Post on 01-Apr-2015
Simulations of ‘Bottom-up’ Fill in Simulations of ‘Bottom-up’ Fill in Via Plating of Semiconductor Via Plating of Semiconductor
InterconnectsInterconnectsUziel LandauUziel Landau11, Rohan Akolkar, Rohan Akolkar11, , Eugene MalyshevEugene Malyshev22, and Sergey , and Sergey
ChivilikhinChivilikhin22
1Department of Chemical EngineeringCase Western Reserve University
Cleveland, OH 44106 and
2L-Chem, IncBeachwood, OH 44122
OutlineOutline• Significance and ObjectivesSignificance and Objectives• Parameters Controlling the Bottom-Parameters Controlling the Bottom-Up FillUp Fill• Simulation MethodSimulation Method• Sample SimulationsSample Simulations• ConclusionsConclusions
Prior WorkPrior Work•Andricacos, Uzoh, Dukovic, Horkans and Deligianni, IBM J. R&D 1998:
- Additives blocking model- Adjustable Parameters + steady-state additives diffusion
•Georgiadou, Veyret, Sani and Alkire, J. Electrochem. Soc. 2001:
- Convective flow + additives transport
•Cao, Taephaisitphongse, Chalupa and West, J. Electrochem. Soc., 2001:
- Diffusion controlled additives transport + adsorption isotherms
• Josell, Baker, Witt, Wheeler and Moffat, J. Electrochem. Soc., 2002:
- Curvature enhanced SPS coverage
ObjectivesObjectives Develop a Simulation for the Bottom-Develop a Simulation for the Bottom-
Up FillUp Fill
Based on Experimental DataBased on Experimental Data
Without Adjustable Parameters & Without Adjustable Parameters &
Without Without Invoking Extreme Invoking Extreme
AssumptionsAssumptions
Simulation should correlate Simulation should correlate
experimental experimental
observations observations
Gap-Fill Gap-Fill ModesModes
Bottom-up Fill
(Good!)
Pinch
Conventional Plating
(unacceptable)
Seam
Conformal Plating
(unacceptable)
Seam
Void
Fill~ 2.5 min~ 50 sec~ 30 sec
‘Conventional’ Plating
Conformal Plating
Bottom-up Plating
Stages in ‘Gap-Fill’
Variable Adsorption leads to Variable Variable Adsorption leads to Variable Kinetics and to ‘Bottom-up’ fill:Kinetics and to ‘Bottom-up’ fill:
Suppressor, e.g. PAG
Slow deposition
Fast deposition
‘Enhancer’, e.g. Organic di-sulfide
Variable Deposition Rates Due to Non-uniform Variable Deposition Rates Due to Non-uniform InhibitionInhibition
i
[mA/cm2]
V
Polarization Curves
Enhanced Kinetics (via)
Suppressed Kinetics
(‘flat’ wafer)10
300 mV
100
< 50 Sec
2-3 Min
Rapid Fill of Vias and Rapid Fill of Vias and TrenchesTrenches
Nernst-Plank Equation (ionic transport):
Navier-Stokes Equation (fluid-flow–momentum balance):
VVVV 2
Pt
C (Boundary
Layer)
Transport Equations --Transport Equations --
Electroneutrality:
Zj Cj = 0
jjjjjjj CCUFZCDt
C
V
Pseudo Steady-State
Diffusion Electric Migration
Convection
Scaling Analysis of the Nernst Plank Scaling Analysis of the Nernst Plank Equation*:Equation*: 02 jjjjj CFUZCD
Diffusion Electric Migration
Cb
2 = 0Thin boundary layerBoundary conditions:
Electrode: = V – E0 – ηa – ηC
Insulator: i = 0 (i = - κ ) = 0
Ohmic Control on the Macro-Scale
μm500mm0.5 L
sticcharacteri iFn
TRL
Thin Boundary Layer Approximation
2 = 0 (Laplace’s eqn. for the potential is solved within the cell)
* U. Landau, The Electrochem. Soc. Proceedings Volume 94-9, 1994.
Scaling Analysis of the Nernst Plank Scaling Analysis of the Nernst Plank Equation*:Equation*: 02 jjjjj CFUZCD
Diffusion Electric Migration
Cb
2 = 0
Mass Transport Control on the Micro-Scale
μm500mm0.5 L
sticcharacteri iFn
TRL
2 C = 0 (Laplace’s eqn. for the Concentration, solved in the boundary layer)Boundary conditions:
Electrode: ηC = V – E0– ηa -
outer edge of diffusion layer: y = C = CB
Insulator: i = 0 (i = - κ ) C = 0
* U. Landau, The Electrochem. Soc. Proceedings Volume 94-9, 1994.
