Apparatus and method for splitting current from a direct drive radio frequency signal generator between multiple coils - Patents.com

Abstract

A radio frequency (RF) power supply system includes a first coil and a second coil. The RF power supply system also includes a first RF power source connected to supply an RF signal of a first frequency to both the first coil and the second coil. The RF power supply system also includes a current splitter variable capacitor connected to control the division of the RF signal of the first frequency between the first coil and the second coil. The RF power supply system also includes a second RF power source connected to supply an RF signal of a second frequency to the second coil. In some embodiments, the first RF power source and the second RF power source are first and second direct drive RF power sources, respectively, that drive the RF signal of the first frequency and the RF signal of the second frequency through a first and second reactance circuit, respectively.

Description

[Background technology]

[0001] Plasma processing systems are used to manufacture semiconductor devices, e.g., chips / dies on semiconductor wafers. In plasma processing systems, the semiconductor wafers are exposed to various types of plasmas to cause a prescribed change in the state of the semiconductor wafer, such as by material deposition and / or material removal and / or material implantation and / or material modification. During plasma processing of a semiconductor wafer, radio frequency (RF) power is transmitted through a process gas in a chamber to convert the process gas into a plasma that is exposed to the semiconductor wafer. Reactive components of the plasma, such as radicals and ions, interact with materials on the semiconductor wafer to achieve a prescribed effect on the semiconductor wafer. In some plasma processing systems, the generated RF power is transmitted to the process gas through a coil located outside the plasma processing chamber. It is in this context that the embodiments described in the present disclosure are carried out. Summary of the Invention

[0002] In one exemplary embodiment, an RF power supply system is disclosed. The RF power supply system includes a first coil and a second coil. The RF power supply system also includes a first RF power source connected to supply an RF signal at a first frequency to both the first coil and the second coil. The RF power supply system also includes a current splitter variable capacitor connected to control the division of the RF signal at the first frequency between the first coil and the second coil. The RF power supply system also includes a second RF power source connected to supply an RF signal at a second frequency to the second coil.

[0003] In an exemplary embodiment, an RF power supply system is disclosed. The RF power supply system includes a first RF power source having an output terminal. The RF power supply system also includes a first reactance circuit having an input terminal and an output terminal. The input terminal of the first reactance circuit is connected to the output terminal of the first RF power source. The RF power supply system also includes a first coil connected to the output terminal of the first reactance circuit. The RF power supply system also includes a current splitter variable capacitor having an input terminal and an output terminal. The input terminal of the current splitter variable capacitor is connected to the output terminal of the first reactance circuit. The RF power supply system also includes a second coil connected to the output terminal of the current splitter variable capacitor. The RF power supply system also includes a second RF power source having an output terminal. The RF power supply system also includes a second reactance circuit having an input terminal and an output terminal. The input terminal of the second reactance circuit is connected to the output terminal of the second RF power source. The RF power supply system also includes a blocking filter having an input terminal and an output terminal. The input terminal of the blocking filter is connected to the output terminal of the second reactance circuit, and the output terminal of the blocking filter is connected to the second coil.

[0004] In an exemplary embodiment, a method for supplying RF power to a plasma processing system is disclosed. The method includes generating an RF signal at a first frequency. The method also includes supplying a first portion of the RF signal at the first frequency to a first coil. The method also includes supplying a second portion of the RF signal at the first frequency to a second coil. The method also includes generating an RF signal at a second frequency. The method also includes supplying the RF signal at the second frequency to the second coil.

[0005] Other aspects and advantages of the embodiments will become more apparent from the following detailed description and accompanying drawings. [Brief description of the drawings]

[0006] [Figure 1]FIG. 1 illustrates an RF power supply system according to some embodiments.

[0007] [Figure 2A] FIG. 2 is a schematic diagram of a direct drive RF signal generator in accordance with some embodiments.

[0008] [Figure 2B] FIG. 13 illustrates a plot of parameters of an exemplary shaped amplified square waveform generated at the output terminals of the first / second RF power supply as a function of time in accordance with some embodiments.

[0009] [Figure 2C] FIG. 13 illustrates a plot of parameters of an exemplary shaped sinusoidal waveform generated at the output terminals of the first / second reactance circuits as a function of time in accordance with some embodiments.

[0010] [Figure 2D] FIG. 2C illustrates a plot of a shaped sinusoidal waveform that corresponds to the shaped amplified square waveform of FIG. 2B in accordance with some embodiments.

[0011] [Figure 3A] 2 illustrates an exemplary plasma processing system that utilizes the RF power supply system of FIG. 1 in accordance with some embodiments.

[0012] [Figure 3B] 3B is a plan view of a first coil and a second coil in the plasma processing system of FIG. 3A according to some embodiments.

[0013] [Figure 4] 1 is a flowchart of a method for supplying RF power to a plasma processing system in accordance with some embodiments.

[0014] [Diagram 5] FIG. 2 is a diagram of a system controller, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one of ordinary skill in the art that embodiments of the present disclosure may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail in order not to unnecessarily obscure the present disclosure.

[0016] Disclosed herein are systems and methods for splitting RF current at a first frequency among multiple coils of an RF power supply system used to drive a plasma for processing a substrate, e.g., a semiconductor wafer, in combination with transmitting RF current at a second frequency to some of the multiple coils, whereby at least one of the multiple coils receives both a portion of the RF current at the first frequency and an RF current at the second frequency. These systems and methods are useful in many plasma processing situations, and are particularly useful in situations where the transmission of RF current at a second frequency to a given coil alone is not sufficient to ignite / strike and maintain a plasma having defined characteristics. In such situations, the portion of the RF current at the first frequency transmitted to a given coil, in combination with the RF current at the second frequency, serves to support igniting / strike and maintaining a plasma having defined characteristics. The above-mentioned situations are just one example of the many possible uses and benefits of the systems and methods disclosed herein.

[0017] FIG. 1 shows an RF power supply system 100 according to some embodiments. The RF power supply system 100 includes a first coil 113 and a second coil 115. In some embodiments, the first coil 113 is an inner coil and the second coil 115 is an outer coil. In some of these embodiments, each of the first coil 113 (inner coil) and the second coil 115 (outer coil) is a planar type helical coil, and the second coil 115 surrounds the first coil 113. The first coil 113 has an input terminal 113i and an output terminal 113o. The input terminal 113i of the first coil 113 is connected to receive an RF signal of a first frequency from a first RF power source 101. The output terminal 113o of the first coil 113 is connected to a reference ground potential 119. The second coil 115 has an input terminal 115i and an output terminal 115o. The input terminal 115i of the second coil 115 is connected to receive an RF signal of the second frequency from the second RF power source 103. The second RF power source 103 is connected to supply an RF signal of the second frequency to the second coil 115. Furthermore, the input terminal 115i of the second coil 115 is also connected to receive an RF signal of the first frequency from the first RF power source 101 according to a capacitance setting of a current splitter variable capacitor 109 connected between the first RF power source 101 and the second coil 115. The current splitter variable capacitor 109 is connected in parallel with the first coil 113. In this way, the first RF power source 101 is connected to supply an RF signal of the first frequency to both the first coil 113 and the second coil 115, and the current splitter variable capacitor 109 is connected to control the division of the RF signal of the first frequency between the first coil 113 and the second coil 115. In addition, the output terminal 115 o of the second coil 115 is connected to a reference ground potential 119 .

