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

Abstract

The present invention is directed to an apparatus and method for detecting electromagnetic radiation or signals emitted by a plasma, the apparatus and method comprising a sensing unit including: a first sensor for detecting the electromagnetic radiation or signals; an electromagnetic barrier configured to surround the first sensor to prevent ambient electromagnetic radiation from reaching the first sensor; a first port through which the electromagnetic radiation can pass, the first port configured to connect to a port of a plasma chamber so that the electromagnetic radiation or signals emitted from the plasma can reach the first sensor; and a first output connected to a balun and a dual coaxial system, whereby a detected signal is connected to ground and an opposite-phase version of the signal is connected to ground. A signal acquisition system (SAS) for detecting electromagnetic radiation emitted by a plasma is also described.

Description

[Technical field]

[0001] The present disclosure is directed to improvements in the control and measurement of plasmas, and in particular to improving the signal-to-noise ratio of measurement signals obtained from the plasma and to improving the electrical noise immunity of the systems used to obtain these measurements. [Background technology]

[0002] Plasmas are very common and are used in many manufacturing and industrial processing environments. For example, low pressure systems are used for advanced material processing, including material deposition and / or etching processes, for example in the semiconductor or medical industry. As a further example, atmospheric pressure plasma processing systems also have industrial applications, for example, material cleaning, bonding, deposition, or etching, for example for the aeronautical, automotive, and other sectors.

[0003] Due to the trend towards increased process automation, improved control over the plasma properties in industrial semiconductor processing equipment is important. One consideration in improving control over the properties of the plasma is the measurement of the plasma properties. Currently, invasive plasma measurement techniques are the oldest and most commonly used procedures for measuring the properties of the plasma. Such techniques involve immersion of one or more probes into the plasma under study.

[0004] However, invasive plasma measurement techniques are undesirable in most industrial environments. In particular, plasmas often create harsh conditions for many of the probes used for measurements. As a result, probes used for invasive plasma measurement techniques are expensive and / or prone to failure. Furthermore, the probes themselves can interact with the plasma, sometimes unpredictably, changing the plasma's characteristics. Such problems reduce the accuracy of the measurements and therefore the control of the plasma.

[0005] Furthermore, the equipment used for invasive plasma measurement techniques is difficult to retrofit into existing manufacturing equipment and infrastructure. In addition to this difficulty, the disruptive impact of installing invasive plasma measurement equipment can introduce additional complexity into the manufacturing line. This can adversely affect the necessary process repeatability that is key to mass production. Thus, the risk of adding complexity and cost to the manufacturing line is slowing improvements in plasma measurement and control.

[0006] Thus, non-invasive plasma measurement techniques may provide a significant improvement in plasma control. For example, a non-invasive plasma measurement device may be easily connected to an existing plasma device. An additional advantage is that the existing plasma device remains in place when connected to the non-invasive plasma measurement device, thereby reducing the risk of adding complexity and cost to the manufacturing line. Non-invasive plasma measurements are also significantly more accurate than invasive plasma measurements. Unlike many existing probe systems, non-invasive plasma measurements do not require a probe to be placed in the plasma. As a result, non-invasive plasma measurements do not disturb the plasma itself (eliminating the risk of the probe altering the measurements being taken). An exemplary system is described in a paper by K Suzuki and M Sato entitled "Advanced technology for monitoring plasma sparking ESD damage using high frequency magnetic field sensors," Electrical Overstress / Electrostatic Discharge Symposium (2003). Various patent publications, such as US 2005 / 0183821, JP 5-188151, JP 11-67732, and EP 1394835, describe electromagnetic field signal acquisition systems for high signal-to-noise ratios and electrical noise immunity.

[0007] The present disclosure is based on the contributions provided by PCT patent application No. PCT / EP2018 / 057556, which describes a Radio Emission Spectroscopy (RES) system, as well as the paper Appl. Phys. Express 10 (2017) 096101 by S. Kelly and PJ McNally. In a typical embodiment, the RES system includes a Near Field (NF) electric field (E-field) antenna and / or a Near Field (NF) magnetic field (B-field) antenna positioned closely (e.g., preferably 40 mm or less) inside the plasma process chamber to measure and control plasma properties in the plasma process chamber. Importantly, the antenna(s) are positioned outside the plasma, i.e., according to the present disclosure, the antenna(s) are not immersed in the plasma and are not in physical contact with the plasma when in use.

