Toroidal plasma source and method of using the same

Abstract

A plasma source, comprises a plasma source body comprising a plurality of magnetic cores, a plurality of primary windings capable of being energized, and a cooling structure, wherein one or more sections of the plasma source body comprise a dielectric material, and wherein when the plurality of primary windings are energized, a plasma forms a loop within the plasma source body, and the cooling structure is positioned between the plasma source body and at least one of the plurality of the magnetic cores.

Description

TOROIDAL PLASMA SOURCE AND METHOD OF USING THE SAMECROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority of U.S. Provisional Application No.: 63 / 638,169, filed April 24, 2024, entitled “Toroidal Plasma Source”, the entire contents of which are incorporated herein by reference.FIELD OF THE INVENTION

[0002] The present application is directed to toroidal plasma sources and methods of operating the plasma sources, and more precisely to miniature toroidal plasma sources functioning with reduced voltage.BACKGROUND

[0003] Toroidal plasma sources are typically used for generating reactive radicals that are delivered to a semiconductor processing chamber. Typical applications for plasma sources are cleaning unwanted material for the chamber, or delivering radicals that are used for on- wafer processes. A toroidal plasma source typically has a plasma loop length of approximately 40 cm and is capable of dissociating several standard liters per minute (slm) of gas flow, at a pressure of several Torr, and operates at several kilowatts. A typical plasma loop voltage under these conditions is approximately 200-300 V.

[0004] A toroidal plasma source is typically constructed of a conductive aluminum vacuum vessel that has a dielectric coating. The vacuum vessel has dielectric breaks, such that it does not form a complete turn through the ferrite core, and therefore prevents the vacuum vessel from forming a shorted turn. During the ignition of a toroidal plasma source, before the toroidal plasma is formed, there is typically a large voltage that is induced, and because the vacuum vessel is conductive, this voltage drop is concentrated on the dielectric break, where it creates strong electric fields. If the induced voltage without a plasma present is large enough, then arcing can occur across these breaks, which can cause damage to the dielectric coating, or electrical breakdown through the dielectric coating. Typically, a dielectric break has 3-4mm, and a plasma source may have between 2 to 4 dielectric breaks. The ratio of dielectric break length to overall length may be as high as 4%.

[0005] To avoid these problems, the voltage during the ignition process should be limited. However, this can limit the ignition performance and narrow the ignition operating windowwith regards to pressure and ability to ignite. Lower ignition voltage can also reduce reliability of ignition with small partial pressures of “poison” gas.

[0006] For example, if a conventional toroidal plasma source has a loop voltage of approximately 40 cm, it may operate with a loop voltage of approximately 200-300 V, and may require more than 600 V to ignite, under ideal conditions. However, under non-ideal gas conditions, it may require an even higher voltage, but the plasma source cannot be configured for the required higher voltage because at that level the ignition voltage will approach the arcing threshold, or the breakdown strength of hard anodize which is approximately 600 V / mil.

[0007] Separately, radicals generated by a remote plasma source typically should be transported to a working surface through a transport tube, and sometimes through a showerhead. This transport path leads to recombination losses of the radicals, and a net reduction in cleaning or processing performance. Typically, with a conventionally sized remote plasma source, it is not possible due to mechanical constraints around a semiconductor chamber to reduce the transport distance or optimize the path for low recombination losses. This is important when using chemistries that have high recombination rates, such as atomic oxygen or atomic hydrogen.

[0008] In light of the foregoing, toroidal plasma sources utilizing an array of plasma loops, of unknown size, have been used. While these plasma loop-based systems have proven somewhat useful, they also have shortcomings. For example, the plasma loop is described as operating at very low pressures (0.3 to 100 mTorr) and substantially low power (400 W distributed over an array of 6 plasma loops, or ~65 W per loop). As such, this arrangement has limited applications for low pressure, low flow, and low power. For many cleaning or processing applications, operation at higher pressures of 1-10 Torr, flows of 500-6000 seem, and powers of 2 - 6 kW is required. In order to operate an array of plasma sources at these conditions, a novel cooling solution is required.

[0009] Therefore, there is an ongoing need for toroidal plasma sources with a plasma loop of small dimensions, that are able to function at high power, but reduced voltage without compromising their ability to ignite.SUMMARY

[0010] The present application discloses embodiments of a toroidal plasma source and its method of operating, that have been conceived and developed aiming to provide solutions to the above stated objective technical needs, as it will be evidenced in the following description.

