Patent Publication Number: US-2021183619-A1

Title: Compact high density plasma source

Description:
BACKGROUND 
     Atomic layer deposition (ALD) is a vapor deposition technique capable of providing highly conformal thin films with atomic scale control. A typical ALD process involves a series of two half-reactions that are separated by purge operations. Thus, one cycle of an ALD process can include the following steps: (1) exposure of a substrate surface to a first reactant, wherein the exposure is self-limiting so as to deposit a single atomic layer of the first reactant; (2) purging of the process chamber with an inert gas to remove any remaining quantities of the first reactant and/or byproducts; (3) exposure of the substrate surface to a second reactant that reacts with the deposited first reactant to form the thin film product; (4) purging of the process chamber with an inert gas to remove any remaining quantities of the second reactant and/or byproducts. The ALD cycle can be repeated for a desired number of iterations to build up the thickness of the thin film product. Because a single ALD cycle typically deposits a single atomic layer of the product material, ALD is capable of providing highly controlled thicknesses of conformal thin film. 
     In some ALD processes, a plasma is employed for either of the half-reactions. It is desirable to use high density plasma in order to achieve high quality film deposition by ALD. However, existing chambers do not provide high density plasma in a small volume process space conducive for ALD. Current inductively coupled plasma (ICP) systems (or transformer coupled plasma (TCP) systems) are designed with a large process space over the substrate (e.g. on the order of a 6 inch (approximately 15 cm) vertical gap over the substrate). The large process space is necessary to accommodate the reach of the global magnetic field generated by the TCP coil, and to minimize the effects of non-uniformity of the plasma distribution. However, such a large process space is not conducive for ALD processes due to the amount of time required to cycle gases into and out of the process chamber, which negatively impacts throughput, especially when the ALD cycle is repeated many times. 
     Also, similar challenges apply to atomic layer etch (ALE) processes. 
     It is in this context that implementations of the disclosure arise. 
     SUMMARY 
     In some implementations, an RF antenna is configured, when powered, to inductively generate plasma in a process region of a chamber, including: an array of parallel conductive lines that are oriented along a plane, the array including a first conductive line, a second conductive line, a third conductive line, and a fourth conductive line; wherein the first and second conductive lines are adjacent, wherein the second and third conductive lines are adjacent, and wherein the third and fourth conductive lines are adjacent; wherein when the RF antenna is powered, current flow in the adjacent first and second conductive lines occurs in an opposite direction, current flow in the adjacent second and third conductive lines occurs in a same direction, current flow in the adjacent third and fourth conductive lines occurs in an opposite direction. 
     In some implementations, the RF antenna includes a first segment that includes the first and second conductive lines connected to each other in series; wherein the RF antenna includes a second segment that includes the third and fourth conductive lines connected to each other in series. 
     In some implementations,the first segment is not connected to the second segment, so that conductive lines of the first segment are not connected to conductive lines of the second segment. 
     In some implementations, each of the first and second segments includes a first end configured to receive RF power and a second end configured to be connected to ground. 
     In some implementations, adjacent conductive lines of a given segment are connected to each other in series by an end connector. 
     In some implementations, the end connector is configured to produce a change in direction of current flow by enabling current flow between the adjacent conductive lines of the given segment. 
     In some implementations, each given segment has a unitary structure formed as a single piece that includes the end connector and the adjacent conductive lines of the given segment. 
     In some implementations, the current flow in the adjacent first and second conductive lines occurring in opposite directions defines a first local counter current inductive array; wherein the current flow in the adjacent third and fourth conductive lines occurring in opposite directions defines a second local counter current inductive array. 
     In some implementations, the conductive lines are configured to occupy an area that covers a surface of a substrate when present in the chamber. 
     In some implementations, the area occupied by the conductive lines is a substantially circular area. 
     In some implementations, the conductive lines are substantially straight. 
     In some implementations, the conductive lines have a vertical thickness in the range of approximately 0.1 to 1 inch. 
     In some implementations, the conductive lines have a horizontal width in the range of approximately 0.1 to 0.5 inches. 
     In some implementations, the first and second conductive lines are spaced at approximately 2 to 3 inches, wherein the second and third conductive lines are spaced at approximately 3 to 4 inches, and wherein the third and fourth conductive lines are spaced at approximately 2 to 3 inches. 
     In some implementations, a radio frequency (RF) antenna for use in an inductive plasma chamber is provided, including: a first hairpin-shaped conductive line having a powered end and a grounded end; a second hairpin-shaped conductive line having a powered end and a grounded end; wherein an RF power source is connectable to the powered end of the first and second hairpin-shaped conductive lines and said grounded ends are connectable to ground; wherein the first hairpin-shaped conductive line is arranged adjacent to and in a parallel orientation to the second hairpin-shaped conductive line, such that the RF antenna is configured to be disposed over a processing region of the chamber. 
     In some implementations, the powered ends and grounded ends of the first and second hairpin-shaped conductive lines are connected to said RF power source to produce a current in each of the first and second hairpin-shaped conductive lines, the current in adjacent segments of the first and second hairpin-shaped conductive lines flowing in either a same direction or an opposite direction, when said RF power source is active to produce said current. 
     In some implementations, the powered ends and grounded ends of the first and second hairpin-shaped conductive lines are connected to said RF power source to produce a current in each of the first and second hairpin-shaped conductive lines, the current in inner adjacent segments of the first and second hairpin-shaped conductive lines flowing in a same direction, when said RF power source is active to produce said current. 
     In some implementations, opposite segments to the inner adjacent segments of the first and second hairpin-shaped conductive lines flow said current in a same direction, when said RF power source is active to produce said current. 
     In some implementations, the first hairpin-shaped conductive line defines a first pair of parallel segments that are spaced apart by about 5 to 8 centimeters (about 2 to 3 inches); wherein the second hairpin-shaped conductive line defines a second pair of parallel segments that are spaced apart by about 5 to 8 centimeters (about 2 to 3 inches). 
     In some implementations, inner adjacent segments of the first and second hairpin-shaped conductive lines are spaced apart by about 7 to 10 centimeters (about 3 to 4 inches). 
     In some implementations, a radio frequency (RF) antenna for use in an inductive plasma chamber is provided, comprising: a first hairpin-shaped conductive line having a powered end and a grounded end; a second hairpin-shaped conductive line having a powered end and a grounded end; a third hairpin-shaped conductive line having a powered end and a grounded end; wherein at least one RF power source is connectable to the powered end of the first, second, and third hairpin-shaped conductive lines and said grounded ends are connectable to ground; wherein the first hairpin-shaped conductive line is arranged adjacent to and in a parallel orientation to the second hairpin-shaped conductive line, and the second hairpin-shaped conductive line is arranged adjacent to and in a parallel orientation to the third hairpin-shaped conductive line, such that the RF antenna is configured to be disposed over a processing region of the chamber. 
     In some implementations, the powered ends and grounded ends of the first, second, and third hairpin-shaped conductive lines are connected to said at least one RF power source to produce a current in each of the first, second, and third hairpin-shaped conductive lines, the current in adjacent segments of the first, second, and third hairpin-shaped conductive lines flowing in either a same direction or an opposite direction, when said at least one RF power source is active to produce said current. 
     In some implementations, the powered ends and grounded ends of the first, second, and third hairpin-shaped conductive lines are connected to said at least one RF power source to produce a current in each of the first, second, and third hairpin-shaped conductive lines, the current in inner adjacent segments of the first and second hairpin-shaped conductive lines flowing in a same direction, the current in inner adjacent segments of the second and third hairpin-shaped conductive lines flowing in a same direction, when said RF power source is active to produce said current. 
     In some implementations, opposite segments to the inner adjacent segments of the first and second hairpin-shaped conductive lines flow said current in a same direction, wherein opposite segments to the inner adjacent segments of the second and third hairpin-shaped conductive lines flow said current in a same direction, when said RF power source is active to produce said current. 
     In some implementations, the powered ends and grounded ends of the first, second, and third hairpin-shaped conductive lines are connected to said at least one RF power source to produce a current in each of the first, second, and third hairpin-shaped conductive lines, the current in inner adjacent segments of the first and second hairpin-shaped conductive lines flowing in opposite directions, the current in inner adjacent segments of the second and third hairpin-shaped conductive lines flowing in opposite directions, when said RF power source is active to produce said current. 
     In some implementations, opposite segments to the inner adjacent segments of the first and second hairpin-shaped conductive lines flow said current in opposite directions, wherein opposite segments to the inner adjacent segments of the second and third hairpin-shaped conductive lines flow said current in opposite directions, when said RF power source is active to produce said current. 
     In some implementations, the first hairpin-shaped conductive line defines a first pair of parallel segments that are spaced apart by about 2 to 8 centimeters (about 1 to 3 inches); wherein the second hairpin-shaped conductive line defines a second pair of parallel segments that are spaced apart by about 2 to 8 centimeters (about 1 to 3 inches); wherein the third hairpin-shaped conductive line defines a third pair of parallel segments that are spaced apart by about 2 to 8 centimeters (about 1 to 3 inches). 
     In some implementations, adjacent segments of the first, second, and third hairpin-shaped conductive lines are spaced apart by about 2 to 8 centimeters (about 1 to 3 inches). 
     In one embodiment, a radio frequency (RF) antenna for use in an inductive a chamber is disclosed. The RF antenna includes a first hairpin-shaped conductive line having a powered end and a grounded end, and a second hairpin-shaped conductive line having a powered end and a grounded end. An RF power source is connectable to the powered end of the first and second hairpin-shaped conductive lines and said grounded ends are connectable to ground. The first hairpin-shaped conductive line is arranged adjacent to and in a parallel orientation to the second hairpin-shaped conductive line. The RF antenna is configured to be disposed over a processing region of the chamber. 
     In some embodiments, the powered ends and grounded ends of the first and second hairpin-shaped conductive lines are connected to said RF power source to produce a current in each of the first and second hairpin-shaped conductive lines, and the current in adjacent segments of the first and second hairpin-shaped conductive lines is configured to flow in either a same direction or an opposite direction, when said RF power source is active to produce said current. 
     In some embodiments, the powered ends and grounded ends of the first and second hairpin-shaped conductive lines are connected to said RF power source to produce a current in each of the first and second hairpin-shaped conductive lines. The current in inner adjacent segments of the first and second hairpin-shaped conductive lines is configured to flow in a same direction, when said RF power source is active to produce said current. In one embodiment, opposite segments to the inner adjacent segments of the first and second hairpin-shaped conductive lines flow said current in a same direction, when said RF power source is active to produce said current. 
     In some implementations, an RF antenna is configured, when powered, to inductively generate plasma in a process region of a chamber, including: an array of parallel conductive lines that are oriented along a plane; wherein the RF antenna includes two or more discrete segments, each segment including two or more of the conductive lines that are connected to each other in series 2. The RF antenna of claim  1 , wherein when the RF antenna is powered, current flow in adjacent conductive lines occurs in one of a same direction or an opposite direction to form a local same-direction current or a local counter current. 
     In some implementations, the current flow in adjacent conductive lines occurring in opposite directions defines a counter current inductive array, such that magnetic fields generated by each of the conductive lines are respectively localized to each of the conductive lines. 
     In some implementations, when the RF antenna is powered, current flow in at least two adjacent conductive lines occurs in a same direction. 
     In some implementations, when the RF antenna is powered, current flow in at least two adjacent conductive lines occurs in opposite directions. 
     In some implementations, each segment is not connected to another segment, so that conductive lines of a given segment are not connected to conductive lines of another segment. 
     In some implementations, each segment includes a first end configured to receive RF power and a second end configured to be connected to ground. 
     In some implementations, adjacent conductive lines of a given segment are connected to each other in series by an end connector. 
     In some implementations, the end connector is configured to produce a change in direction of current flow by enabling current flow between the adjacent conductive lines of the given segment. 
     In some implementations, the given segment has a unitary structure formed as a single piece that includes the end connector and the adjacent conductive lines of the given segment. 
     In some implementations, the conductive lines are configured to occupy an area that covers a surface of a substrate when present in the chamber. 
     In some implementations, the area occupied by the conductive lines is a substantially circular area. 
     In some implementations, the conductive lines are substantially straight. 
     In some implementations, the conductive lines have a vertical thickness in the range of approximately 0.01 to 0.02 inches. 
     In some implementations, the conductive lines have a horizontal width in the range of approximately 0.1 to 0.5 inches. 
     In some implementations, the conductive lines are equally spaced at a pitch of approximately 0.5 to 2 inches, and wherein the conductive lines are embedded within an insulating material. 
     In some implementations, an RF antenna is configured, when powered, to inductively generate plasma in a process region of a chamber, including: an array of equally spaced parallel conductive lines that are oriented along a plane; wherein each pair of adjacent conductive lines of the array is connected in series by a connector, so that when the RF antenna is powered, current flow in adjacent conductive lines of each pair occurs in opposite directions to form a local counter current; wherein for a given connector, at least a portion of the given connector is not oriented along the plane along which the conductive lines are oriented. 
     In some implementations, the each pair of adjacent conductive lines being connected in series by a connector defines a plurality of connectors, including a first set of connectors along a first side of the RF antenna, and a second set of connectors along a second side of the RF antenna opposite the first side, the connectors of the first set being staggered with the connectors of the second set to enable connection of the conductive lines in series. 
     In some implementations, the first set of connectors are substantially oriented along one or more second planes that are not parallel to the plane along which the conductive lines are oriented; wherein the second set of connectors are substantially oriented along one or more third planes that are not parallel to the plane along which the conductive lines are oriented. 
     In some implementations, the one or more second planes are each substantially perpendicular to the plane along which the conductive lines are oriented; wherein the one or more third planes are each substantially perpendicular to the plane along which the conductive lines are oriented. 
     In some implementations, each connector has a curved or semicircular shape. 
     In some implementations, the RF antenna includes a first end configured to receive RF power and a second end configured to be connected to ground. 
