Electromagnetic field signal acquisition system with high signal-to-noise ratio and electrical noise immunity

Abstract

The present invention relates to a device and method for detecting electromagnetic radiation or signals emitted by a plasma. The device includes a sensor unit, and the sensing unit includes: a first sensor for detecting electromagnetic radiation or signals; an electromagnetic barrier, wherein the electromagnetic barrier is configured to surround the first sensor to prevent ambient electromagnetic radiation from reaching the first sensor; a first port through which electromagnetic radiation can pass, and the port is configured to be coupled to a port of a plasma chamber so that electromagnetic radiation or signals emitted from the plasma can reach the first sensor; and a first output, which is coupled to a balun and a double coaxial system, whereby the sensed signal is grounded and an inverted version of the signal is grounded. A signal acquisition system (SAS) for detecting electromagnetic radiation emitted by a plasma is also described.

Description

Technical Field

[0001] This disclosure is directed to improving the control and measurement of plasmas. Specifically, this disclosure is directed to improving the signal-to-noise ratio of measurement signals obtained from plasmas and increasing the electrical noise immunity of systems used to obtain these measurements. Background Art

[0002] Plasmas are very common and are used in many manufacturing and industrial processing environments. For example, low-pressure systems are used in advanced materials processing, including, for example, materials deposition and / or etching processes in the semiconductor or medical industry sectors. As a further example, atmospheric pressure plasma processing systems also have industrial applications, such as materials cleaning, adhesion, deposition, or etching in fields such as the aerospace and automotive industries.

[0003] Due to the increasing trend towards process automation, it is important to improve the control of plasma characteristics in industrial semiconductor processing equipment. One consideration in improving plasma characteristics control is the measurement of plasma characteristics. Currently, invasive plasma measurement techniques are the oldest and most commonly used methods for measuring plasma characteristics. These techniques involve immersing one or more probes into the plasma being studied.

[0004] However, in most industrial environments, invasive plasma measurement techniques are not desirable. In particular, the conditions under which plasmas are generated are typically harsh for many of the probes used for measurement. As a result, the probes used for invasive plasma measurement techniques are expensive and / or prone to failure. In addition, the probes themselves can interact with the plasma, thereby (sometimes unpredictably) altering the characteristics of the plasma. These problems reduce the accuracy of the measurement and, in turn, reduce the control of the plasma.

[0005] In addition, the equipment used for invasive plasma measurement techniques is difficult to retrofit to existing manufacturing equipment and infrastructure. In addition to this difficulty, the disruptive effects of installing invasive plasma measurement equipment can introduce additional complexity to the manufacturing line. This, in turn, can have an adverse effect on process replication, which is a key requirement for high-volume production. Therefore, the risk of increasing manufacturing line complexity and cost slows down the improvement of plasma measurement and control.

[0006] Therefore, non-invasive plasma measurement techniques may offer significant improvements in plasma control. For example, non-invasive plasma measurement devices can be easily coupled to existing plasma equipment. Another advantage is that existing plasma equipment can remain in place when coupled to a non-invasive plasma measurement device, reducing the risk of increasing the complexity and cost of the manufacturing line. Non-invasive plasma measurement is also much more accurate than invasive plasma measurement. Unlike many existing probe systems, non-invasive plasma measurement does not require placing a probe in the plasma. Thus, non-invasive plasma measurement does not disturb the plasma itself (which eliminates the risk of the probe altering the measurement one is trying to obtain). An example system was described by K Suzuki and M Sato in a paper titled "Advanced technology for monitoring plasma sparking ESD damage using high frequency magnetic field sensors" at the 2003 Electrical Overstress / Electrostatic Discharge Symposium. Various patent publications describe electromagnetic field signal acquisition systems with high signal-to-noise ratios and electrical noise immunity, such as US2005 / 0183821; JP H05188151; JP H1167732 and EP 1394835.