[0011] To address the above enumerated problems, a plasma source that is small is required. A small plasma source inherently requires lower voltage for operation and ignition. A small size also enables the plasma source to be located close to the surface that to be cleaned or processed, which substantially reduces the distance of the transport tubing and recombination losses. This allows much more efficient cleaning, and in some cases, enables cleaning regions of the chamber that could not otherwise be adequately cleaned. A challenge in constructing a miniature plasma source at relevant conditions (>1 kW) is in managing the heat dissipation in the ferrite cores, and the heat load from the plasma on the body of the plasma source and its vacuum vessel.

[0012] To address the above technical needs the present application proposes a plasma source having a plasma source body, a plurality of magnetic cores, a plurality of primary windings capable of being energized, and a cooling structure, wherein one or more sections of the plasma source body comprise a dielectric material, wherein when the plurality of primary windings are energized, a plasma forms a loop within the plasma source body, and wherein the cooling structure is positioned between the plasma source body and at least one of the plurality of the magnetic cores. The dielectric material is capable of capacitively coupling energy into the plasma source to form a plasma ignition discharge. A length of the plasma loop is less than 25 cm. A voltage of the plasma is less than about 75 V, and a plasma power is higher than 500 W. The cooling structure comprises a plurality of cooling plates positioned between the plurality of magnetic cores and the plasma source body. The plasma source further comprises a thermally conductive potting material, the thermally conductive potting material providing thermal coupling between the plurality of magnetic cores and the cooling structure, the thermally conductive potting material being capable of facilitating heat transfer from the dielectric break to the cooling structure. The plurality of magnetic cores has more than 60% of the surface area coupled with the cooling structure. The dielectric material comprises a cylindrical dielectric break and a planar dielectric break positioned along the plasma. The plasma source further comprises an electrode formed on a surface of the cylindrical dielectric break. The plasma source body comprises a gas inlet and a gas outlet connected by a vacuum channel. The plasma forms within the vacuum channel when theplurality of primary windings are energized. A portion of the plasma source body has a length that is at least 7% of the overall length of the plasma loop.

[0013] In another embodiment, the present application discloses a method of operating a plasma source, comprising energizing a plurality of primary windings wrapped around a plurality of magnetic cores in a plasma source, forming a plasma within a body of the plasma source, and cooling the plasma source body using a cooling structure positioned between the plasma source body and the plurality of magnetic cores. The method further comprises igniting the plasma using a dielectric barrier discharge igniter. Igniting the plasma comprises operating the dielectric barrier discharge igniter at a power of about 20 W for a period of time between about several milliseconds to about two minutes. The method further comprises transitioning from the dielectric barrier discharge igniter to an inductively coupled plasma mode igniter. Forming the plasma comprises generating a plasma current exceeding 20 A. The plasma is formed at a pressure between about 0.5 to about 10 Torr and with a gas flow rate between about 100 to about 2000 standard cubic centimeters per minute. Cooling the plasma source body comprises circulating water through copper cooling plates positioned between the plurality of magnetic cores and a plasma vessel of the plasma source body.

[0014] In another embodiment, the present application discloses a semiconductor processing system, comprising a processing chamber and a plasma source coupled to the processing chamber, the plasma source comprising a plasma source body, a plurality of magnetic cores, a plurality of primary windings capable of being energized, and a cooling structure, one or more sections of the plasma source body comprising a dielectric material, and when the plurality of primary windings are energized, a plasma forms a loop within the plasma source body, and the cooling structure is positioned between the plasma source body and at least one of the plurality of the magnetic cores.

[0015] The miniature plasma source disclosed herein enables integrated capacitive coupled plasma for ignition. The dielectric break in the main plasma loop has one surface facing the vacuum and one surface facing the region at atmospheric pressure. An electrode is constructed on the atmosphere side of the dielectric. This forms a dielectric barrier discharge structure, or more generally, a capacitively coupled discharge structure that is used for igniting the main inductively coupled toroidal plasma. The ratio of dielectric break length to overall length is larger than 6%.

