Plasma processing apparatus and power supply unit

Abstract

Provided is technology for miniaturizing a power supply unit. This power supply unit includes: a main DC generator configured to generate a main DC signal; a first RF generator configured to generate a first DC signal from the main DC signal, generate a first RF signal from the generated first DC signal, and supply the generated first RF signal to an upper electrode or a lower electrode; a second RF generator configured to generate a second DC signal from the main DC signal, generate a second RF signal from the generated second DC signal, and supply the generated second RF signal to the lower electrode; and a control unit configured to control the distribution of the main DC signal from the main DC generator to the first RF generator and the second RF generator such that the sum of the power level of the first DC signal and the power level of the second DC signal does not exceed the maximum power level of the main DC signal.

Description

Plasma processing apparatus and power supply unit

[0001] SUMMARY OF THE INVENTION An exemplary embodiment of the present disclosure relates to a plasma processing apparatus and a power supply unit.

[0002] Patent Document 1 discloses a distributed power supply apparatus including a set of DC power supply units and a plurality of power generators, each of which is coupled to a different power supply element.

[0003] JP 2015-92483 A

[0004] The present disclosure provides a technique for miniaturizing a power supply unit.

[0005] In one exemplary embodiment of the present disclosure, there is provided a plasma processing apparatus including: a chamber; a substrate support disposed within the chamber and including a lower electrode; an upper electrode disposed above the substrate support; and a power supply unit including: a main DC generator configured to generate a main DC signal; a first RF generator configured to generate a first DC signal from the main DC signal, generate a first RF signal from the generated first DC signal, and supply the generated first RF signal to the upper electrode or the lower electrode; a second RF generator configured to generate a second DC signal from the main DC signal, generate a second RF signal from the generated second DC signal, and supply the generated second RF signal to the lower electrode; and a controller configured to control distribution of the main DC signal from the main DC generator to the first RF generator and the second RF generator such that a sum of a power level of the first DC signal and a power level of the second DC signal does not exceed a maximum power level of the main DC signal.

[0006] According to one exemplary embodiment of the present disclosure, a technology for miniaturizing a power supply unit can be provided.

[0007] FIG. 1 is a diagram for explaining an example of the configuration of a plasma processing system. FIG. 2 is a diagram for explaining an example of the configuration of a capacitively coupled plasma processing apparatus. FIG. 3 is a diagram for explaining an example of the configuration of a power supply 30 of a plasma processing apparatus 1. FIG. 4 is an example of a timing chart relating to distribution control. FIG. 5 is an example of a timing chart relating to distribution control. FIG. 6 is an example of a timing chart relating to distribution control. FIG. 7 is a diagram showing a modified example of the power supply shown in FIG. 3. FIG. 8 is a diagram showing a modified example of the power supply shown in FIG. 3.

[0008] Hereinafter, each embodiment of the present disclosure will be described.

[0009] In one exemplary embodiment, there is provided a plasma processing apparatus comprising: a chamber; a substrate support disposed within the chamber and including a lower electrode; an upper electrode disposed above the substrate support; and a power supply unit including: a main DC generator configured to generate a main DC signal; a first RF generator configured to generate a first DC signal from the main DC signal, generate a first RF signal from the generated first DC signal, and supply the generated first RF signal to one of the upper and lower electrodes; a second RF generator configured to generate a second DC signal from the main DC signal, generate a second RF signal from the generated second DC signal, and supply the generated second RF signal to the lower electrode; and a controller configured to control distribution of the main DC signal from the main DC generator to the first and second RF generators such that a sum of a power level of the first DC signal and a power level of the second DC signal does not exceed a maximum power level of the main DC signal.

[0010] In one exemplary embodiment, the main DC generator includes an AC to DC converter.

[0011] In one exemplary embodiment, the first RF signal has a first power level for a first time period, and the second RF signal has a second power level for the first time period, the sum of the first power level and the second power level being less than or equal to a maximum power level of the main DC signal.

[0012] In one exemplary embodiment, the second power level is a zero power level.

[0013] In one exemplary embodiment, the first RF signal has a third power level during the second time period that is less than the first power level, and the second RF signal has a fourth power level during the second time period that is greater than the second power level, and the sum of the third power level and the fourth power level is less than or equal to the maximum power level of the main DC signal.

[0014] In one exemplary embodiment, the third power level is a zero power level.

[0015] In one exemplary embodiment, the first RF signal has a first power level during a third time period, and the second RF signal has a fourth power level during the third time period, and the sum of the first power level and the fourth power level is less than or equal to the maximum power level of the main DC signal.

[0016] In one exemplary embodiment, the power supply unit further includes a third RF generator configured to generate a third DC signal from the main DC signal, generate a third RF signal from the generated third DC signal, and supply the generated third RF signal to the lower electrode, and the control unit is configured to control distribution of the main DC signal from the main DC generator to the first RF generator, the second RF generator, and the third RF generator so that the sum of the power level of the first DC signal, the power level of the second DC signal, and the power level of the third DC signal does not exceed a maximum power level of the main DC signal.

[0017] In one exemplary embodiment, the power supply unit further includes a secondary DC generator configured to generate a fourth DC signal from the main DC signal, the controller is configured to control distribution of the main DC signal from the main DC generator to the first RF generator, the second RF generator, and the secondary DC generator such that a sum of a power level of the first DC signal, a power level of the second DC signal, and a power level of the fourth DC signal does not exceed a maximum power level of the main DC signal, and the plasma processing apparatus further includes a pulse generator configured to generate a sequence of voltage pulses from the fourth DC signal and supply the generated sequence of voltage pulses to the lower electrode.

[0018] In one exemplary embodiment, there is provided a power supply unit for use in a plasma processing apparatus, the power supply unit comprising: a main DC generator configured to generate a main DC signal; a first RF generator configured to generate a first DC signal from the main DC signal and to generate a first RF signal from the generated first DC signal; a second RF generator configured to generate a second DC signal from the main DC signal and to generate a second RF signal from the generated second DC signal; and a controller configured to control distribution of the main DC signal from the main DC generator to the first RF generator and the second RF generator such that the sum of the power levels of the first DC signal and the second DC signal does not exceed a maximum power level of the main DC signal.

[0019] In one exemplary embodiment, the main DC generator includes an AC to DC converter.

[0020] In one exemplary embodiment, the power converter further includes a third RF generator that generates a third DC signal from the main DC signal and generates a third RF signal from the generated third DC signal, and the control unit is configured to control the distribution of the main DC signal from the main DC generator to the first RF generator, the second RF generator, and the third RF generator so that the sum of the power level of the first DC signal, the power level of the second DC signal, and the power level of the third DC signal does not exceed the maximum power level of the main DC signal.