[0007] This disclosure is based on contributions provided by PCT / EP 2018 / 057556 and a paper by S. Kelly and P. J. McNally in Appl. Phys. Express 10 (2017) 096101, which describes a radio emission spectroscopy (RES) system. In a typical embodiment, for measuring and controlling plasma characteristics in a plasma processing chamber, the RES system involves placing the following near the interior of the plasma processing chamber (e.g., preferably 40 mm or less): a near-field (NF) electric field (E-field) antenna, and / or an NF magnetic field (B-field) antenna. Crucially, the (multiple) antennas are located outside the plasma, i.e., according to this disclosure, the (multiple) antennas are not immersed and do not make physical contact with the plasma during use.

[0008] However, in a typical semiconductor manufacturing facility, for example, the facility generally includes multiple plasma processing systems, each plasma processing system including at least one plasma chamber, and these plasma processing systems are not individually in a state of electromagnetic (radio frequency - RF) isolation from each other. In fact, a manufacturing facility may include dozens or more such systems, all operating simultaneously and all capable of generating RF electromagnetic emissions. Thus, these processing systems may interfere with each other and with the RES system.

[0009] In addition, there may be other local RF sources. As another example, high-speed electrical equipment generates electromagnetic noise. Therefore, it is crucial to design a RES system that is only capable of receiving electromagnetic signals from the single plasma processing chamber it is targeted at. It is crucial that the RES system must be immune to noise signals, such as signals from other electronic systems (including, for example, other plasma processing chambers, auxiliary electrical equipment, etc.) and general broadband local RF background emissions. Signals from the antenna head are vulnerable to "skin" inductive noise from the cable. In the operating environment of a plasma chamber, RF noise from control machines / computers and adjacent plasma chambers is very dense, for example, in an industrial environment where machines are arranged in a long line in a "chasing" manner. This can result in RF interference. In addition, the signal level from one or more antennas is very low, and any local amplification will introduce broadband noise, thus affecting any measurement. Another problem with the RES system is that common-mode currents can occur between the sensor head and the chamber being monitored, which can also cause interference.

[0010] Therefore, to address this and other problems of the prior art, the present disclosure relates to a signal acquisition system (SAS) for a RES system, the SAS: i) having a high signal-to-noise immunity; ii) being suitable for receiving RES signals from the plasma source (such as a plasma processing chamber) it is used to measure; iii) not receiving radio frequency signals from the surrounding environment, such as RES signals from other adjacent chambers on the same processing tool. Summary of the Invention

[0011] The features of the device of the present disclosure are set forth in the appended claims.

[0012] Specifically, the present disclosure relates to a device for detecting electromagnetic radiation emitted by a plasma, the device including a first sensor unit, the first sensing unit including: a first sensor for detecting electromagnetic radiation; an electromagnetic barrier, wherein the electromagnetic barrier is configured to surround the first sensor to prevent ambient electromagnetic radiation from reaching the first sensor; a first port through which electromagnetic radiation can pass, the port being configured for attachment to a port of a plasma chamber such that electromagnetic radiation emitted from the plasma can reach the first sensor; and a first output coupled to the sensor, wherein the output is configured to be coupled to a cable, whereby the signal detected by the first sensor can be provided to a separate receiver, transceiver, or transmitter unit.

[0013] In one embodiment, there is provided a device for detecting electromagnetic radiation or signals emitted by a plasma, the device including a sensor unit, the sensing unit including:

[0014] A first sensor for detecting electromagnetic radiation or signals;

[0015] An electromagnetic barrier, wherein the electromagnetic barrier is configured to surround the first sensor to prevent ambient electromagnetic radiation from reaching the first sensor;

[0016] A first port through which electromagnetic radiation can pass, the port being configured for coupling to a port of a plasma chamber such that electromagnetic radiation or signals emitted from the plasma can reach the first sensor; and a first output coupled to a balun and a twin coaxial system, whereby the sensed signal is grounded and the inverted version of the signal is grounded.

