Mitigating distortion currents in radio frequency plasma processing chambers.

Abstract

Embodiments provided herein generally include plasma processing systems and methods for mitigating distortion currents. An exemplary plasma processing system includes a voltage source coupled to an input node. The input node is coupled to an electrode disposed within the processing chamber. The voltage source is configured to generate a pulsed voltage signal at the input node. The plasma processing system further includes a radio frequency (RF) signal generator having an output. The RF signal generator is configured to provide a first RF signal at a first RF frequency to the input node. The plasma processing system further includes a bandpass filter coupled between the output of the RF signal generator and the input node. The bandpass filter is configured to attenuate a second RF signal outside a range of frequencies that includes the first RF frequency of the first RF signal. The plasma processing system further includes an impedance matching circuit coupled between the bandpass filter and the input node.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE

[0001] Embodiments of the present disclosure generally relate to systems used in semiconductor device manufacturing. In particular, embodiments of the present disclosure relate to plasma processing systems used to process substrates. [Background technology]

[0002]

[0002] Reliably producing high aspect ratio features is one of the key technological challenges for next generation semiconductor devices. One method for forming high aspect ratio features uses a plasma-assisted etching process, in which a plasma is generated in a processing chamber and ions from the plasma are accelerated toward the surface of a substrate to form openings in a layer of material located below a mask layer formed on the surface of the substrate.

[0003]

[0003] In a typical plasma-assisted etching process, a substrate is placed on a substrate support located in a processing chamber, a plasma is generated above the substrate, and ions are accelerated from the plasma across a plasma sheath (i.e., an electron-depleted region created between the plasma and the surface of the substrate) toward the substrate.

[0004] In certain cases, plasma processing may use a combination of input powers having different frequencies. For example, a low-frequency pulsed voltage signal (e.g., 100 kHz to 5 MHz) and a high-frequency radio frequency (RF) signal (e.g., 10 MHz to 200 MHz). The plasma and the oscillating sheath may constitute a nonlinear load. The nonlinear load may generate distortion from the input power. The distortion current may include sidebands of the RF signal, such as bands of frequencies higher or lower than the frequency of the RF signal. For example, if a high RF frequency f1 provided by a first source and a low pulsed voltage signal frequency f2 provided by a second source are used, the distortion current may include the sum and / or difference of f1 and f2, resulting in sideband frequencies f1-f2 and f1+f2 close to the frequency f1. In certain cases, the distortion current may include harmonic distortion. For example, if a rectangular pulse waveform or a regulated waveform is used, the sum of the harmonic frequencies associated with the waveform may contribute to the sidebands. The distortion current can return to the power supply (e.g., an RF signal generator) and appear as reflected power. A signal filter may be placed at the output of the RF signal generator to protect the RF signal generator from the low-frequency bias power provided in the pulsed voltage signal generated from the low-frequency source. The signal filter may not be able to block all of the reflected distortion current returning from the plasma load. RF reflected power can be monitored and trigger a system safety interlock loop to protect against sudden abnormal changes in the process chamber. Such safety measures can interrupt substrate processing operations. In certain cases, reflected power can damage the power supply and / or other electrical components. In certain cases, reflected power can also affect the results of substrate processing.

[0005]

[0005] Therefore, there is a need in the art for plasma treatment and biasing methods that can mitigate the effects of distorting currents on the results of plasma assisted etch processes and plasma assisted etch hardware. Summary of the Invention

[0006]

[0006] Embodiments provided herein broadly include an apparatus, plasma processing system, and method for generating a waveform for plasma processing a substrate in a processing chamber.

[0007] One embodiment of the present disclosure is directed to a plasma processing system. The plasma processing system generally includes a voltage source coupled to an input node. The input node is coupled to an electrode disposed within a processing chamber. In this case, the voltage source is configured to generate a pulsed voltage signal at the input node. The plasma processing system further includes a radio frequency (RF) signal generator having an output. In this case, the RF signal generator is configured to provide a first RF signal at a first RF frequency to the input node. The plasma processing system further includes a bandpass filter coupled between the output of the RF signal generator and the input node. In this case, the bandpass filter is configured to attenuate a second RF signal outside a range of frequencies that includes the first RF frequency of the first RF signal. The plasma processing system further includes an impedance matching circuit coupled between the bandpass filter and the input node.

[0008] One embodiment of the present disclosure is directed to a plasma processing system. The plasma processing system generally includes a voltage source coupled to an input node coupled to an electrode disposed within a processing chamber, where the voltage source is configured to generate a pulsed voltage signal at the input node. The plasma processing system further includes an RF signal generator having an output, where the RF signal generator is configured to generate an RF signal that is superimposed on the pulsed voltage signal at the input node. The plasma processing system further includes an RF circulator coupled between the output of the RF signal generator and the input node. The plasma processing system further includes a memory and a processor coupled to the memory. The processor and the memory are configured to monitor the power of a signal reflected from the processing chamber at the RF circulator and to stop generation of the RF signal at the RF signal generator if the monitored power is equal to or greater than a threshold value for a certain duration.

[0009] One embodiment of the present disclosure is directed to a method for processing a substrate. The method generally includes generating, by a voltage source, a pulsed voltage signal at an input node coupled to an electrode disposed in a processing chamber, and providing, by a signal generator, a first RF signal to the input node through at least a bandpass filter, where the first RF signal has a first RF frequency, the bandpass filter is disposed between the RF signal generator and the input node, and an impedance matching circuit is disposed between the bandpass filter and the input node, and the bandpass filter is configured to attenuate a second RF signal outside a range of frequencies that includes the first RF frequency of the first RF signal.

[0010]

[0010] So that the above features of the present disclosure can be understood in detail, a more particular description of the present disclosure briefly summarized above can be made by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only exemplary embodiments and therefore should not be considered to limit the scope of the present disclosure, as other equally effective embodiments may also be acceptable. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view of a processing system according to one or more embodiments configured to perform the methods described herein. [Figure 2A]

[0012] 1 illustrates a voltage waveform that may be applied to an electrode of a processing chamber according to one or more embodiments. [Figure 2B]

[0013] 3 illustrates a voltage waveform established on a substrate due to a voltage waveform applied to an electrode of a processing chamber. [Figure 3]

[0014] FIG. 1 illustrates an exemplary plasma processing system employing a bandpass filter for mitigating distortion currents. [Figure 4A]

[0015] 4A-4C are diagrams of exemplary bandpass filters. [Figure 4B] 4A-4C are diagrams of exemplary bandpass filters. [Figure 4C] 4A-4C are diagrams of exemplary bandpass filters. [Figure 5]

[0016] 1 is a graph of the frequency response of an exemplary bandpass filter. [Figure 6]

[0017] FIG. 1 is a process flow diagram illustrating a method for mitigating distortion currents using a bandpass filter. [Figure 7]

[0018] FIG. 1 illustrates an exemplary plasma processing system employing an RF circulator for mitigating distortion currents. [Figure 8]

[0019] FIG. 1 is a process flow diagram illustrating a method for mitigating distortion currents using an RF circulator. [Figure 9]

[0020] 1 is an exemplary plasma processing system employing a bandpass filter and an RF circulator for mitigating distortion currents. DETAILED DESCRIPTION OF THE INVENTION

[0012]

[0021] For ease of understanding, where possible, the same reference numerals have been used to designate identical elements common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized in multiple other embodiments without specific recitation.

