Pulse power source device

Abstract

This pulse power source device 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 source device: generates, by inverter control, a ramp waveform voltage, which is a voltage having a voltage gradient that linearly changes over time at a predetermined voltage change rate dv / dt from a ground potential; superimposes a DC voltage and the ramp waveform voltage to generate a trapezoidal waveform voltage; generates a pulse waveform from the trapezoidal waveform voltage; and generates a pulse having the voltage gradient without using a current source.

Description

Pulse Power Supply

[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.

[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 to apply a bias with a pulsed waveform to compensate for the ion deposition effect on the dielectric substrate during the etching or deposition phase. The pulsed waveform consists of a negative voltage gradient that decreases to compensate for the rise in 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, into a switch-mode power supply are known (see Patent Documents 1 and 2).

[0005] Patent No. 7214046 Patent No. 6181792

[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.

[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 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 that changes linearly over time from the first voltage at the predetermined voltage change rate dv / dt through this voltage superposition.

[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 a DC voltage to an AC voltage. By making the voltage change rate dv / dt negative, a trapezoidal waveform voltage with a negative gradient is generated.

[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, with the starting voltage being ground potential and the voltage changing 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. By setting the voltage change rate dv / dt of the ramp waveform voltage to a negative value, a negative trapezoidal waveform voltage is generated.

[0019] The switch unit synchronizes the start of pulse generation in the switch unit with the start of output of the gradient power supply, and generates a pulse waveform by switching between 0 V (ground potential) and a trapezoidal waveform voltage generated by the gradient power supply. The generated pulse waveform has a first section where the potential is 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 0 V 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 0 V and a second section of a 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 Configuration: The voltage superposition circuit of the first configuration is disposed in a rectifier circuit. As an example, there is a configuration in which one output terminal of the rectifier circuit is connected to the output terminal of the first DC power supply.

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

[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.

[0027] FIG. 1 is a diagram for explaining a schematic configuration of a pulsed power supply according to the present invention; FIG. 2 is a timing chart for explaining an example of operation of the pulsed power supply according to the present invention; FIG. 3 is a diagram for explaining an example of operation in the discharge phase of the pulsed power supply according to the present invention; FIG. 4 is a diagram for explaining an example of operation in the discharge phase of the pulsed power supply according to the present invention; FIG. 5 is a diagram for explaining an example of operation in the application phase of the pulsed power supply according to the present invention; FIG. 6 is a diagram for explaining an example of operation in the application phase of the pulsed power supply according to the present invention; FIG. 7 is a schematic diagram of a first configuration example of a gradient power supply according to the present invention; FIG. 8 is a timing chart of the first configuration example of a gradient power supply according to the present invention; FIG. 9 is a schematic diagram of a second configuration example of a gradient power supply according to the present invention; FIG. 10 is a timing chart of the second configuration example of a gradient power supply according to the present invention; FIG. 11 is a diagram for explaining an example of the configuration of a voltage superposition circuit according to the present invention; FIG. 12 is a diagram for explaining an example of the configuration of a voltage superposition circuit according to the present invention; FIG. 13 is a diagram for explaining a smoothing circuit according to the present invention; FIG. 14 is a diagram for explaining a first embodiment including a smoothing circuit according to the present invention; FIG. 15 is a diagram for explaining a second embodiment including a smoothing circuit according to the present invention; FIG. 16 is a diagram for explaining an example of waveforms of the smoothing circuit according to the present invention; FIG. 17 is a diagram for explaining an example where the load of the pulsed power supply according to the present invention is a plasma load; FIG. 18 is a diagram for explaining an example of a switch drive signal, a power supply output Vout, and an output current Iout; FIG. 19 is a diagram for explaining a wafer voltage Vsh, a power supply output Vout, and an ion current Ip.

[0028] (1) General Configuration and Operational Example of the Pulse Power Supply Device of the Present Invention The general configuration and operational example of the pulse power supply device of the present invention will be described below with reference to FIGS. 1 and 2. FIG.

[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 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.

[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, 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 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 from the switch unit 13 is supplied to the load 21 as a power supply output.

[0033] The pulse power supply device 1 may be configured with a smoothing circuit. The smoothing circuit may be configured in two ways: a first way in which the smoothing circuit is connected to the output terminal of the gradient power supply 12; and a second way 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 way suppresses noise contained in the gradient power supply output. The smoothing circuit of the second way 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 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 that changes at a predetermined voltage change rate dv / dt starting from ground potential, and superimposes the first voltage V1 on this ramp waveform voltage Vlamp to generate a trapezoidal waveform voltage.

[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] Because ΔV is the product of the voltage change rate dv / dt and Ton (Ton × dv / dt), voltages ΔV and V2 depend on the voltage change rate dv / dt and Ton, or the duty ratio of the periodic pulse. Therefore, if the voltage change rate dv / dt, Ton, or the duty ratio of the periodic pulse is changed, voltages ΔV and 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 unit output of the switch unit 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 indicates the discharge phase, and the section marked with Ph_add indicates the application phase. During 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, during 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 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.

[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 discharge phase Toff to ground and setting the voltage of the gradient power supply output Vgra to 0V.

[0045] 3A and 3B are diagrams for explaining an example of operation in the discharge phase, and respectively show the operating state at the time when the power supply output Vout rises from V2 to 0 V and the operating state at which the power supply output Vout becomes 0 V in the discharge phase Ph_dis in FIG. 2.