[0016] More detailed explanations regarding these and other aspects and advantages of the various embodiments of the toroidal plasma source are provided herein.BRIEF DESCRIPTION OF DRAWINGS

[0017] The above and other aspects, features and advantages of the toroidal plasma source will become more apparent from the subsequent description thereof, presented in conjunction with the following drawings, wherein

[0018] FIG. l is a diagram of an embodiment of a miniature toroidal plasma source with planar dielectric break;

[0019] FIG. 2 is a diagram of an embodiment of a miniature toroidal plasma source with cylindrical dielectric break;

[0020] FIG. 3 is a diagram of an embodiment of a miniature toroidal plasma source with two ferrite cores;

[0021] FIG. 4 is a representation of a planar array used in an embodiment of a miniature toroidal plasma sources with cylindrical dielectric breaks;

[0022] FIG. 5 is a schematic representation of planar array used in an embodiment of a miniature toroidal plasma sources with cylindrical dielectric break, and

[0023] FIG. 6 is also a diagram of an embodiment of a miniature toroidal plasma source with two ferrite cores.DETAILED DESCRIPTION

[0024] The present application discloses several embodiments of a toroidal plasma source. The following detailed description is not to be taken in a limiting sense and is merely to provide an overview of the various embodiments. Further, the following detailed description will reference the accompanying drawings wherein like numerals refer to like parts throughout.

[0025] As it will be described in detail below, miniaturized remote plasma sources with a short plasma loop can operate at relatively high power but at low voltage compared to a conventional toroidal plasma source. The small plasma source enables reliable ignition with reduced voltages, by operating in a hybrid mode with a capacitively coupled plasma source for ignition that transitions to an inductively coupled toroidal plasma. Due to the small plasma loop, robust transition to high power toroidal mode can be achieved at moderate voltages, which avoids the problems of arcing and voltage breakdown of coatings during the ignition process that appear in conventional, larger toroidal plasma sources. This enables longer life of the plasma vessel and reduced particle output. Additionally, the compact form factor of the plasma source allows it to be positioned close to the surface to be processed,which eliminates recombination losses during radical transport, losses that occur when a conventional large plasma source is positioned remotely.

[0026] In one embodiment, the toroidal plasma source described herein combines the function of the dielectric break with a capacitively coupled ignition electrode. By having a relatively large dielectric break that is more than 7% of the plasma loop length, or approximately 1 cm, the electric field across the dielectric break is substantially reduced, which further reduces the chance of arcing during ignition, even with high induced voltages. A low electric field across the dielectric break also reduces the erosion of the wall surfaces due to sputtering. The size of the dielectric break can vary from approximately 0.5 to 2cm, and one or more dielectric breaks may be present. The plasma loop can be constructed as small as 10 cm, and as large as 25 cm, or of a size anywhere in between, in order to achieve a substantial reduction in operating plasma loop voltage. A large dielectric break could introduce challenges concerning cooling, which can be mitigated by using a potting material to facilitate heat transfer from the dielectric break to a cooling structure. For example, Berquist® GF3500LV potting material has thermal conductivity of 3.6 W / m*k and dielectric strength of 275 V / mil. In accordance with the present disclosure, at least three possible implementations for the dielectric break are proposed, although those skilled in the art will appreciate that any number of implementations of the dielectric break may be used.

[0027] As illustrated in FIG. 1, the dielectric break can be implemented as a flat ceramic disc. As illustrated in FIG. 2 the break may be implemented as a ceramic tube, or as illustrated in FIG. 3, the plasma source may be implemented with two magnetic or ferrite cores and a plurality of dielectric breaks. Exemplarily the ferrite cores may have a toroidal shape, but the plasma source can be constructed with ferrite cores of other shapes and geometries, such as U cores. Herein, the terms “ferrite cores” and “magnetic cores” are used interchangeably. Magnetic cores encompass in addition to ferrite cores, other classes of materials suitable for use as a transformer core, such as amorphous metals, or iron-based materials. Ferrite cores, made from materials such as MnZn or NiZn, are a preferred embodiment due to easy availability of diverse sizes, cost, and material properties. Epcos N87 is an example of a suitable MnZn ferrite core material.

