Monitoring of process stability and chamber matching by ...

Andreas SteinbachSven BarthMemory Development Center - Infineon Technologies Dresden

4th European AEC/APC Conference 2003Grenoble, France

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Monitoring of process stability and chamber matching

by plasma parameter measurementusing High speed- SEERS

Andreas SteinbachSven Barth

Memory Development CenterUnit Process Development Coordination

Infineon Technologies [email protected]

4th European AEC/APC 2003

mailto:[email protected]



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Acknowledgement

We greatly appreciate our colleagues support:Lars Christoph Lincoln O´RiainAndreas Thamm Jörg RadeckerGary Skinner Mark- Stefan Scheftner

Acknow-ledgement

The results presented in this paper were supported:by the EFRE fund of the European Communityand by funding of the State Saxonyof the Federal Republic of Germany, project 7700 / 1220.

The authors are responsible for the content of the paper.



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Outline

High speed SEERS featuresStrategy of plasma parameter application within AEC/APCHigh speed SEERS application examples

Process stabilityChamber matchingFDC - Fault detection and classification

Summary

Outline



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High speed SEERS features

High speedSEERS



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Self Excited Electron Plasma Resonance Spectroscopy -How it does work

RF up to 30th harmonicsPassiv, no impact on process

Easy current sensorqualification

SEERS model limits:One RF frequency higherthan ion plasma frequency(4 … 6 MHz)Pressure max. 300mTorr

Electron Collision Rate [s-1] Mean electron collisions with gas moleculesElectron Density [cm-3] = Plasma Density

Bulk Power [mW/cm²] Power dissipated by electrons in plasma

DC Bias Voltage [V]it`s well known

MeasurementRF Current

RF Peak Voltage

CalculationFFT and

Model SEERS

Resultsin real time

Plasma Parameters

High speedSEERS



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Plasma parameter vs. Process time

1,E+08

3,E+08

5,E+08

7,E+08

9,E+08

1,E+09

200 205 210 215 220time [s]

el. C

oll.

rate

[s-1

]

2,2E+09

2,4E+09

2,6E+09

2,8E+09

3,0E+09

3,2E+09

3,4E+09

3,6E+09

el. d

ensi

ty [c

m-³

]

High speedSEERS

B- field sine wave mode 0,5 Hz:

B- field square wave mode 0,25 Hz:

Dynamic effects in plasma: B- field rotation mode effecton process conditions - Results

Electron DensityElectron Collision Rate

Plasma parameter vs. Process tim e

1,E+08

2,E+08

3,E+08

4,E+08

5,E+08

6,E+08

200 205 210 215 220time [s]

el..

coll.

rate

[s-1

]

2,E+08

4,E+08

6,E+08

8,E+08

1,E+09

el. d

ensi

ty [c

m-³]

Electron DensityElectron Collision Rate



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Dynamic effects in plasma: B- field rotation mode effecton process conditions - Discussion

High speed SEERS modus: up to 15 measurements per secondElectron collision rate and electron density show B- field mode (square or sinus) impact on process conditions.

Oscillation indicate electrically asymmetric chamber geometryElectron density (plasma density) with sine wave B- field mode recipe indicates plasma instabilitiesPhase shift between electron density (= plasma density) and electron collision rate (see B-field square wave mode 0,25Hz)Hypothesis of phase shift root cause: Retardation between plasmaexcitation (electron density) and resulting gas composition

High speedSEERS



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Dynamic effects in plasma: Plasma stabilisation at process start

Electron density vs. Process time

2.E+08

4.E+08

6.E+08

8.E+08

1.E+09

0 5 10 15 20 25 30 35time [s]

elec

tron

den

sity

[cm

-3]

Plasma density oscillationcaused by rotating B- field

Process stability reachedafter about 20 s

High speedSEERS



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Strategy of plasma parameter application

within AEC/APC

ApplicationStrategy



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The Plasma is your Tool

Some parameters can bemeasured, for example:

MFC gas flow, pressure …Other parameters cannot bemeasured, for example:

Gas adsorption and desorption at chamber wall = conditioning

Processes on wafer surfaceare difficult to monitor.

