WO1996013621A1

WO1996013621A1 - An ecr plasma source

Info

Publication number: WO1996013621A1
Application number: PCT/US1995/011648
Authority: WO
Inventors: Ole D. Krogh; Herbert J. Sawin
Original assignee: Krogh Ole D; Sawin Herbert J
Priority date: 1994-10-31
Filing date: 1995-09-18
Publication date: 1996-05-09

Abstract

An apparatus is described as a source of a plasma for gas abatement whereby toxic or environmentally harmful effluent from a process chamber (1) is converted to harmless and stable products. The plasma source may also be used for downstream processing. A substrate can be effected by deposition of a thin film, followed by etching of the substrate surface, or otherwise modifying the surface. The plasma is produced in a gas by magnetic field and microwave energy in ECR mode. The microwave field is coupled to the chamber gas (1) by an antenna rod (2) or through a microwave transparent window (27). Permanent magnets (4) are placed either on the side of the chamber opposite the entrance of the microwave field or along the sides of the chamber or in magnetized rings placed along the entire length of the chamber. This increases the ability of plasma electrons to absorb power and increase the electron density in the plasma by magnetic confinement thereby avoiding excessive loss of electrons to the chamber walls. Process gases can be added either just before or just after passage through the plasma source.

Description

AN ECR PLASMA SOURCE.

BACKGROUND OF THE INVENTION

The present invention is a device used to generate a gaseous plasma in which an oscillating electromagnetic field ionizes neutral species in the gas phase to form ions and electrons, excites neutral species to form electronically excited atoms and molecules, and dissociates molecules to form atoms and radicals. Industrial plasma processing involves the exposure of a workpiece to the plasma effluents in order to remove material from the substrate surface (etching), grow material on the substrate surface (deposition), chemically alter the surface (plasma oxidation, nitration, surface cleaning and passivation), physically modify the surface (surface roughing or smoothing), or generally modify the conditions on the surface or in the body of the workpiece (e.g. plasma sterilization). Another application is gas abatement which involves using the plasma source as a low-temperature incinerator to convert toxic or environmentally harmful industrial emissions into harmless substances. The utility of a plasma source relates for many applications to the density of charged particles in the plasma, ions and electrons. This density, in turn, is governed by the rate of production versus the rate of loss of ions and electrons. Plasmas and plasma sources are characterized and differentiated not only by the density of charged particles in the resulting plasma but in addition by the frequency of the generating electromagnetic field and by the range of gas pressure or vacuum suitable for its operation. The following review of prior art is limited to the technology associated with plasmas generated by microwaves of frequency 2.45 GHz.

ECR. In a plasma electrons oscillate with the electrical component of the generating electromagnetic field. The electrical as well as the magnetic vector is located in a plane perpendicular to the direction of propagation of the electromagnetic field. If a strong magnetic field is imposed on the plasma the electrons are forced to gyrate around the magnetic field lines with a rotation frequency determined by the strength of the magnetic field. The plane of rotation is perpendicular to the magnetic field lines. By proper adjustment of the electromagnetic frequency and magnetic strength the oscillation frequency due to the electromagnetic field and the gyration frequency caused by the superimposed magnetic field can be brought to .coincide. This defines the special condition of electron cyclotron resonance, ECR. In addition to the matching of frequencies the spacial arrangement must be such that the electrical vector of the electromagnetic field is in the plane of gyration. This is the case when the microwave propagation is parallel with the magnetic field lines. With the microwave propagation perpendicular to the magnetic field lines resonance is spatially restricted but in reality the resonance zone is broadened by collisional scattering of the electrons as well as by the Doppler effect associated with the velocity of electrons. The ECR condition is characterized by a drastically increased microwave power absorption by the plasma electrons resulting in much higher densities of charged particles and a much greater degree of dissociation in an ECR plasma than in a microwave plasma without the auxiliary magnetic field. Collisional scattering of electrons by neutrals will interfere with the electron gyration resulting in dampening of the effect as a gas pressure is raised. However, the effect is still substantial in helium at 1 torr as reported by B. Lax, P. Allis, and S.C. Brown, J. Appl. Phys., 21, 1297 (1950).

Electromagnets. In practice, the necessary magnetic field can be produced either by an electromagnet or by a permanent magnet. By far the most common has been to use electromagnets. These magnets are usually in the shape of a solenoid which encloses the process chamber or part of the chamber, the plasma generating subchamber. In order to achieve adequate control of the shape of the magnetic field two or even three solenoid coils are used. This is exemplified by U.S. Patent Nos.

4,876,983, 4,915,979, and 4,970,435. In order to produce a magnetic field of the proper strength currents in excess of 100 amps are needed in the coils producing heat and demanding elaborate cooling efforts. In addition, the circuitry to control the strength of the magnetic fields generated by the coils as well as the considerable size and weight of such electromagnets increase the cost of these systems very significantly. The size, or "footprint", is of particular concern in the semiconductor industry, where cleanroom space is at a premium.

