JP7545608B1 - Pulse Power Supply - Google Patents

Abstract

[Problem] To provide a pulse power supply device equipped with a gradient power supply that can obtain a negative voltage gradient without using a current source. [Solution] In the control of the gradient power supply, the pulse power supply device of the present invention generates a voltage waveform in which the voltage changes linearly over time at a predetermined voltage change rate dv/dt by inverter control, generates a trapezoidal waveform voltage by superimposing a DC voltage on the generated voltage waveform, and outputs a pulse whose pulse waveform repeats at a predetermined period by switching operation in the control of the switch section. The generation of the trapezoidal waveform voltage and the generation of the pulse are synchronized by synchronizing the control of the gradient power supply with the control of the switch section. [Selected Figure] Figure 1

Description

The present invention relates to a pulse power supply device that generates a pulse output including a gradient waveform in which the voltage changes linearly with a predetermined slope.

The pulse output generated by the pulse power supply is used for plasma processing such as film formation and etching, and can be applied to various industrial devices other than plasma processing. For example, in the etching process of semiconductor devices, a negative voltage with respect to ground is applied to a substrate to generate a substantially uniform negative voltage across the entire surface of the substrate when plasma processing a conductor.

In plasma etching and deposition processes, it is known to use a pulsed bias waveform with a broad negative pulse during the etching phase and a short positive pulse during the discharge phase.

It is known that a bias with a pulsed waveform is applied to compensate for the ion deposition effect on the dielectric substrate during the etching or deposition phase. The pulse waveform consists of a negative voltage gradient that decreases to compensate for the rise in the substrate potential during the etching or deposition phase, and a positive voltage pulse to attract electrons to maintain the charge bias during the discharge phase. Configurations that generate a negative voltage gradient by incorporating ion current compensation, such as a current source, in a switched mode power supply are known (Patent Document 1, Patent Document 2).

Patent No. 7214046 Patent No. 6181792

To supply an ion current that maintains the substrate voltage at a constant voltage, it is necessary to set a predetermined negative voltage gradient. In the conventional pulse power supply device described above, the negative voltage gradient and the ion current are related by a predetermined function, so an ion current compensation current source such as a current source is used to realize the negative voltage gradient.

However, current sources with high resistance have the problem that the time constant of the circuit that constitutes the current source becomes large due to the influence of distributed capacitance, resulting in low high-speed response. This problem of high-speed response becomes more pronounced at high-frequency pulse frequencies.

In addition to the issue of high-speed response mentioned above, there are other points to consider when it comes to current sources. Current sources are generally affected by internal resistance and temperature fluctuations, which requires temperature compensation and feedback compensation, and this increases the cost of the components of the pulse power supply device. As mentioned above, pulse power supplies that output high-frequency pulses using a current source have issues with high-speed response and cost due to the use of the current source.

The present invention aims to solve the above-mentioned problems of the conventional technology and provide a pulse power supply device equipped with a gradient power supply that can obtain a negative voltage gradient without using a current source.

In the pulse power supply device of the present invention, in controlling the gradient power supply, a voltage waveform in which the voltage changes linearly over time at a predetermined voltage change rate dv/dt is generated by inverter control, a trapezoidal waveform voltage is generated by superimposing a DC voltage on the generated voltage waveform, and in controlling the switch section, a pulse waveform is output in which a pulse repeats at a predetermined period by switching operation. The generation of the trapezoidal waveform voltage and the generation of the pulse are synchronized by synchronizing the control of the gradient power supply and the control of the switch section.

The pulse power supply device of the present invention includes a DC power supply that generates a first DC voltage, a gradient power supply that generates a trapezoidal waveform voltage, a switch unit that generates a pulse waveform by switching between a ground potential and the trapezoidal waveform voltage of the gradient power supply, and outputs a pulse by repeating the pulse waveform at a predetermined cycle, and a control unit that controls the gradient power supply.

The pulse power supply of the present invention generates a trapezoidal waveform pulse with a predetermined voltage gradient by superimposing a constant DC voltage and a ramp waveform voltage. The ramp waveform voltage is a voltage with a voltage gradient that changes linearly over time at a predetermined voltage change rate dv/dt from the ground potential. The pulse power supply of the present invention generates this ramp waveform voltage by inverter control, generates a trapezoidal waveform voltage by superimposing the DC voltage and the ramp waveform voltage, and generates a pulse waveform from the trapezoidal waveform voltage, thereby generating a pulse with a voltage gradient without using a current source.

The pulse power supply device of the present invention includes a first power supply, which is a DC power supply that generates a first voltage that is a constant DC voltage, a second power supply, which is a gradient power supply that generates a trapezoidal waveform voltage from the generated first voltage and a ramp waveform voltage, and further includes a switch unit that generates a pulse from the trapezoidal waveform voltage generated by the gradient power supply.

The switch unit generates a pulse waveform by switching between the ground potential and the trapezoidal waveform voltage of the gradient power supply of the second power supply, and outputs a pulse by repeating the generated pulse waveform at a predetermined cycle.

The gradient power supply of the present invention uses inverter control to generate a ramp waveform voltage that changes linearly over time from the ground potential at a predetermined voltage change rate dv/dt, superimposes the generated ramp waveform voltage on the first voltage of the DC power supply, and generates a trapezoidal waveform voltage from the first voltage by this voltage superposition, the voltage changing linearly over time at a predetermined voltage change rate dv/dt.

