Modulation of the Station Voltage during Plasma Operation

Abstract

Various embodiments of the present specification relate to systems, apparatuses, and methods for modulating the station voltage during plasma operation. In some embodiments, the system comprises a process chamber, at least one variable reactance element operably coupled to an electrode not powered in the process chamber, and a controller. In some embodiments, the controller is configured to determine one or more target voltages associated with one or more components. The controller may be configured to determine the value of at least one variable reactance element based on the one or more target voltages. The controller may be configured to cause at least one variable reactance element to have the determined value, and causing at least one variable reactance element to have the determined value causes one or more voltages associated with one or more components of the process chamber to move towards the one or more target voltages.

Description

Technical Field

[0001] Incorporation by Reference As part of this application, a PCT application form is filed simultaneously with this specification. As identified in the PCT application form filed simultaneously, each application for which this application claims benefit or priority is incorporated herein by reference in its entirety and for all purposes.

Background Art

[0002] Plasma-based operations, such as plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), atomic layer etching (ALE), etc., are often performed in a plasma reactor that includes two electrodes, and the two electrodes are configured to sustain a plasma in the region between those electrodes. The plasma can be ignited and / or sustained when an RF signal is provided to the powered electrode of the two electrodes.

[0003] The description of the background art provided herein is intended to present the context of the present disclosure in general. The research of the inventors, as currently named, is not to be regarded, whether explicitly or implicitly, as prior art to the present disclosure in the context of this background art section, in the same way as aspects of the description that may not be regarded as prior art separate from the prior art at the time of filing in the scope of that research described in this background art section.

Summary of the Invention

[0004] Systems, apparatuses, and methods for modulating the DC voltage during plasma operation are disclosed herein.

[0005] In some embodiments, a system is provided. The system may include a process chamber configured to perform a semiconductor fabrication process including plasma-based operations, at least one variable reactance element operably coupled to an unpowered electrode of the process chamber, and a controller. The controller may be configured to determine one or more target voltages associated with one or more components of the process chamber during or prior to the performance of the plasma-based operations. The controller may be configured to determine a value of the at least one variable reactance element based at least in part on the one or more target voltages. The controller may be configured to cause the at least one variable reactance element to have the determined value, and causing the at least one variable reactance element to have the determined value causes one or more voltages associated with one or more components of the process chamber to move towards the one or more target voltages.

[0006] In some examples, the unpowered electrode of the process chamber comprises a showerhead of the process chamber, and the at least one variable reactance element is electrically connected to the showerhead or disposed within the showerhead.

[0007] In some examples, the unpowered electrode of the process chamber is a pedestal of the process chamber, and the at least one variable reactance element is electrically connected to the pedestal of the process chamber or disposed within the pedestal of the process chamber.

[0008] In some examples, causing one or more voltages associated with one or more components of the process chamber to move towards the one or more target voltages reduces the likelihood of parasitic plasmas within the process chamber.

[0009] In some examples, at least one of the one or more target voltages is a voltage associated with a showerhead that is not powered in the process chamber.

[0010] In some examples, the system further comprises a pedestal configured to support a wafer undergoing a semiconductor fabrication process, and at least one of the one or more target voltages is a voltage at a location proximate to the rest position of the wafer. In some examples, causing at least one variable reactance element to have a determined value causes the voltage at a location proximate to the rest position of the wafer to be substantially lower than the voltage at the location prior to causing at least one reactance element to have a determined value. In some examples, the system further comprises a radio frequency (RF) generator operably coupled to the pedestal.

[0011] In some examples, the at least one variable reactance element comprises a variable capacitor. In some examples, the system further comprises a stepper motor operably coupled to the variable capacitor, and the controller is configured to cause the variable capacitor to have a determined value by operating the stepper motor. In some examples, the value of the variable capacitor is determined based on the inductance associated with an unpowered electrode.

[0012] In some examples, the at least one variable reactance element comprises a variable inductor.

[0013] In some examples, the at least one variable reactance element comprises a network configured to provide different reactances for different frequencies. In some examples, the different frequencies include DC, multiple RF drive frequencies, multiple harmonics of one or more RF drive frequencies, or any combination thereof.

[0014] In some examples, at least one variable reactance element comprises a replaceable hardware element.

[0015] In some examples, the plasma operation is a plasma-based etch operation or a plasma-based deposition operation.

[0016] In some embodiments, a method is provided. The method includes determining one or more target voltages associated with one or more components of a process chamber during or prior to performing a plasma-based operation in the process chamber, where the process chamber may include determining the one or more target voltages for an electrode that is not powered. The method may include determining a value of at least one variable reactance element operably coupled to the non-powered electrode. The method includes causing the at least one variable reactance element to have the determined value, where causing the at least one variable reactance element to have the determined value causes one or more voltages associated with one or more components of the process chamber to move toward the one or more target voltages.

[0017] In some examples, determining a value of at least one variable reactance element includes using one or more target voltages as key values to a look-up table to identify a value of the at least one variable reactance element that causes one or more voltages associated with one or more components to be within a predetermined range of the one or more target voltages.

[0018] In some examples, determining the value of at least one variable reactance element is based on a circuit model of at least a portion of the process chamber, the circuit model including at least one variable reactance element. In some examples, the circuit model comprises one or more circuit elements associated with a plasma formed in the process chamber. In some examples, the one or more circuit elements associated with the plasma comprise a resistor representing plasma resistance and a capacitor representing capacitance associated with the plasma sheath. In some examples, the at least one variable reactance element comprises a variable capacitor, and the circuit model comprises a variable capacitor coupled in series with an inductor representing the inductance of an electrode that is not powered. In some examples, the value of the variable capacitor is determined as a value that causes the impedance associated with the variable capacitor to substantially cancel out the impedance associated with an inductor representing the inductance of an electrode that is not powered.

[0019] In some examples, the electrode that is not powered comprises a pedestal of the process chamber.

[0020] In some examples, the at least one variable reactance element comprises a variable inductor.

[0021] In some examples, the value of the at least one variable reactance element is determined based at least in part on plasma characteristics determined based on optical data captured from an optical sensor.

[0022] In some examples, the value of the at least one variable reactance element is determined based at least in part on plasma characteristics determined based on power, voltage, current, and / or phase measurements of one or more RF signals measured within one or more regions of the process chamber or within the RF power delivery system.

[0023] In some examples, the value of at least one variable reactance element is determined based at least in part on plasma characteristics determined based on a DC bias signal measured on one or more of the electrodes to which power is supplied or the electrodes to which no power is supplied.

