A high voltage circuit outputting symmetrical positive and negative voltages and a control method thereof

Abstract

The present invention relates to the field of semiconductor processing technology, and in particular to a high-voltage circuit that outputs symmetrical positive and negative voltages and a control method thereof. The circuit comprises: a full-bridge inverter circuit, a transformer, a rectifier circuit, a commutation circuit and a load connected in sequence; the full-bridge inverter circuit performs DC / AC inversion conversion, and performs voltage boosting through a transformer, and the rectifier circuit performs AC / DC conversion on the boosted voltage, and outputs a DC voltage to the commutation circuit; the output end of the commutation circuit is connected to the load, and the current direction of the load is changed through the commutation circuit to achieve neutralization of residual charge on the load or reverse power supply; wherein the rectifier circuit comprises a capacitor, a resistor and a diode; the first tap of the secondary side of the transformer is connected to capacitors C2 and C3, and by adding sampling resistors R2 and R3 at one end of the rectifier circuit, the output current values ​​of the positive and negative poles can be detected, so that the current can be accurately detected in a simple way, and the output voltage and current conditions can be accurately reflected and controlled, so as to achieve accurate control of the neutralization of the load and the residual charge.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor processing technology, and in particular to a high voltage circuit outputting symmetrical positive and negative voltages and a control method thereof. Background Art

[0002] Electrostatic chucks are used in various semiconductor processes to hold the wafer in place during processing. Electrostatic chucks utilize a pressure plate with an integrated electrode that can be biased with a high voltage to create an electrostatic holding force that “clamps” the wafer.

[0003] Electrostatic chucks are divided into two types according to the different adsorption methods: one is the Coulomb force type with insulating material as the medium; the other is the Johnsen-rahbek force type, whose dielectric layer is conductive. When the electrode is energized, a small current will flow in the small gap between the chip and the dielectric interface, resulting in electrostatic polarization. The process of generating electrostatic adsorption force is as follows: Figure 1 The electrostatic chuck 200 includes a plurality of inner electrodes 201. After two adjacent inner electrodes are connected to a voltage circuit 300, the inner electrodes 201 have positive and negative charges respectively under the action of the positive and negative electrodes output by the voltage circuit. The charges 101 on the working component 100 are attracted by the inner electrodes 201, so that the working component 100 is adsorbed on the electrostatic chuck.

[0004] The charges of the workpiece and the electrode are originally evenly distributed. When voltage is applied, polarized charges are generated inside the electrode and the workpiece generates opposite polarized charges. The workpiece is adsorbed on the surface of the electrostatic chuck through the Coulomb force generated by the opposite charges of the two. The actual application of electrostatic chucks can be divided into two types: monopolar and bipolar. The schematic diagram of a bipolar electrostatic chuck is as follows Figure 2 As shown, through the action of the DC electrode 500 , the electric charge of the wafer 300 is adsorbed on the dielectric layer 400 by the attraction of the DC electrode 500 .

[0005] Depend on Figure 2 It can be seen that the electrodes of the bipolar electrostatic chuck have two polarities and require two voltage inputs of opposite polarities. Electrodes of different polarities will generate charges of opposite polarities at corresponding longitudinal positions of the wafer, thereby generating Coulomb force for adsorption. For a bipolar electrostatic chuck, in order to ensure that the wafer is evenly stressed, it is necessary to ensure that the positive and negative polarity paths have the same power supply and the voltage values ​​at both ends are the same.

[0006] In addition, in the environment where the electrostatic chuck is used, there are various plasmas. One of the effects of the plasma in the processing chamber is to generate a voltage offset on the electrostatic chuck, which, together with the electrode voltage, changes the potential difference on the chuck, which may cause discharge of the chuck medium or the wafer itself. Both of these situations may cause damage. Therefore, during the use of the electrostatic chuck, it is necessary to apply a bias voltage to the chuck electrode signal during the presence of plasma.