[0018] In some embodiments, the RF power supply system 100 includes a first reactance circuit 105 having an input terminal 105i connected to the output terminal 101o of the first RF power source 101. In this manner, the first RF power source 101 is connected to supply an RF signal of a first frequency to both the first coil 113 and the second coil 115 through the first reactance circuit 105. Also, in some embodiments, the RF power supply system 100 includes a second reactance circuit 107 having an input terminal 107i connected to the output terminal 103o of the second RF power source 103. In this manner, the second RF power source 103 is connected to supply an RF signal of a second frequency to the second coil 115 through the second reactance circuit 107.

[0019] In some embodiments, each of the first RF power source 101 and the second RF power source 103 is a respective direct drive RF signal generator. FIG. 2A shows a schematic diagram of a direct drive RF signal generator 200 according to some embodiments. The direct drive RF signal generator 200 includes an input section 201 and an output section 203. The input section 201 is electrically coupled to the output section 203. For the first RF power source 101, the output section 203 is electrically connected to the output terminal 101o, as indicated by the arrow 205. Thus, for the first RF power source 101, the output section 203 is electrically connected to the first reactance circuit 105, as indicated by the arrow 205. Similarly, for the second RF power source 103, the output section 203 is electrically connected to the second reactance circuit 107, as indicated by the arrow 205. The input section 201 includes an electrical signal generator 207 and an input portion 209A of a gate driver 209. The output section 203 includes an output portion 209B of the gate driver 209 and a half-bridge transistor circuit 211. The input section 201 generates a plurality of square wave signals and provides the square wave signals to the output section 203. The output section 203 generates an amplified square shaped waveform from the plurality of square wave signals received from the input section 201. The output section 203 also shapes an amplitude envelope, such as a peak-to-peak magnitude, of the amplified square shaped waveform. For example, a shaping control signal is provided from the input section 201 to the output section 203 to generate an amplitude envelope. The shaping control signal has a plurality of voltage values ​​for shaping the amplified square shaped waveform to generate a shaped amplified square waveform in the amplitude envelope. For the first RF power source 101, the shaped and amplified square waveform is transmitted from the output section 203 to the first reactance circuit 105. For the second RF power source 103, the shaped and amplified square waveform is transmitted from the output section 203 to the second reactance circuit 107.

[0020] Each of the first reactance circuit 105 and the second reactance circuit 107 removes, for example, filters out, higher-order harmonics of the shaped and amplified rectangular waveform to generate a shaped sinusoidal waveform having a fundamental frequency. The shaped sinusoidal waveform has the same amplitude envelope as the shaped and amplified rectangular waveform. For the first RF power source 101, RF power is transmitted through the output terminal 105o of the first reactance circuit 105 in the form of a shaped sinusoidal waveform having a fundamental frequency and an amplitude envelope. Similarly, for the second RF power source 103, RF power is transmitted through the output terminal 107o of the second reactance circuit 107 in the form of a shaped sinusoidal waveform having a fundamental frequency and an amplitude envelope.

[0021] FIG. 2B shows a plot of an exemplary shaped amplified square waveform 213 parameter generated at the output terminal 101o / 103o of the first / second RF power source 101 / 103 as a function of time according to some embodiments. The parameter of the shaped amplified square waveform 213 is either power, voltage, or current. FIG. 2B also shows an amplitude envelope 215 (represented by a thick dashed line) of the shaped amplified square waveform 213, which is generated according to a voltage value indicated by a shaped control signal transmitted to the output section 203 of the direct drive RF signal generator 200. In the example of FIG. 2B, the amplitude envelope 215 is controlled such that the absolute value of the parameter of the shaped amplified square waveform 213 transitions between a first level L1 (lower level) and a second level L2 (upper level). However, it should be understood that in various processes, the amplitude envelope 215 may be controlled to have essentially any desired shape by controlling the voltage supplied to the power rails in the output section 203 as a function of time according to a shaping control signal transmitted to the output section 203. For example, in various processes, the shaping control signal may be generated to instruct the amplitude envelope 215 to have a continuous wave shape, a triangular shape, a multi-level pulse shape, or essentially any other defined, controlled shape.

[0022] FIG. 2C shows a plot of parameters of an exemplary shaped sine waveform 217 generated at the output terminal 105o / 107o of the first / second reactance circuit 105 / 107 as a function of time according to some embodiments. The parameters of the shaped sine waveform 217 are either power, voltage, or current. The shaped sine waveform 217 is based on the shaped amplified square waveform 213 transmitted to the input terminal 105i / 107i of the first / second reactance circuit 105 / 107 as a function of time. The shaped sine waveform 217 also has an amplitude envelope 215. The shaped amplified square waveform 213 is a combination of a fundamental frequency sine waveform 213A and multiple higher harmonic frequency sine waveforms 213B, 213C, etc. For example, the sine waveform 213B represents a second harmonic frequency of the fundamental frequency sine waveform 213A. Also, the sinusoidal waveform 213C represents a third harmonic frequency of the fundamental frequency sinusoidal waveform 213A. The first / second reactance circuit 105 / 107 functions to remove the higher harmonic frequency sinusoidal waveforms 213B, 213C, etc. from the shaped amplified square waveform 213 such that only the fundamental frequency sinusoidal waveform 213A is provided as a shaped sinusoidal waveform 217 at the output terminals 105o / 107o of the first / second reactance circuit 105 / 107 as a function of time.

[0023] 2D shows a plot of a shaped sinusoidal waveform 217 corresponding to the shaped amplified square waveform 213 of FIG. 2B according to some embodiments. For the first RF power source 101, the shaped sinusoidal waveform 217 at the output terminal 105o of the reactance circuit 105 is transmitted to the first coil 113 and to the second coil 115 according to the capacitance setting of the current splitter variable capacitor 109. For the second RF power source 103, the shaped sinusoidal waveform 217 at the output terminal 107o of the reactance circuit 107 is transmitted to the second coil 115.

[0024] 1, in some embodiments, the first reactance circuit 105 includes an input terminal 105i connected to the output terminal 101o of the first RF power source 101. The first reactance circuit 105 includes a first tuneable variable capacitor 121 having an input terminal 121i connected to the input terminal 105i of the first reactance circuit 105 and in turn to the output terminal 101o of the first RF power source 101. The first reactance circuit 105 also includes an inductor 123 connected in series with the first tuneable variable capacitor 121. In particular, the input terminal 123i of the inductor 123 is connected to the output terminal 121o of the first tuneable variable capacitor 121. The output terminal 123o of the inductor 123 is connected to the output terminal 105o of the first reactance circuit 105. The output terminal 105o of the first reactance circuit 105 is connected to both the input terminal 113i of the first coil 113 and the input terminal 109i of the current splitter variable capacitor 109. In this manner, the output terminal 123o of the inductor 123 is connected to both the first coil 113 and the input terminal 109i of the current splitter variable capacitor 109.

