JP2013165062A - Discharge device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge device that allows improvement of output efficiency and, furthermore, reduction in switching loss, and is advantageous to cost reduction, by developing the point of view of a tailing pulse.SOLUTION: A discharge device includes: a pair of electrodes (14a and 14b); a pulse generating section 16 applying a pulse to the pair of electrodes; and a pulse control section 18 controlling the pulse generating section 16 so as to cause the pair of electrodes to generate discharge. The pulse control section 18 includes a first control section 52 applying one or more first pulses to the pair of electrodes and causing the pair of electrodes to change from first discharge to second discharge, and a second control section 54 applying two or more second pulses to the pair of electrodes after the pair of electrodes are changed from the first discharge to the second discharge.

Description

  In the present invention, various processes using plasma generated by discharge of a high voltage pulse (ignition process of an internal combustion engine, gas decomposition process, deodorization process, plasma film forming process, plasma etching process, laser oscillation process, gas generation process, etc.) It is related with the discharge device which can perform.

  Recently, techniques for performing deodorization, sterilization, film formation, decomposition of harmful gases, etc. have been applied by plasma by pulse discharge (see, for example, Patent Document 1 and Non-Patent Document 1). In order to perform efficiently, it is necessary to supply a pulse with a high voltage and a very narrow width (see, for example, Non-Patent Document 2).

  Therefore, conventionally, a method has been proposed in which a high-voltage, extremely narrow pulse is continuously supplied to high-speed plasma processing in high pressure, atmospheric pressure, and low pressure (see, for example, Patent Document 2).

  Conventionally, methods for maintaining streamer discharge by improving the electrode structure and electrode material have been proposed (see, for example, Patent Documents 3 to 5).

  Further, conventionally, in a hydrogen generation method in which hydrogen is generated by electrolysis of an electrolytic solution, a short pulse is applied to a pair of electrodes immersed in the electrolytic solution, followed by a tailing pulse in which the voltage gradually decreases. A hydrogen generation method has also been proposed in which the generation efficiency of hydrogen is improved by applying it to the electrode pair for a longer time than the time (see, for example, Patent Document 6).

Japanese Patent No. 2649340 JP 2004-220985 A JP 2010-247139 A JP 2005-267874 A JP 2005-262002 A JP 2006-257480 A

Applied Physics, Vol. 61, No. 10, 1992, p. 1039-1043, "Preparation of amorphous silicon thin film by high voltage pulsed discharge chemical vapor deposition" IEEE TRANSACTION ON PLASTIC SCIENCE, VOL. 28, NO. 2, APRIL 2000, p. 434-442, “Improvement of NOx Removal Efficiency Using Short-Width Pulsed Power”

  However, when high-speed plasma processing is performed by a conventional method such as Patent Document 2, it is necessary to continuously supply a high-voltage pulse in a short cycle, which is inferior in output efficiency and disadvantageous in terms of cost, and switching loss. There is also a problem that increases. The same applies to Patent Documents 3 to 5 that propose a method for maintaining streamer discharge.

  In addition, the conventional method of Patent Document 6 and the like applies a tailing pulse over a long period of time after applying a short pulse between electrodes, and this effectively moves mainly hydrogen ions in the electrolyte to the cathode. Thus, hydrogen generation efficiency is improved, and there is no description about application to high-speed plasma processing using discharge near atmospheric pressure, for example.

  The present invention has been made in view of such problems, and by developing the concept of tailing pulses described in Patent Document 6, output efficiency can be improved, and switching loss can be reduced. It is an object of the present invention to provide a discharge device that can be realized and is advantageous in terms of cost.

[1] A discharge device according to the present invention controls a pair of electrodes, a pulse generator that applies a pulse between the pair of electrodes, and the pulse generator so as to generate a discharge between the pair of electrodes. A first control that applies one or more first pulses between the pair of electrodes, and makes a transition from the first discharge to the second discharge between the pair of electrodes. And a second control unit that applies two or more second pulses between the pair of electrodes after transition from the first discharge to the second discharge, and a peak voltage value of the first pulse and The peak current values are Va and Ia, the peak voltage value and peak current value of the second pulse are Vb and Ib, the conduction time of the current of the first pulse is Ti1, and the conduction time of the current of the second pulse is Ti2. When
Va> Vb
Ia <Ib
Ti1 <Ti2
It is characterized by being.

[2] In the present invention, when the pulse width of the first pulse is Tp1, and the pulse width of the second pulse is Tp2,
Tp1 <Tp2
It is preferable that

[3] In the present invention, the first discharge may be a primary streamer discharge, and the second discharge may be a secondary streamer discharge.

