Substrate processing method and apparatus

Abstract

A method and apparatus for processing a substrate are provided. For example, a matching network comprises a first sensor operably connected to the input of the matching network and an RF generator capable of operating at a first frequency, and a second sensor operably connected to the output of the matching network and a plasma processing chamber. The first and second sensors are configured to measure impedance during the pulse-on time of the RF generator. A variable capacitor is connected to the first and second sensors. A controller is configured to adjust at least one variable capacitor of the matching network during the pulse-on time of the RF generator based on an impedance value measured during at least one of the pulse-on or pulse-off states of a pulse voltage waveform generator connected to the matching network, or an RF signal from another RF generator capable of operating at a second frequency different from the first frequency.

Description

Field

[0001] Embodiments of the present disclosure generally relate to substrate processing methods and apparatuses, and for example, to methods and apparatuses for processing a substrate using impedance lock tuning in a pulse voltage generator (PVT). Background

[0002] Methods and apparatuses for processing a substrate using one or more RF power sources in a vacuum processing chamber are known (for example, one or more RF power sources can be configured into single level pulses, dual level pulses, or multi-level pulses). For example, in a single level pulse (for example, a pulse between an on state and an off state), there is only one state to be adjusted (for example, the on state). However, in a dual level pulse, the RF power source is switched between a high state and a low state (for example, not an off state). In a multi-level pulse, the RF power source is switched between multiple states.

[0003] An RF matching network is often connected between an RF power source (RF generator) and a vacuum processing chamber and is configured to efficiently couple the output of the RF power source to the plasma and maximize the amount of energy coupled to the plasma (for example, called tuning of the RF power supply). The minimum reflected power to the RF power source is one criterion for successful tuning by the RF matching network. However, since sidebands return to the RF power source along with the PVT pulse voltage waveform, the reflected power measured at the RF power source may also be caused by pulse-on time, PVT frequency, matching data processing, etc. Therefore, evaluating matching tuning using the reflected power at the RF power source may not function well enough, especially in a PVT chamber. When the RF matching network is tuned to the time-averaged impedance, the RF matching network is tuned to the combination of PVT on-impedance and PVT off-impedance (for example, depending on the matching signal processing setting).

[0004] Accordingly, the inventors herein provide an improved method and apparatus for processing a substrate using impedance-locked tuning in a pulse voltage generator (PVT).

[0005] A substrate processing method and apparatus are provided. For example, in some embodiments, a matching network configured for use in a plasma processing chamber comprises a first sensor operably connected to the input of the matching network and an RF generator capable of operating at a first frequency, and a second sensor operably connected to the output of the matching network and the plasma processing chamber. The first and second sensors may be configured to measure impedance during the pulse-on time of the RF generator. At least one variable capacitor may be connected to the first and second sensors. A controller may be configured to adjust at least one variable capacitor of the matching network during the pulse-on time of the RF generator based on an impedance value measured during at least one of the pulse-on or pulse-off states of a pulse voltage waveform generator connected to the matching network, or an RF signal from another RF generator capable of operating at a second frequency different from the first frequency.

[0006] According to at least some embodiments, the plasma processing chamber comprises a chamber body and a chamber lid, an RF generator operated at a first frequency and connected to the chamber lid and configured to generate plasma from a gas placed within the processing area of ​​the chamber body, and a matching network. The matching network comprises a first sensor operably connected to the input of the matching network and the RF generator, and a second sensor operably connected to the output of the matching network and the plasma processing chamber. The first and second sensors may be configured to measure impedance during the pulse-on time of the RF generator. At least one variable capacitor may be connected to the first and second sensors. The controller may be configured to adjust at least one variable capacitor of the matching network during the pulse-on time of the RF generator based on an impedance value measured during at least one of the pulse-on or pulse-off states of a pulse voltage waveform generator connected to the matching network, or an RF signal from another RF generator operated at a second frequency different from the first frequency.

[0007] According to at least some embodiments, a substrate processing method includes the steps of detecting the pulse-on time of an RF generator in a matching network connected to an RF generator capable of operating at a first frequency, and adjusting at least one variable capacitor in the matching network during the pulse-on time of the RF generator based on an impedance value measured during at least one of the pulse-on or pulse-off states of a pulse voltage waveform generator connected to the matching network, or an RF signal from another RF generator capable of operating at a second frequency different from the first frequency.

[0008] Other embodiments and further embodiments of this disclosure are described below. [Brief explanation of the drawing]

[0009] The embodiments of this disclosure, briefly summarized above and described in more detail below, can be understood by referring to exemplary embodiments of this disclosure shown in the accompanying drawings. However, the accompanying drawings only illustrate typical embodiments of this disclosure and therefore do not limit the scope of this disclosure. This disclosure may also encompass other embodiments that are equally effective. [Figure 1] This is a cross-sectional view of a processing chamber according to at least some embodiments of the present disclosure. [Figure 2] This is a diagram of a system according to at least some embodiments of the present disclosure. [Figure 3] This is a diagram of a harmonized network according to at least some embodiments of the present disclosure. [Figure 4] This is a graph of sampling impedance according to at least some embodiments of the present disclosure. [Figure 5] This is a diagram of a system according to at least some embodiments of the present disclosure. [Figure 6] This is a diagram of the internal synchronization of dual-level pulses according to at least some embodiments of the present disclosure. [Figure 7] This is a diagram of internal synchronization for flexible pulse control according to at least some embodiments of the present disclosure. [Figure 8] This is a flowchart of a substrate processing method according to at least some embodiments of the present disclosure.

[0010] To facilitate understanding, identical elements common to the drawings are given the same reference numeral whenever possible. The drawings are not drawn to scale and may be simplified for clarity. Elements and features of one embodiment can be usefully incorporated into other embodiments without further explanation. Detailed description

[0011] Embodiments of substrate processing methods and apparatus are provided herein. For example, a matching network configured for use in a plasma processing chamber may include a first sensor operably connected to the input of the matching network and an RF generator, and a second sensor operably connected to the output of the matching network and the plasma processing chamber. The first and second sensors are configured to measure impedance during the pulse-on time of the RF generator. At least one variable capacitor may be connected to the first and second sensors. A controller may be configured to adjust at least one variable capacitor of the matching network during the pulse-on time of the RF generator based on an impedance value measured during at least one of the pulse-on or pulse-off states of a pulse voltage waveform generator connected to the matching network. Advantages of the apparatus and methods described herein include, but are not limited to, adjustment to an optimized plasma impedance value to achieve the minimum total reflected power in all states during multilevel pulse generation, faster etching rates when adjusting during operation (e.g., PVF), spatial power distribution and uniformity, and flexibility in defining adjustment targets based on various processes and pulse conditions.