[0025] In some embodiments, the control component 125 is connected to provide control of the capacitance setting of the first tuned variable capacitor 121. In some embodiments, the control component is a mechanical shaft that extends to a location that is accessible for manual turning of the mechanical shaft, and manual turning of the mechanical shaft provides a change in the capacitance setting of the first tuned variable capacitor 121. In some embodiments, the control component 125 includes a motor, e.g., a stepper motor, and includes a mechanical linkage that extends between the motor and the first tuned variable capacitor 121. In some embodiments, the mechanical linkage translates rotational movement of the motor's shaft into an adjustment of the capacitance setting of the first tuned variable capacitor 121, such as by causing movement of spaced apart conductive members (e.g., plates) of the first tuned variable capacitor 121 relative to one another. In some embodiments, the control component 125 is configured to provide remote control of the capacitance setting of the first tuned variable capacitor 121 through the transmission of an electrical signal to the control component 125. In some embodiments, operation of the control component 125 is directed by an electrical signal transmitted from the system controller 311 (see FIG. 3A ) such that the capacitance setting of the first tuneable variable capacitor 121 can be set remotely and / or programmatically by the system controller 311. In some embodiments, the reactance of the first reactance circuit 105 is modified by transmitting a quality factor control signal to the control component 125, the Q factor control signal directing implementation of a particular change in the reactance of the first reactance circuit 105, such as by directing implementation of a change in the capacitance setting of the first tuneable variable capacitor 121.

[0026] In some embodiments, the current splitter variable capacitor 109 has an output terminal 109o connected to the input terminal 115i of the second coil 115. In some embodiments, a control component 133 is connected to provide control of a capacitance setting of the current splitter variable capacitor 109. In some embodiments, the control component 133 includes a motor, e.g., a stepper motor, and includes a mechanical linkage extending between the motor and the current splitter variable capacitor 109. In some embodiments, the mechanical linkage translates rotational movement of a shaft of the motor into adjustment of a capacitance setting of the current splitter variable capacitor 109, such as, for example, by causing movement of spaced apart conductive members (e.g., plates) of the current splitter variable capacitor 109 relative to one another. In some embodiments, the control component 133 is configured to provide remote control of a capacitance setting of the current splitter variable capacitor 109 through transmission of an electrical signal to the control component 133. In some embodiments, the operation of the control component 133 is directed by electrical signals transmitted from the system controller 311 (see FIG. 3A ) such that the capacitance setting of the current splitter variable capacitor 109 can be set remotely and / or programmatically by the system controller 311.

[0027] The capacitance setting of the current splitter variable capacitor 109 affects the impedance of the second coil 115. By adjusting the capacitance setting of the current splitter variable capacitor 109, the impedance between the first coil 113 and the second coil 115 is changed. When the capacitance setting of the current splitter variable capacitor 109 causes an increase in the impedance of the second coil 115, more of the RF signal of the first frequency generated by the first RF power source 101 will be transmitted to the first coil 113 and less of the RF signal of the first frequency generated by the first RF power source 101 will be transmitted to the second coil 115. Conversely, when the capacitance setting of the current splitter variable capacitor 109 causes a decrease in the impedance of the second coil 115, more of the RF signal at the first frequency generated by the first RF power source 101 will be transmitted to the second coil 115 and less of the RF signal at the first frequency generated by the first RF power source 101 will be transmitted to the first coil 113. In this manner, the current splitter variable capacitor 109 controls the splitting of the RF signal at the first frequency generated by the first RF power source 101 between the first coil 113 and the second coil 115.

[0028] In some embodiments, the second reactance circuit 107 includes an input terminal 107i connected to the output terminal 103o of the second RF power supply 103. The second reactance circuit 107 includes a second tuneable variable capacitor 127 having an input terminal 127i connected to the input terminal 107i of the second reactance circuit 107 and in turn to the output terminal 103o of the second RF power supply 103. The second tuneable variable capacitor 127 has an output terminal 127o connected to the output terminal 107o of the second reactance circuit 107. The second reactance circuit 107 also includes a capacitor 131 connected in parallel with the second tuneable variable capacitor 127. In particular, the input terminal 131i of the capacitor 131 is connected to the input terminal 107i of the second reactance circuit 107 and in turn to the output terminal 103o of the second RF power supply 103. The capacitor 131 has an output terminal 131o connected to the output terminal 107o of the second reactance circuit 107. The capacitor 131 is also referred to herein as a parallel capacitor. The output terminal 107o of the second reactance circuit 107 is connected to transmit an RF signal at a second frequency generated by the second RF power supply 103 to the input terminal 115i of the second coil 115.

[0029] In some embodiments, the control component 129 is connected to provide control of the capacitance setting of the second tuned variable capacitor 127. In some embodiments, the control component 129 is a mechanical shaft that extends to a location that is accessible for manual turning of the mechanical shaft, where manual turning of the mechanical shaft provides for changing the capacitance setting of the second tuned variable capacitor 127. In some embodiments, the control component 129 includes a motor, e.g., a stepper motor, and includes a mechanical linkage that extends between the motor and the second tuned variable capacitor 127. In some embodiments, the mechanical linkage translates rotational movement of the motor's shaft into adjustment of the capacitance setting of the second tuned variable capacitor 127, such as by causing movement of spaced apart conductive members (e.g., plates) of the second tuned variable capacitor 127 relative to one another. In some embodiments, the control component 129 is configured to provide remote control of the capacitance setting of the second tuned variable capacitor 127 through transmission of an electrical signal to the control component 129. In some embodiments, operation of the control component 129 is directed by an electrical signal transmitted from the system controller 311 (see FIG. 3A ) such that the capacitance setting of the second tuneable variable capacitor 127 can be set remotely and / or programmatically by the system controller 311. In some embodiments, the reactance of the second reactance circuit 107 is modified by transmitting a Q-factor control signal to the control component 129, the Q-factor control signal directing implementation of a particular change in the reactance of the second reactance circuit 107, such as by directing implementation of a change in the capacitance setting of the second tuneable variable capacitor 127.

[0030] In some embodiments, the RF signal of the second frequency generated by the second RF power source 103 is transmitted to the input terminal 115i of the second coil 115 through a blocking filter 111 on the way. The blocking filter 111 is configured to prevent the RF signal of the first frequency generated by the first RF power source 101 from proceeding to the second RF power source 103. In this manner, the blocking filter 111 supports the transmission of a portion of the RF signal of the first frequency generated by the first RF power source 101 proceeding to the second coil 115 through the output terminal 109o of the current splitter variable capacitor 109. The blocking filter 111 includes an input terminal 111i and an output terminal 111o, where the input terminal 111i is connected to the output terminal 107o of the second reactance circuit 107, and the output terminal 111o is connected to the input terminal 115i of the second coil 115. In some embodiments, the blocking filter 111 includes a capacitor 135 and an inductor 137 connected in parallel with each other between the input terminal 111i and the output terminal 111o of the blocking filter 111. In particular, the capacitor 135 has an input terminal 135i connected to the input terminal 111i of the blocking filter 111 and an output terminal 135o connected to the output terminal 111o of the blocking filter 111. Also, the inductor 137 has an input terminal 137i connected to the input terminal 111i of the blocking filter 111 and an output terminal 137o connected to the output terminal 111o of the blocking filter 111. In various embodiments, the blocking filter 111 may be configured differently from that shown in the example of FIG. 1, so long as the blocking filter 111 provides for the transmission of an RF signal of a second frequency from the second RF power source 103 to the second coil 115 while blocking the transmission of an RF signal of a first frequency from the first RF power source 101 to the second RF power source 103.

