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Module 1: Physical Vapour Deposition

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Physical Vapor Deposition - Lesson Summary

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Physical Vapour Deposition (PVD) is a thin-film deposition method that allows the deposition of almost all materials that are used in fabrication. In PVD, the surface reaction occurs very rapidly, and so, very little rearrangement of atoms occur on the film surface. As a result, thickness uniformity, shadowing by surface topography and step coverage can be a very important issue in PVD. 

In evaporation techniques of PVD, a vacuum chamber is pumped down to a pressure of less than 10-5 Torr. Heating utilizing electricity causes the source material (typically a metal like gold or aluminium) to melt and evaporate. Evaporation atoms from the source condense on the surface of a wafer forming a thin film material that can then be etched by lithography methods. The interest of these techniques in this course is to understand how these techniques can be used to fabricate EEG electrodes. 

Thermal Evaporation:

• Relies on thermal energy supplied through electricity (voltage) to the crucible or boat where the source material is placed to evaporate atoms from the source. 
• Evaporated atoms travel through the evacuated space between the source and the sample (wafer) and stick to the sample. 
• The surface reaction usually occurs very rapidly and there is very little rearrangement of the surface atoms after sticking. 

E-Beam Evaporation: 
• Electron Beam (e-beam) evaporation is a physical vapour deposition process that allows the user to evaporate materials that are difficult or even impossible to process using the standard resistive thermal evaporation method. Some of these materials include high-temperature materials and some ceramics. 
• To generate an electron beam, an electrical current is applied to a filament which is subjected to a high electric field. This field causes electrons in the filament to escape and accelerate away. The electrons are focused by magnets to form a beam, directed towards a crucible that contains the material. The energy of the e-beam is transferred to the material to start evaporation. 

Sputtering:
• Sputtering uses argon gas to target the molecules and atoms of a source or material we want to deposit. When the argon “hits” the “target” and dislodges the atoms, these atoms will fall down one by one onto a substrate.
• Sputtering can be divided into four categories: DC sputtering, RF sputtering, Magnetron sputtering, and Reactive sputtering.