High-power low-frequency coils

Abstract

To provide coils for a plasma processing device that may decrease losses in voltage and current at high power, and methods of forming the same.SOLUTION: A coil 200 for a plasma processing device comprises: a coil form 205; and a plurality of concentric cross-section wire windings disposed around the coil form 205, the wire 225 having a spacing between adjacent turns of about 0.25 to 1.0 of the radius of the wire and a diameter-to-length ratio between about 2:1 and 3:1.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 62 / 893,066, filed August 28, 2019, and U.S. Non-Provisional Patent Application No. 17 / 006,693, filed August 28, 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] Radio frequency (RF) plasma-induced processing is widely used in semiconductor manufacturing to etch different types of films, deposit thin films at low to medium process temperatures, and perform surface treatment and cleaning. A characteristic of such processes is the use of plasma, i.e., partially ionized gases, which are used to generate neutral species and ions from precursors in a reaction chamber, provide energy for ion bombardment, and / or perform other operations. [Brief explanation of the drawings]

[0003] The present disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to standard industry practice, various features have not been drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or decreased for clarity of discussion. [Figure 1] FIG. 1 is a schematic diagram of an RF plasma processing system according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a side view of a coil according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a side view of the coil of FIG. 2 according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is an end view of the coil of FIG. 2 according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a side perspective view of the coil of FIG. 2 according to an embodiment of the present disclosure. [Figure 6]FIG. 6 is a side view of the coil of FIG. 2 according to an embodiment of the present disclosure. [Figure 7] FIG. 7 is a side view of a coil within a coil block according to an embodiment of the present disclosure. [Figure 8] FIG. 8 is a schematic elevational perspective view of the coil of FIG. 7 within a coil block, according to an embodiment of the present disclosure. [Figure 9] FIG. 9 is a schematic cross-sectional view of a coil according to an embodiment of the present disclosure. [Figure 10] FIG. 10 is a schematic diagram of a trifilar inductor according to an embodiment of the present disclosure. [Figure 11] FIG. 11 is a flowchart of a method for forming a coil for a plasma processing apparatus according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0004] Illustrative examples of the claimed subject matter are disclosed herein. In the interest of clarity, not all features of an actual implementation are described herein. It will be understood that in the development of any such actual implementation, numerous implementation-specific decisions may be made to achieve the developer's particular goals, including compliance with system- and business-related constraints that vary from implementation to implementation. Moreover, it will be understood that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0005] Furthermore, as used herein, the article "a" is intended to have its ordinary meaning in the patent art, i.e., "one or more." As used herein, the term "about," unless otherwise specified, is intended to have its meaning when applied to a value, or a general average value within the tolerances of the equipment used to generate the value, in some cases, the average ±10%, or ±5%, or ±1%. Furthermore, as used herein, the term "substantially" means, for example, most, or nearly all, or all, or an amount in the range 51% to 100%. Furthermore, the examples herein are intended to be merely illustrative and are presented for purposes of discussion and not limitation.

[0006] Typical cylindrical single-layer coils can have many problems and limitations in use. For example, a typical cylindrical single-layer coil can have a reduced Q factor when its length is greater than its diameter. In addition, such coils have experienced poor cooling due to air trapped adjacent to the cylindrical coil form when wound on a dielectric cylinder. The coil also has a relatively long magnetic field return path, which can result in a high coupling coefficient to the aluminum shield housing wall, which creates eddy losses that result in a low Q factor. Typical coils can also have a lower inductance per unit length of wire, which can result in a lower Q factor. Such coils can also have smaller, predictable manufacturing tolerances.