[0031] In some embodiments, a blocking filter 117 is optionally connected between the current splitter variable capacitor 109 and the second coil 115. In particular, an input terminal 117i of the blocking filter is connected to an output terminal 109o of the current splitter variable capacitor 109, and an output terminal 117o of the blocking filter 117 is connected to an input terminal 115i of the second coil 115. In some embodiments, the blocking filter 117 is configured like the blocking filter 111 to include a capacitor and an inductor connected in parallel with each other, similar to the capacitor 135 and the inductor 137. In some embodiments, the portion of the RF signal of the first frequency generated by the first RF power source 101 transmitted through the current splitter variable capacitor 109 is then transmitted to the input terminal 115i of the second coil 115 through the blocking filter 117 on the way. The blocking filter 117 is configured to prevent the RF signal of the second frequency generated by the second RF power source 103 from proceeding to the first RF power source 101. In this manner, the blocking filter 117 supports the transmission of an RF signal at the second frequency generated by the second RF power source 103 to the second coil 115. In various embodiments, the blocking filter 117 may be configured in various ways, so long as the blocking filter 117 provides for the transmission of an RF signal at the first frequency from the first RF power source 101 to the second coil 115 while blocking the transmission of an RF signal at the second frequency from the second RF power source 103 to the first RF power source 101.

[0032] In some embodiments, the RF power supply system 100 includes one or more sensors for measuring the amount of RF power delivered to the first coil 113 and / or the amount of RF power delivered to the second coil 115. For example, in some embodiments, a V / I (voltage / current) sensor 139 is connected to provide a measurement of the amount RF power delivered from the first RF power source 101 to the first coil 113. In some embodiments, the V / I sensor 139 is connected between the output terminal 105o of the first reactance circuit 105 and the input terminal 113i of the first coil 113. In some embodiments, another V / I sensor 141 is connected to provide a measurement of the amount RF power delivered from the first RF power source 101 to the second coil 115. In some embodiments, the V / I sensor 141 is connected between the output terminal 109o of the current splitter variable capacitor 109 and the input terminal 115i of the second coil 115. Also, in some embodiments, the V / I sensor 141 is connected between the output terminal 117o of the blocking filter 117 and the input terminal 115i of the second coil 115. In some embodiments, another V / I sensor 143 is connected to provide a measurement of the amount of RF power delivered from the second RF power source 103 to the second coil 115. In some embodiments, the V / I sensor 143 is connected between the output terminal 111o of the blocking filter 111 and the input terminal 115i of the second coil 115. Also, in some embodiments, the V / I sensor 141 is connected between the output terminal 107o of the second reactance circuit 107 and the input terminal 115i of the second coil 115.

[0033] In some embodiments, the V / I sensor 139 is connected to measure the voltage and current present on the electrical conductors in the RF signal delivery path from the first RF power source 101 to the first coil 113. And in some embodiments, the V / I sensor 141 is connected to measure the voltage and current present on the electrical conductors in the RF signal delivery path from the first RF power source 101 to the second coil 115. And in some embodiments, the V / I sensor 143 is connected to measure the voltage and current present on the electrical conductors in the RF signal delivery path from the second RF power source 103 to the second coil 115. In some embodiments, each of the V / I sensors 139, 141, and 143 measures the root mean square (RMS) voltage (V rms ), RMS current (i rms ), and the measured RMS voltage (V rms ) and the measured RMS current (i rms ) and the phase angle (φ) between V / I sensors 139, 141, and 143. In some embodiments, each of V / I sensors 139, 141, and 143 is also configured to measure the RF power (P) transmitted through the corresponding electrical conductor at a given time in relation to the measured RMS voltage (V rms ), the measured RMS current (i rms ), and the measured RMS voltage (V rms ) and the measured RMS current (i rms ) and the phase angle (φ) between rms )(i rms )cos(φ). It should be appreciated that in various embodiments, each of the V / I sensors 139, 141, and 143 may be configured to determine the real-time RF power transmitted through the corresponding electrical conductor at a given time using essentially any available electrical measurement or measurement calculation technique. In some embodiments, a signal indicative of the RF power (P) determined by the V / I sensors 139, 141, 143 at a given time is communicated to the system controller 311 (see FIG. 3A) through an electrical signal connection. Also, in some embodiments, the measured RMS voltage (Vrms ), the measured RMS current (i rms ), and the measured RMS voltage (V rms ) and the measured RMS current (i rms ) and are communicated from the V / I sensors 130, 141, 143 to the system controller 311 through electrical signal connections.

[0034] In some embodiments, the V / I sensors 139, 141, 143 may be used to determine the amount of RF power being delivered to each of the first coil 113 and the second coil 115. In some embodiments, information obtained from the V / I sensors 139, 141, 143 enables the system controller 311 to determine how to adjust the capacitance setting of the current splitter variable capacitor 109 to achieve a target RF current ratio between the first coil 113 and the second coil 115. In some embodiments, the system controller 311 is configured to use one or more of the RF power measurement(s) provided by the V / I sensors 139, 141, 143 as a feedback signal to control, via the control component 133, the capacitance setting of the current splitter variable capacitor 109 such that a target amount of RF power corresponding to an RF signal at the first frequency is delivered from the first RF power source 101 to the second coil 115. For example, in some embodiments, a plasma processing recipe specifies an initial setting point for the capacitance setting of the current splitter variable capacitor 109 and target RF parameters (voltage, current, and / or power) for each of the first coil 113 and the second coil 115. Then, during performance of the plasma processing recipe on the wafer, measurements provided by the V / I sensors 139, 141, and 143 are used by the system controller 311 as feedback signals to control the capacitance setting of the current splitter variable capacitor 109 to achieve and maintain the target RF parameters (voltage, current, and / or power) for each of the first coil 113 and the second coil 115. In this manner, a closed loop feedback control process is implemented using the system controller 311, the control component 133, the current splitter variable capacitor 109, and one or more of the V / I sensors 139, 141, and / or 143.

[0035] FIG. 3A illustrates an exemplary plasma processing system 300 utilizing the RF power supply system 100 according to some embodiments. FIG. 3A illustrates an exemplary vertical cross-section through an exemplary plasma processing chamber 301. The plasma processing chamber 301 includes an outer structure 302, e.g., side and bottom structures, and an upper window structure 303. The upper window structure 303 is formed from a material, e.g., quartz or a similar material, that provides transmission of RF power from the first coil 113 and the second coil 115 to a plasma processing region 310 in the plasma processing chamber 301. A substrate support structure 305 is disposed within the plasma processing region 310 to provide support for the substrate 307 during plasma processing of the substrate 307. The substrate support structure 305 is configured to hold the substrate 307 for exposure to the plasma processing region 310 during plasma processing operations. The plasma processing chamber 301 is connected to a reference ground potential 119.