The gradient power supply of the present invention includes an inverter circuit that converts a DC voltage into an AC voltage, a rectifier circuit that converts the AC voltage of the inverter circuit into a DC voltage, and a voltage superposition circuit that superposes the output of the DC power supply of the first power supply and the output of the rectifier circuit.

When performing DC-AC voltage conversion using inverter control, the inverter circuit adjusts the AC voltage with the voltage change rate dv/dt. The voltage change rate dv/dt is the rate of change of voltage over time, and the inverter circuit adjusts the voltage change rate dv/dt by changing the control amount over time when converting the DC voltage to an AC voltage. Making the voltage change rate dv/dt negative generates a trapezoidal waveform voltage with a negative gradient.

The rectifier circuit rectifies the AC voltage output from the inverter circuit to a DC voltage, and generates a ramp voltage that changes linearly over time from the ground potential. The voltage change rate of the ramp voltage is adjusted by the inverter control.

The voltage superposition circuit superposes the ramp waveform voltage of the output of the rectifier circuit and the first voltage of the DC power supply of the first power supply to generate a trapezoidal waveform voltage.

The ramp waveform voltage output from the rectifier circuit exhibits a voltage waveform in which the voltage changes linearly over time, but the starting voltage is the ground potential and the voltage changes over time from the ground potential. The trapezoidal waveform voltage is a voltage waveform in which the first voltage starts at the first voltage and changes linearly over time at a predetermined voltage change rate dv/dt by superimposing the first voltage on the ramp waveform voltage. By setting the voltage change rate dv/dt of the ramp waveform voltage to a negative value, a negative trapezoidal waveform voltage is generated.

The switch unit synchronizes the start of pulse generation in the switch unit with the start of output from the gradient power supply, and generates a pulse waveform by switching between 0V, the ground potential, and the trapezoidal waveform voltage generated by the gradient power supply. The generated pulse waveform has a first section in which the potential is the ground potential, and a second section of a trapezoidal waveform voltage that changes linearly over time from the first voltage at a predetermined voltage change rate dv/dt. There is a potential difference of the first voltage between 0V in the first section and the first voltage at the start of the second section.

The second voltage at the end point of the trapezoidal waveform voltage is determined by the voltage change rate dv/dt of the ramp waveform voltage and the time width of the second section of the trapezoidal waveform voltage.

The switch unit generates a pulse waveform from the trapezoidal waveform voltage as one pulse, and outputs a periodic pulse by repeating this pulse waveform at a predetermined period. The time width of one pulse is the sum of the time width of the first section and the time width of the second section, and is determined according to the pulse period.

In the case of a negative polarity trapezoidal waveform voltage, the switch unit outputs a periodic pulse with one pulse being a voltage waveform consisting of two voltage sections: a first section of 0V and a second section of a trapezoidal waveform voltage that changes linearly over time from the negative first voltage.

The control unit of the present invention includes control of a gradient power supply that controls an inverter circuit by inverter control to generate a ramp waveform voltage that changes linearly over time from the ground potential at a predetermined voltage change rate dv/dt, superimposes the ramp waveform voltage with a first voltage, and generates a trapezoidal waveform voltage whose voltage changes linearly over time from the first voltage at a predetermined voltage change rate dv/dt, and control of a switch unit that controls a switching operation that alternates between opening and closing between the gradient power supply and the output terminal, and between the ground potential and the output terminal, and a periodic operation that repeats the switching operation at a predetermined period, and synchronizes the control of the gradient power supply with the control of the switch unit, and synchronizes the generation of the trapezoidal waveform voltage with the generation of the pulse.

The inverter control of the gradient power supply can be performed using PWM control, which controls the duty ratio of the inverter control, PFM control, which controls the period of the inverter control, or phase shift control, which shifts and controls the conduction angle of the inverter.

Two types of inverter control can be applied: voltage control and current control. The first type of inverter control is voltage control, which controls the voltage change of the output voltage detected by the detection unit to a set voltage change rate dv/dt.

On the other hand, the second control form of inverter control is current control, which controls the output current detected by the detection unit to a constant current value. The constant current value can be an external command or a statically constant current value after the first voltage is applied.

As described above, the pulse power supply device of the present invention can achieve high-speed response by providing a gradient power supply that can obtain a predetermined voltage gradient without using a current source.

1 is a diagram for explaining a schematic configuration of a pulse power supply device according to the present invention; 4 is a timing chart for explaining an example of the operation of the pulse power supply device of the present invention. FIG. 4 is a diagram for explaining an example of operation of the pulse power supply device of the present invention in a discharge phase. FIG. 4 is a diagram for explaining an example of operation of the pulse power supply device of the present invention in a discharge phase. FIG. 4 is a diagram for explaining an example of operation of the pulse power supply device of the present invention in an application phase. FIG. 4 is a diagram for explaining an example of operation of the pulse power supply device of the present invention in an application phase. FIG. 13 is a diagram for explaining an example of control of a gradient power supply according to the present invention. 1A and 1B are diagrams for explaining an inverter control mode based on PWM control, an inverter control mode based on PFM control, and phase shift control. FIG. 2 is a schematic diagram of a first configuration example of a gradient power supply of the present invention. 4 is a timing chart of a first configuration example of the gradient power supply of the present invention. FIG. 11 is a schematic diagram of a second configuration example of a gradient power supply of the present invention. 4 is a timing chart of a second configuration example of the gradient power supply of the present invention. FIG. 2 is a diagram for explaining a configuration example of a voltage superposition circuit according to the present invention; FIG. 2 is a diagram for explaining a configuration example of a voltage superposition circuit according to the present invention; FIG. 2 is a diagram for explaining a smoothing circuit according to the present invention; FIG. 2 is a diagram for explaining a first example of a smoothing circuit of the present invention; FIG. 11 is a diagram for explaining a second embodiment of a smoothing circuit according to the present invention; FIG. 4 is a diagram showing an example of a waveform of a smoothing circuit according to the present invention. FIG. 4 is a diagram showing an example of a waveform of a smoothing circuit according to the present invention. FIG. 2 is a diagram for explaining an example of a plasma load as a load of the pulse power supply device of the present invention. 3A to 3C are diagrams illustrating an example of a switch drive signal, a power supply output Vout, and an output current Iout. FIG. 13 is a diagram showing the wafer voltage Vsh, the power supply output Vout, and the ion current Ip.