[0024] In some examples, the value of at least one variable reactance element is determined based at least in part on plasma characteristics determined based on electrical plasma diagnostics in a process chamber.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0031] Glossary The following terms are used throughout this specification.

[0032] The terms "semiconductor wafer", "wafer", "substrate", "wafer substrate", and "partially fabricated integrated circuit" may be used interchangeably. One of ordinary skill in the art will understand that the term "partially fabricated integrated circuit" can refer to a semiconductor wafer at any of many stages of integrated circuit fabrication on a semiconductor wafer. Wafers or substrates used in the semiconductor device industry generally have a diameter of 200 mm, or 300 mm, or 450 mm. In addition to semiconductor wafers, other workpieces that may utilize the disclosed embodiments include printed circuit boards, magnetic recording media, magnetic recording sensors, mirrors, optical elements, display devices, or components such as the backside for a pixelated display device, flat panel displays, microelectromechanical devices, and various other articles. Workpieces can be of various shapes, sizes, and materials.

[0033] As used herein, "semiconductor device fabrication operation" refers to an operation performed during the fabrication of a semiconductor device. Generally, the overall fabrication process includes a plurality of semiconductor device fabrication operations, each of which is performed in its own semiconductor fabrication tool, such as a plasma reactor, an electroplating cell, a chemical mechanical planarization tool, a wet etch tool, etc. Categories of semiconductor device fabrication operations include subtractive processes, such as etch processes and planarization processes, and additive processes, such as deposition processes (e.g., physical vapor deposition, chemical vapor deposition, atomic layer deposition, electrochemical deposition, electroless deposition). In the context of an etch process, a substrate etch process includes a process of etching a mask layer, or more generally, a process of etching any layer of material previously deposited on and / or otherwise present on the substrate surface. Such an etch process can etch a stack of layers in the substrate.

[0034] "Manufacturing equipment" refers to the equipment in which a manufacturing process is performed. Manufacturing equipment often has a processing chamber in which a workpiece is present during processing. Generally, when in use, manufacturing equipment performs one or more semiconductor device fabrication operations. Examples of manufacturing equipment for semiconductor device fabrication include deposition reactors, such as electroplating cells, physical vapor deposition reactors, chemical vapor deposition reactors, and atomic layer deposition reactors, and removal process reactors, such as dry etch reactors (e.g., chemical and / or physical etch reactors), wet etch reactors, and asher. Modulation of the Station Voltage during Plasma Operation

[0035] Plasma-based operations, such as plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), and atomic layer etching (ALE), are often performed in a plasma reactor that includes two electrodes, which are configured to sustain a plasma in the region between those electrodes. The plasma can be ignited and / or sustained when an RF signal is provided to the powered electrode of the two electrodes. The unpowered electrode of the two electrodes, which is attached to the wall of the plasma reactor, can be effectively DC grounded at a relatively low RF frequency. However, at higher RF frequencies, the unpowered electrode can generate a voltage with respect to the wall of the plasma reactor. This voltage can have detrimental effects on the plasma within the reactor, such as causing parasitic plasmas in regions of the reactor outside the region between the two electrodes. The detrimental effects on the plasma can result in unpredictable and / or adverse conditions for semiconductor fabrication operations, such as non-uniformities in the deposited layer, non-uniformities in the etched layer, etc.

[0036] Techniques for modulating voltages in various regions of a station of a process chamber during and / or prior to the implementation of a plasma operation are disclosed herein. In some implementations, one or more target voltages, each associated with a component of the station, are determined. Exemplary components of the station for which a target voltage can be determined include the showerhead of the station (e.g., the target voltage is the voltage between the two ends of the showerhead), the pedestal of the station (e.g., the target voltage is in a region proximate to the upper or top surface of the pedestal where the wafer is present during processing), etc. In some implementations, one or more variable reactance elements can be adjusted to drive the voltage of the station to a value that drives it towards one or more target voltages. The target voltage can be specified in a recipe (e.g., for a particular step or portion of the recipe). As an example, the target voltage for a region proximate to the upper surface of the pedestal can be a value that minimizes the parasitic plasma under the pedestal.

[0037] Note that one or more variable reactance elements may be operably coupled to an electrode that is not powered in the process station. For example, in a case where an RF signal is provided to a pedestal that serves as an electrode to which power is supplied, one or more variable reactance elements may be operably coupled to a showerhead that serves as an electrode that is not powered. As another example, in a case where the showerhead is an electrode to which power is supplied, one or more variable reactance elements may be operably coupled to the pedestal.

[0038] In some embodiments, the value of one or more variable reactance elements that will drive the voltage towards one or more target voltages may be determined using a look-up table. For example, one or more target voltages may be provided as a key to the look-up table, and the value of the variable reactance element may be identified from the values of the look-up table such that the voltage may be driven to approach or substantially match one or more target voltages. In some implementations, the value of one or more variable reactance elements may be determined at least in part based on the near real-time or dominant plasma characteristics of the plasma in the station. In some implementations, the plasma characteristics may be based on, for example, optical data from an optical sensor arranged to capture an image of the plasma within the station. In some implementations, the plasma characteristics may be determined based on the power, voltage, current, and / or phase measurements of one or more RF signals measured in a region (or regions) associated with or within the process chamber apparatus. In some implementations, the plasma characteristics may be determined based on a DC bias signal measured on an electrode to which power is supplied and / or an electrode that is not powered. In some implementations, the plasma characteristics may be determined based on an electrical plasma diagnosis performed in the process chamber. Note that in some embodiments, the plasma characteristics may be determined based on one or more combinations of the techniques described above.

[0039] It should be understood that the recipe used to perform the plasma operation can constrain various process conditions such as the RF signal, process gas, flow rate, pressure, temperature, etc. utilized to generate or maintain the plasma. These process conditions can affect the voltage in various regions of the station. For example, as will be described in more detail below with respect to FIGS. 2 and 3, the plasma characteristics can affect the voltage across the showerhead and / or in proximity to the pedestal, and the plasma characteristics are driven by the process conditions. Thus, the techniques described herein can be utilized to modulate the voltage after other process conditions have been set for a particular recipe step. In other words, the use of a variable reactance element associated with the non-powered electrode of the station for modulating the voltage can introduce an additional variable that can be adjusted after the process conditions have been set.

