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Duane Boning - ICMTS 2003 1 MIT-MTL Pattern Dependent Characterization of Copper Interconnect Prof. Duane Boning Massachusetts Institute of Technology Microsystems Technology Laboratories http://www-mtl.mit.edu/Metrology ICMTS Tutorial, March 2003
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Pattern Dependent Characterization of Copper Interconnect

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Page 1: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 1 MIT-MTL

Pattern Dependent Characterizationof Copper Interconnect

Prof. Duane Boning

Massachusetts Institute of TechnologyMicrosystems Technology Laboratories

http://www-mtl.mit.edu/Metrology

ICMTS Tutorial, March 2003

Page 2: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 2 MIT-MTL

Copper Interconnect Dual Damascene ProcessDeposit dielectric stack; Pattern trenches & vias

Barrier deposition; copper electroplating

CMP

SiO2

SiO2

Si3N4 Etch Stop

SiO2

SiO2

SiO2

Cu

TaN

■ Electroplating❏ “Superfill” used to fill

narrow trenches and vias ❏ Ideally: plated surface

nearly flat

■ Copper CMP❏ Multistep process to

remove bulk copper and barrier metal

❏ Ideally: polished surface nearly flat • no loss in copper wire

thickness• flat for next level

Cu Lines

Repeat for multiple levels of metal

Page 3: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 3 MIT-MTL

Copper Interconnect Problems■ Polishing stages: bulk polish, barrier polish, and overpolish

CMP Process and Problems

Oxide

Oxide

Dishing

Field OxideLoss

Erosion

Non-uniform plating

Oxide

CMP

Overpolish

Evolving Surface Profile

Page 4: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 4 MIT-MTL

Electroplating/CMP Characterization Methodology

Electroplating Process■ Fixed plating recipe

Model ParameterExtraction

■ Plating: Measure step height, array bulge/recess and field copper thickness

■ CMP: Measure dishing, erosion and field copper thickness

Calibrated ECD Pattern Dependent Model

■ Plating: prediction of step height, array height, copper thickness and local pattern density

■ CMP: prediction of clearing time, dishing and erosion, final copper line thicknesses

Chip-LevelSimulation

Product Chip Layout

Electroplating/CMPTest Wafers

CMP Process■ Fixed pad, slurry, process

settings (pressure, speed, etc)■ Variable polish times

Calibrated Copper Pattern Dependent

Model

Page 5: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 5 MIT-MTL

Outline■ Background

❏ Pattern dependent effects in plating and CMP

■ Copper CMP Characterization❏ Polishing Length Scales❏ Test Structure and Mask Design

• Single Layer Test Structures and Mask Design• Multilevel Test Structures and Mask Design

❏ Measurements and Analysis❏ Design Rule Generation❏ Chip Scale Modeling

■ Copper Electroplating Characterization

■ Conclusions

Page 6: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 6 MIT-MTL

Copper CMP Pattern Dependent Effects

Oxide

Dishing Erosion

Copper

0 200 400 600 800 1000 1200 1400 1600−0.24

−0.2

−0.16

−0.12

−0.08

−0.04

0

Scan Length (um)

Rel

ativ

e H

eig

ht

(um

)

0 200 400 600 800 1000 1200 1400 1600−0.24

−0.2

−0.16

−0.12

−0.08

−0.04

0

Scan Length (um)

Rel

ativ

e H

eig

ht

(um

)

Erosion

Dishing

Erosion

Dishing

Sample Profilometer Scans

Line width = 1 µmLine space = 1 µm

Line width = 9 µmLine space = 1 µm

Page 7: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 7 MIT-MTL

Polishing Length Scales

FieldArray Structure

AnotherArray Structure

Oxide

Dishing

Rel

ativ

e T

hick

ness

(Å)

Scan Length (µm)SEM Cross Section(0.5µm wide line)

mm Range

~100µm Range

~1µm RangeInitial Copper Polish

Barrier/Overpolish

■ Three Polishing Length Scales:❏ ~2mm range: copper bulk polish❏ ~100µm range: erosion profile❏ ~1µm range: dishing profile

