Taek-Soo KimDepartment of Materials Science and Engineering, Stanford University

Qiping Zhong, Halbert Tam, Maria Peterson JSR Micro, Sunnyvale, CA

Tomohisa KonnoJSR Corporation Yokkaichi Research Center, Yokkaichi, Japan

Reinhold H. Dauskardt(dauskardt@stanford.edu)

Solution Chemistry Effects on Cracking and Damage during CMP

Work supported by JSR Corporation.

Reliability of Interconnect Structures

0.1 μm

nano-scaledefect

package contact stresses and complex

loading

silicon device

soft/ductile buffer layers

effect of metal density and aspect ratio

thermomechanicalreliability of low k films

cracking depends on flux composition

Process yield and reliability determined by the evolution of defect

distributions….

Evolution of Defects control Yield through Processing

• Lower thin-film stresses – driving force for cracking– structure effects, Z– metal density

• Optimize glass composition, network and pore structure

• Control evolution of defects during processing, packaging and service

0.1 μm

nano-scaledefect

cf

ff GE

hZG ≤=

2σ

WaferAqueous solution

Pressure

package contact stresses and complex loading

silicon device

OSi

CH3

fracture

path

Accelerated Cracking in Chemically Active Environments

M. Lane, R. Ware, Q. Ma, H. Fujimoto, and R. H. Dauskardt - Proc. MRS, 1997.

Subcritical debonding important for reliability

during CMPand

bumping/wire bondingpackaging

strained debondtip bonds

chemical reactionwith H20

applied stress

WaferAqueous solution

Pressure

aol

crack velocity

transport limited zone

debonddielectricbarriercopper

H20

Delaminator 4-Point Adhesion Test System

Delaminator System Features• Software test control• 4-pt. bend adhesion and cohesion• Environmental chamber• Low profile for in-situ microscopy• Automated crack velocity measurement

Conditioning Electronics

Software Control

Test controland analysis

Low Profile Test Frame

(use with microscopy)

System and support available from:DTS CompanyMenlo Park, CA(contact directly: dauskardt@stanford.edu)

4 Point Bend Double Cantilever Beam

DTS Company

Version 4.0

Automated Crack Velocity Testing

Accelerated CrackingIn low k OSG

aqueouspH 3

aqueous pH 11

pH 4.5 3%H2O2

10-111 2

Cra

ck G

row

th V

eloc

ity, d

a/dt

(m/s

)

Applied Strain Energy Release Rate, G (J/m2)

10-10

10-9

10-8

10-7

10-6

10-5

10-4

threshold crucial for reliability

Po

Load

, PC

rack

Len

gth,

a

Time (s)

dP/dt

da/dt

Load Relaxation Crack Growth Technique

Vapor environment Liquid environment

Solution container

Port for vapor injection

Thermocouple

Delaminator Adhesion Test System, DTS Company

fracture

path

cap

liner

Low kOSG

auto analysis

adhesive/cohesivecrack

DTS Company

H2Oδ

δ+

Silicon

Oxygen

Methyl

-OH-

δ-

δ+--

δ--

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

50%RH

pH 7pH 10

(NH4OH)

Increasing pH accelerates crack

growth rates

Michalske and Freiman, 1982

Accelerated Cracking in Non-Buffered Solutions

crack tip reaction

Si – O – Si + nH2O → 2(Si – OH)Si – O – Si + nOH

_→ Si – OH + Si – O

_

crack tip reaction

Crack growth rates are accelerated with increasing pH (increasing hydroxide ion concentration)

OH- mediated reaction

Transport of OH-

10-10

10-9

10-8

10-7

10-6

10-5

10-4

1.2 1.4 1.6 1.8 2 2.2 2.4

pH 5.8

Applied Strain Energy Release Rate, G(J/m2)

Cra

ck P

ropa

gatio

n R

ate,

da/

dt (m

/s)

30ºCPolymeric CapPorous MSSQ

pH 11

pH 14.4

Dielectric Cracking in Non-Buffered Solutions

Si – O – Si + nH2O → 2(Si – OH)Si – O – Si + nOH

_→ Si – OH + Si – O

_

• dominated by [OH]

stagnant boundary layer

aol

crack velocity

bulksolution

Issues:•model predictions•reaction order•what is crack tip [OH]?E. Guyer and R. H. Dauskardt (JMR) - 2005