[0013]

[0022] As technology nodes progress toward 2 nm, the fabrication of smaller features with higher aspect ratios requires atomic precision for plasma processing. In etching processes where plasma ions play a major role, ion energy control is challenging for the semiconductor equipment industry. Traditional RF bias approaches use a sinusoidal wave to excite the plasma and accelerate the ions.

[0014]

[0023] Some embodiments of the present disclosure are generally directed to techniques and apparatus for mitigating distortion currents reflected back to a signal source(s) from a complex plasma load. For example, a bandpass filter may be placed between the output of a radio frequency (RF) signal generator and the plasma load. In certain aspects, the RF signal generator and / or the bandpass filter may be adjusted to increase the input power to the plasma load and / or attenuate distortion currents from the plasma load. In certain aspects, an RF circulator may be placed between the output of the RF signal generator and the plasma load to isolate the RF signal generator from the distortion currents. In some aspects, a bandpass filter, an RF match, and a signal filter may be sequentially placed between the output of the RF signal generator and the plasma load.

[0015]

[0024] The techniques and apparatus for mitigating distorted currents described herein can protect certain electrical devices (e.g., signal sources) from electrical damage, enable substrate processing operations without interruption due to reflected power, and / or facilitate higher energy substrate processing operations.

[0016] Multiple Embodiments of a Plasma Processing System

[0025] 1 is a schematic cross-sectional view of a plasma processing system 10 configured to perform one or more of the plasma processing methods described herein. In some embodiments, the processing system 10 is configured for a plasma-assisted etching process, such as a reactive ion etching (RIE) plasma process. However, it should be noted that the embodiments described herein may also be used with processing systems configured for use in other plasma-assisted processes, such as a plasma deposition process, e.g., 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).

[0017]

[0026] As shown, the processing system 10 is configured to form a capacitively coupled plasma (CCP). In this case, a processing chamber 100 includes an upper electrode (e.g., a chamber lid 123) disposed within a processing space 129. The upper electrode faces a lower electrode (e.g., a substrate support assembly 136) also disposed within the processing space 129. In a typical CCP processing system, a radio frequency (RF) source is electrically coupled to one of the upper or lower electrodes and provides an RF signal configured to ignite and sustain a plasma (e.g., plasma 101). The plasma is capacitively coupled to each of the upper and lower electrodes and disposed within a processing region therebetween. Typically, the other of the upper or lower electrode is coupled to ground or a second RF power source for further plasma excitation. As shown, the processing system 10 includes the processing chamber 100, the support assembly 136, and a system controller 126.

[0018]

[0027] The processing chamber 100 typically includes a chamber body 113. The chamber body 113 includes a chamber lid 123, one or more sidewalls 122, and a chamber base 124, which collectively define a processing space 129. The one or more sidewalls 122 and the chamber base 124 generally comprise a material sized and shaped to provide structural support for the elements of the processing chamber 100 and configured to withstand pressure and additional energy applied thereto. Meanwhile, the plasma 101 is generated in a reduced pressure environment maintained within the processing space 129 of the processing chamber 100 during processing. In one embodiment, the one or more sidewalls 122 and the chamber base 124 are formed from a metal, such as aluminum, an aluminum alloy, or a stainless steel alloy.

[0019]

[0028] A gas inlet 128 disposed through the chamber lid 123 is used to supply one or more process gases to the process space 129 from a process gas source 119 that is in fluid communication with the process space 129. The substrate 103 is loaded into and removed from the process space 129 through an opening (not shown) in one of the one or more sidewalls 122. The opening is sealed by a slit valve (not shown) during plasma processing of the substrate 103.

[0020]

[0029] In some embodiments, a plurality of lift pins (not shown) movably disposed through openings formed in the substrate support assembly 136 are used to facilitate movement of the substrate to and from the substrate support surface 105A. In some embodiments, the plurality of lift pins 132 are coupled to and / or engageable with a lift pin hoop (not shown) disposed above and positioned within the processing volume 129. The lift pin hoop may be coupled to a shaft (not shown) that sealingly extends through the chamber base 124. The shaft may be coupled to an actuator (not shown) for raising and lowering the lift pin hoop. When the lift pin hoop is in the raised position, the lift pin hoop engages the plurality of lift pins 132, raising the upper surfaces of the lift pins above the substrate support surface 105A and lifting the substrate 103 therefrom, allowing a robotic handler (not shown) to access the non-active side (backside) of the substrate 103. When the lift pin hoop is in the lowered position, the plurality of lift pins 132 are flush with or retracted below the substrate support surface 105A, and the substrate 103 rests on the substrate support surface 105A.

[0021]

[0030] The system controller 126, also referred to herein as a processing chamber controller, includes a central processing unit (CPU) 133, memory 134, and support circuits 135. The system controller 126 is used to control the process sequence used to process the substrate 103, which includes performing certain aspects of distortion current mitigation, as described further herein. The CPU 133 is a general-purpose computer processor configured for use in an industrial setting to control the processing chamber and its associated sub-processors. The memory 134, as described herein, is generally non-volatile memory and may include random access memory, read-only memory, floppy or hard disk drives, or other suitable forms of digital storage (local or remote). The support circuits 135 are conventionally coupled to the CPU 133 and include cache, clock circuits, input / output subsystems, power supplies, etc., and combinations thereof. Software instructions (programs) and data may be coded and stored in the memory 134 to instruct and command the processor within the CPU 133. A software program (or computer instructions) readable by CPU 133 within system controller 126 specifies which operations can be performed by components within processing system 10 .

[0022]

[0031] Typically, a program is readable by the CPU 133 in the system controller 126 and includes code that, when executed by the processor (CPU 133), performs operations associated with the plasma processing schemes described herein. The program may include instructions that are used to control various hardware and electrical components within the processing system 10 to perform various process operations and various process sequences used to implement the methods described herein. In one embodiment, the program includes instructions that are used to perform one or more of the operations described below with respect to FIG. 6 and / or FIG. 8.