     In some implementations, the given connector is configured to produce a change in direction of current flow by enabling current flow between the adjacent conductive lines that are connected by the given connector. 
     In some implementations, the RF antenna has a unitary structure formed as a single piece that includes the conductive lines. 
     In some implementations, the conductive lines are configured to occupy an area that covers a surface of a substrate when present in the chamber. 
     In some implementations, the area occupied by the conductive lines is a substantially circular area. 
     In some implementations, the conductive lines are substantially straight. 
     In some implementations, the conductive lines have a vertical thickness in the range of approximately 0.01 to 0.02 inches. 
     In some implementations, the conductive lines have a horizontal width in the range of approximately 0.1 to 0.5 inches. 
     In some implementations, the conductive lines are equally spaced at a pitch of approximately 0.5 to 2 inches. 
     In some implementations, the conductive lines are embedded within an insulating material. 
     In some implementations, a plasma chamber is provided, including: an RF antenna having a plurality of equally spaced parallel conductive lines that are oriented along a plane, wherein when the RF antenna is powered, current flow in adjacent conductive lines occurs in opposite directions, the RF antenna being positioned above a process space of the plasma chamber in which plasma is generated; a plurality of grounded induction lines disposed within the process space, wherein each of the grounded induction lines is positioned below a corresponding one of the conductive lines, the grounded induction lines being configured to be inductively powered when the RF antenna is powered, and the grounded induction lines further being configured to inductively generate plasma within the process space when inductively powered. 
     In some implementations, the grounded induction lines are connected to each other, forming a one-piece structure that is connected to ground. 
     In some implementations, the plasma chamber further includes: a dielectric window; wherein the RF antenna is positioned over the dielectric window; wherein the grounded induction lines are disposed below the dielectric window. 
     In some implementations, the RF antenna includes two or more discrete segments, each segment including two or more of the conductive lines that are connected to each other in series. 
     In some implementations, each segment includes a first end configured to receive RF power and a second end configured to be connected to ground. 
     In some implementations, adjacent conductive lines of a given segment are connected to each other in series by an end connector, the end connector being configured to produce a change in direction of current flow by enabling current flow between the adjacent conductive lines of the given segment. 
     In some implementations, the given segment has a unitary structure formed as a single piece that includes the end connector and the adjacent conductive lines of the given segment. 
     In some implementations, the grounded induction lines have a thickness in the range of approximately 0.2 to 1 inches. 
     In some implementations, the grounded induction lines have a width in the range of approximately 0.2 to 1 inches. 
     In some implementations, an RF antenna is provided that is configured, when powered, to inductively generate plasma in a process region of a process chamber, including: a first set of conductive lines that are parallel to one another and coplanar along a first horizontal plane, the first set of conductive lines being disposed over a dielectric window of a process chamber, the first horizontal plane being at a first height above the dielectric window; a second set of conductive lines that are parallel to one another and coplanar along a second horizontal plane, the second horizontal plane being parallel to the first horizontal plane, the second horizontal plane being at a second height above the dielectric window that is greater than the first height, each conductive line of the second set of conductive lines being disposed substantially over and parallel to a respective conductive line of the first set of conductive lines. 
     In some implementations, each of the conductive lines of the first set and the second set is substantially straight over a region defined by a wafer when present in the process chamber. 
     In some implementations, for each of the conductive lines of the first set and second set, current in a given conductive line of the first set flows in a substantially same direction as current in the conductive line of the second set that is substantially over the given conductive line of the first set. 
     In some implementations, at least one conductive line of the first set is electrically connected to at least one conductive line of the second set. 
     In some implementations, current in at least one pair of adjacent conductive lines of the first set flows in substantially opposite directions. 
     In some implementations, current in at least one pair of adjacent conductive lines of the first set flows in substantially the same direction. 
     In some implementations, the RF antenna is defined by two or more looped structures, each looped structure including two adjacent conductive lines of the first set and, two adjacent conductive lines of the second set that are respectively disposed over the two adjacent conductive lines of the first set. 
     In some implementations, each looped structure is formed from a single continuous length of a conductive material. 
     In some implementations, the each looped structure is configured so that current flow in the two adjacent conductive lines of the first set occurs in opposite directions, and current flow in the two adjacent conductive lines of the second set occurs in opposite directions. 
     In some implementations, the each looped structure is configured so that for each one of the two adjacent conductive lines of the first set, current flow occurs in a same direction as a respective one of the two adjacent conductive lines of the second set that is disposed over the one of the two adjacent conductive lines of the first set. 
     In some implementations, the looped structure further includes a first connector that connects the two adjacent conductive lines of the first set, a second connector that connects the two adjacent conductive lines of the second set, and a third connector that connects one of the two adjacent conductive lines of the first set to one of the two adjacent conductive lines of the second set that is not disposed over the one of the two adjacent conductive lines of the first set. 
     In some implementations, the looped structures receive power from a single RF source. 
     In some implementations, each of the looped structures receives power from a separate RF source. 
     In some implementations, an RF antenna is provided that is configured, when powered, to inductively generate plasma in a process region of a process chamber, including: a plurality of line pairs disposed over a dielectric window of a process chamber, each line pair including two horizontally oriented conductive lines that are parallel and vertically stacked; wherein the plurality of line pairs are parallel to each other. 
     In some implementations, current flow in conductive lines of a given line pair occurs in a same direction. 
     In some implementations, the conductive lines of the plurality of line pairs are substantially straight. 
     In some implementations, lower ones of the conductive lines of the line pairs are disposed along a first horizontal plain at a first height above the dielectric window. 
     In some implementations, upper ones of the conductive lines of the line pairs are disposed along a second horizontal plain at a second height above the dielectric window that is greater than the first height. 
     Other aspects and advantages of the disclosures herein will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate by way of example the principles of the disclosures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross-sectional schematic diagram illustrating a plasma processing system  100 , in accordance with implementations of the disclosure.  FIG. 1B  is a cross-sectional schematic diagram illustrating a plasma processing system  100 , in accordance with implementations of the disclosure. 
         FIG. 2  is an overhead view of an RF antenna for plasma processing, in accordance with implementations of the disclosure. 
         FIG. 3  is a conceptual cross-section view of a portion of a process chamber, in accordance with implementations of the disclosure. 
         FIGS. 4A, 4B, 4C, 4D, 4E, 4F, 4G, and 4H  illustrate various examples of RF antenna  110  having various dimensions and coverage configurations, in accordance with implementations of the disclosure.  FIG. 5  illustrates an overhead view of an RF antenna  110  defined as a single continuous length of a conductive material, in accordance with implementations of the disclosure.  FIG. 6  illustrates an overhead view of RF antenna  110  consisting of two distinct segments, in accordance with implementations of the disclosure. 
         FIG. 7  illustrates an overhead view of an RF antenna  110  having multiple hairpin-shaped segments, in accordance with implementations of the disclosure. 
         FIG. 8  illustrates an overhead view of an RF antenna  110  having multiple segments, in accordance with implementations of the disclosure. 
         FIG. 9A  illustrates an overhead view of an RF antenna  110  having multiple double reverse hairpin segments, in accordance with implementations of the disclosure. 
         FIG. 9B  is a cross-section view of the implementation of  FIG. 9A , in accordance with implementations of the disclosure. 
         FIG. 10A  illustrates a conceptual cross-section of an RF antenna  110  in accordance with implementations of the disclosure. 
         FIG. 10B  illustrates a conceptual cross-section in accordance with the implementation of  FIG. 10A . 
         FIG. 11A  illustrates a perspective view of an RF antenna  110  having raised end loops, in accordance with implementations of the disclosure. 
         FIG. 11B  illustrates a cutaway view of a process chamber  102  including the RF antenna  110  in accordance with the implementation of  FIG. 11A . 
         FIG. 11C  illustrates a perspective view of the process chamber  102  in accordance with the implementation of  FIG. 11B . 
         FIG. 11D  illustrates an overhead view of the process chamber  102  in accordance with the implementation of  FIG. 11B . 
         FIG. 12A  illustrates a cutaway view of a process chamber  102 , in accordance with implementations of the disclosure. 
         FIG. 12B  illustrates a perspective view showing the stacking of components including the RF antenna  110 , in accordance with the implementation of  FIG. 12A . 
         FIG. 12C  illustrates an overhead view of the process chamber  102 , in accordance with implementations of the disclosure. 
         FIG. 12D  illustrates a cross section view of an outer portion of the process chamber  102 , in accordance with the implementation of  FIG. 12C . 
         FIG. 12E  illustrates a cross section view of a portion of the process chamber  102 , in accordance with the implementation of  FIG. 12C . 
         FIG. 12F  illustrates a cross section view of a portion of the process chamber  102 , in accordance with the implementation of  FIG. 12C . 
         FIG. 13A  illustrates an RF antenna  110  in accordance with implementations of the disclosure. 
         FIG. 13B  illustrates an RF antenna  110  in accordance with implementations of the disclosure. 
         FIG. 14A  illustrates an overhead view of an RF antenna disposed over a grounded counter-current inductor for coupling RF power into a chamber, in accordance with implementations of the disclosure. 
         FIG. 14B  illustrates a cross section view of the grounded inductor  1400 , in accordance with implementations of the disclosure. 
         FIG. 14C  is a graph illustrating the relative phases of the currents in the structures of the plasma processing system, in accordance with the implementation of  FIG. 14A . 
         FIG. 14D  illustrates a cross-section view of a grounded inductor line  1402  of the grounded inductor  1400 , in accordance with the implementation of  FIG. 14A . 
         FIGS. 15A and 15B  illustrate overhead and cross-section views, respectively, of a grounded inductor  1500 , in accordance with implementations of the disclosure. 
         FIG. 16  illustrates a single hairpin counter-current inductor segment, in accordance with implementations of the disclosure. 
         FIG. 17  illustrates the effect of 90 degree line-to-line phased spatial-alternating plasma-skin induction currents, in accordance with implementations of the disclosure. 
         FIGS. 18A and 18B  illustrate an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 19A and 19B  illustrate an RF antenna, in accordance with implementations of the disclosure. 
         FIGS. 20A, 20B, and 20C  illustrate a hairpin segment for an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 21A and 21B  illustrate a hairpin segment for an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 22A and 22B  illustrate a hairpin segment for an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 23A, 23B, and 23C  illustrate an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 24A, 24B, and 24C  illustrate an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 25A, 25B, and 25C  illustrate an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 26A, 26B, and 26C  illustrate an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 27A, 27B, and 27C  illustrate an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 28A, 28B, and 28C  illustrate an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 29A, 29B, and 29C  illustrate an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 30A and 30B  illustrate an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 31A, 31B, and 31C  illustrate an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIGS. 32A, 32B, and 32C  illustrate an RF antenna and corresponding experimental results, in accordance with implementations of the disclosure. 
         FIG. 33  illustrates an RF antenna, in accordance with implementations of the disclosure. 
         FIG. 34  illustrates an RF antenna, in accordance with implementations of the disclosure. 
         FIG. 35A  illustrates an overhead view into a process chamber  3500  showing a configuration of an RF antenna  3502 , in accordance with implementations of the disclosure. 
         FIG. 35B  illustrates a perspective cutaway view of the process chamber  3500 , in accordance with implementations of the disclosure. 
         FIG. 35C  illustrates a cutaway view of the process chamber  3500  along a plane perpendicular to the conductive lines of the RF antenna  3502 , in accordance with implementations of the disclosure. 
         FIG. 36A  illustrates an overhead view into a process chamber  3500  showing a configuration of an RF antenna  3600 , in accordance with implementations of the disclosure. 
         FIG. 36B  illustrates a perspective cutaway view of the process chamber  3500  including the RF antenna  3600 , in accordance with implementations of the disclosure. 
         FIG. 36C  illustrates a cutaway view of the process chamber  3500  along a plane perpendicular to the conductive lines of the RF antenna  3600 , in accordance with implementations of the disclosure. 
         FIG. 36D  conceptually illustrates a cross section view of a portion of the dielectric window  3610  and the RF antenna  3600 , in accordance with implementations of the disclosure. 
         FIGS. 37A, 37B, 37C, and 37D  schematically illustrate various configurations of powering and terminating the RF antenna, in accordance with implementations of the disclosure. 
         FIG. 38A  illustrates a portion of an RF antenna, such as one of the halves/sides of the RF antenna  3600 , that is formed as a continuous bent sheet/strip. 
         FIG. 38B  illustrates a portion of an RF antenna formed as a continuous bent tube, in accordance with implementations of the disclosure. 
         FIG. 38C  illustrates a portion of an RF antenna formed from a plurality of tubular fittings, such as a plurality straight tubular fittings and a plurality of curved tubular fittings, in accordance with implementations of the disclosure. 
         FIGS. 39A, 39B, and 39C  illustrate overhead, perspective cutaway, and side cross-sectional views an RF antenna that is powered from the sides, in accordance with implementations of the disclosure. 
         FIG. 40  conceptually illustrates an overhead view of an RF antenna having curved outer conductive lines, in accordance with implementations of the disclosure. 
         FIG. 41  conceptually illustrates an overhead view of an RF antenna having curved inner and outer conductive lines, in accordance with implementations of the disclosure. 
         FIG. 42  conceptually illustrates an overhead view of an RF antenna having adjustable line spacing, in accordance with implementations of the disclosure. 
         FIG. 43  is a simplified schematic diagram of a computer system for implementing implementations of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the example implementations. However, it will be apparent to one skilled in the art that the example implementations may be practiced without some of these specific details. In other instances, process operations and implementation details have not been described in detail, if already well known. 
     As used herein, the terms “about” and “approximately” mean that the specified parameter can be varied within a reasonable tolerance, e.g., ±10% in some implementations, ±15% in some implementations, or ±20% in some implementations. 
     Some implementations of the present disclosure provide a radio frequency (RF) antenna that is configured, when powered, to define a counter current inductor that generates localized magnetic fields for plasma generation. The RF antenna of the present disclosure enables generation of high density plasma (e.g. 1×10{circumflex over ( )}11 per cubic cm or greater in some implementations) with high distribution uniformity in a small volume process space, thereby enabling ALD/ALE in a high density plasma system. At present, ALD/ALE is not performed in high density plasma systems, due to the large process space and the excessive amount of time required to pump gases into, and purge gases from, the process space, which is prohibitive for purposes of throughput. 