[0028] FIG. 1 schematically shows a diagram of an embodiment of a miniature toroidal plasma source with planar dielectric break. As shown in FIG. 1, the plasma source 100 comprises a plasma body having at least one gas inlet 102 and at least one gas outlet 104, that is facilitated by the vacuum channel 114. The plasma loop 116 comprises both the gas inlet 102 and a gas outlet 104. In one embodiment, the length of the plasma loop 116 isapproximately 11 centimeters, although those skilled in the art will appreciate that the miniature toroidal plasma source may be constructed having any desired plasma loop length. The plasma source 100 also comprises a plurality of magnetic cores 106 and a plurality of primary windings 108 capable of being energized. Optionally, one or more cooling plates or structures 118 may be formed in or coupled to the toroidal plasma source 100 and are positioned between the plasma source body and at least one of the plurality of the magnetic cores 106. At least one dielectric break 110 may be positioned on or otherwise coupled to the toroidal plasma source 100. In one embodiment, the dielectric break 110 may be configured to serve as a barrier dielectric. At least one electrode 112 may be formed on the surface of the dielectric break 110, on the surface of the dielectric break 110 that is at atmospheric pressure. Electrode 112 can be formed by bonding a metal film to a surface of the dielectric break 110. In another embodiment, the electrode 112 may be formed using a thick film metallization technique, where a paste containing metal is silk screened on the surface of the dielectric break 110 and then fired. Electrode 112 can also be formed using a co-firing technique, where the metal layer is embedded inside the wall of the dielectric break 110. In all of these cases, the ceramic disc structure 110 serves as dielectric barrier layer, so a barrier dielectric discharge is formed in the vacuum channel 114. A dielectric barrier discharge is considered a subset of a capacitively coupled discharge. The dielectric barrier discharge (DBD) plasma is ignited easily and serves to generate free electrons that facilitate the transition to form a high power inductively coupled plasma, which is energized by the primary windings around the ferrite core.

[0029] FIG. 2 is a diagram of an embodiment of a miniature toroidal plasma source with cylindrical dielectric break.

[0030] The miniature toroidal plasma source 100 of FIG. 2 is identical to the miniature toroidal plasma source of FIG. 1, with the distinction that the dielectric break and the DBD igniter 110, respectively the metal electrode 120 are distinct from dielectric break 110 and electrode 112 in that they have a cylindrical geometry and are situated along the plasma loop 116. In the embodiment of FIG. 2, the miniature toroidal source 100 includes a larger electrode area, due to the particular geometry of the cylindrical dielectric break 110.

[0031] FIG. 3 is a diagram of an embodiment of a miniature toroidal plasma source 300 with two ferrite cores, a first ferrite core 306 and a second ferrite core 314. FIG. 3 shows an embodiment of a miniature toroidal plasma source 300 with dual ferrite cores 306 and 314 with a plurality of cylindrical dielectric breaks 310 and DBD igniter, and with a plasma loop 312 having a length of approximately 15 cm. As shown, the plasma source 300 comprises afirst ferrite core 306 and a second ferrite core 314 disposed side by side within the plasma loop 312. A cooling structure 318 is illustrated adjoining the ferrite cores 306 and 314. The primary windings 308 capable of being energized are also illustrated in FIG. 3 and may be placed adjacent to a dielectric break 310 and an igniter. The plasma source body 320, having at least one gas inlet 302 and at least one gas outlet 304, that is facilitated by a vacuum channel, are also illustrated in the figure.

[0032] The above-described miniature toroidal plasma sources of FIGs. 1 - 3 enable more robust ignition and operation. A dielectric barrier discharge (DBD) igniter can ignite reliably under a broad range of vacuum conditions. A dielectric break igniter 110 will also ignite reliably even in the presence of contaminants that are present in the plasma source 100. The plasma source 100 can be used to reliably generate free electrons, that will enable the transition to a toroidal inductively coupled plasma mode. The dielectric break 110 can also be operated in steady state at moderate power (for example 20 watts) for a substantial period of time, for example several seconds, or several minutes, or 10s of minutes, with a cleaning gas such as oxygen or NF3, such that gaseous or solid contaminants are removed from the toroidal plasma vacuum vessel. In accordance with an embodiment of the present invention, igniting the plasma comprises operating the dielectric barrier discharge igniter at a power of about 20 W for a period of time between about several milliseconds to about two minutes. These contaminants could otherwise prevent reliable operation with the toroidal ICP operation, particularly if the contaminant is a conductive powder that bridges the dielectric break. After a cleaning step using the plasma, the toroidal plasma source 100 or 300 can transition to toroidal ICP mode and operate reliably at higher powers, such as 500 - 1500 W.