Permanent magnets. Permanent magnets have been used in .order to avoid the costly disadvantages of electromagnets. The problem now becomes one of placing the magnets sufficiently close to the plasma and the workpiece considering the rapid decay of the magnetic field strength with the distance from the magnet surface. In U.S. Patent No. 4,433,228 the permanent magnet is placed in the microwave waveguide itself. While this arrangement brings the magnet very close to the workpiece it necessitates that the microwaves pass through the magnetic material thereby limiting the microwave power that can be applied in order to avoid destroying the magnet by the generated heat. In addition, the electromagnetic field of the microwave is perturbed by passage through the magnetic material. This disadvantage is avoided in U.S. Patent No. 5,196,670 where the microwaves are brought in between the magnet and the quartz windows allowing the microwaves, to pass into the chamber without passing through the magnet. However, this effectively moves the magnet further away from the preferable location of the ECR plane in the chamber which, in turn, necessitates a considerably more powerful and costly magnet. Permanent magnets have also been used in connection with high density plasmas in order to reduce the rate of loss of electrons to the chamber walls by magnetic confinement. Here, the magnets function by repelling the electrons away from the walls back into the plasma. This is illustrated by U.S. Patent No. 4,483,737, where the plasma source is a hot filament, and by U.S. Patent No. 5,032,202, where the source is an electromagnetic ECR subchamber. In U.S. Patent No. 5,032,205 permanent magnets provide the necessary magnetic field for ECR operation and the plasma source is an RF electrode in the chamber itself. A similar setup is described in U.S. Patent No. 4,745,337, where the in-chamber electrodes are microwave antennas.

Coupling of microwave power to the plasma. Power can be coupled from a waveguide to the plasma either through a window of microwave transparent material or through an electrode or antenna. Several recent patents describe the use of antennas to couple power into microwave plasmas for substrate processing. Thus, in U.S. Patent No. 4,745,337 mentioned above a series of antenna rods are placed inside the processing chamber at the exact location of the ECR resonance field of permanent magnets located external to the processing chamber. The stated purpose of the arrangement is to create a field free region in the center of the chamber for substrate processing. In U.S. Patent No. 4,866,346 an antenna rod is used to couple microwave power from one waveguide to another with the purpose of creating a circular axisymmetric microwave field in the second waveguide. The power is finally coupled to a substrate processing chamber through a window, specifically a quartz bell jar. The field necessary for ECR resonance is provided by magnets, permanent or electromagnetic, located outside the bell jar.

Remote Processing. Remote processing here designates treatment of a substrate located outside the plasma excitation region in a separate, downstream processing chamber as opposed to and distinct from the in situ plasma generation chamber.

There are a variety of industrial processes that involve the plasma activation of a gas or gas mixture, transport of the activated gas effluent to a downstream region, and reaction to a deposit a film on a substrate, to remove or etch a surface layer from a substrate, or to chemically or physically alter or modify the surface or body of the substrate. The gas or gas mixture can be activated by a number of means such as a hot filament, a microwave discharge, a DC or RF discharge, and plasma jets or torches. U.S. Patent No. 5,206,471 describes a microwave activated gas generator, in which the gas is passed through the MW waveguide in a quartz tube, but with no provisions for creation of ECR conditions and thus much less efficient. Another example is U.S. Patent No. 5,115,166 using a plurality of similar microwave plasma generators, again unsuitable for ECR operation, employing the downstream processing region for substrate sterilization.

There is no prior art in the technology area known as reactive sputter deposition of optical thin films closely related to the present invention. Typically, a substrate is moved from a sputtering zone with an inert atmosphere, where the substrate is coated with a metal or metal alloy, to a reaction zone with a reactive and/or activated atmosphere, where the sputtered material is chemically altered to form the final film. The sputter zone is separated from the reaction zone by either physical means, as in U.S. Patent No. 4,420,385, or by formation of concentration gradients of the proper chemicals, as in U.S. Patent No. 4,851,095. Remote plasma activation of the gases flowing to the reaction zone is expected to accelerate the conversion of the sputtered film to the final, optically transparent film.

The design for in situ plasma sources or substrate processing chambers has been greatly restricted by the need to make room for the workpiece in the process chamber. This concern has prevented more ideal designs which would have the magnet be closer to the plasma so that the necessary magnetic field can be achieved with a much smaller and less costly magnet. The present invention makes this ideal or optimal design possible by moving the workpiece completely out of the source chamber. Remote plasma sources are usually under restrictions too severe to allow for the cost and bulk of the traditional electromagnetic ECR source. The savings in production cost and in space requirements associated with the present invention will for the first time make a remote ECR plasma source production worthy.

Gas abatement. Release of gases that are toxic to humans or generally harmful to the global environment is of growing concern to the Environmental Protection Agency and to the industrial producers of these gaseous emissions. The semiconductor industry is particularly affected by this concern as the fabrication of computer chips involves very toxic chemicals (arsine, phosphine, chlorine) as well as very stable compounds capable of reaching the upper atmosphere inflicting serious and long-term damage to the planetary climate: ozone depletion by chlorofluorocarbons and global warming by perfluorinated compounds. The present invention is thought to be especially suited for abatement of the perfluorinated compounds, CF₄, C₂F₆, and NF₃, used in this film etching and cleaning of chambers for chemical vapor deposition (CVD). The application of the present invention for gas abatement involves location of the plasma source downstream from a processing chamber. The gas molecules in the effluent of the processing chamber are dissociated by electron impact collisions in the plasma, and suitable reaction partners for the molecular fragments can be added either just before or right after passage through the plasma source.

