Compensation of impedance modulation in a plasma generator due to frequency sweep.

Abstract

A plasma processing system is disclosed. A very high frequency (VHF) generator delivers power to a plasma chamber, and a medium frequency (MF) generator delivers power to the plasma chamber. The VHF generator includes a sensor configured to provide a signal indicative of the impedance of a plasma load presented to the VHF generator. The VHF generator further includes a frequency tuner configured to adjust the frequency of the VHF generator within a cycle of the MF generator based on the signal to mitigate impedance modulation caused by the MF generator. Impedance modulation can also be mitigated by a synchronization line between the VHF generator and the MF generator that allows the VHF generator frequency to be preset in synchronization with the cycle of the MF generator.

Description

[Technical Field]

[0001] (Claim of priority under 35 U.S.C. § 119) This application for patent claims priority to U.S. Non-provisional Application No. 18 / 086,307, entitled "COMPENSATION OF IMPEDANCE MODULATION IN A PLASMA GENERATOR BY FREQUENCY SWEEP," filed December 21, 2022, which is incorporated herein by reference.

[0002] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to plasma processing systems, and more particularly to plasma processing systems with modulated plasmas. [Background technology]

[0003] While plasma processing systems for etching and deposition have been available for decades, advances in processing techniques and equipment technology continue to produce increasingly complex systems, which in turn lead to more problematic interactions between multiple generators driving the same plasma system. Summary of the Invention [Means for solving the problem]

[0004] One aspect of the present disclosure can be characterized as a plasma processing system comprising: a very high frequency (VHF) generator configured to deliver power to a plasma chamber; and a medium frequency (MF) generator configured to deliver power to the plasma chamber. The VHF generator comprises a sensor configured to produce at least one signal indicative of an impedance of a plasma load presented to the VHF generator; and a frequency tuner configured to adjust the frequency of the VHF generator within a cycle of the MF generator based on the sensed impedance to mitigate impedance modulation caused by the MF generator.

[0005] Another aspect of the present disclosure may be characterized as a plasma processing system including a very high frequency (VHF) generator configured to deliver power to a plasma chamber, and a medium frequency (MF) generator configured to deliver power to the plasma chamber, wherein a synchronization line is provided between the VHF generator and the MF generator to enable presetting of the frequency of the VHF generator in synchronization with the cycle of the MF generator so as to adjust the frequency of the VHF generator to mitigate impedance modulation caused by the MF generator.

[0006] A further aspect of the present disclosure may be characterized as a method for compensating for impedance modulation in a plasma chamber, the method including delivering power to the plasma chamber using a very high frequency (VHF) generator, delivering power to the plasma chamber using a medium frequency (MF) generator, sensing an impedance of a plasma load presented to the VHF generator, and adjusting the frequency of the VHF generator within a cycle of the MF generator based on the sensed impedance to mitigate impedance modulation caused by the MF generator.

[0007] Yet a further aspect of the present disclosure may be characterized as a method for compensating for impedance modulation in a plasma chamber, the method including delivering power to the plasma chamber using a very high frequency (VHF) generator, delivering power to the plasma chamber using a medium frequency (MF) generator, synchronizing the VHF generator and the MF generator, and presetting a frequency of the VHF generator in synchronization with a cycle of the MF generator to adjust the frequency of the VHF generator to mitigate impedance modulation caused by the MF generator. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a conceptual block diagram of a plasma processing system including VHF and MF generators according to embodiments disclosed herein.

[0009] [Figure 2A] FIG. 2A is a graph depicting RF electrode voltage and sheath voltage in a plasma processing system including VHF and MF generators according to embodiments disclosed herein.

[0010] [Figure 2B] FIG. 2B is a conceptual diagram illustrating an equivalent circuit for the plasma processing system of FIG. 1 according to embodiments disclosed herein.

[0011] [Figure 3] FIG. 3 is a graph depicting an example of impedance modulation within the plasma processing system of FIG. 1 according to embodiments disclosed herein.

