Ion beam

An ion beam is a type of particle beam consisting of ions. Ion beams have many uses in electronics manufacturing (principally ion implantation) and other industries. Today's ion beam sources are typically derived from the mercury vapor thrusters developed by NASA in the 1960s.

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Uses

Ion beam etching or Sputtering

One type of ion beam source is the duoplasmatron. Ion beams can be used for sputtering or ion beam etching and for ion beam analysis.

Ion beam etching, or sputtering, is a technique conceptually similar to sandblasting, but using individual atoms in an ion beam to ablate a target. Reactive ion etching is an important extension that uses chemical reactivity to enhance the physical sputtering effect.

In a typical use in semiconductor manufacturing, a mask is used to selectively expose a layer of photoresist on a substrate such as a silicon dioxide or gallium arsenide wafer. The wafer is developed, and for a positive photoresist, the exposed portions are removed in a chemical process. The result is a pattern left on the surface areas of the wafer that had been masked from exposure. The wafer is then placed in a vacuum chamber, and exposed to the ion beam. The impact of the ions erodes the target, abrading away the areas not covered by the photoresist. This method is frequently enhanced by bleeding a reactive gas into the vacuum system, which is known as reactive ion etching.

Focused Ion Beam (FIB) instruments are also used in the design verification and/or failure analysis of semiconductor devices. Engineering prototype devices may be modified using the ion beam in order to rewire the electrical circuit. The technique may be effectively used to avoid performing a new mask run for the purpose of testing design changes. A device edit (FIB milling operation) is accomplished by focusing the ion beam on selected regions of the device in order to mill through metal or polysilicon structures. In addition to milling, it is also possible to use the ion beam to force the deposit of new conductive lines on the surface of the device. This is accomplished by injecting chemicals into the ion stream near the device surface. The interaction between the ions and the chemicals result in chemical deposition on the surface. This process is typically referred to as a FIB deposit operation.

Sputtering is also used in materials science to thin samples or specific regions of samples for transmission electron microscope analysis, or for extending surface analytical techniques such as secondary ion mass spectrometry or electron spectroscopy (XPS, AES) so that they can depth profile them.

High energy ion beams

High energy ion beams produced by particle accelerators are used in atomic physics, nuclear physics and particle physics.

Weaponry

The use of ion beams as a particle beam weapon is theoretically possible, but has not been demonstrated. See particle beam weapon for more information on this type of weapon.

In science fiction, weaponised ion beam generators are usually dubbed ion cannons.

See also

• Particle beam