In-situ electric field detection method and device

Abstract

Embodiments of the present disclosure include an electric field measurement system comprising: a first light source; a first light sensor configured to receive electromagnetic energy transmitted from the first light source; an electro-optical sensor; and a controller. The electro-optical sensor may include: a package including a first electro-optical crystal disposed within a body; and at least one optical fiber. The optical fiber is configured to transmit electromagnetic energy transmitted from the first light source to a surface of the first electro-optical crystal, and to transmit at least a portion of the electromagnetic energy transmitted to the surface of the first electro-optical crystal and then through at least a portion of the first electro-optical crystal to the first light sensor, the first light sensor is configured to generate a signal based on a property of electromagnetic energy received by the first light sensor from the at least one optical fiber. The controller is configured to generate a command signal based on a signal received from the first light sensor.

Description

Background Art

[0001] field

[0002] Embodiments of the present disclosure generally relate to systems and methods for use in semiconductor device fabrication. More specifically, embodiments provided herein generally include apparatus and methods for measuring electric fields generated in a plasma processing chamber to diagnose and control a generated plasma formed in the plasma processing chamber.

[0003] Related technical description

[0004] Reliably forming high aspect ratio features is one of the key technical challenges for next generation semiconductor devices. One method of forming high aspect ratio features uses a plasma assisted etching process, such as a reactive ion etching (RIE) plasma process, to form a high aspect ratio opening in a material layer (e.g., a dielectric layer) of a substrate. In a typical RIE plasma process, a plasma is formed in a processing chamber and ions from the plasma are accelerated toward a surface of a substrate to form an opening in a material layer disposed below a shielding layer formed on the surface of the substrate.

[0005] A typical reactive ion etch (RIE) plasma processing chamber includes a radio frequency (RF) bias generator that provides an RF voltage to a power electrode, such as a metal plate (more commonly referred to as a "cathode") located near an "electrostatic chuck" (ESC) assembly. The power electrode may be capacitively coupled to the plasma of the processing system through a thick layer of dielectric material (e.g., a ceramic material) that is part of the ESC assembly. In a capacitively coupled gas discharge, the plasma is generated using an RF generator coupled to the power electrode (or a separate power electrode disposed within the processing chamber outside the ESC assembly) through an RF matching network ("RF match") that adjusts the apparent load to 50Ω to minimize reflected power and maximize power transfer efficiency. Application of the RF voltage to the power electrode causes an electron-repelling plasma sheath to form above the processing surface of the substrate, which is positioned on the substrate support surface of the ESC assembly during processing. The nonlinear, diode-like nature of the plasma sheath causes the applied RF field to be rectified, resulting in a direct current (DC) voltage drop or "self-bias" between the substrate and the plasma, causing the substrate potential to be negative relative to the plasma potential. This voltage drop determines the average energy at which the plasma ions are accelerated toward the substrate and thus etch anisotropically. More specifically, ion directionality, feature profiles, and etch selectivity to stop layers and shields are controlled by the ion energy distribution function (IEDF). In a plasma with an RF bias, the IEDF typically has two non-discrete peaks, one at low energy and one at high energy, and a population of ions with an energy range extending between the two peaks. The presence of an ion population between the two peaks of the IEDF reflects the fact that the voltage drop between the substrate and the plasma oscillates at the RF bias frequency. When a lower frequency RF bias generator is used to achieve a higher self-bias voltage, the energy difference between the two peaks can cause processing-related problems, such as causing the walls of the etched features formed on the substrate surface to bend. Compared with high-energy ions, low-energy ions are less efficient at reaching the bottom corners of the etched features (e.g., due to charging effects), but result in less sputtering of the shielding material. This is important in high aspect ratio etching applications, such as hard shield openings or dielectric pattern etching. As feature sizes continue to decrease and aspect ratios increase, while feature profile control requirements become more stringent, having well-controlled substrate bias and, therefore, IEDF at the substrate surface during processing becomes more desirable.

[0006] It has been found that conventional RF plasma assisted etching processes that deliver only a sinusoidal waveform of an RF signal including a conventional plasma generation bias level to one or more electrodes in a plasma processing chamber do not adequately or ideally control sheath characteristics and generated ion energy, which can lead to undesirable plasma processing results. Undesirable processing results may include excessive sputtering of shielding layers and the generation of sidewall defects in high aspect ratio features.

[0007] In addition, the substrate potential or the self-bias generated during the plasma processing is a key parameter to ensure controllable and ideal plasma processing results. The determination of the substrate potential during the plasma processing of the substrate can be used to improve the plasma processing results achieved on the substrate and subsequent substrates processed in the processing chamber. For example, the real-time determination of the substrate potential can be used to better control the actual bias voltage established at the substrate due to the capacitive coupling of the waveform applied to the adjacent positioning bias electrode, and compensate for any drift in the substrate potential caused by changes in the processing environment. In other examples, the determination of the substrate potential can be used for plasma processing diagnosis and optimization, as well as for the control of electrostatic adsorption and desorption of the substrate during plasma processing. Typically, the potential of the substrate can only be inferred by using empirical models, or experimentally measured using offline non-production-value diagnostic processing test methods using specially set virtual substrates or experimental probes. Therefore, using conventional processing, direct real-time measurement of the substrate potential and real-time control based on the measured substrate potential during plasma processing of semiconductor devices including production substrates is impossible.

[0008] Therefore, there is a need in the art for a plasma processing apparatus and a bias method that can at least solve the above problems. Summary of the invention

[0009] Embodiments of the present disclosure include an electric field measurement system. The electric field measurement system also includes: a first light source configured to transmit electromagnetic energy at one or more wavelengths; a first light sensor configured to receive electromagnetic energy transmitted at one or more wavelengths. The system also includes: at least one electro-optical sensor, which may include: a package, which may include a body; a first electro-optical crystal, disposed within the body; and at least one optical fiber, configured to transmit electromagnetic energy transmitted from the first light source to a surface of the first electro-optical crystal; and transmit at least a portion of the electromagnetic energy transmitted to the surface of the first electro-optical crystal and then passing through at least a portion of the first electro-optical crystal to the first light sensor, wherein the first light sensor is configured to generate a signal, the signal varies based on the properties of the portion of the electromagnetic energy received by the first light sensor from at least one optical fiber. The system also includes a controller, the controller configured to receive the generated signal from the first light sensor and generate a command signal based on the received signal. Other embodiments of this aspect include corresponding computer systems, devices, and computer programs recorded on one or more computer storage devices, configured to perform methods.

