RF Measurements from Transmission Line Sensors

Abstract

Embodiments disclosed herein include a sensor, in one embodiment, that includes a board with an aperture formed therethrough, a current loop passing through the board so as to wrap around the aperture, and a voltage ring around the aperture and on an inner circumference of the current loop, the voltage ring including an inner ring, an insulating ring around the inner ring, and an outer ring around the insulating ring.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 17 / 737,682, filed May 5, 2022, the entire contents of which are incorporated herein by reference.

[0002] FIELD OF THE DISCLOSURE

[0002] Embodiments relate to the field of semiconductor manufacturing, and in particular to sensors for measuring voltages and currents within semiconductor tools. [Background technology]

[0003] In plasma processing tools, the plasma is ignited by a cathode coupled to the process gases in the chamber. In most tools, the power source is coupled to the cathode through an impedance matching network (sometimes simply called a "matcher"). The matcher allows the impedance of the system to be adjusted to match the impedance of the load to which the cathode is coupled. The load has a wide range of impedances dictated by parameters such as process conditions and chamber geometry. Impedance matching is important for efficient power transfer from the power source to the load.

[0004] RF coupled sensors are used to provide feedback to modify impedance variation devices and change the impedance of matchers. However, current sensors are not without problems. One issue is that parasitic effects are not well controlled, limiting the effective frequency of operation. In addition, sensor parasitics and port mutual coupling impair the dynamic range of the sensor due to mutual coupling. Yet another issue is that multiple sensors built on a common printed circuit board (PCB) can cause coupling between the sensors, thereby compromising the sensor measurements. Summary of the Invention

[0005] Embodiments disclosed herein include a sensor, in one embodiment, that includes a board with an aperture formed therethrough, a current loop passing through the board so as to wrap around the aperture, and a voltage ring around the aperture and on an inner circumference of the current loop, the voltage ring including an inner ring, an insulating ring around the inner ring, and an outer ring around the insulating ring.

[0006] In additional embodiments, a sensor is described. In one embodiment, the sensor includes a board having an aperture therethrough, a current loop around the aperture with an inner set of vias, an outer set of vias, and a plurality of conductive traces, each conductive trace connecting a via in the inner set to a via in the outer set, the plurality of conductive traces alternating between a top surface of the board and a bottom surface of the board, and a voltage ring on an inner periphery of the current loop, the voltage ring including an inner ring, an insulating ring around the inner ring, and an outer ring around the insulating ring.

[0007] In one embodiment, a processing tool is described that includes a power source, an impedance matching network coupled to the power source, a cathode, where the power source is configured to provide power to the cathode through the impedance matching network, a processing module communicatively coupled to the power source and the impedance matching network, and a first sensor upstream of the impedance matching network and a second sensor downstream of the impedance matching network, the first sensor and the second sensor each including a board having an aperture formed therethrough, a current loop passing through the board so as to wrap around the aperture, and a voltage ring around the aperture and on an inner circumference of the current loop, the voltage ring including an inner ring, an insulating ring around the inner ring, and an outer ring around the insulating ring. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of a plasma processing tool including a central control architecture according to an embodiment. [Figure 2A] FIG. 2 is a plan view of a current loop of a sensor according to an embodiment. [Figure 2B] FIG. 13 is a plan view of a voltage ring of a sensor according to an embodiment. [Figure 3A] FIG. 2 is a plan view of a sensor having a current loop, a voltage ring, and a guard ring according to an embodiment. [Figure 3B] FIG. 2 is a plan view of a printed circuit board having a pair of sensors according to an embodiment. [Figure 4A] FIG. 2 is a plan view of a sensor having multiple baluns coupled to a current loop according to an embodiment. [Figure 4B] FIG. 2 is a circuit diagram of a balun that may be used in a sensor, according to an embodiment. [Figure 5A] FIG. 2 is a perspective view of a sensor according to an embodiment. [Figure 5B] FIG. 13 is a perspective view of a ground plate having a cutout for a sensor according to an embodiment. [Figure 5C] FIG. 1 is a perspective view of a sensor inserted into a ground plate according to an embodiment. [Figure 6A] FIG. 13 is a plan view of a ground plate for a symmetric cathode including a cutout for a sensor, according to an embodiment. [Figure 6B] FIG. 13 is a top view of a ground plate having a sensor inserted into a cutout according to an embodiment. [Figure 7] FIG. 1 illustrates a block diagram of an exemplary computer system that may be used with a processing tool, according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The system described herein includes a sensor for measuring voltage and current in a semiconductor tool from a transmission line sensor. In the following description, numerous specific details are presented to provide a thorough understanding of the embodiments. It will be apparent to one of ordinary skill in the art that the embodiments may be practiced without these specific details. In other instances, well-known aspects have not been described in detail so as not to unnecessarily obscure the embodiments. Furthermore, it should be understood that the various embodiments illustrated in the accompanying figures are illustrative representations and are not necessarily drawn to scale.

