Lecture 20 on-Wafer Sensors

7/30/2019 Lecture 20 on-Wafer Sensors

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Lecture 20: On-Wafer Sensors

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In-chamber and on-wafer sensors

A Paradigm Shift


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Overview

Exact chamber environment control is relatively new

Various sensors (pressure, gas flow, gas composition,temperature) are needed to accomplish it.

An interesting transition to on-wafer sensors holdsmuch promise...


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Thermocouples

operating principlePeltier-Seebeck effect, up to 3000oC

Tgradient along wires of different materials develop different emf

emf measures junction T

platinum rhodium alloy, or silicon based

sensitivity 100-200V /oK

problems

big problems with shield designradiative effects

low signal -- need amplifiers or use thermopile

invasive

gas Tmeasurement is very hard, especially < 10-4 torr

comments

inexpensive, low drift low bandwidth

accuracy ~+/-5oCat 800oC where do you want to measure T?


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Acoustic Wave sensors

operating principle

acoustic wave is transmitted through body

surface and internal waves propagate through body atTdependent speed

interference with source gives beats

beat frequency determines T issues

implementation difficulty

invasive calibration


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Pyrometry

operating principle

hot objects radiate

radiation is wavelength dependent

radiation model for black bodies (Planck's Law)

in microns, Tin oK, R for non-black bodies need to account for emissivity

issues

surface properties affect radiation

multiple internal reflections

emissivity is wavelength and geometry dependent

can change during processing

calibrations via thermocouples, difficult

)1(

37418/143885

=T

e

R


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Pressure Sensors

direct gauges

displacement of a solid or liquid surface

capacitance manometer, McLeod pressure transducer

indirect gauges

measurement of a gas related property

momentum transfer, charge generation

huge range of available sensors cost

sensitivity

range


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Capacitance manometer

basic idea

pressure differential causes

displacement of diaphragm

sense capacitance change

between diaphragm and

fixed electrode

resolution 10

-2

%at 2 hertz and 10-3 torr


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Gas flow meters

differential pressure meters

thermal mass flow meters

mass flow = K/ (T1 - T2)

Kdepends on specific heat of gas etc. must be calibrated for different gases

accuracy ~ 1 sccm at flows of 40 sccm

low bandwidth because of thermal inertia


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Mass Spectrometers

two types

flux analyzers : sample gas through aperture

partial pressure sensors : analysis in exhaust stack

issues

recombination in mass spec tube changes

indistinguishable species : (ex: CO, N2 and Si havesame amu (28))

pressure measurements are removed from

processing chamber


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RGA

basic ideaspecial kind of mass spectrometer

measures gas compositions

works at low vacuum < 10-5 torr

ion beam is produced from gas sample by e-bombardment

beam is collimated by electric fields

q/mratio of ions determines bending in Bfield

detection of ions via a Faraday cup

issues

quadrupole (magnetless design)

very noisy !!good for diagnostics

can withstand 500 oC

can also be used at higher pressures with differential pumps

mass range 50 amu, resolution 2 amu,


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How about placing sensors on the wafer???

Sensarray products


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Calibration is an issue...


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Long Term Reliability also an Issue...


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On-Wafer Etch Rate by Resonant Structure

IEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING, VOL. 11, NO. 2, MAY 1998A Novel In SituMonitoring Technique for Reactive Ion Etching Using a Surface Micromachined Sensor

Michael D. Baker, Frances R. Williams, Student Member, IEEE, and Gary S. May, Senior Member, IEEE


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Remote reading of resonant sensor


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Noise is the biggest problem...

On the bench... In the chamber...

When plasma is on...


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But it works! (almost)

Innovative

noisy

intrusive

maycontaminate...


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Our Vision

In-situsensor array, with integrated power and telemetry

Applications:

process control, calibration,

diagnostics & monitoring,

process design


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Issues

Sensor arrays

inexpensive, modular

environmentally isolated

transparent to wafer handling robotics

on-board power & communications

Operating mode

no equipment modifications !!

Smart dummy wafer for in-situ metrology


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Test Case: Etch Rate

Onboard etch-rate sensor for plasma etch

many sensor points on a wafer

accurate film thickness measurement

real-time data available

etch-friendly materials

wired power and communications (for now)


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Transduction Scheme - Etch Rate

Van der Pauw structure:

=V

It

2ln


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Current Design

Integrated Sensor Wafer Test Design

57 etch-rate sensors on a 4 wafer

Full-wafer addressing of each sensor from a single die Redundant interconnect to enhance yield

Four styles of sensor, selectable from a single die

On-board current-sourcing Wired power and communications (at first)

Expandable to allow wireless power and communication


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Experimental Procedure

Bond wires to wafer

solder wires to strip header

glue header to wafer edge

wire bond from header to wafers bond pads

Verify operation on bench Place wafer in XeF2 Chamber

Measure film-thickness / etch-rate in real time

Calibrate using Nanospec thickness measurements


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Pictures


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Results

8 sensors (in a row) wired together in series

Everything works perfectly! In-SituXeF2 test performed

XeF2 etch rate much too fast(~0.2m/sec)

