4 vacuum pump
Post on 14-Nov-2014
336 Views
Preview:
TRANSCRIPT
Dr. G. Mirjalili, Physics Dept. Yazd University
Vacuum techniques
Pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
Vacuum theory and pumping laws
Vacuum theory and pumping laws
How the vacuum is created?
Dr. G. Mirjalili, Physics Dept. Yazd University
• to reduce gas density in given volume to below atmospheric pressure with pump
• enclosed vessel has continuous sources which launch gas into volume and present pump with continuous gas load
• vacuum achievable at steady state is result of dynamic balance between gas load and ability of pump to remove gas form volume
Production of vacuumProduction of vacuum
Dr. G. Mirjalili, Physics Dept. Yazd University
Vacuum pumps and their characteristics
Vacuum pumps and their characteristics
• Gas transfer pumps:
(a) Positive displacement pumps that transfer repeated volumes of gas from inlet to outlet by compression ( e.g. rotary pump).
(b) Kinetic pumps that continuously transfer gas from inlet to outlet by imparting momentum to gas molecules (e.g. Diffusion pump, turbomolecular pump).
Dr. G. Mirjalili, Physics Dept. Yazd University
• Entrapment/capture pumps,
retain molecules by sorption or condensation on internal surfaces (e.g. sorption pump, sublimation pump, sputter ion pump, cryogenic pump).
Dr. G. Mirjalili, Physics Dept. Yazd University
Low vacuum pumps (1atm-10-3)
mbarRoughing Pumps
1
Dr. G. Mirjalili, Physics Dept. Yazd University
Ultrahigh Vacuum High Vacuum Rough Vacuum
Typical HighPressure
Typical Low Pressure
Vacuum (units)
1 atm.1.3x10-31.3x10-61.3x10-9
760 Torr1 Torr1 mTorr1x10-6 Torr
1 Torr =1 mm-Hg
101,333 Pa133 Pa0.133 Pa0.133x10-3 Pa
1 Pascal =1 N/m2
Dr. G. Mirjalili, Physics Dept. Yazd University
VACUUM PUMPING METHODS
Sliding VaneRotary Pump
MolecularDrag Pump
TurbomolecularPump
Fluid EntrainmentPump
VACUUM PUMPS(METHODS)
ReciprocatingDisplacement Pump
Gas TransferVacuum Pump
DragPump
EntrapmentVacuum Pump
Positive DisplacementVacuum Pump
KineticVacuum Pump
RotaryPump
DiaphragmPump
PistonPump
Liquid RingPump
RotaryPiston Pump
RotaryPlunger Pump
RootsPump
Multiple VaneRotary Pump
DryPump
AdsorptionPump
Cryopump
GetterPump
Getter IonPump
Sputter IonPump
EvaporationIon Pump
Bulk GetterPump
Cold TrapIon TransferPump
Gaseous Ring Pump
TurbinePump
Axial FlowPump
Radial FlowPump
EjectorPump
Liquid JetPump
Gas JetPump
Vapor JetPump
DiffusionPump
DiffusionEjector Pump
Self PurifyingDiffusion Pump
FractionatingDiffusion Pump
Condenser
SublimationPump
Dr. G. Mirjalili, Physics Dept. Yazd University
Name of Pump Mechanism of PumpingMechanical (roughing)* Compression of gasSorption Physical or chemical absorption Diffusion* Intermolecular collisions Turbo Molecular collisions with surfacesIon Ionization and implantation of gasCryo(genic) Solidification of gas by liquid He *used in lab
Dr. G. Mirjalili, Physics Dept. Yazd University
PUMP OPERATING RANGES
10-12 10-10 10-8 10-6 10-4 10-2 1 10+2
P (mbar)
Rough VacuumHigh VacuumUltra High Vacuum
Venturi Pump
Rotary Vane Mechanical Pump
Rotary Piston Mechanical Pump
Sorption PumpDry Mechanical Pump
Blower/Booster Pump
High Vac. PumpsUltra-High Vac. Pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
VACUUM SYSTEM USE
1
2
4
6
5
9
8
8
7
123
3a456789
ChamberHigh Vac. PumpRoughing PumpForeline PumpHi-Vac. ValveRoughing ValveForeline ValveVent ValveRoughing GaugeHigh Vac. Gauge
7
33a
Dr. G. Mirjalili, Physics Dept. Yazd University
Mechanical pumps• Mechanical pumps (displacement pumps) remove gas atoms
from the vacuum system and expel them to atmosphere, either directly or indirectly
• In effect, they are compressors and one can define a compression ratio, K, given by
• K is a fixed value for any given pump for a particular gas species when measured under conditions of zero gas flow.