[0007] Embodiments of the present disclosure can reduce voltage and current losses at high power, resulting in better Q factors due to a better ratio of stored energy to dissipated energy. Embodiments of the present disclosure can also advantageously maximize the inductance per unit length of the wire used, thereby resulting in better Q factors. Such embodiments can further reduce the distributed voltage across the windings, thereby reducing voltage stress potentials internally. By optimizing the magnetic field return path, embodiments can further reduce magnetic field coupling to the aluminum shielding enclosure, thereby reducing eddy coupling losses to the shield. Embodiments may also increase airflow around the inductor wire to improve cooling. Another advantage may be a mechanical form that provides predictable wire dimensional spacing in the X, Y, and Z directions, resulting in tighter manufacturing tolerances. Not all embodiments exhibit all of these characteristics, and to the extent they exhibit two or more, they may not do so to the same degree.

[0008] Embodiments of the present disclosure can provide relatively high-power, low-frequency coils, such as coils having frequencies of approximately 400k. In other embodiments, the coils disclosed herein can have frequencies below and / or above 400k, depending on the application. Additionally, the disclosed geometries compact the magnetic field, reducing coupling interactions with the shielding walls surrounding the coil. Furthermore, the registered start of each winding from the same side reduces voltage stress from layer to layer, allowing for higher voltage operation than continuous filament sequentially wound coils with multiple layers traversing side to side. Furthermore, the geometric positioning of the evenly spaced wires can result in close tolerance repeatability approaching + / - 1 percent.

[0009] 1, a schematic side view of an RF plasma processing system 100 according to an embodiment of the present disclosure is shown. The RF plasma processing system 100 includes a first RF generator 105 and a second RF generator 110, a first impedance matching network 115, a second impedance matching network 120, a sheath 125, a plasma power supply such as a showerhead 130 or equivalent power supply element such as an electrode, and a pedestal 135. As used herein, a plasma power supply can refer to any device that introduces power to generate plasma and may include, for example, the showerhead 130 and / or other types of electrodes, antennas, etc.

[0010] The RF plasma processing system 100 can include one or more first and second RF generators 105, 110 that supply power to a reaction chamber 140 through one or more impedance match networks 115, 120. RF power flows from the first RF generator 105 through the impedance match network 115 to the showerhead 130, to the plasma in the reaction chamber 140, to an electrode (not shown) other than the showerhead 130 or to an inductive antenna (not shown) that electromagnetically supplies power to the plasma, and from the plasma to ground and / or to the pedestal 135 and / or to the second impedance match network 120. Generally, the first impedance matching network 115 compensates for variations in the load impedance inside the reaction chamber 140 so that the combined impedance of the showerhead 130 and the first impedance matching network 115 is equal to the output of the first RF generator 105, e.g., 50 ohms, by adjusting a reactive component (not separately shown) in the first impedance matching network 115, e.g., a variable capacitor.

[0011] The impedance matching networks 115, 120 are designed to adjust their internal reactive elements so that the load impedance matches the source impedance. Embodiments of the present disclosure may be used in impedance matching networks 115, 120, filters (not shown), resonators (not shown), etc.

[0012] Referring to FIG. 2, a side view of a coil according to an embodiment of the present disclosure is shown. In this embodiment, the coil 200 includes a coilform 205 that is shown to have six coilform extensions 210. Although six coilform extensions 210 are shown, in other embodiments, the coilform 205 may have three, four, five, seven, or more coilform extensions 210. The coilform extensions 210 may project radially outward from a coilform center 215. The coilform center 215 may be used to attach the coil 200 to a block (not shown), as illustrated below.

[0013] 3 and 5, one or more spacers 220 / 222 may be disposed on the radially outer edge of one or more coils forming extension 210. In this embodiment, two spacers 220 / 222 are shown with one inner spacer 220 disposed radially inward and a second outer spacer 222 disposed radially outward. Spacers 220 / 222 may be formed from the same material as coilform 205, or may be formed from other materials in other embodiments.

[0014] The wire 225 may be wound concentrically around the coilform 205, forming an extension 210 that begins at the center, i.e., the radially outer edge, of the coilform 205. An inner spacer 220 may then be placed on top of the coilform 205, and the wire 225 may be wound around the inner spacer 220. An outer spacer 222 may then be placed on top of the inner spacer 200, and the wire 225 may be wound through the outer spacer 222.

