RF Voltage and Current (VI) Sensors and Measurement Methods

Abstract

A radio frequency sensor assembly includes a sensor housing disposed about a central aperture, the sensor housing including a first conductive cover and a second conductive cover. The assembly includes a cavity disposed about the central aperture and comprising a dielectric material, the cavity being bounded by a first major outer surface and a second major outer surface in a radial direction from the center of the central aperture, wherein the first conductive cover is electrically coupled to the second conductive cover via a coupling region outside the second major outer surface of the cavity and is electrically insulated from the second conductive cover by the cavity and the central aperture. The assembly includes a current sensor electrically insulated from the sensor housing and comprising current pickups symmetrically disposed about the central aperture, the current pickups being disposed within the cavity and insulated from the sensor housing.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is related to co-pending U.S. non-provisional application No. 16 / 913,526, filed on June 26, 2020, with attorney docket number 190907US01, and U.S. non-provisional application No. 16 / 913,548, filed on June 26, 2020, with attorney docket number 190883US01, and claims priority to U.S. non-provisional application No. 16 / 913,545, filed on June 26, 2020, with attorney docket number 200391US01, which are hereby incorporated by reference into this application. Technical Field

[0003] The present invention relates generally to plasma processing systems and methods, and in particular embodiments to radio frequency (RF) voltage and current sensors and measurement methods. Background Art

[0004] In general, the need to achieve higher functionality at a reduced cost has driven the advancement of semiconductor integrated circuits (ICs). The higher functionality achieved at a lower cost is primarily provided by increasing component packing density through miniaturization. An IC is a network of electronic components (e.g., transistors, resistors, and capacitors) interconnected by a multi-level system of wires, contacts, and vias. The elements of the network are integrated together by sequentially depositing and patterning layers of dielectric material, conductive material, and semiconductor material over a semiconductor substrate using a fabrication process that includes process steps such as chemical vapor deposition (CVD), optical lithography, and etching. The packing density of circuit elements has been increased by periodically reducing the minimum feature size using innovations such as immersion lithography and multiple patterning. Further miniaturization is achieved by reducing the device footprint using three-dimensional (3D) device structures (e.g., FinFETs and stacked capacitor memory cells).

[0005] Plasma processes such as reactive ion etching (RIE), plasma enhanced CVD (PECVD), plasma enhanced atomic layer etching and deposition (PEALE and PEALD), and cyclic plasma processes (e.g., cycles of alternating deposition and etching) are routinely used in the deposition and patterning steps used in semiconductor IC fabrication. However, with the advent of feature sizes down to a few nanometers and structural features controlled at atomic scale dimensions, the challenge of providing manufacturable plasma technologies for advanced IC designs has intensified. Manufacturable plasma processes are expected to provide structures with precise dimensions (e.g., line width, etch depth, and film thickness) and precisely controlled features for plasma etching (e.g., sidewall angle, anisotropy, and selectivity to etch stop layers) and for plasma deposition (e.g., conformality, aspect ratio selectivity, and area selectivity for bottom-up patterning), as well as uniformity across the width (e.g., 300 mm) of the wafer. In many plasma processes used in IC fabrication, the plasma is maintained by RF power. Because plasma properties are affected by the RF power delivered to the processing chamber, precise control of the plasma process may require innovative, undisturbed and accurate metering of the RF signal. Summary of the Invention

[0006] According to an embodiment of the present invention, an RF sensor assembly includes a sensor housing disposed about a central aperture, the sensor housing including a first conductive cover and a second conductive cover. The assembly includes a cavity disposed about the central aperture and comprising a dielectric material, the cavity being bounded by a first major outer surface and a second major outer surface in a radial direction from the center of the central aperture, wherein the first conductive cover is electrically coupled to the second conductive cover via a coupling region outside the second major outer surface of the cavity and is electrically insulated from the second conductive cover by the cavity and the central aperture. The assembly includes a current sensor electrically insulated from the sensor housing and comprising current pickups symmetrically disposed about the central aperture, the current pickups being disposed within the cavity and insulated from the sensor housing.

[0007] According to an embodiment of the present invention, a radio frequency (RF) sensor assembly includes a sensor housing symmetrically disposed about a central aperture, the sensor housing including a first conductive cover and a second conductive cover. The assembly includes a toroidal cavity symmetrically disposed about the central aperture and comprising a first dielectric material, the cavity being bounded radially from the center of the central aperture by a first major outer surface and a second major outer surface, the first major outer surface comprising an annular continuous region in physical contact with the central aperture, and the second major outer surface comprising a closed outer boundary at a radial distance greater than a radius of the first major outer surface; and a current sensor including a current pickup coil symmetrically disposed about the central aperture, the current pickup being insulated from the sensor housing and disposed within the cavity. The assembly includes a toroidal conductive ridge interposed between the current pickup and the central aperture and electrically coupled to the second conductive cover, the conductive ridge being covered with the dielectric material.

[0008] According to an embodiment of the present invention, a plasma system includes a process chamber including an electrode; a radio frequency (RF) power supply configured to power the process chamber with an RF signal; an RF tube coupling the RF power supply to the electrode of the process chamber; a mandrel shaped like a toroidal coil, the mandrel symmetrically disposed about an axis of the RF tube that carries the RF signal; and a voltage pickup symmetrically disposed about the axis of the RF tube and surrounded by the mandrel. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0010] Figure 1A A block diagram of a general plasma processing system used in semiconductor IC fabrication is shown;

[0011] Figure 1B shows a cross-sectional view of a VI sensor for an RF tube according to an embodiment;

[0012] Figure 1C shows a top cross-sectional view of a current sensor for a VI sensor of an RF tube according to an embodiment;

[0013] Figure 2A shows a perspective view of a VI sensor for an RF tube according to an embodiment;

[0014] Figure 2B Shown Figure 2A A cross-sectional view of the VI sensor shown in FIG;

[0015] Figure 3shows a cross-sectional view of a VI sensor for an RF tube according to an embodiment;

[0016] Figure 4 shows a cross-sectional view of a VI sensor for an RF tube according to an embodiment;

[0017] Figure 5 shows a cross-sectional view of a VI sensor for an RF tube according to an embodiment;

[0018] Figure 6A shows a perspective view of a VI sensor for an RF tube according to an embodiment;

[0019] Figure 6B Shown Figure 6A A cross-sectional view of the VI sensor shown in FIG;

[0020] Figure 6C Shown Figure 6A A cross-sectional view of the VI sensor shown in FIG;

[0021] Figure 6D According to one embodiment, Figure 6A A perspective view of a current sensor element of a VI sensor shown in FIG.

[0022] Figure 7A A perspective view of a current sensor assembly for an RF tube according to an embodiment is shown;

[0023] Figure 7B Shown Figure 7A An exploded view of the current sensor assembly shown in FIG.

[0024] Figure 7C Shown Figure 7A an exploded view of a cross-sectional view of a current sensor assembly and an RF conductor for an RF tube;

[0025] Figure 7D Demonstrates that according to one embodiment Figure 7C A cross-sectional view of the current sensor assembly and the RF conductor for the RF tube shown in FIG; and

[0026] Figure 7E Shown Figure 7C A plan view of the current sensor assembly and the bottom portion of the RF conductor shown in FIG.

[0027] Figures 1A to 7E The last two digits of all three-digit reference numbers in the FIG. 1 always denote similar components. DETAILED DESCRIPTION

[0028] The making and using of embodiments of the present disclosure are discussed in detail below. However, it should be understood that the concepts disclosed herein may be embodied in a wide variety of specific situations, and that the specific embodiments discussed herein are intended to be illustrative only and not to limit the scope of the claims.

[0029] This disclosure describes sensor designs and methods for accurately measuring the voltage (V), current (I), and phase angle (Φ) between the voltage and current of radio frequency (RF) electrical signals. Embodiments of the voltage and current (VI) sensors described herein have been applied to detect the electric and magnetic fields of RF electromagnetic waves along coaxial transmission lines known as RF tubes.

[0030] Plasma processes in semiconductor fabrication (e.g., plasma etching and deposition processes) typically use RF power to maintain the plasma. As known to those skilled in the art, the RF signal that maintains the plasma in the plasma chamber affects the plasma's properties. These plasma properties (e.g., electron density, plasma sheath thickness, ion-to-radical flux ratio, etc.) in turn affect the etching and / or deposition characteristics of the plasma process.

[0031] In various embodiments, this application describes an RFV-I sensor for measuring the current and voltage of an RF signal passing through an RF tube. The term RF tube herein refers to a coaxial transmission line that carries RF power from one part of a plasma reactor (referred to as a plasma processing system) to another. The waveforms I and V transmitted through the RF tube are functions of position (x) and time (t), i.e., I(x, t) and V(x, t). When there is a single frequency component f, the current and voltage are compactly written as Re(I(x)e jωt ) and Re(V(x)e j(ωt+Φ) ) is described by a sinusoidal waveform, where ω = 2πf, j 2 = -1, and Re is the real part of the complex variable function. As mentioned above, I and V each have a magnitude and are separated from each other by a phase angle Φ. In general, waveforms I and V can include multiple frequency components. The voltage V(x, t) refers to the potential of the inner conductor (or core) of the RF tube (or coaxial transmission line) relative to the grounded outer conductor (or shield), where ground represents the reference potential of the RF system.

[0032] As described in various embodiments, an RF VI sensor can use geometric symmetry and differential measurement methods to provide V and I with high accuracy at the sensor's location. Multiple VI sensors can be used at various locations along the RF tube to detect RF signals therein. Since V and I are functions of position x, each VI sensor can be positioned as close as possible to the corresponding desired measurement location. For example, if it is desired to monitor and control a plasma process using accurate measurements of the voltage and current of the RF signal provided to the plasma chamber, the VI sensor used for this purpose can be positioned close to the location where the RF signal enters the plasma chamber. The various embodiments described herein improve the measurement accuracy and sensitivity of the VI sensor without increasing cost, thereby providing plasma processing systems with enhanced capabilities to provide plasma processes with better repeatability and tighter process control at the same cost. In addition, the RF probe is designed to be non-intrusive, allowing existing plasma processing equipment to be easily retrofitted with the improved VI sensor without requiring time-consuming and expensive redevelopment of established plasma process recipes in the production flow.

[0033] In this disclosure, reference is first made to Figure 1A The block diagram shown in FIG is used to explain the use of the VI sensor in the plasma processing system. Next, according to an embodiment, reference is made to Figure 1B The basic structure and operating principle of the VI sensor in the plasma processing system are described with reference to the schematic diagram shown in FIG. Figure 2A 、 Figure 2B 、 Figure 3 、 Figure 4 and Figure 5 The example embodiment of the VI sensor shown in FIG. 1 illustrates the VI sensor design (similar to Figure 1B Some innovative aspects of the design of the basic structure in the schematic diagram.