[0010] As discussed above, existing sensor devices have limitations. Thus, impedance matching networks do not work under ideal conditions. Thus, the embodiments disclosed herein include sensors with improved performance. As used herein, a sensor may refer to a sensor capable of measuring current and / or voltage along a coaxial transmission line section. In a particular embodiment, the sensor includes an aperture through which a conductive device (e.g., an RF cable) having a concentric ring of electrically insulating material is threaded. Features on the sensor are capable of picking up the current and voltage passing along the transmission line. For example, a current loop picks up the current and a voltage ring detects the voltage. The current and voltage measurements can be used as sensor measurement feedback to direct changes in the impedance of the impedance matching network.

[0011] In certain embodiments, the sensors described herein exhibit reduced parasitic coupling between pickup elements, which allows for a larger dynamic range over a wider operating frequency range. In some embodiments, a balun is included along the current loop, which allows for increased magnetic field coupling and amplification of current loop induction. In yet another embodiment, isolation between the sensor pickup elements (for current and voltage) reduces mutual coupling between the sensor ports, which allows for a larger dynamic range over a wider operating frequency range. Some embodiments may include multiple sensors within a single printed circuit board (PCB). In such embodiments, a guard ring may be provided around each sensor to eliminate mutual coupling between concentric sensor elements. This allows for higher fidelity measurements and accuracy over a wider dynamic range, while also increasing the frequency range.

[0012] In certain embodiments, the sensors described herein are part of a plasma processing tool. Generally, the plasma processing tool includes a chamber having a cathode. A power supply architecture provides power to the cathode. For example, the power supply architecture includes one or more power supplies and an impedance matching network. The sensors described herein may be provided upstream of the impedance matching network and / or downstream of the impedance matching network. The sensors may provide feedback to a process power processing module that controls the bulk and sheath voltages of the plasma and a power supply coupled to the impedance matching network.

[0013] 1, a more detailed schematic diagram of a plasma processing tool 100 is shown, according to an embodiment. In one embodiment, the plasma processing tool 100 includes a plasma chamber 120. The plasma chamber 120 includes a cathode 122 for coupling received power to one or more gases flowing into the plasma chamber 120. In one embodiment, the plasma chamber 120 may be suitable for any plasma processing typical of a semiconductor manufacturing environment. For example, the plasma chamber 120 may be a plasma etch chamber, a plasma deposition chamber, a plasma processing chamber, etc. In certain embodiments, the plasma chamber 120 may be a plasma enhanced chemical vapor deposition (PECVD) chamber, a physical vapor deposition (PVD) chamber, or a plasma enhanced atomic layer deposition (PEALD) chamber.

[0014] In one embodiment, the plasma chamber 120 may be coupled to a power supply architecture. For example, the power supply architecture may include one or more power sources 1321-132. n In the illustrated embodiment, multiple power sources 132 are shown. However, it should be understood that in some embodiments, a single power source 132 may be used. In an embodiment, the power source 132 may include any type of power source. For example, the power source 132 may be an RF power source, a microwave power source, a direct current (DC) power source, a pulsed DC power source, or the like. A transmission line sensor with an increased dynamic range and wider operating frequency response allows for a wider corpus of plasma-driven power sources.

