JP2011249054A - Charged corpuscular beam apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide measuring technique with which a beam current can be measured and set highly accurately in a short time in a charged corpuscular beam apparatus.SOLUTION: In a charged corpuscular beam apparatus, a sample is irradiated with a charged particle source and a signal generated from the sample is detected. The charged corpuscular beam apparatus includes: a charged particle optical system for converging or radiating a charged corpuscular beam onto the sample; detection means for detecting a signal generated from the sample by scanning of the charged corpuscular beam; a detection element for measuring a current of the charged corpuscular beam; a control section which includes a deflection electrode or a deflection coil for implementing scanning of charged particles and applies a voltage or a current for controlling this deflection electrode or deflection coil; and an arithmetic unit capable of storing an optical condition of the charged corpuscular beam. By previously storing a condition for obtaining a peak current of the beam current and referring to a beam deflection range in accordance with the optical condition, a current value of the charged corpuscular beam is measured while restricting beam deflection only in the vicinity of the detection element.

Description

  The present invention relates to a charged particle beam apparatus that irradiates a sample with a charged particle beam and detects signal particles generated from the sample, and that can perform current measurement and setting of the charged particle beam at high speed and with high accuracy. It is about.

  A charged particle beam device is a device that irradiates a sample with a primary charged particle beam and detects secondary electrons generated from the sample or backscattered electrons (backscattered electrons) backscattered from the sample as secondary signals. The detected secondary signal is used for various measurements and inspections as an image or an image signal. As the current value of the primary charged particle beam changes, the amount of signal emitted from the sample also changes. Therefore, in order to acquire a good image or image signal, it is necessary to make the current amount of the primary charged particle beam to be irradiated as uniform as possible within the acquisition range of the image or image signal. Therefore, when actually performing an image or image signal, it is necessary to measure the current value of the charged particle beam with high accuracy in advance, and to adjust the current value again if the current value deviates from the set value.

  The beam current measuring method of the charged particle beam apparatus is roughly classified into two methods. One is a method of measuring a current by mechanically moving a detection element typified by a Faraday cup on the optical axis of a charged particle beam. The other is a method in which a charged particle beam is incident on a detection element fixed by electromagnetic deflection or electrostatic deflection, and the current value is measured. The latter method does not require mechanical adjustment, can easily measure current, and is used in many charged particle beam apparatuses. For example, Patent Document 1 discloses an invention of a charged particle beam apparatus in which a current amount detector having a vertically long groove shape is provided in the vicinity of an E × B deflector.

JP-A-9-171790

  In the case of the beam current measurement disclosed in Patent Document 1, the current amount detector is arranged not in the sample but in the middle of the electron optical system. Therefore, when beam current measurement is performed, a charged particle beam is first deflected by a predetermined amount and incident on a deep groove-shaped detection element connected to the current detection circuit, and it is determined that the maximum current value obtained by the detection circuit is the current value. Was. In the case of a deep groove-shaped detection element, it is the inner wall surface of the groove on the current measurement surface, and the peak current is obtained when the charged particle beam is successfully irradiated to the groove bottom of the detection element. In this case, when the charged particle beam is irradiated onto the metal parts around the detection element, emission and absorption of charged particles occur in the irradiated metal part. If these charged particles reach the detection element, there is a problem that the current value of the charged particle beam that should be measured cannot be measured accurately.

  Further, the amount of movement necessary for the detection element to detect the charged particle beam or the amount of deflection necessary for the charged particle beam to enter the detection element varies depending on the optical conditions of the charged particle beam. Therefore, in the conventional method, it is necessary to change the control current and the control voltage for controlling the beam deflection over a wide range, and high-speed measurement is difficult.

  An object of the present invention is to provide a charged particle beam apparatus capable of measuring and setting a current value of a charged particle beam at high speed and with high accuracy while eliminating the above-described drawbacks of the prior art.

  In order to achieve the above object, the charged particle beam apparatus of the present invention scans a sample with a primary charged particle beam and outputs a signal based on detected secondary electrons such as reflected electrons and secondary electrons. A charged particle optical system having a function to perform the above, a current detection element for measuring the amount of current of the primary charged particle beam, and a charged particle for controlling the drive voltage or drive current of the scanning deflection means provided in the charged particle optical system And an optical system control unit for controlling the scanning deflection means so that the beam deflection amount becomes an appropriate value when measuring the beam current of the primary charged particles.

