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Modeling Wafer Surface Damage Caused During CMP. Terry A. Ring ◊ , Paul Feeney, Jaishankar Kasthurirangan, Shoutian Li, David Boldridge, James Dirksen. Cabot Microelectronics Corporation and 870 Commons Drive Aurora, IL 60504. ◊ Chemical Engineering Department

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modeling wafer surface damage caused during cmp

Modeling Wafer Surface Damage Caused During CMP

Terry A. Ring◊, Paul Feeney, Jaishankar Kasthurirangan, Shoutian Li, David Boldridge, James Dirksen

Cabot Microelectronics Corporation and

870 Commons DriveAurora, IL 60504

◊Chemical Engineering Department

50 S. Central Campus Drive, MEB3290

University of Utah

Salt Lake City, UT 84112

www.che.utah.edu/~ring

CMP-MIC 2006

overview
Overview
  • Description of Surface Damage
    • Fracture Mechanics
  • Description of Surface Damage Experiments
  • Description of Surface Damage Model
    • Two Simultaneous Population Balances
      • Under Wafer Impurity Particles
      • Surface Damage
  • Comparison of Model with Experiments
  • Conclusions

CMP-MIC 2006

surface damage
Plastic Deformation (Plow) Brittle Fracture gives FlakesSurface Damage

•Indenter = Hard Impurity Particle

•Indenter Forced Into Surface

•Indenter Dragged Across Surface

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surface damage1
Surface Damage
  • ILD (PETEOS)
  • Failure by Brittle Fracture

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surface damage2
Surface Damage
  • Copper
  • Plastic Deformation

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surface damage3
Surface Damage
  • Copper
  • Plastic Deformation

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Dp=1-2 micron

experiments
Copper CMP

Copper Slurry

Fumed SiO2 Abrasive

Same Copper Slurry

With 0.07% wgt

1.1 m -Al2O3 particles

ILD CMP

Copper Slurry

Fumed SiO2 Abrasive

Same Copper Slurry

With 0.07% wgt

1.1 m -Al2O3 particles

Experiments

100 mm Blanket Wafers, 60 s polishing on a Logitech CDP polisher (Logitech Ltd., Glasgow, UK) with an A110 pad with CMC standard concentric grooving (30 mils x 10 mils x 80 mils)

CMP-MIC 2006

experimental results candela instruments
PETEOS

Explosion of Brittle Fractures

Copper

Explosion of Surface Damage

Plow Lines

Rolling Indenter

Experimental Results – Candela Instruments

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depth of defects
Depth of Defects
  • AFM of Copper Surface Damage

δave=9.6 nm

?

δave=1.7 nm

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model equations 1
Model Equations-1
  • 1) Surface Damage type=i; surface material=j,
  • Population No./cm2
  • Population Balance of Surface Damage

s

Removal Generation Uncovery

s=/i

Impurity Particles

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surface damage results
Surface Damage Results

Total Number density of Scratches

  • Evolution of the Initial Size Distribution of Scratches with time, RRo=-400 nm/s, UR=0, PR=0.

Time

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add 0 2 impurity particles
Add 0.2% Impurity Particles

RRo=-400 nm/s,

UR= 0,

PR = - 0.002*0.2*RRo.

20% of RR is mechanical

0.2% Impurity Particles

Time

CMP-MIC 2006

add impurity particles
Add Impurity Particles

2% impurity particles

0.2% impurity particles

0% impurity particles

PR = (% I Particles) RRo(Fraction Mechanical Removal)

RRo= -400 nm/s

CMP-MIC 2006

uncover of pores with scratch production
Uncover of Pores with Scratch Production
  • Total Number of Scratches as a Function of Polishing Time, RRo= -400 nm/s, UR= -RRo commencing at 5 s and continuing until the 4,000 nm pores are uncovered, PR = - 0.02*0.2*RRo.

w uncovery

Pore

w/o uncovery

s

s

s=/i

CMP-MIC 2006

surface damage model conclusions
Surface Damage Model Conclusions
  • Dynamic Population Balance Model of Scratches has been developed
    • With simple models for RR, PR and UR
    • Results are Expected
      • Starting with a large population of surface scratches
        • Low PR results in decreased number of scratches
        • High PR results in increased number of scratches
      • Uncover of pores is a temporal problem

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model equations 2
Model Equations-2
  • 2) Impurity Particle Population No./mL
  • Under Wafer Impurity Particle Population Balance

Dissolution Inflow Outflow Production Removal by Grooves

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impurity particles
Production Rate (ILD only)

Removal Rate in Grooves

Impurity Particles

Particle Mass Transfer

Impurity Particle Rotation

The particle removal frequency, β,

The collision frequency, αc, varies from 10-3 to 104 Hz

β values ranging from 14 Hz to 440 Hz.