     However, implementations of the present disclosure overcome these challenges by enabling localized fields and plasma generation in a small process space (e.g. approximately 3 inch (approximately 7.5 cm) vertical gap or less in some implementations, approximately 1 inch (approximately 2.5 cm) vertical gap or less in some implementations). With such a small process space, it is possible to achieve a low residence time of process gases in the chamber, enabling reduction in the ALD/ALE cycle time as the time required to move gases into and out of the chamber is reduced. 
     Broadly speaking, implementations of the present disclosure provide an RF antenna that includes an array of equally spaced parallel conductive lines that are oriented along a plane. When the RF antenna is powered, current flow in adjacent conductive lines occurs in opposite directions, thereby forming a counter current inductive array that inductively generates plasma in the process space/region of the chamber. The counter current inductive array is such that magnetic fields generated by each of the conductive lines are respectively localized to their originating conductive lines. 
     In some implementations, portions of the conductive lines are connected in series to enable the change in direction of current flow between adjacent conductive lines, as described further below. 
       FIG. 1A  is a cross-sectional schematic diagram illustrating a plasma processing system  100 , in accordance with implementations of the disclosure. The plasma processing system  100  includes a process chamber  102  that is configured to receive a substrate for plasma processing. The componentry of the process chamber  102  encloses and defines a process region  104 , which is a space or volume in which plasma is generated for substrate processing. A pedestal  106  is configured to support the substrate (e.g. a wafer) so that the process region is defined over the substrate during processing. 
     An RF antenna  110  includes an array of conductive lines, which are shown in cross section in the illustrated implementation. The RF antenna  110  is powered by an RF source  118  through a match  116 , and also connected to ground. In some implementations, as further described below, the RF antenna  110  is composed of several individual segments, with each segment being powered (by individual or shared power source(s)) and connected to ground. 
     In some implementations, the RF antenna  110  is disposed between a top insulator  112  and a bottom insulator  114 . A side insulator  108  is also provided, which defines the internal sidewalls of the process region  104 . 
     Process gases are provided from a plurality of gas sources  120 , e.g. including a first reactant gas source for supplying the first reactant for the first half-reaction of the ALD process, a second reactant gas source for supplying the second reactant for the second half-reaction of the ALD process, and an inert gas source for supplying an inert gas for purging the process region  104  of the process chamber  102 . A gas switching module  122  is configured to manage the delivery of process gases from the gas sources  120  to the process chamber  102 . The gas switching module  122  may include a plurality of controllable valves and/or flow controllers to control the delivery of the process gases. 
     Process gases are delivered to a gas plenum  124 . From the gas plenum  124 , in some implementations, the process gases are routed into the process region  104  through a plurality of injectors  126 . The injectors  126  can define throughholes through the top and bottom insulators, and the injectors  126  can be horizontally distributed above the process region  104  so that process gases can be simultaneously introduced and evenly distributed throughout the process region  104 . 
     While a plurality of injectors are shown in the illustrated implementation, in other implementations, other hardware configurations can be employed to deliver process gases to the process region  104 . In some implementations, a center injector and/or side injectors are provided to deliver process gases into the process region  104 . 
     Gases (e.g. process gases, inert gas, reaction byproducts, etc.) are evacuated from the process region  104  through a baffle  130  by a vacuum pump  132 . It will be appreciated that the process region  104  can be maintained under vacuum by the vacuum pump  132 . 
     The process chamber  102  includes outer sidewalls  134  that are grounded. 
     Although not all specifically shown in detail, the process chamber  102  is typically coupled to facilities when installed in either a clean room or a fabrication facility. Facilities include plumbing that provide, among other things, processing gases, vacuum, temperature control, and environmental particle control. These facilities are coupled to the process chamber  102 , when installed in the target fabrication facility. Additionally, process chamber  102  may be coupled to a transfer chamber that will enable robotics to transfer substrates (e.g. semiconductor wafers) into and out of process chamber  102  using automation. 
     A programmable controller  140  is provided for controlling the operation of the process chamber  102  and its associated components, including, by way of example without limitation, the RF source  118  and match  116 , the gas switching module  122 , and the vacuum pump  132 . Broadly speaking, the controller  108  can be programmed to execute a chamber operation defined by a recipe. A given recipe may specify various parameters for the operation, such as the application of power to the RF antenna, the flow of gas into the chamber, and the application of vacuum. It should be appreciated that the timing, duration, magnitude, or any other adjustable parameter or controllable feature can be defined by a recipe and carried out by the controller to control the operation of the process chamber  102  and its associated components. Additionally, a series of recipes may be programmed into the controller  140 . In one implementation, the recipe is configured to process ALD operations. 
       FIG. 1B  is a cross-sectional schematic diagram illustrating a plasma processing system  100 , in accordance with implementations of the disclosure. The implementation of  FIG. 1B  differs from that of  FIG. 1A  primarily in that the RF antenna  110  is disposed over a dielectric window  150  (e.g. ceramic such as quartz), rather than being integrated into or sandwiched between insulators. In some implementations, the dielectric window  150  has a thickness in the range of about one-half to one inch (e.g. about 1 to 3 cm). 
       FIG. 2  is an overhead view of an RF antenna for plasma processing, in accordance with implementations of the disclosure. As shown, the RF antenna  110  has a serpentine shape, consisting of a series of parallel equally spaced conductive lines that are connected in series by looped ends. In other words, the RF antenna is defined by a continuous line that traces a path back and forth over the process region. In the illustrated implementation, the RF antenna  110  is powered at one end by an RF source  118  through a match  116 , and the other end of the RF antenna  110  is connected to ground. 
     Also shown in the overhead view is a substrate  200 . The RF antenna  110  is formed in the illustrated implementation to cover a circular area that encompasses the substrate  200 , and to inductively generate plasma in the process region of the chamber substantially over the entire exposed area of the substrate  200 . 
     In some implementations, the thickness (vertical dimension) of the RF antenna  110  is in the range of approximately 0.01 to 0.02 inches (approximately 0.02 to 0.05 cm). In some implementations, the RF antenna  110  is at a minimum distance from the sidewalls of the chamber, e.g. approximately 0.5 inch (1.3 cm) in some implementations. In some implementations, there is a minimum horizontal distance from the edge of the wafer to the turnaround of a given loop of the RF antenna  110 , e.g. approximately 0.5 inch (1.3 cm) in some implementations. 
       FIG. 3  is a conceptual cross-section view of a portion of a process chamber, in accordance with implementations of the disclosure. As shown, the RF antenna  110  is sandwiched between a top insulator  112  and a bottom insulator  114 . Side insulators  108   a  and  108   b  are joined to the periphery of the top and bottom insulators, so as to form a seal that enables the chamber to be operated under vacuum. The top and bottom insulators can be formed from a ceramic (e.g. quartz) or other insulating materials. 
     In order to achieve an inductively coupled plasma with high uniformity in a small vertical gap, it is important to have a localized magnetic field H (hence, E). Implementations of the present disclosure achieve this, generating a localized H by having the currents in any two adjacent lines running in the opposite direction. Parameters affecting the localization of the magnetic field and ultimately, the characteristics of the plasma generation, include the following: (1) line-line spacing (pitch), s, (2) line-plasma distance, d, (3) inductor line width, w. 
     In some implementations, the pitch s is in the range of about 0.5 to 2 inches (about 1 to 5 cm). In some implementations, s is approximately one inch (2.5 cm) for a vertical small gap on the order of approximately one inch (2.5 cm). In some implementations, s can be further reduced to approximately one-half inch (1.3 cm) in order to further improve the local electron density (Ne) uniformity of the small vertical gap (about one inch) geometry. 
     In order to maximize the plasma-skin induction current, d should be as small as physically and electrically feasible so as to maximize the induced fields. No limits are placed on the ratio s/d. In some implementations, a ratio of s/d&gt;2 is generally considered for practical power-coupling and in fact, a maximum ratio s/d maximizes power-coupling as long as such geometry can be physically and electrically possible. 
     No limits are placed on the ratio of the vertical small-gap/s. In some implementations, small-gap/s&gt;1 is generally considered for practical local Ne uniformity. 
     It is recognized that the field that penetrates into the plasma will become negligible if the spacing between lines (pitch) becomes much less than the thickness of the window. Also, if d is too small, then the conductive lines may be close to a Faraday shield, resulting in high stray capacitance. 
     Additionally, it is recognized that the conductive lines should have sufficient width and/or height to carry current, or they may be at risk of melting. 
     With continued reference to  FIG. 3 , k is the wave vector indicating the direction of energy flow. The wave vector k is equal to the cross product of E and H, e.g. in units of Watts per meter squared. 
     As can be seen, the RF antenna  110  covers the process region in a way that other antennas cannot do. More specifically, the RF antenna  110  provides a very uniform density of flux lines over the entire area with a granularity in accordance with the spacing of the antenna lines. The line-line spacing can be optimized for the line-plasma distance, which may in turn be determined in part by the thickness of the bottom insulator or dielectric window, any distance from the dielectric window, skin depth, etc. The RF antenna  110  provides a uniform source of magnetic flux to drive currents everywhere across the process region area and hence provides uniform plasma production. 
     Existing TCP coils do not achieve uniformity in a small vertical gap because they are designed to generate and diffuse plasma throughout a larger volume and at relatively lower pressure. Such coils are designed to be a global antenna, inducing currents throughout the plasma chamber in a large circular pattern, with attendant stochastic effects. Thus, such existing chambers do not have the property of low residence time. With a conventional TCP coil, it is not possible to achieve high uniformity very close to the window. And thus if the vertical gap of the chamber were simply reduced in an attempt to reduce the residence time, this would bring the non-uniformity close to the wafer surface. 
     However, with the RF antenna provided in accordance with implementations of the present disclosure, there are not the global current circulation and stochastic effects seen in existing coils. But rather, effects are localized, enabling high uniformity of plasma in a narrow vertical gap very close to the window. 
       FIGS. 4A, 4B, 4C, 4D, 4E, 4F, 4G, and 4H  illustrate various examples of RF antenna  110  having various dimensions and coverage configurations, in accordance with implementations of the disclosure. 
     The implementations of  FIGS. 4A-D  illustrate the RF antenna  110  having a substantially circular coverage area, so as to provide coverage over the entire horizontal area of the substrate. In the implementation of  FIG. 4A , the RF antenna  110  has a width of approximately 0.25 inch and a pitch of approximately 1 inch per line. In the implementation of  FIG. 4B , the RF antenna  110  has a width of approximately 0.38 inch and a pitch of approximately 1 inch per line. In the implementation of  FIG. 4C , the RF antenna  110  has a width of approximately 0.50 inch and a pitch of approximately 1 inch per line. In the implementation of  FIG. 4D , the RF antenna  110  has a width of approximately 0.5 inch and a pitch of approximately 1.5 inches per line. 
     The implementations of  FIGS. 4E-H  illustrate the RF antenna  110  having a substantially rectangular coverage area. In the implementation of  FIG. 4E , the RF antenna  110  has a width of approximately 0.25 inch and a pitch of approximately 1 inch per line. In the implementation of  FIG. 4F , the RF antenna  110  has a width of approximately 0.38 inch and a pitch of approximately 1 inch per line. In the implementation of  FIG. 4G , the RF antenna  110  has a width of approximately 0.50 inch and a pitch of approximately 1 inch per line. In the implementation of  FIG. 4I , the RF antenna  110  has a width of approximately 0.25 inch and a pitch of approximately 1.5 inches per line. It will be appreciated that the parameters of the RF antenna  110 , such as the width, pitch, and turns, can be optimized to provide for the desired density and uniformity of plasma when in operation. Currents induced in the plasma mirror the currents going back and forth along the RF antenna  110 . 
       FIG. 5  illustrates an overhead view of an RF antenna  110  defined as a single continuous length of a conductive material, in accordance with implementations of the disclosure. Generally speaking, the RF antenna  110  is defined by an array of parallel equally spaced conductive lines, such as the conductive lines  504   a ,  504   b ,  504   c , and  504   d  as indicated in the illustrated implementation. The conductive lines are substantially straight portions of the RF antenna  110 , and when the RF antenna  110  is powered, current in adjacent ones of the conductive lines runs in opposite directions, forming a local countercurrent. For example, when powered, the current in conductive line  504   c  will run in the opposite direction as the current in adjacent conductive line  504   d . To achieve this countercurrent setup, the conductive lines are connected in series to each other. For example, the conductive lines  504   a ,  504   b ,  504   c , and  504   d  are connected in series. Conductive line  504   a  is connected to conductive line  504   b  by a connector  506   a ; conductive line  504   b  is connected to conductive line  504   c  by a connector  506   b ; and, conductive line  504   c  is connected to conductive line  504   d  by a connector  506   c.    
     In the illustrated implementation, the connectors are shown as curved lines or semicircular shaped. However, in other implementations the connectors can have other shapes. In some implementations, each connector is defined by a single straight line connecting segment. In some implementations, each connector is defined by two or more straight line connecting segments. In some implementations, the RF antenna  110  may have different shaped connectors at different portions of the RF antenna  110 . 
     The RF antenna  110  has a first end  500  that is powered, and a second end  502  that is connected to ground. As shown, the RF antenna  110  has a serpentine shape that defines a current path configured to flow back and forth along and parallel to a first axis, while traversing a second axis perpendicular to the first axis from one side of the chamber to the opposite side of the chamber. The RF antenna  110  thus defines a countercurrent inductor that produces localized plasma induction. 
     In the illustrated implementation, the RF antenna  110  has a single continuous length. In such implementations with and single continuous length, if the length is too long for the frequency at which the system operates, there may be transmission line effects as the whole length may not be sufficiently in phase, and the inductance may be too high. For example, at a frequency of 13.56 MHz, and an RF antenna  110  length of about 3-10 feet, the entire length can be considered to be in phase. However, if the length is significantly longer, then there may be transmission line effects. One possibility to address such issues is to lower the frequency. However, another way is to break down the conductive length into different segments, which lowers the inductance. 
     With continued reference to  FIG. 5 , in some implementations, each of the conductive lines has a segment length of approximately 17 inches (approximately 43 cm); in some implementations, approximately 15-20 inches (approximately 38 to 51 cm). In some implementations, the line-to-line spacing is approximately 1 inch (approximately 2.5 cm); in some implementations, approximately 0.5 to 1.5 inches (approximately 1.3 to 3.8 cm). In some implementations, the line width is approximately 0.25 inch (approximately 0.6 cm); in some implementations, approximately 0.1 to 0.5 inch (approximately 0.2 to 1.3 cm). 
