HK1128358B - Electrode systems and methods of using electrodes - Google Patents

Description

Electrode system and electrode using method

Technical Field

The present invention relates to deposition and material modification processes and systems for use therewith, and more particularly, but not exclusively, to plasma enhanced chemical vapor deposition or material modification processes, electrodes for use in such systems, and methods of using such electrodes.

Background

"plasma enhanced chemical vapor deposition" (or PECVD) is a well-known technique for forming films on different substrates. For example, U.S. patent No.5224441 to Felts et al describes an apparatus for rapid plasma deposition. In plasma enhanced chemical vapor deposition of silicon oxide, a gas stream comprising components such as a volatile organosilicon compound, oxygen, and an inert gas (such as helium or argon) is sent into a closed chamber at reduced pressure, and a glow discharge (glow discharge) plasma is established from the gas stream or components thereof. A silicon oxide layer is deposited on the substrate when the substrate is positioned proximate to the plasma. In such systems, the pressure is typically reduced from atmospheric pressure using a vacuum pumping system. The electrode surface is in electrical communication with the gas introduced into the system, thereby forming an electrical discharge or plasma. The purpose of this discharge is to excite the components in the system and cause them to deposit on the workpiece (work piece) or substrate to be coated.

The use of the "hollow cathode effect" is known from the applicant's own patent application WO2006/019565(Boardman et al) wherein the internal surfaces of tubes and pipes are modified by the treatment process in which the workpiece itself forms the deposition chamber. Treatment is achieved in the workpiece by applying a bias voltage in the workpiece or only between an electrode external to the workpiece and the workpiece itself, while passing a treatment gas through the workpiece and maintaining the interior of the workpiece at a reduced pressure. The process gas includes the desired component to be deposited or implanted, and the pressure is sufficiently low to establish and maintain the "hollow cathode effect" in which the electron mean free path is slightly less than the diameter of the workpiece, resulting in electron oscillation and implantation or deposition of the desired component below or onto the surface of the component itself.

One problem with this system is that the electrodes may be contaminated by the insulating layer of the material used for the composition. The deposit growth on the electrode will cause the voltage/current characteristics of the system to shift over time and as electrode contamination progresses, the required operating voltage for a given current will increase. These changes result in deviations in the quality of the dielectric coating produced on the substrate and require periodic cleaning or replacement of the electrodes.

Furthermore, power is wasted and excessive heat is generated due to the high impedance provided to the plasma by the contaminated electrodes. It is desirable to have a process that is free of drift and has minimal waste heat generation. A similar problem exists when the counter electrode must be placed outside the workpiece electrode. This must be done multiple times when the diameter of the tube being coated is small or if pre-activation of the plasma is required to provide a uniform coating along the tube. In this case, there is a resistance between the high density, hollow cathode plasma and the counter electrode (usually biased as an anode) in the workpiece (usually biased as a cathode as described below) due to the decay of the plasma as it flows from the cathode to the anode. This problem can obviously only be made worse if the anode is coated with a resistive material.

There is also a problem in that the electrodes must be heated to thermionic emission temperatures to release electrons and in some arrangements are so hot that separate and expensive water cooling equipment is required only to prevent heat from the electrodes from adversely affecting surrounding structures. One example of such an arrangement is shown in U.S. patent No.6110540 to Countrywood et al, which discusses a counter electrode used in the deposition process. For example, in fig. 3 and 4, the actual electrode is surrounded by a cooling system that cools the material surrounding the electrode. This patent also discloses the possibility of using a coil of refractory metal wire as an alternative to the electrode of fig. 4, but no other relevant comments are given.

Countrywood et al require the addition of a separate magnetic field generation system to confine the generated plasma within the desired region of the anode structure. This system introduces additional overhead, makes the already complex system more complex, and consumes additional power.

Countrywood et al also require the use of an AC signal so that the counter electrode can alternately function as the anode and then the cathode. In the hollow tube electrode configuration described by Countrywood et al, a negative (cathode) bias on the counter electrode is required for a portion of the waveform to produce a strong low impedance plasma (essentially a hollow cathode plasma). Countrywood et al also describes a DC anode, but it requires a separate DC power source to power the anode. An advantage of the present invention is that no positive bias on the counter electrode is required, nor is a separate power supply for DC or DC pulsing as in Countrywood et al.

