Physics 358 Nanolithography

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Physics 358 Nanolithography
Overview of vacuum and deposition systems
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Deposition techniques
Chemical techniques Electroplating Chemical vapor
deposition (CVD) X Plasma enhanced CVD
X Reactive sputtering X Molecular beam epitaxy
(MBE) X Usually too high temperatures or other
problems with resist in extreme environments
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Deposition techniques (cont.)
Physical Deposition Thermal evaporation Electron
beam evaporation Sputtering (mechanical
ablation) Pulsed laser deposition (PLD) For best
results, need line of sight deposition Thermal
and e-beam evaporation best Sputtering not
considered to be ideal, but can do
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Thermal evaporation
Simple conceptually Heat boat to melt and
evaporate metal Need good vacuum long mean free
path, large distance between source and
substrate Boat material should not alloy with
metal
sample holder
sample substrate
Bell jar
material
Boat or filament
To vacuum pumps
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Electron beam evaporation
Use electrons to heat up material, using an
electron source (e-gun). Very similar to e-gun
in SEM Typical voltages 5 kV
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Comparison of thermal evaporation and e-gun
evaporation
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Sputtering
Good for alloys and hard to evaporate materials
Sputtering gun
Ion gun
Target
sample substrate
sample holder
I
I
To vacuum pumps
To vacuum pumps
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Vacuum production techniques
Why do we need a good vacuum? Mean free path of
atoms is longer, less scattering 10 cm at 10-3
Torr Less contamination Monolayer coverage time
tmn/(s ZA) n density of sites, s sticking
coefficient ZA ?v/4, ? density, v mean velocity
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Vacuum in general
Vacuum ranges Atmosphere 760 mm of Hg 760
Torr Rough vacuum down to 10-3 T High vacuum
10-3 - 10-8 T Ultra high vacuum 10-9 -
10-12 T Metric unit is Pascals, 1 Pascal 1
N/m2 1 Torr 133 Pascals
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Vacuum production
Rough vacuum Sorption pumps adsorption of
gases on cold surface Scroll-pumps
Traditional mechanical pumps belt-driven and
direct drive
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Vacuum production
High and ultra high vacuum Diffusion pumps
Ion pumps Turbo pumps Cryogenic pumps
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Vacuum production
Diffusion pumps Boiling oil (percolator) forms
supersonic jet that that traps gas
molecules Needs to be backed with mechanical
pump! Problem backstreaming of oil in high
vacuum area..solve by using cold trap, either
nitrogen or water
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Vacuum measurement
Rough vacuum Mechanical gauges, Bourdon.
diaphragm gauges Thermal conductivity gauges
Thermocouple (TC) gauges, Pirani gauges Higher
vacuum Ionization gauges (hot and cold
cathode gauges, Penning gauges)
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Film thickness measurement
Quartz crystal thickness monitor Frequency of
oscillation of a quartz crystal is changed by
mass of metal deposited on it Calibrated by
density, acoustic impedance, etc Need to take
into account geometry of chamber (tooling factor)