[0010] Embodiments of the present disclosure may further include: a method of performing electric field measurement using an electric field measurement system, the method may include: detecting an electric field generated by a first component by using a first electro-optical sensor, wherein the first electro-optical sensor may include: a package, which may include a body; a first electro-optical crystal, disposed within the body and positioned so that the generated electric field passes through at least a portion of the first electro-optical crystal; and at least one optical fiber. The method also includes: transmitting electromagnetic energy through at least one optical fiber to a surface of the first electro-optical crystal while the first component generates the electric field. The method also includes: transmitting at least a portion of the electromagnetic energy transmitted to the surface of the first electro-optical crystal and then passing through at least a portion of the first electro-optical crystal to the first optical sensor through at least one optical fiber. The method also includes: generating a first measurement signal by the first optical sensor, the first measurement signal varying based on a property of a portion of the electromagnetic energy received by the first optical sensor from the at least one optical fiber. The method also includes: generating a command signal by a controller based on the generated first measurement signal, the command signal being configured to provide information for adjusting a setting of a process parameter of a plasma process performed in a plasma processing chamber. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, configured to perform the methods.

[0011] Embodiments of the present disclosure include a method for performing electric field measurements using an electric field measurement system. The method includes: detecting an electric field generated by a first component by using a first electro-optical sensor, wherein the first electro-optical sensor includes: a package including a body; a first electro-optical crystal disposed within the body and positioned so that the generated electric field passes through at least a portion of the first electro-optical crystal; and at least one optical fiber. The method also includes: transmitting electromagnetic energy through at least one optical fiber to a surface of the first electro-optical crystal while the first component generates the electric field by using a first light source; transmitting at least a portion of the electromagnetic energy transmitted to the surface of the first electro-optical crystal and then passing through at least a portion of the first electro-optical crystal to the first optical sensor through at least one optical fiber; generating a first measurement signal by the first optical sensor, the first measurement signal varying based on a property of a portion of the electromagnetic energy received by the first optical sensor from the at least one optical fiber; and generating a command signal by a controller based on the generated first measurement signal, wherein the command signal is configured to provide information for adjusting a setting of a processing parameter of a plasma process performed in a plasma processing chamber.

[0012] Embodiments of the present disclosure include an electric field measurement system. The electric field measurement system may include: a first light source configured to transmit electromagnetic energy at one or more wavelengths; a first light sensor configured to receive electromagnetic energy transmitted at one or more wavelengths; at least one electro-optical sensor; and a controller. The at least one electro-optical sensor may include: a package including a body; a first electro-optical crystal disposed within the body; and at least one optical fiber. The optical fiber is configured to transmit electromagnetic energy transmitted from the first light source to a surface of the first electro-optical crystal, and transmit at least a portion of the electromagnetic energy transmitted to the surface of the first electro-optical crystal and then passing through at least a portion of the first electro-optical crystal to the first light sensor, wherein the first light sensor is configured to generate a signal that varies based on a property of a portion of the electromagnetic energy received by the first light sensor from the at least one optical fiber. A controller configured to receive the generated signal from the first light sensor and generate a command signal based on the received signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to understand the above-mentioned features of the present disclosure in more detail, a more specific description of the present disclosure briefly summarized above may be made with reference to embodiments, some of which are shown in the accompanying drawings. However, it should be noted that the accompanying drawings only illustrate exemplary embodiments and are therefore not to be considered as limiting the scope of the embodiments, and other equivalent embodiments may be admitted.

[0014] Figure 1 is a schematic cross-sectional view of a processing system configured to implement the methods set forth herein, according to one or more embodiments.

[0015] Figure 2 is a schematic diagram of a portion of a signal detection assembly according to one embodiment.

[0016] Figure 3A is a top view of a sensing assembly including a signal detection assembly according to one or more embodiments.

[0017] Figure 3B According to an embodiment Figure 3A A side cross-sectional view of the sensing assembly shown in FIG.

[0018] Figure 3C According to an embodiment Figure 3A A side cross-sectional view of an alternative version of the sensing assembly shown in FIG.

[0019] Figure 3D is a side cross-sectional view of a sensing assembly according to one embodiment.

[0020] Figure 4 is a diagram illustrating a method for real-time chip potential measurement in a plasma processing system according to one embodiment.

[0021] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. DETAILED DESCRIPTION

[0022] Embodiments of the present disclosure generally relate to systems for manufacturing semiconductor devices. More specifically, embodiments provided herein generally include apparatus and methods for real-time measurement and control of potentials formed on a substrate or plasma generating component disposed within a plasma processing chamber during processing. The measured potentials can be used for plasma process monitoring, equipment calibration, process and device performance diagnostics, process chamber design optimization, and improving the safety of a plasma processing chamber.

[0023] It has been discovered that an electro-optical (EO) effect sensing device including an EO sensing component (e.g., an EO crystal) has significant advantages over other conventional techniques for detecting electrical potentials generated in one or more regions of a plasma processing chamber. Typical conventional measurement techniques require circuits including devices and conductive components that typically modify and / or interfere with various electromagnetic fields generated in a plasma processing chamber during processing. The electromagnetic fields are typically generated due to the transmission of radio frequency (RF) and / or pulsed direct current (DC) voltage signals that are used to generate and control a plasma formed in a processing region of a processing chamber during operation. Figure 1 is an example of a plasma processing system 10 and a controller 126 configured to perform a plasma processing method. Figure 22 is a simplified schematic diagram of a signal detection assembly 225 that forms part of a sensing assembly 184 that can be positioned in a region of a plasma processing system 10 to sense an electric field strength E, and a voltage (V) generated in the region (i.e., electric field E=-dV / ds, where "s" is the distance over which the electric field extends) can be determined and used to control one or more aspects of a plasma process. The signal detection assembly 225 includes a laser 210 and a photodetector 211 that are optically coupled to one or more fiber optic sensors 250 (e.g., a crystal) using one or more optical fibers. The one or more optical fibers can include a first optical fiber 213 and a second optical fiber 214. The laser 210 is coupled to the fiber optic sensor 250 via a first fiber optic cable 213. The fiber optic sensor 250 is coupled to the photodetector 211 via a second fiber optic cable 214. When the fiber optic sensor 250 is positioned between the first electrode 203 and the second electrode 204, the fiber optic sensor can be used to detect an electric field formed between the first electrode 203 and the second electrode 204. The optical fiber sensor 250 includes an electro-optic (EO) effect sensing component, such as an electro-optic crystal 290, which is configured to detect the magnitude of an electric field E passing through the electro-optic crystal 290, such as the electric field E generated between the first electrode 203 and the second electrode 204 during plasma processing. In one embodiment, the electro-optic (EO) effect sensing component includes a crystal using the Pockel's effect, wherein the birefringence of the crystal changes in proportion to the electric field applied to the optical crystal within the optical fiber sensor 250. In some embodiments, the electro-optic crystal 290 includes a crystal material, such as lithium niobate (LiNbO 3 )、LiTaO 3 , potassium dihydrogen phosphate (KDP) and its isomorphs, crystals of beta-barium borate (BBO), III-V semiconductors, or other non-centrosymmetric media, such as electric field polarized polymers or glasses. Any change in the electric field will cause the characteristics of the light received by the photodetector 211 to change due to the effect of the change in the electric field on the electro-optic effect sensing components and the light generated by the laser 210 passing therethrough. In some embodiments, the laser 210 is configured to transmit light having a wavelength between approximately 200 and 14,000 nanometers (nm). Values ​​associated with the change in the characteristics of the light received by the photodetector 211 can then be relayed to the controller 126 to determine the potential or voltage formed between the electric field generating components in the area of ​​the plasma processing system 10 where the fiber optic sensor 250 is located.

