In-Situ Measurements for Chemical Mechanical Polishing

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