[0007] The existing bipolar electrostatic chuck power supply solutions have the problem of excessively large voltage differences between the positive and negative electrodes, which can cause uneven force on the wafer and pose a risk of unstable adsorption and damage; most cannot implement external bias voltage injection, and cannot compensate for voltage offset during plasma action, posing a risk of discharge damage to the wafer; no discharge circuit suitable for the electrostatic chuck is set, making it impossible to quickly discharge the electrostatic chuck, and after the process is completed, residual charge on the wafer may not be neutralized.

[0008] Figure 3 It is a topological structure diagram of a quadruple voltage rectifier in the prior art (the diagram comes from the patent publication "Bipolar output voltage self-balancing circuit based on bipolar voltage doubling unit", the publication number is CN118137845A). Figure 3 The main defect of the circuit when actually applied to the bipolar electrostatic chuck is that in order to realize the control of the balancing circuit, it is necessary to collect the current value flowing through the positive and negative loads at the output end, and to detect the actual output current, a relatively complex current collection circuit is required. Summary of the invention

[0009] In order to solve the problem of complex current detection circuit, the present invention improves the circuit based on the quadruple voltage rectifier topology diagram in the prior art, and proposes a high voltage circuit and a control method thereof for a bipolar electrostatic chuck.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is:

[0011] A high-voltage circuit that outputs symmetrical positive and negative voltages, comprising a full-bridge inverter circuit, a transformer, a rectifier circuit, and a commutation circuit and a current collection circuit connected to the rectifier circuit in sequence;

[0012] The output end of the commutation circuit is connected to a load, and the current direction of the load is changed by the commutation circuit to achieve neutralization of residual charge on the load;

[0013] Wherein, the rectifier circuit includes a capacitor and a diode;

[0014] One end of capacitor C2 and one end of capacitor C3 are connected to the first tap of the secondary side of the transformer.

[0015] The diode D1 and the diode D2 are connected in series in the same direction to form a first diode series branch, the other end of the capacitor C2 is connected to the midpoint of the diode D1 and the diode D2, the capacitor C4 is connected in parallel to the diode series branch, and the cathode of the diode D1 is connected to the second tap of the secondary side of the transformer after passing through the reversing switch and the load in sequence;

[0016] The diode D3 and the diode D4 are connected in series in the same direction to form a second diode series branch, the other end of the capacitor C2 is connected to the midpoint of the diode D3 and the diode D4, the capacitor C5 is connected in parallel to the diode series branch, and the anode of the diode D3 is connected to the second tap of the secondary side of the transformer after passing through the reversing switch and the load in sequence;

[0017] The current acquisition circuit includes a first detection branch arranged between the anode of the diode D2 and the second tap of the secondary side of the transformer, and a second detection branch arranged between the cathode of the diode D3 and the second tap of the secondary side of the transformer.

[0018] Furthermore, the first detection branch and the second detection branch each include at least one detection device, and the detection device is any one of a Hall sensor, a shunt, and a resistor.

[0019] Furthermore, the detection devices of the first detection branch and the second detection branch are resistors respectively, wherein the resistor R2 in the first detection branch is connected in series between the anode of the diode D2 and the second tap of the secondary side of the transformer, and the resistor R3 in the second detection branch is connected in series between the cathode of the diode D3 and the second tap of the secondary side of the transformer.

[0020] Furthermore, a plurality of loads are symmetrically distributed around a center point E2, the center point E2 is connected to a second tap of a secondary side of the transformer, and an external bias voltage is injected through the center point E2 to offset a voltage offset generated by the loads.

[0021] Further, the commutation circuit includes a plurality of switches, a first input terminal, a second input terminal, a first output terminal and a second output terminal;

[0022] The two ends of switch S1 are connected to the first input end and the first output end respectively; the two ends of switch S4 are connected to the second input end and the second output end respectively, and the two ends of switch S2 are connected to the first input end and the second output end respectively; the two ends of switch S3 are connected to the second input end and the first output end respectively, and the first output end and the second output end are connected to the two ends of the center point E2 respectively.

