Idem µ-PCD: popular non invasive method thanks to fast and good resolution mapping ; and possible Fe "selectivity" for p-type Si doped B
∆Vs-1
α-1µm
slope: S
extrapolation : Ldiff
2.2 SPV
Adrien DANEL, UCPSS 2006 44
2006
∆1/ττττbulk ∝∝∝∝ Feconcentration withLLD < 1011 at/cm 3
Fe quantification using lifetime measurements
FeBbgdbulk
111
τττ+=• Before dissociation of FeB pairs:
• At room temperature, Fe contamination into p-type Si bulk forms stable FeB pairs
Assuming that Fe contaminant dominates and with FeB being an efficient recombination center
under medium or high optical flux excitation (µ-PCD ): ττττbulk ≈ ττττFeB
Under low optical flux excitation (SPV) FeB is a poor recombination center but Feinterstitial is a very efficient one
Feibgdbulk
111
τττ+=• After dissociation of FeB pairs
(by heating or optical):
Assuming measurement on
p-type Si (1/τ or Ldiff) is τvolume
with Fe contribution only:
[ ]Fev11
Fei
i
nth
Febulk
σττ
=≅ [ ]bulk
12E82.1Fe
τ≅
with vth = 107 cm/s and σnFei = 5.5E-14 cm2
(µs)(at/cm3)
Adrien DANEL, UCPSS 2006 45
2006 3 Conclusion: summary of methods for metallic contamination
* Automatic equipment for IC manufacturing
Invasive Mapping Throughput LLD Price* Capability
TXRF No
VPD – TXRF
≈ YesResolution 1cm
Edge exclusion 1cm
5min. per point10sec. per point
≈ 1010
at/cm2
> 1M€ GoodNa → U
≠ surfacesbare and smooth
Yes No
Global, entire surface
45min. <109 at/cm2 > 1.5M€ Good
VPD/LPD/LPE– ICPMS/AAS
Yes No 30min. per wafer
<109 at/cm2 < 0.5M€ Very goodAlmost any
element and any substrate
Surface and bulk
+ wet bench+ people
Lifetime(applied to Si)
Yes
Very good resolution
A few min. per wafer
<1011
Fe at/cm3
0.1 to 1M€ Poor
Complex understanding
of results
≈ Yes
IntradiffusionSurface
passivation
Global, entire surface
Na → U≠ surfaces
bare and smooth
Adrien DANEL, UCPSS 2006 46
2006 3 Conclusion
Yield
Management of contamination
Fab competitiveness • Fast and safe introduction of new materials• Small volume production = shared equipments • High value production
Define "just enough" levels and rules
• Cost issues of ultra cleanliness
Understanding of detrimental impact
• Electrical and physical short loops• Yield and crisis expertise
Knowledge on contamination control
• Cleaning – Metrology – Dissemination
Adrien DANEL, UCPSS 2006 47
2006 3 ReferencesMetrology:• "Contamination-Free Manufacturing for Semiconductors and other Precision Products"
Editor R.P. Donavan, M. Dekker Press, NY, 2001.• "Handbook of Silicon Semiconductor Metrology" Editor A. Diebold, M. Dekker Press,
NY, 2001.• "trace-analytical methods for monitoring contaminations in semiconductor-grade Si
manufacturing", L. Fabry et al., J. Anal. Chem. 349, p. 260-271, 1994.• “Organic contamination: Impact, Characterization, Sources and Cleaning during IC
Manufacturing”, M. Claes and S. De Gendt, Proc. of the Electrochem. Soc., PV 2001-29, pp. 320-335 (2001).
TXRF:• "Handbook of X-Ray Spectrometry", Editor R.E. van Grieken, M. Dekker press, NY, 1992.• “Whole surface analysis of semiconductor wafers by accumulating short-time mapping data of
total-reflection X-ray fluorescence spectrometry”, Y. Mori et al., Anal. Chem., 74, pp 1104-1110, 2002.
• "Trends in total reflection X-ray fluorescence spectrometry for metallic contamination control in semiconductor nanotechnology", D. Hellin, to be published in Spectra Chem. Acta B, 2006.
ICPMS:• "Guide to ICPMS", R. Thomas, www.spectroscopyonline.com
Adrien DANEL, UCPSS 2006 48
2006
Thank you for your attention
2006
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