( )12 2[ ] expν β⎛ ⎞ =⎜ ⎟

⎝ ⎠o

I

da H O Gdt10-9

10-8

10-7

10-6

10-5

10-4

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3

30CSiC Cap

3wt% H2O

2

1.5wt%H

2O

2

10wt% H2O

2

Cra

ck P

ropa

gatio

n R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G(J/m2)

Onset of steric hindrance ~0.8 J/m2 Porous MSSQ

model predictions

Effect of [H2O2] on Accelerated Cracking

[ ]2 22 2

⎛ ⎞ =⎜ ⎟⎝ ⎠

H OII

da A H O Ddt

Porous/SiC

H2O2

Silicon

Oxygen

Methyl

δ-δ+

Model Predictionsreaction

transport

E. Guyer and R. H. Dauskardt (Nature Materials) - 20031

Inglis expression for the stress concentration

2 /t aσ σ ρ=

Decelerated Crack Growth by Crack Tip BluntingAlkali metal ions in solution

result in crack tip blunting by dissolution of silica

pH 10 (NaOH)

50%RH

pH 7

pH 10 (NH4OH)

Electrolytes in DI water w/o surfactants

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt(m

/s)

Applied Strain Energy Release Rate, G (J/m2)

pH 10(KOH)

Tomozawa (1996)

High-voltage electron micrographs of a crack tip of silica glass (a) before and (b) after hot-water-soaking at 90˚C for 7 days.

Decelerated Crack Growth by Crack Tip Blunting

pH 10 (NaOH)

50%RH

pH 7

pH 10 (NH4OH)

Electrolytes in DI water w/o surfactants

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt(m

/s)

Applied Strain Energy Release Rate, G (J/m2)

pH 10(KOH)

Effects of Nonionic Surfactants on Defect Evolution during CMP

CMP slurry

Effects of surfactant molecules on the defect evolution/crack growth

are unknown!

Applied stress

δδ+

-

SiliconOxygen

Methyl

H2O or OH-

Surfactant additions critical for efficient CMP:• enhances wetting of hydrophobic low-k dielectrics

• increases the contact area for slurry/wafer interaction

• optimized CMP rates, reduced dishing…

Hydrophilic head

Hydrophobic tail

Surfactant molecule

CH3(CH2)m-1O(CH2CH2O)nH

polyoxyethylene alkyl ether

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

pH 7

E100E20

E10

CmEn Surfactant Effects on Crack Growth Behavior (pH 7)

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

pH 7

E4

E7

E23E50

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

pH 7

E4E6

E9

C10 En

C10 En C12 En C18 En

Marked effect on crack growthSensitive to hydrophilic chain length

No effect of surfactant molecules

C18 En C12 En

Marked effect on crack growthInsensitive to hydrophilic chain length

0.1 wt% surfactant

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

pH 10

E100

E20E10

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

pH 10

E4E7

E23

E50

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

pH 10

E4E6E9

C10 En C12 En C18 En

C10 En

Marked effect on crack growthSensitive to hydrophilic chain length

Little effect of surfactant molecules

C18 En C12 En

Increased effect on crack growthInsensitive to hydrophilic chain length

0.1 wt% surfactant

CmEn Effects on Crack Growth Behavior (in pH 10 NH4OH)

Nonionic Surfactants Organization and Interaction with Surfaces

organization into aggregates depends on molecular type, concentration, temperature, pH, ionic content, surfaces, confinement….

•CmEn

small n (large m)

large n(small m)

•SiO2 surface binding sites

low

highbi-layer aggregates

surface

surface

micellar aggregates

•confinement in cracks or pores

2-D

1-D

3-D

surfacesurface δ crack surfaces

cylindrical pores

pores

adsorption on SiO2

•pH effectsF. Tiberg, Lund University, 1994

CH3

CH3CH3

Crack Growth

Crack Tip Reaction Region

H2O

StrainedBond

OH

OH

CH3

CH3

CH3 OHOH

OHCH3CH3

OHCH3CH3CH3OHOH

OHOH

HydrophilicHydrophobic

Hydrophilic interaction

Hydrophobic interaction

Hydrophobic and Hydrophilic Interactions

Hydroxyl ions from alkaline solution compete for adsorption sites and at pH levels above 10 all surfactants are displaced from the surface.[F. Tiberg Ph.D. Thesis, Lund University. Sweden, 1994].