       FIG. 6  illustrates an overhead view of RF antenna  110  consisting of two distinct segments, in accordance with implementations of the disclosure. As shown, the RF antenna  110  has a segment  600  and a segment  606 . The RF antenna  110  still consists of an array of conductive lines that are parallel and equally spaced. However, the conductive lines are divided into two segments, with the segment  600  including half of the conductive lines connected in series, and the segment  606  including the other half of the conductive lines connected in series. The segment  600  is powered at a first end  602  and grounded at a second end  604 . The segment  606  is powered at a first end  608  and grounded at a second end  610 . 
     In some implementations, power is split from a single power source to each of the first ends  602  and  608  of the segments  600  and  606  respectively. In other implementations, power is provided from separate power sources to each of the first ends respectively. In either case, when the RF antenna  110  is powered, each pair of adjacent conductive lines of the RF antenna  110  exhibits current flow in opposite directions, so that RF antenna  110  functions as a countercurrent inductor. 
     In some implementations, the RF antenna  110  in accordance with  FIG. 6  has dimensions similar to those described with reference to the implementation of  FIG. 5 . 
       FIG. 7  illustrates an overhead view of an RF antenna  110  having multiple hairpin-shaped segments, in accordance with implementations of the disclosure. In the illustrated implementation, the RF antenna  110  consists of segments  700 ,  702 ,  704 ,  706 ,  708 ,  710 ,  712 ,  714 , and  716 . Each segment has a hairpin shape consisting of two adjacent and parallel conductive lines that are connected by a connector on one side. For example, the segment  700  includes conductive lines  718  and  720 , connected on one side by a connector  722 . An adjacent segment  702  includes conductive lines  728  and  730 , connected on the opposite side by a connector  732 . 
     The segment  700  is powered at a first end  724 , and has a second end  726  connected to ground. The segment  702  is powered at a first end  734 , and has a second end  736  connected to ground. The remaining segments are similarly configured to be powered and grounded. In some implementations, the segments may each receive RF power that is uniformly or adjustably split from a power source. It will be appreciated that the segments are arranged as shown, so that when the RF antenna  110  is powered, adjacent lines exhibit current flow in opposite directions, thereby enabling the RF antenna  110  to function as a countercurrent inductor. 
     In some implementations, the RF antenna  110  is powered at a frequency of 13.56 MHz and a total power W. In some implementations, the power to each segment is equal to W divided by the number of segments of the RF antenna  110 . 
       FIG. 8  illustrates an overhead view of an RF antenna  110  having multiple segments, in accordance with implementations of the disclosure. In the illustrated implementation, each segment includes three conductive lines connected in series. The RF antenna  110  as shown includes segments  800 ,  802 ,  804 ,  806 ,  808 , and  810 . By way of example, the segment  800  includes conductive lines  812 ,  814 , and  816  connected in series by connectors  818  and  820  as shown. Similarly, the segment  802  includes conductive lines  826 ,  828 , and  830  connected in series by connectors  832  and  834 . The remaining segments are similarly configured. Each segment thus exhibits a double reverse hairpin shape, with two 180 degree turns for each segment. 
     The segment  800  receives power at a first end  822 , and a second end  824  is connected to ground Likewise, the segment  802  receives power at a first end  836 , and a second end  838  is connected to ground. The other segments are similarly configured. In some implementations, RF power can be uniformly or adjustably split from a power source to the segments of the RF antenna  110 . It will be appreciated that the segments are arranged as shown, so that when the RF antenna  110  is powered, adjacent lines exhibit current flow in opposite directions, thereby enabling the RF antenna  110  to function as a countercurrent inductor. 
     In some implementations, the RF antenna  110  is powered at a frequency of 13.56 MHz and a total power W. In some implementations, the power to each segment is equal to W divided by the number of segments of the RF antenna  110 . 
       FIG. 9A  illustrates an overhead view of an RF antenna  110  having multiple double reverse hairpin segments, in accordance with implementations of the disclosure. In the illustrated implementation, the RF antenna  110  includes segments  900 ,  916 ,  940 , and  956 . Each segment is powered by a separate power supply, thus enabling the RF power provided to each segment to be individually tuned. This can be leveraged to improve deposition uniformity, for example, or even to intentionally produce a differential deposition profile. Segment  900  is powered by power supply  912  and connected to ground through a termination module  914 ; segment  916  is powered by power supply  928  and connected to ground through a termination module  930 ; segment  940  is powered by power supply  952  and connected to ground through a termination module  954 ; segment  956  is powered by power supply  968  and connected to ground through a termination module  970 . 
     Segment  900  includes conductive lines  902 ,  904 , and  906 , connected in series by connectors  908  and  910 ; segment  916  includes conductive lines  918 ,  920 , and  922 , connected in series by connectors  924  and  926 ; segment  940  includes conductive lines  942 ,  944 , and  946 , connected in series by connectors  948  and  950 ; and segment  956  includes conductive lines  958 ,  960 , and  962 , connected in series by connectors  964  and  966 . 
     As conceptually shown by the arrows on the conductive lines, when the RF antenna  110  is powered, current flow in adjacent conductive lines occurs in opposite directions, thus forming a countercurrent inductor. 
     In some implementations, the RF antenna  110  is powered at a frequency of 13.56 MHz and a total power W. In some implementations, the power to each segment is equal to W divided by the number of segments of the RF antenna  110 . For example, in the case of four segments as shown, the power to each segment is equal to W/4. 
       FIG. 9B  is a cross-section view of the implementation of  FIG. 9A , in accordance with implementations of the disclosure. In  FIG. 9B , the components of the RF antenna  110  are shown disposed over a dielectric window  980 . Shown below the dielectric window  980  is a ground electrode  982 . 
       FIG. 10A  illustrates a conceptual cross-section of an RF antenna  110  in accordance with implementations of the disclosure. Shown is a cross-section view along a length of one of the conductive lines  1000  of the RF antenna  110 . Conductive lines  1000  may also be referred to as inductor lines. The RF antenna  110  is formed between a top insulator  112  and a bottom insulator  114 . Also disposed within the bottom insulator and below the RF antenna  110  is a Faraday shield  1002 . The Faraday shield  1002  includes lines that are oriented perpendicular to the orientation of the conductive lines of the RF antenna  110 . Thus in the illustrated implementation, the Faraday shield  1002  appears as a series of short segments below the conductive line  1000 , as the view is cross-sectional across the Faraday shield&#39;s lines. 
       FIG. 10B  illustrates a conceptual cross-section in accordance with the implementation of  FIG. 10A . The view shown at  FIG. 10B  is perpendicular to that of  FIG. 10A . Thus, the illustrated cross-section of  FIG. 10B  is perpendicular to the orientation of the conductive lines  1000  of the RF antenna  110 , and several individual conductive lines  1000  are visible. In some implementations, between the individual conductive lines  1000 , there is epoxy  1004 , which bonds the top insulator  112  and the bottom insulator  114 . 
     The electrostatic Faraday shield  1002  absorbs the electric field from the conductive lines, so that electric field will not pass through into plasma. The arrows shown at  FIG. 10A  illustrate electric field lines terminating on the Faraday shield  1002 . Thus, only the magnetic fields pass through the ceramic into the plasma skin to be absorbed. 
     In some implementations, the Faraday shield is designed such that the capacitance between the inductor lines and the Faraday shield is a controllable quantity. In some implementations, the Faraday shield  1002  is at ground, so if the stray capacitance is too high compared to the series resonance capacitance, then the ICP match won&#39;t tune. 
     Further illustrated at  FIG. 10B  is the wave vector K, indicated by arrows beneath the inductor lines. Directly below the inductor line the direction of energy flow is straight down. But away from the inductor line, the direction of energy flow changes because the magnetic field is curved. 
     The Faraday shield can function to block capacitive coupling from the RF antenna  110  to plasma. In some implementations, the Faraday shield is grounded; whereas in some implementations, the Faraday shield is floating. 
     In some implementations, the Faraday shield is powered, to sputter the window to keep it clean. Additionally, if the Faraday shield is powered, then this could be used to assist in ignition and plasma stability. 
       FIG. 11A  illustrates a perspective view of an RF antenna  110  having raised end loops, in accordance with implementations of the disclosure. In the RF antenna  110  the looped ends may cause some transformer effect. Therefore, in some implementations, this effect can be reduced by bending the end loops up at an angle (e.g. approximately 90 degree angle). This will also reduce the end loops&#39; current induction into the chamber. 
     In the illustrated implementation, the RF antenna  110  includes conductive lines that are connected in series by raised end loop connectors. For example, the conductive lines  1100 ,  1104 ,  1108 ,  1112 , and  1116  are connected in series by connectors  1102 ,  1106 ,  1110 , and  1114  as shown. The connectors are curved segments (e.g. semicircular) and each is oriented along a plane that is substantially perpendicular to the plane along which the conductive lines are oriented. The connectors define a current path, from one conductive line to another, that travels upward out of the plane of the conductive lines, and then travels downward back into the plane of the conductive lines. 
     In the illustrated implementation, the RF antenna  110  is configured to cover a substantially circular region of the chamber, so as to cover and extend beyond the area of the substrate surface that is beneath it. Accordingly, when the connectors are configured to have substantially the same shape as in the illustrated implementation, then the sizes of the connectors may vary as the distance between the ends of adjacent conductive lines may vary depending upon their positioning within the overall array of conductive lines. As shown, adjacent conductive lines positioned towards the ends of the RF antenna  110  have larger connectors (e.g. connector  1102 ) than adjacent conductive lines positioned towards the center of the RF antenna  110  (e.g. connector  1114 ). 
       FIG. 11B  illustrates a cutaway view of a process chamber  102  including the RF antenna  110  in accordance with the implementation of  FIG. 11A . In some implementations, the RF antenna  110  is positioned above a dielectric window that may consist of top and bottom insulators  112  and  114 . In some implementations, the RF antenna  110  is positioned between the top and bottom insulators  112  and  114 . 
     Also shown are contact structures  1120  and  1122  which define electrical contacts for the RF antenna  110 . For example, the contact structure  1120  may receive RF power from a power source, while the contact structure  1122  is connected to ground. 
       FIG. 11C  illustrates a perspective view of the process chamber  102  in accordance with the implementation of  FIG. 11B . The region of the process chamber  102  above the RF antenna  110  can be provided with airflow to cool this region and more specifically cool the RF antenna  110  and prevent it possibly melting. 
       FIG. 11D  illustrates an overhead view of the process chamber  102  in accordance with the implementation of  FIG. 11B . An advantage of the upturned end loop connectors of the RF antenna  110  is that the straight conductive lines can be extended close to the chamber edge, so that the length/reach and coverage area of each conductive line is maximized. In some implementations, a minimum distance from the chamber edge is defined for the RF antenna  110  (e.g. approximately 0.5 inch, or 1.3 cm), and the conductive lines may therefore extend up to or close to the minimum distance from the chamber edge that is defined. In this manner, the conductive lines extend beyond the edge of the substrate  200  to the maximum extent possible, thereby promoting uniformity of plasma generation over the substrate edge regions. 
       FIG. 12A  illustrates a cutaway view of a process chamber  102 , in accordance with implementations of the disclosure. In the illustrated implementation, the RF antenna  110  and the Faraday shield  1206  are embedded within a lower insulator  1200 . An upper insulator  1202  is positioned above the lower insulator  1200 , forming a space between the upper and lower insulators that defines a gas plenum  1204 . Also visible in cross section are gas through-holes  1210  that pass through the lower insulator  1200 , enabling process gases in the gas plenum  1204  to travel through the lower insulator  1200  into the process region over the wafer pedestal  106 . 
       FIG. 12B  illustrates a perspective view showing the stacking of components including the RF antenna  110 , in accordance with the implementation of  FIG. 12A . As can be seen in this view, the RF antenna  110  is positioned over the Faraday shield  1206 , with the conductive lines of the RF antenna  110  running perpendicular to lines of the Faraday shield  1206 . 
       FIG. 12C  illustrates an overhead view of the process chamber  102 , in accordance with implementations of the disclosure. As shown, the RF antenna  110  is positioned over the Faraday shield  1206 . In the implementation of  FIG. 12C , the line pitch of the Faraday shield is smaller than that of the implementation shown at  FIGS. 12A and 12B . 
       FIG. 12D  illustrates a cross section view of an outer portion of the process chamber  102 , in accordance with the implementation of  FIG. 12C . The gas plenum  1204  is shown between the upper insulator  1202  and the lower insulator  1200 . The illustrated cross section is along the direction of the conductive lines of the RF antenna  110 , and perpendicular to the direction of the lines of the Faraday shield  1206 . 
       FIG. 12E  illustrates a cross section view of a portion of the process chamber  102 , in accordance with the implementation of  FIG. 12C . The illustrated cross section is perpendicular to the lines of the Faraday shield  1206 . In the illustrated view, gas through-holes  1210  are shown, which are positioned so that process gas may travel between the lines of the Faraday shield  1210 . 
       FIG. 12F  illustrates a cross section view of a portion of the process chamber  102 , in accordance with the implementation of  FIG. 12C . The illustrated cross section is perpendicular to the lines of the RF antenna  110 . As shown, the gas through-holes  1210  are positioned so that process gas may travel between the conductive lines of the RF antenna  110 . 
       FIG. 13A  illustrates an RF antenna  110  in accordance with implementations of the disclosure. In the illustrated implementation, the RF antenna  110  includes parallel and equally spaced conductive lines  1300 ,  1302 ,  1306 ,  1308 ,  1310 , and  1312 . The conductive lines of the RF antenna  110  are powered from the same side of the RF antenna  110  and split RF power from a power source  118 . The conductive lines are grounded on the opposite side of the RF antenna  110 . Hence, currents run in parallel in the same direction along the lines  1300 ,  1302 ,  1306 ,  1308 ,  1310 , and  1312 . 
       FIG. 13B  illustrates an RF antenna  110  in accordance with implementations of the disclosure. In the illustrated implementation, the RF antenna  110  includes parallel and equally spaced conductive lines  1314 ,  1316 ,  1320 ,  1322 ,  1326 , and  1328 . Conductive lines  1314  and  1316  are connected in series by a connector  1318 ; conductive lines  1320  and  1322  are connected in series by a connector  1324 ; conductive lines  1326  and  1328  are connected in series by a connector  1330 . As shown, the conductive lines are powered and grounded from the same side of the RF antenna  110 . More specifically, the conductive lines  1314 ,  1320 , and  1326  are powered by an RF power source  118 , and the conductive lines  1316 ,  1322 , and  1328  are connected to ground, along the same side of the RF antenna  110 . 
     A problem for achieving high density plasma with inductively coupled plasma systems is that the voltage and/or power required to achieve the desired high density of plasma is too high. Having too high a voltage and/or power can cause multiple problems. Generally speaking, the plasma sheath forms the outermost part (e.g. about 1 mm thickness) of the plasma skin (e.g. about 1 cm thick). As the electric field in the plasma sheath just below the dielectric window is generally perpendicular to the plane of the dielectric window (whereas the electric field in the plasma skin is generally parallel to the plane of the dielectric window) the high voltage and/or power will result in bombardment of the dielectric window with ions, which can result in contamination of the wafer surface. This further wastes energy by generating heat and also consumes the power being applied, so that it is wasted instead being used for inductive heating of the plasma, rendering the process very inefficient. Additionally, high voltage and/or power may stress related power componentry, producing excessive wear, reducing lifetime, and may even trigger arcing of the match circuitry. 
     In some implementations, it is contemplated how to place the counter-current inductor lines the closest to the plasma while having the least plasma-to-inductor voltage and the most inductor-current. Accordingly, with continued reference to the implementation of  FIG. 5 , for an RF antenna defined having a single continuous length, the following is considered: 
     