[0015] In one embodiment, the power supply 132 may be coupled to the cathode 122 through an impedance matching network 130. The impedance matching network 130 adjusts the impedance of the power delivery architecture to match a load in the chamber 120. Due to changes in process conditions (e.g., gas flow rates, pressure, temperature, etc.), the impedance of the load may vary. Thus, the impedance matching network 130 is used to match the varying impedance in order to efficiently and optimally (i.e., with no or minimal reflected power) deliver power to the coupled plasma in the chamber.

[0016] In one embodiment, the sensors 151 and 152 may be provided on either side of the impedance matching network 130. For example, the sensors 1511-151 n may be upstream of the impedance matching network 130 and the sensor 152 may be downstream of the impedance matching network 130. The "upstream" side refers to the input side of the impedance matching network 130 and the "downstream" side refers to the output side of the impedance matching network 130. As shown, multiple sensors 1511-151 n is provided upstream of the impedance matching network 130. The number of sensors 151 may be equal to the number of power sources 132. That is, each power source 132 has its own dedicated sensor 151. The downstream side of the impedance matching network 130 may have a single sensor 152. However, it should be understood that if there is more than one output from the matching network 130, there may be additional sensors 152. For example, if there are two outputs (e.g., for a center of the chamber 120 and an end of the chamber 120), there may be two sensors 152.

[0017] If there are multiple sensors 151, 1-nmay be fabricated on a single PCB, i.e., a single module may contain multiple sensors. A more detailed description of multiple sensor embodiments is provided below. In general, the embodiments described herein include electrical shielding techniques that limit cross-coupling between sensors on a single PCB.

[0018] In FIG. 1, sensors 151 and 152 are generally shown as blocks. However, it should be understood that sensors 151 and 152 may be similar to any of the sensor architectures described in more detail below. For example, each sensor 151 and / or 152 may be a voltage and current (i.e., V / I) sensor. Voltage may be detected by an embedded voltage ring and current may be detected by a current loop. Each sensor has an aperture through which a conductive device (e.g., an RF cable) having a concentric ring of electrically insulating material passes.

[0019] In one embodiment, the sensors 151 and 152 may be communicatively coupled to the processing module 134. As shown, a generic processing power control module 134 is provided in FIG. 1 . However, it should be understood that the processing module may be a microwave processing module 134, a DC processing module, an RF processing module, etc., depending on the type of power source 132 included in the tool 100. In one embodiment, the sensors 151 and 152 provide voltage and / or current to the processing module 134. In one embodiment, the processing power control module 134 may have external connections for various physical layers and protocols, such as standard industrial connections such as Ethernet (ENET) and EtherCAT.

[0020] In one embodiment, the processing module 134 may be coupled to the impedance matching network. The processing module 134 may be capable of sending a control signal to the impedance matching network 130. For example, the control signal may be used to adjust the capacitance of a variable capacitor in the impedance matching network 130. Furthermore, the processing module 134 may be coupled to the power source 132. Thus, the processing module 134 is capable of coordinated impedance adjustment.

[0021] 2A, a plan view of a portion of a sensor 250 is shown, according to an embodiment. In one embodiment, the sensor 250 may comprise a PCB 253. The PCB 253 may include two or more routing layers. Each routing layer may be separated from the others by a dielectric layer. In one embodiment, vias may pass through the dielectric layer to provide electrical coupling between the routing layers.

