JP5133722B2 - Voltage source circuit - Google Patents

Description

  The present invention relates to a voltage source circuit and an inspection apparatus including the same, and, for example, a voltage that generates a high voltage for realizing acceleration / deceleration and deflection of an electron beam in a length measuring SEM (Scanning Electron Microscope) which is a semiconductor inspection and measurement apparatus. More particularly, the present invention relates to a feedback control type voltage source circuit using a Cockcroft-Walton circuit, and an inspection apparatus including the same.

  Generally, in a voltage source circuit, an input voltage is boosted to generate a high voltage. For example, the Cockcroft-Walton circuit is one of the booster circuits that can easily obtain an output voltage many times the input voltage.

  First, the operation and performance of a single Cockcroft-Walton circuit will be described with reference to FIG. The Cockcroft-Walton circuit counts the charging circuit composed of the AC power supply 13 and the capacitor 11 and the diode 12 as one stage, so that the directions of the diodes alternate between the even and odd stages, and An arbitrary number of stages, usually an even number of stages, are connected in parallel to the preceding diode. Its operation depends on the polarity of the AC power supply and the direction of the diode, charging about half of the current charge from the front capacitor to the rear capacitor, from the odd capacitor to the even capacitor, and vice versa. I will do it. At this time, if the time required for charging / discharging between capacitors is zero as an ideal value without loss, the time required for the charge stored in each capacitor to be approximately saturated depends on the frequency of the AC power supply and the number of stages configured. Dependent. When the number of stages is about 6 to 10, the time required for all capacitors to saturate corresponds to 100 to 150 cycles of the AC power supply cycle. In addition, the size of the output voltage that can be obtained is a maximum of the number of stages of the peak value of the AC power supply in the case of an even number of stages. This can be extracted from the sum of the charges stored in the even-stage capacitors.

  The polarity of the output voltage that can be acquired can be changed between positive and negative depending on the direction of the diode. In the case of the circuit configuration example of FIG. 2, a negative output voltage can be acquired. When all the diode directions are reversed, a positive output voltage can be obtained.

  The Cockcroft-Walton circuit, when supplying a voltage to a capacitive load such as a voltage applied between the electrodes that realizes deflection of the electron beam as a load, has a peak value of a certain AC power source as described above. The dependent DC voltage can be obtained by realizing high stability and a certain degree of responsiveness, although a slight instability factor corresponding to the leakage current of the diode and the degree of insulation of the capacitor remains.

  However, when considering the case where the charge stored in each capacitor is discharged once, the discharge current path is the only path, so when the load current is small, the discharge current is also small and the capacity load is targeted. In such a case, it takes a long discharge time.

  Here, the rapid response means the quickness until the output voltage converges to a steady state (saturated value). The rapid response time is the time taken for the voltage to converge. Furthermore, the term “stability” means that high-frequency ripple generated by charging / discharging between capacitors is stabilized, so that long-term fluctuations such as a change of component constants with time are stabilized.

  The Cockcroft-Walton circuit is often used for a high-voltage power supply circuit that does not require much output current because of its simple circuit configuration and relatively safe and easy generation of a high voltage. However, not only the Cockcroft-Walton circuit but also a high-voltage power supply circuit is required to be able to monitor the output voltage and arbitrarily control the output voltage. Therefore, when the Cockcroft-Walton circuit is used, a voltage source circuit is configured by separately adding a circuit for detecting a high output voltage and a circuit capable of arbitrarily adjusting the peak value of the AC power supply.

  FIG. 2 shows a schematic configuration of a conventional voltage source circuit using a Cockcroft-Walton circuit as disclosed in Patent Documents 1 and 2, for example. The voltage source circuit is composed of only a circuit portion composed of the capacitor 11 and the diode 12 of the Cockcroft-Walton circuit 10 and a smoothing circuit (comprising a capacitor 21 and a resistor 22) connected so as to smooth the output voltage of the Cockcroft-Walton circuit. 20 and a detection resistor 41 connected to the output voltage potential to detect the output current with respect to the smoothed output voltage (for example, a large resistance of mega Ω level, as will be described later) And the difference voltage between the set voltage input to the difference detection circuit from the set voltage terminal 50 and the detected output voltage is input and adjusted from the power supply voltage. A PI operation type feedback control circuit 60 that outputs a possible DC input voltage and an AC voltage having a peak value that can be adjusted from the input voltage. And a switching regulator circuit 80 that outputs from the secondary side of the pull-type high-frequency transformer 83.

