5/2/2005

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FLCC

Wireless Metrology in Semiconductor Manufacturing

Costas J. SpanosFLCC Seminar

5/2/2005

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Outline

Historical perspective• Hardware and software applications• Breakthroughs that have yet to be realized• Distributed control and diagnostics• Hardware requirements

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Past And Present

• Ideas and even patents circulated in the industry since the early 90s.– No known implementation since UCB work started in

late 1997• Commercialized in 2000 by OnWafer

Technologies– Founders from UCB and LAM Research– BakeTemp for Post Exposure Bake– PlasmaTemp– An expanding software applications suite

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Smart Sensor Wafers - 1997In-situ sensor array, with integrated power and telemetry

Applications:process control, calibration, diagnostics & monitoring,process design

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Sacrificial, On-wafer Sensors

I

Exposed

I

Buried

VthVtemp

Temperature Compensated Design of Etch Rate Sacrificial SensorEach sensor has a buried temperature reference

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Wired Proof of Concept Implementation

100mm

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• Wafer placed on bakeplate, Rs measured for both sensorsResults - bakeplate

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Results - XF2 Etch• Temperature-induced offset cancelled

13Å average

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Wireless Prototype ~1999Off-the Shelf Components, Ni on Al, Solder Paste

Mount…

thermistorresistor capacitors

PIC

voltage regulatorLED

batteries

100mm

4 Sensors4oC Accuracy2oC Precision1oC ResolutionPrimary BatteriesNo MemoryFixed Behavior~15grams/ 5mm

4 Sensors4oC Accuracy2oC Precision1oC ResolutionPrimary BatteriesNo MemoryFixed Behavior~15grams/ 5mm

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Thermal Stress Tests on Calibrated Plate

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Autonomous Passage Through Wafer Track

Wafer leaves bake plateWafer leaves bake plate

Wafer arrives at chill plateWafer arrives at chill plate

Non-uniform bake…Non-uniform bake…

Non-uniform coolingNon-uniform cooling

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RF isolation of wafer; isn’t it ugly?• Standard temperature wafer covered with layer

of epoxy• Epoxy is transparent to infrared: LED can be

used for data transmission

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Test results in plasma: RF 50W, 0.76 Torr, O2

sensor 3

sensor 1 sensor 2

sensor 4

Word’s first Wireless Plasma Monitoring – Late 1999!

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Test results in plasma: RF 100W, 0.76 Torr, O2

sensor 3

sensor 1 sensor 2

sensor 4

Word’s first Wireless ~High Power Plasma Monitoring!

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A Commercial Smart Dummy? (Sept 2000)

Courtesy of OnWafer Technologies, Inc.

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Outline

• Historical perspectiveHardware and software applications

• Breakthroughs that have yet to be realized• Distributed control and diagnostics that go beyond

lithography and etch• Hardware requirements

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Today: The BakeTemp Sensor Wafer

module

SiO2polyimid

Courtesy OnWafer Technologies

19994 Sensors4oC Accuracy2oC Precsion1oC ResolutionPrimary BatteriesNo MemoryFixed Behavior~15grams/ 5mm

19994 Sensors4oC Accuracy2oC Precsion1oC ResolutionPrimary BatteriesNo MemoryFixed Behavior~15grams/ 5mm

200564 Sensors0.05oC Accuracy0.02oC Precision0.001oC ResolutionSecondary BatteriesMemoryProgrammable/Adaptive Behavior~1.5grams/ 3mm

200564 Sensors0.05oC Accuracy0.02oC Precision0.001oC ResolutionSecondary BatteriesMemoryProgrammable/Adaptive Behavior~1.5grams/ 3mm

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Much more than you ever wanted to know about Post Exposure Bake

Overshoot

Cooling

Steady

Heating

Chill

200mm ArF90nm

130oC 60sec

Courtesy OnWafer Technologies

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Today: The PlasmaTemp Sensor Wafer

Demonstrated in up to 7,000W ChambersReusableClean and safe enough to be adopted by all the top tier fabs