Page 8: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 8 MIT-MTL

Dishing and Erosion Test Structures

Isolated Line Array Region

Line width/line space mark

500mm

50mm 2mm

2mm

1.0 1.0/2.0

500mm

IsolatedLine

DummyLine

ArrayRegion

0.5/4.5

Electrical

Electrical∆V

∆V

50mm2200mm

2160mm

Physical Test Structure Electrical Test Structure

Region

Measurement

Typical erosionprofilometry scan Measurement

❏ Profilometry: captures surface height over long scans❏ Electrical measurements: extract line thickness by probing

Page 9: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 9 MIT-MTL

Dishing/Erosion Array Test Structures

(a) (b) (c)si

ngle

loop

loop

w/ d

umm

y

50%

den

sity

arr

a

(d)

■ Three Regions: b) Single loop: isolated linec) Small array: loop with surrounding dummy linesd) Large array: multiple taps along length of the array

■ Electrical Sampling: ❏ Each tap is a Van der Pauw structure: measure resistance❏ Uniform sampling: e.g. every 100 µm❏ Edge sampling: place more taps near the transition region

Page 10: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 10 MIT-MTL

Copper Thickness Extraction ProcedureE-TestLineResistance

Line WidthCorrection

CopperThicknessExtraction

CopperThickness

Physical

PhysicalVerification

R

SEM+Profile+Optical

W+∆W

R -> TM TM

Oxide

TM

TL

TL

Copper

W

Barrier

Layer

Simplified Profile

■ R is measured line resistance■ Rs (ρ/t) is sheet resistance■ t is the thickness of a line■ ρ is the resistivity of copper■ L is the length of a line■ W is the width of a line.■ RCu is resistance due to copper

■ RL is resistance due to liner

■ ρL is the resistivity of liner

or by re-arranging variables (1)

and

(2)

(3)

R Rs LW-----×= t ρ

R---LW-----×=

RCuρCu L×

TM TL–( ) W 2TL–( )×----------------------------------------------------------=

RLρL L×

2TM TL×( ) W 2TL–( ) TL×( )+--------------------------------------------------------------------------------=

TMρCu

R---------- L

W 2TL–( )--------------------------× TL+=

Page 11: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 11 MIT-MTL

Additional Structures

Metal 1Metal 2

Top Down View Cross Sectional View

Split Combs Solid Plate

100µm

100µm

Cross Section

Oxide Fill

Cu

Oxide

Slotting

Capacitance

Area

Top Down View

100µm

1000µm

Metal 2Metal 1

Page 12: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 12 MIT-MTL

Single Layer Mask Designs

■ Single-level mask: electrical and physical test structures.■ Key pattern factors: density and pitch and/or linewidth and linespace.■ Structure Interaction: structure size and floor planning.

PITCH BLOCKS

DENSITYBLOCKS

DENSITYBLOCKS

15mm

15mmA. First Generation Mask(“SEMATECH 931 Mask”) B. Second Generation Mask

20mm

20mm

PitchStructures

DensityStructures

AreaStructures

Page 13: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 13 MIT-MTL

Single Layer Surface Profiles and Trends

0 500 1000 1500 2000 2500

−1200

−800

−400

0

0 500 1000 1500 2000 2500

−1200

−800

−400

0

0 500 1000 1500 2000 2500

−1200

−800

−400

0

5.0µm/5.0µm

50µm/50µm

1.0µm/1.0µm

Isolated

Scan Distance in µm

Surface Profiles (in Å)

Lines

ErosionDishing

Lw/Ls

Lw/Ls

Lw/Ls

ErosionErosion

DishingErosion

Dishing

Array Region

Dishing

Dishing

FineFeatures

MediumFeatures

LargeFeatures

Page 14: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 14 MIT-MTL

Extracted and Physical Copper Thickness

10 30 50 70 900

0.2

0.4

0.6

0.8

1

10 30 50 70 900

0.20.40.60.8

1

10 30 50 70 900

0.20.40.60.8

1

o = Extracted* = Physical

Metal Density (%)(for fixed pitch of 5µm)

Rem

aini

ng C

u T

hick

ness

(µm

) 300 sec. Polish Time (~11% Overpolish)

Metal Density (%)(for fixed pitch of 5µm)

Rem

aini

ng C

u T

hick

ness

(µm

) 270 sec. Polish Time (0% Overpolish)

330 sec. Polish Time (~22% Overpolish)

❏ Good correlation between extracted thickness and physical data.