  The output current detected by the detection resistor 41 is compared with the set voltage current flowing from the set voltage resistor 42, and the difference current is output to the difference detection signal terminal 43 as a difference voltage. In the circuit configuration of FIG. 2, a negative output voltage can be acquired from the output voltage terminal 30. In this case, the set voltage is set to a positive polarity. When the output voltage (also referred to as control target voltage) falls below a target value that depends on the set voltage, the difference detection circuit 40 outputs a negative difference voltage.

  The PI operation type feedback control circuit 60 outputs a DC input voltage (voltage at the terminal 61) corresponding to the input differential voltage. In the PI operation type feedback control circuit 60, a proportional element signal and an integral element signal are generated from the differential voltage, and a so-called feedback control signal is output. Actually, the input voltage corresponding to the feedback control signal voltage is extracted from the power supply voltage input from the power supply voltage terminal 70 and output.

  The push-pull switching regulator circuit 80 includes a two-stone switching transistor 82, a switching gate pulse generation circuit 81 that alternately controls OPEN / CLOSE, and a two-stone switching transistor 82 that alternately OPEN / CLOSE. A push-pull type high-frequency transformer 83 that generates an AC voltage at the secondary coil end. This constitutes an AC power supply section of a Cockcroft-Walton circuit that inputs a DC input voltage and outputs an AC voltage.

  The above circuit configuration is called a so-called feedback control system. According to this voltage source circuit, the input voltage can be output and adjusted by inputting the set voltage, and the output voltage can be boosted, adjusted and converged to the target value corresponding to the set voltage, and this can be applied for a long time. Realize the stability to hold.

JP 2003-200573 A JP 2004-96946 A

  By the way, in the length measurement SEM, a demand for improvement in accuracy according to miniaturization in the semiconductor design rule and a demand for improvement in speed called throughput are increasing year by year. One means for realizing this is to improve the performance of the voltage source circuit mounted. The accuracy aspect in the voltage source circuit means the stability of the output voltage, the speed aspect is quick response, and the problem is to increase both at the same time.

  However, as described from the performance of the Cockcroft-Walton circuit alone, in the conventional circuit configuration using the Cockcroft-Walton circuit, the stability and the quick response are in a contradictory relationship.

  When discussing the stability of the voltage source circuit, it is necessary to pay attention to a ripple that fluctuates at a high frequency called a switching frequency, in addition to a change over time, which is a long-term fluctuation factor. The high-frequency ripple is the charge / discharge voltage that is constantly repeated in the capacitor constituting the Cockcroft-Walton circuit, and is proportional to the output current. In order to increase the stability, that is, to reduce the high frequency ripple, it is necessary to suppress the output current (for example, μA level). For this purpose, the resistance value of the detection resistor 41 is increased (for example, the megaΩ level). There is no choice but to do. When the current that can be detected is small, the amount of information that can be obtained is small, so that the response of the desired voltage control is deteriorated and the stability is increased, but it is difficult to realize the quick response.

  On the other hand, when discussing rapid response, attention must be paid to the discharge rate of the output voltage. When performing control with increased responsiveness, it is essential to overshoot the output voltage once exceeding the target value, and it is also necessary to increase the discharge rate for control to step down the current output voltage value. However, in order to discharge the output voltage quickly, that is, to quickly discharge the electric charge charged in the capacitor, it is necessary to increase the discharge current flowing through the detection resistor (load). For this purpose, the resistance value of the detection resistor 41 is required. There is no choice but to make it smaller. In this case, on the contrary, stability is sacrificed.

  As described above, the conventional voltage source circuit using the Cockcroft-Walton circuit cannot achieve both stability and quick response.

  The present invention has been made in view of such a situation, and provides a voltage source circuit capable of achieving both stability and quick response.

  In order to solve the above problems, in the present invention, in addition to the configuration of a conventional voltage source circuit using a Cockcroft-Walton circuit, a switch (analog switch) is connected between a conventional output voltage potential (control target potential) and ground. A resistor dedicated to discharging is provided. The switch has a role of adjusting the timing and amount of the discharge current flowing through the discharge resistor, and controls the discharge current control circuit by providing a circuit. These are collectively referred to as a discharge control circuit, and a discharge control signal serving as a timing signal for starting discharge generated in the feedback control circuit is input.