There does not seem to be any consideration of using plasma abatement for incineration of industrial emissions prior to the recent concern for global warming by perfluorinated compounds. Thus, the prior art for this application is limited to three reports at conferences involving, in all cases, non-ECR plasma abatement. The proof-of-principle report is provided by F.-W. Breitbarth, H.-J. Tiller, and K. Dummke, Proceedings of the 11th International Symposium on Plasma Chemistry, 728 (1993). They demonstrate abatement of C₄F_ and CHF₃ in a capacitively coupled RF discharge. Demonstration of microwave plasma abatement of C₂F₆ was provided in a report by M.T. Mocella, V. Mohindra, and H.H. Sawin at the meeting of The Electrochemical Society, San Francisco, May 1994. An additional report on microwave abatement of C₂F₆ was given by J.D. Cripe at the Global Warming Symposium, Dallas, June 1994. The most significant feature separating the present invention from all reported abatement experiments is the ability to operate in the ECR mode afforded by the permanent magnet. For the application for gas abatement the ECR feature has particular significance as it implies a higher electron density in the plasma, probably by a factor of 10 to 100, which should affect the efficiency in direct proportion. The mechanism of gas abatement by a plasma clearly is based on extensive dissociation of the gas by electron impact collisions and therefore depends on the availability of electrons. Another property of ECR plasmas of special importance to gas abatement is the drastically increased power absorption in the ECR mode. High flow gas abatement, e.g. 2 standard liters per minute of C₂F₆, is expected to require input of 2-5 kWatts power to the plasma, which is far beyond the capability of a non-ECR plasma to absorb for a small reaction volume and low process pressures. In addition, there are specific differences between the present invention and each of the reported experiments. Thus, it is widely recognized that the microwave frequency used in the present invention, 2.45 GHz, is much more efficient for the purpose of plasma dissociation than capacitively coupled RF frequencies, 13.56 MHz or lower, used by Breitbarth, et al .

In a production environment reliability is crucial. Thus, it is important that the pressure and flow oscillations frequently occurring in the semiconductor production environment not cause the plasma to extinguish and the abatement to stop. It is considered an important feature of the present invention that the functional pressure range is very wide, spanning from a fraction of a millitorr to tens of torr. The ECR functionality extends the range to the lowest pressures, and at pressures above 1 to 10 torr the magnets have no effect and the source functions as an ordinary microwave source. If necessary, the re-ignition of the plasma could be further facilitated by a UV radiation source or other means.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a microwave plasma source, operating in the ECR mode, for remote processing and for abatement of toxic or environmentally harmful gases. It is also an object of the present invention to provide an ECR plasma source with smaller power consumption than comparable electromagnetic sources.

It is also an object of the present invention to provide an ECR plasma source with less magnetic material than comparable permanent magnet sources due to the simplicity of the present design which, in turn, is made possible by moving the substrate out of the source chamber.

It is a further object of this invention to provide an ECR plasma source at considerably lower cost than comparable electromagnetic sources.

It is also an object of the present invention to provide an ECR plasma source with a smaller volume than a comparable electromagnetic source. It is a further object of the present invention to provide a plasma source which will function more reliably and with less maintenance than any comparable source.

It is a still further object of the present invention to provide a plasma source which assures reproducibility of processing more than any comparable source.

Finally, it is an object of the present invention to provide a plasma source capable of igniting the plasma at any pressure or of re-igniting the plasma during pressure and flow oscillations often occurring in semiconductor production environments.

These objects are accomplished with the present invention which includes a plasma chamber into which the microwave energy from a magnetron is coupled by an antenna rod or through a microwave transparent window. The magnetic field necessary for ECR plasma conditions is provided by blocks of permanent magnets located outside the chamber itself and arranged around the chamber in different embodiments of the invention. Entrance and exit ports for a gas or gas mixture are located on the remaining unencumbered chamber sides such that gas molecules are forced to pass through or near the ECR surface in order to travel from entrance to exit port. For the purpose of remote processing the source chamber is intended to be coupled to the upstream side of a process chamber holding a workpiece such that the plasma activated effluent flows from the source chamber to the process chamber in order to modify the workpiece chemically or physically. The dimensions and material of the coupling as well as the nature of the interior surfaces are determined by the chemical system and the desired modification of the workpiece specific to a given technological application. For the purpose of gas abatement the source chamber is intended to be coupled to the downstream side of a process chamber in which the gases to be abated are used or produced. The effluent from the process chamber will then flow through the source chamber where abatement will take place.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the vertical cross section according to the present invention. The microwave waveguide is coupled to the plasma chamber through an antenna rod.

FIG. la is a side view of the vertical cross section according to the present invention. The microwave waveguide is coupled to the plasma chamber through a microwave transparent window.

FIG. 2 is a side view of the vertical cross section of an alternative arrangement of the present invention. The microwave waveguide is coupled to the plasma chamber through an antenna rod. FIG. 3 is a side view of the vertical cross section of a further alternative arrangement of the present invention. Here, again, the microwave waveguide is coupled to the plasma chamber through an antenna rod.

FIG. 3 a is a cross-sectional view from the top of the chamber shown from the side in FIG. 3.

FIG. 4 is a side view of the vertical cross section of an alternative embodiment in which the antenna pass all the way through the chamber.

FIGS. 5a-c are cross-sectional views from the top of the chamber shown from the side in FIG.4 illustrating three different arrangements of magnets external to the chamber.

FIG. 6 is a side view of an arrangement in which a tubular magnetic field containing the antenna rod is created by a set of magnetic rings external to the chamber.

FIG. 7 is a block diagram illustrating the application of the present invention as a plasma source for remote processing.

