Secondary RF Plasma System for Mitigation of EUV Source Debris and Advanced Fuels

Diagnostics

Dual In-Situ Crystal• Filters Noise• Extremely Sensetive

Tdepositiojn = KZ-ratio ∆Fxtal2-xtal1 / ρdebris

KZ-ratio = NnaturalF ρquartz / Fxtal12

ρquartz = 2.65 g/cm3

ρdebris = 6.06 g/cm3

Nnatural = 166 kHzFxtal1 = 5.97 MHz

Tdepositiojn = KZ-ratio ∆Fxtal2-xtal1 / ρdebris

KZ-ratio = NnaturalF ρquartz / Fxtal12

ρquartz = 2.65 g/cm3

ρdebris = 6.06 g/cm3

Nnatural = 166 kHzFxtal1 = 5.97 MHz

Dual QCM

QCM Crystals

Debris on Surface Clean Surface

QCM Crystals

Debris on Surface Clean SurfaceDebris on Surface Clean Surface

Faraday Cup

Segregator

• Collects charged particles

• L/D ratio prevents secondary electron emission

• Deflects fast ions away from QCM aperture

• Deflects up to 10 keV Ar

Michael A. Jaworski, Matthew R. Hendricks, Erik L. Antonsen, Brian E. Jurczyk, David N. Ruzic, 1Robert BristolDepartment of Nuclear, Plasma and Radiological Engineering, Plasma Material Interaction Group, University of Illinois at Urbana. Correspondence to druzic@uiuc.edu

3rd International EUVL Symposium, Miyazaki, Japan November 2004

Bulk Plasma at VP

GEA at Ground Potential

Accelerated Ions

Bulk Plasma at VP

GEA at Ground Potential

Accelerated Ions

Collector Grid Current Signal

0

2

4

6

8

10

12

14

-2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00Time [microseconds]

Cur

rent

[mA

]

Current [mA]

Why Not Use a Positive Pulse Voltage?• Anode pulse forces plasma potential up.• Sheath wave propagates new potential

throughout bulk plasma quickly.• Ions already near sheath accelerated even

more into surfaces.• Anomalous current rise measured on

collector grid due to sheath ions.•Large amounts of sputtering due to energetic sheath ions

Bulk Plasma at VP

GEA at Ground Potential

Accelerated Ions

Bulk Plasma at VP

GEA at Ground Potential

Accelerated Ions

Collector Grid Current Signal

0

2

4

6

8

10

12

14

-2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00Time [microseconds]

Cur

rent

[mA

]

Current [mA]

Why Not Use a Positive Pulse Voltage?• Anode pulse forces plasma potential up.• Sheath wave propagates new potential

throughout bulk plasma quickly.• Ions already near sheath accelerated even

more into surfaces.• Anomalous current rise measured on

collector grid due to sheath ions.

• Anode pulse forces plasma potential up.• Sheath wave propagates new potential

throughout bulk plasma quickly.• Ions already near sheath accelerated even

more into surfaces.• Anomalous current rise measured on

collector grid due to sheath ions.•Large amounts of sputtering due to energetic sheath ions

IV Traces of DPF Discharge

• I: Potential Applied to Anode

• II: Breakdown• III: Rundown Initiates• IVa,b: Pinches

I-V Trace No Pre-Ionization

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5Time (s)

Volta

ge (k

V)

-2

-1

0

1

2

3

4

5

6

7

8

Cur

rent

(kA

)

VoltageCurrent

I

IIIII

IVa

I-V Trace No Pre-Ionization

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5Time (s)

Volta

ge (k

V)

-2

-1

0

1

2

3

4

5

6

7

8

Cur

rent

(kA

)

VoltageCurrent

I

IIIIIIIIII

IVaIVaWhy do we go to zero without pre-ionization?•Surface flashover arcs waste much of the energy. No current can be maintained.

•After many arcs oscillations, enough current builds up to initiate rundown. Voltage has dropped considerably.

