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.

• EMPL’s 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 ~ 90°C) - 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 = 4πRγL

]exp[64)( 2221

22

HzeTRkHVR κ

γγπε−=

Particle Removal Mechanism

Etching

Dynamic Driving Force

Interaction Force

• Few Å/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 ΔH (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 ΔG = ΔGLW + ΔGAB 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=-2π(ΔGLW+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 60°C

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 (Å

/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 (Particle’s 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 μm)

Fabricated Colloidal Probe50 μm

2 μm

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

(Å/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