DARPA Advanced Lithography Review Feb 2004 v8a

February 5, 2004© Copyright 2003 Cymer, Inc. DARPA Advanced Lithography Program Review, Las Vegas, NV

Progress on the Development of a Light Source for EUV Lithography.

I.V. Fomenkov, S.T. Melnychuk, O.V. Khodykin, N.R. Böwering, J.R. Hoffman, I.R. Oliver, C.L Rettig, R.M. Ness.

This work was partially funded by DARPA contract N66001-03-C-8017

2February 5, 2004© Copyright 2003 Cymer, Inc. DARPA Advanced Lithography Program Review, Las Vegas, NV

Presentation Outline

EUV Source Requirements Overview of Cymer’s EUV source and development:

DPF Light Source Components: Electrodes, Pulsed Power, Debris Shield, Collector.

DPF Physics/Experimental Results EUV conversion efficiency, plasma modeling High repetition rate operation, pulsed power, gas dynamics Thermal engineering, power loads, modeling Source contamination Source Imaging, Spectroscopy

Alternative Sources Elements: Sn, Li Summary


Central wavelength 13.5 nmEUV Power (2% bandwidth) 80-120 WRepetition frequency >6000 HzIntegrated energy stability (3σ, 50 pulses) +/- 0.3%Etendue of source output* 1-3.3 mm2strMax. solid angle input to illuminator* 0.03-0.2 strSource cleanliness >30,000 hoursSpectral purity* duv/uv, 130-400nm infra-red, >800nm

TBD – 7%TBD

Industry Source Requirements(presented at October 2002 EUV Source Workshop)

* Not agreed among ASML,Nikon and Canon


Cymer DPF Source Technology Roadmap 13.5Central Wavelength (nm)

10B1B100M50M10M10M2M1M1MCritical comp. lifetime (pulses)

power, lifetime

power, lifetime

power, lifetime

thermal, debris

thermal, debris

thermal, debris

thermal, debris

thermal, debris

thermal, debris

Key risk areas

isotropicPulse-pulse pointing stab. (3σ)

isotropicPulse-pulse angular stab. (3σ)

4% 0.3%

6% 0.5%

10% 0.7%

15% 1%

20%2%

21%2%

27%2%

27%2%

27%2%

Pulse-pulse intensity stab. (3σ)Dose stability

506080100150150>250>250>250Pulse-pulse spatial stab (µm 3σ)

100B50B10B1B>50M>50M>50M>5M>0.5MSource-facing condenser life (pulses to 10% reflectance loss)

60403020106210.5Steady state power dissipation (kW)

643210.500.200.10.05Demo’d contin. rep. rate (kHz)

1088642 211Demo’d max rep. rate (kHz)

775333322Etendue (mm2•sr)

0.4 x 2.50.4 x 2.50.4 x 2.50.25 x 1.70.25 x 1.7Source emission volume,diam. x length (mm x mm)

2π available (1.8 used with present collector design, π the future )Available collection angle (sr)

100300

50200

27108

880

440

120

In-band power, 2%BW, 2π sr, (W) • Average, continuous • In-burst maximum (@ rep rate)

Mar-07Mar-06Mar-05Mar-04Mar-03Oct-02Mar-02Oct-01Mar-01Oct-00Metrics13.513.5 13.5 13.5 13.513.5 13.5 13.5 13.5

0.4 x 2.5 0.4 x 2.50.35 x 2.00.25 x 1.7

180480

240480

380630


EUV Light Source System Development Areas

We are pursuing a concurrent R&D program and product development program designed to meet the needs of future EUV lithography systems.

Key areas of investigation: Power scaling and thermal engineering Lifetime and debris mitigation High repetition rate operation, gas dynamics, pre-ionization system Plasma optimization, electrodes geometries Pulsed Power development Metrology and EUV optics Alternative source elements


DPF EUV Light Source System

EUV Source Plasma Chamber

Debris Shield

Intermediate Focus

Collector & Vacuum Vessel

Cymer defines an “EUV light source system” as everything from the source plasma chamber to the intermediate focus

Spectral Purity Filter

EUV Radiation


EUV Source System Concept (5 W)

•Base Concept for Alpha Source

•Test bed for System Development and performance evaluations

•Selects best technology from existing prototypes

•Intial proto based on Cymer 7000 series laser production frame.

