Vacuum Design Constraints and Considerations

Martin P. Aalund, Ph.D.

SummaryIntro to Vacuum Technology

History Terminology Levels of Vacuums Cluster Tools Robotics Motion Across The Barrier Data and Electrically How do we Maintain it Virtual Leaks Material CompatibilityOut gassing

The Vacuum barrier, How do you Cross it?

Design Consideration

Intro to Vacuum TechnologyHistory Why do we need Vacuums Terminology Levels of Vacuums Cluster Tools Robots

Vacuum HistoryEvangelista Torricelli was the first person credited with creating a vacuum 1643 and also invented the barometer. This was in an attempt understand why a suction pump could only raise water to 32 feet. Robert Boyle (1627-1691) used a von Guericke pump, improved by the young Robert Hooke, to investigate the vacuum and the general properties of gases and gas pressure England. Papin invented the Pressure Cooker Currently one of the most impressive bits of artificial emptiness is created in the particle accelerators. The large electronpositron collider (LEP) at CERN gets down to a pressure of 1012 Torr or 1.3*10-10 Pa This corresponds to a particle density of about 1011 hydrogen molecules per cubic meter. To a first approximation the average density of the universe is about 1 hydrogen atom per m3

Why do we need VacuumLimits Contamination

No Airborne Contamination Limits Cross Contamination Slows Oxidation Allows for Controlled Atmospheres

Control Chemistries Many process can be made more predictable or require a vacuum to function

Plasma Production Metallization: Metal is evaporated and deposited onto a substrate Etch Deposition Sputtering Ion Implantation E-beamMetrology Inspection

TerminologyVacuum:

A volume of Space Substantially void of matter (Wikepedia) a space partially exhausted (as to the highest degree possible) by artificial means (as an air pump) (Websters)

P1

P2

Manometer: Liquid scale used to measure vacuum or pressure usually in Inches or mm torr: A unit of measurement for pressure:torr = 1 mm_Hg torr = 0.039in_Hg torr = 1.32 10 torr = 133.32Pa3

P

atm

(it is named after Evangelista Torricelli)

Virtual Leek: A void or trapped volume that slowly released material into a vacuum. Examples include Blind wholes with screws etc.

TerminologyAtmospheric pressure is variable based on weather and location, but is standardized at 101.325 kPa (760 Torr) Low vacuum, also called rough vacuum or coarse vacuum, is vacuum that can be achieved or measured with rudimentary equipment such as a household vacuum cleaner. Can be measure with a simple manmometer Medium vacuum is vacuum that can be achieved with a single pump, but is too low to measure with a liquid or mechanical manometer. It can be measured with a McLeod gauge, thermal gauge or a capacitive gauge. High vacuum is vacuum where the mean free path of residual gases is longer than the size of the chamber or of the object under test. High vacuum usually requires multi-stage pumping and ion gauge measurement. Some texts differentiate between high vacuum and very high vacuum. Ultra high vacuum requires baking the chamber to remove trace gases, and other special procedures. Deep space is generally much more empty than any artificial vacuum that we can create. But it is not uniform and has areas of gas that may be quite dense. Perfect vacuum is an ideal state that cannot be obtained in a lab, nor even in outer space. AMC: Airborne Molecular Contaminates: Gaseous Atoms, Molecules, or clusters

AMCsCan be emitted from Cables, Plastic or Electrometric Parts Airborne molecular Include

Acids: HCl, HF, SOx, NOx, etc. Basis: Amonias: Amines, etc Condensates: Phthalic Ester, Siloxane, Etc Dopants: Boron, Phosphorous Yield Loss Corrosion of metal surfaces on the wafer Surface PollutionHaze on wafers Haze on optics

