Efficient energy recovery in a nanosecond pulser circuit

Abstract

Some embodiments include a nanosecond pulser circuit. In some embodiments, a nanosecond pulser circuit may include: a high voltage power supply; a nanosecond pulser electrically coupled with the high voltage power supply and switches voltage from the high voltage power supply at high frequencies; a transformer having a primary side and a secondary side, the nanosecond pulser electrically coupled with the primary side of the transformer; and an energy recovery circuit electrically coupled with the secondary side of the transformer. In some embodiments, the energy recovery circuit comprises: an inductor electrically coupled with the high voltage power supply; a crowbar diode arranged in parallel with the secondary side of the transformer; and a second diode disposed in series with the inductor and arranged to conduct current from a load to the high voltage power supply.

Description

BACKGROUND

Producing high voltage pulses with fast rise times and/or fast fall times is challenging. For instance, to achieve a fast rise time and/or a fast fall time (e.g., less than about 50 ns) for a high voltage pulse (e.g., greater than about 5 kV), the slope of the pulse rise and/or fall must be incredibly steep (e.g., greater than 10⁻¹¹ V/s). Such steep rise times and/or fall times are very difficult to produce especially in circuits driving capacitive loads. Such pulse may be especially difficult to produce using standard electrical components in a compact manner; and/or with pulses having variable pulse widths, voltages, and repetition rates; and/or within applications having capacitive loads such as, for example, a plasma.

SUMMARY

Some embodiments include a nanosecond pulser circuit. In some embodiments, a nanosecond pulser circuit may include: a high voltage power supply; a nanosecond pulser electrically coupled with the high voltage power supply and switches voltage from the high voltage power supply at high frequencies; a transformer having a primary side and a secondary side, the nanosecond pulser electrically coupled with the primary side of the transformer; and an energy recovery circuit electrically coupled with the secondary side of the transformer. In some embodiments, the energy recovery circuit comprises: an inductor electrically coupled with the high voltage power supply; a crowbar diode arranged in parallel with the secondary side of the transformer; and a second diode disposed in series with the inductor and arranged to conduct current from a load to the high voltage power supply.

In some embodiments, the energy recover inductor comprises an inductance of greater than about 50 μH.

In some embodiments, the nanosecond pulser switches voltage from the high voltage power supply at frequencies greater than about 100 kHz. In some embodiments, the nanosecond pulser switches voltage from the high voltage power supply at frequencies from about 0 kHz to about 500 kHz. In some embodiments, the nanosecond pulser circuit provides voltage greater than about 5 kV to a load.

In some embodiments, the energy recovery circuit comprises a switch. In some embodiments, the energy recovery circuit further comprises a high voltage switch in series with the second diode and the inductor. In some embodiments, the high voltage switch switches voltages greater than about 5 kV.

In some embodiments, the load comprises a capacitive load. In some embodiments, the load comprises a plasma deposition chamber.

In some embodiments, the high voltage power supply provides DC power with a voltage greater than 500 V, 750 V, 1 kV, 1.5 kV, etc.

Some embodiments include circuit comprising: a storage capacitor; a switching circuit coupled with the storage capacitator, the switching circuit outputs waveforms with voltages greater than about 1 kV and with a frequencies greater than about 1 kHz; a transformer having a primary side and a secondary side, the switching circuit may be electrically coupled with the primary side of the transformer; and an energy recovery circuit electrically coupled with the secondary side of the transformer (e.g., through an energy recovery diode) and the storage capacitor. In some embodiments, the energy recovery circuit comprises an inductor electrically coupled with the high voltage power supply; and a second diode disposed in series with the inductor and arranged to conduct current from a load to the high voltage power supply.

In some embodiments, the energy recovery circuit comprises a crowbar diode arranged in parallel with the secondary transformer.

In some embodiments, the inductor comprises an inductance of greater than about 50 μH.

In some embodiments, the switching circuit comprises a nanosecond pulser. In some embodiments, the switching circuit comprises an RF driver. In some embodiments, the RF driver comprises either a half-bridge driver, a full-bridge driver, a high frequency solid state switch(es), an RF generator, an amplifier tube based RF generator, or a tube based RF generator.

In some embodiments, the circuit further comprises a bias compensation circuit includes a bias compensation diode in parallel with the bias compensation switch; and a DC power supply arranged in series with the bias compensation diode and the bias compensation switch.

Some embodiments include a method for creating high voltage pulses. The method may comprise: opening a bias compensation switch within a bias compensation circuit while closing the pulser switch, the bias compensation circuit coupled with the secondary of the transformer; closing a pulser switch of a nanosecond pulser to create a pulse, the nanosecond pulser coupled with a primary side of a transformer and a DC power supply, the pulse having a voltage greater than 1 kV on a secondary side of the transformer; opening an energy recovery switch within an energy recovery circuit while closing the pulser switch, the energy recovery circuit coupled with the secondary side of the transformer and the DC power supply; pausing for a period of time less than about 100 nanoseconds; closing the pulser switch of the nanosecond pulser; and opening the energy recovery switch within the energy recovery circuit while closing the pulser switch.

In some embodiments, the energy recovery circuit comprises an inductor and a diode in series with the energy recovery switch.

In some embodiments, the energy recovery switch comprises a plurality of switches arranged in series and having a plurality of voltage sharing resistors such that each voltage sharing resistor of the plurality of voltage sharing resistors is arranged across a corresponding switch of the plurality of switches.

In some embodiments, the bias compensation circuit comprises a bias compensation diode in parallel with the bias compensation switch; and a DC power supply arranged in series with the bias compensation diode and the bias compensation switch.

Some embodiments include a method for creating high voltage pulses. The method may comprise: prior to a burst of pulses, opening a bias compensation switch within a bias compensation circuit coupled with a nanosecond pulser through a transformer, the bias compensation circuit coupled with the secondary of the transformer; during a burst of pulses, repeatedly opening and closing a pulser switch of a nanosecond pulser to create a plurality of pulses within the burst of pulses, the nanosecond pulser coupled with a primary side of the transformer and a DC power supply, the opening and closing of the pulser switch occurring with a pulse repetition frequency greater than about 1 kHz, and the closing of the pulser switch produces pulses with a voltage greater than 1 kV on the secondary side of the transformer; during the burst of pulses, repeatedly closing and opening an energy recovery switch within an energy recovery circuit such that the energy recovery switch is closed when the pulser switch is open and the energy recovery switch is open when the pulser switch is closed, the energy recovery circuit coupled with a secondary side of the transformer and the DC power supply; and after the burst of pulses, closing bias compensation switch within a bias compensation circuit.

In some embodiments, the method may further comprise pausing for period of time less than about 100 microseconds; prior to a second burst of pulses, opening the bias compensation switch; during the second burst of pulses, opening and closing the pulser switch; and during the second burst of pulses, closing opening an energy recovery switch; and after the second burst, closing the bias compensation switch.

In some embodiments, the energy recovery circuit comprises an inductor and a diode in series with the energy recovery switch.

In some embodiments, the energy recovery switch comprises a plurality of switches arranged in series and having a plurality of voltage sharing resistors such that each voltage sharing resistor of the plurality of voltage sharing resistors is arranged across a corresponding switch of the plurality of switches.

In some embodiments, the bias compensation circuit comprises a bias compensation diode in parallel with the bias compensation switch; and a DC power supply arranged in series with the bias compensation diode and the bias compensation switch.

Some embodiments include a nanosecond pulser circuit comprising: a high voltage power supply; a nanosecond pulser electrically coupled with the high voltage power supply and configured to switch voltage from the high voltage power supply at high frequencies; a transformer having a primary side and a secondary side; and an energy recovery circuit arranged in parallel with the primary side of the transformer. In some embodiments, the energy recovery circuit comprises a switch; an inductor; a first diode arranged in series with the switch and the inductor such that the first diode conducts current from the switch, when the switch is closed, to the inductor; and a second diode arranged to conduct current from a point in the nanosecond pulser circuit between the switch, when the switch is closed, and the first diode to a point in the nanosecond pulser circuit between the high voltage power supply and the nanosecond pulser.

Some embodiments include a nanosecond pulser circuit comprising: a high voltage power supply; a nanosecond pulser electrically coupled with the high voltage power supply and configured to switch voltage from the high voltage power supply at high frequencies; a transformer having a primary side and a secondary side, the nanosecond pulser electrically coupled with the primary side of the transformer; and an energy recovery circuit electrically coupled with the second side of the transformer in parallel with the primary side of the transformer. In some embodiments, the energy recovery circuit comprises an inductor electrically coupled with the high voltage power supply; a crowbar diode arranged in parallel with the secondary side of the transformer; and a second diode disposed in series with the inductor and arranged to conduct current from a load to the high voltage power supply.

In some embodiments, the inductor comprises an inductance of less than about 1,000 nH. In some embodiments, the nanosecond pulser switches voltage from the high voltage power supply at frequencies greater than about 100 kHz. In some embodiments, the nanosecond pulser switches voltage from the high voltage power supply at frequencies from about 0 kHz to about 500 kHz. In some embodiments, the nanosecond pulser circuit provides voltage greater than about 5 kV to a load. In some embodiments, the secondary side of the transformer is coupled with a capacitive load. In some embodiments, the secondary side of the transformer is coupled with one or more electrodes that produce or manipulate a plasma. In some embodiments, the energy recovery circuit comprises a switch.

These illustrative embodiments are mentioned not to limit or define the disclosure, but to provide examples to aid understanding thereof. Additional embodiments are discussed in the Detailed Description, and further description is provided there. Advantages offered by one or more of the various embodiments may be further understood by examining this specification or by practicing one or more embodiments presented.