[0023] Furthermore, it also includes a discharge circuit connected in parallel with the plurality of loads, wherein the discharge circuit includes a discharge switch and a discharge resistor;

[0024] The discharge switch and the discharge resistor are connected in series, the center point PE in the series branch is grounded, the discharge resistors are symmetrically distributed with the center point PE as a reference, and the discharge switches are symmetrically distributed with the center point PE as a reference.

[0025] Furthermore, the actual output voltage and current of the load are differentially calculated with the set voltage and current values, and the obtained result is subjected to PID closed-loop control to output a control signal to the full-bridge inverter circuit for adjusting the output voltage of the full-bridge inverter circuit.

[0026] Furthermore, a resonance unit is connected between the full-bridge inverter circuit and the transformer.

[0027] The full-bridge inverter circuit is used for DC / AC current conversion to output alternating current to the resonant unit;

[0028] The resonance unit outputs a resonance signal to the primary side of the transformer;

[0029] The resonant unit comprises an inductor L and a capacitor C. The inductor L and the capacitor C are connected in series, one end of which is connected to the output end of the full-bridge inverter circuit, and the other end is connected to the first tap of the primary side of the transformer.

[0030] Furthermore, it also includes a resistor R1 and a resistor R4, wherein the resistor R1 is connected in parallel to both ends of the first diode series branch, and the resistor R4 is connected in parallel to both ends of the second diode series branch.

[0031] Based on the same concept, a control method for a high-voltage circuit that outputs symmetrical positive and negative voltages is also proposed. A high-voltage circuit that outputs symmetrical positive and negative voltages as described above is constructed, and the current direction of the symmetrical positive and negative voltage loads is changed by the output end of the commutation circuit to achieve neutralization of the residual charge on the symmetrical positive and negative voltage loads.

[0032] As a preferred solution, the on-time of the power tube in the full-bridge inverter circuit is controlled by controlling the duty cycle of the PWM wave to adjust the effective value of the primary current of the transformer.

[0033] Furthermore, the actual output voltage and current on the symmetrical positive and negative voltage loads are differentially calculated with the set voltage and current values, and PID closed-loop control is performed based on the obtained voltage difference and / or current difference. The PID closed-loop control acts on the duty cycle adjustment of the PWM wave until the output of the full-bridge inverter circuit reaches the set current value.

[0034] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: the circuit and control method of the present invention can realize the precise control of the output voltage and current values, and the positive and negative poles can realize the self-equalizing function. It can be applied to bipolar chucks to realize the neutralization of residual charge, and through the output current sampling resistor of the secondary side of the transformer, the output current can be accurately detected in a simple form with low isolation requirements, and the accurate control of residual charge in the bipolar chuck can be realized. The discharge resistor can realize the rapid discharge of the bipolar chuck and realize the unloading function. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of the electrostatic chuck polarization process in the background technology;

[0036] Figure 2 It is a flow chart of a bipolar electrostatic chuck in the background technology;

[0037] Figure 3 This is a circuit schematic diagram of a high voltage circuit that outputs symmetrical positive and negative voltages in Embodiment 1 of the present invention;

[0038] Figure 4 A high voltage circuit diagram for use in a bipolar electrostatic chuck in Embodiment 2 of the present invention;

[0039] Figure 5 1 is a waveform diagram of the PWM wave and transformer primary current in Example 2 of the present invention.

[0040] Figure numerals: 100 - working part; 101 - charge in the working part; 200 - electrostatic chuck; 201 - inner electrode; 300 - voltage circuit; 400 - dielectric layer; 500 - DC electrode; 600 - wafer. DETAILED DESCRIPTION

[0041] The present invention is described in detail below in conjunction with the accompanying drawings. In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0042] Example 1

[0043] A high voltage circuit that outputs symmetrical positive and negative voltages. The circuit schematic is shown in Figure 3 As shown, it includes a full-bridge inverter circuit, a transformer, a rectifier circuit connected in sequence, and a commutation circuit and a current collection circuit connected to the rectifier circuit;

[0044] The full-bridge inverter circuit boosts the voltage after DC / AC inverter conversion through a transformer, and the rectifier circuit converts the boosted voltage into AC / DC, and outputs a DC voltage to the commutation circuit; the output end of the commutation circuit is connected to the load, and the current direction of the load is changed by the commutation circuit to achieve neutralization of the residual charge on the load.