[0023]

[0032] The plasma control system generally includes a first source assembly 196 for establishing at least a first pulsed voltage (PV) waveform at the bias electrode 104 (of a complex load as shown in FIG. 4 ) and a second source assembly 197 for establishing at least a second PV waveform at the edge control electrode 115. The first PV waveform or the second PV waveform may be generated using one or more components (e.g., PV sources) in a waveform generator assembly 150, which may correspond to a voltage source and / or a current source, as described in more detail herein with respect to FIG. 4 . In some embodiments, the waveform generator assembly 150 is configured to generate a pulsed voltage (PV) waveform. In that case, the PV waveform is a non-sinusoidal voltage pulse. FIGS. 2A and 2B show examples of typical PV waveforms generated at the electrode and substrate, respectively, and may be used in conjunction with one or more embodiments of the disclosure provided herein. In one embodiment, the waveform generator assembly 150 is configured to provide PV pulses at a frequency between approximately 100 kHz and 400 kHz and at a voltage between approximately 100 volts and 10,000 volts.

[0024]

[0033] 1, a separate waveform generator assembly 160 in the third source assembly 198 includes at least an RF signal generator. The RF signal generator is configured to provide an RF signal to the support base 107 (e.g., a powered electrode or cathode) and / or the bias electrode 104. In some embodiments, the plasma generator assembly 160 may be used to provide an RF signal to the support base 107 (e.g., a powered electrode or cathode) and / or the bias electrode 104, and thus generate (sustain and / or ignite) the plasma 101 in a processing region disposed between the substrate support assembly 136 and the chamber lid 123. In some embodiments, the third source assembly 198 may be alternatively coupled to the chamber lid 123, such as in place of a ground as shown in FIG. 1.

[0025]

[0034] In certain aspects, the distortion current manager 152, the impedance matching circuit 153, and / or the signal filter 154 may be disposed between the waveform generator assembly 160 in the third source assembly 198 and the support base 107 (e.g., a power electrode or a cathode) and / or the bias electrode 104. In some embodiments in which the waveform generator assembly 160 is configured to generate an RF signal and the waveform generator assembly 150 is configured to generate a lower frequency signal, the signal filter 154 is a high-pass filter. The high-pass filter is configured to allow the signal provided from the waveform generator assembly 160 to be supplied to the support base 107 and / or the bias electrode 104 through the signal filter 154. The support base 107, the bias electrode 104, and / or the edge control electrode 115 may collectively and / or individually be referred to as input nodes of the process chamber 100. In this example, the impedance matching circuit 153 may be disposed between the distortion current manager 152 and the signal filter 154.

[0026]

[0035] The distortion current manager 152 may be configured to block and / or attenuate distortion currents reflected from the plasma load back to the waveform generator assembly 160. For example, the distortion current manager 152 may include a bandpass filter and / or an RF circulator, as described further herein.

[0027]

[0036] The impedance matching circuit 153 may be configured to match the input impedance of the input node. For example, the output impedance of the waveform generator assembly 150 may be matched to the input impedance of the input node via the impedance matching circuit 153. The impedance matching circuit 153 may enable efficient transfer of power from the waveform generator assembly 160 to the input node.

[0028]

[0037] The signal filter 154 may be configured to allow the RF signal generated by the waveform generator assembly 160 to pass to the input node. In certain aspects, the signal filter 154 may include a bypass filter. The signal filter 154 may isolate the waveform generator assembly 160 of the third source assembly 198 from low frequency signals generated by the other waveform generator assemblies 150 of the first source assembly 196 and / or the second source assembly 197.

[0029]

[0038] The applied waveforms provided from the first source assembly 196, the second source assembly 197, and / or the third source assembly 198 may be configured to generate (sustain and / or ignite) the plasma 101 in a processing region disposed between the substrate support assembly 136 and the chamber lid 123. In some embodiments, an RF signal provided from the waveform generator assembly 160 is used to ignite and sustain the processing plasma 101, which uses a process gas disposed in the processing space 129 and an electric field generated by RF power (RF signal) supplied to the support base 107 and / or the bias electrode 104. In some aspects, the RF signal may be generated by an RF signal generator (not shown) disposed in the waveform generator assembly 160. In some embodiments, the RF signal generator of the waveform generator assembly 160 may be configured to provide an RF signal having a frequency greater than 1 MHz and / or between 2 MHz and 200 MHz, e.g., 13.56 MHz, 40 MHz, 60 MHz, 120 MHz, or 162 MHz.

[0030]

[0039] The processing space 129 is fluidly coupled to one or more dedicated vacuum pumps via a vacuum outlet 120. The one or more dedicated vacuum pumps maintain the processing space 129 at sub-atmospheric pressure and evacuate process gases and / or other gases from the processing space 129. In some embodiments, a substrate support assembly 136 disposed within the processing space 129 is disposed on a support shaft 138 that is grounded and extends through the chamber base 124.

[0031]

[0040] As briefly described above, the substrate support assembly 136 generally includes a substrate support 105 (e.g., an electrostatic chuck (ESC) substrate support) and a support base 107. In some embodiments, the substrate support assembly 136 may further include an insulator plate 111 and a grounded plate 112, as described further below. The support base 107 is electrically insulated from the chamber base 124 by the insulator plate 111, and the grounded plate 112 is interposed between the insulator plate 111 and the chamber base 124. The substrate support 105 is thermally coupled to and disposed on the support base 107. In some embodiments, the support base 107 is configured to regulate the temperature of the substrate support 105 and the substrate 103 disposed on the substrate support 105 during substrate processing. In some embodiments, the support base 107 includes one or more cooling channels (not shown) disposed therein. The one or more cooling channels are fluidly coupled to and in fluid communication with a coolant source (not shown) (such as a refrigerant source or a water source having a relatively high electrical resistance). In some embodiments, the substrate support 105 includes a heater (not shown) (such as a resistive heating element embedded within the dielectric material of the substrate support 105). Here, the support base 107 is formed of a corrosion-resistant, heat-conducting material, such as a corrosion-resistant metal (e.g., aluminum, an aluminum alloy, or stainless steel), and is coupled to the substrate support by adhesive or mechanical means.

[0032]

[0041] Typically, the substrate support 105 is formed of a dielectric material (e.g., a bulk-sintered ceramic material such as a corrosion-resistant metal oxide or metal nitride material), such as aluminum oxide (Al2O3), aluminum nitride (AlN), titanium oxide (TiO), titanium nitride (TiN), yttrium oxide (YO3), mixtures thereof, or combinations thereof. In embodiments herein, the substrate support 105 further includes a bias electrode 104 embedded within the dielectric material.

