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Post CMP Defects; Their Origin and Removal
Jin-Goo Park
Div. of Materials and Chemical Engineering, Hanyang University, Ansan 426-791, Korea
February 15, 2007
KOTEF Lab of Excellence
2007 Levitronix CMP Users Conference
Introduction to EMPL
The Electronic Materials and Processing Laboratory (EMPL) started at Hanyang University in 1994.
EMPLs research focus on the surface and colloidal phenomena in the area of semiconductor and electronic materials and processing.
Laser Shock Cleaning Ozone Cleaning Single Type Megasonic Cleaning
Post CMP Cleaning IPA Drying
Metal CMP (Cu, Ru, Pt, Al and etc)
Oxide and Poly-Si CMP ECMP Slurry Consumables
Bio-Chip/MEMS Fabrication
Mold Fabrication Surface Modification
Cleaning CMP BioMEMS
Nano-level
Defect FreeCleaning
Process
Damage Free Dry Cleaning Laser Shock Cleaning Pattern Damage Force
Measurements
Nano Surface Characterization Electrokinetic Adhesion force
Drying Technology IPA/water solutions Marangoni Effects
D
Non-RCA Wet Chemistry Ozone Chelating agents Surfactants High k/Low k cleanings
N
Nano Particles Adhesion/Removal Mechanism Experimental/Theoretical Interpretation Quantitative/Qualitative Interpretation
N
Cleaning Research at Hanyang University
Cleaning Equip. CMP Equip.
Charactrization
Samsung Hynix Intel, IBM Dongwoo MOICE KOSEF Doosan Siltron, LGM IMT
Korea Cleaning UGM Korea CMPUGM
Cleanroom (Class 10, 100 and 1000)
Wet station @ 2 DI water Generator (500 lpm) IPA Dryer Brush Scrubber Megasonic Cleaner
E-CMP Polisher (4) CMP Polisher (6) Friction Polisher (4, 6 and 8)
Nano-level Defect Free Wafer CleaningStudents (29)
Ph.Ds: 4Masters: 16
Undergrads: 8Secretary: 1
KLA-Tencor Particle Scanner, 6200 Nanometer Particle Scanner Atomic Force Microscopy Zeta-potential Analyzer 273 EG&G Potentiostat
KOTEF Lab of Excellence in Cleaning
EMPL Infra-Structure
12,0008,875 3,125
7,20
05,
750
1,45
0
Wet Bench
Wafer Brush Scrubber
Wet Station Ozone
WetStation
Optical microscope
Fluorescence microscope
Laser Shock Cleaning System
Laminar Flow Hood
&Surface Scan
EUV Cleaning System
EUV Controller
AFM
MCC
Smock Room
Classroom (Class 10,
~700 sq ft)
E.P.S.
U/T R.A S.A
ChemicalStocker
Fix Window
Total Construction Space 1,800 sq ft
New Cleanroom
Summary
Slurry and Cleaning Solution Evaluation
Effect of Slurry, Pads & Surfaces on Defects
Post CMP Cleaning
Introduction to Wet Cleaning
Outline
Next Generation Surface Preparation
Nanometer Feature Size New Materials Nanometer Thin Film Single Wafer Cleaning CMP Process EUVL Process 3D Device
Issues
Clean without Etching- Non RCA (H2O2 based) Chemistry
Clean without Pattern Damage - No Megasonics and Brushes
CMP Induced Defects Zero Defect on EUVL Mask
Challenges
65nm poly Si lines
Semiconductor Cleaning
Wet Cleaning
Dry Cleaning
Si Wafer
Organic contaminant
Metal
Particle
Native oxide