[0012] [Figure 4] 4A, 4B, and 4C are graphs illustrating an example of impedance modulation in the plasma processing system of FIG. 1 according to embodiments disclosed herein. The graphs illustrating impedance modulation compensation by decreasing the VHF frequency according to embodiments disclosed herein are also shown in FIG. 4A, 4B, and 4C, respectively.

[0013] [Figure 5] FIG. 5 is a conceptual block diagram of a VHF generator according to an embodiment disclosed herein.

[0014] [Figure 6] FIG. 6 is a flowchart depicting a method for compensating impedance modulation by frequency control according to embodiments disclosed herein.

[0015] [Figure 7] FIG. 7 is a flowchart depicting a method for compensating impedance modulation by frequency synchronization according to embodiments disclosed herein.

[0016] [Figure 8] FIG. 8 is a conceptual block diagram depicting a computing system that may be utilized in connection with the embodiments disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0017] Detailed Description Interactions between generators (driving the same plasma), where one of the generators modulates the load seen by another generator, are becoming increasingly problematic as power levels are increased, and therefore there is a need for new and improved methods and systems to address this problem.

[0018] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[0019] Some plasma etch applications, such as high aspect ratio contact (HARC) etch applications in one non-limiting example, typically use a dual frequency capacitively coupled plasma (CCP) configuration (sometimes also referred to as a dual frequency bias configuration) that applies both VHF (very high frequency) and MF (medium frequency) power to the plasma chamber. In this regard, this description will focus primarily on the CCP or bias configuration, although the principles of the present disclosure may also be applied to an inductively coupled configuration.

[0020] 1 is a conceptual block diagram of a plasma processing system 100 including a VHF generator 114 and an MF generator 116 according to embodiments disclosed herein. In the following description, the VHF generator 114 may be any type of generator operating at a frequency within a relatively high frequency range (e.g., about 10 MHz to about 200 MHz, etc.), and the MF generator 116 may be any type of generator operating at a frequency within a relatively medium frequency range (e.g., about 100 kHz to about 2 MHz, etc.). A guideline is that the frequency range of the VHF generator 114 should be higher than the frequency range of the MF generator 116. The MF generator 116 may be, for example, a sine wave generator, a pulsed DC voltage (bias supply) generator, or any other type of generator operating at a frequency range lower than that of the VHF generator 114. As a specific example, the MF generator may apply an asymmetric periodic voltage waveform to the substrate support 106. Examples of asymmetric periodic voltage waveforms are described in U.S. Pat. No. 10,707,055, entitled "Spatial and Temporal Control of Ion Bias Voltage for Plasma Processing," issued July 7, 2020, which is incorporated herein by reference.

[0021] 1 , the plasma chamber 102 is coupled to a VHF generator 114 and an MF generator 116 via a matching network 112. In some embodiments, the matching network 112 may be a combined network for both the VHF generator 114 and the MF generator 116, while in other embodiments, the matching network 112 may comprise a matching network for the VHF generator 114 and a separate matching network for the MF generator 116. In other embodiments, the matching network 112 may be omitted, such that there is no matching network between the VHF and MF generators 114, 116 and the plasma chamber 102. The plasma chamber 102 includes a first grounded electrode 104 and a second electrode (RF electrode) or substrate support 106, and a substrate (e.g., wafer) 108 is mounted on the second electrode (RF electrode) or substrate support 106 and exposed to a plasma 110 in the chamber 102. Power is applied to the substrate support 106 by VHF and MF generators 114, 116.

[0022] The operation of the VHF generator 114 and the MF generator 116 may also be capable of being synchronized, as shown by the synchronization line 118 in FIG. 1. For example, in some embodiments, the synchronization line 118 provides a common exciter (CEX) mode so that the VHF generator 114 and the MF generator 116 operate in a fixed phase relationship. In other embodiments, the synchronization line 118 provides a clock signal, and synchronization of the generators 114 and 116 may be based on the clock signal. In short, the synchronization line 118 may be any mechanism capable of synchronizing the VHF generator 114 and the MF generator 116.