(1) Schematic Configuration and Operation Example of a Pulse Power Supply Device of the Present Invention The schematic configuration and operation example of a pulse power supply device of the present invention will be described below with reference to Figs.

The pulse power supply device 1 includes a power supply unit 10, a switch unit 13, a control unit 15, and a detection unit 16. The power supply unit 10 includes a first DC power supply 11 that generates a first constant voltage as a first power supply, and a gradient power supply 12 that generates a trapezoidal waveform voltage as a second power supply.

The gradient power supply 12 generates a ramp waveform voltage Vlamp whose voltage changes at a predetermined voltage change rate dv/dt starting from the ground potential, and by superimposing the first voltage of the first DC power supply 11 on this ramp waveform voltage Vlamp, it generates a trapezoidal waveform voltage whose voltage changes at a predetermined voltage change rate dv/dt starting from the first voltage, and outputs a pulse of the gradient power supply output Vgra.

The switch unit 13 supplies current to the load by alternately repeating a discharge phase in which the charge accumulated on the load side is discharged by switching operation and an application phase in which a periodic pulse is applied to the load side. The switch unit 13 includes a pulse switch unit 13a for outputting a pulse of the gradient power supply output Vgra to the load in the application phase, and a discharge circuit 13b for discharging the charge accumulated in the load. The switching operations of the pulse switch unit 13a and the discharge circuit 13b are controlled by the control unit 15.

In the application phase, the switch unit 13 applies the trapezoidal waveform voltage generated by the gradient power supply 12 to the load as one periodic pulse waveform. In the discharge phase, the charge accumulated on the load side is discharged and the output of the switch unit 13 becomes 0 V, so that the output of the switch unit 13 at the start of the application phase changes from 0 V to the first voltage. The pulse output output from the switch unit 13 is supplied to the load 21 as a power supply output.

The pulse power supply device 1 may be configured to include a smoothing circuit. The smoothing circuit may be in a first form in which the smoothing circuit is connected to the output end of the gradient power supply 12, or in a second form in which the smoothing circuit is connected to the output end of the pulse switch section 13a of the switch section 13. The smoothing circuit of the first form suppresses noise contained in the gradient power supply output. The smoothing circuit of the second form suppresses voltage oscillations of overshoot and undershoot that occur in the switch section 13 due to voltage changes between the discharge phase and the application phase. Note that the smoothing circuit is not shown in FIG. 1.

The detection unit 16 detects the output voltage Vout or the output current Iout of the power output of the pulse power supply device 1 and feeds back the detected value to the control unit 15.

The control unit 15 controls the gradient power supply 12 and the switch unit 13. At this time, the output control of the gradient power supply output Vgra of the gradient power supply 12 and the pulse control of the switch unit 13 are performed in synchronization.

The control unit 15 performs output control of the gradient power supply output Vgra by inverter controlling the gradient power supply. The inverter control can be PWM control that controls the duty ratio, PFM control that controls the inverter control period, or phase shift control that shifts the conduction angle of the inverter.

The first control form of inverter control performs voltage control so that the voltage change of the output voltage becomes the set value of the voltage change rate dv/dt based on the detected voltage value detected by the detection unit 16.

The control unit 15 calculates the voltage change rate dv/dt based on the detected voltage value, compares the calculated value with a set value, and controls the inverter so that the calculated value becomes the set value. The set value of the voltage change rate dv/dt can be stored inside the device or obtained by inputting it from outside.

The second control form of inverter control is current control, which controls the output current value detected by the detection unit 16 to be a constant current value. The control unit 15 compares the detected current value with a set value, and controls the inverter so that the calculated value becomes the set value. Constant current control is performed by determining a constant current value as the set value. The constant current value can be an external command, or a statically constant current value after application of the first voltage.

The third control form of inverter control performs voltage control so that the output voltage becomes a set voltage based on the detected voltage value detected by the detection unit 16. The control unit 15 compares the detected voltage value with a set value and performs phase shift control so that the calculated value becomes the set value. In phase shift control, the output is controlled by controlling the phase shift amount that determines the phase shift of the conduction angle of the lagging leg relative to the leading leg in the full bridge circuit that constitutes the inverter.

Figure 2 is a timing chart for explaining an example of the operation of the pulse power supply device of the present invention.

The power supply unit 10 includes a first power supply, a first DC power supply 11, and a second power supply, a gradient power supply 12. The first DC power supply 11 of the first power supply generates a constant first voltage V1. The gradient power supply 12 of the second power supply generates a ramp waveform voltage Vlamp whose voltage changes at a predetermined voltage change rate dv/dt starting from the ground potential, and generates a trapezoidal waveform voltage by superimposing the first voltage V1 on this ramp waveform voltage Vlamp.