[0024] However, it has been found that the electric field strength measurements made by most EO effect sensor designs are temperature dependent and also depend on the orientation of the sensing crystal and the orientation of the generated electric field lines. Therefore, embodiments of the present disclosure provided herein are configured to compensate for these additional measurement variables. Figure 3A and3B The diagram shows an embodiment of a sensing assembly 184, which includes a detector assembly 301, which includes a plurality of fiber optic sensors 250, such as a first fiber optic sensor 320 and a second fiber optic sensor 321 mounted within a package 310. The package 310 includes a body, which may include a dielectric material capable of supporting and retaining each of the plurality of fiber optic sensors 250, and in some embodiments, the body may include a ceramic material, a polymeric material, or other materials that do not interfere with the operation of the fiber optic sensors and do not significantly degrade when exposed to high temperatures, electric fields, or plasma processing environments. In one embodiment, the first fiber optic sensor 320 includes a pair of optical fibers 341 and 342, each of which is in optical communication with the surface of the electro-optic crystal 290 located at one end of the optical fiber, and is in optical communication with the first optical detection assembly 350A located at the other end of the optical fiber. Similarly, the second fiber optic sensor 321 includes a pair of optical fibers 343 and 344, each of which is in optical communication with the surface of the electro-optic crystal 290 located at one end of the optical fiber, and is in optical communication with the second optical detection assembly 350B located at the other end of the optical fiber. Optical fibers 341, 342 and 343, 344 are respectively disposed in a support sleeve 311 extending between the body surface of the package 310 and the optical detection components 350A, 350B to protect the optical fibers from external environmental interference and avoid damage during installation and / or use. The sleeve 311 can be further protected by using ceramic beads, flexible metal tubes or other useful materials that can provide chemical and thermal insulation and / or resistance to components exposed to them during processing.

[0025] During operation, the optical transmission assembly 351 within the optical detection assembly 350 includes a laser 210 that is configured to transmit electromagnetic radiation (e.g., coherent light) to input optical fibers 341, 343, which transmit the generated radiation to and through the electro-optic crystal 290, which in some configurations causes a majority of the generated radiation to be reflected and / or returned to the output optical fibers 342, 344, which then transmit the generated radiation to the optical detector 352, which is configured to detect aspects of the received radiation (e.g., intensity, polarization, etc.) and transmit information related to the detected aspects of the received radiation to the controller 126. The optical detector 352 is configured to receive the electromagnetic radiation provided from the optical transmission assembly 351 and then provide a signal including information related to the detected aspects of the received electromagnetic radiation. The optical detector 352 may include an optoelectronic device, such as a photoelectric effect type sensor (e.g., a photodiode, a photomultiplier tube), a photoconductive type sensor, a photorefractive effect type sensor, or other useful device configured to convert electromagnetic energy into a signal that can be used by the controller 126. The controller 126 may then use the signal received from the optical detector 352 and generate a command signal to control some aspect of a process performed in the processing chamber 100 or to control the use of a piece of hardware in the processing chamber 100. The controller 126 will generally analyze and use the information provided in the signal received from the optical detector 352 to monitor aspects of the plasma processing, help calibrate and / or improve the performance of one or more processing chamber components, optimize the processing chamber design, and ensure that the plasma processing chamber is safe, as will be discussed further below. The analysis performed by the controller 126 may include a comparison of the information provided in the signal with system configuration data stored in the memory of the controller 126. The system configuration data may include baseline data previously generated from previous processing runs and / or user-defined thresholds that are defined to ensure proper operation of portions of the processing chamber.

[0026] like Figure 3A and 3BAs shown, the first fiber optic sensor 320 and the second fiber optic sensor 321 are spaced apart by a distance in one direction (e.g., the X direction) so that each electro-optic crystal 290 within each fiber optic sensor 250 can detect a different portion of the electric field E passing through various components within the detector assembly 301 during processing. Generally, it is desirable that the surfaces 325, 326 of the first fiber optic sensor 320 and the second fiber optic sensor 321, respectively, are oriented in a desired direction relative to the generated electric field E. In one example, the surfaces 325, 326 of the first fiber optic sensor 320 and the second fiber optic sensor 321 can be aligned with features (e.g., crystal planes) within the electro-optic crystal 290, and the orientation of the electro-optic crystal 290 is perpendicular to the main electric field E line direction (e.g., the Z direction). In some embodiments, it is desirable that the detector assembly 301 includes three or more fiber optic sensors 250. In one example, the package 310 includes a first fiber optic sensor 320, a second fiber optic sensor 321, and a third fiber optic sensor (not shown), which are oriented to measure the electric field E in three different orthogonal directions, respectively, so that each major surface (e.g., surfaces 325, 326) of each fiber optic sensor is oriented perpendicular to a different direction in the X, Y, and Z coordinate directions.