[0023] The VHF generator 114 and the MF generator 116 may each operate over a wide range of frequencies, although typically the VHF generator 114 operates at a higher frequency than the MF generator 116. In some embodiments, for example, the VHF generator 114 may deliver RF power within a frequency range of about 10 MHz to about 200 MHz, and the MF generator 116 may deliver RF power within a frequency range of about 100 kHz to about 2 MHz. In one example, the VHF generator delivers power within a frequency range of about 60 MHz, and the MF generator delivers power within a frequency range of about 400 kHz. While these frequency ranges are typical, they are provided for non-limiting illustrative purposes only, and it should be noted that the frequency ranges of the VHF generator 114 and the MF generator 116 may be wider (or narrower) than these exemplary ranges, so long as the frequency range of the VHF generator 114 is higher than the frequency range of the MF generator 116.

[0024] In some embodiments, the VHF generator 114 is configured to ignite and maintain the plasma 110 in the plasma chamber 102, and the MF generator 116 is configured to bias the substrate (e.g., wafer) 108 by applying a periodic voltage function to the substrate support (RF electrode) 106, thereby resulting in a desired distribution of ion energy at the surface of the substrate 108. In other embodiments, the VHF generator 114 is configured to maintain the plasma, and one or both of the VHF generator 114 and the MF generator 116 may be configured to ignite the plasma. In still further embodiments, the VHF generator 114 is configured to contribute in part to biasing the substrate (e.g., wafer) 108, and the MF generator 116 is configured to contribute in part to maintaining the plasma 110.

[0025] Some applications (such as HARC etching for components such as memory) require very high MF power. In some embodiments, for example, the MF generator 116 may apply a relatively large amount of power (e.g., in one non-limiting example, in the range of about 10 kW to about 30 kW) to the plasma load in the plasma chamber 102. This large amount of power applied to the plasma at low frequency causes the VHF generator 114 to exhibit impedance modulation due to nonlinear plasma properties, which in turn leads to amplitude modulation in the forward and reflected power. As the MF power is increased, the impedance modulation and resulting amplitude modulation of the forward and reflected power become more severe, and the net VHF power into the plasma for a given forward power is reduced. Sometimes, the net VHF power may be half or less of the forward power, requiring an increase in the forward power supplied by the VHF generator to achieve the desired net power. Furthermore, the large amount of reflected power may cause stress and damage to the VHF generator. Known solutions to this problem are expensive and may include, for example, the use of external RF devices to protect the VHF generator from high reflected power and / or the use of a VHF generator with higher power handling capabilities. The present disclosure seeks to provide a more efficient and economical solution to these problems.

[0026] 2A and 2B are illustrative of the causes of impedance modulation, which results in large amounts of reflected power. FIG. 2A is a graph 200 depicting various waveforms in a plasma processing system (such as the plasma processing system 100 of FIG. 1) including a VHF and MF generator. In FIG. 2A, the x-axis represents time and the y-axis represents the RF electrode voltage (the voltage at the substrate support 106). Plasma voltage 201 (which is near ground or zero) is shown as a dotted line for reference. Waveform 202 is the RF electrode voltage when only VHF power is applied, waveform 204 is the RF electrode voltage when VHF power and a relatively higher MF power are applied, and waveform 203 is the RF electrode voltage when VHF power and a relatively lower MF power are applied.

[0027] The sheath voltage, which is the difference between the plasma voltage and the RF electrode voltage, can also be seen in FIG. 2A. When only VHF power is applied, the sheath voltage (the voltage difference between plasma voltage 201 and VHF power-only waveform 202) is lower and is very stable and uniform. In response to the application of relatively high MF and VHF power, as illustrated by waveform 204, the sheath voltage becomes less uniform and undergoes significant fluctuations during the MF cycle. In particular, the sheath voltage cycles between areas of relatively high sheath voltage, as depicted by region 208, and areas of relatively low sheath voltage, as depicted by region 206.