[0015] In other embodiments, more than one wire 225 may be used. For example, a first wire may be wrapped around the coilform 205. A second wire may be wrapped around the inner spacer 220, and a third wire may be wrapped around the outer spacer 222. The three wires may then be connected using one or more electrical connectors, such as an electrical bus.

[0016] In operation, the coil 200 includes a cylindrical winding that includes multiple layers, and in this embodiment, includes three layers. The winding begins at the innermost diameter and continues for seven turns, as described in more detail below. At the tip of the innermost diameter, the wire 225 returns through the center of the coilform 205 to the starting position, then overlaps the first winding and begins a second winding where the first winding began. The second winding continues to its end, which in this embodiment includes eight turns. When the second winding reaches the end, it returns through the center of the coilform 205. The wire 225 can then continue for a third winding, which in this embodiment includes nine turns. At the end of the third winding, the wire may exit the coil 200 for electrical connection to another component, for example, via a lug (not shown) or other type of electrical connector.

[0017] Providing three continuous windings reduces the number of layers used. Thus, using three windings divides the voltage stress by a factor of three. If each winding contains the same length of wire, wire 225 will have the same amount of voltage across its ends. Additionally, such a geometry compacts the magnetic field, reducing coupling interactions with the shielding wall (not shown) surrounding coil 200 during operation.

[0018] Additionally, embodiments of coil 200 may include the start of each winding, coilform 205, and coilform extension 210 starting on the same side of coil 200. Starting on the same side of coil 200 may reduce voltage stress from layer to layer, allowing for higher voltage operation than if multiple layers were sequentially coiled with continuous filaments traversing side-to-side. Additionally, the geometric positioning of the wire provides equal spacing, resulting in close tolerance repeatability, within approximately one percent. Specific design aspects of coil 200 as a multi-trifilar coil are discussed in detail below.

[0019] Referring to FIG. 3 , a side view of a coil 200 according to an embodiment of the present disclosure is shown. As described above, the coil 200 includes a coilform 205, which is shown to have six coilform extensions 210. As shown, the coilform extensions 210 project radially outward from a coilform center 215. One or more spacers 220 / 222 may be disposed on the radially outer edges of one or more coils forming the extensions 210. In this embodiment, two spacers 220 / 222 are shown, with one inner spacer 220 disposed radially inward and a second outer spacer 222 disposed radially outward.

[0020] The wire 225 may be wound concentrically around the coilform 205, with the coilform extension 210 originating at the center, i.e., the radially outer edge of the coilform 205. An inner spacer 220 may then be placed on top of the coilform 205, and the wire 225 may be wound around the inner spacer 220. An outer spacer 222 may then be placed on top of the inner spacer 200, and the wire 225 may be wound through the outer spacer 222.

[0021] Both ends of the wire 225 may include a lug-like electrical connector 230. In certain embodiments, the electrical connector 230 may include other types of connectors, such as, for example, male-female connectors, screw connectors, bolt connectors, and / or any other type of electrical connector used in the art or suitable. In certain embodiments, the electrical connector 230 may be insulated or partially insulated depending on operational requirements.

[0022] Referring to FIG. 4, an end view of a coil 200 according to an embodiment of the present disclosure is shown. As described above, the coil 200 includes a coilform 205, which is shown to have six coilform extensions 210. As shown, the coilform extensions 210 project radially outward from a coilform center 215. One or more spacers 220 / 222 may be disposed on the radially outer edges of one or more coils forming the extensions 210. In this embodiment, two spacers 220 / 222 are provided, one inner spacer 220 disposed radially inward and a second outer spacer 222 disposed radially outward.

[0023] The wire 225 may be wound concentrically around the coilform 205, with the coilform extension 210 originating at the center, i.e., the radially outer edge of the coilform 205. An inner spacer 220 may then be placed on top of the coilform 205, and the wire 225 may be wound around the inner spacer 220. An outer spacer 222 may then be placed on top of the inner spacer 200, and the wire 225 may be wound through the outer spacer 222.