[0021] In one exemplary embodiment, the power supply further includes a secondary DC generator configured to generate a fourth DC signal from the primary DC signal, and a pulse generator configured to generate a sequence of voltage pulses from the fourth DC signal, wherein the controller is configured to control distribution of the primary DC signal from the primary DC generator to the first RF generator, the second RF generator, and the secondary DC generator such that the sum of the power level of the first DC signal, the power level of the second DC signal, and the power level of the fourth DC signal does not exceed a maximum power level of the primary DC signal.

[0022] In one exemplary embodiment, there is provided a power supply unit for use in a plasma processing apparatus, the power supply unit comprising: a main DC generator configured to generate a main DC signal; a first RF generator configured to generate a first DC signal from the main DC signal and to generate a first RF signal from the generated first DC signal; a secondary DC generator configured to generate a fourth DC signal from the main DC signal; a pulse generator configured to generate a sequence of voltage pulses from the fourth DC signal; and a controller configured to control distribution of the main DC signal from the main DC generator to the first RF generator and the secondary DC generator such that a sum of the power levels of the first DC signal and the fourth DC signal does not exceed a maximum power level of the main DC signal.

[0023] In one exemplary embodiment, the main DC generator includes an AC to DC converter.

[0024] Hereinafter, each embodiment of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or similar elements are designated by the same reference numerals, and redundant explanations will be omitted. Unless otherwise specified, the positional relationships, such as up, down, left, and right, will be described based on the positional relationships shown in the drawings. The dimensional ratios in the drawings do not represent actual ratios, and the actual ratios are not limited to the ratios shown in the drawings.

[0025] <Configuration Example of Plasma Processing System> FIG. 1 is a diagram illustrating a configuration example of a plasma processing system. In one embodiment, the plasma processing system includes a plasma processing apparatus 1 and a control unit 2. The plasma processing system is an example of a substrate processing system, and the plasma processing apparatus 1 is an example of a substrate processing apparatus. The plasma processing apparatus 1 includes a plasma processing chamber 10, a substrate support 11, and a plasma generation unit 12. The plasma processing chamber 10 has a plasma processing space. The plasma processing chamber 10 also has at least one gas supply port for supplying at least one processing gas to the plasma processing space and at least one gas exhaust port for exhausting gas from the plasma processing space. The gas supply port is connected to a gas supply unit 20 (described later), and the gas exhaust port is connected to an exhaust system 40 (described later). The substrate support 11 is disposed in the plasma processing space and has a substrate support surface for supporting a substrate.

[0026] The plasma generating unit 12 is configured to generate plasma from at least one processing gas supplied into the plasma processing space. The plasma generated in the plasma processing space may be capacitively coupled plasma (CCP), inductively coupled plasma (ICP), electron-cyclotron-resonance plasma (ECR plasma), helicon wave plasma (HWP), surface wave plasma (SWP), or the like. Various types of plasma generators may be used, including alternating current (AC) plasma generators and direct current (DC) plasma generators. In one embodiment, the AC signal (AC power) used in the AC plasma generator has a frequency in the range of 100 kHz to 10 GHz. Thus, AC signals include radio frequency (RF) signals and microwave signals. In one embodiment, the RF signal has a frequency in the range of 100 kHz to 150 MHz.

[0027] The control unit 2 processes computer-executable instructions that cause the plasma processing apparatus 1 to perform various processes described in this disclosure. The control unit 2 may be configured to control each element of the plasma processing apparatus 1 to perform various processes described herein. In one embodiment, part or all of the control unit 2 may be included in the plasma processing apparatus 1. The control unit 2 may include a processing unit 2a1, a storage unit 2a2, and a communication interface 2a3. The control unit 2 may be implemented by, for example, a computer 2a. The processing unit 2a1 may be configured to read a program from the storage unit 2a2 and execute the read program to perform various control operations. This program may be stored in the storage unit 2a2 in advance or may be acquired via a medium when needed. The acquired program is stored in the storage unit 2a2 and read from the storage unit 2a2 by the processing unit 2a1 for execution. The medium may be various storage media readable by the computer 2a or a communication line connected to the communication interface 2a3. The processing unit 2a1 may be a CPU (Central Processing Unit). The storage unit 2a2 may include a random access memory (RAM), a read-only memory (ROM), a hard disk drive (HDD), a solid state drive (SSD), or a combination thereof. The communication interface 2a3 may communicate with the plasma processing apparatus 1 via a communication line such as a local area network (LAN).

[0028] The following describes a configuration example of a capacitively coupled plasma processing apparatus as an example of the plasma processing apparatus 1. Fig. 2 is a diagram for explaining a configuration example of a capacitively coupled plasma processing apparatus.

[0029] The capacitively coupled plasma processing apparatus 1 includes a plasma processing chamber 10, a gas supply 20, a power supply 30, and an exhaust system 40. The plasma processing apparatus 1 also includes a substrate support 11 and a gas inlet. The gas inlet is configured to introduce at least one process gas into the plasma processing chamber 10. The gas inlet includes a showerhead 13. The substrate support 11 is disposed within the plasma processing chamber 10. The showerhead 13 is disposed above the substrate support 11. In one embodiment, the showerhead 13 forms at least a portion of the ceiling of the plasma processing chamber 10. The plasma processing chamber 10 has a plasma processing space 10s defined by the showerhead 13, a sidewall 10a of the plasma processing chamber 10, and the substrate support 11. The plasma processing chamber 10 is grounded. The showerhead 13 and the substrate support 11 are electrically insulated from the housing of the plasma processing chamber 10.

[0030] The substrate support 11 includes a main body 111 and a ring assembly 112. The main body 111 has a central region 111a for supporting a substrate W and an annular region 111b for supporting the ring assembly 112. A wafer is an example of a substrate W. The annular region 111b of the main body 111 surrounds the central region 111a of the main body 111 in a plan view. The substrate W is disposed on the central region 111a of the main body 111, and the ring assembly 112 is disposed on the annular region 111b of the main body 111 so as to surround the substrate W on the central region 111a of the main body 111. Therefore, the central region 111a is also called a substrate support surface for supporting the substrate W, and the annular region 111b is also called a ring support surface for supporting the ring assembly 112.