  More specifically, the current of the primary charged particle beam is measured using the current detection element, and the relationship between the deflection amount of the primary beam and the current is stored in advance in an appropriate storage unit. Thereafter, when the beam current measurement is performed again, the charged particle optical system control unit refers to the above relationship, and controls the deflection control current or deflection control to limit the deflection range of the charged particle beam only to the vicinity of the current detection element. By applying a voltage, the peak current value can be measured.

  ADVANTAGE OF THE INVENTION According to this invention, it can provide the charged particle beam apparatus which can be measured and set with high precision for a short time regarding the beam current value measurement of a charged particle beam.

Explanatory drawing which showed the Example of the scanning electron microscope. Example 1 Explanatory drawing of a detection element (Faraday cup) and peripheral components. (Example 2) The relationship of the electron beam deflection control voltage necessary to obtain a constant beam deflection amount for a predetermined acceleration voltage. The characteristic view which shows the relationship between the amount of electron beam current detection circuit output currents in each deflection control current, and a deflection control voltage. 5 is a flowchart showing a flow of beam current measurement according to the first or second embodiment. 6 is a flowchart showing a flow of beam current measurement according to the third or fourth embodiment.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to the drawings, taking a scanning electron microscope as an example.

  FIG. 1 is a drawing of an embodiment of a scanning electron microscope. An electron source 1 is attached above the scanning electron microscope, and a beam control electrode 2 is provided in the vicinity of the electron source 1. This is connected to the beam control high voltage power source 5 together with the extraction electrode 3 and the acceleration electrode 4, and is controlled by a power source control unit of the central control unit 6 equipped with a computing unit (CPU) and a storage device. The amount of current emitted from the electron source 1 can be controlled by adjusting the voltage applied to the extraction electrode 3 and the acceleration electrode 4. The electron source 1, the beam control electrode 2, the extraction electrode 3, and the acceleration electrode 4 constitute an electron gun. In the following description, the set of optical elements described above is appropriately referred to as an “electron gun”. In addition, although it may call an electron gun including another optical element, application of this invention is possible even in that case.

  The electron beam 7 formed by the electrons emitted from the electron source 1 forms a crossover above the diaphragm plate 10 by the lens action of the first converging lens 8. The beam diameter of the converged electron beam 7 is mechanically limited by the beam diaphragm plate 10, and then, the second convergent lens 11 and the convergent lens control power source 9 that are mounted below the diaphragm plate 10, and the objective The electron beam 7 is converged on the sample 17 by controlling the lens 12 and the objective lens control power source 13 by the central controller 6. The operations of the first convergent lens 8 and the second convergent lens 11 are controlled by a convergent lens control power supply 9.

  The converged electron beam 7 can be scanned on the sample by beam scanning deflection means, for example, electromagnetic deflection by the deflection coil 14 or electrostatic deflection by the deflection electrode 15. The scanning of the electron beam 7 can be controlled by changing the control voltage or control current of the deflection control power supply 16 in accordance with the observation magnification. In the case of electromagnetic deflection, the coil drive current is supplied from the deflection coil 14 and the deflection control power supply 16. In the case of electrostatic deflection, a control voltage is supplied from the deflection electrode 15 and the deflection control power source 16. Although FIG. 1 shows a case where the deflection control means for both of the deflection coils 14 are mounted, in reality, only one of them is often provided. As the scanning condition of the observation electron beam, the deflection control power supply 16 is controlled according to the control by changing the control voltage or the control current of the deflection control power supply 16 according to the optical conditions such as the observation magnification and the pixel size.

  The secondary electrons 18 generated by irradiating from the sample 17 by irradiating the primary electron beam 7 or the backscattered reflected electrons are directly or via a reflector 19 for increasing the detection efficiency, to the electron detector 20. Is detected. The detection signal detected by the electronic detector 20 is imaged by a signal detection circuit 21 having an amplification function, an A / D conversion function, and an image processing function, and is displayed on the image display device 22.

  Further, the beam current amount of the primary electron beam 7 is measured using the beam current detecting element 23. In the case of the present embodiment, the beam current detection element 23 is disposed below the two-stage deflection coil 14. When a control current is supplied to the deflection coil 14 or a control voltage is applied to the deflection electrode 15, the electron beam 7 is deflected and is incident on the beam current detection element 23. The beam current detection element 23 has a groove-like structure that is long with respect to the optical axis direction of the electron beam, and a detection current proportional to the charged particle dose incident on the electron detector formed on the inner wall surface of the groove is a current. Output to the detection circuit 24.

