L07-Sputtering_a

L07-Sputtering_a - Sputtering Vacuum Evaporation Recap Use...

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Sputtering
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Vacuum Evaporation Recap Use high temperatures at high vacuum to evaporate (eject) atoms or molecules off a material surface. Use ballistic flow to transport them to a substrate and deposit. Film uniformity can be an issue. Alloy evaporation is very complicated and in most cases, not possible.
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An Alternative Method Instead of using heat to eject material from a source, we can bombard them with high speed particles. The momentum transfer from the particles to the surface atoms can impart enough energy to allow the surface atoms to escape. Once ejected, these atoms (or molecules) can travel to a substrate and deposit as a film. There are several considerations here: Creating, controlling and directing a high speed particle stream. Interaction of these particles with the source surface and emission yields. Deposition of the emitted atoms on the substrate and film quality. Source Substrate
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Some Terminology Atomic particles can best be easily controlled by electromagnetic methods if they are charged. A weakly charged gas of particles that exhibit collective behavior is called a plasma . The source material is called the target and the emitted atoms or molecules are said to be sputtered off.
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Sputtering So in sputtering, the target material and the substrate is placed in a vacuum chamber. A voltage is applied between them so that the target is the cathode and the substrate is attached to the anode. A plasma is created by ionizing a sputtering gas (generally a chemically inert, heavy gas like Argon). The sputtering gas bombards the target and sputters off the material we’d like to deposit. -V Target (cathode) Substrates Anode Sputtering gas Plasma
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Generating and Controlling the Plasma Ions can be generated by the collision of neutral atoms with high energy electrons. The interaction of the ions and the target are determined by the velocity and energy of the ions. Since ions are charged particles, electric and magnetic fields can control these parameters. The process begins with a stray electron near the cathode is accelerated towards the anode and collides with a neutral gas atom converting it to a positively charged ion. The process results in two electrons which can then collide with other gas atoms and ionize them creating a cascading process until the gas breaks down. The breakdown voltage depends on the pressure in the chamber and the distance between the anode and the cathode.
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This document was uploaded on 02/29/2012.

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L07-Sputtering_a - Sputtering Vacuum Evaporation Recap Use...

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