6 - Physical Vapor Deposition (PVD) Himanshu J. Sant...

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Physical Vapor Deposition (PVD) Himanshu J. Sant Fundamentals of Microfabrication Evaporation • Material is heated to attain gaseous state • Carried out under high-vacuum conditions (~5x10 -7 torr) • Advantages – Films can be deposited at high rates (e.g., 0.5 μ m/min) – Low energy atoms (~0.1 ev) leave little surface damage – Little residual gas and impurity incorporation due to high-vacuum conditions – No substrate heating – Alloys can be deposited
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Evaporation • Limitations – Accurate alloy compounds difficult – No in situ substrate cleaning – Poor step coverage – Variation of deposit thickness for large/multiple substrates – X-ray damage – Relatively poor adhesion Evaporation • Resistive evaporation – Uses resistive heating to evaporate a metallic filament – Drawbacks • Limited to low melting point metals • Small filament size limits deposit thickness • Electron-beam evaporation – Uses a stream of high energy electrons (5-30 keV) to evaporate source material – Can evaporate any material – Electron-beam guns with power up to 1200 kw – Drawbacks • At >10 kV incident electrons can produce x-rays • Redeposition of metal droplets blown of source by vapor • Ion beam evaporation • Inductive heating evaporation – Essentially eddy current losses
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Evaporation System Evaporation System Requirements • Vacuum: – Need 10 -6 torr for medium quality films. – Can be accomplished in UHV down to 10 -9 torr. • Cooling water: – Hearth – Thickness monitor – Bell jar • Mechanical shutter: – Evaporation rate is set by temperature of source, but this cannot be turned on and off rapidly. A mechanical shutter allows evaporant flux to be rapidly modulated. • Electrical power: – Either high current or high voltage, typically 1-10 kW.
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Evaporation Support Materials • Refractory metals: – Tungsten (W); MP = 3380°C, P* = 10 -2 torr at 3230°C – Tantalum (Ta); MP = 3000°C, P* = 10
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This note was uploaded on 09/02/2010 for the course MEEN 5050 taught by Professor Himanshuj.sant during the Spring '10 term at University of Utah.

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6 - Physical Vapor Deposition (PVD) Himanshu J. Sant...

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