Pulse power supply device

Abstract

To provide a pulse power supply device having a gradient power supply capable of obtaining a negative voltage gradient without using a current source.SOLUTION: A pulse power supply device according to the present invention generates a pulse having a trapezoidal waveform with a predetermined voltage gradient by superimposing a DC voltage of a constant voltage and a ramp waveform voltage. The pulse power supply device generates, through inverter control, a ramp waveform voltage that is a voltage having a voltage gradient that changes linearly over time from a ground potential at a predetermined voltage change rate dv / dt, as well as generating a trapezoidal waveform voltage by superimposing the DC voltage and the ramp waveform voltage, and generates a pulse waveform from the trapezoidal waveform voltage and generates a pulse having a voltage gradient without using a current source.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pulse power supply that generates a pulse output including a gradient waveform in which the voltage changes linearly with a predetermined slope. [Background technology]

[0002] The pulse output generated by the pulse power supply is used for plasma processing such as film formation processing and etching processing, and can also be applied to various industrial devices other than plasma processing. For example, in etching processing of semiconductor devices, a negative voltage relative 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.

[0003] In plasma etching and deposition processes, it is known to use a pulsed bias waveform comprising a broad negative pulse during the etching phase and a short positive pulse during the discharge phase.

[0004] 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 that attracts electrons to maintain the charge bias during the discharge phase. A configuration that generates a negative voltage gradient by incorporating ion current compensation such as a current source into a switch-mode power supply is known (Patent Document 1 and Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7214046 [Patent Document 2] Patent No. 6181792 Summary of the Invention [Problem to be solved by the invention]

[0006] In order 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 described above, the relationship between the negative voltage gradient and the ion current is determined by a predetermined function, so an ion current compensation current source such as a current source is used to realize the negative voltage gradient.

[0007] 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, and the problem of low high-speed response becomes more pronounced at high pulse frequencies.

[0008] In addition to the issue of high-speed response mentioned above, there are other points to consider with current sources. Generally, current sources are affected by internal resistance and temperature fluctuations, so temperature compensation and feedback compensation are required, which increases the cost of the components of the pulsed power supply device. As mentioned above, pulsed power supplies that output high-frequency pulses using a current source have issues such as high-speed response and cost due to the use of the current source.

[0009] SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and 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. [Means for solving the problem]

[0010] The pulse power supply of the present invention generates a trapezoidal waveform pulse with a predetermined voltage gradient by superimposing a constant DC voltage on 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 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 on 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.

[0011] The pulse power supply device of the present invention includes a first power supply that is a first DC power supply that generates a first voltage that is a constant DC voltage, a second power supply that 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 of the second power supply.

[0012] 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 pulses by repeating the generated pulse waveform at a predetermined cycle.

[0013] The gradient power supply of the present invention uses inverter control to generate a ramp waveform voltage that changes linearly over time from ground potential at a predetermined voltage change rate dv / dt, superimposes the generated ramp waveform voltage on a first voltage of a first DC power supply, and generates a trapezoidal waveform voltage from the first voltage that changes linearly over time at the predetermined voltage change rate dv / dt.

[0014] 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 a first DC power supply and the output of the rectifier circuit.

[0015] When performing DC-AC voltage conversion using inverter control, an inverter circuit adjusts the AC voltage using 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 variable over time when converting DC voltage to AC voltage. Making the voltage change rate dv / dt negative generates a trapezoidal waveform voltage with a negative slope.

[0016] The rectifier circuit rectifies the AC voltage output from the inverter circuit to DC voltage, and generates a ramp voltage that changes linearly over time from ground potential. The voltage change rate of the ramp voltage is adjusted by inverter control.

[0017] The voltage superposition circuit superposes the ramp waveform voltage output from the rectifier circuit on the first voltage of the first DC power supply to generate a trapezoidal waveform voltage.

