Transcript Slide 1

Modeling The Deposit Thickness
Distribution in Copper Electroplating of
Semiconductor Wafer Interconnects
Eugene Malyshev 1, Uziel Landau 2,
and
Sergey Chivilikhin 1
1 L-Chem,
Inc
Beachwood, OH 44122
and
2 Department of Chemical Engineering,
Case Western Reserve University,
Cleveland OH 44106
AIChE Annual Meeting,San Fransisco, CA.
Objectives
• Analyze the effects of the different process
parameters
• Provide a convenient (for non-expert users) &
comprehensive tool for:
Cell Design
Scale-up
Process Optimization
Issues in Design
Deposit-
• Deposit thickness uniformity (+/- ~3% across the
wafer)
• Minimal edge exclusion (<5 mm)
• Deposit texture/appearance
• Good gap-fill
• Extreme electrical/mechanical/chemical properties
Process-
• Stable
• Controllable
• Scalable
Parameters Analyzed
• Cell Configuration (Dimensions, Edge gap, Shields)
• Flow (Rotation and Convective Flow)
• Seed Layer Thickness
• Electrolyte Composition
Acid Concentration (Conductivity)
Reactant Concentration (Mass-Transport)
Additives (Kinetics/Polarization Curve)
• Operating Parameters: Current/Voltage
Cell “Generic” configuration
Base Case: r = 100 mm, gap =10 mm
i = 20 mA/cm2, K= 0.55 S/cm,
seed thickness = 1000A
rotation = 60 rpm
impinging flow = 4 gpm
HOLDER
60 rpm
WAFER
GAP
HOLDER
100 mm
150 mm
ANODE
GAP
10 mm
10 mm
DISTRIBUTED FLOW = 4 gpm
WAFER
Seed thickness
Applied Voltage
Flow effects
Rotating Disk vs. Combined Flow
Flow Map:
Modified Design
Flow Map:
Base Case
Delta, cm
0.0090
Base case
0.0075
0.0060
0.0045
Modified
Levich eqn.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
r/R
Numerical comparison with analytical model
Delta, cm
Model system: rotating disk,
r = 7 mm, Cb = 0.28 mole/L, D = 6.7*10-6 cm2/s
0.04
Cell-Design
0.03
0.02
Levich eqn.
0.01
0.00
0
1
2
3
4
5
6
7
8
9
10
11
10
11
i lim, A/cm2
1/2 [rad/sec]1/2
0.30
Levich eqn.
0.20
0.10
Cell-Design
0.00
0
1
2
3
4
5
6
7
1/2 [rad/sec]1/2
8
9
Effect of edge-gap
i lim, A/cm2
Wafer r = 100 mm
Simulated gaps: 5 mm, 10 mm, and 15 mm;
Cb = 0.28 mole/L, D = 6.7*10-6;
Impinging flow = 4 gpm
0.090
5 mm
0.070
50 mm
0.050
100 mm
150 mm
0.030
0
1
2
3
4
5
6
7
8
Radial coordinate, cm
9
10
Resistive substrate effect
HOLDER
WAFER
HOLDER
GAP
100 mm
10 mm
150 mm
10 mm
Seed thickness
Applied Voltage
DISTRIBUTED FLOW = 4 gpm
Seed thicknesses = 500, 1000 and 2000 Å.
iaverage = 10 and 40 mA/cm2. Wafer r = 100 mm.
Rotation = 60 rpm. Impinging flow = 4 gpm.
Cb= 0.28 mol/L, k = 0.55 S/cm, D = 6.7*10—6cm2/s.