[0017] While Faraday cage implementations can provide an electromagnetic barrier, there are many problems with existing prior art systems in the field of measuring plasma signals, such as noise generated by common mode currents. The present invention overcomes these problems by providing a twin coaxial configuration at both ends of the system in combination with coupling and decoupling baluns.

[0018] In a preferred embodiment of the present invention, the balun / twin coax / balun system is positioned near the sensor head. In fact, the balun / twin coax / balun method of the present invention (wherein the signal and the inverted version of the signal of the signal line are noise isolated in two different cables) overcomes the noise and common mode current problems associated with signal acquisition when measuring signals emitted from a plasma source.

[0019] The signal acquisition system is designed to be electrically isolated from its environment, and only NF E-field and NF B-field sensors (such as antennas) connected to the signal acquisition system can receive RF signals.

[0020] Provide the first sensor as a separate unit, allow it to be mounted remotely from a receiver, transmitter, or transceiver, and reduce the number of components local to the first sensor that may interfere with the first sensor's readings.

[0021] Provide the first sensor as a separate unit, allow it to be mounted remotely from a receiver, transmitter, or transceiver, and reduce the size of the first sensor for most effective attachment to a first port in a space-constrained plasma system. Additionally, for a system with multiple chambers, the remote first port can be coupled to a separate receiver, transceiver, or transmitter unit or multiple units.

[0022] Preferably, the first sensor is a near-field antenna, but if desired, the system can also be configured for mid-field or far-field operation.

[0023] Preferably, the first output is a balanced output configured to be coupled to one or more cables to provide a differential signal. This allows the first output to be coupled to a balanced differential cable (which is an off-the-shelf component). Advantageously, the use of a balanced cable means that the resulting system rejects common-mode interference from external sources.

[0024] Preferably, the sensor unit includes a balun configured to convert an unbalanced signal provided by the first sensor into a balanced signal provided to the first output.

[0025] In one embodiment, the sensor unit includes a second sensing unit, where the second sensing unit includes: a second sensor for detecting electromagnetic radiation; an electromagnetic barrier configured to surround the second sensor to prevent ambient electromagnetic radiation from reaching the second sensor; a second port through which electromagnetic radiation can pass, the port being configured for attachment to a matching unit of a plasma chamber such that electromagnetic radiation emitted from the matching unit can reach the second sensor; and a second output coupled to the second sensor, where the second output is configured to be coupled to a cable.

[0026] This arrangement produces a differential signal that is a measurement of the current and / or voltage phase difference on a substrate / workpiece being plasma processed.

[0027] Additionally, in the case where the connector of the antenna is in a receive or transmit mode, a directional coupler can be attached, the directional coupler being configured to allow implementation of reflection / transmission measurements. For example, this can be used to obtain a basic impedance measurement of the transmission line consisting of the antenna and the attached balun and cable.

[0028] Preferably, the first output and the second output are balanced outputs.

[0029] Preferably, the first output and the second output are cross-coupled to a balun to generate a third output, wherein the third output is a balanced output that is a function of the current and / or voltage phase difference between the signal received by the first sensor and the signal received by the second sensor.

[0030] In another embodiment, a method for detecting electromagnetic radiation or signals emitted by a plasma is provided, the method comprising the steps of:

[0031] Detecting electromagnetic radiation or signals;

[0032] Configuring an electromagnetic barrier to surround a first sensor to prevent ambient electromagnetic radiation from reaching the first sensor;

[0033] Coupling a first port associated with the sensor and through which electromagnetic radiation can pass to a port of the plasma chamber such that electromagnetic radiation or signals emitted from the plasma can reach the first sensor; and

[0034] Coupling the first output to a balun and a twin coaxial system, whereby the sensed signal is grounded and an inverted version of the signal is grounded.