FIG. 8 is a block diagram illustrating the application of the present invention for gas abatement.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is an ECR plasma source for remote processing or for gas abatement and is illustrated in FIG. 1. It involves a vacuum chamber 1, an antenna rod 2, a waveguide 3 for microwaves, a permanent magnet or composite magnet block 4, chamber cooling means 5, magnet cooling means 6, and entrance 7 and exit 8 ports for gas or gas mixture.

The plasma chamber 1 has a cylindrical sidewall 9 which is made hollow to accommodate cooling liquid constantly flowing through chamber cooling means 5 and magnet cooling means 6. The chamber 1 is constructed of non-ferromagnetic metallic material or quartz, and made to tolerate total evacuation of the chamber. The antenna rod 2 is made of inert material like stainless steel and is hollow to allow water cooling. Externally to the chamber 1 and located under the bottom of the chamber is a magnet or magnet pack 4 designed such that the magnetic field lines are perpendicular to the bottom of the chamber 1 as shown by arrows 12 and of such strength that the decaying field drops to about 875 Gauss in a plane near the middle of the chamber and parallel to the top and bottom, and the surface so defined is often referred to as the ECR resonance surface. The magnet pack 4 is protected from excessive heating by the plasma by having the wall between plasma chamber and magnet pack hollow to accommodate cooling liquid the same way as described for the sidewall. The interior surfaces of the chamber are coated with a hard, wear resistant and inert coating the nature of which depends on the chemical system used in the plasma. The coating is designed to protect the chamber from chemical and physical attack by the plasma activated species and to minimize the deactivation and recombination of these species on the walls of the chamber.

The permanent magnet 4 is positioned below the chamber 1 with its N-S poles aligned with the propagation of the microwave field coupled into the chamber 1 by the antenna 2 and shown by arrows 11. This geometry assures that the center magnetic field line is at right angle to the electric field associated with the microwaves.

The plasma source is operated by introduction of a gas or gas mixture through entrance port 7 or a plurality of such ports, and the inlet flow and exit flow through port 8 is adjusted so as to keep the total pressure sufficiently reduced in order to limit collisional scattering of the gyrating electrons by neutrals, preferably below about 1 torr. The nature of the gas or gas mixture depends on the mode of application of the plasma source. For the purpose of remote processing in a downstream chamber the choice of gases is entirely determined by the chemistry and nature of the downstream activity. For the purpose of abatement of perfluorinated compounds (PFC's) the effluent mixture entering through port 7 will in part consist of unreacted PFC's and in part of other gas additives and reaction products specific to the upstream activity. In addition, suitable reaction partners, e.g. oxygen and hydrogen, can be added to the effluent mixture in order to facilitate the conversion of the carbon in the PFC to CO₂ and the fluorine to HF. The microwave power supply (not shown) generates microwaves which travel down the waveguide 3 and are coupled to the plasma by the -11- antenna rod 2.

In the resulting microwave plasma electrons are accelerated by the electrical component of the electromagnetic field which oscillates in a plane perpendicular to the direction of propagation. In a magnetic field electrons gyrate around the magnetic field lines with a rotational frequency determined by and proportional with the strength of the magnetic field. The plane of rotation is perpendicular to the magnetic field lines. The microwave field propagates radially from the antenna and it becomes possible for its electrical component to cooperate with the magnetic field in the acceleration of electrons where the plane of gyration coincides spacially with the electrical vector of the microwave field. While the microwave frequency here is fixed at 2.45 GHz the magnetic field strength and therefore the gyration frequency decays monotonously with the distance from the magnet surface. Resonance between the electrical field oscillation and the magnetic field gyration occurs at 875 Gauss for the microwave frequency of 2.45 GHz. At this point the two forces are in phase and a drastically increased power absorption by the electrons becomes possible. This condition is termed electron cyclotron resonance or ECR. With the proper design of the magnet pack 4 this will occur near the center of the described plasma chamber 1 in a surface roughly parallel to the top and bottom of the chamber. The increased power absorption possible in the ECR surface will result in increased electronic excitation, ionization, and dissociation of the plasma gas.

Adjusting spacers 13 are placed between the magnet pack 4 and the plasma chamber 1 in order to be able to vary the spacial distance between the chamber and the magnet. By adjusting this distance, the precise location of the ECR resonance surface can be varied. The teflon sleeve 14 allows the antenna rod 2 to couple the microwave energy in the waveguide 3 to the plasma chamber 1; yet, the vacuum integrity of the plasma chamber is maintained. The waveguide recess 15 is dimensioned such as to maximize the transfer of microwave energy from the waveguide to the antenna rod. The waveguide flange 17 facilitates the interface to microwave power supply and associated tuning equipment. Flange 16 on the plasma chamber is provided to make a vacuum seal between the top lid 18 and the chamber side wall 9. For the purpose of remote processing the creation of ions and electrons is considered a necessary feature of operation of no consequence to the workpiece as the lifetime of these species under all operating conditions is too short to allow transport form the plasma chamber 1 to any process chamber. Electrons and ions are eliminated by recombination on surfaces largely before exit from the source chamber and this results in generation of a large amount of heat. Thus, efficient cooling of the chamber and magnet is necessary. Atoms and radicals in their electronic ground states have much longer lifetimes than electrons and ions and some electronically excited neutrals likewise can be quite stable, sometimes labeled metastable species. Generally, the lifetime or stability depends on experimental conditions such as gas pressure and nature of gas phase collision partners as well as the dimensions and interior surface of the container. With the proper choice of these experimental conditions the plasma activated species can survive the transport from the source chamber to the process chamber to reach the workpiece and modify it as intended. In order to ensure that all feed gas species benefit from the special conditions in the ECR resonance surface it is desirable to force the gas through this resonance surface by locating the gas inlet 7 on one side of the ECR resonance surface and locating the gas exit port 8 for the activated gas effluent on the side of the ECR resonance surface opposite the inlet port 7. Thus, if the inlet port 7 is located below the ECR resonance surface, then the exit port 8 is located above the ECR resonance surface, and vice versa.