[0012] Figure 1 is a cross-sectional view of an example of a processing chamber 100 suitable for performing the etching process according to this disclosure. Suitable processing chambers that can be adapted to use the teachings disclosed herein include, for example, one or more etching processing chambers available from Applied Materials, Inc., Santa Clara, California. Other processing chambers can also be adapted to benefit from one or more methods of this disclosure.

[0013] The processing chamber 100 includes a chamber body 102 and a chamber lid 104 that enclose an internal volume 106. The chamber body 102 is typically manufactured from aluminum, stainless steel, or other suitable material. The chamber body 102 generally includes side walls 108 and a bottom 110. A substrate support access port (not shown) is typically defined in the side wall 108 and selectively sealed by a slit valve to facilitate the loading and unloading of the substrate 103 into the processing chamber 100. An exhaust port 126 is defined in the chamber body 102 and connects the internal volume 106 to a pump system 128. The pump system 128 generally includes one or more pumps and throttle valves used to evacuate the internal volume 106 of the processing chamber 100 and regulate the pressure. In this embodiment, the pump system 128 typically maintains the pressure in the internal volume 106 at an operating pressure between approximately 1 mTorr and approximately 500 mTorr, between approximately 5 mTorr and approximately 100 mTorr, or between approximately 5 mTorr and approximately 50 mTorr, depending on the needs of the process.

[0014] In one embodiment, the chamber lid 104 is sealed and supported on the side wall 108 of the chamber body 102. The chamber lid 104 can be opened to allow access to the internal volume 106 of the processing chamber 100. The chamber lid 104 includes a window 142 to facilitate optical process monitoring. In one embodiment, the window 142 is made of quartz or other suitable material that transmits signals used by an optical monitoring system 140 installed outside the processing chamber 100.

[0015] The optical monitoring system 140 is positioned to allow observation of at least one of the internal volume 106 of the chamber body 102 and / or the substrate 103 placed on the substrate support assembly 148 through the window 142. In one embodiment, the optical monitoring system 140 is coupled to the chamber lid 104 and enables an integrated deposition process that uses optical measurements to provide information that allows for process adjustments to compensate for discrepancies in features (e.g., thickness) of the incoming substrate pattern and provides process state monitoring (e.g., plasma monitoring, temperature monitoring, etc.) as needed.

[0016] The processing gas and / or cleaning gas can be introduced into the internal volume 106 of the chamber body 102 via a showerhead assembly 130 from a gas panel 158 coupled to the processing chamber 100. A vacuum pump system, such as a pump system 128, maintains the pressure inside the chamber body 102 while removing deposited by-products.

[0017] In some embodiments, a gas panel 158 is provided. In the example shown in Figure 1, the chamber lid 104 is provided with inlet ports 132' and 132'', allowing gas to be supplied from the gas panel 158 to the internal volume 106 of the processing chamber 100. In some embodiments, the gas panel 158 is configured to supply an inert gas such as argon, a processing gas of oxygen and helium, or a gas mixture to the internal volume 106 of the processing chamber 100 via the inlet ports 132' and 132''. In one embodiment, the processing gas supplied from the gas panel 158 includes a processing gas containing at least an oxidizing agent such as oxygen gas. In some embodiments, the processing gas containing an oxidizing agent may further include an inert gas such as argon or helium. In some embodiments, the processing gas may include a reducing agent such as hydrogen and may be mixed with an inert gas such as argon, or other gases such as nitrogen or helium. In some embodiments, chlorine gas can be provided alone or in combination with at least one of an inert gas such as nitrogen, helium, and argon. Non-limiting examples of oxygen-containing gases include one or more of O2, CO2, N2O, NO2, O3, H2O, etc. Non-limiting examples of nitrogen-containing gases include N2, NH3, etc. Non-limiting examples of chlorine-containing gases include HCl, Cl2, CCl4, etc. In the embodiment, the showerhead assembly 130 is coupled to the inner surface 114 of the chamber lid 104. The showerhead assembly 130 includes a plurality of openings, which allow gas to flow from the inlet ports 132', 132'' into the internal volume 106 of the processing chamber 100 via the showerhead assembly 130 in a predetermined distribution across the entire surface of the substrate 103 being processed in the processing chamber 100.

[0018] In some embodiments, the processing chamber 100 can utilize capacitively coupled RF energy for plasma processing, and in some embodiments, the processing chamber 100 can use inductively coupled RF energy for plasma processing. In some embodiments, a remote plasma source 177 is additionally coupled to a gas panel 158 to facilitate the separation of the gas mixture from the remote plasma before it enters the internal volume 106 for processing. In some embodiments, an RF power supply 143 is coupled to a showerhead assembly 130 via a matching circuit 141. The RF power supply 143 typically generates up to about 5000W, for example, about 200W to about 5000W, or 1000W to 3000W, or about 1500W, and can optionally generate an adjustable frequency in the range of about 50kHz to about 200MHz.

[0019] Furthermore, the showerhead assembly 130 includes a region that transmits optical measurement signals. The light-transmitting region or passage 138 is suitable for allowing the optical monitoring system 140 to observe the substrate 103 placed on the internal volume 106 and / or substrate support assembly 148. The passage 138 may be one or more openings formed or disposed within the showerhead assembly 130, made of a material that substantially transmits the wavelength of energy generated by and reflected to the optical monitoring system 140. In one embodiment, the passage 138 includes a window 142 to prevent gas leakage through the passage 138. The window 142 may be a sapphire plate, a quartz plate, or other suitable material. Alternatively, the window 142 may be located on the chamber lid 104.

[0020] The showerhead assembly 130 can consist of multiple zones that allow for individual control of the gas flowing into the internal volume 106 of the processing chamber 100. In the example shown in Figure 1, the showerhead assembly 130 consists of an inner zone 134 and an outer zone 136, which are individually coupled to the gas panel 158 via inlet ports 132', 132''.