[0024] As shown in Figure 4, the third winding, or outermost radial winding, includes nine windings. As noted above, the middle or second winding includes eight windings, while the innermost radial winding includes seven windings. In this manner, a triangular winding shape is obtained, which may provide one or more of the advantages described above. The triangular winding shape is illustrated and discussed in more detail below.

[0025] Referring to FIG. 5, a side perspective view of a coil 200 according to an embodiment of the present disclosure is shown. In FIG. 5, certain portions of the wire 225 have been removed for clarity regarding the geometry of other components, such as the coilform 205 and spacers 220 / 222. As noted above, the coil 200 includes a coilform 205, which is shown to have six coilform extensions 210. As shown, the coilform extensions 210 project radially outward from the coilform center 15. One or more spacers 220 / 222 may be disposed on the radially outer edges of one or more coils forming the extensions 210. In this embodiment, two spacers 220 / 222 are provided, one inner spacer 220 disposed radially inward and a second outer spacer 222 disposed radially outward.

[0026] The wire 225 may be wound concentrically around the coilform 205, with the coilform extension 210 starting at the center, i.e., the radially outer edge of the coilform 205. An inner spacer 220 may then be placed on top of the coilform 205, and the wire 225 may be wound around the inner spacer 220. An outer spacer 222 may then be placed on top of the inner spacer 200, and the wire 225 may be wound through the outer spacer 222.

[0027] Referring to FIG. 6, a side view of a coil 200 according to an embodiment of the present disclosure is shown. As described above, the coil 200 includes a coilform 205, which is shown to have six coilform extensions 210. As shown, the coilform extensions 210 project radially outward from a coilform center 215. One or more spacers 220 / 222 may be disposed on the radially outer edges of one or more coils forming the extensions 210. In this embodiment, two spacers 220 / 222 are shown, with one inner spacer 220 disposed radially inward and a second outer spacer 222 disposed radially outward.

[0028] The wire 225 may be wound concentrically around the coilform 205, with the coilform extension 210 originating at the center, i.e., the radially outer edge of the coilform 205. An inner spacer 220 may then be placed on top of the coilform 205, and the wire 225 may be wound around the inner spacer 220. An outer spacer 222 may then be placed on top of the inner spacer 200, and the wire 225 may be wound through the outer spacer 222.

[0029] 5, the outermost winding 235 returns to the center of the winding 240 before exiting the coil 200 to be connected to another device. Similarly, the intermediate winding 245 also returns to the center of the winding 240 before being wound onto the third winding 240. Also, the innermost winding 250 returns to the center of the winding 240 and enters the intermediate winding 245.

[0030] Referring to FIG. 7, a side view of a coil within a coil block according to an embodiment of the present disclosure is shown. In this embodiment, a coil 200 includes a coilform 205 shown having six coilform extensions 210. As shown, the coilform extensions 210 protrude radially outward from the coilform center. One or more spacers 220 / 222 may be disposed on the radially outer edges of one or more coils forming the extensions 210. In this embodiment, two spacers 220 / 222 are provided, one inner spacer 220 disposed radially inward and a second outer spacer 222 disposed radially outward.

[0031] In this illustration, coil 200 is positioned within coil block 255. Coil 200 may be connected to coil block 255 via various types of mechanical attachments 260, such as bolts. Coil block 255 may be formed from various materials, including those from which coil 200 is formed. Coil block 255 may be used to hold coil 200 in place during operation and may be connected to a housing (not shown) or other element using one or more attachment points 265. Coil block 255 and the winding of wire 225 are described in more detail with respect to FIG. 8.