       
         
           
             
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                   τ 
                   
                     C 
                     S 
                   
                 
               
               = 
               
                 
                   I 
                   0 
                 
                  
                 ω 
                  
                 
                   L 
                   S 
                 
               
             
           
         
       
     
     where V S  is the RF antenna&#39;s peak-voltage, 
     I 0  is the inductor peak current, 
     L S  is the RF antenna&#39;s inductance, 
     ω is the angular frequency and τ is the angular period. 
     It will be noted that for an unbalanced ICP where the inductor-end is tied directly to ground without C S2 , its phase-cap was C=C S /2 and the unbalanced ICP peak-voltage is double that of the balanced ICP. 
     On the lowest order, a constant I 0  keeps a constant n e  for the ICP. Thus, a challenge is how to maintain a constant I 0  while keeping V S  as low as possible. If V S  can be kept under 400V at maximum power, then Faraday shield may not be needed. 
     As noted previously, by way of example without limitation, an RF antenna having the following dimensions is considered: 17″ line-segment (18 lines), 1″ line-to-line, 0.25″ line width. 
     One strategy for reducing the voltage is to divide the RF antenna into multiple segments, such as indicated by the implementation of  FIG. 7 . Considering such an implementation, then the following is considered: 
     let, L=Serpentine-cell&#39;s inductance, 
     L 0 =Serpentine-cell Array&#39;s inductance, 
     Then, it is approximately correct to have, 
     
       
         
           
             L 
             = 
             
               
                 L 
                 S 
               
               9 
             
           
         
       
       
         
           
             
               L 
               0 
             
             = 
             
               
                 L 
                 9 
               
               = 
               
                 
                   L 
                   S 
                 
                 
                   8 
                    
                   1 
                 
               
             
           
         
       
     
     and the matcher would then have, 
     
       
         
           
             
               C 
               0 
             
             = 
             
               8 
                
               1 
                
               
                 C 
                 S 
               
             
           
         
       
       
         
           
             ω 
             = 
             
               
                 2 
                 
                   
                     L 
                     0 
                   
                    
                   
                     C 
                     0 
                   
                 
               
             
           
         
       
     
     and then the inductor&#39;s peak-voltage becomes, 
     
       
         
           
             
               V 
               0 
             
             = 
             
               
                 9 
                  
                 
                   I 
                   0 
                 
                  
                 
                   τ 
                   
                     C 
                     0 
                   
                 
               
               = 
               
                 9 
                  
                 
                   I 
                   0 
                 
                  
                 ω 
                  
                 
                     
                 
                  
                 
                   L 
                   0 
                 
               
             
           
         
       
       
         
           
             
               V 
               0 
             
             = 
             
               
                 
                   I 
                   0 
                 
                  
                 
                   τ 
                   
                     9 
                      
                     
                       C 
                       S 
                     
                   
                 
               
               = 
               
                 
                   I 
                   0 
                 
                  
                 ω 
                  
                 
                   
                     L 
                     S 
                   
                   9 
                 
               
             
           
         
       
       
         
           
             
               V 
               0 
             
             = 
             
               
                 V 
                 S 
               
               9 
             
           
         
       
     
     Thus, by dividing the RF antenna into nine segments, the voltage is approximately divided by nine, while each line segment still passes the same current, I 0 . A possible complication is that the phase-caps of the matcher will need to be 81 times larger than that of the matcher for the RF antenna having only a single continuous length. The 400V peak-voltage for the 9-segment array RF antenna is equivalent to 3600V for the single continuous length RF antenna, and that is equivalent to 7200V unbalanced ICP. A ±7200V peak-voltage of an unbalanced ICP is typically associated with 5 kW to 10 kW of RF power. 
     While a 400V peak-voltage is achievable as discussed above, such a voltage and power requirement may still be too high. Another way to reduce the voltage is to couple the RF power through a grounded counter-current inductor as discussed below. 
       FIG. 14A  illustrates an overhead view of an RF antenna disposed over a grounded counter-current inductor for coupling RF power into a chamber, in accordance with implementations of the disclosure. The RF antenna  110  in accordance with the implementation of  FIG. 7  (including segments  700 ,  702 ,  704 ,  706 ,  708 ,  710 ,  712 ,  714 , and  716 ) is shown disposed over a grounded (counter current) inductor  1400 . The RF antenna  110  is positioned above the dielectric window, while the grounded inductor  1400  is positioned below the dielectric window in the process region of the chamber. Broadly speaking, the RF antenna  110  is powered as previously discussed and induces currents in the grounded inductor  1400 , which in turn inductively generate the plasma in the process region. 
     As shown, the grounded inductor  1400  includes grounded inductor lines  1402  that are positioned directly beneath the conductive lines of the RF antenna  110 . 
       FIG. 14B  illustrates a cross section view of the grounded inductor  1400 , in accordance with implementations of the disclosure. The conductive lines  718  and  720  of the segment  700  of the RF antenna  110  are shown disposed over the dielectric window  150 , and separated therefrom by an air-gap of approximately 0.050 inch (0.13 cm) in some implementations. The grounded inductor lines  1402   a  and  1402   b  are aligned below the conductive lines  718  and  720 , respectively. In some implementations, the dielectric window  150  has a thickness of approximately 0.125 inch (0.32 cm). At such a thickness, the dielectric window may not be structurally strong enough to withstand the difference in pressure when the chamber is operated under vacuum conditions. Therefore, the grounded inductor lines  1402  of the grounded inductor  1400  may further serve to support the dielectric window  150 , enabling the dielectric window  150  to be constructed with low thickness (e.g. less than about 0.25 inch (0.6 cm) in some implementations). 
     In some implementations, a typical current flowing in a hairpin segment such as segment  718  of the RF antenna  110  is about 80 amps. However, because the segment is thin, it has a certain inductance. The grounded inductor line  1402   a  has a much larger cross sectional area so its inductance, in some implementations, is about four times lower than that of the segment  718 . So assuming conservation of flux for the sake of simplification, then the current in the grounded inductor line  1402   a  becomes about four times higher than the current in the segment  718 . So the 80 amps flowing in the segment  718  becomes approximately 320 amps flowing in the grounded induction line  1402   a . And with the current amplified four times, then the voltage in the grounded induction line  1402   a  is reduced by a factor of four. 
     Thus, the voltage can be reduced both by the segmentation of the RF antenna  110  and by using the grounded inductor  1400 . By way of example without limitation, at for example, 3 kW of power and 80 amps current, the voltage in a single continuous line RF antenna design (as in implementation of  FIG. 5 ) may be in the range of about 8000 V. However, by splitting the RF antenna into, for example, a nine segmented hairpin design (as in implementation of  FIG. 7 ), the voltage is approximately divided by the number of segments, so instead of 8000 V, the voltage in the segments is reduced (divided by nine) to approximately 900 V. And using the grounded inductor  1400   e , because the inductance is lower, the current is further amplified about four times from 80 to 320 Amps, and when the current is amplified four times, the voltage drops four times. Thus, the 900 V in the RF antenna  110  drops down to a voltage in the grounded inductor  1400  in the range of about 200 to 300 V. 
     The grounded inductor lines  1402  are immersed in the plasma, so the magnetic flux generated by current in the grounded inductor lines  1402  will be strongly coupled to the plasma. A typical inductor is much further away from the plasma, and typically separated by a thicker window. However, implementations of the present disclosure provide for the inductor line to be located in the plasma with current amplified so the voltage drops. 
     In some implementations, the RF antenna  110  is powered with approximately 2 to 5 kW of power, to produce a high density plasma. 
     As shown, in some implementations, the grounded inductor lines  1402  have a cross-sectional width of about 0.4 inch (1 cm) and a cross-sectional height of about 0.5 inch (1.3 cm). The pitch of the grounded inductor lines  1402  is the same as that of the conductive lines of the RF antenna  110 . Hence, in some implementations, the pitch of the grounded inductor lines  1402  is about 1 inch (2.5 cm). 
     In some implementations, a frame  1404  of the grounded inductor  1400  is formed as a one-piece structure that forms part of the sidewalls of the process chamber, acting as a vacuum wall to structurally maintain the integrity of the chamber under vacuum. A gasket  1406  is embedded in the frame  1404  to provide a seal between the dielectric window  150  and the frame  1404  of the grounded inductor  1400 . It will be appreciated that the inductor lines  1402  of the grounded inductor  1400  are attached at their ends to the frame  1404 , and in some implementations, are formed as a continuous structure with the frame  1404 . 
     It will be appreciated that the grounded inductor  1400  also serves as the Faraday shield, and thus there is no need for an additional Faraday shield to block the electric field from the RF antenna  110 , as the electric field is absorbed by the grounded inductor  1400 . 
     Additionally, in some implementations, the gap between the conductive lines of the RF antenna  110  and the grounded inductor lines of the grounded inductor  1400  can be configured to be the smallest possible to maximize inductive coupling while also being large enough to support a stray capacitance that can facilitate the series resonance. 
       FIG. 14C  is a graph illustrating the relative phases of the currents in the structures of the plasma processing system, in accordance with the implementation of  FIG. 14A . As shown, but without being bound by any particular theory of operation, it is submitted that in some implementations, the current in the grounded induction lines of the grounded inductor  1400  is approximately 90 degrees phase-shifted from the current in the respective conductive lines (hairpin current) of the RF antenna  110 . Further, the current in the plasma is submitted to be approximately 90 degrees phase-shifted from the current in the grounded inductor  1400 . Thus, the current in the plasma is submitted to be approximately 180 degrees phase-shifted from the current in the RF antenna  110 . 
       FIG. 14D  illustrates a cross-section view of a grounded inductor line  1402  of the grounded inductor  1400 , in accordance with the implementation of  FIG. 14A . As shown, in some implementations, the structure includes an aluminum central body  1410 , which provides suitable strength to support the dielectric window  150  during vacuum processes. However, while, aluminum is strong, it is not a good RF conductor. Therefore, the aluminum body  1410  can be coated with a highly conductive material such as Cu or Ni—Ag—Ni, to form a conductive coating  1412  over the central body  1410 . Then a protective coating  1414  can be deposited over the conductive coating  1412 , the protective coating  1414  consisting of a material that will be chemically non-reactive during process conditions, such as yttrium oxide (Y 2 O 3 ). 
     Additionally, in some implementations, cooling channels  1420  can be defined within the grounded inductor lines  1402 , to enable a coolant to be circulated within the grounded inductor  1400  and provide for temperature control of the grounded inductor  1400 . 
     Further, in some implementations, gas channels  1422  can be run within the grounded inductor lines  1402 , which allow process gases to be fed into the chamber through the grounded inductor  1400 . Process gases can be routed into the gas channels  1422  and distributed into the process region through exit holes  1424 . The integration of a showerhead is generally always a problem for any system with a dielectric window. However, the grounded inductor  1400  disclosed herein provides a metal piece within which channels for liquid cooling and process gases can be run, so that the dielectric window  150  does not need to have any holes as in other systems. 
       FIGS. 15A and 15B  illustrate overhead and cross-section views, respectively, of a grounded inductor  1500 , in accordance with implementations of the disclosure. The grounded inductor  1500  of  FIGS. 15A and 15B  differs from the grounded inductor  1400  of  FIGS. 14A and 14B  primarily in that the width of the grounded inductor lines  1502  is widened to have a width of approximately 0.8 inch (2 cm). 
     In existing ICP systems, it is generally desirable to have the Faraday shield oriented with lines running perpendicular to the inductor lines, and for the Faraday shield to have gaps so that magnetic flux to come through the Faraday shield into the process region. However, in the present design of the grounded inductor structure, it is desired to not have any magnetic flux from the RF antenna  110  to come in to the plasma. Rather, it is desirable to have the magnetic flux induce electric field above and below. 
     For the currents indicated by the X and the dot, indicating the current traveling in/out of the page, respectively, 
     
       
         
           
             
               ∮ 
               
                 E 
                 · 
                 dl 
               
             
             = 
             
               
                 
                   
                     
                       - 
                       
                         d 
                         dt 
                       
                     
                      
                     
                       ∮ 
                       
                         B 
                         · 
                         dS 
                       
                     
                   
                    
                   
                       
                   
                   &amp; 
                 
                  
                 
                     
                 
                  
                 J 
               
               = 
               
                 σ 
                  
                 
                     
                 
                  
                 E 
               
             
           
         
       
