Christopher LittekenDaniel Maidenberg

Sven StrohbandLouise Wang

Eric Guyer

Reinhold H. Dauskardt(dauskardt@stanford.edu)

Work supported by the DOE, SRC, MARCO, and ATP Dept. of Commerce. Industry support from INTEL, IBM, TI, AMAT, JSR, Hitachi Chemical.

Reliability of Advanced Interconnect Structures:

New Materials and Length Scale Challenges

Mechanical Reliability of Thin-Film Interconnect Structures

Issues:• Measurement of thin-film adhesion• Subcritical debonding (moisture,

temperature, mechanical fatigue)

• Relationship to processing and composition (interface chemistry and morphology, surface treatment, seed layers)

• Integration of new materials• Simulation and reliability modeling

debonding

Device

Substrate (Ceramic or Polymer)

Solder Interconnect Polymer Underfill

100 µ m

applied mixed mode K-field(KI, KII)

ductile layerplasticzone

elastic

elastic substrate

cohesive zone elasticlayer

BC domain dia 25 – 50 µm

applied mixed mode K-field(KI, KII)

ductile layerplasticzone

elastic

elastic substrate

cohesive zone elasticlayer

BC domain dia 25 – 50 µm

Multi-ScaleSimulations

1 µm

Outline• Adhesion and Fracture Involving Brittle Dielectric Layers

– barriers and dielectrics in interconnect structures (TiN, TaN, SiNx, SiO2)– new low-k dielectric materials (e.g. CDO, MSSQ, SiLK, porosity)

• Moisture and Implications for CMP

– moisture assisted subcritical debonding– kinetic models and understanding

• Multi-Scale Simulations of Adhesion– interface cohesive zones and plasticity in ductile layers– barrier layer stiffness, thickness and effects of pre-stressed thin films

• Patterned Structures– elastic constraint and stress state– effect of line geometry

Interface Fracture Resistance and Reliability

Gtotal = Go + Gzone

interface chemistry

frictional contactductile adjacent layer

Plastic Zone

Fracture ProcessZone, Go

Adsorbed layer

Elastic Layer

Elastic Substrate

SurfaceRoughness, λ Ductile Layer, hD

BarrierLayer, hb

Interface Fracture Energy

Of interest….• New materials

• brittle glasses• ductile polymers• porosity (density)

• Length scales effects• mechanical properties• adhesion• 1-D, 2-D, complex

structures

Thin-Film Adhesion Testing

Subcritical Debonding(temperature and moisture effects)

1 10Debond Driving Force, G (J/m2)

10-8

10-7

10-6

10-5

10-4

10-3

m ~ 80

m ~ 14mGCdtda

=

Deb

ond

Gro

wth

Rat

e, d

a/dt

(m/s

)

TaNx

Ta

1.00

Sample Type

0.0

4.0

8.0

12.0

Ta TaNInte

rface

Fra

ctur

e E

nerg

y, G

c(J

/m2 ) Delamination Resistance

Lane, Krishna, Hashim, Dauskardt - J. Mater. Res. 15 [1] 2000

Thin films sandwiched between elastic substrates

EnvironmentalChamberLow Profile Test Frame

(use with microscopy)

4-pt. Delaminator Tool

Research Activities in Low K MaterialsMaterial Class Feature Examples

DielectricConstant

Silica (SiO2) Silicon dioxide glass ThermalTEOS

3.9 – 4.1

Modified Silica Fluorinated silicaCarbon doped silica

CVD fluorinated silica (FSG)SiCOH

3.5< 3.0

Porous Silica Nanoporous silica AerogelZerogel

1.0 – 3.0

Inorganic Polymer Organically modifiedsilicate

Polysilesquioxanes (SSQ) 2.5 – 3.5

Porous Hybrids Phase separatedorganic/inorganic

PCL/SSQ hybrids 2.3 – 3.0

Organic Polymers Fluorinated and non-fluorinated polymers

Polyimide, parylene andpolynaphthalene familiesBenzocyclobutene (BCB)Aromatic Hydrocarbon (SiLK)Amorphous carbon films