[0021] The substrate support assembly 148 is positioned within the internal volume 106 of the processing chamber 100, below the gas distribution assembly, such as the showerhead assembly 130. The substrate support assembly 148 holds the substrate 103 during processing. The substrate support assembly 148 typically includes several lift pins (not shown) through which the substrate 103 is lifted from the substrate support assembly 148, facilitating the replacement of the substrate 103 by a robot (not shown) in a conventional manner. An inner liner 118 can closely surround the substrate support assembly 148.

[0022] The substrate support assembly 148 includes a mounting plate 162, a base 164, and an electrostatic chuck 166. The mounting plate 162 is coupled to the bottom 110 of the chamber body 102 and includes passages for routing utilities such as fluids, power lines, and sensor leads to the base 164 and the electrostatic chuck 166. The electrostatic chuck 166 is equipped with electrodes 180 (e.g., clamp electrodes) for holding the substrate 103 below the showerhead assembly 130. The electrostatic chuck 166 is driven by a chuck power supply 182, as is conventionally known, to generate electrostatic force to hold the substrate 103 on the chuck surface. Alternatively, the substrate 103 may also be held to the substrate support assembly 148 by clamping, vacuum, or gravity.

[0023] The base 164 or the electrostatic chuck 166 includes a heater 176, at least one optional embedded isolator 174, and a plurality of conduits 168, 170, and can control the lateral temperature profile of the substrate support base assembly 148. The conduits 168, 170 are fluidly coupled to a fluid source 172 that circulates a temperature-regulating fluid. The heater 176 is controlled by a power source 178. The conduits 168, 170 and the heater 176 are used to control the temperature of the base 164, heat and / or cool the electrostatic chuck 166, and ultimately control the temperature profile of the substrate 103 disposed thereon. The temperatures of the electrostatic chuck 166 and the base 164 can be monitored using a plurality of temperature sensors 190, 192. Further, the electrostatic chuck 166 can include a plurality of gas passages (not shown), such as grooves, formed on the substrate support base support surface of the electrostatic chuck 166 and fluidly coupled to a heat transfer (or backside) gas source such as helium (He). During operation, the backside gas is supplied to the gas passages at a controlled pressure to improve heat transfer between the electrostatic chuck 166 and the substrate 103. In an embodiment, the temperature of the substrate can be maintained between 20°C and 450°C, for example, between 100°C and 300°C, or between 150°C and 250°C.

[0024] The substrate support base assembly 148 can be configured as a cathode assembly and includes electrodes 180 coupled to a plurality of RF bias power supplies 184, 186. The RF bias power supplies 184, 186 are coupled between an electrode 180 disposed within the substrate support base assembly 148 and another electrode such as the showerhead assembly 130 (or the chamber lid 104) of the chamber body 102. The RF bias power excites and maintains a plasma discharge formed from a gas disposed within the processing region of the chamber body 102.

[0025] Continuing to refer to FIG. 1, in some embodiments, the dual RF bias power supplies 184, 186 are coupled to the electrodes 180 disposed within the substrate support assembly 148 via a matching network 188. The signals generated by the RF bias power supplies 184, 186 are sent to the substrate support assembly 148 in a single feed via the matching network 188 to ionize the gas mixture provided within a plasma processing chamber such as the processing chamber 100. This provides the ion energy necessary to perform etching deposition and other plasma enhanced processes. Generally, the RF bias power supplies 184, 186 can generate RF signals having a frequency of about 50 kHz to about 200 MHz (e.g., about 13.56 MHz ± 5%) and a power of about 0 watts to about 10,000 watts (e.g., about 50 W for low power operation and about 10,000 W for high power operation), 1 watt (W) to about 100 W, or about 1 W to about 30 W. Additional bias power can be connected to the electrode 180 to control the characteristics of the plasma.

[0026] In at least some embodiments, the impedances at the input and output ports of the matched network 188 and / or matched network 141 can be measured in all states of a multilevel pulse. The impedances at the input and output ports of the matched network can be used to determine weighted input and output impedances for tuning. For example, the apparatus and method described herein uses weighted average tuning in a multilevel pulse. In at least some embodiments, for feedforward tuning, a weighted combination of measured output impedances can be selected, and the weighted impedance can be defined from the measured input impedances in a multilevel pulse state. Furthermore, in at least some embodiments, for hybrid tuning, frequency tuning can be used in combination with weighted average tuning. The matched network described herein can receive a TTL synchronization signal from an RF generator and / or an advanced waveform generator 202 (advanced voltage waveform generator), as will be described in more detail below. Alternatively or additionally, the matched network can receive a TTL synchronization signal that is internally triggered by the rising or falling edge of a detected pulse.

[0027] The controller 150 is connected to the processing chamber 100 and controls the operation of the processing chamber 100. The controller 150 includes a central processing unit 152, memory 154, and support circuits 156, which are used to control the processing sequence and adjust the gas flow rate from the gas panel 158. The central processing unit 152 may be any form of general-purpose computer processor available for use in an industrial environment. Software routines can be stored in the memory 154, such as random access memory, read-only memory, floppy disks, hard disk drives, or other forms of digital storage devices. The support circuits 156 are connected to the central processing unit 152 in a conventional manner and may include a cache, clock circuit, input / output system, power supply, etc. Bidirectional communication between the controller 150 and the various components of the processing chamber 100 is performed via a number of signal cables.

[0028] Figure 2 is a diagram of System 200 according to at least some embodiments of the present disclosure.

[0029] For example, in at least some embodiments, one or more RF power supplies (e.g., RF bias power supply 184 and / or RF source power supply 143) can be configured to supply RF power for plasma generation to the RF base plate of the cathode assembly (e.g., electrostatic chuck 166). In such embodiments, the upper electrode (e.g., showerhead assembly 130 (or chamber cover 104)) can be grounded. The frequency of one or more RF power supplies can range from 13.56 MHz to an ultra-high frequency band such as 60 MHz, 120 MHz, or 162 MHz. Also, in at least some embodiments, one or more RF power supplies can be supplied via the upper electrode. One or more RF power supplies can operate in continuous mode or pulsed mode. For example, in pulsed mode, the pulse frequency is 100 Hz to about 10 kHz, and the duty cycle is about 5% to about 95%.

[0030] To optimize power supply efficiency, an RF impedance matching network (e.g., matching network 188 and / or matching network 141) is connected between one or more RF power supplies and the processing chamber 100. This matching network is configured for use in plasma processing chambers such as, for example, a physical vapor deposition chamber, a chemical vapor deposition chamber, an atomic layer deposition chamber, an etching chamber, or other processing chambers that use a matching network. For illustrative purposes, this specification describes the matching network (e.g., matching network 141 and / or matching network 188) in relation to an etching chamber, such as the processing chamber 100.