[0018] 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 ground potential and the voltage changes over time from ground potential. The trapezoidal waveform voltage is a voltage waveform in which the first voltage is superimposed on the ramp waveform voltage, and the voltage changes linearly over time at a predetermined voltage change rate dv / dt, starting from the first voltage. A negative trapezoidal waveform voltage is generated by setting the voltage change rate dv / dt of the ramp waveform voltage to a negative value.

[0019] 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, which is the ground potential, and the trapezoidal waveform voltage generated by the gradient power supply. The generated pulse waveform has a first section where the potential is the ground potential, and a second section where the trapezoidal waveform voltage 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.

[0020] 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.

[0021] 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.

[0022] In the case of a negative trapezoidal waveform voltage, the switch unit outputs a periodic pulse, one pulse of which is a voltage waveform consisting of two voltage sections: a first section of 0V and a second section of the trapezoidal waveform voltage that changes linearly over time from the negative first voltage.

[0023] In the gradient power supply of the present invention, the voltage superposition circuit can be arranged in a number of different positions.

[0024] First form: The voltage superposition circuit of the first embodiment is disposed in a rectifier circuit, and as an example, one output terminal of the rectifier circuit is connected to an output terminal of the first DC power supply.

[0025] Second form: In the second embodiment, a transformer is provided between the inverter circuit and the rectifier circuit, the voltage superposition circuit is disposed in the transformer, and the output terminal of the first DC power supply is connected to one end of the secondary side of the transformer. [Effects of the Invention]

[0026] As described above, the pulse power supply device of the present invention can achieve high speed response by including a gradient power supply that can obtain a predetermined voltage gradient without using a current source. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a diagram illustrating a schematic configuration of a pulse power supply device according to the present invention; [Figure 2] 4 is a timing chart for explaining an example of the operation of the pulse power supply device of the present invention. [Figure 3A] 10A and 10B are diagrams for explaining an example of operation in a discharge phase of the pulse power supply device of the present invention. [Figure 3B] 10A and 10B are diagrams for explaining an example of operation in a discharge phase of the pulse power supply device of the present invention. [Figure 4A] 10A and 10B are diagrams for explaining an example of operation of the pulse power supply device of the present invention in the application phase. [Figure 4B] 10A and 10B are diagrams for explaining an example of operation of the pulse power supply device of the present invention in the application phase. [Figure 5] FIG. 1 is a schematic diagram illustrating a first configuration example of a gradient power supply according to the present invention. [Figure 6] 4 is a timing chart of a first example configuration of the gradient power supply of the present invention. [Figure 7] FIG. 10 is a schematic diagram of a second example of the gradient power supply of the present invention. [Figure 8] 10 is a timing chart of a second example configuration of the gradient power supply of the present invention. [Figure 9A] 1 is a diagram for explaining a configuration example of a voltage superposition circuit according to the present invention; [Figure 9B] 1 is a diagram for explaining a configuration example of a voltage superposition circuit according to the present invention; [Figure 10] FIG. 2 is a diagram for explaining a smoothing circuit according to the present invention. [Figure 11] FIG. 1 is a diagram illustrating a first embodiment of a smoothing circuit according to the present invention. [Figure 12] FIG. 4 is a diagram for explaining a second embodiment including a smoothing circuit of the present invention. [Figure 13A] 4A and 4B are diagrams illustrating examples of waveforms of a smoothing circuit according to the present invention. [Figure 13B] 4A and 4B are diagrams illustrating examples of waveforms of a smoothing circuit according to the present invention. [Figure 14] FIG. 10 is a diagram for explaining an example in which the load of the pulse power supply device of the present invention is a plasma load. [Figure 15] 3A and 3B are diagrams illustrating an example of a switch drive signal, a power supply output Vout, and an output current Iout. [Figure 16] FIG. 10 is a diagram showing the wafer voltage Vsh, the power supply output Vout, and the ion current Ip. DETAILED DESCRIPTION OF THE INVENTION

[0028] (1) Schematic configuration and operation example of the pulse power supply device of the present invention The schematic configuration and operation example of the pulse power supply device of the present invention will be described below with reference to FIGS.