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On-Wafer Plasma Monitoring200mm Poly Etching

Routine He Reduced He

pre-etchpre-etch

main etchmain etch

de-chuckde-chuckover etchover etch

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Cool chuck - 200mm Poly Etching

main etch

Temperature fluctuations during main etch

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Can see rotating magnetic field !

phase delay in temp fluctuationCan calculate B-field periodCan see rotation is clockwise

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What are the Killer Apps?• Temperature Monitoring has intuitive diagnostic

value for some users.• To expand use from Pilot to Production, we must

address different, routine needs.– Calibration– Acceptance– SPC/SQC– …

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PEB Evolved from a Single Zone to Multi-Zone Control System Why?

Multi-Zone Control

Single Zone Control

10 Years of Product

Evolution

Post Exposure Bake Track Equipment Complexity is Increasing

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PEB Hotplate Thermal Profile Optimization System

Baseline Thermal Profile

Condition

Offset Generator

Engine

Plate Type Specific Thermal Profile Modeling

Engine

Offset ValuesOptimized for Both Within-Plate and

Plate-to-Plate Thermal Profile

Uniformities

Output

Input

BakeTemp™& OnView™

AutoCal™

Input

OnWafer Technologies

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PEB Temp Control

16 plates, 120 ºC Target

2.700oC

Target = 120oC

0.175oC

Before After

OnWafer Technologies

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Spatial PEB/CD Distribution Correlation• Plotting both the bake plate temperature trajectory and R2

from temperature-CD correlation against bake time:

Max R2 during the transient heating period

Continued high R2

during steady state due to poor temperature control in single-zone plate design

• Plotting both the bake plate temperature trajectory and R2

from temperature-CD correlation against bake time:

Max R2 during the transient heating period

Continued high R2

during steady state due to poor temperature control in single-zone plate design

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PEB Hotplate Critical Dimension Optimization System

Baseline Thermal Profile

Condition

Offset Generator

Engine

Plate Type Specific Thermal Profile Modeling

Engine

Offset ValuesOptimized for Both Within-Plate and

Plate-to-Plate Critical Dimensions

Uniformities

Output

Input

BakeTemp™& OnView™

AutoCal™

Input

Input

Resist & Litho Cell Specific CD

Modeling Engine

AutoCD™

Baseline CD Profiles per Plate Customer

Provided

Input

OnWafer Technologies

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CDU Improvement

AcrossPlate Plate to

Plate

AutoCD

AutoCalPOR

0

0.5

1

1.5

2

2.5

3

3.5

AutoCDAutoCalPOR

OnWafer Technologies

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What we learned about Lithography• Weight / Form Factor

– module electronics, height, wafer flatness• Precision• Speed• Equipment Compatibility• Contamination

• COST OF OWNERSHIP– Lifetime– Ease of Use

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0

0

0

0

0

0

W 1 W 2 W 3 Avg W 1 W 2 W 3 Avg W 1 W 2 W 3 Avg

Plate A Plate B Plate C

beforeafter

Killer Lithography Applications• Monitor/Diagnose

– Multi-zone plates, complex exhaust systems, precise transport timing and placement. Plate C is still

stabilizing…

Plate response errors.

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What we learned from Plasma

• RF/heat tolerance• Arcing resistance• Shape/size• Contamination• Lifetime and reliability

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Killer Plasma Apps

• Temperature monitoring• Automatic Calibration/Diagnosis???• Equipment Compatibility

– Power Range– RF Tolerance– Chemistry– Contamination– Arcing Tolerance

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Outline

• Historical perspective• Hardware and software applications

Breakthroughs that have yet to be realized• Distributed control and diagnostics• Hardware requirements

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The limitations• Shape, Size and Weight

– Surface mount electronics – min ~2mm– Needs thin film wafer interconnect to achieve ~10µm

flatness– Integrated (in Si) electronics still prohibitive for a

consumable product• Lifetime

– Battery– Films (Plasma, CMP)

• Performance Envelope– Battery up to 200oC– Electronics up to 300oC

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Shape Size and Weight – Zero Footprint Wafer

