flcc september 25, 2006 1 fiona m. doyle and shantanu tripathi* university of california at berkeley...

September 25, 2006

1

FLCC

Fiona M. Doyle and Shantanu Tripathi*Fiona M. Doyle and Shantanu Tripathi*University of California at BerkeleyUniversity of California at Berkeley

Department of Materials Science and EngineeringDepartment of Materials Science and Engineering210 Hearst Mining Building # 1760210 Hearst Mining Building # 1760

Berkeley, CA 94720-1760Berkeley, CA 94720-1760

[email protected]@berkeley.edu

*Department of Mechanical Engineering*Department of Mechanical Engineering

TRIBO-CHEMICAL MECHANISMS AND TRIBO-CHEMICAL MECHANISMS AND MODELING IN COPPER CMPMODELING IN COPPER CMP

TRIBO-CHEMICAL MECHANISMS AND TRIBO-CHEMICAL MECHANISMS AND MODELING IN COPPER CMPMODELING IN COPPER CMP

September 25, 2006

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FLCC

FLCC CMP ApproachFLCC CMP ApproachFLCC CMP ApproachFLCC CMP Approach

• Our approach is to develop integrated Our approach is to develop integrated feature-level process models linked to basic feature-level process models linked to basic process mechanicsprocess mechanics

• These models will drive process optimization These models will drive process optimization and the development of novel consumables and the development of novel consumables to minimize feature-level defects and pattern to minimize feature-level defects and pattern sensitivitysensitivity

• Current effort aims to integrate mechanical Current effort aims to integrate mechanical and chemical phenomenaand chemical phenomena

• Need to capture synergism between the two Need to capture synergism between the two

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FLCC

CMP OverviewCMP OverviewCMP OverviewCMP Overview

ALUMINA PARTICLES average size ~ 120 nm

from EKC Tech.

Cross-sectional View ofSUBA 500 Pad, Rodel

Corp. (courtesy Y.Moon)

SLURRY • Abrasive particles • Chemicals

Wafer

Carrier

Slurry feeder

Polishing Plate

POLISHING PAD

Pressure

Rotation

Polishing padPad

asperities

Patterned wafer

September 25, 2006

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FLCC

Kaufman’s Model for PlanarizationFor effective planarization, must maintain higher

removal at protruding regions and lower removal at recessed regions on the wafer

1- removal of passivating film by mechanical action

at protruding areas

3- planarization by repetitivecycles of (1) and (2)

Metal Passivating film

2- wet etch of unprotected metal by chemical action. passivating film reforms

Passive films, or corrosion inhibitors, are key Passive films, or corrosion inhibitors, are key to attaining planarizationto attaining planarization

Passive films, or corrosion inhibitors, are key Passive films, or corrosion inhibitors, are key to attaining planarizationto attaining planarization

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FLCC

Mechanical Phenomena

Chemical Phenomena

Interfacial and Colloid

Phenomena

Chemical Mechanical

Planarization

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Chemistry interacts synergistically with Chemistry interacts synergistically with mechanical/colloidal phenomenamechanical/colloidal phenomena

Chemistry interacts synergistically with Chemistry interacts synergistically with mechanical/colloidal phenomenamechanical/colloidal phenomena

Mechanical forces on copper introduce defects, increasing reactivity

Mechanical properties of films appear to be strongly dependent on chemistry, and probably potential

Chemistry affects degree of aggregation of abrasive particles.

Copper nanoparticles have dramatic effect

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FLCC

Integrated Cu CMP Model

ColloidAgglomeration

OxidizerInhibitor

Complexing agentSurface Film

PadPressure/ Velocity

Abrasive

The ProblemNeeded: an Integrated Copper CMP Model

Fluid MechanicsMass TransferNeeded:

understanding of the synergy between different components

Interactions:Interactions:•Asperity-copperAsperity-copper•Abrasive-copperAbrasive-copper

Fluid pressureContact pressure

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FLCC

Tribo-Chemical Model of Copper CMP

•Synergism between frequent

mechanical interactions and

action of chemical slurry make

copper CMP process

electrochemically TRANSIENT;

but to date•NO study of transient

behavior, focus on steady

state.•NO mechanistic models

of tribo-chemical

synergism.

