GB2601106A - High density plasma source - Google Patents

Abstract

A gas plasma source 3 for attachment to and use with a vacuum chamber 1 of a plasma processing apparatus comprises a radio frequency antenna 11 placed external to the vacuum chamber, a RF transparent (e.g. dielectric) window construct 12 attached to the vacuum chamber in proximity to the antenna, and one or more magnets (6, 13) for guiding and extending the plasma across a region 22 where plasma processing is required. The RF transparent window construct includes means to control and limit the extent of coating or deposition of stray material on the window, e.g. by ensuring any coating formed is electrically discontinuous and isolated other than in a form that replicates and is aligned to the antenna shape and size. The means may be a shielding strip or mask 24 placed proximate to the window. Alternatively, separate RF transparent window sections separated by electrically isolating elements may be provided. The invention may eliminate coating induced loss of plasma source efficiency without need to reduce or eliminate the coating itself.

Description

I

High Density Plasma Source This invention relates to a novel means of producing high density vacuum gas plasma, primarily but not uniquely for use in apparatus that sputter deposit thin film coatings onto other surfaces and materials.

Vacuum gas plasmas are extensively used in a diverse range of research and production processes, especially within the semiconductor and large area flat panel electronics industries, e.g. for solar panel and flat display panel production. In general, economies of scale mean that it is highly desirable to generate such plasmas uniformly over as large an area as possible whilst simultaneously achieving plasma densities in excess of 1012 cm-3 to support fast processing; this is a challenging objective.

One class of plasma sources commonly used in industry inductively couples radio frequency (RF) energy into the vacuum process environment to produce the plasma: this is generically referred to as an Inductively Coupled Plasma (ICP). Typically, but not exclusively, radio frequencies of about 13.561MHz are used, this being the centre frequency of a band reserved for industrial, scientific and medical (ISM) use; many multiples of 13.56MHz, for example about 40MHz, are also used where process benefits may be realised. The simplest versions of these ICP sources produce plasma (i.e. ion and electron) densities of about 1010 cm', more advanced systems can achieve greater than 1012 cm'.

Large area ICP systems can be constructed to produce large areas of plasma, the RF energy being transmitted via an equivalently large shaped 'serpentine' or large diameter 'coil' antenna placed within the vacuum process chamber and defining the extent of the plasma area. However, these tend to be restricted to lower than desirable plasma density, less than about 1011 cm-3, partly due to issues arising from the direct electrical contact of the antenna to the plasma. More complex designs, utilising local magnetic plasma density enhancement and segregation of the (metal) antenna from the plasma are disclosed in the literature and can improve on this but remain limited to less than 1012 plasma density. Additionally, the plasma antenna itself overlays the process region, limiting its application.

There also exist a class of inductive plasma sources capable of generating plasma densities of 1013cm' or greater, though without large area capability unless used as a multi-source array, a potentially very expensive and/or complex arrangement. Examples of these are summarised by Popov in 'High Density Plasma Sources' (1995) and Chen in 'Lecture Notes on Principles of Plasma Processing' (2003). A further, highly efficient plasma source is used in a sputter deposition system invented by Thwaites (UK patent GB2343992, US Patent No.6463873). This utilises a helically wound multi-turn coil ICP antenna in conjunction with particular magnetic field arrangements to both produce a high density plasma within a plasma chamber attached to the sputter process chamber and to extend this plasma to a sputter target surface out of line of sight of the plasma source The Thwaites plasma source has subsequently been adapted by the inventors to produce derivative systems that permit the generation of large area plasmas of "slab" form, i.e. one dimension (thickness) being significantly less than the other two. These deliver an acceptably uniform, high plasma density (10" cm' or greater) over a large area from a single smaller plasma source. An early example of these is described by Hockley and Thwaites in Patent Application GB1006567.0 A key feature of the developed sources is that the plasma generation zone defines only two dimensions of the plasma region, the width (typically 10-50cm) and thickness (typically a few cm). The third dimension (typically 20-40cm) results from the extension of the plasma from the source by the magnetic field. Unlike other large area ICP sources mentioned above, this allows the plasma to pass between a sputter target (or targets) and substrate(s) to be coated, without any plasma source components blocking the coating flux path, making it suitable for use as the plasma generating component of a large area sputter coating system, especially when close spacing of the target and substrate is required.

