MEMS_16-17 gw chat 3_physical vapor deposit 02

MEMS_16-17 gw chat 3_physical vapor deposit 02 - Physical...

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Physical vapor deposition Thermal evaporation One of the oldest techniques for film deposition Based on boiling off or sublimating of a heated material onto a substrate in a vacuum Flux: number of molecules leaving an unit area of evaporant per second
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Physical vapor deposition Thermal evaporation equ. (3.22) based on thermodynamics F l = N 0 exp-(Φ e /kT) F l : flux N 0 : slow vary function of T T : temperature Φ e : activation energy (in eV) required to evaporate one molecule of the evaporant material Φ e = H/(e x N) H : enthalpy of formation of the evaporant N : Avogadro’s number
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Physical vapor deposition Thermal evaporation Resistive heating : in lab setting, a metal is evaporated by passing a high current through a highly refractory metal containment structure (e.g. filament) Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. Simple but easily spreads contaminations that are preset in the filament Small size of filament limits the thickness of the film O 2 pressure should be low -> reduce chemical reaction
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Physical vapor deposition Thermal evaporation
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Physical vapor deposition Thermal evaporation In industry, resistive heating is surpassed by e-beam induction evaporation : RF induction evaporation laser Heat sources
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Physical vapor deposition Thermal evaporation e-beam: fig. 3.5B High intensity e-beam gun (3-20 keV) is focused on the target material that is placed in a recess in a H 2 O cooled copper hearth The e-beam is magnetically directed onto the evaporant, which melts locally The metal forms its own crucible The contact with the hearth is very cool -> few chemical reaction -> resulting in fewer source- contamination
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Physical vapor deposition Thermal evaporation: e-beam
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Physical vapor deposition Thermal evaporation E-beam evaporation: High quality film High deposition rate 50-500 nm/min Disadvantage Might induce x-ray damage Possibly even some ion damage to the substrate At v >10 kV, the incident e-beam will cause x-ray emission Could be avoided by using a high power laser beam instead of e-beam Deposition equipment is more complex
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Physical vapor deposition Thermal evaporation RF induction heating H 2 O cooled RF coupling coil surround a crucible with the material to be evaporated 2/3 RF energy is absorbed with one skin depth of the surface -> Frequency decreases Skin depth : also known as classical skin depth, is a measure of the distance an alternating current can penetrate beneath the surface of a conductor Materials: refractory metals: Pt molebdenum ,
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Physical vapor deposition Sputtering The target material to be evaporate: a disk at high –potential Bombarded with + ion created in plasma The target material is sputtered away as neutral atoms by momentum transfer The ejected surface atoms are deposited onto the substrate placed on the anode
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MEMS_16-17 gw chat 3_physical vapor deposit 02 - Physical...

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