We must study:We must study:•Transient passivation Transient passivation

behavior of copper: first few behavior of copper: first few

moments of copper moments of copper

passivation.passivation.•Abrasive-copper Abrasive-copper

interactions: frequency, interactions: frequency,

duration and force.duration and force.•Properties of passive Properties of passive

film: mechanical, electrical, film: mechanical, electrical,

chemicalchemical

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iactive

ipassive

Ox

ida

tio

n

rate

i0

Interval between two abrasive-

copper contacts

(τ): stochastic

Abrasive-copper

interaction: stochastic

Bare copper

Thick passive film

Stochastic variation in i0

t0Time (t’)

Copper oxidized

Copper: transient passivation behavior

i(t’)

Copper oxidation influenced by abrasive

interactions

More frequent interactions

Average removal rate between abrasive-copper

contacts

0

0 )( dtttinF

MV CuCW

September 25, 2006

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Transient Passivation Behavior

-2

-3

-4

-5

-6

Region I II III IV V

-2 -1 0 1 2

Log

i (A

/cm2

)

Log t (s)

Log

i

Log t

•No direct study on copper

CMP slurry constituents.•Observed behavior for other

metal-chemical combinations:

log-log (oxidation rate – time) [Jones DA “Principles and prevention of

corrosion” Prentice Hall; 2nd edition, 1995]

•Complex behavior observed

for Cu-AHT (inhibitor) behavior [Beier M, Schultze JW, Electrochimica Acta

37 (12): 2299-2307 1992]

•Wide variation observed in

decay kinetics for different

systems: milliseconds to

minutes.

[Beier & Schultze]

September 25, 2006

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Parabolic Rate Law for Corrosion Kinetics?Parabolic Rate Law for Corrosion Kinetics?Parabolic Rate Law for Corrosion Kinetics?Parabolic Rate Law for Corrosion Kinetics?

0

1

2

3

4

5

6

7

8

9

0 100 200 300 400 500

time

curr

ent

den

sity

Cu

Film thickness x(t)

Passive film

CMP Slurry containing

oxidant

{oxidant} in slurry (fixed)

{oxidant} in copper (fixed)

dt

dxk

x

oxidantoxidantD Cuslurry

}{}{

dtoxidantoxidantk

Dxdx Cuslurry }{}{

20

2 ' xtkx 2

0' xtkx

Flux of oxidant =

20'

"

xtk

ki

0

5

10

15

20

25

0 100 200 300 400 500 600

time

thic

kn

es

s

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Differing wear

distance

Relative motion

Contact area in

plan view

Wear distance

Pad asperity

Abrasive

Copper

Passive filmAbrasive

Duration between contact events.

•Passive film thickness ↔ corresponding oxidation rate

•Duration/Force of contact ↔ Thickness of Passive film removed

MechanicalInteractions

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Interaction Frequency & Duration

Elmufdi & Muldowney,Mater. Res. Soc. Symp. Proc.

Vol. 91, 2006 Spring

•Interval between asperity-copper contact ≈ 1ms•Duration of contact ≈ 10μs •Needed: study of abrasive-copper interactions

C-RICM image of real contact area

September 25, 2006

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Tribological Properties of Passive Films

Film

thic

knes

s (n

m)

Wear Distance (μm)

Film

thic

knes

s (n

m)

Wear Distance (μm)

Film

thic

knes

s (n

m)

Wear Distance (μm)

Linear wear till passive film removed

Bi-layer passive film ‘Loading’ of abrasive

Passive film properties varying with slurry chemistry

•Wear of passive film depends on mechanical properties of passive film and abrasive particle, and force of contact.

•Mechanical properties of passive film affected by chemical conditions (inhibitor, oxidation potential)

Wear distance (μm)

Conditions (a)

Conditions (b)

September 25, 2006

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Quartz Crystal MicrobalanceQuartz Crystal MicrobalanceQuartz Crystal MicrobalanceQuartz Crystal Microbalance

• Sauerbrey equation:

where q is the shear modulus of the quartz crystal, q the density, and f0 the resonant frequency

• for an AT-cut quartz crystal with a resonant frequency of 5 MHz gives that m/f is –1.77 x 10-8

g/cm2Hz

2

0

2

1

2 ff

m qq

• The changes in frequency of a piezoelectric quartz crystal, f, are related to changes in mass, m, of a substrate (e.g. Cu) that is attached to the quartz crystal:

September 25, 2006

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EQCM Experimental apparatus and materials(a) Maxtek Research

Quartz Crystal Microbalance

(b) Maxtek 1-inch diameter quartz crystals and the electrode configuration

(c) Maxtek crystal holder

(d) Schematic diagram of experimental setup for EQCM measurements. (left) chemical reagents introduced against the wall of cell, (right) a tube 10 mm from the crystal) for injecting chemicals

September 25, 2006

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pH 4, OCP, 0.01 M glycine premixed in pH 4, OCP, 0.01 M glycine premixed in acetate bufferacetate buffer

pH 4, OCP, 0.01 M glycine premixed in pH 4, OCP, 0.01 M glycine premixed in acetate bufferacetate buffer

Temporary loss in Temporary loss in weight, followed by weight, followed by significant gain in significant gain in weight, more weight, more pronounced at higher pronounced at higher concentration of Hconcentration of H22OO22..