[0028] 2B is a conceptual diagram depicting an equivalent circuit 250 for a plasma processing system including a VHF generator 252 and an MF generator 254. The circuit 250 includes an equivalent resistance 256 presented by the plasma load, as well as an equivalent sheath capacitance 258 between the substrate (e.g., wafer) 108 and the plasma 110, and an equivalent sheath capacitance 260 between the electrode 104 and ground. Variations in the sheath voltage result in variations in the equivalent sheath capacitance 258 and the equivalent sheath capacitance 260 (sheath capacitance 258 is the dominant mechanism) during the MF cycle, as shown in FIG. 2A, which in turn modulates the impedance seen by the VHF generator 114 and, consequently, the amplitude of the forward and reflected power. In particular, when the sheath voltage is low (region 206), the sheath capacitance 258 is larger, and when the sheath voltage is high, the sheath capacitance 258 is smaller. The plasma load may also vary to some extent during the MF cycle, which may also contribute to impedance modulation and power amplitude modulation.

[0029] 3 is a graph (Smith chart) 300 illustrating an example of impedance modulation seen by the VHF generator 114 due to the high-power MF generator 116. The impedance (the "target impedance"), in this example, is around point B in the graph, or approximately 50 ohms. While 50 ohms is typical, this is a non-limiting example, and the target impedance may be other values. Variations in sheath capacitance, as described above, cause variations in the impedance seen by the VHF generator 114. In particular, the impedance may "swing" between a first impedance (point A) and a second impedance (point C). More specifically, at a first impedance (point A), the impedance varies in a first direction from the target impedance (point B) (and at point A, the sheath capacitance is greater than the target sheath capacitance), and at a second impedance (point C), the impedance varies in a second direction from the target impedance (point B), the second direction being opposite to the first direction (relative to point B), and at the second impedance (point C), the sheath capacitance is less than the target sheath capacitance.

[0030] In accordance with an aspect of the present disclosure, applicant has discovered that impedance swings or modulation caused by high levels of power applied by MF generator 116 can be compensated for (reduced) by utilizing the frequency tuning capabilities of VHF generator 114. VHF generator 114 typically has a range of frequencies that can be generated beyond its rated power. A 60 MHz VHF generator, for example, typically has a range of + or -5 percent. Thus, a 60 MHz VHF generator can typically be operated within a range of approximately 57 MHz to approximately 63 MHz. By adjusting the frequency of the VHF generator within this range, applicant has discovered that the impedance modulation swings can be "pushed" back toward an ideal target impedance of approximately 50 ohms.

[0031] This concept is illustrated in the graphs of Figures 4A-4C. In graph 410 of Figure 4A, the VHF generator 114 operates at 57.6 MHz and the MF generator 416 operates at 400 kHz. Under this condition of operation, the impedance seen by the VHF generator 114 "swings" between a first impedance (point A) when the sheath capacitance is at its maximum and a second impedance (point C) when the sheath capacitance is at its minimum.

[0032] When the sheath capacitance is at its maximum and the impedance consequently swings to point A, the impedance can be pushed back toward the target impedance of, for example, 50 ohms (point B) by decreasing the frequency of the VHF generator 114. In this regard, as shown in graph 420 of FIG. 4B, when the impedance swings to point A, the frequency of the VHF generator 114 is reduced to 57.3 MHz. As a result, the impedance swings back toward the target impedance of 50 ohms (FIG. 4B; point A * ) and swings back.