[0008] However, for example, in a typical semiconductor fabrication facility that typically includes multiple plasma processing systems, each including at least one plasma chamber, the plasma processing systems are not individually located and electromagnetically (radio frequency (RF)) isolated from one another. In fact, a fabrication facility may consist of dozens or more such systems, all functioning simultaneously and all capable of generating RF electromagnetic radiation. As a result, the processing systems may interfere with one another and with the RES system.

[0009] Additionally, there may be other local RF sources. As another example, high speed electrical equipment may generate electromagnetic noise. It is therefore important to invent a RES system that can receive only the electromagnetic signals from the individual plasma process chambers targeted by the RES system. Importantly, the RES system needs to be immune to noise signals, such as signals emanating from other electronic systems (including, for example, other plasma process chambers, auxiliary electrical equipment, etc.), and general wideband local RF background emissions. The signals from the antenna head are susceptible to "skin" induced noise from the cables. The operating environment of the plasma chamber is dense with RF noise from both the control machines / computers and the adjacent plasma chambers, for example, in industrial environments, the machines are arranged in long lines in "chases". This results in RF interference. Furthermore, the signal levels from the antenna or antennas are very low, and any local amplification tends to result in wideband noise that affects any measurements. A further problem with the RES system is that common mode currents are found to occur between the sensor head and the chamber being monitored, also resulting in interference.

[0010] Therefore, to address this and other problems with the prior art, the present disclosure is directed to a Signal Acquisition System (SAS) for a RES system that i) has high signal-to-noise tolerance, ii) is adapted to receive a RES signal from the plasma source (e.g., plasma process chamber) being used to measure, and iii) is not susceptible to radio frequency signals from the surrounding environment, e.g., receiving RES signals from other adjacent chambers in the same processing tool. Summary of the Invention [Means for solving the problem]

[0011] The present disclosure is directed to an apparatus having the features set out in the appended claims.

[0012] In particular, the present disclosure is directed to an apparatus for detecting electromagnetic radiation emitted by a plasma comprising a first sensing unit, the first sensing unit comprising: a first sensor for detecting electromagnetic radiation; an electromagnetic barrier configured to surround the first sensor to prevent ambient electromagnetic radiation from reaching the first sensor; a first port through which the electromagnetic radiation may pass, the port configured to be attached to a port of the plasma chamber such that electromagnetic radiation emitted from the plasma may reach the first sensor; and a first output connected to the sensor, the first output configured to be connected to a cable whereby a signal detected by the first sensor may be provided to another receiver, transceiver, or transmitter unit.

[0013] In one embodiment, an apparatus is provided for detecting electromagnetic radiation or signals emitted by a plasma, comprising a sensing unit, the sensing unit comprising: a first sensor for detecting the electromagnetic radiation or signals; an electromagnetic barrier configured to surround the first sensor to prevent ambient electromagnetic radiation from reaching the first sensor; a first port through which the electromagnetic radiation may pass, the first port configured to connect to a port of the plasma chamber such that the electromagnetic radiation or signals emitted from the plasma may reach the first sensor; and a first output connected to a balun and dual coaxial system whereby the signal to be detected is grounded and an inverted phase version of the signal is grounded.

[0014] Although Faraday cage type implementations can provide an electromagnetic barrier, existing prior art systems in the field of measuring plasma signals suffer from many problems such as noise from generated common mode currents, etc. The present invention overcomes such problems by providing a dual coaxial configuration combined with coupling and decoupling baluns at both ends of the system.

[0015] In a preferred embodiment of the present invention, the balun / dual coax / balun system is located in close proximity to the sensor head. In effect, both the signal and the opposite phase version of the signal line are noise isolated separately on two different cables. The balun / dual coax / balun solution of the present invention overcomes the noise and common mode current problems associated with signal acquisition when measuring signals emanating from a plasma source.