[4] In the present invention, when the reaction time of radicals generated between the pair of electrodes is Tr, the conduction time Ti2 of the current of the second pulse is
0.75Tr ≦ Ti2 ≦ 2.00Tr
It is preferable that

[5] In the present invention, when the first control unit applies two or more first pulses, the pulse period of the first pulse is Ta, and the pulse period of the second pulse is Tb,
Ta <Tb
It may be.

[6] In the present invention, the number of pulses of the first pulse is preferably 1-10.

[7] In the present invention, the pulse generation unit includes a transformer and a switch connected in series to both ends of a DC power supply unit, and accumulates inductive energy in the transformer by ON control of the switch of the pulse control unit. And a pulse generation circuit that generates the pulse on the secondary side of the transformer by turning off the switch of the pulse control unit.

[8] In this case, the second control unit may change the accumulation time of the induction energy in the transformer at the start of control by the second control unit.

[9] Further, the start time of the control by the second control unit may be a time when a preset time has elapsed from the start time of the control by the first control unit.

[10] Further, the pulse control unit includes a discharge detection unit that detects transition to the second discharge between the pair of electrodes, and the start point of control by the second control unit is the discharge detection. It may be a point in time when a preset time has elapsed since it was detected that the part transitioned to the second discharge between the pair of electrodes.

[11] In this case, the discharge detection unit is configured to acquire the first moving image based on the camera that acquires the moving image of the discharge generated between the pair of electrodes and the moving image of the discharge acquired by the camera. And an image processing unit that detects the timing of transition from the discharge to the second discharge.

[12] Alternatively, the discharge detection unit determines that the discharge has transitioned to the second discharge when the voltage between the pair of electrodes decreases and becomes equal to or lower than a preset threshold voltage. You may make it have.

  According to the discharge device according to the present invention, it is possible to reduce the power supply, reduce the running cost and the like, and increase the output efficiency.

It is a lineblock diagram showing the discharge device concerning this embodiment. It is a circuit block diagram which shows the structure of the discharge device concerning this Embodiment. It is a time chart which shows operation | movement of a pulse generation circuit. It is a time chart which shows the processing operation of the discharge device (Example) which concerns on this Embodiment. It is a time chart which shows the voltage waveform and current waveform of a 1st pulse. It is a time chart which shows the voltage waveform and current waveform of a 2nd pulse. It is a time chart which shows the processing operation of the discharge device concerning a reference example. It is a characteristic view which shows the difference in the output efficiency of an Example and a reference example. It is a circuit block diagram which shows the structure of the discharge device which concerns on a 1st modification. It is a circuit block diagram which shows the structure of the discharge device which concerns on a 2nd modification.

  Hereinafter, an embodiment of a discharge device according to the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the discharge device 10 according to the present embodiment includes a pair of electrodes 14a and 14b installed in, for example, the plasma processing chamber 12 and a pulse for applying a pulse between the pair of electrodes 14a and 14b. It has the production | generation part 16 and the pulse control part 18 which controls the pulse production | generation part 16 so that discharge may be generated between a pair of electrodes 14a and 14b.

  The pulse generation unit 16 includes a pulse generation circuit 20 as shown in FIG. The pulse generation circuit 20 includes a transformer 24, an SI thyristor 26, and a switching element 28 connected in series at both ends of the DC power supply unit 22. The positive electrode of the DC power supply unit 22 is connected to one first terminal 32 a of the primary winding 30 of the transformer 24, and the anode of the SI thyristor 26 is connected to the other first terminal 32 b of the primary winding 30 of the transformer 24. . A diode 34 and a resistor 36 are connected in parallel between the gate of the SI thyristor 26 and one first terminal 32 a of the primary winding 30. The diode 34 has a cathode connected to one first terminal 32 a of the primary winding 30 and an anode connected to the gate of the SI thyristor 26.

  The switching element 28 is configured by, for example, a MOSFET, an IGBT, or the like, and an input terminal 38 is connected to the gate electrode thereof, and a control signal (ON signal Son / OFF signal Soff) is supplied from the pulse control unit 18 to the input terminal 38. It has become so.

  One electrode 14a (cathode) is connected to one second terminal 42a of the secondary winding 40 of the transformer 24, and the other electrode 14b (anode) is connected to the other second terminal 42b of the secondary winding 40. Has been.

  Further, for example, a diode 44 is connected between the other second terminal 42b of the secondary winding 40 and the other electrode 14b. The connection direction of the diode 44 is such that when the high voltage pulse is generated, when the current flows from the secondary winding 40 → the other second terminal 42b → the other electrode 14b (anode), the diode 44 is in the forward direction. It is connected. That is, the diode 44 has an anode connected to the other second terminal 42b and a cathode connected to the other electrode 14b.

