TWG -- February 21, 2016ieuvi.org/TWG/Resist/2016/20160221Meeting/14_CNSE...2016/02/21 · SPIE TWG...

SPIE TWG 2-21-16 1

What Don’t We Know About

EUV Exposure Mechanisms? TWG -- February 21, 2016

Amrit Narasimhan,a Steven Grzeskowiak,a Liam Wisehart,a Adam Janover,a

Mark Neisser,b Leonidas E. Ocola,c Greg Denbeaux,a and Robert L. Brainarda

(a) CNSE, (b) SUNY Poly SEMATECH, (c) Argonne National Laboratories

SPIE TWG 2-21-16 2

What Don’t We Know About

EUV Exposure Mechanisms? TWG -- February 21, 2016

Amrit Narasimhan,a Steven Grzeskowiak,a Liam Wisehart,a Adam Janover,a

Mark Neisser,b Leonidas E. Ocola,c Greg Denbeaux,a and Robert L. Brainarda

(a) CNSE, (b) SUNY Poly SEMATECH, (c) Argonne National Laboratories

A Lot!

This Talk: Ask several questions

Goal: Share some thoughts on the answers

SPIE TWG 2-21-16 3

EUV

hn = 92 eV

e-

EUV

hn = 92 eV

e-

Will a Photoelectron fall into

another Photon’s Hole?

Major Questions:

(A) Will a Photoelectron Fall into another Photon’s Hole?

(B) How Many e- are Made?

(C) What are the Reactions of Ultra-Low Energy (RULE)

Electrons?

(D) How Far do e- Travel?

SPIE TWG 2-21-16 4

Experiments:

PAG X-Sections (Tues @ 8:40AM)

Fluorescence (Tues @ 9:40 AM)

(1) de Schepper Expt*

(2) Dielectric Breakdown (Here)

(3) Depth of Penetration (Here)

* de Schepper et al.

SPIE 942507 (2015)

Major Questions:



(C) What are the Reactions of Ultra-Low Energy (RULE)

Electrons?


SPIE TWG 2-21-16 5

= Core Electrons

= Valence Electrons

(3) Elastic Scattering:

e-

DE = 0

(1) Photoionization:

EUV hn

e-

DE = 10-12 eV

Binding Energy

e- e- (4) Plasmon

Generation:

DE ≈ 3-24 eV

A plasmon is a wave of bound

valence electrons in a solid

e- e-

e- (2) Ionization:

DE = 10-12 eV

Binding Energy

LESiS* (Low-energy Electron Scattering in Solids): Monte Carlo Model of Photons and Electrons

Follows Four Fundamental Reactions

*Torok PhotopolySciTech 611 (2014)

*Narasimhan JM3 043502 (2015)

SPIE TWG 2-21-16 6

Fundamental Reactions between e-, hn and Matter: Currently Not Part of the LESiS Model

DE ≈ 2-3 eV M M*

Internal Excitation

PAG is “Exposed” similar to photolysis.

e- + PAG PAG* + e- H+

(DE = 2-3 eV)

Electron Trapping Electron Trapped by PAG:

e- + PAG H+

(DE = 2-3 eV)

e- + Ph3S+ X- Ph3S

. X- H+

Hole-Initiated Chemistry (Kozawa Mechanism)

p+ + Polymer H+

See Narasimhan

Tues. 9:40

SPIE TWG 2-21-16 7

(A) Will a Photoelectron Fall into

another Photon’s Hole? EUV

hn = 92 eV

e-

EUV

hn = 92 eV

e-

In order to answer this question we must know:

1) The cross-section for electron/hole recombination (vs. e- energy)

2) The lifetimes of the electrons and holes

3) The arrival rates of photons (it is slower than you think).

Our current thinking is that this is very, very unlikely

SPIE TWG 2-21-16 8

(B) How Many Electrons Are Made?

LESiS: 1.8 ± 0.7 e- / Absorbed Photon

Secondary e-

Secondary e-

Input e-

(80 eV)

2 nm

2.5

nm

One Secondary is Made:

Two total electrons

*Torok PhotopolySciTech 611 (2014)

e1- e1

-

e2-

hn

SPIE TWG 2-21-16 9

(B) How Many Electrons Are Made? PROLITH: 4.03 ± 0.04 e- / Absorbed Photon

* de Schepper et al. SPIE 942507 (2015)

(1) De Schepper et al.* assert that all

electrons made by EUV photons can

be measured via an ammeter.

e-(1) = e-(2) = e-(total)

no reaction e- + hole

e- + PAG no reaction

And,

Resist

EUV hn e-(1)

Silicon

e-(2) A

Therefore,

Assumptions: • e-/p+ cross-section is very small

• e-/PAG cross-section is very small

• Thermal electrons injected from the

silicon can diffuse through the film

and neutralize the holes.

