Rf voltage and current (v-i) sensor and measurement method

Abstract

A radio frequency (RF) system includes an RF power supply configured to power a load with an RF signal, an RF tube including an inner conductor and an outer conductor connected to ground, the conductors coupling the RF power supply to the load, and a current sensor aligned with a center axis of the RF tube carrying the RF signal. A sensor housing is disposed around the RF tube, wherein the sensor housing includes a conductive material connected to the outer conductor of the RF tube. A gallery is disposed within the sensor housing and outside the outer conductor of the RF tube, wherein the current sensor is disposed in the gallery. A slit in the outer conductor of the RF tube exposes the current sensor to a magnetic field resulting from a current of the RF signal in the inner conductor of the RF tube.

Description

[0001] Cross-references to related applications

[0002] This application relates to co-pending U.S. non-provisional application No. 16 / 913,545, filed June 26, 2020, agent file number 200391US01, U.S. non-provisional application No. 16 / 913,548, filed June 26, 2020, agent file number 190883US01, and claims priority to U.S. non-provisional application No. 16 / 913,526, filed June 26, 2020, agent file number 190907US01, which are hereby incorporated herein by reference. Technical Field

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

[0004] Typically, the need to achieve higher functionality at reduced costs has driven advancements in semiconductor integrated circuits (ICs). Higher functionality at lower costs is primarily achieved through increased component density via 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 network's elements are integrated together by sequentially depositing and patterning dielectric, conductive, and semiconductor layers on a semiconductor substrate using fabrication processes including chemical vapor deposition (CVD), photolithography, and etching. The 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 conventionally used in the deposition and patterning steps of semiconductor IC fabrication. However, with the emergence of feature sizes shrinking to a few nanometers and structural features controlled at the atomic scale, the challenges of providing fabricatable plasma technologies for advanced IC design have intensified. Fabricable plasma processes are expected to provide structures with: precise dimensions (e.g., linewidth, etch depth, and film thickness), features for precise control of plasma etching (e.g., sidewall angles, anisotropy, and selectivity for etch stop layers), features for precise control of plasma deposition (e.g., conformality, aspect ratio selectivity, and bottom-up patterning region selectivity), and uniformity across wafer widths (e.g., 300 mm). In many plasma processes used in IC manufacturing, the plasma is maintained by RF power. Since the properties of plasma are affected by the RF power delivered to the processing chamber, precise control of plasma processes may require innovative, interference-free, and accurate measurement of the RF signal. Summary of the Invention

[0006] According to an embodiment of the present invention, a radio frequency (RF) system includes: an RF power supply configured to power a load with an RF signal; an RF tube including an inner conductor and an outer conductor connected to ground, the conductors coupling the RF power supply to the load; and a current sensor aligned with the central axis of the RF tube carrying the RF signal. The current sensor is configured to monitor the current of the RF signal and includes a conductive half-loop disposed near the RF tube, wherein the conductive half-loop includes a first end and an opposing second end. The current sensor is configured to output an output signal between the first end and the second end. A sensor housing is disposed around the RF tube, wherein the sensor housing includes a conductive material connected to the outer conductor of the RF tube. A corridor is disposed within the sensor housing and outside the outer conductor of the RF tube, wherein the current sensor is disposed in the corridor. A slit in the outer conductor of the RF tube exposes the current sensor to a magnetic field generated by the current of the RF signal in the inner conductor of the RF tube.

[0007] According to an embodiment of the present invention, a radio frequency (RF) system includes: an RF power supply configured to power a load with an RF signal; an RF tube including an inner conductor and an outer conductor connected to a reference potential node, the conductors coupling the RF power supply to the load; and a first voltage sensor axially symmetrically disposed around the axis of the RF tube carrying the RF signal, wherein the first voltage sensor is configured to monitor the voltage of the RF signal.

[0008] According to an embodiment of the present invention, a method for measuring a radio frequency (RF) signal includes aligning a current sensor with the axis of an RF tube carrying the RF signal, wherein the current sensor is disposed in a corridor disposed within a sensor housing and outside the outer conductor of the RF tube. The sensor housing is disposed around the RF tube. The current sensor includes a conductive half-loop, wherein the conductive half-loop includes a first end and an opposing second end. The method includes determining the current of the RF signal based on measuring an output signal between the first end and the second end. Attached Figure Description

[0009] To gain a more complete understanding of the 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-purpose plasma processing system for semiconductor IC fabrication is shown.

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

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

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

[0014] Figure 2B Showing Figure 2A The cross-sectional view of the VI sensor shown in the image;

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

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

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

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

[0019] Figure 6B Showing Figure 6A The cross-sectional view of the VI sensor shown in the image;

[0020] Figure 6C Showing Figure 6A The cross-sectional view of the VI sensor shown in the image;

[0021] Figure 6D An example of one embodiment is shown. Figure 6A A 3D view of the current sensor element of the VI sensor shown in the image;

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

[0023] Figure 7B Showing Figure 7A An exploded view of the current sensor assembly shown in the image;

[0024] Figure 7C Showing Figure 7A An exploded view of the cross-sectional view of the current sensor assembly and the RF conductor for the RF tube.

[0025] Figure 7D Demonstrates an embodiment of the present invention. Figure 7C The current sensor assembly and the RF conductor for the RF tube shown in the figure are cross-sectional views; and

[0026] Figure 7E Showing Figure 7C The diagram shows a plan view of the current sensor assembly and the bottom portion of the RF conductor.

[0027] Figures 1A to 7E In all three-digit figure labels, the last two digits always indicate a similar part. Detailed Implementation

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

[0029] This disclosure describes sensor designs and methods for accurately measuring voltage (V), current (I), and the phase angle (Φ) between voltage and current in 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 a coaxial transmission line known as an RF tube.

[0030] Plasma processes in semiconductor fabrication (e.g., plasma etching and deposition processes) typically use RF power to sustain the plasma. As is known to those skilled in the art, the RF signal sustaining the plasma in the plasma chamber affects plasma properties. 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 refers herein 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 a single frequency component f is present, the current and voltage are compactly written as Re(I(x)e^(-f / f)). jωt ) and Re(V(x)e j(ωt+Φ) The waveform is described by a sine wave, where ω = 2πf, j 2 = -1, and Re is the real part of the complex function. As mentioned above, I and V each have magnitudes and are separated from each other by a phase angle Φ. Typically, waveforms I and V can include multiple frequency components. Voltage V(x,t) refers to the potential of the inner conductor (or core) of an 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 the various embodiments, RF VI sensors can provide V and I with high accuracy at the sensor location using geometric symmetry and differential measurement methods. Multiple VI sensors can be used at various locations along the RF tube to detect the RF signal there. 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 the plasma process using accurate measurements of the voltage and current provided to the plasma chamber by the RF signal, 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 VI sensors without increasing cost, thereby providing enhanced capabilities to plasma processing systems to deliver plasma processes with better repeatability and tighter process control at the same cost. Furthermore, the RF probes are designed to be undisturbed to allow for easy retrofitting of existing plasma processing equipment using improved VI sensors without the time-consuming and costly redevelopment of established plasma process formulations in the production process.

[0033] In this disclosure, we first refer to Figure 1A The block diagram shown illustrates the use of the VI sensor in a plasma processing system. Next, based on an embodiment, refer to... Figure 1B The schematic diagram shown illustrates the basic structure and operating principle of the VI sensor in the plasma processing system. Then, refer to... Figure 2A , Figure 2B , Figure 3 , Figure 4 and Figure 5 The example embodiments of the VI sensor shown in the document explain the design of the VI sensor (similar to...). Figure 1B Some innovative aspects of the design of the basic structure shown in the schematic diagram.