  Here, the circuit operation in the pulse generation circuit 20 will be described with reference to FIG.

  First, when a control signal (ON signal Son: for example, a high level signal) indicating ON is supplied from the pulse control unit 18 to the input terminal 38 of the pulse generation circuit 20 at the start time ta of the cycle 1 in FIG. The switching element 28 is turned on, whereby the SI thyristor 26 is turned on after being turned on. When the SI thyristor 26 is turned on, substantially the same voltage as the voltage E of the DC power supply unit 22 is applied to the transformer 24, and when the primary inductance of the transformer 24 is L1, the current I1 that flows through the primary winding 30 of the transformer 24 Increases linearly with the elapse of time at the gradient (E / L1), and induction energy is accumulated in the transformer 24.

  At this time, during the period in which the SI thyristor 26 is on (on period Ton), the diode 44 is connected to the secondary side and the current flow is interrupted, so that the current between the pair of electrodes 14a and 14b is interrupted. The voltage V2 is the reference voltage Vx. The reference voltage Vx is a voltage generated due to the pair of electrodes 14a and 14b being equivalent to a capacitor, etc., and varies depending on the type of plasma processing.

Thereafter, at the time tb when the value of the primary-side current I1 reaches a predetermined peak value (peak value) Ip1, a control signal (OFF) is output from the pulse control unit 18 to the input terminal 38 of the pulse generation circuit 20. When an off signal Soff (for example, a low level signal) is supplied, the switching element 28 is turned off, whereby the SI thyristor 26 is turned off through turn-off. When the SI thyristor 26 is turned off, the supply of the high voltage pulse Pa between the pair of electrodes 14a and 14b is started. Here, when the voltage of the DC power supply unit 22 is E, the period during which the switching element 28 is on (on period) is Ton, and the primary inductance of the transformer 24 is L1, the peak value Ip1 is
Ip1 = E × Ton / L1
It becomes.

  When the SI thyristor 26 is turned off, a pulse-like induced electromotive force Vp1 is generated in the transformer 24. Along with this, the secondary-side current I2 rapidly flows in the forward direction of the diode 44, and a pair of electrodes A pulsed high voltage Vp2 (high voltage pulse P) corresponding to the induced electromotive force Vp1 is applied between 14a and 14b.

  Thereafter, when the peak of the high voltage Vp2 is passed, energy is consumed in the plasma processing chamber 12, so that the secondary-side current I2 is gradually attenuated and the predetermined off period Toff (the switching element 28 is changed). The reference level (0 (A)) is reached before the time period during which the power is turned off. Accordingly, the time from the time tb to the time when the reference level is reached is the current conduction time Ti.

  Cycle 2 is started when the off period Toff has elapsed, and the same operation as cycle 1 described above is repeated.

  Next, the pulse control unit 18 will be described. As shown in FIG. 2, the pulse control unit 18 includes a switching control unit 50 that supplies an on signal Son and an off signal Soff to the switching element 28 of the pulse generation circuit 20, a first control unit 52, and a second control unit. 54, a first time measurement unit 56, and a control switching unit 58.

  In the first section T1 (see FIG. 4) in each cycle of plasma processing (different from cycle 1 and cycle 2 in FIG. 3), the first controller 52 applies one or more first pulses P1 of high energy to a pair. Application is performed between the electrodes 14a and 14b, and control is performed so as to transition from the first discharge to the second discharge between the pair of electrodes 14a and 14b. Here, the first discharge is, for example, a primary streamer discharge, and the second discharge is, for example, a secondary streamer discharge.

  The first control unit 52 generates a first on-timing generation unit 60 that generates an on-timing signal So1 that turns on the switching element 28 in the first section T1, and an off-timing that turns off the switching element 28 in the first section T1. And a first off-timing generator 62 that generates the signal Sf1. For example, the first off-timing generator 62 delays the on-timing signal So1 from the first on-timing generator 60 by a preset time and outputs it as the off-timing signal Sf1. The switching controller 50 turns on the switching element 28 based on the on-timing signal So1 from the first on-timing generator 60, and turns off the switching element 28 based on the off-timing signal Sf1 from the first off-timing generator 62. To. Therefore, the output cycle of the off timing signal Sf1 from the first off timing generation unit 62 is the pulse cycle Ta (= 1 / pulse frequency) of the first pulse P1. Further, although not shown, the time from the output timing of the on-timing signal So1 to the output timing of the off-timing signal Sf1 corresponds to the accumulation time of induced energy for the first pulse P1.

