JP2010232129A - Charged particle beam device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charged particle beam device capable of accurately detecting abnormal discharge of a charged particle source. <P>SOLUTION: The charged particle beam device is provided with a charged particle source 12, an accelerating voltage source 3 impressing accelerating voltage on the charged particle source 12, a transformer 30 having a gap G at a core C and a primary-side winding connected between the accelerating voltage source 3 and the charged particle source 12, a primary-side current detecting circuit detecting a current flowing in the primary-side winding N1 based on a current flowing in, or a voltage generated at, a secondary-side winding N2 of the transformer, and a discharge detecting circuit detecting discharge based on an output of the primary-side current detecting circuit. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a discharge detection circuit used in a charged particle beam apparatus.

  The charged particle beam device generates charged particles by causing thermionic emission or electric field emission, accelerates the generated charged particles, and irradiates an object to be irradiated. There are many such charged particle beam devices such as electron microscopes, X-ray tubes, electron beam heating devices, electron beam exposure devices, etc., and they are used in a wide range of fields such as observation, analysis, processing, heating, and X-ray generation devices in minute areas. ing.

  A configuration example of an electron beam irradiation apparatus which is one of such charged particle beam apparatuses is shown in FIG.

  In the figure, reference numeral 1 denotes a filament that emits thermoelectrons, and reference numeral 2 denotes a filament power source that supplies current to the filament 1. Reference numeral 3 denotes an acceleration voltage power source for applying an acceleration voltage to the filament 1. Reference numeral 50 denotes a sample irradiated with a charged particle beam, and the sample 50 is electrically connected to the ground. Reference numeral 5 denotes an electron beam emitted from the filament 1.

  The portion through which the electron beam passes from the filament 1 to the sample 50 is in the vacuum chamber 6, and the vacuum chamber 6 is evacuated by a vacuum pump (not shown). The vacuum chamber 6 is electrically connected to the ground. The filament 1 at the potential on the acceleration voltage is insulated by an insulator 7 and held in a chamber 6. A Wehnelt 8 is attached to the insulator 7 so as to surround the filament 1. A Wehnelt power supply 4 is connected between the Wehnelt 8 and the filament 1, and a negative (minus) potential is applied to the filament 1. A cathode 10 is attached so as to surround the Wehnelt 8. The cathode is electrically connected to the ground.

  A Wehnelt hole 9 is formed in the Wehnelt 8 and a cathode hole 11 is formed in the cathode 10 so that the electron beam 5 is irradiated from the tip of the filament 1 to the sample 50. The filament 1, Wehnelt 8, and cathode 10 constitute an electron gun 12 that is a charged particle beam source.

  A voltage divider 20 divides the acceleration voltage with two resistors. Reference numeral 21 denotes a comparator which compares the voltage obtained by dividing the acceleration voltage by the voltage divider 20 with the reference voltage Vref output from the comparison reference voltage source 22 and outputs a discharge detection signal. Reference numeral 23 denotes a protection circuit which operates upon receiving a discharge detection signal from the comparator 21.

  In such an apparatus, a current is passed from the filament power source 2 to the filament 1 to heat the filament 1. Thermoelectrons are emitted from the heated filament 1. However, a Wehnelt 8 is applied around the filament 1 to a negative (minus) potential with respect to the filament 1 by a Wehnelt power source 4. Therefore, thermoelectrons having a negative charge repel the Wehnelt 8. Then, the thermoelectrons are attracted to the cathode 10 through the hole 9 formed in the Wehnelt 8 and accelerated, and become an electron beam and irradiated to the sample 4 through the hole 11 of the cathode 10.

  The acceleration voltage for accelerating electrons is at least about 1 kV, sometimes up to 1000 kV, and unnecessary discharge often occurs between the acceleration voltage and the ground. This is called unnecessary discharge. When unnecessary discharge occurs, the output of the acceleration voltage source 3 is in the same state as short-circuited to the ground, and a rapid discharge current flows. Continuous unnecessary discharge may cause destruction of the acceleration voltage power supply 3. In addition, when the charged particle beam apparatus is used as an electron beam vapor deposition apparatus, a uniform vapor deposition film cannot be formed due to fluctuations in acceleration voltage due to unnecessary discharge, which may cause defective products. A method of detecting the unnecessary discharge and controlling the acceleration voltage to be stable even if the unnecessary discharge occurs, and a method of stopping and protecting the application of the acceleration voltage when an unnecessary discharge occurs have been devised.