September 25, 2006

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pH 9, OCP, 0.01 M glycine added to pH 9, OCP, 0.01 M glycine added to carbonate buffer after stabilizationcarbonate buffer after stabilization

pH 9, OCP, 0.01 M glycine added to pH 9, OCP, 0.01 M glycine added to carbonate buffer after stabilizationcarbonate buffer after stabilization

Slow loss in weight Slow loss in weight upon adding glycine. upon adding glycine. Temporary sharp loss Temporary sharp loss in weight after adding in weight after adding peroxide, followed by peroxide, followed by significant gain in significant gain in weight.weight.

September 25, 2006

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Effect of adding additional glycine, Effect of adding additional glycine, afterafter adding 2.09% hydrogen peroxideadding 2.09% hydrogen peroxide

Effect of adding additional glycine, Effect of adding additional glycine, afterafter adding 2.09% hydrogen peroxideadding 2.09% hydrogen peroxide

pH 9pH 9Deionized Deionized waterwater

September 25, 2006

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Open circuit potential of copper, pH 9, 0.01 M Open circuit potential of copper, pH 9, 0.01 M glycine and 2.09% hydrogen peroxideglycine and 2.09% hydrogen peroxide

Open circuit potential of copper, pH 9, 0.01 M Open circuit potential of copper, pH 9, 0.01 M glycine and 2.09% hydrogen peroxideglycine and 2.09% hydrogen peroxide

No passivation without No passivation without HH22OO2. 2. See that behavior See that behavior is strongly dependent is strongly dependent on history of glycine on history of glycine additions; oxidized additions; oxidized layers must resist layers must resist dissolutiondissolution

No HNo H22OO22. . Potential Potential same as that same as that induced by induced by HH22OO22

September 25, 2006

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Effect of glycine and HEffect of glycine and H22OO22 additions at additions at

different potentials, pH 9, 0.01 M glycinedifferent potentials, pH 9, 0.01 M glycine

Effect of glycine and HEffect of glycine and H22OO22 additions at additions at

different potentials, pH 9, 0.01 M glycinedifferent potentials, pH 9, 0.01 M glycine

Iron disk-Au ring Iron disk-Au ring electrode. Helectrode. H22OO22 produced during produced during reduction of Oreduction of O22 is is rapidly reduced rapidly reduced at high and low at high and low potentials, but potentials, but can escape can escape electrode at electrode at intermediate intermediate potentialspotentials

S. Zečević, D.M. S. Zečević, D.M. Dražić, S. Gojkivić; Dražić, S. Gojkivić; J. J. Electroanal. Chem, Electroanal. Chem, 265 (1989) 179265 (1989) 179

At controlled potentials, At controlled potentials, either oxidizing or either oxidizing or reducing, Hreducing, H22OO22 does does NOT lead to weight NOT lead to weight increase. Protective increase. Protective film must be sensitive film must be sensitive to potentialto potential

However, this is not consistent However, this is not consistent with passivation at high with passivation at high concentrations of Hconcentrations of H22OO22

September 25, 2006

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Environmental AFM

AFM scanner

Cu sample in a flow through cell

Peristaltic pump6 port valve

inout

3 2 1

In-situ flow through experiment (flow rate = 0.675ml/min)Slurry constituents1) DI water (introduced at time t = 0min)2) Glycine in pH 4 acetic acid/acetate buffer

(at time t = 22 min)3) Glycine + Hydrogen Peroxide in pH 4 acetic

acid/acetate buffer (at time t = 56 min)

September 25, 2006

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FLCC

AFM in Air of Copper Pre-exposed to Different Slurry Components Ex-situ

Copper in Air

Copper pre-exposed to 0.01M glycine @ pH4 for 1 minute

Copper pre-exposed to 2% H2O2 and 0.01M glycine @ pH4 for about 1 hour

Glycine at pH 4 (albeit short exposure) does not affect surface morphology significantly

With peroxide, original surface morphology is changed dramatically

Although there is some ambiguity, peroxide is much more likely to be adding a surface film rather than etching, which would affect grain boundaries preferentially

Topography Deflectionx=y=1.13μm

z range = 47.6nm z range = 0.74nm





September 25, 2006

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t=29min t=32min t=35min

t=44mint=41min t=47min

Corrosion of Copper in 0.01M glycine, pH 4In-situ imaging: Buffered glycine solution introduced at t=22 min. See slight etching, correlates with very slightly negative gradient in EQCM work before peroxide addition

x=y=1.13μm, Deflection images

September 25, 2006

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Copper in 2% H2O2, 0.01M Glycine at pH 4

•Contact mode imaging gives very noisy AFM images

•Consistent with presence of very porous and mechanically weak film on copper

•Possible deterioration of AFM probe tips in this chemistry

Effect of changing the flow through constituent:

•Instant drift and noise in AFM imaging, then stabilization.

