Vacuum technology
Chambers and pumps
 Vacuum (Latin vacuo): nothingness, empty space, lack of gas
 lack of gas is measured by pressure 
 SI unit: Pa
 widely used in engineering: mbar
 common sense as scientist: atm
Pressure units
2
Vacuum range
mbar
Pa
Particle density
Mean free path
Kn
Rough vacuum
1000 - 1
105 - 100
1025 - 1022 m-3
l << d
<< 1
1 - 10-3
100 - 0.1
1022 - 1019 m-3
l≈d
≈1
10-3 - 10-7
10-1 - 10-5
1019 - 1015 m-3
l>d
>1
< 10-7
< 10-5
< 1015 m-3
l >> d
>> 1
< 10-11
< 10-9
< 1011 m-3
l >>> d
>>> 1
RV
Medium vacuum
MV
High vacuum
HV
Ultra-high vacuum
UHV
Extremely-high
vacuum (XHV)
 vacuum chamber: recipient of dimension d suitable for holding a low pressure for long
periods of time - implosion proofed!
 typical materials: steel (304, 316), glass (only HV)
Vacuum chambers
3
Vacuum chambers
4
 vacuum chambers are interconnected using flanges and valves available in various systems:
 ISO-KF (kleinflansch): 10 - 50 mm
 KF10, KF16, KF25, KF40, KF50
 ISO-F: 63 - 630 mm
 F63, F80, F100, F160(150), F200,
F250, F320, F400, F500, F630
 ISO-K: 63 - 630 mm
 K63, K80, K100, K160(150), K200,
K250, K320, K400, K500, K630
HV vacuum flange systems
http://eu.trinos.com
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 components:
 blank flanges
 full or half nipples
 flex hoses
 centering rings
 clamps
 various connectors are available for standardized constructions
 sealing material for rings: Neoprene, Silicone, Teflon, Viton, metal (aluminum)
 suitable for multiple use except for metal sealings
 suitable pressure range: RV to HV
 metal sealing must be used for pressures below 10-6 mbar (10-4 Pa)
HV vacuum flange systems
http://eu.trinos.com
6
 vacuum valves are critical points in a vacuum system since are most prone to leakages
diaphragm valves
angle valves
in-line valves
gate valves
control valves
(butterfly)
Vacuum valves
http://www.vatvalve.com
7
 a proper selection of vacuum pumps is critical for vacuum applications
 gas transfer pumps
 positive displacement pumps - this pumps suck! 
 oil sealed pumps: rotary vanes, rotary piston
 trapped volumes of gas are isolated using oil
 dry pumps: roots, scroll, piston/diaphragm
 trapped volumes of gas are isolated using close clearances
between moving parts or O-rings - oil free pumps
 kinetic (momentum transfer) vacuum pumps
 diffusion pumps, turbomolecular pumps
 gas binding pumps - molecules are removed through adsorption or condensation on surfaces
inside the pump
 cryo-pumps, getter pumps, sublimation pumps, sputtering pumps
Vacuum pumps
8
a) rotary vanes pump
b) rotary piston pump
 a volume of gas is trapped
inside the pump due to
mechanical movement of a rotor
 from inlet, the gas is
compressed and forced out
through outlet
 the rotor is partially submerged
in an oil bath for a better sealing
or isolation between zones with
various partial pressures
 pumping speeds: 1 - 1500 m3 h-1
 working temperature: 20 - 90°C
 ultimate pressure:
 single stage: 1 Pa (10-2 mbar)
 dual stage: 10-2 Pa (10-4 mbar)
Oil sealed pumps
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 pump oil selection must be done accordingly with the application and its special requirements
 for commonly used oils (mineral) the oil viscosity specified by the pump manufacturer must
always be respected - too low viscosity leads to leakage and noise, too high viscosity leads to
difficulty of starting at room temperature and occasionally seizures
 oil types:
 Hydrocarbon oils - highly refined mineral oil - the most usual oil used - may contain
additives for minimizing the corrosion effects of vapors being pumped
 Synthetic organic-type oils - used for heavy-duty applications at high temperatures - have
improved oxidation resistance
 Fluorinated (perfluoropolyether) fluids - higher grade oils used for an increased operation
time between pump maintenance periods. Advantages:
 chemical inertness - ideal for pumping aggressive materials (semiconductor industry)
 noninflamable - no fire risk
 high thermal resistance - no residual “tar” is formed by overheating
 oxygen-compatible - allows safe pumping of oxygen
Oil sealed pumps
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 momentum


p  mv
m1
 elastic collision - momentum conservation
 massive target m1<<m2
'

 v1  v1
m2



p  0  m1v1  m2 v2

v
 momentum transfer pumps
 momentum is transferred to gas molecules so that
a continuous flow is ensured between inlet and outlet
moving surface