[0032] Referring to FIG. 8 , a schematic cross-sectional view of a coil according to an embodiment of the present disclosure is shown. As described above, the coil 200 includes a coilform 205, which is shown to have six coilform extensions 210. As shown, the coilform extensions 210 project radially outward from the coilform center 215. One or more spacers 220 / 222 may be disposed on the radially outer edges of one or more coils forming the extensions 210. In this embodiment, two spacers 220 / 222 are shown, with one inner spacer 220 disposed radially inward and a second outer spacer 222 disposed radially outward.

[0033] The wire 225 may be wound concentrically around the coilform 205, with the coilform extension 210 starting at the center, i.e., the radially outer edge of the coilform 205. An inner spacer 220 may then be placed on top of the coilform 205, and the wire 225 may be wound around the inner spacer 220. An outer spacer 222 may then be placed on top of the inner spacer 200, and the wire 225 may be wound through the outer spacer 222. The wire 225 may pass through respective sets of grooves 223 formed in the coilform 205, the inner spacer 220, and the outer spacer 222.

[0034] Coil 200 is also shown having two electrical connectors 230 / 232. First electrical connector 230 begins the innermost, first winding, while second electrical connector terminates the outermost, third winding. As shown, both electrical connectors 230 / 232 are shown as tabs, although other electrical connectors, such as those described above, may be used.

[0035] In this illustration, coil 200 is placed within coil block 255. Coil 200 may be connected to coil block 255 via various types of mechanical attachments 260, such as bolts. Coil block 255 may be formed from various materials, including those from which coil 200 is formed. Foil block 255 may be used to hold coil 200 in place. During operation, one or more attachment points 265 may be used to connect to a housing (not shown) or other element.

[0036] Referring to FIG. 9, a schematic cross-sectional view of a coil 200 according to an embodiment of the present disclosure is shown. In this embodiment, the coil 200 is shown having three windings of wire 225: an innermost first winding 250, a central second winding 245, and an outermost third winding 235. Each winding is spaced a fixed distance both axially and radially relative to each adjacent wire, so that the cross-section of the completed concentric layers of the winding forms a half-sided triangle, with all conductor centers aligned. The half-sided triangle geometry is indicated by reference numeral 270. The progression of one turn per layer can thereby optimize the field return path. The one turn per layer winding is indicated by reference numeral 275.

[0037] Thus, embodiments of the present disclosure can provide multiple concentric cylindrical or polygonal cross-section windings of wire, with equal spacing between any adjacent windings and a wire radius on the order of 0.25 to 1. Such embodiments can include starting a first winding, continuing to the end of the winding, then returning axially to the same starting end of the first winding to start a new, larger diameter cylindrical winding layer concentric with the first winding, thereby surrounding and connecting the first winding to a concentric cylinder of wire. Starting a second winding, continuing to the end of the winding, then returning axially to the same starting end as the first and second windings to start a new cylindrical winding concentric with the first winding.

[0038] This allows the concentric coils to have common location beginning and ending points for each winding. The collective cross section of the windings includes a diameter 280 and a length, which collectively form an average diameter to length ratio 285 of 2:1 to 3:1, in certain embodiments 2.4:1 to 2.5:1, and in yet other embodiments, about 2.46:1.

[0039] The wire windings may be parallel and perpendicular to the coil axis for 5 / 6 of a turn, or may step from one guide groove to the next for 1 / 6 of a turn. Such mechanical techniques may simplify the construction of the coil during manufacturing. Increasing the number of windings per layer may provide improved magnetic field coupling and wire advantage. Separation may be maintained as the wire rises radially from the lower layer to the next.

[0040] Referring to FIG. 10, a schematic diagram of a trifilar inductor according to an embodiment of the present disclosure is shown. As shown, a first electrical connector 230, which in this embodiment is a first knob, is connected to an electrical source (not shown). A wire 225 is then wound into three concentric windings. The first winding 250 includes seven windings and forms the innermost portion of the coil. The second winding 245 includes eight windings and forms the middle portion of the coil. The third winding 235 includes nine windings and forms the outermost portion of the coil. The wire 225 then exits the coil and is severed at the second end connector 232.