[0016] The signal acquisition system is designed such that it is electrically isolated from its environment and only NF electric and NF magnetic field sensors (e.g., antennas) connected to the signal acquisition system can receive RF signals.

[0017] Providing the first sensor as a separate unit allows for remote location of the first sensor from the receiver, transmitter, or transceiver, reducing the number of components local to the first sensor that may interfere with the measurement of the first sensor.

[0018] Providing the first sensor as a separate unit allows for remote placement of the first sensor from the receiver, transmitter, or transceiver, reducing the size of the first sensor for most efficient mounting to the first port in space-constrained plasma systems. Further, in systems having multiple chambers, the remote first port may be connected to a separate receiver, transceiver, or transmitter unit or units.

[0019] Preferably, the first sensor is a near-field antenna, but the system may also be configured for mid-field or far-field operation if desired.

[0020] Preferably, the first output is a balanced output configured to connect to one or more cables to provide a differential signal. This allows the first output to be connected to a balanced differential cable, which is a readily available component. Advantageously, the use of a balanced cable means that the resulting system rejects common mode interference from external sources.

[0021] Preferably, the sensing unit comprises a balun configured to convert an unbalanced signal provided by the first sensor into a balanced signal provided at the first output.

[0022] In one embodiment, the sensing unit comprises a second sensing unit comprising 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 the electromagnetic radiation may pass, the port configured to be attached to a matching unit of the plasma chamber such that electromagnetic radiation emitted from the matching unit may reach the second sensor, and a second output connected to the second sensor, the second output configured to be connected to a cable.

[0023] This arrangement produces a differential signal that is a measurement of the current and / or voltage phase difference between the substrate / workpiece being manipulated by the plasma.

[0024] Additionally, a directional coupler may be attached and configured to allow reflection / transmission measurements to be made when the connector to the antenna is in either receive or transmit mode. For example, this may be used to obtain a basic impedance measurement for the transmission line consisting of the antenna and attached balun and cable.

[0025] Preferably, the first and second outputs are balanced outputs.

[0026] Preferably, the first and second outputs are cross-coupled in a balun to generate a third output, the third output being 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.

[0027] In another embodiment, a method for detecting electromagnetic radiation or signals emitted by a plasma includes the steps of: detecting an electromagnetic radiation or signal; configuring an electromagnetic barrier to surround the first sensor to prevent ambient electromagnetic radiation from reaching the first sensor; connecting a first port corresponding to the sensor through which electromagnetic radiation can pass to a port of the plasma chamber such that electromagnetic radiation or signals emanating from the plasma can reach the first sensor; connecting the first output to a balun and dual coaxial system whereby the signal to be sensed is coupled to ground and an out-of-phase version of the signal is coupled to ground; A method is provided that includes:

[0028] The present disclosure is also directed to, but is not limited to, a signal acquisition system (SAS) for detecting electromagnetic radiation emitted by a plasma, the SAS comprising any of the above-described devices for detecting electromagnetic radiation, a receiver, transmitter, or transceiver for wirelessly providing a signal obtained by the device to a control unit, and a further housing comprising an electromagnetic barrier configured to surround the receiver, transmitter, or transceiver to prevent ambient electromagnetic radiation from reaching the receiver, transmitter, or transceiver, and at least one cable for providing a signal received by the device to the receiver, transmitter, or transceiver.

[0029] Preferably, the cable is a balanced cable. More preferably, the cable is a pair of coaxial cables, the cable being configured to provide a ground connection from the device to a further housing. [Brief description of the drawings]

[0030] The invention will be more clearly understood from the following description of embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which: [Figure 1] An example of unbalanced wiring is shown below. [Diagram 2]An example of balanced wiring is shown below. [Diagram 3] 1 shows an example circuit for a balanced line from an antenna. [Figure 4] 1 shows an example of an antenna head and a remote transceiver. [Diagram 5] 4 shows another example of an antenna head and a remote transceiver. [Figure 6] 1 shows a circuit for connecting an unbalanced antenna to a balanced line. [Figure 7] 1 shows a transceiver connected to an antenna for transmitting the signal received by the sensor to a control unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] A typical RES comprises a sensor (e.g., an antenna) for measuring the plasma, which is connected to a receiver or transceiver for providing measurements from the sensor to a control system and, optionally, receiving control signals from the control system. The examples of a receiver or transceiver are illustrative and, optionally, a transmitter could be used instead.