[0022] In one embodiment, the sensor 250 may include a current loop 254. The current loop 254 may include one or more conductive windings that pass through the PCB 253 and surround the aperture 260. In the particular embodiment shown in FIG. 2A, the current loop 254 includes two windings. However, it should be understood that in other embodiments, a single winding or more than two windings may be used. In one embodiment, each winding consists of a trace 257 (solid line) on the top surface of the PCB 253 and a trace 256 (dashed line) on the bottom surface of the PCB 253. The transition through the PCB 253 may be provided by vias 255. As shown, a first concentric ring of vias 255A and a second concentric ring of vias 255B are provided around the aperture 260. Each via 255 is paired with a via 255B. In some cases, the vias 255A may be referred to as outer vias and the vias 255B may be referred to as inner vias.

[0023] As shown, the windings are alternately implemented as traces 256 on the top surface of PCB 253 and as traces 257 on the bottom surface of PCB 253. Furthermore, each winding is alternated between inner via 255B and outer via 255A. Furthermore, the windings cross each other. For example, a first winding may pass along the top surface of PCB 253 as trace 256 and a second winding may pass along the bottom surface of PCB 253 as trace 257 between a first pair of vias 255A and 255B and an adjacent second pair of vias 255A and 255B.

[0024] In one embodiment, a first end of current loop 254 may be coupled to pad 2591 by trace 258. Similarly, a second end of current loop 254 may be coupled to pad 2592 by trace 258. In one embodiment, the first end of current loop 254 and the second end of current loop 254 may be provided on the same side of PCB 253. For example, in FIG. 2A , pads 2591 and 2592 are provided on the top side of PCB 253.

[0025] In the illustrated embodiment, 16 inner vias 255B and 16 outer vias 255A (32 vias 255 total) are shown. However, it should be understood that more or less vias 255 may be used according to various embodiments. In certain embodiments, there may be 24 inner vias 255B and 24 outer vias 255 (48 vias 255 total). In some cases, increasing the number of vias 255 may increase the coupling with the cable's magnetic field through the aperture 260, which may improve sensor performance.

[0026] 2B, a plan view of a portion of a sensor 250 according to an embodiment is shown. In one embodiment, the sensor 250 of FIG. 2B shows a voltage pick-up structure. For example, a recessed voltage ring 265 may be inserted into the PCB 253 surrounding the aperture 260. More specifically, it is noted that the voltage ring 265 is physically inserted into the PCB 253 and is not etched out of traditional PCB material. This creates a 3D type PCB assembly. Although shown as separate sensor 250 for clarity, it will be understood that the current loop 254 and the voltage ring 265 may be implemented on a single PCB 253. In such an embodiment, the voltage ring 265 may be provided around the aperture 260 within the inner circumference of the current loop 254.

[0027] In one embodiment, the voltage ring 265 may include a first conductive ring 266 and a second conductive ring 268. In one embodiment, an insulating ring 267 may be provided between the first conductive ring 266 and the second conductive ring 268. In a particular embodiment, the first conductive ring 266 and the second conductive ring 268 may comprise copper or another conductive material. The first conductive ring 266 and the second conductive ring 268 may be concentric rings with respect to each other. The thickness of the first conductive ring 266 and the second conductive ring 268 may be substantially equal to the thickness of the PCB 253.

[0028] In one embodiment, the first ring 266 may be used as a voltage pick-up surface. The second ring 268 may be grounded, i.e., the second ring 268 may be connected to an electrical ground. Although not shown, it will be understood that tabs connected to either the first ring 266 and / or the second ring 268 may be folded over the top and / or bottom surfaces of the insulating ring 267. In one embodiment, the recessed voltage ring 265 is concentric with an aperture 260 that penetrates the PCB 253. In one embodiment, the recessed voltage ring 265 is recessed within the aperture 260. In other embodiments, the recessed voltage ring is internally embedded within the underlying structure of the PCB 253.

[0029] 3A, a top view of a sensor 350 according to an embodiment is shown. As shown, the sensor 350 is fabricated on a PCB 353. The sensor 350 may include a current loop 354 and a voltage ring 365 within the current loop 354. The current loop 354 and the voltage ring 365 may extend through the PCB 353 and surround an aperture 360.