Other benefits of being able to produce such large area, high density plasma are reported in the literature. The separation of the plasma generation task (by the plasma source) from the sputter coating target material source provides more process options with commensurate advantages when optimising materials properties (for example as reported by Vospariou et al, WEE Transactions on Magnetics, Vol.40, No.4, July 2004) whilst full target material surface sputtering at high plasma currents delivers the very high coating rates needed for high volume manufacturing and, as reported for example by Flewitt et al, Semicond. Sci. Technol. 24 (2009), delivers highly stable reactive sputter deposition processes, further greatly increasing the coating rates achievable for dielectric materials when compared to conventional sputtering techniques In general, the work undertaken by the applicants to develop these large area, high density plasma sources has shown that many of the physical elements defined in the Thwaites design are able to be varied significantly: as an example, the multi-turn coil antenna may instead be an elongated partial loop (extended "U" shape) allowing non-circular plasma cross section to be generated. The new knowledge we have gained from this work has prompted us to experiment further with design variations to optimise performance for a range of individual applications of large area sputter coating. This work has resulted in the discovery of an unexpected and previously unobserved limitation and an associated novel solution.

In essence, the inventors found that replacement of the dielectric tube element of the Thwaites source with a planar dielectric window and appropriate reshaping and repositioning of the RF antenna and magnets, whilst delivering the desired operational high density large area plasma source, did not deliver the expected stable performance usual to the above-mentioned Thwaites design developments when used in a coating process. It was observed that the usual, largely unavoidable coating of the dielectric window on the vacuum side by even thin layers of stray sputtered metal both rapidly reduced the efficiency of plasma generation and significantly changed overall operational parameters of the plasma source so as to ultimately, typically within a few minutes, prevent its further use until said metallic coating on the dielectric window was removed. Later optical assessment of these layers indicated that said coating thicknesses in the range of only 10-100nm were sufficient to cause the above loss of plasma source operation.

This was in contrast to experience with the earlier developed tube based ICP systems in which, as expected from standard RF shielding theory, internal tube coating had not been an issue even following long periods of operation, typically many months to years, and the build up of extensive coatings of materials in the range 0.1 to 1mm thickness. The inventors therefore started a series of experiments to determine how best to minimise coating of the window without compromising other aspects of the design or performance.

During one experiment it was seen that, despite a metal coating still forming rapidly on the dielectric window, the previously observed reduction of plasma source efficiency occurred far more slowly than before. On further investigation and following small alterations of the design, it was found possible to fully eliminate the coating induced loss of plasma source efficiency without any need to reduce or eliminate the coating itself, thereby re-establishing the long-term operational stability usual with sources based on the Thwaites designs.

Further experimentation and analysis of the coated, but working, plasma source showed that this was due to a particular spatial coating discontinuity being present as a result of shadowing by an internal structural element: more critically, this was not a region of the dielectric window that was directly required to transmit RF energy to the plasma generation regions.

Subsequent work has shown that the means of controlling coating of the RF transparent window construct so as to avoid above said reduction of plasma source efficiency is essentially to ensure that any coating formed on the window construct components, notably those through which the RF energy is to be transmitted into the vacuum chamber and those associated with the mechanical support and vacuum integrity of those components, is electrically discontinuous and isolated other than, at most, in a form that replicates and is aligned to the antenna shape and size.

Considered in another way, the coating of the RF transparent parts of the window construct must be electrically discontinuous and isolated such that, if the coating itself is imagined to be brought into physical contact with the antenna along its length, as if separation was reduced to zero without otherwise changing the coating and antenna positioning and alignment, no parts of the antenna would have a significantly shorter electrical path between them through the coating than that already inherent in the antenna itself. An example of this requirement will be given in the description below for clarity.