BRIEF DESCRIPTION OF THE FIGURES

These and other features, aspects, and advantages of the present disclosure are better understood when the following Detailed Description is read with reference to the accompanying drawings.

FIG. 1 is a circuit diagram of a nanosecond pulser system with an energy recovery circuit driving a capacitive load according to some embodiments.

FIG. 2 illustrates waveforms of the voltage and current within the circuit diagram shown in FIG. 1.

FIG. 3 is a circuit diagram of a nanosecond pulser system that includes a nanosecond pulser with an energy recovery circuit having an energy recover switch according to some embodiments.

FIG. 4 is a circuit diagram of a nanosecond pulser system that includes a passive bias compensation circuit with the energy recovery circuit according to some embodiments.

FIG. 5 is a circuit diagram of a nanosecond pulser system that includes an active bias compensation circuit with the energy recovery circuit according to some embodiments.

FIG. 6 is a circuit diagram of a nanosecond pulser system that includes an active bias compensation circuit with an energy recovery circuit according to some embodiments.

FIG. 7 is a circuit diagram of an RF driver system that includes an RF driver, the active bias compensation circuit, and the energy recovery circuit according to some embodiments.

FIG. 8 are waveforms of the voltage and currents within a nanosecond pulser system.

FIG. 9 is a schematic of a spatially variable wafer bias system according to some embodiments.

FIG. 10 is a circuit diagram of a nanosecond pulser system with the energy recovery circuit according to some embodiments.

FIG. 11 illustrates waveforms of the voltage and current within a nanosecond pulser system.

FIG. 12 is a circuit diagram of a nanosecond pulser system with the energy recovery circuit driving a capacitive load according to some embodiments.

FIG. 13 illustrates waveforms of the voltage and current within the nanosecond pulser system.

FIG. 14 is a block diagram of a high voltage switch with isolated power according to some embodiments.

FIG. 15 is a block diagram of a process for operating a nanosecond pulser system with an active energy recovery circuit and an active bias compensation circuit according to some embodiments.

FIG. 16 shows an illustrative computational system for performing functionality to facilitate implementation of embodiments described herein.

FIG. 17 is a schematic of a spatially variable wafer bias system according to some embodiments.

FIG. 18 is a circuit diagram of an RF driver system that includes an RF driver, the active bias compensation circuit, and the energy recovery circuit according to some embodiments.

DETAILED DESCRIPTION

Some embodiments include a nanosecond pulser system that provides energy recovery from a load (e.g., a capacitive load) using an energy recovery circuit. In some embodiments, the nanosecond pulser system may include a high voltage, high frequency nanosecond pulser, which may, for example, drive a plasma deposition system, plasma etch system, plasma sputtering system, e-beam system, ion beam system, etc. (the load).

In some embodiments, the energy recovery circuit may recover charge from the load to charge an energy storage capacitor. For example, the energy recover circuit may recover energy that was stored by or charge held by various circuit element including capacitors or inductors. These elements, for example, might include stray or parasitic capacitance or inductances which may normally be dissipated or wasted. The energy recovery circuit, for example, may recover energy by acting to recharge an energy storage capacitor and/or inductor. This energy may be available and/or reutilized by the circuit.

FIG. 1 is a circuit diagram of a nanosecond pulser system 100 that includes a nanosecond pulser stage 101 with an energy recovery circuit 110, a transformer T1, a lead stage 103, a DC bias circuit 104, and a load stage 106.

In some embodiments, the load stage 106 may represent an idealized or effective circuit for semiconductor processing chamber such as, for example, a plasma deposition system, semiconductor fabrication system, plasma sputtering system, etc. The capacitance C2, for example, may represent the capacitance of an electrostatic chuck upon which a semiconductor process wafer may sit. The chuck, for example, may comprise a dielectric material (e.g., aluminum oxide, or other ceramic materials and a conductor housed within the dialectic material). For example, the capacitor C1 may have small capacitance (e.g., about 10 pF, 100 pF, 500 pF, 1 nF, 10 nF, 100 nF, etc.).

The capacitor C3, for example, may represent the sheath capacitance between the plasma to the wafer. The resistor R6, for example, may represent the sheath resistance between the plasma and the wafer. The inductor L2, for example, may represent the sheath inductance between the plasma and the wafer. The current source I2, for example, may be represent the ion current through the sheath. For example, the capacitor C1 or the capacitor C3 may have small capacitance (e.g., about 10 pF, 100 pF, 500 pF, 1 nF, 10 nF, 100 nF, etc.).

The capacitor C9, for example, may represent the plasma sheath capacitance to the wall of the chamber. The resistor R7, for example, may represent resistance between the plasma and the chamber wall. The current source I1, for example, may be representative of the ion current in the plasma. For example, the capacitor C1 or the capacitor C9 may have small capacitance (e.g., about 10 pF, 100 pF, 500 pF, 1 nF, 10 nF, 100 nF, etc.).

In some embodiments, the plasma voltage may be the voltage measured from ground to circuit point 123; the wafer voltage is the voltage measured from ground to circuit point 122 and may represent the voltage at the surface of the wafer; the chucking voltage is the voltage measured from ground to circuit point 121; the electrode voltage is the voltage measure from ground to circuit point labeled 124 (e.g., on the electrode); and the input voltage is the voltage measured from ground to circuit point 125.

In this example, the DC bias circuit 104 does not include any bias compensation. The DC bias circuit 104 includes an offset supply voltage V5 that may, for example, bias the output voltage either positively or negatively. In some embodiments, the offset supply voltage V5, can be adjusted to change the potential between the wafer voltage and the chuck voltage. In some embodiments, offset supply voltage V5 can have a voltage of about ±5 kV, ±4 kV, ±3 kV, ±2, kV, ±1 kV, etc. kV.

In some embodiments, the bias capacitor C12 can isolate (or separate) the DC bias voltage from other circuit elements. The bias capacitor C12, for example, may allow for a potential shift from one portion of the circuit to another. In some embodiments, this potential shift may ensure that the electrostatic force holding the wafer in place on the chuck remains below the voltage threshold. The resistor R2 may isolate the DC bias supply from the high voltage pulsed output from the nanosecond pulser stage 101.

The bias capacitor C12, for example, may have a capacitance less than about 100 pF, 10 pF, 1 pF, 100 μF, 10 μF, 1 μF, etc. The resistor R2, for example, may have a high resistance such as, for example, a resistance of about 1 kOhm, 10 kOhm, 100 kOhm, 1 MOhm, 10 MOhm, 100 MOhm, etc.

The resistor R13, for example, may represent the resistance of the leads or transmission lines that connect from the output of the high voltage power system to the electrode (e.g., the load stage 106). The capacitors C1, for example, may represent stray capacitance in the leads or transmissions line.

In some embodiments, the nanosecond pulser stage 101 may produce pulses with high pulse voltage (e.g., voltages greater than 1 kV, 10 kV, 20 kV, 50 kV, 100 kV, etc.), high frequencies (e.g., frequencies greater than 1 kHz, 10 kHz, 100 kHz, 200 kHz, 500 kHz, 1 MHz, etc.), fast rise times (e.g., rise times less than about 1 ns, 10 ns, 50 ns, 100 ns, 250 ns, 500 ns, 1,000 ns, etc.), fast fall times (e.g., fall times less than about 1 ns, 10 ns, 50 ns, 100 ns, 250 ns, 500 ns, 1,000 ns, etc.) and/or short pulse widths (e.g., pulse widths less than about 1,000 ns, 500 ns, 250 ns, 100 ns, 20 ns, etc.).

For example, the nanosecond pulser stage 101 may include all or any portion of any device described in U.S. patent application Ser. No. 14/542,487, titled “High Voltage Nanosecond Pulser,” which is incorporated into this disclosure for all purposes, or all or any portion of any device described in U.S. patent application Ser. No. 14/635,991, titled “Galvanically Isolated Output Variable Pulse Generator Disclosure,” which is incorporated into this disclosure for all purposes, or all or any portion of any device described in U.S. patent application Ser. No. 14/798,154, titled “High Voltage Nanosecond Pulser With Variable Pulse Width and Pulse Repetition Frequency,” which is incorporated into this disclosure for all purposes.

In some embodiments, the nanosecond pulser stage 101 may include one or more nanosecond pulsers coupled together in any number of ways.

In some embodiments, the nanosecond pulser stage 101 may include a DC power supply providing a consistent DC voltage that is switched by switch S6 and provides the switched power to the transformer T1. The DC power supply may include a voltage source V5 and an energy storage capacitor C7. If the transformer T1 has a 1:10 turn ratio, then the transformer may produce 10 kV on the load C1.

In some embodiments, if the load capacitance (e.g., capacitance C3 and capacitance C9) is small in comparison with the capacitance of the energy storage capacitor C7, voltage doubling may (or may not) occur at the transformer input. For example, if the energy storage capacitor C7 provides 500 V, then 1 kV may be measured at the input of the transformer T1.

The switch S6, for example, may include one or more solid state switches such as, for example, an IGBT, a MOSFET, a SiC MOSFET, SiC junction transistor, FETs, SiC switches, GaN switches, photoconductive switch, etc. The switch S6 may be switched based on a signal from a controller labeled Sig6+ and Sig6−.

In some embodiments, the nanosecond pulser stage 101 may include snubber circuit that may include any type of snubber circuit. In some embodiments, the snubber circuit may include a capacitor. In some embodiments, the snubber circuit may include a capacitor and a resistor. In some embodiments, the snubber circuit may include a capacitor, an inductor, and a resistor

In some embodiments, the snubber circuit may include snubber resistor R3 in parallel with snubber diode D4, and a snubber capacitor C5. The snubber circuit may also include stray inductance. In some embodiments, the snubber resistor R3 and/or the snubber diode D4 may be placed between the collector of switch S6 and the primary winding of the transformer T1. The snubber diode D4 may be used to snub out any over voltages in the switching. A large and/or fast capacitor C5 may be coupled on the emitter side of the switch S6. The freewheeling diode D2 may also be coupled with the emitter side of the switch S1. Various other components may be included that are not shown in the figures. One or more switches and or circuits can be arranged in parallel or series.