The above-mentioned patent also discloses the use of a gas purification system in which the electrode is protected from the process gas by a shielding gas which is transported over the electrode and exits the chamber in which the electrode is located through small holes provided therein. The shielding gas is provided at a higher pressure than the process gas and thus serves to prevent any process gas from entering the electrode chamber and depositing thereon. The gas source associated with the electrode may maintain a gas pressure around the electrode greater than the gas pressure in other areas of the evacuated chamber. These gases form a relatively high density plasma associated with the electrode, which acts as an extension of the metal electrode surface and reduces the impedance of the electrode. This electrode system is commonly referred to as a gas purged electrode. The benefit of using a gas purge electrode is that it provides a constant, low impedance electrical contact with the processing plasma. Because the impedance is constant, the process does not deviate; due to the low impedance, the whole process is performed at a lower voltage and less power is wasted. The greater gas pressure surrounding the gas-purging electrode is continually replenished by the gas source, and the difference in gas pressure between the area surrounding the gas-purging electrode and the rest of the evacuated chamber prevents the reactive gas or other components from the primary gas source from approaching the gas-purging counter electrode. The gas used is typically an inert gas such as helium, neon or argon or a mixture such as helium/neon or neon/argon. In a reactive sputtering process, it may be oxygen, nitrogen, or other reactive gas. Each of these gases may be used in the apparatus and method of the present invention.

Disclosure of Invention

The present invention provides a gas purged electrode arrangement wherein electrode material is provided in the form of a metal coil having a longitudinal axis about which a plurality of turns of said coil are wound and said gas outlet is positioned for supplying plasma generating gas substantially along said longitudinal axis of said coil. It is understood that the electrodes may form either the anode or the cathode. The coil generates a magnetic confinement field that helps confine and intensify the plasma field while more easily confining electrons, including thermionically emitted electrons and electrons flowing from the electrode material, within the field and acquiring high energy levels before being released therefrom. In one particularly preferred arrangement, the electrode material may be surrounded by a shield effective to enclose the electrode material and also to protect the electrode material from the main process gas in which it may be operated. The walls of the shield are provided with one or more outlets through which, in operation, the shielding gas is delivered into the process chamber. It has also been found that forming the electrode material into an arc shape or preferably a perfect circle shape helps to enhance the energy of the emitted electrons and may in some cases result in a significant increase in the intensity of the plasma. In the case of electrode material remote from the cathode, this arcuate geometry will provide full plasma activation of the entire diameter of the gas volume as it flows between the cathode and electrode material, thereby providing a lower resistance than straight electrode material. In each such arrangement, it has been found that as the distance from the gas supply increases, the uniformity of the emission can be enhanced by varying the number of outlets so that the outlets are further away from the gas inlet, the number or physical size of which increases. It has been found that an enhanced plasma effect can be produced by varying the exit angle around the arrangement of the circular electrode material such that the plasma emitted therefrom converges in a conical manner. Other forms of outlets may be used, such as a single outlet at the end of the shroud, or multiple outlets provided along the shroud or indeed around the circumference of the shroud, and this arrangement is discussed in detail below. The electrode material is preferably made of a refractory material, such as tantalum, tungsten or molybdenum, since these materials can operate at high temperatures and can thus contribute to the generation of a higher number of thermionically emitted electrons.

In one preferred arrangement, the electrode comprises an electrode material formed as a coil having a longitudinal axis about which a plurality of turns of the coil are wound and a gas inlet for directing a shielding gas generally along the axis whilst being confined by a shroud arrangement surrounding the electrode material. The shield is provided with an outlet at its surface so as to allow plasma gas to be transported out of the shield. This arrangement provides enhanced electron generation and protection of the electrode material from potentially harmful coating atmospheres outside the electrode arrangement.