[0033] Similarly, when the sheath capacitance is at its minimum and after the impedance has swung in the opposite direction from the impedance at point A to the impedance at point C, the impedance can be pushed back toward the target impedance of 50 ohms (point B) by increasing the frequency of the VHF generator 114. In this regard, as shown in graph 430 of FIG. 4C, when the impedance swings to its high point C, the frequency of the VHF generator 114 is increased to 57.9 MHz. As a result, the impedance swings back toward the target impedance of 50 ohms (FIG. 4C; point C * ).

[0034] Accordingly, aspects of the present disclosure tune the frequency of the VHF generator 114 and adjust the modulation impedance presented to the VHF generator 114. In this regard, FIG. 5 illustrates a block diagram of a VHF generator 500 that may be used to implement the VHF generator 114 described with reference to FIG. 1. As shown, the VHF generator includes an exciter 502, a power amplifier 504, a sensor 506, and a frequency tuner 508. The exciter 502 generates an oscillating signal at an RF frequency, typically in the form of a sine wave or square wave. The power amplifier 504 amplifies the signal generated by the exciter 502, resulting in an amplified oscillating signal. For example, the power amplifier 504 may amplify a 1 mW exciter output signal to 3 kW. The sensor 506 measures one or more aspects of the power applied by the VHF generator and produces at least one signal 507 indicative of the impedance Z of the plasma load presented to the VHF generator 500. The sensor 506 may be, for example, without limitation, a VI sensor for producing voltage and current signals or a directional coupler for producing forward and reflected voltage signals.

[0035] The frequency tuner 508 receives measurements indicative of the impedance of the plasma load seen by the VHF generator 500 and processes those measurements to produce frequency adjustments that are supplied to the exciter 502 to adjust the frequency generated by the exciter 502. In particular, as described with reference to Figures 4A-4C, when the sheath capacitance is greater than the target sheath capacitance and the impedance sensed by the sensor 506 swings to point A, the frequency tuner 508 may decrease the frequency of the VHF generator 500, pushing the impedance back toward the target impedance (point B) of, for example, 50 ohms. Similarly, when the sheath capacitance is less than the target sheath capacitance and the impedance sensed by the sensor 506 swings to point C, the frequency tuner 508 may increase the frequency of the VHF generator 500, lowering the impedance or pushing it back toward the target impedance (point B) of 50 ohms.

[0036] Depending on the hardware configuration, it is contemplated that when the sheath capacitance is less than the target sheath capacitance, the frequency tuner 508 may need to decrease the frequency of the VHF generator 500 to reduce the impedance or push it back toward the target impedance of, for example, 50 ohms (point B). Similarly, depending on the hardware configuration, it is contemplated that when the sheath capacitance is less than the target sheath capacitance, the frequency tuner 508 may need to decrease the frequency of the VHF generator 500 to reduce the impedance or push it back toward the target impedance of, for example, 50 ohms (point B). Also, while sheath capacitance has been identified as one reason for impedance modulation, it should be recognized that sheath capacitance is not the only reason for impedance modulation. For example, both the plasma body impedance and the sheath capacitance contribute to the total impedance.

[0037] Additionally, as described with reference to FIG. 1 , the operation of the VHF generator 114 and the MF generator 116 may be capable of being synchronized, as indicated by the MF synchronization line 118. For example, the synchronization line 118 may provide a common exciter (CEX) mode such that the VHF generator 114 and the MF generator 116 operate in a fixed phase relationship. Synchronization of the generators 114 and 116 may also be provided on the synchronization line 118, for example, by a clock signal or the like. This manner of synchronization may allow the frequency of the VHF generator 114 to be preset in sync with the cycle of the MF generator 116, such that the frequency of the VHF generator 114 is increased and decreased at the appropriate times so that the impedance seen by the VHF generator 114 is continuously modulated to be as close to the target impedance as possible.