[0033] In order to operate a toroidal plasma source 100 or 300 with a high flow of electronegative gas such as NF3 or O2 at 100 seem - 2000 seem, with a pressure of 0.5 - 10 Torr, a high plasma current such as 20-50 A is required. For example, with an electric field strength of 3 V / cm, and a loop voltage of approximately 35 V, and a plasma current of 40 A, the plasma source 100 or 300 will operate at approximately 1400 W. At substantially lower plasma current, such as 10-15 A, the plasma can only be sustained in limited operating conditions, if at all. To keep the plasma loop 116 or 312 small, a small ferrite core 106 or 306, 314 should be used. Because of the small core surface area, and the high powers in the plasma body 320, power densities are quite high and require aggressive conductive cooling. In accordance with the present disclosure, a voltage of the plasma loop source is less than about 75 V, and a plasma power is higher than 500 W. In this construction, heat from the plasma body 320 is dissipated in the cooling structures 118 or 318 (exemplarily implementedas cold plates 118 or 318, or cooling plates) and has minimal impact on the temperature of the ferrite cores 106 or 306, 314, if the ferrite cores 106 or 306, 314 are sandwiched between two cooling plates 118 or 318. The plurality of magnetic cores has more than 60% of their surface area coupled with the cooling structure. Alternatively, the cooling structures 118 or 318 are exemplarily implemented as water cooled copper cooling plates 118 or 318 that are situated between the core 106 or 306, 314 and the plasma body 320, such that three of four sides of the toroidal ferrite cores 106 or 306, 314 are in close contact with the cooling plates 118 or 318. The entire body 320 is potted with a thermally conductive potting, that may also be electrically insulating, to further increase the cooling capability and provide voltage insulation. The thermally conductive potting material, providing thermal coupling between ferrite cores 106 or 306, 314 and the cooling structure 118 or 318 is capable to facilitate heat transfer from the dielectric break 110 or 310 to the cooling structure 118 or 318.

[0034] Another advantage of the various embodiments of the plasma sources disclosed herein consists of the ability of these devices to be located close to the surface to be cleaned or processed. The plasma sources disclosed herein are used to generate reactive radicals such as F*, O*, or H*. These radicals typically travel from the plasma source, through a transport tube, possibly through elbows, and usually a distribution plate or shower head before reaching the surface to be treated or cleaned with the radicals. During this transport, some of the radicals will recombine into molecular species which are far less reactive. Particularly with oxygen or hydrogen radicals, this recombination loss is severe to the point where <10%, or with higher pressures and longer transport distances, even <1% of the radicals survive the transport.

[0035] A solution to this problem is to have a small plasma source that can be located close to the surface to be cleaned with minimal transport distance, which can greatly improve the transport efficiency and overall delivered radicals, even if the plasma source operates at relatively low power and generates fewer radicals. Due to the space constraints in modem etch and deposition chambers for semiconductor applications, it is usually not possible to position a conventional toroidal remote plasma source within about 150mm of the location where the radicals are to be delivered, simply due to the size of a conventional toroidal remote plasma source. An advantage of the embodiments of the toroidal plasma source disclosed herein is a very small loop length, of less than 25 cm, such that the plasma source can be located close to the point of use with minimal transport distance, such as 25-100 mm, or as much as 150 mm. In conventional systems, a transport tube is 40 mm or 50 mm in diameter and uses a standard KF style vacuum connection such as a KF25, KF40, or KF50.However, with the miniature toroidal plasma source 100 or 300 it is possible to use a larger, non-standard flange, such that the outlet of the toroidal plasma source forms a relatively large opening (for example 25 x 75mm), and mates to a matched large opening in the chamber. This enables direct, line of sight exposure of the toroidal plasma to surfaces in the chamber. This will further minimize recombination losses, since the transport tube is eliminated.

[0036] It is expected that multiples of the miniature toroidal plasma sources 100 or 300 would be positioned around various parts of the semiconductor chamber in order to provide even cleaning of the chamber. For example, a source 100 or 300 could be installed at the top of the chamber above the showerhead, one or more near the wafer pedestal, one or more near the bottom of the chamber, and one or more in the foreline or pumping line. In a chamber with multiple wafer pedestals, miniature toroidal plasma sources 100 or 300 can be placed in the corners of the chamber, or in regions that are hard to clean with conventional cleaning gas flow patterns. Sources should be positioned at locations where most byproducts accumulate. With multiple plasma sources 100 or 300, an individual mass flow controller could deliver cleaning gas to each plasma source, or one mass flow controller could be used, but with the gas passing through a flow splitter, with orifices installed in each leg of the flow splitter, such that the flow going to each plasma source is evenly balanced.