[0035] The present disclosure also relates to, but is not limited to, a signal acquisition system (SAS) for detecting electromagnetic radiation emitted by a plasma, the SAS comprising: means for detecting electromagnetic radiation according to any of the preceding claims; another housing comprising: a receiver, a transmitter or a transceiver for wirelessly providing the signal obtained by the means to a control unit; and an electromagnetic barrier, wherein the electromagnetic barrier is configured to surround the receiver, the transmitter or the transceiver to prevent ambient electromagnetic radiation from reaching the receiver, the transmitter or the transceiver; and at least one cable for providing the signal received by the means to the receiver, the transmitter or the transceiver.

[0036] Preferably, the cable is a balanced cable. More preferably, the cable is a pair of coaxial cables, wherein the cables are configured to connect the ground wire of the means to the another housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] With reference to the accompanying drawings, the present invention will be more clearly understood from the following description of its embodiments given by way of example only, in which: -

[0038] Figure 1 An example of unbalanced wiring is shown;

[0039] Figure 2 An example of balanced wiring is shown;

[0040] Figure 3 An example circuit of a balanced line from an antenna is shown;

[0041] Figure 4 shows an example of an antenna head and a remote transceiver;

[0042] Figure 5 shows another example of an antenna head and a remote transceiver;

[0043] Figure 6 shows a circuit for connecting an unbalanced antenna to a balanced line; and

[0044] Figure 7 shows a transceiver connected to an antenna, which is used to transmit the signal received by the sensor to a control unit. DETAILED DESCRIPTION

[0045] Typical RESs include sensors (such as antennas) for measuring plasma, which are coupled to a receiver or transceiver that is used to provide the measurements obtained from the sensors to a control system and optionally receive control signals from the control system. Examples of receivers or transceivers are exemplary, and optionally a transmitter can be used instead.

[0046] In a RES system, it is important to ensure that the signals received by the sensors are from the plasma system (such as a plasma chamber) being observed or tested. Thus, the sensors of a RES system (such as E-field and / or B-field antennas, or similar sensors) are typically placed near the access port of the plasma system being tested. The access port typically consists of a glass / quartz / dielectric window, which may or may not provide a direct visual observation of the plasma. Whether or not there is a direct visual access, the RF emissions of the plasma can still pass through the access port. The present invention can be applied to both cases where the plasma is directly visible or not. In addition to using off-the-shelf NF B-field, NF E-field, or similar antennas, custom sensors can also be constructed or manufactured. This can include manually or automatically depositing dielectric and / or conductive components on glass, dielectric, wood, or similar substrates in order to custom-build sensors or antennas suitable for the requirements of the RES system. Such a system is described in detail in PCT patent application number PCT / EP2018 / 057556 assigned to Dublin City University, which is hereby incorporated by reference in its entirety.

[0047] Very high precision and accuracy are required to detect small changes in the amplitude or intensity of the signals received by the sensors. To do this, the noise must be minimized, i.e., the signal-to-noise ratio of the signals received by the RES must be maximized.

[0048] However, placing the sensor near the access port of the plasma system does not guarantee that the received signal is only from the plasma system being tested. The typical RF signals detected by the sensor have extremely low amplitudes (e.g., about -60 dBm to -100 dBm), and the received signals are typically or often in the near-field region of the electromagnetic field (see S. Kelly and P. J. McNally, Appl. Phys. Express 10 (2017) 096101).

[0049] Many other plasma systems can and in practice often are very close to the plasma system being tested. In many cases, plasma systems will be designed to be similar or nearly identical to their neighbors, including the plasma system being measured by the RES system. Another issue is that the receiver or transceiver of the RES may interfere with the sensor.

[0050] The sensor (e.g., one or more RF antennas) typically operates in the near field and is limited in size by the actual construction of the individual plasma system being tested. A suitable sensor that can be used is a broadband EM sensor. Thus, the RF sensors of the RES system tend to be very small. The size of a typical RF sensor may be about 1 cm 2 . These small transceiver sensors must not be overwhelmed by unwanted RF signals. Additionally, the interference levels due to strong E-fields and B-fields generated by uncontrolled RF emissions from other sources in the environment can be quite high. This disclosure describes a SAS for the RES that ensures good isolation from such interference.

