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ImpactofBondPadCorrosion

June6to9,2010SanDiego,CA USA

Terence Q. CollierCVInc

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June6to9,2010 IEEESWTestWorkshop 2

Overview

Cleanthewafer nottheprobecard Historyofcontamination Corrosionremoval ExamplesofPreandPostCleans Analysisofpackagedunitsreliability Summary

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Cleanthewafer nottheprobecardRoot cause of high contact resistance (CRES)

is corrosion and contamination, not the probecard. Goal should be to eliminate fluorinecorrosion on bond pads

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WhyCleantheWafer Aprocessthatwillstripthecorrosion/oxidationbutnot

attackthebasemetalsisdesired.Traditionalmethods

includeplasma,phosphoric(PANordilutephosphoric)

acidderivatives

and

even

dilute

TMAH

for

aluminum.

Unfortunatelyphosphoricgoesaftergoodaluminumas

wellandanystrongbasewillhaveadramatic,notagood

one,impactonaluminum.

Improvecostofownership:

Extendhardwarelife. Improveassemblyyield. Reducescrapdieandwafers.

Reducereliabilityriskandregainprocesscontrol.

Damagedpadsleadtocustomerreturns

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Historyofcontamination

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Two items impact post fab yield:Test hardware

Bond pad conditions.

Removing the highly resistive layer can improve yield, extend probe card life, minimizereliability issues and help manage process control constraintsGoal: Remove the resistive layer without damaging the underlying metal layer.

What process has the following capabilities:No etch rate on metalsLow etch rate on passivation layers and Si.Love oxide and corrosion.

TheProblem ContactResistanceDue

to

Corrosion,

Not

Oxidation

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Dry Box Conditions - Fluorine contamination is apparent at time zero asreceived. As time continues the pads become more corroded. Conditions ofthese pads are typical and are the root of poor contact resistance. If the padsare not cleaned then poor yield is likely as well as die and hardware damage.

Zero

Time

One

Week

SixWeeks

ThreeWeeks

AlBondPadAnalysisOverTime

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ProbedPads

Prior

to

Clean

Brown corrosion layer variesfrom pad to pad. Some pads aremore corroded than otherswhich is why a solution isrequired that does not attack

aluminum.

A material that attacksaluminum would likely etch

away the top pad prior toreaching pure aluminum on thebottom pad.

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CorrosionRemovalinFiveMinutes

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CleaningImprovements

AsRecvd

BPS100

5min

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Cleaningand

rinsing

BPS100 can be used to clean thepads but as with any pure aluminumsurface DI water is an enemy.

An oxidized aluminum surface will

be more resilient to DI water than afresh layer.

An example of a cleaned surfaceleft in DI water shows the etching of

the probe mark on the wafer after90 minutes.

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ComparisonofSurfaceTexture

Sharp Al2O3 oxide peaks replacedby spongy corrosion layers.

Clockwise from left, Al+oxide, Al atambient for 3 days, Al + ambient +CF4 plasma.

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Voltage(mV

)

Touchdowns

BeforeBPS

AfterBPS

Lower CRES

Less Noise

Fewer false fails

Less CRES increaseover touchdowns

DramaticResultsAfterBPSonAl

Real resistancebetween two pinson the pad at10um overtravel

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BaselineSample;

No

Clean

Fuzzy, oxidized aluminum pads.

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BPS100(Sample

100

5)

Well defined grain boundaries..

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SideBy

Side

Comparison

of

the

BondPads

As Received, without BPS100.With BPS100 for 5 minutes.

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AugerDepthProfiles 3DaysC09ZG15711.pro: Sample 0 EAG

2009 Oct 19 10.0 keV 0 FRR 1.5904e+005 max

Al2/Full

0 20 40 60 80 100 120 140 160 180 2000

10

20

30

40

50

60

70

80

90

100C09ZG15711.pro

Sputter Depth ( )

AtomicConc

entration(%)

O

F

Al(O)

Si Ti

Al

O1.ls1C1.ls1F1.ls1

Al4.ls1Al2.ls2Si4.ls1Ti1.ls1

C09ZG15721.pro: 100-5 EAG2009 Oct 19 10.0 keV 0 FRR 9.8344e+001 max

Al2/Full

0 20 40 60 80 100 120 140 160 180 2000

10

20

30

40

50

60

70

80

90

100C09ZG15721.pro

Sputter Depth ( )

AtomicConce

ntration(%)

Al

O

C

F

Al2O1.ls1C1.ls1F1.ls1

Sample 0

100-5

70

20

F present until 40A

Si3N4 at 25A

Ti unusually present

AlO up to 80A; typicalfor Al

O at +120A

90% Al at 200A

F removed at 10A

Si3N4 eliminated

Ti eliminated

AlO eliminated

O in some form up to40A

90% Al at 40A

As Received

BPS100

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Analysisofpackagedunitsreliability

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WireBond

Evaluation

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CrossSections

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WireBondTestatMSL3

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CrossSectionsatMSL3

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Low etch rate on baseline aluminum pad.

Five minutes in BPS will remove CRES layer for up to 3-4 days.

Pads can be brought to t=0 from nitride etch.

Reduces bottlenecks and hardware costs.Improves yield and cycle time.

Decreases reliability risks with no detrimental impact to assembly

Clean the wafer, not the probes!

Summary

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ThankYou!Thankyoufortakingtimetolistingtothispresentation.TheauthorwouldalsoliketothankthefollowingfolksatAirProductsfortheirhelpandsupport:

DavidRennieRajRamamurthi

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S03 04 Collier SWTW2010