[0031] The matching network includes an input stage 201 connected to one or more RF power supplies (e.g., RF bias power supplies 184, 186) of the plasma processing chamber and configured to receive one or more high-frequency (RF) signals. The matching network also includes an output stage 203 connected to a substrate support assembly (e.g., substrate support assembly 148) of the processing chamber and configured to transmit one or more RF signals to the processing chamber.

[0032] The matching network includes one or more variable (adjustable) capacitors, such as a first variable capacitor 205 (e.g., a series variable capacitor) and a second variable capacitor 207 (e.g., a shunt variable capacitor), which can be connected in series or in parallel. Each of the first variable capacitor 205 and the second variable capacitor 207 has a variable capacitance that can be adjusted to one or more frequencies. For example, in at least some embodiments, the capacitances of the first variable capacitor 205 and the second variable capacitor 207 can range from about 3 pF to about 2500 pF. In at least some embodiments, when the processing chamber is operating in a high-power or low-power state, the first variable capacitor 205 and the second variable capacitor 207 can be adjusted to one or more of the aforementioned frequencies, for example, target frequency ±10% and target frequencies from 100 kHz to about 250 MHz.

[0033] In at least some embodiments, one or more additional capacitors, inductors, transistors, etc. (not shown) may be provided and connected in parallel and / or series with the first variable capacitor 205 and the second variable capacitor 207.

[0034] The first variable capacitor 205 and the second variable capacitor 207 may be the same or different from each other. In at least some embodiments, the first variable capacitor 205 may be connected to the output stage 203 and the second variable capacitor 207 may be connected to the input stage 201, or vice versa.

[0035] In at least some embodiments, one or more RF filters can be connected to the matching network to allow power in a selected frequency range and to isolate RF power supplies from each other. For example, in at least some embodiments, an RF filter 204 (RF circulator) used to regulate and isolate power flow between ports is connected to the matching network 188 and / or the substrate support assembly 148 and / or the RF bias power supply 184 and the matching network 188. In the latter case, a dummy load 210 can be connected to the RF filter 204 to direct reflected power to the dummy load 210.

[0036] In at least some embodiments, the advanced waveform generator 202 can be used to supply one or more waveforms (e.g., pulse voltage waveforms and / or regulated voltage waveforms (which may be the sum of harmonic frequencies associated with the regulated voltage waveform)). One or more voltage waveforms can be coupled to bias electrodes (e.g., electrodes 180 of the substrate support assembly 148) via one or more filter assemblies. For example, in at least some embodiments, an RF filter 206 is connected to the advanced waveform generator 202 and electrodes 180. The advanced waveform generator 202 is connected to a matching network 188 and can output a synchronization signal to the matching network 188. For example, in at least some embodiments, the synchronization signal can generate a transistor-transistor logic (TTL) 209 signal, which will be described in more detail below. Alternatively or additionally, the RF power supply can be configured to output a synchronization signal to the matching network 188. Alternatively or additionally, the matching network 188 can be configured to generate an internal synchronization signal, which will be described in more detail below.

[0037] Figure 3 shows a harmonized network 188 configured for use in a processing chamber 100 according to at least some embodiments of the present disclosure. In at least some embodiments, the harmonized network 188 can be an L-type or pi-type harmonized network.

[0038] The harmonized network 188 consists of a local controller, one or more sensors, and one or more electric capacitors, all connected via EtherCAT (shown as dashed line 301). EtherCAT is a real-time industrial Ethernet protocol that provides fast and accurate synchronization during plasma processing due to its short cycle time and low jitter. One or more other interfaces can be used to interconnect the components of the harmonized network 188 and to connect the RF generator and the plasma processing chamber to the harmonized network 188. For example, RF power can be supplied to the plasma processing chamber by using transmission line 303 (shown as solid line) to connect the RF generator to the harmonized network 188 and the harmonized network 188 to the plasma processing chamber.

[0039] In at least some embodiments, the local controller 300 functions as a local EtherCAT master, and all network components (e.g., sensors, electric capacitors) are EtherCAT slave devices controlled by the local controller 300. For example, commands sent from the local controller 300 (e.g., the EtherCAT master controller) are sent to all EtherCAT slave devices. A first electric capacitor 302 (vacuum capacitor) with an EtherCAT interface can be connected to the local controller 300 and a second electric capacitor 304 (vacuum capacitor) with an EtherCAT interface. The first electric capacitor 302 can be connected in series or parallel to the second electric capacitor 304. For example, in the illustrated embodiment, the first electric capacitor 302 (e.g., a shunt variable capacitor) is connected in parallel with the second electric capacitor 304 (e.g., a series variable capacitor). The first electric capacitor 302 and the second electric capacitor 304 are electric variable capacitors and are configured to be adjusted during operation. For example, the local controller 300 can be configured to adjust the first motorized capacitor 302 and the second motorized capacitor 304 in order to minimize reflected power during plasma processing.

[0040] The local controller 300 is connected (directly or indirectly) to the first sensor 306 located on the input side of the matching network 188 and the second sensor 308 (when in use) located on the output side of the matching network 188, and can acquire inline RF voltage, current, phase, harmonics, and impedance data, respectively. In at least some embodiments, the first sensor 306 and the second sensor 308 may be multi-frequency voltage / current probes. The measurement data can be used for automatic impedance adjustment, load impedance monitoring, etc.

[0041] In at least some embodiments, the interlock circuit 307 can be connected to the local controller 300 and configured to prevent failure of the RF generator. For example, the interlock circuit 307 may include a fault protection circuit configured to shut off the RF power output from the RF generator when the reflected RF power exceeds a certain percentage (e.g., more than 20%) of the forward power (RF power sent from the RF generator through the matching network 188 to the load (e.g., plasma in the processing chamber)).

[0042] As described above, the EtherCAT communication interface connects the local controller 300 to the first motorized capacitor 302, the second motorized capacitor 304, the first sensor 306, and the second sensor 308. The EtherCAT communication interface connects an RF generator (e.g., RF bias power supplies 184, 186 (and / or RF bias power supply 189)) directly to each of the first sensor 306 and the second sensor 308, and transmits a TTL signal 305 from the RF generator to each of the first sensor 306 and the second sensor 308, for example, fast response and short adjustment time.