1.8 – 3.5

2.72.62.7 – 3.5

CH3

Si

CH3O

Si

O

O

O

Si OH3C

O

Si O

SiO

Si

OCH3

CH3

Effect of Carbon Doping on Adhesion of CDO

4.61

8.5

2.412.8

3.57

5.355.57

3.2

3.8

4.5

0

1

2

3

4

5

6

7

8

9

10

0% 10% 20% 30% 40% 50% Graded

Inte

rface

Fra

ctur

e E

nerg

y G

c (J/

m2 )

Sample Set 2Sample Set 1

Si-CH3 / Si-O FTIR ratioSi

O

Si OO

O

Si

Si

OO

O

O

SiO

Si

O

O

O

OO

O

silica

carbon-doped

Cu

SiNx

SiO2

Si

SiNx

CDO 0.5 µm debond

J. Rim, F. Shi and R.H. Dauskardt - 2000

0 10 20 30 40 502.02.22.42.62.83.03.23.43.6

Die

lect

ric C

onst

ant k

(at 1

0KH

z)

Initial Content of Porogen (wt%)

0 10 20 30 40 500.8

1.0

1.2

1.4

1.6

Den

sity

(g/c

m3 )

Initial Content of Porogen (wt%)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

5010 20 25 30 400

Frac

ture

Ene

rgy

(J/m

2 )

Initial Content of Porogen (wt%)

SoG Porosity Effects on Properties

L. Wang, J. Rim, and R.H. Dauskardt - 2002

fracture MSQ(Hitachi Chemical)

0 20 40 60 80 100

2.6

2.8

3.0

3.2

3.4

Die

lect

ric C

onst

ant k

(at 1

0KH

z)

NaOH Promoter Content (ppm)

0 20 40 60 80 1000.975

0.980

0.985

0.990

0.995

Den

sity

(g/c

m3 )

NaOH Promoter Content (ppm)0.0

0.5

1.0

1.5

2.0

2.5

3.0

10 25 50 75 1000

Frac

ture

Ene

rgy

(J/m

2 )

Promoter Content (ppm)

• Step 2: Condensation

• Step 1: Hydrolysis

Si(OR')3R + H2O ------ Si(OR')2ROH + HOR'

Si(OR')4 + H2O ------ Si(OR')3OH + HOR'

Si(OR')2CH3OH + Si(OR')3OH

CH3(OR')2Si-O-Si(OR')3 +H2O

NaOH

NaOH

SoG NaOH Promoter Effects on PropertiesL. Wang, J. Rim, and R.H. Dauskardt - 2002

R = CH3

CH3

Si

HO

Si

O

O

O

Si OH3C

O

Si O

SiO

Si

O

CH3CH3

H R = H

SoG Composition Effects on Fracture PropertiesFr

actu

re E

nerg

y, G

c(J

/m2 )

0

2

4

6

8

10

0 1 2 3

Si-O Bond Ratio, SiOx

CH3/H

CH3

SiO2“Rule of Mixture”

Models

Methyl Side Groups(R = CH3)

Hydrogen Side Groups(R = H)

L. Wang, J. Rim, F. Oota and R.H. Dauskardt - 2001

OSi

CH3

OSi

C6H5

OSi

C2H3

Methyl Vinyl Phenyl

increasing functional group size

0

1

2

3

4

5

0 20 40 60 80(Effective Functional Group Content) x (Size)

Frac

ture

Ene

rgy,

Gc

(J/m

2 )

MethylVinylPhenyl

Functional Group SizeConstant CH3, Varying H

Porous Brittle Dielectrics (MSSQ)

200 nm50%

Porous MSSQ/Resin-1/Porogen DMAEMA-MMA

0

5

10

15

20

25

0% 10% 20% 30% 40% 50%

UntreatedTreated

Porosity

Fracture path:MSSQ-Silica

All others show fracture atMSSQ-chromium

Inte

rfaci

al A

dhes

ion,

G (J

/m2 )

Maidenberg, Miller, Volksen, and Dauskardt - 2002

Porosity, ρ

Ela

stic

and

Fra

ctur

e P

rope

rties

Isostrain

Isostress

actual

ff

f EE

hG ∝≈2σβ

TEff ∆∆≈ ασdriving “force” for thin film cracking:

…anticipate fracture problemsin complex structures…

film stress:

…but some surprises!