[0027] To compensate for temperature drift or changes in the measured electric field strength (and therefore, the measured voltage), the measurements provided by controller 126 from the signal received from optical detector 352 may be adjusted by using fiber optic sensor calibration data stored in the memory of controller 126. In one embodiment, the effect of temperature on the measurements from each fiber optic sensor 320, 321 may be stored in the form of a time-varying formula or as data in a lookup table created based on a known process train. In one example, changes in the optical properties of electro-optic crystal 290 for a plurality of standard plasma process trains performed in a first plasma processing chamber are collected and stored in memory, and the stored data is used in subsequent plasma process trains to help adjust measurements made in a similarly configured second plasma processing chamber that is running one of the plurality of standard plasma process trains. In another embodiment, the effect of temperature changes on the measurement results can be determined by synchronously pausing or stopping the transmission of the electric field generating signal to the electrode, radio frequency (RF) coil or electric field generating component for a brief period of time, allowing the fiber optic sensor 250 to collect at least one measurement in the absence of the electric field E, so that the change in the optical characteristics of the electro-optic crystal 290 can be collected by comparing the measurement made during the cessation of the electric field E with the previous measurement made when the electric field E was also absent. In one example, the optical characteristics of the electro-optic crystal 290 are measured at one or more intervals when the generated electric field E is stopped and compared with the optical characteristics of the electro-optic crystal 290 performed at a time before the plasma processing begins. In one processing example, the optical detector 352 is adapted to provide a measurement signal to the controller 126 in real time, wherein the measurement signal includes a first portion and a second portion, in which the electric field is sensed by the fiber optic sensor 250 and in which the fiber optic sensor 250 does not sense the electric field, thereby allowing the effect of temperature to be determined by comparing the two portions of the measurement signal. In either case, a temperature effect compensation factor determined by using a formula, data in a lookup table, or by comparing measurements taken at different times can then be used to adjust the optical data collected by one or more fiber optic sensors to improve the accuracy of the derived voltage measurement.

[0028] Figure 3CAn embodiment of a sensing assembly 184 is shown that includes a detector assembly 301 that includes at least one fiber optic sensor 250 that is configured to detect changes in an electric field (i.e., a first fiber optic sensor 320) and at least one fiber optic sensor 250 that is similarly configured but shielded from the electric field E by using a shielding element 360 (i.e., a second fiber optic sensor 321). The shielding element 360 may include a conductive layer (e.g., a metal layer) that is sized and positioned within the body of the package 310 so as to act as a Faraday shield for the shielded fiber optic sensor. In this configuration, due to the proximity of the two fiber optic sensors 250 and their thermal coupling to each other due to their position within the package 310, the measured optical properties of the electro-optic crystal 290 within the shielded fiber optic sensor (which is substantially unaffected by the presence of the electric field E passing through the body of the package 310) can be used as a baseline value to adjust measurements made by another fiber optic sensor that is exposed to the electric field E. In one example, the measurement baseline value measured by the shielded second optical fiber sensor 321 may be subtracted from the measurement value of the first optical fiber sensor 320 , thereby eliminating the influence of temperature change on its measurement result.

[0029] Figure 3D An embodiment of a sensing assembly 184 is shown, the sensing assembly 184 includes a detector assembly 301, the detector assembly 301 includes at least one fiber optic sensor 250 configured to detect changes in an electric field (i.e., a first fiber optic sensor 320) and at least one optical temperature measurement assembly 370 configured to measure the temperature of the electro-optic crystal 290 when the fiber optic sensor 250 performs an electric field E measurement. The optical temperature measurement assembly 370 may include an optical fiber 371 positioned to collect radiation emitted from the electro-optic crystal 290 at one end and transmit the collected electromagnetic radiation to a detector disposed within an optical detection assembly 372 located at an opposite end. In this case, the temperature measurement signal generated by the electronics in the optical detection assembly 372 as a result of receiving radiation emitted from the surface 327 of the electro-optic crystal 290 may be transmitted to the controller 126 so that the measurement collected by the fiber optic sensor 250 may be adjusted based on previous calibration data stored in the memory to compensate for temperature changes of the electro-optic crystal 290. Conventional optical temperature measurement components are available from Omega Engineering, Inc. of Norwalk, Connecticut, USA or Advanced Energy Inc. of Fort Collins, Colorado, USA, and are configured to make measurements during processing over the desired temperature range to which electro-optic crystal 290 is exposed.

[0030] In some alternative embodiments, a temperature sensor (eg, an optical temperature sensor probe) may be used that is external to the detector assembly 301 and not affected by the electric field E. In this case, the temperature signal generated by the external temperature sensor is transmitted to the controller 126 for processing and electric field compensation.

[0031] Measuring equipment and processing methods

[0032] As described above, for example, the sensing assembly 184 includes a detector assembly 301 and an optical detection assembly 350A, wherein the detector assembly 301 includes a package 310, the package 310 includes one or more fiber optic sensors 250, and the optical detection assembly 350A is optically coupled to the fiber optic sensors 250 via optical fibers 341, 342. Return to Reference Figure 1 , each sensing assembly 184 is communicatively coupled to the controller 126 via the communication line 165. The controller 126 can then use the output signals received from each optical detection assembly to display the results or measurements performed by the fiber optic sensor 250 and / or control some portion of the processing chamber 100 during processing. As explained in further detail below, the processing chamber 100 may include one or more sensing assemblies 184 that are positioned to detect electric fields, and therefore voltages generated in areas of the processing chamber 100, and provide feedback to the controller 126. Changes in the sensed parameters detected by the fiber optic sensor 250 are transmitted from the sensing assembly 184 to the controller 126. The controller 126 can then subsequently use the input received from the sensing assembly 184 to change one or more plasma processing variables, such as changing the characteristics of the RF signal or the pulsed voltage (PV) waveform generated by the PV waveform generator 175, and / or the amount of current provided from the current source 177 to the bias electrode 104 within the processing chamber 100.

[0033] Figure 1 is a schematic cross-sectional view of a plasma processing system 10 that can be configured to perform one or more plasma processing methods. In some embodiments, the plasma processing system 10 is configured for a plasma-assisted etching process, such as a reactive ion etching (RIE) plasma process. The plasma processing system 10 can also be used in other plasma-assisted processes, such as a plasma-enhanced deposition process, such as a plasma-enhanced chemical vapor deposition (PECVD) process, a plasma-enhanced physical vapor deposition (PEPVD) process, a plasma-enhanced atomic layer deposition (PEALD) process, a plasma treatment process, or a plasma-based ion implantation process (e.g., a plasma doping (PLAD) process). In one configuration, such as Figure 1As shown, the plasma processing system 10 is configured to form a capacitively coupled plasma (CCP). However, in some embodiments, the plasma may alternatively be generated by an inductively coupled source disposed above a processing region of the plasma processing system 10. In this configuration, the RF coil may be placed on top of a ceramic lid (vacuum boundary) of the plasma processing system 10.