7000 series SSPPM set(pre-ionization)

AC-DC Distribution

XLA Control System

3ea XLF series HVPS(main pinch)

7000 seriesWater Distribution

Module XLF seriesResonant Charger

(main pinch)

Fluid Management Module

Vacuum VesselIncludes:

Debris ShieldCollector

Spectral Purity Filter

EUV Dense Plasma Focus Light Source


Electrode Development Input Power is Limited by inner electrode diameter (Limited

Cooling Surface Area). EUV conversion efficiency and gas recipe are dependent on

electrode geometry. Plasma initiation and propagation depend on electrode details Source size and stability dependent on inner electrode.


Pulsed Power


Grazing Incidence Collector Status and Plan

Procured several small proof-of-concept collectors from various suppliers Carbon contamination and insufficient debris mitigation

makes working with the collectors impractical to date(ultrashort expected lifetimes)

No integrated testing to date with collectors Pursuing two paths to meet schedule and performance:

Use existing Zeiss collector to meet early milestones Develop new collector

0 5 10 15 20 25 300.0

0.2

0.4

0.6

0.8

1.0FILE: 981022a.opj

Published Reflectivity vs. Grazing Incidence Angle

Li

W

Au Pd

Rh

Ru

Mo

Refle

ctivi

ty

Grazing Incidence Angle (Degrees)


Debris Mitigation Status and PlanInitial evaluation of physical barrier concept underway

Limited testing on initial ceramic samples Working with supplier to develop prototypes

Team to survey and evaluate multiple concepts Physical barrier (ceramic and refractory metal) Alternatives (gas curtains, electromagnetic,…) Conduct optical modeling of integrated collector and debris shield to optimize the

design


Prototype of Cymer EUV Source

Power Scaling and Thermal Engineering Setup

February 5, 2004© Copyright 2003 Cymer, Inc. DARPA Advanced Lithography Program Review, Las Vegas, NV

Modeling and Results


MHD Model A MHD model of plasma dynamics is being utilized to

model dependencies and scaling in the Cymer dense plasma focus EUV light source. Plasma condition are coupled to a collisional-radiative model of

Xe emission to predict radiation scaling. Calculated features of the model dynamics are being

compared to experimental measurements, including pinch timing, pinch time scaling, pinch size, EUV output scaling,

current peak and waveform, inductance. The goal of plasma modeling effort is to guide design

efforts toward an optimum configuration.


Pinch Dynamics


Comparison of Waveforms Experimental discharge

current, and pinch timing are compared to MHRDR calculations.

A sharp maximum in radial kinetic energy coincides with the time of the magnetic pinch.

Two cases for simulation shown are Low inductance, low

pressure (blue) High inductance, high

pressure (black) Simulation can be made to

match experimental current and pinch timing by reasonable model.

-100 0 100 200 300 4000.0

0.5

1.0Fill pressurecontrols pinch timing

Experimental vs Calculated Waveforms

EUV

Ligh

t, Ra

dial

KE

(AU)

Time (nS)

EUV Light (Measured) Radial Kinetic Energy Radial Kinetic Energy

0

15

30

45

60

MeasuredComputed:

high fill pressure, high inductance

low pressure, low inductance

Circuit parameters controlcurrent waveform

Plas

ma

Curre

nt (k

A) Current

05

10152025

Volta

ge (k

V)

Capacitor Voltage


Positive DPF Singe Pulse Pinch FormationRun 18, Delay 100ns, Gate 20 ns

A fast framing camera (courtesy of Cooke Corp.) was tested for visible pinch formation imaging during a single pulse.

Pinch formation follows “expected” behavior with plasma formation between inner and outer electrodes followed by a compression phase.