[0036] The plasma processing system 300 is an inductively coupled system in which RF power is transferred from the first coil 113 and the second coil 115 to the plasma processing region 310. In the exemplary plasma processing system 300, the first coil 113 is an inner coil and the second coil 115 is an outer coil. FIG. 3B shows a plan view of the first coil 113 and the second coil 115 in the plasma processing system 300, according to some embodiments. In the example of FIG. 3B, the first coil 113 (the inner coil) includes a pair of interleaved helical coils 113A and 113B. Each of the coils 113A and 113B has a respective first end connected to receive an RF signal from the output terminal 105o of the first reactance circuit 105. Each of the coils 113A and 113B has a respective second end connected to a reference ground potential 119. Also in the example of FIG. 3B, the second coil 115 (outer coil) includes a pair of interleaved helical coils 115A and 115B collectively positioned to surround the coils 113A and 113B of the first coil 113 (inner coil). Each of the coils 115A and 115B has a respective first end connected to receive an RF signal from the output terminal 111o of the blocking filter 111 and from the output terminal 109o of the current splitter variable capacitor 109 (either directly or via an optional blocking filter 117). Each of the coils 115A and 115B has a respective second end connected to a reference ground potential 119. In various embodiments, each of the first coil 113 and the second coil 115 can have essentially any configuration suitable for transmitting RF power through the upper window structure 303 and to the plasma processing region 310. In various embodiments, each of the first coil 113 and the second coil 115 can have any number of turns and any cross-sectional size and shape (circular, elliptical, rectangular, trapezoidal, etc.) as appropriate to provide transmission of RF power through the upper window structure 303 and to the plasma processing region 310.

[0037] The plasma processing region 310 is fluidly connected to a process gas supply system 313 such that one or more process gases can be supplied to the plasma processing region 310 in a controlled manner, as represented by arrow 315. The process gas supply system 313 includes one or more process gas sources and an arrangement of valves and mass flow controllers to enable provision of one or more process gases to the plasma processing region 310 at controlled flow rates and with controlled flow times. Also, in various embodiments, the one or more process gases are delivered to the plasma processing region 310 in both a temporally controlled manner and a spatially controlled manner relative to the substrate support structure 305 and a substrate 307 held thereon. The plasma processing system 300 also includes an exhaust system that provides controlled removal of process gases from the plasma processing region 310, as indicated by arrow 317. The plasma processing system 300 operates by causing a process gas supply system 313 to flow one or more process gases to the plasma processing region 310 and by transmitting RF power from the first coil 113 and / or the second coil 115 to the plasma processing region 310 to convert the one or more process gases into a plasma 309 (represented by the dashed oval area) in the plasma processing region 310. In some embodiments, a system controller 311 is connected to control the operation of the process gas supply system 313 and to control the operation of the RF power supply system 100.

[0038] The plasma 309 is generated to cause a change in the substrate 307 in a controlled manner. In various fabrication processes, the change in the substrate 307 can be a change in a material or a surface condition on the substrate 307. For example, in various fabrication processes, the change in the substrate 307 can include one or more of etching a material from the substrate 307, depositing a material on the substrate 307, or modifying a material present on the substrate 307. It should be understood that the plasma processing system 300 can be any type of plasma processing system in which RF power is delivered from a first coil 113 and a second coil 115 disposed outside the plasma processing chamber 301 to a process gas in the plasma processing region 310 to generate a plasma 309 in the plasma processing region 310.

[0039] In some embodiments, the substrate 307 is a semiconductor wafer that has undergone a fabrication procedure. However, it should be understood that in various embodiments, the substrate 307 can be essentially any type of substrate that undergoes a plasma-based fabrication process. For example, in some embodiments, the substrate 307 referred to herein can be a substrate formed from silicon, sapphire, GaN, GaAs, or SiC, or other substrate materials, and can include glass panels / substrates, metal foils, metal sheets, polymeric materials, and the like. Also, in various embodiments, the substrate 307 referred to herein can vary in form, shape, and / or size. For example, in some embodiments, the substrate 307 referred to herein can correspond to a 200 mm (millimeter) diameter semiconductor wafer, a 300 mm diameter semiconductor wafer, or a 450 mm diameter semiconductor wafer, among other semiconductor wafer sizes. Also, in some embodiments, the substrate 307 referred to herein can correspond to a non-circular substrate, such as a rectangular substrate for a flat panel display, among other shapes.

[0040] 4 shows a flowchart of a method for supplying RF power to a plasma processing system according to some embodiments. The method includes an operation 401 for generating an RF signal at a first frequency (e.g., by operating a first RF power supply 101). The method also includes an operation 403 for supplying a first portion of the RF signal at the first frequency to a first coil (e.g., 113). The method also includes an operation 405 for supplying a second portion of the RF signal at the first frequency to a second coil (e.g., 115). In some embodiments, the method includes using a current splitter variable capacitor (e.g., 109) to control an amount of the first portion of the RF signal at the first frequency and an amount of the second portion of the RF signal at the first frequency. The method also includes an operation 407 for generating an RF signal at a second frequency (e.g., by operating a second RF power supply 103). The method also includes an operation 409 for supplying an RF signal at the second frequency to a second coil (e.g., 115). In some embodiments, the method includes using a blocking filter (e.g., 111) to prevent the RF signal at the first frequency from passing to a source of the RF signal at the second frequency (e.g., to prevent the RF signal generated by the first RF power supply 101 from passing to the second RF power supply 103).

[0041] In some embodiments, the method includes an operation for controlling a capacitance setting of the current splitter variable capacitor (e.g., 109) to increase an amount of a second portion of the RF signal at the first frequency generated by the first RF power source (e.g., 101) delivered to the second coil (e.g., 115) to support ignition / striking of a plasma driven by the second coil (e.g., 115). Also, in some of these embodiments, the method includes an operation for controlling a capacitance setting of the current splitter variable capacitor (e.g., 109) to decrease an amount of the second portion of the RF signal at the first frequency generated by the first RF power source (e.g., 101) delivered to the second coil (e.g., 115) after ignition / striking of the plasma. In some embodiments, the method includes an operation for controlling a capacitance setting of a current splitter variable capacitor (e.g., 109) to control an amount of a second portion of a RF signal of a first frequency generated by a first RF power source (e.g., 101) delivered to the second coil (e.g., 115) to support stability of a plasma driven by the second coil (e.g., 115). In some embodiments, the method includes an operation for measuring an amount of RF power delivered to the second coil (e.g., 115) by the second portion of the RF signal of a first frequency generated by the first RF power source (e.g., 101). Also, in these embodiments, the method includes an operation for using the measured amount of RF power as a feedback signal to control a capacitance setting of the current splitter variable capacitor (e.g., 109) such that a target amount of RF power is delivered to the second coil (e.g., 115) by the second portion of the RF signal of a first frequency generated by the first RF power source (e.g., 101).