Moisture Assisted Subcritical Debonding

M. Lane and R. H. Dauskardt - Proc. MRS, 1999.

Subcritical debonding important for reliability

during CMP

strained debondtip bonds

chemical reactionwith H20

applied stress

WaferAqueous solution

Pressure

aol

crack velocity

transport limited zone

debonddielectricbarriercopper

H20

Require Gc > 5 J/m2 to survive CMP.

Block, Scherban, et.al. INTELProc. IEEE 2001 Int. Interconnect Tech.

Conf., June 2001

Crack Driving Energy, G

Region II

Region I

GC

TH

(Reaction-controlled)

(Transport-controlled)

Region III

+−

=

RTbGE

PP

Adtda tip

n

oOH

*

exp2

Moisture-Assisted Debonding

)complex activated() tipdebond( *2 BBOnH →+

[ ] [ ]BOHkrate nr 2=

strained debondtip bonds

chemical reactionwith H20

applied stress• Interaction of moisture with strained debond tip bonds

• Chemical reaction rate theory:

Wiederhorn et. al. model (1980)

• Atomistic crack-growth models:

−=

ηγ2

sinh tipo

Gv

dtda

Lawn and Cook model (1990)

−−

−= −+

kTU

kTUfrate o

**

expexp

Subcritical Delamination Behavior in Moist Environments: Temperature and Humidity Effects

−=

ηγ2sinh Gv

dtda

o

Crack-Growth Model

SiO2/TaN/Cu

debond

10Debond Driving Force, G (J/m2)

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

153

95% RH

50% 20%5%

T = 50oC

Del

amin

atio

n G

row

th R

ate,

da/

dt(m

/s)

10-11

10-10

10 -9

10 -8

10 -7

10 -6

10 -5

10 -4

1 10

20 at.% C

90% RH

30% RH

5 at.% C

Del

amin

atio

n G

row

th R

ate,

da/

dt(m

/s)

Debond Driving Energy, G (J/m2)

TaN/SiO2(25oC and 50% RH)

Debonding in CDO Dielectrics

threshold values crucial for reliability

M. Lane and R. H. Dauskardt - Proc. MRS, 1999.

J. Rim, F. Shi and R.H. Dauskardt - 2000

Effect of CMP Solution on Subcritical Debonding

10-10

10-9

10-8

10-7

10-6

10-5

10-4

1 2

Deb

ond

Gro

wth

Rat

e, d

a/dt

(m/s

)

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

pH 11.0

pH 3.0

T = 30oC

Increasing pH acceleratesdelamination growth rates

E. Guyer, M. Patz and R. H. Dauskardt - 2002

Delamination observed in MSSQ

pH 3.0 solution (e.g. dielectric slurry)1.0 wt.% potassium hydrogen phthalate, hydrogen chloride 0.07 wt.%, formaldehyde 0.05 wt.%, methanol 0.02 wt.%, balance H2O

pH 11.0 solution (e.g. barrier metal slurry)0.08 wt.% Glycine, 0.03 wt.% sodium chloride, 0.02 wt.% sodium hydroxide, 0.01 wt.% disodiumethylenediaminetetraacetate anhydrous, balance H2O

Materials:JSR - LKD6103 with Poly X Cap

H2O

+− +↔ NaOHNaOH

−+ +↔ OHOHOH 3222 lone pair

orbitals1 lone pair(shields)

3 lone pairs(accelerates)

−+ +↔+ ClOHOHHCl 32

1 lone pair(shields)

3 lone pairs(accelerates)

Cra

ck G

row

th R

ate,

da/

dt(m

/s)

10-4

10-12

10-10

10-8

10-6

Stress Intensity Factor, K (MPa√m)0.3 0.4 0.5 0.6

Bulk Silica Glass(Wiederhorn – 1973)

