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A Simulation Framework For Lithography Process Monitor & Control

Using Scatterometry

SFR WorkshopMay 24, 2001

Junwei Bao, Costas SpanosBerkeley, CA

2001 GOAL: to demonstrate simulator tuning for full profile matching over a range of focus and exposure conditions by

9/30/2001.

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Motivation

• Lithography process parameter drift is one of the major sources of CD variation.

• Sub-0.25m patterning has greatly reduced the depth of focus. This makes the printed profile sensitive to the focus drift.

• Due to requirements of later process steps, a tight control of sidewall angle is needed, so it is not feasible to compensate the focus drift by just adjusting the exposure.

• Scatterometry has been proven to be a promising candidate as an in-situ, full-profile metrology tool for advanced process monitoring and control.

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The Lithography Control Framework Using Scatterometry

Lithographymodule

Feedbackcontroller

Control parameter Patterned wafer

Extracted control parameters

Noise

+/-

Measured spectrum

Measured profile

Adj

uste

d o

ffse

t

Ellipsometer

Scatterometrylibrary

Control param. extractor

Noise

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The Simulation Framework For Process Control Using Scatterometry

Prolith processsimulator

Prolith processsimulator

Control parameter Patterned wafer

Noise

+/-

Grating responsesimulator

Grating responsesimulator

Feedbackcontroller

Extracted control parameters

+/-

Measured spectrum

Measured profile

Adj

uste

d o

ffse

t

Scatterometrylibrary

Control param. extractor

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-300 -200 -100 0 100 200 3000

50

100

150

200

250

300

350

400

450

500original measured best matched

Structure, Profiles and Spectrum:Process Simulation and Scatter Predictions match well

Resist 505 nmARC 61 nm

480 nm 160 nm

200 300 400 500 600 700 800-2

-1.5

-1

-0.5

0

0.5

1TanPsi

measuredfitted

200 300 400 500 600 700 800-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1CosDel

measuredfitted

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Parameter Disturbance Emulating Process Drift

0 10 20 30 40 50 60 70 80 90 100-0.2

0

0.2

focu

s (u

m)

0 10 20 30 40 50 60 70 80 90 1000

2

4

expo

sure

(m

J/cm

2 )

0 10 20 30 40 50 60 70 80 90 100-2

0

2

PE

B T

emp

(deg

ree)

0 10 20 30 40 50 60 70 80 90 100-5

0

5

Res

ist

Thk

(nm

)

0 10 20 30 40 50 60 70 80 90 100-2

0

2

AR

C T

hk (

nm)

wafer patterning sequence number

1kaka1kdkd jjjjj First order integrated moving average disturbance model ( = 0.3)

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-0.16 -0.14 -0.12 -0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04-0.2

-0.15

-0.1

-0.05

0

input focus (um)

extr

acte

d fo

cus

(um

)

23.2 23.4 23.6 23.8 24 24.2 24.4 24.6 24.8 25 25.223

23.5

24

24.5

25

25.5

input exposure (mJ/cm2)

extr

acte

d ex

posu

re (

mJ/

cm2 )

Extracted vs. Input Focus and Exposure Settings: Full Profile Extraction detects process inputs

Standard deviation of detection error: 0.025 m (focus), 0.23 mJ/cm2 (exposure)

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No control CD only Full profile

Bottom CD (m) 8.9 4.5 3.4

Sidewall angle (degree)

0.35 0.23 0.14

0 10 20 30 40 50 60 70 80 90 100120

140

160

180

Bot

tom

CD

(nm

)

0 10 20 30 40 50 60 70 80 90 10087

87.5

88

88.5

89

side

wal

l ang

le (

degr

ee)

wafer patterning sequence number

full profile monitored

CD monitored no control

full profile monitored CD monitored

no control

CD and Sidewall Angle Variation

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Conclusions and Future WorkBoth focus and exposure drifts can be monitored with scatterometry.

CD and sidewall angle variations are reduced by feedback control of focus and exposure according to simulation.

Next Goals:

Study the effect of disturbance model and controller parameters on control results.

Study the case of multi-wafer delay between metrology and control.

Demonstrate lithography simulator tuning for full statistical profile matching over a range of conditions, by 9/30/2002.

Implement lithography controller that merges full profile in-line information with available metrology, by 9/30/2003.