[0040] FIG. 1 shows a fabrication tool shown as a substrate processing apparatus 100. The apparatus 100 can be configured to deposit a film on or across a semiconductor substrate using any number of processes. For example, the apparatus 100 can be adapted to perform PECVD, ALD, or ALE in particular.

[0041] The processing apparatus 100 of FIG. 1 can employ a single process station 102 of a process chamber having a single substrate holder 108 (e.g., a pedestal) in an internal volume that can be maintained under vacuum by a vacuum pump 118. A showerhead 106 and a gas delivery system 101 that are fluidly coupled to the process chamber can permit the delivery of, for example, film precursors, as well as carrier and / or purge and / or process gases, secondary reactants, etc.

[0042] In FIG. 1, the gas delivery system 101 includes a mixing vessel 104 for blending and / or conditioning a process gas for delivery to the showerhead 106. One or more mixing vessel inlet valves 120 may control the introduction of the process gas into the mixing vessel 104. Certain reactants may be stored in liquid form prior to vaporization and subsequent delivery to the process station 102 of the process chamber. The implementation of FIG. 1 includes a vaporization point 103 for vaporizing a liquid reactant that is to be supplied to the mixing vessel 104. In some implementations, the vaporization point 103 may include a heated liquid injection module. In some other implementations, the vaporization point 103 may include a heated vaporizer. In still other implementations, the vaporization point 103 may be removed from the process station. In some implementations, a liquid flow controller upstream of the vaporization point 103 may be provided to control the mass flow rate of the liquid for vaporization and delivery to the process station 102.

[0043] The showerhead 106 may operate to distribute process gas and / or reactants (e.g., film precursors) to the substrate 112 in the process station, and the flow thereof may be controlled by one or more valves (e.g., valves 120, 120A, 105) upstream from the showerhead. In the implementation shown in FIG. 1, the substrate 112 is shown as being located below the showerhead 106 and is shown as being placed on the pedestal 108. The showerhead 106 may include any suitable shape and may include any suitable number and arrangement of ports for distributing process gas to the substrate 112. In some implementations with two or more stations, the gas delivery system 101 may independently control the flow of process gas and / or reactants to each station so as to permit the flow of gas to one station while prohibiting the flow of gas to a second station, including valves or other flow control structures upstream from the showerhead. Further, the gas delivery system 101 may be configured to independently control the process gas and / or reactants delivered to each station in a multi-station apparatus such that the gas compositions provided to different stations are different, e.g., such that the partial pressures of the gas components may vary simultaneously between stations.

[0044] In the implementation form of FIG. 1, the gas volume 107 is shown as being located below the shower head 106. In some implementation forms, the pedestal 108 can be raised or lowered to expose the substrate 112 to the gas volume 107 and / or to vary the size of the gas volume 107. The separation between the pedestal 108 and the shower head 106 is sometimes referred to as a "gap". Optionally, the pedestal 108 can be lowered and / or raised during part of the deposition process to modulate the process pressure, reactant concentration, etc. within the gas volume 107. The shower head 106 and the pedestal 108 are shown as being electrically coupled to an RF signal generator 114 and a matching network 116 to couple power to a plasma generator. Thus, the shower head 106 can function as an electrode for coupling radio frequency power to the process station 102. The RF signal generator 114 and the matching network 116 can be operated at any suitable RF power level that can operate to form a plasma having a desired composition of radical species, ions, and electrons. Further, the RF signal generator 114 can provide RF power having two or more frequency components, such as a low frequency component (e.g., less than about 2 MHz) and a high frequency component (e.g., greater than about 2 MHz). In some implementation forms, the plasma ignition and maintenance conditions are controlled by appropriate hardware and / or appropriate machine-readable instructions in a system controller that can provide control instructions via a sequence of input / output control instructions.

[0045] As described above with respect to FIG. 1, the process station can include a shower head and a pedestal, each of which can be considered an electrode. As described above, an RF signal can be applied to one of the electrodes, such as the pedestal. In such an example, the shower head can be considered an electrode that is not powered. The shower head can be considered to have an inductance, which is generally referred to as L in this specification shdis called. The showerhead inductance can generally be in the range of 10 nH to 50 nH. Due to the showerhead inductance, the impedance related to the showerhead (generally denoted as Z shd in this specification) is Z shd = jωL shd . At relatively low RF frequencies, the influence of the showerhead inductance can have a negligible impact on the impedance related to the showerhead. Therefore, the voltage across the showerhead may also be negligible. In other words, at relatively low RF frequencies, the showerhead is effectively DC grounded and can thereby have the same potential as the chamber. However, at higher RF frequencies (e.g., above 20 MHz, above 30 MHz, above 40 MHz, etc.), the impedance related to the showerhead increases, thereby causing a corresponding increase in the voltage across the showerhead with respect to the chamber (generally denoted as V shd in this specification). It should be understood that when an RF signal is applied to the showerhead, the pedestal can be considered as an electrode not powered. In the case where the showerhead is an electrode not powered, similar to what was described above regarding the voltage generated across the showerhead at higher RF frequencies, in the case where the pedestal is an electrode not powered, a voltage can be generated across the pedestal.

[0046] The components of the reactor, including the pedestal, the showerhead, and the plasma sustained between the pedestal and the showerhead, can be represented as an equivalent circuit of a resistor, an inductor, and / or a capacitor. In particular, the equivalent circuit can be a series RLC circuit. In the case where the pedestal is an electrode powered, the RLC circuit can include an RF signal generator electrically coupled to an inductor representing the pedestal supply hardware, a series capacitor and resistor representing the plasma sustained between the pedestal and the showerhead, and an inductor representing the showerhead. As described above, the voltage across the showerhead (V Shd) can be affected by the characteristics of the RF signal applied to the pedestal. The voltage at the upper portion of the pedestal, which corresponds to the surface of the pedestal on which the substrate undergoing processing is placed (generally referred to herein as V ped The voltage across the showerhead (called V) can also be affected by the characteristics of the RF signal. Shd ) and the voltage at the top of the pedestal (V ped ). Thus, an undesired voltage across the showerhead (e.g., due to the inductance of the showerhead) can cause undesired voltage changes at the surface of the pedestal, which can cause undesired changes in plasma conditions within the reactor. For example, such undesired voltage changes across various components in the reactor can cause parasitic plasmas. As further specific examples, such parasitic plasmas can include plasma between the showerhead and a wall, plasma under a portion of the pedestal, etc. Moreover, such undesired voltage changes can cause undesired fabrication effects on wafers undergoing processing in the reactor, such as non-uniform deposition, non-uniform etching, etc. It should be understood that in embodiments in which the powered electrode is the showerhead and the unpowered electrode is the pedestal, an RF signal generator can be electrically coupled to the inductor representing the showerhead.