  The second control unit 54 performs the first pulse P1 in the second period T2 (see FIG. 4) after the transition from the primary streamer discharge to the secondary streamer discharge between the pair of electrodes 14a and 14b during each cycle of the plasma processing. 2 or more second pulses P2 having a higher peak current value and a longer pulse period are applied.

  The second control unit 54 includes a second on-timing generation unit 64 that generates an on-timing signal So2 that turns on the switching element 28 in the second section T2, and an off-timing that turns off the switching element 28 in the second section T2. And a second off-timing generator 66 that generates the signal Sf2. Also in this case, for example, the second off-timing generator 66 delays the on-timing signal So2 from the second on-timing generator 64 by a preset time and outputs it as the off-timing signal Sf2. The switching controller 50 turns on the switching element 28 based on the on-timing signal So2 from the second on-timing generator 64, and turns off the switching element 28 based on the off-timing signal Sf2 from the second off-timing generator 66. To. Accordingly, the output cycle of the off-timing signal Sf2 from the second off-timing generator 66 is the pulse cycle Tb (= 1 / pulse frequency) of the second pulse P2. Although not shown, the time from the output timing of the on-timing signal So2 to the output timing of the off-timing signal Sf2 corresponds to the accumulation time of induced energy for the second pulse P2. Therefore, the second on-timing generator 64 and the second off-timing generator 66 constitute an accumulation time changing unit 68 that changes the accumulation time of the induced energy.

  The first time measurement unit 56 outputs the first switching signal Sc1 at the start time of each cycle of the plasma processing (start time t1 of the first section T1), and counts the reference clock clk from the start time t1 of the first section T1. Then, the second switching signal Sc2 is output when a preset time has elapsed from the start time t1 of the first section T1 (start time t2 of the second section T2).

  Based on the input of the first switching signal Sc1 from the first time measuring unit 56, the control switching unit 58 stops the control by the second control unit 54 and starts the control by the first control unit 52. Is output. Further, based on the input of the second switching signal Sc2 from the first time measuring unit 56, the control by the first control unit 52 is stopped and the instruction signal is output so as to start the control by the second control unit 54.

  Next, the processing operation of the discharge device 10 according to the present embodiment will be described with reference to the time chart of FIG. In FIG. 4, in order to simplify the description, the signal waveform on the primary side of the transformer 24 is omitted, and the voltage waveform (see the upper part of FIG. 4) generated on the secondary side of the transformer 24 and the current waveform ( FIG. 4 schematically shows the lower part).

  First, as shown in FIG. 4, at the start time of each cycle of the plasma processing (start time t1 of the first section T1), the control by the first control unit 52 is started, and the first high energy energy from the pulse generation unit 16 is started. A pulse P1 is generated and applied between the pair of electrodes 14a and 14b. The first pulse P1 has a voltage waveform in which the voltage V2 rises steeply and falls sharply between the pair of electrodes 14a and 14b, and the current I2 also rises steeply and is not as sharp as the voltage waveform, but slightly steeply rises. The current waveform decreases. The generation of the first pulse P1 is performed at least once.

When a high-energy first pulse P1 is applied between the pair of electrodes 14a and 14b, a discharge is caused between the pair of electrodes 14a and 14b. In the discharge, electrons of about 1 to 10 eV are generated and collide with neutral particles (N ₂ , O ₂ , H ₂ O, etc.) existing between the pair of electrodes 14a and 14b. As a result, a collisional dissociation reaction or an adhesion dissociation reaction is performed to generate primary radicals such as N, O, OH, and H. Other, O ^- and H ^- ions or the like, excited species is also generated. After the primary radical is generated, secondary radicals such as O ₃ and HO ₂ are generated by the reaction of the primary radical.

  That is, when the application time of the first pulse P1 reaches a predetermined time, a glow discharge is generated in which new positive ions are generated by secondary electrons emitted when positive ions collide with the cathode 14a. At this time, as shown in FIG. 5, when the rising rate of the voltage V2 at the rising edge of the first pulse P1 (voltage increasing rate (dV / dt)) is approximately 30 to 500 kV / μs and the rising edge is steep, In this steep rise time Tx1, the glow discharge shifts to the primary streamer discharge. Specifically, at the above-described time Tx1, the growth of the primary streamer from the cathode 14a to the anode 14b starts (occurrence of primary streamer discharge), and when the application time of the first pulse P1 is further increased, the primary streamer becomes a pair of electrodes. It progresses while ionizing the gas between 14a and 14b. A conductive region is formed in the region through which the primary streamer has passed.