The arrangement shown in FIG. la is different from FIG. 1 only in the way the microwave field is coupled to the plasma. In FIG. la the top wall of the chamber 1 is flat and entirely or in part occupied by the microwave window 27 made of microwave transparent material like quartz or aluminum oxide. The window 27 is vacuum sealed to the chamber 1 with a metal o-ring 10 in order to permit evacuation of the chamber, to prevent leakage of radiation, and to withstand the plasma generated heat. The waveguide 3 has in the absence of an antenna rod a different shape but the same function. An alternative location of the permanent magnet 4 is shown in FIG. 2, where the magnet is placed between the waveguide 3 and the plasma chamber 1. The wafer cooling means 6 has been extended to the top lid, and the labeling is otherwise identical to FIG. 1. This arrangement has the advantage of a so-called high-field launch of the microwave energy. This is achieved by the antenna rod extending to the center of the chamber through a volume now with a magnetic field higher than the resonance value of 875 Gauss. In FIG. 1 the field in this volume was lower than the resonance field and that condition impedes the power absorption in the plasma.

In FIG. 3 permanent magnets 4 are placed parallel to the antenna rod 2 on either side of the plasma chamber 1. Soft iron backing 19 can be placed on the magnets in order to "shorten" the external magnetic field lines and thereby increase the field between the magnets 4, i.e. in the plasma chamber 1. The use of a highly permeable material like soft iron for backing of the magnets can be applied to any of the embodiments described for this invention. The magnets 4 are oriented such that a north pole on one magnet faces a south pole on the other resulting in a magnetic field across the chamber 1 and perpendicular to the antenna rod 2. In this geometry the plane of gyration of electrons around the magnetic field lines is perpendicular to the radial electrical component of the microwave field from the antenna. While this tends to limit the ECR surface area, the Doppler shift of the ECR absorption caused by the high velocity electrons and collisional scattering by neutrals will tend to expand the ECR heating volume. The geometry shown in FIG. 3 has the advantage of making it possible to maintain optimal conditions for transfer of microwave power between the antenna rod and the plasma over the entire length of the antenna. Two alternative positions of the antenna rod are shown in FIG. 3 a: center location, 2 a, or off-center location, 2 b. The dotted curves illustrate a possible location of the ECR resonance surfaces. The off-center location of the antenna, 2 b, establishes a high- field launch as the antenna is located between a magnet and its ECR resonance surface. The charged particles generated at the antenna will flow downstream in the magnetic field towards the center of the chamber and the plasma will fill the entire chamber volume more completely than with the antenna in the center position.

In an alternative embodiment, FIG. 4, the antenna exciting the plasma can also pass entirely through the chamber and be connected to the bottom chamber wall rather than terminating inside the plasma chamber. This allows the flow of coolant through a tubular antenna with the antenna being electrically grounded in both ends. The length of the antenna in this and other embodiments can be adjusted so as to set up a resonance standing wave before the plasma is struck. The resonance standing wave condition allows high electrical fields to build up, thereby facilitating the breakdown of the gas and forming a plasma without other means of initiation.

FIGS. 5 a-c are illustrations of three different arrangements of external magnets 4 and can be applied to the chamber shown in either FIG. 3 or FIG. 4. The radial spokes indicate the electrical field emanating from the antenna rod 2 towards the chamber wall 9. In FIG. 5a two magnets 4 are placed on opposite sides of the chamber/antenna assembly such that a north pole on one magnet faces a south pole on the other magnet resulting in a magnetic field across the chamber and perpendicular to the antenna rod 2. In FIG. 5b each magnet has been split into two while retaining the geometry of the pole orientation resulting in a magnetic field in the chamber which can be more advantageous for the abatement efficiency. Finally, in FIG. 5c the same four magnets have been arranged in an pole orientation which alternates the north/south polarity around the perimeter of the tube to form the tubing equivalent of the classical magnetic bucket arrangement.

FIG. 6 is a side view of an arrangement in which a tubular magnetic field containing the antenna rod is created by a set of magnetic rings external to the chamber. The magnetic or magnetized rings 4 are of alternating north/south polarity of sufficient magnetic strength and placed with appropriate spacing along the entire length of the chamber (i.e. not necessarily limited to four rings as shown in FIG. 6) to form a bevelled ECR surface around the antenna rod 2. The outline of the chamber is indicated by the dotted line 9a. With particular reference to FIG. 7, the practice of remote processing involves not only a plasma source such as the present invention described in FIGURES 1 through 6, but in addition a process chamber 20, containing a workpiece or substrate 21, and a vacuum pump 23 which is capable of reducing the pressure in both the source chamber 1 and the process chamber 20 to at least lxl 0^"4 torr. The source chamber 1 is operatively connected to the process chamber 20 through the gas exit port 8, and the process chamber 20 is operatively connected the the vacuum pump 23 by the gas conduit 22, which can be located opposite and below port 8.