[0046] The discharge phase Ph_dis1 in Fig. 3A is the point in time when the switch SWA of the pulse switch unit 13a is switched to the OFF state and the switch SWB of the discharge circuit 13b is switched to the ON state. This point in time corresponds to the section indicated by Dis1 in Fig. 2. During 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, 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. 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] 4A and 4B are diagrams for explaining an example of operation in the application phase, and respectively show the operating state at the time when the power supply output Vout falls from 0 V to V1 and the operating state at which the power supply output Vout changes from V1 to V2 in the application phase Ph_app in FIG. 2.

[0049] The application phase Ph_app1 in Fig. 4A is the time when the switch SWA of the pulse switch unit 13a is switched on and the switch SWB of the discharge circuit 13b is switched off. This time corresponds to the time indicated by App1 in Fig. 2. At this 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 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, the switch SWA of the pulse switch unit 13a is on, and the switch SWB of the discharge circuit 13b is off. 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 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. 15.

[0051] (2) Gradient Power Supply The gradient power supply 12 of the present invention includes an inverter circuit that converts DC voltage into AC voltage, a rectifier circuit that converts the AC voltage of the inverter circuit into 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 it as the gradient power supply output Vgra.

[0052] The gradient power supply of the present invention can be configured in a variety of forms, in which the voltage superposition circuit that superimposes the output of the DC power supply and the ramp waveform voltage Vlamp is located at different positions in the gradient power supply circuit. Below, first and second configuration examples of the gradient power supply of the present invention will be described with reference to Figures 5 to 8. Figures 5 and 6 are diagrams illustrating the first configuration example of the gradient power supply, and Figures 7 and 8 are diagrams illustrating the second configuration example of the gradient power supply. Furthermore, Figure 9 is a diagram illustrating an example configuration of the voltage superposition circuit.

[0053] (a) First Configuration Example of Gradient Power Supply FIG. 5 shows a schematic configuration of a first configuration example of the gradient power supply of the present invention, and FIG. 6 shows a timing chart of the first configuration 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, or may 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 example circuit configuration 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] 6 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 an output pulse period T, and resumes after an 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.

[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 needs to be higher than the output pulse frequency f_pulse, and it is desirable for it to be 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 whose voltage changes at a predetermined voltage change rate dv / dt. The ramp waveform voltage is output during an on-time Ton and not during an 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 Configuration Example of Gradient Power Supply FIG. 7 shows a schematic configuration of a second configuration example of the gradient power supply of the present invention, and FIG. 8 shows a timing chart of the second configuration 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, a description 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 described.

[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] 8, like FIG. 6, 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 an output pulse period T, and resumes 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.

[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 needs to be higher than the output pulse frequency f_pulse, and it is desirable for it to 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 Fig. 10 shows an example of the configuration of the smoothing circuit 14. The smoothing circuit 14 is configured as an LC circuit having 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 present 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 Smoothing Circuit A first example of a smoothing circuit 14A will be described with reference to Fig. 11. Fig. 11 shows a configuration example 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 switch 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.

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

[0076] 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 by 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 abruptly switched 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 switch 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 switch 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 at a predetermined time constant, and a power supply output Vout with suppressed fluctuations is output.

[0078] FIG. 13 shows example waveforms of the smoothing circuit 14B. FIG. 13A shows a case where the constants of the inductor Lf and capacitor Cf are small, while FIG. 13B 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, 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 required to be constant, thereby maintaining the wafer voltage Vsh of the substrate 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, which is 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 has a value 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.

[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.

[0087] REFERENCE SIGNS LIST 1 Pulse power supply device 2 Plasma chamber 10 Power supply unit 11 First DC power supply 12, 12A, 12B, 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, 14A, 14B Smoothing circuit 15 Control unit 16 Detector 17 Discharge circuit 21 Load Ph_dis Discharge phase Ph_add Application phase Cf, Cp, Cw Capacitor Iout Output current Ip Ion current Iq, Ir Current Lf, Lp Inductor SWA, 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

1. A pulse power supply device comprising: a first DC power supply that generates a first DC voltage; a gradient power supply that generates a trapezoidal waveform voltage; and 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 period, wherein the gradient power supply generates a ramp waveform voltage that changes linearly over time from the ground potential at a predetermined voltage change rate dv / dt through inverter control, and superimposes the ramp waveform voltage on the first voltage to generate a trapezoidal waveform voltage that changes linearly over time at the predetermined voltage change rate dv / dt from the first voltage.

2. The pulse power supply according to claim 1, wherein said gradient power supply comprises: a second DC power supply; an inverter circuit that converts the DC voltage of said second DC power supply into an AC voltage; a rectifier circuit that converts the AC voltage of said inverter circuit into a DC voltage; and a voltage superposition circuit that superimposes the output of said first DC power supply and the output of said rectifier circuit, wherein said inverter circuit adjusts the voltage change rate dv / dt of the AC voltage in the DC-to-AC voltage conversion, said rectifier circuit rectifies the output of said inverter circuit to generate a ramp waveform voltage that varies linearly with time from ground potential, and said voltage superposition circuit superimposes said first voltage of the output of said first DC power supply and the ramp waveform voltage of the output of said rectifier circuit to generate a trapezoidal waveform voltage that varies linearly with time at a predetermined voltage change rate dv / dt from said first voltage of said first DC power supply.

3. A pulse power supply according to claim 2, wherein the voltage superposition circuit is provided in the rectifier circuit, and an output terminal of the first DC power supply is connected to one output terminal of the rectifier circuit.

4. The pulse power supply according to claim 2, further comprising a transformer between said inverter circuit and said rectifier circuit, said voltage superposition circuit being provided in said transformer, and an output terminal of said first DC power supply being connected to one end of the secondary side of said transformer.

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