  The optical elements such as the electron source 1, the extraction electrode 3, the acceleration electrode 4, or the various lenses such as the converging lenses 8 and 11 and the objective lens 12 described above constitute an electron optical system. In the following description, the set of optical elements described above may be referred to as “electron optical system” or “charged particle optical system”.

  FIG. 2 shows an arrangement relationship between the beam current detection element 23 and peripheral components. The beam current detection element 23 is attached to the inside of the inner wall surface of the metal member constituting the shield 101 provided in the electron microscope via the insulator 102, and is installed so as to be at the ground potential in cases other than the beam current measurement. Is done. When measuring the beam current value, the current detection element 23 is disconnected from the ground and connected to the beam current detection circuit 24. Then, the control voltage of the deflection control power supply 16 is set by the CPU mounted on the central control device 6, and the electron beam 7 is incident on the beam detection element 23 so as not to irradiate the shield 101 and the upper metal part 103. The peak value of the output of the beam current detection circuit 24 at that time can be measured as the beam current value.

  Here, by applying a suppressing material such as carbon having an effect of suppressing generation of secondary electrons or reflected electrons to the inner wall surface of the groove of the beam current detecting element 23, the detection surface of the secondary electrons or reflected electrons becomes the groove surface. It can be limited to the bottom only. As a result, the current amount of the primary charged particle beam can be measured only from the bottom surface of the groove, which is relatively difficult to reach, rather than the inner wall surface of the groove where the charged particles emitted from the metal parts around the beam current detection element 23 are relatively easy to reach. Therefore, noise components caused by causes other than the primary charged particle beam included in the detection signal of the beam current detection element 23 can be reduced, and the measurement accuracy of the beam current amount can be improved.

  Further, by applying a suppression material to the inner wall surface, it is possible to suppress the generation amount of secondary electrons or reflected electrons generated by irradiation of the inner wall surface of the groove of the electron beam 7. As a result, the amount of secondary electrons or reflected electrons incident on the bottom surface of the groove, which is a charged particle beam detector, is reduced, so that the noise component contained in the detection signal of the beam current detector 23 can also be reduced. it can.

  As described above, in order to perform accurate beam current amount measurement, the primary electron beam 7 needs to be incident only on the beam detection element 23. For this purpose, it is necessary to perform precise beam deflection so that the primary electron beam 7 does not irradiate the shield 101, the metal part 103, etc., but the deflection amount of the primary electron beam 7 depends on the acceleration voltage of the electron gun and the beam. Influenced by control voltage. Hereinafter, the relationship between the deflection amount of the electron beam 7 and the acceleration voltage of the electron gun will be described with reference to FIG.

  FIG. 3 shows the relationship between the acceleration voltage Vacc of the electron gun and the beam deflection amount. FIG. 3 is a diagram showing the relationship between Vacc and the amount of beam deflection in the case of electromagnetic deflection. The horizontal axis of the figure is the square root (1/2 power) of Vacc, and the vertical axis is a fixed amount of electron beam 7. A deflection control current amount to be supplied to the deflection coil 14 necessary for deflection is shown. As shown in the figure, the amount of deflection coil current required to obtain a constant beam deflection amount increases with the acceleration voltage Vacc. Also in the case of electrostatic deflection, the relationship between the electrostatic deflection voltage and the acceleration voltage is substantially the same, and the voltage applied to the electrostatic deflection electrode 15 necessary for obtaining a constant beam deflection amount increases with Vacc. .

  The beam current value (Ip) is influenced not only by the acceleration voltage Vacc but also by the voltage applied to the beam control electrode 2 in the electron beam electron gun (hereinafter referred to as the electron beam control voltage Vs), and the control voltage Vs. The amount of electron beam current can be controlled by adjusting.

  The relationship between the acceleration voltage and the deflection control current amount indicated by the solid line in FIG. 3 is expressed by the following equation (1).

  In the case of electrostatic deflection, the relationship between the acceleration voltage and the deflection control voltage applied to the electrostatic deflection electrode 15 is expressed by the following equation (2).

Here, L is an electron beam deflection amount, Vacc is an effective acceleration voltage of the electron gun, Idef is a control current flowing through the deflection coil 14 in the case of electromagnetic deflection, and Vdef is applied to the deflection electrode 15 in the case of electrostatic deflection. The applied deflection control voltages, α ₁ and α ₂ , mean proportional constants determined by the electron optical conditions of the electron beam 7.