[0042] In some embodiments, the first frequency of the RF signal generated by the first RF power source 101 is about 13 megahertz (MHz), and the second frequency of the RF signal generated by the second RF power source 103 is about 2 MHz. In these embodiments, the capacitance setting of the current splitter variable capacitor 109 is controlled within a range ranging from about 5 picofarads (pF) to about 500 pF. Also, in some of these embodiments, the capacitance setting of the first tuning variable capacitor 121 is controlled within a range ranging from about 5 pF to about 1000 pF, and the inductor 123 has an inductance within a range ranging from about 300 nanohenries (nH) to about 1000 nH. Also, in some of these embodiments, the capacitance setting of the second tuning variable capacitor 127 is controlled within a range ranging from about 5 pF to about 2000 pF, and the capacitor 131 has a capacitance within a range ranging from about 2000 pF to about 3500 pF. Also in some of these embodiments, blocking filter 111 is comprised of capacitor 135 having a capacitance in the range ranging from about 50 pF to about 500 pF and inductor 137 having an inductance in the range ranging from about 200 nH to about 2000 nH. Also in some of these embodiments, optional blocking filter 117 is configured similarly to blocking filter 111.

[0043] In some embodiments, the plasma processing system 300 is programmed via the system controller 311 to perform a plasma processing recipe that includes generating a plasma 309 in a plasma mode in which it is difficult to ignite / light and maintain the plasma 309 using only the transmission of a second frequency RF signal to the second coil 115 in combination with the transmission of a first frequency RF signal to only the first coil 113. For example, for some plasma processing recipes and prescribed plasma modes, the second frequency, e.g., 2 MHz, RF signals generated by the second RF power supply 103 do not provide enough RF power by themselves to ignite / light and maintain the plasma driven by the outer coil 115. Thus, for these plasma processing recipes and prescribed plasma modes, the current splitter variable capacitor 109 is controlled via the control component 133 to transfer some of the first frequency, e.g., 13 MHz, RF signal to the outer coil 115 to assist in igniting / lighting and maintaining the plasma 309 driven by the outer coil 115.

[0044] In various plasma processing recipes, the plasma 309 can be generated either in E-mode, where the plasma 309 is driven primarily by the capacitive electric field between the coil 113 / 115 and the plasma 309, or in H-mode, where the plasma 309 is driven primarily by the magnetic field generated by the coil 113 / 115. In some circumstances, when the plasma 309 is to be generated in H-mode, the RF power supplied by the RF signal at the second frequency transmitted from the second RF power source 103 to the second coil 115 is not sufficient to ignite / ignite and maintain the plasma 309. Also, due to a transition region in the plasma 309 generation, it will be necessary to increase the RF power supplied by the RF signal at the second frequency transmitted from the second RF power source 103 to the second coil 115 by an order of magnitude, for example, from about 300 watts to more than 2 kilowatts, to ignite / ignite and maintain the plasma 309. However, increasing the RF power supplied by the RF signal at the second frequency to such a high level would result in driving an extremely high current through the second coil 115, which is not possible. For example, driving an extremely high current through the second coil 115 may increase the voltage on the second coil 115 to an unacceptable level that would cause problematic plasma sputtering of the upper window structure 303. Thus, in such a situation, generation of the plasma 309 in the H-mode cannot be reliably performed by simply increasing the RF power supplied by the RF signal at the second frequency from the second RF power source 103 to the second coil 115. The RF power supply system 100 provides a solution in this situation that allows reliable ignition / striking and maintaining of the plasma 309 in the H-mode without the need to drive an unacceptably high current through the second coil 115.For example, in this situation, the system controller 311 and control component 133 operate to set the capacitance of the current splitter variable capacitor 109 to transfer a sufficient amount of the RF signal of the first frequency generated by the first RF power supply 101 to the second coil 115 to extend the RF power provided by the RF signal of the second frequency supplied from the second RF power supply 103 to the second coil 115 to support ignition / ignition and maintenance of the plasma 309 in H-mode without resulting in an unacceptably high voltage on the second coil 115 that could cause sputtering of the upper window structure 303.

[0045] In various embodiments, the capacitance setting of the current splitter variable capacitor 109 can be changed between plasma processing steps as needed. For example, a plasma processing recipe can include a processing step in which a majority of the RF signal at the first frequency is transmitted to the first coil 113, followed by another processing step in which some of the RF signal at the first frequency is transferred to the second coil 115 via the current splitter variable capacitor 109 to support coupling of an RF signal at a second frequency from the second coil 115 to the plasma 309. Also, in some embodiments, the system controller 311 is programmed to control the capacitance setting of the current splitter variable capacitor 109 via the control component 133 such that a sufficiently large portion of the RF signal at the first frequency is transmitted from the first RF power source 101 to the second coil 115 for the ignition / ignition phase of plasma 309 generation, followed by a reduction in the portion of the RF signal at the first frequency transmitted from the first RF power source 101 to the second coil 115 after ignition / ignition of the plasma 309, such that the voltage on the second coil 115 is maintained below a level that may cause plasma sputtering of the upper window structure 303, e.g., 1500V. The programmable ability to transfer some of the first frequency RF signal to the second coil 115 provided by the RF power supply system 100, and in particular by the current splitter variable capacitor 109, provides increased reliability of ignition / strike of the plasma 309, improved stability of the plasma 309 during plasma processing operations, and a sufficiently low voltage on the coil 115 to prevent / reduce plasma sputtering of the upper window structure 303.

[0046] The RF power supply system 100 disclosed herein provides a way to split RF power provided by a first frequency, e.g., 13 MHz RF signal between a first coil 113, e.g., an inner coil, and a second coil 115, e.g., an outer coil. The RF power supply system 100 is particularly useful when each of the first RF power source 101 and the second RF power source 103 is a respective direct drive RF signal generator 200. The splitting of a portion of the RF signal at the first frequency to the second coil 115 enables the use of the direct drive RF signal generator 200 for each of the first RF power source 101 and the second RF power source 103 in situations where the RF power provided to the second coil 115 by the RF signal at the second frequency does not result in ignition of the plasma 309, causes instability in the plasma 309, and / or causes sustainability issues for the H-mode plasma 309.

[0047] In some embodiments, by applying a small amount of RF current corresponding to a first frequency, e.g., 13 MHz RF signal, to the second coil 115, both ignition / ignition of the plasma 309 is more likely and the plasma 309 stability window is increased. Also, in some embodiments, the RF current corresponding to a first frequency, e.g., 13 MHz RF signal, provided to the second coil 115 helps to put the plasma 309 into H-mode, and the H-mode maintenance of the plasma 309 is more likely because the RF current corresponding to a second frequency, e.g., 2 MHz RF signal, provided to the second coil 115 cannot put the plasma 309 into H-mode by itself. Furthermore, by applying a small amount of RF current corresponding to a first frequency, e.g., 13 MHz RF signal, to the second coil 115, it is possible to control the spatial distribution of plasma 309 properties such as ion density, electron density, and electron temperature, among other properties of the plasma 309.