[0045] The rectifier circuit includes a capacitor, a resistor and a diode; one end of the capacitor C2 and the capacitor C3 are both connected to the first tap of the secondary side of the transformer.

[0046] The diode D1 and the diode D2 are connected in series in the same direction to form a first diode series branch, the other end of the capacitor C2 is connected to the midpoint of the diode D1 and the diode D2, the capacitor C4 is connected in parallel to the diode series branch, and the cathode of the diode D1 is connected to the second tap of the secondary side of the transformer after passing through the reversing switch and the load in sequence;

[0047] The diode D3 and the diode D4 are connected in series in the same direction to form a second diode series branch, the other end of the capacitor C2 is connected to the midpoint of the diode D3 and the diode D4, the capacitor C5 is connected in parallel to the diode series branch, and the anode of the diode D3 is connected to the second tap of the secondary side of the transformer after passing through the reversing switch and the load in sequence;

[0048] The current collection circuit includes a first detection branch arranged between the anode of the diode D2 and the second tap of the secondary side of the transformer, and a second detection branch arranged between the cathode of the diode D3 and the second tap of the secondary side of the transformer;

[0049] The second tap of the secondary side of the transformer is also connected to the center point E2 of the load.

[0050] As a preferred solution, the first detection branch and the second detection branch each include at least one detection device, and the detection device may be any one of a Hall sensor, a shunt, and a resistor.

[0051] Furthermore, the detection devices of the first detection branch and the second detection branch are resistors respectively, wherein the resistor R2 in the first detection branch is connected in series between the anode of the diode D2 and the second tap of the secondary side of the transformer, and the resistor R3 in the second detection branch is connected in series between the cathode of the diode D3 and the second tap of the secondary side of the transformer. Resistors are used for current detection, and the resistors have low cost, can collect both AC and DC signals, and are easy to match to suitable sampling signals.

[0052] As a preferred solution, the commutation circuit includes a plurality of switches, a first input terminal, a second input terminal, a first output terminal, and a second output terminal;

[0053] The two ends of switch S1 are connected to the first input end and the first output end respectively; the two ends of switch S4 are connected to the second input end and the second output end respectively; the two ends of switch S2 are connected to the first input end and the second output end respectively; the two ends of switch S3 are connected to the second input end and the first output end respectively. Preferably, a single-pole double-throw switch can be used, wherein S1 and S2 are the first single-pole double-throw switches, and S3 and S4 are the second single-pole double-throw switches. When switching, S1 and S4 are opened and closed at the same time, and S2 and S3 are opened and closed at the same time. The connection diagram of the switching circuit is shown in FIG. Figure 4 shown.

[0054] Further, such as Figure 4As shown, several loads are symmetrically distributed around a center point E2, the center point E2 is connected to the second tap of the secondary side of the transformer, and an external bias voltage is injected through the center point E2 to offset the voltage offset generated by the load. When the load is a bipolar electrostatic chuck, an external bias voltage is injected through the center point E2 to offset the voltage offset generated by the chuck.

[0055] Furthermore, it also includes a discharge circuit connected in parallel with the load, and the discharge circuit includes a discharge switch and a discharge resistor; the discharge switch and the discharge resistor are connected in series, the center point PE in the series branch is grounded, the discharge resistor is symmetrically distributed with respect to the center point PE of the series branch as a reference, and the discharge switch is symmetrically distributed with respect to the center point PE of the series branch as a reference.

[0056] It can accurately reflect and control the output voltage and current, and accurately neutralize the residual charge of the bipolar electrostatic chuck. The second tap of the secondary side of the transformer can add an external bias relative to PE to match the asymmetric positive and negative polarity voltage caused by the self-bias when the electrostatic chuck is used.