  That is, the voltage source circuit according to the present invention includes a switching regulator circuit that inputs a DC voltage and converts it into an AC voltage, and a Cockcroft-Walton circuit that is supplied with the AC voltage and outputs a DC voltage boosted to a multiple of the peak value. A detection resistor connected to the potential of the output DC voltage and detecting an output current; a differential detection circuit that outputs a differential voltage between the DC voltage and the set voltage; and a DC input from the differential voltage to the switching regulator circuit A feedback control circuit having proportional and integral elements for realizing a PI operation for extracting a voltage from a power supply voltage, and a discharge control circuit for controlling discharge of an output voltage of the Cockcroft-Walton circuit. Then, the discharge control circuit is configured to turn on / off the switch based on a discharge resistor for supplying a discharge current from the Cockcroft-Walton circuit, a switch for controlling ON / OFF of the discharge current, and an output from the feedback control circuit. A discharge current control circuit for generating a discharge control signal for controlling OFF. In the Cockcroft-Walton circuit, it is desirable that the stage for taking the output DC voltage and the stage for the output voltage to be discharged are the same.

  Further features of the present invention will become apparent from the best mode for carrying out the present invention and the accompanying drawings.

  According to the voltage source circuit of the present invention, both stability and rapid response can be achieved.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be noted that this embodiment is merely an example for realizing the present invention, and does not limit the technical scope of the present invention. In each drawing, the same reference numerals are assigned to common components.

<Configuration of voltage source circuit>
FIG. 3 is a diagram showing a schematic configuration of the voltage source circuit according to the embodiment of the present invention. The voltage source circuit 1 includes a discharge control circuit 90 including a discharge current control circuit 91, an analog switch 92, and a discharge resistor 93 in addition to the above-described conventional circuit configuration (see FIG. 2). In this case, whether the output voltage exceeds the target value or the step-down control is performed by lowering the set voltage, a positive differential voltage is supplied to the differential detection signal terminal. The PI operation type feedback control circuit 60 generates a discharge control signal voltage for controlling the discharge timing and the amount of discharge current from the differential voltage, and supplies it to the discharge control signal terminal 62.

  The discharge control signal voltage is multiplied by a gain in the discharge current control circuit 91 in the discharge control circuit 90, and an offset is added. The analog switch 92 is subjected to OPEN / CLOSE control, and the discharge flowing from the output voltage through the discharge resistor 93. It becomes a signal source for adjusting and controlling the amount of current. That is, when the capacitor 21 needs to be discharged, the analog switch 92 is set to CLOSE (ON) and a current is passed through the discharging resistor 93 to realize rapid discharge. For this purpose, the resistance value of the discharge resistor 93 needs to be set sufficiently smaller than the resistance value of the detection resistor 41.

  In some cases, the discharge rate may be changed depending on the situation. For discharge when the output voltage approaches the target value and converges a slight difference, we want to suppress the discharge current amount and speed so as not to fall into oscillation. Also, when the output voltage is once set to zero (off), it is desired to increase the discharge current amount to discharge at once. In order to respond to such a wide range and various situations, the circuit configuration of FIG. 3 assumes that the amount of discharge current can be varied and adjusted.

  However, there may be a restriction that the desired discharge rate cannot be realized as the range in which the discharge can be varied and adjusted is widened. In this case, a plurality of analog switches and discharge resistors may be prepared, and discharge resistors having resistance values corresponding to the discharge control signal voltage range may be selected and discharged.

  In the Cockcroft-Walton circuit 10, the stage for providing the output terminal for taking the output voltage and the stage for the capacitor to be discharged must be the same. This condition will be described below with reference to FIG.

  FIG. 4 shows a circuit configuration example in the case where the potential for connecting the analog switch 92 of the discharge control circuit 90 is connected to the potential of the second-stage capacitor 18 of the eight-stage Cockcroft-Walton circuit 16 instead of the output voltage potential. It is. In FIG. 4, the PI operation type feedback control circuit 60 is omitted.