[0047] FIG. 2 shows a schematic diagram illustrating components of a reactor utilizing a pedestal as a powered electrode, represented as equivalent circuit elements, according to some embodiments. As shown, an RF generator 202 is represented by a current source 204. As described above with respect to FIG. 1, the RF signal generator 202 may be configured to provide an RF signal at one or more frequencies, including low frequencies (e.g., about 2 MHz) and / or high frequencies (e.g., greater than 2 MHz). The RF signal generator 202 is electrically coupled to a pedestal 206. A stem of the pedestal is connected to an inductor 208 (L pedis represented by (referred to as). As shown in FIG. 2, the voltage at the upper portion of the pedestal 206 is generally V in this specification ped is referred to as. When present, the plasma 210 is sustained between the pedestal 206 and the showerhead 216. The plasma 210 can be represented by a series capacitor 212 (generally C in this specification plasma is referred to as) and a resistor 214 (generally R in this specification plasma is referred to as). Generally, R plasma represents the plasma slab resistance, and C plasma represents the plasma sheath capacitance. The showerhead 216 is represented by an inductor 220 (generally L in this specification Shd is referred to as) when fixed to the wall of the reactor (as in the case of a conventional configuration), and the inductor 220 is coupled to ground (i.e., the station wall). This configuration is sometimes referred to as a "grounded showerhead configuration". The voltage V Shd across the showerhead corresponds to the voltage at the node of the ungrounded inductor 220 as shown in FIG. 2.

[0048] In some implementations, a variable reactance element can be used to modulate one or more voltages associated with the station. Examples of variable reactance elements include variable capacitors, variable inductors, and networks that can provide different behaviors at different frequencies (e.g., at DC, harmonics at the RF drive frequency, and / or at multiple RF drive frequencies) by providing different reactances for different frequencies through different reactance elements. In some embodiments, the variable reactance element can be operably coupled to an electrode of the station that is not powered. For example, in the case where the pedestal is the powered electrode of the station, the variable reactance element can be operably coupled to the showerhead. As another example, in the case where the showerhead is the powered electrode, the variable reactance element can be operably coupled to the pedestal.

[0049] Circuit elements representing various station components or regions (e.g., as shown in and described above with respect to FIG. 2) are generally connected in series, so varying the variable reactance element can modulate the voltage across the entire station. For example, varying the reactance of the variable reactance element can vary the voltage associated with the pedestal (e.g., V ped ) and / or the voltage across the showerhead (e.g., V shd ) as shown in and described above with respect to FIG. 2.

[0050] FIG. 3 shows a schematic diagram of the components of the reactor of FIG. 2 according to some implementations, including a variable reactance element operably coupled to a showerhead (i.e., the non-powered electrode of the reactor of FIG. 2). As shown, a variable capacitor 302 is operably coupled to the showerhead 216. By adjusting the variable capacitor 302, the voltage (V shd ) across the showerhead 216 and the voltage (V ped ) associated with the pedestal can be varied or modulated.

[0051] As described above, modulation of the variable reactance element can cause a voltage change for one or more voltages associated with the station. The one or more voltages can include the voltage across the showerhead, the voltage at the upper or top portion of the pedestal (e.g., where the wafer is present during processing), etc. Note that the voltage change can occur whether the variable reactance element is operably coupled to the showerhead (e.g., when the pedestal is the powered electrode) or the variable reactance element is operably coupled to the pedestal (e.g., when the showerhead is the powered electrode).

[0052] Note that the change in one or more voltages may depend on the properties of the plasma present in the station. For example, as shown in FIGS. 2 and 3 and described above with respect to FIGS. 2 and 3, the plasma can be represented by a series resistor (R plasma ) and a capacitor (C plasma ). Continuing with this example, the properties of the plasma can affect the values for the resistance and / or capacitance that represent the plasma. The values of the resistance and / or capacitance that represent the plasma can affect the change in one or more voltages. In some implementations, the value of C plasma can range from about 200 pF to about 1200 pF, which can correspond to a plasma sheath thickness of about 0.25 millimeters to about 1.5 millimeters. In some implementations, the voltage in a particular region of the station can be modulated within a range that is at least partially dependent on the resistance (R plasma ) associated with the plasma. For example, in some embodiments, a larger voltage change can be possible for a relatively lower plasma resistance (e.g., about 0.5 ohms, about 1 ohm, about 1.5 ohms, about 2 ohms, etc.) compared to a higher plasma resistance (e.g., greater than about 9 ohms, greater than about 10 ohms, greater than about 15 ohms, etc.).

[0053] FIG. 4A shows a contour plot of the voltage change (V ped ) in a pedestal that responds to the varying reactance of a variable capacitor operably coupled to a showerhead of a station. As shown, the pedestal voltage can be varied over a range from about 20 to 100 (using any voltage units). The contour plot of FIG. 4A was generated assuming a fixed plasma resistance of 1 ohm and for various plasma capacitances (as shown on the y-axis). The x-axis shows the varying values of the variable showerhead capacitance. Note that for a given plasma capacitance (e.g., 1200 pF), the pedestal voltage can be varied over a dynamic voltage range by adjusting the showerhead capacitor from 100 pF to 500 pF.

[0054] FIG. 4B shows the voltage change (V shd ) contour plot in the showerhead in response to the varying reactance of a variable capacitor operably coupled to the showerhead. In other words, FIGS. 4A and 4B both vary the reactance of the variable showerhead capacitor but show the voltage change in different regions of the station (i.e., the pedestal in FIG. 4A and the showerhead in FIG. 4B). Similar to what was described above with respect to FIG. 4A, the contour plot of FIG. 4A was generated assuming a fixed plasma resistance of 1 ohm and for various plasma capacitances (as shown on the y-axis). The x-axis shows the varying values of the variable showerhead capacitance. Note that for a given plasma capacitance (e.g., 1200 pF), the showerhead voltage can be varied over a dynamic voltage range by adjusting the showerhead capacitor from 100 pF to 500 pF.