[0057] The actual output voltage and current of the load are differentially calculated with the set voltage and current values, and the obtained results are used for PID closed-loop control to output a control signal to the full-bridge inverter circuit. The duty cycle of the PWM waveform is used to control the on and off of the switch tubes Q1, Q2, Q3, and Q4 in the full-bridge inverter circuit to adjust the output parameters of the full-bridge inverter circuit.

[0058] A resonant unit is also connected between the full-bridge inverter circuit and the transformer.

[0059] The full-bridge inverter circuit is used for DC / AC current conversion to output AC current to the resonant unit;

[0060] The resonance unit outputs a resonance signal to the primary side of the transformer;

[0061] The resonant unit comprises an inductor L and a capacitor C. One end of the inductor L and the capacitor C are connected in series and connected to the output end of the full-bridge inverter circuit, and the other end is connected to the first tap of the primary side of the transformer.

[0062] The use of a resonant unit solves the problem of transformer bias. By matching reasonable LC parameters, the inverter part can work in discontinuous mode, which can better achieve smooth regulation of the output voltage.

[0063] The schematic diagram of the high-voltage circuit that outputs symmetrical positive and negative voltages also includes resistors R1 and R4. The resistor R1 is connected in parallel to both ends of the first diode series branch, and the resistor R4 is connected in parallel to both ends of the second diode series branch.

[0064] A control method for a high-voltage circuit that outputs symmetrical positive and negative voltages, any of the above-mentioned high-voltage circuits that output symmetrical positive and negative voltages, changes the current direction of the symmetrical positive and negative voltage loads through the output end of the commutation circuit to achieve neutralization of the residual charge on the symmetrical positive and negative voltage loads.

[0065] The on-time of the power tube in the full-bridge inverter circuit is controlled by controlling the duty cycle of the PWM wave, thereby adjusting the effective value of the primary current of the transformer.

[0066] The actual output voltage and current on the symmetrical positive and negative voltage loads are differentially calculated with the set voltage and current values, and PID closed-loop control is performed based on the obtained voltage difference and / or current difference. The PID closed-loop control acts on the duty cycle adjustment of the PWM wave until the output of the full-bridge inverter circuit reaches the set current value.

[0067] Example 2

[0068] Figure 4 The circuit diagram shown is a high-voltage circuit for a bipolar electrostatic chuck. It is a specific application of a high-voltage circuit that outputs symmetrical positive and negative voltages in Example 1 in a bipolar electrostatic chuck voltage circuit. It is composed of Q1 / Q2 / Q3 / Q4 / Cr / L1 to form a full-bridge inverter structure for DC / AC circuit processing. The processed voltage is input to the transformer. The PWM wave and the transformer primary current waveform are as follows: Figure 5 As shown, U1 is the Q2 / Q3 drive signal, U2 is the Q1 / Q2 drive signal, and I is the primary current of the transformer.

[0069] Due to the existence of the LC resonant circuit, the primary current is a smooth triangular waveform, so the effective value is linearly related to the rise time, and the larger L1 is, the smaller the slope is; an external control chip is used to output PWM waves U1 and U2, and the duty cycle of U1 and U2 is controlled by programming to control the turn-on time of the power tubes Q1 / Q2 / Q3 / Q4, and the corresponding turn-on time is the primary current rise time, thereby adjusting the effective value of the primary current to achieve the purpose of controlling the proportion of energy transmitted to the secondary side of the transformer.

[0070] The transformer T1 can be designed by controlling the turns ratio to control the maximum output voltage of the secondary rectifier circuit after rectification, thereby achieving high-voltage output. The secondary rectifier circuit includes D1 / D2 / C2 / R1 / C4 / R2 / R3 / D3 / D4 / C3 / R4 / C5, wherein R1 and R4 are output-end dummy loads (a typical value of which is 50MΩ), and the incorporation of R1 / R4 shunts the current, and the current shunt accounts for about 5%, which is beneficial to the stable regulation of the output by the primary power tube; C4 and C5 are output voltage filter capacitors for reducing output voltage ripple; C2 and C3 are DC blocking capacitors for AC / DC circuit isolation; R2 and R3 are output-end current sampling resistors for detecting the positive and negative output current values. The current detection method is simple. Since the AC signal flowing through the sampling resistor is positive and negative symmetrical, the DC signal is the current value of the output load end. Therefore, according to the KCL law, the current flowing through the resistor is the load end current.