❏ Clear trend of total remaining thickness is shown from the electrical data.

Page 15: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 15 MIT-MTL

Analysis: Dishing and Erosion in Copper CMP

240 270 300 330 3600

500

1000

1500

2000

2500

0 50 100 150 2000

500

1000

1500

2000

2500

Dis

hing

(Å)

Polish Time (sec.)(270 = “just cleared”)

Dis

hing

and

Ero

sion

(Å)

o = Dishing+ = Erosion

Pitch Values (µm)(for fixed 50% metal density)

Dishing and Erosion Dependencies on Polish Time and Pitch

300 sec. Polish Time (~11% Overpolish)

5µm Pitch3µm Pitch

20µm Pitch

50µm Pitch

100µm Pitch

150µm Pitch200µm Pitch

10µm Pitch

■ Profilometry surface scan for dishing and oxide thicknessmeasurement for erosion.

■ Constant dishing after initial transition for smaller pitch structures.

Page 16: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 16 MIT-MTL

Multilevel Process Sequence and Pattern Problems

Metal 1

Metal 2

Oxide

Oxide M1 Copper Lines

M2 Recess

M2 Remaining

As Dep.Oxide Profile

Oxide

Oxide

As Dep.Oxide Profile

ThicknessOxide

Metal 2

Oxide

Oxide

1. M1 Polish

2. M2 Oxide Deposition

3. M2 Cu Deposition

4. M2 Polish

Metal 1

Page 17: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 17 MIT-MTL

Multilevel Copper CMP Test Mask Design■ Multi-level mask: M1, Via, and M2

❑ electrical and physical test structures■ Single level effects: Layout factors on M1 to

study creation of topography❑ Density❑ Pitch (Line Width & Line Space)

■ Multiple metal level effects: Overlay M2 structures to study topography impact

20mm

20mm

Metal 1 Metal 2

Multi-Level Mask

Metal 2Metal 1

Page 18: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 18 MIT-MTL

M1 Structure Design Space M1 Structure Design Space (in µm): < P2D50 = Pitch of 2 and Density of 50% >

LWLS 0 0.18 0.25 0.5 1 1.5 2 3 4 5 7 9 10 50 90 1000 D100

Solid0.18 P0.36

D500.25 P0.5

D500.5 P1

D50P2

D671 P2

D50P4

D75P6

D83P10D90

P51D98

P101D99

1.5 P2D33

2 P4D50

3 P4D25

P10D70

45 P6

D17P10D50

7 P10D30

9 P10D10

10 P20D50

P100D90

50 P51D2

P100D50

90 P100D10

100 P101D1

P200D50

Page 19: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 19 MIT-MTL

Multilevel CMP Test Structure Design

Half Overlap Structure

Mask Layout

20mm

20mm

Metal 1: BlueMetal 2: Magenta

Arrays M2 Bond

M2 Bond

M1 Bond

M1 Bond

Iso.Lines

Pad (Top)

Pad (Bottom)

Pad (Top)

Pad (Bottom)

(“SEMATECH 954 Mask”)

■ Multi-level mask: M1, Via, and M2 with electrical and physical test structures.

■ Layout factors: Line width/line space combinations

■ Focus: Multi-level pattern effects■ Overlap structures: direct, half, and dual

Page 20: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 20 MIT-MTL

Direct Overlap: Structure

Metal 1 Metal 2

Oxide

Oxide

M1 BottomPad

M1 TopPad

M2 TopPad

M2 BottomPad

CrossSectionalView

TopDownView

Metal 2

Metal 1

Page 21: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 21 MIT-MTL

Direct Overlap: Data Analysis

OxideAs Dep.Oxide Profile

Metal 2

Metal 1Oxide

0.5

0.6

0.7

0.8

−2000

−1000

0

−500 0 500 1000 1500 20000.5

0.6

0.7

0.8

M2

Rem

ain.