• CAN THIS HAPPEN?

SPIE TWG 2-21-16 10

(C) What are the Reactions of Ultra-Low

Energy (RULE) Electrons?

Classic e- pathlength vs. energy V

plot.

If electrons are slow enough, will

they bounce around forever?

“Universal” curve for electron

inelastic mean free path

Seah and Dench, 1979

Thermal

(~ 0.03 eV)

e-

Hole

p+

5 nm

Will Electrons Slow-Down

and Stop?

Or do the bounce around until

they find a trap or leave the film?

Dis

tan

ce

be

twe

en

Sc

att

eri

ng

SPIE TWG 2-21-16 11

1. A fine metal mesh is gently placed on a commercial EUV resist

(only a few points of contact).

2. DC voltage is applied across the resist between the mesh and the

back of the silicon wafer.

lP – Power Supply

lA – Pico-Ammeter

lR – 0.12 MΩ Resistor Substrate

Commercial Resist

Mesh

A

P

R

(2) Dielectric Break-Down Experiments: Can “thermal electrons” diffuse through an

insulating resist?

SPIE TWG 2-21-16 12

(2) Dielectric Break-Down Experiments

Breakdown at ~29V.

Behaves as a conductor post

breakdown.

Breakdown at ~33V.

Hysteresis indicates a temporary conductive

stage induced by dielectric breakdown.

After breakdown, Ohm’s Law behavior: iR = V

Same Sample

5-minute Delay

050

100150200250300350400

0 20 40 60

Cu

rren

t (µ

A)

Applied Voltage (V)

Forward Bias Only

050

100150200250300350400

0 20 40 60

Cu

rren

t (µ

A)

Applied Voltage (V)

Voltage Cycle

External

Resistance

External

Resistance

Sample +

Ext. R

Sample +

Ext. R

SPIE TWG 2-21-16 13

What is Happening on a Molecular Level

During Dielectric Breakdown?

Conduction

Band

Valence

Band

SPIE TWG 2-21-16 14

Thickness Loss was measured as a function of

e- energy and dose.


(3) Depth of Penetration Experiment

Bake and

Develop

Vary Dose

& Voltage

e- e- e-

Resist Resist

EUV

hn Thickness Loss

(Ellipsometry)

Depth of reactions

SPIE TWG 2-21-16 15

Thickness Loss of Open-Source Resist

(OS2)

0

10

20

30

40

50

60

0.01 0.1 1 10 100 1000

Th

ickn

ess L

oss (

nm

)

Dose (µC/cm2)

2000 eV 700 eV

250 eV

80 eV

15 wt.%

1.5 wt% TBAL

SPIE TWG 2-21-16 16

LESiS Model

Strategy: = Core Electrons

= Valence Electrons

(3) Elastic Scattering:

e-

DE = 0

(1) Photoionization:

EUV hn

e-

DE = 10-12 eV

Binding Energy

e- e- (4) Plasmon

Generation:

DE ≈ 3-24 eV

A plasmon is a wave of bound

valence electrons in a solid

e- e-

e- (2) Ionization:

DE = 10-12 eV

Binding Energy

Follow Location of

Energy-Loss Events

SPIE TWG 2-21-16 17

Energy Loss Events per e- vs. Resist

(OS2) Depth

15 wt.%

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 10 20 30 40 50 60

Num

ber

of E

vents

per

Ele

ctr

on

Depth in Resist (nm)

80 eV

250 eV

700 eV

2000 eV

Nu

mb

er

of

En

erg

y L

oss E

ven

ts

Per

Incid

en

t E

lectr

on

per

0.1

nm

SPIE TWG 2-21-16 18

0

0.2

0.4

0.6

0.8

1

1.2

0 10 20 30 40 50 60

Energ

y L

oss E

vents

per

Ele

ctr

on


8x

4x

2x

1x 0.5x

Thickness Loss Simulation (OS2, 700 eV)