[0032] In a RES system, it is important to ensure that the signal received by the sensor originates from the plasma system (e.g., plasma chamber) being observed or tested. Thus, the sensor of the RES system (e.g., electric and / or magnetic field antenna, or similar sensor) is often located near an access port of the plasma system being tested. This access port is typically constructed of a glass / quartz / dielectric window and may or may not allow direct viewing and observation of the plasma. Regardless of direct viewing access, RF radiation from the plasma may still pass through this access port. The present invention can function in both situations where the plasma is either directly visible or not. In addition to the use of off-the-shelf NF, magnetic, electric, or similar antennas, custom sensors can be built or manufactured. This may involve manual or automated deposition of dielectric and / or conductive members onto glass, dielectric, wood, or similar substrates to custom build a sensor or antenna appropriate to the requirements of the RES system. Such systems are described in detail in PCT Patent Application No. PCT / EP2018 / 057556, assigned to Dublin City University, and incorporated herein in its entirety by reference.

[0033] Very high precision and accuracy are required to detect small changes in the amplitude or strength of the signal received by the sensor. To this end, noise needs to be minimized, i.e. the signal-to-noise ratio of the signal received by the RES needs to be maximized.

[0034] However, placing the sensor close to the access port of the plasma system does not guarantee that the signals received are exclusively from the plasma system under test. Typical RF signals detected by the sensor have very low amplitudes (e.g., on the order of -60 to -100 dBm), and the received signals are usually or often in the near-field region of the electromagnetic field (see S. Kelly and P.J. McNally, Appl. Phys. Express 10 (2017) 096101).

[0035] Many other plasma systems may be, and typically are, in close proximity to the plasma system under test. In many situations, the plasma systems will be designed to be similar or nearly identical to the neighboring plasma systems, including the plasma system being measured by the RES system. A further problem is that the receiver or transceiver of the RES may interfere with the sensor.

[0036] The sensors (e.g., one or more RF antennas) typically operate in the near field and are constrained in size by the actual geometry of the particular plasma system under test. A suitable sensor that may be used is a broadband EM sensor. As a result, RF sensors for RES systems tend to be very small. Typical RF sensor dimensions are on the order of 1 cm. 2 The RF power of the small transceiver sensor may be on the order of 100 MHz. Such a small transceiver sensor needs to be protected from being overwhelmed by unwanted RF signals. Furthermore, interference levels from strong electric and magnetic fields of uncontrolled RF radiation from other sources in the environment may be very high. This disclosure describes a SAS for a RES that ensures very good isolation from such interference.

[0037] The present disclosure achieves this objective by isolating the sensor through separation of the sensor from the receiver or transceiver. In particular, the sensor is provided in a separate enclosure from the receiver or transceiver. In one embodiment, the SAS comprises an Antenna Head Enclosure (AHE) comprising a sensing member of the SAS. The sensing member is preferably one or more of a single-ended NF electric field and / or NF magnetic field antenna(s). The AHE is positioned in proximity to a plasma system (e.g., a plasma process chamber) such that the AHE is in an electromagnetic near-field generated by the plasma of the plasma system. The signal received by the sensor of the AHE is then transmitted via an electrical cable to another Remote Transceiver Head (RTH). The RTH includes a signal transceiver subsystem.

[0038] One example of a cable is a coaxial cable ("coax"), which is a type of electrical cable that has an inner conductor surrounded by a tubular insulating layer, which is surrounded by a tubular conductive shield.

[0039] Another example cable is the twinaxial cable "Twinax." Twinax is a type of cable similar to coaxial cable, but with two inner conductors instead of one. Due to its cost effectiveness, it has become popular in modern ultra-short distance high-speed differential signaling applications.