[0041] 11, a flowchart of a method of forming a coil for a plasma processing apparatus according to an embodiment of the present disclosure is shown. The method includes the step of feeding a wire through a coil forming a coil-form central portion of the coil-form (Block 300). The coil-form central portion may include one or more openings that allow the wire to pass through the coil-form.

[0042] The method may further include winding a wire around the coilform to form a first winding (block 305). The wire may first pass through an opening in the coilform and then around a radially outer portion of the coilform. The wire may pass through a pre-formed groove in the coilform or may be pressed against the coilform, depending on operational requirements.

[0043] The method may further include returning the wire to a central portion of the coil that is centered in the coilform (block 310), thereby allowing the wire to return to the central portion at a location on the same side as where the first winding began. Although the final location of the first winding is on the same side of the coilform, the initially threaded wire may be located at a different longitudinal position relative to the opening.

[0044] The method may further include winding wire around the coilform (block 315) to form a second winding that is radially further away from the central portion of the coilform center than the first winding. The second winding may therefore be outside the first winding. The second winding may begin by passing through a second opening on the same side of the coilform as the first opening, but at a different longitudinal position.

[0045] The method can further include returning the wire to a central portion of the coil that is centered in the coilform (block 320), such that the wire can return to the central portion at a location on the same side as where the first winding began and ended. The final location of the second winding is on the same side of the coilform, but the wire that was first passed through to begin the second winding can be located longitudinally at a different location relative to the opening.

[0046] The method may further include winding wire around the coilform (block 325) to form a third winding that is radially farther from a central portion of the coilform than the second winding, thereby allowing the wire to return to the central portion at a location on the same side as where the first and second windings began and ended. The final location of the third winding may be on the same side of the coilform, but may be located longitudinally at a different location relative to the opening through which the wire initially passed to initiate the first and / or second windings.

[0047] In certain embodiments, a first winding is disposed on at least a portion of the coilform, a second winding is disposed on at least a portion of the first spacer, the first spacer is disposed in a radially distal portion of the coilform, a third winding is disposed on at least a portion of the second spacer, and the second spacer is disposed on the first spacer. The first spacer may be added to the coil after the first winding is generated. The second spacer may be added to the coil after the second winding is generated. Because the spacers are added sequentially, assembly of the coil may be easier due to access to the radially outermost edge of the coil during any given winding.

[0048] In certain embodiments, the first winding can include seven windings, the second winding can include eight windings, and the third winding can include nine windings. In other embodiments, the number of windings for any given winding can vary based on the number of coilform extensions and the desired outcome of a particular operation. For example, in certain implementations, the coil can include three progressive windings of four, five, and six windings. Those skilled in the art will understand that varying the number of windings to facilitate winding can vary based on the desired outcome.

[0049] In certain embodiments, advantages of the present disclosure can reduce voltage and current losses at high power, which can result in an increased quality factor compared to a typical cylindrical single-layer coil.

[0050] In certain embodiments, advantages of the present disclosure may provide an increased quality factor due to the ratio of stored energy to dissipated energy.

[0051] In certain embodiments, the advantages of the present disclosure can provide optimized / maximized inductance per unit length of the wire used.

[0052] In certain embodiments, an advantage of the present disclosure may be reduced distributed voltage across the windings which reduces internal voltage stress potentials.

[0053] In certain embodiments, an advantage of the present disclosure is that it can reduce magnetic field coupling to the aluminum shield housing by optimizing the magnetic field return path, thereby reducing eddy coupling losses to the shield.

[0054] In certain embodiments, an advantage of the present disclosure can be increased airflow around the inductor wire for improved cooling.

[0055] In certain embodiments, an advantage of the present disclosure may be to provide a mechanical form that provides predictable wire dimensional spacing along the X, Y, and Z axes, thereby allowing for tighter manufacturing tolerance spread.

