University College Dublin
School of Electrical, Electronic and Mechanical Engineering
Modelling of Compliance in Chemical Mechanical
Planarisation (CMP)
Padraig Timoney, Eamonn Ahearne, Gerald Byrne, Centre of Manufacturing Engineering,
School of Electronic, Electrical & Mechanical Engineering, University College Dublin, Belfield, Dublin 4, Ireland
Planarisation - Motivation
3-D Finite Element Analysis
Literature sources report a correlation between wafer
von Mises stress and polishing uniformity 1
von Mises
Stress
(MPa)
FEA - Wafer Radial von Mises Stress
Distribution
Planar
Surface
Max Stress 5.97 MPa
Average Stress 0.64 MPa
8.00
6.00
4.00
2.00
0.00
-100
-50
0
50
100
Wafer Radius (mm)
Wafer contact pressure is measurable
Role of CMP Wafer Carrier
DF
DF – Force through Carrier Shaft
Wafer Carrier
Retaining Ring
Polishing Pad
Platen
Wafer Carrier and retaining
ring hold wafer in polishing
Polishing uniformity (post CMP planarity) depends on:
• Interfacial Pressure Distribution (wafer loading)
• Relative Velocity (polishing pad & wafer motion)
IPEC 200mm Wafer Carrier
• Carrier on CMP tool in UCD
• Wafer edge sits into lip seal to create
pressurised bladder behind wafer, allows
wafer pressure control
• Static finite
element analysis
(FEA) undertaken
to evaluate contact
pressure between
pad and wafer
• Fujifilm Prescale
TM pressure
measurement film
used to validate
model
Max Pressure 0.34 MPa
0.40
0.30
0.20
0.10
0.00
Average Pressure 0.10 MPa
-100
-50
0
50
100
Wafer Radius (mm)
Validation - Pressure Measurement
Observations
Similar range of values between FEA and measured
Higher resolution in measurement than model
Pad surface roughness and grooves not modelled
PrescaleTM film limited to range of 0.05 to 0.25 MPa
rcc
Pmax, FEA
Paverage, FEA
Pmax, Meas
Paverage, Meas
Path 1
Path 2
(large rcc effect) (small rcc
effect)
76mm 170mm 76mm 170mm
0.39
0.78
0.376 0.285
0.085 0.084
0.086 0.087
0.25
0.22
0.17
0.25
0.046 0.049
0.051 0.041
Filtered Path 1 Filtered Path 2
0.05 < P < 0.25 0.05 < P < 0.25
76mm
0.25
0.25
0.25
0.069
170mm
0.25
0.25
0.22
0.069
76mm
0.25
0.09
0.17
0.068
170mm
0.22
0.09
0.25
0.066
FEA vs Measured Wafer
Contact Pressure Distribution
Fujifilm PrescaleTM film.
Contact Pressure
(MPa)
Ideal CMP Process
Cross Section of 7 Metal
layer micro-processor chip
(C-H Jan, Intel)
Contact
Pressure
(MPa)
FEA - Wafer Radial Contact Pressure Distribution
0.25
0.20
FEA, r_cc = 76mm
FEA, r_cc = 170mm
Meas, r_cc = 76mm
Meas, r_cc = 170mm
0.15
0.10
0.05
-100
-50
0
50
Wafer Radius (mm)
100
(Above) Tabulated data and
corresponding graph of results
References
(Left) Pressure distribution for
IPEC wafer carrier on CMP tool
[1] D. Wang et al., J. Electrochem. Soc. 1997
Acknowledgements
Components of tool in FE model
Machine and technical support provided by Intel Ireland
Funding for this research by Enterprise Ireland