AMC Related Problems include

Changes in contact resistance Use materials with High Molecular weight and Low Volatility Use High Purity Materials Control Cross Contamination during Manufacturing and Installation Testing is performed in vacuum. Sample from 100 to 300 grams in placed in special aluminum boat and heated to 398K inside a copper container with a 6.3 mm hole for 24 hours. A Chromium plated disk is placed in front of a 6.3 mm hole. TML Total Mass Loss CVCM Collected Volatile Condensable Material WVR Water Vapor Regained (Exposed to 50% Humidity for 24 Hours)

AMC Control

Outgassing Measurements

Levels of VacuumName Atmospheric Pressure (variable) Low, Rough or Course Vacuum Medium Vacuum High Vacuum Ultra High Vacuum Extremely High Vacuum Outer Space Perfect Vacuum Start torr (Pa) 760 (101.325 kPa) 760 (101kPa) 25 (3kPa) 1x10-3 (100nPa) 1X10-9 (100mPa) 1x10-12 (100pPa) 1x10-6 (100uPa) 0 (0) 3x10-17 (3fPa) 25 (3kPa) 1x10-3 (100mPa) 1x10-9 (100pPa) 1x10-12 Stop torr (Pa)

Vacuum Cluster ChallengesProcess Challenges

Time to purge Temperature Chemistries

Vacuum Robot High VacuumProcess Chambers Process Chambers

Clusters used for alternate atmospheres Operate near strong electro-magnetic fields

No magnetic signature Static electricity

Integrated Process Chambers Orienter / Degas

Cool-Down/ PreClean Chambers Orienter / Degas

Moving the Wafer

Low Vacuum

Wafer Cassette Loadlocks

Vacuum RobotsVery high reliability Operate in vacuum

10-8 Torr Material compatibility No virtual leaks MESC compatibility Minimize chamber volume Increase wafer throughput Prevent wafer slippage Time optimized trajectories

Low profile

Sophisticated controls

7 to 9" arm links

Robot ARM TypesFrog Leg

More Bearings Second Wafer Moves at Low Speed Higher Throughput for Same Accel Simple Design Must Have Bands or Belts in Vacuum Speed of Extension limited by Second Wafer No Bands More Bearings

SCARA

Four-Bar Linkage

Vacuum Robot VendorsVendor Brooks IDE Rorze Genmark Yaskawa JEL AITEC SankyoSVHR3163, STVHR4000, DVHR3200 AR-SV300, AR-WV300 SR8600 RR452, RR713 AVR3000

ModelsMag 7

TechnologyPermanent Magnet

Ferrofluidic Seals Ferrofluidic Seals, Only in Japan Ferrofluidic Seals Single and Dual Single and Dual Arm

Motion and VacuumCannot use a vacuum P chuck to hold a substrate

Edge Grip Highly Optimized Motion Special Materials

Motion can be created either inside or outside the vacuum barrier, both create challenges. We will look at some of these challenges for robotics, but could be applied to any general device.

The Vacuum barrier, How do you CrossMechanically

How do We transmit Motion or Torque Across the Barrier Need to get Signals and Power Across the Barrier Need to See and measure thingsQuarts Encoders Lasers

Electrically

Information

Two Main ChoicesCreate Motion in the vacuum Create Motion outside of vacuum and then provide feed through transferring motion to the vacuum.

Bellows Ferro fluidic Seals Lip Seals Mag Coupling

Permanent MagnetPros Good Vacuum Isolation Simple Design Cons Bearings in Vacuum Magnets and epoxy in vacuum Can Stack for extra DOF Brooks has Patent

Vacuum

Flux

Magnet Flux

N

Magnet Flux

S

Flux

Bearings

Magnetic CouplingPros Good Vacuum Isolation Cons Bearings in Vacuum Magnets and epoxy in vacuum Two air gaps produces control and stiffness issues Can Stack for extra DOF AMAT has Patent

Vacuum

Flux

S N SMagnet Flux

S N N

Flux

Magnet Flux

Magnet Flux Magnet Flux

Bearing

Ferrofluidic SealsPros No Bearing in Vacuum Motor and Sensors can be standard Cons Seal can Burp during pump down Seal can Outgas Reliability of Seal Concentric shaft for added DOFs Used by Yaskawa, Brooks has some Patents via Smartmachines Vacuum