v
 positive displacement pumps are trapping volumes of
gas between inlet and outlet - fundamental difference
 momentum can be transported by:
 high speed vapor streams - diffusion pumps
 continuously moving parts - turbomolecular pumps
Kinetic vacuum pumps
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 concept:
 vapors from liquids (e.g. Hg or petroleum) are produced
in a boiler (D)
 when inserted in an evacuated chamber through a small
opening (nozzle), the vapors will expand acquiring a high
forward mass velocity - vapor jet (P)
 expansion of the vapor jet is limited by the gas present in
the pump - at low pressures a diffuse layer of vapor mixed
with penetrating gas molecules is formed
 gas diffused into vapors is moved in the jet direction
 separation of vapors and gas is done through
condensation on cold surfaces (walls of the pump) (F)
 gas molecules are trapped by vapor barriers
 special design of the nozzles (e.g. umbrella-type)
 diffusion pumps require backing (forevacuum) pumps (N)
Diffusion vacuum pumps
Langmuir’s diffusion pump
12
 multistage pumps - more efficient in trapping gas under
several jet barriers
 the narrowing neck in front of the vapor jet - diffuser (Venturi
tube)
 diffusion not necessarily happen - jet speed is high
enough so that the barrier is very efficient
 diffusion pumps - historical name from Venturi
 small molecules can diffuse back - not efficient for H, He, etc
 used for achieving HV in “dirty” processing chambers
 special diffusion oil chemically inert (resistant to oxidation)
 operating pressure: 10-1 - 10-6 mbar
 pumping speeds: up to 1000 l s-1 (3600 m3 h-1)
 Q gas throughput (load)
Q  SP
 S pumping speed
 P desired pressure
Diffusion vacuum pumps
Edward’s diffusion pump
13
 momentum transfer from a fast rotating surface
(turbine blade) to the gas molecules - molecular drag
 rotors and stators alternating lead to a controlled
direction of the moving gas molecules
 successive collisions/deflections produce a net
molecular flow from the inlet to the outlet
 progressive inclinations of the blades minimize
the back-deflection
 extremely high-speed motors (up to 1.25 kHz - 75000 RPM)
 Boeing turbo jet engine - 36500 RPM 
 huge compression factors: N2 up to 1011 (1:10 for Boeing)
 if mean free path of the gas molecules higher than
the distance between rotor and stator blades:
 molecules interact mainly with the blades
 backing is needed
 pumping speeds: up to 3200 l s-1
 operating pressure: 10-2 - 10-10 mbar
Turbomolecular vacuum pumps
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 various designs available - single rotation axis - most common
 critical point: mechanic support of the rotors
 mechanical rotor suspension (ceramic ball bearings - zirconia)
 magnetic rotor suspension - for low vibration, hydrocarbon free vacuum
 service intervals:
 bearing exchange 10000 - 15000 h (14 - 21 months)
 rotor axis exchange 45000 - 100000 h (5 - 12 years)
 magnetic suspension are service-free pumps
 frequency converters are necessary to be used with turbo pumps
 extra caution should be used when mounting a turbo pump to a vacuum chamber!!!
 always use steel screw/bolts (as many as possible, at least M8)

v
 never start a turbopump if is not properly connected to the chamber (big mass)
 r = 0.05 m, f = 1.25 kHz - circumference L = π/10 m - radial speed v = Lf = 395 m/s
 m = 0.001 kg rotor imbalance - dropping a peanut E 
1 2
mv  80 J  80 N  m
2
 distance to the chamber d = 0.01 m, F = 8 kN - similar with a cannonball energy

r
Turbomolecular vacuum pumps
http://www.oerlikon.com
15
Vacuum technology
Vacuum measurement
 gauge = pressure sensor (transducer) - various phenomena can be exploited:
 displacement of a liquid column, diaphragm, or other deformable element by force due
to a pressure differential (RV)
 viscous drag acting upon a moving element (MV - HV)
 thermal conductivity (HV)
 ionization by electrons, nuclear radiation, or laser photons, and sensing either ion
current or emitted light (UHV)
 Capacitance diaphragm gauge
 Piston pressure gauge
 U-tube manometer
P1  P2  gh
P1  P2  mg / A
Vacuum gauges
a2
C Y 
P
4T
T = membrane radial tension
17
 a hot filament loses heat by: radiation, conduction to supports, transfer to the surrounding gas
 total energy
WT  WR  WC  WG
 Thermocouple gauge: temperature is
measured from the potential drop arising at
the junction between two dissimilar metals
 Pirani gauge: temperature of the
filament is measured from its resistance
 energy loss due to gas pressure - temperature loss electrical resistance change
 the filament resistance is
measured in a Wheatstone
bridge
 the gauge measures the
pressure correctly in the
linear regime
Thermal conductivity gauges
18
 Bayard-Alpert gauge
 hot cathode electron emission
 triode design
 the collector current iC is
proportional with the pressure
iC  Ki P  ir
 K depends on cell geometry
 i- - incident electron current
 ir - residual current due to photoelectrons ejected
from grid and collector
 positioning the BA gauge inside vacuum is critical
 the entire volume of the triode must be inside the
bulk vacuum
 the flanges containing the gauge cannot be placed
inside tubes - more X-rays can be generated
 pressure range: 10-3 - 10-12 mbar
Ionization gauges
19
Thermal evaporation
 a conductor having a potential difference between two planes will accelerate electrons in a field E

E

Fe
 the electric force Fe will be opposite to a material specific
resistance force Fr
 