[0034] As referenced below Figure 1B Describe in detail, Figure 2A 、 Figure 2B 、 Figure 3 、 Figure 4 and Figure 5 The voltage sensor in the embodiment of the invention has an axisymmetric conductive ring designed to be placed inside the RF tube and arranged around a central longitudinal axis extending parallel to the direction of current flow. The advantages provided by the axisymmetric design have been discussed below with reference to Figure 2B Explained.

[0035] The corresponding current sensor in the example embodiment is located in a sleeve or gallery around the circumference of the RF tube exterior. The gallery is a cavity inside the sensor housing. The sensor housing has a conductive wall covering the gallery and can be connected to the outer conductor of the RF tube and thus to ground. Figure 1B Described in detail, the current sensor is a single conductive loop (referred to as a half loop) with two open ends; the loop is completed using a component of an external VI analyzer connected to the current sensor, for example, via a coaxial cable. The VI analyzer is a measurement system that analyzes the raw signals received from the current sensor and the voltage sensor. As further explained below, the two ends of the current sensor can be connected to the VI analyzer to perform differential measurement to obtain accurate analysis. However, in order to simplify the system at the expense of accuracy, only one of the ends of the current sensor can be connected to the VI analyzer, and the other end is terminated to ground or shorted to ground through a load impedance (e.g., through a 50 ohm load). The ground connection can be a direct connection to the sensor housing. In this configuration, the outer ground cover of the corridor is located in the circuit between the two ends of the half loop, which is very helpful in completing the loop. In an alternative RF system using an embodiment of the current sensor described in this disclosure, the entire closed loop can be contained in a corridor with appropriate impedance matching and one or more external signal connections.

[0036] In reference Figures 1B to 5 In the described exemplary embodiment, the current loop of the half-loop current sensor has a conductive turn comprising three conductive elements. The three conductive elements of the half-loop of the current sensor are two identical vertical branches connected by a horizontal branch oriented parallel to the central axis of the RF tube. Accordingly, the current sensor design discussed herein has mirror symmetry about a mirror plane normal to the central axis of the RF tube and passing midway between the two vertical branches. Figure 2B The advantages of having reflection symmetry are explained in the discussion. However, the single-turn half-loop current sensor lacks axisymmetry due to being located on one side of the RF tube. Figures 6A to 7E An axisymmetric multi-turn half-loop current sensor design is described, wherein these embodiments utilize an annular mandrel to mechanically support a multi-turn current pickup.

[0037] The innovative aspects of the VI sensor design described in the present disclosure can provide multiple advantages. For example, non-intrusive detection of the electric and magnetic fields of electromagnetic waves has been used to allow VI measurements to be performed with negligible interference on the RF signal in the RF tube. In addition, geometric symmetry and differential measurement techniques are advantageously used in the sensor design to provide measurements that may be insensitive to machining errors due to standard tolerances of the tools used to form the components, as well as positioning errors during assembly of the VI sensor. In addition, various structural enhancement techniques have been utilized; for example, elements of the VI sensor can be repetitively positioned to enhance geometric symmetry, and parts designed to provide additional mechanical support can be positioned to reduce / suppress even small deformations in the shape of critical sensor components due to mechanical stresses during assembly. Thus, by using the embodiments described in the present disclosure, RF VI measurements can be performed with improved accuracy without the increased cost of tighter machining tolerances.

[0038] Figure 1A This is a block diagram of a general plasma processing system that can be used in semiconductor IC manufacturing.

[0039] Now refer to Figure 1A In a plasma processing system, an RF signal may be generated by a high power RF power source 10 (e.g., an RF oscillator coupled to an RF power amplifier). The RF signal waveform (e.g., frequency, amplitude, pulsed / continuous, etc.) may be adjusted by a programmable controller 20 and associated electronic circuitry. The RF signal may be transmitted via a conduit (e.g., an RF tube 110) to deliver RF power to a plasma processing system coupled to a plasma processing system. Figure 1A The electrodes of the plasma are indicated inside the box of the plasma chamber 30 .

[0040] As known to those skilled in the art, the RF signal in the RF tube 110 can be represented as a combination of traveling RF electromagnetic waves. The impedance mismatch between the output impedance of the RF power source 10 and the load impedance causes a portion of the RF power traveling from the RF power source 10 toward the load to be reflected back to the RF power source 10. In order to suppress such undesirable reflections, a matcher 40 including a matching network can be inserted into the RF signal path between the RF power source 10 and the plasma chamber 30, as shown in FIG. Figure 1A The ratio of the reflected power to the incident power of the matching network can be sensed by the matcher 40 (e.g., using a VI sensor and an analyzer) and provided to the programmable controller 20. The programmable controller 20 can be controlled by using, for example, a feedback control loop (in Figure 1A The impedance of the matching network is adjusted to reduce the RF power reflected back from the matching network to the RF power supply 10 (indicated by the two arrows between the matcher 40 and the programmable controller 20).

[0041] The plasma may be maintained in the plasma chamber 30 using RF power delivered from the RF power supply 10 to the electrodes of the plasma chamber 30, for example, through the RF tube 110. Figure 1A As shown in FIG, the VI sensor 100 can be used to sense the current and voltage of an RF signal provided to an electrode. In various plasma chamber designs, the electrode can be internal to the chamber wall, such as a disk-shaped electrode in a capacitively coupled plasma (CCP) chamber, or an antenna external to the chamber wall. For example, in an inductively coupled plasma (ICP) chamber, the antenna can be a conductive planar spiral placed on a dielectric window or a conductive spiral wrapped around a dielectric cylinder. Figure 1A The block designated as plasma chamber 30 includes electrodes and antennas coupled to the plasma. For simplicity, in this disclosure, the term electrode refers to both electrodes and / or antennas. Plasma chamber 30 includes at least two electrodes, for example, a top electrode and a bottom electrode electrically coupled to the plasma located between these electrodes. In some designs, it may be advantageous for the bottom electrode to also serve as a substrate holder.

[0042] although Figure 1A The block diagram in FIG. 1 shows an RF tube 110 delivering RF power from a single RF power source 10 to the plasma chamber 30, but there may be more than one RF power source providing RF power to more than one electrode. For example, the RF power source 10 may provide RF power to an electrode (e.g., a top electrode) of the plasma chamber 30, and a second RF bias power source may supply RF bias power to another electrode (e.g., a bottom electrode) of the plasma chamber 30 using corresponding RF tubes, a matcher, and a VI sensor positioned proximate the plasma chamber to sense the voltage and current of the RF signal provided to the bottom electrode.

[0043] exist Figure 1AIn FIG, a VI sensor 100 for sensing and measuring the current and voltage of the RF signal, located near an electrode receiving the RF signal, is connected to a VI analyzer 60. The VI analyzer 60 can receive raw output waveforms reflecting V(t) and I(t) from the VI sensor 100, as indicated by the arrows. The VI analyzer 60 can be a signal processor (e.g., a digital signal processor) that can extract various RF signal characteristics from the raw waveforms. The various RF signal characteristics can include the magnitude |V|, |I|, the phase angle (Φ) between V and I, and the peak RF power |V||I|cosΦ. In addition, harmonic analysis can be performed to extract multiple frequency components. The measured RF signal characteristics can reflect plasma impedance and plasma properties, such as free electron and ion density and ion / radical flux and energy. The VI analyzer 60 can be pre-calibrated using, for example, an RF calibration signal within a certain frequency range (e.g., from about 0.4 MHz to about 1 GHz) and power range (e.g., from about 0.015 kW to about 30 kW), a standard load impedance (e.g., short circuit, open circuit, 50 ohms, etc.), and a vector network analyzer (VNA).

[0044] As in Figure 1A Various RF signal characteristics reflecting plasma properties, indicated by arrows in FIG. , can be provided by VI sensor 100 and VI analyzer 60 to programmable controller 20 and used, for example, for process monitoring or endpoint detection. Additionally, programmable controller 20 can use the received RF measurements for process control. As known to those skilled in the art, plasma properties can be modified by altering the RF signal coupled to the plasma. Programmable controller 20 can use information from the RF measurements to control the plasma process, for example, by adjusting the settings of RF power source 10 or the impedance of the matching network of matchbox 40.

[0045] In embodiments where the VI sensor 100 is used to estimate and control parameters of a plasma, it may be advantageous to position the VI sensor 100 close to the plasma chamber 30. The V and I of the RF signal at an electrode location can be estimated based on the V and I measured at a different location by the VI sensor 100 positioned there. However, the measurement errors of V and I at the electrode may increase as the distance between the electrode and the VI sensor increases. In theory, the transfer matrix used to transform the sensor signal between two locations deviates further from the identity matrix as the distance between the two locations increases. Accordingly, the V and I estimated for an electrode location become increasingly sensitive to any errors in estimating the corresponding transfer matrix.

[0046] Now refer to Figure 1BAccording to one embodiment, the VI sensor 100 is attached to an RF tube 110, which is connected to the plasma chamber 30. The RF tube 110 can be a coaxial structure including two conductive tubes (e.g., aluminum or copper tubes) concentrically placed around a shared longitudinal axis. The inner conductive tube, referred to as the inner conductor 120, can be electrically connected to the output terminal of the matcher 40 indicated by the arrow pointing to the left. The outer conductive tube, referred to as the outer conductor 130, can be a grounded sheath connected to a reference potential, typically referred to as ground. The RF tube 110 can be referred to as a main coaxial line because it carries RF power from the matcher 40 to the plasma chamber 30. Other coaxial lines in the present disclosure are referred to as coaxial signal lines (e.g., a coaxial line that can be used to carry signals from the VI sensor 100 to the VI analyzer 60).

[0047] The VI sensor 100 includes two main components: a current sensor 140 and a voltage sensor 150. The current sensor 140 may be disposed in an annular gallery 160 within a sensor housing 165 having conductive walls (e.g., aluminum, brass, stainless steel, or copper). Figure 1B In the embodiment schematically illustrated in FIG, corridor 160 is a hollow, annular region that follows the complete circumference of the outer conductor 130 and is axisymmetric about the axis of RF tube 110. The axisymmetric design of corridor 160 provides the advantage of preventing additional reflections and non-axisymmetric wave modes of RF electromagnetic waves propagating in RF tube 110. Corridor 160 and conductive sensor housing 165 can be integrally formed with RF tube 110 or symmetrically attached around RF tube 110 and positioned during assembly to help avoid misalignment between the longitudinal axis of RF tube 110 and current sensor 140. In either case, conductive sensor housing 165 and outer conductor 130 are electrically and physically connected. Accordingly, sensor housing 165 can be considered an extension of outer conductor 130 of coaxial RF tube 110.

[0048] although Figure 1B The embodiment in FIG. 1 has an annular corridor 160, but in certain other embodiments, the corridor may not be annular. In certain other embodiments, the axial symmetry of the RF tube 110 may already be unavoidably disrupted by, for example, a bend in the RF tube 110, and therefore, the additional loss of axial symmetry due to the asymmetry in the VI sensor design may not be significant. It may then be reasonable to relax the axial symmetry in the VI sensor design. For example, the corridor may partially follow the circumference of the outer conductor 130 without forming a complete loop of the RF tube 110.