In an alternative arrangement, the electrode comprises electrode material formed as a circular coil having a longitudinal axis about which a plurality of turns of the coil are wound and a gas inlet for directing a shielding gas generally along the axis whilst being confined by a shroud arrangement surrounding the electrode material. The shield provides an outlet at its surface so as to allow plasma gas to pass out of the shield, while the circular arrangement helps to confine any generated electrons. The arrangement also providesFor enhanced electron generation and protection of the electrode material from potentially harmful coating atmospheres outside the electrode arrangement. The shield may be formed using any of a number of suitable materials, but preferably comprises a non-metallic material such as quartz, which may be in a transparent form. The use of non-metallic materials significantly reduces the build-up of any deposited coating on its outer surface, whilst the use of transparent materials allows the plasma generation to be observed, which has significant advantages when the hollow cathode effect is first established. The shield conveniently comprises a portion which fits over the base portion of the electrode and includes a seal therebetween to ensure that the shielding gas is maintained in the desired region. The electrical connection from the electrode material to the power source is preferably achieved by an insulating connector that insulates the electrode from the base portion (through which it must be connected to the source of electrical power). A gas inlet also positioned in the base portion is for receiving shielding gas into an optional gas chamber for distributing the supply gas to a single or multiple gas inlets associated with the electrode material. To ensure that a good quality thermionic emission is generated, a wire comprising an open coil of tungsten or any other refractory metal such as tantalum or molybdenum may be used. When a tungsten wire is used, its diameter is preferably 0.2 mm. The electrode material is preferably connected to a source of pulsed current which, in operation, causes the electrode material to first heat and generate thermionic emission electrons and subsequently cool to prevent overheating before heating is again allowed and additional thermionic emission is generated. The thickness and length of the wire will control the resistance to be R ═ ρ L/a, whereFor resistivity, L is the length and A is the cross-sectional area. The wire heating is proportional to the resistance and thermionic electron emission is proportional to the heating.

According to another aspect of the present invention, there is provided a method for generating a plasma field, comprising the steps of: providing an electrode material in the form of a wire coil having a longitudinal axis X, a plurality of turns of said coil being wound about said longitudinal axis, and providing a plasma generating gas directed generally along said axis and over said electrode material. The electrode material is grounded and the element 10 (fig. 1) is connected to a positive voltage source to generate a plasma around the electrode material. The electrode material may also be protected by providing a shield surrounding the electrode material and transporting the plasma generating gas between the shield and the electrode material. If desired, a shield in the form of a tube having a sidewall and a plurality of outlets in the sidewall for exhausting plasma gas from the shield may be provided.

One particularly preferred method further comprises the step of protecting the electrode material by providing a shield surrounding the electrode material in the form of a tube having a sidewall, by providing a plurality of outlets in the sidewall and transporting the plasma generating gas between the shield and the filament and out of the outlets in the shield. Preferably, the method comprises the steps of: providing the electrode material as a loop of coiled wire, protecting the electrode material by providing a shield around the electrode material in the form of a circular tube having a sidewall and a plurality of outlets in the sidewall, and transporting the plasma generating gas between the shield and the wire and out of the outlets in the shield. The method further includes the step of directing the exiting plasma gas from the outlet such that any gas flows generally converge, and preferably converge in a manner to form a cone or torroidal plasma gas adjacent the electrode. When emitting gas according to the above method, the coating or treatment process may also be enhanced by passing any treatment gas through the center of the circular tube and into an annular or conical emitting plasma gas.

The gas purged counter electrode may be used in a plasma enhanced chemical vapor deposition system using a pulsed DC or AC power source. These electrodes use the purge gas to generate a strong plasma jet which is emitted into an evacuated process chamber, which may be formed at least in part by the component to be treated. The relatively high density plasma jet is conductive and acts as a counter electrode to the processing plasma. The processing plasma is sustained by an electrical current applied between the gas-purging counter electrode and the other electrode. The other electrode may be a second gas-purging electrode, or other forms may be used such as a simple metal rod or plate, or may be the element itself. This latter arrangement has particular advantages when coating or treating the internal surfaces of small diameter pipes or treating elements in the field. Electrons or ions are readily extracted from the plasma associated with the gas purging counter electrode, as required for processing the plasma, and therefore the net impedance (net impedance) of the plasma-based electrode is low.

In order to produce a consistent quality dielectric coating, it is necessary to generate a stable plasma. Even for plasma deposition systems using alternating current, any growth of dielectric deposits on the electrodes can cause the voltage/current characteristics of the system to shift over time. The required operating voltage will increase and thus the current decreases for a given level of power. These changes will cause the properties of the dielectric coating produced by the process to shift and require periodic cleaning of the electrodes. The aim of the invention is to reduce and eliminate as far as possible this effect, while enhancing the plasma intensity and facilitating the generation of the plasma itself.