  In general, the unnecessary discharge is detected by detecting that the acceleration voltage changes due to the unnecessary discharge. However, since the acceleration voltage is high, it is difficult to detect a change in the acceleration voltage directly. Therefore, a voltage dividing resistor 20 composed of two resistors is connected between the output of the acceleration voltage power supply 3 and the ground, and the acceleration voltage is divided to about 10 volts. When the acceleration voltage drops due to unnecessary discharge, the divided voltage also drops. The comparison reference voltage source 22 is set in advance to determine the reference voltage Vref. If the divided voltage drops below the reference voltage Vref, it is determined that the discharge is unnecessary, and the comparator 21 outputs an unnecessary discharge detection signal. The comparator 21 determines that the discharge is unnecessary, and the protection circuit 23 receives the output signal to lower the acceleration voltage or stop application of the acceleration voltage.

JP-A-8-22797

  As shown in FIG. 1, a voltage dividing resistor 20 configured by connecting two resistors in series between the acceleration voltage and the ground is connected between the acceleration voltage and the ground.

  In the case of an electron beam generator, the acceleration voltage power supply 3 outputs a negative voltage to accelerate the electron beam. Therefore, a current flows through the voltage divider 20 from the ground toward the acceleration voltage power supply 3. The acceleration voltage power supply 3 is a high voltage power supply, and in order to obtain a large load current, not only the power supply becomes large but also very expensive. Therefore, in order to prevent the current from flowing through the voltage divider 20 as much as possible, a voltage divider having a large resistance value such as several hundred MΩ is used.

  However, if the current flowing through the voltage dividing resistor 20 is reduced, the current flowing into the input terminal of the comparator 21 cannot be ignored. For this reason, the divided voltage of the acceleration voltage cannot be obtained only by the voltage dividing ratio by the resistance, and the unnecessary discharge cannot be accurately determined.

  Further, when the acceleration voltage is changed, the voltage of the voltage divider also changes. Therefore, it is necessary to reset the comparison reference voltage source 22 as a reference for the comparator 21 and change the reference voltage Vref to the acceleration voltage each time. .

  In addition, even if the voltage dividing resistor 20 is discharged, the same unnecessary discharge is generated, so that the voltage dividing resistor 20 is placed in an insulating oil so as not to cause unnecessary discharge or is solid-molded with silicon or the like. A measure is needed. This not only reduces the size but also increases the cost.

  FIG. 2 shows an example in which a plurality of charged particle sources 12 and 12b are used with one acceleration voltage power source 3. In this case, the acceleration voltage fluctuates regardless of which of the electron guns 7 and 7b generates an unnecessary discharge. Therefore, the electron gun that caused the unnecessary discharge could not be determined.

  A charged particle source, an acceleration voltage source for applying an acceleration voltage to the charged particle source, a transformer having a gap in the core and having a primary winding connected between the acceleration voltage source and the charged particle source, and the transformer A primary current detection circuit for detecting a current flowing in the primary winding based on a current flowing in the secondary winding or a generated voltage, and a discharge for detecting discharge based on the output of the primary current detection circuit A charged particle beam apparatus comprising a detection circuit.

  ADVANTAGE OF THE INVENTION According to this invention, the charged particle beam apparatus which can detect the abnormal discharge of a charged particle source correctly can be provided.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 3 shows a schematic example of a charged particle beam apparatus according to the present invention. Moreover, what was made into the symbol same as the symbol used in FIG. 1 is the same component.

  Filament 1, filament power source 2, acceleration voltage power source 3, sample 50, electron beam 5, vacuum chamber 6, insulator 7, Wehnelt 8, Wehnelt power source 4, cathode 10, Wehnelt hole 9 and cathode hole 11 are the same as in the prior art. is there. Reference numeral 30 denotes a current transformer. The current transformer 30 has a structure in which a primary winding N1 and a secondary winding N2 are wound around a core C having a gap G. A cable between the acceleration voltage power source 3 and the filament 1 is wound around the primary side of the current transformer 30, and detection resistors 31 are attached to both ends of the secondary side winding. One side of the detection resistor 31 is connected to the ground, and the opposite end is connected to the comparator 21. The comparator 21 is connected to compare the reference voltage Vref, which is the output of the comparison reference voltage source 22, with the voltage of the detection resistor 31.

  In such an apparatus, a current is passed through the filament 1 to heat it as in the prior art, and an acceleration voltage is applied to the filament 1 to irradiate the sample 50 with the electron beam 5.