Dose

Thic

kness L

oss

Thickness loss at 8x dose

Nu

mb

er

of

En

erg

y L

oss E

ven

ts

Per

Incid

en

t E

lectr

on

per

0.1

nm

SPIE TWG 2-21-16 19

Thickness Loss Simulation Results (OS2)

0

10

20

30

40

50

60

0.01 1 100 10000

Thic

kness L

oss (

nm

)

Dose (μC/cm2)

700 eV

LESiS

Experiment

0

10

20

30

40

50

60

0.01 0.1 1 10 100

Thic

kness L

oss (

nm

)

Dose (μC/cm2)

2000 eV LESiS

Experiment

Threshold set to match 700 eV

simulation and experimental data

SPIE TWG 2-21-16 20


0

10

20

30

40

50

60

0.01 1 100 10000T

hic

kness L

oss (

nm

)

Dose (μC/cm2)

80 eV

LESiS

Experiment

0

10

20

30

40

50

60

0.01 1 100 10000

Thic

kness L

oss (

nm

)

Dose (μC/cm2)

250 eV

LESiS

Experiment

Currently, LESiS does not adequately model Very Low-Energy Electrons.



SPIE TWG 2-21-16 21

Maybe these Energy Loss Events Don’t

Properly Model Chemical Reactions

Internal Excitation e- + PAG PAG* + e- H+

(DE = 2-3 eV)

Electron Trapping e- + PAG H+

(DE = 2-3 eV)

Hole-Initiated Chemistry p+ + Polymer H+

e- e-(4) Plasmon

Generation:

DE ≈ 3-24 eV

e-e-

e-(2) Ionization:

DE = 10-12 eV

Binding Energy

5 eV

Count when

Electrons

“Fall below 5 eV”

Energy-

Loss

Events

Ionization

Plasmon

(CSD) Continuous

Slowing-Down

Approximation

SPIE TWG 2-21-16 22

Energy Loss Events per e-

vs. Resist (OS2) Depth

Ionization + Plasmon

Ionization, Plasmon

& e- fall below 5 eV

700 eV

2000 eV

SPIE TWG 2-21-16 23

Energy Loss Events per e-

vs. Resist (OS2) Depth


Ionization, Plasmon


80 eV

250 eV

SPIE TWG 2-21-16 24

0

10

20

30

40

50

60

0.01 1 100 10000

Thic

kness L

oss (

nm

)

Dose (µC/cm2)

0

10

20

30

40

50

60

0.01 1 100 10000

Thic

kness L

oss (

nm

)

Dose (µC/cm2)




No

Transition

5 eV

Transition

Experiment Experiment

5 eV

Transition No

Transition

2000 eV 700 eV

SPIE TWG 2-21-16 25

0

10

20

30

40

50

60

0.01 1 100 10000

Thic

kness L

oss (

nm

)

Dose (µC/cm2)

0

10

20

30

40

50

60

0.01 1 100 10000

Thic

kness L

oss (

nm

)

Dose (µC/cm2)


A better model when 3 or 5 eV transitions are included.

No

Transition



3 eV

Transition

5 eV

Transition

No

Transition

Experiment 5 eV

Transition

3 eV

Transition

Experiment

250 eV 80 eV

SPIE TWG 2-21-16 26

Summary

Experiments:

PAG X-Sections (Tues @ 8:40AM)

Fluorescence (Tues @ 9:40 AM)

(1) de Schepper Expt*

(2) Dielectric Breakdown (Here)

(3) Depth of Penetration (Here)

Major Questions:



(C) What are the Reactions of Ultra-Low Energy (RULE) Electrons?


SPIE TWG 2-21-16 27

Acknowledgements

Partial Funding By:

SUNY Polytechnic Institute (CNSE)

Tanzid Sultan

Sean Wang

Alex Comerford

Argonne National Laboratories

This work was performed, in part, at the Center

for Nanoscale Materials, a U.S. Department of

Energy Office of Science User Facility under

Contract No. DE-AC02-06CH11357.

SPIE TWG 2-21-16 28

Appendix

SPIE TWG 2-21-16 29

Photo- and Secondary Electrons

Photoelectron energies

For 92ev EUV photons, average

photoelectron energy is 80.4 ± 3.5 eV.

