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EUV Lithography –Vacuum ChallengesEUV Lithography –

Vacuum Challenges

Paul A. Blackborow – Energetiq Carolyn Hughes - BOC EdwardsPaul A. Blackborow – Energetiq Carolyn Hughes - BOC Edwards

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AbstractAbstract

• The semiconductor industry is moving to next generation lithography (NGL) as device dimensions shrink to 32nm and below.

– The leading candidate for NGL is Extreme Ultra Violet Lithography (EUVL) with a much shorter wavelength, 13.5nm.

• EUV Lithography requires new technologies and poses new challenges. – Optical elements, including masks, are reflective, rather than refractive; – New light sources that produce adequate power at 13.5nm are required; – The entire light source, optical stem and wafer are under high vacuum.

• In this talk we will look at some of the challenges related to EUV light generation and to the challenges of maintaining a clean vacuum environment in high throughput manufacturing.

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The EUV transition in Semiconductor LithographyThe EUV transition in Semiconductor Lithography

• EUV is a practical technique for high volume manufacturing

– EUV is optical lithography, like today’s DUV

– High throughput is possible unlike other forms of next generation lithography (NGL)

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EUV LithographyEUV Lithography• Extreme Ultra Violet (EUV) lithography is expected at device

dimensions ≤ 32nm

• EUV light is also absorbed by air, so the entire tool including the light source, optical train and wafer must be maintained in an ultra clean vacuum environment

• Light at 13.5nm is absorbed by all materials including traditional transmissive lens materials used in conventional lithography, so reflective optics & masks are required

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Vacuum Challenges of the EUV Tool EnvironmentVacuum Challenges of the EUV Tool Environment• EUV mirrors are made with multilayer mirrors with up to 100 layers of Molybdenum and

Silicon

• One of the principal challenges for success of EUV lithography is maintaining the optics lifetime – 1% reflectivity loss over 10 years! (entire optic train)

• The multilayer mirrors are expensive and highly sensitive to contamination from hydrocarbons and moisture, in the presence of EUV light reactions occur to produce carbon growth and oxidation which can seriously degrade reflectivity

Pictures from C Gwyn, EUVL Symposium 2003

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Vacuum Challenges of the EUV Tool EnvironmentVacuum Challenges of the EUV Tool Environment

• Contamination levels need to be strictly controlled and monitored in the EUVL tool environment, defined specifications: (ASML – SPIE 2003 vol. 5037 pp24)

– CxHy - 1x10-9 mbar, – H2O - 1x10-7 mbar

• In addition, there are mechanical and thermal challenges– The tool must achieve stringent alignment and overlay characteristics, so any

sources of vibration must be minimised– Temperature control of the optical train must be carefully maintained, thus

radiant heat load from vacuum pumps & gauges must be minimised - +/- 0.001K

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Addressing the Vacuum Challenges – DesignAddressing the Vacuum Challenges – Design• Advanced system modelling can be employed in the

design phase to optimise contamination levels and vacuum performance

• Miles of cabling and 100s actuators & sensors are required inside the vacuum system,

– extensive outgassing measurements are made to select the best materials/components and preparation methods for the tool

-210

-110

010

110

210

13.0 13.5 14.0 14.5 15.0 15.5 16.0

Pres

sure

(mba

r)

Time (s)

1: Loadlock 1: Transfer Chamber 1: Process Chamber

OEM Subsystems Group

v2.1

Sample id: Pump speed: 68.0 l/sDescription: Tested by:Materials: At location:Sample area: cm² Date:Mass: kg Background test:

Comments:

Q total mbar.l/s Q total 2.9E-04 mbar.l/sQ H20 mbar.l/s Q H20 7.2E-05 mbar.l/sQ CxHy mbar.l/s Q CxHy 1.4E-05 mbar.l/sP ion gauge mbar P ion gauge 4.26E-06 mbar

Time exponent - α, according to Q (t )=Q 10t-α

αCxHy =

EUVL Standard Outgassing Test Report

b-20030924-01Test details

Neil CondonBOC Edwards, OEMSS lab

Ziconia cupYitttia Stabilised Zirconia

No cleaning - detailed history unknown

10-Dec-2002n/a0.1 bg20030902

(background subtracted) (background subtracted)Sample outgassing rate at 1h Sample outgassing rate at 10h

0.260.09αH20 =

2.6E-041.4E-042.1E-054.00E-06

Outgassing vs time

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

0:00 2:00 4:00 6:00 8:00 10:00 12:00

time (hh:mm)

mba

r.l/s

H20 (Sample)H20 (B.ground)CxHy (Sample)CxHy (B.ground)

Pressure vs time

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

0:00 2:00 4:00 6:00 8:00 10:00 12:00

time (hh:mm)

Pion

(mba

r)

P (Sample)P (B.ground)

Mass spectrum (10 hrs)

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96

SampleBackground

• Modelling Distributed outgassing is particularly valuable

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Addressing the Vacuum Challenges – Pump TechnologyAddressing the Vacuum Challenges – Pump Technology

• Maintaining ultra low contamination levels is a significant challenge for the vacuum EUV tool

– System baking is not possible

• It is likely that continuous or intermittent cleaning strategies will be employed to control carbon or oxide growth

– E.g. introduction of gas mixtures and active chemistry

• The principal vacuum pump technology will be maglev turbo pumps and regenerative stage type pumps

• The use of cryo technology inside the EUV tool is not ideal due to the need for optical and thermal shielding and the need for regeneration