[0037] Similarly, to power each of the plasma sources 100 or 300, an RF generator power supply could be dedicated to each plasma source, or one common RF generator could have multiple output stages, so each plasma source is driven by its own RF output stage, but all output stages are housed in a common enclosure with common support electronics. Alternatively, each plasma source 100 or 300 can be powered by its own dedicated RF generator. Alternatively, a remote RF generator can be used to power the toroidal plasma or one or more plasma sources 100 or 300, while the RF power supply for the ignition can be located local to the plasma source 100 or 300. The ratio of dielectric break length to overall length may is >6%. A portion of the plasma source body has a length that is at least 7% of the overall length of the plasma loop.

[0038] It is also possible to construct a planar array 400 of miniature plasma sources 100, as illustrated in FIG. 4, where multiple plasma loops 404 form through multiple bores in the plate 408. A variation of this configuration is to construct the plasma source 100 such that the current of two loops combine for each section of the bore 408. The primary windings 108 of the plasma sources 100 can be powered individually, or with the primary windings of each loop driven in series. A planar array 400 with six 1000 W plasma sources will be operating with a total of 6 kW. The construction of the plasma sources is similar to that of the singlesources described above in connection with FIGs 1 to 3. The dielectric break 110 can be planar across multiple sources, or have a cylindrical tubular structure, as discussed in connection with the configuration illustrated either in connection with FIGs. 1 or 2. Dielectric barrier discharge is used for ignition. Aggressive cooling structures 118 with cooling plates closely coupled to the ferrite cores are implemented. At least one surface of each ferrite core 106 is in close communication with the cooling structure 118. As shown in FIG 5, the ferrite cores 106 are all in direct contact with the cooling structure 118. Thermally conductive, electrically insulating potting material substantially fills the interior cavity. A cylindrical dielectric break 110 prevents a shorted turn in the housing 408 and serves as a dielectric barrier for a capacitively coupled ignition discharge using electrode 120. A structural housing 408 with a material such as aluminum provides a vacuum barrier between the internal components and the outer vacuum environment that contains the plasma loops 406. Vacuum facing aluminum surfaces have a coating such as anodization or Plasma Electrolytic Oxidation (PEO). O-rings 502 form seals between the cylindrical dielectric breaks 110 and the vacuum structure. An alternative structure would form the housing top plate 504 of a dielectric material, so this serves as the dielectric break and barrier dielectric for the capacitively coupled discharge for ignition. Alternatively, all or some segments of the housing structure can be fabricated from a ceramic or dielectric material. In another alternative arrangement, an additional cooling structure 118 could be integrated between the ferrite cores 106 and the housing top plate, such that the ferrite cores 106 are cooled on two surfaces, and are well isolated from the top and bottom surfaces of the housing 408. The cooling structure 118 can be positioned between the ferrite cores 106 and the body of the plasma source 408 and 504 such that thermal power dissipated in the body minimally affects the temperature of the ferrite core 106. The aggressive cooling of the ferrite cores 106 and substantially isolating the ferrite cores 106 from the heat load of the plasma body allows smaller ferrite cores to be selected for utilization. Smaller cores enable the plasma loop to be smaller. The ratio of dielectric break length to overall length may is >6%.

[0039] The length of the plasma loop 404 for an arrangement as the one illustrated in FIG. 4 is of approximately 15 cm or less, while the primary windings 108 may be wired either in series or in parallel, and the single plasma loops 406 are disposed in parallel. In FIG. 4 numerals 402 indicate the gas flow, numeral 404 the plasma loop and numerals 406 indicate single plasma loops with a direction of the plasma flow. A portion of the plasma source body has a length that is at least 7% of the overall length of the plasma loop.

[0040] FIGs. 4 and 5 are schematic representations of planar array of miniature toroidal plasma sources with cylindrical dielectric break, in accordance with an embodiment of the present invention. As may be seen in the figures, a plurality of miniature toroidal plasma sources with cylindrical dielectric breaks and with a plasma loop length of approximately 15 cm are arranged adjacent to each other.

[0041] As opposed to the solutions proposed in the art, the configuration of the present invention has an operating regime of 250 mTorr - 10 Torr, at power levels that are 10 to20 times higher (700-1500 W) than those possible with the configurations in known in the art. These high power levels are required for the plasma source to operate reliably with the chemistry, flows, and pressures required for cleaning applications. Higher pressure operation also serves to reduce ion energy for the same plasma loop voltage.