out
in
PK
P
Dr. G. Mirjalili, Physics Dept. Yazd University
Rotary Vane, Oil-Sealed Mechanical Pump
Dr. G. Mirjalili, Physics Dept. Yazd University
Pump Mechanism
Dr. G. Mirjalili, Physics Dept. Yazd University
Gas ballastting
Dr. G. Mirjalili, Physics Dept. Yazd University
The Molecular Sieve/Zeolite Trap
Dr. G. Mirjalili, Physics Dept. Yazd University
Rotary pump Trap
Dr. G. Mirjalili, Physics Dept. Yazd University
Single &Dual Stage
Dr. G. Mirjalili, Physics Dept. Yazd University
How 2-stage rotary pump Works
Dr. G. Mirjalili, Physics Dept. Yazd University
OIL BACKSTREAMING
2
PRESSURE LEVELS: LESS THAN 0.2 mbar
Dr. G. Mirjalili, Physics Dept. Yazd University
Other types of Mechanical pumps
Rotary Piston
Roots
Rotary Vane
Dry pump
Dr. G. Mirjalili, Physics Dept. Yazd University
Dry Vacuum Pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
Root pump
Dr. G. Mirjalili, Physics Dept. Yazd University
How Root Pump works
Dr. G. Mirjalili, Physics Dept. Yazd University
One Stage Roots Blower Pump Assembly
Dr. G. Mirjalili, Physics Dept. Yazd University
Vacuum system use for Root pumps
123456789
101112
ChamberForelineRoughing ValveRoughing GaugeRoughing PumpForelineForeline ValveForeline GaugeHigh Vacuum ValveBooster/BlowerVent ValveHigh Vacuum Gauge
1
9
3
12
4
11
5
2
678
10
Dr. G. Mirjalili, Physics Dept. Yazd University
Diaphragm pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
Diaphragm pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
Diaphragm Pump• Eccentric shaft produces
alternate expansion / compression process
• Inlet / outlet via reed valves
• Ultimate vacuum 100 - 0.1 torr - limited by external leakage past valves, internal back-streaming, dead volume
• Compression ratio typically 10 - 30
• Pumping speed: single unit 0.1-0.7 l/s, parallel units up to 5.3 l/s
Dr. G. Mirjalili, Physics Dept. Yazd University
Diaphragm Pump
• High resistance to chemical attack
• Oil free - used with roots blower or cryopump for completely oil-free system
• Lifetime ~ 5000 hours
Dr. G. Mirjalili, Physics Dept. Yazd University
Diaphragm pump
Dr. G. Mirjalili, Physics Dept. Yazd University
Sorption Pump Components
Dr. G. Mirjalili, Physics Dept. Yazd University
The sorption pump has no moving parts and therefore no oils or other lubricants. (5 liters of liquid nitrogen)
Sorption pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
HIGH VACUUM PUMPS
2
Dr. G. Mirjalili, Physics Dept. Yazd University
VACUUM PUMPING METHODS
Sliding VaneRotary Pump
MolecularDrag Pump
TurbomolecularPump
Fluid EntrainmentPump
VACUUM PUMPS(METHODS)
ReciprocatingDisplacement Pump
Gas TransferVacuum Pump
DragPump
EntrapmentVacuum Pump
Positive DisplacementVacuum Pump
KineticVacuum Pump
RotaryPump
DiaphragmPump
PistonPump
Liquid RingPump
RotaryPiston Pump
RotaryPlunger Pump
RootsPump
Multiple VaneRotary Pump
DryPump
AdsorptionPump
Cryopump
GetterPump
Getter IonPump
Sputter IonPump
EvaporationIon Pump
Bulk GetterPump
Cold TrapIon TransferPump
Gaseous Ring Pump
TurbinePump
Axial FlowPump
Radial FlowPump
EjectorPump
Liquid JetPump
Gas JetPump
Vapor JetPump
DiffusionPump
DiffusionEjector Pump
Self PurifyingDiffusion Pump
FractionatingDiffusion Pump
Condenser
SublimationPump
Dr. G. Mirjalili, Physics Dept. Yazd University
PUMP OPERATING RANGES
10-12 10-10 10-8 10-6 10-4 10-2 1 10+2
P (Torr)