Current, A/cm2
ANODE
0.08
0.06
GAP
WAFER
no seed resistance
iaverage = 40
mA/cm2
500 Å
1000 Å
2000 Å
0.04
0.02
iaverage = 10 mA/cm2
no seed resistance
500 Å
1000 Å
2000 Å
0.00
0
1
2
3
4
5
6
7
Radial coordinate, cm
8
9
10
Effect of edge-gap
60 rpm
WAFER
HOLDER
i = 20 mA/cm2
gap = variable
seed = 1000 A
Gap
DISTRIBUTED FLOW = 4 gpm
ANODE
Deposit,
[micron]
Gap = 0 mm
Deposit,
[micron]
Gap = 10 mm
Deposit,
[micron]
2.5
2.5
2.5
2.0
2.0
2.0
1.5
1.0
150 sec
1.5
1.0
150 sec
1.5
1.0
0.5
0.5
0.5
0.0
0.0
0.0
Gap = 50 mm
180 sec
0 1 2 3 4 5 6 7 8 9 10
0 1 2 3 4 5 6 7 8 9 10
0 1 2 3 4 5 6 7 8 9 10
Radial coordinate, cm
Radial coordinate, cm
Radial coordinate, cm
1-3 time steps = 20 sec, 4-7 time steps = 30 sec
Shield design
60 rpm
60 rpm
HOLDER
60 rpm
HOLDER
WAFER
HOLDER
WAFER
WAFER
DISTRIBUTEDFLOW
FLOW ==44gpm
DISTRIBUTED
gpm
DISTRIBUTED FLOW = 4 gpm
DISTRIBUTED FLOW = 4 gpm
ANODE
ANODE
ANODE
i, A/cm2
i, A/cm2
i, A/cm2
0.05
0.05
0.05
0.04
0.04
0.04
0.03
0.03
0.03
0.02
0.02
0.02
0.01
0.01
0.01
0.00
0.00
10% variation
0.00
0 1 2 3 4 5 6 7 8 9 10
0 1 2 3 4 5 6 7 8 9 10
0 1 2 3 4 5 6 7 8 9 10
Radial coordinate, cm
Radial coordinate, cm
Radial coordinate, cm
200 mm wafer vs. 300 mm wafer
60 rpm
WAFER
GAP
Seed thickness = 1000 Å.
Cb= 0.28 mol/L, k = 0.55 S/cm, D = 6.7*10—6cm2/s.
200 mm wafer
100 mm
150 mm
10 mm
DISTRIBUTED FLOW = 4 gpm
Deposit, micron
HOLDER
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0.00
deposit(r/R=1) / deposit(r/R=0) =
0
0.2
0.4
0.6
180 sec
150 sec
120 sec
90 sec
60 sec
40 sec
20 sec
1.646
0.8
1
r/R
150 mm
150 mm
10 mm
DISTRIBUTED FLOW = 9 gpm
Deposit, micron
300 mm wafer
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0.00
deposit(r/R=1) / deposit (r/R=0) = 1.847
0
0.2
0.4
0.6
0.8
180 sec
150 sec
120 sec
90 sec
60 sec
40 sec
20 sec
1 r/R
Electrolyte conductivity (pH)
200 mm wafer
Deposit,
[micron]
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Deposit,
[micron]
k = 0.55 S/cm
iaverage = 20 mA/cm2
seedth = 1000 A
180 sec
150 sec
120 sec
90 sec
60 sec
40 sec
20 sec
0
0.2
0.4
0.6
0.8
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
iaverage = 20 mA/cm2
seedth = 1000 A
180 sec
150 sec
120 sec
90 sec
60 sec
40 sec
20 sec
0
1
k = 0.055 S/cm
0.2
0.4
r/R
0.6
0.8
1
r/R
300 mm wafer
Deposit,
[micron]
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Deposit,
[micron]
k = 0.55 S/cm
iaverage = 20 mA/cm2
seedth = 1000 A
180 sec
150 sec
120 sec
90 sec
60 sec
40 sec
20 sec
0
0.2
0.4
0.6
0.8
High (normal) acidity
1 r/R
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
k = 0.055 S/cm
iaverage = 20 mA/cm2
seedth = 1000 A
180 sec
150 sec
120 sec
90 sec
60 sec
40 sec
20 sec
0
0.2
0.4
0.6
Low acidity
0.8
1 r/R
Additives effect
Current density,
[A/cm2]
0.043
0.038
Pure copper sulfate
(0.5 M, pH = 2, no additives )
0.033
0.028
With additives *
0.023
0.018
0.013
0
0.2
0.4
0.6
0.8
1
r/R
* - Plating from copper sulfate in the presence of 70 ppm Cl - ,
50 ppm SPS and 200 ppm Polyethylene glycol [‘PEG’] (molecular weight = 4000 )
Conclusions
• The effects of the various process parameters have
been simulated
• The simulated results are in general agreement with
observations. Some Specifics:
• A proper shield design at the wafer edge significantly
enhances uniformity
• Electrode rotation has a larger effect than the convective
flow (in the practiced range)
• Wafer plating (macroscopic scale) does not typically operate
under mass transport control
• The edge-gap has a major effect on the flow and the
current density near the wafer edge
• The resistive seed effect is noticed mostly at higher current
densities (~40 mA/cm2)
• Scaling to 300 mm enhances the non-uniformity effects,
unless compensating measures are taken,.