[0038] 6 is a flowchart depicting a method 600 for compensating impedance modulation through frequency control according to embodiments disclosed herein. In step 602, power is applied to the plasma chamber 102 using the VHF generator 114 / 500. As explained above, the power applied by the VHF generator 114 / 500 is typically in the range of about 60 MHz and typically serves to sustain (and potentially ignite) the plasma 110 in the plasma chamber 102. In step 604, power is applied to the plasma chamber 102 using the MF generator 116. As explained above, the power applied by the MF generator 116 is typically in the range of about 400 kHz and typically serves to bias the substrate 108 by applying a periodic voltage function to the substrate support 106, thereby providing a desired distribution of ion energy at the surface of the substrate 108.

[0039] In step 606, the impedance presented to the VHF generator 114 / 500 by the plasma load is sensed. The impedance may be sensed, for example, by a sensor (such as sensor 506 in FIG. 5). In step 608, if the impedance is swinging or modulating to point A (FIGS. 3 and 4), the frequency of the VHF generator 114 / 500 is reduced in step 610 to push the impedance back toward the target impedance (typically, but of course not always, 50 ohms). Step 610 may be performed, for example, by frequency tuner 508 of FIG. 5. In step 612, if the impedance sensed by sensor 506 is swinging or modulating to point C (FIGS. 3 and 4), the frequency of the VHF generator 114 / 500 is increased in step 614 to push the impedance back toward the target impedance. Step 614 may be performed, for example, by frequency tuner 508 of FIG. 5.

[0040] 7 is a flowchart depicting an alternative method 700 for compensating for impedance modulation through frequency synchronization according to embodiments disclosed herein. In step 702, power is applied to the plasma chamber 102 using the VHF generator 114 / 500. As explained above, the power applied by the VHF generator 114 / 500 is typically in the 60 MHz range and serves to ignite and sustain the plasma 110 in the plasma chamber 102. In step 704, power is applied to the plasma chamber 102 using the MF generator 116. As explained above, the power applied by the MF generator 116 may be in the 400 kHz range and serves to bias the substrate 108 by applying a periodic voltage function to the substrate support 106, thereby providing a desired distribution of ion energy at the surface of the substrate 108.

[0041] In step 706, the VHF generator 114 / 500 is preset to be synchronized with the cycle of the MF generator 116. As described above, for example, a common exciter (CEX) mode may be provided by synchronization line 118 so that the VHF generator 114 and the MF generator 116 operate in a fixed phase relationship. Synchronization of the generators 114 and 116 may also be provided on synchronization line 118, for example, by a clock signal or the like. By presetting the frequency modulation of the VHF generator 114 / 500 in this manner, the frequency of the VHF generator 114 / 500 is automatically adjusted to correspond to the cycle of the MF generator 116, thereby eliminating the need to continually sense the impedance seen by the VHF generator 114 / 500 and adjust the frequency output of the VHF generator 114 / 500 accordingly.

[0042] In step 708, according to the preset of the VHF generator 114 / 500, the VHF frequency is decreased as directed by the synchronization signal to modulate the impedance seen by the VHF frequency generator back towards the target impedance. Similarly, in step 710, the VHF frequency is increased as directed by the synchronization signal to modulate the impedance seen by the VHF frequency generator back towards the target impedance.

[0043] Those skilled in the art will understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, the data, instructions, commands, information, signals, bits, symbols, and chips that may be referred to throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0044] Those skilled in the art will further understand that the various illustrative logic blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or a combination of both. The various illustrative logic blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed using a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof, designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but alternatively, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0045] The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

[0046] FIG. 8 is a conceptual diagram of a computing system 800 that may be implemented within the MF generator 116 and / or the VHF generator 114. A display portion 802 and non-volatile memory 804 are coupled to a bus 806, which is also coupled to a random access memory (“RAM”) 808, a processing portion 810 (including N processing components), a field programmable gate array (FPGA) 812, and a transceiver component 814, including N transceivers. While the components depicted in FIG. 8 represent physical components, FIG. 8 is not intended to be a detailed hardware diagram; thus, many of the components depicted in FIG. 8 may be realized by common construction or distributed among additional physical components. It is also contemplated that other existing and yet-to-be-developed physical components and architectures may be utilized to implement the functional components described with reference to FIG. 8.