[0071] The wafer residual charge processing circuit is composed of S1 / S2 / S3 / S4, S1, S2, S3, and S4 are reversing switches, wherein S1 / S4 and S2 / S3 are two groups of switches that are opened and closed at the same time. When S1 / S4 is closed and S2 / S3 is disconnected, E1 outputs positive polarity to E3, and vice versa, E1 outputs negative polarity to E3. The residual charge on the wafer is neutralized by circuit reversal; the discharge circuit is composed of S5 / S6 / R5 / R6, wherein S5 and S6 are discharge switches, and R5 and R6 are discharge resistors. After the voltage input is turned off, the discharge switch is closed, and the electrostatic chuck will discharge to the ground through the discharge resistor.

[0072] The output current is the current value flowing through the output loads Zload1 and Zload2; Zload1 and Zload2 are used to simplify the simulation of a bipolar electrostatic chuck. When the voltage offset on the electrostatic chuck is detected externally, an external bias voltage is injected through E2 between Zload1 and Zload2 to offset the voltage offset. The actual output voltage and current on Zload1 and Zload2 can be differentially calculated with the set voltage and current values, and the result is used for PID closed-loop control to adjust the duty cycle of the PWM wave until the output reaches the set value.

[0073] The bias voltage value of the electrostatic chuck is collected externally, and then the voltage is injected externally to the center tap of E2, thereby preventing damage to the wafer or the electrostatic chuck.

[0074] The high voltage circuit applied to the electrostatic chuck has the following beneficial effects:

[0075] 1. An effective solution is provided to realize the power supply to the bipolar electrostatic chuck to generate electrostatic adsorption force, and the topology structure automatically symmetrizes the positive and negative output voltage values ​​under different load conditions to achieve uniform symmetry of the electrostatic chuck's holding force.

[0076] 2. The output voltage and current detection are both performed relative to E2. A very simple method is used to detect the output current. The isolation pressure is small, and the isolation standard only needs to meet the requirements of E2 to the ground.

[0077] 3. The electrostatic chuck can be introduced externally to the plasma chamber bias voltage into the center tap of the high voltage topology, thereby protecting the electrostatic chuck and the wafer.

[0078] 4. Set up a commutation circuit to reverse the input voltage and inject opposite charges at the residual charge position to achieve the purpose of neutralizing the charge.

[0079] 5. Set up a discharge circuit, suitable for chuck discharge.

[0080] 6. High control accuracy, the output voltage and current can be programmed by controlling the power tube of the full-bridge inverter part.

[0081] 7. The setting of dummy load reduces the influence of load condition at output end, reduces output ripple, ensures the stability of clamping force and prevents shaking fragments.