In operation, a working feedgas or gas mixture is introduced to the source chamber 1 through gas entrance 7. After plasma activation the gas effluent is transported from the source chamber 1 to the process chamber 20 through the exit port 8 to act on the workpiece or substrate 21. Finally, the effluent is exhausted to the vacuum pump 23 through the gas conduit 22. As described earlier for the source chamber, all interior surfaces in the process chamber 20 and the conduits 8 and 22 are coated with a hard, inert coating designed to protect the surfaces from chemical attack and to minimize loss of plasma activated species by deactivation or recombination on the surfaces.

With reference to FIG. 8, the practice of gas abatement involves a process chamber 20 in which in one embodiment a workpiece 21 is exposed to a gas or gas mixture. In another embodiment the process chamber 20 is exposed to a gas or gas mixture for the purpose of cleaning the interior of the process chamber while no workpiece is in place. In either embodiment the effluent from the process chamber

20 is pulled through the plasma source 1 by the vacuum pump 23. The plasma source 1 is operatively connected to the process chamber 20 by the conduit 7 and to the vacuum pump 23 by the conduit 8. In addition, reaction partners for the abatement process taking place in the plasma source 1 can be added upstream from the source through the conduit 24 or immediately downstream from the source through the conduit 25. Alternatively, a solid reaction partner such as silicon or silicon dioxide can be located in place of the conduits 24 or 25.

In operation, a working feedgas or gas mixture is introduced to the process chamber 20 through gas entrance port 26 and exposed to a workpiece 21. The effluent from the process chamber 20, consisting now of process reaction products and unreacted feedgas, is pulled through conduit 7 to the plasma source 1 by the vacuum pump 23. This effluent from the process chamber 20 can be mixed with an appropriate reaction partner added through conduit 25. The abatement process is facilitated by the intense plasma in the source chamber 1, and the abated gas mixture is pumped out through the conduit 8, possibly after addition of alternative reaction partners through conduit 25. The advantages associated with the present invention have been described above and can be reviewed as follows: The present invention does not consume any electrical power in order to provide the magnetic field needed for ECR functionality nor is any external circuitry needed to control the strength of this magnetic field. Generation of the magnetic field is not associated with any heat generation and no cooling is necessary other than protection of the magnet from other heat sources (i.e. the plasma). The permanency of the magnetic field assures reproducibility of processing and this is considered a very valuable characteristic of this source. Further, for applications in a production environment it is considered an important feature of the present invention that the functional pressure range is very wide, spanning from a fraction of a millitorr to tens of torr.

By comparison with other ECR sources based on permanent magnets the present design has the advantage of being able to locate the magnet much closer to the plasma without putting magnets in the path of the microwave field. This advantage originates with the removal of the workpiece from the plasma chamber. The proximity enables the establishment of the necessary magnetic field in the plasma with much smaller and less expensive magnets than any previous design. The reduced cost of this invention is essential for its exploitation as a plasma source fore gas abatement. ECR plasma sources have in the past most commonly been used for in situ processing of a workpiece, and these sources have been considered too costly to use for remote processing as disclosed here. The cost, bulk, and complexity of alternative sources explain the scarcity of prior art in the field of remote plasma processing and would suggest widespread application of the present invention in the technology areas of semiconductors, superconductors, optical thin films, plasma sterilization, and gas abatement.

The foregoing detailed description has been given for clarity of understanding only, and no unnecessary limitations should be inferred therefrom, as some modifications will be obvious to those skilled in the art. Accordingly, the scope of the present invention is defined by the claims which follow.

Claims

CLAIMSWhat is claimed:

1. A plasma producing device for remote processing comprising: a chamber having at least one opening sealed by a window formed of microwave transparent material; means for transporting microwave energy having a direction of propagation and an associated electric field with said microwave energy through said opening and said window into said chamber; permanent magnet means having an axial magnetic field and located externally to said chamber and opposite to said window and with a north and south pole aligned such that the axial magnetic field of said magnet is parallel to the direction of propagation of microwaves entering said chamber wherein an ECR resonance surface is located within said chamber; an inlet port for feedgas mixture located on one side of said ECR resonance surface and an exit port for the activated gas effluent located on the side of said ECR resonance surface opposite to said inlet port; a process chamber operatively connected to said chamber through said exit port; a workpiece in said process chamber; and vacuum means operatively connected to said process chamber.

2. A plasma producing device for remote processing according to claim 1, the device further comprising: a hard, wear resistant coating on all appropriate internal surfaces designed to minimize loss of plasma activated species.

3. A plasma producing device for remote processing according to claim 1 wherein said vacuum means forces said feedgas mixture to pass through said ECR resonance surface.

4. A plasma producing device for remote processing according to claim 1 wherein said permanent magnet means are formed by a composite block of smaller magnets.

5. A plasma producing device for remote processing according to claim 1, the device further comprising: means for adjusting the distance between said permanent magnet means and said chamber while preserving the parallelism between the resulting magnetic field of said magnet means and the direction of propagation of said microwave field.

6. A plasma producing device for remote processing according to claim 1, the device further comprising: means for adjusting the precise location of said ECR resonance surface.

7. A plasma producing device for remote processing according to claim 1 wherein, said means for transporting microwave energy are connected to a microwave source which produces microwaves at about 2.45 GHz and said permanent magnet means produce a magnetic field of 875 Gauss in said chamber.