I-V Trace With Pre-Ionization

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Time (s)

Volta

ge (k

V)

-4.2

-3.6

-3.0

-2.4

-1.8

-1.2

-0.6

0.0

0.6

1.2

Cur

rent

(kA

)

CurrentVoltage

II IIII IIIIIIIVaIVa

IVbIVb

Dense Plasma Focus Device

• Electrode cross-sectional view

•Pinch visible at electrode tip

• Pulsing system utilizes a fast hydrogen Thyratronswitch:

• 690 nanosecond current rise time

• L = 89 nH• C=3.33 µF• Repeatable DPF firing

at 0-40 Hz• Well defined pinches

by visual inspection

Picture yellowed by Kapton film

Illinois Debris mitigation for EUV Applications Laboratory (IDEAL)

• IDEAL facility is capable of collecting and analyzing data relevant to EUVL sources•300Vs Varian Turbo Pump•Ebara High-Throughput Dry Roughing Pump•ENI A-500 Tunable RF Amplifier•RF Tube amplifier•DPF Charging Supply (12kW max)•DPF Pulsing System (50 Hz)•Adaptive Pressure Control System•Tetramethyl Tin Bubbler System

• Components•Differential pressure gas manifold scheme•3 turn RF antenna for secondary plasma (1-500W @ 10-35 MHz)•Tin injection and waste retention system

Dense Plasma Focus

RF CoilsFaraday Shield

Faraday Cup

Langmuir Probe

QCM Segregator Tool

Fuel Entrance

Secondary Plasma Source

Oscillator0.1-50 MHz

RF Amplifier0-500W

0.3 – 35 MHz

RF Tube Amplifier

• Three-turn immersed antenna

• Faraday shielded to reduce plasma potential

• Plasma provides debris mitigation and pre-ionization

Plasma ConditionsPlasma Parameters at 300 WTe=3.9 eV, ne=5.9X1010 cm-3

Vp=95V, Vf=80

Faraday Shielded RF Antenna

RF Compensated Langmuir Probe

Mirror for visual inspection of pinch

•Raw data is analyzed to produce the measured slopes at right•Deposition items and erosion items are listed in the table elements and are modified by the segregator or foil trap or both•A system of equations is built by balancing deposition against erosion and the QCM measurement

Ionization Fraction Measurement

.309γ αBi δASnXXX

.516γ β αBj δASnXXXX

.565β αBδASnXXX

.359αBδASnXX

.606γ BASnXLOWX

.825γ β BASnXXLOWX

.744β BASnXLOWX

.373BASnLOWX

Measurement (+/- 0.05)

ErosionTerms

Deposition Terms

GasSegregatorFoilTrap

RFPulse

.309γ αBi δASnXXX

.516γ β αBj δASnXXXX

.565β αBδASnXXX

.359αBδASnXX

.606γ BASnXLOWX

.825γ β BASnXXLOWX

.744β BASnXLOWX

.373BASnLOWX

Measurement (+/- 0.05)

ErosionTerms

Deposition Terms

GasSegregatorFoilTrap

RFPulse

Data Table for Analysis

Index of Symbols

Dense Plasma Focus

RF Coils

Faraday Shield

QCM

β

Fuel Entrance

γ

Erosive

Diffusive

Dense Plasma Focus

RF Coils

Faraday Shield

QCMQCM

β

Fuel Entrance

γ

Erosive

Diffusive

Problem Statement•Different components of debris must be separated

•Intense magnetic field in segregator deflects much of the erosive fast ions from the pinch region

•Foil trap also attenuates some fast ions

•Used in conjunction, a table of variables can be built to study the effect of the RF plasma

The Process

Screening factor of RF plasma (due to physical presence of Foil Trap alone)

i

Screening Factor of RF plasma (due to physical presence of Foil Trap and Segregator)

j

Attenuation of fast ions due to passing through RF plasmaα

Screening factor of RF plasma (due to physical boundaries, but not Foil Trap)

δ

Foil Trap attenuation of fast ionsγ

Segregator attenuation of fast ionsβ

Fast erosive ions from DPFB

Sputtered electrode material and condensable fuel debrisA

Screening factor of RF plasma (due to physical presence of Foil Trap alone)

i

Screening Factor of RF plasma (due to physical presence of Foil Trap and Segregator)

j

Attenuation of fast ions due to passing through RF plasmaα

Screening factor of RF plasma (due to physical boundaries, but not Foil Trap)