Therefore, viewed from a first aspect, the present invention relates to a high density gas plasma source capable of being used with a vacuum chamber and associated systems to produce gas plasma of density greater than 10' cm', the plasma source comprising: a radio frequency (RF) antenna positioned on one external side of the vacuum chamber in dose proximity to an RF transparent window construct of similar dimension to the antenna in or on said chamber, the whole being constructed and configured to selectively and controllably permit the transmission of radio frequency (RF) energy into the vacuum chamber to excite a plasma therein; at least one magnet being provided within or external to the vacuum chamber, positioned and of strength sufficient to interact with said plasma to both restrict the plasma excitation region in two orthogonal directions whilst extending the plasma excitation region from the antenna enclosure in a third orthogonal direction; and the RF transparent window construct being fabricated such that any process induced coating of the RF transparent components of the construct is specifically controlled and spatially restricted so as to prevent said coating from reducing the efficiency of plasma source operation.

Viewed from a further aspect, the invention described above is constructed such that the antenna and associated RF transparent window construct has a non-circular, elongate plan form, thereby giving rise to a plasma generation zone where one dimension (nominally width) is significantly Greater than the other (nominally height), typically by a factor of 5-10.

At least in preferred embodiments, we have accordingly invented a new form of a high density plasma source that is of especial utility when applied to large area plasma processing, including sputter deposition for which it delivers greatest benefit. Whilst the invention could be used in a form replicating the usual circular antenna geometry of Thwaites, a superior and preferred design is to elongate the transverse cross section of the plasma source through elongation of the antenna in a plane orthogonal to the plasma source longitudinal axis, to produce an essentially rectangular or rounded rectangular or oval or elliptical cross section plasma This is a particularly advantageous configuration, with a wide range of application in the coating and surface modification industries.

Detailed specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which Figure 1 is a schematic cross section of a preferred elongate embodiment of the gas plasma source shown in the gas plasma source longitudinal cross section as applied to use in sputter apparatus; and Figure 2 is the schematic cross section A-A' shown in figure 1 viewed from the right hand side of figure 1, showing a transverse cross section of the gas plasma source; and Figure 3 is the schematic cross section B-B' shown in figure 1 viewed from the bottom of figure 1.

Figure 4 is a schematic to elucidate the coating electrical discontinuity and isolation requirement for an example elongate shaped antenna and window construct Figure 5 is a schematic to elucidate the coating electrical discontinuity and isolation requirement for an example elongate "serpentine" shaped antenna and window construct.

In a preferred embodiment of the apparatus for use as a vacuum coating system, a vacuum chamber 1 and controllable means of vacuum pumping the chamber by a pumping system 2, both well known in the art, are fitted with an elongate remote gas plasma generation system 3, a planar rectangular target assembly 4, a DC power supply 5, an electromagnet 6 and associated DC power supply 7 capable of producing an axial magnetic field strength of up to 500 Oersted, substrate carrier or chuck 8, optional shutter assemblies 9 and a controllable process gas feed system 10 The elongate remote plasma generation system 3, as further shown in figures 2 and 3, comprises an assembly mounting a RF antenna II in close proximity, usually a few mm, to an aperture 23 in the vacuum chamber that is fitted with a window construct 12 that is at least in part transparent to RF radiation, in this embodiment being a quartz or ceramic or other dielectric plate of thickness able to withstand the vacuum -atmosphere pressure differential, typically a thickness of 12mm, with a coating shielding strip or mask 24 fitted within the vacuum chamber in close proximity to the window thereby limiting the zones over which any metal coating of the RF transparent window can occur. Examples of allowed coating zones 25 are shown in Figures 4 and 5, for different example antenna designs; it is to be noted that the example coated regions shown are electrically isolated from each other and from the electrically conducting vacuum chamber or elements thereof and are discontinuous other than in a path following part of the antenna pattern. An example of a dis-allowed coating zone 26 is also indicated in both figures; this will compromise plasma source operation as the adjacent coating zones are no longer isolated from each other and the disallowed coating zone does not follow the antenna path. The means of fabricating and fitting this window construct without compromising the integrity of the vacuum system will be well known by those skilled in the art.