The gradient power supply 12 generates a ramp waveform voltage Vlamp based on the gradient power supply control signal from the control unit 15, superimposes the generated ramp waveform voltage Vlamp with the first voltage V1 to generate a trapezoidal waveform voltage, and outputs it as the gradient power supply output Vgra.

The gradient power supply control signal has the same output pulse period T as the switch control signal that controls the switch unit 13, and is synchronized with the switch control signal. The generation of the ramp waveform voltage Vlamp by the gradient power supply control signal and the start of the pulse application phase by the switch control signal occur at the same time A. The end of the ramp waveform voltage Vlamp by the gradient power supply control signal and the end of the pulse application phase and the start of the discharge phase by the switch control signal occur at the same time B.

Here, when the duty ratio for the output pulse period T (= Ton + Toff) is Ton/T, the on time of the gradient power supply control signal and the time of the application phase are the same Ton, and the off time of the gradient power supply control signal and the time of the discharge phase are the same Toff.

The ramp waveform voltage Vlamp changes from 0V at the start of the application phase at a predetermined voltage change rate dv/dt, and at the end of the application phase, it becomes a voltage ΔV determined by the product of the voltage change rate dv/dt and Ton (Ton x dv/dt). The gradient power supply output Vgra changes from the first voltage V1 at the start of the application phase at a predetermined voltage change rate dv/dt, and at the end of the application phase, it becomes a voltage V2 (=V1+ΔV) in which a voltage ΔV is superimposed on the first voltage V1.

Voltage ΔV and voltage V2 are voltages that depend on the voltage change rate dv/dt and Ton or the duty ratio of the periodic pulse, because ΔV is the product of the voltage change rate dv/dt and Ton (Ton x dv/dt). Therefore, if the voltage change rate dv/dt, Ton, or the duty ratio of the periodic pulse is changed, voltage ΔV and voltage V2 will have different values.

The first type of smoothing circuit suppresses noise contained in the gradient power supply output, and the second type of smoothing circuit suppresses voltage oscillations of overshoot and undershoot contained in the switch unit output of the switch unit 13. The power supply output of the pulse power supply device 1 is supplied to the load 21.

In FIG. 2, the section marked with Ph_dis represents the discharge phase, and the section marked with Ph_add represents the application phase. In the discharge phase, the switch SWA of the pulse switch unit 13a is in the OFF state, and the switch SWB of the discharge circuit 13b is in the ON state. On the other hand, in the application phase, the switch SWA of the pulse switch unit 13a is in the ON state, and the switch SWB of the discharge circuit 13b is in the OFF state.

The switch SWA of the pulse switch unit 13a switches from the discharge phase to the application phase by switching from the off state to the on state, and outputs the gradient power supply output Vgra as a pulse output during the application phase Ton.

The switch SWB of the discharge circuit 13b switches from the application phase to the discharge phase by switching from the off state to the on state, discharging the charge accumulated in the load during the discharge phase Toff to ground, and setting the voltage of the gradient power supply output Vgra to 0 V.

Figure 3 is a diagram for explaining an example of operation in the discharge phase, and Figures 3A and 3B respectively show the operating state at the point in time when the power supply output Vout rises from V2 to 0 V during the discharge phase Ph_dis in Figure 2, and the operating state when the power supply output Vout becomes 0 V.

The discharge phase Ph_dis1 in FIG. 3A is the point in time when the SWA of the pulse switch unit 13a switches to the OFF state and the SWB of the discharge circuit 13b switches to the ON state. This point in time corresponds to the section represented by Dis1 in FIG. 2. In this Dis1, the power supply output Vout rises from V2 to 0 V, and the output current Iout is a steep discharge current that decreases toward 0 A. The current Ip in the application phase corresponds to the ion current Ip in the case of a plasma load.

In the discharge phase Ph_dis2 in FIG. 3B, the SWA of the pulse switch unit 13a is in the OFF state, and the SWB of the discharge circuit 13b is in the ON state. This state corresponds to the section represented by Dis2 in FIG. 2. In this Dis2, the power supply output Vout is 0 V, and the output current Iout is 0 A.

Figure 4 is a diagram for explaining an example of operation in the application phase, and Figure 4A and Figure 4B respectively show the operating state at the time when the power supply output Vout falls from 0V to V1 and the operating state when the power supply output Vout changes from V1 to V2 during the application phase Ph_app in Figure 2.

The application phase Ph_app1 in FIG. 4A is the point in time when SWA of the pulse switch unit 13a switches to the ON state and SWB of the discharge circuit 13b switches to the OFF state. This point in time corresponds to the point in time represented as App1 in FIG. 2. At this point in time App1, the power supply output Vout falls from 0V to V1, and a current Iq flows toward the load. The voltage change at the point in time App1 is determined by the time constant of the circuit connected downstream of the switch unit.

In the application phase Ph_app2 in FIG. 4B, SWA of the pulse switch unit 13a is on, and SWB of the discharge circuit 13b is off. This state corresponds to the section represented by App2 in FIG. 2. In this App2, the power output Vout changes from V1 at the voltage change rate dv/dt, and at the end point of App2, the power output Vout becomes V2. In the case of a plasma load, a constant current Ir equivalent to an ion current determined based on the voltage change rate dv/dt flows in the output current Iout. An example of the current Ir and the current Iq is shown in FIG. 17.

(2) Gradient Power Supply The gradient power supply 12 of the present invention includes an inverter circuit that converts a DC voltage into an AC voltage, a rectifier circuit that converts the AC voltage of the inverter circuit into a DC voltage, and a voltage superposition circuit that generates a trapezoidal waveform voltage by superimposing the output of the DC power supply of the first power supply and the ramp waveform voltage Vlamp output through the rectifier circuit, and outputs the trapezoidal waveform voltage as the gradient power supply output Vgra.