[0030] In one embodiment, the current loop 354 may include an inner via 355B and an outer via 355A. The vias 355 may be coupled together by a trace 356 on the top surface of the PCB 353 and by a trace 357 on the bottom surface of the PCB 353. In the illustrated embodiment, the current loop 354 includes a pair of windings around an aperture 360. In one embodiment, the current loop 354 may be substantially similar to the current loop 254 described in more detail above.

[0031] In one embodiment, the voltage ring 365 may include an inner conductive ring 366 and an outer conductive ring 368. An insulating ring 367 may be provided between the inner ring 366 and the outer ring 368. The inner ring 366 may be a voltage pick-up surface and the outer ring 368 may be grounded. In one embodiment, the inner ring 366 may define an outer periphery of the aperture 360. The voltage ring 365 may be substantially similar to the voltage ring 265 described in more detail above.

[0032] In one embodiment, the sensor 350 may further include a guard ring 370 that surrounds the outer periphery of the current loop 354. In one embodiment, the guard ring 370 may be grounded. The guard ring 370 may include vias (not shown) that connect the guard ring 370 to a similarly sized and shaped ring on the bottom side of the PCB 353. Thus, an electrical shielding barrier is provided around the pickup components of the sensor 350. This may improve sensor performance.

[0033] In one embodiment, the voltage ring 365 may be coupled to a pick-up circuit 381 on the PCB 353. The pick-up circuit 381 in FIG. 3 is shown diagrammatically as a dashed box. However, it should be understood that the pick-up circuit 381 may include features such as filters and amplifiers. In one embodiment, a pad 383 is provided. The pad 383 may be suitable for attachment of a connector (not shown) to feed back voltage information to a processing module (e.g., a processing module as described in more detail above).

[0034] In one embodiment, the current loop 354 may be coupled to a pick-up circuit 382 on the PCB 353. The pick-up circuit 382 in FIG. 3A is shown diagrammatically as a dashed box. However, it should be understood that the pick-up circuit 382 may include features such as filters and amplifiers. In one embodiment, a pad 384 is provided. The pad 384 may be suitable for attachment of a connector (not shown) to feed back the current information to a processing module (e.g., a processing module as described in more detail above).

[0035] In one embodiment, the pick-up circuit 381 is electrically isolated from the pick-up circuit 382. The two sets of pick-up circuits 381 and 382 allow for reduced mutual coupling between the two circuits. Thus, the performance of the sensor 350 can be improved. In one embodiment, the electrical isolation can be achieved by a conductive strip 385 provided between the two sets of pick-up circuits 381 and 382. In one embodiment, the conductive strip 385 can be grounded. In some embodiments, the conductive strip 385 is electrically coupled to the guard ring 370. The conductive strip 385 can be provided on the top surface of the PCB 353. In other embodiments, vias can be provided below the strip 385 to extend the electrical isolation through the thickness of the PCB 353.

[0036] 3B, a plan view of a sensor 350 according to an additional embodiment is shown. In the embodiment shown in FIG. 3B, the sensor 350 may include a pair of apertures 3601 and 3602. Each aperture 360 ​​may be surrounded by a current loop 354 and a voltage ring 365. For example, a current loop 3541 and a voltage ring 3651 are around the aperture 3601, and a current loop 3542 and a voltage ring 3652 are around the aperture 3602. Similarly, a first guard ring 3701 may be around the current loop 3541 and a second guard ring 3702 may be around the current loop 3542. Although two sets of pickup elements are shown, it will be understood that any number of apertures 360 and corresponding current loops 354, voltage rings 365, and guard rings 370 may be included on the PCB 353. The current loop 354 and the voltage ring 365 may be substantially similar to the current loop 254 and the voltage ring 265 described in more detail above.

[0037] 3B, guard ring 370 includes via 371. Via 3711 is below guard ring 3701 and via 3712 is below guard ring 3702. In one embodiment, the orientation of vias 3711 and 3712 may be rotated relative to each other. Rotating the orientation of via 371 may result in greater electrical isolation between the two sets of pickup elements.