[0049] refer to Figure 1B and Figure 1C, the corridor 160 is shown as being completely enclosed by the sensor housing 165 and the conductive surface of the outer conductor 130, except for the slot 132 connecting the corridor 160 to the hollow region of the RF tube 110. The current pickup 141 of the current sensor 140 is shown as being located in the corridor 160 directly above the slot 132. Figure 1B In the embodiment shown in , the current pickup 141 includes three conductive branches (called half loops) arranged as three sides of a rectangle: two vertical branches 142 and one horizontal branch 143. In one embodiment, the two vertical branches 142 are each screwed into an opening in the horizontal branch 143.

[0050] exist Figure 1B In the embodiment of FIG, the vertical and horizontal branches of the current pickup 141 are formed using three separate parts. In certain other embodiments, a different number (fewer / more) of parts may be used.

[0051] Slots 132 are designed to allow magnetic flux to penetrate into gallery 160. Current flowing in inner conductor 120 causes magnetic flux to circulate around inner conductor 120 in the region between inner and outer conductors 130, around longitudinal axis LA1. Without slots 132, the magnetic flux outside outer conductor 130 would be substantially zero because, according to Ampere's law, an equal but opposite return current flowing on the inner surface of outer conductor 130 would cancel the circulating magnetic flux generated by the current in inner conductor 120. Slots 132, by disrupting the continuity in cylindrical outer conductor 130, divert the return current to flow along the inner surface of the outer conductive body of sensor housing 165. Consequently, the hollow region of gallery 160, containing half-loop current pickup 141, falls within the region between the current flowing in inner conductor 120 and the corresponding return current. According to Ampere's law, a magnetic field now exists within gallery 160, passing through the rectangular half-loop of current pickup 141. In one example, the slot 132 may extend along the entire circumference of the cylindrical outer conductor 130 to help maximize the magnetic flux through the half loop of the current pickup 141 .

[0052] In addition to the magnetic flux, there is also an electric flux emanating from the inner conductor 120 due to the voltage difference between the inner conductor 120 and the grounded outer conductor 130. Undesirable electric flux may leak into the gallery 160 through the gap in the grounded sheath provided by the slot 132 formed in the outer conductor 130. The changing magnetic flux passing through the half loop of the current pickup 141 induces an electric signal, which is a measure of I(t) at that location. However, the electric flux entering the gallery 160 may couple with the current pickup 141 and contaminate the signal generated by the magnetic flux. Accordingly, as shown in FIG. Figure 1CAs shown in FIG, the slot 132 has been designed to have a width (dimension parallel to LA1) of about 1 mm to about 5 mm. The width of the slot 132 can be kept narrow to help reduce the electrical flux from the interior of the RF tube 110 into the gallery 160.

[0053] Although used for reference Figures 1B to 5 The slot design of the described embodiment of the VI sensor is shaped like a ring along the circumference of the outer conductor, but it should be understood that various other designs are possible. For example, a zigzag slot design has been used in reference to 7A to 7E In the current sensor assembly described.

[0054] The conductive parts of the current sensor 140 may pass through an air gap (or other insulator) and through an insulating member for mechanical support (e.g., insulating member 162 in FIG. 1 b ) (and Figures 2A to 5 ) are insulated from the outer conductor 130 and the conductive surface of the sensor housing 165.

[0055] The current pickup 141 is topologically a half-loop (a loop with two open ends) that forms one turn around a region having a rectangular cross-section (having two vertical branches 142 and one horizontal branch 143). The single-turn half-loop current pickup 141 can be positioned in the presence of a time-varying magnetic field originating from an RF electromagnetic wave traveling along the RF tube 110. According to Faraday's law, a time-varying voltage difference proportional to the time-varying magnetic flux can be induced between the two ends of the current pickup 141. The two ends of the current pickup 141 can be attached to a Figure 1B 1 and 2. A pair of symmetrical terminals 144 are shown on the sensor housing 165. In one embodiment, the terminals 144 may be coaxial cable connectors for connecting coaxial signal lines.

[0056] As explained in further detail below, it is advantageous to use a symmetrical design for the current pickup 141. Figure 1A and Figure 1B The VI analyzer 60 in FIG. 1 exploits the symmetry to cancel parasitic signals in the two vertical branches 142 by measuring, for example, the differential voltage between the two terminals 144 of the current sensor 140. For this measurement method, the differential signal from the current sensor 140 is its output signal and can be detected using, for example, a differential amplifier.

[0057] The half-loop of current pickup 141 is completed outside the VI sensor by a combination of the termination impedance, the input impedance of the primary detection system, and the impedance of the cable (if a cable is used to transmit the output signal of current sensor 140 to the primary detection system of the measurement system). If the primary detection system is located at current sensor 140 itself, the requirement to match the detector impedance to the cable impedance can be eliminated. If the measurement system is remote from current sensor 140, a coaxial signal line, such as a coaxial cable, can be used to connect terminal 144 to the primary detection system of the measurement system. The impedance of a coaxial cable typically ranges from approximately 20 ohms to approximately 300 ohms. It is advantageous to terminate the coaxial signal line with matched impedance to avoid reflections from the measurement system due to impedance mismatch. It is also advantageous to connect the two end terminals 144 of current sensor 140 to symmetrical coaxial signal lines terminated in a symmetrical manner to preserve the symmetry of the output signal of current sensor 140. For example, in one embodiment, a pair of identical 50-ohm coaxial cables with 50-ohm terminations can be used.

[0058] As mentioned above, using a differential signal as the output signal of the current sensor provides higher accuracy when measuring I. In order to detect the differential signal, it is necessary to use, for example, a pair of coaxial cables to provide the paired signals from the paired terminals 144 to the initial detection system. However, with some loss of accuracy, the current sensor can also be used in conjunction with a measurement system that detects the signal at one of the paired terminals 144. In a system that detects the signal at the first terminal in the paired terminals 144 (rather than detecting the differential signal), the second terminal in the paired terminals 144 can be connected to an impedance that reflects the impedance at the first terminal as closely as possible. For example, the first terminal can be connected to a first 50-ohm coaxial cable to transmit the signal to the 50-ohm input port of the initial detection system, and the second terminal can be connected to a second identical 50-ohm coaxial cable with a 50-ohm termination at the end of the cable instead of a detector. It should be noted that some other appropriate impedance can be used for the termination; the impedance does not need to be 50 ohms. In addition, the second coaxial cable can be omitted and the termination of the appropriate impedance can be directly fixed to the second terminal in the paired terminals 144.

[0059] The design of the measurement system including the elements for connecting the current sensor 140 also takes into account the impedance to ground due to the parasitic capacitance of the electronic components. Due to the frequency dependence of the parasitic capacitance impedance, the impedance of the component at RF frequencies may be significantly different from the impedance of the component at low frequencies or at DC (zero frequency). For example, due to the parasitic capacitance to ground associated with the resistor structure, the impedance of the resistor component at DC may decrease as the frequency of the electrical signal increases to the RF range. The impedance of resistors with higher resistance values is more sensitive to the frequency of the RF signal. Since the parasitic capacitance to ground depends on the geometric structure and the geometric environment in which the resistor is placed, it is difficult to control the impedance variation from unit to unit if the resistor has a high resistance value. Therefore, in order to maintain measurement accuracy, it is advantageous to limit the design of the initial detection system to using resistors with a resistance value less than 0.1 of their parasitic RF reactance even when the initial detection system is placed at the sensor location.

[0060] The voltage pickup 151 of the voltage sensor 150 includes a conductive ring that can be placed along the inner surface of the outer conductor 130. The outer conductor 130 and the conductive voltage pickup 151 can be insulated from each other by an insulating ring 152, as shown in FIG. Figure 1B . Insulating ring 152 may comprise Teflon, some other plastic material, or some other suitable dielectric. In one embodiment, voltage pickup 151, such as a conductive ring, may be exposed to the air (or other insulator) between inner conductor 120 and outer conductor 130. In another embodiment, voltage pickup 151 may be embedded in an insulating housing. In all embodiments, voltage pickup 151 (e.g., a conductive ring) may be electrically insulated from outer conductor 130 and mechanically supported by an insulating structure.

[0061] In one embodiment, the inner diameter of the voltage pickup 151 (e.g., a conductive ring) can be the same as the inner diameter of the outer conductor 130. In certain other embodiments, the inner diameter of the voltage pickup 151 (e.g., a conductive ring) can be different (smaller or larger than the inner diameter of the outer conductor 130). When the inner diameter of the voltage pickup 151 (e.g., a conductive ring) is equal to the inner diameter of the outer conductor 130, the perturbation of the electric and magnetic fields in the RF tube 110 caused by the insertion of the voltage pickup 151 is relatively minimal. The output signal from the voltage pickup 151 increases as the inner diameter of the voltage pickup 151 (e.g., a conductive ring) decreases, as explained in further detail below. The contact to the voltage pickup 151 extends outside the outer conductor 130 and terminates at a third terminal 153 (e.g., a third coaxial cable connector) attached to the sensor housing 165. The current pickup 141 , the voltage pickup 151 , and the contacts to the respective terminals 144 and 153 may comprise a metal with high conductivity (eg, copper) and may all be insulated from other conductive elements such as the outer conductor 130 and the conductive sensor housing 165 .

[0062] Considerations for the termination impedance and design of the coaxial signal line connecting the initial detection system to the terminal 153 of the voltage sensor 150 can be similar to the considerations for the termination impedance and design of the coaxial signal line connecting the initial detection system to the terminal 144 of the current sensor 140, as discussed above. The discussion above with reference to the current sensor 140 includes considerations for preserving the symmetry of the differential output signal. However, this portion of the discussion does not apply to the voltage sensor because, in the embodiment of the VI sensor 100, the voltage sensor 150 has only one ring-shaped voltage pickup 151 and one terminal 153, while the current sensor 140 has a pair of terminals 144. Symmetry considerations may be applicable in another embodiment in which the two voltage pickup rings are symmetrically placed and may, for example, be positioned in reference to the voltage sensor 150. Figure 3 In the described VI sensor 300 , the arithmetic mean of the two signals is used.

[0063] As in Figure 1B and Figure 1C As shown in FIG, the longitudinal axis LA1 of the RF tube 110 is in the plane P1 of the current pickup 141. The longitudinal axis LA1 is also parallel to the direction of the current in the RF tube 110. In addition, as shown in FIG. Figure 1CAs can be more easily seen in FIG, along a direction orthogonal to the longitudinal axis LA1 of the RF tube 110, the current pickup 141 includes: a first mirror symmetry plane M1, which includes the longitudinal axis LA1 of the RF tube 110; and a second mirror symmetry plane M2, which is orthogonal to the first mirror symmetry plane M1. In one or more embodiments, the first mirror symmetry plane M1 of the current pickup 141 is coplanar with the longitudinal axis LA1 of the RF tube 110.