  In the circuit configuration of FIG. 4, although there is a merit that it is not necessary to be a high withstand voltage analog switch, the expected effect cannot be obtained. In other words, in this case, the discharge control circuit 90 can quickly discharge the charges stored in the first-stage charging capacitor 17 and the second-stage charging capacitor 18 through the discharging resistor, but is stored in the remaining capacitors. The electric charge is discharged only through the detection resistor 41. Therefore, even if the output voltage falls below the target value by executing the discharging operation by the detection resistor 41 and the discharging operation of the second-stage charging capacitor, the analog capacitor 92 is opened and the second-stage capacitor is immediately left as it is. It is immediately charged to the charge stored in the capacitor. For this reason, it is not different from the case of controlling and discharging only through the conventional detection resistor 41.

  As described above, in the Cockcroft-Walton circuit 10, if the stage for taking the output voltage is different from the stage for discharging the capacitor, it is not possible to achieve both stability and responsiveness. Therefore, it is desirable to set them to the same stage.

<Another configuration example of the voltage source circuit>
FIG. 5 is a diagram illustrating another configuration example of the voltage source circuit, and illustrates a circuit configuration example in the case where the analog switch 92 cannot achieve a withstand voltage as high as the output voltage.

  As shown in FIG. 5, in the eight-stage Cockcroft-Walton circuit 16, an analog switch 92 and a discharging resistor 93 are connected to each of the even-numbered four capacitors constituting the output voltage. The withstand voltage of the analog switch 92 only needs to be equal to or higher than the charge charged in each even-stage capacitor. In this case, it is necessary to apply a signal (current or voltage) from the discharge current amount control terminal 94 so that the same timing and discharge current amount can be controlled for all analog switches 92.

<Application to measuring SEM>
In the length measurement SEM, a disk (called a wafer) on which semiconductor circuits are stacked is placed in a vacuum chamber and observed. The wafer is carried on a table called a holder on which a wafer is fixed and is transferred into a vacuum chamber. In the vacuum chamber, there is a stage that receives a holder on which a wafer is placed and can move in a plane.

  A high voltage is applied to the holder in the current measuring machine of the length measuring SEM in order to help the length measuring performance, and a conventional voltage source circuit configuration method is adopted for this. In the operation of applying a high voltage to the holder, when the holder is taken out of the vacuum chamber (unloading), it is necessary to consider the time for waiting for the discharge to be completed. In the case where the battery is not fully discharged and remains in a charged state, there is a high possibility of causing a phenomenon that leads to deterioration of the apparatus performance such as discharge and adsorption of foreign matter.

  However, if the unload operation is waited until the discharge is completed, there is a problem that the throughput of the length measuring SEM is lowered.

  Therefore, if the voltage source circuit according to the present invention is used for the length measurement SEM, selective discharge becomes possible, and the time for waiting for the completion of discharge can be reduced as much as possible. As a result, parallel processing can be performed without waiting for the completion of discharge, and the time of the unload sequence can be reduced. That is, the throughput of the length measurement SEM can be improved.

  Further, if the voltage source circuit according to the present invention is used, the output current and the high frequency ripple can be intentionally increased, and the output voltage can be fluctuated and oscillated from the steady stable state. As a result, there is a possibility that in the charging of the wafer itself that has not yet been elucidated and in the local charging in the observation, the elucidation and elimination can be effective.

<Summary>
Close the analog switch of the discharge control circuit (switch ON) only when overshooting exceeding the target value that requires discharging of the output voltage, when controlling to step down, and when turning off to zero volts. ) A discharge current can flow through the discharge resistor. In this case, the discharge resistor 93 is set to a value sufficiently smaller than the resistance value of the detection resistor 41 that constantly monitors the output voltage, so that the effect can be exhibited more quickly and the discharge can be performed quickly.

  In addition, the detection resistor 41 can always prioritize realizing high stability, and the effect of reducing high-frequency ripple can be obtained at the same time by using a resistor having a large resistance value.

  Further, as described above, in the Cockcroft-Walton circuit, it is desirable that the stage for taking the output DC voltage and the stage for the output voltage to be discharged are the same. In addition, when adopting a configuration that can take an output DC voltage from a predetermined stage (including a plurality of stages) of the Cockcroft-Walton circuit, if a discharge control circuit is connected to that stage, the input voltage or Without changing the set voltage, the output voltage boosted to various values can be generated while achieving both stability and quick response.