(2-1) Control of Gradient Power Supply An example of control of the gradient power supply 12 will be described with reference to Fig. 5. Note that Fig. 5 shows only a part of the configuration of the gradient power supply 12.

The gradient power supply output of the gradient power supply 12 is controlled by the control unit 15. The control unit 15 obtains the detection value of the power supply output detected by the detection unit 16 through feedback, and the comparison unit 15a compares the detection value with a comparison value. The control command generation unit 15b generates a control command for inverter controlling the inverter circuit 12b based on the comparison result.

In the control of the control unit 15, the feedback control can be voltage control or current control. In addition, in each control, the inverter control can be PWM control that controls the duty ratio, PFM control that controls the inverter control period, or phase shift control that controls the amount of phase shift of the inverter.

Therefore, as the control form by the control unit 15, it is possible to selectively apply a control form in which feedback control of voltage control is performed by PWM controlled inverter control, PFM controlled inverter control, or phase shift control, and a control form in which feedback control of current control is performed by PWM controlled inverter control, PFM controlled inverter control, or phase shift control.

(a) Control Form by Voltage Control In the control form of voltage control using feedback control, voltage control is performed based on the output voltage Vout detected by the detection unit 16 so that the voltage change of the output voltage becomes the set value of the voltage change rate dv/dt. The control unit 15 calculates the voltage change rate dv/dt based on the output voltage Vout, compares the calculated value with the set value, performs feedback control so that the calculated value becomes the set value, and generates a control command. The set value of the voltage change rate dv/dt can be stored inside the device or obtained by inputting it from outside.

(b) Control Form by Current Control In the control form of current control using feedback control, current control is performed to control the output current Iout detected by the detection unit 16 to a constant current value. The control unit 15 compares the output current Iout with a set value and performs feedback control so that the output current Iout becomes the set value. Constant current control is performed by determining a constant current value as the set value. The constant current value can be an external command or a statically constant current value after application of the first voltage.

(c) Inverter control Fig. 6 shows an example of an inverter control form by PWM control, an inverter control form by PFM control, and phase shift control. Fig. 6 shows the cycle of inverter control, inverter output by PWM control, inverter output by PFM control, inverter output by a combination of PWM control and PFM control, and each signal example of phase shift control in order. Note that each signal is shown as an outline for convenience of explanation, and does not represent an actual signal.

In the example of the inverter control cycle signal shown in FIG. 6, the inverter control cycle T has a period Ton during which inverter control is performed and a period Toff during which inverter control is stopped. The period Ton during which inverter control is performed is synchronized with the same time width as the section during which the switch unit outputs pulses, and the period Toff during which inverter control is stopped is synchronized with the same time width as the section during which the switch unit stops outputting.

(c1) Inverter control form by PWM control In the example of inverter output by PWM control shown in Fig. 6, in the inverter control by PWM control, the inverter is turned on/off in the same cycle Tinv during the period Ton. Each cycle Tinv includes an on section ton_w1, ton_w2, ..., ton_wi in which the switch is in the on state, and an off section toff_w1, toff_w2, ..., toff_wi in which the switch is in the off state. The duty ratio at this time is expressed as (Ton/Tinv).

By controlling the duty ratios of Ton_w1/Tinv, Ton_w2/Tinv, ..., Ton_wi/Tinv to gradually increase, the output voltage obtained by rectifying the output of the inverter circuit 12b increases linearly. When performing PWM control, the duty ratio in each cycle of the inverter control is adjusted.

(c2) Inverter control by PFM control In the inverter output example of PFM control shown in Figure 6, in the inverter control by PFM control, the inverter is turned on/off in a period Ton with a cycle Tinv, similar to the inverter control by PWM control. Each cycle Tinv has an on-section ton1_f1, ton_f2, ..., ton_fi in which the switch is in an on state, and an off-section toff_f1, toff_f2, ..., toff_fi in which the switch is in an off state. The duty ratio at this time is represented by (Ton/T), and the pulse frequency is modulated by the time width of the cycle Tinv.

In PFM control, frequency modulation corresponds to modulation of the time width of the cycle Tinv. By controlling the time width of the cycles Tinv_f1, Tinv_f2, ..., Tinv_fi to gradually decrease, the output voltage obtained by rectifying the output of the inverter circuit 12b increases linearly. When performing PFM control, the cycle time of each cycle of the inverter control is adjusted.

(c3) Inverter Control by Combination of PWM Control and PFM Control The present invention may be a control form in which inverter control by PWM control and inverter control by PFM control are combined.

In an example of inverter output that combines inverter control by PWM control and inverter control by PFM control as shown in FIG. 6, the same period Tinv_f1 is used for several periods from the start of control, and PWM control is performed to gradually increase the on-section ton1_f during these several periods, and PFM control is performed to shorten the period Tinv_f2 for the next several periods, and PWM control is performed to gradually increase the on-section ton1_f during these several periods.

In this way, by combining PWM control and PFM control for inverter control, it is possible to allow some leeway in adjusting the duty ratio in PWM control and the cycle width in PFM control.

(c4) Inverter Control by Phase Shift Control The phase shift control example shown in Fig. 6 shows a change in the phase shift amount φ. This phase shift amount φ is the amount of phase shift of the driver signal that drives the switching element of the lag leg relative to the driver signal that drives the switching element of the lead leg in the full bridge circuit. By controlling the phase shift amount φ to gradually decrease, the output voltage obtained by rectifying the output of the inverter circuit 12b increases linearly.