[0031] In one embodiment, the main body 111 includes a base 1110 and an electrostatic chuck 1111. The base 1110 includes a conductive member. The conductive member of the base 1110 can function as a lower electrode. The electrostatic chuck 1111 is disposed on the base 1110. The electrostatic chuck 1111 includes a ceramic member 1111a and an electrostatic electrode 1111b disposed within the ceramic member 1111a. The ceramic member 1111a has a central region 111a. In one embodiment, the ceramic member 1111a also has an annular region 111b. Note that the annular region 111b may also be provided by another member surrounding the electrostatic chuck 1111, such as an annular electrostatic chuck or an annular insulating member. In this case, the ring assembly 112 may be disposed on the annular electrostatic chuck or the annular insulating member, or may be disposed on both the electrostatic chuck 1111 and the annular insulating member. Furthermore, at least one RF / DC electrode coupled to an RF power supply 31 and / or a DC power supply 32, which will be described later, may be disposed within the ceramic member 1111a. In this case, the at least one RF / DC electrode functions as a lower electrode. When a bias RF signal and / or a DC signal, which will be described later, is supplied to the at least one RF / DC electrode, the RF / DC electrode is also called a bias electrode. Note that the conductive member of the base 1110 and the at least one RF / DC electrode may function as multiple lower electrodes. Furthermore, the electrostatic electrode 1111b may function as a lower electrode. Therefore, the substrate support 11 includes at least one lower electrode.

[0032] The ring assembly 112 includes one or more annular members. In one embodiment, the one or more annular members include one or more edge rings and at least one cover ring. The edge rings are formed of a conductive or insulating material, and the cover rings are formed of an insulating material.

[0033] The substrate support 11 may also include a temperature adjustment module configured to adjust at least one of the electrostatic chuck 1111, the ring assembly 112, and the substrate to a target temperature. The temperature adjustment module may include a heater, a heat transfer medium, a flow passage 1110a, or a combination thereof. A heat transfer fluid such as brine or a gas flows through the flow passage 1110a. In one embodiment, the flow passage 1110a is formed in the base 1110, and one or more heaters are disposed in the ceramic member 1111a of the electrostatic chuck 1111. The substrate support 11 may also include a heat transfer gas supply configured to supply a heat transfer gas to a gap between the backside of the substrate W and the central region 111a.

[0034] The showerhead 13 is configured to introduce at least one process gas from the gas supply unit 20 into the plasma processing space 10s. The showerhead 13 has at least one gas supply port 13a, at least one gas diffusion chamber 13b, and multiple gas inlets 13c. The process gas supplied to the gas supply port 13a passes through the gas diffusion chamber 13b and is introduced into the plasma processing space 10s from the multiple gas inlets 13c. The showerhead 13 also includes at least one upper electrode. In addition to the showerhead 13, the gas inlet may also include one or more side gas injectors (SGIs) attached to one or more openings formed in the sidewall 10a.

[0035] The gas supply unit 20 may include at least one gas source 21 and at least one flow controller 22. In one embodiment, the gas supply unit 20 is configured to supply at least one process gas from a corresponding gas source 21 to the showerhead 13 via a corresponding flow controller 22. Each flow controller 22 may include, for example, a mass flow controller or a pressure-controlled flow controller. Additionally, the gas supply unit 20 may include at least one flow modulation device that modulates or pulses the flow rate of the at least one process gas.

[0036] The power supply 30 includes an RF power supply 31 coupled to the plasma processing chamber 10 via at least one impedance matching circuit. The RF power supply 31 is configured to supply at least one RF signal (RF power) to at least one lower electrode and / or at least one upper electrode. This generates a plasma from at least one processing gas supplied to the plasma processing space 10s. Therefore, the RF power supply 31 can function as at least a part of the plasma generation unit 12. Furthermore, by supplying a bias RF signal to the at least one lower electrode, a bias potential is generated on the substrate W, thereby attracting ion components in the formed plasma to the substrate W.

[0037] In one embodiment, the RF power supply 31 includes a first RF generating unit 31a and a second RF generating unit 31b. The first RF generating unit 31a is coupled to at least one lower electrode and / or at least one upper electrode via at least one impedance matching circuit and is configured to generate a source RF signal (source RF power) for plasma generation. In one embodiment, the source RF signal has a frequency in the range of 10 MHz to 150 MHz. In one embodiment, the first RF generating unit 31a may be configured to generate multiple source RF signals having different frequencies. The generated one or more source RF signals are supplied to at least one lower electrode and / or at least one upper electrode.

[0038] The second RF generator 31b is coupled to at least one lower electrode via at least one impedance matching circuit and is configured to generate a bias RF signal (bias RF power). The frequency of the bias RF signal may be the same as or different from the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency lower than the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency in the range of 100 kHz to 60 MHz. In one embodiment, the second RF generator 31b may be configured to generate multiple bias RF signals having different frequencies. The generated one or more bias RF signals are supplied to at least one lower electrode. In various embodiments, at least one of the source RF signal and the bias RF signal may be pulsed.

[0039] The power supply 30 may also include a DC power supply 32 coupled to the plasma processing chamber 10. The DC power supply 32 includes a first DC generator 32a and a second DC generator 32b. In one embodiment, the first DC generator 32a is connected to the at least one lower electrode and configured to generate a first DC signal. The generated first DC signal is applied to the at least one lower electrode. In one embodiment, the second DC generator 32b is connected to the at least one upper electrode and configured to generate a second DC signal. The generated second DC signal is applied to the at least one upper electrode.

[0040] In various embodiments, the first and second DC signals may be pulsed. In this case, a sequence of voltage pulses is applied to at least one lower electrode and / or at least one upper electrode. The voltage pulses may have a rectangular, trapezoidal, triangular, or combination thereof pulse waveform. In one embodiment, a waveform generator for generating the sequence of voltage pulses from the DC signal is connected between the first DC generator 32a and at least one lower electrode. Thus, the first DC generator 32a and the waveform generator constitute a voltage pulse generator. When the second DC generator 32b and the waveform generator constitute a voltage pulse generator, the voltage pulse generator is connected to at least one upper electrode. The voltage pulses may have either positive or negative polarity. Furthermore, the sequence of voltage pulses may include one or more positive voltage pulses and one or more negative voltage pulses within one period. The first and second DC generating units 32a and 32b may be provided in addition to the RF power supply 31, or the first DC generating unit 32a may be provided instead of the second RF generating unit 31b.

[0041] The exhaust system 40 may be connected to, for example, a gas exhaust port 10e provided at the bottom of the plasma processing chamber 10. The exhaust system 40 may include a pressure regulating valve and a vacuum pump. The pressure in the plasma processing space 10s is regulated by the pressure regulating valve. The vacuum pump may include a turbomolecular pump, a dry pump, or a combination thereof.