Thi

ck. (

µm)

M2

Rec

ess

M1

Rem

ain.

Thi

ck. (

µm)

µm

M2: Surface Scan

M2: Electrically Extracted

M1: Electrically Extracted

No Overlap

Overlap

Iso. Lines

Iso. Lines

(Å)

Page 22: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 22 MIT-MTL

Multilevel Half Overlap Structure

As Dep.Oxide Profile

Metal 1 Metal 2

Oxide

Oxide

M1 BottomPad

M1 TopPad

M2 TopPad

M2 BottomPad

CrossSectionalView

TopDownView

Metal 2

Metal 1

Page 23: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 23 MIT-MTL

Half Overlap: Erosion to Erosion

0.5

0.6

0.7

0.8

−2000

−1000

0

0 500 1000 1500 2000 25000.5

0.6

0.7

0.8

Iso. Lines

Over OverStruct. Oxide

M2: Electrically Extracted

M2: Surface Scan

M1: Electrically Extracted

µm

Ref.

Oxide

Oxide

As Dep.Oxide Profile

M2

Rem

ain.

Thi

ck. (

µm)

M2

Rec

ess

M1

Rem

ain.

Thi

ck. (

µm)

(Å)

Metal 2

Metal 1

Page 24: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 24 MIT-MTL

Half Overlap: Dishing to Erosion

0 500 1000 1500 2000 2500 3000−2000−1500−1000

−5000

0 500 1000 1500 2000 2500 3000−2000−1500−1000

−5000

M2 Profile (Å) No OverlapRegion Over

Oxide0.5µm Lw/ OverStruct.

M1 Profile (Å)

Scan Distance (µm)

0.5µm Ls

50µm Lw/50µm Ls

M2 Array

DishingDominant

Page 25: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 25 MIT-MTL

Half Overlap: Erosion to Dishing/Erosion

0 500 1000 1500 2000 2500 3000−2000−1500−1000

−5000

0 500 1000 1500 2000 2500 3000−2000−1500−1000

−5000

Dark bandindicates dishing

M2 Profile (Å) No OverlapRegion Over

Oxide5µm Lw/ OverStruct.

M1 Profile (Å)

Scan Distance (µm)

5µm Ls

1µm Lw/1µm Ls

M2 Array

ErosionDominant

Page 26: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 26 MIT-MTL

Dual Overlap: Structure

Oxide

Oxide

As Dep.Oxide Profile

Metal 2

Metal 1

Metal 1

Metal 2

M1 BottomPad

M1 TopPad

M2 TopPad

M2 BottomPad

CrossSectionalView

TopDownView

Page 27: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 27 MIT-MTL

Dual Overlap: Data Analysis

0.5

0.6

0.7

0.8

−2000

−1000

0

0 500 1000 1500 2000 2500 30000.5

0.6

0.7

0.8

OverStruct.1

M2 Electrically Extracted

Ref.

M2: Surface Scan

M1: Electrically Extracted

µm

OverStruct.2

Iso. Lines

Oxide

OxideMetal 2

Metal 1

M2

Rem

ain.

Thi

ck. (

µm)

M2

Rec

ess

M1

Rem

ain.

Thi

ck. (

µm)

(Å)

As Dep.Oxide Profile

Page 28: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 28 MIT-MTL

Multilevel Electrical Impact: M2 Line Thickness

■ Metal 2 thickness (0.5 µm line/space) as function of space from the edge of the metal 1 array (3 µm line/1mm sapce)

■ Change in resistance of a 0.5 µm mtetal 2 line/space structure at a transition in metal 1 density

Lakshminarayanan et al. (LSI Logic), IITC 2002.

Page 29: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 29 MIT-MTL

Design Rule Generation

Lakshminarayanan et al. (LSI Logic), IITC 2002.

