TFUG 8/21/2002

Cu Plating Today and Tomorrow:Cu Plating Today and Tomorrow:Managing the Terminal EffectManaging the Terminal Effect

John Klocke

TFUG 8/21/2002

Ionized PVD Seed and BarrierIonized PVD Seed and Barrier≈ 250Å Barrier Layers≈ 1000Å Seed Layers

0.13µµµµm Tech. Node0.15 µm Vias1.6:1 AR

ECD Films≈ 1.0 µm ThickFlat Profile

200mm Wafers

High Volume Production: TodayHigh Volume Production: Today

TFUG 8/21/2002

0.07µµµµm Tech. Node0.085 µm Vias1.7:1 AR

300mm Wafers

50Å ALD Barrier200Å Seed Layer (Direct Barrier Deposition?)

ECD Films≤ 0.5 µm ThickMatched CMP Profile

Over 5x Sheet Resistance

(Global Uniformity)

More Aggressive (Feature Filling)

Reduce Overburden

(Local Uniformity)

High Volume Production: TomorrowHigh Volume Production: Tomorrow

TFUG 8/21/2002

ECD Copper for InterconnectsECD Copper for Interconnects

• Feature Filling /Film Properties• Seed and Barrier Layers• Plating Chemistry• Plating Recipe

• Local Uniformity• Global Uniformity

TFUG 8/21/2002

Seed and Barrier LayersSeed and Barrier Layers

Good Seed = Good Fill

Side Voids

Seam Voids

Bottom Voids

Assuming proper current densityand chemical conditions:

TFUG 8/21/2002

Chemistry: CompositionChemistry: Composition

• Organic• Suppressor• Accelerator• Leveler (Optional)

• Inorganic• Copper Sulfate• Sulfuric Acid• HCl

TFUG 8/21/2002

Chemistry: Fill MechanismChemistry: Fill Mechanism

Two Component

TFUG 8/21/2002

Std. PotentialCu2+ + 2e- � Cu + 0.34Cu2+ + e- � Cu+ + 0.16

50 100

H2SO4 (g/l)Et

ch R

ate

Copper Etch Rate In Plating Bath

Thin Seed0

Recipe: Cathodic ProtectionRecipe: Cathodic Protection

TFUG 8/21/2002

Too Low Current

Too High Current

Current Density

Bad

Good

HighLow

Gap

Fill

Current Density

0.35micron, 4.3:1 AR Vias 0.35micron, 4.3:1 AR Vias

0.18micron, 5.1:1 AR Trench 0.18micron, 5.1:1 AR Trench

Optimum Fill

Conformal(Center Void)

CuDepletion(Pinch Off)

Recipe: Current DensityRecipe: Current Density

Optimum Current

Optimum CurrentVoids

TFUG 8/21/2002

ECD Copper for InterconnectsECD Copper for Interconnects

• Feature Filling /Film Properties• Local Uniformity

• Chemistry Effects• Recipe Effects

• Global Uniformity

TFUG 8/21/2002

Feature Scale UniformityFeature Scale Uniformity

• Recipe• Simple Chemistry• Proven Process

Integration• Chemistry (Leveler)

• Three Components• Simplified CMP

Two Component: DC

Two Component: Optimized

TFUG 8/21/2002

OverplatingRecession

Planar Deposition

Insufficient LevelerOver Suppression

Optimized Organic Conditions DC Process

Three Component Bump MinimizationThree Component Bump Minimization

TFUG 8/21/2002

ECD Copper for InterconnectsECD Copper for Interconnects

• Feature Filling /Film Properties• Local Uniformity• Global Uniformity

• Definition: Terminal Effect• Transient Nonuniformity• Compensating for Terminal Effect

TFUG 8/21/2002

Relectrolyte

RAnode

V1+

ElectrolyteEdgeLoop

CenterLoop

Cathode(Thin Seed)

Anode(Thick)

1) Disregard fluid flow.

2) Assume a uniformboundary layer andinterfacial resistance.

3) Assume bathconductivity muchlower than bulkconductivity of Copper(Equipotential Anode).

Consider two arbitrarysurface elements in thesystem. One at the centerand one at the edge.

RCathode

Relectrolyte

First Approximation: Terminal EffectFirst Approximation: Terminal Effectiedge icenter

4) Fixed ReactorGeometry

TFUG 8/21/2002

)R(RR

eelectrolytcathode

eelectrolytedgecenter +

= ii

The full treatment...The full treatment...