(c5) Inverter control by combination of PWM control or PFM control and phase shift control The present invention may be a control form in which inverter control by PWM control or inverter control by PFM control is combined with phase shift control. In the control form in which phase shift control is combined, the phase shift amount for shifting the conduction angle between the leading leg and the lagging leg in each on-section ton1_w or ton1_f in PWM control or PFM control is sequentially adjusted. By combining phase shift control, it is possible to provide a margin for adjusting the duty ratio in PWM control and the period width in PFM control. Note that this inverter control is not shown in FIG. 6.

The gradient power supply of the present invention can be configured in a number of forms in which the voltage superimposition circuit that superimposes the output of the DC power supply and the ramp waveform voltage Vlamp is placed at different positions in the gradient power supply circuit. Below, the first and second configuration examples of the gradient power supply of the present invention will be described with reference to Figures 7 to 11.

Figures 7 and 8 are diagrams for explaining a first example configuration of the gradient power supply, and Figures 9 and 10 are diagrams for explaining a second example configuration of the gradient power supply. Figure 11 is a diagram for explaining an example configuration of the voltage superposition circuit.

(2-2) Configuration Examples of Gradient Power Supply (a) First Configuration Example FIG. 7 shows a schematic configuration of a first configuration example of the gradient power supply of the present invention, and FIG. 8 shows a timing chart of the first configuration example of the gradient power supply of the present invention.

The gradient power supply 12A in the first configuration example includes a second DC power supply 12a, an inverter circuit 12b, a transformer 12c, and a rectifier circuit 12d, and the voltage superposition circuit 12e is provided within the rectifier circuit 12d.

The second DC power supply 12a may be an AC/DC power supply that converts AC to DC and outputs a DC voltage, or may be a normal DC power supply. The source of AC (alternating current) may be either an external power supply or an internal power supply. The inverter circuit 12b converts the input DC voltage into an AC voltage and adjusts and outputs the voltage value of the converted AC voltage. The transformer 12c converts the amplitude of the AC voltage from the inverter circuit 12b based on a transformation ratio determined by a predetermined winding ratio. The rectifier circuit 12d rectifies the AC voltage of the transformer 12c and converts it into a DC voltage.

The inverter circuit 12b is inverter-controlled based on a control command output from the control unit 15. The control command of the control unit 15 may be generated based on a feedback signal of the voltage and/or current of the gradient power supply output, or may be generated based on an external signal from an external device (not shown).

The inverter circuit 12b is driven at a high frequency of, for example, several hundred kHz to several tens of MHz. The inverter circuit 12b may be a one-transistor flyback inverter using one switching element, a two-transistor half-bridge inverter using two switching elements, or a four-transistor full-bridge inverter using four switching elements.

The voltage superposition circuit 12e is incorporated in the rectifier circuit 12d, and superimposes the first voltage V1 of the first DC power supply 11 on the rectified output of the rectifier circuit 12d. FIG. 11A shows an example of the configuration of the voltage superposition circuit 12e incorporated in the rectifier circuit 12d. Here, an example of a circuit configured of a diode bridge is shown as the rectifier circuit 12d. In the circuit configuration example of FIG. 11A, the output terminal of the voltage superposition circuit 12e is connected to one output terminal of the rectifier circuit 12d, and the rectified output on which the first voltage V1 is superimposed is output as a gradient power supply output.

Figure 8 shows a case where PWM control is used for inverter control. Inverter control is performed during the on-time Ton based on the duty ratio within the output pulse period T, and is resumed after the off-time Toff has elapsed. PWM control controls the pulse width for each inverter period Tinv (= 1/f_inv) determined by the drive frequency f_inv. The output voltage is adjusted by gradually increasing or decreasing the pulse width to increase or decrease the peak value of the output voltage.

When generating the ramp waveform voltage Vlamp and the gradient waveform of the voltage of the gradient power supply output Vgra by inverter control, taking into consideration the responsiveness when a smoothing circuit is connected downstream of the gradient power supply 12, the drive frequency f_inv of the PWM control that performs the inverter control must be higher than the output pulse frequency f_pulse, and preferably is at least five times higher.

The transformer 12c adjusts the peak value of the inverter output of the inverter circuit 12b based on a transformation ratio determined by the winding ratio, and outputs the result to the rectifier circuit 12d. The rectifier circuit 12d rectifies the inverter output and outputs a ramp waveform voltage whose voltage changes at a predetermined voltage change rate dv/dt. The ramp waveform voltage is output during the on-time Ton, and is not output during the off-time Toff. The voltage superposition circuit 12e generates a superposed output by superposing a first voltage V1 on the rectified output of the rectifier circuit 12d.

(b) Second Configuration Example of Gradient Power Supply FIG. 9 shows a schematic configuration of a second configuration example of the gradient power supply of the present invention, and FIG. 10 shows a timing chart of the second configuration example of the gradient power supply of the present invention.

The gradient power supply 12B of the second configuration example includes a second DC power supply 12a, an inverter circuit 12b, a transformer 12c, and a rectifier circuit 12d, and includes a voltage superposition circuit 12e within the transformer 12c.

The gradient power supply 12B of the second configuration example includes a second DC power supply 12a, an inverter circuit 12b, a transformer 12c, and a rectifier circuit 12d, similar to the gradient power supply 12A of the first configuration example, but differs in that the voltage superposition circuit 12e is incorporated into the transformer 12c. Here, the explanation of the second DC power supply 12a, the inverter circuit 12b, the transformer 12c, and the rectifier circuit 12d will be omitted, and only the voltage superposition circuit 12e will be explained.

