CMP FtF9 Nov 06

Friction Updates1. Last FtF

• Past issues & solutions

2. Latest data• CoF vs. slurry dilution• CoF vs. rotation rate• Fz vs. slurry dilution

3. Laser displacement sensor tests

• Feasibility• Specifications

4. Thesis Roadmap• Microscale friction and

polishing model• Macroscale

measurements

5. Questions/Requests6. Future work

Jim VlahakisPhD. CandidateTufts University

CMP FtF9 Nov 06

Friction Updates – Last FtF

• External noise issues• New wafer motor power

supply eliminated noise

• Issues concerning slurry dilution

• Moved from 9:1 to 3:2 dilution, more in line with industry practice

• Data runs at 30/60rpm• Now using 60/120rpm (.5

& 1m/s), more in line with industry practice

• Irregularities due to changes in wafer shape

• Controls in place to monitor wafer shape

CMP FtF9 Nov 06

Friction Updates – Latest Data

• CoF vs. slurry dilution• 60rpm & 1.7psi• Note large CoF (and

large σ) for pure slurry. A result of shear thickening?

• CoF remains fairly constant over a wide range of slurry dilutions

• CoF for pure H2O seems strongly dependent on pH

• Next steps• study slurry

compositions in the range of 1 part H2O to 2/3/5/7 parts slurry

• Investigate pH dependence for H2O

• Perform experiment “backwards”

CoF vs. slurry composition

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0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

pure slurry 1 to 1 3 to 2 3 to 1 5 to 1 7 to 1 9 to 1 pHadjusted

H2O

slurry composition

Co

F

CMP FtF9 Nov 06

Friction Updates – Latest Data

CoF vs. rotation rate, note development of CoF plots and spectra

CMP FtF9 Nov 06

Friction Updates – Latest Data

CoF vs. rotation rate, note development of CoF plots and spectra

CMP FtF9 Nov 06

Friction Updates – Latest Data

• Fx vs. slurry dilution• 60rpm - 1.7psi• Decrease in Fz tracks

decrease in density of slurry as it is mixed with H20

• Increasing σ corresponds to increasing chatter (except for pure slurry case)

• Next steps• study slurry

compositions in the range of 1 part H2O to 2/3/5/7 parts slurry

• Investigate pH dependence for H2O

Fz vs. slurry composition

50

52

54

56

58

60

pure slurry 1 to 1 3 to 2 3 to 1 5 to 1 7 to 1 9 to 1 pHadjusted

H2O

slurry composition

Fz

CMP FtF9 Nov 06

Friction Updates – Latest Data

• CoF vs. rotation rate• 60rpm - 1.7psi• CoF remains fairly

constant over a wide range of velocities

• Below 30rpm data is unreliable – motion of wafer drive is noticeably non-uniform

• Next step• Investigating deeper

into the Stribeck curve will require lower pressures and much higher velocities. Likely not possible with our current setup

CoF vs. Rotation Rate

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0.25

0.27

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0.31

0.33

0.35

30rpm-.32m/s

45rpm-.48m/s

60rpm-.64m/s

75rpm-.80m/s

90rpm-.96m/s

105rpm-1.12m/s

120rpm-1.28m/s

rotation rate - velocity

Co

F

CMP FtF9 Nov 06

Friction Updates – Laser Sensor

• Feasibility of using multiple laser sensors to monitor wafer displacement

• How much does support frame displace during worst case polishing• 60rpm–2.5psi–pure

H20 (strong chatter)

• Frame displacements are on the order of .1mm

• Spectrum of displacement signal is very familiar

• Safe to say that wafer motion won’t be lost in frame motion

CMP FtF9 Nov 06

Friction Updates – Laser Sensor

• Generate rough idea of wafer displacement

• 60rpm-1.7psi-3:2 (minimal chatter)

• range = +/- 1mm

• Wafer regularly moving out of range

• To be safe, we should require a range of at least +/- 2mm or even +/-5mm

• Must design a system that allows for quick adjustment of sensor position

• Given the accuracy of the laser (~1μ), is this a good way to measure fluid film thickness?

• Sensor size is an important consideration

CMP FtF9 Nov 06

Friction Updates – Thesis Roadmap

1. Develop a micro-friction model utilizing the expertise of the BostonCMP group

• Identify the processes that contribute to CoF and/or MRR

• Examples• CoF = μfluid+μpad+μparticles

• Polishing is more a “plucking” (chemical) process, rather than a “plowing” (mechanical) process

2. Make changes on the microscale and measure their effect on the macroscale, for example

• Vary roughness and moduli of pads• Various particle loads• Maintain constant particle loading,

while varying the load of particles that participate in the polishing

3. Measure effect on both CoF and MRR• Which changes effect CoF or MRR

only• Which effect both• Does this confirm our model or do we

need to make adjustments?

Microscale Changes and Their Effect on Macroscale Process

Variables in Chemical Mechanical Planarization

Submitted by

James Vlahakis

In Partial Fulfillment of the Requirements for a PhD.

School of Engineering

Tufts University

May 2008

CMP FtF9 Nov 06

Friction Updates - Questions/Requests

Questions1. How can we measure MRR?

• Can we etch a radial channel in our wafers and measure the change in step heights?

2. Can we replace slurry silica particles with particles that do not participate in the chemistry?

Requests1. More slurry please!

2. Pads of various roughness and modulus

CMP FtF9 Nov 06

Friction Updates – Future Work

High Level View

1. Continue to develop models with Boston CMP group

2. Identify the experiments that will show the accuracy (or inaccuracy) of our models

3. Perform the experiments and, if necessary, iterate until our models can explain our data

4. Write it up!

Low Level View

1. Complete CoF vs. slurry dilution experiments

2. Determine μ and shear thickening effects for various slurry dilutions

3. Purchase and begin installation of laser displacement package

4. Prepare for various conferences and papers