[0029] The pulse power supply device 1 includes a power supply unit 10, a switch unit 13, and a control unit 15. 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.

[0030] The gradient power supply 12 generates a ramp waveform voltage Vlamp that 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 that 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.

[0031] The switch unit 13 supplies current to the load by alternately repeating a discharge phase in which electric charge accumulated on the load side is discharged by switching operation and an application phase in which periodic pulses are applied to the load side. The switch unit 13 includes a pulse switch unit 13a for outputting pulses of the gradient power supply output Vgra to the load in the application phase, and a discharge circuit 13b for discharging electric 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.

[0032] In the application phase, switch unit 13 applies the trapezoidal waveform voltage generated by 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 switch unit 13 becomes 0 V, so the output of switch unit 13 at the start of the application phase changes from 0 V to the first voltage. The pulse output from switch unit 13 is supplied to load 21 as a power supply output.

[0033] The pulse power supply device 1 may be configured with a smoothing circuit. There are two types of smoothing circuits: a first type in which a smoothing circuit is connected to the output terminal of the gradient power supply 12, and a second type in which a smoothing circuit is connected to the output terminal of the pulse switch unit 13a of the switch unit 13. The smoothing circuit of the first type suppresses noise contained in the gradient power supply output. The smoothing circuit of the second type suppresses voltage oscillations such as overshoot and undershoot that occur in the switch unit 13 due to voltage changes between the discharge phase and the application phase. Note that the smoothing circuit is not shown in FIG. 1.

[0034] 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.

[0035] 2 is a timing chart illustrating an example of the operation of the pulse power supply 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 that changes at a predetermined voltage change rate dv / dt starting from ground potential, and generates a trapezoidal waveform voltage by superimposing the first voltage V1 on this ramp waveform voltage Vlamp.

[0036] The gradient power supply 12 generates a ramp waveform voltage Vlamp based on a gradient power supply control signal from the control unit 15, and superimposes the generated ramp waveform voltage Vlamp on the first voltage V1 to generate a trapezoidal waveform voltage, which is output as a gradient power supply output Vgra.

[0037] 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.

[0038] Here, when the duty ratio with respect to 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.

[0039] The ramp waveform voltage Vlamp changes from 0 V at the start of the application phase at a predetermined voltage change rate dv / dt, and at the end of the application phase becomes a voltage ΔV determined by the product of the voltage change rate dv / dt and Ton (Ton × 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 becomes a voltage V2 (= V1 + ΔV) obtained by superimposing a voltage ΔV on the first voltage V1.

[0040] Voltage ΔV and voltage V2 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 × 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.

[0041] The smoothing circuit of the first type suppresses noise contained in the gradient power supply output, and the smoothing circuit of the second type suppresses voltage oscillations of overshoot and undershoot contained in the switch section output of the switch section 13. The power supply output of the pulse power supply device 1 is supplied to a load 21.

[0042] 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.

[0043] The switch SWA of the pulse switch unit 13a switches from the off state to the on state to switch from the discharge phase to the application phase, and outputs the gradient power supply output Vgra as a pulse output during the application phase Ton.

[0044] The switch SWB of the discharge circuit 13b switches from the OFF state to the ON state, thereby switching from the application phase to the discharge phase, discharging the charge accumulated in the load during the Toff of the discharge phase to ground, and setting the voltage of the gradient power supply output Vgra to 0V.

[0045] 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 0V and the operating state when the power supply output Vout becomes 0V in the discharge phase Ph_dis in Figure 2.

[0046] 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 indicated by Dis1 in FIG. 2. In Dis1, the power supply output Vout rises from V2 to 0 V, and the output current Iout sharply decreases toward 0 A as a discharge current. The current Ir in the application phase corresponds to the ion current Ip in the case of a plasma load.