[0043] In at least some embodiments, the local controller 300 connected to the RF generator and plasma processing chamber is configured as an EtherCAT master device to control and monitor local EtherCAT slave devices such as sensors and stepping motors. Alternatively, the local controller 300 is integrated with an EtherCAT slave controller, so that the local controller 300 functions as an EtherCAT slave device and the controller 150 functions as an EtherCAT master device. That is, the local controller 300 is configured to perform master / slave conversion with the controller 150. The tool controller may be implemented on an industrial computer and may have the necessary drivers built in. In such embodiments, the local controller 300 can receive feedback requests from the controller 150 during plasma processing and provide feedback to the controller 150. For example, the local controller 300 can receive inline RF voltage, current, phase, harmonics, and impedance data acquired via the first sensor 306 and the second sensor 308. Sensor data and the position of the variable capacitor are transmitted to the controller 150 and combined with other system processing data such as forward power data and reflected power data from the RF bias power supplies 184 and 186, enabling cooperative, intelligent, real-time control during operation.

[0044] The harmonized network 188 may include at least one of a first network port 310 (e.g., dual RJ45 ports) configured to connect to a controller 150, and a second serial port configured to connect to an external computing device (e.g., a laptop or other suitable computing device) for manual control of the harmonized network 188. For example, in at least some embodiments, the controller 150 can be connected to the first network port 310 of the harmonized network 188 for plasma process control. The local controller 300 can receive inline RF voltage, current, phase, harmonic, and impedance data acquired via the first sensor 306 and the second sensor 308. The sensor data and the position of the variable capacitor are transmitted to the controller 150 and combined with other system processing data, such as forward and reflected power data from the RF bias power supplies 184 and 186, to enable cooperative intelligent real-time control during operation. In at least some embodiments, the harmonized network 188 may include a second serial port 312 configured to connect to a computing device 314 for uploading algorithms and for manual control of the harmonized network using, for example, external software and an application programming interface (API). In at least some embodiments, external software and APIs are uploaded, stored in memory 154, and can be accessed from the memory (not shown) of the controller 150 and / or the local controller 300. In at least some embodiments, sensor data obtainable from the first sensor 306 and the second sensor 308 can be accessed from a computing device 314. Furthermore, the computing device 314 connected to the second serial port 312 can be configured to control the first electric capacitor 302 and the second electric capacitor 304. The inclusion of the first network port 310 and the second serial port 312 significantly improves the flexibility of the harmonized network 188 compared to conventional harmonized networks.For example, advanced process-related control algorithms can be deployed in real time, and the harmonized network 188 can operate fully autonomously, in conjunction with the controller 150, and / or manually controlled via the computing device 314. During processing, if necessary, the EtherCAT-based distributed RF impedance harmonized network described herein allows the user to use the computing device 314 to fully control the harmonized network 188 and its associated components.

[0045] Figure 4 is a graph 400 of sampling impedance according to at least some embodiments of the present disclosure. For example, in at least some embodiments, a voltage waveform or RF power pulse applied to a substrate (e.g., substrate 103) in a processing chamber 100 may include two stages. The impedance of the plasma sheath changes in accordance with the supplied pulse voltage waveform and RF power pulse, and the matching network 188 monitors the TTL synchronous signal from the waveform generator 202 or RF power supply. For example, in a pulse cycle, the matching network 188 may collect two or more pulse data points to collect impedance at different stages. In at least some embodiments, a first data sample may be collected for impedance Z1 in a first stage (e.g., 404 corresponding to the sheath collapse stage), and a second data sample may be collected for impedance Z2 in a second stage (e.g., 402 corresponding to the ion current stage). The collected data samples can be used to obtain a weighted impedance value. In at least some embodiments, the data samples need to be collected after a time delay defined, for example, based on the pulse frequency, duty cycle, and / or the rising edge of the TTL synchronous signal.

[0046] In at least some embodiments, a high-voltage DC power supply 208 can be used to supply power to the electrode 180 that chucks the substrate (e.g., wafer) during processing, and thermal control can be performed. In at least some embodiments, a third electrode (not shown) can be provided on the edge of the cathode assembly for edge uniformity control. In such embodiments, a third low-frequency RF power supply in the frequency range of 50 kHz to 2 MHz can be supplied to the edge electrode and operated in continuous mode.

[0047] Figure 5 shows a diagram of System 500 according to at least some embodiments of the present disclosure. System 500 is substantially identical to System 200. Therefore, only features specific to System 500 will be described herein.

[0048] For example, one or more RF power supplies (e.g., RF power supply 143) are connected to the upper electrode for plasma generation. The frequency of one or more RF power supplies can operate in the range of approximately 13.56 MHz to approximately 200 MHz, for example, 60 MHz, 120 MHz, or 162 MHz, as needed. One or more RF power supplies can operate in continuous mode or pulsed mode. The pulse frequency is in the range of 100 Hz to approximately 10 kHz, and the duty cycle is in the range of approximately 5% to approximately 95%. An RF bias power supply (e.g., RF bias power supply 184) is connected to the lower electrode at a frequency in the range of approximately 100 kHz to approximately 15 MHz. The RF bias power supply can operate in continuous mode or pulsed mode. The pulse frequency is 100 Hz to 10 kHz, and the duty cycle can be approximately 5% to approximately 95%. One or both of the RF power supply 143 and the RF bias power supply can be configured to transmit synchronous TTL signals to matching network 141 and matching network 188, respectively. As mentioned above, a third electrode can be used on the edge of the cathode assembly for edge uniformity control. In such embodiments, a third low-frequency RF power in the frequency range of 50 kHz to 2 MHz can be supplied to the edge electrode and operated in continuous mode. Similar to system 200, the RF filter can be connected to a matching network 188 (not shown), and can be connected to a matching network 141 and a high-voltage DC power supply 208. In at least some embodiments, the RF filter can be connected to the matching network 188.

[0049] Figure 6 shows internal synchronization for dual-level pulsing according to at least some embodiments of the present disclosure. For example, as described above, a trigger signal can be generated externally (e.g., via one or more RF power supplies or advanced waveform generators) or internally (e.g., via a matching network) to obtain impedance values ​​for determining a weighted average. In the latter embodiment, voltage and current sensors (e.g., first sensor 306 and second sensor 308) of the matching network are configured to internally detect the start of the pulse signal. The voltage and current sensors can detect multiple impedance samples during the pulse period. For example, at the start of the trigger signal, and at first and second sample times typically defined with respect to the rising edge of the pulse, multiple impedances can be measured at the same pulse level or at different levels and can be used in the weighted average adjustment algorithm. Thus, the matching network uses the weighted impedance obtained from all measured samples at the same pulse level or at different levels.

