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III. Vacuum PumpsIII. Vacuum Pumps
MechanismGas transferGas capture
FunctionFunctionRoughing (backing, mechanical pumps)
Rotary vaneSorption Rotary lobe Scroll ScrewSorption, Rotary lobe, Scroll, Screw
High vacuumOil diffusion, Turbomolecular, Cryo, Ion
AuxiliaryTitanium Sublimation, LN2
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IIIIII--A. Roughing: Rotary Vane Pump A. Roughing: Rotary Vane Pump (Gas Transfer)(Gas Transfer)(Gas Transfer)(Gas Transfer)
Single-stage10-2 torr
Dual-stage10-3 torr
Speed: 1-100 cfmOil: lubricant, coolant, sealant, contaminationForeline trap: copper gauze, molecular sieve, LN2Pumping reactive/flammable/O2 gas:
Chemically inert fluid: Fomblin PFPE (perfluoropolyethers)
Liu, UCD Phy250-1, 2011, NanoFab17
Chemically inert fluid: Fomblin PFPE (perfluoropolyethers)Ballast valve; Gas bubbler; Venting (anti-suckback); Exhaust; Vibration
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Roughing: Sorption Pump Roughing: Sorption Pump (Gas Capture)(Gas Capture)( p )( p )
10-3 - 10-4 torr10 10 torrOil free, no moving partsDrawback:
Initial cooling
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gLimited capacity, need regenerationGas selective- difficulty w/ inert gases
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Roughing: Diaphragm Pumps Roughing: Diaphragm Pumps (Dry, Gas Transfer)(Dry, Gas Transfer)( y, )( y, )
< 10cfm
1-10 torr
Exhaust into atmosphereExhaust into atmosphere
Low cost
Liu, UCD Phy250-1, 2011, NanoFab20
Kurt J. Lesker
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Roughing: Roots (Rotary Lobe) Pump Roughing: Roots (Rotary Lobe) Pump (Dry, Gas Transfer)(Dry, Gas Transfer)( y, )( y, )
RootsGas transfer0.01-10 torr(10-4 torr when backed) Handle high gas loadsHandle high gas loads
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Kurt J. Lesker
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Roughing: Other Dry PumpsRoughing: Other Dry Pumps
Kurt J. Lesker
ScrollG f
ScrewGas transferGas transfer
10-2 torr12-25 cfm
Gas transfer10-3 torr30-320 cfmMay handle aggressive gases
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May handle aggressive gases
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IIIIII--B. High Vacuum: Oil Diffusion PumpB. High Vacuum: Oil Diffusion Pump(Wet, Gas Transfer)(Wet, Gas Transfer)( , )( , )
Momentum transfer
10-7 -10-8 torr or better30 L/s - 50,000 L/sOil: Very low vapor pressure
O2 resistantBaffles & LN2 trap
Kurt J. LeskerBaffles & LN2 trap
Advantages: Inexpensive, simple, non-gas-selective, durable, quietDisadvantages: oil backstreaming (LN2 trap, baffles)
Liu, UCD Phy250-1, 2011, NanoFab23
upright, load < 300mtorr, need backingslow start/shut-down
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High Vacuum: Turbomolecular PumpHigh Vacuum: Turbomolecular Pump(Dry, Gas Transfer)(Dry, Gas Transfer)( y, )( y, )
10-7 -10-10 torr10 -10 torr 50 L/s - 3500 L/sCrossover P: ~ 1000 mtorr
Gas selective: Easy w/ heavy moleculesdifficulty w/ H2, He
High speed, screenOften verticalOften verticalBearings
Ceramic M ti ll l it t d
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Magnetically levitated
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High Vacuum: Cryo PumpHigh Vacuum: Cryo Pump(Dry, Gas Capture)(Dry, Gas Capture)( y, p )( y, p )
Cryo-condensation + cryo-sorptionClosed-cycle He cryocompressor10-9 torr or betterAny orientationNo backing neededNo backing neededCrossover P: ~ 500 mtorr
Gas selecti e: diffic lt / HeGas selective: difficulty w/ HeRegeneration & replacement
KJL
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KJL
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UHV Pump: Ion PumpUHV Pump: Ion Pump(Gas Capture)(Gas Capture)( p )( p )
KJLKJL
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Chemical reaction w/ Ti (getter) + burial (ion implantation)
Reactive gases All gases
10-12 torrCross over P: ~<1mtorrAny orientationAny orientationClean, bakeable, vibration-freePermanent magnet: ionization; heavy
Gas selective: difficulty w/ inert gasLow throughput
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Ti refurbish necessary
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HV Pump ComparisonHV Pump Comparison
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IIIIII--C. Auxiliary: Titanium Sublimation PumpC. Auxiliary: Titanium Sublimation Pump(Dry, Gas Capture)(Dry, Gas Capture)( y, p )( y, p )
Sublime Ti-Mo, continuous/pulseChemical reactionGas selective: no inert gasGas selective: no inert gasBetter at LN2:
Pump speed & heat insulationProper partitionOperates < 10-6 torr
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Auxiliary: LNAuxiliary: LN22(Gas Capture)(Gas Capture)( p )( p )
Cryopumping
LN trapLN2 trapCryopanel
Continuous LN2 feed$0.25 /L
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IIIIII--D. Vacuum SystemsD. Vacuum SystemsExample: Diffusion pump system
Safeguards:Water interlockT i l k
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Temperature interlockPressure interlock