ex) SC1, SC2, Piranha, HF etc
ex) Laser shock cleaning, Plasma, Anhydrous HF, Jet Fluid, Cryogenic etc
Attached Particle
Interaction Force
Traditional Wafer Cleaning Chemicals
SC-1(NH4OH+H2O2+H2O=1:1:5 at 80 ~ 90C) - Particles and organic contamination removal
SC-2(HCl+H2O2+H2O=1:1:5) at 80 ~ 90 C )- Trace and Noble Metal removal
Piranha(H2SO4:H2O2=4:1 at 90 ~ 120 C)- Organic Contamination removal and PR strip
HF (+ H2O2) : Last wet cleaning- HF : Native oxide and H2O2 : Metal removal
Particle Adhesion Mechanism
Physisorption (Van Der Waals Forces)
Electrostatic Attraction
Chemisorption
Capillary Condensation
E= - AR / 6H2
Surface charge : Zeta-Potential
Chemical reaction between particles and surfaces
Fc = 4RL
]exp[64)( 2221
22
HzeTRkHVR
=
Particle Removal Mechanism
Etching
Dynamic Driving Force
Interaction Force
Few /min/Dissolution
Surface charge and Electrostatic repulsion Wettability of surfaces and particles
Mobility of liquid molecules Megasonic irradiation, Higher temperature, Hydrodynamic force
Electrochemical Deposition
Redox Reaction E (V vs. NHE)
O3 + 2H+ +2e- = O2 +H2OH2O2 + 2H+ + 2e- = 2H2OAu+ +e- = AuO2 + 4H+ + 4e- = 2H2O
Cu+ + e- = Cu
2H+ +2e- = H2
Ag+ + e- = Ag
Na+ + e- = Na
Pb2+ + 2e- = PbNi2+ + 2e- = NiFe2+ + 2e- = Fe
SiO2 + 4H+ + 4e- = Si + 2H2O
Cu2+ + 2e- = Cu
K+ + e- = KCa2+ + 2e- = Ca
Al3+ + 3e- = Al
2.0761.7781.6921.2280.7990.5200.3370.000-0.126-0.250-0.440-0.857-1.663-2.714-2.866-2.924
More Noble
More Active
Oxide Formation
Oxide H (kJ/mol)
Al2O3 -1,675
Cr2O3CrO2CrO3
-1,130
-583
-580
Fe3O4 -1,118
Fe2O3 -822
SiO2 -909NiO -241CuO -155
Tendency to be included in the oxide film
Metal Contamination Mechanism
Electrochemical Deposition
Hydroxide Formation
Film Inclusion
Etching
Interruption of oxidation/reduction reactionChange of Eh and pH and complexation of ions
Surface modification and complexationParticle removal mechanism
Metal Removal Mechanism
CMP Process and Defects
WaferPolishing Pad
Wafer Carrier
Rotating Platen
Polishing Slurry
Slurry Supply
CMP induced particles, metal ions
Physical damages: scratch, pits, stress
Chemical damages: corrosion
Slurry particles: SiO2, Al2O3, CeO2
Requirements for Post CMP Cleaning
Post CMP Cleaning
Particle/Metal Removal Mechanism
Slurry/Cleaning Chemistry
Particle/Metal Adhesion Mechanism
Post CMP Cleaning Equipments
Copper CMP CleaningCopper CMP Cleaning- Surface properties
- No Damages- Specific contamination
- Single/batch- Brush/Megasonic
- Low k integration- Corrosion
Defects Types in CMP
Dishing / Erosion/N.U.
Particles / Scratch
Origins of these defects: Tool, Consumables, Substrate Materials
Random Particle Defects in WCMP
Slurry residue on dielectric
Slurry residue in W-plug Organic particle
Particle on surface and trench
Slurry residue in trench
Post CMP Scheme on W Plug
for particle removal in trench for particle removal on surface film
Dielectric (SiO2)
Etch amount
??