[0050] The collected data samples can be measured in pulses or averaged from multiple pulses. For example, a threshold 601 for pulse detection can be defined. The threshold 601 can be set between two pulse state levels. The start of a pulse is detected when the voltage measured by a sensor (not shown) exceeds the threshold 601. In at least some embodiments, sample 1 and sample 2 can be obtained from different pulses. In at least some embodiments, sample 1 and sample 2 may be the average of a number of pulse data points collected from multiple pulses. For example, in at least some embodiments, to calculate the average, the high state of a pulse can be measured 10 times with 10 pulses to obtain average sample 1, and the low state of a pulse can be measured 10 times with the same or different pulses to obtain average sample 2. Measurement of data points starts after a delay of a first sample time and a second sample time from the start of the pulse. The first and second sample times determine when the measurement takes place within the pulse.

[0051] For example, the first data sample 602 and the second data sample 604 can be acquired in a high state and a low state, respectively, by defining the first pulse time and the second pulse time with respect to a trigger signal, such as the rising edge 606 of a pulse.

[0052] The inventors have found that the plasma load impedance can be changed in response to multilevel pulse conditions depending on the power levels and combinations of the RF power supplies (e.g., RF bias power supply 184 and RF source power supply 143). Furthermore, vacuum capacitor motors commonly used in conventional matching networks cannot respond (e.g., move) fast enough within the pulse period, and conventional matching networks cannot adjust both impedances simultaneously.

[0053] Accordingly, the inventors provide weighted combinations of impedances (e.g., various impedance samples obtained via either an external or internal trigger) in single-level or multi-level pulses. For example, in a dual-level pulse, a first impedance Z1 can be measured at a first pulse level during a first sampling time, and a second impedance Z2 can be measured at a second pulse level during a second sampling time, using either or both an external or internal trigger. The weighted target impedance can then be calculated using equation (1). Z W =Z1*W+Z2*(1-W), where W ranges from 0 to 1... (1)

[0054] Here, W is a weight value between 0 and 1. In at least some embodiments, a multi-state weighting algorithm may also be available, in which case more weight values ​​may be required. For example, W1 and W2 may be weight values ​​when a 3-level pulse is generated. During operation, the weighted target impedance of the matched network described herein changes depending on the weight values ​​in the two impedance states. For example, when W is 0, the matched network is tuned to an impedance equal to the second level of the pulse. When W is 1, the matched network is tuned to an impedance equal to the first level.

[0055] In at least some embodiments, the optimized W value can be determined based on the minimum total reflected power in both states. For example, the reflected power changes in response to changes in the weight value in a two-stage pulse. For instance, the reflected power may be minimized at W=1 in the first level and at W=0 in the second level. For example, the total reflected power in both states is minimized when W=0.8. Other criteria can also be used to select appropriate weight values.

[0056] Similarly, the matched network provides a measured and weighted output impedance in dual-level (or multi-level) pulses. For example, the plasma load impedance changes with the pulse power level, the on / off state of the bias power, or the pulse voltage waveform. Thus, Z1 and Z2 can be the measured impedance at the output of the matched network, either through external or internal synchronization. As mentioned above, since motors in conventional matched networks cannot keep up with rapidly changing impedance states, the weighted output impedance can be calculated and used as the target plasma load impedance. For example, in at least some embodiments, the weighted impedance at the output of the matched network can be used as a tuning target in a feedforward tuning algorithm.

[0057] In at least some embodiments, the weighted input impedance and weighted output impedance can be stored in a lookup table (e.g., in memory 154) or a circuit model can be used to directly move the variable capacitor in the RF match to the target position. In some embodiments, a learning-based tuning algorithm can be employed to determine the appropriate weighted target impedance at the input and / or output of the RF match.

[0058] Figure 7 shows internal synchronization for flexible pulse control according to at least some embodiments of the present disclosure. For example, the inventors have found that during operation, a matching network (e.g., matching network 188) can be configured to perform impedance measurements (e.g., impedance lock tuning) during the pulse-on and / or pulse-off times of the advanced waveform generator 202. For example, the matching network 188 can perform impedance measurements in one or more time slots (e.g., data windows) corresponding to the pulse-on and / or pulse-off times of the advanced waveform generator 202. One or more slots are flexible and can have variable width and storage for multilevel pulsed operation. In at least some embodiments, one or more slots can have a slot time of about 10 ns to about 100 μs and a slot width of about 0.1 μs to about 50 μs. In at least some embodiments, the matching network 188 can be configured to perform impedance measurements only during the pulse-on time 702 of the advanced waveform generator 202. For example, the matching network 188 can use slot 706, which corresponds only to the pulse-on time 702(Z1) of the advanced waveform generator 202. The time and width of slot 706 fall within the range of the on-state 708 of the TTL logic signal received from the RF bias power supplies 184 and 186. The on-state of the TTL logic signal corresponds to the sheathless state in 402 (measurement performed at a relatively high impedance). Additionally or alternatively, in at least some embodiments, the matching network 188 can use slot 710 (which may be different from or the same as slot 706), which corresponds only to the pulse-off time 704(Z2) of the advanced waveform generator 202. The time and width of slot 710 fall within the range of the off-state 712 of the TTL logic signal received from the RF bias power supplies 184 and 186. The off-state 712 of the TTL logic signal corresponds to the sheath-collapsed state in 404 (relatively low impedance).When impedance measurements are performed only during the pulse-on time 702 (or pulse-off time 704), the matching network 188 tunes and synchronizes with the pulse-on time 702 and / or pulse-off time 704 of the advanced waveform generator 202, resulting in a higher etching rate compared to a tuning-time averaged impedance measurement. Slots 706 and 710 can be changed based on at least one of the following: the pulse-on and pulse-off states of the advanced waveform generator 202 (e.g., 5% to approximately 95% of the pulse-on and pulse-off states), the pulse frequency of the advanced waveform generator 202 (e.g., 10kHz to approximately 500kHz), the duty cycle of the RF bias power supply (e.g., approximately 1% to approximately 99% of the RF generator duty cycle), or the pulse frequency of the RF bias power supply (1Hz to approximately 500kHz). Furthermore, during tuning, the matching network 188 can repeat impedance measurements and average the impedance values.