Rough VacuumHigh VacuumUltra High Vacuum
Roughing Pumps
Turbo Pump
Diffusion Pump
Cryo Pump
Ion Pump
Tit. Subl. Pump
Liquid Nitrogen Trap
Dr. G. Mirjalili, Physics Dept. Yazd University
VACUUM SYSTEM USE (high vacuum)
1
4
6
5
9
8
8123
3a456789
ChamberHigh Vac. PumpRoughing PumpFore PumpHi-Vac. ValveRoughing ValveForeline ValveVent ValveRoughing GaugeHigh Vac. Gauge
7
33a
28
2
Dr. G. Mirjalili, Physics Dept. Yazd University
Diffusion pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
Diffusion pumps
• diffusion pump is one form of a fluid entrapment pump– a fluid (usually oil) is heated and vaporized– the vapor is A sent through a nozzle with supersonic speed– the pump fluid vapor is condensed on a cooled surface
• Gas molecules are transported to the bottom of the pump by the pump fluid, where it is evacuated by a backing pump (usually a rotary vane pump) through the pump exhaust (the foreline)
• In order to work, the pump cannot be started until the foreline pressure is sufficiently low (~millitorr)
Dr. G. Mirjalili, Physics Dept. Yazd University
Water ejector pump (Liquid Jet pump)
Dr. G. Mirjalili, Physics Dept. Yazd University
Pump Construction
Dr. G. Mirjalili, Physics Dept. Yazd University
How the Pump Works
Dr. G. Mirjalili, Physics Dept. Yazd University
How the Pump Works
-A coil heater (1) raises the temperature of the oil pool (2) inside the pump body (3) with external cooling coils (4)
-The pump body is bolted to the vacuum system by a flange (5)
-The oil vapor rises through the housing that has 4 exit nozzles (A – D).
- The oil vapor exits the nozzles at high velocity (7) and collides with gas molecules (6), imparting a downward momentum to them.
Dr. G. Mirjalili, Physics Dept. Yazd University
First stage vapors are separated from others
Dr. G. Mirjalili, Physics Dept. Yazd University
Pumping Speed
10-10 10--3 10--1
Pu
mp
ing
Sp
eed
(A
ir)
1 2 3 4
Inlet Pressure (Torr)
Critical Point
1. Compression Ratio Limit2. Constant Speed3. Constant Q (Overload)4. Mechanical Pump Effect
Dr. G. Mirjalili, Physics Dept. Yazd University
Maximum Tolerable Foreline Pressure
(critical pressure)
Dr. G. Mirjalili, Physics Dept. Yazd University
LN2 reservoir with baffles
Dr. G. Mirjalili, Physics Dept. Yazd University
How the LN2 Trap Works
GasApproximate Vapor
Pressure (mbar)
Water (H2O)Argon (A)Carbon Dioxide (CO2)Carbon Monoxide (CO)Helium (He)Hydrogen (H2)Oxygen (O2)Neon (Ne)Nitrogen (N2)Solvents
10-22
500 10 -7
>760>760>760 350>760 760 <10 -10
Dr. G. Mirjalili, Physics Dept. Yazd University
Diffusion pump characters
Dr. G. Mirjalili, Physics Dept. Yazd University
Diffusion pump Fluids
Dr. G. Mirjalili, Physics Dept. Yazd University
Diffusion pumps -- additional information
• “The only justification for calling them diffusion pumps is due to the observation that the molecules of the pumped gas penetrate some distance into the vapor jet in a manner resembling diffusion of one gas into another.” (Hablanian, High Vacuum Technology)
• Original pumping fluid (before 1928) was mercury, since it did not break down and early oils did -- over 99% today use oil
• The boiler pressure inside a nozzle is 1 to 2 torr, while at the center of the vapor stream it is about 0.1 torr
• A cold trap is often used in the high vacuum side to reduce oil backstreaming
Dr. G. Mirjalili, Physics Dept. Yazd University