Drawings

The foregoing and other features and aspects of the present invention will become apparent from the following detailed description, when read in conjunction with the accompanying drawings, wherein:

【0018】 FIG. 1 is a schematic diagram showing a processing apparatus incorporating the present invention;

【0019】 FIG. 2 shows a cross-sectional view of a first electrode arrangement according to an aspect of the invention;

【0020】 Figure 3 shows a cross-sectional view of a second electrode arrangement according to a second aspect of the invention;

【0021】 FIG. 4 shows another cross-sectional view of the second electrode in the direction of arrows A-A shown in FIG. 3;

【0022】 The schematic diagram of fig. 5 shows the magnetic field and the electron path in the above arrangement.

Detailed Description

Referring to FIG. 1, a conduit or "workpiece" 10 is shown connected to a system including a gas supply subsystem 12 and a process control subsystem 14. The workpiece is shown as a single piece, which may also be an assembly of pipes or tubes. A readily available process gas, such as methane or acetylene, is provided to the first gas supply vessel 16. This gas is used in the injection or coating step described below. Argon or any other suitable inert gas is provided for this purpose from a second gas supply vessel 18 to allow plasma "pre-cleaning" of the pipe surfaces and mixing of argon (Ar) with the process gas.

A DC pulsed power supply 20 is used to apply a negative bias to the workpiece 10. This bias is used to (a) create a plasma between the cathode and ground electrode materials, (b) attract the ionized reactant gas to the surface to be treated, (c) allow ion bombardment of the film to improve film properties such as density and stress levels, and (d) allow control of film uniformity by adjusting the duty cycle so as to allow replenishment of the source gas during the "off" portion of the cycle. Here the workpiece acts as a cathode and has grounded anodes 22 and 24 at opposite ends of the workpiece. Through which turbo pump 26 and vacuum pump 28 draw gases from within workpiece 10. The pressure controller 30 receives information from an optical probe 32 and a Langmuir (langeuler) probe 34, the probes being positioned such that: an optical probe has a line of sight to the plasma, and the Langmuir probe contacts the plasma. Both probes sense the plasma intensity and generate information indicative of the intensity level. This information is used by the controller to determine the correct setting for the adjustable flow element 36 (which may be a valve). The arrangement should be such that the pressure within the workpiece 10 establishes a condition where the electron mean free path is slightly less than the internal diameter of the workpiece, resulting in electron oscillation and increased ionizing collisions by the "hollow cathode" effect. Thereby, a stronger plasma is generated in the workpiece. Since the electron mean free path increases as the pressure decreases, it is necessary to decrease the pressure as the diameter of the pipe increases. For example, an 1/4 inch (6.35 mm) diameter gas tube would produce a hollow cathode plasma at a pressure of about 200 mTorr, while a four inch (101.6 mm) diameter pumped exhaust would produce a plasma at a pressure of about 12 mTorr. The values used are approximate to illustrate the general tendency for lower pressures for larger diameters, but the pressure range can vary significantly from these values and still maintain a hollow cathode plasma.

Since only the ionized gas is accelerated through the plasma sheath into the workpiece, the level of ionization, or plasma intensity, is important for effective Plasma Immersion Ion Implantation and Deposition (PIIID) techniques. The hollow cathode effect provides a stronger plasma than would otherwise be available in a DC or RF plasma. This increase in intensity can be achieved without complicating other means of generating a strong plasma, such as magnets or microwave plasma sources, which are very difficult to achieve for internal surfaces (particularly for "in-field" applications). This process also does not require separate heating of the workpiece 10, as heating can result from ion bombardment. When a strong hollow cathode is correctly produced, the optical and Langmuir probes are located at the anode end of the connection monitor. A computer software control 38 is shown connected to the DC pulsed power supply 20 and the pressure controller 30. In addition, computer software control may generate and send control signals to the gas supply subsystem 12 via the interface cable 40 for the purpose of controlling operation.