[0033]

[0042] In one configuration, the bias electrode 104 is a chucking pole used to secure (i.e., chuck) the substrate 103 to the substrate support surface 105A of the substrate support 105 and to bias the substrate 103 relative to the processing plasma 101 using one or more of the pulsed voltage biasing schemes described herein. Typically, the bias electrode 104 is formed of one or more conductive components, such as one or more metal meshes, foils, plates, or combinations thereof.

[0034]

[0043] In some embodiments, the bias electrode 104 is electrically coupled to a clamping network or high-voltage DC supply 312 (FIG. 3). The clamping network or high-voltage DC supply 312 provides a chucking voltage, such as a static DC voltage between about −5000 V and about 5000 V, to the bias electrode 104 using an electrical conductor, such as a coaxial power supply line 106 (e.g., a coaxial cable). The clamping network includes a DC power supply 155 (e.g., a high-voltage DC (HVDC) supply) and a filter 151 (e.g., a low-pass filter).

[0035]

[0044] The substrate support assembly 136 may further include an edge control electrode 115. The edge control electrode 115 is disposed below the edge ring 114, surrounds the bias electrode 104, and / or is spaced apart from the center of the bias electrode 104. Typically, in a processing chamber 100 configured to process a circuit substrate, the edge control electrode 115 is ring-shaped, made of a conductive material, and configured to surround at least a portion of the bias electrode 104. In some embodiments, such as shown in FIG. 1, the edge control electrode 115 is disposed within the region of the substrate support 105. In some embodiments, as shown in FIG. 1, the edge control electrode 115 comprises a conductive mesh, foil, and / or plate disposed a similar distance (i.e., in the Z direction) from the substrate support surface 105A of the substrate support 105 as the bias electrode 104.

[0036]

[0045] The edge control electrode 115 may be biased through the use of a waveform generator assembly that is different from the waveform generator assembly 150 used to bias the bias electrode 104. In some embodiments, the edge control electrode 115 may be biased using the waveform generator assembly 150 that is also used to bias the bias electrode 104 by splitting a portion of the power to the edge control electrode 115. In one configuration, a first waveform generator assembly 150 of a first source assembly 196 is configured to bias the bias electrode 104, and a second waveform generator assembly 150 of a second source assembly 197 is configured to bias the edge control electrode 115.

[0037]

[0046] In one embodiment, a power supply line 157 electrically connects the output of the waveform generator assembly 150 of the first source assembly 196 with the bias electrode 104. While the following description primarily describes the power supply line 157 of the first source assembly 196 used to couple the waveform generator assembly 150 to the bias electrode 104, the power supply line 158 of the second source assembly 197 coupling the waveform generator assembly 150 to the edge control electrode 115 and / or the power supply line 159 of the third source assembly 198 coupling the waveform generator assembly 160 to the support base 107 will include the same or similar components. The electrical conductor(s) in the various portions of the voltage supply line 157 include the following: That is, (a) one or a combination of coaxial cables, such as a flexible coaxial cable connected in series with a rigid coaxial cable; (b) insulated high voltage corona resistant circuit wire; (c) bare wire; (d) metal rod; (e) electrical connector; or (f) any combination of the electrical elements (a)-(e).

[0038]

[0047] In some embodiments, the processing chamber 100 further includes a quartz tube 110 or collar that at least partially circumscribes portions of the substrate support assembly 136 to prevent the substrate support 105 and / or support base 107 from contacting corrosive process gases or plasmas, cleaning gases or plasmas, or by-products thereof. Typically, the quartz tube 110, insulator plate 111, and ground plate 112 are circumscribed by a liner 108 (e.g., a cathode liner). In some embodiments, a plasma screen 109 is disposed between the cathode liner 108 and the sidewall 122 to prevent plasma generation in the space below the plasma screen 109 between the liner 108 and one or more sidewalls 122.

[0039]

[0048] FIG. 2A illustrates an exemplary voltage waveform that may be established at an electrode or input node (e.g., bias electrode 104 and / or support base 107) of a processing chamber. FIG. 2B illustrates an example of different types of voltage waveforms 225 and 230 established at a substrate due to a different voltage waveform similar to the voltage waveform illustrated in FIG. 2A that is separately established at an electrode in the processing chamber. As illustrated, the waveform includes two phases: an ion current phase and a sheath collapse phase. As illustrated in FIG. 2A, the exemplary voltage waveform may include a pulsed voltage signal (e.g., a 100 kHz to 5 MHz pulsed signal with a duty cycle ranging from 5% to 95%) superimposed with an RF signal (e.g., a sinusoidal radio frequency signal with a frequency greater than 10 MHz). For current compensation (e.g., during the ion current phase), the exemplary voltage waveform illustrated in FIG. 2A may also include a voltage ramp with a negative slope superimposed with an RF signal. At the beginning of the ion current phase, the drop in substrate voltage creates a high voltage sheath above the substrate, accelerating positive ions to the substrate.

[0040]

[0049] Positive ions impinging on the substrate surface during the ion current phase deposit positive charge on the substrate surface, which, if uncompensated, gradually increases the substrate voltage during the ion current phase, as shown by voltage waveform 225 in FIG. 2B. However, uncontrolled accumulation of positive charge on the substrate surface undesirably gradually discharges the sheath and chuck capacitors, slowly reducing the sheath voltage drop and causing the substrate potential to approach zero, as shown by voltage waveform 225. The accumulation of positive charge results in voltage droop in the voltage waveform established at the substrate surface (FIG. 2B). However, as shown in FIG. 2A, a voltage waveform established at the electrode having a negative slope during the ion current phase can be desirably generated to establish a square-shaped region (e.g., a slope near zero) for the established substrate voltage waveform, as shown by the curve labeled 230 in FIG. 2B. Implementing a slope in the waveform established at the electrode during the ion current phase (FIG. 2A) may be referred to as current compensation. The voltage difference between the beginning and end of the ion current phase determines the width of the ion energy distribution function (IEDF). A larger voltage difference results in a wider IEDF, which is undesirable in most current high-precision plasma processes. To achieve monoenergetic ions and a narrower IEDF width, ion current compensation is used to operate to flatten the substrate voltage waveform during the ion current phase.

[0041] Mitigating distortion currents for substrate processing.

[0050] Certain embodiments of the present disclosure are generally directed to techniques and apparatus for mitigating distortion currents reflected from a plasma load to a signal source of a plasma processing system.

[0042]

[0051] In certain aspects, the distortion current manager may employ a bandpass filter to attenuate the distortion current. FIG. 3 illustrates an exemplary plasma processing system 300 employing a bandpass filter 306 for distortion current mitigation in accordance with certain aspects of the present disclosure. The plasma processing system 300 may represent one embodiment of the processing system 10. As illustrated, the plasma processing system 300 may include a voltage source 302 (e.g., the waveform generator assemblies 150 of the first and second source assemblies 196, 197), an RF generator 304 (e.g., the waveform generator assembly 160 of the third source assembly 198), a bandpass filter 306 (e.g., the distortion current manager 152), and an impedance matching circuit 308 (e.g., the impedance matching circuit 153).