W-Plug
Trench pattern
Pad fragment Slurry residueOrganic particle
Post CMP Cleaning Processes
Clean configurations
Wet Sand Indexer
Wet Sand Indexer
Dual Brush Module
Dual Brush Module
Rinse, Spin Dry Station
Rinse, Spin Dry Station
NH4OH HF
Shapes of Organic Defects after Poly CMP
Ameba type defects on hydrophobic surface
Sources of Organic Residues
Pho-Pho
Phil-Phil
Phil-Pho
Pho-Pho
Phil-PhoPhil-Phil
Theoretical Calculation Adhesion Force Measurement
Repulsive
Attractive
Ref. : Alexandre M. Freitas and Mukul M. Sharma, Journal of Colloid and Interface Science, 233, 73-82, (2001)
Substrate Colloidal Probe
Phi-Phi SiO Wafer Glass (30mm)
Pho-Phi Silanated Glass Glass (15mm)
Pho-Pho Silanated Glass Silanated Glass (15mm)
Liquid Pho-Pho Phi-Phi Phi-Pho
Water -71.47 10 -18
Net Free Energy at contact G = GLW + GAB values (mN/m) for a number of interacting system according to Acid-Base theory
The AB parameters for liquids were taken from van Oss. Silica was used as the model substrate. The force can be calculated using the Derjaguin approximation F/R=-2(GLW+AB)
More positive : More repulsive, More negative : More attractive
Net Free Energy
Hydrophobic Forces
Contact angle of poly Si decreased as function of Sol. A concentrations
Slurry Modification to reduce defects Surface wettability change
Contact Angle of Poly Si Wafer Treated with Sol. A
0 2 4 6 8 10
20
30
40
50
60
70
80
Contact Angle of Poly Si Wafer
Con
tact
Ang
le (
Deg
ree
)
Concentration of H2O2 ( vol % )Concentration of Sol. A ( vol % )
Adhesion force measurement of pad particle on poly Si wafer surface at pH 11 (Spring constant : 0.03 N/m cantilever)pH 11 was adjusted by KOHHydrophilic poly Si : Lower adhesion force than hydrophobic poly Si surface
6
8
10
12
14
16
Adhesion Force of Polymeric Particle on Poly Si
Adhesion Force of Polymer Particle
Adhe
sion
For
ce (n
N)
H2O2 0% H2O2 1% H2O2 3% H2O2 10%Sol. A 0% Sol. A 1% Sol. A 3% Sol. A 10%
After CMP : Contact Angle of poly Siwith slurry and Sol. A mixture solution
Contact Angle : 52
After CMP : Contact Angle of poly Si with SS12 slurry
Contact Angle :
No additive (KOH, pH 11), Hydrophobic Surface (KOH + lower additive ), Hydrophilic Surface
(KOH + medium additive ), Hydrophilic Surface (KOH + higher additive), Hydrophilic Surface
1 min dipping in alkaline KOH solutions which have abraded pad particles, and then dried in N2 atmosphere at 60C
Abraded Pad Particle
FESEM Images of Polymeric Particle Contamination on Poly Si
Defect Maps with Modified Slurry
Effect of Polishing Byproducts on CMP
Typical form of stains caused by polish byproducts on the padThe effects of stains on CMP performance such as erosion, dishing and
non-uniformity were evaluated No removal by DI buffing
Polish-Byproduct or Stain on Pad in Cu CMP
Slurry chemistry induced defects
Effect of Byproducts on Polishing
2000
3000
4000
5000
6000
0 5 10 15 20 25
Number of Wafer
Rem
oval
Rat
e (
/min
)
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
N.U
(%)
Removal RateNon Uniformity
- RR, Erosion, Selectivity and Dishing
Temperatures and Friction
0
10
20
30
40
50
0 50 100 150Polishing Time (sec)
Tem
pera
ture
()
0
1
2
3
4
5
0 10 20 30 40 50 60
Time (sec)Fr
ictio
n Fo
rce
(A.U
.)