[0055] In some implementations, one or more target voltages associated with components of the station at which a plasma operation is being or is to be performed are determined during and / or prior to the performance of the plasma operation. The one or more target voltages can be associated with a pedestal of the station (e.g., the upper portion of the pedestal where the wafer is present during processing), a showerhead of the station, etc. The plasma operation can be a plasma-based etch operation or a plasma-based deposition operation. In some embodiments, the one or more target voltages can be determined based on the target voltages indicated in a recipe to be implemented at the station. In some embodiments, the target voltage among the one or more target voltages can be, for example, 0 volts or another minimum voltage if the goal is to minimize the voltage across the ends of the showerhead. In some cases, the target voltage can be specified for a particular component at a plurality of frequencies, such as a plurality of RF drive frequencies, harmonics of the plurality of RF drive frequencies, DC, etc. In some implementations, the target voltage for a particular component can be determined based on an estimate of substantially real-time or dominant plasma characteristics (e.g., during the performance of the plasma operation). In some embodiments, the substantially real-time or dominant plasma characteristics can be estimated or determined using an optical sensor (e.g., one or more camera devices) having a viewport directed at the station.

[0056] In some embodiments, the value of at least one variable reactance element associated with a component of the station can be determined based at least in part on one or more target voltages. In some embodiments, the variable reactance element can be a variable inductor and / or a variable capacitor. In some implementations, the variable reactance element can be a network of reactance elements (e.g., a plurality of reactance elements), and thus, for example, at different frequencies, different reactances can be selected by selecting different nodes of the network. In some implementations, the variable reactance element can be a fixed hardware element that can be easily replaced in the field. Such fixed hardware elements can include capacitors, inductors, etc., that are relatively low cost and / or easily replaceable.

[0057] In some embodiments, at least one variable reactance element can be associated with a particular component of the station. This component can correspond to an electrode of the station that is not powered. For example, as described above with respect to FIG. 3, in the case where the pedestal is the powered electrode, at least one variable reactance element can be operably coupled to the showerhead. As another example, in the case where the showerhead is the powered electrode, at least one variable reactance element can be operably coupled to the pedestal.

[0058] In some embodiments, the value of at least one variable reactance element can be determined using a look-up table. For example, one or more target voltages can be used as keys to the look-up table to determine the value of at least one variable reactance element that will result in a voltage closer to the one or more target voltages relative to the dominant voltage value. Note that in some cases, it may be possible to drive the voltage associated with a particular component to substantially match the target voltage associated with that component. For example, the voltage can be within a predetermined range (e.g., + / -1%, + / -5%, + / -10%, etc.) of the target voltage associated with the component. In other cases, it may only be possible to drive the voltage associated with a particular component to be closer to the target voltage relative to the dominant voltage associated with that component. Additionally, note that in cases where multiple target voltages (e.g., a target voltage for a showerhead and a target voltage for a pedestal) are utilized, it may not be possible to match the multiple target voltages by adjusting at least one variable reactance element. In such cases, the value of at least one reactance element that optimizes the values of the multiple voltages can be selected. Additionally or alternatively, the value of at least one reactance element that prioritizes a subset of the one or more target voltages can be selected. As an example, in a case where the target voltages include a pedestal voltage and a showerhead voltage, one or the other can be prioritized in determining the value of at least one variable reactance element to drive the voltage of the prioritized component voltage towards the corresponding target voltage with less consideration for the other component voltage.

[0059] After determining the value of at least one variable reactance element, the at least one variable reactance element can be adjusted or actuated to have the determined value. For example, a stepper motor can be utilized to cause the at least one variable reactance element to have the determined value. As a further specific example, the stepper motor can rotate the plates of a variable capacitor to achieve the determined reactance value. As another example, in the case where the at least one variable reactance element includes a variable inductor, the solid core within the solenoid can be moved or positioned (e.g., using a stepper motor) to achieve the target inductance.

[0060] FIG. 5 is a flowchart of an exemplary process 500 for adjusting a variable reactance element to modulate the voltage associated with a station at which plasma operation is being or will be performed. In some implementations, the blocks of process 500 can be performed by a controller or processor associated with the station or a process chamber associated with the station. In some embodiments, the blocks of process 500 can be performed in an order other than that shown in FIG. 5. In some implementations, two or more blocks of process 500 can be executed substantially in parallel. In some implementations, one or more blocks of process 500 can be omitted.

[0061] Process 500 can start, at 502, by determining one or more target voltages associated with components of the station during or prior to the implementation of the plasma operation, where the plasma operation is being or is to be implemented. The plasma operation can be a plasma-based etch operation or a plasma-based deposition operation. The one or more voltages can be associated with, for example, the showerhead of the station, the pedestal of the station (e.g., the upper portion of the pedestal where the wafer is present during processing), etc. The one or more target voltages can be determined based on a recipe implemented or to be implemented in the station. For example, the recipe can specify one or more target voltages. In some embodiments, the one or more target voltages can be based on the determination of the dominant plasma characteristics of the plasma within the station (e.g., during the implementation of the plasma operation). The dominant plasma characteristics can indicate plasma uniformity or plasma centroid location within the station or within a region of the station. In some embodiments, the plasma characteristics can be determined based on optical data obtained from one or more optical sensors (e.g., camera sensors) of the station. In some implementations, the one or more target voltages can be determined to modify the plasma characteristics towards desired or optimal plasma characteristics. In some embodiments, at least one target voltage can be 0 or some other minimum voltage value. For example, the target voltage associated with an electrode that is not powered in the station can be determined to be 0 at a particular frequency, and thus the non-powered electrode can be considered to be DC grounded when the target voltage is achieved.

[0062] At 504, process 500 can determine the value of at least one variable reactance element associated with a component of the station, at least in part based on one or more target voltages. For example, as described above, process 500 can use one or more target voltages as keys to a lookup table to identify the value of at least one variable reactance element suitable for driving the voltage of a component of the station towards one or more target voltages. In some implementations, the value of at least one reactance element can be determined by considering multiple target voltages associated with multiple components. Additionally or alternatively, in some implementations, the value of at least one reactance element can be determined by prioritizing a certain target voltage associated with a single component of the station. As described above, at least one variable reactance element can include a variable capacitor, a variable inductor, and / or a variable reactance network that can be selectively adjusted for different frequencies. At least one variable reactance element can be associated with an electrode that is not powered by the station.

[0063] At 506, process 500 can cause at least one variable reactance element to have the determined value, thereby causing one or more voltages associated with a component of the station to move towards one or more target voltages. For example, process 500 can cause a stepper motor to actuate the plates of a variable capacitor to achieve the target reactance of the variable capacitor. As another example, process 500 can actuate the core within a solenoid to achieve the target reactance of a variable inductor.

