role of stress and solution chemistry for reduced damage ...role of stress and solution chemistry...

Role of Stress and Solution Chemistry for Reduced Damage During CMP of Ultra-Low-k Materials

July 17, 2007July 17, 2007

Taek-Soo Kim1, Katherine Mackie1, Qiping Zhong2, Maria Peterson2, Halbert Tam2, Tomohisa Konno3, and Reinhold H. Dauskardt1a be t a , o o sa o o , a d e o d aus a dt

1Stanford University, Stanford, CA 94305 USA2JSR Micro, Inc., 1280 N. Mathilda Ave., Sunnyvale, CA 94089, USA

33JSR Corporation, Yokkaichi Research Center, 100 Kawajiri-cho, Yokkaichi, Japan

Reliable Processing of Interconnect Structures Applied CMP down force

Applied CMP shear loadSi Via Low-k

abrasiveCMP Slurry

ULKcracking delaminationσf

P

nano-scaledefect

Via Low k

PAD0.1 μm

ff t f t l

silicon device

effect of metal density and aspect ratio

thermomechanical reliability of low k films

Process yield and yreliability determined by the evolution of defect

CMP and package contact stresses

soft/ductile buffer layers

cracking depends on flux composition

Crack Driving Force

Applied CMP down forceP

elastic-plastic contact

Applied CMP down force

Applied CMP shear loadSi

cracking d l i ti

σf

Crack Driving ForceGGGG ++

abrasiveCMP Slurry

ULKcracking delaminationσf

CMPcontactfilmtotal GGGG ++=

f

fffilm E

hZG

2σ=

2Pχ l ti l ti

film stressP

PAD damage initiated by abrasive or pad asperity

3aEPG

fcontact ⋅

⋅=χ elastic-plastic

contact

),( pressureshearfnGCMP =

In the absence of chemically active environmental species, crack propagates if

2( / )total cG G J m≥

Environment-Assisted Cracking

Applied CMP down forceStress: applied, residual Silicon

OApplied CMP shear load

Si

ULKcracking delaminationσf δ-

H2O δ+

Oxygen

CMP aqueous

OH-

PAD

abrasiveCMP Slurryf

P

Strained crack tip bonds

δsolution OH

p

2stressSi O Si H O Si OH Si OH− − + ⎯⎯⎯→ − + −stressSi O Si OH Si OH Si O− −− − + ⎯⎯⎯→ − + −

In the presence of chemically active species, crack propagates even if

2( / )total cG G J m< Kinetic fracture

Load Relaxation Crack Growth Technique Double Cantilever Beam (DCB) Specimen

Liquid environment Delaminator v4.0

SiSi

UKD

CMP aqueous solution

Solution container

aqueous pH 11/d

t (m

/s)

10-5

10-4

Po

aqueouspH 3

pH 11

pH 4.5 3%H2O2

Velo

city

, da/

10-7

10-6

Load

, Pa

dP/dt

auto analysis pck

Gro

wth

V

10-10

10-9

10-8

threshold crucial for reliabilityC

rack

Len

gth,

a

da/dt

auto analysis

System and support:DTS Company, Menlo Park, CA ([email protected])

10-111 2

Cra

c

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

10 reliabilityC

Time (s)

Relevance to CMP Damage Thierry FARJOT – Patrick LEDUC. LETI

NH4OH 79Citric acid 70TMAH 68DI water 65H2O2 50

45 s CMP

NH4OHDI waterCitric acid

10-4

10-3

a/dt

(m/s

)

NH4OH

DI Water Citric Acid TMAH H2O2

10-3

(m/s

)

TMAHH2O2

10-6

10-5

Gro

wth

Rat

e, d

a

10-4

NH4 OH

DI waterocity

, da/

dt

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.810-7

Cra

ck G


10

citric acidTMAH

H O. Cra

ck V

elo

40 45 50 55 60 65 70 75 80 85 9010-5

H2O2

Ave.