[0064] The magnetic field lines are approximately concentric about the longitudinal axis LA1 and pass vertically through the plane P1 of the half loop. In this configuration, the magnetic field is inductively coupled to the current pickup 141 (as desired). Undesired coupling with the electric field is greatly reduced by positioning the current pickup 141 outside the outer conductor 130. The inductively coupled oscillating magnetic field induces an electromotive force (emf) in the current pickup 141 (three-sided half loop). According to Faraday's law, the induced emf is related to the changing magnetic flux. Since the strength of the magnetic field around a conductor carrying a current reflects the corresponding current, the current sensor 140 can generate a time-varying electrical signal that reflects the RF current at the corresponding position in the RF tube 110. One aspect of the current sensor 140 is that the electrical signals at the two terminals 144 can be received by a detection system and the differential voltage between the two terminals 144 is used as the output signal of the current sensor 140. Reference is made below to Figure 2B The advantages provided by the differential output technology are explained in further detail.

[0065] The potential and electric field magnitude profile is roughly a circle centered on the longitudinal axis LA1 of the RF tube 110. The circular profile is contained within a series of planes normal to the longitudinal axis LA1. Therefore, electric field lines are directed radially from the inner conductor 120 perpendicular to the longitudinal axis LA1. The annular voltage pickup 151 is located approximately on one of the circular profiles. With this configuration, the oscillating electric field in the space outside the inner conductor 120 capacitively couples to the voltage pickup 151. According to the physical laws of electromagnetism, the conductive ring acquires an oscillating potential that is roughly proportional to the potential of the inner conductor at the corresponding location. This oscillating potential can be used as the output signal of the voltage sensor 150. According to Gauss's law, the magnitude of the radial electric field between the inner conductor 120 and the outer conductor 130 decreases with increasing radial distance from the longitudinal axis LA1. Accordingly, the output signal of the voltage sensor 150 can be increased by, for example, positioning the voltage pickup 151 of the voltage sensor closer to the inner conductor 120 by reducing the inner diameter of the voltage pickup ring.

[0066] Although the voltage pickup 151 is capacitively coupled to the electric field, there is almost no coupling to the magnetic field because the magnetic flux normal to the plane of the annular voltage pickup 151 is negligible for this geometry. Since the strength of the electric field around the conductive tube (in this example, the inner conductor 120) reflects the potential of the conductor, the voltage sensor 150 can generate a time-varying electrical signal that reflects the RF voltage at the corresponding position on the RF tube 110.

[0067] The raw output signals (eg, one pair from current sensor 140 and another pair from voltage sensor 150) may be transmitted to VI analyzer 60 as indicated by the arrows (see also Figure 1A ).

[0068] Figure 2A A perspective view of the VI sensor 200 and the outer conductor 230 (outer tube) of the RF tube is shown. Figure 2B A cross-sectional view of the same VI sensor 200 along axis 2B- 2B′ is shown. Figure 2A and Figure 2B The VI sensor 200 in is similar to Figure 1B The VI sensor 100 in FIG. The current sensor 240 and the voltage sensor 250 are placed in the annular corridor 260 of the VI sensor 200. Figure 2A and Figure 2B In FIG, the inner conductor of the RF tube has been removed to better show the voltage pickup ring 251 of the voltage sensor 250 inside the outer conductor 230. Figure 2A ) shows three terminals (coaxial cable connectors in this example) of the VI sensor 200. The paired terminals 244 extending above the top of the corridor 260 are connected to the current pickup 241 of the current sensor 240, as shown in FIG. Figure 2B The third terminal 253 is connected to the voltage pickup 251 of the voltage sensor 250 .

[0069] refer to Figure 2B , the current pickup 241 of the current sensor 240 is a half loop comprising three conductors. The two conductive vertical branches 242 of the current pickup 241 are insulated from the metal sensor housing 265 by plastic (or other insulating material). The vertical branches 242 are connected to the two ends of the horizontal branch 243, which is a third conductor arranged horizontally inside the gallery 260 above the outer conductor 230. The slits 232 along the circumference of the outer conductor 230 allow the magnetic field to pass through the plane of the half loop and induce an electromotive force in the conductive branches of the current pickup 241. The horizontal branches 243 of the current pickup 241 can be attached to a horizontal non-conductive (e.g., plastic) part 262 along the side of the conductor. In Figure 2A and Figure 2BIn the example embodiment of VI sensor 200 shown in FIG, horizontal branch 243 is insulated from grounded metal sensor housing 265 and outer conductor 230 by plastic parts 262 on the sides and by the air in the gap between the bottom of horizontal branch 243 and the top of outer conductor 230. In another embodiment described in further detail below, the mechanical support for horizontal branch 243 can be enhanced by additional plastic parts placed in the air gap below the horizontal conductor.

[0070] Current pickup (e.g. Figure 2B The current pickup 240 in the VI sensor 200 provides an electrical signal through its interaction with the RF electromagnetic field. As explained above, the magnetic field (not the electric field) reflects the RF current. The slot 232 allows the magnetic field to penetrate from the RF tube into the gallery 260 where the current pickup 241 is located. Any coupling of the current pickup 241 with the electric field will degrade the measurement accuracy of the magnetic field. The current sensor 240 can suppress measurement errors that may be caused by undesirable interactions with the electric field, as explained herein. First, the current sensor 240 in the VI sensor 200 is placed outside the grounded outer conductor 230, thereby using the outer conductor 230 to shield the electric field. As described above with reference to Figure 1B and Figure 1CAs mentioned, the RF electric field is in the radial direction (perpendicular to the coaxial axis LA1 of the RF tube), and accordingly, the electric flux leaking into the gallery is approximately proportional to the slot width, defined above as the dimension parallel to LA1. The width of slot 232 can be selected to be relatively small to reduce the amount of electric flux entering gallery 260 due to the gap formed by slot 232 in outer conductor 230. Furthermore, a differential signal can be used as the output signal to further reduce the impact of the portion of the electric field that may penetrate into the cavity regardless of outer conductor 230. Ideally, according to electromagnetic theory, the differential voltage between the two terminals 244 of the current sensor is approximately proportional to the oscillating magnetic field. However, due to the presence of slot 232, the weak electric field within gallery 260 can capacitively couple to current pickup 241. However, current pickup 241, slot 232, and gallery 260 can be configured to be mirror-symmetric about a plane passing through the center of slot 232 and oriented perpendicular to the longitudinal axis of the RF tube. Due to the aforementioned geometric mirror symmetry of half-loop current pickup 241, perturbations along vertical branch 242 are approximately equal in magnitude and phase to the perturbations to the potentials appearing at the two terminals 244. This symmetry can be advantageously exploited because it means that the differential signal is unaffected by parasitic signals induced in current pickup 241 by interaction with the penetrating electric field in gallery 260. In other words, the potential difference between the first and second terminals of the paired terminals 244 remains undisturbed and correct to first order. These aspects of the current sensor 240 design can advantageously enable current measurements with high accuracy, particularly in applications such as providing an RF bias signal to an electrostatic substrate holder in a plasma chamber, where the load impedance can be such that the amplitude of the electric field is relatively high and the amplitude of the magnetic field is relatively low near the point where the RF signal enters the plasma chamber.

[0071] Still refer to Figure 2B The ring-shaped conductor placed inside the outer conductor 230 near its inner surface is the voltage pickup 251 of the voltage sensor 250. The strength of the signal generated by the voltage pickup 251 can depend on its size. While the diameter can be roughly determined by the diameter of the outer conductor 230, the width and thickness are adjustable design parameters. In this embodiment, the conductive voltage pickup 251 is a ring that is electrically connected at one point to the third terminal 253 of the VI sensor 200 (e.g., a coaxial cable connector). The conductive voltage pickup 251 is insulated from the conductive outer conductor 230 by a ring-shaped dielectric member 252 attached to the voltage pickup 251.

[0072] As explained above, the voltage pickup 251 provides an electrical signal at the third terminal 253 of the VI sensor 200 due to the charge polarization induced by the RF electromagnetic field. The potential at the third terminal 253 reflects the potential of the inner conductor (not shown for clarity). Figure 2B The RF electric field is capacitively coupled to the voltage pickup 251. However, the interaction with the magnetic field is negligible because the longitudinal axis is normal to the plane of the ring, as described above with reference to Figure 1B Explained.

[0073] The ring-shaped design of the voltage pickup 251 uses axial symmetry to reduce the sensitivity of the output of the voltage sensor 250 to some errors in placement and size errors, as explained herein. First, the circular symmetry can eliminate the need for precise placement of the voltage pickup 251 because, to a first order, the potential at the conductive surface of the ring is independent of the center position of the ring from the central axis ( Figure 2A Axis 2B-2B' and Figure 1B LA1 in the circuit). In contrast, the potential of voltage pickup 251 depends primarily on the dimensions of the ring (e.g., inner diameter, outer diameter, and thickness). In contrast, in an asymmetric voltage pickup design, the voltage pickup conductor will acquire a potential that depends, to a first order, on the size and placement of the asymmetric voltage pickup. For example, a mushroom-shaped voltage pickup may be sensitive not only to the size of the conductive surface at the mushroom head but also to its position relative to the inner conductor. In such a design, the distance between the voltage pickup and the longitudinal axis of the RF tube may have to be precisely adjusted during assembly, sometimes manually using a micrometer screw. Furthermore, the design of voltage pickup 251 can substantially offset any centering errors during assembly of voltage sensor 250 into VI sensor 200. The axial symmetry of voltage pickup 251 ensures that, to a first order, the total electric flux remains constant even if the center of voltage pickup 251 is slightly displaced from the longitudinal axis of the inner conductor. The increase in electric flux in the half of the ring that may be displaced closer to the inner conductor is balanced by a concomitant decrease in electric flux in the other half of the conductive ring that will now be further from the longitudinal axis due to the circular geometry of the ring.

[0074] Figure 3 A cross-sectional view of another embodiment of a VI sensor 300 is shown having a current sensor 340 located in a corridor 360 inside a sensor housing 365. A horizontal branch 343 is shown supported by an insulating part 362 and connected to two vertical branches 342 of the current sensor 340. A slot 332 running in a mirror symmetry plane M2 is shown above the horizontal branch 343.

[0075] Similar to reference Figure 2A and Figure 2BIn the depicted VI sensor 200, a first voltage sensor 350 is shown inside the outer conductor 330. Additionally, the VI sensor 300 has a second voltage sensor 355 symmetrically located on the opposite side of the current sensor 340. In this embodiment, the voltage pickups and housings of the first and second voltage sensors 350 and 355 are recessed into the body of the outer conductor 330 to maintain the inner surface of the outer conductor 330 as smooth as possible. The smooth inner surface of the outer conductor 330 provides the advantage of reducing disturbances to the electromagnetic field caused by the insertion of the voltage sensors 350 and 355. In this embodiment, the VI sensor 300 causes negligible disturbances to the electromagnetic field in the RF tube.