  Now, if the formula (1) or the formula (2) is used, the beam deflection amount with respect to the set acceleration voltage Vacc can be known. Therefore, the beam for making the electron beam incident on the beam current detection element 23 so that the target beam deflection amount, that is, the component that affects the electron beam current amount measurement such as the shield 101 and the metal part 103 is not irradiated with the electron beam. When the deflection amount is determined, the current value of the deflection coil 14 or the voltage value of the electrostatic deflection electrode 15 for realizing a predetermined beam deflection is determined under a given acceleration voltage Vacc.

  Next, the deflection control of the electron beam will be described with reference to FIG. FIG. 4 shows the relationship between the current (deflection control current) flowing through the deflection coil 14 during scanning of the electron beam 7 and the amount of electron beam current in the case of electromagnetic deflection. The horizontal axis in FIG. 4 indicates the current value applied to the deflection coil 14, and the vertical axis indicates the detection current value of the beam current detection element 23.

  In conventional current measurement, as described above, the beam current is simply deflected over a wide range and the peak current is measured. In this case, the electron beam 7 may irradiate the shield 101 around the beam current detection element 23 or the metal part 103 attached above, and many reflected electrons and secondary electrons 18 are generated from the metal part. When the beam current detection element 23 captures these, or the yield of secondary electrons, a peak current value larger than the original electron beam current value is detected. In this case, in the case of FIG. 4, a current value as shown as “a current value at the time of beam irradiation to a metal part” is detected as a current value to be originally measured, which causes a problem. Therefore, first, the deflection amount L such that the beam is incident on the groove wall of the current detection element 23 is calculated from the equation (1), and the electron beam 7 is not irradiated to the peripheral shield 101 or the insulator 102 attached above. The deflection control power supply 16 is set so as to achieve such deflection, and the beam current is measured.

  When measuring the detected current value on the vertical axis in FIG. 4, the electron beam 7 is deflected so that the electron beam 7 is incident on the inner wall of the beam current detecting element 23. The output of the current detection circuit 24 when entering the inner wall surface (bottom surface when the suppression material is coated) becomes the measurement value of the electron beam current value. The beam deflection amount L required for measuring the electron beam current value can be calculated from the equation (1) or (2). However, since the electron beam 7 may be displaced from the optical axis 104, the beam current amount is shown in advance. It is necessary to measure the deflection control current at which the current peak value is obtained by measuring in the deflection range as large as indicated by the arrow “beam deflection control range for reference data generation” in 4.

  In order to realize the beam deflection only in the peripheral portion including the peak as shown in FIG. 4, as described with reference to FIG. 3, a table or formula (1) describing the relationship between the beam current amount and the acceleration voltage Vacc. ) Or the proportionality constant information of the formula (2) is stored in a memory provided in the central control unit 6, and the relationship information between the beam current amount and the electron beam control voltage Vs is further stored in the memory. When measuring the beam current, the central control device 6 refers to each data stored in the memory, and makes a target deflection amount under the conditions of the currently set electron beam irradiation conditions (for example, acceleration voltage Vacc). By calculating the deflection current value or deflection voltage value for obtaining the value, and controlling the deflection control power supply 16 according to the calculated deflection current value or deflection voltage value, only the vicinity where the peak current value is obtained is scanned. Such a deflection control range is set. As a result, the beam current can be measured without being affected by the axial deviation of the electron beam 7 or the influence of the peripheral insulator 102.

  The procedure for measuring the beam current with high accuracy and high speed using the above means can be represented by the flowchart of the figure. A detailed beam current measurement and beam setting sequence is shown in the flowchart of FIG. The procedure for measuring the beam current with high accuracy and high speed using the above means is represented by the flowchart of FIG. First, the charged particle beam apparatus is started up (step S01), the apparatus parameters are set by the initial setting (step S02), and then the charged particle optical conditions are set and adjusted (step S03; hereinafter, the optical conditions are the basic optical conditions). Abbreviated condition). The basic optical conditions for changing the beam current amount include acceleration voltage, extraction voltage, beam control voltage controlled by the beam control high-voltage power supply 5, and condenser lens excitation current controlled by the convergent lens control power supply 9 and objective lens control power supply 13. There are settings such as. The basic optical conditions are set, and the amount of control current flowing through the deflection coil 14 or the voltage applied to the deflection electrode 15 is controlled by the deflection control power supply 16 to deflect the charged particle beam. In the measurement of the charged particle beam current value, the beam is deflected so as to enter the current detection element 23, and the output value in the beam current detection circuit 24 is measured. Here, the relationship between the voltage applied to the beam control high-voltage power supply 5 and the control current applied to the deflection coil 14 or the control voltage applied to the deflection electrode 15 is stored in the storage device (step S04). Using this result, the beam irradiation range is in the vicinity of the peak value of the beam current value so that the charged particle beam can be deflected so that the peak value of the beam current value can be obtained at high speed. (Step S05). The above five steps are the work of the equipment manufacturer.