  If an unnecessary discharge occurs between the acceleration voltage and the ground while the sample 50 is irradiated with the electron beam 5, a discharge current flows from the ground to the acceleration voltage power source 3. The primary winding N1 of the current transformer 30 is connected between the filament 1 and the acceleration power source 3. Then, the discharge current flows from the ground to the acceleration power supply 30 via the primary winding N1 of the current transformer 30. A current proportional to the primary current flowing in the primary winding is generated in the secondary winding N2 of the current transformer 30. If the detection resistor 31 is connected to both ends of the secondary winding of the current transformer 30, the current generated by the secondary winding flows in the detection resistor 31, and the voltage Vs is generated at both ends of the detection resistor 31 due to a voltage drop. To do. The voltage at both ends of the detection resistor 31 is 0 V when there is no unnecessary discharge, and the voltage Vs is generated when discharge occurs, so that it operates as a primary current detection circuit. Thus, unnecessary discharge can be detected by observing the voltage Vs generated across the detection resistor 31.

  The voltage Vs generated at both ends of the detection resistor 31 is input to the comparator 21 and compared with the reference voltage Vref that is the output of the comparison reference voltage source 22. If the comparator 21 determines that the discharge is unnecessary, the comparator 21 outputs an unnecessary discharge detection signal. The unnecessary discharge detection signal output from the comparator 21 is input to the protection circuit 23. Upon receiving the unnecessary discharge detection signal, the protection circuit 23 lowers the acceleration voltage and stops applying the acceleration voltage.

  However, there are many cases where it is desired to protect only during a large discharge without operating the protection circuit of the device with a slight discharge. In that case, it is only necessary to change the setting of the comparison reference voltage source 22 connected to the comparator 21 to increase the reference voltage Vref and detect only the discharge with a large discharge current.

  FIG. 4 shows the current transformer 30. The current transformer 30 is formed by winding a primary winding N1 and a secondary winding N2 around a ferromagnetic core such as ferrite.

  FIG. 5 shows a graph of the magnetic flux density of the core C with respect to the external magnetic flux of the current transformer 30 (the magnetic flux generated by the primary winding N1).

  A current I is passed through the primary winding N1 of the current transformer 31, and a magnetic field is applied from the primary winding N1 to the core C made of a ferromagnetic material. When the external magnetic field H is zero, the magnetic flux density B is also zero. When the strength of the external magnetic field H is increased, the magnetic flux density B of the core C increases in proportion to the saturation magnetic flux density Bm. Increasing H beyond that does not increase the magnetic flux density B. This is because the core C is saturated.

  In the transmission of energy from the primary winding N1 of the current transformer 31 to the secondary winding N2, the magnetic field generated by the primary winding N1 changes the magnetic flux density B of the core C. The change causes a current to be generated in the secondary winding N2. When the core C is saturated, the magnetic flux density B does not change, and energy is not transmitted to the secondary winding N2.

  The strength of the magnetic field applied to the core C is determined by the number of turns on the primary side and the current that flows. The discharge of the acceleration voltage is almost equivalent to the short-circuit of the acceleration power supply 3 which is a high voltage, and the discharge current is very large. Even if the number of turns of the primary winding is reduced, the discharge current is large and the core may be saturated. In order not to saturate the core, it is necessary to increase the cross-sectional area of the core or lower the magnetic permeability of the core.

  When the cross-sectional area of the core is increased and saturation is avoided, the core itself is enlarged and the current transformer 30 becomes large, which is not realistic. Further, in order to change the magnetic permeability of the core, the material of the core may be changed, but it is difficult to select a material having the optimum magnetic permeability.

  Therefore, a gap is provided in the core of the current transformer 30. FIG. 4B shows a state where a gap G is provided in the core C of the current transformer 30.

  Returning to FIG. 5, the change in the magnetic flux density with respect to the external magnetic flux when there is a gap in the core of the current transformer 30 will be described.