[0076] The measurements from first voltage sensor 350 and current sensor 340 have relative phase errors due to the difference in measurement locations between these sensors. In this embodiment, the oppositely positioned second voltage sensor 355 has opposite phase errors due to this symmetrical location relative to current sensor 340 (i.e., the mirror-image symmetry plane M2 of current sensor 340 is equidistant from first voltage sensor 350 and second voltage sensor 355). Due to symmetry, the relative phase error between the voltage and current in the RF signal waveform sensed by first voltage sensor 350 and the corresponding error in the RF signal waveform sensed by second voltage sensor 355 cancel out, at least to a first order, in the sum of the two sensed voltage signals. Accordingly, a more accurate voltage measurement can be provided by combining the signal from first voltage sensor 350 with the signal from second voltage sensor 355. By using, for example, the arithmetic mean of the measurements from first voltage sensor 350 and second voltage sensor 355, the phase error can be reduced or even eliminated to produce a voltage measurement that reflects the voltage at the mirror-image symmetry plane.

[0077] Additionally, the presence of the second voltage sensor 355 helps ensure that the two vertical branches 342 and the left and right halves of the horizontal branch 343 of the current pickup 341 experience the same electric and magnetic fields. As explained above, parasitic electrical signals may be generated by the current pickup undesirably coupling to the electric field in the cavity penetrating into the gallery 360. By improving the geometric symmetry, the second voltage sensor 351 helps ensure that perturbations in the potential shown at the first and second terminals 344 of the current sensor 340 are more accurately canceled by using differential current measurements, as described above with reference to FIG. Figure 2A and Figure 2B In some embodiments, using the output of the second voltage sensor 355 may be optional.

[0078] Figure 4Yet another embodiment of a VI sensor 400 is shown attached to an RF tube 410 comprising an inner conductor 420 and an outer conductor 430 .

[0079] Similar to reference Figure 2A and Figure 2B As described above, the VI sensor 400 includes a current sensor 440 and a voltage sensor 450 placed in a corridor 460. The design of the VI sensor 400 has been modified relative to the design of the VI sensor 200 (see FIG. 1 ) by providing additional mechanical support to the horizontal conductor 443 of the current pickup 441 of the current sensor 440. Figure 2A and Figure 2B ) has been improved.

[0080] exist Figure 4 In the design of the VI sensor 400 shown in FIG. 1 , the support components (e.g., plastic parts 462 and 470) are connected to the Figure 2B 462 and 470 can more securely secure the horizontal branches 443 than the corresponding parts (e.g., plastic parts 262) in the VI sensor 200 shown in FIG. For example, in one embodiment, the plastic parts 262 at both ends of the horizontal branches 243 in the VI sensor 200 are rings with a set of holes in which the horizontal branches 243 can be placed, while in the design of the VI sensor 400, plastic parts such as parts 462 and 470 contain more horizontal branches 443 and can have bosses that fit tightly into matching cavities in the metal sensor housing 465 and the metal outer surface of the outer conductor 430.

[0081] As in Figure 4 As shown in FIG, a support structure 470 (e.g., made of plastic or other non-conductive material) placed in addition to the insulating support 462 holds the conductive horizontal branch 443 of the current pickup 441 from all sides. The support structure 470 includes a first portion for supporting the first portion of the horizontal branch and a second portion for supporting the second portion of the horizontal branch, separated by a gap. In contrast, as in FIG Figure 2B As shown in FIG, the plastic part 262 (similar to the support 462) does not support the horizontal branch from below. Figure 2BIn FIG. 4 , an overhead space exists between the horizontal branch 243 of the current pickup 241 of the current sensor 240 and the outer conductor 230. When the vertical branch 442 of the current pickup 441 is placed in contact with the horizontal branch 443, the additional support prevents the horizontal conductor 443 from bending. Furthermore, the support structure 470 can prevent the vertical branch 442 from being overtightened to the horizontal branch 443. Variations in the magnetic flux coupled to the current pickup 441 are affected by variations in the shape and area of the half-loop geometry of the current pickup 441. Therefore, stabilizing the shape of the current pickup 441 reduces variations in the electrical output of the current sensor 440 and improves the accuracy of the current measurement.

[0082] Figure 5 VI sensor 500 is shown attached to RF tube 510 including inner conductor 520 and outer conductor 530. Current sensor 540 is shown having a pair of terminals 544 disposed above sensor housing 565 and a single-turn half-loop current pickup 541 disposed inside gallery 560. Current pickup 541 includes two vertical branches 542 attached to horizontal branches 543. Similar to Figure 4 In the VI sensor 400 , the plastic part 570 has been used to prevent over-tightening of the vertical branch 542 and bending of the horizontal branch 543 of the current pickup 541 during assembly of the current sensor 540 .

[0083] The VI sensor 500 includes improvements that reduce machining complexity, thereby providing a more precise and precise measurement compared to the VI sensor 400 (in FIG. Figure 4 By using the voltage sensor 550 (wherein the insulator piece 555 that centers the inner conductor 520 of the RF tube 510 is also used to support the conductive voltage pickup ring of the voltage sensor 550), the design of the VI sensor 500 is improved compared to the design of the VI sensor 400, as shown in Figure 5 Using the same plastic part 555 for multiple purposes allows eliminating some of the plastic parts used in, for example, the VI sensor 400. This reduces the machining complexity and manufacturing cost of the VI sensor 500.

[0084] Figure 5 The conductive voltage pickup ring of the voltage sensor 550 in FIG. 5 has been positioned closer to the inner conductor 520 by designing the diameter of the voltage pickup ring to be smaller than the diameter of the outer conductor 530. The smaller diameter of the voltage pickup ring improves the output signal strength of the voltage sensor 550, as described above with reference to FIG. Figure 1B and Figure 1C Explained.

[0085] Although the single-turn half-loop current pickup has been used in the above reference figures 1 to Figure 5The VI sensor described herein is shown in FIG. 1 , but it should be understood that multiple turns can also be used in the design of the current pickup of the current sensor. Figure 5 The current pickup in the VI sensor shown in FIG can include a plurality of rectangular turns between two ends of the current pickup connected to two terminals of the current sensor. As mentioned above, the multi-turn current pickup can also be constructed by winding the conductive wire on a core shaft (e.g., a toroidal core shaft). The conductive wire can be wound in the form of a coil on a circular shaft of donut-shaped insulating material, which is symmetrically coiled around the inner conductor of the RF tube that passes vertically through the center hole of the toroidal coil. Figures 6A to 7E A multi-turn current pickup using a toroidal mandrel is described.

[0086] It should be understood that the mandrel may not exactly conform to the mathematical definition of a toroid, but it will generally resemble a toroid with structures for attaching the coil, making connections to terminals, and the like.

[0087] Figure 6A A perspective view of a VI sensor 600 is shown, Figure 6B shows a cross-sectional view, and Figure 6C A cross-sectional view along axis AA′ of the VI sensor 600 is shown.

[0088] Figure 6A The conductive sensor housing 665 of the VI sensor 600 is shown. Figure 6A The current and voltage pickups, which are not visible in FIG, are housed within the space enclosed by the conductive sensor housing 665. Figures 6A to 6C In the embodiment, the inner conductor will pass through the center hole 621. For clarity purposes Figures 6A to 6C The various views of the VI sensor 600 in FIG. 6 omit the inner conductor itself. The outer conductor of the RF tube will be connected to flanges at the top and bottom of the conductive sensor housing 665. The two neck regions 631 are shown with Figure 6A The flanges at the top and bottom portions of the sensor housing 665 are adjacent. The shape and size of the neck region 631 can be designed to be similar to the shape and size of the outer conductor of the RF tube. Therefore, the sensor housing 665 can be interpreted as an extension of the outer conductor that extends from the neck region 631 into a wider central portion including a top cover 663 and a bottom cover 666 having a conductive wall with a larger diameter. The sensor housing 665 and the outer conductor form an outer shield of the coaxial structure and can be connected to ground. As described below with reference Figure 6B and Figure 6C As depicted, the wider central portion of the sensor housing 665 houses an annular dielectric cavity 661 around the inner conductor passing through the central aperture 621 .

[0089] Figure 6AThe perspective view in FIG also shows three coaxial cable connectors assembled on the outside of sensor housing 665. The three coaxial cable connectors are the three terminals of VI sensor 600. The outer pair of coaxial connectors 645 connect to the terminals of current sensor 641, which are connected to the current pickup, and the middle coaxial connector connects to the center terminal 654, which is connected to the voltage pickup 651 of the voltage sensor. The current and voltage pickups are located between the top cover 663 and the bottom cover 666.

[0090] Figure 6B The cross-sectional view and Figure 6C Along the cutting plane A-A' (in Figure 6A The cross-sectional view of FIG. 6 (shown in FIG. 6 ) shows the internal structure of the VI sensor 600. The inner conductor of the RF tube is omitted for clarity. Figure 6B and Figure 6C The inner surface 638 of the central bore 621 shown within the neck region 631 in FIG. 1 forms the sidewall of what may be interpreted as the interior of the main coaxial structure of the RF tube. The neck region 631 expands into the wider diameter top cover 663 and wider diameter bottom cover 666 of the sensor housing 665, thereby enclosing the dielectric cavity 661 in the section surrounding the central bore 621 of the VI sensor assembly 600. The inner wall 638 continues as the surface 627 of the top cover 663 and bottom cover 666 until it is interrupted by a slit 671. As shown in FIG. Figure 6C As shown in FIG, dielectric cavity 661 is between first major outer surface 627 and second major outer surface 628 along a radial direction from the center of central hole 621. First major outer surface 627 includes a continuous annular region in physical contact with central hole 621. Vertically, annular first major outer surface 627 is divided into two portions by a slit region 671. Second major outer surface 628 is located at a radial distance greater than the radius of first major outer surface 627.

[0091] Cavity 661 includes a slit region 671. As in Figure 6B and Figure 6C As shown in FIG, the slot region 671 comprises a physical break in the inner surface 627 of the cylindrical wall of the central bore 621 that forms a gap in the joint between the top cover 663 and the bottom cover 666 of the sensor housing 665. The surface 627 is an extension of the surface 638 of the cylindrical wall of the central bore 621. When viewed radially from the center of the central bore 621, the slot region 671 has the appearance of an insulating ring in physical contact with the central bore 621. Further radially outward, the slot region 671 takes on a tortuous shape that circumvents the annular conductive voltage pickup 651, as indicated by Figure 6B and Figure 6CThe continuous insulating annular region of the cavity 661 radially disposed between the physical contact portion with the central hole 621 and the inner radius of the annular current sensor 641 is referred to as the slit region 671 of the VI sensor 600. Figure 6B and Figure 6C As shown in FIG, the slot region 671 forms a dielectric barrier interposed between the conductive voltage pickup 651 and the current sensor 641 and the sensor housing 665. In the region radially between the first major outer surface 627 and the second major outer surface 628, the cavity 661 (including the insulating slot region 671) electrically isolates the top cover 663 from the bottom cover 666. For radial distances less than the first major outer surface 627, the top cover 663 is electrically isolated from the bottom cover 666 by the central hole 621. The top cover 663 is electrically coupled to the bottom cover 666 via a coupling region 629 radially outside the second major outer surface 628 of the dielectric cavity 661.