  The transition from the primary streamer discharge to the secondary streamer discharge is made at a time Ty1 from the time tx1 after the time Tx1 has passed to the application end time ty1 of the first pulse P1. Specifically, when the primary streamer advances toward the counter electrode (anode 14b) at the time Ty1 described above and the tip of the primary streamer reaches the counter electrode (anode 14b), the streamer is again along the conductive region. (Secondary streamer) will progress. That is, secondary streamer discharge is started. The secondary streamer advances only partway between the pair of electrodes 14a and 14b and does not reach the counter electrode (anode 14b). Then, primary radicals such as N, O, OH, and H are generated mainly in the secondary streamer. The generated primary radical is reduced by the subsequent recombination reaction or the like, and a secondary radical is generated instead.

  Then, after the transition to the secondary streamer discharge between the pair of electrodes 14a and 14b, the control by the second control unit 54 is started from the start time t2 of the second section T2.

  When control by the second control unit 54 is started, a second pulse P2 having a waveform different from that of the first pulse P1 and having a trailing waveform Pt is generated, and the pair of electrodes 14a and 14b is generated. Applied between. The second pulse P2 is applied between the pair of electrodes 14a and 14b in order to maintain the secondary streamer discharge over the reaction time of at least a target radical (hereinafter referred to as a target radical). Specifically, in the second pulse P2, the current conduction time Ti2 is long, and accordingly, the peak current value Ib is also high.

  Conversely, the peak voltage value Vb is lower than the peak voltage value Va of the first pulse P1. This is considered to be caused by the following. That is, assuming that the pair of electrodes 14a and 14b are both plate electrodes, for example, the primary streamer generated in, for example, one portion (local portion) of the cathode 14a reaches the counter electrode (anode 14b). In the advanced stage, a secondary streamer is generated, but in the next second pulse P2, a primary streamer is generated from another portion at a steep rise time Tx2. In this case, since the impedance between the pair of electrodes 14a and 14b is reduced by the discharge (secondary streamer discharge) by the secondary streamer generated by the application of the first pulse P1, the first pulse is generated due to heat generation. It is considered that a primary streamer is generated from another portion described above in a shorter time than P1, that is, a primary streamer is generated at a peak voltage value Vb lower than the peak voltage value Va of the first pulse P1. .

  Then, at the time Ty2 from the time tx2 when the time Tx2 has passed to the time ty2 when the trailing waveform Pt is started, the primary streamer transitions from the primary streamer discharge to the secondary streamer discharge, and the primary radical including the target radical is generated. To do. Thereafter, from the start time ty2 of the trailing waveform Pt to the end time tz of the trailing waveform Pt, the secondary streamer discharge is maintained, and the primary radicals react to generate secondary radicals. Become.

  The long conduction time Ti2 and the high peak current value Ib of the current of the second pulse P2 are output from the second off-timing generation unit 66 from the output timing of the on-timing signal So2 from the second on-timing generation unit 64 in the second control unit 54. This is realized by setting the time until the output timing of the off-timing signal Sf2 to be output, that is, the accumulation time of the induction energy for the second pulse P2, to be long. The pulse period Tb of the second pulse P2 is realized by setting the output period of the on-timing signal So2 after the current conduction time Ti2 is set.

  The conduction time Ti2 of the current set by the second control unit 54 and the pulse period Tb of the second pulse P2 are determined in advance through experiments, simulations, etc. based on the type of plasma treatment, the reaction time of the target radical, etc. It is preferable to obtain an optimal range for each, and select and set an appropriate range from the optimal range determined in advance based on the type of plasma treatment to be performed, the reaction time of the target radical, and the like.

Specifically, first, when the peak voltage value of the first pulse P1 is Va and the peak voltage value of the second pulse P2 is Vb,
Va> Vb
It is.

When the conduction time of the current of the first pulse P1 is Ti1, and the conduction time of the current of the second pulse P2 is Ti2,
Ti1 <Ti2
It is preferable to have the following relationship. In this case, when the reaction time of the target radical is Tr, the conduction time Ti2 of the current of the second pulse P2 is preferably 0.75Tr ≦ Ti2 ≦ 2.00Tr, more preferably 0.85Tr ≦ Ti2 ≦. 1.50Tr, particularly preferably 0.90Tr ≦ Ti2 ≦ 1.20Tr. For example, the conduction time Ti2 of the current of the second pulse P2 is Ti2 = 20 to 30 μsec when the target radical is a vibrationally excited OH radical (v = 4), and Ti2 = 50 to when the target radical is a vibrationally excited OH radical (v = 3). When 100 μsec, vibration-excited OH radical (v = 2), Ti 2 = 100 to 200 μsec, and when vibration-excited OH radical (v = 1), Ti 2 = 300 to 400 μsec can be preferably used. Note that if the conduction time Ti2 of the current of the second pulse P2 is too short, the output efficiency (ratio of the amount of secondary radicals to the input power) is reduced. If the conduction time Ti2 is too long, the generated secondary streamer discharge may not be maintained.