[0042] <Configuration Example of Power Supply Unit> An example of a power supply unit used in a plasma processing apparatus will be described below. FIG. 3 is a diagram illustrating a configuration example of the power supply 30 of the plasma processing apparatus 1. As shown in FIG. 3, in one embodiment, the power supply 30 includes a main DC generator 300, a first RF generator 310, a second RF generator 320, and a power supply controller PCU. The main DC generator 300 is electrically connected to the input terminal (IN) of the power supply 30 via a transmission line TL0. The first RF generator 310 is electrically connected to the output terminal (ND) of the main DC generator via a transmission line TL1. The second RF generator 320 is electrically connected to the output terminal (ND) of the main DC generator via a transmission line TL2. In one embodiment, the components of the power supply 30 are integrated into a single power supply unit. The components of the power supply 30 may be housed in a single housing.

[0043] The main DC generator 300 is configured to generate a main DC signal. The main DC generator 300 is an example of a main DC generator in the present disclosure. A signal from an external power supply is input to the main DC generator 300 via a transmission line TL0. The external power supply may be an AC power supply such as a commercial power supply. That is, the signal input to the main DC generator 300 may be an AC (alternating current) signal. In this case, the main DC generator 300 includes an AC-DC converter 302. The AC-DC converter 302 rectifies the input AC signal based on a control signal from the power supply controller PCU to convert it to a predetermined maximum power level P ｍａｘ In one embodiment, the external power source may be a DC (direct current) power source. In this case, the main DC generator 300 may include a DC-DC converter instead of the AC-DC converter 302.

[0044] A part or all of the main DC signal generated by the main DC generator 300 is distributed to the first RF generator 310 and the second RF generator 320 based on a control signal from the power supply controller PCU. Details of the distribution control will be described later.

[0045] In one embodiment, the main DC generator 300 may include a capacitor bank 304. The capacitor bank 304 may be disposed on the transmission line TL0 on the output side of the AC-DC converter 302. The capacitor bank 304 is configured to store a portion of the power of the main DC signal (e.g., excess power of the main DC signal that is not distributed from the main DC generator 300 to the first RF generator 310 and the second RF generator 320). The capacitor bank 304 may be configured by combining one or more capacitors.

[0046] The first RF generator 310 is configured to transform and modulate the main DC signal to generate an RF signal (hereinafter referred to as the "first RF signal") of a predetermined frequency. That is, the first RF generator 310 functions as a power amplifier. The first RF generator 310 is an example of the first RF generator in the present disclosure. In one embodiment, the first RF signal has a frequency in the range of 10 MHz to 150 MHz. In one embodiment, the first RF signal may be a source RF signal for plasma generation.

[0047] In one embodiment, the first RF generator 310 includes a DC-DC converter 312 and a DC-RF converter 314. The first RF generator 310 may include a filter 316. The DC-DC converter 312, the DC-RF converter 314, and the filter 316 are arranged on the transmission line TL1 in this order from the input side (ND) to the output side (OUT1) of the first RF generator 310.

[0048] The DC-DC converter 312 receives a part or all of the main DC signal via the transmission line TL1. The DC-DC converter 312 is configured to convert the input main DC signal into a DC signal (hereinafter referred to as a "first DC signal") of a given voltage value based on a control signal from the power supply controller PCU, and output the DC-DC signal to the DC-RF converter 314. In one embodiment, the control signal may include a PAM (Pulse Amplitude Modulation) signal. The DC-DC converter 312 has a function of controlling the power level of the first RF signal output from the DC-RF converter 314.

[0049] The DC-RF converter 314 receives a first DC signal via a transmission line TL1. The DC-RF converter 314 is configured to generate a first RF signal by modulating the input first DC signal based on a control signal from the power supply controller PCU. In one embodiment, the control signal may include a PDM (Pulse Density Modulation) signal or a PWM (Pulse Width Modulation) signal.

[0050] The filter 316 is configured to remove or reduce noise, such as harmonics, from the first RF signal output from the DC-to-RF converter 314 .

[0051] The first RF signal generated in the first RF generator 310 is output to a first output terminal (OUT1) of the power supply 30 via a transmission line TL1. The output first RF signal is supplied to the upper electrode or the lower electrode of the plasma processing apparatus 1 via an impedance matching circuit or the like.

[0052] The second RF generator 320 is configured to transform and modulate the main DC signal to generate an RF signal (hereinafter referred to as the "second RF signal") of a predetermined frequency. That is, the second RF generator 320 functions as a power amplifier. The second RF generator 320 is an example of a second RF generator in the present disclosure. In one embodiment, the frequency of the second RF signal may be the same as or different from the frequency of the first RF signal. In one embodiment, the second RF signal has a frequency lower than the frequency of the first RF signal. In one embodiment, the second RF signal has a frequency in the range of 100 kHz to 60 MHz. In one embodiment, the second RF signal may be a bias RF signal.

[0053] In one embodiment, the second RF generator 320 includes a DC-DC converter 322 and a DC-RF converter 324. The second RF generator 320 may include a filter 326. The DC-DC converter 322, the DC-RF converter 324, and the filter 326 are arranged on the transmission line TL2 in this order from the input side (ND) to the output side (OUT2) of the second RF generator 320.

[0054] The DC-DC converter 322 receives a part or all of the main DC signal via the transmission line TL2. The DC-DC converter 322 is configured to convert the input main DC signal into a DC signal (hereinafter referred to as a "second DC signal") of a given voltage value based on a control signal from the power supply controller PCU, and output the DC-DC signal to the DC-RF converter 324. In one embodiment, the control signal may include a PAM (Pulse Amplitude Modulation) signal. The DC-DC converter 322 has a function of controlling the power level of the second RF signal output from the DC-RF converter 324.

[0055] The DC-RF converter 324 receives a second DC signal via a transmission line TL2. The DC-RF converter 324 is configured to generate a second RF signal by modulating the input second DC signal based on a control signal from the power supply controller PCU. In one embodiment, the control signal may include a pulse density modulation (PDM) signal or a pulse width modulation (PWM) signal.

[0056] The filter 326 is configured to remove or reduce noise, such as harmonics, from the second RF signal output from the DC-to-RF converter 324 .

[0057] The second RF signal generated in the second RF generator 320 is output to the second output terminal (OUT2) of the power supply 30 via a transmission line TL2. The output second RF signal is supplied to the lower electrode of the plasma processing apparatus 1 via an impedance matching circuit or the like.