Area fraction of DelaminationCourtesy of Markus D. Ong and Reinhold H. Dauskardt, MRS Spring Meeting, 2007

Effects of Solution pH on Crack GrowthSilicon Methyl

H2Oδ

Oxygen

-10-5

10-4

Increasing pH accelerates crack δ

δ+

-

10-6

10

da/d

t (m

/s) accelerates crack

growth rates

OH -

δ- --10-8

10-7

owth

Rat

e, d

δ+- δ-

10-10

10-9

o

Cra

ck G

ro

50%RHpH 7

pH 10NH4OH

TaNEpoxy

Si

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10 30oC

2

JSR-LKD 5537

MSSQTa/TaN

Si


Alkali metal ion + crack tip decelerated crack growth by crack tip bluntingg y p g

Electrolytes in DI water w/o surfactants

Crack tip gets blunted by dissolution of the silica backbone.

10-5

10-4

m/s

)

Electrolytes in DI water w/o surfactants

Inglis expression for the t t ti

10-7

10-6

Rat

e, d

a/dt

(m

pH 10 (NH4OH)

stress concentration

2 /t aσ σ ρ=

10-9

10-8

Cra

ck G

row

th R

50%RH

pH 7 Wijnen (1989)

Silica gel dissolution in aqueous alkali metal hydroxides

Tomozawa (1996)

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

30oC

C pH 7

pH 10 (KOH)

pH 10 (NaOH)

Wijnen (1989)

JSR-LKD 5537


Effects of Nonionic Surfactants on Defect Evolution during CMP

Effects of surfactant molecules on the defect

l ti / k th

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

• stabilizes CMP slurry evolution/crack growth are unknown!

stabilizes CMP slurry

• optimized CMP removal rates, reduced dishing…

Silicon

MethylCH3(CH2)m-1O(CH2CH2O)nH

polyoxyethylene alkyl ether

CMP slurry δδ+

-

SiliconOxygenHydrophilic

headHydrophobic

tail

CMP slurry

H2O or OH-

Surfactant molecule

Applied stress

2

Nonionic Surfactants: Polyoxyethylene Alkyl Ethers

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

Monomeric surfactant

C i l # f C # f EO Molecular Molarity of 0 1 t%

Hydrophobic hydrocarbon chain

Hydrophilic ethylene oxide (EO) chain

Commercial name

# of C,m

# of EO,n HLB

Molecular weight (g/mol)

0.1wt% surfactant

solution (M)

ETHALL DA-4

10

4 10.5 334 2.99 x 10-3

DA 6 6 12 4 423 2 37 10 3

Hydrophilic-Lipophilic Balance (HLB)lipophilic 1 20 hydrophilic10DA-6 6 12.4 423 2.37 x 10-3

DA-9 9 14.3 555 1.80 x 10-3

ETHALL LA-4 4 9.2 363 2.76 x 10-3

LA 7 7 12 2 495 2 02 10-3

lipophilic 1 20 hydrophilic

(oil soluble) (water soluble)

12LA-7 7 12.2 495 2.02 x 10-3

LA-23 23 16.8 1200 8.34 x 10-4

LA-50 50 18.3 2389 4.19 x 10-4

BRIJ 76 10 12 4 711 1 41 x 10-3

CMC @25˚C

BRIJ 76: 4x10-3 wt%

BRIJ 78: 9.5x10-4 wt%BRIJ 76

18

10 12.4 711 1.41 x 10 3

78 20 15.3 1152 8.68 x 10-4

700 100 18.8 4676 2.14 x 10-4

CmEn Effects on Crack Growth Behavior (in pH 7 NH4OH)

C18 En

10-5

10-4

C10 En

0.1 wt% surfactant 10-5

10-4

0.1 wt% surfactant10-5

10-4

C12 En

0.1 wt% surfactant

10-8

10-7

10-6

Rat

e, d

a/dt

(m/s

)

pH 7 10-7

10-6

Rat

e, d

a/dt

(m/s

)

pH 7E100

8

10-7

10-6

Rat

e, d

a/dt

(m/s

)

pH 7

10-10

10-9

10-8

30oC

Cra

ck G

row

th

E6

E9 10-10

10-9

10-8

30oC

Cra

ck G

row

th R E20

E10

10-10

10-9

10-8

30oC

Cra

ck G

row

th R

E4

E7

E23

E50 JSR-LKD 5537

M k d ff t k th N ff t f f t t l l

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

30 C


E4E6

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

30oC


M k d ff t k th

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

30 C


7

C10 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

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

C10 En C12 En C18 En

10-5

10-4


10-4


10-4

0.1 wt% surfactant

8

10-7

10-6

Rat

e, d

a/dt

(m/s

)