The pulse period Ta of the first pulse P1 and the pulse period Tb of the second pulse P2 are:
Ta <Tb
It is preferable that In this case, Ta <Tb <100Ta is preferable, Ta <Tb <50Ta is more preferable, and Ta <Tb <10Ta is particularly preferable. When the pulse period Tb is too short, the output efficiency is lowered. If the pulse period Tb is too long, the generated secondary streamer discharge may not be maintained.

The peak current value Ia of the first pulse P1 and the peak current value Ib of the second pulse P2 are:
Ia <Ib
It is preferable that In this case, Ia <Ib <100Ia is preferable, Ia <Ib <50Ia is more preferable, and Ia <Ib <10Ia is particularly preferable.

  In some cases, the transition from the primary streamer discharge to the secondary streamer discharge can be made only by applying one first pulse P1 between the pair of electrodes 14a and 14b. Although it may be possible to make transition to secondary streamer discharge by applying to, the number of first pulses P1 is preferably 1-10. This is because if the number of the first pulses P1 is too large, the first pulse P1 is applied unnecessarily even after the secondary streamer discharge is generated, and the improvement in output efficiency may be insufficient.

  The number of the first pulses P1 described above includes the pulse period Ta of the first pulse P1 and the time set in the first time measuring unit 56 (from the start time t1 of the first section T1 to the start time t2 of the second section T2). Time). Therefore, it is preferable that the period of the first pulse P1 and the time set in the first time measurement unit 56 are appropriately selected and adjusted so that the number of the first pulses P1 is 1 to 10.

  Here, the difference in output efficiency between the reference example and the example described below will be described.

In the reference example, as shown in FIG. 7, one first pulse P1 is applied in the first period T1, and the first pulse P1 is also applied to the second period T2 after the primary streamer discharge transitions to the secondary streamer discharge. It supplied continuously to a pair of electrodes 14a and 14b. The number of pulses per second of the first pulse P1 in the second section T2 is 100 × 10 ³ pulses. The peak voltage value Va between the pair of electrodes 14a and 14b due to the first pulse P1 gradually decreases as the impedance between the pair of electrodes 14a and 14b decreases, but is constant from the stage when the number of pulses exceeds a certain value. Level voltage value. The average peak voltage value Va was approximately 40 kV. The voltage increase rate dV / dt at the rising edge of the first pulse P1 is about 50 V / μsec. The current conduction time Ti1 of the first pulse P1 is about 7 μsec, and the pulse period Ta is 10 μsec.

In the embodiment, as shown in FIG. 4, one first pulse P1 is applied in the first period T1, and the second pulse P2 is applied in the second period T2 after the primary streamer discharge has changed to the secondary streamer discharge. It supplied continuously to a pair of electrodes 14a and 14b. The number of pulses per second of the second pulse P2 in the second section T2 is 10 × 10 ³ pulses. The peak voltage value Va between the pair of electrodes 14a and 14b by the first pulse P1 was 30 kV, and the average of the peak voltage value Vb between the pair of electrodes 14a and 14b by the second pulse P2 was approximately 8 kV. The voltage increase rate dV / dt at the rising edge of the first pulse P1 is about 50 V / μsec. The conduction time Ti2 of the current of the second pulse P2 is about 75 μsec (assuming vibrationally excited OH radical (v = 2) as the target radical), and the pulse period Tb is 100 μsec. The peak current value Ib of the second pulse P2 is approximately 10 times the peak current value Ia of the first pulse P1.

In the reference example, the first pulse P1 of 100 × 10 ³ pulses per second is applied to the pair of electrodes 14a and 14b. Therefore, since the next first pulse P1 is applied before the target radical generated in the secondary streamer by the previous first pulse P1 reacts, not only the amount of the target radical increases, but the pair of electrodes 14a and The amount of neutral particles and other primary radicals existing between 14b are reduced, and as a result, the recombination reaction of the target radical disappears without being induced or the recombination reaction of the target radical is induced. The reaction amount is small, and the amount of secondary radicals does not increase so much.

On the other hand, in the embodiment, since the current conduction time Ti2 continuously applies the second pulse P2 corresponding to the reaction time Tr of the target radical in the second section T2, the previous first pulse P1 or the previous first pulse P2 is applied. When the target radical generated in the secondary streamer by the two-pulse P2 is almost recombined and the secondary radical is generated, the next second pulse P2 is applied. It can contribute to the production of secondary radicals efficiently. Further, 10 × 10 ³ pulses per second are sufficient, and the average peak voltage value Vb applied to the pair of electrodes 14a and 14b is 8 kV lower than that of the reference example (40 kV). The power supplied to 14b is less than in the reference example. That is, as shown in FIG. 8, the amount of secondary radicals generated with respect to the input power is higher in the example than in the reference example, and the output efficiency of the example is higher than in the reference example.