8. A plasma producing device for remote processing according to claim 1 , the device further comprising: means for cooling the wall between said chamber and said magnet means in order to carry away heat generated by the plasma in said chamber.

9. A plasma producing device for gas abatement comprising: a plasma abatement chamber having at least one opening sealed by a window formed of microwave transparent material; means for transporting microwave energy having a direction of propagation and an associated electric field with said microwave energy through said opening and said window into said chamber; permanent magnet means having an axial magnetic field and located externally to said chamber and opposite to said window and with a north and south pole aligned such that the axial magnetic field of said magnet is parallel to the direction of propagation of microwaves entering said chamber wherein an ECR resonance surface is located within said chamber; an inlet port for introducing effluent from a process chamber located on one side of said ECR resonance surface and an exit port for removing the abated gas mixture located on the side of said ECR resonance surface opposite to said inlet port; a process chamber operatively connected to said plasma abatement chamber through said inlet port; and vacuum means operatively connected to said plasma abatement chamber.

10. A plasma producing device for gas abatement according to claim 9, the device further comprising: a hard, wear resistant coating on all appropriate internal surfaces.

11. A plasma producing device for gas abatement according to claim 9 wherein said vacuum means forces said process chamber effluent to pass through said ECR resonance surface.

12. A plasma producing device for gas abatement according to claim 9 wherein said permanent magnet means are formed by a composite block of smaller magnets.

13. A plasma producing device for gas abatement according to claim 9, the device further comprising: means for adjusting the distance between said permanent magnet means and said plasma abatement chamber while preserving the parallelism between the resulting magnetic field of said magnet means and the direction of propagation of said microwave field.

14. A plasma producing device for gas abatement according to claim 9, the device further comprising: means for adjusting the precise location of said ECR resonance surface.

15. A plasma producing device for gas abatement according to claim 9 wherein said means for transporting microwave energy are connected to a microwave source which produces microwaves at about 2.45 GHZ and said permanent magnet means produce a magnetic field of 875 Gauss in said plasma abatement chamber.

16. A plasma producing device for gas abatement according to claim 9, the device further comprising: means for cooling the wall between said plasma abatement chamber and said magnet means in order to carry away heat generated by the plasma in said chamber.

17. A plasma producing device for gas abatement according to claim 9, the device further comprising: means for adding suitable reaction partners into said inlet port.

18. A plasma producing device for gas abatement according to claim 9, the device further comprising: means for adding suitable reaction partners into said exit port.

19. A plasma producing device for gas abatement according to claim 9 wherein said process chamber effluent contains perfluorinated compounds.

20. A plasma producing device for remote processing comprising; a chamber having means to couple a microwave field from an external waveguide into said chamber through an antenna rod; permanent magnet means located externally to said chamber and having a magnetic field of sufficient strength to provide the magnetic field in said chamber needed to be in electron cyclotron resonance (ECR) with said microwave field; and an inlet port for a feedgas mixture and an exit port for the activated gas mixture; and vacuum means operatively connected to said chamber; and gas at reduced pressure within said chamber; a process chamber operatively connected to said chamber through said exit port; a workpiece in said process chamber.

21. A plasma producing device for remote processing according to claim

20 wherein said antenna rod is water cooled and extends through any part of said chamber.

22. A plasma producing device for remote processing according to claim

21 wherein said antenna rod enters said waveguide through a plate in a tubular recession so that the point of attachment of said antenna rod to said waveguide can be adjusted relative to the center of said waveguide for optimum coupling of microwave energy from said waveguide to said antenna rod.

23. A plasma producing device for remote processing according to claim 21 wherein said antenna rod enters said chamber at an off-center location and extends through any part of said chamber.

24. A plasma producing device for remote processing according to claim 20 wherein a permanent magnet is located externally to said chamber on the side of said chamber opposite to said antenna rod or said window and external waveguide and of sufficient strength to provide the magnetic field in said chamber needed to be in electron cyclotron resonance (ECR) with the microwave field; and a backing of highly permeable material placed on said magnet in order to increase the field on the front side of said magnet where said chamber is located.

25. A plasma producing device for remote processing according to claim 20 wherein permanent magnets are located externally to said chamber and parallel with said antenna inside said chamber and of sufficient strength to provide the magnetic field in said chamber needed to be in electron cyclotron resonance (ECR) with the incoming microwave field; and said magnets are oriented such as to maximize the crossing of the resulting magnetic field lines with the radial electrical microwave field at angles as close to 90 degrees as possible; and a backing of highly permeable material placed on said magnets in order to increase the field between said magnets where said chamber is located.

26. A plasma producing device for remote processing according to claim 20 wherein said permanent magnet means are formed by a composite block of smaller magnets.

27. A plasma producing device for remote processing according to claim

20, the device further comprising: means for adjusting the distance between said permanent magnet means and said chamber while preserving the direction of the resulting magnetic field of said magnet means relative to the propagation of said microwave field.

28. A plasma producing device for remote processing according to claim

27, the device further comprising: an ECR resonance surface located in said chamber; the precise location of said ECR resonance surface being variable by said means for adjusting the distance between said permanent magnet means and said chamber while preserving the direction of the resulting magnetic field of said magnet means relative to the propagation of said microwave field.

SUBSTITUTE SHEET (RULE _6)

29. A plasma producing device for remote processing according to claim 20, the device further comprising: an ECR resonance surface located in said chamber; and an inlet port for a feedgas mixture located on one side of said ECR resonance surface and an exit port for the activated gas mixture located on the side of said ECR resonance surface opposite of said inlet port.