[0048] 5 illustrates a diagram of the system controller 311 according to some exemplary embodiments. In some embodiments, the system controller 311 includes a processor 509, a storage hardware unit (HU) 511 (e.g., memory), an input HU 501, an output HU 505, an input / output (I / O) interface 503, an I / O interface 507, a network interface controller (NIC) 515, and a data communication bus 513. The processor 509, the storage HU 511, the input HU 501, the output HU 505, the I / O interface 503, the I / O interface 507, and the NIC 515 are in data communication with each other via the data communication bus 513. Examples of the input HU 501 include a mouse, a keyboard, a stylus, a data acquisition system, a data acquisition card, and the like. Examples of the output HU 505 include a display, a speaker, a device controller, and the like. Examples of the NIC 515 include a network interface card, a network adapter, and the like. In various embodiments, the NIC 515 is configured to operate according to one or more communication protocols and associated physical layers, such as Ethernet and / or EtherCAT, among others. Each of the I / O interfaces 503 and 507 is defined to provide compatibility between different hardware units coupled to the I / O interface. For example, the I / O interface 503 may be defined to convert signals received from the input HU 501 to a format, amplitude, and / or speed compatible with the data communication bus 513. Also, the I / O interface 507 may be defined to convert signals received from the data communication bus 513 to a format, amplitude, and / or speed compatible with the output HU 505. While the various operations described herein are performed by the processor 509 of the system controller 311, it should be understood that in some embodiments, the various operations may be performed by multiple processors of the system controller 311 and / or by multiple processors of multiple computing systems connected to the system controller 311.

[0049] In various embodiments, the plasma processing system 300 is integrated with electronics for controlling its operation before, during, and after processing of the substrate 307, which electronics are implemented in a system controller 311 configured and connected to control various components and / or sub-portions of the plasma processing system 300, including the RF power supply system 100. Depending on the substrate 307 processing requirements and / or the particular configuration of the plasma processing system 300, the system controller 311 is programmed to control any of the processes and / or components disclosed herein, including, among others, delivery of process gas(es) by the process gas supply system 313, temperature settings (e.g., heating and / or cooling), pressure settings, vacuum settings, power settings, RF power supply system 100 settings, electrical signal frequency settings, gas flow rate settings, fluid delivery settings, position and operation settings, substrate 307 transfer to and from the plasma processing chamber 301 and / or to and from load locks connected to or interfaced with the plasma processing system 300.

[0050] In various embodiments, the system controller 311 is defined as electronics having various integrated circuits, logic, memory, and / or software that direct and control various tasks / operations such as receiving instructions, issuing instructions, controlling device operations, enabling cleaning operations, enabling endpoint measurements, enabling metrology measurements (optical, thermal, electrical, etc.), among other tasks / operations. In some embodiments, the integrated circuits in the system controller 311 include one or more of firmware that stores program instructions, digital signal processors (DSPs), application specific integrated circuit (ASIC) chips, programmable logic devices (PLDs), one or more microprocessors, and / or one or more microcontrollers that execute the program instructions (e.g., software), among other computing devices. In some embodiments, the program instructions are communicated to the system controller 311 in the form of various individual settings (or program files) that define operational parameters for performing processes on the substrate 307 in the plasma processing system 300. In some embodiments, the operational parameters are included in a recipe defined by a process engineer to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and / or die on the substrate 307.

[0051] In some embodiments, the system controller 311 is part of, connected to, or a combination of a computer that is integrated with, connected to, or otherwise networked to the plasma processing system 300. For example, in some embodiments, the system controller 311 is implemented in all or part of a “cloud” or fab host computer system, which allows remote access for control of substrate 307 processing by the plasma processing system 300. The system controller 311 allows remote access to the plasma processing system 300 to provide monitoring of the current progress of a fabrication operation, provide examination of the history of past fabrication operations, provide examination of trends or performance metrics from multiple fabrication operations, provide changes to process parameters, provide settings for subsequent processing steps, provide specification of RF power supply system 100 operating parameters, and / or provide initiation of a new substrate fabrication process.

[0052] In some embodiments, a remote computer, such as a server computer system, provides the process recipe to the system controller 311 over a computer network, including a local network and / or the Internet. The remote computer includes a user interface that allows entry or programming of parameters and / or settings, which are then communicated from the remote computer to the system controller 311. In some examples, the system controller 311 receives instructions in the form of settings for processing a substrate 307 in the plasma processing system 300. It should be understood that those settings are specific to the type of process to be performed on the substrate 307 and the type of tools / devices / components that the system controller 311 interfaces with or controls. In some embodiments, the system controller 311 is distributed, such as by including one or more individual system controllers 311 that are networked together and synchronized to work toward a common purpose, such as operating the plasma processing system 300 to perform a defined process on the substrate 307. One example of a distributed system controller 311 for such purposes includes one or more integrated circuits on the chamber in communication with one or more integrated circuits located remotely (such as at the platform level or as part of a remote computer) that are combined to control the process in the chamber. Depending on the process operations to be performed by the plasma processing system 300, the system controller 311 also communicates with various entities throughout the semiconductor fabrication factory, such as other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, nearby tools, distributed tools, a main computer, another controller, or one or more of the tools used in material transport to carry containers of substrates 307 to and from tool locations and / or load ports in the semiconductor fabrication factory.

[0053] Various embodiments described herein may be practiced with a variety of computer system configurations, including portable hardware units, microprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers, and the like. Various embodiments described herein may also be practiced with distributed computing environments in which tasks are performed by remote processing hardware units linked through a computer network. It should also be understood that various embodiments disclosed herein include the performance of various computer-implemented operations involving data stored in computer systems. These computer-implemented operations manipulate physical quantities. In various embodiments, the computer-implemented operations are performed by either general-purpose or special-purpose computers. In some embodiments, the computer-implemented operations are performed by selectively activated computers and / or are directed by one or more computer programs stored in computer memory or retrieved over a computer network. When the computer programs and / or digital data are retrieved over a computer network, the digital data may be processed by other computers on the computer network, e.g., a cloud of computing resources. The computer programs and digital data are stored as computer-readable code on a non-transitory computer-readable medium. A non-transitory computer readable medium is any data storage hardware unit, such as a memory device, that stores data, which is thereafter readable by a computer system. Examples of non-transitory computer readable media include hard drives, network attached storage (NAS), ROM, RAM, compact disk ROM (CD-ROM), CD recordable (CD-R), CD rewriteable (CD-RW), digital video / versatile disk (DVD), magnetic tape, and other optical and non-optical data storage hardware units.In some embodiments, computer programs and / or digital data are distributed among multiple computer readable media in different computer systems within a network of coupled computer systems such that the computer programs and / or digital data are executed and / or stored in a distributed fashion.