CMP-MIC 2006

slide18
Size of scratch debris particles (red line) versus the size of the indenter causing the damage to the wafer surface (ILD).

Pointed Particle with 1/10th radius of curvature

2

1

Evans, A.G. and Marshall, D.B. Fundamentals of Friction and Wear of Materials, (ASM: 1980), p. 441

α(s)

Flake

Results

1/8

s

n=1

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flow in grooves
Flow in Grooves

Velocity Vectors for Flow of Slurry in Groove, Vrel= 1 m/s

Particle Trajectories for Flow of Slurry in Groove, Vrel= 1 m/s

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solution for impurity particles
Solution for Impurity Particles
  • Impurity Particle Population Balance
  • Separation of Variables
  • Solve for functions individually
  • Initial Condition

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solution for impurity particles1
Solution for Impurity Particles
  • Cases – Impurity Particle Equation
    • with particle dissolution
    • with particle generation
    • with particle removal
  • Flow Types
    • Wafer Center – Dead (Stagnant) Zone
      • Batch
    • Wafer Periphery
      • Well mixed
      • Plug flow

CMP-MIC 2006

impurity particles stagnant zone
Impurity Particles - Stagnant Zone
  • Analytical Solutions
  • Stagnant Zone – dissolution + generation, n=0
  • Stagnant Zone – dissolution + generation
  • Stagnant Zone – dissolution + generation + Groove removal

CMP-MIC 2006

stagnant zone dissolution
Stagnant Zone – dissolution

Impurity Particles

Plot of impurity particle population with time for the conditions, n = 0, αc = 10-4 Hz, sc= 500 nm, D = 30 nm/s, No=1/mL, so=103nm. ηI_o(s) is given by the red solid line, the population ηI(s,t) is given by all the other lines with the dotted blue line for t = 0.1 τ, the dashed green line for t = 2 τ, the dot-dash magenta line for t = 4 τ, the dotted cyan line for t = 6 τ, the dotted brown line for t = 8 τ, the dashed black line for t = 10 τ, the dot-dash red line for t = 12 τ and the solid blue line for t = 14 τ where τ = 10 s. Scratch Debris Batch-2.mcd.

CMP-MIC 2006

stagnant zone dissolution generation
Stagnant Zone – dissolution + generation

Impurity Particles

αc = 0.0001 Hz

αc = 0.01 Hz

Plot of impurity particle population with time for the conditions, n = 2, αc = 10-2 Hz and 10-4 Hz, sc=500 nm, D = 30 nm/s, No=1/mL, so=103nm. ηI_o(s) is given by the red solid line, the population ηI(s,t) is given by all the other lines with the dotted blue line for t = 0.1 τ, the dashed green line for t = 2 τ, the dot-dash magenta line for t = 4 τ, the dotted cyan line for t = 6 τ, the dotted brown line for t = 8 τ, the dashed black line for t = 10 τ, the dot-dash red line for t = 12 τ and the solid blue line for t = 14 τ where τ = 10 s. Scratch Debris Batch-2.mcd.

CMP-MIC 2006

stagnant zone dissolution generation groove removal
Stagnant Zone – dissolution + generation + groove removal

αc = 0.00001 Hz

 =1 Hz

 =10 Hz

Plot of groove enhanced impurity particle population with time for the conditions, β = 1 Hz (A) and 10 Hz (B), d50= 1000 nm, n = 2, αc = 10-4 Hz, sc=500nm, D = 30 nm/s, No=1/mL, so=103nm. ηI_o(s) is given by the red solid line, the population ηI(s,t) is given by all the other lines with the dotted blue line for t = 0.1 τ, the dashed green line for t = 2 τ, the dot-dash magenta line for t = 4 τ, the dotted cyan line for t = 6 τ, the dotted brown line for t = 8 τ, the dashed black line for t = 10 τ, the dot-dash red line for t = 12 τ and the solid blue line for t = 14 τ where τ = 10 s. Scratch Debris Batch-2.mcd.