In some embodiments, the switch S6 may switch so fast that the switched voltage may never be at full voltage (e.g., the voltage of the energy storage capacitor C7 and/or the voltage source V5). In some embodiments, a gate resistor coupled with the switch S6 may be set with short turn on pulses.

In some embodiments, the nanosecond pulser stage 101 may include a freewheeling diode D2. In some embodiments, the freewheeling diode D2 may be used in combination with inductive loads to ensure that energy stored in the inductive load may be allowed to dissipate after the switch S6 is opened by allowing current to keep flowing in the same direction through the inductor and energy is dissipated in the resistive elements of the circuit. If a freewheeling diode D2 is not included, then this can, for example, lead to a large reverse voltage on the switch S6.

In some embodiments, the nanosecond pulser stage 101 may include stray inductance L1 and/or stray resistance R1. The stray inductance L1, for example, may be less than about 10 nH, 100 nH, 1,000 nH, 10,000 nH, etc. The stray resistance R1, for example, may be less than about 1 Ohm, 100 mOhm, 10 mOhm, etc.

In some embodiments, the energy recovery circuit 110 may be electrically coupled with the secondary side of the transformer and/or with the energy storage capacitor C7. The energy recovery circuit 110, for example, may include a diode 130 (e.g., a crowbar diode) across the secondary side of the transformer T1. The energy recovery circuit 110, for example, may include energy recovery diode 120 and the energy recovery inductor 115 (arranged in series), which can allow current to flow from the secondary side of the transformer T1 to charge the energy storage capacitor C7. The energy recovery diode 120 and the energy recovery inductor 115 may be electrically connected with the secondary side of the transformer T1 and the energy storage capacitor C7. In some embodiments, the energy recovery circuit 110 may include diode 130 and/or inductor 140 electrically coupled with the secondary of the transformer T1. The inductor 140 may represent the stray inductance and/or may include the stray inductance of the transformer T1.

In some embodiments, the energy recovery inductor 115 may include any type of inductor such as, for example, a ferrite core inductor or an air core inductor. In some embodiments, the energy recovery inductor 115 may have any type of geometry such as, for example, a solenoidal winding, a toroidal winding, etc. In some embodiments, the energy recovery inductor 115 may have an inductance greater then about 10 μH, 50 μH, 100 μH, 500 μH, etc. In some embodiments, the energy recovery inductor 115 may have an inductance of about 1 μH to about 100 mH.

In some embodiments, when the nanosecond pulser is turned on, current may charge the load stage 106 (e.g., charge the capacitor C3, capacitor C2, or capacitor C9). Some current, for example, may flow through energy recovery inductor 115 when the voltage on the secondary side of the transformer T1 rises above the charge voltage on the energy storage capacitor C7. When the nanosecond pulser is turned off, current may flow from the capacitors within the load stage 106 (e.g., capacitor C1) through the energy recovery inductor 115 to charge the energy storage capacitor C7 until the voltage across the energy recovery inductor 115 is zero. The diode 130 may prevent the capacitors within the load stage 106 from ringing with the inductance in the load stage 106 or the DC bias circuit 104.

The energy recovery diode 120 may, for example, prevent charge from flowing from the energy storage capacitor C7 to the capacitors within the load stage 106.

The value of energy recovery inductor 115 can be selected to control the current fall time. In some embodiments, the energy recovery inductor 115 can have an inductance value between 1 μH-600 μH. In some embodiments, the energy recovery inductor 115 can have an inductance value greater than 50 μH. In some embodiments, the energy recovery inductor 115 may have an inductance less than about 50 μH, 100 μH, 150 μH, 200 μH, 250 μH, 300 μH, 350 μH, 350 μH, 400 μH, 400 μH, 500 μH, etc.

For example, if the energy storage capacitor C7 provides 500 V, then 1 kV will be measured at the input of the transformer T1 (e.g., as noted above due to voltage doubling). The 1 kV at the transformer T1 may be divided among the components of the energy recovery circuit 110 when the switch S6 is open. If the values are chosen appropriately (e.g., inductor L3 has an inductance less than the inductance of energy recovery inductor 115), the voltage across the energy recovery diode 120 and the energy recovery inductor 115 may be greater than 500 V. Current may then flow through energy recovery diode 120 and/or charge the energy storage capacitor C7. Current may also flow through diode D3 and inductor L6. Once the energy storage capacitor C7 is charged, the current may no longer flow through diode D3 and energy recovery inductor 115.

In some embodiments, the energy recovery circuit 110 may transfer energy (or transfer charge) from the load stage 106, for example, on fast time scales (e.g., 1 ns, 10 ns, 50 ns, 100 ns, 250 ns, 500 ns, 1,000 ns, etc. time scales). The stray resistance of the energy recovery circuit may be low to ensure the pulse across the load stage 106 has a fast fall time t_f. The stray resistance of the energy recovery circuit 110, for example, may have a resistance less than about 1 Ohm, 100 mOhm, 10 mOhm, etc. In some embodiments, the energy transfer efficiency from the load stage 106 may be high such as, for example, greater than about 60%, 70%, 80%, or 90%, etc.

Any number of components shown in FIG. 1 may or may not be required such as, for example, the diode 135 or the diode 130 or the inductor 140.

In some embodiments, a diode may be placed between the voltage source V1 and the point where the energy recovery circuit 110 connects with the voltage source V1 and/or the energy storage capacitor C7. This diode, for example, may be arranged to allow current to flow from the voltage source V1 to the energy storage capacitor C7 but may not allow current to flow from the energy recovery circuit to the energy storage capacitor C7.

FIG. 2 illustrates waveforms of the voltage and current within the nanosecond pulser system 100 shown in FIG. 1. The waveform 205 represents the voltage into the load stage 106 measured at the point labeled 124 (e.g., on the electrode) in the nanosecond pulser system 100. The waveform 220 represents the voltage at the point labeled 122 (e.g., on the wafer). The waveform 215 represents the current through the energy recovery inductor 115. The waveform 215 shows that the current through the energy recovery inductor 115 when the nanosecond pulser stage 101 is turned on (e.g., as shown by the light blue waveform rising). When the nanosecond pulser stage 101 is turned off, the current through the energy recovery inductor 115 continues to rise to a maximum prior to falling. The current should stop flowing through the energy recovery inductor 115 when the voltage across the energy recovery inductor 115 goes to zero; however, in this example, the nanosecond pulser stage 101 is turned on again before the voltage across the energy recovery inductor 115 goes to zero.

In some embodiments, the potential at the point labeled 121 in FIG. 1 is shown as negative, however, the chucking potential could also be positive.

FIG. 3 is a circuit diagram of a nanosecond pulser system 300 that includes a nanosecond pulser stage 101 with an active energy recovery circuit 111 having an energy recover switch S5 according to some embodiments. The energy recovery switch S5 may be switched based on a signal from a controller labeled Sig5+ and Sig5−.

In FIG. 3, the active energy recovery circuit 111 may include an energy recovery switch S5 that can be used to control the flow of current through the energy recovery inductor 115. In some embodiments, the energy recovery switch S5 may include a freewheeling diode arranged across the energy recovery switch. The energy recovery switch S5, for example, may be placed in series with the energy recovery inductor 115. In some embodiments, the energy recovery switch S5 may be opened and closed based on a signal from Sig5+ and/or Sig5−. In some embodiments, the switching input V5 may close the energy recovery switch when the switch S1 is open and/or no longer pulsing to allow current to flow from the load stage 106 back to the high voltage load C7. In some embodiments, the switching signal from Sig5+ and/or Sig5− may open the energy recovery switch when the switch S1 is closed and/or pulsing to restrict current from flowing to the high voltage load C7.

The energy recovery switch S5 in FIG. 3 is shown in series with the energy recovery diode 120 and the energy recovery inductor 115 and is placed between the secondary side of the transformer T1 and both the energy recovery diode 120 and the energy recovery inductor 115. In some embodiments, both the energy recovery diode 120 and the energy recovery inductor 115 may be placed between the energy recovery switch S5 and the secondary side of the transformer T1. In some embodiments, the energy recovery switch S5 may be placed between the energy recovery diode 120 and the energy recovery inductor 115. The energy recovery diode 120, the energy recovery inductor 115, and the energy recovery switch S5 may be arranged in any order.

The energy recovery switch S5, for example, may include a high voltage switch such as, for example, the high voltage switch 1400.

In some embodiments, the load stage 106 may be charged by the nanosecond pulser stage 101 while the energy recovery switch S5 is open. It may be beneficial to remove the charge from the load stage 106 such as, for example, on fast time scales (e.g., less than about 1 ns, 10 ns, 50 ns, 100 ns, 250 ns, 500 ns, 1,000 ns, etc.). To remove the charge from the load stage 106, the energy recovery switch S5 may be closed.

FIG. 4 is a circuit diagram of a nanosecond pulser system 400 that includes a passive bias compensation circuit 114 with the energy recovery circuit 110 according to some embodiments.

In this example, the passive bias compensation circuit 114 is a passive bias compensation circuit and can include a bias compensation diode 405 and a bias compensation capacitor 410. The bias compensation diode 405 can be arranged in series with offset supply voltage V5. The bias compensation capacitor 410 can be arranged across either or both the offset supply voltage V5 and the resistor R2. The bias compensation capacitor 410 can have a capacitance less than 100 nF to 100 μF such as, for example, about 100 μF, 50 μF, 25 μF, 10 μF, 2 μF, 500 nF, 200 nF, etc.