[0051] This disclosure achieves this purpose by separating the sensor from the receiver or transceiver to isolate the sensor. In particular, the sensor is provided in a housing separate from the receiver or transceiver. In one embodiment, the SAS includes an antenna head housing (AHE) that includes the sensing components of the SAS. The sensing components are preferably one or more of (a plurality of) single-ended NF E-field and / or NF B-field antennas. The AHE is placed near the plasma system (e.g., a plasma processing chamber) so that the AHE is in the electromagnetic near field generated by the plasma of the plasma system. The signals received by the sensors of the AHE are then transmitted via a cable to a separate remote transceiver head (RTH). The RTH contains the signal transceiver subsystem.

[0052] An example of the cable is a coaxial cable or "coax". Coax is a cable in which the inner conductor is surrounded by a tubular insulating layer and then by a tubular conductive shield.

[0053] Another example of a cable is a twinaxial cable or "Twinax". Twinax is a cable similar to a coaxial cable but with two internal conductors instead of one. Due to cost - effectiveness, it has become increasingly common in modern ultra - short - reach high - speed differential signal applications.

[0054] A further example of a cable is a triaxial cable, commonly referred to as "Triax". Triax is a cable similar to a coaxial cable but with an additional insulating layer and a second conductive sheath. It offers greater bandwidth and interference rejection compared to coaxial or twinaxial cables.

[0055] The electromagnetic sensor preferably includes an antenna. The antenna has two connection ports. One port is typically connected to a signal line, while the other port is connected to ground. Thus, when coupling the antenna to a cable, twinax or triax cables are commonly used in the art. Referring Figure 1 to the cable shown, the cable consists of two wires 101 (signal wire 102 and ground / sheath 103) inside the cable. Inside the cable itself, the signal wire 102 is typically located at the center of the cable, while the ground / sheath 103 surrounds the signal wire. The outer ground sheath conducts a portion of the RF signal and to some extent protects the main signal wire from external RF interference. This type of cable arrangement is called an unbalanced cable.

[0056] However, any length of cable can act like an antenna. As a result, the inner wire 102 can act like an antenna and pick up unwanted RF noise 105 (such as a common - mode current signal), degrading the signal.

[0057] To avoid this problem, a differential balun is used. A differential balun (an abbreviation for "balanced - unbalanced") is a two - port component placed between a single - ended source (i.e., a source such as an antenna, having a single signal port and a ground - reference port) and a differential load (i.e., a load having two ports that each receive two signals, where the load responds to the electrical difference between the two signals), or vice versa. In other words, a balun is used to convert a single - ended signal (also called an unbalanced signal) to a differential signal (also called a balanced signal) or a differential signal to a single - ended signal. A balun typically uses a dual - winding transformer, with one side grounded and the other side floating (differential). A balun does not have a definite "input" and "output" port, i.e., it is generally a reciprocal device.

[0058] By using a differential balun, a single - ended source such as an antenna can be coupled to a (multi -) differential cable.

[0059] Figure 2A balanced cable is shown that includes the following three wires 201: two signal wires 202a and 202b plus a separate ground sheath 203. As in an unbalanced cable, the ground sheath 203 still surrounds the signal wires and serves as an anti-interference shield. The balanced cable uses the two signal wires 202a and 202b to convey copies of a signal 205, namely a positive copy 202a and a negative copy 202b (i.e., these two copies are sent with opposite polarities). Figure 2 An antenna 206 is shown that includes an electromagnetic RF isolation barrier 207 that cooperates with a plasma chamber 208 to form an RF isolation channel or "pipe" from the plasma chamber 208 to the antenna 206. When the two copies of the signal propagate along the cable, they are exposed to the same RF noise signal. Therefore, inverting the negative copy and adding it to the positive signal has the effect of canceling out the RF noise signal. This results in improved noise immunity. Preferably, the signal from the antenna within the housing of the RF barrier 207 is conveyed within the cable to the housing of a remote receiver head 209 while maintaining an RF seal unit from the antenna 207 to the receiver head 209.