The chamber is the tool box only.The plasma in the chamber – that´s your Tool really.

Cathode, chamber kit,RF Power installation

E- chuck

Plasma

Wafer

ApplicationStrategy



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Plasma parameters = key indicators of process conditions

How electron collision rate νe and electron density neindicate process conditions in plasma (simplified equations):

RF power input Gas PressureB- Field Gas Temperature

Gas Composition

Plasma parameters summarise process impacts, which are:known and measured easilyknown and difficult to measureunknown and cannot be measured at all

Plasma parameters = key indicators of process conditions

ne ~ B02 Upeak f(pGas)

)veσ1(ve-1)

ε02νe =

e2 ne2

B2

pgas

kBTgas( p1

p + ...

ApplicationStrategy



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Plasma parameter application as a process health indicator in AEC/APC

Detection of statistical significant process drift:Caused by measurable effects with very high sensitivityCaused by indirectly measurable effectsCaused by recipe parameters, chamber, wafer

Data compression:By the measured parameter, „by Physics“ itself

Plasma parameters give youdirect information about the plasma - your Tool.

Plasma parameters arereal time process health indicators.

ApplicationStrategy



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High speed SEERS applications within AEC/APC

Process stabilityChamber matching

FDC

ApplicationExamples



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Process stability & chamber matching of an etch process

Stability and Matching

Electron Collision Rate Electron Density

Mainframe 14 chambers





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Process stability and chamber matching of mainframe 2

Superimposition of long term drift and short term processcondition drift in plasmaWet clean impacton processconditions is clearlyseen by bothparameters



Mainframe 24 chamber



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Process stability and chamber matchingof mainframe 2, chamber B and C

Electron collision rate and electron density indicate different effects on processconditions(see page 11)


Mainframe 2chamber B,C

Mainframe 2chamber B,C



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Wet clean monitoring with plasma parametersof an etch chamber

Electron collision rate shows normal and abnormal wet clean clearly

Wet clean abnormal Wet clean normal

Stabilityand FDC



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FDC: E- chuck fault detection in an etch chamber

Electron collision rate and electron density show e-chuck faults clearly

Stabilityand FDC

Plasma unstableafter wet clean

Plasma stable afterESC exchange



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FDC: Detection of unstable plasma and arcing in an etch chamber with rotating B- field

Detection of unstable plasma and arcingby electron density(= plasma density) measurement

FDC



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FDC: Conditioning monitoring and leak detection of CVD process

Leakdetected

Stabilityand FDC

Tool down

Abnormal firstwafer effectafter dry clean



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Conditioning monitoring –First wafer effect after dry clean of CVD process

is normal First wafer effect is abnormal

First product waferafter dry clean

one point - one wafer one point - one wafer

one curve - one wafer one curve - one wafer

First product wafer after dry clean

Stabilityand FDC



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FDC: First wafer effect and leak detection - discussion

Conditioning:Dry clean every 5th wafer Impact on chamber wall surfaceChamber re- conditioning takes about 20 .. 25s on followingproduct waferConditioning effects are not detected by tool parameters

Electron collision rate = „Conditioning indicator“Leak detection:

Leak was detected by increase of chamber pressure and electroncollision rateBut electron collision rate rise was about ten times higher thanpressure increase !

Electron collision rate detects very small leaks, which cannotbe found using tool parameters, e.g. pressure

Stabilityand FDC



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Chamber matching: CVD chamber redesign effect on process stability

Same recipe afterchamber redesignElectron collision rate less noisy, butsignificant drift (gas composition)

Increase of electrondensity indicatesincreased plasmadensity (effectivepower input)


before redesignafter redesign

before redesignafter redesign



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Summary

Plasma parameters, like electron collision rate and electron density, characterise process conditions in plasma directly.High speed SEERS enables real time plasma parameter measurement with fast response time Short dynamic processes in plasma can be monitored.Applications of High speed SEERS were demonstrated with etch and CVD processes:

Process stability monitoring Chamber matching FDC

Plasma parameters can be used as real time process health indicators.

Summary

Monitoring of process stability and chamber matching by ...

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