Boundary layer
The Software PackageThe Software Package‘Cell-Design’ Features:
Current Distribution + Fluid Flow (BEM + FD)
Current Distribution: (BEM)
• Macro-scale:
• Micro-scale:• Moving boundaries• Variable Kinetics
Fluid-Flow (FD):
• Complete solution of the Navier-Stokes equation
• Integrated with the electrochemical modeling
• Solution of the Nernst-Plank equation• Export C
Fast, Robust, Menu driven
2 2 C = 0C = 0
22 = 0 = 0
Boundary Element (BEM)
Finite Differences (FD)
Simulation of Deposit Simulation of Deposit PropagationPropagationVariable kinetics + Moving
boundaries
2 =0 2 C =0
i = f (η)
Passivated kinetics (PEG+SPS) [Measured, f(t)]
Accelerated kinetics (SPS)
Variable kinetics [Partially passivated, f(t)]
Virtual electrode;Outer edge of diffusion layer
C
Flow SimulationsFlow Simulations
60 RPM + 4 GPM Impinging Flow
Wafer Wafer ScaleScale
‘Cell-Design’ Simulations
Flow Flow SimulationsSimulationsMicro-ScaleMicro-Scale
Transport within the via is due to diffusion
‘Cell-Design’ Simulations
‘Cell-Design’ Simulations
Concentration MapConcentration Map
0
10
20
30
40
50
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
Activation Overpotential, a, [V]
i
[mA/cm2]
SPS (Stagnant
) PEG (Stagnant
)
Steady-State Polarization Steady-State Polarization DataData
0.00 0.05 0.10 0.15 0.20 0.25 0.300
10
20
30
40
50
60
70
80 SPS steady state PEG+SPS unsteady state PEG steady state
slow SPSactivity
t=50s t=20st=10s
t=0s(PEG)
Current Density, i [mA/cm2]
Activation Overpotential, a [V]
Initial state
Polarization Transients: PEG + SPSPolarization Transients: PEG + SPS
50 s 20 s10 sec
0 sec(PEG)
SPS Steady-
state
Time
0 2 4 6 8 100.0
0.2
0.4
0.6
0.8
1.0PEG Penetration Depth, z*=z/h
Time, t (s)
Fast PEG transport to upper via sidewalls
Slow PEG transport to the via-bottom
PEG Penetration PEG Penetration DepthDepth
Short time SPS
coverage
Short time PEG
coverage
0 2 4 6 8 100.0
0.2
0.4
0.6
0.8
1.0PEG Penetration Depth, z*=z/h
Time, t (s)
Fast PEG transport to upper via sidewalls
Slow PEG transport to the via-bottom
PEG Penetration PEG Penetration DepthDepth
Longer time PEG coverage
Longer time SPS
coverage
Slow SPS depolarizati
on
SiO2
2 sec
4 sec
8 sec
12 sec
16 sec
24 sec
32 sec
40 sec
44 sec
Electrolyte
47 sec
‘Cell-Design’ Simulations
Via Fill Via Fill SimulationSimulationFill Time: 47 sec.
Overpotential: - 124 mV
Bottom: i = 60 mA/cm2
i0 = 1.12 mA/cm2 C = 0.83
Top & Sidewalls: i = 0.24 mA/cm2 3.4 mA/cm2
Depolarization by SPS:i0 = 3.1 μA/cm2 46 μA/cm2
C = 0.9
SiO2
Electrolyte
2 sec
6 sec
16 sec
32 sec
10 sec
22 sec
42 sec
50 sec
‘Cell-Design’ Simulations
Via Fill Via Fill SimulationSimulationFill Time: 49 sec.
Overpotential: - 124 mV
Bottom: i = 60 mA/cm2
i0 = 1.12 mA/cm2 C = 0.83
Top & Sidewalls: i = 0.24 mA/cm2 6.8 mA/cm2
Depolarization by SPS:i0 = 3.1 μA/cm2 92 μA/cm2
C = 0.9
SiO2
Electrolyte
‘Cell-Design’ Simulations
SiO2
Electrolyte
1 sec time intervals
Variable Kinetics along the Sidewalls
Via Fill Via Fill SimulationSimulation
Fill Time: 48 sec.
Overpotential: - 124 mV
Bottom: i = 60 mA/cm2
i0 = 1.12 mA/cm2 C = 0.83
Top: i = 0.24 mA/cm2 3.4 mA/cm2
Depolarization by SPS:i0 = 3.1 μA/cm2 46 μA/cm2
C = 0.9
Sidewalls: Interpolated kinetics between Top and Bottom
SiO2
Electrolyte
Seam
‘Cell-Design’ Simulations
Via Fill Via Fill SimulationSimulation
Plating Time: ~147 sec.
Overpotential: - 80 mV
Bottom: i = 10 mA/cmi = 10 mA/cm22
i0 = 1.12 mA/cm2 C = 0.83
Top: i = 0.05 mA/cm2 4.8 mA/cm2
High Depolarization by SPS:i0 = 3.1 μA/cm2 0.28 mA/cm2 C = 0.9
Sidewalls: Interpolated kinetics between Top and Bottom
Current density has been Current density has been lowered: lowered: No Bottom-Up FillNo Bottom-Up Fill
1 sec time intervals
Deposit Propagation in Deposit Propagation in Feature Clusters and Wide Feature Clusters and Wide
FeaturesFeatures
Flat regions - Passivated: i0 =5x10-4 A/cm2
Ac
Bottom – Pure copper: i0 =10-3 A/cm2
Ac
Side-walls - interpolated
Cluster
Wide Feature
‘Cell-Design’ Simulations
ConclusionsConclusions Simulation of bottom-up fill has been carried Simulation of bottom-up fill has been carried
w/o invoking arbitrary assumptions w/o invoking arbitrary assumptions
Simulation is based on, and implements Simulation is based on, and implements ‘variable‘ kinetics = f(time, position)‘variable‘ kinetics = f(time, position)
A commercial CAD program that accomodates A commercial CAD program that accomodates moving boundaries and variable kinetics was moving boundaries and variable kinetics was usedused
Different process parameters have been Different process parameters have been explored: explored:
Transport and adsorption kinetics of inhibiting Transport and adsorption kinetics of inhibiting and depolarizing additives must match processand depolarizing additives must match process
Operating conditions (i, V) must be within Operating conditions (i, V) must be within
rangerange
AcknowledgementAcknowledgementss
• Yezdi Dordi – Yezdi Dordi – Applied materialsApplied materials• Peter Hey – Peter Hey – Applied MaterialsApplied Materials• Andrew Lipin – Andrew Lipin – L-ChemL-Chem
Thank you for Thank you for your your
attentionattention