• Low cost per unit pumping speed, very high pumping speeds• Very well understood• Hard to destroy
• Continuous operating expense (LN2)
• Potential for serious vacuum accidents• “Open system”:Forbidden in certain applications
Diffusion pumps -- additional information
Dr. G. Mirjalili, Physics Dept. Yazd University
•Turbomolecular pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
Turbomolecular pumps (high vacuum and UHV)
Turbomolecular pumps (high vacuum and UHV)
• Medium to high cost per unit pumping speed• Very clean, pumps rare gases• Requires periodic maintenance which can be
expensive• Difficult to reach very low UHV base pressures• “Open system”:Forbidden in certain
applications
Dr. G. Mirjalili, Physics Dept. Yazd University
Pump OperationMolecule V
Moving Wall with Speed V
Principle of the Turbomolecular Pump
Dr. G. Mirjalili, Physics Dept. Yazd University
Turbomolecular pumps• Operation can be extended to higher pressure
by adding a drag stage
Dr. G. Mirjalili, Physics Dept. Yazd University
Principal of Turbomolecular pump
Dr. G. Mirjalili, Physics Dept. Yazd University
Rotor - stator assembly
Dr. G. Mirjalili, Physics Dept. Yazd University
Turbomolecular pump principle• To maximise the compression ratio, blade tip velocities
need to be comparable to molecular thermal velocities.• For a single blade, at zero flow
• where α12 is the forward transmission probability
• and α21 is the reverse transmission probability
• It can be shown that
• where Vb is the blade velocity
12
21
out
in
PK
P
0
exp2bV M
KTkN
Dr. G. Mirjalili, Physics Dept. Yazd University
Compression ratio
Dr. G. Mirjalili, Physics Dept. Yazd University
high pressurestages
fore vacuum
high vacuum
low pressurestages
moving rotors impartdownward momentumto gas molecules
fixed stators decelerate the molecule for thenext rotor “hit”
without the stators,the next rotor couldnot impart additionalvelocity to the gasmolecule
med. pressurestages
moving rotors only:a “molecular dragpump”
Dr. G. Mirjalili, Physics Dept. Yazd University
Turbomolecular Pump
ROTOR BODY
HIGH PUMPING SPEED
HIGH COMPRESSION
EXHAUST
HIGH FREQ. MOTOR
INLET FLANGE
STATOR BLADES
BEARING
BEARING
Dr. G. Mirjalili, Physics Dept. Yazd University
A typical turbomolecular pumpA typical turbomolecular pump
Dr. G. Mirjalili, Physics Dept. Yazd University
Turbomolecular Pumps
• Similar in design to a jet engine. Alternating rotor and stator blade assemblies turn at 20,000-90,000 rpm to force out molecules. Requires a region of low or medium vacuum behind and in front of pump.
Pfeiffer Vacuum GmbH
Dr. G. Mirjalili, Physics Dept. Yazd University
Turbomolecular pump.
• Turbo pumps cannot pump from atmosphere and cannot eject to atmosphere, so they require: 1-roughing (fore vacuum) pumps to reduce the pressure in the vacuum system before they can be started and
2-backing pumps to handle the exhaust.• There are many types of roughing and backing
pumps. Most accelerators now use clean (dry) pumps to avoid oil contamination in the system.
Dr. G. Mirjalili, Physics Dept. Yazd University
Turbopump (con’t)
• contains no oil and is capable of reducing the pressure into the ultrahigh
vacuum range
• operates as a “molecular bat”
- rotor blades spinning at speeds as high as 6x104 rpm,
- gives a blade velocity at a radius of 10 cm of 3.8x106 cm/s.