[0040] Another example of a cable is a triaxial cable, often referred to as a "Triax." A Triax is a type of electrical cable similar to a coaxial cable, but with the addition of another layer of insulation and a second conductive sheath. The Triax offers better bandwidth and interference rejection than coaxial or twinaxial cables.

[0041] The electromagnetic sensor preferably comprises an antenna. The antenna has two connection ports. Typically, one port is connected to a signal line and the other port is connected to a ground line. Thus, when connecting an antenna to a cable, typically either twinaxial or triaxial cables are used in the art. With reference to the cable shown in FIG. 1, the cable is composed of two wires 101 inside the cable: a signal line 102 and a ground line / sheath 103. Within the cable itself, typically the signal line 102 is in the center of the cable and the ground line / sheath 103 surrounds said signal line 102. The outer ground sheath carries part of the RF signal and serves to shield the main signal line to some extent from external RF interference. This type of cable arrangement is known as an unbalanced cable.

[0042] However, any length of cable can behave like an antenna. As a result, the inner wire 102 can behave like an antenna and pick up unwanted RF noise 105, such as common mode current signals, thereby degrading the signal.

[0043] To avoid this problem, differential baluns are used. A differential balun (short for "balanced-unbalanced") is a two-port member placed between a single-ended source (i.e., a source such as an antenna with a single signal port and a ground-referenced port) and a differential load (i.e., a load with two ports, each receiving two signals and the load responding 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 known as an unbalanced signal) to a differential signal (also known as a balanced signal) or to convert a differential signal to a single-ended signal. Baluns typically use a two-winding transformer with one side grounded and the other side floating (differential). Baluns do not have identified "input" and "output" ports, i.e., they are typically reciprocal devices.

[0044] Through the use of a differential balun, a single-ended source, such as an antenna, can be connected to a differential cable(s).

[0045] FIG. 2 shows a balanced cable with three wires 201, two signal wires 202a and 202b plus another ground sheath 203. As in the unbalanced cable, the ground sheath 203 still surrounds the signal wires and is used as a shield against interference. The balanced cable uses two signal wires 202a and 202b to carry copies of the signal 205, a positive copy 202a and a negative copy 202b, respectively (i.e., the two copies are transmitted with their polarities reversed). FIG. 2 shows an antenna 206 with 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. As the two copies of the signal travel along the cable, they are exposed to the same RF noise signal. As a result, inverting the negative copy and adding it to the positive signal has the effect of canceling the RF noise signal. This leads to improved noise immunity. Preferably, the signal from the antenna within the RF barrier 207 housing is carried in a cable to the remote receiver head 209 housing, maintaining an RF sealed unit from the antenna 206 to the receiver head 209 .

[0046] Thus, as shown in Fig. 4, through the use of 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 use of a balanced differential cable 412 to transmit the received signal from the antenna head housing (AHE) 400 to another remote receiver head (RTH) 450. Due to the use of the differential balun 410, two coaxial cables can be used to transmit the differential / balanced signal towards the RTH 450. Preferably, the antenna head housing (AHE) 400 that runs all the way to the other remote receiver head (RTH) 450 is in an RF sealed unit to define a channel or pipe from the antenna head 400 to the receiver head (RTH) 450.

[0047] 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 connects directly to the transceiver system.

[0048] It will be appreciated that the combination of the balun, the differential signal passing through the dual coaxial cable completes the RF isolation pipe between the head unit and the remote receiver. In effect, the present invention provides RF containment of the signals from measurements in the plasma chamber 208 and the signals transmitted to the receiver 209.

[0049] Optionally, a control line 425 may be provided to provide power and / or control signals from the RTH to the AHE.

[0050] Figure 3 shows a circuit diagram of an exemplary embodiment using a differential balun with an RF sensor (antenna) in an electrically isolated antenna housing. As shown in Figure 3, an antenna 310 (preferably a magnetic loop antenna) is connected to a high frequency transformer 320 that 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 a capacitor 330 to remove unwanted galvanic currents from the signal. The transmission line is terminated with a combination of resistors 340. The balanced point of the line may be terminated using an electrical load 350, such as a resistor.