  The user sets only the desired acceleration voltage and the current value of the charged particle beam from the interface when measuring the current amount of the charged particle beam or setting the current amount. Thereby, the optical condition necessary for the inspection is called from the basic optical condition (step S03) stored in the central controller 6, and the set value of the beam control high voltage power source 5 is determined. At the same time, the beam irradiation range stored in the central controller 6 is called up and the deflection control power supply 16 is set. As a result, the charged particle beam is irradiated only in the vicinity of the beam current detecting element 23, and the beam current value can be measured and set at high speed and with high accuracy (step S06).

  Next, FIG. 6 shows a current measurement flowchart in the charged particle beam apparatus. First, a desired acceleration voltage and beam current amount are selected (step S07). In accordance with the set conditions, the central controller 6 sets the control voltage and basic optical conditions to be applied to the beam control high voltage power source 5. At this time, the beam current detection element 23 connected to the ground is connected to the current detection circuit 24 (step S08), and the relationship between the set acceleration voltage and the previously acquired deflection control current amount or applied voltage is obtained. The deflection control power supply 16 is set so that the deflection range of the electron beam 7 is only in the vicinity of the groove of the beam detection element 23 (step S09). As a result, the beam deflection control range for detecting the current peak value is limited, and the beam current detection element 23 detects the peak value of the beam current within this deflection range (step S10). Thereby, since the charged particle beam can be incident on the current detection element 23 with high accuracy and instantaneously, both high-speed current measurement and high accuracy can be achieved. When setting the amount of electron beam current, after step S10, the control voltage is called from the reference data recorded in the central controller 6 so that the control voltage of the beam control high-voltage power supply 5 is changed to a desired increase / decrease. Thus, the beam current amount can be set at a high speed (step S11). Thereby, the beam current amount is measured at high speed, and the measurement result is displayed on the image display device 22 or the like (step S12). After the measurement, the beam detection element 23 is again connected to the ground, and the measurement is finished (step S13).

1 Electron Source 2 Beam Control Electrode 3 Extraction Electrode 4 Acceleration Electrode 5 Beam Control High Voltage Power Supply 6 Central Controller 7 Electron Beam 8 First Converging Lens 9 Converging Lens Control Power Supply 10 Aperture Plate 11 Second Converging Lens 12 Objective Lens 13 Objective Lens Control Power supply 14 Deflection coil 15 Deflection electrode 16 Deflection control power supply 17 Sample 18 Secondary electron 19 Reflector 20 Electron detector 21 Signal detection circuit 22 Image display device 23 Beam current detection element 24 Current detection circuit 101 Shield 102 Insulator 103 Metal component 104 optical axis

Claims (6)

In a charged particle beam apparatus including a charged particle optical system having a function of outputting a secondary signal detected by irradiating a sample with a primary charged particle beam,
The charged particle optical system includes:
A scanning deflector for scanning the sample with the primary charged particle beam;
A current detection element for measuring a current value of the primary charged particle beam deflected by the scanning deflector,
The charged particle beam device is configured to measure a beam current of the primary charged particle beam.
The charged particle beam apparatus further comprising control means for controlling the scanning deflector so that a deflection range with respect to the primary charged particle beam is started in the vicinity of a detection current peak position of the current detection element. The charged particle beam apparatus according to claim 1,
The charged particle optical system includes an electron gun capable of adjusting an acceleration voltage of the primary charged particle beam,
A charged particle beam apparatus that controls the primary charged particle beam deflection start position in accordance with the acceleration voltage. The charged particle beam apparatus according to claim 2,
The charged particle beam apparatus according to claim 1, wherein the control unit includes a table in which a deflection voltage value supplied to the scanning deflector is stored in accordance with the acceleration voltage. The charged particle beam apparatus according to claim 2,
The charged particle beam apparatus according to claim 1, wherein the control unit calculates a deflection voltage supplied to the scanning deflector based on a predetermined arithmetic expression and the acceleration voltage. The charged particle beam apparatus according to claim 1,
A charged particle beam apparatus comprising display means for displaying the measured current value of the charged particle beam. In the charged particle beam device according to any one of claims 1 to 5,
The charged particle beam device according to claim 1, wherein a shape of the current detection element is a groove shape long in an optical axis direction of the primary charged particle beam.

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