Referring now to fig. 2 and 3, the above briefly mentioned electrodes are described in more detail, and it can be seen that they comprise a number of different shapes, but all use the same basic operating principle. Referring to fig. 2, it can be seen that this electrode material 50 is formed as a coil of wire formed from a plurality of said coils of wire and arranged to extend along said axis X, such that the open loop of said coils surrounds said axis and creates an inner region 52, the function of which inner region 52 is described below. A shield 54 surrounds the coil of electrode material 50, the shield 50 being formed from, for example, transparent quartz and having a sidewall 56 provided with one or more holes 56a extending therethrough. The holes may be singular, in which case the position of the holes is selected to be appropriate for the desired direction of plasma generation, or a series of holes in the side wall are positioned to direct the discharge of plasma generating gas in the desired collective direction or into the general area surrounding the electrodes 22, 24. Figure 2 shows a series of holes for creating a plasma region generally surrounding the electrodes and located within region R. The wire may be made of a variety of materials, but preferably a refractory metal such as tungsten, tantalum or molybdenum is used and if provided as a tungsten element, may be between 0.1mm and 1.0mm in diameter, preferably 0.2mm, which may be found sufficient for general processing purposes. The other free end 56 of the electrode material 50 passes through the insulating block 58 and into the base portion 60 of the electrode where it is electrically coupled to the terminal 62. The terminals 62 are located on the exterior of the base portion so as to allow connection thereof to the power supply 20 of fig. 1. A gas supply tube 64 is positioned for supplying gas from the container 18 to the base portion 60 so as to enter a region 66 between the electrode material 50 and the shield 54 before being directed along the longitudinal axis X-X of the coil itself. The base portion 60 is also provided with a region 66 around which a pair of seals 68 are provided for sealing any gap between the shroud 54 and the portion 66, whilst also retaining the shroud on the base portion.

Fig. 3 and 4 show a preferred alternative electrode arrangement in which the wire of electrode material is formed as an open coil comprising a plurality of turns of said wire extending around a longitudinal axis X and in a circular arc and preferably in a complete or substantially complete circle having an inner bore 70. The shield 54 is similarly shaped as an arc of a circle, or preferably a complete circle, and surrounds the electrode material 54 in the manner described above in connection with fig. 1. While it is understood that the outlet 56a may be provided in any of a number of locations within the sidewall 54, it has been found that providing an outlet on one side thereof and positioning the axis of the aperture such that any plasma gas emitted therefrom is directed to converge with the gas emitted from the associated aperture can produce an enhanced plasma region in the region R adjacent the electrode itself. In a particularly desirable arrangement, the apertures are positioned to direct the plasma gas from the circular electrode arrangement so that it converges in a conical manner as shown. This arrangement helps to intensify the generated plasma and, when a circular arrangement is used, produces a conical plasma into which any process gas G can be directed. To ensure uniform emission of the plasma gas from the electrode, it may prove desirable to vary the size and/or distance between the outlets such that the concentration of the outlets is higher the further away from the source of plasma generating gas. Alternatively, the size of the holes may simply be varied, with the diameter increasing further away from the gas inlet. This causes electrons to flow through all of the electrode material and a magnetic field to be generated by all of the electrodes (by entering furthest from the electrical inlet connection), and also causes gas G to flow through all of the electrodes. In some arrangements it may be desirable to provide a single or relatively small number of outlets at locations remote from the gas input point, thereby ensuring that the plasma gas has a high residence time adjacent to the electrode material. Other features of fig. 3 and 4 include a gas/electrode supply portion 72 for allowing shielding gas to be introduced into the electrode and assembly portion at schematic representation 74.

The operation of the electrode shown in fig. 2 to 4 is better illustrated with reference to fig. 5, which shows the coil of electrode material at 50 and the plurality of magnetic field lines F1, F2 and F3 that result directly from the transmission of electrical current through the coil arrangement 50 in fig. 5. Inert plasma generating gas is introduced at 72 and is directed generally along the longitudinal axis of the electrode material and preferably within the coil itself.