[0047] The display portion 802 generally operates to provide a user interface and, in some implementations, is realized by a touchscreen display. The non-volatile memory 804 is generally non-transitory memory that functions to persistently store data and machine-readable (e.g., processor-executable) code (including executable code associated with effecting the methods described herein). In some embodiments, the non-volatile memory 804 includes boot loader code, operating system code, file system code, and non-transitory processor-executable code to facilitate execution of the methods described herein, including the methods described with reference to FIGS. 6 and 7.

[0048] In some implementations, non-volatile memory 804 is realized by flash memory (e.g., NAND memory or ONENAND memory), although it is contemplated that other memory types may be utilized as well. While it is possible to execute code from non-volatile memory 804, executable code in non-volatile memory 804 is typically loaded into RAM 808 and executed by one or more of the N processing components in processing portion 810.

[0049] In operation, the processing portion 810 associated with RAM 808 may generally operate to execute instructions stored in non-volatile memory 804 to implement aspects of the frequency tuner 508 and to control aspects of the VHF generator 114 / 500, the mid-frequency generator 116, and the matching network 112. For example, non-transient processor-executable instructions for effecting aspects of the methods described with reference to Figures 6 and 7 may be persistently stored in non-volatile memory 804 and executed by the processing portion 810 associated with RAM 808. As one skilled in the art would understand, the processing portion 810 may include a video processor, a digital signal processor (DSP), a graphics processing unit (GPU), and other processing components.

[0050] Additionally or alternatively, FPGA 812 may be configured to effect one or more aspects of the methods described herein (e.g., the methods described with reference to Figures 6 and 7). For example, non-transient FPGA configuration instructions may be persistently stored in non-volatile memory 804 and accessed by FPGA 812 (e.g., during boot-up) to configure FPGA 812, implement aspects of frequency tuner 508, and control aspects of VHF generator 114 / 500, mid-frequency generator 116, and matching network 112.

[0051] The input component 816 may operate to receive signals (e.g., from the sensor 506 (and / or a synchronization line between the VHF generator and the MF generator when the VHF generator operates as a satellite)) indicative of one or more aspects of power, such as, for example, voltage, current, forward power, reflected power, and plasma load impedance. The output component 818 generally operates to provide one or more analog or digital signals to affect operational aspects of the generator 114 / 500 and the generator 116. For example, the output component 818 may provide control signals utilized by the generator 114 / 500 and the generator 116. The output component 818 may also provide synchronization signals when operating as a master device.

[0052] The transceiver component 814 includes N transceiver chains that can be used to communicate with external devices over wireless or wired networks. Each of the N transceiver chains can represent a transceiver associated with a particular communication scheme (e.g., Wifi, Ethernet, Profibus, etc.).

[0053] This description is provided to enable any person skilled in the art to make or use the invention. Various modifications will be readily apparent to those skilled in the art, and the principles disclosed herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not limited to the embodiments disclosed herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. 1. A plasma processing system comprising: a very high frequency (VHF) generator configured to deliver power to the plasma chamber; a medium frequency (MF) generator configured to deliver power to the plasma chamber; and and the VHF generator comprises: a sensor configured to produce at least one signal indicative of the impedance presented to said VHF generator; a frequency tuner configured to adjust the frequency of the VHF generator within a cycle of the MF generator based on the at least one signal indicative of the impedance to mitigate impedance modulation caused by the MF generator; A plasma processing system comprising:

2. the frequency tuner decreases the frequency of the VHF generator when the impedance swings in a first direction from a target impedance; the frequency tuner increasing the frequency of the VHF generator when the impedance swings from the target impedance in a second direction opposite to the first impedance.