•Transient noise prevents capturing any transient material removal upon adding peroxide



Flow through imaging, H2O2 solution introduced at t=56min, after solution 1 & 2

Imaging in standing solution, no pre-exposure to solutions 1 & 2


z range = 65nm z range = 0.66nm

t=68min

Consistent with plateau in weight gain after adding peroxide, with passivation seen in glycine/peroxide chemistries, and with signficant acceleration of material removal

September 25, 2006

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FLCC

Future AFM WorkFuture AFM WorkFuture AFM WorkFuture AFM Work

• Use of AFM tip to damage existing passive Use of AFM tip to damage existing passive filmsfilms

• Observe effect of chemistry on mechanical Observe effect of chemistry on mechanical properties of filmsproperties of films

• Observe transient currents, and correlate Observe transient currents, and correlate with area of damaged surface to obtain with area of damaged surface to obtain current densities as a function of timecurrent densities as a function of time

• Study passive film formation kinetics, to Study passive film formation kinetics, to identify best model for transient behavioridentify best model for transient behavior

September 25, 2006

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Testing of ModelTesting of ModelTesting of ModelTesting of Model

• Earlier electrochemical studies (under SFR, Earlier electrochemical studies (under SFR, by Serdar Aksu) will be used to test model by Serdar Aksu) will be used to test model predictionspredictions– Synergy between mechanical and chemical Synergy between mechanical and chemical

factors of particular interestfactors of particular interest

• EQCM work done under FLCC by Ling Wang EQCM work done under FLCC by Ling Wang will provide reference for short time frameswill provide reference for short time frames

September 25, 2006

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Polarization Curves in Cu-Glycine-HPolarization Curves in Cu-Glycine-H22OO

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

0 2 4 6 8 10 12 14 16pH

E,

V v

s. S

HE

Cu2+

CuL2Cu

L+

Cu

O2

2-

Cu

OCu2O

Cu

i, A/m2

10-4 10-3 10-2 10-1 100 101 102 103

E m

V v

s. S

HE

-800

-600

-400

-200

0

200

400

600

800

1000

1200

1400

1600

1800

pH 4pH 9pH 12

{CuT} = 10-5, {LT} = 10-2

{LT} = 10-2

September 25, 2006

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In-situIn-situ Polarization Polarization

i, A/m2

10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1

E m

V v

s. S

HE

-800

-600

-400

-200

0

200

400

600

800

1000

1200

1400

1600

1800

No abrasionPolishing with pad onlyPolishing with pad and5 % alumina particles

i, A/m2

10-4 10-3 10-2 10-1 100 101 102 103

E m

V v

s. S

HE

-800

-600

-400

-200

0

200

400

600

800

1000

1200

1400

1600

1800


i, A/m2

10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1

E m

V v

s. S

HE

-800

-600

-400

-200

0

200

400

600

800

1000

1200

1400

1600

1800


Aqueous 10-2 M glycine, 27.6 kPa, 200 rpm

pH 4

pH 9

pH 12

September 25, 2006

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ConclusionsConclusionsConclusionsConclusions

• Earlier mechanistic studies of copper CMP are Earlier mechanistic studies of copper CMP are providing insight for coupling of chemical and providing insight for coupling of chemical and mechanical modelsmechanical models– Mechanistic approach is designed to capture the synergy Mechanistic approach is designed to capture the synergy

between the twobetween the two– Work on colloidal properties of abrasives will also be Work on colloidal properties of abrasives will also be

invokedinvoked

• FLCC CMP team well positioned to capture relevant FLCC CMP team well positioned to capture relevant developments in other fieldsdevelopments in other fields

• In addition to the intrinsic utility of a combined In addition to the intrinsic utility of a combined chemical/mechanical model for CMP, this should chemical/mechanical model for CMP, this should resolve remaining questions on material removal resolve remaining questions on material removal mechanismsmechanisms

• This in turn will allow more efficient developments in This in turn will allow more efficient developments in futurefuture

flcc september 25, 2006 1 fiona m. doyle and shantanu tripathi* university of california at berkeley...

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