The current is selected to be sufficient to heat the electrode material 50 to thermionic temperatures and allow electrons to be released from its surface. Once the electrons are released, it is desirable to keep them within the confines of the magnetic field for as long as possible, in order to allow them to attain high energy levels and to allow them to collide with a plurality of neutral gas atoms, which results in more ionization. Path 76 shows the flight of the electrons and their confinement boundaries in the magnetic field. Electrons will rotate along the magnetic field lines according to the equation F-qv × B, where q is the electron charge, v electron velocity and B is the magnetic field. Once the electrons pass along the length of the coil in fig. 2, they are released from the confines of the magnetic field and allowed to emit from the electrode. The plasma generating gas is directed along the axis of the coiled electrode material to ensure that the gas remains in contact with the electrode material for as long as possible and to confine any emitted electrons for as long as possible to accumulate before being released in a particular controlled direction. In the arrangement of fig. 2, the electrons are constrained to travel in a "racetrack" fashion around a circular arrangement of electrode material, so that the electrons are further concentrated before being released from the confining boundaries of the magnetic field. This is because the field lines meet in a circle and the electrons will tend to follow the circular field lines, especially at low voltages. The magnetic field strength can also be increased by increasing the number of turns of the coil, following the following formula: b ═ ρ NI/L, where ρ is permeability, N is the number of turns, I is current and L is length. Furthermore, when bipolar pulses of AC or DC are used, the counter electrode may be given a negative bias with respect to the workpiece for some limited portion of the waveform. This also has the effect of increasing the density of the plasma around the counter electrode due to the higher bias that occurs between the plasma and the negatively biased electrode relative to the positively biased electrode (since the plasma potential tends to rise to a few electron volts above the maximum positive electrode potential). This higher bias will result in increased ion bombardment, resulting in increased heating and thermionic emission of electrons. These electrons are then confined by the magnetic field and subsequently collide with gas neutrals which increase the plasma density. This increased plasma density is available before decay when the positive portion of the waveform is applied to the counter electrode. It will be understood that by "racetrack" is meant herein that the coil is completely circular, such that any gas that is transported around it (if desired) can complete more than one complete circle.

The different process steps are now described by way of example only to assist the reader in understanding the possibilities of the proposed invention of the above-described apparatusThe application is as follows. It will be appreciated that the apparatus described above and the electrodes of figures 1 to 5 may be used in any one or more of the following steps and their use is not limited to use in a process employing all of the following steps. In a first example, a pre-cleaning step may be used and facilitated by introducing a sputtering gas (such as argon) from the first gas supply vessel 18. Down to 1X 10 under pumping^-3Tray or preferably 1X 10^-4After the tray is lowered, pre-cleaning may begin. When a negative DC pulse is applied by the power supply 20, contaminants on the interior surface of the workpiece are sputtered off.

An optional implantation step of nitriding or carbon implantation may be used in some applications. For example, carbon implantation forms a subsurface carbon layer in the workpiece material (which may be stainless steel). This layer improves adhesion to any subsequently deposited layers and other materials. The carbon implantation is provided at a higher magnitude bias than experienced in other steps of the coating process. Suitable biases are in excess of 5 kV. Care must be taken at this step for small diameter tubes so that the plasma sheath is not dimensioned larger than the radius of the workpiece.

A precursor deposition step may be used in which one precursor is introduced into the workpiece 10. Acceptable precursors include methane, acetylene or toluene. In this process step, the DC pulse voltage is reduced in order to provide thin film deposition, rather than implantation. During the coating step, argon may be mixed with the carbon-containing precursor, thereby providing increased ion bombardment and/or reduced impedance of the plasma. The coating parameters may be dynamically adjusted during the coating process to produce a desired combined coating. The probe provides information that can be used by the computer software control 42 and the pressure controller 34 to keep the different parameters within their tolerable ranges. Thus, the factor that determines the pressure within the workpiece may be adjusted as needed, or the amplitude and duty cycle of the pulsed bias may be adjusted if necessary.

Claims (29)

1. An electrode for a deposition process in which deposition is from a process gas, comprising:

an electrode material;

a gas inlet for directing a shielding gas over an outer surface of the electrode material to shield the electrode material from the process gas;

a non-metallic shield surrounding the electrode material;

wherein the electrode material comprises a metal coil having a longitudinal central axis X around which a plurality of turns of the metal coil are wound, and wherein the gas inlet is positioned for directing the shielding gas substantially along the axis X.

2. An electrode as claimed in claim 1 wherein the shield comprises a surface and an outlet in the surface through which the shielding gas may be delivered in operation.

3. The electrode of claim 1, wherein the shield comprises a surface and an outlet, and wherein the shield comprises a tube having a sidewall with a plurality of outlets.