  Furthermore, the number of pulses of the second pulse P2 in the second section T2 of the embodiment is 1/10 of the number of pulses of the first pulse P1 in the second section T2 of the reference example. That is, the number of times of switching in the embodiment can be reduced to 1/10 that of the reference example, and the switching loss can be greatly reduced. In the embodiment, the pulse period Tb of the second pulse P2 and the current conduction time Ti2 are appropriately selected within the above-described preferable ranges, thereby improving the output efficiency and reducing the supply power per unit time. The degree can be changed variously.

As described above, the discharge device 10 according to the present embodiment applies one or more first pulses P1 between the pair of electrodes 14a and 14b, and performs the first discharge between the pair of electrodes 14a and 14b (this example). Then, after the transition from the first discharge to the second discharge after the transition from the first discharge to the second discharge (secondary streamer discharge), two or more second between the pair of electrodes 14a and 14b. A second control unit 54 for applying the pulse P2, and Va and Ia for the peak voltage value and the peak current value of the first pulse P1, and Vb and Ib for the peak voltage value and the peak current value of the second pulse P2, respectively. Ib, when the conduction time of the current of the first pulse P1 is Ti1, and the conduction time of the current of the second pulse P2 is Ti2,
Va> Vb
Ia <Ib
Ti1 <Ti2
Therefore, the output efficiency can be improved and the switching loss can be reduced. This is advantageous in reducing the cost.

  Next, two modifications of the discharge device 10 will be described with reference to FIGS. 9 and 10.

  First, as shown in FIG. 9, the discharge device 10 a according to the first modification has substantially the same configuration as the discharge device 10 according to the above-described embodiment, but differs in the following points.

  That is, the pulse control unit 18 further includes a discharge detection unit 76, and includes a second time measurement unit 78 instead of the first time measurement unit 56 described above.

  The discharge detection unit 76 acquires a moving image of the discharge generated between the pair of electrodes 14a and 14b, and the primary streamer discharge to the secondary streamer based on the moving image of the discharge acquired by the camera 80. And an image processing unit 82 that detects the timing of transition to discharge.

  The camera 80 transmits, in real time, a moving image of light emitted by the primary streamer generated at a certain portion of one electrode (cathode 14a) to the image processing unit 82. The image processing unit 82 detects a motion vector between frames of the transmitted light emission moving image, and acquires coordinates of the light emission image that has moved. Then, the image processing unit 82 outputs a detection signal Sd to the second time measurement unit 78, assuming that a secondary streamer has occurred when the acquired coordinates substantially coincide with the coordinates of the counter electrode (anode 14b).

  The second time measurement unit 78 outputs the first switching signal Sc1 at the start time of each cycle of the plasma processing (start time t1 of the first section T1), and the detection signal Sd from the image processing unit 82 of the discharge detection unit 76. Based on the input of the detection signal Sd, the second switching is performed when a preset time (including the preset time in the first time measuring unit 56 includes 0 hour) has elapsed since the input time of the detection signal Sd. The signal Sc2 is output.

  Next, as shown in FIG. 10, the discharge device 10 b according to the second modification has substantially the same configuration as the discharge device 10 a according to the first modification described above, but differs in the following points.

  That is, the discharge detector 76 detects that the transition from the primary streamer discharge to the secondary streamer discharge has occurred between the pair of electrodes 14a and 14b based on the voltage between the pair of electrodes 14a and 14b. Specifically, the discharge detection unit 76 includes a voltage determination unit 84. The voltage determination unit 84 compares, for example, the voltage between the pair of electrodes 14a and 14b with a preset threshold voltage, and the voltage between the pair of electrodes 14a and 14b is equal to or lower than the threshold voltage. To output the detection signal Sd. The threshold voltage is obtained by applying a high voltage pulse between the pair of electrodes 14a and 14b in advance to measure the voltage between the pair of electrodes 14a and 14b when the primary streamer discharge is changed to the secondary streamer discharge. It is performed a plurality of times, and the average value is taken. Further, for example, a voltage 1/100 to 1/10 of the average value is added to the average value to obtain a threshold voltage. Which ratio is adopted among 1/100 to 1/10 can be appropriately selected depending on the type of plasma treatment.

  The second time measurement unit 78 outputs the first switching signal Sc1 at the start time of each cycle of the plasma processing (start time t1 of the first section T1), and based on the input of the detection signal Sd from the discharge detection unit 76. The second switching signal Sc2 is output when a preset time (including 0 hours, which is different from the preset time in the first time measuring unit 56) has elapsed since the input time of the detection signal Sd. .

