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31 Cards in this Set
- Front
- Back
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Elastic collision
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Energy and momentum are conserved and no attractive or repulsive forces between molecules
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Kinetic Theory Assumptions (4)
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1. Large number of Molecules per volume
2. Adjacent Molecules are separated by distances Large compared to their diameters 3, Molecules are in a constant state of random motion 4. Collisions are elastic |
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Maxwell-Boltzmann Distribution
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The distribution of molecular velocities is proportional to Molecular weight and absolute temperature
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Mean Free path
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The distance traveled by Molecules between successive Collisions
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Gas impingement flux
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The frequency with which Molecules collide on a surface
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Contamination Time
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The time it tales for a surface to be coated by a monolayer of gas molecules
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Molecular Flow
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Large distance between Collisions where pressure is reduced and kinetic theory is observed
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Viscous Flow
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Low mean free path at elevated pressure meaning more intermolecular interactions To molecule/wall, very complex
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Knudsen Number
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Distinguishes between Molecular and Viscous flow regimes. Ratio between mean free path and a characteristic diameter
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Conductance
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The volume of gas traveling through An orifice Per second
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Pumping Speed
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The volume of gas passing through the vacuum inlet or a given plan eper unit time
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Gas transfer pumps
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Remove gas molecules from pumped volume and Convey them to ambient in Compression
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Entrapment pump
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Condense or chemically bind Molecules to surfaces situated within the chamber being pumped
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Rotary mechanical Pump
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Positive displacement pump drawing gas into space . Minimum pressure 10^ -2 To 10^-4 torr
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Roots Pump
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Oil-free seal and very high pumping speeds popular in sputtering and LPCVD
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Diffusion Pump
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No moving parts. Molecular flow regime so Mechanical fore pump required but subject to backsteaming at very low pressures
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Turbo molecular Pump
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Directs Molecular motion by rapidly whirring turbine and requires no traps or baffles
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Cryopump
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Rely on the Condensation of Vapor molecules on surfaces colder than 120k by Van der Waals forces but require low initial fore pressure
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Sputter Ion Pump
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Relies on sorption processes initiated by ionized gas to permanently remove gas
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Physical Vapor Deposition
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Reliance on solid or molten Sources.
Physical mechanisms release atoms. Released source transported through vacuum Evaporation and Plasma assisted sputtering |
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Clausius-clapeyron
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Equation expressing connection between temperature and Vapor pressure
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Coefficient of Evaporation
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= 1 for Knudsen Cell
about 1 for many molten metal <1 for sublimation from a solid source |
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Strategies for compound or Alloy deposition
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Separate Sources, evaporate t anneal, pulsed Laser deposition
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Pulsed Laser Deposition
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Small point vaporizes before heat is conducted away
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Sputter Deposition
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Argon + ions bombard target
Atoms dislodged from source Sputter everywhere |
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Plasma Creation
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Chamber evacuated to 10^-7 for purity
Bleed in Argon Negative potential to source e-is created and collides to form Ar ions Ar ions accelerate Toward source, self sustaining |
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Paschen Curve
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Relates voltage to Pressure and inter cathode distance
Low Pd → too few collisions High Pd → too many collisions quenching discharge |
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Cathode glow
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Highly luminous layer clings to cathode probably by ion neutralization
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Cathode dark Space
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A region of relatively little ionizations
Dropped discharge voltage accelerate ion to cathode |
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Negative Glow
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Visible emission due to excitation and de excitation
Substrate goes here |
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Magnetron Sputtering
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Magnets direct path of electron
Less pressure required |