     
     J is current; sigma is conductivity; E is the electric field. 
     The grounded inductor  1400  is in some implementations, aluminum coated with copper (Cu) (as noted above) which has significantly better conductivity than the plasma. Thus, the flux of the RF antenna  110  would not substantially generate plasma current, as the current in the RF antenna  110  would principally become current in the copper of the grounded inductor  1400 . Thus the magnetic flux by the RF antenna  110  is substantially completely blocked by the grounded inductor lines. In some implementations, the gap between the grounded inductor lines can be a very small gap, e.g. less than about 0.5 inch (1.3 cm) in some implementations, about 0.2 inch (0.5 cm) in some implementations. 
     The proximity of the grounded induction lines (e.g., 0.2″) could force a ˜90° line-to-line current phase; its effect of enhancing “spatial stochastic” heating is discussed further below. The proximity also increases counter-current mutual induction resulting in a reduced inductance for the grounded induction line and that, reduces the peak voltage on the grounded induction line for a given current. The wider grounded induction line could also benefit the local plasma-density uniformity. 
       FIG. 16  illustrates a single hairpin counter-current inductor segment, in accordance with implementations of the disclosure. The segment  1600  as shown can be part of an array of such segments organized to form a counter-current inductor RF antenna  110  in accordance with implementations discussed above. An issue to consider is the precise current phase along the two conductive lines of the segment  1600 , indicated as line- 1  and line- 2  in the illustrated implementation. 
     Without being bound by any particular theory of operation, it is nonetheless posited that each ladder piece is likely not a uniform-current inductor. For line-to-line induction is believed to play a part in affecting the current phase. A graph  1602  illustrates by way of example without limitation, a 90 degree line-to-line current phase, that is believed to occur if line-to-line induction dominates. However, it is noted that if line-to-line conduction (real current) dominates, then the line-to-line current phase is 180 degrees, as the 180 degree direction change forced by the hairpin turn geometry will produce this. 
     In view of both line-to-line conduction and induction effects on current phase, it is therefore possible that perhaps the line-to-line current phase is a mixture from 90 degrees to 180 degrees varying along the length of a line to the current/voltage nodes. 
       FIG. 17  illustrates the effect of 90 degree line-to-line phased spatial-alternating plasma-skin induction currents, in accordance with implementations of the disclosure. 
     ∇XE is the highest within Δx˜1 mm (simply due to ωB in Δx) and it will lead to “spatial” stochastic collisionless heating of the electrons as the electrons drift across Δx. In the absence of Landau damping and cyclotron resonance, such spatial stochastic collisionless heating occurs when electrons drift across Δx under a coincident phase condition. If the line-to-line phase were 180°, such coincident phase is very small. However, for the 90° line-to-line phase, such coincident phase is π⇒½ the time collisionless heating occurs. If the plasma is collisional, such a spatial stochastic process simply enhances ionization through collisional relaxation. 
     Thus, the effect of a 90 degree line-line current phase, if it exists, is enhanced ionization in addition to EEDf mixing among regions under the lines which normally occur even in the pure 180 degree condition. 
       FIG. 18A  illustrates an overhead view of an RF antenna  1800  having a series serpentine configuration, in accordance with implementations of the disclosure. The RF antenna has an inductance of 2.4 μH, a 0.25 inch line width, and the parallel lines are equally spaced and have a 1 inch pitch. 
       FIG. 18B  is a graph showing ion density as a function of lateral position for a plasma generated using RF antenna  1800  under various powers. The lateral position is the position along a center line in the chamber running perpendicular to the lines of the RF antenna. In the illustrated implementation, results are shown for a 30 cm distance that is equivalent to measuring edge-to-edge across a 300 mm wafer plane. Ion density was measured using a moving Langmuir probe. Plasma was generated with 50 mT Ar, in a chamber having a 2 inch vertical gap from the dielectric window to the wafer plane. 
     The curves  1810 ,  1812 ,  1814 ,  1816 ,  1818 , and  1820  correspond to results for power levels of 500 W, 1000 W, 1500 W, 2000 W, 2500 W, and 3000 W, respectively. 
     In the following disclosure, several different examples of RF antenna configurations are shown and tested. The inductor lines generally have a height of approximately ½ inch and a width of approximately ⅛ inch. However it will be appreciated that in other implementations the height and width of the inductor lines may vary. Broadly speaking, an inductor line height greater than its width can be beneficial to reduce capacitive coupling versus inductive coupling. For purposes of experimentation, RF power was applied at a frequency of 13.56 MHz. However, it will be appreciated that in other implementations the frequency of the power may vary, e.g. in a range of about 400 kHz to about 2 MHz. 
       FIG. 19A  schematically illustrates an RF antenna having five hairpin segments  1900 ,  1902 ,  1904 ,  1906 , and  1908 . The segments are arranged so that when powered, the RF antenna operates a counter-current inductor. 
       FIG. 19B  illustrates an overhead view of an RF antenna in accordance with the implementation of  FIG. 19A , including five hairpin segments  1910 ,  1912 ,  1914 ,  1916 , and  1918 , that form a counter-current inductor. 
       FIG. 20A  illustrates a single hairpin element  2000  having a 1.5 inch spacing between lines, in accordance with implementations of the disclosure. 
       FIG. 20B  is a graph of ion density versus lateral position for a plasma generated using the single hairpin element  2000 . The curves  2010  and  2012  illustrate results at 500 W and 1000 W, respectively. 
       FIG. 20C  is a graph showing normalized density versus normalized power for the results shown at  FIG. 20B . 
       FIG. 21A  illustrates a perspective view of a single hairpin element  2100  with a 0.125″ spacing introduced between the antenna and the dielectric window  2102  to reduce capacitive coupling. As shown, the spacing was accomplished by using spacers  2104  and  2106  mounted on the dielectric window  2102 . The thickness of the dielectric window  2102  is approximately ¾ inch. 
       FIG. 21B  is a graph of ion density versus lateral position for a plasma generated at 250 mT Ar using the single hairpin element  2100  with the 0.125 inch spacing off the dielectric window. The curves  2110 ,  2112 ,  2114 , and  2116  illustrate results at 500 W, 750 W, 1000 W, and 1250 W, respectively. 
       FIG. 22A  schematically illustrates a single hairpin element  2200  having a 3 inch spacing. 
       FIG. 22B  is a graph of ion density versus lateral position for a plasma generated at 250 mT Ar using the single hairpin element  2200 . The curves  2210 ,  2212 ,  2214 , and  2216  illustrate results at 500 W, 750 W, 1000 W, and 1250 W, respectively. 
       FIG. 23A  schematically illustrates an RF antenna consisting of two segments  2300  and  2302 , having a line spacing of 2.5″/2.5″/2.5″ as shown, and configured as a counter-current inductor. 
       FIG. 23B  illustrates an overhead view of an RF antenna having segments  2310  and  2312 , in accordance with the implementation of  FIG. 23A . 
       FIG. 23C  is a graph of ion density versus lateral position for a plasma generated at 250 mT Ar using the RF antenna of  FIG. 23B . The approximate lateral locations of the antenna lines are shown at reference  2320 . The curves  2322 ,  2324 ,  2326 , and  2328  illustrate results at 500 W, 750 W, 1000 W, and 1250 W, respectively. 
       FIG. 24A  schematically illustrates an RF antenna consisting of two hairpin segments  2400  and  2402 , having a line spacing of 2.5″/2.5″/2.5″ as shown, and configured as a partially parallel-current and partially counter-current inductor. As can be seen, the segments are configured and arranged so that within a single hairpin segment, current in adjacent lines runs in opposite directions, whereas between the two hairpin segments, current in the adjacent lines runs in the same direction. In some embodiments, the separation between the inner segments of the hairpin conductive lines can be adjusted to be increased or decreased as a tuning knob, to influence uniformity across the wafer. In the example of  FIG. 24A , two hairpin conductive lines are shown. In other embodiments, additional hairpin conductive lines can be added, e.g., four hairpin conductive lines. The connections of power and ground to each hairpin conductive line can be made to set whether the current in adjacent inner lines run in the same direction or in opposite directions. In other cases, the power source connected to each segment can be separately controlled, e.g., to provide different power, voltage, and/or frequency to each hairpin conductive line. In this manner, not only can the structural placement of the hairpin conductive lines be set at different separations, but the power/current provided to each segment can also be individually set or dynamically adjusted to achieve the desired uniformity profiles. By way of example,  FIGS. 31C and 32C  show how uniformity can be achieved by the set relative orientation of the hairpin conductive lines, e.g., relative to each other, and the connections to the RF power source and ground. 
       FIG. 24B  illustrates an overhead view of an RF antenna having segments  2410  and  2412 , in accordance with the implementation of  FIG. 24A . 
       FIG. 24C  is a graph of ion density versus lateral position for a plasma generated at 120 mT Ar using the RF antenna of  FIG. 24B . The approximate lateral locations of the antenna lines are shown at reference  2420 . The curves  2422 ,  2424 ,  2426 , and  2428  illustrate results at 500 W, 750 W, 1000 W, and 1250 W, respectively. 
       FIG. 25A  schematically illustrates an RF antenna consisting of two hairpin segments  2500  and  2502 , having a line spacing of 2.5″/3.5″/2.5″ as shown, and configured as a partially parallel-current and partially counter-current inductor. The implementation of  FIG. 25A  is similar to that of  FIG. 24A , but with a wider center spacing. 
       FIG. 25B  illustrates an overhead view of an RF antenna having segments  2510  and  2512 , in accordance with the implementation of  FIG. 25A . 
       FIG. 25C  is a graph of ion density versus lateral position for a plasma generated at 250 mT Ar using the RF antenna of  FIG. 25B . The approximate lateral locations of the antenna lines are shown at reference  2520 . The curves  2522 ,  2524 ,  2526 , and  2528  illustrate results at 500 W, 750 W, 1000 W, and 1250 W, respectively. 
       FIG. 26A  schematically illustrates an RF antenna consisting of two hairpin segments  2600  and  2602 , having an even line spacing of 3.5″/3.5″/3.5″ as shown, and configured as a partially parallel-current and partially counter-current inductor. The implementation of  FIG. 26A  is similar to that of  FIG. 25A , but with a wider even spacing. 
       FIG. 26B  illustrates an overhead view of an RF antenna having segments  2610  and  2612 , in accordance with the implementation of  FIG. 26A . 
       FIG. 26C  is a graph of ion density versus lateral position for a plasma generated at 250 mT Ar using the RF antenna of  FIG. 26B . The curves  2622 ,  2624 ,  2626 , and  2628  illustrate results at 500 W, 750 W, 1000 W, and 1250 W, respectively. 
       FIG. 27A  schematically illustrates an RF antenna consisting of several lines  2700 ,  2702 ,  2704 , and  2706 , connected in parallel, and having a line spacing of 2.5″/3.5″/2.5″ as shown, and configured as an anti-counter current array/inductor or parallel-current array/inductor. That is, when the RF antenna is powered, the current in the inductor lines runs parallel in the same direction. The implementation of  FIG. 27A  is similar to that of  FIG. 25A  in terms of line spacing, but with complete parallel current as noted. 
       FIG. 27B  illustrates an overhead view of an RF antenna having lines  2710 ,  2712 ,  2714 , and  1716 , in accordance with the implementation of  FIG. 27A . 
       FIG. 27C  is a graph of ion density versus lateral position for a plasma generated at 250 mT Ar using the RF antenna of  FIG. 27B . The approximate lateral locations of the antenna lines are shown at reference  2720 . The curves  2722 ,  2724 ,  2726 ,  2728 , and  2730  illustrate results at 500 W, 750 W, 1000 W, 1250 W, and 1500 W, respectively. 
       FIG. 28A  schematically illustrates an RF antenna having three hairpin segments  2800 ,  2802 , and  2804 , having an even line spacing of two inches as shown, and configured as a counter current inductor. 
       FIG. 28B  illustrates an overhead view of an RF antenna having hairpin segments  2810 ,  2812 , and  2814 , in accordance with the implementation of  FIG. 28A . 
       FIG. 28C  is a graph of ion density versus lateral position for a plasma generated at 250 mT Ar, 1000 W, using the RF antenna of  FIG. 28B . The curves  2820  and  2822  illustrate results at 20% and 45%, respectively. 
       FIG. 29A  schematically illustrates an RF antenna consisting of three hairpin segments  2900 ,  2902 , and  2904 , having an even spacing of two inches as shown, and configured as a partially parallel-current and partially counter-current inductor. 
       FIG. 29B  illustrates an overhead view of an RF antenna having segments  2910 ,  2912 , and  2914 , in accordance with the implementation of  FIG. 29A . 
       FIG. 29C  is a graph of ion density versus lateral position for a plasma generated at 250 mT Ar using the RF antenna of  FIG. 29B . The curves  2922 ,  2924 ,  2926 , and  2928  illustrate results at 500 W, 750 W, 1000 W, and 1250 W, respectively. 
       FIG. 30A  illustrates an overhead view of an RF antenna consisting of three hairpin segments  3010 ,  3012 , and  3014 , having an even spacing of two inches as shown, and configured as a counter-current inductor, but with an alternating reverse setup of the hairpin segments, so that adjacent hairpin segments powered/grounded from opposite sides. The implementation of  FIG. 30A  is similar to that of  FIG. 28A and 28B , except that the middle hairpin segment  3002  is powered and grounded from the opposite side when compared to the outer two hairpin segments  3002  and  3004 . 
       FIG. 30B  is a graph of ion density versus lateral position for a plasma generated at 250 mT Ar using the RF antenna of  FIG. 30A . The curves  3022  and  3024  illustrate results at 1000 W and 1500 W, respectively. 
       FIG. 31A  schematically illustrates an RF antenna consisting of two hairpin segments  3100  and  3102 , having a line spacing of 2.5″/4.5″/2.5″ as shown, and configured as a partially parallel-current and partially counter-current inductor. 
       FIG. 31B  illustrates an overhead view of an RF antenna having segments  3110  and  3112 , in accordance with the implementation of  FIG. 31A . 
       FIG. 31C  is a graph of ion density versus lateral position for a plasma generated at 250 mT Ar using the RF antenna of  FIG. 31B . The curves  3122 ,  3124 ,  3126 , and  3128  illustrate results at 500 W, 750 W, 1000 W, and 1250 W, respectively. 
       FIG. 32A  schematically illustrates an RF antenna consisting of two hairpin segments  3200  and  3202 , having a line spacing of 2.5″/4.0″/2.5″ as shown, and configured as a partially parallel-current and partially counter-current inductor. 
       FIG. 32B  illustrates an overhead view of an RF antenna having segments  3210  and  3212 , in accordance with the implementation of  FIG. 32A . 
       FIG. 32C  is a graph of ion density versus lateral position for a plasma generated at 250 mT Ar using the RF antenna of  FIG. 32B . The curves  3222 ,  3224 ,  3226 , and  3228  illustrate results at 500 W, 750 W, 1000 W, and 1250 W, respectively. 
     Table 1 below shows additional data analysis for the results illustrated at  FIG. 32C . 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 std dev 
                 range 
               
               
                 power 
                 average 
                 max 
                 std dev 
                 range 
                 (−3pts) 
                 (−3pts) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 500 
                 4.35E+11 
                 6.85E+11 
                 35% 
                 57% 
                 31% 
                 47% 
               
               
                 750 
                 6.03E+11 
                 7.67E+11 
                 25% 
                 46% 
                 17% 
                 26% 
               
               
                 1000 
                 8.46E+11 
                 9.92E+11 
                 20% 
                 39% 
                  9% 
                 15% 
               
               
                 1250 
                 1.18E+12 
                 1.33E+12 
                 20% 
                 47% 
                  7% 
                 14% 
               
               
                   
               
            
           
         
       
     