[0034] See below for reference Figure 1B A detailed description, Figure 2A , Figure 2B , Figure 3 , Figure 4 and Figure 5 The voltage sensor in the embodiment is axisymmetric and designed as a conductive ring placed inside the RF tube, looping around a central longitudinal axis extending parallel to the current direction. The advantages provided by the axisymmetric design are referenced in the discussion below. Figure 2B An explanation was provided.

[0035] In the example embodiment, the corresponding current sensor is located in a sleeve or channel surrounding the circumference of the RF tube. The channel is a cavity inside the sensor housing. The sensor housing has a conductive wall covering the channel and can be connected to the outer conductor of the RF tube, thereby connecting to ground. See below for further details. Figure 1B In detail, the current sensor is a single conductive loop (referred to as a half-loop) with two open ends; this loop is completed using components, for example, an external VI analyzer connected to the current sensor via a coaxial cable. The VI analyzer is a measurement system that analyzes the raw signals received from the current sensor and voltage sensor. As explained further below, both ends of the current sensor can be connected to the VI analyzer for differential measurements to obtain accurate analysis. However, to simplify the system at the expense of accuracy, only one end of the current sensor can be connected to the VI analyzer, and the other end is connected to ground or shorted to ground via 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 external ground cover of the corridor is located in the circuit between the two ends of the half-loop, which greatly facilitates loop completion. In alternative RF systems using embodiments of the current sensor described in this disclosure, the entire closed loop can be contained within a corridor with appropriate impedance matching and one or more external signal connections.

[0036] Reference Figures 1B to 5 In the described example 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 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 between the two vertical branches. References are made below. Figure 2B The advantages of reflective symmetry are explained in the discussion. However, due to its location on one side of the RF transistor, the single-turn half-loop current sensor lacks axisymmetry. (Reference) Figures 6A to 7E The design of axisymmetric multi-turn half-loop current sensor is described, wherein these embodiments utilize a ring-shaped mandrel to mechanically support the multi-turn current pickup.

[0037] The innovative aspects of the VI sensor design described in this disclosure offer several advantages. For example, non-invasive detection of the electric and magnetic fields of electromagnetic waves has been used to allow for VI measurements with negligible interference to RF signals in RF tubes. Furthermore, geometric symmetry and differential measurement techniques are advantageously used in sensor design to provide measurements that are insensitive to machining errors resulting from standard tolerances of the tools used to form the components, as well as positioning errors during the assembly of the VI sensor. Additionally, various structural enhancement techniques have been utilized; for example, the elements of the VI sensor can be repeatedly placed to enhance geometric symmetry, and parts designed to provide additional mechanical support can be placed to reduce / suppress even minor deformations of the shape of critical sensor components due to mechanical stress during assembly. Therefore, by using the embodiments described in this disclosure, RF VI measurements can be performed with improved accuracy without increasing costs due to tighter machining tolerances.

[0038] Figure 1A This is a block diagram of a general-purpose plasma processing system that can be used in the fabrication of semiconductor ICs.

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

[0040] As those skilled in the art will know, the RF signal in RF tube 110 can be represented as a combination of traveling RF electromagnetic waves. Impedance mismatch between the output impedance of RF power supply 10 and the load impedance causes a portion of the RF power traveling from RF power supply 10 toward the load to be reflected back to RF power supply 10. To suppress such undesirable reflection, a matching network including a matching adapter 40 can be inserted into the RF signal path between RF power supply 10 and plasma chamber 30, as shown in... Figure 1A As shown in the diagram, the ratio of reflected power to incident power of the matching network can be sensed by the matching unit 40 (e.g., using a VI sensor and analyzer) and provided to the programmable controller 20. The programmable controller 20 can then use, for example, a feedback control loop (in... Figure 1A (Indicated by the two arrows between the matching network 40 and the programmable controller 20) Adjust the impedance of the matching network to reduce the RF power reflected back to the RF power supply 10 from the matching network.

[0041] The plasma can be maintained in the plasma chamber 30 using, for example, RF power supplied from the RF power supply 10 to the electrodes of the plasma chamber 30 via the RF tube 110. Figure 1A As shown, the VI sensor 100 can be used to sense the current and voltage of the RF signal provided to the electrodes. In various plasma chamber designs, the electrodes can be inside the chamber wall, for example, a disk-shaped electrode in a capacitively coupled plasma (CCP) chamber, or an antenna outside the chamber wall. For example, in an inductively coupled plasma (ICP) chamber, the antenna can be a conductive planar helix placed on a dielectric window or a conductive helix wound around a dielectric cylinder. Figure 1A The block labeled plasma chamber 30 includes electrodes and an antenna coupled to the plasma. For simplicity, in this disclosure, the term electrode refers to an electrode and / or an antenna. 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 be a substrate support.

[0042] although Figure 1A The block diagram illustrates an RF tube 110 supplying RF power from a single RF power supply 10 to the plasma chamber 30, but there may be more than one RF power supply providing RF power to more than one electrode. For example, using appropriate RF tubes, matching circuits, and VI sensors, RF power supply 10 may supply RF power to an electrode of the plasma chamber 30 (e.g., the top electrode), and a second RF bias power supply may supply RF bias power to another electrode of the plasma chamber 30 (e.g., the bottom electrode), the VI sensor being positioned close to the plasma chamber to sense the voltage and current of the RF signal supplied to the bottom electrode.

[0043] exist Figure 1AIn this configuration, a VI sensor 100, located near the electrode receiving the RF signal, is connected to a VI analyzer 60 for sensing and measuring the current and voltage of the RF signal. The VI analyzer 60 receives 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) capable of extracting various RF signal characteristics from the raw waveform. These various RF signal characteristics can include magnitudes |V|, |I|, the phase angle (Φ) between V and I, and the peak RF power |V||I|cosΦ. Additionally, 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, RF calibration signals 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), standard load impedances (e.g., short circuit, open circuit, 50 ohms, etc.), and a vector network analyzer (VNA).

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

[0045] In embodiments where the VI sensor 100 is used to estimate and control plasma parameters, positioning the VI sensor 100 close to the plasma chamber 30 can be advantageous. The V and I values ​​of the RF signal at the electrode location can be estimated based on V and I measured by the VI sensor 100 at different locations. However, the measurement errors of V and I at the electrode may increase with the distance between the electrode and the VI sensor. Theoretically, 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 the electrode locations become increasingly sensitive to any errors in estimating the corresponding transfer matrix.

[0046] Now for reference 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 may be a coaxial structure comprising two conductive tubes (e.g., aluminum or copper tubes) placed concentrically around a shared longitudinal axis. The inner conductive tube, referred to as the inner conductor 120, may be electrically connected to the output terminal of the matching unit 40, indicated by the left-pointing arrow. The outer conductive tube, referred to as the outer conductor 130, may be a grounded sheath connected to a reference potential generally referred to as ground. The RF tube 110 may be referred to as the primary coaxial line because it carries RF power from the matching unit 40 to the plasma chamber 30. Other coaxial lines in this disclosure are referred to as coaxial signal lines (e.g., coaxial lines that may 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 can be disposed within an annular channel 160 inside a sensor housing 165 having conductive walls (e.g., aluminum, brass, stainless steel, or copper). Figure 1B In the schematically illustrated embodiment, the corridor 160 is a hollow annular region that follows a complete circumference of the outer conductor 130 and is axisymmetric about the axis of the RF tube 110. The axisymmetric design of the corridor 160 provides the advantage of preventing additional reflections and non-axisymmetric wave modes of the RF electromagnetic waves propagating in the RF tube 110. The corridor 160 and the conductive sensor housing 165 can be integrally formed with the RF tube 110 or can be symmetrically attached around the RF tube 110 and are positioned during assembly to help avoid alignment errors between the longitudinal axis of the RF tube 110 and the current sensor 140. In either case, the conductive sensor housing 165 and the outer conductor 130 are electrically and physically connected. Accordingly, the sensor housing 165 can be considered as an extension of the outer conductor 130 of the coaxial RF tube 110.