Page 30: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 30 MIT-MTL

Modeling of Pattern Effects in Copper CMP

bulk

OxideErosion

MetalDishing

Stage 1 copperremoval

Stage 2 barrierremoval

Stage 3

over-polish

■ Approach: Apply density/step-height model to each stage in the copper polish process

■ “Removal Rate” Diagrams:❑ Track RR for metal and oxide

during each phase■ Approximation: neglect barrier

removal phase

Page 31: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 31 MIT-MTL

Pattern-Density / Step-Height Effects

■ For large step heights: ❒ step height reduction goes as

1/pattern-density

■ For small step heights (less than the “contact height”): ❒ height reduction proportional

to height❒ height decays with time constant τ:

H t( ) H0e t τ⁄–=

H

tdd H t( ) 1

τ---H t( )–=

tdd H t( ) K

ρ----–=td

dH

Step HeightHc

Wafer

Wafer

CMP Pad

CMP Pad

Hc

X

PL

■ Calculate effective density by averaging local pattern densities over some window/weighting function

EffectiveDensity MapOver Chip

Ouma et al., IITC ‘98;Smith et al., CMPMIC ‘99Grillaert et al., CMP-MIC ‘98.

Page 32: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 32 MIT-MTL

Chip-Scale CMP Simulation

0

500

1000

1500

2000

Cu Dishing after step 2 polish

50 100 150 200 250 300 350 400 450 500

100

200

300

400

500

600

700

Dishing after step two

RMS Error = 155 Å

Å

0 5 10 15 20 25 30 35 40 450

50

100

150

200

250

300

Site number

Dis

hin

g (

A)

Data Model

Site number

Dis

hing

(Å)

Page 33: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 33 MIT-MTL

Outline■ Background

■ Copper CMP Characterization

■ Copper Electroplating Characterization❏ Definitions❏ Test Structure and Measurement Plan❏ Trend Analysis❏ Chip Scale Modeling❏ Integrated Plating/CMP Chip-Scale Modeling

■ Conclusions

Page 34: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 34 MIT-MTL

Copper Electroplating Non-UniformitiesIsolatedLine

Array Region

Conventional Fill Super Fill(Bottom-Up Fill)

■ Isolated line and array region are recessed

■ Isolated line sticks up and array region is bulged

Page 35: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 35 MIT-MTL

Electroplating Pattern Dependent Effects

0

Sample Profilometer

Oxide

SH

AH

0

Fine Line Large Line Fine Line Large LineFine Space Large Space Medium Space Fine Space

AH

AH

SH

AH: Array Height SH: Step Height

SH

AH

Scans

Page 36: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 36 MIT-MTL

Measurement Plan and Sample Profile Scan■ Profile scans taken across each line/array structure

Isolated Line Array Region

Thickness Measurement

Bulge

Zoom

Recess

Step Height

Step Height

Step Height(Isolated Line)

(Isolated Line)

(Array Line)

into array

Superfill

Conformal Fill

Test Mask

X X

Profile Scan

Page 37: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 37 MIT-MTL

Electroplated Profile Trends: Pitch Structures

0 1000 2000 3000

−5000

0

5000

2um/2um

0 1000 2000 3000

−5000

0

5000

5um/5um

0 1000 2000 3000

−5000

0

5000

10um/10um

0 1000 2000 3000

−5000

0

5000

20um/20um

0 1000 2000 3000

−5000

0

5000

50um/50um

0 1000 2000 3000

−5000

0

5000

100um/100um

0 1000 2000 3000

−5000

0

5000

0.25um/0.25um

0 1000 2000 3000

−5000

0

5000

0.3um/0.3um

0 1000 2000 3000

−5000

0

5000

0.35um/0.35um

0 1000 2000 3000

−5000

0

5000

0.5um/0.5um

0 1000 2000 3000

−5000

0

5000

0.7um/0.7um

0 1000 2000 3000

−5000

0

5000

1um/1um

Hei

ght (

Å)

Trace Length (µm)

Lw/Ls

Hei

ght (

Å)

0.25/0.25µm 0.35/0.35µm0.3/0.3µm

0.5/0.5µm 1/1µm0.7/0.7µm

2/2µm 10/10µm5/5µm

20/20µm 100/100µm50/50µm

Superfill

ConformalBehavior

Behavior

Page 38: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 38 MIT-MTL

Step Height Data Analysis

10−1

100

101

102

−6000

−4000

−2000

0

2000

10−1

100

101

102

−6000

−4000

−2000

0

2000

Line Width (µm) - Log Scale

ArrayLine

IsolatedLine

LW

Step

Hei

ght (

Å)