pH 10 NH4OH

8

10-7

10-6

Rat

e, d

a/dt

(m/s

)

pH 10 NH4OH

8

10-7

10-6

Rat

e, d

a/dt

(m/s

)

pH 10 NH4OH

10-10

10-9

10-8

30oC

Cra

ck G

row

th R

E4E6

E9 10-10

10-9

10-8

30oC

Cra

ck G

row

th R

E

E23

E50

10-10

10-9

10-8

30oC

Cra

ck G

row

th R

E100

E20

E

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

30 C


46

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

30 C


E4 E71.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

10-11

30 C


E10

C10 En

Marked effect on crack growthSensitive to hydrophilic chain length

Little effect of surfactant molecules

C18 En C12 En

some effect on crack growthInsensitive to hydrophilic chain length

Alkali metal ion + EO Complexation

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

Alkali metal ion + EO Complexation

10-4 KOH pH10 + 0.1wt% surfactant

Carbon

Oxygen

EO of Polyoxyethylene Alkyl Ether

10-7

10-6

10-5

, da/

dt (m

/s)

NH4OH

Metal ion10-9

10-8

10 7

ck G

row

th R

ate

KOH

Okada (1993)

The EO chain locked by the cation stabilzed1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

10-11

10-10

30oC

Cra

c

C18E10

C18E20C18E100

The EO chain locked by the cation, stabilzed by electron-rich oxygen atoms, decreases mobility

Crack tip blunting effects suppressed by shielding of potassium ion


shielding of potassium ion.

Also, complexation reduces hydrogen bonding sites ↓ Gbridging ↓

Nonionic Surfactants: Surfynol 400 Series

CH3 CH3 CH3 CH3I I I I

CH3 – CH – CH2 – C – C ≡ C – C – CH2 – CH – CH3I IO O CH2 CH2CH2 m CH2 nI I

• Dimeric (Gemini) surfactant

• Low foaming (defoaming) and rapid s rface ettingI I

OH OH

m + n = number of moles of ethylene oxide (EO)

and rapid surface wetting

Commercial name Surfynol 420 Surfynol 440 Surfynol 465 Surfynol 485

Ethylene Oxide ContentMoles

Percent by Weight1.320

3.540

1065

3085Percent by Weight 20 40 65 85

Specific Gravity @ 25˚C 0.943 0.982 1.038 1.068

HLB 4 8 13 17

VOC (Volatile Organic Compound) Content (wt %) 28 4 <0.01 <0.01Compound) Content (wt %)

Molecular weight (g/mol) 284 381 667 1548

Molarity of 0.1wt% surfactant solution (M) 3.53 x 10-3 2.63 x 10-3 1.50 x 10-3 6.46 x 10-4

Nonionic Gemini (Dimeric) Surfactants Effects on Crack Growth Behavior

10-4

pH10 KOH + 0.1wt% surfactant10-4

pH 7 + 0.1wt% surfactant

465

pH10 NH4OH + 0.1wt% surfactant10-4

465

10-7

10-6

10-5

e, d

a/dt

(m/s

)

H 1010-7

10-6

10-5

, da/

dt (m

/s)

pH 7

420

440

465

10-7

10-6

10-5

da/

dt (m

/s)

420465

485 pH 10

10-10

10-9

10-8

10

Cra

ck G

row

th R

ate pH 10

KOH

440

485

10-10

10-9

10-8

10

Cra

ck G

row

th R

ate, pH 7

485 10-10

10-9

10-8

10

Cra

ck G

row

th R

ate,

440

485 pH 10NH4OH

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10 10

30oC


420440465

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10 30oC

C


485

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10 30oC

C


440

Low foaming (defoaming) and rapid surface wetting

EO length: S420 < S440 < S465 < S485

Low foaming (defoaming) and rapid surface wetting

accelerated crack growth

Controlling Crack Growth Rate by Surfactant

C18 En10-4

10-4

C10 En10-4

Dimeric surfactant

10-6

10-5

10

/dt (

m/s

)

0.1 wt% surfactant

10-6

10-5

10

/dt (

m/s

)

0.1 wt% surfactant

10-6

10-5

10

/dt (

m/s

)