[0058] The power supply controller PCU is configured to control each component of the power supply 30 based on a control signal input from the control unit 2 (see FIGS. 1 and 2). The power supply controller PCU may be configured to include a processing unit, a storage unit, and a communication interface, similar to the control unit 2. Some or all of the functions of the power supply controller PCU may be executed by the control unit 2. In other words, each component of the power supply 30 may be directly controlled by the control unit 2. The power supply controller PCU and the control unit 2 are examples of the control unit in the present disclosure.

[0059] 3, the power supply 30 is configured to distribute a main DC signal generated by the main DC generator 300 to the first RF generator 310 and the second RF generator 320. That is, the first RF generator 310 and the second RF generator 320 share one main DC generator 300. This allows the power supply 30 to be made smaller than when the first RF generator 310 and the second RF generator 320 are each provided with a main DC generator.

[0060] <Distribution Control of Primary DC Signal> The power supply controller PCU is configured to execute control (hereinafter also referred to as "distribution control") to distribute a part or all of the primary DC signal generated by the primary DC generator 300 to the first RF generator 310 and the second RF generator 320. In one embodiment, the power supply controller PCU controls the distribution of ... ｍａｘ In one embodiment, the power supply controller PCU performs distribution control so that the power level of the first DC signal and the power level of the second DC signal vary periodically. This will be described below with reference to Figures 4A to 4C.

[0061] 4A to 4C are examples of timing charts for explaining distribution control. In FIGS. 4A to 4C, "P1" and "P2" respectively indicate the power level of the first DC signal and the power level of the second DC signal. Also, "V1" and "V2" respectively indicate the voltage level of the first DC signal and the voltage level of the second DC signal. Also, "P ｍａｘ " and "V ｍａｘ " are the maximum power level and maximum voltage level of the main DC signal, respectively.

[0062] In the example shown in Fig. 4A, the power level P1 of the first DC signal varies with a period T1. Also, the power level P2 of the second DC signal varies with a period T1. That is, the first DC signal and the second DC signal are each pulse waves having a period T1. The period T1 includes a period T11 and a period T12 that follows the period T11. The period T11 is an example of a first period in the present disclosure. The period T12 is an example of a second period in the present disclosure.

[0063] In the periods T11 and T12, the sum of the power level P1 of the first DC signal and the power level P2 of the second DC signal is equal to the maximum power level P of the main DC signal. ｍａｘ That is, in the period T11, the power level (P ｍａｘ ) and the power level (zero power level) of the second DC signal (P ｍａｘ ) is the maximum power level P of the main DC signal ｍａｘ In addition, in the period T12, the power level (P １１ <P ｍａｘ ) and the power level of the second DC signal (P ２１ >0) and the sum (P １１ +P ２１ ) is the maximum power level P of the main DC signal ｍａｘ In the period T12, the power level of the first DC signal may be zero, and in this case, the power level of the second DC signal is equal to or less than the maximum power level P ｍａｘ In one embodiment, the power supply controller PCU controls the voltage level V1 (V ｍａｘ →V １１ ) and the voltage level V2 (0 → V ２１ ) may be controlled to achieve the power level control described above.

[0064] In the example shown in FIG. 4B , the power level P1 of the first DC signal fluctuates with a period T2. The power level P2 of the second DC signal fluctuates with a period T2. That is, the first DC signal and the second DC signal are each pulse waves having a period T2. The period T2 includes a period T21, a period T22, a period T23, and a period T24, which are successively arranged in this order. The period T21 is an example of a first period in the present disclosure. The period T22 is an example of a third period in the present disclosure. The period T23 is an example of a second period in the present disclosure.

[0065] During the period T21 to the period T24, the sum of the power level P1 of the first DC signal and the power level P2 of the second DC signal is equal to the maximum power level P ｍａｘ That is, in the period T21, the power level (P １２ <P ｍａｘ ) and the power level (zero power level) of the second DC signal (P １２ ) is the maximum power level P of the main DC signal ｍａｘ During the period T22, the power level (P １２ ) and the power level of the second DC signal (P ２２ >0) and the sum (P １２ +P ２２ ) is the maximum power level P of the main DC signal ｍａｘ In addition, in a period T23, the power level (0≦P １３ <P １２ ) and the power level of the second DC signal (P ２２ >0) is the maximum power level P of the main DC signal. ｍａｘ In addition, during a period T24, the power level (P １３ <P １２ ) and the power level of the second DC signal (zero power level) is the maximum power level P ｍａｘ In one embodiment, the power supply controller PCU adjusts the voltage level V1 (V １２ →V １３ ) and the voltage level V2 (0 → V ２２→0), the above-mentioned power level control may be performed.

[0066] In the example shown in Figure 4C, the power level P1 of the first DC signal fluctuates with a period T3. The power level P2 of the second DC signal fluctuates with a period T3. That is, the first DC signal and the second DC signal are each pulse waves having a period T3. The period T3 includes a period T31, a period T32, a period T33, and a period T34, which are successively arranged in this order. The period T31 is an example of a first period in the present disclosure. The periods T32 and T33 are each an example of a second period in the present disclosure.

[0067] During the period T31 to the period T34, the sum of the power level P1 of the first DC signal and the power level P2 of the second DC signal is equal to the maximum power level P ｍａｘ That is, in the period T31, the power level (P ｍａｘ ) and the power level (zero power level) of the second DC signal (P ｍａｘ ) is the maximum power level P of the main DC signal ｍａｘ In addition, in the period T32, the power level (P １４ <P ｍａｘ ) and the power level of the second DC signal (P ２３ >0) and the sum (P １４ +P ２３ ) is the maximum power level P of the main DC signal ｍａｘ In addition, during a period T33, the power level (P １５ <P １４ ) and the power level of the second DC signal (P ２３ >0) is the maximum power level P of the main DC signal. ｍａｘ In addition, during a period T24, the power level (P １５ <P １４ ) and the power level of the second DC signal (zero power level) is the maximum power level P ｍａｘ In one embodiment, the power supply controller PCU adjusts the voltage level V1 (V ｍａｘ →V １４ →V １５) and the voltage level V2 (0 → V ２３ →0), the above-mentioned power level control may be performed.

[0068] As described above, the power supply controller PCU determines whether the sum of the power level of the first DC signal and the power level of the second DC signal is equal to the maximum power level P of the main DC signal. ｍａｘ That is, the power used by the first RF generator 310 and the second RF generator 320 increases simultaneously (for example, the maximum power level P ｍａｘ This prevents the maximum power level of the main DC generator 300 from being set too low, which allows the main DC generator 300 to be made smaller.