  When the external magnetic field H is zero, the magnetic flux density B is also zero. When the strength of the external magnetic field H is increased, the magnetic flux density B increases in proportion. When the saturation magnetic flux density Bm is reached, the magnetic flux density B does not increase even if the external magnetic field strength H is increased further. However, when there is no core gap, the strength of the external magnetic field reaches the saturation magnetic flux density Bm at point A, whereas when there is a core gap, the strength of the external magnetic field saturates at point B greater than point A. Here, when the core gap G is increased (expanded), the strength of the external magnetic field reaching the saturation magnetic flux density Bm is increased, and when the core gap G is decreased (decreased), the external magnetic field reaching the saturation magnetic flux density Bm is increased. The strength approaches point A. This is the same as changing the magnetic permeability of the core C of the current transformer 31. Furthermore, the optimum magnetic permeability can be obtained by adjusting the gap of the core C of the current transformer 31.

  Since the magnetic permeability of the core C is optimized as described above, even if the core C of the current transformer 31 is downsized, the core C of the current transformer 31 is not saturated and discharge can be detected accurately.

  Further, since the change in the acceleration voltage is not detected but the discharge current is detected, it is necessary to reset the comparison reference voltage Vref referred to by the comparator 21 by the comparison reference power source 22 even if the acceleration voltage is changed. Disappears.

  In addition, the high-voltage part is simply wound around the insulation cable between the accelerating power source 3 and the filament 1 (passing through the core in the case of one turn), so that the detection resistor 31 and the current transformer 30 are immersed in insulation oil or solid. There is no need for special insulation such as a mold.

  Next, FIG. 6 shows an example in which one acceleration voltage power source 3 is connected to a plurality of electron guns. The electron beam irradiation apparatus configured in the configuration of FIG. As a result, the expensive acceleration voltage power supply 3 is shared by the two charged particle guns, thereby reducing the cost.

  Here, when there is an unnecessary discharge in the first electron gun 12, the discharge current flows only to the current transformer 30 and does not flow to the current transformer 30b. Further, when there is an unnecessary discharge in the second electron gun 12b, a discharge current flows only in the current transformer 30b, and no discharge current flows in the current transformer 30. Therefore, if an accelerating voltage power source is connected to a plurality of electron guns, it can be recognized which electron gun has caused an unnecessary discharge.

  In the above description, the protection circuit 23 is activated by detecting the unnecessary discharge, and the acceleration voltage is lowered to stop the application of the acceleration voltage for protection. However, a recorder is connected to the output of the comparison circuit 21 to monitor the frequency of unnecessary discharge. However, it may be used as a guide for maintenance of the charged particle gun.

  In addition, although the said best form demonstrated the case where it implemented to the electron beam irradiation apparatus, it cannot be overemphasized that it can implement also to an ion generator.

The outline of the discharge detector of the conventional electron beam irradiation apparatus is shown. The outline at the time of using the conventional acceleration voltage power supply with several electron beam irradiation apparatus is shown. The outline of the discharge detector of the electron beam irradiation apparatus of this invention is shown. The outline of a current transformer is shown. It is a graph which shows the relationship between the intensity | strength of an external magnetic field, and magnetic flux density. The outline at the time of using the acceleration voltage power supply of this invention with a several electron beam irradiation apparatus is shown.

DESCRIPTION OF SYMBOLS 1,1b ... Filament, 2, 2b ... Filament power supply, 3, ... Acceleration voltage power supply, 4, 4b ... Wehnelt power supply, 5, 5b ... Electron beam, 6, 6b ... Vacuum chamber, 7, 7b ... Insulator, 8, 8b: Wehnelt, 9, 9b: Wehnelt hole, 10, 10b ... Cathode, 11, 11b ... Cathode hole, 12, 12b ... Electron gun, 20 ... Voltage dividing resistor, 21, 21b ... Comparator, 22, 22b ... Comparative reference voltage source, 23 ... protection circuit, 30, 30b ... current transformer, N1 ... primary winding of current transformer, N2 ... secondary winding of current transformer, C ... core of current transformer, G ... current transformer Core gap, detection voltage ... Vs, Vs2, reference voltage ... Vref, Vref2

Claims (2)

A charged particle source;
An acceleration voltage source for applying an acceleration voltage to the charged particle source;
A transformer having a gap in the core and a primary winding connected between the acceleration voltage source and the charged particle source;
A primary current detection circuit for detecting a current flowing in the primary winding based on a current flowing in the secondary winding of the transformer or a generated voltage;
A charged particle beam apparatus comprising a discharge detection circuit that detects discharge based on an output of the primary current detection circuit. Have multiple charged particle sources,
Configured to apply an accelerating voltage from one accelerating voltage source to a plurality of charged particle sources;
The charged particle beam apparatus according to claim 1, wherein the transformer is arranged between the charged particle sources and the acceleration voltage source.

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