Formation of plasma instabilities can be clearly observed.

T=0 ns

T=300 nsT=200 ns

T=100 ns


NDPF Single Pulse Pinch FormationRun 25, Delay 20 ns, Gate 10 ns

T=0 ns T=20 ns

T=40 ns T=60 ns

Negative polarity configuration shows that plasma is initiated inside the inner electrode. No “rundown” phase is observed.

Self-pre-ionization is possible, dependent on electrode configuration.

Current MHD models do not predict the observed behavior.


Negative vs.Positive Polarity

Operation of DPF configuration with different polarity inner electrodes shows very different plasma behavior.

Positive DPF with pre-ionization behaves similar to classical DPF with a rundown and compression phase.

Negative polarity device shows characteristics similar to hollow cathode with self-preionization. No rundown phase is observed.

Similar CE observed for both devices, but NDPF source size is generally smaller. Additional advantages of NDPF include reduced power dissipation on inner electrode at the expense of more plasma in the discharge vessel.


Non-Axis-Symmetric Electrode By creating an asymmetry in the

azimuthal dimension, we can tailor the inductance dynamic as the conducting sheath moves down the electrode. e.g. by introducing a cutout on the

end, the effective length is reduced at those azimuthal angles

The pinch occurs at varying times in varying cross-sections – possibly increasing the pulse length to improve efficiency

Other techniques to destroy the axial symmetry are waiting for testing.

Asymmetric electrode geometry spreads out the pinch in time and space – a possible avenue to higher conversion efficiency.

More sophisticated technique to stabilize pinch by current pulse shaping are possible.

Initial test shown uses simple asymmetry.


Visible Characteristics of Non-Axisymmetric Pinch are Pronounced

Sequence of visible images of pinch plasma, pulse integrated over a 60 pulse burst.

Dim spot observed inside shorter pinch dimension.


Energy of Non-axisymmetric electrode Negative DPF

General shape is similar to gas dependency plots as other electrodes. Maximum CE ~0.5%.

Xe injection into a very low pressure buffer gas produces more spherical EUV source.

Source size at highest power: 3.0 mm x 0.4 mm.

40 60 80 100 120 140 160 180 20020

30

40

50

60 Ptot100_EEUV Ptot60_EEUV Ptot40_EEUV Ptot30_EEUV Ptot20_EEUV

In-B

and

Ener

gy /

pulse

(mJ/

2π/2

% B

W)

Xe Flow Rate (sccm)


Time Evolution Shows Very Early Pinch

Series of visible images shows pinch shortly after breakdown.

No visible signs of an axial rundown preceding the radial pinch phase.


Positive Polarity DPF Source Size vs. Rep. Rate Demonstrated > 50 mJ/pulse at 2 kHz,

and approx. 32 mJ/pulse at 5 kHz. Source length ~ 5 mm. Diam. ~ 0.35 mm up to 2 kHz. Increased size above 2 kHz likely due to reduction in Xe density in un-cooled electrode.

At wavelength imaging of the source with un-cooled electrodes shows an increase in source size and reduction in energy as the electrodes heat up, possibly due to a reduction in local Xe gas density. The source size and output can be recovered by addition of Xe.

100

1000

10000

1 10 100 1000 1000010

100

1000

Phot

odio

de S

igna

l, XC

M, Y

CM [n

V-s]

,[pixe

l],[p

ixel]

Rep Rate [Hz]

Photodiode

X,Y

[micr

on]

Source Size FWHM X Source Size FWHM Y

X CM (pixel) Y CM (pixel)

Xe = 100 Xe = 50


Dependence of EUV Energy on Coupled Energy at 5 kHz.

0.0 1.0 2.0 3.0 4.0 5.0 6.00.000.010.020.030.04

6.0 7.0 8.0 9.0 10.0 11.0 12.0.000.010.020.030.04

6.0 7.0 8.0 9.0 10.0 11.0 12.0.000.010.020.030.04

EUV

In-b

and

Ener

gy in

2pi

sr.

