Particle Characterization of AbrasivesChemical Mechanical Polishing (CMP) Smooth (planarize) silicon wafer surface with combination of chemical & mechanical forces Uses abrasive &

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Particle Characterization of Abrasives

Mark [email protected]


Factors Affecting Abrasion Mechanics

Difference in hardness between the two substances: a much harder abrasive will cut faster and deeper Grain size (grit size): larger grains will cut faster as they also cut deeper Grain shape: sharp corners helpAdhesion between grains, between grains and backing, between grains and matrix: determines how quickly grains are lost from the abrasive and how soon fresh grains, if present, are exposed


Factors Affecting Abrasion Mechanics

Contact force: more force causes faster abrasion Loading: worn abrasive & cast off work material fill spaces between abrasive grains, reducing cutting efficiency while increasing friction Use of lubricant/coolant/metalworking fluid: Can carry away swarf (preventing loading), transport heat (may affect physical properties of the workpiece or the abrasive), decrease friction (with the substrate or matrix), suspend worn work material and abrasives allowing for a finer finish, conduct stress to the workpiece.


Macro vs. Microgrits

Macrogrits:Greater than ~ 60 µmTraditional size test is sieving

Microgrits:Less than ~ 60 µmTraditional testing is sedimentometer

2 mm

40 µm


Macrogrits


Microgrits


ISO 6344Macrogrits P12 to P220


Sieve Analysis

InexpensiveTime consumingAlternative: Dynamic Image Analysis by CAMSIZER

Higher throughputComplete distributionShape informationParticle images

Size and shape from 30 µm – 30 mm


Dynamic Image AnalysisBy choosing proper size parameter, Xc min, results can match historic sieve Data. Also generates shape data provenTo correlate with abrasive performance.


Sand: Round vs. “Edgy” by CAMSIZER

Similar in size.Shape difference seenin b/l and sphericity.Edgy would makebetter abrasive.

Sphericity

Breadth/length (b/l)


ISO 6344Microgrits P240 to P1200


ISO 6344

Microgrits P1500 to P2500


Sedimentometer

Sample is pre-wet, then placed in settling medium at top of tube, time is recordedTime is recorded when the first material reaches the collecting tubeTimes are recorded as sample reaches various graduations in settling tubeExample: If the 2mm height was reached in 4 minutes, that means 8% of the material is 39.8 microns and coarserStill in use, but being replaced by newer technology (laser diffraction)


Laser Diffraction

Powders (in air) and suspensions30 nm – 3000 µmQuick, easy, reproducibleHighly automatedMost popular particle sizing techniqueLA-950 highest performance available but workhorse dependability

Dry powder feeder


Laser Diffraction DataDiamond Abrasives

Silicon Carbide

slurry


Chemical Mechanical Polishing (CMP)

Smooth (planarize) silicon wafer surface with combination of chemical & mechanical forcesUses abrasive & corrosive colloidal slurry, polishing pad, and retainer ringCMP slurry contains small abrasive particlesLarge particles in slurry cause scratches (defects)Want to know mean size + presence of larger particles


Particle Sizing Techniques

NoVery poorVery poor (statistics)ExcellentMicroscopy

(SEM, TEM)

YesVery poorExcellentVery goodDisc Centrifuge

YesPoorGoodVery goodLight Obscuration

NoGoodExcellentVery goodAcoustic Spectroscopy

YesVery goodVery poorExcellentDynamic Light Scattering

YesExcellentExcellentVery goodLaser Diffraction

Dilution Required?Analysis SpeedOversize Measurement

Nano-Particle MeasurementTechnique


Laser Diffraction Data

Ludox colloidal slurry (31 nm)

Geltech silica (1.65 µm)

0.05 wt % Geltech in Ludox


Acoustics: DT-1201 Experiment

0

1

2

3

4

5

6

7

8

9

Atte

n uat

ion

[dB

/cm

/MH

z]

10 0 10 1 10 2

Frequency [MHz]

diameter 1 microndiameter 0.5 micron

Attenuation [dB/cm/MHz]

out

in

II

cmLMHzflog

][][10

=α



Materials: Ludox colloidal silica, Geltech silica, commercially available CMP slurriesSpike SS25 CMP slurry with Geltech silicaNote: all measurements made with no dilution, major benefit of acoustics



Attenuation spectra for single component silica slurries

Corresponding particle size distributions



Particle size distributions of silica Cabot SS25, diluted down to 12 wt %, with various additions of silica Geltech 0.5


Image Analysis Experiment

Samples: small, medium, large abrasive particlesMeasure size & shape using static image analysis (PSA300)Prepare sample using Sampler DisperserCalculate size, shape, custom calculation to define angularity


Image Analysis Experiment

Small abrasive, high angularity (left), low angularity (right)

Medium abrasive, high angularity (left), low angularity (right)

Large abrasive, high angularity (left), low angularity (right)


Shape Parameters


Spike Parameter*

* Stachowiak, W., Image Analysis of Abrasive Grits, Tribology and Interface Engineering, Vol 44


PSA300 Calculation

Find sharp edges at the tips of the particlesCount number of tips (child count)Number of tips alone not sufficient, long particles w/2 tips not as good as hexagon w/6 tipsDefine angularity roundness as child count x roundnessThus triangle w/3 points less angular than octagon of 4 sharp edges & 4 rounded edges


PSA300 Calculation


PSA300 Calculation


PSA300 Calculation


Image Analysis Results


Conclusions

For particle size analysisLaser diffraction offers many benefits over sedimentometerCAMSIZER offers many advantages over sievesDT-1201 for undiluted size and zeta potential

For particle size and shapeCAMSIZER for 30 µm – 30 mmPSA300 for 0.5 µm – 2000 µm

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Particle Characterization of AbrasivesChemical Mechanical Polishing (CMP) Smooth (planarize) silicon wafer surface with combination of chemical & mechanical forces Uses abrasive &