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In-Situ Measurements for Chemical Mechanical Polishing. James Vlahakis Caprice Gray CMP-MIC February 20, 2006. Outline. Slurry layer imaging using Dual Emission Laser Induced Fluorescence (DELIF) Why DELIF works How to take data Ways to interpret data In-Situ Force measurements - PowerPoint PPT Presentation
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In-Situ Measurements for Chemical Mechanical Polishing
James VlahakisCaprice Gray
CMP-MICFebruary 20, 2006
Outline
• Slurry layer imaging using Dual Emission Laser Induced Fluorescence (DELIF)– Why DELIF works– How to take data– Ways to interpret data
• In-Situ Force measurements– Experimental Equipment/Setup– Coefficient of Friction– Downforce frequency analysis
In Situ Slurry Layer Image Acquisition in Chemical Mechanical Planarization
Caprice Gray
PhD. Candidate
Tufts University
20 February 2006
3
Dual Emission Laser Induced Fluorescence (DELIF)
• Types of Measurements– Dye choice– pH, temperature, fluid layer thickness
• How to make DELIF measurements– time averaged (no laser)– 2 Dye System– 1 Dye System
• DELIF Images and Analysis– Qualitative examination of data– Calibration procedure for quantitative – Types of quantitative measurements
Is a DELIF system hard to set up?
• YES
Types of Measurements
Time averaged
Low Resolution Instantaneous
High Resolution Instantaneous
1”
1 cm
1mm
Why Examine 2 Emissions?
Pad
Slurry
Division of 2 images cancels variationsin image source intensity
=
Ratio
DELIF Light Paths
Laser Shot
Camera Mirror
Laser Mirror
Camera 1
Camera 2 Fluorescent Light
Optics Box
BK7 Optical Glass Wafer
Optics Box
CalceinCamera
Pad Camera
DELIF Spectral Analysis (1 dye)
0
0.2
0.4
0.6
0.8
1
300 400 500 600
Wavelength (nm)
Inte
nsi
ty (
au)
Pad Abs. 346nm
Laser Em.355 nm
0
0.2
0.4
0.6
0.8
1
300 400 500 600
Wavelength (nm)
Inte
nsi
ty (
au)
Pad Em.392 nm
Pad Abs. 346nm
Laser Em.355 nm
0
0.2
0.4
0.6
0.8
1
300 400 500 600
Wavelength (nm)
Inte
nsi
ty (
au)
Pad Em.392 nm
Calcein Abs492 nm
Pad Abs. 346nm
Laser Em.355 nm
0
0.2
0.4
0.6
0.8
1
300 400 500 600
Wavelength (nm)
Inte
nsi
ty (
au)
Pad Em.392 nm
Calcein Abs492 nm
Calcein Em.530 nm
Pad Abs. 346nm
Laser Em.355 nm
Spectral Filter Regions
How DELIF works
DCzbazd
dA
I
I
bazzAzAAzA
d
dzA
I
I
dzAAII
zAAIIzAzI
dAIdII
AII
cam
cam
cam
cam
Lcam
Lff
Lfcam
Lf
)()(
)()()(),(
),(
),()355(
),()355()(),(),(
)355()(
)355()(
2
1
4
3
2
1
4
3
4
3
2
1
2
1
2
1
2
2
22
1
2
21212
21211222
1111
111
• Variables
– I1f, I2f = Fluorophore fluorescent intensity
– IL = laser intensity– Icam = light collected by
camera– = quantum
efficiency– A = absorption– = wavelength– z = passive scalar– a, b, C, D = constants
Sources of Error• Measurements are independent of viewing geometry• Short wavelength absorber/emitter:
– Independent of the passive scalar (type 3 conflict*)– Does not absorb its own emission– Does not absorb the long wavelength absorber’s emission
• Long wavelength absorber/emitter:– Does not absorb its own emission– Does not absorb Laser emission– Absorption must be a linear function of z (true for thin films)
• Choose a short wavelength filter band outside the absorption region of the long wavelength absorber/emitter (type 2 conflict*)
• Choose filter bands where emissions do not overlap (type 1 conflict*)
*Spectral conflict types as identified by Coppeta and Rogers Experiments in Fluids, 25 (1998) 1-15.