[0092] With this design, almost none of the RF current flowing in the grounded sensor housing 665 can flow in the region surrounded by the ring-shaped current sensor 641. The current will flow vertically in the neck region 631 along the inner wall 638 and then detour around the current sensor 641 due to the physical break in the inner surface 638 formed by the dielectric slit 671. Due to the slit 671, the current will turn radially outward around the ring-shaped current sensor 641, flowing laterally along the conductive wall of the annular dielectric cavity 661, returning radially, and then continuing vertically along the inner wall 638 of the neck region 631.

[0093] refer to Figure 6B and Figure 6C , the current sensor 641 is an annular structure inside the annular dielectric cavity 661 in the outer portion of the cavity (i.e., the area farther from the central hole 621). The current sensor 641 includes a conductive coil 647 and an annular core 642. The coil 647 includes multiple turns of continuous conductive wire wrapped around the central circular axis of the annular core 642. The two opposite ends of the coil 647 can be attached to the coaxial connector 645, as shown in Figure 6B The conductive wire of coil 647 can be a bare conductor, an enameled conductor or a conductor coated with an insulator. Figure 6D The annular core shaft 642 is described in further detail. The current sensor 641 is electrically isolated from the conductive sensor housing 665.

[0094] As in Figure 6B and Figure 6CAs shown in FIG, the conductive voltage pickup 651 of the voltage sensor is shaped like a conductive ring. The voltage pickup 651 is shown as being disposed in the region of the annular dielectric cavity 661 between the ring current sensor 641 and the central hole 621. Solid dielectric material (e.g., plastic) can be used for the parts used to provide mechanical support for the voltage pickup 651. The slit region 671 of the cavity 661 and the dielectric support parts electrically isolate the conductive voltage pickup 651 from the conductive sensor housing 665. Figure 6B The connection between the voltage pickup 651 and the center terminal 654 is shown in FIG. (The coaxial connector 645 and the center terminal 654 are not included in the cutting plane AA'; therefore, Figure 6C Not visible in the cross-section view shown in .)

[0095] The function of the voltage pickup 651 is to sense the RF voltage of the inner conductor at the center of the central bore by sensing the radial electric field between the inner and outer conductors of the RF tube. Typically, the outer conductor of the RF tube and the conductive sensor housing 665 are grounded. Accordingly, if the conductive ring of the voltage pickup 651 is shielded from the inner conductor of the RF tube by, for example, a grounded metal ring placed in the annular dielectric area between the inner conductor of the RF tube and the voltage pickup 651, the voltage pickup 651 may not function properly. In the case of excessive shielding, the voltage sensor output will be too weak to be useful. As shown in Figure 6B and Figure 6C As shown in FIG, the voltage pickup 651 extends vertically partially into the cavity 661 above and below the slot region 671 of the annular dielectric cavity 661. The cavity is formed above by grooves in the metal top cover 663 and below by corresponding grooves in the metal bottom cover 666. Although the grounded conductive inner walls of these grooves are interposed between the conductive ring of the voltage pickup 651 and the central axis of the central hole 621 for the inner conductor, the grounded metal does not completely shield the voltage pickup 651. There is Figure 6B and Figure 6C The dielectric slot 671 separating the top cover 663 from the bottom cover 666 is shown in FIG. The slot 671 is considered to be in the mirror plane M (defined by Figure 6C 6 (indicated by the dashed line in FIG), the dielectric region in FIG671 resembles a cylindrical disk because there is no inner conductor in the center hole 621. When the inner conductor is in place, the dielectric slot 671 will resemble an annular disk surrounding the inner conductor. The unshielded radial electric field in the dielectric slot 671 will be sensed by capacitive coupling between the inner conductor and the center portion of the annular voltage pickup 651. The voltage pickup 651 can now provide a usable electrical signal proportional to the RF voltage of the inner conductor at that location.

[0096] The function of the current pickup coil 647 is to sense the RF current in the inner conductor at the center of the central aperture by sensing a circulating magnetic field passing through the coil in a direction parallel to the central axis of the annular core 642. According to Faraday's law, an oscillating electrical signal is induced in the coil, which is proportional to the oscillating magnetic flux in the annular core 642 enclosed within the turns of the conductive wire of the coil 647. According to Ampere's law, the strength of the magnetic field passing through the current sensor 641 is proportional to the total current flowing through the planar area enclosed within the central aperture of the annular current sensor (analogous to the donut-shaped aperture of a donut). As is true for any coaxial structure, the current passing through the inner conductor at any location in the RF tube is exactly equal to the opposite current in the outer conductor. The sensor housing 665 of the VI sensor 600 can be considered the equivalent outer conductor of the RF tube, with the inner conductor passing through the central aperture 621. Therefore, the current sensor 641 may not function properly unless the RF current in the sensor housing 665 is constrained to flow outside the disk-shaped area enclosed by the outer circumference of the annular core 642. For example, if the top cover 663 makes electrical contact with the bottom cover 666 at a radial distance from the central axis that is shorter than the inner radius of the annular core 642, a portion of the current in the conductive housing can flow through the contact. This current, opposing the current in the inner conductor, will reduce the magnitude of the total current enclosed by the current sensor 641, thereby reducing the magnetic flux through the coil 647. If the total current passing through the contacts inside the area enclosed by the annular current sensor 641 is too low, the magnetic field may not be sufficient to induce a usable electrical signal in the current pickup coil 647. In addition, the dielectric slit region 671 prevents electrical contact between the top cover 663 and the bottom cover 666 at a radial distance less than the inner radius of the annular current sensor 641, as shown in FIG. Figure 6B and Figure 6C As shown in .

[0097] The uninterrupted, continuous dielectric region that separates the top cover 663 from the bottom cover 666 up to the outer periphery of the ring current sensor 641 is achieved by designing the voltage pickup 651 to be smaller than the vertical height of the cavity 661. The conductive ring of the voltage pickup 651 can be positioned approximately symmetrically between the top cover 663 and the bottom cover 666 by a support member comprising insulating material. Thus, in all directions, there is insulating material immediately adjacent to the conductive voltage pickup 651. As described above, this insulating material is within the slit region 671 of the cavity 661. The shape of the dielectric above the conductive ring of the voltage pickup 651 is determined by Figure 6B It can be noted that, as in Figure 6C As shown by the dashed lines in FIG, a meandering dielectric slot region 671 exists both above and below the voltage pickup 651 because the conductive ring of the voltage pickup 651 must be electrically isolated from the grounded sensor housing 665.

[0098] The current pickup of a current sensor is typically shielded from RF electric fields by grounded conductive parts. Shielding the current pickup is advantageous in applications where the electric field is strong and the magnetic field is weak, such as near a high impedance load. In the VI sensor 600, the current pickup coil 647 is located in a dielectric cavity 661 inside the sensor housing 665. The conductive parts encountered when moving radially inward from the ring current sensor 641 to the inner conductor include, first, the conductive voltage pickup 651 and, second, a portion of the inner wall of the conductive sensor housing 665, as shown in FIG. Figure 6B and Figure 6C 6 and also described above. These interposed conductive features can help shield the current sensor 641 from radial electric fields. Some of the electric field lines emanating from the inner conductor can terminate on the grounded inner wall of the conductive sensor housing 665. In addition, the conductive voltage pickup 651 serves a dual purpose by partially shielding the coil 647 from the RF electric field. Because the voltage pickup 651 is not short-circuited to ground, the reduction in electric field provided by the conductive ring depends on the magnitude of the impedance to ground at the center terminal 654.

[0099] The structures of the current sensor 641 and the voltage pickup 651 of the VI sensor 600 are axisymmetric with respect to a common axis passing through the center and in a direction normal to the plane of the central hole 621. In addition, the current sensor 641 and the voltage pickup 651 both share the same mirror plane perpendicular to the longitudinal axis (at Figure 6C The symmetry of the structure of the VI sensor 600 helps reduce / eliminate any measured differences in the phase angle (Φ) between the voltage and current. In addition, the first-order cancellation effect due to the axial symmetry makes the sensor output signal of the VI sensor 600 less sensitive to machining tolerances and positioning errors during assembly.

[0100] Figure 6D Demonstrated that it can be used as Figure 6B The example annular structure of the core shaft 642 of the annular current sensor 641 is shown in FIG. The annular core shaft 642 has a continuous groove on its outer surface, in which a conductive wire can be placed to form a coil 647 (in FIG. Figure 6B The two opposite ends of the coil 647 can pass through the Figure 6D and then attached to the pair of coaxial connectors 645 (see Figure 6B ). Voltage pickup 651 (see Figure 6B ) can be connected by a conductive element passing through a hole in the annular core shaft 642 and an opening 653 to be attached to the center terminal 654.

[0101] The annular mandrel 642 comprises plastic or other insulating materials and can be fabricated using, for example, 3D printing techniques. After the coil 647 has been mounted on the grooved annular mandrel 642, the structure can be optionally encased in a resin coating using, for example, resin embedding techniques. The resin encapsulation securely holds the wound multi-turn current pickup 647 in place.

[0102] The integrated assembly of the VI sensor 600 described above, including the current sensor 641 and the combined electric field shield and voltage pickup 651 , provides the advantage of a compact VI sensor design.

[0103] Figures 7A to 7E A current sensor assembly 701 is shown that is similar in design to the design of VI sensor 600. Unlike VI sensor 600, current sensor assembly 701 does not sense voltage. Additionally, the design of annular mandrel 742 used for current sensor assembly 701 differs from grooved annular mandrel 642, as further described below.

[0104] Figure 7A A perspective view of a current sensor assembly 701 using a ring current sensor 741 is shown, which is placed in a dielectric cavity between a top cover 782 and a bottom cover 784 of a sensor housing 765. Figures 7C to 7E The current sensor 741 is further described. The top cover 782 and the bottom cover 784 may comprise a metal (e.g., copper or aluminum). The current sensor assembly 701 has a central hole 710. The inner conductor of a coaxial transmission line (e.g., an RF tube) that may be used with the current sensor assembly 701 will pass through the central hole 710. Thus, the current sensor assembly 701 will be positioned symmetrically about the longitudinal axis of the coaxial transmission line.

[0105] Figure 7B An exploded view of the current sensor assembly 701 is shown. Figure 7B , the current sensor 741 has been removed from the sensor housing 765 to illustrate the structure of the dielectric cavity 720 and the lower half of the bottom cover 784. (See below for details.) Figure 7C The upper half of the structure is further described.) The dielectric cavity 720 can be divided into an outer dielectric region 723 and an inner dielectric region referred to as a meandering dielectric slot 725. The outer dielectric region is the region above the outermost groove in the bottom plate of the bottom cover 784. Outside the outer circle of this outermost groove, the metal top cover 782 and the metal bottom cover 784 can be physically and electrically connected together, but inside the outer circle of the outermost groove, no electrical contact can be made between the top cover 782 and the bottom cover 784.