Step Height vs. Line Width

■ Trends• SH depends on line width: near zero or positive (superfill) for small features

and becomes more conformal as line width increases■ Saturation Length: fill becomes fully conformal and SH = Trench Depth• Line width LW

= 10µm

0.5µm

Copper

Oxide 3µm 10µm

d

d

NarrowTrench

WideTrench

MediumTrench

Step Height Behavior

Page 39: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 39 MIT-MTL

Array Height Data Analysis

10−1

100

101

102

−4000

−2000

0

2000

4000

6000

■ Trends• Positive (superfill) for small features, and becomes negative (conformal),

and saturates to field level as line width increases■ Saturation length: fill becomes fully conformal and AH = 0Å• Line width LW

= 10µm

Line Width (µm) - Log Scale

LW

Arr

ay H

eigh

t (Å

)

Array Height vs. Line Width

0.3µm 5µm 20µmOxide

NarrowTrench

WideTrench

MediumTrench

Array Height Behavior

Copper

Page 40: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 40 MIT-MTL

SH and AH vs. Line Space

■ Trends• Line space dependency for SH and AH is similar to line width dependency

■ Saturation length: similar value is observed for line space• Line space LS = 10µm

Array Height vs. Line Space

10−1

100

101

102

−4000

−2000

0

2000

4000

6000

Arr

ay H

eigh

t (Å

)

LS

10−1

100

101

102

−6000

−5000

−4000

−3000

−2000

−1000

0

1000

2000

LS

Step

Hei

ght (

Å)

Step Height vs. Line Space

ArrayLine

Line Space (µm) - Log ScaleLine Space (µm) - Log Scale

Page 41: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 41 MIT-MTL

Transition Length Scale in Electroplating■ Plating depends on local feature (feature scale) and nearest

neighbors within 2-5µm range

720 730 740 750 760 770 780−1000

0

1000

2000

2720 2730 2740 2750 2760 2770 2780−1000

0

1000

2000

700 750 800 850−4000

−3000

−2000

−1000

0

2650 2700 2750 2800−4000

−3000

−2000

−1000

0

Arr

ay H

eigh

t (Å

)

Array Height Profile Scans

Right Edge

Left Edge

~5µm

~5µm

Right Edge

Left Edge

Scan Length (µm) Scan Length (µm)

Arr

ay H

eigh

t (Å

)

Superfill Conventional fill

0.5µm/0.5µm Array 5µm/5µm Array

Sharp Transition

4.5µm/0.5µm Array

1.5µm/3.5µm Array

Array to ArrayTransition

Page 42: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 42 MIT-MTL

Semi-Empirical Model for Topography Variation■ Physically Motivated Model Variables:

❏ Width, Space, 1/Width, and Width*Space

■ Semi-Empirical Model Development❏ Capture both conformal regime and superfill regime in one model frame

❏ 1/W2 and W2 terms explored as well

■ Model Form❏ Array Height:

❏ Step Height:

AH aEW bEW 1– cEW 2– dES eEW S× ConstE+ + + + +=

SH aSW bSW 1– cSW2 dSS e+S

W S× ConstS+ + + +=

Page 43: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 43 MIT-MTL

Model Fit: Step Height and Array Height

10−1

100

101

102

−6000

−4000

−2000

0

2000

10−1

100

101

102

−6000

−4000

−2000

0

2000

Line Width (µm)

ArrayLine

IsolatedLine

Step

Hei

ght (

Å)

Step Height vs. Line Width

* = Datao = Model Fit

10−1

100

101

102

−4000

−2000

0

2000

4000

6000

Line Width (µm)

Env

elop

e H

eigh

t (Å

)

Array Height vs. Line Width

* = Datao = Model Fit

■ The models capture both trends well❏ Step Height RMS error = 327 Å❏ Array Height RMS error = 424 Å