The antenna requires further enclosure with RF shielding materials to block hazardous or otherwise undesirable RF emissions other than via the RF transmissive elements into the further RF blocking enclosure formed by the vacuum system. This antenna enclosure can be made capable of sustaining a vacuum, thereby removing the requirement that the window construct be able to support the vacuum to atmospheric pressure differential. This is not a preferred embodiment of the invention as it introduces complications with window construct cooling and requires the provision of additional vacuum system parts.

A further electromagnet 13 and associated DC power supply 16 are ideally used with the plasma source, being designed to be capable of producing an axial magnetic field strength of up to 500 Oersted. It is desirable but not necessary for both electromagnets to have a similar cross-sectional shape to the antenna 11. In this embodiment of the apparatus, this is an elongated "Ti' shape as shown in Figure 2, The RF antenna 11 is constructed most simply from shaped copper tube, though alternate electrically conducting materials, for example brass or aluminium, could be used. as can differing cross sectional shapes, for example rod, strip or a combined assembly, for example of strip and tube. The use of tubular construction for the RF antenna has the advantage of allowing it to be water cooled, hence allowing the use of higher RF powers than would otherwise be the case.

By well known means the RF antenna 11 is connected to and powered by a 13.56MIlz RF generator 14 and impedance matching network 15.

The construction of the target assembly 4 will be obvious to those skilled in the art, comprising a vacuum chamber feedthrough 17 that feeds cooling water and electrical power to a mounting assembly 18, the target being thereby water cooled and capable of having a voltage applied to it from power sources external to the vacuum chamber. A target material 19 is fitted to the face of the mounting assembly 18 that faces the substrate, ensuring good electrical and thermal contact by well known means, for example bonding with silver loaded epoxy. Additionally in order to prevent sputtering of the mounting assembly 18 a shield 20 that is electrically grounded is provided around this item, allowing only the target material 19 to be directly exposed to the plasma; the requirements and design of this shield are also well known.

The substrate carrier 8 essentially provides a means to position and hold the substrates 21 that are to be coated within the vacuum chamber. By well known means, the carrier may be water cooled or include heaters to control the substrates temperature, be capable of having a voltage applied to it to assist control of deposited film properties, include means of rotating and / or tilting the substrates to improve coating thickness uniformity, and itself be capable of being moved and / or rotated within the vacuum chamber.

The optional moveable shutter assembly 9 is provided such that in the 'closed' position target sputtering can take place without coating the substrates. There are many means of achieving this, all well known to those skilled in the art The process gas feed system 10 comprises one or more gas inlets for one or more process gases or process gas mixtures, each gas flow being controllable for example using commercial mass flow controllers, and optionally including gas mixing manifolds and / or gas distribution systems within the vacuum chamber, the detailed design of such systems is well known. In the simplest embodiment of the invention, a single gas inlet is provided to the vacuum chamber, the process gas or gases then being distributed to all parts of the vacuum by normal low pressure diffusion processes or directed pipework.

It will be appreciated by those skilled in the art that the positioning, orientation, size and form of the items described above can be significantly different to that shown, depending on the precise coating application. Configurations suited to roll-to-roll (-web") coating, vertically orientated substrate plates, semiconductor wafer coating, for example, can all be realised with the plasma source.

An example of the operation of the above example system will now be described with reference to figure 1.

The substrates 21 to be coated are loaded onto the substrate carrier 8 and the shutter 9 set to the closed position. The vacuum chamber 1 is then pumped by the pumping system 2 to a vacuum pressure suitable for the process, for example less than 1x10' torr. The process gas feed system 10 is then used to flow at least one process gas, for example argon, into the vacuum chamber. The flow rate and optionally the rate of vacuum pumping are adjusted to provide a suitable operating pressure for the sputter process, for example 3x10-3 torr. The electromagnets 6 and 13 in conjunction with their respective power supplies 7 and 16 are then used to produce a magnetic field of strength approximately 100 to 300 Oersteds between them and across the vacuum chamber. The magnetic 'polarity' of each electromagnet is set to be identical in this example (i.e. they attract).