30. A plasma producing device for remote processing according to claim 20 wherein said means for transporting microwave energy are connected to a microwave source which produces microwaves at about 2.45 GHz and said permanent magnet means produce a magnetic field of 875 Gauss in said chamber.

31. A plasma producing device for remote processing according to claim 20, the device further comprising: means for cooling the wall between said chamber and said magnet means in order to carry away heat generated by the plasma in said chamber.

32. A plasma producing device for remote processing according to claim

20, the device further comprising: a hard, wear resistant coating on all appropriate internal surfaces designed to minimize loss of plasma activated species.

33. A plasma producing device for remote processing according to claim 20 wherein said vacuum means force said feedgas mixture to pass through or near said ECR resonance surface.

34. A plasma producing device for remote processing according to claim 20 wherein magnetized rings of alternating north/south polarity are locates externally along the length of said chamber resulting in a bevelled ECR surface around said antenna rod.

35. A plasma producing device for gas abatement comprising: a plasma abatement chamber having means to couple a microwave field from an external waveguide into said chamber through ar antenna rod; permanent magnet means located externally to said chamber and having a magnetic field of sufficient strength to provide the magnetic field in said chamber needed to be in electron cyclotron resonance (ECR) with the microwave field; and an inlet port for a feedgas mixture and an exit port for the abatement effluent; and a process chamber operatively connected to said plasma abatement chamber through said inlet port; and vacuum means operatively connected to said plasma abatement chamber; and gas at reduced pressure within said plasma abatement chamber.

36. A plasma producing device for gas abatement according to claim 35 wherein said antenna rod is water cooled and extends through any part of said chamber.

37. A plasma producing device for gas abatement according to claim 35 wherein said antenna rod enters said waveguide through a plate in a tubular recession so that the point of attachment of said antenna rod to said waveguide can be adjusted relative to the center of said waveguide for optimum coupling of microwave energy from said waveguide to said antenna rod.

38. A plasma producing device for gas abatement according to claim 35 wherein said antenna rod enters said chamber at an off-center location and extends through any part of said chamber.

39. A plasma producing device for gas abatement according to claim 35 wherein a permanent magnet is located externally to said chamber on the side of said chamber opposite to said antenna rod or said window and external waveguide and of sufficient strength to provide the magnetic field in said chamber needed to be in electron cyclotron resonance (ECR) with the microwave field; and a backing of highly permeable material placed on said magnet in order to increase the field on the front side of said magnet where said chamber is located.

40. A plasma producing device for gas abatement according to claim 35 wherein permanent magnets are located externally to said chamber and parallel with said antenna inside said chamber and of sufficient strength to provide the magnetic field in said chamber needed to be in electron cyclotron resonance (ECR) with the incoming microwave field; and said magnets are oriented such as to maximize the crossing of the resulting magnetic field lines with the radial electrical microwave field at angles as close to 90 degrees as possible; and a backing of highly permeable material placed on said magnets in order to increase the field between said magnets where said chamber is located.

41. A plasma producing device for gas abatement according to claim 35 wherein said permanent magnet means are formed by a composite block of smaller magnets.

42. A plasma producing device for gas abatement according to claim 35, the device further comprising: means for adjusting the distance between said permanent magnet means and said chamber while preserving the direction of the resulting magnetic field of said magnet means relative to the propagation of said microwave field.

43. A plasma producing device for gas abatement according to claim 35, the device further comprising: an ECR resonance surface located in said chamber; the precise location of said ECR resonance surface being variable by said means for adjusting the distance between said permanent magnet means and said chamber while preserving the direction of the resulting magnetic field of said magnet means relative to the propagation of said microwave field.

44. A plasma producing device for gas abatement according to claim 35, the device further comprising: an ECR resonance surface located in said chamber; and an inlet port for a feedgas mixture located on one side of said ECR resonance surface and an exit port for the activated gas mixture located on the side of said ECR resonance surface opposite of said inlet port. 45. A plasma producing device for gas abatement according to claim 35 wherein, said means for transporting microwave energy are connected to a microwave source which produces microwaves at about 2.

45 GHz and said permanent magnet means produce a magnetic field of 875 Gauss in said chamber.

46. A plasma producing device for gas abatement according to claim 35, the device further comprising: means for cooling the wall between said chamber and said magnet means in

SUBSTITUTE SHEET (RULE 2ffl order to carry away heat generated by the plasma in said chamber.

47. A plasma producing device for gas abatement according to claim 35, the device further comprising: a hard, wear resistant coating on all appropriate internal surfaces.

48. A plasma producing device for gas abatement according to claim 35 wherein said vacuum means force said feedgas mixture to pass through or near said ECR resonance surface.

49. A plasma producing device for gas abatement according to claim 35 wherein magnetized rings of alternating north/south polarity are located externally along the length of said chamber resulting in a bevelled ECR surface around said antenna rod.

50. A plasma producing device for gas abatement according to claim 35, the device further comprising: means for adding suitable reaction partners into said inlet port.

51. A plasma producing device for gas abatement according to claim 35, the device further comprising: means for adding further reaction partners into said exit port.

52. A plasma producing device for gas abatement according to claim 35 wherein said feedgas mixture contains perfluorinated compounds.

SUBSTITUTE SHEET (RULE 2β