[0047] In the discharge phase Ph_dis2 in Fig. 3B, SWA of the pulse switch unit 13a is in the OFF state, and SWB of the discharge circuit 13b is in the ON state. This state corresponds to the section indicated by Dis2 in Fig. 2. In this Dis2, the power supply output Vout is 0 V, and the output current Iout is 0 A.

[0048] Figure 4 is a diagram for explaining an example of operation in the application phase, and Figures 4A and 4B respectively show the operating state at the point in 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 in the application phase Ph_app in Figure 2.

[0049] 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 indicated by App1 in FIG. 2. At this point in time App1, the power supply output Vout falls from 0 V 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.

[0050] In the application phase Ph_app2 of FIG. 4B, SWA of the pulse switch unit 13a is in the ON state, and SWB of the discharge circuit 13b is in the OFF state. This state corresponds to the section indicated by App2 in FIG. 2. In App2, the power supply output Vout changes from V1 at a voltage change rate dv / dt, and at the end of App2, the power supply output Vout becomes V2. In the case of a plasma load, a constant current Ir corresponding to the ion current Ip 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. 15.

[0051] (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 via the rectifier circuit, and outputs the trapezoidal waveform voltage as the gradient power supply output Vgra.

[0052] The gradient power supply of the present invention can be configured in a number of ways, with the voltage superposition circuit, which superimposes the output of the DC power supply and the ramp waveform voltage Vlamp, being located at different positions in the gradient power supply circuit. Hereinafter, first and second configuration examples of the gradient power supply of the present invention will be described with reference to Figs. 5 to 8. Figs. 5 and 6 are diagrams illustrating the first configuration example of the gradient power supply, and Figs. 7 and 8 are diagrams illustrating the second configuration example of the gradient power supply. Also, Fig. 9 is a diagram illustrating an example configuration of the voltage superposition circuit.

[0053] (a) First example of gradient power supply configuration FIG. 5 shows a schematic configuration of a first example of the gradient power supply of the present invention, and FIG. 6 shows a timing chart of the first example of the gradient power supply of the present invention.

[0054] The gradient power supply 12A of 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.

[0055] 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 AC (alternating current) source 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 the voltage value of the converted AC voltage before outputting it. 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 from the transformer 12c and converts it into a DC voltage.

[0056] The inverter circuit 12b is inverter-controlled based on a control command output from the control unit 15. The control command from the control unit 15 is generated based on a feedback signal of the voltage and / or current of the gradient power supply output, and may also be generated based on an external signal from an external device (not shown).

[0057] 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 single-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.

[0058] The voltage superposition circuit 12e is incorporated into 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. 9A shows an example configuration of the voltage superposition circuit 12e incorporated into the rectifier circuit 12d. Here, an example circuit formed of a diode bridge is shown as the rectifier circuit 12d. In the circuit configuration example of FIG. 9A, 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.

[0059] Figure 6 shows the 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 resumes after the off-time Toff has elapsed. PWM control controls the pulse width for each inverter period Tinv (= 1 / f_inv), which is 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.

[0060] 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.

[0061] The transformer 12c adjusts the peak value of the inverter output from the inverter circuit 12b based on a transformation ratio determined by the winding ratio, and outputs the adjusted value to the rectifier circuit 12d. The rectifier circuit 12d rectifies the inverter output and outputs a ramp waveform voltage that changes at a predetermined voltage change rate dv / dt. The ramp waveform voltage is output during the on-time Ton and not during the off-time Toff. The voltage superposition circuit 12e generates a superposed output by superposing a first voltage V1 on the rectified output from the rectifier circuit 12d.

[0062] (b) Second example of gradient power supply configuration FIG. 7 shows a schematic configuration of a second example of the gradient power supply of the present invention, and FIG. 8 shows a timing chart of the second example of the gradient power supply of the present invention.