[0069] As described above, according to one exemplary embodiment of the present disclosure, the power supply unit can be made smaller.

[0070] <Example of Plasma Processing Method> The plasma processing performed using the plasma processing apparatus 1 includes an etching process that uses plasma to etch a film on the substrate W. In one embodiment, the plasma processing is executed by the control unit 2.

[0071] First, the substrate W is carried into the plasma processing chamber 10 by the transport arm, placed on the substrate support 11 by the lifter, and held by suction on the substrate support 11 as shown in FIG.

[0072] Next, the processing gas is supplied to the shower head 13 by the gas supply unit 20, and is then supplied to the plasma processing space 10s from the shower head 13. The processing gas supplied at this time includes a gas that generates activated species necessary for etching the substrate W.

[0073] Next, a source RF signal for generating plasma is supplied to the lower electrode and / or the upper electrode. In one embodiment, a bias signal for attracting ions may be supplied to the lower electrode. At this time, the atmosphere in the plasma processing space 10s may be exhausted through the gas exhaust port 10e, and the pressure in the plasma processing space 10s may be reduced to a predetermined pressure. As a result, plasma is generated in the plasma processing space 10s, and the substrate W is etched.

[0074] 3 , the source RF signal may be supplied, for example, as follows: Part or all of the main DC signal generated by the main DC generator 300 is input to the first RF generator 310 by the distribution control described above. The input main DC signal is transformed and modulated in the first RF generator 310 to generate a first RF signal. The generated first RF signal is output from a first output terminal (OUT1) of the power supply 30 and supplied as a source RF signal to the upper electrode or the lower electrode of the plasma processing apparatus 1 via an impedance matching circuit or the like.

[0075] 3 , the bias signal may be supplied, for example, as follows: Part or all of the main DC signal generated by the main DC generator 300 is input to the second RF generator 320 by the distribution control described above. The input main DC signal is transformed and modulated in the second RF generator 320 to generate a second RF signal. The generated second RF signal is output from the second output terminal (OUT2) of the power supply 30 and supplied to the lower electrode of the plasma processing apparatus 1 as a bias RF signal via an impedance matching circuit or the like.

[0076] <Modifications> Figures 5A to 5C are diagrams showing modifications of the power supply shown in Figure 3. Below, differences from the configuration shown in Figure 3 will be mainly described, and a description of the common configuration will be omitted.

[0077] 5A , the power supply 30 may further include a third RF generator 330. The third RF generator 330 is electrically connected to the output terminal (ND) of the main DC generator via a transmission line TL3. A part or all of the main DC signal generated by the main DC generator 300 is distributed to the first RF generator 310, the second RF generator 320, and the third RF generator 330 based on a control signal from the power supply controller PCU. In one embodiment, the power supply controller PCU controls the power level of the first DC signal, the power level of the second DC signal, and the power level of the third DC signal to be equal to the maximum power level P of the main DC signal. ｍａｘ Distribution control is performed so as not to exceed

[0078] The third RF generator 330 is configured to transform and modulate the input main DC signal to generate an RF signal (hereinafter referred to as the "third RF signal") of a predetermined frequency. In other words, the third RF generator 330 functions as a power amplifier. The third RF generator 330 is an example of a third RF generator in the present disclosure. In one embodiment, the frequency of the third RF signal may be the same as or different from the frequency of the second RF signal. In one embodiment, the third RF signal has a frequency lower than the frequency of the second RF signal. In one embodiment, the third RF signal has a frequency in the range of 100 kHz to 600 kHz. In one embodiment, the third RF signal has a frequency in the range of 100 kHz to 2 MHz. In one embodiment, the third RF signal may be a bias RF signal.

[0079] The third RF generator 330 includes a DC-DC converter 332 and a DC-RF converter 334. The third RF generator 330 may include a filter 336. The DC-DC converter 332, the DC-RF converter 334, and the filter 336 are arranged on the transmission line TL3 in this order from the input side (ND) of the third RF generator 330 toward the output side (OUT3). The DC-DC converter 332, the DC-RF converter 334, and the filter 336 may be configured in the same manner as those described for the first RF generator 310 and the second RF generator 320. That is, the DC-DC converter 332 converts the main DC signal into a third DC signal and outputs it to the DC-RF converter 334. The DC-RF converter 334 modulates the input third DC signal to generate a third RF signal. The filter 336 removes or reduces noise such as harmonics from the third RF signal output from the DC-to-RF converter 334 .

[0080] The third RF signal generated in the third RF generator 330 is output to a third output terminal (OUT3) of the power supply 30 via a transmission line TL3. The output third RF signal is supplied to the lower electrode of the plasma processing apparatus 1 via an impedance matching circuit or the like.

[0081] As shown in Fig. 5B, the power supply 30 may include a secondary DC generator 340 and a waveform generating unit 350 instead of the second RF generator 320. Also, as shown in Fig. 5C, the power supply 30 may include a secondary DC generator 340 and a waveform generating unit 350 in addition to the second RF generator 320. The secondary DC generator 340 is electrically connected to the output terminal (ND) of the main DC generator via a transmission line TL4. The waveform generating unit 350 is electrically connected to the output terminal of the secondary DC generator 340 via a transmission line TL4.

[0082] 5B , a part or all of the primary DC signal generated by the primary DC generator 300 is distributed to the first RF generator 310 and the secondary DC generator 340 based on a control signal from the power supply controller PCU. In one embodiment, the power supply controller PCU controls the power level of the first DC signal to be equal to the maximum power level P of the primary DC signal. ｍａｘ Distribution control is performed so as not to exceed

[0083] 5C , a part or all of the primary DC signal generated by the primary DC generator 300 is distributed to the first RF generator 310, the second RF generator 320, and the secondary DC generator 340 based on a control signal from the power supply controller PCU. In one embodiment, the power supply controller PCU determines whether the sum of the power level of the first DC signal, the power level of the second DC signal, and the power level of the fourth DC signal is equal to the maximum power level P of the primary DC signal. ｍａｘ Distribution control is performed so as not to exceed

[0084] 5B and 5C , the secondary DC generator 340 is configured to transform the input primary DC signal to generate a DC signal (hereinafter referred to as a "fourth DC signal") at a predetermined voltage level. The secondary DC generator 340 is an example of a secondary DC generator in the present disclosure. The secondary DC generator 340 includes a DC-DC converter 342 that converts the primary DC signal into the fourth DC signal. The secondary DC generator 340 may include a filter 346 that removes or reduces noise from the fourth DC signal.