[0060] Thus, as Figure 4 shown, by using a first differential balun 410, the output from a single-ended source 411 such as an antenna can be provided as a balanced signal. This allows the received signal to be transmitted from an antenna head housing (AHE) 400 to a separate remote receiver head (RTH) 450 using a balanced differential cable 412. Due to the use of the differential balun 410, two coaxial cables can be used to transmit the differential / balanced signal to the RTH 450. Preferably, the antenna head housing (AHE) 400 that extends all the way to a separate remote receiver head (RTH) 450 is located within an RF seal unit so as to define a channel or pipe from the antenna head 400 to the receiver head (RTH) 450.

[0061] Within the RTH 450, another differential balun 451 is used to convert the balanced differential signal back to a single-ended unbalanced signal for connection to a receiver or transceiver 452. In other words, the signal is converted back to a signal configuration such as a single coaxial Bayonet Neill-Concelman (BNC) or SubMiniature Version A (SMA) plug connector that is directly connected to a transceiver system.

[0062] It should be understood that the combination of the balun and the differential signal through the twin coaxial cables accomplishes an RF isolation pipe between the head unit and the remote receiver. In fact, the present invention provides RF containment of the signal measured at the plasma chamber 208 and the signal sent to the receiver 209.

[0063] Optionally, a control line 425 can be provided to supply power and / or control signals from the RTH to the AHE.

[0064] Figure 3 A circuit diagram of an exemplary embodiment using a differential balun and an RF sensor (antenna) within an electrically isolated antenna housing is shown. As Figure 3 shown, the antenna 310 (preferably, a B-field loop antenna) is connected to a high-frequency transformer 320, which acts as a balun and transfers any unbalanced signals received to a balanced differential transmission line. The transmission line is AC-coupled to connectors X1 and X2 using capacitors 330 to remove unwanted currents from the signal. The transmission line is terminated with a combination of resistors 340. The balance point of the line can be terminated using an electrical load 350, such as a resistor.

[0065] This disclosure also relates to a system and component layout for the RTH that also utilizes a differential balun. As Figure 6 shown, an exemplary circuit for coupling a dual coaxial balanced input from the AHE to a single-ended transceiver. In particular, ports X8 and X13 are configured for coupling to the dual coaxial balanced input and are AC-coupled to the transmission line using capacitors 610 to remove unwanted currents from the signal. The transmission line is terminated with a combination of resistors 620. The balance point of the line can be terminated using an electrical load 650, such as a resistor. The transmission line supplies the received differential signal to a high-frequency transformer 630, which acts as a balun to convert the differential signal to a single-ended signal. The single-ended signal is provided to port X1 to connect to a single-ended transceiver. Those skilled in the art will again note that other configurations can use different circuit components (such as resistors, capacitors, etc. with different values) and topologies, and the embodiments shown above are illustrative.

[0066] As Figure 2 and Figure 6 shown, the signal lines are conveyed in a grounded coaxial cable, and the anti-phase signal is also conveyed in a separate coaxial cable. Each of these cables is self-shielded, and when the signal is transmitted to the analysis chamber via two coaxial lines, the process is reversed. This balun / dual coax / balun configuration ensures a common ground from the sensor unit to the signal processing unit.

[0067] This includes the application of a dual coax system where the coax common ground is the ground of the RF field system and balanced differential signals are included in the system. This unique system reduces RF current induction due to environmental tool noise (e.g., from the plasma chamber under study and adjacent operating chambers) via the coax and also uses the balanced differential system included in the system, which helps significantly reduce the induced noise. This configuration enables the active processing components to be located away from the chamber itself while still maintaining the integrity of the low-intensity signals that need to be processed. This configuration allows the system to position the sensor head adjacent to the chamber wall and deliver very low-level broadband signals to a remote detection system for processing while preventing inter-chamber noise and other external noise.

