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Negative Ion Source Disclosure Number: IPCOM000050750D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 33K

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Cuomo, JJ: AUTHOR [+3]


A solid sputter ion source is described for extracting negative ions by selecting materials with proper negativity.

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Negative Ion Source

A solid sputter ion source is described for extracting negative ions by selecting materials with proper negativity.

In reactive plasma etching it is generally desirable to deliver to a substrate highly reactive atoms, molecules or radicals which undergo various physical and chemical interactions with the substrate material. In standard etching processes, the substrates are subjected to a combination of neutral gas flow and positive ion bombardment, whether they are immersed in the glow discharge, mounted on the cathode of a diode or triode RF system, or bombarded by the effluents from an ion milling type source. While a certain degree of control can be exercised over the positive ion flux density and energy in these processes, these ions generally contain a very small percentage of the most highly reactive species, namely the halogen atoms. This fact arises from the high electronegativity characteristic of these elements.

In the figure, a negative ion source with a unique extraction arrangement 10 is illustrated. This source generates a beam of negative ions which contains a much higher percentage of halogen and highly electronegative atoms (e.g. , oxygen, if desired). Thus, this source provides the ion flux control features available in ion milling sources and also an enhanced chemical etching feature from the higher reactive species content in the beam.

A particular disadvantage associated with this source design is the susceptibility of the discharge chamber walls and particularly the cathode 12 to chemical reactions with the gases used in the source, leading to reduced source lifetime. This problem can be overcome by selecting the material for the cathode 12 from a class of materials which yield a large flux of negative ions (in particular, the desired halogens) when bombarded with positive ions. Such materials include LaF(3), TbF(3), TbCl(3), TEFLON(Trademark of E. I. du Pont de Nemours, & Co.), etc. These materials act as a solid source of reactive halogen ions which are sputtered into the discharge plasma 14...