       FIG. 33  schematically illustrates an RF antenna consisting of two S-shaped (S-pin/mini-serpentine) segments  3300  and  3302 , having a line spacing of 2″/2″/3.5″/2″/2″ as shown, and configured as a partially parallel-current and partially counter-current inductor. Each of the S-pin segments is configured individually as a counter-current inductor. However, the adjacent ones of the lines of the segments  3300  and  3302  (innermost two adjacent lines) are configured for parallel current in the same direction. 
       FIG. 34  schematically illustrates an RF antenna consisting of four hairpin segments  3400 ,  3402 ,  3404 , and  3406 , and having an even line spacing of 1.5″, and configured as a partially parallel-current and partially counter-current inductor. 
     In some implementations, a controller is part of a system, which may be part of the above-described examples. Such systems can comprise semiconductor processing equipment, including a processing tool or tools, chamber or chambers, a platform or platforms for processing, and/or specific processing components (a wafer pedestal, a gas flow system, etc.). These systems may be integrated with electronics for controlling their operation before, during, and after processing of a semiconductor wafer or substrate. The electronics may be referred to as the “controller,” which may control various components or subparts of the system or systems. The controller, depending on the processing requirements and/or the type of system, may be programmed to control any of the processes disclosed herein, including the delivery of processing gases, temperature settings (e.g., heating and/or cooling), pressure settings, vacuum settings, power settings, radio frequency (RF) generator settings, RF matching circuit settings, frequency settings, flow rate settings, fluid delivery settings, positional and operation settings, wafer transfers into and out of a tool and other transfer tools and/or load locks connected to or interfaced with a specific system. 
     Broadly speaking, the controller may be defined as electronics having various integrated circuits, logic, memory, and/or software that receive instructions, issue instructions, control operation, enable cleaning operations, enable endpoint measurements, and the like. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and/or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files), defining operational parameters for carrying out a particular process on or for a semiconductor wafer or to a system. The operational parameters may, in some implementations, be part of a recipe defined by process engineers to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and/or dies of a wafer. 
     The controller, in some implementations, may be a part of or coupled to a computer that is integrated with, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may be in the “cloud” or all or a part of a fab host computer system, which can allow for remote access of the wafer processing. The computer may enable remote access to the system to monitor current progress of fabrication operations, examine a history of past fabrication operations, examine trends or performance metrics from a plurality of fabrication operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g. a server) can provide process recipes to a system over a network, which may include a local network or the Internet. The remote computer may include a user interface that enables entry or programming of parameters and/or settings, which are then communicated to the system from the remote computer. In some examples, the controller receives instructions in the form of data, which specify parameters for each of the processing steps to be performed during one or more operations. It should be understood that the parameters may be specific to the type of process to be performed and the type of tool that the controller is configured to interface with or control. Thus as described above, the controller may be distributed, such as by comprising one or more discrete controllers that are networked together and working towards a common purpose, such as the processes and controls described herein. An example of a distributed controller for such purposes would be one or more integrated circuits on a chamber in communication with one or more integrated circuits located remotely (such as at the platform level or as part of a remote computer) that combine to control a process on the chamber. 
     Without limitation, example systems may include a plasma etch chamber or module, a deposition chamber or module, a spin-rinse chamber or module, a metal plating chamber or module, a clean chamber or module, a bevel edge etch chamber or module, a physical vapor deposition (PVD) chamber or module, a chemical vapor deposition (CVD) chamber or module, an atomic layer deposition (ALD) chamber or module, an atomic layer etch (ALE) chamber or module, an ion implantation chamber or module, a track chamber or module, and any other semiconductor processing systems that may be associated or used in the fabrication and/or manufacturing of semiconductor wafers. 
     As noted above, depending on the process step or steps to be performed by the tool, the controller might communicate with one or more of other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, neighboring tools, tools located throughout a factory, a main computer, another controller, or tools used in material transport that bring containers of wafers to and from tool locations and/or load ports in a semiconductor manufacturing factory. 
       FIG. 35A  illustrates an overhead view into a process chamber  3500  showing a configuration of an RF antenna  3502 , in accordance with implementations of the disclosure. The RF antenna  3502  is disposed over a dielectric window (not shown) and is configured to inductively generate plasma in the process chamber  3500  when powered. The RF antenna  3502  includes several conductive lines that are parallel to each other and coplanar (oriented along the same plane above the dielectric window of the process chamber). These include outer conductive lines  3504   a  and  3504   b , and inner conductive lines  3506   a  and  3506   b . In the illustrated implementation current flow in the inner conductive lines  3506   a  and  3506   b  occurs in the same given direction, while current flow in the outer conductive lines  3504   a  and  3504   b  occurs in the opposite direction. 
     The conductive lines  3504   a ,  3504   b ,  3506   a , and  3506   b , are substantially straight portions of the RF antenna. As shown, the conductive lines  3504   a  and  3506   a  are connected by a connecting portion  3508   a , and the conductive lines  3504   b  and  3506   b  are connected by a connecting portion  3508   b , enabling current flow between the inner and outer conductive lines. The connecting portions function as turnarounds, so that current flow in the outer conductive lines flows in the opposite direction to current flow in the inner conductive lines. 
     The inner conductive lines  3506   a  and  3506   b  are spaced apart at a pitch spacing S 1  (center-to-center distance) of about 1 to 6 inches (about 2.5 to 15 cm) in some implementations, about 3 to 5 inches (about 7.5 to 12.5 cm) in some implementations, or about 4 inches (about 10 cm) in some implementations. 
     The adjacent outer and inner conductive lines  3504   a  and  3506   a , as well as  3504   b  and  3506   b , are spaced apart at a pitch spacing S 2  (center-to-center distance) of about 2 to 6 inches (about 5 to 15 cm) in some implementations, about 2 to 3 inches (about 5 to 7.5 cm) in some implementations, or about 2.5 inches (about 6 to 6.5 cm) in some implementations. 
     In some implementations, the inner and outer conductive lines are configured to be substantially straight throughout the region that is over the wafer&#39;s surface. That is, relative to an axis that is orthogonal through the center of the wafer surface, the conductive lines extend in a substantially straight manner to a point that is at or beyond the radius of the wafer. In the illustrated implementation, the radius R 1  of the wafer is shown, and the radius R 2  of the connecting portions  3508   a  and  3508   b  is greater than the radius R 1 . 
       FIG. 35B  illustrates a perspective cutaway view of the process chamber  3500 , in accordance with implementations of the disclosure. As shown, the RF antenna  3502  is disposed over the dielectric window  3510 . In some implementations the thickness of the dielectric window  3510  is in the range of about 0.5 to 2 inches (about 1 to 5 cm). In some implementations the distance of the RF antenna  3502  from the dielectric window  3510  is about 0 to 0.5 inch (about 0 to 1.5 cm). 
     The RF antenna  3502  receives RF power from a generator  3512  through a match  3514 , which together define an RF source for the RF antenna. As shown, in some implementations the outer conductive lines  3504   a  and  3504   b  connect to the RF source, or are positioned upstream (the RF feed side of the RF antenna) relative to the RF source, as compared to the inner conductive lines  3506   a  and  3506   b  which are positioned downstream relative to the RF source (the ground/return side of the RF antenna). In some implementations the inner conductive lines  3506   a  and  3506   b  connect to a termination cap  3516  that includes a variable capacitor and connects to ground. 
     It is further noted that as shown in the illustrated implementation, the ends of the RF antenna  3502  are raised above the plane of the conductive lines. More specifically, the ends of the RF antenna on the feed side (ref.  3518 ) serve to electrically link the outer conductive lines for connection to the same RF source. Similarly, the ends of the RF antenna on the ground/return side (ref.  3520 ) link the inner conductive lines for connection to the same termination cap. 
     In an alternative implementation, the inner conductive lines are positioned upstream and connected to the RF source, and the outer conductive lines are positioned downstream and connected to the termination cap. 
     In the illustrated implementation the upstream and downstream ends of the RF antenna  3502  are joined so as to be powered by the same RF source and grounded through the same termination cap. However, it will be appreciated that in some implementations the upstream ends of the RF antenna  3502  can be powered by separate RF sources. Further, in some implementations the downstream ends of the RF antenna  3502  can be terminated by separate termination caps. 
       FIG. 35C  illustrates a cutaway view of the process chamber  3500  along a plane perpendicular to the conductive lines of the RF antenna  3502 , in accordance with implementations of the disclosure. 
       FIG. 36A  illustrates an overhead view into a process chamber  3500  showing a configuration of an RF antenna  3600 , in accordance with implementations of the disclosure. 
       FIG. 36B  illustrates a perspective cutaway view of the process chamber  3500  including the RF antenna  3600 , in accordance with implementations of the disclosure. 
     The RF antenna  3600  has a stacked configuration of conductive lines extending over the wafer region, such that in addition to the set of conductive lines shown and described in the RF antenna  3502 , the RF antenna  3600  additionally includes a second set of parallel conductive lines that are disposed directly over the first set of conductive lines. That is, there is RF antenna  3600  includes a bottom set of coplanar parallel conductive lines, and an upper set of coplanar parallel conductive lines that are respectively aligned over the conductive lines of the bottom set as shown. 
     In the illustrated implementation the RF antenna  3600  includes an upper set of coplanar and parallel conductive lines including upper inner conductive lines  3602   a  and  3602   b , and upper outer conductive lines  3606   a  and  3606   b . The RF antenna  3600  further includes a lower set of coplanar and parallel conductive lines including upper inner conductive lines  3610   a  and  3610   b , and upper outer conductive lines  3614   a  and  3614   b.    
     The upper inner conductive line  3602   a  connects via a connecting segment  3604   a  to the upper outer conductive line  3606   a , which connects via a connecting segment  3608   a  to the lower inner conductive line  3610   a , which connects via an additional connecting segment (not shown, directly below connecting segment  3604   a ) to the lower outer conductive line  3614   a . In this manner, these lines and segments form a looped structure that substantially defines one half of the RF antenna  3600 . The other half of the RF antenna  3600  is similarly substantially defined by a similar looped structure, wherein the upper inner conductive line  3602   b  connects via a connecting segment  3604   b  to the upper outer conductive line  3606   b , which connects via a connecting segment  3608   b  to the lower inner conductive line  3610   b , which connects via an additional connecting segment (not shown, directly below connecting segment  3604   b ) to the lower outer conductive line  3614   b.    
     In some implementations the wafer has a diameter of about 12 inches (about 30 cm) or a radius R 1  of about 6 inches (about 15 cm). Accordingly, the straight conductive lines may extend to or past the diameter of the wafer, so that the turns of the RF antenna are not substantially over the wafer. In some implementations the connecting segments are configured at a diameter of about 14 inches (about 35 cm) or a radius R 2  of about 7 inches (about 17.5 cm). 
     In the illustrated implementation, the upper inner conductive lines  3602   a  and  3602   b  are connected to an RF source  3620 , and are thus at the RF feed side of the antenna structure. The lower outer conductive lines  3614   a  and  3614   b  are connected to a termination cap  3622 , and are thus at the ground/return side of the antenna structure. In the illustrated implementation the ends of the upper inner conductive lines  3602   a  and  3602   b , and the ends of the lower outer conductive lines  3614   a  and  3614   b , are turned vertically upward out of the horizontal planes of the conductive lines to provide connection points for connection to the RF source  3620  and termination cap  3622 . 
     It is recognized that in the RF antenna  3600  the looped ends (turnaround segments) may cause some transformer effect. Therefore, in some implementations, this effect can be reduced by bending the end loops up at an angle (e.g. approximately 90 degree angle). This will also reduce the end loops&#39; current induction into the chamber. Thus in some implementations, the RF antenna  3600  includes conductive lines that are connected in series by raised end loop connectors. For example, the conductive lines  3602   a ,  3606   a ,  3610   a , and  3614   a  are connected in series by connectors  3604   a ,  3608   a , and an additional connector (not shown) below connector  3604   a . The connectors can be configured as curved segments oriented along a plane that is substantially perpendicular to the horizontal plane(s) along which the conductive lines are oriented. Such connectors can define a current path, from one conductive line to another, that travels upward out of the plane of the conductive lines, and then travels downward back into the plane of the conductive lines. Similarly, the conductive lines  3602   b ,  3606   b ,  3610   b , and  3614   b  are connected in series by connectors  3604   b ,  3608   b , and an additional connector (not shown) below connector  3604   b , and the connectors can be similarly configured and define a current path as described above. 
     It will be appreciated that that such connectors and the conductive lines can be configured to maintain a predefined separation between the various lines. For example, the upper conductive lines  3602   a  and  3606   a  may extend to certain lengths (e.g. past the wafer edge) at which the raised connector  3604   a  is formed. Whereas the lower conductive lines  3610   a  and  3614   a , which are below the upper conductive lines  3602   a  and  3606   a , may extend to lengths beyond those of the conductive lines  3602   a  and  3606   a , at which the raised connector connecting the lower conductive lines is formed. In this way, a given spacing between the lines can be maintained while accommodating the raised end loop structure for both the upper and lower deck of the RF antenna. 
     In other implementations, each side of the RF antenna  3600  is independently powered, such that the upper inner conductive lines  3602   a  and  3602   b  are powered by separate RF sources. In some implementations, each side of the RF antenna  3600  is independently terminated, such that the lower outer conductive lines  3614   a  and  3614   b  are connected to separate termination caps. 
       FIG. 36D  conceptually illustrates a cross section view of a portion of the dielectric window  3510  and the RF antenna  3600 , in accordance with implementations of the disclosure. The inner conductive lines  3602   a  and  3602   b  are horizontally separated at a pitch spacing S  1  as shown, which can be the same as that described above with respect to the RF antenna  3502 . As the inner conductive lines  3602   a  and  3602   b  are vertically stacked directly over the inner conductive lines  3610   a  and  3610   b , the same pitch spacing S 1  applies to inner conductive lines  3610   a  and  3610   b . The inner conductive line  3602   a  is separated from the outer conductive line  3606   a  at a pitch spacing S 2 , which can be the same as that described above with respect to RF antenna  3502 . The same pitch spacing S 2  also applies to the separation of inner conductive line  3602   b  from outer conductive line  3606   b , as well as to the separation of inner conductive line  3610   a  from outer conductive line  3614   a , and the separation of inner conductive line  3610   b  from outer conductive line  3614   b.    
     As shown, the dielectric window  3510  has a thickness H 1 . In some implementations, the thickness H 1  is in the range of about 0.25 to 1.5 inch (about 0.6 to 3.8 cm); in some implementations, H 1  is in the range of about 0.5 to 1 inch (about 1.3 to 2.5 cm); in some implementations, H 1  is about 0.75 inch (about 2 cm). The vertical distance H 2  from the bottom of the dielectric window  3510  to the lower set of conductive lines ( 3610   a ,  3610   b ,  3614   a , and  3614   b ) in some implementations can range from about 0.5 to 2 inches (about 1 to 5 cm). In some implementations the lower set of conductive lines are vertically separated from the top of the dielectric window  3510  by a vertical distance H 3 . In some implementations, H 3  is in the range of about 0 (i.e. no separation, with conductive lines touching dielectric window) to 0.5 inch (about 0 to 1.2 cm); in some implementations, H 3  is in the range of about 0 to 0.25 inch (about 0 to 0.6 cm); in some implementations, H 3  is about 0.25 inch (about 0.6 cm). Generally, the closer the conductive lines to the dielectric window, the better the inductive coupling into the chamber, but also the greater the sputtering of the dielectric window. 