In some embodiments, the bias compensation diode 405 can conduct currents of between 10 A and 1 kA at a frequency of between 10 Hz and 500 kHz.

In some embodiments, the bias capacitor C12 may allow for a voltage offset between the output of the nanosecond pulser stage 101 (e.g., at the position labeled 125) and the voltage on the electrode (e.g., at the position labeled 124). In operation, the electrode may, for example, be at a DC voltage of −2 kV during a burst (a burst may include a plurality of pulses), while the output of the nanosecond pulser alternates between +6 kV during pulses and 0 kV between pulses.

The bias capacitor C12, for example, 100 nF, 10 nF, 1 nF, 100 μF, 10 μF, 1 μF, etc. The resistor R2, for example, may have a high resistance such as, for example, a resistance of about 1 kOhm, 10 kOhm, 100 kOhm, 1 MOhm, 10 MOhm, 100 MOhm, etc.

In some embodiments, the bias compensation capacitor 410 and the bias compensation diode 405 may allow for the voltage offset between the output of the nanosecond pulser stage 101 (e.g., at the position labeled 125) and the voltage on the electrode (e.g., at the position labeled 124) to be established at the beginning of each burst, reaching the needed equilibrium state. For example, charge is transferred from capacitor C12 into bias compensation capacitor 410 at the beginning of each burst, over the course of a plurality of pulses (e.g., maybe about 5-100 pulses), establishing the correct voltages in the circuit.

In some embodiments, the pulse repetition frequency (e.g., the frequency of pulses within a burst) may be between 200 kHz and 800 MHz such as, for example, 2 MHz, 13.56 MHz, 27 MHz, 60 MHz, and 80 MHz etc. In some embodiments, the burst repetition frequency (e.g., the frequency of bursts) may be about 10 kHz, 50 Hz, 100 kHz, 500 kHz, 1 MHz, etc. such as, for example, 400 kHz

The energy recovery circuit 110 may or may not include an energy recovery switch as shown in FIG. 3.

FIG. 5 is a circuit diagram of a nanosecond pulser system 500 that includes an active bias compensation circuit 134 with the energy recovery circuit 110 according to some embodiments.

The active bias compensation circuit 134 may include any bias and/or bias compensation circuit known in the art. For example, the active bias compensation circuit 134 may include any bias and/or bias compensation circuit described in U.S. patent application Ser. No. 16/523,840 titled “NANOSECOND PULSER BIAS COMPENSATION,” which is incorporated into this disclosure in its entirety for all purposes.

In some embodiments, the active bias compensation circuit 134 of nanosecond pulser system 500 shown in FIG. 5 may include a bias capacitor C6, blocking capacitor C12, a blocking diode D8, bias compensation bias compensation switch S8 (e.g., a high voltage switch), an offset supply voltage V5, resistance R2, and/or resistance R4. In some embodiments, the switch S8, for example, may include a high voltage switch such as, for example, the high voltage switch 1400 shown in FIG. 14. The bias compensation switch S8 may be switched based on a signal from a controller labeled Sig8+ and Sig8−.

In some embodiments, the offset supply voltage V5 may include a DC voltage source that can bias the output voltage either positively or negatively. In some embodiments, the capacitor C12 may isolate/separate the offset supply voltage V5 from other circuit elements. In some embodiments, the active bias compensation circuit 134 may allow for a potential shift of power from one portion of the circuit to another. In some embodiments, the active bias compensation circuit 134 may be used maintain a constant chucking force between a process wafer and an electrostatic chuck. Resistance R2, for example, may protect/isolate the DC bias supply from the driver. As another example, the resistance R2 may be used to ensure that the DC supply V5 does not go into overcurrent failure.

In some embodiments, the bias compensation switch S8 may be open while the nanosecond pulser stage 101 is not actively producing pulses at greater than 10 kHz or providing a burst of pulses and closed when the nanosecond pulser stage 101 is not pulsing. While closed, the bias compensation switch S8 may, for example, allow current in the direction prevented by the blocking diode D8. Shorting this current may allow the bias between the wafer and the chuck to be less than 2 kV, which may be within acceptable tolerances.

In some embodiments, the load stage 106 may be coupled with the active bias compensation circuit 134. In some embodiments, the energy recovery circuit 110 may or may not include an energy recovery switch as shown in FIG. 3.

FIG. 6 is a circuit diagram of a nanosecond pulser system 600 that includes an active bias compensation circuit 134 with an active energy recovery circuit 111 according to some embodiments.

FIG. 7 is a circuit diagram of a matchless RF driver system 700 that includes an RF driver 705, the active bias compensation circuit 134, and the energy recovery circuit 110 according to some embodiments.

In this example, the matchless driver system 700 may include an RF driver 705 rather than a nanosecond pulser stage 101. The RF driver 705, for example, may be a half-bridge driver or a full-bridge driver. The RF driver 705 may include a voltage source V1 that may be a DC voltage source (e.g., a capacitive source, AC-DC converter, etc.). In some embodiments, the RF driver 705 may include four switches S1, S2, S3, and S4. In some embodiments, the RF driver 705 may include a plurality of switches S1, S2, S3, and S4 in series or in parallel. These switches S1, S2, S3, and S4, for example, may include any type of solid-state switch such as, for example, IGBTs, a MOSFETs, a SiC MOSFETs, SiC junction transistors, FETs, SiC switches, GaN switches, photoconductive switches, etc. These switches S1, S2, S3, and S4 may be switched at high frequencies and/or may produce a high voltage pulses. These frequencies may, for example, include frequencies of about 400 kHz, 0.5 MHz, 2.0 MHz, 4.0 MHz, 13.56 MHz, 27.12 MHz, 40.68 MHz, 50 MHz, etc.

Each switch of switches S1, S2, S3, and S4 may be coupled in parallel with a respective diode D1, D2, D3, and D4 and may include stray inductance represented by inductor L1, L2, L3, and L4. In some embodiments, the inductances of inductor L1, L2, L3, and L4 may be equal. In some embodiments, the inductances of inductor L1, L2, L3, and L4 may be less than about 50 nH, 100 nH, 150 nH, 500 nH, 1,000 nH, etc. The combination of a switch (S1, S2, S3, or S4) and a respective diode (D1, D2, D3, or D4) may be coupled in series with a respective inductor (L1, L2, L3, or L4). Inductors L3 and L4 are connected with ground. Inductor L1 is connected with switch S4 and the resonant circuit 710. And inductor L2 is connected with switch S3 and the opposite side of the resonant circuit 710.

The switches S1, S2, S3, and S4 may include a high voltage switch such as, for example, the high voltage switch 1400 shown in FIG. 14.

In some embodiments, the RF driver 705 may be coupled with a resonant circuit 710. The resonant circuit 710 may include a resonant inductor L5 and/or a resonant capacitor C2 coupled with a transformer T1. The resonant circuit 710 may include a resonant resistance R5, for example, that may include the stray resistance of any leads between the RF driver 705 and the resonant circuit 710 and/or any component within the resonant circuit 710 such as, for example, the transformer T1, the capacitor C2, and/or the inductor L5. In some embodiments, the resonant resistance R5 comprises only stray resistances of wires, traces, or circuit elements. While the inductance and/or capacitance of other circuit elements may affect the driving frequency, the driving frequency can be set largely by choice of the resonant inductor L5 and/or the resonant capacitor C2. Further refinements and/or tuning may be required to create the proper driving frequency in light of stray inductance or stray capacitance. In addition, the rise time across the transformer T1 can be adjusted by changing L5 and/or C2, provided that:

$f_{\mathrm{resonant}}=\frac{1}{2\pi \sqrt{\left(L5\right)\left(C2\right)}}=\mathrm{constant}.$

In some embodiments, large inductance values for L5 can result in slower or shorter rise times. These values may also affect the burst envelope. As shown in FIG. 17, each burst can include transient and steady state pulses. The transient pulses within each burst may be set by L5 and/or the Q of the system until full voltage is reached during the steady state pulses.

If the switches in the RF driver 705 are switched at the resonant frequency, f_resonant, then the output voltage at the transformer T1 will be amplified. In some embodiments, the resonant frequency may be about 400 kHz, 0.5 MHz, 2.0 MHz, 4.0 MHz, 13.56 MHz, 27.12 MHz, 40.68 MHz, 50 MHz, etc.

In some embodiments, the resonant capacitor C2 may include the stray capacitance of the transformer T1 and/or a physical capacitor. In some embodiments, the resonant capacitor C2 may have a capacitance of about 10 μF, 1 μF, 100 nF, 10 nF, etc. In some embodiments, the resonant inductor L5 may include the stray inductance of the transformer T1 and/or a physical inductor. In some embodiments, the resonant inductor L5 may have an inductance of about 50 nH, 100 nH, 150 nH, 500 nH, 1,000 nH, etc. In some embodiments, the resonant resistor R5 may have a resistance of about 10 ohms, 25 ohms, 50 ohms, 100 ohms, 150 ohms, 500 ohms, etc.

In some embodiments, the resonant resistor R5 may represent the stray resistance of wires, traces, and/or the transformer windings within the physical circuit. In some embodiments, the resonant resistor R5 may have a resistance of about 10 mohms, 50 mohms, 100 mohms, 200 mohms, 500 mohms, etc.

In some embodiments, the transformer T1 may comprise a transformer as disclosed in U.S. patent application Ser. No. 15/365,094, titled “High Voltage Transformer,” which is incorporated into this document for all purposes. In some embodiments, the output voltage of the resonant circuit 710 can be changed by changing the duty cycle (e.g., the switch “on” time or the time a switch is conducting) of switches S1, S2, S3, and/or S4. For example, the longer the duty cycle, the higher the output voltage; and the shorter the duty cycle, the lower the output voltage. In some embodiments, the output voltage of the resonant circuit 710 can be changed or tuned by adjusting the duty cycle of the switching in the RF driver 705.