[0068] In one embodiment, it is possible to implement the measurement of the phase difference between current and voltage variations inside the plasma itself. The electric field (E-field) sensor / antenna effectively detects voltage variations via capacitive coupling to the antenna; the magnetic field (B-field) sensor / antenna most effectively detects current variations, which is inductively coupled to the conduction current and displacement current inside the plasma.

[0069] Inside the plasma, there are "layers" with different characteristics where different frequencies propagate in these different regions. This has the effect of changing the phase of different frequencies for different operating points of the plasma. By measuring the phase differences of these different frequencies, a lot of data on the physical properties of plasma operation can be obtained. By examining the phase spectrum generated from the data processing of the signals, a lot of information about the current state of the plasma can be obtained.

[0070] Additional sensors can be used in conjunction with the present invention. For example, RF sensors placed at different locations around the plasma port (e.g., in the microwave region of the spectrum) are sensitive to microwave emissions from different regions in the plasma chamber, where the plasma itself is not spatially uniform. In an inductively coupled plasma, the waveguide effect between the induction power coil and the plasma body will generate microwave emissions, which are fundamentally different from the microwave emission components from the plasma body.

[0071] Figure 5 An alternative embodiment of the present disclosure is shown. In particular, this alternative embodiment relates to the use of two antennas within the AHE1000. Refer to Figure 5, the first antenna 1011a is located in a first RF shield (e.g., a shield housing) for mounting to a port of the plasma chamber 1001 as described above. The first antenna 1011a is connected to a first balun 1010a to convert the signal received by the first antenna into a first differential signal 1013a. Optionally, in this embodiment (and previous embodiments), the balun can be further shielded with metal (e.g., copper). The second antenna 1011b is located in a second RF shield (e.g., a shield housing) for mounting within a matching unit 1002 on the output side of the plasma chamber. Similar to the first antenna 1011a, the second antenna 1011b is connected to a second balun 1010b to convert the signal received by the second antenna 1011b into a second differential signal 1013b.

[0072] The first 1013a and second 1013b are cross-coupled to a third balun 1020a and a fourth balun 1020b to generate an output differential signal 1012. As described above with reference to Figure 4 The output differential signal is provided to the RTH 450. An optional control and / or power line 425 can be provided from the RTH 450 to the AHE 1000.

[0073] An advantage of this arrangement is that the output differential signal provided by the AHE 1000 is a function of the phase shift between the first antenna 1011a and the second antenna 1011b. In other words, the output differential signal 1012 is a measurement of the phase difference on the substrate / workpiece being processed in the plasma chamber 1001.

[0074] Figure 7 An example block diagram of the present invention is shown, similar to Figure 2 , showing a transceiver connected to an antenna 206 for transmitting the signal received by the sensor to a receiver 209. The antenna 206 includes an RF isolation barrier 207 that cooperates with the plasma chamber 208 to form an RF isolation channel or "pipe" from the plasma chamber 208 to the antenna 206, as described above with reference to Figures 2 to 6 The combination of the balun and the differential signal through the coaxial cable 700 completes the RF isolation pipe between the antenna 206 and the remote receiver 209 that can house the control unit. The cable 700 can be arranged in parallel and arranged without kinks or the like so that the signal is not degraded or impaired.

[0075] Of course, the above examples are merely exemplary, and those skilled in the art will recognize that there are many alternative ways to implement the systems, methods, and devices disclosed herein without departing from the spirit and scope of this disclosure.

[0076] For example, differential amplification can be performed on the input of the balun of the RTH, rather than on the single-ended output from the balun of the RTH.

[0077] It should be understood that the methods described herein with reference to the figures can be used simultaneously for more than two antennas, for example, several antennas at several viewports can be implemented. In other words, multiple versions of the "balun - dual coax - balun" topology can be used to transmit signals from multiple connected antennas to the AHE and then to the SAS, which itself cannot handle signals from one, two, three, or more antennas at the AHE.