Sensor structure only 0.45 m thick, gone in 2 sec Sensors wired in series so when one etches through,

all measurements stop

Data collected during etch, but no calibrationavailable


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Data - Etch #3

0 1 2 3 4 5 6 7 8 9 1 00

1000

2000

3000

4000

5000

Po lys i li con Th ick ness vs . T ime fo r Ex per im ent #3

T ime (sec )

MeasuredThickness(A)

0 1 2 3 4 5 6 7 8 9 1 00

50 0

1000

1500

2000

Po lys i li con E tch -Rate vs . T ime fo r Ex per im ent #3

T ime (sec )

FilteredEtch-Rate(A/sec)


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How about completely wireless???

S


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Smart dummy developed in 1998

Developed and tested at the UC BerkeleyMicrofabrication Laboratory.

4 sensors, wafer covered with layer of epoxy LED used for real-time, one-way transmission

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First Test results in plasma, 1999

13.56MHz, 100W, 0.76 Torr, O2

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An Update on OnWafer Sensors

OnWafer technologies Inc, a Berkeley startup,was founded in 2000.

Today OnWafer products are in use in all of themajor fabs around the world, and by all themajor tool makers (LAM, Applied, TEL, Nikon).

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Basic OnWafer System

IR DongleIR Dongle

Base StationBase Station

SensorWaferSensorWafer

ShipperShipper

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feedback

process control

processing

equipment

data

OnWafer

base station

The Approach

wafers to be processed

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42 sensors/wafer, 1Hz

0.5 C accuracy

Rechargeable.

Functional up to 140 C, several kW RF

Suitable for oxide/poly plasma etch

Non-contaminating, cleanable and reusable

PlasmaTemp SensorWafer

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E l P M it i


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Lecture 20: On-Wafer Sensors 36

Example - Process Monitoringof 200mm Poly Etching

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C l h k 200


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Cool chuck - 200mmPoly 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 period

Can see rotation is clockwise

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Example - Gas flow trouble in TEL DRM Etcher

before data is hotter, further, the pre-

etch step is significantly less uniform

before data is hotter, further, the pre-

etch step is significantly less uniform

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Example Comparison between 8 PEB plates on a


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Example - Comparison between 8 PEB plates on a193nm wafer track (+/- 0.1C accuracy)

11 12 13 14 21 22 23 24

Best!

Worst!

Data collection in two 10-minute cassette-to-cassette missionsData collection in two 10-minute cassette-to-cassette missions

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On-Wafer PEB / CD Analysis

P6P6P5P5P4P4P3P3P2P2P1P1

Six TEL ACT 8 plates used for 90nm CD lines (193nm Lithography)Six TEL ACT 8 plates used for 90nm CD lines (193nm Lithography)

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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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PEB Evolved from a Single Zone to Multi-Zone Control SystemWhy?

Multi-ZoneControl

Single ZoneControl

10 Years ofProduct

Evolution

Post Exposure Bake Track Equipment

Complexity is Increasing

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PEB Hotplate Thermal Profile Optimization System

Baseline

Thermal ProfileCondition

Offset

GeneratorEngine

Plate TypeSpecific Thermal

Profile Modeling

Engine

Offset Values

Optimized for BothWithin-Plate and

Plate-to-Plate

Thermal ProfileUniformities

Output

Input

BakeTemp& OnView

AutoCal

Input


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PEB T m C t l


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PEB Temp Control

16 plates, 120 C Target

2.700oC

Target = 120oC

0.175oC

Before After


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S ti l PEB/CD Di t ib ti C l ti


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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 thetransient heating period

Continued high R2

during steady state dueto 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 thetransient heating period

Continued high R2

during steady state dueto poor temperature

control in single-zone

plate design

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PEB Hotplate Critical Dimension Optimization

System

Baseline

Thermal ProfileCondition

Offset

GeneratorEngine

Plate Type

Specific ThermalProfile Modeling

Engine

Offset Values

Optimizedfor Both

Within-Plate andPlate-to-Plate

Critical DimensionsUniformities

Output

Input

BakeTemp

& OnView

AutoCal

Input

Inpu

t

Resist & Litho CellSpecific CD

Modeling Engine

AutoCD

BaselineCD Profilesper Plate Customer

Provided

Input


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CDU Improvement


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CDU Improvement

AcrossPlate Plate to

Plate

AutoCD

AutoCal

POR

0

0.5

1

1.5

2

2.5

3

3.5

AutoCD

AutoCal

POR


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The New Problem


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The New Problem

How can we improve the across-wafer CDU?How much can we improve CDU?