For example, the duty cycle of the switches can be adjusted by changing the duty cycle of signal Sig1, which opens and closes switch S1; changing the duty cycle of signal Sig2, which opens and closes switch S6; changing the duty cycle of signal Sig3, which opens and closes switch S3; and changing the duty cycle of signal Sig4, which opens and closes switch S4. By adjusting the duty cycle of the switches S1, S2, S3, or S4, for example, the output voltage of the resonant circuit 710 can be controlled.

In some embodiments, each switch S1, S2, S3, or S4 in the resonant circuit 710 can be switched independently or in conjunction with one or more of the other switches. For example, the signal Sig1 may be the same signal as signal Sig3. As another example, the signal Sig2 may be the same signal as signal Sig4. As another example, each signal may be independent and may control each switch S1, S2, S3, or S4 independently or separately.

In some embodiments, the resonant circuit 710 may be coupled with a half-wave rectifier 715 that may include a blocking diode D7.

The active bias compensation circuit 134 may include the active bias compensation circuit described in conjunction with FIG. 5.

The matchless driver system 700 does not include a traditional matching network such as, for example, a 50 ohm matching network or an external matching network or standalone matching network. In some embodiments, the matchless driver system 700 does not require a 50 ohm matching network to tune the switching power applied to the wafer chamber. In some embodiments the matchless driver system 700 may include a variable output impedance RF generator without a traditional matching network. This can allow for rapid changes to the power drawn by the plasma chamber. Typically, this tuning of the matching network can take at least 100 μs-200 μs. In some embodiments, power changes can occur within one or two RF cycles, for example, 2.5 μs-5.0 μs at 400 kHz.

In this example, the energy recovery circuit 110 may be positioned on or electrically coupled with the secondary side of the transformer T1. The energy recovery circuit 110, for example, may include a diode 130 (e.g., a crowbar diode) across the secondary side of the transformer T1. The energy recovery circuit 110, for example, may include energy recovery diode 120 and the energy recovery inductor 115 (arranged in series), which can allow current to flow from the secondary side of the transformer T1 to charge the energy storage capacitor C7 and current to flow to the load stage 106. The energy recovery diode 120 and the energy recovery inductor 115 may be electrically connected with the secondary side of the transformer T1 and coupled with the energy storage capacitor C7. In some embodiments, the energy recovery circuit 110 may include diode 130 and/or inductor 140 electrically coupled with the secondary of the transformer T1. The energy recovery inductor 115 may represent the stray inductance and/or may include the stray inductance of the transformer T1.

When the nanosecond pulser is turned on, current may charge capacitors in the load stage 106 (e.g., charge the capacitor C3, capacitor C2, or capacitor C9). Some current, for example, may flow through energy recovery inductor 115 when the voltage on the secondary side of the transformer T1 rises above the charge voltage on the energy storage capacitor C7. When the nanosecond pulser is turned off, current may flow from the capacitors within the load stage 106 (e.g., capacitor C1) through the energy recovery inductor 115 to charge the energy storage capacitor C7 until the voltage across the energy recovery inductor 115 is zero. The diode 130 may prevent the capacitors within the load stage 106 from ringing with the inductance in the load stage 106 or the active bias compensation circuit 134.

The energy recovery diode 120 may, for example, prevent charge from flowing from the energy storage capacitor C7 to the capacitors within the load stage 106.

The value of energy recovery inductor 115 can be selected to control the current fall time. In some embodiments, the energy recovery inductor 115 can have an inductance value between 1 μH-500 μH.

In some embodiments, the energy recovery circuit 110 may include a switch that can be used to control the flow of current through the energy recovery inductor 115. The switch, for example, may be placed in series with the energy recovery inductor 115. In some embodiments, the switch may be closed when the switch S1 is open and/or no longer pulsing to allow current to flow from the load stage 106 back to the energy storage capacitor C7.

A switch in the energy recovery circuit 110, for example, may include a high voltage switch such as, for example, the high voltage switch 1400 shown in FIG. 14.

FIG. 8 are waveforms of the voltage and current within the matchless driver system 700. The waveform 805 represents the voltage on the wafer measured at the point labeled 124 (e.g., on the electrode). The waveform 810 represents the voltage into the load stage 106 measured at the position labeled 122 (e.g., on the wafer). The waveform 815 represents the current through the energy recovery diode 120.

FIG. 9 is a schematic of a spatially variable wafer bias system 900 according to some embodiments. The spatially variable wafer bias system 900 may include a first high voltage pulser 925 coupled with a first energy recovery circuit 926 and a second high voltage pulser 930 coupled with a second energy recovery circuit coupled with a plasma chamber 935. Either or both the first energy recovery circuit 926 and the second energy recovery circuit 931 may include all or some of the components of energy recovery circuit 110 or the active energy recovery circuit 111.

In this example, the first high voltage pulser 925 is coupled with the first energy recovery circuit 926 and a first bias capacitor 915, and/or the second high voltage pulser 930 is coupled with a second energy recovery circuit 931 and a second bias capacitor 921.

A first electrode 950 and a second electrode 955 may be disposed in the plasma chamber 935. In this example, the first electrode 950 is disc shaped and disposed within a central aperture of the second electrode 955. The first high voltage pulser 925 is electrically coupled with the first electrode 950 and the second high voltage pulser 930 is electrically coupled with the second electrode 955. In some embodiments, a stray coupling capacitance 965 can exist between the first high voltage pulser 925 and the second high voltage pulser 930. The stray coupling capacitance 965, for example, may be less than about 100 pF, about 1 nF, about 10 nF, etc.

In some embodiments, either or both the first high voltage pulser 925 and the second high voltage pulser 930 may be coupled with a bias circuit such as, for example, DC bias circuit 104, passive bias compensation circuit 114, or the active bias compensation circuit 134.

In some embodiments, the energy storage capacitor C7₁ in the first nanosecond pulser 925 can be coupled with a first DC power supply and the energy storage capacitor C7₁ in the second nanosecond pulser 930 may be coupled with a second DC power supply.

In some embodiments, the energy storage capacitor C7₂ in the first nanosecond pulser 925 and the energy storage capacitor C7₂ in the second nanosecond pulser 930 may be coupled with a single DC power supply.

In some embodiments, both the first nanosecond pulser 925 and the second nanosecond pulser 930 may be coupled with the same energy storage capacitor, which may be coupled with a DC power supply.

In some embodiments, the switch S6 may be turned on for a different period of time than switch S7. The amount of time a switch is closed may correspond to the voltage applied to the respective electrode. In order to provide different voltages to different electrodes, each switch may be turned on for a different period of time.

Either or both the first nanosecond pulser 925 and the second nanosecond pulser 930 may include a passive bias compensation circuit 114, an active bias compensation circuit 134, or a DC bias circuit 104.

FIG. 10 is a circuit diagram of a nanosecond pulser system 1000 with the energy recovery circuit 110 according to some embodiments. In this example, the nanosecond pulser system 1005 is similar to the nanosecond pulser system 100 with the nanosecond pulser stage 101 switching the other polarity of the energy storage capacitor C7. When switch S6 is open, charge on the capacitor C1 flows through the energy recovery circuit 110 to the high voltage energy storage capacitor C7 and may charge the high voltage energy storage capacitor C7. When the charge on the capacitor C1 is less than the charge on the high voltage energy storage capacitor C7 the current stops flowing through the energy recovery circuit 110. In some embodiments, the DC bias circuit 104 may be replaced with the passive bias compensation circuit 114 or the active bias compensation circuit 134. In some embodiments, the energy recovery circuit 110 may be replaced with the active energy recovery circuit 111.

In some embodiments, a nanosecond pulser (or switches) are included that switch the ground side (see e.g., FIG. 1) or the positive side of the power supply V1 and/or C7 (see e.g., FIG. 10). Either arrangement may be used. A figure showing one arrangement may be replaced with the other arrangement.

FIG. 11 illustrates waveforms of the voltage and current within the nanosecond pulser system 1000 shown in FIG. 10. The waveform 1105 represents the current through the energy recovery inductor 115. The waveform 1110 represents the voltage into the load stage 106 measured at the position labeled 124 (e.g., on the electrode). The waveform 1115 represents the wafer voltage measured at the position labeled 122 (e.g., on the wafer). As shown, when the pulse is turned off, current flows through energy recovery inductor 115, which charges the high voltage energy storage capacitor C7. In this one specific example, the capacitive load is 500 pF and the energy recovery inductor 115 is 10 μH.

FIG. 12 is a circuit diagram of a nanosecond pulser system 1200 with the energy recovery circuit 110 driving a capacitive load 1205 according to some embodiments. In this example, the nanosecond pulser system 1200 is similar to the nanosecond pulser system 100 without the DC bias circuit 104 and is driving a capacitive load 1205. The capacitive load 1205 may include any type of load such as, for example, a plasma load, a plurality of grids, a plurality of electrodes, physical capacitor, a photoconductive switch capacitance, etc.

FIG. 13 illustrates waveforms of the voltage and current within the nanosecond pulser system 1200 shown in FIG. 12. The waveform 1305 represents the voltage at the capacitive load 1205; and the waveform 1310 represents the current through the energy recovery inductor 115. As shown, when the pulse is turned off, current flows through energy recovery inductor 115 to charge the high voltage energy storage capacitor C7. In this one specific example, the load C1 is 500 pF and the energy recovery inductor 115 is 10 μH.