The remote gas plasma is generated by applying RF power, for example 2kW, from the generator 14 via the impedance matching network 15 to the antenna 11. In combination with the magnetic field produced as described above, these result in visible high density plasma being produced across the chamber and under the target assembly 4, as approximately indicated by the region 22 in figure 1 The DC power supply 5 is then used to apply a negative polarity voltage to the target assembly 4. This results in ions from the plasma in the vicinity of the target being attracted to the target and, if the voltage is above the sputter threshold value for the target material (typically in excess of 65 volts), sputtering of the target material will occur. As the sputter rate for this example system is approximately proportional to the voltage above this threshold value, voltages of 400 volts or more will usually be applied; for very high rate applications higher voltages may be used, for example 1200 volts.

After an optional time delay to allow the target surface to clean and stabilise, for example 5 minutes, the shutter assembly 9 is set to the open position to expose the surface of substrates 21 facing the target assembly to the sputtered material, thereby coating the substrate surfaces with a film of the target material 19. After a time determined by the required film thickness and the deposition rate at the substrate surface, the shutter assembly 9 is set to the closed position and deposition onto the substrates ceases.

The various power supplies and gas flows can then be turned off as required and the vacuum system vented to atmospheric pressure using a suitable gas, for example nitrogen or air, to permit recovery and subsequent use of the coated substrates. All these procedures will be obvious and well known to those skilled in the art.

In an alternate embodiment of the gas plasma source, the RF transparent window may be made using two or more RF transparent sections, each section having a part of the antenna construct in close proximity to it; this is most effectively used with the elongate antenna embodiment of the invention, with for example two separate RF transparent window sections of comparable long dimension to the linear elements of the antenna being placed proximate to and aligned with said antenna elements. Arrangements for ensuring that coatings received on these separate windows are not electrically connected by the intervening chamber walls, fittings or other elements of the window construct are as used internally for other electrical connector isolation requirements in the vacuum coating industry and will be known to those skilled in the art. This construction has the benefit of eliminating the need for the internal mask 24 whilst providing a more robust window construct.

Typically, the antenna designs used for the Thwaites plasma sources cover a wide set of options The described invention is clearly also relevant to many of these, in particular those of planar serpentine form of Figure 5 in which a series of alternating coat free zones will be needed to maintain the required power coupling to the plasma chamber, potentially though a series of square dielectric windows to provide a highly robust elongate window assembly.

It will be appreciated by those skilled in the art that the usual stray coating reduction techniques can still be applied to the invention with benefits when considering long term coating build up, delamination debris impact and coating system maintenance issues. Such techniques include as examples the use of coating baffles, line of sight to target avoidance, recessed window placement and debris collection traps.

The results achieved in experimenting with plasma sources based on the above example embodiments will now be described.

A vacuum system fitted with a plasma source was constructed substantially as shown in figure 1 and described above. Two electromagnets of dimension equivalent to that of the antenna were installed either side of the vacuum chamber and plasma source. The antenna was constructed from 6mm diameter copper tube in the form of an elongated "U" shape, as shown in figure 2, the two linear sections passing in close proximity to the chamber window, which was a 12mm thick slab of quartz, of approximate planar dimensions 550mm by 120mm. In the initial experiments, the window shielding strip or mask was not fitted.

The sputter target, in this case being copper, was operated substantially according to the example description above. The following observations and results were obtained.

The process conditions were set as follows: an argon gas flow of 150sccm resulting in a vacuum system pressure of about 5x10-3 ton, 800W, 13.56Milz RF power applied to the RF antenna and the electromagnet 13 and electromagnet 6 operated so as to produce a suitably strong, greater than about 500e, essentially planar magnetic field across the chamber width. When powered, the elongate gas plasma source produced a visible plasma region of approximately 460mm by 40mm cross section extending across the chamber width of about 300mm from the RF transparent window, visible as an intense argon plasma of characteristic purple -blue colouration typical of the presence of a plasma density of between loll and 1013 CM-3 The visible plasma generation zone originating from the elongate gas plasma source could be guided and shaped using the electromagnets 6 and 13 to pass completely across the chamber width and thereby completely cover the whole target material surface; the presence of the target material did not visibly affect the plasma, whether grounded or not, or with a low, approximately 20V, negative electrical bias i.e. below the target material sputter threshold. Furthermore, the target assembly did not substantially heat up despite being placed in proximity to the high density plasma.