δ

Foil Trap attenuation of fast ionsγ

Segregator attenuation of fast ionsβ

Fast erosive ions from DPFB

Sputtered electrode material and condensable fuel debrisA

. . : 0.825Deposition Erosion Measuremente g A Bγβ

− =− =

20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

3570.53571.03571.53572.03572.53573.03573.53574.03574.53575.03575.53576.03576.53577.03577.53578.0

QCM Raw Data HIgh Power RF

Foil Trap In & Seg Off

Foil Trap In & Seg On

Foil trap Out & Seg On

Foil Trap Out & Seg Off

Cry

stal

Fre

quen

cy D

iffer

ence

(H

z)

Time (minutes)

(1 ) .371(1 )(1 )

B MB N

B O

βγγβ

− = =− =− =

The above equations can be rearranged into:

βγ

γβ

γβ

=−−

−=−

=−−

)1(1

)1(1

)1()1(

NM

NM

NM

The resulting set of equations can be reduced by linearly combining terms to obtain for the first four equations:

12 14 16 18 20 22 24 26

3552

3554

3556

3558

3560

3562

Foil Trap In,Seg Off

Foil TrapIn,Seg OnFoil Trap

Out,Seg On

Foil Trap Out,Seg Off

Cry

stal

Fre

quen

cy D

iffer

ence

(Hz)

Time (minutes)

QCM RAW DATA MINIMUM POWER RF

12 14 16 18 20 22 24 26

3552

3554

3556

3558

3560

3562

Foil Trap In,Seg Off

Foil TrapIn,Seg OnFoil Trap

Out,Seg On

Foil Trap Out,Seg Off

Cry

stal

Fre

quen

cy D

iffer

ence

(Hz)

Time (minutes)

QCM RAW DATA MINIMUM POWER RF

•High pressure discharge

•Large deposition

•Quick coating of witness plate sample

Initial Tetramethyltin Operation in July

Latest Tetramethyltin Operation•Stable TMSnoperation achieved•QCM measurements indicate additional fuel deposition

•High pressure discharge

•Large deposition

•Quick coating of witness plate sample

Initial Tetramethyltin Operation in July

Latest Tetramethyltin Operation•Stable TMSnoperation achieved•QCM measurements indicate additional fuel deposition

Faraday Cup MeasurementFaraday Cup Signal

Time of Flight Analysis ofPinch Energy Distribution

-50

0

50

100

150

200

250

300

350

400

-1 0 1 2 3 4 5 6 7

Time [microseconds]Fa

rada

y C

up S

igna

l [m

V]

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

Elec

trod

e Vo

ltage

[kV]

Faraday Cup SignalElectrode Voltage

t = 0

E = 4380 eV

E = 930 eV

trundown=350ns

• Distance from Pinch to Faraday Cup = 40 cm

• Large Positive Signal (2-2.5 µs) Corresponds to Plasma Pulsed Positive

• Rundown time corresponds to a sheath velocity that is 4390 eV

• 200 mV peak signal indicates flux of 3e16 ions/cm2-s assuming singly ionized particles

Tetramethyltin Sn(CH3)4Operation

Acknowledgements•INTEL Corporation for funding this research under contract SRA159-03.•Cymer Inc. and Xtreme Technologies GmbH for collaborative discussions.

Which can then be further simplified, allowing for the value of γ to be found as:

2

1 4 1

2

1M O M ON N N N

MN

M ON N

γ

⎛ ⎞ ⎛ ⎞− + ± − −⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

=

⎛ ⎞− +⎜ ⎟⎝ ⎠

After obtaining γ, it is a simple matter to return to the first set of equations and obtain a solution for all of the variables in the system.

Results and ConclusionError

.734i

.861j

.555α

.716δ

.590γ

.347β

.568B

.941A

ResultsVariable Error

.734i

.861j

.555α

.716δ

.590γ

.347β

.568B

.941A

ResultsVariableIDEAL has shown the ability to mitigate debris using a secondary RF discharge. A large amount of sputtered material from both the electrode and the fuel itself is diverted away from the QCM by the presence of a plasma. We also note the ability of a strong magnetic field to divert erosive ions. Used in combination, the effect is multiplied.

A higher density plasma is need. Our next experiments will increase the power of the plasma, while maintaining a low plasma potential to minimize coil sputtering with the Faraday shield. An improved foil trap will lead to more realistic simulations of commercial EUV DPP sources.