[0063] 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 in the transformer 12c.

[0064] 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 a voltage superposition circuit 12e is incorporated into the transformer 12c. Here, explanations 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.

[0065] 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. 9B shows an example of the configuration of the voltage superposition circuit 12e.

[0066] In the circuit configuration example of FIG. 9B, 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 voltage converted by the transformer 12c.

[0067] Like Figure 6, Figure 8 shows a case where PWM control is used for inverter control. Inverter control is performed during an on-time Ton based on the duty ratio within the output pulse period T, and resumes after the off-time Toff has elapsed. PWM control controls the pulse width for each inverter period Tinv, which is 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.

[0068] 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 account 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 it is desirable that it be at least five times higher.

[0069] The transformer 12c adjusts the peak value of the inverter output from the inverter circuit 12b based on a transformation ratio.

[0070] The voltage superposition circuit 12e superposes the first voltage V1 on the inverter output converted by the transformer 12c to generate a transformer output, which is output to the rectification circuit 12d. The rectification circuit 12d rectifies the inverter output and outputs a ramp waveform voltage that 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.

[0071] (3) Smoothing circuit 10 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.

[0072] The smoothing circuit of the pulse power supply 1 of the present invention can be configured in a first form in which the smoothing circuit is connected to the output terminal of the gradient power supply 12, or in a second form in which the smoothing circuit is connected to the output terminal of the pulse switch unit 13a of the switch unit 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 such as overshoot and undershoot that occur in the switch unit 13 due to voltage changes between the discharge phase and the application phase.

[0073] (a) First example of a smoothing circuit The smoothing circuit 14A of the first embodiment will be described with reference to Fig. 11. Fig. 11 shows an example of the configuration of a gradient power supply 12A that performs voltage superposition in a rectifier circuit 12d.

[0074] 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 when 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 mode, a discharge circuit 17 is connected to discharge the voltage charged in the capacitor in the smoothing circuit 14A.

[0075] (b) Second example of smoothing circuit The smoothing circuit 14B of the second embodiment will be described with reference to Figures 12 and 13. Figure 12 shows an example of the configuration of a gradient power supply 12A that performs voltage superposition in a rectifier circuit 12d, and Figure 13 shows an example of the waveform of the smoothing circuit 14B.

[0076] The smoothing circuit 14B of the second embodiment is connected between the pulse switch unit 13a and the discharge circuit 13b in the switch unit 13. Due to the switching operation performed by the pulse switch unit 13a of the switch unit 13, the voltage changes sharply from V2 to the first voltage V1 during discharge, and also changes sharply from the ground potential of 0V to the first voltage V1. This voltage change causes an overshoot or undershoot in the output waveform.

[0077] 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 such as overshoot and undershoot caused by voltage changes are suppressed, the voltage value of the power supply output is settled with a predetermined time constant, and a power supply output Vout with suppressed fluctuations is output.

[0078] FIG. 13 shows an example of a waveform of the smoothing circuit 14B. FIG. 13A shows a case where the constants of the inductor Lf and the capacitor Cf are small, and FIG. 13B shows a case where the constants of the inductor Lf and the capacitor Cf are large. By selecting small constants for the inductor Lf and the capacitor Cf, the time constant of the LC circuit is set to a small value, thereby shortening 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 the discharge period long, 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.

[0079] (4) Example of plasma load An example of a plasma load as the load of the pulse power supply of the present invention will be described using Figure 14. 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. Capacitor Cw is the intrinsic capacitance of components such as the substrate provided in the plasma chamber, and Cp is the variable capacitance of the sheath capacitance and stray capacitance.

[0080] In the plasma chamber 2, the ion current Ip supplied to the substrate placed in the chamber is kept constant, and thereby the wafer voltage Vsh of the substrate is required to be maintained at a constant voltage.