[0051] The present disclosure is also directed to systems and component layouts for RTHs that also utilize differential baluns. As shown in FIG. 6, one exemplary circuit is for connecting dual coaxial balanced inputs from an AHE to a single-ended transceiver. In particular, ports X8 and X13 are configured to connect to the dual coaxial balanced inputs and are AC-coupled to the transmission line using capacitors 610 to remove unwanted galvanic currents from the signal. The transmission line is terminated with a combination of resistors 620. The balance point of the line may be terminated using an electrical load 650, such as a resistor. The transmission line provides the received differential signal to a high frequency transformer 630, which functions as a balun that converts the differential signal to a single-ended signal. The single-ended signal is provided to port X1 for connection to the single-ended transceiver. Those skilled in the art will again note that other configurations may use different circuit components (e.g., different values ​​of resistors, capacitors, etc.) and topologies, and the embodiment shown above is illustrative.

[0052] As shown in Figures 2 and 6, the signal line is carried on a grounded coaxial cable and the opposite phase signal is also carried on another coaxial cable. Each of the cables is itself shielded, and the process is reversed when the signal is transmitted to the analysis chamber via two coaxial lines. This balun / dual coax / balun configuration ensures that there is a common ground that runs from the sensing unit to the signal processing unit.

[0053] This consists of the application of a dual coax system where the common ground of the coax is the ground of the RF live system and where a balanced differential signal is included. With this unique system, the coax not only reduces the induction of RF currents due to ambient tool noise (e.g. from the plasma chamber under investigation and from adjacent operating chambers), but the use of a balanced differential system included within the system contributes to a significant reduction in induced noise. This configuration allows the active processing elements 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 carry very low-level wideband signals to a remote detection system for processing, while still protecting against inter-chamber and other external noise, despite placing the sensor head adjacent to the chamber wall.

[0054] In one embodiment, measurements of the phase difference of current and voltage changes within the plasma itself may be achieved: voltage changes are efficiently detected by electric field (E-field) sensors / antennas via capacitive coupling to an antenna, and current changes are most effectively detected by magnetic field (B-field) sensors / antennas inductively coupled to the conduction and displacement currents within the plasma.

[0055] Within a plasma there are "layers" with different properties, where different frequencies move in different regions. This has the effect of changing the phase of the different frequencies for different operating points of the plasma. By measuring the phase difference of the different frequencies, a lot of data can be obtained about the physical attributes of the operation of the plasma. By examining the phase spectrum resulting from data processing of the signal, a lot of information can be obtained about the current state of the plasma.

[0056] Additional sensors may be used in combination with the present invention. For example, RF sensors located at different locations around the plasma port, e.g., in the microwave region of the spectrum, are sensitive to microwave radiation from different regions in the plasma chamber where the plasma itself is not spatially uniform. Waveguiding effects between the inductive power coil and the plasma body in an inductively coupled plasma produce microwave radiation that is fundamentally different from the microwave radiation component from most plasmas.

[0057] FIG. 5 shows an alternative embodiment of the present disclosure. In particular, this alternative embodiment includes the use of two antennas in the AHE 1000. Referring to FIG. 5, the first antenna 1011a is disposed in a first RF shield (e.g., a shielding case) for mounting to a port of the plasma chamber 1001, as described above. The first antenna 1011a is connected to a first balun 1010a for converting a signal received by the first antenna into a first differential signal 1013a. Optionally, in this embodiment (and the previous embodiment), the balun may be further shielded with metal (e.g., copper). The second antenna 1011b is disposed in a second RF shield (e.g., a shielding case) for mounting in a matching unit 1002 of the plasma chamber on the output side. Similar to the first antenna 1011a, the second antenna 1011b is connected to a second balun 1010b for converting the signal received by the second antenna 1011b into a second differential signal 1013b.

[0058] 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. The output differential signal is provided to the RTH 450, as described above with reference to Figure 4. Optional control and / or power lines 425 may be provided from the RTH 450 to the AHE 1000.

[0059] The 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 measure of the phase difference between the substrates / workpieces being processed in the plasma chamber 1001.