[0085] 5B and 5C, the waveform generating unit 350 pulses the input fourth DC signal based on a control signal from the power supply controller PCU. This generates a DC signal including a sequence of voltage pulses (hereinafter referred to as a "pulsed DC signal"). The waveform generating unit 350 is an example of a pulse generator in the present disclosure. In one embodiment, the sequence of voltage pulses has a pulse frequency in the range of, for example, 100 kHz to 600 kHz. The voltage pulses may have positive polarity or negative polarity.

[0086] The pulsed DC signal generated in the waveform generating unit 350 is output to a fourth output terminal (OUT4) of the power supply 30 via a transmission line TL4. In one embodiment, the pulsed DC signal output from the power supply 30 is supplied to a lower electrode of the plasma processing apparatus 1. In one embodiment, the pulsed DC signal output from the power supply 30 is supplied to an upper electrode of the plasma processing apparatus 1. Note that the pulse generator 350 does not have to be included in the power supply 30, and may be provided, for example, on a transmission line between the power supply 30 and the lower electrode or the upper electrode.

[0087] In the examples shown in FIGS. 5A to 5C, the power supply unit can be made smaller in size, similar to the configuration shown in FIG.

[0088] Embodiments of the present disclosure further include the following aspects.

[0089] (Supplementary Note 1) A plasma processing apparatus comprising: a chamber; a substrate support disposed within the chamber and including a lower electrode; an upper electrode disposed above the substrate support; and a power supply unit including: a main DC generator configured to generate a main DC signal; a first RF generator configured to generate a first DC signal from the main DC signal, generate a first RF signal from the generated first DC signal, and supply the generated first RF signal to the upper electrode or the lower electrode; a second RF generator configured to generate a second DC signal from the main DC signal, generate a second RF signal from the generated second DC signal, and supply the generated second RF signal to the lower electrode; and a controller configured to control distribution of the main DC signal from the main DC generator to the first RF generator and the second RF generator such that a sum of a power level of the first DC signal and a power level of the second DC signal does not exceed a maximum power level of the main DC signal.

[0090] (Supplementary Note 2) The plasma processing apparatus of Supplementary Note 1, wherein the main DC generator includes an AC-DC converter.

[0091] (Supplementary Note 3) The plasma processing apparatus according to Supplementary Note 1 or Supplementary Note 2, wherein the first RF signal has a first power level during a first period, the second RF signal has a second power level during the first period, and a sum of the first power level and the second power level is less than or equal to a maximum power level of the main DC signal.

[0092] (Supplementary Note 4) The plasma processing apparatus according to Supplementary Note 3, wherein the second power level is a zero power level.

[0093] (Supplementary Note 5) The plasma processing apparatus according to Supplementary Note 3 or Supplementary Note 4, wherein the first RF signal has a third power level during a second period that is lower than the first power level, the second RF signal has a fourth power level during the second period that is higher than the second power level, and a sum of the third power level and the fourth power level is equal to or lower than a maximum power level of the main DC signal.

[0094] (Supplementary Note 6) The plasma processing apparatus according to Supplementary Note 5, wherein the third power level is a zero power level.

[0095] (Supplementary Note 7) The plasma processing apparatus according to Supplementary Note 5 or Supplementary Note 6, wherein the first RF signal has the first power level during a third period, the second RF signal has the fourth power level during the third period, and a sum of the first power level and the fourth power level is less than or equal to a maximum power level of the main DC signal.

[0096] (Supplementary Note 8) The plasma processing apparatus according to any one of Supplementary Notes 1 to 7, wherein the power supply unit further comprises a third RF generator configured to generate a third DC signal from the main DC signal, generate a third RF signal from the generated third DC signal, and supply the generated third RF signal to the lower electrode, and the control unit is configured to control distribution of the main DC signal from the main DC generator to the first RF generator, the second RF generator, and the third RF generator so that a sum of a power level of the first DC signal, a power level of the second DC signal, and a power level of the third DC signal does not exceed a maximum power level of the main DC signal.

[0097] (Supplementary Note 9) The plasma processing apparatus according to any one of Supplementary Notes 1 to 8, wherein the power supply unit further comprises a secondary DC generator configured to generate a fourth DC signal from the main DC signal, the control unit is configured to control distribution of the main DC signal from the main DC generator to the first RF generator, the second RF generator, and the secondary DC generator such that a sum of a power level of the first DC signal, a power level of the second DC signal, and a power level of the fourth DC signal does not exceed a maximum power level of the main DC signal, and the plasma processing apparatus further comprises a pulse generator configured to generate a sequence of voltage pulses from the fourth DC signal and supply the generated sequence of voltage pulses to the lower electrode.

[0098] (Supplementary Note 10) A power supply unit for use in a plasma processing apparatus, comprising: a main DC generator configured to generate a main DC signal; a first RF generator configured to generate a first DC signal from the main DC signal and to generate a first RF signal from the generated first DC signal; a second RF generator configured to generate a second DC signal from the main DC signal and to generate a second RF signal from the generated second DC signal; and a control unit configured to control distribution of the main DC signal from the main DC generator to the first RF generator and the second RF generator so that a sum of a power level of the first DC signal and a power level of the second DC signal does not exceed a maximum power level of the main DC signal.

[0099] 11. The power supply unit of claim 10, wherein the main DC generator includes an AC-DC converter.

[0100] (Supplementary Note 12) The power supply unit according to Supplementary Note 10 or Supplementary Note 11, further comprising a third RF generator that generates a third DC signal from the main DC signal and generates a third RF signal from the generated third DC signal, wherein the control unit is configured to control distribution of the main DC signal from the main DC generator to the first RF generator, the second RF generator, and the third RF generator so that a sum of a power level of the first DC signal, a power level of the second DC signal, and a power level of the third DC signal does not exceed a maximum power level of the main DC signal.

[0101] (Supplementary Note 13) The power supply unit according to any one of Supplementary Notes 10 to 12, further comprising: a secondary DC generator configured to generate a fourth DC signal from the main DC signal; and a pulse generator configured to generate a sequence of voltage pulses from the fourth DC signal, wherein the controller is configured to control distribution of the main DC signal from the main DC generator to the first RF generator, the second RF generator, and the secondary DC generator such that a sum of a power level of the first DC signal, a power level of the second DC signal, and a power level of the fourth DC signal does not exceed a maximum power level of the main DC signal.