[0034] The plasma processing system 10 includes a processing chamber 100, a substrate support assembly 136, a gas system 182, a DC power system 183, an RF power system 189, one or more sensing assemblies 184, and a controller 126. The processing chamber 100 includes a chamber body 113, which includes a chamber lid 123, one or more sidewalls 122, and a chamber base 124. The chamber lid 123, one or more sidewalls 122, and the chamber base 124 collectively define a processing space 129. The one or more sidewalls 122 and the chamber base 124 generally include a material (e.g., aluminum, an aluminum alloy, or a stainless steel alloy) of a size and shape designed to form a structural support for the components of the processing chamber 100, and the material is configured to withstand the pressure and increased energy applied to the material while generating a processing plasma 101 in a vacuum environment maintained in the processing space 129 of the processing chamber 100 during processing. The substrate 103 is loaded into and removed from the processing space 129 through an opening (not shown) in one of the sidewalls 122. The opening is sealed with a slit valve (not shown) during plasma processing of the substrate 103. A gas system 182 coupled to the processing space 129 of the processing chamber 100 includes a processing gas source 119 and a gas inlet 128 disposed through the chamber lid 123. The gas inlet 128 is configured to deliver one or more processing gases from the plurality of processing gas sources 119 to the processing space 129.

[0035] The processing chamber 100 further includes a chamber lid 123, an RF coil 181, and a lower electrode (eg, a substrate support assembly 136) disposed in the processing space 129. The chamber lid 123 and the lower electrode are positioned to face each other. Figure 1 As shown, in one embodiment, a radio frequency (RF) source 171 is electrically coupled to the lower electrode. The RF source 171 is configured to transmit an RF signal to ignite and maintain a plasma (e.g., plasma 101) between the upper electrode and the lower electrode. In some alternative configurations, the RF source can also be electrically coupled to the upper electrode. For example, the RF source can be electrically coupled to the chamber lid. In another example, the RF source can also be electrically coupled to the substrate support base 107.

[0036] The substrate support assembly 136 includes a substrate support 105, a substrate support base 107, an insulating plate 111, a ground plate 112, a plurality of lift pins 186, and a bias electrode 104. Each lift pin 186 is disposed through a through hole 185 formed in the substrate support assembly 136 and is used to assist in transferring the substrate 103 to and from the substrate support surface 105A of the substrate support 105. The substrate support 105 is formed of a dielectric material. The dielectric material may include a bulk sintered ceramic material, a corrosion resistant metal oxide (e.g., alumina (Al2O3), or a dielectric material. 2 O 3 ), titanium oxide (TiO), yttrium oxide (Y 2 O 3 ), metal nitride materials (such as aluminum nitride (AlN), titanium nitride (TiN)), mixtures thereof, or combinations thereof.

[0037] The substrate support pedestal 107 is formed of a conductive material (e.g., aluminum, aluminum alloy, or stainless steel alloy). The substrate support pedestal 107 is electrically insulated from the chamber base 124 by an insulating plate 111, and a ground plate 112 is interposed between the insulating plate 111 and the chamber base 124. In some embodiments, the substrate support pedestal 107 is configured to adjust the temperature of the substrate support 105 and the substrate 103 disposed on the substrate support 105 during substrate processing. In some embodiments, the substrate support 105 includes a heater (not shown) to heat the substrate support 105 and the substrate 103 disposed on the substrate support 105.

[0038] The bias electrode 104 is embedded in the dielectric material of the substrate support 105. Generally, the bias electrode 104 is formed by one or more conductive parts. The conductive part generally includes a mesh, a foil, a plate or a combination thereof. Here, the bias electrode 104 is used as an adsorption rod (i.e., an electrostatic adsorption electrode), which is used to fix (e.g., electrostatically adsorb) the substrate 103 to the substrate support surface 105A of the substrate support 105. Generally speaking, a parallel plate structure is formed by the bias electrode 104 and a dielectric material layer disposed between the bias electrode 104 and the substrate support surface 105A. The dielectric material can generally have an equivalent capacitance CE between about 5nF and about 50nF. Generally, the dielectric material layer (e.g., aluminum nitride (AlN), aluminum oxide (Al 2 O 3) and the like) has a thickness between about 0.05 mm and about 5 mm, such as between about 0.1 mm and about 3 mm, such as between about 0.1 mm and about 1 mm, or even between about 0.1 mm and 0.5 mm. The bias electrode 104 is electrically coupled to a clamping network that provides a clamping voltage to the bias electrode 104. The clamping network includes a DC voltage source 173 (e.g., a high voltage DC power supply) coupled to a filter 178A of a filter assembly 178, the filter 178A being disposed between the DC voltage source 173 and the bias electrode 104. In one example, the filter 178A is a low pass filter that is configured to block RF frequencies and pulsed voltage (PV) waveform signals provided by other bias components within the processing chamber 100 from reaching the DC voltage source 173 during plasma processing. In one configuration, the static DC voltage is between about -5000 V and about 5000 V and is transmitted using an electrical conductor (e.g., a coaxial power transmission line 160).

[0039] In some configurations, the substrate support assembly 136 further includes an edge control electrode 115. The edge control electrode 115 is formed of one or more conductive parts. The conductive parts generally include meshes, foils, plates, or combinations thereof. The edge control electrode 115 is located below the edge ring 114 and surrounds the bias electrode 104 and / or is disposed at a distance from the center of the bias electrode 104. Generally speaking, for a processing chamber 100 configured to process a circular substrate, the edge control electrode 115 is annular in shape, made of a conductive material, and configured to surround at least a portion of the bias electrode 104. Figure 1 As shown, the edge control electrode 115 is located within the region of the substrate support 105 and is biased using a pulsed voltage (PV) waveform generator 175 .