     The upper and lower conductive lines are vertically separated by a vertical distance H 4 . In some implementations, H 4  is in the range of about ⅛ to 1 inch (about 0.3 to 2.5 cm); in some implementations, H 4  is in the range of about 0.25 to 0.75 inch (about 0.6 to 2 cm); in some implementations, H 4  is about 0.5 inch (about 1.3 cm). Broadly speaking, closer vertical spacing between the conductive lines provides for greater induction but also increased risk of arcing. 
     The double stack configuration of the RF antenna  3600  provides advantages over a single level configuration (e.g. as demonstrated by RF antenna  3502 ) in terms of ease of powering the RF antenna and induction efficiency for generating plasma. For with the single level configuration of RF antenna  3502 , a high current is required to drive both sides of the RF antenna  3502 . One possible solution is to use separate generators to drive each side of the RF antenna. Another possibility is to apply power at a high frequency (e.g. about 40 MHz). However, using additional generators or applying a high frequency requires additional and/or costly hardware, increasing expense. 
     The double stack configuration of the present implementation solves these problems by increasing the inductance of the RF antenna, thus reducing the current while increasing the voltage. Power loss (e.g. through inductive heating which wastes power) in inductively coupled plasma systems is proportional to the square of the current (follows I 2 R). Thus, doubling the current, as required by the single level configuration of RF antenna  3502  which splits power into two halves, results in four times the loss. But by employing the double stack configuration of RF antenna  3600 , it is possible to raise the inductance of the RF antenna  3600 , to enable running at half the current of the single level RF antenna  3502 . This produces a four-fold reduction in power loss (reduced by 75%) for RF antenna  3600 , and provides better distribution of power and more efficient inductive coupling of power into the process chamber to generate the plasma. 
     With the single level configuration of RF antenna  3502 , the current is higher, but the voltage is lower, so the danger of capacitive coupling is reduced. However, it is desirable to achieve some capacitive coupling for purposes of plasma ignition. Thus, sufficient voltage is sought to ignite the plasma, while less voltage is sought once running to provide for more efficient inductive power coupling. The double stack configuration of RF antenna  3600  can also provide solutions to this issue because the bottom level of the RF antenna can shield high voltage from the upper level. The termination capacitance can be tuned so that there is sufficient voltage to ignite the plasma, but once running under steady state, while the upper level is at a higher voltage, the lower level is at a lower voltage. Each turn of the RF antenna is like a voltage divider, so that there may be twice as much voltage on the top versus the bottom, and this allows for the high voltage to be kept away from the dielectric window  3610 . High voltage in proximity of the dielectric window may sputter the dielectric window, and thus it is desirable to keep high voltage away from the dielectric window. 
       FIGS. 37A, 37B, 37C, and 37D  schematically illustrate various configurations of powering and terminating the RF antenna, in accordance with implementations of the disclosure.  FIG. 37A  illustrates the RF antenna  3600  being powered by a single RF source  3620 , and terminated by a single termination cap  3622 . In the illustrated implementation, the RF antenna  3600  is schematically represented as a pair of inductors that split power from the RF source  3620 , which includes a generator  3700  (e.g. oscillator) coupled to a match  3702 . On the downstream side, both inductors of the RF antenna  3600  terminate to the termination cap  3622 , which includes a variable capacitor coupled to ground. 
       FIG. 37B  illustrates the RF antenna  3600  wherein each half is powered by a separate RF source. More specifically, one coil (one inductor) of the RF antenna  3600  is powered by an RF source  3710 , including a generator  3712  coupled to a match  3714 . The other coil of the RF antenna  3600  is powered by an RF source  3716 , including a generator  3718  coupled to a match  3720 . In the illustrated implementation, both coils are connected to the same termination cap  3622 , which includes a variable capacitor coupled to ground. It will be appreciated that the separate RF sources can be individually tuned to provide a desired power distribution through the two sides of the RF antenna  3600 . 
       FIG. 37C  illustrates the RF antenna  3600  being powered by a single RF source  3620 , and terminated by separate termination caps  3720  and  3722 . Each termination cap includes a variable capacitor coupled to ground. It will be appreciated that each termination cap can be adjusted/tuned to provide for balanced distribution of voltage/current through the two inductor halves of the RF antenna  3600 . 
       FIG. 37D  illustrates the RF antenna  3600  being powered by separate RF sources  3710  and  3716 , and terminated by separate termination caps  3720  and  3722 . In this configuration, both the upstream and downstream sides of each inductor half of the RF antenna  3600  can be tuned to provide optimal power distribution. 
     It will be appreciated that the RF power applied to the antenna can be tuned to a desired state. For example, in some implementations the RF power is configured to achieve running under a balanced condition, so as to minimize capacitive coupling (thereby minimizing sputtering of the dielectric window). In such a state, the RF power is tuned so that a node (zero-voltage condition) exists at approximately halfway around the turn of the coil that is nearest the dielectric window. In the case of a single stack design as described with reference to  FIGS. 35A-35C , the RF power would be tuned so that nodes exist along the connecting portions  3508   a  and  3508   b . Whereas in the case of a double stack design as described with reference to  FIGS. 36A-36C , the RF power would be tuned so that nodes exist along the connecting segments that are below the connecting segments  3604   a  and  3604   b  (not shown, as noted above). It is noted that when capacitive coupling is minimized, plasma ignition may become more difficult. Therefore in some implementations the RF power may be tuned to permit an amount of capacitive coupling sufficient to achieve plasma ignition under desired conditions. 
     It will be appreciated that the antenna lines can be formed to have various kinds of cross-sectional shapes, in accordance with implementations of the disclosure. While various segments have been described, it will be appreciated that each half of the RF antenna  3600  can be formed from a single continuous length of conductive material that is bent/formed to have the desired antenna shape (e.g. double stacked shape having a double looped structure).  FIG. 38A  illustrates a portion of an RF antenna, such as one of the halves/sides of the RF antenna  3600 , that is formed as a continuous bent sheet/strip. In the illustrated implementation, the portions consists of a single strip of conductive material that has been bent to the desired shape, such that the cross-sectional shape is a vertically oriented (height greater than width) substantially rectangular shape. 
       FIG. 38B  illustrates a portion of an RF antenna formed as a continuous bent tube, in accordance with implementations of the disclosure. 
       FIG. 38C  illustrates a portion of an RF antenna formed from a plurality of tubular fittings, such as a plurality straight tubular fittings and a plurality of curved tubular fittings, in accordance with implementations of the disclosure. 
       FIGS. 39A, 39B, and 39C  illustrate overhead, perspective cutaway, and side cross-sectional views an RF antenna that is powered from the sides, in accordance with implementations of the disclosure. In the illustrated implementation, the RF antenna  3900  is similar in structure to the RF antenna  3502  described above, including two portions/sides/halves  3902   a  and  3902   b , with each antenna portion including inner and outer conductive lines that are parallel and oriented along the same horizontal plane, extending over the wafer and to the edges of the wafer region. However, in the RF antenna  3900 , each outer conductive line is not continuous through the middle, but actually consists of two segments that are respectively connected to the RF source and to the termination cap/ground. The outer ends of these segments are connected, via connectors, to the adjacent inner conductive line, thereby forming a loop (from RF source to termination cap). Thus, current flow from the RF source begins from the side, through a side connector to one of the segments of the outer conductive line, through a connector to the inner conductive line, through another connector to the other segment of the outer conductive line, and through another side connector to a termination cap. It will be appreciated that though each half has been described as consisting of various segments, each half of the RF antenna  3900  can be formed from a single length of conductive material, such as a tube or sheet/strip. 
     While the RF antenna  3900  as shown and described consists of a single level structure, it will be appreciated that in other implementations, the RF antenna  3900  can have a double stack structure similar to that of RF antenna  3600  described above, with each half formed as a double looped structure with upper and lower conductive lines that are directly above/below one another, while also being powered/grounded from the side. 
       FIG. 40  conceptually illustrates an overhead view of an RF antenna having curved outer conductive lines, in accordance with implementations of the disclosure. In the illustrated implementation, the RF antenna  4000  includes inner conductive lines  4002   a  and  4002   b , and outer conductive lines  4004   a  and  4004   b . The inner conductive lines  4002   a  and  4002   b  are substantially straight, while the outer conductive lines  4004   a  and  4004   b  have are substantially curved outward along the horizontal plane. In some implementations the RF antenna  4000  can have a double stack configuration including two loops that are vertically aligned. 
       FIG. 41  conceptually illustrates an overhead view of an RF antenna having curved inner and outer conductive lines, in accordance with implementations of the disclosure. In the illustrated implementation, the RF antenna  4100  includes inner conductive lines  4102   a  and  4102   b , and outer conductive lines  4104   a  and  4104   b . The inner conductive lines  4102   a  and  4102   b , as well as the outer conductive lines  4104   a  and  4104   b  have are substantially curved outward along the horizontal plane. In some implementations the RF antenna  4100  can have a double stack configuration including two loops that are vertically aligned. 
       FIG. 42  conceptually illustrates an overhead view of an RF antenna having adjustable line spacing, in accordance with implementations of the disclosure. As shown, the RF antenna  4200  includes inner conductive lines  4202   a  and  4202   b , as well as outer conductive lines  4204   a  and  4204   b . The inner and outer conductive lines are configured to be horizontally movable, so that the spacing between the lines is adjustable. In some implementations, an adjustment mechanism is provided at each end of the conductive lines to enable horizontal movement of the conductive lines. In the illustrated implementation, adjusters  4206   a  and  4206   b  are configured to enable horizontal adjustment of the conductive line  4202   a ; adjusters  4208   a  and  4208   b  are configured to enable horizontal adjustment of the conductive line  4202   b ; adjusters  4210   a  and  4210   b  are configured to enable horizontal adjustment of the conductive line  4204   a ; adjusters  4212   a  and  4212   b  are configured to enable horizontal adjustment of the conductive line  4204   b.    
     The adjusters can include movement mechanisms (e.g. electric motors, stepper motors, servos, etc.) for moving the conductive lines. Further, the adjusters can include flexible conductive materials, such as cabling or flexible fittings, to accommodate the movement of the conductive lines. This may also ensure that the RF path length of the antenna does not substantially change when the conductive lines are moved to different positions. 
     It will be appreciated that as the conductive lines are moved, so the spacing between the conductive lines changes. Thus, the spacing S 1  between the inner conductive lines  4202   a  and  4202   b  is adjustable, as is the spacing S 2  between the inner and outer conductive lines  4202   a  and  4204   a , and between the inner and outer conductive lines  4202   b  and  4204   b . In some implementations, by adjusting the layout of the conductive lines, the spacing between the inner and outer conductive lines  4202   a  and  4204   a  can differ from that between the inner and outer conductive lines  4202   b  and  4204   b . By enabling adjustment of the positioning of the conductive lines, it is possible to adjust/tune the spacing of the lines to achieve optimal plasma generation and process performance for given processes. 
       FIG. 43  is a simplified schematic diagram of a computer system for implementing implementations of the present disclosure. It should be appreciated that the methods described herein may be performed with a digital processing system, such as a conventional, general-purpose computer system. Special purpose computers, which are designed or programmed to perform only one function may be used in the alternative. The computer system  4300  includes a central processing unit (CPU)  4304 , which is coupled through bus  4310  to random access memory (RAM)  4328 , read-only memory (ROM)  4312 , and mass storage device  4314 . System controller program  4308  resides in random access memory (RAM)  4328 , but can also reside in mass storage  4314 . 
     Mass storage device  4314  represents a persistent data storage device such as a floppy disc drive or a fixed disc drive, which may be local or remote. Network interface  4330  provides connections via network  4332 , allowing communications with other devices. It should be appreciated that CPU  4304  may be embodied in a general-purpose processor, a special purpose processor, or a specially programmed logic device. Input/Output (I/O) interface  4320  provides communication with different peripherals and is connected with CPU  4304 , RAM  4328 , ROM  4312 , and mass storage device  4314 , through bus  4310 . Sample peripherals include display  4318 , keyboard  4322 , cursor control  4324 , removable media device  4334 , etc. 
     Display  4318  is configured to display the user interfaces described herein. Keyboard  4322 , cursor control (mouse)  4324 , removable media device  4334 , and other peripherals are coupled to I/O interface  4320  to communicate information in command selections to CPU  4304 . It should be appreciated that data to and from external devices may be communicated through I/O interface  4320 . The implementations can also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a wire-based or wireless network. 
     Implementations may be practiced with various computer system configurations including hand-held devices, microprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers and the like. The implementations can also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a network. 
     With the above implementations in mind, it should be understood that the implementations can employ various computer-implemented operations involving data stored in computer systems. These operations are those requiring physical manipulation of physical quantities. Any of the operations described herein that form part of the implementations are useful machine operations. The implementations also relates to a device or an apparatus for performing these operations. The apparatus may be specially constructed for the required purpose, such as a special purpose computer. When defined as a special purpose computer, the computer can also perform other processing, program execution or routines that are not part of the special purpose, while still being capable of operating for the special purpose. Alternatively, the operations may be processed by a general purpose computer selectively activated or configured by one or more computer programs stored in the computer memory, cache, or obtained over a network. When data is obtained over a network the data may be processed by other computers on the network, e.g., a cloud of computing resources. 
     One or more implementations can also be fabricated as computer readable code on a computer readable medium. The computer readable medium is any data storage device that can store data, which can be thereafter be read by a computer system. Examples of the computer readable medium include hard drives, network attached storage (NAS), read-only memory, random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes and other optical and non-optical data storage devices. The computer readable medium can include computer readable tangible medium distributed over a network-coupled computer system so that the computer readable code is stored and executed in a distributed fashion. 
     Although the method operations were described in a specific order, it should be understood that other housekeeping operations may be performed in between operations, or operations may be adjusted so that they occur at slightly different times, or may be distributed in a system which allows the occurrence of the processing operations at various intervals associated with the processing, as long as the processing of the overlay operations are performed in the desired way. 
     Accordingly, the disclosure of the example implementations is intended to be illustrative, but not limiting, of the scope of the disclosures, which are set forth in the following claims and their equivalents. Although example implementations of the disclosures have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications can be practiced within the scope of the following claims. In the following claims, elements and/or steps do not imply any particular order of operation, unless explicitly stated in the claims or implicitly required by the disclosure.