[0048] although Figure 1B The embodiment in question has an annular corridor 160, but in another embodiment, the corridor may not be annular. In another embodiment, the axisymmetry of the RF tube 110 may have been unavoidably disrupted, for example, by bending within the RF tube 110, and therefore, the additional axisymmetry loss due to asymmetry in the VI sensor design may be insignificant. Relaxing the axisymmetry in the VI sensor design may then be reasonable. For example, the corridor may partially follow the circumference of the outer conductor 130 without forming a complete loop in the RF tube 110.

[0049] refer to Figure 1B and Figure 1CThe corridor 160 is shown as being completely enclosed by the sensor housing 165 and the conductive surfaces of the outer conductor 130, except for the slit 132 connecting the corridor 160 and the hollow area of ​​the RF tube 110. The current pickup 141 of the current sensor 140 is shown located in the corridor 160 directly above the slit 132. Figure 1B In the embodiment shown, the current pickup 141 includes three conductive branches (referred to as a half-loop) arranged in a rectangular shape on three sides: 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 one embodiment, the vertical and horizontal branches of the current pickup 141 are formed using three separate parts. In another embodiment, a different number (fewer / more) of parts may be used.

[0051] Slit 132 is designed to allow magnetic flux to penetrate into corridor 160. The current flowing in inner conductor 120 causes the magnetic flux to circulate around the longitudinal axis LA1 of inner conductor 120 in the region between inner conductor 120 and outer conductor 130. Without slit 132, the magnetic flux outside outer conductor 130 would be approximately zero because, according to Ampere's law, the equal but opposite return current flowing on the inner surface of outer conductor 130 would cancel out the circulating magnetic flux caused by the current in inner conductor 120. Slit 132 deflects the return current to flow along the inner surface of the outer conductive body of sensor housing 165 by disrupting the continuity in cylindrical outer conductor 130. Therefore, the hollow region of corridor 160 containing semi-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 inside corridor 160 through a rectangular semi-loop of current pickup 141. In one example, the slit 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 magnetic flux, there is also an electrical flux emanating from the inner conductor 120 due to the voltage difference between the inner conductor 120 and the grounded outer conductor 130. Undesirable electrical flux may leak into the corridor 160 through the gap in the grounded sheath provided by the slit 132 formed in the outer conductor 130. The changing magnetic flux through the half-loop of the current pickup 141 induces an electrical signal, which is a measure of I(t) at that location. However, the electrical flux entering the corridor 160 may couple with the current pickup 141 and contaminate the signal generated by the magnetic flux. Accordingly, as in Figure 1CAs shown, slit 132 has been designed to have a width of approximately 1 mm to approximately 5 mm (parallel to the dimensions of LA1). The width of slit 132 can be kept narrow to help reduce the electrical flux entering the corridor 160 from inside the RF tube 110.

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

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

[0055] The current pickup 141 is topologically a half-loop (a loop with two open ends), forming a turn around a region with a rectangular cross-section (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 RF electromagnetic waves 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... Figure 1B The image shows a pair of symmetrical terminals 144 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. This is due to the measurement system (e.g., Figure 1A and Figure 1B The VI analyzer 60 in the middle utilizes 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 the current pickup 141 is completed outside the VI sensor by a combination of the termination impedance, the input impedance of the initial detection system, and the impedance of the cable (if the cable is used to transmit the output signal of the current sensor 140 to the initial detection system of the measurement system). If the initial detection system is located at the current sensor 140 itself, the requirement to match the detector impedance with the cable impedance is eliminated. If the measurement system is located away from the current sensor 140, the terminals 144 can be connected to the initial detection system of the measurement system using a coaxial signal line, including, for example, a coaxial cable. The impedance of the coaxial cable is typically in the range of about 20 ohms to about 300 ohms. It is advantageous to terminate the coaxial signal line with a 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 the current sensor 140 to symmetrically terminated coaxial signal lines to preserve the symmetry of the output signal of the 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 a current sensor provides higher accuracy when measuring I. To detect the differential signal, a pair of coaxial cables, for example, must be used to provide the paired signal 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 terminals in 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 the detector. It should be noted that some other suitable impedance can be used for the termination; the impedance does not need to be 50 ohms. Furthermore, the second coaxial cable can be omitted, and a termination with a suitable impedance can be directly attached to the second terminal in the paired terminals 144.

[0059] The design of the measurement system, including the elements used to connect the current sensor 140, also considers the impedance to ground due to the parasitic capacitance of the electronic components. Because of the frequency dependence of parasitic capacitance impedance, the impedance of a component at RF frequencies may differ significantly from its impedance 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 a resistor component at DC may decrease as the frequency of the electrical signal increases into the RF range. Resistors with higher resistance values ​​are more sensitive to the frequency of the RF signal. Since the parasitic capacitance to ground depends on the geometry and the geometry in which the resistor is placed, it is difficult to control impedance variations from cell to cell if the resistor has a high resistance value. Therefore, to maintain measurement accuracy, it is advantageous to restrict the design of the initial detection system to use resistors with resistance values ​​less than 0.1 times 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... Figure 1B As shown in the illustration. The insulating ring 152 may comprise Teflon or some other plastic material or some other suitable dielectric. In one embodiment, a voltage pickup 151, such as a conductive ring, may be exposed to air (or other insulator) between the inner conductor 120 and the outer conductor 130. In another embodiment, the voltage pickup 151 may be embedded in an insulating housing. In all embodiments, the voltage pickup 151 (e.g., a conductive ring) may be electrically insulated from the 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) may be the same as the inner diameter of the outer conductor 130. In another embodiment, the inner diameter of the voltage pickup 151 (e.g., a conductive ring) may 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 disturbance to 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 contacts of the voltage pickup 151 extend outside the outer conductor 130 and terminate at a third terminal 153 (e.g., a third coaxial cable connector) attached to the sensor housing 165. The current pickup 141, voltage pickup 151, and contacts to the corresponding terminals 144 and 153 may comprise a highly conductive metal (e.g., copper) and may be entirely insulated from other conductive elements such as the outer conductor 130 and the conductive sensor housing 165.

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

[0063] As in Figure 1B and Figure 1C As shown, the longitudinal axis LA1 of the RF transistor 110 lies 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 transistor 110. Furthermore, as in... Figure 1CAs can be more easily observed, along a direction orthogonal to the longitudinal axis LA1 of the RF tube 110, the current pickup 141 includes: a first mirror-symmetric plane M1, which includes the longitudinal axis LA1 of the RF tube 110; and a second mirror-symmetric plane M2, which is orthogonal to the first mirror-symmetric plane M1. In one or more embodiments, the first mirror-symmetric 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 around the longitudinal axis LA1 and vertically pass through the plane P1 of the half-loop. In this configuration, the magnetic field is inductively coupled to the current pickup 141 (as desired). Undesirable 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 the current-carrying conductor reflects the corresponding current, the current sensor 140 can generate a time-varying electrical signal reflecting the RF current at the corresponding location 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 the detection system, and the differential voltage between the two terminals 144 is used as the output signal of the current sensor 140. See below for reference. Figure 2B The advantages offered by differential output technology will be explained in further detail.