[0043]

[0052] The voltage source 302 may include a waveform generator 310 and an HVDC supply 312. The waveform generator 310 may generate a pulsed voltage signal. The HVDC supply 312 may provide a DC bias for the voltage waveform. The voltage source 302 may be coupled to an input node 314. The input node 314 may be coupled to an electrode 316 (e.g., support base 107 and / or bias electrode 104) disposed within a process chamber 318 (e.g., process chamber 100). The voltage source 302 may be configured to generate a pulsed voltage signal (e.g., a 100 kHz to 5 MHz pulsed signal with a duty cycle ranging from 5% to 95%) at the input node 314.

[0044]

[0053] The RF generator 304 may have an output 320 coupled to an input node 314 via at least a bandpass filter 306 and an impedance matching circuit 308. The RF generator 304 may generate a first RF signal that is superimposed on the pulsed voltage signal at the input node 314, for example, as described herein with respect to Figures 1 and 2A. The first RF signal may have at least one first RF frequency, for example, greater than 1 MHz and / or between 1 MHz and 200 MHz, for example, 13.56 MHz, 40 MHz, 60 MHz, 120 MHz, or 162 MHz. The RF generator 304 may be referred to as an RF plasma generator or an RF signal generator.

[0045]

[0054] The bandpass filter 306 may be coupled between the output 320 of the RF generator 304 and the input node 314. The bandpass filter 306 may prevent or attenuate harmful reflected power signals from damaging the RF generator 304. For example, the bandpass filter 306 may be configured to attenuate distorted currents reflected back to the RF generator 304 from a plasma load in the processing chamber 318. The bandpass filter 306 may have a high quality factor (e.g., a quality factor of 50 or greater) with low insertion loss. The bandpass filter 306 may have a narrow bandwidth (e.g., measured at the half-power point or cutoff frequency) of ±0.1% to ±0.5% from the center frequency of the bandpass filter 306. A bandwidth of ±0.1% to ±0.5% from the center frequency may represent a bandwidth of 0.2% to 1% of the center frequency. In that case, for example, the lower cutoff frequency is −0.1% to −0.5% from the center frequency, and the upper cutoff frequency is 0.1% to 0.5% from the center frequency. For example, the bandwidth of the bandpass filter 306 may be 100 kHz to 800 kHz. The bandpass filter 306 may be configured to attenuate the second RF signal (e.g., distortion currents described herein) outside a range of frequencies that includes the first RF frequency of the first RF signal (e.g., a bandwidth of ±0.1% to ±0.5% from the center frequency of the bandpass filter 306).

[0046]

[0055] The impedance matching circuit 308 may be coupled between the bandpass filter 306 and the input node 314. For example, the output impedance of the RF generator 304 and / or the bandpass filter 306 may be matched to the input impedance of the input node 314 via the impedance matching circuit 308.

[0047]

[0056] In certain aspects, a signal filter 322 (e.g., signal filter 154) may be disposed between impedance matching circuit 308 and input node 314. Signal filter 322 may isolate RF generator 304 from the pulse signal generated by voltage source 302. A low-pass filter 324 (e.g., filter 151) may be coupled between voltage source 302 and input node 314. Low-pass filter 324 may isolate voltage source 302 from the RF signal generated by RF generator 304.

[0048]

[0057] The processing chamber 318 may include a substrate support comprising a dielectric layer disposed over the electrode 316, for example, as described herein with respect to FIG. 1. The plasma processing system 300 may also include a system controller 126. The system controller 126 may perform one or more of the operations described herein with respect to FIG. 6 and / or FIG. 8.

[0049]

[0058] 4A-4C illustrate several embodiments of a bandpass filter for mitigating distortion currents. The bandpass filter(s) illustrated in FIGS. 4A-4C may be examples of bandpass filter 306 shown in FIG. 3. In certain cases, the bandpass filter(s) illustrated in FIGS. 4A-4C may include lumped electrical components. The bandpass filter may be configured to allow RF signals with frequencies greater than 1 MHz, e.g., greater than 10 MHz, or greater than 60 MHz, or even greater than 100 MHz, to pass.

[0050]

[0059] 4A, bandpass filter 400A may include a capacitor 402 and an inductor 404 coupled in parallel along a signal line 406, which may represent power supply line 159. For example, inductor 404 may have an inductance of 0.1 μH to 5 μH, and capacitor 404 may have a capacitance of 3 pF to 100 pH. Bandpass filter 400A may provide various advantages and / or benefits, such as low cost and a small footprint.

[0051]

[0060] In certain aspects, the bandpass filter may include a distributed-element filter. Referring to FIG. 4B , the bandpass filter 400B may include a decompression capacitor 408 coupled in parallel with a power line inductor 410 to an inner surface of a metal housing 412. The metal housing 412 may be coupled to a shield of an RF coaxial cable (e.g., power supply line 159), which may provide an RF return path. The inductance of the distributed inductor 410 may be varied by the conductor length. The conductor length may be, for example, shorter than a quarter wavelength of the RF signal. In certain embodiments, the decompression capacitor 408 may include an electrically actuated decompression capacitor to adjust the center frequency of the bandpass filter 400B. In other words, the bandpass filter 400B may include an adjustable element, such as an adjustable capacitor. The adjustable bandpass filter 400B may be adjusted so that the center frequency of the bandpass filter 400B matches the output frequency used by an RF signal generator (e.g., RF generator 304 shown in FIG. 3 ). Bandpass filter 400B may provide various advantages and / or benefits, such as reduced filter-to-filter variation and improved control over frequency accuracy of center frequency and / or cutoff frequency.

[0052]

[0061] In certain aspects, a bandpass filter may employ reactive components, which may facilitate a narrow bandwidth and a high quality factor. Referring to FIG. 4C , a bandpass filter 400C may include a first shunt capacitor 414, a second shunt capacitor 416, and a third capacitor 418 coupled in series with an inductor 420 along a signal line 422, which may represent the power supply line 159. The third capacitor 418 and the inductor 420 may be coupled between the first shunt capacitor 414 and the second shunt capacitor 416. The shunt capacitors 414, 416 may be coupled along separate shunt branches 424, 426, respectively, from the signal line 422. As an example, the inductor 420 may have an inductance of 0.1 μH to 5 μH. The first and second shunt capacitors 414, 416 may each have a capacitance between 200 pF and 1000 pF, and the third capacitor 418 may have a capacitance between 3 pF and 100 pF. The first, second, and third capacitors 414, 416, 418 may have fixed or adjustable capacitances, such as electrically driven voltage-reducing capacitors. As an adjustable filter, the center frequency of the bandpass filter 400C can be adjusted to match the output frequency of an RF generator (e.g., the RF generator 304 shown in FIG. 3). The bandpass filter 400C may provide various advantages and / or benefits, such as providing desired filter performance with a narrow bandwidth and a high quality factor.