[0102] (Supplementary Note 14) A power supply unit for use in a plasma processing apparatus, comprising: a main DC generator configured to generate a main DC signal; a first RF generator configured to generate a first DC signal from the main DC signal and to generate a first RF signal from the generated first DC signal; a secondary DC generator configured to generate a fourth DC signal from the main DC signal; a pulse generator configured to generate a sequence of voltage pulses from the fourth DC signal; and a controller configured to control distribution of the main DC signal from the main DC generator to the first RF generator and the secondary DC generator such that a sum of a power level of the first DC signal and a power level of the fourth DC signal does not exceed a maximum power level of the main DC signal.

[0103] 15. The power supply unit of claim 14, wherein the main DC generator includes an AC-DC converter.

[0104] The above embodiments are described for the purpose of explanation and are not intended to limit the scope of the present disclosure. Various modifications can be made to the above embodiments without departing from the scope and spirit of the present disclosure. For example, some components in one embodiment can be added to other embodiments. Also, some components in one embodiment can be replaced with corresponding components in other embodiments.

[0105] REFERENCE SIGNS LIST 1: Plasma processing apparatus, 2: Control unit, 10: Plasma processing chamber, 30: Power supply, 300: Main DC generator, 310: First RF generator, 320: Second RF generator, 330: Third RF generator, 340: Secondary DC generator, 350: Waveform generator, PCU: Power supply controller

Claims

1. A plasma processing apparatus comprising: a chamber; a substrate support disposed within the chamber and including a lower electrode; an upper electrode disposed above the substrate support; and a power supply unit including: a main DC generator configured to generate a main DC signal; a first RF generator configured to generate a first DC signal from the main DC signal, generate a first RF signal from the generated first DC signal, and supply the generated first RF signal to the upper electrode or the lower electrode; a second RF generator configured to generate a second DC signal from the main DC signal, generate a second RF signal from the generated second DC signal, and supply the generated second RF signal to the lower electrode; and a controller configured to control distribution of the main DC signal from the main DC generator to the first RF generator and the second RF generator such that a sum of a power level of the first DC signal and a power level of the second DC signal does not exceed a maximum power level of the main DC signal.

2. The plasma processing apparatus of claim 1, wherein the primary DC generator comprises an AC-DC converter.

3. A plasma processing apparatus as described in claim 1 or claim 2, wherein the first RF signal has a first power level during a first period, the second RF signal has a second power level during the first period, and the sum of the first power level and the second power level is less than or equal to a maximum power level of the main DC signal.

4. The plasma processing apparatus of claim 3, wherein the second power level is a zero power level.

5. The plasma processing apparatus of claim 3, wherein the first RF signal has a third power level during the second time period that is less than the first power level, and the second RF signal has a fourth power level during the second time period that is greater than the second power level, and the sum of the third power level and the fourth power level is less than or equal to a maximum power level of the main DC signal.

6. The plasma processing apparatus of claim 5, wherein the third power level is a zero power level.

7. The plasma processing apparatus of claim 5, wherein the first RF signal has the first power level during a third period of time, the second RF signal has the fourth power level during the third period of time, and the sum of the first power level and the fourth power level is less than or equal to a maximum power level of the main DC signal.

8. The plasma processing apparatus of claim 1, wherein the power supply unit further comprises a third RF generator configured to generate a third DC signal from the main DC signal, generate a third RF signal from the generated third DC signal, and supply the generated third RF signal to the lower electrode, and the control unit is configured to control distribution of the main DC signal from the main DC generator to the first RF generator, the second RF generator, and the third RF generator so that a sum of a power level of the first DC signal, a power level of the second DC signal, and a power level of the third DC signal does not exceed a maximum power level of the main DC signal.

9. The plasma processing apparatus of claim 1, wherein the power supply unit further comprises a secondary DC generator configured to generate a fourth DC signal from the main DC signal, the control unit is configured to control distribution of the main DC signal from the main DC generator to the first RF generator, the second RF generator and the secondary DC generator such that a sum of a power level of the first DC signal, a power level of the second DC signal and a power level of the fourth DC signal does not exceed a maximum power level of the main DC signal, and the plasma processing apparatus further comprises a pulse generator configured to generate a sequence of voltage pulses from the fourth DC signal and supply the generated sequence of voltage pulses to the lower electrode.

10. A power supply unit for use in a plasma processing apparatus, comprising: a main DC generator configured to generate a main DC signal; a first RF generator configured to generate a first DC signal from the main DC signal and to generate a first RF signal from the generated first DC signal; a second RF generator configured to generate a second DC signal from the main DC signal and to generate a second RF signal from the generated second DC signal; and a control unit configured to control distribution of the main DC signal from the main DC generator to the first RF generator and the second RF generator such that a sum of a power level of the first DC signal and a power level of the second DC signal does not exceed a maximum power level of the main DC signal.

11. The power supply unit of claim 10, wherein the main DC generator includes an AC-DC converter.

12. The power supply unit of claim 10, further comprising a third RF generator that generates a third DC signal from the main DC signal and generates a third RF signal from the generated third DC signal, and the control unit is configured to control distribution of the main DC signal from the main DC generator to the first RF generator, the second RF generator and the third RF generator so that the sum of the power level of the first DC signal, the power level of the second DC signal and the power level of the third DC signal does not exceed a maximum power level of the main DC signal.

13. The power supply unit of claim 10, further comprising: a secondary DC generator configured to generate a fourth DC signal from the main DC signal; and a pulse generator configured to generate a sequence of voltage pulses from the fourth DC signal, wherein the control unit is configured to control distribution of the main DC signal from the main DC generator to the first RF generator, the second RF generator and the secondary DC generator such that a sum of a power level of the first DC signal, a power level of the second DC signal and a power level of the fourth DC signal does not exceed a maximum power level of the main DC signal.

14. A power supply unit for use in a plasma processing apparatus, comprising: a main DC generator configured to generate a main DC signal; a first RF generator configured to generate a first DC signal from the main DC signal and to generate a first RF signal from the generated first DC signal; a secondary DC generator configured to generate a fourth DC signal from the main DC signal; a pulse generator configured to generate a sequence of voltage pulses from the fourth DC signal; and a controller configured to control distribution of the main DC signal from the main DC generator to the first RF generator and the secondary DC generator such that a sum of a power level of the first DC signal and a power level of the fourth DC signal does not exceed a maximum power level of the main DC signal.

15. A power supply unit as claimed in claim 14, wherein the main DC generator comprises an AC-DC converter.

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