[0065] The potential and electric field magnitude profiles are approximately circles 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 radially guided from the inner conductor 120 perpendicular to the longitudinal axis LA1. A ring-shaped voltage pickup 151 is approximately located on one of these circular profiles. In this configuration, an oscillating electric field in the space outside the inner conductor 120 is capacitively coupled to the voltage pickup 151, and according to the physical laws of electromagnetism, the conductive ring acquires an oscillating potential approximately 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, for example, by reducing the inner diameter of the voltage pickup ring to position the voltage pickup 151 of the voltage sensor closer to the inner conductor 120.

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

[0067] The raw output signals (e.g., one pair from current sensor 140 and another pair from voltage sensor 150) can be transmitted to the 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 the middle is similar to Figure 1B The VI sensor 100 is located within the VI sensor 200. A current sensor 240 and a voltage sensor 250 are placed within the annular channel 260 of the VI sensor 200. Figure 2A and Figure 2B In the diagram, the inner conductor of the RF tube has been removed to better showcase the voltage pickup ring 251 of the voltage sensor 250 inside the outer conductor 230. (3D view) Figure 2A The diagram shows the three terminals of the VI sensor 200 (coaxial cable connectors in this example). Pairs of terminals 244 extending to the top of the corridor 260 connect to the current pickup 241 of the current sensor 240, as shown in... Figure 2B As shown in the diagram, 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 semi-loop comprising three conductors. 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 a horizontal branch 243, which is a third conductor horizontally positioned inside a corridor 260 above the outer conductor 230. A slit 232 along the circumference of the outer conductor 230 allows a magnetic field to pass through the plane of the semi-loop and induce an electromotive force in the conductive branches of the current pickup 241. The horizontal branch 243 of the current pickup 241 can be attached along the side of the conductor to a horizontal non-conductive (e.g., plastic) part 262. Figure 2A and Figure 2BIn the example embodiment of the VI sensor 200 shown, the horizontal branch 243 is insulated from the grounded metal sensor housing 265 and the outer conductor 230 by means of a plastic part 262 on the side and by air in the gap between the bottom of the horizontal branch 243 and the top of the outer conductor 230. In another embodiment, described in further detail below, the mechanical support for the horizontal branch 243 may be reinforced by means of an additional plastic part 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. Slit 232 allows the magnetic field to penetrate from the RF tube into the corridor 260 where the current pickup 241 is located. Any coupling between the current pickup 241 and 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 referenced above... Figure 1B and Figure 1CAs mentioned, the RF electric field is in the radial direction (vertical to the coaxial axis LA1 of the RF tube), and correspondingly, the current flux leaking into the corridor is approximately proportional to the slit width, defined above as a dimension parallel to LA1. The width of slit 232 can be chosen to be relatively small to reduce the amount of current flux entering the corridor 260 due to the gap formed by slit 232 in the outer conductor 230. Secondly, a differential signal can be used as the output signal to further reduce the influence of the portion of the electric field that may penetrate into the cavity regardless of the 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 slit 232, the weak electric field inside the corridor 260 can be capacitively coupled to the current pickup 241. However, the current pickup 241, slit 232, and corridor 260 can be configured to be mirror-symmetric about a plane oriented about the center of slit 232 and perpendicular to the longitudinal axis of the RF tube. Due to the geometric mirror symmetry of the semi-loop current pickup 241 mentioned above, the perturbation along the vertical branch 242 is approximately equal in magnitude and phase to the perturbation of the potential appearing at the two terminals 244. This symmetry property can be advantageously used because it means that the differential signal is unaffected by parasitic signals in the current pickup 241 caused by interaction with the penetrating electric field in the corridor 260. In other words, the potential difference between the first and second terminals of the paired terminals 244 remains undisturbed and correct on the first order. These aspects of the current sensor 240 design can advantageously enable current measurement with high accuracy, particularly in applications such as providing RF bias signals to an electrostatic substrate support in a plasma chamber, where the load impedance allows for a relatively high amplitude of the electric field and a relatively low amplitude of the magnetic field near the point where the RF signal enters the plasma chamber.

[0071] Still referencing Figure 2B The annular conductor located near the inner surface of the outer conductor 230, inside the outer conductor, 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 loop 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 an annular dielectric component 252 attached to the voltage pickup 251.

[0072] As explained above, voltage pickup 251 provides an electrical signal at the third terminal 253 of VI sensor 200, generated by charge polarization induced by the RF electromagnetic field. The potential at the third terminal 253 reflects the inner conductor (not shown for clarity). Figure 2B The oscillation voltage is shown in the figure. 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 loop, as shown in the reference above. Figure 1B The explanation given.

[0073] The ring design of the voltage pickup 251 utilizes axisymmetry to reduce the sensitivity of the voltage sensor 250's output to some errors in placement and size, as explained herein. First, circular symmetry eliminates the need for precise placement of the voltage pickup 251 because, on the first order, the potential at the conductive surface of the ring is independent of the ring's center position from the central axis (…). Figure 2A The axis 2B-2B' in Figure 1B The potential of voltage pickup 251 is primarily dependent 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, in first order, depends on the size and placement of the asymmetric voltage pickup. For example, a mushroom-shaped voltage pickup may be sensitive not only to the dimensions 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, sometimes manually, using a micrometer during assembly. Secondly, the design of voltage pickup 251 can largely offset any centering errors during the assembly of voltage sensor 250 into VI sensor 200. The axisymmetry of voltage pickup 251 ensures that, in first order, even if the center of voltage pickup 251 is slightly displaced from the longitudinal axis of the inner conductor, the total flux remains constant. The increase in current flux in the half of the ring that could be displaced closer to the inner conductor is balanced by the accompanying decrease in current flux in the other half of the conducting ring, which is now farther 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 with a current sensor 340 located in a corridor 360 inside a sensor housing 365 is shown. A horizontal branch 343 is shown as two vertical branches 342 supported by an insulating part 362 and connected to the current sensor 340. A slit 332 that winds around in a mirror-symmetric plane M2 is shown above the horizontal branch 343.

[0075] Similar to a reference Figure 2A and Figure 2BThe described VI sensor 200 includes a first voltage sensor 350 shown inside an 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 keep 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 the first voltage sensor 350 and the current sensor 340 have relative phase errors due to the difference in their measurement positions. In this embodiment, the opposing second voltage sensor 355 has opposite phase errors due to its symmetrical position relative to the current sensor 340 (i.e., the mirror symmetry plane M2 of the current sensor 340 is equidistant from the first voltage sensor 350 and the second voltage sensor 355). Due to symmetry, the relative phase error between the voltage and current in the RF signal waveform sensed by the first voltage sensor 350 and the corresponding error in the RF signal waveform sensed by the second voltage sensor 355 cancel each other out at least on the 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 the first voltage sensor 350 with the signal from the second voltage sensor 355. By using, for example, the arithmetic mean of the measurements from the first voltage sensor 350 and the second voltage sensor 355, the phase error can be reduced or even eliminated to produce a voltage measurement reflecting the voltage at the mirror symmetry plane.

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

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

[0079] Similar to a reference Figure 2A and Figure 2B The described VI sensor 200 and VI sensor 400 include a current sensor 440 and a voltage sensor 450 placed in a corridor 460. The design of the VI sensor 400 has been improved relative to the design of the VI sensor 200 by providing additional mechanical support to the horizontal conductor 443 of the current pickup 441 of the current sensor 440 (see [link to design details]). Figure 2A and Figure 2B The improvements have been made.

[0080] exist Figure 4 In the design of the VI sensor 400 shown, the support components (e.g., plastic parts 462 and 470) and Figure 2B The corresponding parts (e.g., plastic parts 262) in the VI sensor 200 shown can more securely fix the horizontal branch 443 compared to those in the VI sensor 200. For example, in one embodiment, the plastic parts 262 at both ends of the horizontal branch 243 in the VI sensor 200 are rings with a set of holes in which the horizontal branch 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 outer surface of the metal sensor housing 465 and the outer conductor 430.