Reduces to:

Relectrolyte

RCathode

Relectrolyte

Ohm’s LawOhm’s Law

iedge = V1/Relectrolyte

)R(RV

eelectrolytcathodecenter

1

+=i

iedge icenter

V1+Relectrolyte: Inverse to Bath Conductivity

Rcathode : Proportional seed thickness and wafer size

TFUG 8/21/2002

Conventional Process: Thickness ProfilesConventional Process: Thickness Profiles

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

-150 -100 -50 0 50 100 150

Radial Location (mm)

Nor

mal

ized

Thi

ckne

ss 5 sec

10 sec

20 sec

40 sec

122 sec80 sec

1200Å Seed Layer

TFUG 8/21/2002

Uniformity Trajectory for Various Conventional Reactors

0

5

10

15

20

25

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

Film Thickness in µm(Minimum Uniformity - 3σ)

Non

-Uni

form

ity (3

σ)

(0.40%)(0.35% )(0.88%)

1µm

Edge Thick Center Thick

Note: Changes made are with shields, thieves and/or diffusers

Hardware Controlled UniformityHardware Controlled Uniformity

TFUG 8/21/2002

Seed Layer ThicknessSeed Layer Thickness

Optimized at 1.0µm Thickness200mm Wafer

Initial Current Density:600Å vs 1000Å seed layer

15

17

19

21

23

25

27

29

-100 -50 0 50 100

Cur

rent

Den

sity

(mA/

cm2)

600Å (42% 3σ)

1000Å (24% 3σ)

TFUG 8/21/2002

Wafer SizeWafer Size

Optimized at 1.0µm Thickness600Å Seed Layer

Initial Current Density: 200mm vs. 300mm

10

15

20

25

30

35

-150 -100 -50 0 50 100 150

Cur

rent

Den

sity

(mA/

cm2 )

200mm (42% 3σ)

300mm (79% 3σ)

TFUG 8/21/2002

Dynamically Controlled Current DistributionDynamically Controlled Current Distribution

Dynamically Controlled Process Conventional Process

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

-150 -100 -50 0 50 100 150

Radial Location (mm)

Nor

mal

ized

Thi

ckne

ss

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

-150 -100 -50 0 50 100 150

Radial Location (mm)

Nor

mal

ized

Thi

ckne

ss

1200Å Seed Layer

TFUG 8/21/2002

0

2

4

6

8

10

12

14

16

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2Film Thickness (Microns)

Film

Non

-Uni

form

ity (%

3σσ σσ)

1000Å seed layer (Flat)

Conventional Process

Dynamic Process

Modeling DataModeling Data

TFUG 8/21/2002

0.8

1.0

1.2

1 11 21 31 41 51 61 71 81 91 1 11 21 31 41 51 61 71 81 91

1 1 21 31 41 51 61 71 81 910.8

1.0

1.2

1 21 31 41 51 61 71 81 91

0.1 Micron 1.0 Micron

Dyn

amic

Con

vent

iona

l 1 11 21 31 41 51 61 71 81 91

1 1 21 31 41 51 61 71 81 91

1.5 Micron

Plated Film GrowthPlated Film Growth

TFUG 8/21/2002

0100200300400500600

Low Acid Bath Standard Acid Bath

Con

duct

ivity

(mS/

cm) 175 g/l H2SO4

17 g/l Cu

10 g/l H2SO450 g/l Cu

High Acid vs. Low Acid

Bath ConductivityBath Conductivity

)R(RR

eelectrolytcathode

eelectrolytedgecenter +

= ii

500mS/cm

70mS/cm

TFUG 8/21/2002

14

18

22

26

30

34

-150 -100 -50 0 50 100 150

Radius (mm)

Cur

rent

Den

sity

(mA/

cm^2

) 0sec

120sec

14

18

22

26

30

34

-150 -100 -50 0 50 100 150Radius (mm)

Cur

rent

Den

sity

(mA/

cm^2

)

0sec

120sec

14

18

22

26

30

34

-150 -100 -50 0 50 100 150Radius (mm)

Cur

rent

Den

sity

(mA/

cm^2

)

0sec

120sec

500mS/cm

250mS/cm70mS/cm

1000Å seed layer, 11000Å seed layer, 1µµm depositionm depositionModeling DataModeling Data

20%70%

>100%

TFUG 8/21/2002

14

18

22

26

30

34

-150 -100 -50 0 50 100 150

Cur

rent

Den

sity

(mA/

cm2 )

500mS/cm

Dynamic Control

Modeling DataModeling Data

8%

14

18

22

26

30

34

-150 -100 -50 0 50 100 150

Radius (mm)

Cur

rent

Den

sity

(mA/

cm^2

) 0sec

120sec

14

18

22

26

30

34

-150 -100 -50 0 50 100 150Radius (mm)

Cur

rent

Den

sity

(mA/

cm^2

)

0sec

120sec

14

18

22

26

30

34

-150 -100 -50 0 50 100 150Radius (mm)

Cur

rent

Den

sity

(mA/

cm^2

)

0sec

120sec

500mS/cm

250mS/cm70mS/cm

1000Å seed layer, 11000Å seed layer, 1µµm depositionm deposition

20%70%

>100%

TFUG 8/21/2002

CMP Profile Matching

1000

3500

6000

8500

11000

13500

-100 -50 0 50 100

Nor

mal

ized

Thi

ckne

ssFill Profile vs. CMP ProfileFill Profile vs. CMP Profile

Desired Profile

Plating Results

Fill Step

0.4

0.7

1.0

1.3

1.6

TFUG 8/21/2002

SummarySummary

• Feature Filling/Film Properties• Optimized Organic and Inorganic Conditions• Current Density

• Local Uniformity• Recipe• 3 Component Chemistries

• Global Uniformity• Bath Conductivity (Seed Limited)• Dynamic Control Current Distribution