[0038] In one embodiment, voltage ring 3651 may be coupled to pick-up circuit 3811 and pad 3831, and current loop 3541 may be coupled to pick-up circuit 3821 and pad 3841. Similarly, voltage ring 3652 may be coupled to pick-up circuit 3812 and pad 3832, and current loop 3542 may be coupled to pick-up circuit 3822 and pad 3842. Pick-up circuits 381 / 382 may be substantially similar to the pick-up circuits described in more detail above.

[0039] Conductive strips 3851 and 3852 may be provided to provide electrical isolation between various instances of pick-up circuitry 381 / 382. Conductive strip 386 may be provided to provide electrical isolation between pick-up circuits 3821 and 3812. Conductive strips 385 and 386 may be on the top surface of PCB 353. In other embodiments, vias below conductive strip 385 may extend the electrical isolation through the thickness of PCB 353. In one embodiment, conductive strips 385 and 386 may be grounded.

[0040] 4A, a plan view of a sensor 450 according to an embodiment is shown. In one embodiment, the sensor 450 may comprise a PCB 453 having an aperture 460. In one embodiment, the pickup element may include a current loop 454 and a voltage ring 465. The current loop 454 and the voltage ring 465 may be substantially similar to the current loop and voltage ring described in more detail above. In one embodiment, the sensor 450 may further comprise a guard ring 470 surrounding the outer periphery of the current loop 454.

[0041] In one embodiment, the current loop 454 may be electrically coupled to one or more baluns 475. The baluns 475 in FIG. 4 are shown installed in a notch into the guard ring 475. However, it should be understood that the baluns 475 may be provided in any convenient location on the PCB 453. In the illustrated embodiment, four baluns 475 are provided. However, it should be understood that any number of baluns 475 may be used. The presence of the baluns 475 may increase the signal-to-noise ratio and improve the performance of the sensor. In a particular embodiment, each balun 475 may double the amount of current. In one embodiment, the transformers are evenly spaced in each loop, with each transformer geometrically positioned 180 degrees opposite its pair. For example, four transformers are positioned with one pair per loop, and the pairs are 180 degrees circumferentially spaced from each other.

[0042] 4B, an electrical circuit of a balun 475 is shown, according to an embodiment. In one embodiment, the balun 475 may include a transformer-based circuit. Although a particular balun 475 architecture is shown in FIG. 4B, it should be understood that the balun 475 circuit may include any suitable structure that provides the functionality of a balun.

[0043] 5A, a top view of a sensor 550 according to an embodiment is shown. In one embodiment, the sensor 550 may include a roughly circular end 547 and a rectangular end 548. The circular end 547 may include an aperture 560 through which a cable or the like passes. In one embodiment, a current loop and a voltage ring (both not shown for simplicity) are provided around the aperture 560. In one embodiment, the rectangular end 548 may be used to support a pick-up circuit and connector.

[0044] 5B, a plan view of a ground plate 590 of a fixed cathode device is shown, according to an embodiment. As shown, the ground plate 590 may include a notch 591 that substantially matches the shape of the sensor 550. The notch 591 may have a depth that substantially matches (or is greater than) the thickness of the sensor 550. In one embodiment, the notch 591 covers an aperture 561 that extends through the ground plate 590. The aperture 561 may be a location where an electrical cable (e.g., an RF cable) passes through the ground plate 590.

[0045] 5C, a top view of the ground plate 590 after a sensor 550 has been inserted is shown, according to an embodiment. As shown, aperture 560 in the sensor 550 aligns with aperture 561 to allow the passage of a cable. The cable causes current and voltage detection by the sensor's pickup surface (e.g., current loop and voltage ring), which is fed back to the process power processing module. For example, this feedback may be used in part to control an impedance matching network or process power, which contributes to plasma density and / or plasma sheath voltage.

[0046] 6A, a plan view of a ground plate 695 for a symmetric cathode is shown, according to an embodiment. Similar to the embodiment described in Figures 5A-5C, the ground plate 695 can include a notch 691 sized to receive a sensor.