- the mean velocity of a molecule of N2 at 300 K is 4.8x104 cm/s
• Because the rotor blades are slanted downward, the gas
molecules are driven towards the pump outlet
Blade sizes increase towards the high pressure exit port Stator (stationary) blade sets are placed between rotor blade sets
• Pumping efficiency is greatest when the spacing between blades is less than the mean free path of the molecules. (~5 cm at 10-3 Torr)
Dr. G. Mirjalili, Physics Dept. Yazd University
Turbo pumps speed
Dr. G. Mirjalili, Physics Dept. Yazd University
Vacuum system use for Turbo pumps
123456
ChamberTurbo PumpRoughing PumpVent ValveRoughing GaugeHigh Vac. Gauge
1
67
4
3
25
2
Rotary pump
Dr. G. Mirjalili, Physics Dept. Yazd University
Turbo pump &Rotary pump
Process chamber
Turbomolecular Pump
High rotation speed turbine imparts momentum to gas atoms
Inlet pressures: <10 mTorr
Foreline pressure: < 1 Torr
Requires a rough pump
Good choice for toxic and explosive gases –
-gases are not trapped in pump
All gases are pumped at approx. the same rate
Pumping Speeds:
20 – 2000 liters per sec
foreline
adapted from Lesker.com
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion Pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion Getter Pump
A getterIs a materialthat reactswith a gasmolecule toform a solid nonvaporizable material
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion pump• The ion pump works by ionizing
gas molecules and accelerating them into walls coated with freshly-evaporated titanium– the gas ions strike a titanium
cathode and cause sputtering– the sputtered Ti is reactive and
will getter reactive gases (N2, O2)
– the gas ions can be buried by self-ion implantation
• A strong magnetic field is applied to cause the electrons to move in helical paths and increase the ionization efficiency
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion pump (sputter- Ion pump, getter Ion pump)
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion pumps
• Main components– Array of parallel
stainless tubes– Various charged
surfaces– Titanium or tantalum
coated surfaces
• Trap molecules with varying speeds via chemical reactions
Varian Scientific Instrumentation, Inc.
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion pumps• Ion pumps have several serious disadvantages
– low pumping speeds (inert gases are pumped especially poorly)
– can only be started at low pressures (~ 10-4 torr)– can “arc-over” if pressure increases suddenly
• However, ion pumps are very clean and can produce very high vacuums (<10-12 torr)
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion pump
• Expensive per unit pumping speed
• Low pumping speed
• Generates hydrocarbons
• Has a memory effect
• Very low maintenance
• Moderately difficult to destroy
• Excellent base pressures
Dr. G. Mirjalili, Physics Dept. Yazd University
• Does not pump rare gases well
• Does not pump hydrogen
• Closed system: very safe against vacuum accidents
A typical A typical ion-pumpion-pump
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion Pumps• Current (per cell) – and hence pumping
speed – depends on voltage, magnetic field, pressure and history.
nI kP 1.05 < n < 1.2
Pump life depends on quantity of gas pumped
> 20 years at 10-9 mbar
Prone to generate particulates
Leakage current unpredictable, so pressure indication below 10-8 mbar unreliable
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion Pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion PumpsDiode Differential
DiodeStarcell Triode
Voltage +7kV +7kV +2-5kV -5kV
Pumping Speed (Active gases)
Highest Good Good Lowest
Pumping Speed (Noble gases)
Lowest Good Higher Highest
Starting Pressure Lowest Lowest Good Highest
UHV Low Low Good Highest
Cost Lowest Higher Low Highest
Dr. G. Mirjalili, Physics Dept. Yazd University
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion PumpsPumping in the basic diode Penning cell
Dr. G. Mirjalili, Physics Dept. Yazd University
Ion Pumps
• The Diode pump has poor pumping speed for noble gases
• Remedies– Differential Ion; Noble Diode
• “Heavy” cathode
– Triode– Special Anode shape e.g. Starcell
Dr. G. Mirjalili, Physics Dept. Yazd University
•Cryopumps
Dr. G. Mirjalili, Physics Dept. Yazd University
Cryo-condensation
Dr. G. Mirjalili, Physics Dept. Yazd University
Cryopumps
Dr. G. Mirjalili, Physics Dept. Yazd University
Pumping by Cryocondensation
Cold surface
molecules
Dr. G. Mirjalili, Physics Dept. Yazd University
Cryopumps
• Similar in principle to the ion pump but uses a cryogenically cooled surface of activated charcoal or zeolites to condense and trap gas molecules.