 


 Newton law: Fe  Fr  ma  eE  kv  ma

 eE
V1
V2
 when the movement is uniform, a=0
V1 > V2
v
e 
and the speed of the electrons is:
k


 the current density through the conductor ca be
j  V ve
expressed as a function of the volume charge density:

Fr
 Ohm’s law can be directly derived




eE
j  V
 j  E
k
where  is the electrical conductivity
 the resistance force Fr is the classical description of the interactions (collisions) between moving
carriers (electrons) and the phonons of the crystalline structure of the conductor
 kinetic energy is transferred to the material
Ohm’s law for electric conductivity
21
 Joule effect: electrons passing through a conductor will generate heat due interactions with
the crystalline structure of the conductor - kinetic energy transfer
 must depend on material’s electrical resistivity (resistance)  r 
- characterizes the intensity with which the material opposes
the current flow
1

l V

Fe
 must depend on the current intensity
 must depend on the time
V
 



 the electrostatic force Fe produces work: W  Fe l  qEve t  V V Eve t  j EVt
 work is transformed into heat:
W Q
j2

Vt 
I2
Sn 
2
Vt  I 2
l
t
S n
 where the electric current depends on the current density j and normal surface Sn:
 Joule-Lenz law expresses the heat produced in any
portion of resistive and homogeneous solid:
Q  I Rt
2
R
j
I
Sn
l
 l
 r
S n
Sn
Joule effect
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 Joule effect is used for heat generation in furnaces - evaporation sources in vacuum
 evaporation sources (thermal elements)
 high melting point metals (W, Ta, Mo, and their alloys)
 direct evaporation
 the material to be evaporated comes in direct contact with the thermal element
 risk of alloying between the thermal element and the material - short lifetime
 indirect evaporation - the thermal element is used for heating a crucible (e.g. Al2O3)
Thermal
filaments
 point source
 loop source
 small amounts of material
 for wire materials
 coils
 baskets
 serpentines
 spirals
 low deposition temperatures
 average amounts of
material (mg)
 for small flakes, pellets
 higher deposition
temperatures possible
Evaporation sources
www.lesker.com
23
Thermal boats
 dimple
 notched
Thermal boxes
 top hat
 long through
 canoe
 single or multiple reservoirs for plane source simulation
Rod sources (Cr on W)
 high amounts of material
 high deposition rates
Evaporation sources
 high temperatures
www.lesker.com
24
Coated thermal elements (alumina)
 inverted hat
 basket
 interaction with the thermal
element is minimized
 alloying is avoided
 lifetime is extended
Crucibles - heated by coils or baskets
 alumina
 quartz
C
 Ta, Mo, W
 boron nitride
 used when indirect deposition sources are necessary
 evaporated material should not alloy (or diffuse into) with the crucible
 e.g. Al suitable for deposition from alumina or W, but not from C
Evaporation sources
www.lesker.com
25
 designs of single or multiple sources are possible
 two highly conductive electrodes (pure Cu) are used for transporting high currents (300A DC
or AC) to the thermal element
 cooling of the current feedthroughs is necessary
 liquid (the inner part of the rods is hollow) or air (outside the chamber ventilators are
used for cooling the entire rod)
Thermal evaporator design
26
 most of the time, thermal / evaporation shielding has to be used for protecting the chamber
1)
pumping unit
2) pressure measurement
3)
power source
4) vacuum chamber with implosion protection
Thermal evaporator design
27
Thin film uniformity
Thickness distribution
 point source evaporation
 equal amounts of material go in
all directions
Ms
 total evaporated mass Me
dAs
 total deposited (condensed) mass Ms
dAs
r
r0
 substrate plane at distance r0 from source
 elementary substrate surface dAs

dAc
d
Me
 arbitrary condensation surface on the
sphere dAc cut by a solid angle d
 arbitrary elementary surface projected
through the solid angle d
 distance to dAs is r
 evaporation angle 
Thin films thickness
29
 condensation surface depends on dAs
dAc  dAs cos 
Ms
dAs
dAs
r
r0
 the fraction of material accumulated on substrate
must be proportional to the surface fraction through
each the evaporand escapes the sphere
dM s : M e  dAc : 4r

dAc
d
Me
2
 simple mathematics:
dM s
Me
dM s
Me



cos 
2
2
dAc 4r
dAs
4r
 if Ms0 is the amount deposited at zero angle, then:
3
M s r0
 r0 
3

cos



cos



0
2
Ms r
r
2
 cos law for point source
Thin films thickness
30

 plane source (Knudsen cell) - similar to Lambert law:
2
dM s M e
M s r0
 2 cos  cos   0  2 cos  cos 
dAs r
Ms r
 general case:
dM s M e n  1
n



cos
cos
2
dAs
2r

d
2
M s r0
n


 n0
cos
cos
0
2
Ms r
 If the evaporation angle and the deposition angle are the same:
3
M s  r0 
4

cos


cos



0
Ms  r 
plane
3
M s  r0 
n
n 3

cos


cos



0
Ms  r 
Thin films thickness
general
31
32
33
34
35
 material: Al; evaporation distance: 65 mm
Experimental data
36