[0042] FIG. 6 shows another embodiment with more aggressive cooling of the ferrite cores 606 and 614. The plasma source 600 has a gas inlet 602, and a gas outlet 604. In this embodiment the copper cooling structure 618 fully surrounds the ferrite cores 606 and 614. All four surfaces of the ferrites 606 and 614 are in close proximity (within about 2 mm) and closely coupled with the cooling structure 618. Thermally conductive potting material 622 is used to fill the small gaps between the cooling structure 618 and the ferrite cores 606, 614. Water channels 624 are formed in the cooling structure 618, for example using well known brazing techniques, or bolting two parts together with an O-ring in between in order to contain a water channel. Castellations, fingers, or holes can be formed in the cooling structure to allow potting material 622 to reach all desired surfaces. The potting material also serves as an electrical dielectric insulator to isolate voltage between the electrode 620 and the cooling structure 618. The cooling fingers 626 between the inner diameter of the ferrite cores 606, 614 and the plasma bore 602 prevent heat from the plasma bore from affecting the temperature of the ferrite cores 606, 614. The cooling structure 618 and cooling fingers 626 cannot form an electrically conductive path around the ferrite core. In this embodiment at least 60%, or as much as 95% of the core surface area is directly cooled. The aggressive cooling structure allows for higher power operation of the toroidal plasma source, while maintaining small geometry. For example, this structure with a 17 cm plasma loop length can operate at 3000 W while maintaining ferrite core temperatures of 60 °C or less, and aluminum plasma vessel 630 temperatures of 90 °C or less.

[0043] Therefore to conclude, the present application proposes a miniature toroidal plasma source with cylindrical dielectric break, with a small plasma loop length of smaller or equal with 25 cm.

[0044] The source exhibits high plasma current > 20 A, therefore power levels of 0.6 - 2 kW, and high pressure > 0.25 Torr. A typical condition could be a plasma current of 40 A, power level of 1.2 kW, and a pressure of 3 Torr.

[0045] Within the plasma source aggressive cooling of all ferrite cores and plasma source body (implemented exemplarily as a vacuum vessel) surfaces that face the plasma are possible. Aggressive cooling of the ferrite cores is as well possible.

[0046] Within the proposed plasma source potting is used to provide thermal conduction and electrical insulation. The ferrite cores are directly cooled while minimizing a thermal conduction path between the plasma facing source body and the ferrite cores.

[0047] The miniature toroidal plasma source of the present invention enables integrated capacitive coupled plasma for ignition.

[0048] Other advantages of the miniature plasma source array of the present invention are: enables transition from capacitively coupled plasma to toroidal inductively coupled plasma; operation of capacitively coupled plasma steady state for sustained periods (for example, several seconds to many minutes) to remove materials that would prevent reliable toroidal inductively coupled plasma operation; an extended DC break in toroidal plasma channel to lower electric fields during ignition; integration of the capacitively coupled plasma electrode with the extended DC break; having capacitively coupled plasma electrode / DC break in a planar implementation; having capacitively coupled plasma CCP electrode / DC break in a cylindrical format; a small plasma source enables short transport tubes and minimal recombination loss; multiple miniature toroidal sources are arranged around the vacuum chamber; individual mass flow controllers deliver gas to separate plasma sources; only one mass flow controller with an array of flow balancing orifices to balance flow to multiple plasma sources is used; a common power supply is used to power multiple plasma sources; non-standard connection flange may be used with the chamber with a large opening to allow direct coupling of radicals to the process chamber with minimal recombination loss.

[0049] A method of operating a plasma source is as well part of the present invention. The method may comprise energizing a plurality of primary windings wrapped around a plurality of magnetic cores in a plasma source, forming a plasma within a body of the plasma source, and cooling of the plasma source body using a cooling structure positioned between the plasma source body and the plurality of magnetic cores. The method of operating a plasma source of the present invention further comprises igniting the plasma using a dielectric barrier discharge igniter. Igniting the plasma comprises operating the dielectric barrier discharge igniter at a power of about 20 W for a period of time between about several milliseconds toabout two minutes. The method may further comprises transitioning from the dielectric barrier discharge igniter to an inductively coupled plasma mode igniter. Forming the plasma comprises generating a plasma current exceeding 20 A. The plasma is formed at a pressure between about 0.5 to about 10 Torr and with a gas flow rate between about 100 to about 2000 standard cubic centimeters per minute. Cooling the plasma source body comprises circulating water through copper cooling plates positioned between the plurality of magnetic cores and a plasma vessel of the plasma source body.