FIG. 14 is a block diagram of a high voltage switch 1400 with isolated power according to some embodiments. The high voltage switch 1400 may include a plurality of switch modules 1405 (collectively or individually 1405, and individually 1405A, 1405B, 1405C, and 1405D) that may switch voltage from a high voltage source 1460 with fast rise times and/or high frequencies and/or with variable pulse widths. Each switch module 1405 may include a switch 1410 such as, for example, a solid state switch.

In some embodiments, the switch 1410 may be electrically coupled with a gate driver circuit 1430 that may include a power supply 1440 and/or an isolated fiber trigger 1445 (also referred to as a gate trigger or a switch trigger). For example, the switch 1410 may include a collector, an emitter, and a gate (or a drain, a source, and a gate) and the power supply 1440 may drive the gate of the switch 1410 via the gate driver circuit 1430. The gate driver circuit 1430 may, for example, be isolated from the other components of the high voltage switch 1400.

In some embodiments, the power supply 1440 may be isolated, for example, using an isolation transformer. The isolation transformer may include a low capacitance transformer. The low capacitance of the isolation transformer may, for example, allow the power supply 1440 to charge on fast time scales without requiring significant current. The isolation transformer may have a capacitance less than, for example, about 100 pF. As another example, the isolation transformer may have a capacitance less than about 30-100 pF. In some embodiments, the isolation transformer may provide voltage isolation up to 1 kV, 5 kV, 10 kV, 25 kV, 50 kV, etc.

In some embodiments, the isolation transformer may have a low stray capacitance. For example, the isolation transformer may have a stray capacitance less than about 1,000 pF, 100 pF, 10 pF, etc. In some embodiments, low capacitance may minimize electrical coupling to low voltage components (e.g., the source of the input control power) and/or may reduce EMI generation (e.g., electrical noise generation). In some embodiments, the transformer stray capacitance of the isolation transformer may include the capacitance measured between the primary winding and secondary winding.

In some embodiments, the isolation transformer may be a DC to DC converter or an AC to DC transformer. In some embodiments, the transformer, for example, may include a 110 V AC transformer. Regardless, the isolation transformer can provide isolated power from other components in the high voltage switch 1400. In some embodiments, the isolation may be galvanic, such that no conductor on the primary side of the isolation transformer passes through or makes contact with any conductor on the secondary side of the isolation transformer.

In some embodiments, the transformer may include a primary winding that may be wound or wrapped tightly around the transformer core. In some embodiments, the primary winding may include a conductive sheet that is wrapped around the transformer core. In some embodiments, the primary winding may include one or more windings.

In some embodiments, a secondary winding may be wound around the core as far from the core as possible. For example, the bundle of windings comprising the secondary winding may be wound through the center of the aperture in the transformer core. In some embodiments, the secondary winding may include one or more windings. In some embodiments, the bundle of wires comprising the secondary winding may include a cross section that is circular or square, for example, to minimize stray capacitance. In some embodiments, an insulator (e.g., oil or air) may be disposed between the primary winding, the secondary winding, or the transformer core.

In some embodiments, keeping the secondary winding far from the transformer core may have some benefits. For example, it may reduce the stray capacitance between the primary side of the isolation transformer and secondary side of the isolation transformer. As another example, it may allow for high voltage standoff between the primary side of the isolation transformer and the secondary side of the isolation transformer, such that corona and/or breakdown is not formed during operation.

In some embodiments, spacings between the primary side (e.g., the primary windings) of the isolation transformer and the secondary side of the isolation transformer (e.g., the secondary windings) can be about 0.1″, 0.5″, 1″, 5″, or 10″. In some embodiments, typical spacings between the core of the isolation transformer and the secondary side of the isolation transformer (e.g., the secondary windings) can be about 0.1″, 0.5″, 1″, 5″, or 10″. In some embodiments, the gap between the windings may be filled with the lowest dielectric material possible such as, for example, vacuum, air, any insulating gas or liquid, or solid materials with a relative dielectric constant less than 3.

In some embodiments, the power supply 1440 may include any type of power supply that can provide high voltage standoff (isolation) or have low capacitance (e.g., less than about 1,000 pF, 100 pF, 10 pF, etc.). In some embodiments, the control voltage power source may supply 1420 V AC or 240 V AC at 60 Hz.

In some embodiments, each power supply 1440 may be inductively electrically coupled with a single control voltage power source. For example, the power supply 1440A may be electrically coupled with the power source via a first transformer; the power supply 1440B may be electrically coupled with the power source via a second transformer; the power supply 1440C may be electrically coupled with the power source via a third transformer; and the power supply 1440D may be electrically coupled with the power source via a fourth transformer. Any type of transformer, for example, may be used that can provide voltage isolation between the various power supplies.

In some embodiments, the first transformer, the second transformer, the third transformer, and the fourth transformer may comprise different secondary winding around a core of a single transformer. For example, the first transformer may comprise a first secondary winding, the second transformer may comprise a second secondary winding, the third transformer may comprise a third secondary winding, and the fourth transformer may comprise a fourth secondary winding. Each of these secondary winding may be wound around the core of a single transformer. In some embodiments, the first secondary winding, the second secondary winding, the third secondary winding, the fourth secondary winding, or the primary winding may comprise a single winding or a plurality of windings wound around the transformer core.

In some embodiments, the power supply 1440A, the power supply 1440B, the power supply 1440C, and/or the power supply 1440D may not share a return reference ground or a local ground.

The isolated fiber trigger 1445, for example, may also be isolated from other components of the high voltage switch 1400. The isolated fiber trigger 1445 may include a fiber optic receiver that allows each switch module 1405 to float relative to other switch modules 1405 and/or the other components of the high voltage switch 1400, and/or, for example, while allowing for active control of the gates of each switch module 1405.

In some embodiments, return reference grounds or local grounds or common grounds for each switch module 1405, for example, may be isolated from one another, for example, using an isolation transformer.

Electrical isolation of each switch module 1405 from common ground, for example, can allow multiple switches to be arranged in a series configuration for cumulative high voltage switching. In some embodiments, some lag in switch module timing may be allowed or designed. For example, each switch module 1405 may be configured or rated to switch 1 kV, each switch module may be electrically isolated from each other, and/or the timing of closing each switch module 1405 may not need to be perfectly aligned for a period of time defined by the capacitance of the snubber capacitor and/or the voltage rating of the switch.

In some embodiments, electrical isolation may provide many advantages. One possible advantage, for example, may include minimizing switch to switch jitter and/or allowing for arbitrary switch timing. For example, each switch 1410 may have switch transition jitters less than about 500 ns, 50 ns, 20 ns, 5 ns, etc.

In some embodiments, electrical isolation between two components (or circuits) may imply extremely high resistance between two components and/or may imply a small capacitance between the two components.

Each switch 1410 may include any type of solid state switching device such as, for example, an IGBT, a MOSFET, a SiC MOSFET, SiC junction transistor, FETs, SiC switches, GaN switches, photoconductive switch, etc. The switch 1410, for example, may be able to switch high voltages (e.g., voltages greater than about 1 kV), with high frequency (e.g., greater than 1 kHz), at high speeds (e.g., a repetition rate greater than about 500 kHz) and/or with fast rise times (e.g., a rise time less than about 25 ns) and/or with long pulse lengths (e.g., greater than about 10 ms). In some embodiments, each switch may be individually rated for switching 1,200 V-1,700 V, yet in combination can switch greater than 4,800 V-6,800 V (for four switches). Switches with various other voltage ratings may be used.

There may be some advantages to using a large number of lower voltage switches rather than a few higher voltage switches. For example, lower voltage switches typically have better performance: lower voltage switches may switch faster, may have faster transition times, and/or may switch more efficiently than high voltage switches. However, the greater the number of switches, for example, the greater the need for switch timing precision.

The high voltage switch 1400 shown in FIG. 14 includes four switch modules 1405. While four are shown in this figure, any number of switch modules 1405 may be used such as, for example, two, eight, twelve, sixteen, twenty, twenty-four, etc. For example, if each switch in each switch module 1405 is rated at 1200 V, and sixteen switches are used, then the high voltage switch can switch up to 19.2 kV. As another example, if each switch in each switch module 1405 is rated at 1700 V, and sixteen switches are used, then the high voltage switch can switch up to 27.2 kV.

In some embodiments, the high voltage switch 1400 may switch voltages greater than 5 kV, 10 kV, 14 kV, 20 kV, 25 kV, etc.

In some embodiments, the high voltage switch 1400 may include a fast capacitor 1455. The fast capacitor 1455, for example, may include one or more capacitors arranged in series and/or in parallel. These capacitors may, for example, include one or more polypropylene capacitors. The fast capacitor 1455 may store energy from the high voltage source 1460.

In some embodiments, the fast capacitor 1455 may have low capacitance. In some embodiments, the fast capacitor 1455 may have a capacitance value of about 1 μF, about 5 μF, between about 1 μF and about 5 μF, between about 100 nF and about 1,000 nF etc.

In some embodiments, the high voltage switch 1400 may or may not include a crowbar diode 1450. The crowbar diode 1450 may include a plurality of diodes arranged in series or in parallel that may, for example, be beneficial for driving inductive loads. In some embodiments, the crowbar diode 1450 may include one or more Schottky diodes such as, for example, a silicon carbide Schottky diode. The crowbar diode 1450 may, for example, sense whether the voltage from the switches of the high voltage switch is above a certain threshold. If it is, then the crowbar diode 1450 may short the power from switch modules to ground. The crowbar diode, for example, may allow an alternating current path to dissipate energy stored in the inductive load after switching. This may, for example, prevent large inductive voltage spikes. In some embodiments, the crowbar diode 1450 may have low inductance such as, for example, 1 nH, 10 nH, 100 nH, etc. In some embodiments, the crowbar diode 1450 may have low capacitance such as, for example, 100 μF, 1 nF, 10 nF, 100 nF, etc.

