Division of Plasma Physics

Commercial Applications

surface reactions

PLASMA DISCHARGES used in materials processing cause bombardment of solid surfaces with free radicals and ions, inducing a variety of processes such as ion implantation, sputtering, etching and deposition.

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PLASMA SPRAY TORCHES are used to deposit thermal barrier layers on jet engine components. [Courtesy of General Electric Co., Aircraft Engines Division]

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PLASMA ETCHING is used to fabricate high-density integrated circuits. A microscopic blowup of the etched surface is shown in the upper right.

As one manifestation of such behavior, a skin or sheath forms around a plasma when it is in contact with a solid surface. Plasma sheaths, like so many collective effects in plasma, can be either a blessing or a curse to the engineers who try to put this elusive state of matter to work for them. When a plasma is created above a semiconducting wafer in a microprocessing fab, the strong electric fields in the sheath at the wafer's surface accelerate plasma ions nearly straight downward, and some of them zip through the gaps in a "photoresist," or mask, that bears the pattern of an integrated circuit. Those ions crash into the silicon-based material and pump energy into the chemical reactions that etch the narrow, deep trenches-often less than a micron across-out of which the circuits are made. Earlier techniques, based on wet chemistry, tended to undercut the trench walls and couldn't pack as much memory and logic circuitry onto a wafer.

Related methods are supplementing and supplanting wet chemistry in applying thin, high-quality coatings to everything from jet engine components to human prosthetics. Unfortunately, the physics of a plasma's edge doesn't always spin a happy tale for the engineers, and such boundary effects can cause withering problems for plasma applications in other settings: When high-energy particles hurtle from hot fusion plasmas, they can knock cold particles loose from the container's walls, quenching and contaminating the plasma within.

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ELECTRON CYCLOTRON RESONANCE plasma reactors are used to deposit silicon dioxide and silicon nitride. Precise control of the deposited materials' properties is achieved by varying the parameters of the plasma. [Courtesy of Engineering Research Center for Plasma Aided Manufacturing, University of Wisconsin, Madison; Photographer, Bruce Fritz]

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