[0059] In addition or alternatively, in at least some embodiments, the matching network 188 can use slots 714 corresponding to the pulse-on time 702 and pulse-off time 704 of the advanced waveform generator 202. The time and width of slot 714 are adapted to span one or more on-states 708 and off-states 712 of the TTL logic signals received from the RF bias power supplies 184 and 186. In such embodiments, the matching network can use weighted average calculations (Z1 and Z2) as described above.

[0060] In at least some embodiments, for example, when the RF bias power supply uses a multilevel pulse signal, the matching network 188 can be tuned to the rising or falling edge of the multilevel pulse signal. For example, the matching network can be tuned to the first level of the multilevel pulse signal using slot 706 and to the second level of the multilevel pulse signal using slot 710 (which may be different from or the same as slot 706).

[0061] In at least some embodiments, for example, when the advanced waveform generator 202 is not used and a second RF bias power supply (e.g., RF bias power supply 186) is used in conjunction with RF bias power supply 184, two matching networks 188 (e.g., two independent matching networks) can be configured to perform impedance matching as described above. For example, an RF bias power supply 186, which can operate at frequencies from approximately 100 kHz to approximately 20 MHz, can be connected to the first matching network, and an RF bias power supply 184, which can operate at frequencies from approximately 10 MHz to approximately 180 MHz, can be connected to the second matching network. The first and second matching networks can each operate with respect to the matching network 188 as described above. Furthermore, in embodiments, when two RF bias power supplies are used, the advanced waveform generator 202 can be used with one or both of the RF bias power supplies as described above.

[0062] Figure 8 shows a flowchart of a substrate processing method 800 according to at least some embodiments of the present disclosure. For illustrative purposes, the method 800 is described herein using an example in which a substrate 103 is etched using a processing chamber 100.

[0063] In 802, method 800 includes detecting the pulse on-time of an RF generator capable of operating at a first frequency using a matching network connected to the RF generator. For example, the matching network 188 can receive a TTL synchronization signal from an RF bias power supply 184 (capable of operating at pulse frequencies from approximately 1 Hz to approximately 500 kHz) or an advanced waveform generator 202, and / or a TTL synchronization signal that is internally triggered on the rising or falling edge of the detected pulse.

[0064] Next, in 804, method 800 includes adjusting at least one variable capacitor of the matching network during the pulse-on time of an RF generator, based on an impedance value measured during at least one of the pulse-on or pulse-off states (e.g., pulse-on state and / or pulse-off state of the pulse-voltage waveform generator) of a pulse-voltage waveform generator connected to a matching network (e.g., matching network 188), or an RF signal from another RF generator capable of operating at a second frequency different from the first frequency (e.g., RF bias power supply 186 operates at a frequency of approximately 100 kHz to approximately 20 MHz). For example, in at least some embodiments, the matching network 188 may measure impedance values ​​in slots for performing impedance measurements corresponding to the pulse-on time (e.g., measured during the pulse-on time of the advanced waveform generator 202) and / or the pulse-off time (e.g., measured during the pulse-off time of the advanced waveform generator 202). A variable capacitor (e.g., a second motorized capacitor 304) can be lock-tuned based on output impedance and input impedance values ​​measured only when the advanced waveform generator 202 is pulse-on. Similarly, a variable capacitor (e.g., a second motorized capacitor 304) can be lock-tuned based on output impedance and input impedance values ​​measured only when the advanced waveform generator 202 is pulse-off. In at least some embodiments, when more RF power is applied, the variable capacitor (e.g., a second motorized capacitor 304) can be lock-tuned to a combination of pulse voltage waveforms, and for example, by using a customized sensor data acquisition window, the matched network 188 can be lock-tuned to a specific impedance under different power combination conditions.

[0065] Similarly, when two RF bias power supplies are used together (for example, with or without the waveform generator 202), each matching network connected to each RF bias power supply can be configured to measure impedance using the method described above. In at least some embodiments, each matching network can communicate the measured impedance to each other when adjusting the variable capacitor. In at least some embodiments, since the signal of RF bias power supply 186 is substantially an infinite sine wave, the measurement slot time (window) of RF bias power supply 186 can measure impedance Z using a relatively short measurement slot time within a selected range (for example, the measurement slot time can correspond to the peak (and / or trough) of the signal of RF bias power supply 186). Alternatively or additionally, since the on-time of the RF bias power pulse is typically longer than the measurement slot time, in at least some embodiments, the matching network can adjust synchronization using the time-averaged impedance Z (see Equation 1 above).

[0066] In at least some embodiments, at least one capacitor may include two variable capacitors (e.g., a first electric capacitor 302 and a second electric capacitor 304). In such embodiments, at least two variable capacitors can be adjusted simultaneously or at different times.

[0067] In at least some embodiments, for example, when the second sensor 308 is not used, the variable capacitor can be adjusted based on the output impedance stored in a lookup table (e.g., in memory 154) or a circuit model.

[0068] In at least some embodiments (e.g., a single-level pulsed signal configuration including an RF signal provided by an RF bias power supply, an RF signal provided by an RF source power supply, and / or a pulsed voltage waveform), the impedance value can only be obtained from the pulse-on or pulse-off state of the advanced waveform generator 202. Furthermore, the first and second sample times may be the same or different, based on the pulse frequency, duty cycle, or rising edge of a transistor-to-transistor logic (TTL) synchronous signal.

[0069] Similarly, in at least some embodiments (e.g., a multilevel pulsed signal configuration including at least one RF signal and / or pulsed voltage waveform provided by an RF power supply), impedance values ​​can be acquired in high-level and low-level pulse stages. In such embodiments, the high-level pulse stage is acquired at a first sample time, and the low-level pulse stage is acquired at a second sample time different from the first sample time. Furthermore, the first and second sample times are triggered after a delay from the start of the detected pulse when the voltage of the measured pulse exceeds a threshold.

[0070] In at least some embodiments, for example, when a pulse voltage waveform generator is used, the matching network 188 may be configured to adjust at least one variable capacitor based on pulse-on state sideband data of the pulse voltage waveform generator reflected to the RF bias power supply 184. Alternatively or additionally, in at least some embodiments, for example, when impedance matching is performed during the pulse-off state of the pulse voltage waveform generator, the matching network 188 is configured to adjust at least one variable capacitor based on nominal sideband data reflected to the RF bias power supply 184.

