Inductively coupled plasma source using induced eddy currents

Abstract

Methods and apparatus are provided for generating an inductively coupled plasma using induced eddy currents. An inductively coupled plasma source of the invention generally comprises a body constructed substantially of a conductive material interrupted by at least one dielectric gap. Radio frequency power is coupled from a current carrier into the conductive body. The one or more dielectric interruptions in the conductive body are disposed so as to cause eddy currents to circulate about portions of the body and thereby couple RF power into a plasma in proximity to the conductive body. By utilizing induced eddy currents to couple power into a plasma, the invention allows for substantial bodies of conductive materials, such as structural metals, to be interposed between the induction coils that receive power from a power generator and the plasma.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates generally to plasma processing sources, and more particularly to apparatus and methods for inductively coupled plasma processing. [0003] 2. Brief Description of the Prior Art [0004] Inductively coupled plasma sources in a variety of configurations are employed in a broad range of industrial applications. Inductively coupled plasma processing chambers are used abundantly for modifying the surface properties of materials, as for example in the manufacture of modern integrated circuits. Inductively coupled plasma sources may also operate as remote sources of activated gas species for downstream processing operations, or as abatement devices for treatment of toxic or environmentally harmful materials. [0005] In one form of well known inductively coupled plasma source, radio frequency (RF) power is coupled from inductive coils into a plasma contained within a dielectric enclosure. For example, the ...

AI Technical Summary

Benefits of technology

[0011] By utilizing induced eddy currents to couple power into a plasma, the invention allows for substantial bodies of conductive materials to be interposed between the induction coils that receive power from a power generator and the plasma. Thus, in one embodiment of the invention, an inductively coupled plasma source may be constructed in the form of a simple linear or solenoidal discharge tube, but wherein the tube is composed almost entirely of a conductive material such as a metal. The use of a nearly all-metal plasma chamber can have many advantages, including simplified manufacturability and thermal management. A plasma chamber that is substantially conductive also largely avoids the problem of ion bombardment of the chamber walls by reducing or eliminating capacitive coupling between the induction coils and the plasma. As a result, an inductively coupled plasma source of the invention has enhanced performance and durability compared to sources that rely substantially upon structural dielectric materials for confinement of the plasma.

[0013] In forming a plasma chamber of conductive segments, the dielectric breaks between segments may extend along the entire length of the chamber. The chamber may also be formed by joining the segments at their longitudinal ends using caps or rings of dielectric material. Alternatively, the conductive segments may be joined at their longitudinal ends with a conductive material. Although this provides a leakage current path that reduces the power coupled from the induction coils into the plasma, power loss may be minimized by making the path of the leakage current substantially longer than that of the eddy currents.

Problems solved by technology

The use of dielectric chamber materials to separate induction coils from the plasma discharge body can significantly limit the scale and operational range of an inductively coupled plasma source.

Structural dielectric materials, such as quartz or sapphire, typically suffer from mechanical and thermal constraints when used in high power density and chemically reactive applications.

The need to extract and dissipate thermal energy transferred from the plasma to the chamber walls is also more challenging when the chamber is constructed of dielectric materials.

Cooling mechanisms such as forced air or circulating fluids are not only complicated and expensive to implement, but also typically result in reduced coupling efficiency of power to the plasma.

Moreover, electrostatic coupling between the induction coils and the plasma can result in localized ion bombardment of the chamber walls, which not only exacerbates the problem of chamber heat extraction but may over time impair the structural integrity of the chamber itself.

A topologically toroidal plasma source is a complex apparatus, however, that does not lend itself to simple design and manufacturing for commercial applications.

Moreover, the performance a toroidal source is limited by the quality, expense, and ability to cool the high permeability ferrite materials that must typically be employed for operation with RF power sources in medium to high frequency ranges.

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