semitool confidential 1 copper damascene plating 1/5/06 brandon brooks process development engineer
TRANSCRIPT
1Semitool ConfidentialSemitool ConfidentialSemitool ConfidentialSemitool Confidential
Copper Damascene Plating
1/5/06
Brandon BrooksProcess Development Engineer
2Semitool ConfidentialSemitool Confidential
Outline
•Why Cu Interconnects?
•Damascene Process Flow
•Parameters Affecting Cu Interconnects
•Backside Clean and Bevel Etch
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Damascene Plating?
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Why Cu Interconnects?
Al Cu W
Melting Pt (°C) 660 1,083 3,410
Oxidation in Air Rapid; Self-Sealing
Slow; Not Self-Sealing
Inert
Resistivity (m-cm)
Crystalline 2.82 1.77 5.6
As Deposited 3.0-3.3* 1.8-2.0 8-11
Self-Diffusion Coefficient (cm2s-1) @ 100 °C 2.1·10-20 2.1·10-30
Coefficient of Thermal Expansion (Unit/°C)
24·10-6 17·10-6 4.3·10-6
* Alloy (Si, Cu)
Resistivity Melting PointThermal Expansion Electromigration
Al
Resistivity Melting PointThermal Expansion Electromigration
Cu
Best!
Interconnect Metal Properties
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Why Cu Interconnects?
Al Cu Ag
Etch Properties Cl & Br Plasmas Cl & Br Plasmas F & Cl Plasmas
Etch Rate (Å/min)
5,000 500 5,000
Cu has a very slow etch rate•Cu halides are solid at normal temperatures
Changing from Al to Cu interconnects requires new process flow•Enter Damascene plating
Interconnect Metal Properties
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Damascene Process Flow
Typical Damascene Process Flow
1. Dielectric Deposition2. Photoresist Deposition3. UV Exposure4. Develop Photoresist5. Etch Dielectric6. Remove Photoresist7. Barrier Deposition8. Seed Layer Deposition9. Electrochemical Deposition (ECD)10. Backside Clean and Bevel Etch11. Anneal12. Chemical Mechanical Polish (CMP)13. Repeat Steps 1-10 for Every Metal Layer
Today’s Main Topics
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Damascene Process Flow
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Copper Interconnect Parameters
Key Factors Affecting Cu Interconnect Performance
1. Gap-Fill2. CD Uniformity3. Overburden4. Anneal
AMD’s 9 Cu Levels
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Copper Interconnect Parameters: Gap-Fill
Key Parameters for Gap-Fill
1. Seed and Barrier Layers1. Uniformity2. Thickness
2. Plating Recipe1. Hot Start (Initiation)2. Fill Current Density3. Waveform
3. Plating Chemistry1. Inorganic2. Organic
0.12m, 8.3:1AR Trenches
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Copper Interconnect Parameters: Gap-Fill
Physical Vapor Deposition (PVD) Effects
Seed and Barrier Layers
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Edge Shadowing Optimized Seed Layer
Copper Interconnect Parameters: Gap-Fill
Seed and Barrier Layer Uniformity
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1500Å Total Seed Thickness 2000Å Total Seed Thickness
0.30micron, 4.8:1 AR Vias 0.30micron, 4.8:1 AR Vias
Copper Interconnect Parameters: Gap-Fill
Seed and Barrier Layer Thickness
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Copper Interconnect Parameters: Gap-Fill
Plating Recipe Hot Start
0.180 m Line Width Trenches48 Coulombs ECD
No Hot Start 2V Hot Start
2X Fill Rate on the 2V Hot Start
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Copper Interconnect Parameters: Gap-Fill
Plating Recipe Current Density
Current too Low
Current too High
The Effect of Current Density upon Gap Fill
Bad
Good
0.35μm, 4.3:1 AR Vias 0.35μm, 4.3:1 AR Vias
0.18μm, 5.1:1 AR Trench 0.18μm, 5.1:1 AR Trench
Gap
Fill
Current Density
Low High
Optimum Fillfor feature D
Optimum Current
Optimum Current
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Copper Interconnect Parameters: Gap-Fill
Plating Recipe Waveform
Waveform Cu Diffusion Additive Adsorption Bottom Up Fill
Direct Current (DC)
- + 0
Pulse DC + - 0
Pulse Reverse (PR) + - 0
DC plating provides better additive adsorption