[0106] The zigzag dielectric slot 725 comprises a dielectric region above two grooves on either side of a conductive ridge 750 shaped like a ring protruding from the bottom plate of the bottom cover 784. The conductive bottom surface of the dielectric cavity 720 including the conductive ridge 750 will be electrically and physically separated from the corresponding conductive top plate of the dielectric cavity 720 by an uninterrupted continuous dielectric region. Accordingly, the top of the conductive ridge 750 can protrude into the corresponding groove in the top metal cover 782 but cannot make contact with the top plate. Thus, the combined top and bottom portions of the zigzag dielectric slot 725 will be a zigzag dielectric region that winds around and over the conductive ridge 750, as shown in FIG. Figure 7B Indicated by the zigzag dashed line.

[0107] Figure 7C A portion of an RF system 700 is shown that includes an inner conductor 711 of an RF tube passing through a central hole 710 of a current sensor assembly 701 and symmetrically positioned around the inner conductor 711. A grounded outer conductor will be physically and electrically attached to the top cover 782 from above and to the bottom cover 784 from below, thereby grounding the sensor housing 765. Similar to the sensor housing 665 of the VI sensor 600, this sensor housing will serve as a grounded outer conductor for the portion of the inner conductor 711 that passes through the central hole 710.

[0108] exist Figure 7C , the current sensor assembly 701 is shown by a cutaway view including an exploded view of the current sensor 741. The current sensor 741 includes an annular core shaft 742 and a conductive current pickup coil 747. The annular core shaft 742 includes a solid dielectric material having a winding channel. The winding channel can be accessed through access holes 749 at various locations on the surface of the annular core shaft 742. An attachment 743 having two holes has been placed over one of the access holes 749. Two opposing ends of the conductive wire of the coil 747 are shown protruding upward through the holes in the attachment 743. A portion of the annular core shaft 742 has been cut away to show the conductive wire of the coil 747 tunneling through the winding channel in the solid dielectric material of the annular core shaft 742. The coil 747 is embedded inside the core shaft 742. The design of the core shaft 742 provides greater mechanical support relative to the grooved design of the core shaft 642, thereby eliminating the previously referenced Figure 6D The resin encapsulation step is described.

[0109] exist Figure 7C , the annular core shaft 742 has been placed in the outer dielectric region 723 and the corresponding groove on the bottom plate of the bottom cover 784 (see Figure 7B). The exploded view of the current sensor assembly 701 shows that the upper half of the annular mandrel 742 can be fitted into a groove in the top cover 782 within the outer dielectric region 723 of the dielectric cavity 720. The conductive ridge 750 can similarly extend into an adjacent groove in the top cover 782 and into the meandering dielectric slot 725 of the dielectric cavity 720. The conductive ridge 750 is a continuous ring interposed between the annular current sensor 741 and the inner conductor 711, effectively shielding the current sensor 741 from RF electric fields.

[0110] As explained above, electrical contact between the grounded top cover 782 and the grounded bottom cover 784 in the area surrounded by the ring current sensor 741 would reduce the strength of the magnetic field passing through the current pickup coil 747 and could excessively reduce the output signal of the current signal. Therefore, the top of the conductive ridge 750 is electrically isolated from the top cover 782 by the tortuous dielectric slot 725. Figure 7C The meandering shape of the dielectric region is indicated by the meandering dashed line.

[0111] exist Figure 7D The cross-sectional view of a portion of the RF system 700 shown in FIG. 7 shows a current sensor assembly 701 with a top cover 782 mounted over a bottom cover 784. Figure 7D The meandering shape of the dielectric slit 725 is indicated by the meandering dashed line.

[0112] Figure 7E A plan view of the bottom portion of the current sensor assembly 701 and the inner conductor 711 of the RF tube passing through the central hole 710 of the current sensor assembly is shown. The current sensor 741, including the annular mandrel 742 and the current pickup coil 747, is shown above the bottom cover 784. The two opposite ends of the coil 747 pass through holes in the attachment 743. The attachment 743 can be placed over an opening similar to the access hole 749. An annular conductive ridge 750 is shown interposed between the inner conductor 711 and the current sensor 741. Dielectric slots 725 are shown on either side of the conductive ridge 750.

[0113] The use of mandrels such as mandrels 642 and 742 allows current sensor designs to utilize coils with many turns as current pickups. A larger number of turns increases the sensitivity of the corresponding current sensor. The increased sensitivity allows each turn to have a smaller cross-section, and thus the size of the entire current sensor can be reduced, allowing the current sensor to be placed in otherwise inaccessible areas.

[0114] Although the mandrel described in this disclosure is shaped like a toroid, it should be understood that other shapes may be used, such as a square or a regular polygon with any number of sides. Additionally, pickups of various shapes may be implemented without the use of a mandrel.

[0115] Various aspects of the embodiments described in this disclosure can be applied to fabricate VI sensors using various other fabrication techniques. For example, a current pickup can be fabricated in layers of dielectric and conductive material connected by vias, such as using printed circuit board (PCB) technology.

[0116] The embodiments of the toroidal current sensor described above offer the following advantages: axisymmetry of the toroid, higher immunity to noise from multi-turn current pickups, and ease of use due to a compact structure.

[0117] The VI sensor and measurement method described in this disclosure provide embodiments that can achieve extremely high-precision measurements at low manufacturing costs. High precision can be achieved at low manufacturing costs by including design features intended to reduce the sensitivity of the VI measurement to machining errors and assembly errors. The accuracy of the current sensor depends on machining tolerances that cause variations in the size of the geometric structure that determines the current pickup (e.g., the area enclosed by the rectangular half-loop). The accuracy of the measured current may also be limited by assembly tolerances, for example, the accuracy with which the current pickup can be placed, including the radial distance from the longitudinal axis and the angle between the plane of the half-loop and the longitudinal axis. The accuracy of the voltage measurement similarly depends on machining tolerances (e.g., the accuracy of the diameter and circumference of the voltage pickup ring) and assembly tolerances (e.g., the angle between the plane of the ring and the longitudinal axis). The inventors have performed detailed computer simulations of the sensitivity of the VI sensor signal to variations in the size and placement of the current and voltage pickups and found that a high accuracy of 1% can be achieved for standard machines and a placement tolerance value of 0.005 inches can be achieved. Computer simulations were performed using a calibrated 3D finite element solver for Maxwell's equations over a wide range of RF power, RF frequency, and load impedance used in plasma processing.

[0118] Example embodiments of the present application are summarized here. Other embodiments are also apparent from the overall description and claims presented herein.

[0119] Example 1. A radio frequency (RF) sensor assembly includes a sensor housing disposed about a central aperture, the sensor housing including a first conductive cover and a second conductive cover. The assembly includes a cavity disposed about the central aperture and comprising a first dielectric material, the cavity being bounded by a first major outer surface and a second major outer surface in a radial direction from a center of the central aperture, the first major outer surface including a continuous annular region in physical contact with the central aperture, and the second major outer surface being at a radial distance greater than a radius of the first major outer surface, wherein the first conductive cover is electrically coupled to the second conductive cover via a coupling region outside the second major outer surface of the cavity, and wherein the first conductive cover is electrically insulated from the second conductive cover by the cavity and the central aperture. The assembly includes a current sensor electrically insulated from the sensor housing and including a current pickup symmetrically disposed about the central aperture, the current pickup disposed within the cavity and insulated from the sensor housing.

[0120] Example 2. The sensor assembly of Example 1, wherein the current sensor includes a core shaft shaped like a toroidal coil.

[0121] Example 3. A sensor assembly as described in either Example 1 or 2, wherein the core shaft includes a second dielectric material surrounding a continuous hollow channel, the hollow channel being symmetrically wound on an inner circular axis, wherein the current pickup includes a continuous conductive wire having two opposite ends, and wherein the wire is shaped like a coil passing through the hollow channel.

[0122] Example 4. The sensor assembly of any one of Examples 1 to 3 further comprises: a plurality of access holes extending from the outer surface of the core shaft to the hollow channel; and two electrical terminals insulated from the sensor housing, wherein the two electrical terminals are electrically connected to corresponding two opposite ends of the wire extending from the core shaft through the plurality of access holes.

[0123] Example 5. A sensor assembly as described in any of Examples 1 to 4, wherein the core shaft includes a second dielectric material having grooves on a major outer surface of the core shaft, the grooves being symmetrically wound on the inner circular shaft, wherein the current pickup includes a continuous conductive wire having two opposite ends, wherein the wire is shaped like a coil disposed in the grooves of the annular coil.

[0124] Example 6. The sensor assembly of any one of Examples 1 to 5, further comprising: two electrical terminals insulated from the sensor housing, wherein the two electrical terminals are electrically coupled to respective opposite ends of the wire outside the core shaft.

[0125] Example 7. The current sensor of any one of Examples 1 to 6, wherein the core shaft and the current pickup are encapsulated with resin.

[0126] Example 8. The sensor assembly of one of Examples 1 to 7 further includes a voltage sensor, the voltage sensor including a voltage pickup and an electrical terminal, wherein the voltage pickup is disposed in the cavity, inserted between the current sensor and the center hole, and wherein the electrical terminal is electrically connected to the voltage pickup; and wherein the voltage sensor is electrically insulated from the sensor housing.

[0127] Example 9. A sensor assembly as described in one of Examples 1 to 8, wherein the voltage pickup is a ring-shaped electrode symmetrically arranged around the central hole, and wherein the voltage pickup is mechanically supported by a third dielectric material arranged in the cavity between the first conductive cover and the second conductive cover.

[0128] Example 10. The sensor assembly of any of Examples 1 to 9, wherein the third dielectric material is a solid dielectric material and the first dielectric material is a gas.

[0129] Example 11. A voltage sensor as described in one of Examples 1 to 10, wherein the voltage pickup is electrically insulated from the sensor housing by a slit region, the slit region includes a continuous meandering region shaped like a ring, and wherein the slit region is in physical contact with the center hole, the voltage pickup and the current sensor.

[0130] Example 12. A radio frequency (RF) sensor assembly includes a sensor housing symmetrically disposed about a central aperture, the sensor housing including a first conductive cover and a second conductive cover. The assembly includes a toroidal cavity symmetrically disposed about the central aperture and comprising a first dielectric material, the cavity being bounded radially from the center of the central aperture by a first major outer surface and a second major outer surface, the first major outer surface comprising an annular continuous region in physical contact with the central aperture, and the second major outer surface comprising a closed outer boundary at a radial distance greater than a radius of the first major outer surface; a current sensor including a current pickup coil symmetrically disposed about the central aperture, the current pickup being insulated from the sensor housing and disposed within the cavity. The assembly includes a toroidal conductive ridge interposed between the current pickup and the central aperture and electrically coupled to the second conductive cover, the conductive ridge being covered with the dielectric material.

[0131] Example 13. A sensor assembly as described in Example 12, wherein the first conductive cover includes, along the radial direction from the center of the center hole, a first groove shaped like a ring, the first groove being vertically arranged on the conductive ridge; a second groove shaped like a ring at a radial distance farther from the center hole; and a beam shaped like a ring, the beam including a conductive area between the first groove and the second groove; and wherein the second conductive cover includes a third groove shaped like a ring vertically arranged below the beam and the second groove; and wherein the current sensor includes: an upper part, the upper part being arranged in the part of the cavity including the second groove; and a lower part, the lower part being arranged in the part of the cavity including the third groove.