[0050] The present application also discloses an embodiment of a semiconductor processing system. The system in accordance with the invention comprises a processing chamber and a plasma source coupled to the processing chamber, the plasma source comprising a plasma source body, a plurality of magnetic cores, a plurality of primary windings capable of being energized, and a cooling structure. One or more sections of the plasma source body comprise a dielectric material. When the plurality of primary windings are energized, a plasma forms a loop within the plasma source body, and the cooling structure is positioned between the plasma source body and at least one of the plurality of the magnetic cores.

[0051] Although the foregoing descriptions of certain preferred embodiments of the present invention have shown, described and pointed out some fundamental novel features of the invention, it will be understood that various omissions, substitutions, and changes in the form of the detail of the apparatus as illustrated as well as the uses thereof, may be made by those skilled in the art, without departing from the spirit of the invention. Consequently, the scope of the present invention should not be limited to the foregoing discussions and subsequent claims.

Claims

What is claimed is:

1. A plasma source, comprising: a plasma source body, a plurality of magnetic cores, a plurality of primary windings capable of being energized, and a cooling structure; wherein one or more sections of said plasma source body comprise a dielectric material; wherein when said plurality of primary windings are energized, a plasma forms a loop within said plasma source body, and wherein the cooling structure is positioned between the plasma source body and at least one of said plurality of the magnetic cores.

2. The plasma source of claim 1, wherein said dielectric material is capable of capacitively coupling energy into said plasma source to form a plasma ignition discharge.

3. The plasma source of claim 1, wherein a length of the plasma loop is less than 25 cm.

4. The plasma source of claim 1, wherein a voltage of said plasma loop is less than about 75 V, and a plasma source power is higher than 500 W.

5. The plasma source of claim 1, wherein said cooling structure comprises a plurality of cooling plates positioned between said plurality of magnetic cores and said plasma source body.

6. The plasma source of claim 1, further comprising a thermally conductive potting material, wherein said thermally conductive potting material provides thermal coupling between the plurality of magnetic cores and the cooling structure, said thermally conductive potting material being capable of facilitating heat transfer from a dielectric break to the cooling structure.

7. The plasma source of claim 1, wherein the plurality of magnetic cores has more than 60% of their surface area coupled with the cooling structure.

8. The plasma source of claim 6, wherein said dielectric material comprises one of a cylindrical dielectric break and a planar dielectric positioned along said plasma.

9. The plasma source of claim 8, further comprising an electrode formed on a surface of said cylindrical dielectric break.

10. The plasma source of claim 1, wherein said plasma source body comprises a gas inlet and a gas outlet connected by a vacuum channel.

11. The plasma source of claim 10, wherein said plasma forms within said vacuum channel when said plurality of primary windings are energized.

12. The plasma source of claim 1, wherein a portion of said plasma source body has a length that is at least 7% of the overall length of the plasma loop.

13. A method of operating a plasma source, comprising: energizing a plurality of primary windings wrapped around a plurality of magnetic cores in a plasma source; forming a plasma within a body of said plasma source, and cooling off said plasma source body using a cooling structure positioned between said plasma source body and the plurality of magnetic cores.

14. The method of claim 13, further comprising igniting the plasma using a dielectric barrier discharge igniter.

15. The method of claim 14, wherein igniting the plasma comprises operating the dielectric barrier discharge igniter at a power of about 20 W for a period of time between about several milliseconds to about two minutes.

16. The method of claim 15, further comprising transitioning from the dielectric barrier discharge igniter to an inductively coupled plasma mode igniter.

17. The method of claim 13, wherein forming the plasma comprises generating a plasma current exceeding 20 A.

18. The method of claim 17, wherein the plasma is formed at a pressure between about 0.5 to about 10 Torr and with a gas flow rate between about 100 to about 2000 standard cubic centimeters per minute.

19. The method of claim 13, wherein cooling the plasma source body comprises circulating water through copper cooling plates positioned between the plurality of magnetic cores and a plasma vessel of the plasma source body.

20. A semiconductor processing system, comprising: a processing chamber; and a plasma source coupled to said processing chamber, said plasma source comprising: a plasma source body, a plurality of magnetic cores, a plurality of primary windings capable of being energized, and a cooling structure; wherein one or more sections of said plasma source body comprise a dielectric material; wherein when said plurality of primary windings are energized, a plasma forms a loop within said plasma source body, and wherein the cooling structure is positioned between the plasma source body and at least one of said plurality of the magnetic cores.

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