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• Patented concepts for mounting vacuum sensors mid-way along the blade stack of a turbomolecular pump offer significant system design advantages

Addressing the Vacuum Challenges – Gauges and SensorsAddressing the Vacuum Challenges – Gauges and Sensors

– Main chamber is isolated from any impact of the sensor e.g. thermal emissions, outgassing, charged particle emissions etc. through the high compression ratio of the turbopump

– System response time is unaffected or improved

– Sensor is buffered, by the high compression ratio of the turbopump, from back diffusion of species in the exhaust line

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EUV Lithography ToolsEUV Lithography Tools

Exitech’s EUV Micro Exposure Tool, at Intel, with BOC Edwards vacuum equipment & vacuum control systems

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EUV Light SourcesEUV Light Sources

• EUV lithography will require more than 115 watts of power for production applications in the near future, and more than 230W ultimately

• Debris from the light source can destroy the precision light-collection mirrors costing ~$500,000 each

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How is EUV light made?How is EUV light made?

• Two technologies to generate EUV light – Laser Produced Plasma (LPP)

Being developed by Cymer and GigaPhoton– Discharge Produced Plasma (DPP)

Being developed by Xtreme and Philips

• Both techniques heat a gas to high enough temperatures to emit EUV light– Gas or vapor must be heated to ~500,000°C to produce EUV at 13.5nm– Choices of gas/vapor are:

Xenon – inert gasTin Vapor – will contaminate opticsLithium Vapor – will contaminate optics and is very corrosive

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Laser Produced PlasmaLaser Produced Plasma

High Power Pulsed Laser

Nozzle

Target Material e.g. Xe, Sn, Li,

EUV

•High cost/photon •Debris from target can damage optics

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HVM EUV Source Challenges: Laser Produced Plasma (LPP)HVM EUV Source Challenges: Laser Produced Plasma (LPP)• LPP Sources will be very costly

and complex using multiple high power lasers

• Cost estimates range from $4M-$10M per light source

• To reduce the number of high power lasers required, developers have chosen Lithium or Tin vapor as the EUV target

• Lithium and Tin are contaminants for the expensive optics

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Traditional Discharge PlasmaTraditional Discharge Plasma

Electrode

Target Gas Plasma e.g. Xe, Sn, Li,

Target Gas Plasma e.g. Xe, Sn, Li,

Electrode

High Current Pulse

High Current Pulse

Magnetic Field

Magnetic Field

EUVZ-Pinched Plasma

Z-Pinched Plasma

•Lower cost/photon •Debris from target and electrodes can damage optics

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HVM EUV Source Challenges: Discharge Produced Plasma (DPP)HVM EUV Source Challenges: Discharge Produced Plasma (DPP)• DPP Sources are more cost effective, but

present designs cannot be scaled to high power without introducing e.g. Tin vapor

• All present DPP sources use Electrodes which vaporize, contaminating the optical system

• Tin vapor adds a major level of complexity and cost to the light source, to keep the tin vapor from contaminating the extremely expensive collection optics

• Stepper manufacturers and chip makers would much prefer to use Xenon if possible

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Electrodeless Z-Pinch™ EUV SourceElectrodeless Z-Pinch™ EUV Source

Induced High Current Pulse

Induced High Current Pulse

Inductively Coupled Gas Plasma (Xe)

Inductively Coupled Gas Plasma (Xe)

Z-Pinched Plasma

Z-Pinched Plasma

EUV

Magnetic Field

Magnetic Field

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Electrodeless Z-Pinch™EUV SourceElectrodeless Z-Pinch™EUV Source

Magnetically Confined z-Pinch Region

•Source of EUV radiation

Magnetically Confined z-Pinch Region

•Source of EUV radiation

Inductively Coupled Plasma Loops

Inductively Coupled Plasma Loops

• Unique inductive design

– No electrodes → no electrode debris

• Plasma is magnetically confined

– Reduces debris further

• Inert Xenon operation– No debris from

source gas

• Lower cost and complexity

• Six patent applications filed

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Visible Light from PlasmaVisible Light from Plasma

Plasma Return LoopsPlasma Return Loops

Z-Pinch RegionZ-Pinch Region

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Addressing the Vacuum Challenges – The SourceAddressing the Vacuum Challenges – The Source

• Xenon presents challenges for vacuum pumps– poor thermal conductivity and large mass

• Pumping performance and continuous maximum gas flow rate is improved through enhanced design– High performance and optimized rotor/stator blade

design – Optimized heat transfer structure– New platform structure cooling system– Advanced modeling for Xenon operation

• Innovative high emissivity coatings improves thermal dissipation from the rotor– Increases maximum gas flow capability for low thermal

conductivity gases such as xenon– Designed for corrosive gas duty also

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EQ-10M EUV SourceEQ-10M EUV Source

• EQ-10M EUV and Soft X-Ray source introduced in mid-2005

• Delivers more than adequate power for EUV research – EUV Resist Development– EUV Resist Out-gassing Studies– EUV Optics Measurement– EUV Metrology

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SummarySummary

• EUV will most likely be the Next Generation Lithography (NGL)• EUV is a great opportunity for vacuum equipment makers• Creating a vacuum environment for EUV presents specific challenges• EUV light sources present additional vacuum challenges, especially those

using metal vapors such as tin and lithium• Novel approaches such as the Electrodeless Z-pinch using Xenon are

proving useful for EUV lithography

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AcknowledgmentsAcknowledgments

• Carolyn Hughes, Anthony Keen, Rob Grant at BOC Edwards• Friends and former colleagues at MKS Instruments

• The Energetiq team….