It was observed that the visible plasma profile followed the expected magnetic field profile between the electromagnets. In further experiments, the electromagnets were set so as to oppose (i.e. physically repel) each other, resulting in a major change to the magnetic field profile, which again the plasma was observed to follow.

Upon applying negative electrical voltage of 350V to the sputter target, plasma colour was observed to take on a greenish hue, typical of that seen when copper is present in the plasma, demonstrating that sputtering was occurring. The initial target current was about 2A, indicating a plasma density in excess of about 1013 cm'.

The plasma rapidly reduced in intensity, with a commensurate reduction in target current, as the RF transparent window became coated in 'stray' copper from the sputter process, effectively shutting down the plasma and sputter process in less than 10 seconds. Cleaning the coating from the window recovered plasma source and target operation, but this again rapidly diminished with coating formation as before, implying that the coating was attenuating the RF power coupling through the window.

Longitudinal metal strips were therefore positioned within the vacuum chamber in close proximity to the RF transparent window and aligned to the central region of the antenna loop: this was intended to attenuate the window coating without significantly impeding plasma source operation, as the plasma originates at the window vacuum regions closest to the antenna conductor in the Thwaites designs.

With the window again cleaned of previous coatings, the sputter experiment was then repeated: whilst it was seen that there was only a slightly slower window coating rate, it was noticed that the plasma attenuation occurred far more slowly than that rate implied. On examination it was discovered that the window had been coated non-uniformly, having a far thinner central region where the longitudinal strips had best masked the window. Thus the inventors surmised that it was not, as expected from the art, the formation of a RF shielding coating on the window region in closest proximity to the antenna conductor that was the problem, but the formation of a coating between those regions.

Based on that deduction, the experiment was again repeated, this time placing the metal strips in very close proximity to the window to essentially fully stop coating of the central longitudinal region. This resulted in near complete elimination of the plasma attenuation effect, despite there being no significant change in the coating rate of the unmasked window regions close to the antenna.

Hence an elongate remote gas plasma source built according to the invention has produced a stable volume of high density plasma, greater than 1012 cm-3, of cross sectional long dimension in excess of 400mm and of uniformity at least adequate to allow uniform sputtering of a like dimensioned metal sputter target of width 125mm It will be apparent that the inventive step of controlling and limiting coating of the RF transparent window to specific regions is essential to achievement of this capability in a stable and hence useful manner and thereby distinguishes the invention from other disclosed remote plasma generation systems.

The invention can also be used in a reactive sputter process, that is a process in which at least one of the previously mentioned process gases is a reactive gas or vapour introduced via the gas feed system 10 or by other equivalent controllable means to react with the sputtered target material or materials and thereby deposit a compound thin film on the substrate. For example, oxygen gas can be introduced into the sputter process with any of the embodiments previously described in order to deposit oxide thin films, for example to deposit alumina by sputtering of an aluminium target in the presence of oxygen gas or silica by sputtering of a silicon target in the presence of oxygen gas It is to be noted that although dielectric reactive coatings themselves are non-conducting, the 'stray' coatings arriving at the RF transparent window will usually be metal rich and therefore still capable of reducing plasma source efficiency if not controlled and limited in extent as for metals.

It should also be noted that the inventors had, prior to the above described invention, constructed elongate plasma sources using a single essentially linear antenna in place of the already described elongate loop, as it will be apparent from the above descriptions that this inherently avoids the observed coating issues. However, performance of such systems was found to be inferior to that of the loop antenna plasma sources described above which are therefore a preferred solution.