[0081] As in Figure 4 As shown, in addition to the insulating support 462, a support structure 470 (e.g., made of plastic or other non-conductive material) holds the conductive horizontal branches 443 of the current pickup 441 from all sides. The support structure 470 includes a first portion for supporting a first part of the horizontal branch and a second portion for supporting a second part of the horizontal branch, separated by a gap. In contrast, as shown in... Figure 2B As shown, plastic part 262 (similar to support 462) does not branch off horizontally from below. Figure 2BIn this configuration, an overhead space exists between the horizontal branch 243 of the current pickup 241 in the current sensor 240 and the outer conductor 230. When the vertical branch 442 of the current pickup 441 is positioned to contact the horizontal branch 443, additional support prevents the horizontal conductor 443 from bending. Furthermore, the support structure 470 prevents the vertical branch 442 from being overly tightened to the horizontal branch 443. Changes in the magnetic flux coupled to the current pickup 441 are affected by variations in the shape and area of ​​the semi-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 current measurement.

[0082] Figure 5 A VI sensor 500 is shown attached to an RF tube 510 comprising an inner conductor 520 and an outer conductor 530. A current sensor 540 is shown having a pair of terminals 544 disposed above a sensor housing 565 and a single-turn half-loop current pickup 541 disposed within a corridor 560. The current pickup 541 includes two vertical branches 542 attached to a horizontal branch 543. Similar to... Figure 4 In the VI sensor 400, 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, thus providing a significant advantage over the VI sensor 400 (in...). Figure 4 (As shown) Reduced manufacturing costs. By using a voltage sensor 550 (where an insulator 555, which centers the inner conductor 520 of the RF tube 510, also serves 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 As shown in the diagram, using the same plastic part 555 for multiple purposes allows for the elimination of some plastic parts, such as those used in 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 has been positioned closer to the inner conductor 520 by designing its diameter to be smaller than that of the outer conductor 530. The smaller diameter of the voltage pickup ring improves the output signal strength of the voltage sensor 550, as referenced above. Figure 1B and Figure 1C The explanation given.

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

[0086] It should be understood that the mandrel may not perfectly conform to the mathematical definition of a toroidal coil, but it generally resembles a toroidal coil with structures for attaching coils, forming connections with terminals, etc.

[0087] Figure 6A A 3D view of the VI sensor 600 is shown. Figure 6B A sectional view was shown, and Figure 6C A cross-sectional view along axis A-A' of sensor VI 600 is shown.

[0088] Figure 6A The conductive sensor housing 665 of the VI sensor 600 is shown. Figure 6A The invisible current and voltage pickups are housed within a space enclosed by a conductive sensor housing 665. Figures 6A to 6C In the middle, the inner conductor will pass through the central hole 621. For clarity purposes, from Figures 6A to 6C Various views of the VI sensor 600 omit the inner conductor itself. The outer conductor of the RF tube connects to flanges at the top and bottom of the conductive sensor housing 665. Two neck regions 631 are shown as... Figure 6A The sensor housing 665 has adjacent flanges at its top and bottom portions. The neck region 631 can be designed to resemble the shape and size of the outer conductor of an RF tube. Therefore, the sensor housing 665 can be interpreted as an extension of the outer conductor extending from the neck region 631 into a wider central portion comprising a top cover 663 and a bottom cover 666 with conductive walls of a larger diameter. The sensor housing 665 and the outer conductor form a coaxial outer shield and can be connected to ground. See below for reference. Figure 6B and Figure 6C As described, the wider central portion of the sensor housing 665 accommodates an annular dielectric cavity 661 surrounding the inner conductor passing through the central aperture 621.

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

[0090] Figure 6B Sectional views and Figure 6C Along the cutting plane A-A' (in Figure 6A The cross-sectional view shown illustrates the internal structure of the VI sensor 600. The inner conductor of the RF tube is omitted for clarity. (As shown in...) Figure 6B and Figure 6C The inner surface 638 of the central hole 621 shown inside the neck region 631 forms a sidewall that can be interpreted as the interior of the main coaxial structure of the RF tube. The neck region 631 extends 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 hole 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 the inner wall is interrupted by a slit 671. Figure 6C As shown, the dielectric cavity 661 is located between a first major outer surface 627 and a second major outer surface 628 along a radial direction from the center of the central aperture 621. The first major outer surface 627 includes a continuous annular region that is in physical contact with the central aperture 621. Vertically, the annular first major outer surface 627 is divided into two parts by a slit region 671. The second major outer surface 628 is located at a radial distance greater than the radius of the first major outer surface 627.

[0091] Cavity 661 includes slit region 671. (As in...) Figure 6B and Figure 6C As shown, slit region 671 includes a physical fracture in the inner surface 627 of the cylindrical wall of central hole 621, which forms a gap in the joint between the top cover 663 and the bottom cover 666 of sensor housing 665. Surface 627 is an extension of surface 638 of the cylindrical wall of central hole 621. When viewed radially from the center of central hole 621, slit region 671 has the appearance of an insulating ring physically in contact with central hole 621. Further radially outward, slit region 671 presents a tortuous shape that bypasses the annular conductive voltage pickup 651, as if... Figure 6B and Figure 6CThe zigzag dotted line in the diagram indicates this. The continuous insulating annular region radially disposed between the physical contact portion of cavity 661 and the inner radius of the annular current sensor 641 is referred to as the slit region 671 of the VI sensor 600. (As shown in...) Figure 6B and Figure 6C As shown, slit region 671 forms a dielectric barrier between the conductive voltage pickup 651 and the current sensor 641 and the sensor housing 665. In the region radially located between the first major outer surface 627 and the second major outer surface 628, cavity 661 (including insulating slit region 671) electrically isolates top cover 663 from bottom cover 666. For radial distances smaller than the first major outer surface 627, top cover 663 is electrically isolated from bottom cover 666 via central hole 621. Top cover 663 is electrically coupled to bottom cover 666 via coupling region 629 radially outside the second major outer surface 628 of dielectric cavity 661.

[0092] Using this design, almost no RF current flowing in the ground sensor housing 665 can flow within the area surrounded by the annular current sensor 641. The current will flow vertically along the inner wall 638 in the neck region 631 and then around the current sensor 641 due to a physical break in the inner surface 638 formed by the dielectric slit 671. Due to the slit 671, the current will be turned radially outward around the annular current sensor 641, thus 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 located within the annular dielectric cavity 661, in the outer portion of the cavity (i.e., the area farther from the central aperture 621). The current sensor 641 includes a conductive coil 647 and an annular mandrel 642. The coil 647 includes multiple turns of continuous conductive wire wound around the central circular axis of the annular mandrel 642. The two opposite ends of the coil 647 can be attached to a coaxial connector 645, as shown in... Figure 6B As shown in the diagram. The conductive wire of coil 647 can be a bare conductor, an enameled conductor, or a conductor coated with an insulator. See below for reference. Figure 6D The annular mandrel 642 is described in further detail. The current sensor 641 is electrically insulated from the conductive sensor housing 665.

[0094] As in Figure 6B and Figure 6CAs shown, the conductive voltage pickup 651 of the voltage sensor is shaped like a conductive ring. The voltage pickup 651 is shown disposed in a region of an annular dielectric cavity 661 between the annular current sensor 641 and the central hole 621. A solid dielectric material (e.g., plastic) can be used for the parts that 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 diagram illustrates the connection between voltage pickup 651 and center terminal 654. (Coaxial connector 645 and center terminal 654 are not included in the cut plane A-A'; therefore, in...) Figure 6C (Not visible in the cross-sectional view shown.)