Pulsed plating provides better Cu diffusion
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Copper Interconnect Parameters: Gap-Fill
Plating Chemistry
Inorganic Components
1. Copper Sulfate (CuSO4)2. Hydrochloric Acid (HCl)3. Sulfuric Acid (H2SO4)
Organic Components
1. Suppressor (PEG)2. Accelerator (SPS)3. Leveler (Amine)
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Copper Interconnect Parameters: Gap-Fill
Inorganic Plating Chemistry
Copper Effect on Gap Fill
High Copper
Low Copper
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Inorganic Plating Chemistry
Copper Interconnect Parameters: Gap-Fill
Chloride Effect on Gap-Fill
Cl- Effect on Suppressor
0
2
4
6
8
10
12
14
16
18
20
0 50 100 150 200
Cl Concentration ppm
CV
S S
trip
pin
gP
ea
k A
rea
(m
C)
Bad
Good
HighLow
Ga
p F
ill
Chloride (ppm)
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Copper Interconnect Parameters: Gap-Fill
Inorganic Plating Chemistry
Bad
Good
HighLow
Ga
p F
ill
Acid (g/l)
pH 3
pH 2
Acid Effect on Gap Fill
pH 2
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• Accelerator– Catalytic effect
– Requires very small amount of Cl-
– Increased current for a given potential
• Suppressor– Suppresses deposition
– Requires Cl- to adsorb onto copper surface
– Decreases current for a given potential
• Leveler– Suppresses deposition at high current density areas
– Very low concentration (diffusion limited)
Copper Interconnect Parameters: Gap-Fill
Organic Plating Chemistry
Organic Effect on Gap Fill
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A
C
B
A = VMS
B = VMS + Suppressor
C = VMS + Sup. & Accel.
I
V
Cyclic Voltammetric Stripping Analysis (CVS)
Copper Interconnect Parameters: Gap-Fill
Organic Plating Chemistry
Plating Region
Stripping Region
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0
0.1
0.2
0.3
0 0.01 0.02 0.03 0.04 0.05
Suppressor Concentration
80 g/l
Low Acid (10g/l)
High Acid 150 g/l
0
5
10
15
20
25
30
0 1 2 3 4 5
Accelerator Concentration
80 g/l H2SO4
High Acid 150 g/l
Wors
eB
ett
er
Str
ippi
ng A
rea
Wors
eB
ett
er
Str
ipp
ing
Are
aCopper Interconnect Parameters: Gap-Fill
Organic Plating Chemistry
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Copper Interconnect Parameters: Gap-Fill
Organic Plating Chemistry
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Organic Plating Chemistry
Copper Interconnect Parameters: Gap-Fill
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Organic Plating Chemistry
Copper Interconnect Parameters: Gap-Fill
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Organic Plating Chemistry
Copper Interconnect Parameters: Gap-Fill
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Organic Plating Chemistry
Copper Interconnect Parameters: Gap-Fill
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Organic Plating Chemistry
Copper Interconnect Parameters: Gap-Fill
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Key Parameters for Current Density Uniformity
1. Chemistry1. High Acid2. Low Acid
2. CFD Reactor1. Electric Field Control
Intel: 8 Cu Levels
Copper Interconnect Parameters: CD Uniformity
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Copper Interconnect Parameters: CD Uniformity
+
Cathode(Reduction)
Current Path
Anode(Oxidation)
Cu2++2e- Cu0Cu0 Cu2++2e-
e- e-e- e-
Cu2+
V0
Electrolyte
Cu2+
Generalized Electrochemical SchematicElectrolytic Copper Deposition
Ammeter
Surface Area
Current Density = Current Surf. Area
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Copper Interconnect Parameters: CD Uniformity
= Surface Area
Relec 1/Bath Conductivity
Rcat 1/Seed Thickness
Rcat Wafer Radius
Relec
Ranode= 0
V+
Electrolyte
Cathode(Thin)
Anode(Thick)
Rcat
Relec
elecedge R
VI
)R(R
VI
cateleccenter
= Area
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Relec
Ranode= 0
V+
Electrolyte
Cathode (Thin)
Anode (Thick)
Rcat
Relec
Edge I Loop
Center I Loop
)( catelecelec
catECcenteredge RRR
VRIII
How To Make ECI Small?