Hydrogen peroxide effects on reaction kineticspH 3

Buffered HCl

pH 11 Buffered NaOH

pH 4.5 3%H2O2

T=30oC

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

1 2

Deb

ond

Gro

wth

Rat

e, d

a/dt

(m/s

)

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

E. Guyer, M. Patz and R. H. Dauskardt - 2002

−+ +↔+ HOOHOHOH 23222

5 lone pairs(accelerates)

Delamination observed in MSSQ

Materials:JSR - LKD6103 with Poly X Cap

Effect of CMP Solution on Subcritical Debonding

Debond Driving Energy, G (J/m2)1 1010 -8

10-7

10 -6

10 -5

10 -4

10 -3

Deb

ond

Gro

wth

Rat

e, d

a/dt

(m/s

)TaNx

Ta

prematurethreshold

• chemically-active species in aqueous slurries crucial for survival through CMP

Engineer interfaces immune to stress corrosion?• barrier-oxide effect on steric hindrance

Moisture and Loading Effects during CMP

ao

SiO2

TaCu

oxide

2uopH2O

SiO2

adsorbate

Competing rate effects: crack growth rate and Ta oxidization rate

Multi-Scale Simulations of 3-D Interconnect Structures

Microprocessor

n+/p+

n+/p+ n+/p+

Gate

Gate

n+/p+n+/p+

Gate

n+/p+

Reliability of Complex 3-D Structures

debond

Use simulations to predict adhesion and mechanical reliability

of more complex structuresCu

plasticzone

elastic

elastic substrate

Cohesivezone

elasticlayer

Computational Model

• finite deformation elasticity (FEM)

• large strain elastic/plastic (with hardening)

• VIB debond layer or cohesive zone

Separation, δ

Stre

ss, σ

Go ~ 5 J/m2

σmax ~ E/60

δmax

(developed from Klein and Gao - 1999)

10-2 10-1 1 100

20

40

60

80

100

20

Copper Layer Thickness, h (µm)

Inte

rface

Fra

ctur

e E

nerg

y, G

c(J

/m2 )

Dielectric layer

Si wafer

Copper layer

Barrier layer debond

2 4 6 8

250

300

350

400

450

500measured yield properties

0Copper Layer Thickness, h (µm)

Cop

per Y

ield

Stre

ss, σ

ys(M

Pa)

+

h1~ β

ασys

simulated yield properties

+h1~ β

ασys

Lane, Vainchtein, Gao, R.H. Dauskardt - J. Mater. Res. 16 [1] 2001

Cu layer thickness300 Å - 16.4 µm

Multi-Scale Simulations of Interface Fracture Resistance

Elastic barrier layer, D

Ductile copper layer, hCu

Cu metal

Ductile Organic Dielectrics: Thickness Effects on Adhesion

SiO2

CuCrSiXy

SiLK

(0.2 µm)

(0.4 µm)(0.02 µm)

(0.25 – 5.12 µm) debond

Litteken and Dauskardt - 2000

Organic Dielectric Thickness, h (µm)

Inte

rfaci

al A

dhes

ion,

Gc

(J/m

2 )

0

10

20

30

40

50

60

0.01 0.1 1 10

SiLK/SiO2

SiLK/SiO2(ozone clean)

FLARE/SiN

Yie

ld S

tress

, σys

(MP

a)

Film Thickness-1, 1/h (µm)-1

Cu

SiLK0

200

400

600

800

0 2 4 6

Technologically Relevant Values:hb ~ 5 – 100 nm

0.8 - 2.3 005 - 20066.160/

≈

≈≈≈

YS

c

YS

c

MPaGPaE

σσ

σσ

1µm Cubarrier

SiO2 dielectric

silicon

Barrier Layer Thickness Effects on Adhesion

3 4 5 6 7 8 9 10 11 12

1

2

3

4

100

50

25

10

Parameters:

H = 10 GPa

Eb

= 250 GPa

hpl

= 1.0 µm

G0

= 4 J/m2

barrier thicknesshb (nm)