Magnet Flux

Magnet Flux Magnet Flux Magnet Flux

N SMagnet Flux

N SMagnet Flux

Ferrofluidic LiquidFluxMagnet Flux

N

S

Flux

Magnet Flux

Bearings

Harmonic DrivePros Motor and Sensors can be standard Gear Reduction reduces motor and sensor costs. Cons Bearings in Vacuum Flex Spline Circular Spline Interface in Bearing Costs Circular Spline Flex Spline Wave Generator

Vacuum

Placing Motor in VacuumStandard Motors not suitable for less than 10^-4 Torr.

bearing grease, paper slot liners, conformal coatings, winding insulation

Lubricants are not suitable and will vaporize resulting in bearing failures and fouling other components. Some lubricants boil off very quickly others such as Silicon dont vaporize as fast but create low level contamination on all components and are very hard to clean. Cooling. How do we get the heat out.

Heat Sink Heat Pipes Radiation Laminations Non Vented Screws.

Micro Leaks due to construction Micro Environments make create voltage discharge paths

Electrical Challenges in A VacuumInsulation Getting rid of heat Out gassing Exiting the Vacuum

ElectricallyExposed conductors should be insulated

Arcing can be an Issue

Vacuum approved Solders Virtual Leaks Electronics Components in Vacuum

EnclosingEnclose in Box Must monitor pressure Shields device from vacuum (issue for some chips) Prevents Out gassing

PottingCompletely cover with Potting material such as vacuum compatible epoxy. Should Minimize area by placing in recess Whole assembly often must be scrapped if there is a component failure Can actually improve heat transfer.

VentingSame as Enclosing, but vent supplied to atmosphere.

Out gassing in CablesConstruction

Stranded Cables can have voids between wires creating virtual leaks Trapped Air can cause Cable Ruptures and expose Interior materials Must select Materials that have low Out gassing.

Materials

Position InformationType of Rotary Actuator

EncodersEasy to Interface Lower Cost

RevolversAbsolute Position Robust

Capacitive EncodersLow Cost Absolute and Incremental Could be Made Vacuum Compatible

In VacuumDisc in Vacuum Sensor Outside Use Quarts viewing Window (Adds Costs) New Vacuum Compatible Read heads can be placed in vacuum

Use a Window to View Sensor

Code Wheel Sensor Window Quarts Windows Vacuum Barrier

Design ConsiderationHow do we Maintain it

Virtual Leaks Material Compatibility Out gassing

Pump down Speed is Critical How do we optimize itMinimize the Volume Eliminating the cracks, crevices and other areas that trap gasses Fine machine finishes hold less air Porous metals typically require cleaning and sealing Machined metals are preferable to castings Avoid Leaks and Virtual Leaks

Leaks: Leaks can take the form of air leaking through seals, or air or other contaminates leaking from contained volume or voids. Vent Screw

Select the correct Components

How To Select MaterialsOut-gassing

Evaporation Sublimation

Thermal Compatibility Use

Material CompatibilityCarefully Selected Wet Lubricants Vacuum Lubricants Dry Lubricant

Low Vacuum (Mechanical Pump) Many Commercial Plastics

High Vacuum Turbo Pump

Limited PlasticsMost Natural Materials Must be eliminated

No Plastics

AT M

7

1

2

3

4

5

6

10 -

8

10 -

10 -

10 -

10 -

10 -

10 -

10 -

10 -

9

Vacuum LubricantsSolid

MoS2 (molybdenum disulphide) Good down to 10-12 torr WS2 (Tungsten Disulfide) Lubricant is often provided by cage or Spacer. TorrLube Good Down to 10-9 torr Fomblin Y perfluoroalkylpolyether (PFPE) Isoflex Krytox (PFPE) Barrierta

Grease/Oil

Common MaterialsStainless Steal

Strength Corrosion Resistance Available in Magnetic and Non-Magnetic Forms Common Alloys IncludeXxx Mag XXx non Mag