[J]

Recovered EnergyCorrelation Coef. = 0.931

Energy [J]

Dissipated EnergyCorrellation Coef. = 0.845

Stored EnergyCorrelation Coef. = 0.037

50050 200 250 300 350 400 450

5000 200 250 300 350 400 450

500200 250 300 350 400 450

C2 Voltage

Anode Voltage

Photodiode Voltage variation on output stage < 0.9% in

open loop. Evolution of discharge waveforms shows a

change in coupling during the burst. Observed effects may be due to electrode

heating during the burst resulting in a change in local gas density.


Modeling of the SpectraHartree-Fock calculations with configuration interaction for Xe7+ to Xe12+, atomic physics only.

Assume quasi-stationary plasma in partial thermal equilibrium,no plasma dynamics. For Corona equilibrium the line strengths (not the ion populations) are weighted by a Boltzmann factor at electron temperature Te. LTE is not required.

Ion populations are obtained from equilibrium between ionization and recombination (H. Langhoff, to be published). The dependence of the optical density on oscillator strength and wavelength is included explicitly.The calculated spectra are folded to a given experimental resolution.

Te = 30 eV, with opacity, resolution ∆E = 0.15 eV, (calculation by Dr. M. Martins, DESY, Hamburg)


Calculated Spectra at Different Electron Temperatures

Spectra for different electron temperatures, including ion stage populations and opacity effects.Comparison of spectra for the 13 - 14 nm region


Modeling and CE Summary A computational MHD plasma modeling tool for simulating the

Cymer DPF is in place at Cymer, and reasonable results are becoming available.

Comparison of model to experimental results is ongoing and is providing guidance for further tuning of the geometric model, gas conditions, pre-ionization model, circuit model.

The comparison may include pinch size and timing (and scaling), EUV output scaling, and geometrical scalings.

Preliminary modeling confirms that the timing of the pinch as controlled by gas, geometry, and the pulsed power driver have great influence on performance of the pinch.

Favorable comparison of measured Xe spectrum with calculations will provide further guidance to experiments, and modeling.


EUV DPF SSPPM DevelopmentPrevious Output Circuit Characterization

Inductance and Resistance Measurements Made with Output Circuit Mockup to Understand Current Limitations Source Estimates Inductance Resistance

C2 Capacitors 0.075 nH (~3%) 0.6-1.2 mΩ C2 Layout (PCBs, etc.) 2.1 nH (~70%) ~0.3 mΩ LS3 Magnetic Switch 0.8 nH (~27%) ~0.02 mΩ

Load Estimates ~3 nH ~16 mΩ

If Source L Can Be Further Reduced, Higher Output Currents Possible Leading to Higher EUV Output C2 Layout is Dominant Inductance Factor


EUV DPF SSPPM DevelopmentOutput Drive Improvements

Multiple Approaches to Increasing Peak Output Current by Reducing Output Circuit Inductance Modified C2 Capacitor Bank with Reduced Associated

Inductance Using High Voltage Ceramic Capacitors Additional Compression Stage Hardware (C3 and LS4) to

Achieve Faster Output Rise Time


EUV DPF SSPPM DevelopmentHigher Rep-Rates

DPF SSPPM Design Currently 4-6 kHz Capable (for Bursts at Limited Duty Cycle) Thermal Management Necessary for Higher Duty Cycles

Water Cooled Cold Plates for Solid State IGBTs and Diodes Now Being Procured

Magnetic Switch Cooling Design Modifications in Process

Currently Collecting Thermal Data on Several DPFs Thermal DPF Experiment Running up to 2 kHz

Continuous for Several Minutes Other DPF Experiments Running Long Bursts (100's of

Pulses) at up to 4-6 kHz


Calorimetry of Positive and Negative Polarity DPF

Heat removal distribution Inner electrode: Pos. ~ 50%; Neg. ~ 35% Outer electrode: Pos. ~ 40%; Neg. ~ 40% Chamber: Pos ~ 10%; Neg. ~ 25%