[0064] Note that in some implementations, the blocks of process 500 may be looped multiple times. For example, process 500 may be performed during or before each step of a recipe. As another example, process 500 may be performed after certain process conditions are implemented (e.g., as specified in a recipe), and after other process conditions are locked or fixed, to perform further modulation of the process, i.e., by modulating the voltages of various components. Context for the disclosed computing implementations

[0065] Some embodiments disclosed herein relate to a computing system for modulating voltage during plasma operation.

[0066] Many types of computing systems having any of various computer architectures may be employed as the disclosed systems for implementing the algorithms described herein. For example, the system may include software components that execute on one or more general-purpose processors or specially designed processors, such as application-specific integrated circuits (ASICs) or programmable logic devices (e.g., field-programmable gate arrays (FPGAs)). Further, the system may be implemented on a single device or distributed across multiple devices. The functions of the computing elements may be merged with each other or further divided into multiple sub-modules.

[0067] In some embodiments, the code executed during the generation or execution of the techniques described herein on a properly programmed system may be embodied in the form of software elements stored in a non-volatile memory medium (such as optical disks, flash memory devices, mobile hard disks, etc.) that includes some instructions for creating a computer device (such as a personal computer, server, network device, etc.).

[0068] At a certain level, software elements are implemented as a set of commands prepared by a programmer / developer. However, modular software that can be executed by computer hardware is executable code that is committed to memory using "machine code", or "native instructions", selected from a specific set of machine language instructions designed into a hardware processor. The machine language instruction set, or native instruction set, is known to the (one or more) hardware processors and is essentially built into it. This is the "language" for the system and application software to communicate with the hardware processor. Each native instruction can specify a particular register for arithmetic, addressing, or control functions recognized by the processing architecture, a particular memory location or offset, and a particular addressing mode used to interpret the operand, and is an individual code. By combining these simple native instructions, which are executed continuously or as otherwise directed by control flow instructions, more complex operations are built.

[0069] The interrelationship between executable software instructions and a hardware processor is structural. In other words, the instructions are, in themselves, a series of symbols or numerical values. They do not inherently convey any information. It is the processor, which is intentionally preconfigured to interpret the symbols / numerical values, that gives meaning to the instructions.

[0070] The methods and techniques used herein can be configured to execute on a single machine at a single location, on multiple machines at a single location, or on multiple machines at multiple locations. When multiple machines are employed, the individual machines can be adapted for their particular tasks. For example, operations that require large blocks of code and / or significant processing capacity can be implemented on large and / or fixed machines.

[0071] Furthermore, some embodiments relate to tangible and / or non-transitory computer-readable media or computer program products that include program instructions and / or data (including data structures) for performing various computer-implemented operations. Examples of computer-readable media include, but are not limited to, semiconductor memory devices, phase change devices, magnetic media such as disk drives, magnetic tapes, optical media such as CDs, magneto-optical media, and hardware devices specially configured to store and execute program instructions, such as read-only memory devices (ROM) and random access memory (RAM). The computer-readable media can be directly controlled by an end user, or the media can be indirectly controlled by the end user. Examples of directly controlled media include media located in user facilities and / or media not shared with other entities. Examples of indirectly controlled media include media that are indirectly accessible to a user via an external network and / or via a service that provides shared resources, such as "the cloud". Examples of program instructions include both machine code, such as that produced by a compiler, and files that contain higher-level code that can be executed by a computer using an interpreter.

[0072] In various embodiments, the data or information employed in the disclosed methods and apparatuses is provided in electronic format. Such data or information can include various coefficients used in calculations and the like. As used herein, data or other information provided in electronic format is available for storage in machines and transmission between machines. Conventionally, data in electronic format has been provided digitally and can be stored as bits and / or bytes in various data structures, lists, databases, and the like. The data can be embodied electronically, optically, and the like.

[0073] System software generally interfaces with computer hardware and associated memory. In some embodiments, the system software includes operating system software and / or firmware, as well as any middleware and drivers installed on the system. The system software provides the basic non-task-specific functions of the computer. In contrast, modules and other application software are used to accomplish specific tasks. Each native instruction for a module is stored in a memory device and represented numerically.

[0074] FIG. 6 is a block diagram of an example of a computing device 600 suitable for use in implementing some embodiments of the present disclosure. For example, the device 600 may be suitable for implementing some or all of the functions of the image analysis logic disclosed herein.

[0075] The computing device 600 may include a bus 602 that directly or indirectly couples the following devices: a memory 604, one or more central processing units (CPUs) 606, one or more graphics processing units (GPUs) 608, a communication interface 1010, an input / output (I / O) port 612, input / output components 614, a power supply 616, and one or more presentation components 618 (e.g., one or more displays). In addition to the CPU 606 and the GPU 608, the computing device 600 may include additional logic devices not shown in FIG. 6, such as, but not limited to, an image signal processor (ISP), a digital signal processor (DSP), an ASIC, an FPGA, etc.

[0076] The various blocks of FIG. 6 are shown as being connected via bus 602 by lines, which is for clarity only and not limiting. For example, in some embodiments, a presentation component 618, such as a display device, may be considered an I / O component 614 (e.g., if the display is a touch screen). As another example, the CPU 606 and / or GPU 608 may include memory (e.g., memory 604 may represent a storage device in addition to the memory of the GPU 608, CPU 606, and / or other components). In other words, the computing device of FIG. 6 is merely exemplary. Distinctions between categories such as "workstation," "server," "laptop," "desktop," "tablet," "client device," "mobile device," "handheld device," "electronic control unit (ECU)," "virtual reality system," and / or other device or system types are not made as all are contemplated within the scope of the computing device of FIG. 6.

[0077] Bus 602 may represent one or more buses, such as an address bus, a data bus, a control bus, or a combination thereof. Bus 1002 may include one or more bus types, such as an Industry Standard Architecture (ISA) bus, an Extended Industry Standard Architecture (EISA) bus, a Video Electronics Standards Association (VESA) bus, a Peripheral Component Interconnect (PCI) bus, a Peripheral Component Interconnect Express (PCIe) bus, and / or another type of bus.

[0078] Memory 604 may include any of a variety of computer-readable media. A computer-readable media may be any available media that can be accessed by computing device 600. Computer-readable media may include both volatile and nonvolatile media and removable and non-removable media. By way of example and not limitation, computer-readable media may comprise computer storage media and / or communication media.