The voltage superposition circuit 12e is configured to be incorporated in the transformer 12c, and superimposes the first voltage V1 of the first DC power supply 11 on the inverter output of the inverter circuit 12b. FIG. 11B shows an example of the configuration of the voltage superposition circuit 12e.

In the circuit configuration example of FIG. 11B, the first DC power supply 11 is connected to one output terminal on the secondary side of the transformer 12c, so that the first voltage V1 is superimposed on the inverter output that has been voltage converted by the transformer 12c.

As with FIG. 6, FIG. 8 shows a case where PWM control is used for inverter control. Inverter control is performed during an on-time Ton based on a duty ratio within the range of the output pulse period T, and is resumed after an off-time Toff has elapsed. PWM control controls the pulse width for each inverter period Tinv determined by the drive frequency f_inv. The output voltage is adjusted by gradually increasing or decreasing the pulse width to increase or decrease the peak value of the output voltage.

As in the first configuration example, when generating the ramp waveform voltage Vlamp and the gradient waveform of the voltage of the gradient power supply output Vgra by inverter control, taking into consideration the responsiveness when a smoothing circuit is connected downstream of the gradient power supply 12, the drive frequency f_inv of the PWM control that performs the inverter control needs to be higher than the output pulse frequency f_pulse, and it is desirable for it to be at least five times higher.

Transformer 12c adjusts the peak value of the inverter output of inverter circuit 12b based on the transformation ratio.

The voltage superposition circuit 12e generates a transformer output by superposing the first voltage V1 on the inverter output voltage-converted by the transformer 12c, and outputs the transformer output to the rectification circuit 12d. The rectification circuit 12d rectifies the inverter output and outputs a ramp waveform voltage whose voltage changes at a predetermined voltage change rate dv/dt. The ramp waveform voltage is output during the on-time Ton and is not output during the off-time Toff.

(3) Smoothing Circuit Fig. 12 shows an example of the configuration of the smoothing circuit 14. The smoothing circuit 14 is configured as an LC circuit of an inductor Lp connected in series and a capacitor Cp connected in parallel. Note that this smoothing circuit 14 is just an example, and the invention is not limited to this LC circuit.

The smoothing circuit of the pulse power supply device 1 of the present invention can be configured in a first form in which the smoothing circuit is connected to the output end of the gradient power supply 12, and a second form in which the smoothing circuit is connected to the output end of the pulse switch section 13a of the switch section 13. The smoothing circuit of the first form suppresses noise contained in the gradient power supply output. The smoothing circuit of the second form suppresses voltage oscillations of overshoot and undershoot that occur in the switch section 13 due to voltage changes between the discharge phase and the application phase.

(a) First embodiment of the smoothing circuit A smoothing circuit 14A of the first embodiment will be described with reference to Fig. 13. Fig. 13 shows a configuration example of a gradient power supply 12A that performs voltage superposition in a rectifier circuit 12d.

The smoothing circuit 14A is connected between the output terminal of the rectifier circuit 12d of the gradient power supply 12A and the input terminal of the switch unit 13, and suppresses high-frequency noise components contained in the gradient power supply output generated by the rectifier circuit, etc. In this circuit configuration, even if the SWA of the pulse switch unit 13a in the switch unit 13 is switched to the off state, the voltage charged in the capacitor in the smoothing circuit 14A does not drop to the voltage of the V1 power supply. Therefore, in the first form, a discharge circuit 17 is connected to discharge the voltage charged in the capacitor in the smoothing circuit 14A.

(b) Second embodiment of the smoothing circuit A second embodiment of the smoothing circuit 14B will be described with reference to Fig. 14 and Fig. 15. Fig. 14 shows a configuration example of a gradient power supply 12A that performs voltage superposition in a rectifier circuit 12d, and Fig. 15 shows an example of a waveform of the smoothing circuit 14B.

The smoothing circuit 14B of the second embodiment is connected between the pulse switch section 13a and the discharge circuit 13b in the switch section 13. Due to the switching operation performed in the pulse switch section 13a of the switch section 13, the voltage is abruptly switched from V2 to the first voltage V1 during discharge, and also from the ground potential of 0V to the first voltage V1. This voltage change causes an overshoot or undershoot in the output waveform.

When the SWA of the pulse switch unit 13a is in the on state, the capacitor of the smoothing circuit 14B is charged. After that, when the SWA of the pulse switch unit 13a is switched to the off state, the voltage charged in the capacitor of the smoothing circuit 14B is discharged because the discharge circuit 13b is switched to the on state. As a result, between the discharge phase and the application phase, when the pulse switch unit 13a switches between the on state and the off state, voltage oscillations of overshoot and undershoot caused by voltage changes are suppressed, the voltage value of the power supply output is settled at a predetermined time constant, and a power supply output Vout with suppressed fluctuations is output.

Figure 15 shows an example of the waveform of the smoothing circuit 14B. Figure 15A shows a case where the constants of the inductor Lf and capacitor Cf are small, and Figure 15B shows a case where the constants of the inductor Lf and capacitor Cf are large. By selecting small constants for the inductor Lf and capacitor Cf, the time constant of the LC circuit is set to a small value, which makes it possible to shorten the voltage rise time. If the time constant of the LC circuit is large, the voltage rise time t2 becomes long, making it necessary to set a long discharge time, which affects the setting of the high-frequency output pulse frequency f_pulse. It is desirable that the voltage rise time t1 be shorter than, for example, 10% of the pulse period.