200 400 600 800 1000 1200 1400 1600 1800 2000

10

20

30

40

50

60

Solid: Negative PolarityOpen Positive Polarity

, Inner Electrode, Outer Electrode, Vacuum Vessel

% o

f Tot

al P

ower

Rem

oved

Repetition Rate (Hz)0 100 200 300 400 500 600

18

20

22

24

26

28

30

32

34

36

38

2000 Hz

1750 Hz

1500 Hz

1250 Hz

1000 Hz

Total Power Extracted: 21 kW

Inner In Inner Out Outer In 1 Outer Out 1 Outer In 2 Outer Out 2 Outer In 3 Outer Out 3 Outer In 4 Outer Out 4 Vessel In Vessel Out/Lid In Lid Out

Tem

pera

ture

(°C)

Ti ( d )

First generation porous metal inner electrode test power = 8.4 kW


Direct Water Cooling Flow Optimization

Utilizing actual measured temperature distributions for un-cooled electrodes to derive the heat flux distribution on the electrode results in a 2 x increase in the calculated wall temperatures.

Modeling shows that flow reversal can result in lower wall temperatures. Heat transfer can be improved by addition of structures which add turbulence to the

flow.


Electrode Cooling Summary We have tested direct flow electrodes, porous metal, and

micro-channel based electrodes. Best performance to date was achieved with porous metal based electrodes.

New calculated temperature profiles show that the maximum temperature on the electrode surface coincides with the region of maximum electrode erosion.

Optimization of flow conditions in the direct flow electrode channels is possible by proper design of the flow partition and choice of flow direction. The FEA analysis shows that expected improvement is ~ 10%.

Simulation of direct flow electrodes indicates high sensitivity to small changes in the flow geometry.

Demonstrated 2 kHz CW operation with 8.4 kW extracted from inner electrode.


Direct Pinhole Source Imaging

Direct imaging of the DPF source was tried with several filter combinations to in order to obtain average source images by direct integration on the CCD chip at high repetition rate operation.

Due to presence of high energy x-rays we observed a skewed source distribution showing the presence of small high energy “micro-pinches”.

1000 nm Be300 nm Silicon Nitride



20 pulses at 2 kHz with Be+700 nm SiN stack.

Single pulse showing image of SiN Filter holder.


Correlation of Photodiode and Imaging CCD Detectors

A CCD imaging system was constructed using a pinhole aperture, a series of foil filters and a 45 degree ML mirror for 13.5 nm.

97% correlation is observed between the EUV energy measured with a photodiode and the integrated intensity on a ML/CCD combination.

CCD Array

1 1010-4

10-3

10-2

10-1

100

Tran

smis

sion

Wavelength [nm]

1.0 µm Be,0.3 µm Si3N4



0 20 40 60 80 1000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Norm

aliz

ed C

CD S

igna

l

Pulse Number

CCD Detector

Correlation Coefficient = 0.973

Photodiode Detector

Nor

mal

ized

Pho

todi

ode

Sign

al


EUV Metrology For CW Source Operation at 1 kHz. EUV monitor with debris suppression tube Source size measurements with CCD camera and 45 deg ML mirror 76 Watts of in-band EUV radiation (2 % b.w., into 2 π) obtained at 2

kHz repetition rate

Repetition Rate: 1000 Hz, 3.55 mm length, 0.35 mm width (FWHM)


Negative DPF Operation with Sn

Initial experiments conducted with crude Sn delivery system show that approximately a 4x increase in EUV output can be achieved. This implies conversion efficiencies near 2%.

Spectra were measured with Sn and Ar compared with Ar only.

6 7 8 9 10 11 12 13 14 15 160

200

400

600

800

1000

1200

1400 Ar only Sn+Ar

Spec

tral I

nten

sity

(AU)

Wavelength (nm)

13.5 nmTin line

Electrical to EUV conversionapprox. 1.8%

EUV Emission Spectrawith and without Sn.

DARPA Advanced Lithography Review Feb 2004 v8a

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Transcript of DARPA Advanced Lithography Review Feb 2004 v8a