In some embodiments, the crowbar diode 1450 may not be used such as, for example, when the load 1465 is primarily resistive.

In some embodiments, each gate driver circuit 1430 may produce less than about 1000 ns, 100 ns, 10.0 ns, 5.0 ns, 3.0 ns, 1.0 ns, etc. of jitter. In some embodiments, each switch 1410 may have a minimum switch on time (e.g., less than about 10 μs, 1 μs, 500 ns, 100 ns, 50 ns, 10, 5 ns, etc.) and a maximum switch on time (e.g., greater than 25 s, 10 s, 5 s, 1 s, 500 ms, etc.).

In some embodiments, during operation each of the high voltage switches may be switched on and/or off within 1 ns of each other.

In some embodiments, each switch module 1405 may have the same or substantially the same (±5%) stray inductance. Stray inductance may include any inductance within the switch module 1405 that is not associated with an inductor such as, for example, inductance in leads, diodes, resistors, switch 1410, and/or circuit board traces, etc. The stray inductance within each switch module 1405 may include low inductance such as, for example, an inductance less than about 300 nH, 100 nH, 10 nH, 1 nH, etc. The stray inductance between each switch module 1405 may include low inductance such as, for example, an inductance less than about 300 nH, 100 nH, 10 nH, 1 nH, etc.

In some embodiments, each switch module 1405 may have the same or substantially the same (±5%) stray capacitance. Stray capacitance may include any capacitance within the switch module 1405 that is not associated with a capacitor such as, for example, capacitance in leads, diodes, resistors, switch 1410 and/or circuit board traces, etc. The stray capacitance within each switch module 1405 may include low capacitance such as, for example, less than about 1,000 pF, 100 pF, 10 pF, etc. The stray capacitance between each switch module 1405 may include low capacitance such as, for example, less than about 1,000 pF, 100 pF, 10 pF, etc.

Imperfections in voltage sharing can be addressed, for example, with a passive snubber circuit (e.g., the snubber diode 1415, the snubber capacitor 1420, and/or the freewheeling diode 1425). For example, small differences in the timing between when each of the switches 1410 turn on or turn off or differences in the inductance or capacitances may lead to voltage spikes. These spikes can be mitigated by the various snubber circuits (e.g., the snubber diode 1415, the snubber capacitor 1420, and/or the freewheeling diode 1425).

A snubber circuit, for example, may include a snubber diode 1415, a snubber capacitor 1420, a snubber resistor 1416, and/or a freewheeling diode 1425. In some embodiments, the snubber circuit may be arranged together in parallel with the switch 1410. In some embodiments, the snubber capacitor 1420 may have low capacitance such as, for example, a capacitance less than about 100 μF.

In some embodiments, the high voltage switch 1400 may be electrically coupled with or include a load 1465 (e.g., a resistive or capacitive or inductive load). The load 1465, for example, may have a resistance from 50 ohms to 500 ohms. Alternatively or additionally, the load 1465 may be an inductive load or a capacitive load.

In some embodiments, the energy recovery circuit 110 or the active energy recovery circuit 111 can decrease the energy consumption of a high voltage nanosecond pulser system and/or the voltage required to drive a given load with the same energy output performance as systems without an energy recover circuit. For example, the energy consumption, for the same energy output performance as systems without an energy recover circuit, can be reduced as much as 10%, 15% 20%, 25%, 30%, 40%, 45%, 50%, etc. or more.

In some embodiments, the diode 130, the diode 135, and/or the energy recovery diode 120 may comprise a high voltage diode.

FIG. 15 is a block diagram of a process 1500 for operating a nanosecond pulser system with an active energy recovery circuit and an active bias compensation circuit according to some embodiments. The process 1500 may include additional blocks. The blocks shown in the process 1500 may be removed, replaced, skipped, or performed in any order.

The process 1500, for example, may be executed using the nanosecond pulser system 600 with the active energy recovery circuit 111 and the active bias compensation circuit 134 or similar circuits.

In some embodiments, a nanosecond pulser may be used to produce a plurality of bursts, where each burst includes a plurality of pulses. A pulse can be produced by turning the switches of a nanosecond pulser on and off. The pulse width of each pulse, for example, may vary from 10 seconds to 10 ns. The pulse frequency, for example, may vary from 10 kHz to 1 MHz such as, for example, 400 kHz. Each burst may include a set number of pulses. Each burst may have a burst width, which defines the time to complete a plurality of pulses.

The process 1500 may begin at block 1505 where the counter n is set initialized to 1. The counter n counts the number of pulses in a given burst.

At block 1510 the bias compensation switch (e.g., switch S8) may be opened.

At block 1515 the nanosecond pulser switch (e.g., switch S6) may be closed.

At block 1520 the energy recovery switch (e.g., switch S5) may be opened.

In some embodiments, the blocks 1510, 1515, and 1520 may occur at substantially the same time or within 10 ns or 100 ns, etc. In some embodiments, the blocks 1515 and 1520 may occur at substantially the same time.

At block 1525, the process 1500 may pause (e.g., a pulse) for a time period that defines the pulse width of each pulse. In some embodiments, the pulse width of a pulse may define the voltage of the pulse at the load such as, for example, a capacitive load by defining the amount of time the load is charged to a particular voltage. The output voltage at a capacitive load produced by a pulse, for example, may depend on the amount of time the nanosecond pulser switch is closed and, therefore, the amount of time the pulse is charging the capacitive load. Thus, the output voltage at the load of the pulse may be defined by the voltage pause time period up to the maximum output voltage of the nanosecond pulser or some multiple of the maximum output voltage of the nanosecond pulser if it is pulsing into an inductor and/or capacitor that produces some voltage ring up. The voltage pause, for example, may be about 10 ns—about 500 ns nanoseconds or about 50 ns to about 200 ns, or 500 ns, 73.75 ns, 27 ns, 16 ns, or 12.5 ns.

At block 1530 the nanosecond pulser switch (e.g., switch S6) may be opened.

At block 1535 the energy recovery switch (e.g., switch S5) may be closed.

In some embodiments, the blocks 1530 and 1535 may occur at substantially the same time.

At block 1540 it can be determined whether counter n is equal to the number of desired pulses N. While there is no limit to the number of pulses within a burst, the number of desired pulses N, for example, may be 5-1,000. In some embodiments, the pulses may run continuously. As such N may be nearly infinite. If the counter n is not equal to the number of desired pulses N (i.e., fewer than the desired number of pulses have occurred in the burst) then process 1500 proceeds to block 1545.

At block 1545, the process 1500 may pause for a period of time (e.g., pulse pause) that may, in part, define the pulse frequency. For example, the pulse pause time period may be less than 500 ns, 250 ns, 100 ns, 50 ns, 10 ns, 5 ns, etc. The pulse pause time period, for example, may include any time period.

At block 1550, the counter n is incremented, and portions of process 1500 may repeat by proceed to block 1515 to create an additional pulse. At block 1540, if the counter n is equal to the number of desired pulses N (i.e., the desired number of pulses have been created then process 1500 proceeds to block 1555. At block 1555 the bias compensation switch (e.g., switch S8) may be closed.

At block 1560, the process 1500 pauses for a time period (e.g., burst pause) that defines the amount of time between bursts. The burst pause time period may, for example, be as small as 1 ms or as long as 20 seconds. For example, the pulse pause may include a time period between 2.5 microseconds (pulse frequency of 200 Hz) and 100 ms. As another example, the pulse pause may be from 10 ms to a number of hours. Any other time period may be used. After the time period has passed, process 1500 may return to block 1505 where counter n is initialized and the process 1500 may be repeated to create an additional burst with additional pulses.

When the nanosecond pulser switch is closed, the energy recover switch is open, and the bias compensation switch is open, a high voltage pulse (e.g., greater than 1 kV) may be produced at the circuit position 124.

In some embodiments, the pulse pause time period may be less than the burst pause time period.

In some embodiments, block 1520 and block 1535 may be eliminated from process 1500. In such embodiments, when the energy recovery switch is not used, the nanosecond pulser switch is closed and the bias compensation switch is open, a high voltage pulse (e.g., greater than 1 kV) may be produced at the circuit position 124.

In some embodiments, the blocks of process 1500 may be executed using a controller (or processor) such as, for example, the computational system 1600, shown in FIG. 16. The controller, for example, may be in communication with switch S6 via Sig6+ and Sig6−, bias compensation switch S8 via Sig8+ and Sig8−, and/or energy recovery switch S5 via Sig5+ and Sig5−. The controller may provide signals that open and close the nanosecond pulser switch, the energy recovery switch, and/or the bias compensation switch.

The computational system 1600, shown in FIG. 16 can be used to perform any of the embodiments of the invention. For example, computational system 1600 can be used to execute process 1500. As another example, computational system 1600 can be used perform any calculation, identification and/or determination described here. Computational system 1600 includes hardware elements that can be electrically coupled via a bus 1605 (or may otherwise be in communication, as appropriate). The hardware elements can include one or more processors 1610, including without limitation one or more general-purpose processors and/or one or more special-purpose processors (such as digital signal processing chips, graphics acceleration chips, and/or the like); one or more input devices 1615, which can include without limitation a mouse, a keyboard and/or the like; and one or more output devices 1620, which can include without limitation a display device, a printer and/or the like.