Aluminum

Good Stiffness To Weight Ration Easily machined Non MagneticCommon Alloys Include

Ceramics

Chemical Resistance Temperature Resistance Thermal and Electrical Insulation Alumina Quarts Beryllium Oxide? PolyBenzImidazole (Celazole) High Temp, Brittle, Hard to Machine. Bushings, Bearings, Rollers PolyimideVespel High Temp, Expensive Duration, Lower Cost than Vespel, similar Properties

Plastics

PolyAmide-Imide (Torlon) Low Thermal Expansion, typically used for Insulators, spaces. Can be glass filled. PTFE

Low Outgassing PlasticsPolyBenzImidazole

Celazole is the highest temperature-capable plastic available. However, it is very brittle (almost ceramic-like) and quite difficult to machine. That said, is it frequently used for bushings, bearings, rollers, and spacers in extreme environments. Polyimide DuPont Vespel SP-1 is one of the most-used high-temperature plastic materials used in applications where high-purity and electrical properties are needed. Vespel is frequently used in ultra-clean semiconductor and chemical applications. It is also one of the most expensive materials sold, but is flight-approved for NASA, USAF and other aerospace agencies. Duratron XP is the first real alternative to Vespel ... it was developed specifically to replace Vespel in extreme applications at a slightly lower price. It contains less than 1% metallic impurities as measured using the ICP-MS test standard. Duratron XP is ideal for use in high-energy gas plasma etch and strip processes. Unfilled Torlon 4203 has high dielectric properties and low thermal expansion, and is much less expensive than some advanced polymers. Torlon 4203 is typically used for insulators, spacers, and mechanical parts up to 520F. Torlon 5530 (30% glass-filled) is typically used for applications where dimensional stability over a wide temperature range is needed, as with temperature test sockets, nests, and fixtures. : Torlon's moisture absorption is a bit high, so critical dimensional stability can be an issue.

PolyAmide-Imide

Semitron ESd 500HR (filled PTFE) Semitron ESd 500HR is antistatic/conductive PTFE. This material is relatively clean, readily machinable, dissipates static electricity reliably ... as a result it is used in test handling equipment, fixtures, and other applications where static generation may cause failures and/or errors in production environments. PTFE has good mechanical properties up to approximately 500F. Neoflon PCTFE (PolyChloroTetraFluoroEthylene) PCTFE exhibits high chemical resistance, low and high temperature capability, resistance to most chemicals (including strong acids and bases), low friction, electrical and thermal insulation, and "slipperiness".

Low Outgassing PlasticsPEEK (PolyEtherEtherKetone) PEEK is pure, easily machinable, chemically resistant, stable, and also has relatively low outgassing values. PEEK has good mechanical properties, but will not take temperatures over 350F, so it may not have the mechanical or thermal performance needed. Techtron PPS (PolyPhenylene Sulfide) Techtron PPS is easily machined to close tolerance, has excellent mechanical, thermal and chemical stability and has one of the lowest outgassing thermoplastic material. Techtron PPS is generally a bit less expensive than PEEK or Torlon, but will not take as high temperatures. Ultem PEI (PolyEtherImide) Ultem has good dielectric properties and low thermal expansion, and is considerably less expensive than some other polymers. PEI is also clean and stable, but is not particularly resistant to chemicals or solvents . PEI has good mechanical properties up to approximately 410F. Semitron ESd 410C (filled PEI) Semitron ESd 410C is antistatic/conductive PEI. This material is relatively clean, readily machinable, dissipates static electricity reliably ... as a result it is used in test handling equipment, fixtures, and other applications where static generation may cause failures and/or errors in production environments. PEI has good mechanical properties up to approximately 340F. Ertalyte PET-P (Polyethylene Terephthalate) Ertalyte offers the dimensional stability of acetal with the wear resistance of nylon. Ertalyte PETPolyester is clean, chemically resistant, stable, PET-P is considerably less expensive than most of the other materials listed above, but may not have the mechanical or thermal performance needed for all applications. Semitron ESd 225 (filled acetal) Semitron ESd 225 is antistatic/conductive acetal. This material is relatively clean, readily machinable, dissipates static electricity reliably ... as a result it is used in test handling equipment, fixtures, and other applications where static generation may cause failures and/or errors in production environments. Acetal has good mechanical properties up to approximately 180F.