[0082] 8. Low cost and high efficiency, few components are used, and the overall cost is low; it can be expanded on this basis, such as adding voltage doubling rectification and other methods to achieve the control of various bipolar electrostatic chucks.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high voltage circuit that outputs symmetrical positive and negative voltages, comprising a full-bridge inverter circuit, a transformer, and a rectifier circuit connected in sequence, characterized in that: It also includes a commutation circuit and a current collection circuit connected to the rectifier circuit; The output end of the commutation circuit is connected to a load, and the current direction of the load is changed by the commutation circuit to achieve neutralization of residual charge on the load; Wherein, the rectifier circuit includes a capacitor and a diode; One end of capacitor C2 and one end of capacitor C3 are connected to the first tap of the secondary side of the transformer. The diode D1 and the diode D2 are connected in series in the same direction to form a first diode series branch, the other end of the capacitor C2 is connected to the midpoint of the diode D1 and the diode D2, the capacitor C4 is connected in parallel to the diode series branch, and the cathode of the diode D1 is connected to the second tap of the secondary side of the transformer after passing through the reversing switch and the load in sequence; The diode D3 and the diode D4 are connected in series in the same direction to form a second diode series branch, the other end of the capacitor C2 is connected to the midpoint of the diode D3 and the diode D4, the capacitor C5 is connected in parallel to the diode series branch, and the anode of the diode D3 is connected to the second tap of the secondary side of the transformer after passing through the reversing switch and the load in sequence; The current collection circuit includes a first detection branch arranged between the anode of the diode D2 and the second tap of the secondary side of the transformer, and a second detection branch arranged between the cathode of the diode D3 and the second tap of the secondary side of the transformer; A plurality of loads are symmetrically distributed around a center point E2, the center point E2 is connected to a second tap of a secondary side of the transformer, and an external bias voltage is injected through the center point E2 to offset a voltage offset generated by the loads; The commutation circuit includes a plurality of switches, a first input terminal, a second input terminal, a first output terminal, and a second output terminal; The two ends of switch S1 are connected to the first input end and the first output end respectively; the two ends of switch S4 are connected to the second input end and the second output end respectively, and the two ends of switch S2 are connected to the first input end and the second output end respectively; the two ends of switch S3 are connected to the second input end and the first output end respectively, and the first output end and the second output end are connected to the two ends of the center point E2 respectively.

2. A high voltage circuit for outputting symmetrical positive and negative voltages as claimed in claim 1, characterized in that: The first detection branch and the second detection branch each include at least one detection device, and the detection device is any one of a Hall sensor, a shunt, and a resistor.

3. A high voltage circuit for outputting symmetrical positive and negative voltages as claimed in claim 2, characterized in that: The detection devices of the first detection branch and the second detection branch are resistors respectively, wherein the resistor R2 in the first detection branch is connected in series between the anode of the diode D2 and the second tap of the secondary side of the transformer, and the resistor R3 in the second detection branch is connected in series between the cathode of the diode D3 and the second tap of the secondary side of the transformer.

4. A high voltage circuit for outputting symmetrical positive and negative voltages as claimed in claim 1, characterized in that: Also includes a discharge circuit connected in parallel with the load, the discharge circuit includes a discharge switch and a discharge resistor; The discharge switch and the discharge resistor are connected in series, the center point PE in the series branch is grounded, the discharge resistors are symmetrically distributed with the center point PE as a reference, and the discharge switches are symmetrically distributed with the center point PE as a reference.

5. A high voltage circuit for outputting symmetrical positive and negative voltages as claimed in any one of claims 1 to 4, characterized in that: A resonance unit is also connected between the full-bridge inverter circuit and the transformer. The full-bridge inverter circuit is used for DC / AC current conversion to output alternating current to the resonant unit; The resonance unit outputs a resonance signal to the primary side of the transformer; The resonant unit comprises an inductor L and a capacitor C. The inductor L and the capacitor C are connected in series, one end of which is connected to the output end of the full-bridge inverter circuit, and the other end is connected to the first tap of the primary side of the transformer.

6. A high voltage circuit for outputting symmetrical positive and negative voltages as claimed in claim 1, characterized in that: The device also includes a resistor R1 and a resistor R4. The resistor R1 is connected in parallel to both ends of the first diode series branch, and the resistor R4 is connected in parallel to both ends of the second diode series branch.

7. A control method for a high voltage circuit that outputs symmetrical positive and negative voltages, characterized in that: A high voltage circuit that outputs symmetrical positive and negative voltages as described in any one of claims 1 to 6 is constructed, and the current direction of the load is changed by the output end of the commutation circuit to achieve neutralization of the residual charge on the load.

8. A control method for a high voltage circuit that outputs symmetrical positive and negative voltages as claimed in claim 7, characterized in that: The actual output voltage and current on the load are differentially calculated with the set voltage and current values, and PID closed-loop control is performed based on the obtained voltage difference and / or current difference. The PID closed-loop control acts on the duty cycle adjustment of the PWM wave until the output of the full-bridge inverter circuit reaches the set current value.

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