[0053]

[0062] 5 is a graph of an example frequency response 500 of a bandpass filter for mitigating distortion currents, according to certain embodiments of the present disclosure. The frequency response 500 shows the output power of the bandpass filter versus frequency. In this example, the frequency response may have a center frequency 502 that may correspond to the output frequency of the signal generator and a bandwidth 504 that may be ±0.1% to ±0.5% from the center frequency 502. In embodiments, the bandwidth 504 may be determined at the half-power point from the power of the center frequency 502.

[0054]

[0063] 6 is a process flow diagram illustrating a method 600 for mitigating distortion currents using a bandpass filter. The method 600 may be performed by a plasma processing system, such as processing system 10.

[0055]

[0064] At activity 602, a voltage source (e.g., voltage source 302) may generate a pulsed voltage signal at an input node (e.g., input node 314) coupled to an electrode (e.g., support base 107 and / or bias electrode 104) disposed within a process chamber (e.g., process chamber 100, 318). For example, the voltage source may generate a pulsed voltage signal as described herein with respect to FIG. 2A. The pulsed voltage signal may be pulsed at a frequency of 100 kHz to 5 MHz with a duty cycle ranging from 5% to 95%.

[0056]

[0065] At activity 604, an RF signal generator (e.g., RF generator 304) may provide a first RF signal at a first RF frequency (and / or another RF frequency) to an input node. The RF signal generator may pass the first RF signal through at least a bandpass filter (e.g., bandpass filter 306) to generate the first RF signal to be superimposed on a pulsed voltage signal. For example, the RF signal may be superimposed on the pulsed voltage signal as described herein with respect to FIG. 2A. The bandpass filter may be disposed between the RF signal generator and the input node. An impedance matching circuit (e.g., impedance matching circuit 308) may be disposed between the bandpass filter and the input node. The bandpass filter may be configured to attenuate a second RF signal (e.g., a distortion current from a plasma load) outside a range of frequencies (e.g., ±0.1% to ±0.5% from the output frequency of the RF signal generator) that includes the first RF frequency of the first RF signal.

[0057]

[0066] In certain aspects, the output frequency of the RF signal generator may be adjusted to improve the power delivered to the plasma load and / or improve the attenuation of distortion current. At activity 608, the RF signal generator may sweep a range of output frequencies of the RF signal. In this case, the RF signal generator is configured to sweep through a range of output frequencies. At activity 610, a processor and memory (e.g., system controller 126) may select a frequency from the range of output frequencies that provides a peak power of the RF signal that passes through a bandpass filter. At activity 612, the RF signal generator may generate an RF signal at the selected frequency. In some embodiments, the frequency adjustment may begin after the pulsed voltage waveform or the tuned voltage waveform is applied to the plasma chamber. In other embodiments, the frequency adjustment may begin before the pulsed voltage waveform or the tuned voltage waveform is applied to the plasma chamber. The frequency adjustment may continue until a minimum reflected power and / or a maximum delivered power is achieved. The frequency scan range may be 0.1% to 1% of the initial output frequency. The frequency adjustment may allow distortion current mitigation to compensate for variations in the performance of the bandpass filter due to, for example, variations in the impedance of the bandpass filter's components. Due to variations in the component impedance, the center frequency of the bandpass filter may be offset from its design value, and the RF signal generator then adjusts its output frequency to match the center frequency of the bandpass filter. The frequency adjustment scan can compensate for the center frequency shift by changing the output frequency of the RF signal generator to the actual center frequency.

[0058]

[0067] In certain embodiments, the bandpass filter may be adjusted to improve the power delivered to the plasma load and / or to improve the attenuation of distortion currents. At activity 606, the bandpass filter may be adjusted.

[0059]

[0068] In activity 614, the center frequency of the bandpass filter (e.g., center frequency 502) may be adjusted. For example, the center frequency of the bandpass filter may be adjusted until the center frequency matches the output frequency of the RF signal generator. In certain cases, the center frequency may be adjusted until a maximum power delivery is observed at the plasma load. The center frequency of the bandpass filter may be adjusted using at least one capacitor (e.g., third capacitor 418) of the bandpass filter to match the output frequency of the first RF signal, allowing a peak power of the first RF signal at the output frequency. For example, a range of center frequencies of the bandpass filter may be set, and the center frequency providing the maximum power delivery may be considered the peak power of the RF signal. In some embodiments of activity 614, the capacitance of a variable capacitor (e.g., a powered voltage reducing capacitor) is adjusted to change the center frequency of the bandpass filter. FIGS. 4A-4C illustrate various configurations of bandpass filters that may be adjusted to desirably match the frequency setpoint of the RF generator. As an example, referring to FIG. 4C, the capacitance of the third capacitor 418 may be adjusted to adjust the center frequency of the bandpass filter 400C.

[0060]

[0069] In activity 616, the bandwidth of the bandpass filter (e.g., bandwidth 504) may be adjusted. The bandwidth of the bandpass filter may be adjusted to attenuate the second RF signal reflected from the process chamber. For example, the bandwidth may be adjusted until a minimum reflected power from the plasma load is observed. The bandwidth may be adjusted to be within ±5% of the output frequency of the first RF signal, for example, after the center frequency has been adjusted. In certain aspects, adjusting the bandpass filter may include adjusting the capacitance of at least one of the capacitors, such as the capacitors shown in FIGS. 4A-4C. The bandpass filter may be adjusted within 5% of the adjustment range of the bandpass filter until a minimum reflected power and / or a maximum delivered power is observed. As an example, referring to FIG. 4C, the capacitance of the first capacitor 414 and / or the second capacitor 416 may be adjusted to adjust the bandwidth of the bandpass filter 400C.

[0061]

[0070] In certain embodiments, an RF signal superimposed on a pulsed voltage signal may be used for plasma etching applications. For example, a plasma may be generated on a substrate support disposed in a processing chamber as described herein with respect to Figure 1. The substrate support assembly may include an electrode and a dielectric layer disposed between the electrode and the substrate support surface.

[0062]

[0071] In certain aspects, the distortion current manager may employ an RF circulator to isolate the RF signal generator from distortion currents reflected from the plasma load. Figure 7 illustrates an exemplary plasma processing system 700 in accordance with certain aspects of the present disclosure. The plasma processing system 700 may represent one embodiment of the processing system 10. As shown, the plasma processing system 700 may include a voltage source 302, an RF generator 304, an RF circulator 730, and a system controller 126.