It will be obvious to those skilled in the art that the ability of the elongate gas plasma source to operate independently of any sputter target allows further application to be realised. Thus the above described elongate gas plasma source may be used as a substrate cleaning, surface modification or etch tool with especial utility where large dimensioned substrates are to be processed at high throughput rates, for example in roll to roll (-web") coating. It is well known that merely running the substrate through or in proximity to high density plasma is sufficient to achieve great improvement in the adhesion of subsequent coatings, or to cause beneficial changes to the substrate surface. If substrate etching is required, then it is well known in the art that this may be achieved through the application of an electrical bias to the substrate, resulting in substrate surface sputtering, or by introducing a gas or vapour into the process which is then activated by the high density plasma to react with and etch the substrate surface, or by a combination of the two processes.

The elongate gas plasma source could also be used as a 'plasma assist' tool for other coating processes, as is typically used in evaporative coating process tools.

The elongate gas plasma source could also be applied to coating processes based on the technique of Plasma Enhanced Chemical Vapour Deposition (PECVD).

The disclosed elongate gas plasma source is of particular utility in all these processes due to the innate ability to generate uniform high density plasma over very long lengths and widths, thereby allowing its use with large dimensioned substrates. The means for realising such applications will be readily apparent to those skilled in the art, for example essentially comprising vacuum systems of the form described in the preferred embodiments above, but with the omission of the sputter target assembly and, for the plasma assist tool, its replacement with another coating source.

Claims (22)