5

Inte

rface

Fra

ctur

e E

nerg

y, G

ss/G

o

Normalized Cohesive Stress, σc/σys

typical values

strong interfaceweak ductile layer

weak interfacestrong ductile layer

debond

Effect of Barrier Stiffness

3 4 5 6 7 8 9 10 11 121

2

3

500

Elastic modulusEb (GPa)

125

300250200

Inte

rface

Fra

ctur

e E

nerg

y, G

ss/G

o

Normalized Cohesive Stress, σc/σys

typical values

S. Stroband and R.H. Dauskardt - 2002

Pre-Stressed Metal and Multi-Layer Structures

silicon substrate

brittle dielectricbarrier

plastic zone

barrier

σR

S. Stroband and R.H. Dauskardt, Interface Science – 2002 (In review)

-80 -60 -40 -20 0 20 40 60 80

1.4

1.8

2.2

2.6

3.0

σR = 1/3 σys

Nor

mal

ized

Fra

ctur

e E

nerg

y, G

c/Go

Phase Angle, Ψ (degrees)

σR = -1/3 σys

2 3 4 5 6 7 8 9 10 11 12

03

58

1013151820

single layer

bi-layer

bi-layer

Inte

rface

Fra

ctur

e E

nerg

y, G

ss/G

o

Normalized Cohesive Stress, σc/σys

typical values

hb = 10 nm

hb = 20 nm

ILD (4.0µm)

ILD (0.5µm)

plastic (1.0µm)

barrier hb

plastic (1.0µm)

ILD (4.0µm)

barrier hb

Multi-Layer Structures

Films with Residual Stress

C. Litteken and Dauskardt, Int. J. Fracture – 2002 (in review)

Adhesion of Complex Patterned Structures• Does feature size and aspect ratio effect interface adhesion and reliability?• Establish guidelines for interface reliability in complex structures

top surface

Optical Micrographs

bottom surface

SiliconMetal LayerSiO2

Polymer

Silicon

w h = 1 µm

debond

0

2

4

6

8

10

12

14

5 10 15 20

patterned line adhesion

Inte

rfaci

al A

dhes

ion,

Gc

(J/m

2 )

Aspect Ratio (w/h)

blanket thin-film adhesion

shear lip model prediction

400 nm 400 nm210 nm 210 nm

210 nm

210 nm

debond propagation

Cu CDO/SiLK

SiSiO2

SiC or SiN

SiC or SiN

CuTaN

690 nm

Landed Trench

Cu/ILD Patterned Structures (300 mm Wafers)

SiSiO2

SiN or SiC

SiC or SiNSiLK or CDO

690 nm

360 nm

Hanging Trench

narrow features

orthogonal features

wide features

SiLK or CDO

330 nm

C. Litteken, T. Scherban, G. Xu and Dauskardt - 2002

0

1

2

3

4

5

6

Landed Patterned Structures –Etch Stop versus Passivation Cap Debond

pattern/passivationdebond

etch stop debond

Inte

rfaci

al A

dhes

ion,

Gc

(J/m

2 )

SiSiO2SiC

SiC

CuTaN

CDO

debonded interface

orth

ogon

al fe

atur

es

wid

e fe

atur

es

narro

w fe

atur

es

Debond Path Morphology

RMS roughness 3.8nm

RMS roughness 2.9nm

debond direction

KIKII

KIKII

Summary• Adhesion and Fracture Involving Brittle Dielectric Layers

– barriers and dielectrics in interconnect structures (TiN, TaN, SiNx, SiO2)– new low-k dielectric materials (e.g. CDO, MSSQ, SiLK, porosity)

• Moisture and Implications for Debonding– moisture assisted subcritical debonding– kinetic models and understanding

• Multi-Scale Simulations of Adhesion– interface cohesive zones and plasticity in ductile layers– barrier layer stiffness, thickness and pre-stressed thin films

• Patterned Structures– elastic constraint and stress state– effect of line geometry

σx

Dielectric layer

Si wafer

Copper layer

Barrier layer

WaferAqueous solution

Pressure