Kurt J. Lesker Vacuum Technology
Dr. G. Mirjalili, Physics Dept. Yazd University
Cryosorption in charcoal
Dr. G. Mirjalili, Physics Dept. Yazd University
Charcoal placement
Dr. G. Mirjalili, Physics Dept. Yazd University
CryopumpsCryopumps condense gases on cold
surfaces to produce vacuum
Typically there are three cold surfaces:
(1) Inlet array condenses water and hydrocarbons (60-100 Kelvin)
(2) Condensing array pumps argon, nitrogen and most other gases (10-20 K)
(3) Adsorption is needed to trap helium, hydrogen and neon in activated carbon at 10-12 K. These gases are pumped very slowly!
Warning: all pumped gases are trapped inside the pump, so explosive, toxicand corrosive gases are not recommended. No mech. pump is needed until regen.
adapted from www.helixtechnology.com
(Campbell)
Dr. G. Mirjalili, Physics Dept. Yazd University
CryopumpsCryopumps
• Expensive per unit pumping speed
• Very high pumping speeds are possible
• Pumping hydrogen (pumps everything)
• Requires periodic recharging
• Vibration can be a serious problem
Dr. G. Mirjalili, Physics Dept. Yazd University
Types of Cryogenic Pumps
• There are two major classes of such pumps– Liquid Pool
• Liquid helium temperature (~4K)
– Closed cycle• Refrigerator (~12K)• Supplemented by cryosorption
Dr. G. Mirjalili, Physics Dept. Yazd University
Cyro pump (Liquid Pool)
Dr. G. Mirjalili, Physics Dept. Yazd University
Cyro pump (Closed cycle )
Dr. G. Mirjalili, Physics Dept. Yazd University
Cryogenic Pump Speed
Dr. G. Mirjalili, Physics Dept. Yazd University
Getter Pumps
• When a gas molecule impinges on a clean metal film, the sticking probability can be quite high.
• For an active gas with the film at room temperature, values can be between 0.1 and 0.8. These fall with coverage.
• For noble gases and hydrocarbons sticking coefficients are very low (essentially zero)
• Evaporated films, most commonly of titanium or barium, are efficient getters and act as vacuum pumps for active gases.
Dr. G. Mirjalili, Physics Dept. Yazd University
Getter pumps
• In recent times, thin films of getter material have been formed on the inside of vacuum vessels by magnetron sputtering
• These have the advantage of – pumping gas from the vacuum chamber by gettering – and of stopping gases from diffusing out of the walls
of the vessels
Dr. G. Mirjalili, Physics Dept. Yazd University
Getter Pumps
• For vacuum use, the most common getter pump is the titanium sublimation pump
Dr. G. Mirjalili, Physics Dept. Yazd University
Titanium sublimation pumps (HV and UHV)
Titanium sublimation pumps (HV and UHV)
• Very inexpensive and simple
• Requires periodic maintenance, which is cheap
• Often misused, which limits their performance
• Selective in what it pumps (good for oxygen, N2, air, not for rare gases)
Dr. G. Mirjalili, Physics Dept. Yazd University
A typical titanium sublimation pumpA typical titanium sublimation pump
Dr. G. Mirjalili, Physics Dept. Yazd University
Dr. G. Mirjalili, Physics Dept. Yazd University
Others Getter Pumps
• An important class of getter pumps are the Non Evaporable Getters (NEGs)
• These are alloys of elements like Ti, Zr, V, Fe, Al which after heating in vacuo present an active surface where active gases may be gettered
• Traditionally, the getters take the form of a sintered powder either pressed into the surface of a metal ribbon or formed into a pellet
Dr. G. Mirjalili, Physics Dept. Yazd University
Getter Pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
Getter Pumps
Dr. G. Mirjalili, Physics Dept. Yazd University
•Vacuum cycle
Dr. G. Mirjalili, Physics Dept. Yazd University
Pumpdown Curve• Conditions:
– Chamber closed and sealed– Vacuum pump on and all isolation valves open– No gas flowing into the chamber
• What would an ideal pumpdown curve look like?• What effect would the following have on the ideal