[0095] The function of voltage pickup 651 is to sense the RF voltage at the center of the central aperture 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 voltage pickup 651 is shielded from the inner conductor due to, for example, a grounded metal ring placed in the annular dielectric region between the inner conductor of the RF tube and voltage pickup 651, voltage pickup 651 may not function properly. In the case of excessive shielding, the voltage sensor output will be too weak to be usable. As in Figure 6B and Figure 6C As shown, the voltage pickup 651 extends vertically above and below the slit region 671 of the annular dielectric cavity 661. The cavity is formed above by a recess in the metal top cover 663 and below by a corresponding recess in the metal bottom cover 666. Although the grounded conductive inner walls of these recesses 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. Figure 6B and Figure 6C The dielectric slit 671 shown separates the top cover 663 from the bottom cover 666. The slit 671 is considered in a mirror plane M (by...). Figure 6C The dielectric region (indicated by the dashed line in the diagram) resembles a cylindrical disk because there is no inner conductor in the central aperture 621. When the inner conductor is in place, the dielectric slit 671 will resemble an annular disk surrounding the inner conductor. The unshielded radial electric field in the dielectric slit 671 will be sensed through capacitive coupling between the inner conductor and the central 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 the cyclic magnetic field passing through the coil in a direction parallel to the central circular axis of the annular mandrel 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 mandrel 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 passing through the planar region within the central aperture (analogous to the donut-shaped aperture of a donut) enclosed in the annular current sensor. As applicable to 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 as the equivalent outer conductor of the RF tube, wherein the inner conductor passes through the central aperture 621. Therefore, the current sensor 641 may not function properly unless the RF current in the sensor housing 665 is confined to flow outside the disk-shaped region enclosed by the outer circumference of the annular mandrel 642. For example, if the top cover 663 and the bottom cover 666 form electrical contact at a radial distance from the central axis shorter than the inner radius of the annular mandrel 642, a portion of the current in the conductive housing can flow through that contact. This current, flowing in the opposite direction to the current in the inner conductor, will reduce the magnitude of the total current enclosed by the current sensor 641, thus reducing the magnetic flux through the coil 647. If the total current through the contacts inside the region enclosed by the annular current sensor 641 is too low, the magnetic field may be insufficient to induce a usable electrical signal in the current pickup coil 647. Furthermore, the dielectric slit region 671 prevents electrical contact between the top cover 663 and the bottom cover 666 at a radial distance smaller than the inner radius of the annular current sensor 641, as in Figure 6B and Figure 6C As shown in the document.

[0097] The uninterrupted, continuous dielectric region separating the top cover 663 and the bottom cover 666 up to the outer circumference of the annular 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 means of a support member comprising insulating material. Therefore, 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 The text describes a winding, dotted line depicting a scene. Note the example of... Figure 6C As shown by the dashed line, the tortuous dielectric slit 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 grounding 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 as the current sensor 641 moves radially inward from the inner conductor include, firstly, a conductive voltage pickup 651, and secondly, a portion of the inner wall of the conductive sensor housing 665, as shown in... Figure 6B and Figure 6C As shown and described above, these inserted conductive parts help shield the current sensor 641 from the radial electric field. Some electric field lines emanating from the inner conductor can be terminated on the grounded inner wall of the conductive sensor housing 665. Additionally, the conductive voltage pickup 651 serves a dual purpose by partially shielding the coil 647 from the RF electric field. Since the voltage pickup 651 is not short-circuited to ground, the reduction in the electric field provided by the conductive ring depends on the magnitude of the impedance to ground at the center terminal 654.

[0099] The current sensor 641 and voltage pickup 651 of the VI sensor 600 are both axially symmetrical about a shared axis passing through the center and in a direction normal to the plane of the central hole 621. Furthermore, the current sensor 641 and voltage pickup 651 share the same mirror plane perpendicular to the longitudinal axis (in... Figure 6C (Indicated by the dashed line M). The symmetry of the structure of the VI sensor 600 helps reduce / eliminate any measurement difference in the phase angle (Φ) between voltage and current. Furthermore, the first-order cancellation effect attributable to axisymmetry makes the sensor output signal of the VI sensor 600 less sensitive to machining tolerances and positioning errors during assembly.

[0100] Figure 6D It demonstrates what can be used as Figure 6B The annular current sensor 641 shown is an example of annular structure for its spindle 642. The annular spindle 642 has continuous grooves on its outer surface, in which conductive wires can be placed to form a coil 647. Figure 6B (As shown in the diagram). The two opposite ends of coil 647 can pass through... Figure 6D The two openings 643 shown in the figure are subsequently attached to a pair of coaxial connectors 645 (see [reference]). Figure 6B Voltage pickup 651 (see...) Figure 6B It can be connected by a conductive element passing through a hole in the annular mandrel 642 and an opening 653 to be attached to the center terminal 654.

[0101] The annular mandrel 642 comprises plastic and other insulating materials and can be fabricated using, for example, 3D printing technology. After the coil 647 has been mounted on the grooved annular mandrel 642, the structure can optionally be encapsulated in a resin coating using, for example, resin embedding technology. 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, which includes a current sensor 641 and a combined electric field shield and voltage pickup 651, provides the advantages of a compact VI sensor design.

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

[0104] Figure 7A A perspective view of a current sensor assembly 701 using a ring-shaped 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. See below for reference. Figures 7C to 7E The current sensor 741 is further described. The top cover 782 and bottom cover 784 may comprise 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 can be used with the current sensor assembly 701 will pass through the central hole 710. Therefore, the current sensor assembly 701 will be symmetrically positioned 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 In this diagram, the current sensor 741 has been removed from the sensor housing 765 to show the structure of the lower half of the dielectric cavity 720 and the bottom cover 784. (See below for reference) 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 tortuous dielectric slit 725. The outer dielectric region is the region above the outermost recess in the base plate of the bottom cover 784. Outside the outer circle of this outermost recess, 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 recess, no electrical contact can be formed between the top cover 782 and the bottom cover 784.

[0106] The tortuous dielectric slit 725 includes a dielectric region above two recesses on either side of a conductive ridge 750 resembling a ring projecting from the bottom plate of the bottom cover 784. The conductive bottom surface of the dielectric cavity 720, including the conductive ridge 750, is 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 may protrude into a corresponding recess in the top metal cover 782, but may not contact the top plate. Therefore, the combined top and bottom portions of the tortuous dielectric slit 725 will be a tortuous dielectric region that winds around and above the conductive ridge 750, as shown in... Figure 7B The middle part is indicated by the zigzag dotted line.

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

[0108] exist Figure 7C In the image, the current sensor assembly 701 is shown in a cross-sectional view including an exploded view of the current sensor 741. The current sensor 741 includes an annular mandrel 742 and a conductive current pickup coil 747. The annular mandrel 742 includes a solid dielectric material with winding channels. The winding channels can be accessed through access holes 749 at various locations on the surface of the annular mandrel 742. An attachment 743 with two holes has been placed above one of the access holes 749. The two opposite 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 mandrel 742 has been cut away to show the conductive wire of the coil 747 tunneling through the winding channels in the solid dielectric material of the annular mandrel 742. The coil 747 is embedded inside the mandrel 742. The design of the mandrel 742 provides greater mechanical support compared to the grooved design of the mandrel 642, thereby eliminating the foregoing references. Figure 6D The resin encapsulation steps described.

[0109] exist Figure 7C In the middle, the annular mandrel 742 has been placed in the corresponding grooves on the base plate of the outer dielectric area 723 and the bottom cover 784 (see...). Figure 7BThe exploded view of the current sensor assembly 701 shows that the upper half of the annular mandrel 742 can be fitted into a recess in the top cover 782 within the outer dielectric region 723 of the dielectric cavity 720. A conductive ridge 750 can similarly extend into an adjacent recess in the top cover 782 and into the tortuous dielectric slit 725 of the dielectric cavity 720. The conductive ridge 750, being a continuous ring inserted between the annular current sensor 741 and the inner conductor 711, effectively shields the current sensor 741 from the effects of RF electric fields.