[0063]

[0072] The RF circulator 730 may be disposed between the output 320 of the RF generator 304 and the input node 314. The RF circulator 730 may be configured to isolate the RF generator 304 from distortion currents reflected back from the plasma load. The RF circulator 730 may include a first port 732, a second port 734, and a third port 736. The first port 732 may be coupled to the output 320 of the RF generator 304, the second port 734 may be coupled to at least the input node 314, and the third port 736 may be coupled to at least a dummy load 738. The RF circulator 730 may allow an RF signal from the RF generator 304 to travel from the first port 732 to the second port 734 (but not to the third port 736). The RF circulator may allow distortion currents traveling towards the RF circulator 730 to travel from the second port 734 to the third port 736 (but not to the first port 732).

[0064]

[0073] The system controller 126 may monitor the power of the signal reflected from the processing chamber 318 at the RF circulator 730 through the dummy load 738. For example, a power meter 740 may be coupled between the dummy load 738 and the third port 736 of the RF circulator 730. The system controller 126 may communicate with the power meter 740 to receive the measured power at the third port 736 of the RF circulator 730. The RF circulator 730 may direct the reflected distortion current to the dummy load 738, which may include a high-power resistive load (e.g., 50 ohms). The system controller 126 may stop generating the RF signal in the RF generator 304 if the monitored power is equal to or greater than a threshold for a specific duration (e.g., 5 seconds). In other words, the RF generator 304 may be shut off if the reflected distortion current exceeds a specific threshold power. Triggering a shutdown of the RF generator 304 can prevent distortion currents from damaging the signal generator 304 , the RF circulator 730 , and / or other electrical components within the plasma processing system 700 .

[0065]

[0074] 8 is a process flow diagram illustrating a method 800 for mitigating distortion currents using an RF circulator. The method 800 may be performed by a plasma processing system, such as processing system 10.

[0066]

[0075] At activity 802, a voltage source (e.g., voltage source 302) may generate a pulsed voltage signal at an input node (e.g., input node 314) coupled to an electrode (e.g., support base 107 and / or bias electrode 104) disposed within a process chamber (e.g., process chamber 100, 318). For example, the voltage source may generate a pulsed voltage signal as described herein with respect to FIG. 2A.

[0067]

[0076] At activity 804, an RF signal generator (e.g., RF generator 304) may provide an RF signal to the input node. The RF signal generator may generate an RF signal that is superimposed on a pulsed voltage signal (e.g., as described herein with respect to FIG. 2A) through at least an RF circulator (e.g., RF circulator 730). For example, the RF signal generator may generate an RF signal that is superimposed on a pulsed voltage signal as described herein with respect to FIG. 2A.

[0068]

[0077] At activity 806, a processor and memory (eg, system controller 126) may monitor the power of the signal reflected from the processing chamber at an RF circulator, for example, as described herein with respect to FIG.

[0069]

[0078] At activity 808, the processor and memory may stop generation of the RF signal in the RF signal generator if the monitored power is above a threshold for a specified duration (e.g., 5 seconds), as described herein with respect to FIG.

[0070]

[0079] In certain aspects, the distortion current manager may employ an RF circulator and a bandpass filter. Figure 9 illustrates an example of a plasma processing system 90 including a bandpass filter 306, an RF circulator 730, a dummy load 738, and a power meter 740, as described herein with respect to Figures 3 and 7. In one embodiment, signals monitored by the system controller 126 and various control elements within the system controller 126, as described above in conjunction with Figure 7, are used to adjust the center frequency and / or adjust the bandpass filter to maximize delivered power and / or attenuate RF signals reflected from the process chamber, as described above in conjunction with activities 614 and 616 of method 600. Thus, during plasma processing, if the system controller 126 detects an undesirable amount of reflected power passing through the bandpass filter and reaching the power meter 740, the system controller 126 provides a signal that causes adjustment or fine-tuning of components within the bandpass filter (e.g., adjusting the capacitance within bandpass filter 400A, 400B, or 400C) to adjust the center frequency and / or adjust the bandpass filter to minimize the amount of energy delivered to the dummy load 738.

[0071]

[0080] The techniques and apparatus described herein can protect certain electrical devices (e.g., RF signal sources) from electrical damage, enable substrate processing operations without interruption due to reflected power, and / or facilitate higher energy substrate processing operations.

[0072]

[0081] The term "coupled" is used herein to refer to a direct or indirect coupling between two objects. For example, if object A is in physical contact with object B, and object B is in physical contact with object C, objects A and C may be considered coupled to one another even though they are not in direct physical contact. For example, a first object may be coupled to a second object even though the first object is not in direct physical contact with the second object.

[0073]

[0082] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof, which scope is defined by the following claims.

Claims

1. 1. A method of processing a substrate, comprising: generating, by a voltage source, a pulsed voltage signal at an input node coupled to an electrode disposed within the processing chamber; providing, by a radio frequency (RF) plasma generator, a first RF signal through at least a bandpass filter to the input node; the first RF signal has a first RF frequency; the bandpass filter is disposed between the RF plasma generator and the input node; an impedance matching circuit disposed between the bandpass filter and the input node; a signal filter disposed between the impedance matching circuit and the input node; The method, wherein the bandpass filter is configured to attenuate a second RF signal outside a range of frequencies that includes the first RF frequency of the first RF signal.

2. 1. A method of processing a substrate, comprising: generating, by a voltage source, a pulsed voltage signal at an input node coupled to an electrode disposed within the processing chamber; providing, by a radio frequency (RF) plasma generator, a first RF signal through at least a bandpass filter to the input node; the first RF signal has a first RF frequency; Generating the first RF signal includes: sweeping through a range of output frequencies of the first RF signal; selecting a frequency from the range of output frequencies that provides a peak power of the first RF signal passing through the bandpass filter; and generating the first RF signal at the selected frequency; the bandpass filter is disposed between the RF plasma generator and the input node; an impedance matching circuit disposed between the bandpass filter and the input node; The method, wherein the bandpass filter is configured to attenuate a second RF signal outside a range of frequencies that includes the first RF frequency of the first RF signal.

3. 1. A method of processing a substrate, comprising: generating, by a voltage source, a pulsed voltage signal at an input node coupled to an electrode disposed within the processing chamber; providing, by a radio frequency (RF) plasma generator, a first RF signal through at least a bandpass filter to the input node; the first RF signal has a first RF frequency; Generating the first RF signal includes: generating the first RF signal through at least an RF circulator and the bandpass filter; monitoring the power of a signal reflected from the processing chamber at the RF circulator; and ceasing generation of the first RF signal if the monitored power is equal to or greater than a threshold for a duration; the bandpass filter is disposed between the RF plasma generator and the input node; an impedance matching circuit disposed between the bandpass filter and the input node; The method, wherein the bandpass filter is configured to attenuate a second RF signal outside a range of frequencies that includes the first RF frequency of the first RF signal.