curve?– Real (Gross) Leak– Virtual Leak– Permeation Leak– Outgassing– Backstreaming
Dr. G. Mirjalili, Physics Dept. Yazd University
Pumpdown procedure
Dr. G. Mirjalili, Physics Dept. Yazd University
Venting procedure
Dr. G. Mirjalili, Physics Dept. Yazd University
Dr. G. Mirjalili, Physics Dept. Yazd University
Dr. G. Mirjalili, Physics Dept. Yazd University
Dr. G. Mirjalili, Physics Dept. Yazd University
Dr. G. Mirjalili, Physics Dept. Yazd University
System pumpdown
Dr. G. Mirjalili, Physics Dept. Yazd University
Standard Vacuum Cycle• Step 0: Start at atmospheric pressure at t=o
– load wafer and close chamber– alternative, start at loadlock pressure (~100mT)
• a loadlock is a separate vacuum chamber that prevents the chamber from being exposed to atmosphere
• Step 1: Pump down to base pressure– remove atmospheric contaminants from the chamber– verify system integrity– continue to next step: when pressure falls below a trigger
point– abort: if base pressure is not reached within a certain
amount of time, indicating a leak or a pump problem
Dr. G. Mirjalili, Physics Dept. Yazd University
Standard Vacuum Cycle• Step 2: Introduce gasses and stabilize pressure
– pressure increases from base pressure to process pressure
– most reactive gas is introduced last– throttle valve controls conductance to achieve desired
process pressure (effects residence time of gasses)– continue to next step: when pressure reads within a
specified range– abort: if process pressure is not reached within a
certain amount of time, indicating a pressure control problem
Dr. G. Mirjalili, Physics Dept. Yazd University
Standard Vacuum Cycle• Step 3: Process
– equilibrium is maintained through controlled gas flow and controlled (throttled) pressure
– RF power (if applicable) is introduced– continue to next step: when pre-set time is reached,
or endpoint is detected (for etch process)– abort: if pressure drifts outside of desired range
Dr. G. Mirjalili, Physics Dept. Yazd University
Standard Vacuum Cycle• Step 4: Pump Out
– gas flows and RF Power (if applicable) are turned off– throttle valve opens wide– purpose is to remove the majority of the reactive gasses from the
chamber– continue to next step: when base pressure is reached for a
minimum length of time
• Step 5: Purge– inert gas (usually nitrogen - why?) is introduced into the chamber– pressure inside the chamber increases to a trigger point– presence of nitrogen restores viscous flow allowing residual
reactive gasses to be efficiently pumped (rinsed) out– continue to next step: when a minimum pressure is reached
indicating adequate nitrogen has entered the chamber
Dr. G. Mirjalili, Physics Dept. Yazd University
Standard Vacuum Cycle• Step 6: Second Pump Out
– turn off nitrogen– pump out nitrogen and residual reactive gasses to base pressure– continue to next step: when base pressure is reached for a
minimum length of time– Note: steps 5 and 6 may be repeated
• Step 7: Vent– close all valves between chamber and pump– flow nitrogen directly into chamber– pressure increases from base pressure to atmospheric (or
loadlock) pressure– continue to next step: when atmospheric pressure is reached
• Step 8: Open Chamber and Unload Wafer
Dr. G. Mirjalili, Physics Dept. Yazd University
Abort Conditions• Abort = Failure to meet all conditions required to
continue processing.– Pressure not in range, Gas flow not in range, Electrical or
mechanical malfunction, Timeout, Interlock tripped.– Accompanied by an audible and visible alarm.
• Abort Priority:– 1. System immediately goes to safest possible state.– 2. Possible recovery of product material.
• Safest Possible State:– Shut off all gas flows.– Shut off RF power (if applicable).– Pump(s) on, all isolation and throttle valve(s) wide open.
top related