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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 [email protected] +33 438 782 069


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


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


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)


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


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


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


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 …


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


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


2006 1.5 Management issues

Yield

Management of contamination

Clean ability ?

Monitoring capabilities ?

What do we face ?

Detrimental impact ?

Cross contamination ?

Different fab areas


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


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


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.


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:


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


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


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


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


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:


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


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


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


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


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)


2006 2.1 TXRF: performances

after D. Hellin


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!


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


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


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°)


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


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


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


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


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


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


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


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

!


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


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


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


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


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


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)


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


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


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


2006

Thank you for your attention

2006

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