1. Claims 1. A gas plasma source capable of being used with a vacuum system to produce high density plasma, of density greater than 1011 cm', the gas plasma source being attached to said vacuum system, in total comprising: means of controllably producing a vacuum of one or more gases in a vacuum chamber or chambers that may also contain facilities needed for a given desired vacuum process and to at least one of which said chambers said gas plasma source is mounted, said gas plasma source comprising means of coupling energy into said vacuum gases to produce a vacuum gas plasma by means of an electrically conducting antenna placed external to said vacuum chamber or chambers, in proximity to a window construct attached to at least one of the vacuum chambers, at least a portion of the window construct permitting the transmission of radio frequency (RF) energy into said vacuum chamber means of producing a magnetic field within the vacuum chamber(s) using at least one magnet, the magnetic field being of magnitude, alignment and shape that results in the extension of said plasma to and across or onto those regions where a plasma process is required having the characteristic feature that the RF transparent window construct includes means to r control and limit, in a manner determined by the physical shape of the above mentioned antenna, ('I the extent of any coating by the above mentioned process of the RF transmitting components.
2. (3) 2. A gas plasma source as claimed in claim 1 in which the RF transparent window construct includes means to control and limit the extent of any coating of the RF transmitting components by the above mentioned process such as to introduce electrical discontinuity and isolation of the coated regions other than in a form which, at most, essentially follows the path of the RF antenna C\I that is intended to transmit the RF energy to the vacuum chamber or chambers.
3. 3 A gas plasma source as claimed in claims 1 and 2, wherein the RF transparent window construct includes RF transparent materials positioned and designed to preferentially excite plasma in a chosen position or positions within the vacuum chamber at the RF transparent window construct, the means of ensuring that any coating of the RF transmitting components is electrically isolated and discontinuous being the placement of a masking plate proximate to the RF transmitting elements within the vacuum chamber to which the gas plasma source is fitted.
4. 4. A gas plasma source as claimed in claims 1 and 2, wherein the RF transparent window construct includes RF transparent materials positioned and designed to preferentially excite plasma in a chosen position or positions within the vacuum chamber at said window construct, the means of ensuring that any coating of the RF transmitting components is electrically isolated and discontinuous being the use of two or more separate RF transmitting components mounted so as to ensure their individual electrical isolation when subject to process coating.
5. 5. A gas plasma source as claimed in any one of the preceding claims 1 to 4 inclusive, wherein the RF transparent window construct has at least one of the RF transmitting components recessed on the vacuum chamber side to reduce process coating and thereby reduce maintenance requirements.
6. 6. A gas plasma source as claimed in any one of the preceding claims 1 to 5 inclusive in which the antenna is formed from two linear electrical conductors, joined at one end to form a single loop antenna.
7. 7. A gas plasma source as claimed in claim 6 in which further linear conductors are placed in parallel with the single loop linear conductors and joined so as to form a multiple loop antenna.
8. 8. A gas plasma source as claimed in claims 6 and 7 in which the resulting antenna is between 1 and 5 turns.
9. 9. A gas plasma source as claimed in any one of the preceding claims, wherein in plan form the antenna has a length and a width, the ratio of the length to the width of the antenna being greater than or equal to two (2), three (3), five (5), ten (10), or fifteen (15).
10. 10. A gas plasma source as claimed in any one of the preceding claims, wherein the antenna has a planar form which is generally rectangular, rounded rectangular, polygonal, elliptical, U-shaped, or a series of loops or a series of spirals.
11. 11. A gas plasma source as claimed in any of the preceding claims in which the antenna is a construct of materials in rod, tube, plate and sheet form or a mixture of rod, tube, plate and sheet forms having the property of being able to be powered with radio frequency (RF) electrical energy.C\I
12. 12. A gas plasma source as claimed in any one of the preceding claims, wherein the antenna or ^ antennae are supplied with power from one or more radio frequency power supply system(s) * operating at a frequency between 30 kHz and 3 GHz; a frequency between 300 kHz and 300 O MHz; a frequency between 3 MHz and 30 MHz; or at a frequency of approximately 13.56 MHz o or multiples thereof C\I
13. 13. A gas plasma source as claimed in any one of the preceding claims, wherein said at least one magnet generates a magnetic field of strength greater than or equal to 5 Oersteds, and preferably between 50 and 500 Oersteds, measured at a location proximate to, within 5mm distance of, any part of the RF transparent window construct.
14. 14. A gas plasma source as claimed in any one of the preceding claims, wherein said at least one magnet is positioned at least substantially aligned to one of the longer dimensioned sides of the antenna and proximate to said antenna
15. 15. A gas plasma source as claimed in any one of the preceding claims, wherein said at least one magnet comprises: (i) one or more electromagnets; (ii) one or more permanent magnets; or (iii) a combination of one or more permanent magnets and one or more electromagnets; wherein preferably at least one of said electromagnets is controllable.
16. 16. A gas plasma source as claimed in any of the preceding claims, further comprising power supply means for supplying the electromagnets with an alternating current (AC) or a pulsed source to induce changes to the plasma.
17. 17. Use of a gas plasma source as claimed in any one of claims 1 to 16 in a vacuum system for the purposes of sputter coating, through exposure of an electrically negatively biased sputter target material to the gas plasma generated by said source.
18. 18. Use of a gas plasma source as claimed in any one of claims 1 to 16 in a vacuum system for the purposes of substrate cleaning, surface modification or other preparation processes through exposure of said substrate to the gas plasma generated by said source.
19. 19. Use of a gas plasma source as claimed in any one of claims 1 to 16 in a vacuum system for the purposes of substrate etching through application of a negative bias voltage, either intermittently or continuously, to said substrate and optionally with heating or cooling of the substrate and resulting sputtering of said substrate surface by the gas plasma generated by said source.
20. 20. Use of a gas plasma source as claimed in any one of claims 1 to 16 in a vacuum system for the purposes of substrate etching through use of a chemically reactive gas or vapour, optionally with application of a negative bias voltage, either intermittently or continuously, to said substrate and optionally with heating or cooling of the substrate and resulting in etching of said substrate surface by the gas plasma generated by said source.
21. 21. Use of a gas plasma source as claimed in any one of claims 1 to 16 in a vacuum system for the purposes of providing a plasma assist to any physical vapour deposition (PVD) coating process, with said plasma assist being provided by the gas plasma generated by said source, optionally with application of a bias voltage, either intermittently or continuous, to said substrate and optionally with heating or cooling of the substrate.(\I
22. 22. Use of a gas plasma source as claimed in any one of claims 1 to 16 in a vacuum system for the purposes of substrate coating by the process of Plasma Enhanced Chemical Vapour (3) Deposition (PECVD) using an appropriate chemically reactive gas or vapour with said plasma enhancement being provided by the gas plasma generated by said source, optionally with application of a bias voltage, either intermittently or continuous, to said substrate and optionally with heating or cooling of the substrate. C\I23. A gas plasma source substantially as herein described with reference to the accompanying Figures.