[0056] The above description, for purposes of explanation, used specific terminology to provide a thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that specific details are not required to implement the systems and methods herein. The foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the disclosure to the precise forms described. Obviously, many modifications and variations are possible in light of the above teachings. The embodiments have been shown and described to best explain the principles and practical applications of the present disclosure, thereby enabling others skilled in the art to best utilize the present disclosure and various embodiments with various modifications as suited to the particular uses intended. It is intended that the scope of the present disclosure be defined by the following claims and their equivalents.

Claims

1. Coil form and a plurality of concentric cross-section wire windings disposed around the coilform, the wire having a spacing between adjacent windings of between about 0.25 and 1.0 of the wire radius; A coil having

2. The coil of claim 1 , wherein the plurality of concentric cross-section wire windings are in the form of at least one of a cylinder and a polygon.

3. 2. The coil of claim 1, wherein the plurality of concentric cross-section wire windings are connected such that a start of a first winding continues to an end, returns axially to the start of the first winding, and begins a second winding that is larger than the first winding.

4. The coil of claim 3 , wherein the second winding substantially surrounds the first winding.

5. 2. The coil of claim 1, wherein the start of the second winding continues to the end of the winding, returns axially to the start of the first and second windings, and begins the third winding.

6. 2. The coil of claim 1, wherein the plurality of concentric cross-section wire windings have common location beginning and ending points for each winding.

7. 10. The coil of claim 1, wherein the plurality of concentric cross-section wire windings have a diameter to length ratio of between about 2:1 and about 3:

1.

8. 2. The coil of claim 1, wherein the plurality of concentric cross-section wire windings have a diameter to length ratio of between about 2.4:1 and about 2.5:

1.

9. 10. The coil of claim 1, wherein said plurality of concentric cross-section wire windings have a diameter to length ratio of approximately 2.46:

1.

10. The coil of claim 1 , wherein each of the plurality of concentric cross-section wire windings is spaced apart axially and radially by a fixed distance.

11. The coil of claim 10 , wherein the plurality of concentric cross-section wire windings form a one-sided triangle at the location of all conductor centers.

12. The coil of claim 1 , wherein the plurality of concentric cross-section wire windings comprises a progression of turns of one winding per layer.

13. The coil of claim 1 , wherein the coil is disposed in at least one of an impedance matching network, a filter, and a resonator.

14. A plasma processing apparatus, Coil form and a plurality of concentric cylindrical cross-section wire windings disposed about the coilform, the wire having a spacing between adjacent windings of about 0.25 to 1.0 of the radius of the wire and a diameter to length ratio of about 2:1 to 3:1; A plasma processing apparatus comprising:

15. 15. The coil of claim 14, wherein the plurality of concentric cross-section wire windings have a diameter to length ratio of between about 2.4:1 and about 2.5:

1.

16. 15. The coil of claim 14, wherein the plurality of concentric cylindrical cross-section wire windings have a diameter to length ratio of approximately 2.46:

1.

17. 1. A method of forming a coil for a plasma processing apparatus, comprising: feeding a wire through a coil forming a central portion of the coilform; winding the wire around the coilform to form a first winding; returning the wire to a central portion of the coil that is centered in the coilform; winding the wire around the coilform to form a second winding radially spaced from a central portion of the coil that is more central than the first winding; returning the wire to a central portion of the coil that is centered in the coilform; winding the wire around the coilform to form a third winding radially spaced from a central portion of the coil that is more central than the second winding; A method having the following.

18. 18. The method of claim 17, wherein the first winding is disposed on at least a portion of the coilform, the second winding is disposed on at least a portion of a first spacer, the first spacer is disposed on a radially distal portion of the coilform, the third winding is disposed on at least a portion of a second spacer, and the second spacer is disposed on the first spacer.

19. 18. The method of claim 17, wherein the first winding, the second winding, and the third winding return to a central portion of the coil centered on the same side of the coil.

20. 18. The method of claim 17, wherein the first winding has seven turns, the second winding has eight turns, and the third winding has nine turns.

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