[0040] The DC power system 183 includes a DC voltage source 173, a pulse voltage (PV) waveform generator 175, and a current source 177. The RF power system 189 includes a radio frequency (RF) waveform generator 171, a matcher 172, and a filter 174. As previously described, the DC voltage source 173 provides a constant clamping voltage, while the RF waveform generator 171 transmits an RF signal to the processing region, and the PV waveform generator 175 establishes a PV waveform at the bias electrode 104. A sufficient amount of RF power is applied to an electrode, such as a substrate support pedestal 107, so that a plasma 101 is formed in the processing region 129 of the processing chamber 100. In one configuration, the RF waveform has a frequency range between about 1 MHz and about 200 MHz.

[0041] In some embodiments, the power system 183 further includes a filter assembly 178 to electrically isolate one or more components included in the power system 183. Figure 1As shown, power transmission line 163 electrically connects the output of RF waveform generator 171 to impedance matching circuit 172, RF filter 174, and substrate support base 107. Power transmission line 160 electrically connects the output of voltage source 173 to filter assembly 178. Power transmission line 161 electrically connects the output of PV waveform generator 175 to filter assembly 178. Power transmission line 162 connects the output of current source 177 to filter assembly 178. In some embodiments, current source 177 is selectively coupled to bias electrode 104 by using a switch (not shown) disposed in transmission line 162 to allow current source 177 to transmit a desired current to bias electrode 104 during one or more phases (e.g., ion current phase) of the voltage waveform generated by PV waveform generator 175. In one example, the voltage waveform provided from the PV waveform generator 175 may include a plurality of asymmetric voltage pulses having a voltage pulse peak voltage range between ±5000 volts, a pulse on time between 10% and 90% of the asymmetric voltage pulse period, and delivered at a pulse repetition frequency between 100 kHz and 500 kHz. Figure 1 As shown, the filter assembly 178 may include a plurality of individual filter assemblies (i.e., discrete filters 178A-178C), each of which is electrically coupled to the output node via the power transmission line 164. The power transmission lines 160-164 include electrical conductors, which include a combination of coaxial cables, such as a flexible coaxial cable connected in series with a rigid coaxial cable, an insulated high voltage anti-corona connecting wire, a bare wire, a metal rod, an electrical connector, or any combination thereof.

[0042] The controller 126, also referred to herein as a processing chamber controller, includes a central processing unit (CPU) 133, a memory 134, and a support circuit 135. The controller 126 is used to control the processing sequence for processing the substrate 103. The CPU is a general-purpose computer processor configured for use in an industrial environment to control a processing chamber and its associated subprocessors. The memory 134 described herein is generally a non-volatile memory and may include a random access memory, a read-only memory, a hard disk drive, or other suitable forms of local or remote digital memory. The support circuit 135 is coupled to the CPU 133 in a conventional manner and may include caches, frequency circuits, input and output subsystems, power supply devices, etc., and combinations thereof. Software instructions (programs) and data may be encoded and stored in the memory to instruct the processor within the CPU. The program (or computer instructions) readable by the CPU 133 in the system controller 126 determines which tasks can be performed by the components in the processing system 10.

[0043] Generally, the program readable by the CPU 133 in the controller 126 includes code that, when executed by the CPU 133, performs tasks associated with the plasma processing schemes described herein. The program may include instructions for controlling various hardware and electronic components within the processing system 10 to perform various processing tasks and various process sequences for implementing the methods described herein. In one embodiment, the program includes instructions for performing the following with respect to Figure 4 An instruction that describes one or more operations.

[0044] The controller 126 is in communication with the pulsed voltage (PV) waveform generator 175 and the radio frequency (RF) waveform generator 171 such that during processing one or more command signals provided from the controller 126 may be used to control aspects (e.g., waveform characteristics) of output signals provided by the pulsed voltage (PV) waveform generator or the radio frequency (RF) waveform generator.

[0045] Processing method examples

[0046] Figure 4 4 is a diagram illustrating a method for measuring in real time the chip potential of a substrate or plasma generating component disposed within a plasma processing chamber. The method 400 includes generating a plasma in a processing region of the processing chamber, monitoring an electrical characteristic of a sensor within a detector assembly 301 disposed within a sensing assembly 184, forming a set of adjustment parameters based on the electrical characteristic, and adjusting one or more plasma processing parameters based on the monitored electrical characteristic of the sensor. Prior to performing the method 400, one or more detector assemblies 301 (and therefore, one or more fiber optic sensors 250 disposed within the body of the package 310 of each detector assembly 301) are positioned and aligned within one or more regions of the processing chamber 100 to detect a portion of an electric field formed therein.

[0047] At activity 402, method 400 includes forming a plasma 101 in a processing chamber 100 due at least in part to an RF signal provided from an RF waveform generator 171 of an RF power system 189 transmitted to an electrode within the processing chamber. In some embodiments of activity 402, an asymmetric voltage waveform is also provided from a PV waveform generator 175 to an electrode (e.g., bias electrode 104) disposed within the processing chamber 100.

[0048] At activity 404, method 400 includes measuring one or more sensed parameters based on measurements collected by one or more sensors disposed within processing chamber 100. The one or more sensed parameters may include one or more of electric field strength measured by fiber optic sensor 250, changes in optical properties of electro-optic crystal 290, and in some cases may also include temperature measurements provided by a temperature sensor. In some embodiments, the sensed parameters include real-time measurements of the electric field E generated within a region of processing chamber 100 using one or more of the one or more fiber optic sensors 250 within sensing assembly 184. Activity 404 may include measuring ... fiber optic sensors 250 within sensing assembly 184. Activity 404 may include measuring the electric field E generated within a region of processing chamber 100 using one or more fiber optic sensors 250 within sensing assembly 184. Activity 404 may include measuring the electric field E generated within a region of processing chamber 100 using one or more fiber optic sensors 250 within sensing assembly 184. Activity 404 may include measuring the electric field E generated within a region of processing chamber 100 using one or more fiber optic sensors 250 within sensing assembly 184. Activity 404 may include measuring the electric field E generated within a region of processing chamber 100 using one or more fiber optic sensors 250 within sensing assembly 184. Activity 40 Figure 1 ) in order to detect areas of the RF coil 181 that include higher or lower than expected electric fields E and may therefore be susceptible to arcing or plasma inhomogeneities. The measurements associated with the area of ​​the RF coil 181 being measured are relayed to the controller 126 via the communication line 165 for analysis. Prior to taking measurements during activity 404, the detector assembly 301 (and therefore, one or more fiber optic sensors 250 disposed within the body of the package 310) is positioned and aligned such that a surface of the one or more fiber optic sensors 250 (e.g., such as a Figure 3A The surfaces 325 , 326 ) are shown aligned in a desired direction to detect the electric field E generated by the region of the RF coil 181 .