Choosing Dyes
Quantity Dye Candidates
pH Fluorescien(5-8), HPTS(6-9), Rhodamine B(<6), LDS 698(<6), 1-4 DHPN(6-9)
pH Independent Lucifer Yellow, Sulforhodamine, Kiton Red, Phloxine B
Temperature Fluorescien, HPTS, Rhodamine B, Kiton Red, Phloxine B, LDS 698, 1-4 DHPN
Temperature Independent
Sulforhodamine
Thickness Calcein, Pyrromethene 650
Thickness Independent
Coumarin 4, Pyrromethene 567
References:J. Copetta, C. Rogers. Experiments in Fluids, 25 (1998) 1-15.
C. Hidrovo, D. Hart. Measurement Science and Technology, 12 (2001) 467-477J. Lu, et. al. Journal of The Electrochemical Society, 151 (4) (2004)
Time Averaged DELIF
Slurry Layer
Pad
z
UV LampLight
Dye 1Dye 2
• NO LASER, uses UV lamp– Mostly qualitative – global
slurry behavior– Quantitative- average fluid
layer thickness, average pH, or average temperature
• Must suppress the natural fluorescence of the pad with carbon black
• Need 2 dyes
2 Dye System
Slurry Layer
Pad
z
Laser Shot355 nm
Dye 1Dye 2
• Laser allows instantaneous measurements
• Need laser beam expander for low resolution images
• Must suppress the natural fluorescence of the pad with carbon black
1 Dye System
Slurry Layer
Pad
z
Laser Shot355 nm
Dye Particle
• Laser allows instantaneous measurements
• Must use pads with natural fluorescence and spectra that fit the model– Polyurethane based pads
work well– Surface coatings are not
good enough• Depending on laser power,
may need beam expander to prevent pad burning
Calibration Methods
1mm = 232 pixels
X-Y CalibrationCapture image of millimeter ruler and measure pixels/mm
2-Dye CalibrationInject dyed slurry between 2 microscope slide shimmed on 1 side
1-Dye Calibration•Flat wafer shimmed by microscope slide•Need very flat pad•Must image near wafer edge (difficult)
Most Recent Calibration Method• Etch wells into glass wafer to
different depths– Depth must be greater than pad
surface roughness• Relative calibration
– Need wafers with 2 different well depths
– Can acquire pixel to pixel slurry depth differences
• Absolute calibration– Need wafers with at least 3 different
well depths– Know slurry thickness under every
pixel
DCzI
I
pad
slurry
Pad Images (Low Ra Flat)
(a) Flat wafer(b) 14 um deep 1mm2
square well
We can see striations in the pad due to the motion of the conditioner.
Striations direction is along the dotted line.
Slurry flow direction is indicated by arrows
http://www.tuftl.tufts.edu/CMPWebsite2/Public/PictureGallery/pics.htm
Air Pockets
Low Resolution
High Resolution
Air pockets get trapped in features
Grooves help to transport air pockets under the wafer features
Histogram Analysis
• The asperity size distribution is the same shape as the fluid layer thickness distribution.
• When force is applied to the wafer, the distribution changes both shape and location.
• Standard deviation comparison → pad compression
• Peak location → fluid layer thickness.
• Compression factor: 0
0
Histogram Data
Red line = 10psi, White Line = 0psiHistograms of 2mm2 regions at different points on the pad.
Pad Shape Near Wafer Features
DELIF Summary
• How and why DELIF works– Must be very careful in choosing dyes/fluorophores
and filter regions
• Different ways to employ DELIF• Calibration methods• Types of image analysis
– Qualitative: slurry starvation, air travel under the wafer– Quantitative: Pad compression using sub-region
histograms, Pad shape near wafer features
Pad Images (Low Ra Grooved)
Fruedenberg FX9
K-grooved Fruedenberg FX9
K-grooved Rodel IC1000
http://www.tuftl.tufts.edu/CMPWebsite2/Public/PictureGallery/pics.htm
Pad Images (High Ra)
Flat Experimental
Pad
xy-grooved experimental
Pad
Thin-grooved Experimental
Pad
http://www.tuftl.tufts.edu/CMPWebsite2/Public/PictureGallery/pics.htm
Polishing Setups
Old Setup New Setup