(4) Example of Plasma Load An example of the load of the pulse power supply device of the present invention will be described with reference to Fig. 16. In the case of a plasma load, the plasma load in the plasma chamber 2 is represented by capacitors Cw and Cp, and an ion current Ip. The capacitor Cw is the inherent capacitance of components such as the substrate that the plasma chamber has, and Cp is the variable capacitance of the sheath capacitance and stray capacitance.

In plasma chamber 2, the ion current Ip supplied to the substrate placed in the chamber is kept constant, thereby maintaining the substrate wafer voltage Vsh at a constant voltage.

The pulse power supply of the present invention supplies a constant ion current Ip as described above, and supplies power to the load of the plasma chamber 2 to maintain the substrate wafer voltage Vsh at a constant voltage.

The pulse power supply device of the present invention feeds back the power output Vout and/or output current Iout detected by the detection unit 16 to the control unit 15, generates a control value that keeps the power output Vout or the output current Iout at a constant value, and controls the switch SWA of the pulse switch unit 13a and the switch SWB of the discharge circuit 13b.

Figure 17 shows an example of a drive signal for driving the switch, a power supply output Vout, and an output current Iout, and Figure 18 shows the wafer voltage Vsh, the power supply output Vout, and the ion current Ip.

When switching from the discharge phase to the application phase, the power supply output Vout changes from the ground potential of 0 V to V1 with the time constant of the smoothing circuit 14B, and a current Iq flows for a time tq. After the time tq has elapsed, the power supply output Vout changes with a voltage change rate dv/dt, and the current Ir is maintained at a constant current. This current Ir is a current that is statically determined to a constant current after the time tq has elapsed, and can be used as the constant current value of the set value set in the constant current control performed in the control form of the current control of the feedback control described above.

At the end of the application phase, the power supply output Vout becomes voltage V2. This voltage V2 is a voltage value determined by the voltage change rate dv/dt and the time width of the application phase. The time width of the gradient section of the application phase corresponds to the on time Ton of the output pulse period T.

The pulse power supply device of the present invention can be used for plasma processing as well as for loads that require a constant voltage pulse output.

1 Pulse power supply device 2 Plasma chamber 10 Power supply unit 11 First DC power supply 12 Gradient power supply 12A Gradient power supply 12B Gradient power supply 12C Gradient power supply 12a Second DC power supply 12b Inverter circuit 12c Transformer 12d Rectifier circuit 12e Voltage superposition circuit 12f Rectified output smoothing circuit 13 Switch unit 13a Pulse switch unit 13b Discharge circuit 14 Smoothing circuit 15 Control unit 16 Detection unit 21 Load Ph_dis Discharge phase Ph_add Application phase Cf Capacitor Cp Capacitor Cw Capacitor Iout Output current Ip Ion current Ir Current Iq Current Lf Inductor Lp Inductor SWA Switch SWB Switch T Output pulse period Tinv Inverter period Toff Off time Ton On time V1 First voltage Vgra Gradient power supply output Vlamp Ramp waveform voltage Vout Power supply output Vsh Wafer voltage dv/dt Voltage change rate f_inv Drive frequency f_pulse Output pulse frequency

Claims (4)

a first DC power supply generating a first voltage of a DC voltage;
A gradient power supply that generates a trapezoidal waveform voltage;
a switch unit that generates a pulse waveform by switching between a ground potential and the trapezoidal waveform voltage of the gradient power supply, and outputs a pulse by repeating the pulse waveform at a predetermined cycle;
A control unit that controls the gradient power supply;
Equipped with
The gradient power supply comprises:
A second DC power source;
An inverter circuit that converts DC voltage into AC voltage;
a rectifier circuit that converts the AC voltage of the inverter circuit into a DC voltage to generate a ramp waveform voltage;
a voltage superposition circuit that generates a trapezoidal waveform voltage by superposing an output of the first DC power source and an output of the rectifier circuit;
Equipped with
The control unit is
Controlling an inverter circuit by inverter control to generate a ramp waveform voltage that changes linearly over time at a predetermined voltage change rate dv/dt from a ground potential, and controlling a gradient power supply that superimposes the ramp waveform voltage and the first voltage to generate a trapezoidal waveform voltage whose voltage changes linearly over time from the first voltage at a predetermined voltage change rate dv/dt;
a switch unit that controls a switching operation for alternately switching between opening and closing between the gradient power supply and the output terminal and between opening and closing between a ground potential and the output terminal, and a periodic operation for repeating the switching operation at a predetermined period;
Equipped with
Synchronizing control of the gradient power supply with control of the switch unit, and synchronizing generation of the trapezoidal waveform voltage with generation of the pulse.
Pulse power supply. a detection unit for detecting a smoothed output of the switch unit,
The inverter control of the gradient power supply performs voltage control by PWM control for controlling the duty ratio of the inverter control or PFM control for controlling the period of the inverter control so that the voltage change of the output voltage detected by the detection unit becomes a set voltage change rate dv/dt.
2. The pulse power supply of claim 1. a detection unit for detecting a smoothed output of the switch unit,
The inverter control of the gradient power supply performs current control by PWM control that controls the duty ratio of the inverter control or PFM control that controls the cycle of the inverter control so that the output current detected by the detection unit becomes a constant current value.
2. The pulse power supply of claim 1. The constant current value is an external command or a statically constant current value after application of the first voltage.
4. The pulse power supply of claim 3.

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