4. 4. The method of claim 2, wherein a signal filter is disposed between the impedance matching circuit and the input node.

5. The method of any one of claims 1 to 3, wherein the bandpass filter comprises a capacitor and an inductor coupled in parallel.

6. The method according to any one of claims 1 to 3, wherein the bandpass filter includes a distributed constant filter.

7. 4. The method of claim 1, wherein the bandpass filter includes a capacitor coupled in series with a first shunt capacitor, a second shunt capacitor, and an inductor, the capacitor and the inductor being coupled between the first shunt capacitor and the second shunt capacitor.

8. The method according to any one of claims 1 to 3, wherein the bandpass filter has a quality factor of 50 or greater.

9. A method described in any one of claims 1 to 3, further comprising adjusting the center frequency of the bandpass filter having at least one capacitor to match the first RF frequency of the first RF signal, thereby enabling peak power of the first RF signal at the first RF frequency.

10. 4. The method of claim 1, further comprising adjusting a bandwidth of the bandpass filter to attenuate the second RF signal reflected from the processing chamber, wherein adjusting the bandwidth of the bandpass filter comprises adjusting the bandwidth to within ±5% of the first RF frequency of the first RF signal.

11. Generating the first RF signal includes: sweeping through a range of output frequencies of the first RF signal; selecting a frequency from the range of output frequencies that provides a peak power of the first RF signal passing through the bandpass filter; and 4. The method of claim 1, further comprising generating the first RF signal at the selected frequency.

12. 3. The method of claim 1, wherein generating the first RF signal comprises generating the first RF signal through at least an RF circulator and the bandpass filter.

13. monitoring the power of a signal reflected from the processing chamber at the RF circulator; and The method of claim 12 , further comprising ceasing generation of the first RF signal if the monitored power is equal to or greater than a threshold for a duration.

14. a voltage source coupled to an input node, the input node coupled to an electrode disposed within a process chamber, the voltage source configured to generate a pulsed voltage signal at the input node; a radio frequency (RF) signal generator having an output, the RF signal generator configured to provide a first RF signal at a first RF frequency to the input node; a bandpass filter coupled between the output of the RF signal generator and the input node, the bandpass filter configured to attenuate a second RF signal outside a range of frequencies that includes the first RF frequency of the first RF signal; an impedance matching circuit coupled between the bandpass filter and the input node; and The plasma processing system further comprises a signal filter disposed between the impedance matching circuit and the input node.

15. a voltage source coupled to an input node, the input node coupled to an electrode disposed within a process chamber, the voltage source configured to generate a pulsed voltage signal at the input node; a radio frequency (RF) signal generator having an output, the RF signal generator configured to sweep through a range of output frequencies for a first RF signal to generate the first RF signal at a selected frequency, and to provide the first RF signal at the first RF frequency to the input node; a bandpass filter coupled between the output of the RF signal generator and the input node, the bandpass filter configured to attenuate a second RF signal outside a range of frequencies that includes the first RF frequency of the first RF signal; an impedance matching circuit coupled between the bandpass filter and the input node; and 10. The plasma processing system of claim 9, further comprising: a memory; and a processor coupled to the memory, the processor and the memory configured to select a frequency from the range of output frequencies that provides a peak power of the first RF signal that passes through the bandpass filter.

16. a voltage source coupled to an input node, the input node coupled to an electrode disposed within a process chamber, the voltage source configured to generate a pulsed voltage signal at the input node; a radio frequency (RF) signal generator having an output, the RF signal generator configured to provide a first RF signal at a first RF frequency to the input node; a bandpass filter coupled between the output of the RF signal generator and the input node, the bandpass filter configured to attenuate a second RF signal outside a range of frequencies that includes the first RF frequency of the first RF signal; an impedance matching circuit coupled between the bandpass filter and the input node; and 1. A plasma processing system comprising: a memory; and a processor coupled to the memory, the memory including instructions that, when executed by the processor, are configured to: monitor a power of a signal reflected from the processing chamber in an RF circulator; and stop generation of the first RF signal in the RF signal generator if the monitored power is equal to or greater than a threshold value for a certain duration.

17. 17. The plasma processing system of claim 15, further comprising a signal filter disposed between the impedance matching circuit and the input node.

18. The plasma processing system of any one of claims 14 to 16, wherein the bandpass filter includes a capacitor and an inductor coupled in parallel.

19. 17. The plasma processing system of claim 14, wherein the bandpass filter includes a distributed constant filter.

20. 17. The plasma processing system of claim 14, wherein the bandpass filter includes a capacitor coupled in series with a first shunt capacitor, a second shunt capacitor, and an inductor, the capacitor and the inductor being coupled between the first shunt capacitor and the second shunt capacitor.

21. The plasma processing system of any one of claims 14 to 16, wherein the bandpass filter has a quality factor of 50 or greater.

22. A plasma processing system as described in any one of claims 14 to 16, further comprising adjusting the center frequency of the bandpass filter having at least one capacitor to match the first RF frequency of the first RF signal, thereby enabling peak power of the first RF signal at the first RF frequency.

23. the RF signal generator is configured to sweep through a range of output frequencies of the first RF signal; the plasma processing system includes: Memory, and further comprising a processor coupled to the memory, the processor and the memory configured to select a frequency from the range of output frequencies that provides a peak power of the first RF signal that passes through the bandpass filter; 17. The plasma processing system of claim 14, wherein the RF signal generator is configured to generate the first RF signal at the selected frequency.

24. Memory, and and a processor coupled to the memory, the memory including instructions that, when executed by the processor, monitoring the power of a signal reflected from the processing chamber at an RF circulator; and 16. The plasma processing system of claim 14, further configured to: stop generating the first RF signal in the RF signal generator if the monitored power is equal to or greater than a threshold value for a certain duration.

25. a voltage source coupled to an input node coupled to an electrode disposed within the processing chamber, the voltage source configured to generate a pulsed voltage signal at the input node; a radio frequency (RF) signal generator having an output, the RF signal generator configured to generate an RF signal superimposed on the pulsed voltage signal at the input node; an RF circulator coupled between the output and the input node of the RF signal generator; Memory, and a processor coupled to the memory, the processor and the memory comprising: monitoring the power of a signal reflected from the processing chamber at the RF circulator; and If the monitored power is equal to or greater than a threshold value for a certain duration, ceasing generation of the RF signal in the RF signal generator.

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