420

440

4650.1 wt% surfactant

10-9

10-8

10-7

Gro

wth

Rat

e, d

a/pH 7

E100

E20

E10 10-9

10-8

10-7

Gro

wth

Rat

e, d

a/

pH 7

10-9

10-8

10-7

Gro

wth

Rat

e, d

a/ pH 7

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10

30oC

Cra

ck

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10

30oC

Cra

ck G

E4E6

E9

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.610-11

10-10

10

30oC

Cra

ck G

485

No effect of surfactant additions

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

Accelerated crack growth Suppressed crack growth

Diffusion of Aqueous Surfactant Solutions into MSSQ

Cleavededge

Diffusion front

Solutions diffuse NSiNx

edge front

200 nmSolutions diffuse into porous films

change RI

Nanoporous ULK

Silicon

500 nm

50 μm

Diffusion of Aqueous Surfactant Solution

(pH 7 NH OH + 0 1wt% C E )(pH 7 NH4OH + 0.1wt% C10En)

1 8x10-3

x Dt=

3

1.2x10-3

1.4x10-3

1.6x10-3

1.8x10 w/o surfactant C10E4

C10E6

C10E9

nce,

x (m

)

Increasing HLB and MWC10E4 (HLB = 10.5) C10E6 (HLB = 12.4) C10E9 (HLB = 14.3)

4.0x10-4

6.0x10-4

8.0x10-4

1.0x10-3

fusi

on D

ista

n

0 200 400 600 800 10000.0

2.0x10-4Diff

Square Root Time, t0.5 (sec0.5)



1 4x10-3

1.6x10-3

1.8x10-3

C12E4

C12E7

C Ex (m

)

4

8.0x10-4

1.0x10-3

1.2x10-3

1.4x10

C12E23

C12E50

n D

ista

nce,

x

Increasing HLB and MWC12E4 (HLB = 9.2) C12E7 (HLB = 12.2) C12E23 (HLB = 16.8) C12E50 (HLB = 18.3)

0 200 400 600 800 10000.0

2.0x10-4

4.0x10-4

6.0x10-4

Diff

usio

n

0 200 400 600 800 1000




4.0x10-4

C18E10

m)

2.0x10-4

3.0x10-4

C18E20

C18E100

stan

ce, x

(m


1.0x10-4

Diff

usio

n D

i

0 200 400 600 800 10000.0


Diffusion Coefficient (pH 7 NH4OH + 0.1wt% CmEn)

M l l Diff iCommercial name

# of C,m

# of EO,n HLB

Molecular weight,

M (g/mol)

Diffusion coefficient, D (m2s-1)

ETHALL DA-4 4 10.5 334 2.77E-12

x Dt=

11

10DA-6 6 12.4 423 2.19E-12

DA-9 9 14.3 555 1.14E-12

ETHALL LA-4 4 9.2 363 3.12E-12 10-12

10-11

ent,

D (m

2 s-1)

1.85~D M −

12LA-7 7 12.2 495 2.4E-12

LA-23 23 16.8 1200 1.9E-13

LA-50 50 18.3 2389 7.8E-14

10-13

usio

n C

oeffi

cie

-1.85

BRIJ 76

18

10 12.4 711 1.45E-13

78 20 15.3 1152 1.18E-13

700 100 18 8 4676 3 28E-14

102 103 10410-14Diff

u

Molecular Weight (g mol-1)700 100 18.8 4676 3.28E-14

Polymer Reptation Theory

Polymer self-diffusion in polymer melts

Aqueous surfactant solution diffusion in nanoporous MSSQin polymer melts

2~D M −

diffusion in nanoporous MSSQ

2~D M − ?

10-12

10-11

t, D

(m2 s-1

)

1.85~D M −

Experimentally,2.3~D M −

Experimentally,

10-13

10

ion

Coe

ffici

ent

-1.85-2

102 103 10410-14Diff

usi

Molecular Weight (g mol-1)

Data for poly(butadiene)

Jones, Soft Condensed Matter, p. 92

Diffusion of Pure Surfactant in Liquid Phase (C10En)

1 8x10-3

3

1.2x10-3

1.4x10-3

1.6x10-3

1.8x10 C10E4

C10E6

C10E9

nce,

x (m

)


4.0x10-4

6.0x10-4

8.0x10-4

1.0x10-3

fusi

on D

ista

n

0 200 400 600 800 10000.0

2.0x10-4

Diff


Diffusion of Pure Surfactant in Liquid Phase (C12En)