10. The plasma processing system of claim 1.

3. the frequency tuner reduces the frequency of the VHF generator when the sheath capacitance is greater than the target sheath capacitance; the frequency tuner increases the frequency of the VHF generator when the sheath capacitance is less than the target sheath capacitance; 10. The plasma processing system of claim 1.

4. 2. The plasma processing system of claim 1, wherein said frequency tuner increases or decreases said frequency of said VHF generator within about 5 percent of the frequency at which said VHF generator normally operates.

5. 10. The plasma processing system of claim 1, wherein the VHF generator delivers power in a frequency range of approximately 60 MHz and the MF generator delivers power in a frequency range of approximately 400 kHz.

6. 10. The plasma processing system of claim 1, wherein the MF generator applies a power in a range of about 10 kW to about 30 kW to the plasma chamber.

7. 10. The plasma processing system of claim 1, wherein the VHF generator is configured to maintain a plasma in the plasma chamber, and the MF generator is configured to bias a substrate in the plasma chamber by applying a periodic voltage function to produce a desired distribution of ion energy at a surface of the substrate.

8. 1. A plasma processing system comprising: a very high frequency (VHF) generator configured to deliver power to the plasma chamber; a medium frequency (MF) generator configured to deliver power to the plasma chamber; a synchronization line between the VHF generator and the MF generator, the synchronization line being for enabling presetting of the frequency of the VHF generator in synchronization with the cycle of the MF generator so as to adjust the frequency of the VHF generator to mitigate impedance modulation caused by the MF generator; A plasma processing system comprising:

9. 9. The plasma processing system of claim 8, wherein the synchronization line is a line for providing a common exciter (CEX) mode.

10. 9. The plasma processing system of claim 8, wherein the synchronization line is a line for providing a clock signal.

11. the frequency of the VHF generator is adjusted to be lower as the impedance presented to the VHF generator swings in a first direction from a target impedance; the frequency of the VHF generator is adjusted to be higher as the impedance presented to the VHF generator swings from the target impedance in a second direction opposite the first impedance; 9. The plasma processing system of claim 8.

12. the frequency of the VHF generator is adjusted to be lower when the sheath capacitance is greater than the target sheath capacitance; the frequency of the VHF generator is adjusted to be higher when the sheath capacitance is smaller than the target sheath capacitance; 9. The plasma processing system of claim 8.

13. 9. The plasma processing system of claim 8, wherein said frequency tuner increases or decreases said frequency of said VHF generator within about 5 percent of the frequency at which said VHF generator normally operates.

14. 9. The plasma processing system of claim 8, wherein the VHF generator delivers power in a frequency range of approximately 60 MHz and the MF generator delivers power in a frequency range of approximately 400 kHz.

15. 10. The plasma processing system of claim 8, wherein the MF generator applies a power in a range of about 10 kW to about 30 kW to the plasma chamber.

16. 10. The plasma processing system of claim 8, wherein the VHF generator is configured to maintain a plasma in the plasma chamber, and the MF generator is configured to bias a substrate in the plasma chamber by applying a periodic voltage function to produce a desired distribution of ion energy at a surface of the substrate.

17. 1. A method for compensation of impedance modulation in a plasma chamber, comprising: delivering power to the plasma chamber using a very high frequency (VHF) generator; delivering power to the plasma chamber using a medium frequency (MF) generator; adjusting the frequency of the VHF generator to mitigate impedance modulation caused by the MF generator; A method comprising:

18. decreasing the frequency of the VHF generator when the sensed impedance deviates in a first direction from a target impedance; increasing the frequency of the VHF generator when the sensed impedance swings from the target impedance in a second direction opposite to the first impedance; 20. The method of claim 17, further comprising:

19. 18. The method of claim 17, comprising adjusting the frequency based on an indication of the impedance of a plasma load.

20. 18. The method of claim 17, comprising presetting the frequency of the VHF generator in synchronization with a cycle of the MF generator to mitigate impedance modulation caused by the MF generator.

Images