[0049] Additionally or alternatively, during activity 404, measurements of the electric field E generated in the region of the RF match 172 or filter assembly 178 are performed to detect regions of the RF match 172 or filter assembly 178 that include higher or lower electric fields E than expected. Regions that include higher or lower electric fields may be prone to arcing or be a sign that the electric field generating components are prone to premature failure. Measurements related to regions of the RF match 172 and / or filter assembly 178 measured during processing are relayed to the controller 126 via the communication line 165 for analysis. It is believed that detecting electric fields generated by various electrical components (e.g., fixed or variable inductors, variable capacitors, and grounding components (e.g., ground straps) within the RF match 172 and filter assembly 178 that are outside of a desired range can be used to prevent any of these electronic components from causing changes in processing results or damaging portions of the processing chamber 100.

[0050] Additionally or alternatively, during activity 404, measurements of the electric field E generated in the processing region 129 of the processing chamber 100 are performed using a movable probe assembly (not shown) that is configured to be adjustably positioned in the processing region 129 of the processing chamber 100 during plasma processing using an articulated arm (not shown) that is attached to a wall of the processing chamber 100. The movable probe assembly can be used to map the electric field E generated in various regions of the processing chamber 100. The mapped electric field can then be used to adjust the characteristics of the electrical signal or electrical power delivered to the plasma generation components, and / or even physically adjust the plasma generation components to alter plasma uniformity and / or prevent arcing or other undesirable properties of the processing chamber design.

[0051] Additionally or alternatively, during activity 404, measurement of the electric field E generated at the surface of the substrate 103 is performed by using an instrumented substrate. The instrumented substrate includes one or more detector assemblies 301 aligned, oriented, and distributed in an array in each region on the substrate surface to detect skewness of plasma density and / or plasma non-uniformity formed on different regions of the substrate surface. Figure 1 In some embodiments, the support sleeve 311 and its associated optical fiber are connected to a vacuum compatible connector 137, which is configured to transmit optical signals transmitted between the fiber sections inside and outside the processing chamber and between the fiber optic sensor 250 and the optical detection assembly 350. Measurements related to the electric field E in various regions of the substrate surface being measured are relayed to the controller 126 via the communication line 165 for analysis.

[0052] In some alternative configurations, the measurement of the electric field E generated at the surface of the substrate 103 is performed using an array of fiber optic sensors 250 (not shown) arranged, oriented, and embedded within the substrate support 105, such as in the region between the bias electrode 104 and the substrate support surface 105A. In this configuration, the support sleeve 311 and its associated optical fiber can be positioned away from the bottom of the substrate support assembly 136 so that they can be connected to their associated optical detection assembly 350, which is configured to transmit signals to the controller 126.

[0053] At activity 406, the method 400 includes monitoring and analyzing changes in a sensed parameter detected by one or more fiber optic sensors 250 and other sensing components (e.g., optical temperature measurement components 370) within the one or more sensing components 184. During activity 406, the controller 126 compares the data received from the one or more fiber optic sensors 250 and other sensing components with information stored in a memory of the controller 126 or other received sensor data to determine a desired correction amount required to compensate for a temperature drift experienced by the one or more fiber optic sensors 250. The stored information may include an equation or a lookup table configured to provide a correction amount based on data received by the controller 126 related to temperature changes using one of the above-described techniques. In one example, the sensed parameter is a change in the electric field strength between points over time when the electric field E is not present in the region of the processing chamber 100. In another example, the sensed parameter is determined by a difference in the electric field E detected by the first fiber optic sensor 320 and the second fiber optic sensor 321, the second fiber optic sensor 321 being shielded from the electric field E using a shielding element 360. The controller 126 then analyzes and uses the data received over time to determine the amount of adjustment required for the electric field E measurement to correct for temperature changes.

[0054] At activity 408, the controller 126 then uses the determined adjustment amount and the resulting adjusted measurement data to generate a command signal for adjusting one or more plasma processing parameters based on the adjusted measurement. Plasma processing parameters may include any plasma processing variable that will affect the processing results seen on the substrate during or after the plasma processing, and may include, but are not limited to, the RF power level provided from the RF source, the PV power level provided from the PV source, the act of stopping the plasma processing, the gas flow rate, the processing chamber pressure, and the substrate temperature. In one example, due to the comparison of the adjusted measurement data with the stored system configuration data, the controller 126 determines that a set of adjusted measurement data provided from the detector assembly 301 is higher than expected, and then generates a command signal for stopping the process performed in the processing chamber due to the possibility of arcing in the processing chamber. In some embodiments of activity 408, the controller may also calculate an adjusted voltage measurement value based on the determined adjusted electric field E measurement value, and display information related to this measurement value on a graphical user interface (GUI) or store the result in a memory for later use. In one example, the controller 126 determines that an adjusted set of measurement data provided from the detector assembly 301 in the region of the plasma processing chamber is higher or lower than expected due to a comparison of the adjusted measurement data with the stored system configuration data, and then generates a command signal, which is used to provide information to the user that the electric field E in the chamber region is outside the desired range, and therefore one or more chamber components may need to be adjusted, repaired or replaced.

[0055] Embodiments of the present disclosure described herein can be used to measure and control in real time the electrical potential formed on a substrate or plasma generating component disposed within a plasma processing chamber during processing. As described herein, the measured electrical potential can be used for plasma process monitoring, equipment calibration, process and device performance diagnostics, process chamber design optimization, and improving the safety of a plasma processing chamber.

[0056] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be envisaged without departing from the basic scope of the disclosure and the scope of the disclosure is determined by the appended claims.

Claims

1. An electric field measurement system, the electric field measurement system include: a first light source configured to transmit electromagnetic energy at one or more wavelengths; a first light sensor configured to receive said electromagnetic energy transmitted at said one or more wavelengths; At least one electro-optical sensor comprising: Encapsulation, including the body; A first electro-optic crystal is disposed in the body; and at least one optical fiber configured to transmit the electromagnetic energy transmitted from the first light source to a surface of the first electro-optical crystal; and transmitting at least a portion of the electromagnetic energy transmitted to the surface of the first electro-optical crystal and subsequently passing through at least a portion of the first electro-optical crystal to the first photosensor, wherein the first light sensor is configured to generate a signal that varies based on a property of the portion of the electromagnetic energy received by the first light sensor from the at least one optical fiber; and A controller is configured to receive the generated signal from the first light sensor and generate a command signal based on the received signal.