[0054] Although the above disclosure includes some details for the purpose of clarity of understanding, it will be apparent that some changes and modifications can be practiced within the scope of the appended claims. For example, it should be understood that one or more features from any embodiment disclosed herein can be combined with one or more features of any other embodiment disclosed herein. Therefore, the present embodiments should be considered as illustrative rather than restrictive, and the claims should not be limited to the details given herein, but can be modified within the scope and equivalents of the described embodiments.

[0055] The claims are as follows:

Claims

1. a first coil; a second coil; and a first radio frequency power source connected to provide a radio frequency signal at a first frequency to both the first coil and the second coil; a current splitter variable capacitor connected to control the division of the radio frequency signal at the first frequency between the first coil and the second coil; a second radio frequency power source connected to provide a radio frequency signal at a second frequency to the second coil; A radio frequency power supply system comprising:

2. 2. The radio frequency power supply system of claim 1, a first reactance circuit connected such that the first radio frequency power source supplies the radio frequency signal at the first frequency through the first reactance circuit to both the first coil and the second coil; a second reactance circuit, the second radio frequency power source connected to supply the radio frequency signal at the second frequency through the second reactance circuit to the second coil; The radio frequency power supply system further comprises:

3. 3. The radio frequency power supply system of claim 2, wherein the first reactance circuit includes a first tunable variable capacitor and an inductor connected in series with the first tunable variable capacitor, an input terminal of the first tunable variable capacitor being connected to an output of the first radio frequency power source, and an output terminal of the inductor being connected to both the first coil and an input terminal of the current splitter variable capacitor.

4. 4. The radio frequency power supply system of claim 3, wherein the second reactance circuit includes a second tunable capacitor and a parallel capacitor connected in parallel with the second tunable capacitor.

5. 3. The radio frequency power supply system of claim 2, a blocking filter connected between the second reactance circuit and the second coil, the blocking filter configured to block the radio frequency signal at the first frequency from passing to the second radio frequency power source; The radio frequency power supply system further comprises:

6. 6. The radio frequency power supply system of claim 5, wherein the blocking filter includes a capacitor connected in parallel with an inductor.

7. 6. The radio frequency power supply system of claim 5, wherein the blocking filter is a first blocking filter, and the radio frequency power supply system includes a second blocking filter connected between the current splitter variable capacitor and the second coil, the second blocking filter configured to block the radio frequency signal at the second frequency from passing to the first radio frequency power source.

8. 10. The radio frequency power supply system of claim 1, wherein the first radio frequency power source is a first direct drive radio frequency power source and the second radio frequency power source is a second direct drive radio frequency power source.

9. 2. The radio frequency power supply system of claim 1, a control component connected to control the capacitance setting of said current splitter variable capacitor in accordance with an electrical control signal received from a system controller; The radio frequency power supply system further comprises:

10. 10. The radio frequency power supply system of claim 9, a first sensor connected to measure a first amount of radio frequency power delivered to the first coil from the first radio frequency power source; a second sensor connected to measure a second amount of radio frequency power delivered to the second coil from the first radio frequency power source; The radio frequency power supply system further comprises:

11. 11. The radio frequency power supply system of claim 10, wherein the system controller is configured to use at least one of the first amount of radio frequency power and the second amount of radio frequency power as a feedback signal for generating the electrical control signal for transmission to the control component.

12. a first radio frequency power source having an output terminal; a first reactance circuit having an input terminal and an output terminal, the input terminal of the first reactance circuit being connected to the output terminal of the first radio frequency power source; a first coil connected to the output terminal of the first reactance circuit; a current splitter variable capacitor having an input terminal and an output terminal, the input terminal of the current splitter variable capacitor being connected to the output terminal of the first reactance circuit; a second coil connected to the output terminal of the current splitter variable capacitor; a second radio frequency power source having an output terminal; a second reactance circuit having an input terminal and an output terminal, the input terminal of the second reactance circuit being connected to the output terminal of the second radio frequency power source; a blocking filter having an input terminal and an output terminal, the input terminal of the blocking filter being connected to the output terminal of the second reactance circuit, and the output terminal of the blocking filter being connected to the second coil; A radio frequency power supply system comprising:

13. 13. The radio frequency power supply system of claim 12, wherein the blocking filter includes a capacitor having an input terminal and an output terminal, the input terminal of the capacitor being connected to the input terminal of the blocking filter and the output terminal of the capacitor being connected to the output terminal of the blocking filter; and the blocking filter includes an inductor having an input terminal and an output terminal, the input terminal of the inductor being connected to the input terminal of the blocking filter and the output terminal of the inductor being connected to the output terminal of the blocking filter.

14. 13. The radio frequency power supply system of claim 12, wherein the first reactive circuit includes a first tunable variable capacitor having an input terminal and an output terminal, the input terminal of the first tunable variable capacitor being connected to the input terminal of the first reactive circuit; the first reactive circuit includes an inductor having an input terminal and an output terminal, the input terminal of the inductor being connected to the output terminal of the first tunable variable capacitor, and the output terminal of the inductor being connected to the output terminal of the first reactive circuit; the second reactance circuit includes a second tunable variable capacitor having an input terminal and an output terminal, the input terminal of the second tunable variable capacitor being connected to the input terminal of the second reactance circuit and the output terminal of the second tunable variable capacitor being connected to the output terminal of the second reactance circuit; the second reactance circuit includes a parallel capacitor having an input terminal and an output terminal, the input terminal of the parallel capacitor being connected to the input terminal of the second reactance circuit and the output terminal of the parallel capacitor being connected to the output terminal of the second reactance circuit.

15. 1. A method for supplying radio frequency power to a plasma processing system, comprising: generating a radio frequency signal at a first frequency; providing a first portion of the radio frequency signal at the first frequency to a first coil; providing a second portion of the radio frequency signal at the first frequency to a second coil; generating a radio frequency signal at a second frequency; providing the radio frequency signal at the second frequency to the second coil; A method comprising:

16. 16. The method of claim 15, using a current splitter variable capacitor to control the amount of the first portion of the radio frequency signal at the first frequency and the amount of the second portion of the radio frequency signal at the first frequency; The method further comprises:

17. 17. The method of claim 16, controlling a capacitance setting of the current splitter variable capacitor to increase the amount of the second portion of the radio frequency signal at the first frequency to support ignition of a plasma driven by the second coil; controlling the capacitance setting of the current splitter variable capacitor to decrease the amount of the second portion of the radio frequency signal at the first frequency after ignition of the plasma; The method further comprises:

18. 17. The method of claim 16, controlling a capacitance setting of the current splitter variable capacitor to control the amount of the second portion of the radio frequency signal at the first frequency to support stability of a plasma driven by the second coil. The method further comprises:

19. 17. The method of claim 16, measuring an amount of radio frequency power delivered to the second coil by the second portion of the radio frequency signal at the first frequency; using the measured amount of radio frequency power as a feedback signal to control a capacitance setting of the current splitter variable capacitor such that a target amount of radio frequency power is delivered to the second coil by the second portion of the radio frequency signal at the first frequency; The method further comprises:

20. 16. The method of claim 15, using a blocking filter to prevent the radio frequency signal at the first frequency from traveling to the source of the radio frequency signal at the second frequency; The method further comprises:

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