BearingsBall Cross Roller Magnetic Chamberlink Actuator

Puts Bearing on Outside

Bearings

EXAMPLE A:RINGS: Stainless Steel BALLS: Stainless Steel RETAINER: Vespel or PEEK LUBRICATION: Solid, MOS2. Solid, WS2 (Tungsten Disulfide) FEATURES: Clean, high temperature, corrosion resistant, solid lubricated, inexpensive. RINGS: Stainless Steel BALLS: Solid Lube Coated Stainless Steel RETAINER: PEEK LUBRICATION: Solid, MOS2 FEATURES: Clean, high temperature, corrosion resistant, solid lubricated, increased life, increased performance, more expensive.

EXAMPLE B

Materials InformationGood Information Available Use Your Suppliers Use the Web

NASAhttp://outgassing.nasa.gov/

ReferencesLow Outgassing Cables for Clean Room

HITACHI CABLE REVIEW No.24 (AUGUST 2005)

http://outgassing.nasa.gov/ http://en.wikipedia.org/wiki/Main_Page

Backups

Design Considerationsreliability, product safety, efficiency, response time, flexibility, and maintenance issues. Thermal

SummaryCost Patent Clean Proven Stiffness

Magnetic Coupling Ferro Fluidic Permanent Magnets Harmonic Drive

10 9 7 8

10 3 10 3

5 10 5 7

3 3 3 5

10 3 4 2

How do we create a VacuumThis vacuum is produced by pumping air out of a chamber or chambers At pressures above 10-6 Torr a standard Mechanical Pump can be used. At pressures below 10-6 Torr a standard turbo pumps are often used.

Types of Vacuum PumpsPositive Displacement (.1Pa)

Diaphragm Piston Pump Scroll Pump Gear Pump Diffusion (10-8 to 1 pascals ) Turbo Molecular (intermediate vacuum (~10-4) up to ultra-high vacuum levels (~10-10 Torr). ) Cryopumps Ion pump Sorption Pumps

Momentum Transfer (

Entrapment

ClusterVacuum Loadlocks Vacuum Robot Vacuum Transport Chamber

View From Front End (EFEM Interface)

Top View Looking Towards Front End

Vacuum ChallengesOperating in vacuum

Limits material selection Limits lubrication No out gassing Ferofluidic seals Magnetic coupling Cooling Highly optimized motion Special materials

Motion across vacuum barrier

No Vacuum to Grip

Reliability

Methods of Getting Power Across

Ferofluidic seals Magnetic coupling Cooling Limits material selection Limits lubrication No out gassing

Operating in vacuum

Reliability

How do we create a VacuumThis vacuum is produced by pumping air out of a chamber or chambers At pressures above 10-6 Torr a standard Mechanical Pump can be used. At pressures below 10-6 Torr a standard turbo pumps are often used.

Sin/Cosine

Linked Slides

Median SpeedFriction between silicon and stainless steel is about .24 G Must Grip the Wafer to move faster, or use a polymer to increase Friction We must limit the acceleration of the robot when it has a wafer on either end-effector.

Thus the Kinematics of the robot may affect the overall Throughput.

Paschens Law

ResolverUses an AC signal to excite the rotor winding. Stator has two windings at 90 degrees to each other. As the rotor turns the coupling to the two windings will change Can have multiple poles, but you lose absolute capability. Converters usually are analog and can be expensive, $200 for 14-16 bits. Rotor current normally passed through an inductive coupling. Could be placed in vacuum environment.Cosine Reference

Sin