Adsorption on the silica surface

OH- OH-

OH-

Competition for adsorption sites at

high pH

CH3

Molecular Bridging in Aqueous Solution

= −tip applied bridgingG G G

CH3

Crack Growth

Crack Tip Reaction Region

H2O

OH

OH

CH3

CH3

CH3 OHOH

OHCH3CH3

OHCH3CH3OHOH

OHOH OH

OH-

OH OH

OH

Mono/bi-layer aggregates

Micellar Bridging

Cylindrical aggregates

CH3

Crack Growth

Crack Tip Reaction Region

H2O

OH

OH

CH3

CH3

CH3 OHOH

OH CH3CH3

CH3CH3OHOH

OH OH

OH-

OH OH

OHCH3

CH3

0.1 wt% surfactant

pH 10

C10En C18EnC12En

pH 10

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

0.1 wt% surfactant

pH 7

C10En

C18EnC12En

pH 7

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

CmEn Concentration Effects on Crack Growth

pH7 + 0.01wt% surfactant

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

pH 7

E20

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

E100E20

E10

pH7 + 0.1wt% surfactant

pH7

C18 En

Crack Tip Reaction Region

H2O

StrainedBond

OH-

Crack Tip Reaction Region

H2O

StrainedBond

OH-

Tem

pera

ture

(°C

)

Concentration

Phase diagram of water-C12E6 binary mixture

Reduction of surfactant concentration from 0.1 to 0.01wt% may result in different phase near the crack tip – further characterization needed.

Decelerated Crack Growth by Crack Tip Blunting

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

50%RH

pH 7

pH 10 (NH4OH)

pH 10 (KOH)

pH 10 (NaOH)

Electrolytes in DI water w/o surfactants

Wijnen, 1989

Silica gel dissolution in aqueous alkali metal hydroxides

Alkali metal ions in solution result in crack tip blunting by

dissolution of silica

Alkali metal ion + EO Complexation

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

30oC

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G (J/m2)

KOH

C18E10

KOH pH10 + 0.1wt% surfactant

NH4OH

C18E20C18E100

Carbon

Oxygen

Metal ion

Okada (1993)

EO of Polyoxyethylene Alkyl Ether

Before: side chains, straight and mainly repulsive polar hydrophilic chains

After: side chains locked by the cation, stabilzedby two electron-rich oxygen atoms, decreases mobility

Crack tip blunting effects suppressed by shielding of potassium ion.

Decelerated Crack Growth by Crack Tip Blunting

Commercial Post-CMP Cleaning Solutions

Cohesive failure at high growth rates

interfacial failure

10-10

10-9

10-8

10-7

10-6

10-5

10-4

0.5 1 1.5 2 2.5 3 3.5

waterpH 11

pH 1

Cra

ck P

ropa

gatio

n R

ate,

da/

dt (m

/s)

Black Diamond30C

30C250A TaN

Black Diamond

pH 11ESC-797

pH 1.5Kanto

~0.05 wt% TMAH and

~0.5 wt% alkanolamine

ESC-797

~0.5 wt% organic acid

Kanto M02

G

Si

Si

CDO

TaN

Fracture path switches from cohesive to interfacial

Cu

10-10

10-9

10-8

10-7

10-6

10-5

10-4

0.5 1 1.5 2 2.5 3 3.5

pH 11 bufferwaterpH 11 non buff

30C250A TaN

Black Diamond

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G(J/m2)

10-10

10-9

10-8

10-7

10-6

10-5

10-4

0.5 1 1.5 2 2.5 3 3.5

water

pH 1 kanto

ESC ph 11

30C250A TaN

Black Diamond

Cra

ck G

row

th R

ate,

da/

dt (m

/s)

Applied Strain Energy Release Rate, G(J/m2)

CMP Solution Effects on Cracking in CVD Glasses

E. Guyer and R. H. Dauskardt - 2005

• Aqueous solution chemistry affects kinetics of defect evolution during CMP having important effects on damage and process yield.

• Crack growth rates accelerated in basic solutions, inhibited in acidic solutions.

• Nonionic surfactant additions have marked effects on crack growth rates depending on hydrophilic and hydrophobic interactions with crack surfaces micellar bridging effects.

• Possible micellar bridging effects are sensitive to the pH or the choice of electrolyte.

• Aqueous solution chemistry of CMP slurries and post-CMP cleaning solutions must be optimized to reduce damage in interconnect structures for next technology nodes.

Conclusions