Number of secondary electrons

For 92ev EUV photons, on average

1.8 ± 0.7 (primary + secondary) electrons are

generated per incident photon.

For 80 eV electrons, on average 0.65 ± 0.73

secondary electrons are generated.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

70 72 74 76 78 80 82 84

Fra

cti

on

of

Ion

izati

on

Even

ts

Photoelectron Energy (eV)

C 2p

O 2P

F 2P

I 5sH 1s

SPIE TWG 2-21-16 30

Electron-Hole Generation & Lifetime

ΔT

ime

Distance 0

1000X

Time (s)

10-4 10-5 10-6 10-7 10-8 10-9 10-10

Recombination time

in semiconductors

Expected Δt between

two absorption events

within 5 nm

Electrons produced in EUV

exposure are expected to migrate

up to 5 nm from the photon

absorption site.

If the electron and hole recombine

before another photon absorption

occurs nearby, the probability of

recombination an electron and a

hole produced elsewhere is zero.

It takes ~10-14

sec. for a thermal

electron to travel

5 nm to a fixed

hole using basic

mechanics

SPIE TWG 2-21-16 31

Model Comparisons LESiS:

• Bottom Up, based on published first

principle physics

• Attempts to catalog and describe all

physical processes

PROLITH:

• Top Down, starts with litho results.

• Designs model to take 1st results as input

and predict future results given changes to

parameters.

5 eV

SPIE TWG 2-21-16 32

de Schepper Experiment

* de Schepper et al. SPIE 942507 (2015)

SPIE TWG 2-21-16 33

Open-Source Photoresist: OS2

15 wt.% 1.5 wt% TBAL

For most of our work, we use an Open Source Chemically Amplified

Resist, Called OS2.*

In some cases, we replace the PAG with equal weight (15 wt%) of these

Photoacid Generators (PAGs):

*Higgins, Brainard et al.

JJAP 50, 036504, 2011

SPIE TWG 2-21-16 34

Maybe these Energy Loss Events Don’t

Properly Model Chemical Reactions

e- e- (4) Plasmon

Generation:

DE ≈ 3-24 eV

e- e-

e- (2) Ionization:

DE = 10-12 eV

Binding Energy

Internal Excitation

e- + PAG PAG* + e- H+

(DE = 2-3 eV)

Electron Trapping Electron Trapped by PAG:

e- + PAG H+

(DE = 2-3 eV)

Hole-Initiated Chemistry (Kozawa Mechanism)

p+ + Polymer H+

SPIE TWG 2-21-16 35

I. LESiS (Low-energy Electron Scattering in Solids)

Monte Carlo Model of Photons and Electrons Interactions with Matter

LESiS is a fully stochastic simulation

program designed originally by Leo

Ocola. • Cross-sections are calculated in real time.

• Monte Carlo is implemented in real time.

LESiS can simulate exposures by

electrons or photons.

LESiS outputs data for each scattering

event • Energy

• Trajectory

• Identity, location, and orbital of the involved

atom

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1965 1975 1985 1995 2005 2015

Energ

y (

eV

)

Year

Green,

Murata, NBS

Special

Publications

460

Kyser,

Murata

Liljequist

Mack,

Ocola

(LESiS)

Murata,

Kotera,

Ho

Lithography

Motivated

SPIE TWG 2-21-16 36

Electron Resist Interaction Chamber (ERIC)

Mass

Spectrometer Electron

Gun

Expose EUV resist from 80-2000 eV across a wide range of doses and collect

real-time outgassing information using mass spectrometry

SPIE TWG 2-21-16 37

0

0.05

0.1

0.15

0.2

0.25

0 20 40 60 80 100 120Nu

mb

er

of E

ne

rgy L

oss E

ve

nts

pe

r In

cid

en

t E

lectr

on

pe

r 0

.1 n

m



(OS2) Depth


Ionization, Plasmon


700 eV

2000 eV Figure is still an excel plot

SPIE TWG 2-21-16 38


(OS2) Depth

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 5 10 15 20 25

Num

ber

of E

nerg

y L

oss E

vents

p

er

Incid

en

t E

lectr

on

pe

r 0

.1 n

m



Ionization, Plasmon


80 eV

250 eV

Figure is still an excel plot

TWG -- February 21, 2016ieuvi.org/TWG/Resist/2016/20160221Meeting/14_CNSE...2016/02/21 · SPIE TWG...

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