2. The electric field measurement system according to claim 1, further comprising: include: a second light source configured to transmit electromagnetic energy at one or more wavelengths; as well as a second optical sensor configured to receive said electromagnetic energy transmitted at said one or more wavelengths, wherein said at least one electro-optical sensor further comprises: a second electro-optic crystal disposed in the body; and at least one optical fiber configured to transmit the electromagnetic energy transmitted from the second light source to a surface of the second electro-optical crystal; and transmitting at least a portion of the electromagnetic energy transmitted to the surface of the second electro-optical crystal and subsequently passing through at least a portion of the second electro-optical crystal to the second photosensor, wherein the second light sensor is configured to generate a signal that varies based on a property of the portion of the electromagnetic energy received by the second light sensor from the at least one optical fiber; and Wherein the controller is further configured to receive the generated signal from the second light sensor and generate the command signal based on the signals received from the first light sensor and the second light sensor.

3. The electric field measurement system of claim 2, wherein the at least one electro-optical sensor further include: A shielding element is positioned above the second electro-optical crystal and is configured to shield the second electro-optical crystal from an electric field E passing through the body.

4. The electric field measurement system of claim 1 , wherein the controller is configured to communicate with at least one of a pulsed voltage (PV) waveform generator and a radio frequency (RF) waveform generator, and the command signal is configured to cause the pulsed voltage (PV) waveform generator or the radio frequency (RF) waveform generator to adjust an output signal provided from the pulsed voltage (PV) waveform generator or the radio frequency (RF) waveform generator.

5. The electric field measurement system of claim 1 , wherein the controller has a processor configured to execute computer readable instructions that cause the system to measure the strength of the electric field within a region of a plasma processing chamber over time using the at least one electro-optical sensor.

6. The electric field measurement system of claim 1 , wherein the controller has a processor configured to execute computer readable instructions that cause the system to: applying a first radio frequency (RF) waveform to the first electrode using a radio frequency (RF) generator, measuring the strength of the electric field within a region of the plasma processing chamber over time by using the at least one electro-optical sensor; and The first RF waveform generated by the RF generator is altered based on the measured electric field strength.

7. The electric field measurement system of claim 1, wherein the controller has a processor configured to execute computer readable instructions that cause the system to: applying a first voltage waveform to the first electrode using a pulse voltage (PV) waveform generator, measuring the strength of the electric field within a region of the plasma processing chamber over time by using the at least one electro-optical sensor; and A pulsed voltage (PV) waveform generated by the pulsed voltage (PV) waveform generator is altered based on the measured electric field strength.

8. An electric field measurement system as described in claim 1, wherein the at least one electro-optical sensor is disposed in an RF matching component, the RF matching component having an input and an output, the input of the RF matching component is coupled to the output of an RF generator, and the output of the RF matching component is adapted to be coupled to an electrode disposed in a plasma processing chamber, wherein the at least one electro-optical sensor is positioned to detect an electric field generated by one or more components within the RF matching component.

9. The electric field measurement system of claim 1 , wherein the at least one electro-optical sensor is positioned adjacent to a portion of an RF coil disposed within a plasma processing chamber, wherein the at least one electro-optical sensor is positioned to detect an electric field generated by at least a portion of the RF coil during a process performed in the plasma processing chamber.

10. The electric field measurement system of claim 1, wherein the at least one electro-optical sensor further comprises an electro-optical sensor array positioned on a surface of a substrate, the substrate being configured to be positioned on a substrate support in a plasma processing chamber during a process performed in the plasma processing chamber.

11. A method for performing electric field measurement using an electric field measurement system, the method include: By detecting the electric field generated by the first component using a first electro-optical sensor, wherein the first electro-optical sensor comprises: Encapsulation, including the body; a first electro-optic crystal disposed within the body and positioned such that the generated electric field passes through at least a portion of the first electro-optic crystal; and at least one optical fiber; while generating said electric field by the first component, transmitting electromagnetic energy through said at least one optical fiber to a surface of said first electro-optical crystal using a first light source; transmitting at least a portion of the electromagnetic energy transmitted to the surface of the first electro-optic crystal and subsequently passing through at least a portion of the first electro-optic crystal to a first light sensor via the at least one optical fiber; generating, by the first light sensor, a first measurement signal that varies based on a property of the portion of the electromagnetic energy received by the first light sensor from the at least one optical fiber; and A command signal is generated by a controller based on the generated first measurement signal, wherein the command signal is configured to provide information for adjusting a setting of a processing parameter of a plasma process performed in the plasma processing chamber.

12. The method of claim 11, wherein the processing parameter comprises modifying a first voltage waveform generated by a pulsed voltage (PV) waveform generator or a radio frequency (RF) waveform generated by a RF generator.

13. The method of claim 12, wherein the first component is selected from the group consisting of: a component in an RF match; a component in a filter assembly; and a portion of an RF coil.

14. The method of claim 12, wherein Generating the first measurement signal include: generating a first portion of the first measurement signal during a first time period; as well as generating a second portion of the first measurement signal during a second time period, wherein the first component generates the electric field during the first time period and the first component does not generate the electric field during the second time period, and Generating the command signal based on the generated first measurement signal further comprises: comparing the first portion of the measurement signal with the second portion of the measurement signal; as well as The information in the command signal providing for adjusting a setting of a processing parameter is altered based on the comparison.

15. The method of claim 11, further comprising: include: detecting an electric field generated by the first component by using a second electro-optical sensor; while generating said electric field by the first component, by transmitting electromagnetic energy through at least one optical fiber using a second light source to a surface of a second electro-optical crystal disposed within said body of said package; transmitting at least a portion of the electromagnetic energy transmitted to the surface of the second electro-optic crystal and subsequently passing through at least a portion of the second electro-optic crystal to a second light sensor via the at least one optical fiber; as well as generating, by the second light sensor, a second measurement signal, the second measurement signal varying based on a property of the portion of the electromagnetic energy received by the second light sensor from the at least one optical fiber, wherein the controller generating the command signal further comprises: comparing the first measurement signal with the second measurement signal; as well as The information in the command signal providing for adjusting a setting of a processing parameter is altered based on the comparison.

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