VCurrent DensityThroughput
Rcat
Seed Layer ThicknessWafer Radius
Relec
Bath Conductivity
Copper Interconnect Parameters: CD Uniformity
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Conductivity at Various Bath ConditionsConductivity at Various Bath Conditions
0
100
200
300
400
500
600
Con
du
ctiv
ity
(mS
/cm
)
175 g/l H2SO4
17 g/l Cu
80 g/l H2SO4
50 g/l Cu
10 g/l H2SO4
50 g/l Cu
“Low” Acid
“High” Acid
70
247
511
Copper Interconnect Parameters: CD Uniformity
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0sec
5sec
15sec
30sec
60sec
120sec
Cu
rren
t D
ensi
ty
Wafer Radius
Plating Time
(0,0)
Copper Interconnect Parameters: CD Uniformity
Terminal Effect
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Current too Low
Current too High
The Effect of Current Density upon Gap FillThe Effect of Current Density upon Gap Fill
Bad
Good
0.35mm, 4.3:1 AR Vias 0.35mm, 4.3:1 AR Vias
0.18mm, 5.1:1 AR Trench 0.18mm, 5.1:1 AR Trench
Gap
Fill
Current Density
Low High
Optimum Fillfor feature D
Optimum Current
Optimum Current
Copper Interconnect Parameters: CD Uniformity
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Are the center and edge receiving the same process?
Copper Interconnect Parameters: CD Uniformity
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Cathode
Anode2
V1+
V2+
Anode1
Advanced Reactor Design: Multiple Anodes
Robust system that can handle multiple chemistries
Built for the future with the ability to handle shrinking die size
Cost effective ability to handle increasing wafer diameters
Copper Interconnect Parameters: CD Uniformity
0 ECIV1 and V2 adjusted until Independent of Rc and Relec
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Dielectric
Electrolyte Virtual Anodes
Physical Anodes
WaferConventional Reactor CFD Reactor
Electrolyte
Copper Interconnect Parameters: CD Uniformity
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ConcentricAnnular Anodes
ElectrolyteBubble Trap
Rotating Wafer
Dielectric
Flow Inlet
Overflow
Virtual Anode
Copper Interconnect Parameters: CD Uniformity
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Superposition of Electric Field
-120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120
Wafer Diameter (mm)
Nor
mal
ized
Vol
tage
at C
atho
de (
V)Anode 1
Anode 2Anode 3
Anode 4
Summed Field
Copper Interconnect Parameters: CD Uniformity
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100 nm Seed layer, 1100 nm Seed layer, 1m depositionm depositionH
igh
Aci
d51
1mS/
cmL
ow A
cid
70m
S/c
m
Conventional SEMITOOL - CFD
14
18
22
26
30
34
Cu
rren
t D
ensi
ty (
mA
/cm
^2) 0sec
5sec
15sec30sec60sec120sec
133%
14
18
22
26
30
34
0 25 50 75 100 125 150
Cu
rren
t D
ensi
ty (
mA
/cm
^2)
0sec
120sec
20%
<5%
0 25 50 75 100 125 150
<5%
Wafer Radius (mm)
Copper Interconnect Parameters: CD Uniformity
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Dynamic Compensation for Constant Current DensityDynamic Compensation for Constant Current Density
1.0
1.5
2.0
2.5
0 20 40 60 80 100 120Deposition Time (sec)
An
ode
Cu
rren
t (A
mp
s)
Anode 2
Anode 3Anode 1
Anode 4
Copper Interconnect Parameters: CD Uniformity
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Key Parameters for Overburden
A. Local Overburden (Overplating) – Fill Step1. Chemistry
1. 3-Component2. 2-Component
2. Waveform1. Direct Current2. Pulse Reverse
B. Global Overburden – Cap Step1. Chemistry
1. High Acid2. Low Acid
2. CFD Reactor
Copper Interconnect Parameters: Overburden
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Copper Interconnect Parameters: Local Overburden
Direct Current POR
3-Component Organic Package
Moderate Acid Electrolyte
Pulse Reverse POR 2-Component Organic Package
High Acid Electrolyte
Step Up No Step Up
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Copper Interconnect Parameters: Local Overburden
Insufficient Leveler
Planar Deposition
Optimized Organic Conditions
Overplating
Post-CMP Residual Cu
No Post-CMP Residual Cu
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Copper Interconnect Parameters: Global Overburden
-100mm 0 100-800
-600
-400
-200
0
200
400
600
800Å
Radial control of Thickness Variation (Å)
Cu
Th
ick
nes
s (Å
)
Wafer Diameter (mm)
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Copper Interconnect Parameters: Global Overburden
Raider CFD Profile Before & After 30s CMP
4,000
8,000
12,000
16,000
Th
ick
ness
(A
)
POR Profile Before & After 30s CMP
4,000
8,000
12,000
16,000
Wafer Diameter
Th
ick
ness
(A
)
Early Clearing!