  The discharge device 10a according to the first modification described above and the discharge device 10b according to the second modification exhibit the effects of the discharge device 10 according to the above-described embodiment, and after making a transition to the secondary streamer discharge without fail. Since the control can be shifted to the control by the second control unit 54, the reliability can be improved.

  In the above example, the first discharge is a primary streamer discharge and the second discharge is a secondary streamer discharge. However, the first discharge may be a glow discharge, the second discharge may be a streamer discharge, and the first discharge may be a streamer discharge. The discharge and the second discharge may be arc discharge.

  In addition, the discharge device according to the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10, 10a, 10b ... Discharge device 12 ... Plasma processing chamber 14a, 14b ... A pair of electrode 14a ... One electrode (cathode)
14b ... the other electrode (anode) 16 ... pulse generator 18 ... pulse controller 20 ... pulse generator 44 ... diode 50 ... switching controller 52 ... first controller 54 ... second controller 56 ... first time measuring unit 58 ... Control switching unit 60 ... First on-timing generator 62 ... First off-timing generating unit 64 ... Second on-timing generating unit 66 ... Second off-timing generating unit 68 ... Accumulation time changing unit 76 ... Discharge detecting unit 78 ... Second time measurement unit 80 ... Camera 82 ... Image processing unit 84 ... Voltage discrimination unit

Claims (12)

A pair of electrodes, a pulse generation unit that applies a pulse between the pair of electrodes, and a pulse control unit that controls the pulse generation unit to generate a discharge in the pair of electrodes,
The pulse control unit
A first control unit that applies one or more first pulses to the pair of electrodes, and causes a transition from a first discharge to a second discharge at the pair of electrodes;
A second control unit that applies two or more second pulses to the pair of electrodes after transition from the first discharge to the second discharge;
The peak voltage value and peak current value of the first pulse are Va and Ia, the peak voltage value and peak current value of the second pulse are Vb and Ib, the conduction time of the current of the first pulse is Ti1, and the second pulse When the conduction time of the pulse current is Ti2,
Va> Vb
Ia <Ib
Ti1 <Ti2
A discharge device characterized by the above. The discharge device according to claim 1, wherein
When the pulse width of the first pulse is Tp1, and the pulse width of the second pulse is Tp2,
Tp1 <Tp2
A discharge device characterized by the above. The discharge device according to claim 1 or 2,
The first discharge is a primary streamer discharge;
The discharge device, wherein the second discharge is a secondary streamer discharge. In the discharge device according to any one of claims 1 to 3,
When the reaction time of radicals generated between the pair of electrodes is Tr, the conduction time Ti2 of the current of the second pulse is
0.75Tr ≦ Ti2 ≦ 2.00Tr
A discharge device characterized by the above. The discharge device according to any one of claims 1 to 4,
The first control unit applies two or more first pulses,
When the pulse period of the first pulse is Ta and the pulse period of the second pulse is Tb,
Ta <Tb
A discharge device characterized by the above. In the discharge device according to any one of claims 1 to 5,
The number of pulses of the first pulse is 1-10. In the discharge device according to any one of claims 1 to 6,
The pulse generation unit includes a transformer and a switch connected in series at both ends of a DC power supply unit, accumulates inductive energy in the transformer by ON control with respect to the switch of the pulse control unit, A discharge device comprising: a pulse generation circuit that generates the pulse on the secondary side of the transformer by turning off the switch. The discharge device according to claim 7, wherein
The discharge device according to claim 2, wherein the second control unit changes an accumulation time of induction energy in the transformer at a start time of control by the second control unit. The discharge device according to claim 8, wherein
The starting point of control by the second control unit is a point in time that is set in advance from the starting point of control by the first control unit. The discharge device according to claim 8, wherein
The pulse control unit
A discharge detector that detects the transition to the second discharge with the pair of electrodes;
The start point of the control by the second control unit is a point in time when a preset time has elapsed since the discharge detection unit detected that the transition to the second discharge was performed between the pair of electrodes. Discharge device. The discharge device according to claim 10, wherein
The discharge detector is
A camera that acquires a moving image of the discharge generated between the pair of electrodes;
And an image processing unit configured to detect a timing at which the first discharge is changed to the second discharge based on a moving image of the discharge acquired by the camera. The discharge device according to claim 10, wherein
The discharge detector is
A discharge device, comprising: a voltage determining unit that determines that transition to the second discharge has occurred when a voltage between the pair of electrodes decreases and becomes equal to or lower than a preset threshold voltage.

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