[0078] Embodiments of the invention described with reference to the figures include a computer device and / or a process executed in a computer device. However, the invention also extends to a computer program, particularly a computer program stored on or in a carrier adapted to put the invention into practice. The program can be in the form of source code, object code, or code intermediate between source and object code, such as in a partially compiled form or any other form suitable for implementing the method according to the invention. The carrier can include a storage medium such as a ROM, for example, a memory stick or a hard disk. The carrier can be an electrical or optical signal that can be transmitted via a cable or an optical fiber or by radio or other means.

[0079] In the specification, the terms "comprise, comprises, comprised, and comprising" or any of their variants and the terms "include, includes, included, and including" or any of their variants are considered to be fully interchangeable, and they should all be given the broadest possible interpretation, and vice versa.

[0080] The invention is not limited to the embodiments described above, but can vary in both structure and detail.

Claims

1. An apparatus for detecting electromagnetic radiation or signals emitted by a plasma, the apparatus comprising a sensor unit, the sensor unit comprising: a first sensor for detecting electromagnetic radiation or signals; an electromagnetic barrier, wherein the electromagnetic barrier is configured to surround the first sensor to prevent ambient electromagnetic radiation from reaching the first sensor; a first port through which electromagnetic radiation can pass, the port being configured to be coupled to a port of a plasma chamber such that electromagnetic radiation or signals emitted from the plasma can reach the first sensor; and a first output coupled to a balun and a twin coaxial transmission system, wherein the balun and the twin coaxial transmission system are electrically coupled to the first sensor to receive a signal representing the detected electromagnetic radiation or signal and thereby sense the signal with respect to ground and also sense an inverted version of the signal with respect to ground.

2. The apparatus according to claim 1, wherein, the first output is a balanced output configured to be coupled to one or more cables to provide a differential signal.

3. The apparatus according to claim 1, wherein, the balun converts an unbalanced signal provided by the first sensor into a balanced signal provided to the first output.

4. The apparatus according to claim 2, wherein, the balun converts an unbalanced signal provided by the first sensor into a balanced signal provided to the first output.

5. The apparatus according to any one of the preceding claims 1 to 4, wherein, the sensor unit includes a second sensing unit, wherein the second sensing unit includes: a second sensor for detecting electromagnetic radiation; an electromagnetic barrier, wherein the electromagnetic barrier is configured to surround the second sensor to prevent ambient electromagnetic radiation from reaching the second sensor; a second port through which electromagnetic radiation can pass, the port being configured to be attached to a matching unit of a plasma chamber such that electromagnetic radiation emitted from the matching unit can reach the second sensor; and a second output coupled to the second sensor, wherein the second output is configured to be coupled to a cable.

6. The apparatus according to claim 5, wherein, the first output and the second output are balanced outputs.

7. The apparatus according to claim 5, wherein, the first output and / or the second output are cross-coupled to a balun to produce a third output, wherein the third output is a balanced output that is a function of the phase difference between the electromagnetic radiation or signal received by the first sensor and the electromagnetic radiation or signal received by the second sensor.

8. The apparatus according to claim 6, wherein, the first output and / or the second output are cross-coupled to a balun to produce a third output, wherein the third output is a balanced output that is a function of the phase difference between the electromagnetic radiation or signal received by the first sensor and the electromagnetic radiation or signal received by the second sensor.

9. A signal acquisition system (SAS) for detecting electromagnetic radiation emitted by a plasma, the SAS comprising: a device for detecting electromagnetic radiation according to any one of the preceding claims; another housing comprising: a receiver, a transmitter or a transceiver for providing the signal obtained by the device to a control unit; and an electromagnetic barrier, wherein the electromagnetic barrier is configured to surround the transmitter or the transceiver to prevent ambient electromagnetic radiation from reaching the transmitter or the transceiver; and at least one cable for providing the signal received by the device to the transmitter or the transceiver.

10. The SAS according to claim 9, wherein the cable is a balanced cable.

11. The SAS according to claim 9 or 10, wherein, the cable is a pair of coaxial cables, wherein the cable is configured to connect the ground wire of the device to the another housing.

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