The computational system 1600 may further include (and/or be in communication with) one or more storage devices 1625, which can include, without limitation, local and/or network accessible storage and/or can include, without limitation, a disk drive, a drive array, an optical storage device, a solid-state storage device, such as a random access memory (“RAM”) and/or a read-only memory (“ROM”), which can be programmable, flash-updateable and/or the like. The computational system 1600 might also include a communications subsystem 1630, which can include without limitation a modem, a network card (wireless or wired), an infrared communication device, a wireless communication device and/or chipset (such as a Bluetooth device, an 802.6 device, a Wi-Fi device, a WiMax device, cellular communication facilities, etc.), and/or the like. The communications subsystem 1630 may permit data to be exchanged with a network (such as the network described below, to name one example), and/or any other devices described herein. In many embodiments, the computational system 1600 will further include a working memory 1635, which can include a RAM or ROM device, as described above.

The computational system 1600 also can include software elements, shown as being currently located within the working memory 1635, including an operating system 1640 and/or other code, such as one or more application programs 1645, which may include computer programs of the invention, and/or may be designed to implement methods of the invention and/or configure systems of the invention, as described herein. For example, one or more procedures described with respect to the method(s) discussed above might be implemented as code and/or instructions executable by a computer (and/or a processor within a computer). A set of these instructions and/or codes might be stored on a computer-readable storage medium, such as the storage device(s) 1625 described above.

In some cases, the storage medium might be incorporated within the computational system 1600 or in communication with the computational system 1600. In other embodiments, the storage medium might be separate from a computational system 1600 (e.g., a removable medium, such as a compact disc, etc.), and/or provided in an installation package, such that the storage medium can be used to program a general-purpose computer with the instructions/code stored thereon. These instructions might take the form of executable code, which is executable by the computational system 1600 and/or might take the form of source and/or installable code, which, upon compilation and/or installation on the computational system 1600 (e.g., using any of a variety of generally available compilers, installation programs, compression/decompression utilities, etc.) then takes the form of executable code.

FIG. 17 is a schematic of a spatially variable wafer bias system 1700 according to some embodiments. The spatially variable wafer bias system 1700 may include the first high voltage pulser 1725, a second high voltage pulser 1730, a first energy recovery circuit 1726, and a second energy recovery circuit 1731. Both the first energy recovery circuit 1726, and the second energy recovery circuit 1731 are coupled with a single energy storage capacitor C7. In some embodiments, each of the energy recovery circuit 1726 or the energy recovery circuit 1731 may include one or more diodes and/or inductors coupled with the secondary side of each transformer. In some embodiments, the energy recovery circuit 1726 or the energy recovery circuit 1731 may include a switch (e.g., as described above) to allow current to flow through the energy recovery circuit after each pulse.

FIG. 18 is a circuit diagram of an RF driver system 1800 that includes an RF driver 1805, the active bias compensation circuit 134, and the energy recovery circuit 110 according to some embodiments. In this example, the RF driver system 1800 is similar to the matchless RF system 700 with the RF driver 705 and resonant circuit 710 replaced by a RF driver 1805. The RF driver 705 shown in FIG. 7 comprises a full wave rectifier and a resonant circuit 710, which is replaced with a RF driver 1805.

In some embodiments, the RF driver 1805 may include a plurality of high frequency solid state switch(es), an RF generator, an amplifier tube based RF generator, or a tube based RF generator.

The RF driver system 1800 may not include a traditional matching network such as, for example, a 50 ohm matching network or an external matching network or standalone matching network. In some embodiments, the RF driver system 1800 does not require a 50 ohm matching network to optimize the switching power applied to the wafer chamber. An RF generator without a traditional matching network can allow for rapid changes to the power drawn by the plasma chamber. Typically, this optimization of the matching network can take at least 100 μs-200 μs. In some embodiments, power changes can occur within one or two RF cycles, for example, 2.5 μs-5.0 μs at 400 kHz.

In some embodiments, the RF driver 1805 may operate at frequency about 400 kHz, 0.5 MHz, 2.0 MHz, 4.0 MHz, 13.56 MHz, 27.12 MHz, 40.68 MHz, 50 MHz, etc.

Either or both the first nanosecond pulser 1725 and the second nanosecond pulser 1730 may include a passive bias compensation circuit 114, an active bias compensation circuit 134, or a DC bias circuit 104.

Unless otherwise specified, the term “substantially” means within 5% or 10% of the value referred to or within manufacturing tolerances. Unless otherwise specified, the term “about” means within 5% or 10% of the value referred to or within manufacturing tolerances.

The term “or” is inclusive.

Numerous specific details are set forth herein to provide a thorough understanding of the claimed subject matter. However, those skilled in the art will understand that the claimed subject matter may be practiced without these specific details. In other instances, methods, apparatuses or systems that would be known by one of ordinary skill have not been described in detail so as not to obscure claimed subject matter.

Embodiments of the methods disclosed herein may be performed in the operation of such computing devices. The order of the blocks presented in the examples above can be varied—for example, blocks can be re-ordered, combined, and/or broken into sub-blocks. Certain blocks or processes can be performed in parallel.

The use of “adapted to” or “configured to” herein is meant as open and inclusive language that does not foreclose devices adapted to or configured to perform additional tasks or steps. Additionally, the use of “based on” is meant to be open and inclusive, in that a process, step, calculation, or other action “based on” one or more recited conditions or values may, in practice, be based on additional conditions or values beyond those recited. Headings, lists, and numbering included herein are for ease of explanation only and are not meant to be limiting.

While the present subject matter has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, it should be understood that the present disclosure has been presented for purposes of example rather than limitation, and does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.

Claims

1. A nanosecond pulser circuit comprising: a high voltage power supply, wherein the high voltage power supply provides DC power with a voltage greater than 1 kV;a plurality of switches electrically coupled with the high voltage power supply, the plurality of switches switch voltage from the high voltage power supply at high frequencies;a transformer having a primary side and a secondary side, the plurality of switches electrically coupled with the primary side of the transformer; andan energy recovery circuit electrically coupled with the secondary side of the transformer, the energy recovery circuit comprising: an energy recovery inductor electrically coupled with the high voltage power supply; anda diode disposed in series with the energy recovery inductor and arranged to restrict current flowing from the high voltage power supply through the energy recovery inductor to a load located on the secondary side of the transformer.

2. The nanosecond pulser circuit according to claim 1, wherein the energy recovery inductor comprises an inductance greater than about 50 μH.

3. The nanosecond pulser circuit according to claim 1, wherein the nanosecond pulser switches voltage from the high voltage power supply at frequencies of about 400 kHz.

4. The nanosecond pulser circuit according to claim 1, wherein the nanosecond pulser circuit provides voltage greater than 5 kV to the load.

5. The nanosecond pulser circuit according to claim 1, wherein the load comprises a capacitive load.

6. The nanosecond pulser circuit according to claim 1, wherein the load comprises an electrode disposed in a plasma deposition chamber.

7. The nanosecond pulser circuit according to claim 1, wherein the energy recovery circuit further comprises a high voltage switch in series with the diode and the energy recovery inductor.

8. The nanosecond pulser circuit according to claim 7, wherein the high voltage switch switches voltages greater than 5 kV.

9. The nanosecond pulser circuit according to claim 1, wherein the plurality of switches are arranged in a half-bridge or a full-bridge configuration.

10. A circuit comprising: a high voltage storage capacitor;a switching circuit coupled with the storage capacitator, the switching circuit outputs waveforms with voltages greater than 1 kV and with a frequencies greater than 1 kHz, the switching circuit comprising a plurality of switches arranged in a half-bridge or a full-bridge configuration;a transformer having a primary side and a secondary side, the switching circuit electrically coupled with the primary side of the transformer; andan energy recovery circuit electrically coupled with the secondary side of the transformer and the storage capacitor, the energy recovery circuit comprising: an energy recovery inductor electrically coupled with the high voltage power supply having an inductance greater than 50 μH; anda diode disposed in series with the energy recovery inductor and arranged to restrict current flowing from the high voltage power supply through the energy recovery inductor to a load located on the secondary side of the transformer.

11. The circuit according to claim 10, wherein the energy recovery circuit comprises a crowbar diode arranged across the secondary side of the transformer.

12. The circuit according to claim 10, wherein the stray resistance of the energy recovery circuit may be less than 1 ohm.

13. The circuit according to claim 10, wherein the diode conducts current from a load through the energy recovery inductor to the high voltage power supply.

14. The circuit according to claim 13, wherein the energy recovery circuit comprises a crowbar diode arranged across the secondary side of the transformer.

15. The circuit according to claim 10, further comprising a bias compensation circuit that includes a bias compensation diode in parallel with the bias compensation switch; and a DC power supply arranged in series with the bias compensation diode and the bias compensation switch.

16. The circuit according to claim 10, wherein the circuit does not include a matching network.

17. A plasma system comprising: a plasma chamber;an electrode disposed within the plasma camber;a circuit disposed outside the plasma chamber comprising: a high voltage storage capacitor;a switching circuit coupled with the storage capacitator, the switching circuit outputs waveforms with voltages greater than 1 kV and with a frequencies greater than 1 kHz, the switching circuit comprising a plurality of switches arranged in a half-bridge or a full-bridge configuration;a transformer having a primary side and a secondary side, the switching circuit electrically coupled with the primary side of the transformer; andan energy recovery circuit electrically coupled with the secondary side of the transformer and the storage capacitor, the energy recovery circuit comprising: an energy recovery inductor electrically coupled with the high voltage power supply having an inductance greater than 50 μH; anda diode disposed in series with the energy recovery inductor and arranged to restrict current flowing from the high voltage power supply through the energy recovery inductor to the electrode.

18. The plasma system according to claim 17, wherein the energy recovery circuit comprises a crowbar diode arranged across with the secondary side of the transformer.

19. The plasma system according to claim 17, wherein the stray resistance of the energy recovery circuit may be less than 1 ohm.

20. The plasma system according to claim 17, wherein the plasma system does not include a matching network.