POR Profile before CMP
Profile after 30s CMP
Profile after 30s CMP
EdgeResidual!
CFD Profile before CMP
Uniform Post-CMP Profile
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Copper Interconnect Parameters: Global Overburden
CMP Profile Matching
0.96
0.98
1
1.02
1.04
1.06
1.08
1.1
-150 -100 -50 0 50 100 150
Wafer Radius (mm)
No
rma
lize
d T
hic
kn
ess
ECD Profile CMP Profile
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Copper Interconnect Parameters: Anneal
Key Parameters for Anneal1. Temperature
2. Feature Size
3. Barrier Layer
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As Deposited
Self Annealed
Thermally Annealed
Small Grains
Large Grains
Copper Interconnect Parameters: Anneal
Effect of Temperature
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Copper Interconnect Parameters: Anneal
1.0m Trenches
0.25m Trenches
Effect of Feature Size
Furnace AnnealSelf-Anneal
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Copper Interconnect Parameters: Anneal
Ta Barrier Layer
TiNx Barrier Layer
•Strong Surface Interaction
•Reduced Migration
•Weak Surface Interaction
•Increased Migration
•Large Voids
Effect of Barrier Layer
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Copper Interconnect Parameters: Anneal
Anneal Temp
Lin
e R
esis
tanc
e
Ta
TaNx
TiNx
Grain Growth
Void Formation
Optimum
Optimum Anneal Condition
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Backside Clean and Bevel Etch
Why Backside Clean and Bevel Etch?• Cu is a highly mobile ion
• Backside contamination can have adverse effects across the fab
• Unstable films on the edge of the wafer can cause surface damage at CMP
Objective1. Remove bulk Cu on the edge of the wafer
1. Delamination
2. Flaking
3. Yield Problems
2. Remove atomic Cu on the back of the wafer1. Common Photolithography
2. Common Metrology
3. Cu ion diffusion
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Backside Clean and Bevel Etch
Capsule 1 Chamber Cut Away
Edge Exclusion Hardware
Capsule 1 Features
1. Hardware control of bevel etch (BE)
2. 0-4mm BE edge exclusion (EE) range
3. No front side protection needed
4. BE & backside clean simultaneously
5. Clean N2 purged microenvironment
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Backside Clean and Bevel Etch
Capsule Dynamics
WaferDevice Up
Seal
Chamber Rotation
Back Side Inlet: -Dilute Piranha Solution-DI H2O-N2
Front Side Inlet: -DI H2O-N2
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Backside Clean and Bevel Etch
Capsule Dynamics
Seal
Chamber Rotation
Back Side Inlet: -Dilute Piranha Solution-DI H2O-N2
Front Side Inlet: -DI H2O-N2
WaferDevice Up
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Backside Clean and Bevel Etch
A concentric 1.5mm EE BE clears the notch
Precision Control of Chemical Wrap-Around
Critical Bevel Etch Parameters1. Concentricity
2. Complete Cu Clearing
3. Clearing the Notch
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Backside Clean and Bevel Etch
Precision Control of Concentricity
Concentricity Spec (a) ≤ 0.2mm
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Backside Clean and Bevel Etch
E Beam Spot Magn WD 10 µm
10.0kV 2.0 3500x 17.1 STI. Bevel Etch
No Copper on Edge Exclusion Zone
No undercut
Target ECD 1.0µm
1 µm ECD Copper
1.5 mm Edge Exclusion Profilometer Reading
52º Tilt on SEM
<10 µm
Precision Control of Copper Removal
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Why Cu Interconnects?•Resistivity•Reliability
Damascene Process Flow•Photolithography to CMP
Parameters Affecting Cu Interconnects•Gap-Fill•Current Density Uniformity•Overburden•Anneal
•Backside Clean and Bevel Etch•Bulk Cu on the Edge •Atomic Cu on the Backside
Summary
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Acknowledgements
John Klocke – Cu Damascene Group Leader
Kevin Witt – Cu Damascene Business Development Leader
Tom Ritzdorf – Director of ECD Technology
Jake Cook – Marketing Communications
All Semitool personnel that have contributed data to this presentation