4. The electrode of claim 1, wherein the shield comprises a surface and an outlet, and wherein the axis comprises an arc of a circle.

5. The electrode of claim 1, wherein the shroud includes a surface and an outlet, and wherein the axis extends through a complete circle.

6. The electrode of claim 1, wherein said shield comprises a surface and an outlet, and wherein said shield has a plurality of said outlets, and wherein the distance between said outlets decreases as the distance between said outlets and the gas inlet increases.

7. The electrode of claim 1, wherein the shield comprises a surface and a plurality of outlets, wherein the outlets increase in diameter as the distance between the outlets and the gas inlet increases.

8. The electrode of claim 1, wherein the shield comprises a surface and a plurality of outlets, and wherein the outlets comprise a central axis and the axes converge.

9. The electrode of claim 1, wherein the electrode material comprises a refractory metal.

10. The electrode of claim 1, wherein the electrode material is selected from the list comprising: tantalum, tungsten and/or molybdenum.

11. An electrode as claimed in claim 1 wherein the shield has an outlet located away from the gas inlet, thereby causing gas to be transported along the electrode material before exiting the shield.

12. The electrode of claim 1, wherein the shield is comprised of a transparent material.

13. The electrode of claim 1, wherein the shield is comprised of quartz.

14. The electrode of claim 1, further comprising a base portion.

15. The electrode of claim 1, further comprising a base portion and a seal between said base portion and said shield.

16. The electrode of claim 1, further comprising a base portion, wherein the base portion comprises an insulator.

17. The electrode of claim 1, further comprising a base, wherein the base comprises a gas inlet and one or more gas outlets positioned for directing gas toward and around the electrode material.

18. The electrode of claim 1, further comprising a base having an inlet and one or more outlets, wherein the base comprises a gas chamber between the inlet and the one or more outlets.

19. The electrode of claim 1, further comprising a base, wherein the base comprises an external coupling for coupling to an aperture in a wall of the process chamber.

20. The electrode of claim 1, wherein the coil comprises an open coil.

21. The electrode of claim 1, wherein the coil includes an end portion for electrical connection to the mounting portion.

22. The electrode of claim 1 further comprising a base portion and an electrode mounting portion, wherein said mounting portion is located in said base portion of said electrode and has an external electrical connector for connection to an external source of electrical power.

23. The electrode of claim 1, wherein the electrode material comprises tungsten wire.

24. The electrode of claim 23, wherein the wire comprises a 0.2mm diameter tungsten wire.

25. The electrode of claim 1, further comprising a pulsed electrical supply source for supplying a pulsed electrical current to said electrode.

26. An electrode for a deposition process in which deposition is from a process gas, comprising:

an electrode material;

a gas inlet for directing a shielding gas over an outer surface of the electrode material to shield the electrode material from the process gas;

a shield surrounding the electrode material, the shield having a plurality of outlets along a length of the shield and around a circumference thereof;

wherein the electrode material comprises a metal coil having a longitudinal central axis X around which the plurality of turns of the metal coil are wound, and wherein the gas inlet is positioned for directing the shielding gas along the axis.

27. An electrode for a deposition process in which deposition is from a process gas, comprising:

an electrode material;

a gas inlet for directing a shielding gas over an outer surface of the electrode material to shield the electrode material from the process gas;

a shield surrounding the electrode material, the shield comprising a surface and an outlet in the surface;

wherein the electrode material comprises a metal coil having a longitudinal axis extending in a circle, and the gas inlet is positioned for directing the shielding gas along the axis.

28. A method of generating a plasma field in a deposition process, comprising the steps of:

providing an electrode material in the form of a wire coil having a longitudinal axis;

providing a plasma generating gas;

protecting the electrode material by providing a shield around the electrode material in the form of a tube having a sidewall and a plurality of outlets provided in the sidewall;

applying an electrical current to the electrode material and conveying the plasma generating gas between the shield and the coil of wire substantially along the axis and over the electrode material for exiting an outlet in the shield to create a plasma region around the electrode material, the plasma region being different from a main processing plasma for the deposition process.

29. The method of claim 28, further comprising the steps of: providing the electrode material as a loop of coiled wire and protecting the electrode material by providing a shield in the form of a circular tube having the sidewall and the plurality of outlets.