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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
fmdoyle@berkeley.edufmdoyle@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
2
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
September 25, 2006
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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
September 25, 2006
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FLCC
Mechanical Phenomena
Chemical Phenomena
Interfacial and Colloid
Phenomena
Chemical Mechanical
Planarization
September 25, 2006
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FLCC
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
September 25, 2006
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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
September 25, 2006
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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
September 25, 2006
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FLCC
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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FLCC
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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FLCC
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
September 25, 2006
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FLCC
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
September 25, 2006
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FLCC
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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FLCC
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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FLCC
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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FLCC
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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FLCC
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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FLCC
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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FLCC
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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FLCC
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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FLCC
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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FLCC
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
Topography Deflectionx=y=1.13μm
z range = 31.3nm z range = 0.59nm
Topography Deflectionx=y=1.94μm
z range = 320.1nm z range = 4.93nm
September 25, 2006
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FLCC
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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FLCC
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
Topography Deflectionx=y=1.13μm
z range = 98.4nm z range = 1.2nm
Flow through imaging, H2O2 solution introduced at t=56min, after solution 1 & 2
Imaging in standing solution, no pre-exposure to solutions 1 & 2
Topography Deflectionx=y=2.09μm
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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FLCC
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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FLCC
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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FLCC
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
No abrasionPolishing with pad onlyPolishing with pad and5 % alumina particles
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
Aqueous 10-2 M glycine, 27.6 kPa, 200 rpm
pH 4
pH 9
pH 12
September 25, 2006
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FLCC
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
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