It is a figure which shows the structural example of a Cockcroft-Walton circuit. It is a figure which shows the circuit example which employ | adopted the feedback control system in the conventional voltage source circuit. It is a figure which shows schematic structure of the voltage source circuit by embodiment of this invention. It is a figure for demonstrating that the stage which provides the output terminal which takes an output voltage, and the stage of the capacitor | condenser to discharge must be the same in the Cockcroft-Walton circuit. It is a figure which shows another structure of the voltage source circuit by embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Cockcroft-Walton circuit (CW circuit), 11 ... Capacitor, 12 ... Diode, 13 ... AC power supply, 14 ... First stage capacitor charging circuit, 15 ... Second stage capacitor charging circuit, 16 ... Eight-stage cockcroft Walton Circuit: 17 ... First stage charging capacitor, 18 ... Second stage charging capacitor, 20 ... Smoothing circuit, 21 ... Smoothing capacitor, 22 ... Smoothing resistor, 30 ... Output voltage terminal (control target voltage), 40 ... Difference detection circuit, 41 Detecting resistor, 42 Setting voltage resistor, 43 Differential detection signal terminal (differential voltage), 50 Setting voltage terminal (setting voltage), 60 PI operation feedback control circuit, 61 Input voltage terminal (input voltage), 62 ... discharge control signal terminal (discharge control signal voltage), 70 ... power supply voltage terminal (power supply voltage), 80 ... push-pull type switching resistor Regulator circuit, 81... Switching gate pulse generation circuit, 82... Switching transistor, 83 .. push-pull type high frequency transformer, 90... Discharge control circuit, 91. ... Discharge current control terminal (Discharge current control voltage)

Claims (5)

A switching regulator circuit that inputs a DC voltage and converts it to an AC voltage;
A Cockcroft-Walton circuit that is supplied with the AC voltage and outputs a DC voltage boosted up to several times the peak value;
A detection resistor connected to the potential of the output DC voltage and detecting an output current;
A difference detection circuit for outputting a difference voltage between the output DC voltage and a set voltage,
A feedback control circuit having proportional and integral elements for realizing a PI operation for extracting a DC voltage input to the switching regulator circuit from the differential voltage from a power supply voltage;
A discharge control circuit for controlling the discharge of the output voltage of the Cockcroft-Walton circuit,
The discharge control circuit includes:
A resistor for discharging the discharge current from the Cockcroft-Walton circuit;
A switch for controlling ON / OFF of the discharge current;
A discharge current control circuit that generates a discharge control signal for controlling ON / OFF of the switch based on an output from the feedback control circuit;
And a voltage source circuit for converging the output DC voltage of the Cockcroft-Walton circuit to a target value proportional to a set voltage.   2. The voltage source circuit according to claim 1, wherein the discharge resistor is sufficiently smaller than the detection resistor such that most of the discharge current flows through the discharge resistor.   3. The voltage source circuit according to claim 1, wherein in the Cockcroft-Walton circuit, the stage for taking the output DC voltage and the stage for the output voltage to be discharged are the same. A switching regulator circuit that inputs a DC voltage and converts it to an AC voltage;
A Cockcroft-Walton circuit that is supplied with the AC voltage and outputs a DC voltage boosted up to several times the peak value;
A detection resistor connected to the potential of the output DC voltage and detecting an output current;
A difference detection circuit for outputting a difference voltage between the output DC voltage and a set voltage,
A feedback control circuit having proportional and integral elements for realizing a PI operation for extracting a DC voltage input to the switching regulator circuit from the differential voltage from a power supply voltage;
A discharge control circuit for controlling the discharge of the output voltage of the Cockcroft-Walton circuit,
The discharge control circuit includes a switch and a discharge resistor for each capacitor of each stage so as to discharge the electric charge stored in all of the even-stage capacitors that generate the output DC voltage of the Cockcroft-Walton circuit. And a discharge current control circuit that outputs a control signal for adjusting a discharge current amount from the feedback control circuit to all the switches, and the output DC voltage of the Cockcroft-Walton circuit is proportional to a set voltage. A voltage source circuit that converges to a target value.   An inspection apparatus comprising the voltage source circuit according to claim 1.

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