Prototyping a zero-footprint optical metrology wafer for real-time monitoring of dielectric film deposition/etching, resist curing/development and metal etch end-pointing

Metrology wafer to monitor and map optical reflectance and interference of surface layers

Data Transmission

Photo-/RF Transmitter

Dielectric Layer as Optical Window

Battery Data Acquisition Unit

500µm

Si

Data Transmission

Photo-/RF Transmitter

Dielectric Layer as Optical Window

Battery Data Acquisition Unit

500µm

Si

Professor Nathan Cheung and Students

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Lifetime• Batteries

– Button cell secondary commercial solutions not available above 80oC.

– Primary solutions are a bit bulky but can go up to 140oC.– Lithium-based thin film technologies still immature, not focused

on high temp applications.– Temporary solution: screen commercial batteries, make them

field replaceable (160oC ceiling, 10s of hours of operation)– Long term solution: wait for high temperature cathode thin film

batteries (~200oC ceiling, 100s of hours)

• Films– Inherent Limitation in Etch – just make it thick and provide visible

“thread wear” marks.– Might be replaceable in CMP

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Performance Envelope• High Temperature Electronics

– Off the shelf electronics (surface mount or hybrid) ~ 180oC.

– Off the shelf electronics with custom clocking ~240oC.• High Temperature Batteries will probably not

happen above 200oC– Parasitic power sources / caps

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Expanding• Aerial Image• Chemical Mechanical Planarization• Wet processing• Ion Beam• PVD• CVD• RTP???• Automatic Deployment

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Aerial Image Sensor Concept• Data acquisition process:

High spatial frequency aerial image

Aperture mask transmission

Low spatial frequency detector signal

x

xPnm ∆+⋅+ )(

Aperture MaskPhotodetector

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x

xPnm ∆+⋅+ )(

Choosing Aperture Width & Thickness (cont.)

• Near-Field Simulation:

Illumination phase shift 0oIllumination phase shift 180o Aperture groups phase “moving” at max positionAperture groups phase “moving” at min position

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Outline

• Historical perspective• Hardware and software applications• Breakthroughs that have yet to be realized

Distributed control and diagnostics• Hardware requirements

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Pattern Transfer Control

Spin

HMDS

PA Bake

Exposure

PEB

Develop

PD Bake

Photoresist Removal

Electrical Testing

Electrical Testing

Poly Etch SystemEtch

Etch

Etch

TemperatureFeed-forward control

TemperatureFeed-forward control

Temperature, Plasma Voltage, Ion CurrentFF/FB Control, chuck diagnostics

Temperature, Plasma Voltage, Ion CurrentFF/FB Control, chuck diagnostics

Aerial ImageAerial Image

ScatterometryProfile InversionFeedback Control

ScatterometryProfile InversionFeedback Control

Thin FilmFB/FF Control

Thin FilmFB/FF Control

ScatterometryFeedback ControlScatterometry

Feedback ControlScatterometryFB/FF ControlScatterometryFB/FF Control

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Outline

• Historical perspective• Hardware and software applications• Breakthroughs that have yet to be realized• Distributed control and diagnostics

Hardware requirements

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Automatic Deployment

• Wireless Wafers must resemble “real” wafers as much as possible.

• In a 300mm factory, they must reside in FOUPsand move around via overhead transport.

• Deployment, data collection, analysis and resulting actions must be automated.

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Other Breakthroughs Needed• Batteries!

– Or, maybe, parasitic power sources– full-wafer gate cap is 2 orders of magnitude too small– RF pickup coils in plasma have almost unlimited

power• High temperature electronics!

– Silicon Carbide Devices about 250oC– Or, maybe thermal isolation for limited time

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Conclusion• Wireless Semiconductors Metrology has gone a

long way since we started in 1998– Three vendors– Officially Adopted by Fabs and Tool Makers– “Best Known Method” (BKM) in several applications

• Target processes remain in Lithography and Etch, but others are not too far behind

• Next generation of “zero footprint” metrology is likely to expand the application base even more