[0060] FIG. 7 illustrates an exemplary block diagram of the invention similar to FIG. 2, showing a transceiver connected to an antenna 206 for transmitting signals received by a sensor to a receiver 209. The antenna 206 includes an 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, as described above with respect to FIGS. 2-6. A combination of baluns, a differential signal passing through a dual coaxial cable 700 completes the RF isolation pipe between the antenna 206 and a remote receiver 209 that may house a control unit. The cable 700 may be arranged in parallel, free of twists, etc., so that the signal is not degraded or impaired.

[0061] Of course, the above examples are merely illustrative, and those skilled in the art will recognize that there are many alternative ways in which the systems, methods, and apparatus disclosed herein may be implemented without departing from the spirit and scope of the present disclosure.

[0062] For example, differential amplification may be performed on the input of the RTH balun rather than on a single-ended output from the RTH balun.

[0063] It will be understood that the solutions described herein with respect to the figures may be used for more than two antennas simultaneously, for example, several antennas at several viewports may be implemented. In other words, multiple versions of the "balun dual coaxial balun" topology may be used to direct signals from multiple antennas connected towards the AHE and then the SAS, but the AHE cannot process signals from one, two, or more than two antennas alone.

[0064] The embodiments of the invention described with reference to the drawings include a computer device and / or a process executed on a computer device. However, the invention also extends to a computer program, in particular a computer program stored on or in a carrier adapted to carry out the invention. The program may be in the form of source code, object code, or a code intermediate source code and object code, such as in a partially compiled form, or any other form suitable for use in implementing the method according to the invention. The carrier may comprise a storage medium such as a ROM, for example a memory stick or a hard disk. The carrier may be an electrical or optical signal, which may be transmitted via an electrical or optical cable, or by radio or other means.

[0065] As used herein, the terms "comprise, comprise, comprised, and comprising" or any variations thereof, and the terms "include, includes, included, and including" or any variations thereof, are considered to be fully interchangeable and all of them should be given the broadest possible interpretation, and vice versa.

[0066] The invention is not limited to the embodiments described hereinabove, which may be varied in both structure and detail.

Claims

1. 1. An apparatus for detecting electromagnetic radiation or signals emitted by a plasma, comprising a sensing unit, the sensing unit comprising: a first sensor for detecting electromagnetic radiation or signals; an electromagnetic barrier 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 first port being configured to connect to a port of a plasma chamber such that electromagnetic radiation or a signal emanating from the plasma can reach the first sensor; a first output connected to a balun and dual coaxial system whereby a signal is sensed relative to ground and an opposite phase version of said signal is also sensed relative to ground; An apparatus comprising:

2. 10. The apparatus of claim 1, wherein the first output is a balanced output configured to connect to one or more cables to provide a differential signal.

3. The apparatus of claim 1 or 2, wherein the balun converts an unbalanced signal provided by the first sensor to a balanced signal provided at the first output.

4. The sensing unit includes a second sensing unit, the second sensing unit comprising: 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 may 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 may reach the second sensor; a second output connected to the second sensor, the second output configured to be connected to a cable; 4. The apparatus according to claim 1 , further comprising:

5. 5. The apparatus of claim 4, wherein the first and second outputs are balanced outputs.

6. 5. The apparatus of claim 4, wherein the first and / or second outputs are cross-coupled to a balun to produce a third output, the third output being a balanced output that is a function of a phase difference between the signal received by the first sensor and a signal received by a second sensor.

7. 1. A Signal Acquisition System (SAS) for detecting electromagnetic radiation emitted by a plasma, comprising: An apparatus for detecting electromagnetic radiation according to any one of claims 1 to 6, a further housing comprising a receiver, transmitter or transceiver for providing the signal obtained by the device to a control unit, and an electromagnetic barrier configured to surround the transmitter or transceiver to prevent ambient electromagnetic radiation from reaching the transmitter or transceiver; at least one cable for providing the signals received by the device to the transmitter or transceiver; SAS equipped with.

8. The SAS of claim 7 , wherein the cable is a balanced cable.

9. 9. A SAS as claimed in claim 7 or 8, wherein the cable is a pair of coaxial cables, the cable being arranged to provide a ground connection from the device to the further housing.

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