[0079] A computer storage medium can include both volatile and non-volatile media and / or removable and non-removable media implemented in any method or technology for storing information, such as computer-readable instructions, data structures, program modules, and / or other data types. For example, memory 1004 can store computer-readable instructions that represent (one or more) programs and / or (one or more) program elements, such as (one or more) operating systems. A computer storage medium can include, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disk (DVD) or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and can be accessed by computing device 1000. As used herein, a computer storage medium does not itself comprise a signal.

[0080] A communication medium can embody computer-readable instructions, data structures, program modules, and / or other data types in a modulated data signal, such as a carrier wave, or other transport mechanism, and includes any information delivery medium. The term "modulated data signal" can refer to a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example and not limitation, a communication medium can include wired media such as a wired network or direct wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Any combination of the above should also be included within the scope of computer-readable media.

[0081] (One or more) CPUs 606 may be configured to execute computer-readable instructions to control one or more components of computing device 600 to perform one or more of the methods and / or processes described herein. (One or more) CPUs 606 may each include one or more cores (e.g., 1, 2, 4, 8, 28, 72, etc.) capable of handling multiple software threads simultaneously. (One or more) CPUs 606 may include any type of processor and may include different types of processors depending on the type of computing device 600 being implemented (e.g., in the case of a mobile device, a processor with fewer cores, and in the case of a server, a processor with more cores). For example, depending on the type of computing device 600, the processor may be an ARM processor implemented using reduced instruction set computing (RISC) or an x86 processor implemented using complex instruction set computing (CISC). Computing device 600 may include one or more CPUs 606 in addition to one or more microprocessors or auxiliary coprocessors such as a math co-processor.

[0082] (One or more) GPUs 608 can be used by computing device 600 to render graphics (e.g., 3D graphics). (One or more) GPUs 608 can include many (e.g., dozens, hundreds, or thousands) of cores that can handle many software threads simultaneously. (One or more) GPUs 608 can generate pixel data for an output image in response to rendering commands (e.g., rendering commands from (one or more) CPUs 606 received via a host interface). (One or more) GPUs 608 can include graphics memory, such as display memory, for storing pixel data. The display memory can be included as part of memory 604. (One or more) GPUs 608 can include two or more GPUs that operate in parallel (e.g., via a link). When combined, each GPU 608 can generate pixel data for different portions of an output image or for different output images (e.g., a first GPU for a first image and a second GPU for a second image). Each GPU can include its own memory or can share memory with other GPUs.

[0083] In an example where computing device 600 does not include (one or more) GPUs 608, (one or more) CPUs 606 can be used to render graphics.

[0084] The communication interface 610 may include one or more receivers, transmitters, and / or transceivers that enable the computing device 600 to communicate with other computing devices via an electronic communication network, including wired and / or wireless communication. The communication interface 610 may include components and functions for enabling communication over any of several different networks, such as a wireless network (e.g., Wi-Fi, Z-Wave, Bluetooth, Bluetooth LE, ZigBee, etc.), a wired network (e.g., communicating over Ethernet), a low-power wide-area network (e.g., LoRaWAN, SigFox, etc.), and / or the Internet.

[0085] The I / O port 612 can enable the computing device 600 to be logically coupled to other devices including I / O components 614, presentation component(s) 618, and / or other components, some of which may be incorporated (e.g., integrated) into the computing device 600. Exemplary I / O components 614 include a microphone, a mouse, a keyboard, a joystick, a trackpad, a satellite dish, a scanner, a printer, a wireless device, etc. The I / O component 614 can provide a natural user interface (NUI) that processes air gestures, voice, or other physiological inputs generated by a user. In some cases, the input can be sent to an appropriate network element for further processing. The NUI can implement any combination of voice recognition, stylus recognition, face recognition, biometric recognition, both on-screen gesture recognition and off-screen gesture recognition, air gestures, head and gaze tracking, and touch recognition (described in more detail below) related to the display of the computing device 600. The computing device 600 can include a depth camera such as a stereoscopic camera system, an infrared camera system, an RGB camera system, a touch screen technology, and combinations thereof for gesture detection and recognition. Additionally, the computing device 600 can include an accelerometer or gyroscope (e.g., as part of an inertial measurement unit (IMU)) to enable motion detection. In some examples, the output of the accelerometer or gyroscope can be used by the computing device 600 to render immersive augmented reality or virtual reality.

[0086] The power supply 616 can include a hard-wired power supply, a battery power supply, or a combination thereof. The power supply 616 can provide power to the computing device 600 to enable the components of the computing device 600 to operate.

[0087] (One or more) presentation components 618 may include a display (e.g., a monitor, touch screen, television screen, head-up display (HUD), other display types, or combinations thereof), a speaker, and / or other presentation components. The (one or more) presentation components 618 may receive data from other components (e.g., the (one or more) GPUs 608, the (one or more) CPUs 606, etc.) and output that data (e.g., as an image, video, sound, etc.).

[0088] The present disclosure may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer or other machine, such as a personal information appliance or other handheld device. Generally, program modules include routines, programs, objects, components, data structures, etc., which refer to code that performs particular tasks or implements particular abstract data types. The present disclosure may be practiced in a variety of system configurations, including handheld devices, consumer electronics, general-purpose computers, more specialized computing devices, etc. The present disclosure may also be practiced in a distributed computing environment where tasks are performed by remote processing devices linked through a communications network. Conclusion

[0089] In the description, numerous specific details are set forth in order to provide a thorough understanding of the presented embodiments. The disclosed embodiments may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail so as not to unnecessarily obscure the disclosed embodiments. While the disclosed embodiments have been described with respect to specific embodiments, it will be understood that the specific embodiments are not intended to limit the disclosed embodiments.

[0090] Unless otherwise indicated, the method operations and device features disclosed herein involve techniques and devices commonly used in metrology, semiconductor device fabrication technology, software design and programming, and statistics, which are within the skill of the art.

[0091] Unless otherwise defined herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Various scientific dictionaries containing the terms included herein are well known and available to those of ordinary skill in the art. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the embodiments disclosed herein, some methods and materials are described.

[0092] Numeric ranges include the numbers defining the range. Every maximum numerical limitation given throughout this specification shall include every lower numerical limitation, as if such lower numerical limitations were expressly written herein. Every minimum numerical limitation given throughout this specification shall include every higher numerical limitation, as if such higher numerical limitations were expressly written herein. Every numerical range given throughout this specification shall include every narrower numerical range that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein.