[0132] Example 14. A sensor assembly as described in one of Examples 12 or 13, wherein the cavity includes a slit region along the radial direction from the center of the central hole, the slit region including a continuous tortuous dielectric region shaped like a ring, wherein the slit region is in physical contact with the central hole, the conductive ridge and the current sensor.

[0133] Example 15. A sensor assembly as described in any of Examples 12 to 14, wherein the first conductive cover is electrically coupled to the second conductive cover through an area outside the second major outer surface of the cavity, and wherein the first conductive cover is electrically insulated from the second conductive cover through the cavity and the central hole in the area enclosed by the closed outer boundary.

[0134] Example 16. A plasma system comprising: a process chamber including an electrode; a radio frequency (RF) power supply configured to power the process chamber with an RF signal; an RF tube coupling the RF power supply to the electrode of the process chamber; a core shaft shaped like a toroidal coil, the core shaft symmetrically arranged around the axis of the RF tube carrying the RF signal; and a voltage pickup symmetrically arranged around the axis of the RF tube and surrounded by the core shaft.

[0135] Example 17. The system of Example 16 further includes a current sensor comprising: the core shaft, the core shaft comprising a dielectric material; and a current pickup, the current pickup comprising a continuous conductive wire having two opposite ends, wherein the wire is symmetrically wound on an inner circular axis of the core shaft; and two electrical terminals, the two electrical terminals being electrically connected to corresponding two opposite ends of the wire outside the core shaft.

[0136] Example 18. The plasma system of one of Examples 16 or 17, further comprising a sensor assembly comprising: a central hole, wherein the inner conductor of the RF tube is disposed in the central hole; and a sensor housing shaped like a ring, the sensor housing being disposed in contact around the central hole and comprising a first conductive cover and a second conductive cover, the sensor housing being divided into a first annular region and a second annular region, the first annular region being adjacent to the central hole on one side and adjacent to the second annular region on an opposite side, and wherein, in the first annular region, the first conductive cover is electrically insulated from the second conductive cover by a cavity comprising a dielectric material, and wherein the core shaft and the voltage pickup are disposed in the cavity, and wherein, in the second annular region, the first conductive cover is electrically coupled to the second conductive cover.

[0137] Example 19. The plasma system of any of Examples 16 to 18, wherein the first conductive cover and the second conductive cover are electrically coupled to the outer conductor of the RF tube in a first annular region of the sensor housing, and wherein the first conductive cover and the second conductive cover are electrically coupled to the outer conductor of the RF tube in a second annular region of the sensor housing.

[0138] Example 20. The plasma system of any one of Examples 16 to 19, further comprising a voltage sensor comprising the voltage pickup and an electrical terminal, wherein the voltage sensor is electrically insulated from the sensor housing, and wherein the voltage pickup is a ring-shaped electrode symmetrically disposed about the central hole, wherein the voltage pickup is mechanically supported by a solid dielectric material disposed in a cavity between the first conductive cover and the second conductive cover, and wherein the voltage pickup is electrically coupled to the electrical terminal.

[0139] Example 21. A plasma system as described in any one of Examples 16 to 20, wherein the voltage pickup is electrically insulated from the sensor housing by a slit region, the slit region comprising a continuous tortuous dielectric region shaped like a ring, wherein the slit region is in physical contact with the center hole, the voltage pickup and the core shaft.

[0140] Although the present invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art with reference to the description. Accordingly, the appended claims are intended to cover any such modifications or embodiments.

Claims

1. A radio frequency sensor assembly, comprising: a sensor housing disposed around the central hole, the sensor housing including a first conductive cover and a second conductive cover; a cavity disposed about the central bore and comprising a first dielectric material, the cavity being bounded in a radial direction from a center of the central bore by a first major outer surface and a second major outer surface, the first major outer surface comprising a continuous annular region in physical contact with the central bore, and the second major outer surface being at a radial distance greater than a radius of the first major outer surface, wherein the first conductive cover is electrically coupled to the second conductive cover through a coupling region external to the second major outer surface of the cavity, and wherein the first conductive cover is electrically insulated from the second conductive cover by the cavity and the central bore; and A current sensor is electrically insulated from the sensor housing and includes current pickups symmetrically disposed around the central hole, the current pickups being disposed within the cavity and insulated from the sensor housing.

2. The sensor assembly of claim 1, wherein: The current sensor includes a core shaft shaped like a toroidal coil.

3. The sensor assembly of claim 2, wherein: The mandrel includes a second dielectric material surrounding a continuous hollow passage symmetrically wound on an inner circular shaft, wherein the current pickup includes a continuous conductive wire having two opposing ends, and wherein the continuous conductive wire is shaped like a coil passing through the hollow passage.

4. The sensor assembly of claim 3, further comprising: a plurality of access holes extending from an outer surface of the mandrel into the hollow passage; as well as Two electrical terminals are insulated from the sensor housing, wherein the two electrical terminals are electrically connected to respective opposite ends of the wire extending from the core shaft through the plurality of access holes.

5. The sensor assembly of claim 2, wherein: The mandrel comprises a second dielectric material having grooves on a major outer surface of the mandrel, the grooves being symmetrically wound around an inner circular shaft, wherein the current pickup comprises a continuous conductive wire having two opposite ends, wherein the continuous conductive wire is shaped like a coil disposed in the grooves of the toroidal coil.

6. The sensor assembly of claim 5, further comprising: Two electrical terminals are insulated from the sensor housing, wherein the two electrical terminals are electrically coupled to respective opposite ends of the wire outside the core shaft.

7. The sensor assembly of claim 1 , further comprising a voltage sensor comprising a voltage pickup and electrical terminals, in, The voltage pickup is disposed in the cavity, interposed between the current sensor and the central hole, and wherein the electrical terminal is electrically connected to the voltage pickup; and The voltage sensor is electrically insulated from the sensor housing.

8. The sensor assembly according to claim 7, in, The voltage pickup is a ring-shaped electrode symmetrically arranged around the central hole, and The voltage pickup is mechanically supported by a third dielectric material disposed in the cavity between the first conductive cover and the second conductive cover.

9. The sensor assembly of claim 8, wherein: The third dielectric material is a solid dielectric material and the first dielectric material is a gas.

10. The voltage sensor according to claim 8, wherein The voltage pickup is electrically isolated from the sensor housing by a slot region comprising a continuous meandering region shaped like a ring, and wherein the slot region is in physical contact with the central hole, the voltage pickup, and the current sensor.

11. A radio frequency sensor assembly, comprising: a sensor housing symmetrically disposed around the central hole, the sensor housing comprising a first conductive cover and a second conductive cover; a toroidal cavity symmetrically disposed about the central bore and comprising a first dielectric material, the cavity being bounded in a radial direction from a center of the central bore by a first major outer surface and a second major outer surface, the first major outer surface comprising an annular continuous region in physical contact with the central bore, and the second major outer surface comprising a closed outer boundary at a radial distance greater than a radius of the first major outer surface; a current sensor comprising a current pickup coil symmetrically disposed about the central hole, the current pickup being insulated from the sensor housing and disposed within the cavity; and A conductive ridge shaped like a ring is interposed between the current pickup and the central hole and electrically coupled to the second conductive cover, the conductive ridge being covered with the dielectric material.

12. The sensor assembly according to claim 11, in, The first conductive cover includes a a first groove shaped like a ring, the first groove being vertically arranged on the conductive ridge, a second groove shaped like a ring at a greater radial distance from the central hole, and a ring-shaped beam comprising a conductive region between the first groove and the second groove; and The second conductive cover comprises a third groove shaped like a ring and vertically arranged below the beam and the second groove; and The current sensor includes: an upper portion, which is disposed in the portion of the cavity including the second groove; and a lower portion, which is disposed in the portion of the cavity including the third groove.

13. The sensor assembly according to claim 11, in, The cavity includes a slit region along the radial direction from the center of the central hole, the slit region including a continuous meandering dielectric region shaped like a ring, The slit region is in physical contact with the central hole, the conductive ridge and the current sensor.

14. The sensor assembly of claim 11, wherein: The first conductive cover is electrically coupled to the second conductive cover through a region outside the second major exterior surface of the cavity, and wherein the first conductive cover is electrically insulated from the second conductive cover through the cavity and the central aperture in a region enclosed by the closed exterior boundary.

15. A plasma system comprising: a processing chamber comprising an electrode; a radio frequency power supply configured to power the processing chamber with a radio frequency signal; a radio frequency tube coupling the radio frequency power source to an electrode of the processing chamber; A core shaft shaped like a toroidal coil, the core shaft being symmetrically arranged around the axis of the radio frequency tube carrying the radio frequency signal; as well as A voltage pickup is symmetrically arranged around the axis of the radio frequency tube and surrounded by the core shaft.

16. The system of claim 15, further comprising a current sensor comprising: the mandrel, the mandrel comprising a dielectric material; as well as a current pickup comprising a continuous conductive wire having two opposite ends, wherein the wire is symmetrically wound around the inner circular axis of the mandrel; and Two electrical terminals are electrically connected to respective opposite ends of the wire outside the mandrel.

17. The plasma system of claim 15, further comprising a sensor assembly comprising Center hole, where The inner conductor of the radio frequency tube is arranged in the central hole; and A sensor housing shaped like a ring is disposed around the central hole and includes a first conductive cover and a second conductive cover. The sensor housing is divided into a first annular area and a second annular area. The first annular region is connected to the central hole on one side and to the second annular region on the opposite side, and wherein, in the first annular region, the first conductive cover is electrically insulated from the second conductive cover by a cavity comprising a dielectric material, and wherein the mandrel and the voltage pickup are disposed in the cavity, and Wherein, in the second annular region, the first conductive cover is electrically coupled to the second conductive cover.

18. The plasma system of claim 17, in, The first conductive cover and the second conductive cover are electrically coupled to the outer conductor of the radio frequency tube in a first annular region of the sensor housing, and The first conductive cover and the second conductive cover are electrically coupled to the outer conductor of the radio frequency tube in the second annular region of the sensor housing.

19. The plasma system of claim 17, further comprising a voltage sensor comprising the voltage pickup and an electrical terminal, in, The voltage sensor is electrically insulated from the sensor housing, and The voltage pickup is a ring-shaped electrode symmetrically arranged around the central hole. wherein the voltage pickup is mechanically supported by a solid dielectric material disposed in a cavity between the first conductive cover and the second conductive cover, and The voltage pickup is electrically coupled to the electrical terminal.

20. The plasma system of claim 19, wherein: The voltage pickup is electrically isolated from the sensor housing by a slot region comprising a continuous meandering dielectric region shaped like a ring, wherein the slot region is in physical contact with the central hole, the voltage pickup, and the core shaft.

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