Poor Across-WaferCD Uniformity

Processing Tool

EtchEtch

Wafer

LithoLitho

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Supervisory Control with Wireless Metrology


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Supervisory Control with Wireless Metrology

Compensate for systematic spatial non-uniformities acrossthe litho-etch sequence using all available control authority:

Exposure step: die to die dose

PEB step: temperature of multi-zone bake plate

Etch: backside pressure of dual-zone He chuck

Exposure PEB /Develop

Etch

Wafer-level

CD MetrologyOptimizer

Scatterometry/CDSEM

dose temperature He pressure

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Next Step: Zero-Footprint Metrology Wafer

Prototyping a zero-footprint metrology wafer with opticaldetection unit and encapsulated power source.

Data Transmission

Photo-/RFTransmitter

Data Processing,Storage Unit

Dielectric Layer

Si

BatteryData Acquisition Unit

500m

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Self-contained wireless

transmitter

+ -Power

+ -

Power Management& RF Transmission Unit

Measurement Units

Integrated excitation/detection Unit

Power UnitThin film Battery

Proposed Architecture

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3 x 3 Pixels Optical Metrology Prototype


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3 x 3 Pixels Optical Metrology Prototype

Bottom Wafer with LEDPhotodetector integrated

Top Wafer

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Feasibility Test: Thickness Measurement

LED

PD Si

Packaging Substrate

Glass Slide

Test Coating

Filter

5mm

Green LED

Blue LED

1500 1600 1700 1800 1900 2000 2100 2200-16

-14

-12

-10

-8

-6

-4

-2

ReflectionIntensity(a.u.)

PR Thickness (nm)

Excitation=525nm

TheoreticalCurve

1500 1600 1700 1800 1900 2000 2100 2200-16

-14

-12

-10

-8

-6

-4

-2

ReflectionIntensity(a.u.)

PR Thickness (nm)

Excitation=525nm

TheoreticalCurve

Shipley S1818 PR

on Glass Slide

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Wireless Aerial Image Metrology

Mask

light

Image system

Wafer

NAPartial coherenceIllumination aberrationsDefocusmagnification

Aerial image

Latent image

Resist image

Mask image

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An Integrated Aerial Image Sensor

How can a m detectorretrieve nanometer-scale resolution of theaerial image?

How can a m detectorretrieve nanometer-scale resolution of theaerial image?

Dark contact mask forms a moving aperture tocapture incident electromagnetic field.

Poly-siliconmask

Substrate

Photo-detector

Maskaperture

1 2 3 1 2 3

p-Si

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Moir Patterns for Spatial Frequency Shift


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Moir Patterns for Spatial Frequency Shift

Patterns Overlap Pattern rotates 4o Pattern rotates 8o Pattern rotates 16o

Narrow

CD

Wid

eCD

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Aperture pattern shift testing

Image pattern

Detect pattern

4.4

2.2

2

4.4

d

Detector mask layout design

Mask layout

-40 -20 0 20 40 60 80 100 120 140 160

35000

40000

45000

50000

55000

60000

-20 0 20 40 60 80 100 120 140 160

60000

70000

80000

90000

100000

110000

120000

image pattern

intensity

x(pixel)

Measurement result

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Near-Field Optical Simulation


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p

Intensity at the center of the simulation domain

mask

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Present Status of Active CD Control


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Spin

HMDS

PABake

Exposure

PEB

Develop

PDBake

PhotoresistRemoval

ELMELM

Poly Etch

System

ADIADI AEIAEI

Etch

Etch

Etch

Present Status of Active CD Control

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On-wafer and in-line metrology in pattern transfer


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O a e a d e et o ogy patte t a s e

Spin

HMDS

PABake

Exposure

PEB

Develop

PDBake

PhotoresistRemoval

ELMELM

Poly Etch

SystemEtch

Etch

Etch

T (t, x, y)T (t, x, y)

T (t, x, y)V (t, x, y)E (t, x, y)

T (t, x, y)V (t, x, y)E (t, x, y)

I (x, y)I (x, y)

OCDOCD

Thin FilmThin Film

OCDOCD OCDOCD

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CDU control hasto incorporate many strategies


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p y g

Spin

HMDS

PABake

Exposure

PEB

Develop

PDBake

PhotoresistRemoval

ELMELM

Poly Etch

SystemEtch

Etch

Etch

T (t, x, y)

FF control

T (t, x, y)

FF control

T (t, x, y)V (t, x, y)E (t, x, y)FF/FB Control, chuck diagnostics

T (t, x, y)V (t, x, y)E (t, x, y)FF/FB Control, chuck diagnostics

I (x, y)Optimal Pattern Design

I (x, y)Optimal Pattern Design

OCDProfile Inversion

FB Control

OCDProfile Inversion

FB Control

Thin Film

FB/FF Control

Thin FilmFB/FF Control

OCDFB Control

OCDFB Control

OCDFB/FF Control

OCDFB/FF Control

Documents

Lecture 20 on-Wafer Sensors