CMP-MIC 2006

conclusions impurity particle model
Conclusions-Impurity Particle Model
  • When Impurity Particle Production Rate is Dominant
    • Explosion of Impurity Particles
  • When Impurity Particle Removal Rate is Dominant
    • Decreasing Population of Under Wafer Impurity Particles

CMP-MIC 2006

apply to several types of surface damage
Apply to Several Types of Surface Damage
  • ILD
    • Brittle Fracture
  • Copper
    • Plastic Plow
    • Rolling Indenter
  • One Equation for Each type of Surface Damage

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surface damage4
Surface Damage
  • Coupled to Impurity Population Balance

Removal Generation Uncovery

Surface Damage type=i; surface material=j,

s=/i

s

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scratch depth
Scratch Depth

δ

δ

κ

κ

s

s

Particle Pressed into Pad Asperity by Wafer Surface

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rate of surface damage
ILD Surface Damage (i=1)

Surface Damage Mechanism (j)

kij(s = δ/κi)

κi

Comment

Brittle Fracture Scratching

FDK.P_MT(s)

0.1

Only valid for impurity particles above a certain size

Chatter Surface Damage

FDK.P_RC(s)(1-(s/δgap))

>0.1

Impurity particles must be larger than the gap between wafer and pad

Copper Surface Damage (i=2)

Surface Damage Mechanism (j)

kij (s = δ/κi)

κi

Comment

Plastic plow surface deformation

(line scratches)

FDK.P_MT(s)

0.54

Only valid for impurity particles between certain sizes, the size associated with the elastic limit and the plastic yield point

Rolling Indenter Particle Surface Damage

FDK.P_RC(s)(s/δgap)

0.54

Impurity particles must be larger on one axis than the gap between wafer and pad

Rate of Surface Damage

FD is the fraction of particle collisions with the wafer surface that cause surface damage.

K.P_RC(s) is the particle collision rate with wafer surface due to particle rotation.

K.P_MT(s) is the particle collision rate with wafer surface due to particle mass transfer.

CMP-MIC 2006

model comparison
Model Comparison
  • Measure the number, types and location of surface defects on a wafer polished under a given set of CMP operating conditions
    • Standard Slurry
    • Spiked with Impurity Particles

CMP-MIC 2006

conclusions
Conclusions
  • Surface Damage Mechanisms
    • Copper Plastic Deformation
      • Line Scratch & Rolling Indenter
    • ILD Brittle Fracture
      • Chatter Scratch & Brittle Fracture
  • Model Gives Size Distribution of Defects as it Changes with Polish Time
  • Slightly More Scratching in Stagnant Zone (Wafer Center)
  • When there is an excess of debris production compared to debris removal by either washout or removal in the pad grooves, the impurity particles will build up and cause surface damage

CMP-MIC 2006

extra slides
Extra Slides

CMP-MIC 2006

die yield
Die Yield
  • N = No. metal layers
  • n = No. metal CMP )perations
  • m = No. ILD CMP Operations
  • o = No. Barrier CMP Operations
  • Pi = Probability of die failure due to CMP

CMP-MIC 2006

surface damage at wafer rim
Surface Damage at Wafer Rim
  • Scratching in Wafer Rim
  • Production Rate (BSG only)

x = Rw - r

x=5 micron

x=50 micron

x=500 micron

x=5 mm

Impurity Particle Rotation

Across Gap

CMP-MIC 2006

model equations
Model Equations
  • Impurity Particle Population No./mL
  • Under Wafer Impurity Particle Population Balance
  • Surface Damage type=i; surface material=j,
  • Population No./cm2
  • Population Balance of Surface Damage

Dissolution Inflow Outflow Production Removal by Grooves

s

Removal Generation Uncovery

s=/i

CMP-MIC 2006

increase generation rate stagnant zone dissolution generation groove removal
Increase Generation RateStagnant Zone – dissolution + generation + groove removal

αc = 0.01 Hz

 =1 Hz

 =10 Hz

Plot of groove enhanced impurity particle population with time for the conditions, β = 1 Hz (A) and 10 Hz (B), d50= 1000 nm, n = 2, αc = 10-2 Hz, sc=500nm, D = 30 nm/s, No=1/mL, so=103nm. ηI_o(s) is given by the red solid line, the population ηI(s,t) is given by all the other lines with the dotted blue line for t = 0.1 τ, the dashed green line for t = 2 τ, the dot-dash magenta line for t = 4 τ, the dotted cyan line for t = 6 τ, the dotted brown line for t = 8 τ, the dashed black line for t = 10 τ, the dot-dash red line for t = 12 τ and the solid blue line for t = 14 τ where τ = 10 s. Scratch Debris Batch-2.mcd.

CMP-MIC 2006

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