Slurry A
Slurry B
Interaction Forces between Wafer and Surface
+Electrostatic Force
(Zeta Potential) + Repulsiveor - Attractive
van der Waals Force (Particles size )
- Attractive
Total Interaction Forcewaferparticle
Total InteractionForce
Electrostatic Force
Van der Waals Force
: Key factorcontrollingdeposition
In liquid media
Adhesion Force Measurements
Force-Distance Curve by AFM
Polystyrene particle (2 m)
Fabricated Colloidal Probe50 m
2 m
Measured Interaction Forces Using AFM
SILK TEOS Cu TaN0.0
-0.5
-1.0
-1.5
-2.0
TaNCuTEOS
Inte
ract
ion
forc
e (n
N)
Wafers
pH 11 slurry pH 7 slurry pH 3 slurry
SiLKTM
Force-Distance Curve Measurements with Silica particle
Park et. al., J. Electrochem. Soc., 150 (5), pp. G327-G322 (2003)
Particle Contamination After Polishing
Cu TaN TEOS SiLK
pH 11
pH 7
pH 3
Adhesion Force in Cleaning Solutions
The least adhesion force of silica is measured in the citric acid and BTA with NH4OHThe largest adhesion force is measured in the citric acid and BTA with TMAHThe pH and its adjustor selection are very important in cleaning solution design
-11.0
-10.5
-10.0
-9.5
-9.0
-8.5
-8.0
(pH2) (pH6) (pH6)
Adhesion Force
Adhe
sion
For
ce (
log
N )
D.I Citric acid+BTA Citric acid+BTA+NH4OH Citric acid+BTA+TMAH
Park et. al., J. Electrochem. Soc., 151(10), pp. G327-G322 (2004)
FESEM Images of Cu Surfaces after Polishing
- Large numbers of residual particles are observed on Cu surfaces cleaned in DI water, citric acid only solution, and citric acid solution with TMAH- Citric acid and BTA solution with NH4OH shows the complete removal of particles
Pre-Cleaned Cu Contaminated Cu D.I water
Citric acid with BTA Citric acid BTA with NH4OH Citric acid BTA with TMAH
Removal Rates in Alumina and Silica slurry
- Slurry evaluation: RR, friction and adhesion force measurements
-1000
0
1000
2000
3000
4000
5000
6000
7000
Removal rate of Cu
Rem
oval
rate
(/m
in)
DI+Alumina DI+Silica Citric+Alumina Citric+Silica
Park et. al., J. Electrochem. Soc., 153(1), pp. H36-H40 (2007)
Friction Forces in Alumina and Silica slurry
0 10 20 30 40 50 60
0
2
4
6
8
10
12
14
DI Water + Alumina DI Water + Silica
Fric
tion
( Kgf
)
Time (Sec.)0 10 20 30 40 50 60
0
2
4
6
8
10
12
14
Time (Sec.)
Citric Acid + Alumina + H2O2 + NH4OH, pH6 Citric Acid + Silica + H2O2 + NH4OH, pH6
Fric
tion
( Kgf
)
- In DI water, higher friction in alumina- In citric acid, higher friction in silica- The higher the adhesion force, the higher the friction force
Adhesion Forces of Alumina on Cu in Slurries
1.00E-009
2.00E-009
3.00E-009
4.00E-009
5.00E-009
6.00E-009
AluminaSilicaAluminaSilica
Cu Wafer - Particle Adhesion
DI Water
1.00E-009
2.00E-009
3.00E-009
4.00E-009
5.00E-009
6.00E-009
Ad
hesi
on F
orce
( N
)
Citric Acid+NH4OH
Scratches and Defects in Alumina and Silica Slurry
DI - Alumina DI - Silica
Cit - SilicaCit - AluminaLower friction/adhesion force
Higher friction/adhesion force
Summary
Origin of Defects- Tool, Consumables, Surfaces
Consumables- Slurry, Pad Related
Surfaces- Wettability- Metallic vs. Non-metalic
Slurry and cleaning solution modification Evaluation of Slurry and Cleaning Solutions
- Adhesion force- Friction force
Acknowledgements
Fundings fromMOICE, KOSEF, MOSTSamsung, Hynix, Intel
Doosan, Siltron, IMT
Lab of Excellence Program
Through MOE, MOCIE and MOLAB
Post Brain Korea 21 Program
through MOE
AND
Members of EMPL at Hanyang University
Introduction to EMPLCleaning Research at Hanyang UniversityEMPL Infra-StructureNew CleanroomOutlineSemiconductor CleaningEffect of Polishing Byproducts on CMPEffect of Byproducts on PolishingTemperatures and FrictionSummaryAcknowledgements Members of EMPL at Hanyang University