[0110] As explained above, the electrical contact between the grounded top cover 782 and the grounded bottom cover 784, within the area surrounded by the annular current sensor 741, will weaken the strength of the magnetic field passing through the current pickup coil 747 and may excessively attenuate the output signal of the current signal. Therefore, the top of the conductive ridge 750 is electrically isolated from the top cover 782 by a tortuous dielectric slit 725. Figure 7C The meandering shape of the dielectric region is indicated by the zigzag dashed lines.

[0111] exist Figure 7D A cross-sectional view of a portion of the RF system 700 shown in the image illustrates a current sensor assembly 701, with a top cover 782 mounted above a bottom cover 784. Figure 7D The zigzag dashed line in the middle indicates the zigzag shape of the dielectric slit 725.

[0112] Figure 7E A plan view shows the bottom portion of the inner conductor 711 of the current sensor assembly 701 and the RF tube passing through the central hole 710 of the current sensor assembly. 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 positioned above an opening similar to the inlet hole 749. An annular conductive ridge 750 is considered to be inserted between the inner conductor 711 and the current sensor 741. A dielectric slit 725 is considered to be on either side of the conductive ridge 750.

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

[0114] Although the mandrel described in this disclosure resembles a toroidal coil, it should be understood that other shapes can be used, such as a square or a regular polygon with any number of sides. Furthermore, pickups of various shapes can be implemented without using a mandrel.

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

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

[0117] The VI sensor and measurement method described in this disclosure provide embodiments that enable extremely high-precision measurements at low manufacturing costs. High precision can be achieved at low manufacturing costs by including design features designed to reduce the sensitivity of VI measurements to machining and assembly errors. The accuracy of a current sensor depends on machining tolerances that cause variations in the dimensions of the geometry that determines the current pickup (e.g., the area enclosed by a rectangular semi-loop). The accuracy of current measurement can also be limited by assembly tolerances, such as the accuracy of the current pickup's placement, including the radial distance from the longitudinal axis and the angle between the plane of the semi-loop and the longitudinal axis. Similarly, the accuracy of voltage measurement 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 on the sensitivity of VI sensor signals to variations in the size and placement of current and voltage pickups and have found that high accuracy of 1% and placement tolerance values ​​of 0.005 inches can be achieved for standard machines. The computer simulation was performed using a calibrated 3D finite element solver on Maxwell's equations within a wide range of RF power, RF frequency, and load impedance used in plasma processing.

[0118] The exemplary embodiments of this application are summarized herein. Other embodiments can also be understood from the full text of the specification and the claims filed herein.

[0119] Example 1. A radio frequency (RF) system includes: an RF power supply configured to power a load with an RF signal; an RF tube including an inner conductor and an outer conductor connected to ground, the conductors coupling the RF power supply to the load; and a current sensor aligned with the central axis of the RF tube carrying the RF signal. The current sensor is configured to monitor a current in the RF signal and includes a conductive half-loop disposed near the RF tube, wherein the conductive half-loop includes a first end and an opposing second end. The current sensor is configured to output an output signal between the first end and the second end. A sensor housing is disposed around the RF tube, wherein the sensor housing includes a conductive material connected to the outer conductor of the RF tube. A corridor is disposed within the sensor housing and outside the outer conductor of the RF tube, wherein the current sensor is disposed in the corridor. A slit in the outer conductor of the RF tube exposes the current sensor to a magnetic field generated by the current in the inner conductor of the RF tube due to the RF signal.

[0120] Example 2. A system as described in one of Examples 1, wherein the slit has a length along the inner circumference of the outer conductor and a width parallel to the central axis of the RF tube, and wherein the width is between 0.5 mm and 5 mm.

[0121] Example 3. A system as described in either Example 1 or 2, wherein, along a direction orthogonal to the central axis of the RF tube, the conductive half-loop includes: a first mirror symmetry plane including the central axis of the RF tube; and a second mirror symmetry plane orthogonal to the first mirror symmetry plane, wherein the first mirror symmetry plane of the conductive half-loop is coplanar with the central axis of the RF tube.

[0122] Example 4. A system as described in any one of Examples 1 to 3, wherein the conductive half-loop includes: a branch aligned parallel to the axis of the RF tube; a second branch coupled to a first end of the first branch, the second branch being orthogonal to the first branch; and a third branch coupled to a second end of the first branch, the third branch being orthogonal to the first branch and parallel to the second branch.

[0123] Example 5. The system as described in any one of Examples 1 to 4 further includes: insulating support structures for supporting various branches of the conductive half-loop.

[0124] Example 6. A system as described in any one of Examples 1 to 5, wherein the RF tube includes: an inner conductor electrically coupled to the RF power supply and the load; and an outer conductor electrically coupled to a reference potential node.

[0125] Example 7. The system as described in any one of Examples 1 to 6 further includes: a first voltage sensor for monitoring the voltage of the RF signal, the first voltage sensor being arranged axially symmetrically around the RF tube.

[0126] Example 8. A system as described in any one of Examples 1 to 7, wherein the first voltage sensor includes: a conductive ring disposed along the inner surface of the outer conductor of the RF tube; and an insulating ring disposed between the conductive ring and the outer conductor of the RF tube, wherein the insulating ring electrically insulates the conductive ring from the RF tube.

[0127] Example 9. The system as described in any one of Examples 1 to 8 further includes: a second voltage sensor symmetrically disposed around the RF tube, wherein the first voltage sensor is located at a first position on the axis of the RF tube, the second voltage sensor is located at a second position on the axis of the RF tube, and wherein a first distance between the first position and a mirror-symmetric plane of the current sensor is approximately the same as a second distance between the second position and the mirror-symmetric plane.

[0128] Example 10. A radio frequency (RF) system comprising: an RF power supply configured to power a load with an RF signal; an RF tube including an inner conductor and an outer conductor connected to a reference potential node, the conductors coupling the RF power supply to the load; and a first voltage sensor axially symmetrically disposed around an axis of the RF tube carrying the RF signal, the first voltage sensor being configured to monitor the voltage of the RF signal.

[0129] Example 11. The system as described in Example 10 further includes: a second voltage sensor symmetrically disposed around the RF tube, wherein the first voltage sensor is located at a first position on the axis of the RF tube, and the second voltage sensor is located at a second position on the axis of the RF tube.

[0130] Example 12. The system as described in any one of Examples 10 or 11 further includes: a current sensor disposed at a third location around the RF tube, the current sensor being aligned with the axis of the RF tube carrying the RF signal, the current sensor being configured to monitor the current of the RF signal.

[0131] Example 13. A system as described in any one of Examples 10 to 12, wherein the third position is disposed between the first position and the second position.

[0132] Example 14. A system as described in any one of Examples 10 to 13, wherein the current sensor includes a conductive half-loop comprising a first end and an opposing second end, wherein, along a direction orthogonal to the axis of the RF transistor, the conductive half-loop includes: a first mirror-symmetric plane including the axis of the RF transistor; and a second mirror-symmetric plane orthogonal to the first mirror-symmetric plane, wherein the first mirror-symmetric plane of the conductive half-loop is coplanar with the axis of the RF transistor.

[0133] Example 15. A system as described in any one of Examples 10 to 14, wherein the first distance between the first position and the mirror symmetry plane is approximately the same as the second distance between the second position and the mirror symmetry plane.