[0047] 6B, a ground plate 695 is shown after a sensor 650 has been inserted into a notch 691, according to an embodiment. As shown, an aperture 660 of the sensor 650 is positioned to receive a cable. The voltage and current of the cable may be measured by the sensor 650.

[0048] It should be understood that while two examples of sensor integration into a plasma tool are shown, the embodiments are not limited to such configurations. For example, other plasma tool architectures may require the sensor to be moved to various locations other than the ground plate. Additionally, as described in more detail above, a similar sensor architecture may be used to measure current and voltage before an impedance matching network. That is, the embodiments generally include sensors that measure current and voltage through the use of current loops and voltage rings formed concentrically around an aperture.

[0049] Referring now to FIG. 7, a block diagram of an exemplary computer system 700 of a processing tool is shown according to an embodiment. In one embodiment, the computer system 700 is coupled to the processing tool and controls processing within the processing tool. The computer system 700 may be connected (e.g., networked) to other machines in a local area network (LAN), an intranet, an extranet, or the Internet. The computer system 700 may operate in the role of a server or a client machine in a client-server network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The computer system 700 may be a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a mobile phone, a web appliance, a server, a network router, switch, or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify operations to be performed by that machine. Additionally, although only a single machine is shown as computer system 700, the term "machine" should further be interpreted to include any collection of machines (e.g., computers) that individually or in concert execute a set (or sets) of instructions to perform any one or more of the methodologies described herein.

[0050] The computer system 700 may include a computer program product, or software 722, having a non-transitory machine-readable medium having instructions stored thereon that may be used to program the computer system 700 (or other electronic devices) to perform processes according to embodiments. A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable (e.g., computer-readable) medium includes a machine (e.g., computer) readable storage medium (e.g., read-only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.), a machine (e.g., computer) readable transmission medium (in the form of electrical, optical, acoustic, or other propagated signals (e.g., infrared signals, digital signals, etc.)), etc.

[0051] In one embodiment, computer system 700 includes a system processor 702, a main memory 704 (e.g., read only memory (ROM), flash memory, dynamic random access memory (DRAM), such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM)), a static memory 706 (e.g., flash memory, static random access memory (SRAM), etc.), and a secondary memory 718 (e.g., a data storage device), which communicate with each other via a bus 730.

[0052] The system processor 702 represents one or more general-purpose processing devices, such as a microsystem processor or a central processing unit. More specifically, the system processor may be a complex instruction set computing (CISC) microsystem processor, a reduced instruction set computing (RISC) microsystem processor, a very long instruction word (VLIW) microsystem processor, a system processor that executes other instruction sets, or a system processor that executes a combination of instruction sets. The system processor 702 may also be one or more special-purpose processing devices, such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal system processor (DSP), a network system processor, etc. The system processor 702 is configured to execute processing logic 726 for performing the operations described herein.

[0053] The computer system 700 may further include a system network interface device 708 for communicating with other devices or machines. The computer system 700 may further include a video display unit 710 (e.g., a liquid crystal display (LCD), a light emitting diode display (LED), or a cathode ray tube (CRT)), an alphanumeric input device 712 (e.g., a keyboard), a cursor control device 714 (e.g., a mouse), and a signal generating device 716 (e.g., a speaker).

[0054] The secondary memory 718 may include a machine-accessible storage medium 732 (or, more specifically, a computer-readable storage medium) having stored thereon one or more sets of instructions (e.g., software 722) that embody any one or more of the methods or functions described herein. The software 722 may also reside, completely or at least partially, within the main memory 704 and / or the system processor 702 while being executed by the computer system 700, and the main memory 704 and the system processor 702 may also constitute machine-readable storage media. The software 722 may further be transmitted and received over the network 720 via the system network interface device 708. In one embodiment, the network interface device 708 may operate using RF, optical, acoustic, or inductive coupling.