2.5x10-3

3.0x10-3

C12E4

C12E7(m) C12E4 (HLB = 9.2)

C E (HLB = 12 2)Increasing HLB and MW

1.5x10-3

2.0x10-3

12 7

Dis

tanc

e, x

C12E7 (HLB = 12.2)

0 0

5.0x10-4

1.0x10-3

Diff

usio

n D

0 200 400 600 800 10000.0


Diffusion Coefficient (100wt% pure surfactant)

0.1wt% 100wt%

Commercial name

# of C,m

# of EO,n HLB

Molecular weight,

M (g/mol)



Hydrophobic tail length

ETHALL DA-4

10

4 10.5 334 2.77E-12 2.72E-12

DA-6 6 12.4 423 2.19E-12 1.99E-12

DA-9 9 14 3 555 1 14E 12 1 44E 12

1/ 2 2 3~ [ ]mD M C − −

10-11

(m2 s-1

)

DA-9 9 14.3 555 1.14E-12 1.44E-12

ETHALL LA-4

12

4 9.2 363 3.12E-12 7.67E-12

LA-7 7 12.2 495 2.4E-12 5.11E-12

Coe

ffici

ent,

D

-2.99

LA-23 23 16.8 1200 1.9E-13

LA-50 50 18.3 2389 7.8E-14

BRIJ 76 10 12.4 711 1.45E-13 10-1 1.5x10-1 2x10-1 2.5x10-1 3x10-1

10-12

Diff

usio

n M1/2C-2 ( 1/2 l-1/2 -2)

1878 20 15.3 1152 1.18E-13

700 100 18.8 4676 3.28E-14

M1/2C 2m (g

1/2mol 1/2m 2)

Increase of Carbon Content by Surfactant Diffusion

Atom % SiNx 200 nm

Ar ion etching (2 mm x 2 mm)

XPS scan (0.1 mm x 0.1 mm)

(1) (2) (3)

O 27 97 42 88 47 82

C10E9 pure surfactantin liquid phase

Nanoporous ULK

x

Silicon

200 nm

500 nmSide view(1) (2) (3)

O 27.97 42.88 47.82

C 41.30 23.84 22.27

Si 30.73 33.28 29.90Top view

0.5 mm

pH7 NH4OH DI water+ 0.1wt% C10E9(1) (2) (3)

O 36.63 45.76 46.01

0.5 mm

45

Diffusion distance

C 35.80 21.61 21.15

Si 27.57 32.63 32.84

25303540

Car

bon

%

C10E9 pure surfactant

0 1 2 3 42025

C10E9 surfactant solution

C

x (mm)

Gibbs-Marangoni Effects

In foams, the Gibbs-Marangoni effect provides a resisting force to the thinning of liquid filmsa resisting force to the thinning of liquid films.

appliedG appliedGapplied applied

bridgingGbridgingG

SiSi

UKD

CMP aqueous solution

bridgingbridging

= −tip applied bridgingG G G

Schramm, 2000

Conclusion

• The growth of damage is a kinetic process involving stress and the presence of active chemical species.

• Careful surfactant additions can control the defect evolution.

C18 En C10 EnDimeric surfactant

Careful surfactant additions can control the defect evolution.

C18 En

10-6

10-5

10-4

(m/s

)0.1 wt%

surfactant

10-6

10-5

10-4

(m/s

)

C10 En

0.1 wt% surfactant

10-6

10-5

10-4

(m/s

)

4204650.1 wt%

surfactant

Dimeric surfactant

10-8

10-7

0

owth

Rat

e, d

a/dt

pH 7E100

E20

E10-8

10-7

10

owth

Rat

e, d

a/dt

(

pH 7

10-8

10-7

10

owth

Rat

e, d

a/dt

(

pH 7440

1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 610-11

10-10

10-9

30oC

Cra

ck G

ro E10

1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 610-11

10-10

10-9

30oC

Cra

ck G

ro

E4E6

E9

1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 610-11

10-10

10-9

30oC

Cra

ck G

ro

485

No effect of surfactant additions

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6


1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6


1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6


Accelerated crack growth Suppressed crack growth

Thank you!Thank you!

Q&AQ&A

role of stress and solution chemistry for reduced damage ...role of stress and solution chemistry...

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