[0134] Example 16. A method for measuring a radio frequency (RF) signal, the method comprising: aligning a current sensor with an axis of an RF tube carrying the RF signal, the current sensor being disposed in a corridor disposed within a sensor housing and outside an outer conductor of the RF tube, the sensor housing being disposed around the RF tube, the current sensor including a conductive half-loop including a first end and an opposing second end; and determining a current of the RF signal based on measuring an output signal between the first end and the second end.

[0135] Example 17. The method as described in Example 16, wherein the RF tube includes an inner conductor electrically coupled to an RF power supply and a load, and an outer conductor, wherein the method further includes grounding the outer conductor.

[0136] Example 18. The method as described in any one of Examples 16 or 17, further comprising: arranging a first voltage sensor axially symmetrically around the RF tube; and determining the voltage of the RF signal based on measuring an electrical signal at a terminal of the first voltage sensor.

[0137] Example 19. The method of any one of Examples 16 to 18, further comprising: symmetrically distributing a second voltage sensor around the RF tube, wherein the first voltage sensor is located at a first position on the axis of the RF tube, and the second voltage sensor is located at a second position on the axis of the RF tube; and measuring another electrical signal at a terminal of the second voltage sensor, wherein the voltage of the RF signal is determined based on the electrical signal and the other electrical signal.

[0138] Example 20. The method as described in any one of Examples 16 to 19, wherein the conductive half-loop comprises: a first mirror-symmetric plane including the axis of the RF transistor; and a second mirror-symmetric plane orthogonal to the first mirror-symmetric plane, wherein the first mirror-symmetric plane of the conductive half-loop is coplanar with the axis of the RF transistor.

[0139] Although the invention has been described with reference to illustrative embodiments, this description is not intended to be limiting. Various modifications and combinations of the description, illustrative embodiments, and other embodiments of the invention will be apparent to those skilled in the art. Therefore, the appended claims are intended to cover any such modifications or embodiments.

Claims

1. A radio frequency (RF) system, comprising: Radio frequency (RF) power supply, which is configured to supply power to a load using RF signals; An RF transistor, comprising an inner conductor and an outer conductor connected to ground, which couples the RF power supply to the load; A current sensor is aligned with the central axis of the RF tube carrying the RF signal. The current sensor is configured to monitor the current of the RF signal. The current sensor includes a conductive half-loop disposed near the RF tube. The conductive half-loop includes a first end and an opposing second end. The current sensor is configured to output an output signal between the first end and the second end. A sensor housing disposed around the RF tube, wherein the sensor housing includes a conductive material connected to an outer conductor of the RF tube; A corridor, disposed within the sensor housing and outside the outer conductor of the RF tube, wherein the current sensor is disposed within the corridor; and A slit in the outer conductor of the RF tube is used to expose the current sensor to the magnetic field generated by the current of the RF signal in the inner conductor of the RF tube.

2. The system as claimed in claim 1, wherein, The slit has a length along the inner circumference of the outer conductor and a width parallel to the central axis of the RF tube, wherein the width is between 0.5 mm and 5 mm.

3. The system as described in claim 1, wherein, Along a direction orthogonal to the central axis of the RF transistor, the conductive half-loop includes: a first mirror symmetry plane including the central axis of the RF transistor; and a second mirror symmetry plane orthogonal to the first mirror symmetry plane, wherein the first mirror symmetry plane of the conductive half-loop is coplanar with the central axis of the RF transistor.

4. The system as claimed in claim 1, wherein, The conductive half-loop includes: The first branch is aligned parallel to the axis of the RF tube; A second branch is coupled at the first end of the first branch, the second branch being orthogonal to the first branch; and A third branch is coupled at the second end of the first branch, the third branch being orthogonal to the first branch and parallel to the second.

5. The system of claim 4, further comprising: Insulating support structures are used to support the first, second, and third branches of the conductive semi-loop.

6. The system as claimed in claim 1, wherein, The RF transistor includes: The inner conductor, which is electrically coupled to the RF power supply and the load; and An outer conductor that is electrically coupled to a reference potential node.

7. The system of claim 1, further comprising: A first voltage sensor, used to monitor the voltage of the RF signal, is arranged axially symmetrically around the RF tube.

8. The system of claim 7, wherein, The first voltage sensor includes: A conductive ring, the conductive ring being disposed along the inner surface of the outer conductor of the RF tube; and An insulating ring is disposed between the conductive ring and the outer conductor of the RF tube, wherein the insulating ring electrically insulates the conductive ring from the RF tube.

9. The system of claim 8, further comprising: A second voltage sensor is symmetrically disposed around the RF tube, wherein the first voltage sensor is located at a first position on the axis of the RF tube, the second voltage sensor is located at a second position on the axis of the RF tube, and wherein the first distance between the first position and the mirror symmetry plane of the current sensor is approximately the same as the second distance between the second position and the mirror symmetry plane.

10. A radio frequency (RF) system, comprising: Radio frequency (RF) power supply, which is configured to supply power to a load using RF signals; An RF transistor, comprising an inner conductor and an outer conductor connected to a reference potential node, which couples the RF power supply to the load; A first voltage sensor is axially symmetrically disposed around the axis of the RF tube carrying the RF signal. The first voltage sensor is configured to monitor the voltage of the RF signal and is located at a first position on the axis of the RF tube. as well as A current sensor is disposed at a second location around the RF transistor, aligned with the axis of the RF transistor carrying the RF signal, and configured to monitor the current of the RF signal. The current sensor includes a conductive half-loop, which includes a first end and a second end.

11. The system of claim 10, further comprising: A second voltage sensor is symmetrically disposed around the RF tube, wherein the second voltage sensor is located at a third position on the axis of the RF tube.

12. The system of claim 11, wherein, The second position is set between the first position and the third position.

13. The system of claim 11, wherein, Along a direction orthogonal to the axis of the RF transistor, the conductive half-loop includes: a first mirror symmetry plane including the axis of the RF transistor; and a second mirror symmetry plane orthogonal to the first mirror symmetry plane, wherein the first mirror symmetry plane of the conductive half-loop is coplanar with the axis of the RF transistor.

14. The system of claim 13, wherein, The first distance between the first position and the mirror-symmetric plane is approximately the same as the second distance between the third position and the mirror-symmetric plane.

15. A method for measuring radio frequency (RF) signals, the method comprising: Aligning the current sensor with the axis of the RF transistor carrying the RF signal, the current sensor is disposed in a corridor located within a sensor housing and outside the outer conductor of the RF transistor. The sensor housing is disposed around the RF transistor. The current sensor includes a conductive half-loop comprising a first end and an opposing second end; and The current of the RF signal is determined by measuring the output signal between the first terminal and the second terminal.

16. The method of claim 15, wherein, The RF tube includes an inner conductor electrically coupled to an RF power supply and a load, and an outer conductor, wherein the method further includes grounding the outer conductor.

17. The method of claim 15, further comprising: The first voltage sensor is arranged symmetrically around the RF tube. as well as The voltage of the RF signal is determined by measuring the electrical signal at the terminals of the first voltage sensor.

18. The method of claim 17, further comprising: The second voltage sensor is symmetrically arranged around the RF tube, wherein the first voltage sensor is located at a first position on the axis of the RF tube, and the second voltage sensor is located at a second position on the axis of the RF tube; and Another electrical signal is measured at the terminal of the second voltage sensor, wherein the voltage of the RF signal is determined based on the first electrical signal and the second electrical signal.

19. The method of claim 18, wherein, The conductive half-loop includes: a first mirror symmetry plane including the axis of the RF transistor; and a second mirror symmetry plane orthogonal to the first mirror symmetry plane, wherein the first mirror symmetry plane of the conductive half-loop is coplanar with the axis of the RF transistor.

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