[0071] The calculated impedance value is stored in memory 154 and is automatically accessed by controller 150 during operation of 804 to adjust the first variable capacitor and / or the second variable capacitor to the weighted target impedance value.

[0072] The foregoing applies to embodiments of the present disclosure, but other embodiments and further embodiments of the present disclosure can be created without departing from the fundamental scope of the present disclosure.

Claims

1. A matching network configured for use in a plasma processing chamber, A first sensor operably connected to the input of a matched network and an RF generator capable of operating at a first frequency, and a second sensor operably connected to the output of the matched network and a plasma processing chamber, the first and second sensors configured to measure impedance during the pulse-on time of the RF generator, A variable capacitor connected to the first sensor and the second sensor, A matched network comprising a controller configured to adjust at least one variable capacitor of the matched network during the pulse-on time of an RF generator, based on an impedance value measured during at least one of the pulse-on or pulse-off states of a pulse voltage waveform generator connected to the matched network, or an RF signal from another RF generator capable of operating at a second frequency different from a first frequency.

2. The matching network according to claim 1, wherein the controller is configured to adjust at least one variable capacitor of the matching network during the pulse-on or pulse-off state of the pulse voltage waveform generator, and the time slots for performing impedance measurements during the pulse-on and pulse-off states are based on at least one of the pulse-on time of the pulse voltage waveform generator, the pulse-off time of the pulse voltage waveform generator, the pulse frequency of the pulse voltage waveform generator, the duty cycle of the RF generator, or the pulse frequency of the RF generator.

3. The matching network according to claim 2, wherein the pulse-on and pulse-off time slots are based on the ratio of pulse-on time and / or pulse-off time of the pulse voltage waveform generator, the ratio being approximately 5% to approximately 95%.

4. The matching network according to claim 2, wherein the pulse-on and pulse-off time slots are based on the pulse frequency of the pulse voltage waveform generator, and the pulse frequency of the pulse voltage waveform generator is approximately 10 kHz to approximately 500 kHz.

5. The harmonized network according to claim 2, wherein the pulse-on and pulse-off time slots are based on the duty cycle of the RF generator, and the duty cycle of the RF generator is approximately 1% to approximately 99%.

6. The matching network according to claim 2, wherein the pulse-on and pulse-off time slots are based on the pulse frequency of the RF generator, and the pulse frequency of the RF generator is approximately 1 Hz to approximately 500 kHz.

7. The matching network according to claim 2, wherein the resolution of the time slots for the pulse-on state and pulse-off state is approximately 10 ns to approximately 100 μs.

8. The matching network according to claim 2, wherein the time slot widths for the pulse-on state and pulse-off state are approximately 0.1 μs to approximately 50 μs.

9. The matching network according to any one of claims 1 to 8, wherein the controller is further configured to adjust at least one variable capacitor based on pulse-on sideband data.

10. The matching network according to any one of claims 1 to 8, wherein the controller is further configured to adjust at least one variable capacitor of the matching network during operation based on an impedance value measured during the pulse-on state.

11. The matching network according to any one of claims 1 to 8, wherein the controller is further configured to adjust at least one variable capacitor of the matching network during operation based on an impedance value measured during the pulse-off state.

12. The matching network according to claim 1, wherein the controller is configured to adjust at least one variable capacitor of the matching network in the RF signal of another RF generator, and the time slot for performing impedance measurements is based on a selected range corresponding to at least one peak or trough of the RF signal.

13. A harmonized network according to any one of claims 1 to 8 or 12, wherein one RF generator operates at a frequency of approximately 10 MHz to approximately 180 MHz, and another RF generator operates at a frequency of approximately 100 kHz to approximately 20 MHz.

14. A plasma processing chamber, Chamber body and chamber lid, A first frequency-operable RF generator connected to the chamber lid and configured to generate plasma from gas placed within the processing area of ​​the chamber body, It is a harmonized network, A first sensor operably connected to the input of a matched network and an RF generator, and a second sensor operably connected to the output of a matched network and a plasma processing chamber, the first sensor and the second sensor configured to measure impedance during the pulse-on time of the RF generator, A variable capacitor connected to the first sensor and the second sensor, A plasma processing chamber comprising a matched network, the controller configured to adjust at least one variable capacitor of the matched network during the pulse-on time of an RF generator, based on an impedance value measured during at least one of the pulse-on or pulse-off states of a pulse voltage waveform generator connected to the matched network, or an RF signal from another RF generator capable of operating at a second frequency different from a first frequency.

15. Plasma processing chamber according to claim 14, wherein the controller is configured to adjust at least one variable capacitor of the matching network during the pulse-on or pulse-off state of the pulse voltage waveform generator, the time slots for performing impedance measurements during the pulse-on and pulse-off states are based on at least one of the pulse-on time of the pulse voltage waveform generator, the pulse-off time of the pulse voltage waveform generator, the pulse frequency of the pulse voltage waveform generator, the duty cycle of the RF generator, or the pulse frequency of the RF generator.

16. The plasma processing chamber according to claim 15, wherein the pulse-on and pulse-off time slots are based on the ratio of pulse-on time and / or pulse-off time of the pulse voltage waveform generator, the ratio being approximately 5% to approximately 95%.

17. The plasma processing chamber according to claim 15, wherein the time slots for the pulse-on and pulse-off states are based on the pulse frequency of the pulse voltage waveform generator, and the pulse frequency of the pulse voltage waveform generator is approximately 10 kHz to approximately 500 kHz.

18. The plasma processing chamber according to claim 15, wherein the pulse-on and pulse-off time slots are based on the duty cycle of the RF generator, and the duty cycle of the RF generator is approximately 1% to approximately 99%.

19. A plasma processing chamber according to any one of claims 14 to 18, wherein the time slots for the pulse-on state and the pulse-off state are based on the pulse frequency of the RF generator, and the pulse frequency of the RF generator is approximately 1 Hz to approximately 500 kHz.

20. A substrate processing method, A step of detecting the RF generator pulse on-time in a matched network connected to an RF generator capable of operating at a first frequency, A method comprising the step of adjusting at least one variable capacitor in a matching network during the pulse-on time of an RF generator, based on an impedance value measured in the RF signal of at least one pulse-on or pulse-off state of a pulse voltage waveform generator connected to a matching network, or in the RF signal of another RF generator capable of operating at a second frequency different from a first frequency.

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