[0081] The pulse power supply device of the present invention supplies the above-mentioned constant ion current Ip, and supplies the load in the plasma chamber 2 with power to maintain the substrate wafer voltage Vsh at a constant voltage.

[0082] The pulse power supply device of the present invention feeds back the power output Vout and / or output current Iout detected by the detector 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.

[0083] FIG. 15 shows an example of a drive signal for driving a switch, a power supply output Vout, and an output current Iout, and FIG. 16 shows a wafer voltage Vsh, a power supply output Vout, and an ion current Ip.

[0084] When switching from the discharge phase to the application phase, the power supply output Vout changes from 0 V, the ground potential, 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 at a voltage change rate dv / dt, and the current Iq is maintained at a constant current.

[0085] At the end of the application phase, the power supply output Vout becomes voltage V2. This voltage V2 is determined by the voltage change rate dv / dt and the duration of the application phase. The duration of the gradient section of the application phase corresponds to the on-time Ton of the output pulse period T. [Industrial Applicability]

[0086] The pulse power supply device of the present invention can be applied to a load that requires a constant voltage pulse output, in addition to being applied to plasma processing. [Explanation of symbols]

[0087] 1 Pulse power supply 2. Plasma chamber 10 Power supply section 11 1st DC power supply 12 Gradient Power Supply 12A gradient power supply 12B Gradient Power Supply 12C gradient power supply 12a 2nd DC power supply 12b Inverter circuit 12c transformer 12d rectifier circuit 12e Voltage superposition circuit 12f rectifier output smoothing circuit 13 Switch section 13a Pulse switch section 13b Discharge circuit 14 Smoothing circuit 15 Control Unit 16 detectors 17 Discharge circuit 21 Load Ph_dis Discharge phase Ph_add application phase Cf capacitor Cp capacitor Cw capacitor Iq current Iout Output current Ip ion current Iq current Ir current Lf inductor Lp inductor SWA switch SWB switch T output pulse period Tinv inverter cycle Toff Off time Ton On time V1 First voltage Vgra gradient power output Vlamp Ramp waveform voltage Vout Power output Vsh wafer voltage dv / dt Voltage change rate f_inv driving frequency f_pulse output pulse frequency

Claims

1. a first 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 pulses by repeating the pulse waveform at a predetermined cycle; Equipped with the gradient power supply generates a ramp waveform voltage that changes linearly over time at a predetermined voltage change rate dv / dt from a ground potential by inverter control, and superimposes the ramp waveform voltage on the first voltage to generate a trapezoidal waveform voltage that changes linearly over time at a predetermined voltage change rate dv / dt from the first voltage; Pulse power supply.

2. The gradient power supply a second DC power source; an inverter circuit that converts a DC voltage of the second DC power supply into an AC voltage; a rectifier circuit that converts the AC voltage of the inverter circuit into a DC voltage; a voltage superposition circuit that superposes the output of the first DC power supply and the output of the rectifier circuit; Equipped with the inverter circuit adjusts the voltage change rate dv / dt of the AC voltage in the DC-AC voltage conversion; the rectifier circuit rectifies the output of the inverter circuit to generate a ramp waveform voltage that changes linearly over time from a ground potential; the voltage superposition circuit superposes the first voltage of the output of the first DC power supply and the ramp waveform voltage of the output of the rectifier circuit to generate a trapezoidal waveform voltage that changes linearly with time from the first voltage of the first DC power supply at a predetermined voltage change rate dv / dt.

2. The pulse power supply of claim 1.

3. the voltage superposition circuit is provided in the rectification circuit, an output terminal of the first DC power supply is connected to one output terminal of the rectifier circuit; 3. The pulse power supply of claim 2.

4. a transformer is provided between the inverter circuit and the rectifier circuit; the voltage superposition circuit is provided in the transformer, an output terminal of the first DC power source is connected to one end of the secondary side of the transformer; 3. The pulse power supply of claim 2.

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