■ Model coefficients are calibrated and used for chip-scale simulations

Page 44: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 44 MIT-MTL

Chip-Scale Simulation Calibration Results

■ Simulated over the entire test mask used to calibrate the model■ RMS errors are slightly greater (about 90Å and 10Å more) than fitting RMS

errors since distribution values are used

1

1.2

1.4

1.6

1.8

2

2.2

x 104Final Thickness Average: Simulated Result

50 100 150 200 250 300 350 400 450 500

50

100

150

200

250

300

350

400

450

500

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Step Height Average: Simulated Result

50 100 150 200 250 300 350 400 450 500

50

100

150

200

250

300

350

400

450

500

−4000

−2000

0

2000

4000

6000

Envelope Average: Simulated Result

50 100 150 200 250 300 350 400 450 500

50

100

150

200

250

300

350

400

450

500

Array

Step

Final

Test

Thickness

HeightMask

RMS Error=440Å

RMS Error=420Å

Height

Page 45: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 45 MIT-MTL

Integration of Electroplating and CMP Models■ Integration is done by feeding forward the simulated result

from electroplating to copper CMP simulation

■ Electroplating Simulation:• Array Height• Step Height• Topography Pattern Density

Prediction of dishing and erosion

Calibrated Copper Pattern Dependent

CMP ModelChip-Scale Simulation

Layout ParameterExtraction

Product Chip

Oxide

CopperLayout

Surface Envelope

■ CMP model needs:❏ Surface “envelope”:

Array Height❏ Step Height❏ Topography Pattern

Density

Page 46: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 46 MIT-MTL

Topography Pattern Density■ Topography density: as-plated surface topography pattern

density of raised features❏ Depends on plating characteristics❏ Important as an input for CMP pattern density model

Topography DensityLayout Density

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Grid Density: Layout Extracted

50 100 150 200 250 300 350 400 450 500

100

200

300

400

500

600

700

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1ECD Density: Simulated Result

50 100 150 200 250 300 350 400 450 500

100

200

300

400

500

600

700

Page 47: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 47 MIT-MTL

Plating/CMP: Final Dishing

−400

−200

0

200

400

600

800

1000

1200

Dishing after step 3 polish

50 100 150 200 250 300 350 400 450 500

100

200

300

400

500

600

700

Dishing after step three

RMS Error = 140 Å

Å

0 5 10 15 20 25 30 35 40 45−220

−200

−180

−160

−140

−120

−100

−80

−60

−40

−20

0

20

Site number

Dis

hin

g (

A)

Data Model

Site number

Dis

hing

(Å)

Page 48: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 48 MIT-MTL

Plating CMP: Final Erosion

1000

1500

2000

2500

3000

3500

4000

4500

Erosion after step 3 polish

50 100 150 200 250 300 350 400 450 500

100

200

300

400

500

600

700

Erosion after step three

RMS Error = 420 Å

Å

0 5 10 15 20 25 30 35 40 451400

1600

1800

2000

2200

2400

2600

2800

3000

3200

Site number

Ero

sio

n (

A)

Data Model

Site number

Ero

sion

(Å)

Page 49: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 49 MIT-MTL

Conclusion■ Electroplating and CMP are Highly Pattern Dependent

■ Copper Interconnect Pattern Dependent Characterization❏ Test Structure Design

• Capture Key Pattern Effects: Isolated vs. Array, Density, Pitch, etc.• Three Polishing Length Scales: mm, 100µm, and 1µm Ranges.

❏ Mask Design• Single layer• Multi layer

❏ Physical and Electrical Measurements❏ Data Analysis

■ Can Be Applied to Support Process Development, Optimization, and Formulation Of Design Rules

■ Provides Data for Chip-Scale Modeling of Copper Interconnect

Page 50: Pattern Dependent Characterization of Copper Interconnect

Duane Boning - ICMTS 2003 50 MIT-MTL

Acknowledgments■ Past and current students: Tae Park, Tamba Tugbawa, Brian

Lee, Xiaolin Xie, Hong Cai

■ Support and collaboration with SEMATECH, Texas Instruments, Conexant, Praesagus, SKW, Philips Analytical