[0055] Although the machine-accessible storage medium 732 is shown as a single medium in an exemplary embodiment, the term "machine-readable storage medium" should be interpreted to include a single or multiple media (e.g., a centralized or distributed database, and / or associated caches and servers) that store one or more sets of instructions. Furthermore, the term "machine-readable storage medium" should be interpreted to include any medium that is capable of storing or encoding a set of instructions for execution by a machine and causing the machine to perform any of one or more of the methods. Thus, the term "machine-readable storage medium" should be interpreted to include, but is not limited to, solid-state memories, optical media, and magnetic media.

[0056] In the foregoing specification, certain exemplary embodiments have been described. It will be apparent that various modifications may be made thereto without departing from the scope of the following claims. The specification and drawings are therefore to be regarded in an illustrative rather than a restrictive sense.

Claims

1. A sensor comprising: a board having an aperture formed therethrough; a current loop passing through the board so as to wrap around the aperture; and a voltage ring around the aperture and on an inner circumference of the current loop, An inner ring; an insulating ring around the inner ring; an outer ring around the insulating ring; Voltage ring with A sensor comprising:

2. The sensor of claim 1 , wherein the current loop comprises a first winding and a second winding.

3. The sensor of claim 1 , wherein the current loop comprises 16 or more vias through the board.

4. The sensor of claim 1 , further comprising a balun along the current loop.

5. The sensor of claim 4 further comprising a total of four baluns along the current loop.

6. The sensor of claim 1 further comprising a guard ring around the current loop.

7. 2. The sensor of claim 1, wherein a set of pick-up circuits for the current loops is electrically isolated from a set of pick-up circuits for the voltage rings.

8. The sensor of claim 7 , wherein an insulating feature between the current loop and the voltage ring is a ground via through the board.

9. 2. The sensor of claim 1, wherein the inner ring is an electric field pickup surface and the outer ring is grounded.

10. a second aperture through the board; a second current loop around the second aperture; and A second voltage ring on the outer periphery of the current loop. The sensor of claim 1 further comprising:

11. a first guard ring around the current loop; and a second guard ring around the second current loop; The sensor of claim 10 further comprising:

12. 12. The sensor of claim 11, wherein a position of a second via in the second guard ring is in a rotated position relative to a position of a first via in the first guard ring.

13. A sensor comprising: A board having an aperture therethrough; a current loop around the aperture, an inner set of vias; an outer set of vias; a plurality of conductive traces, each conductive trace connecting a via in the inner set of vias to a via in the outer set of vias, the plurality of conductive traces being arranged in alternating fashion on a top surface of the board and a bottom surface of the board; a current loop comprising: a voltage ring on the inner circumference of the current loop, An inner ring; an insulating ring around the inner ring; an outer ring around the insulating ring; Voltage ring with The sensor comprises:

14. The sensor of claim 13 , wherein the number of vias in the inner set is equal to the number of vias in the outer set.

15. The sensor of claim 13 , further comprising a plurality of baluns coupled to the current loop.

16. The sensor of claim 13 further comprising a guard ring around the current loop.

17. 14. The sensor of claim 13, wherein a set of pick-up circuits for the current loops are electrically isolated from a set of pick-up circuits for the voltage rings.

18. 1. A processing tool, comprising: power supply, an impedance matching network coupled to the power source; a cathode, the power supply configured to supply power to the cathode through the impedance matching network; a processing module communicatively coupled to the power source and the impedance matching network; and a first sensor disposed upstream of the impedance matching network and a second sensor disposed downstream of the impedance matching network, the first sensor and the second sensor each having: a board having an aperture formed therethrough; a current loop passing through the board so as to wrap around the aperture; a voltage ring around the aperture and on an inner circumference of the current loop, Inner ring, an insulating ring around the inner ring; and An outer ring around the insulating ring A voltage ring with A first sensor and a second sensor comprising: A processing tool comprising:

19. The processing tool of claim 18 , wherein the current loop comprises a first winding and a second winding.

20. The processing tool of claim 18 , further comprising a guard ring around the current loop.

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