[0093] The headings provided herein do not limit the disclosure.

[0094] As used herein, the singular forms "a", "an", and "the" include the plural unless the context clearly dictates otherwise. As used herein, the term "or" refers to a non-exclusive or unless otherwise indicated.

[0095] Various computational elements, including processors, memories, instructions, routines, models, or other components, may be described or claimed as "configured to" perform one or more tasks. In such a context, the phrase "configured to" is used to imply a structure by indicating that the component includes a structure (e.g., stored instructions, circuitry, etc.) that performs one or more tasks during operation. Thus, a unit / circuit / component may be said to be configured to perform a task even when the specified component is not necessarily currently operable (e.g., off).

[0096] A component used with the phrase "configured to" may refer to hardware, such as circuitry, a memory storing program instructions executable to implement an operation, etc. Further, "configured to" can refer to a general structure (e.g., a general circuit) that is operated by software and / or firmware (e.g., an FPGA or a general-purpose processor that executes software) to operate in a manner capable of performing the (one or more) recited tasks. Further, "configured to" can refer to one or more memories or memory elements that store computer-executable instructions for performing the (one or more) recited tasks. Such memory elements may include memory on a computer chip having processing logic. In some contexts, "configured to" may also include adapting a manufacturing process (e.g., semiconductor manufacturing equipment) to fabricate a device (e.g., an integrated circuit) adapted to implement or perform one or more tasks.

Claims

1. A substrate processing system, A process chamber configured for carrying out semiconductor fabrication processes, including plasma-based operations, At least one variable reactance element operably coupled to an electrode of the process chamber that is not powered, Controller and A substrate processing system comprising, the controller, During or prior to the execution of the plasma-based operation, determine one or more target voltages associated with one or more components of the process chamber, The value of the at least one variable reactance element is determined at least partially based on the one or more target voltages, The at least one variable reactance element having the determined value causes the at least one variable reactance element to have the determined value, which in turn causes one or more voltages associated with one or more components of the process chamber to move toward one or more target voltages, A substrate processing system configured to perform the following actions.

2. A substrate processing system according to claim 1, A substrate processing system wherein the non-powered electrodes of the process chamber are provided with a shower head of the process chamber, and the at least one variable reactance element is electrically connected to or disposed within the shower head.

3. A substrate processing system according to claim 1, A substrate processing system wherein the unpowered electrode of the process chamber is a pedestal of the process chamber, and the at least one variable reactance element is electrically connected to the pedestal of the process chamber or disposed within the pedestal of the process chamber.

4. A substrate processing system according to any one of claims 1 to 3, A substrate processing system in which the one or more voltages associated with one or more components of the process chamber move toward the one or more target voltages, thereby reducing the possibility of parasitic plasma within the process chamber.

5. A substrate processing system according to any one of claims 1 to 3, A substrate processing system in which at least one of the one or more target voltages is a voltage associated with an unpowered showerhead of the process chamber.

6. A substrate processing system according to any one of claims 1 to 3, A substrate processing system further comprising a pedestal configured to support a wafer subjected to the semiconductor manufacturing process, wherein at least one of the one or more target voltages is a voltage at a location close to the resting position of the wafer.

7. A substrate processing system according to claim 6, A substrate processing system in which causing the at least one variable reactance element to have the determined value causes the voltage at the location close to the stationary position of the wafer to be substantially lower than the voltage at the location prior to causing the at least one variable reactance element to have the determined value.

8. A substrate processing system according to claim 6, A substrate processing system further comprising a radio frequency (RF) generator operably coupled to the pedestal.

9. A substrate processing system according to any one of claims 1 to 3, The substrate processing system comprises at least one variable reactance element, which is a variable capacitor.

10. A substrate processing system according to claim 9, further comprising a stepper motor operably coupled to the variable capacitor, wherein the controller is configured to cause the variable capacitor to have the determined value by operating the stepper motor.

11. A substrate processing system according to claim 9, A substrate processing system in which the value of the variable capacitor is determined based on the inductance associated with the electrode that is not supplied with power.

12. A substrate processing system according to any one of claims 1 to 3, The substrate processing system comprises at least one variable reactance element, which includes a variable inductor.

13. A substrate processing system according to any one of claims 1 to 3, A substrate processing system comprising a network or interchangeable hardware element configured to provide different reactances for different frequencies, wherein the at least one variable reactance element is the variable reactance element.

14. A method for modulating the voltage of a process chamber, the method being Determining one or more target voltages associated with one or more components of the process chamber during or prior to the performance of plasma-based operation within the process chamber, wherein the process chamber includes electrodes that are not powered, and the determination of one or more target voltages, Determining the value of at least one variable reactance element operably coupled to the electrode that is not supplied with power, The at least one variable reactance element having the determined value causes the at least one variable reactance element to have the determined value, which in turn causes one or more voltages associated with one or more components of the process chamber to move toward one or more target voltages, Methods that include...

15. The method according to claim 14, A method for determining the value of the at least one variable reactance element, comprising using the one or more target voltages as a key value to a lookup table in order to identify the value of the at least one variable reactance element such that the one or more voltages associated with the one or more components fall within a predetermined range of the one or more target voltages.

16. The method according to claim 14 or 15, A method for determining the value of the at least one variable reactance element, based on a circuit model of at least a portion of the process chamber, wherein the circuit model includes the at least one variable reactance element.

17. The method according to claim 16, The method wherein the at least one variable reactance element comprises a variable capacitor, and the circuit model comprises the variable capacitor coupled in series with an inductor representing the inductance of the unpowered electrode.

18. The method according to claim 17, A method in which the value of the variable capacitor is determined as a value such that the impedance associated with the variable capacitor substantially cancels out the impedance associated with the inductor, which represents the inductance of the unpowered electrode.

19. The method according to claim 14 or 15, A method wherein the value of the at least one variable reactance element is determined at least in part on plasma characteristics determined based on optical data captured from an optical sensor.

20. The method according to claim 14 or 15, A method wherein the value of the at least one variable reactance element is determined at least in part on 1) power, voltage, current, and / or phase measurements of (one or more) RF signals measured in one or more regions of the process chamber, an RF power delivery system, or any combination thereof; or 2) a DC bias signal measured on at least one of the powered electrode and the unpowered electrode; or 3) plasma characteristics determined based on an electrical plasma diagnostic within the process chamber.

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