JP2011129257A - Slit position control method and device of monochromator, as well as analytical electron microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a slit position control method and its device of a monochromator enabled to carry out adjustment of a monochromator in a short time, in the slit position control device of a monochromator. <P>SOLUTION: The monochromator including an energy filter for generating energy dispersion by receiving incident charged particle beams, and extracting electron beams with a desired energy width through energy selecting slits fitted on an energy dispersion surface, is structured having a current detection means 4 for detecting a current flowing in the energy selecting slits 22, and a slit position control means 5 for controlling a position of the energy selecting slits 22 so as to have the current value detected by the current detection means 4 minimum. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a monochromator slit position control method and apparatus and an analytical electron microscope, and more particularly to a monochromator slit position control method and apparatus and an analytical electron microscope that enable electron energy loss spectroscopy with high energy resolution.

  With the miniaturization and miniaturization of semiconductor devices and magnetic head elements, it is necessary to analyze a minute region, and observation with an electron microscope has become important. By reducing the energy width of the incident electron beam with an energy filter device (also called a monochromator), the electron beam probe on the sample surface can be reduced, and the spatial resolution of the electron microscope can be improved.

  The energy filter device is a device that causes an incident charged particle, for example, an electron beam to act on a magnetic field or an electric field to cause energy dispersion and takes out an electron beam having a desired energy width using a slit installed on the energy dispersion surface. It is. The intensity of the magnetic field and electric field of the energy spectroscopic unit, which mainly has an energy spectroscopic unit for causing energy dispersion, a slit unit having an opening for transmitting an electron beam with a width of several μm to several tens of mm in the direction of energy dispersion. It is comprised by the spectrum control part which controls.

  In SEM and STEM, it is necessary to reduce the size of the electron probe in order to improve the spatial resolution. Thus, by dispersing the energy of the electron beam emitted by the energy filter and selecting the electron beam with the slit, the energy width of the electron beam can be reduced and the electron probe can be reduced.

  TEM and STEM are devices that disperse energy of an electron beam transmitted through a sample, select an electron beam with a slit, and form an image with the selected electron beam for observation. When the electron beam passes through the sample, an energy loss inherent to the element occurs due to the interaction with the element constituting the sample. Electron Energy Loss Spectroscopy (EELS), which analyzes the energy of electrons transmitted through a sample with an electron spectrometer, is an analysis method that can perform elemental analysis in a sample. Further, even for the same element, it appears as an energy shift of about several eV, reflecting the chemical bonding state of the element (particularly the difference in the electronic structure of the element). By selecting an electron beam with high accuracy, high-accuracy measurement is possible.

  A monochromator (energy filter device) forms an electron beam that is dispersed by the energy filter and forms a spectrum on the slit, and selectively passes the electron beam through a slit having a certain width. Make the line monochromatic. Here, monochromatization means selecting an electron beam having a certain energy width. Since the monochromator selectively allows only an electron beam having a certain energy to pass through the slit, the amount of beam current is reduced. A decrease in the amount of beam current results in a decrease in the brightness of the electron beam, which greatly affects the performance of the analytical electron microscope.

  Therefore, it is necessary to suppress the decrease in the beam current amount by the monochromator as much as possible. In order to ensure high energy resolution, which is the basic performance of the monochromator, and to suppress the decrease of the electron beam, the position of the energy selection slit is set so that the beam current passing through the slit with a certain width is maximized. Need to be optimized.

  As a conventional device of this type, when the electron beam deviates from the center of the opening of the slit, the deviation is corrected with high accuracy based on the intensity of secondary electrons generated from the sample or the like, and the center of the opening of the slit is corrected. There is known an apparatus for observing a sample using an electron beam transmitted through (see, for example, Patent Document 1).

JP 2007-266016 A (paragraphs 0029 to 0035, FIG. 1)

  The adjustment of the installation position of the energy selection slit in the conventional monochromator largely depends on the operator. The operator determines the increase / decrease of the current amount from the difference in the brightness of the beam by direct observation of the beam, and determines the installation position of the slit. In this case, it is difficult to quantitatively evaluate the installation position of the energy selection slit, and there is no guarantee that the energy selection slit is at an optimal position.

  Another possible method is to measure the beam that has passed through the energy selection slit in a Faraday cup or the like with an ammeter and adjust the installation position of the energy selection slit. In this case, all the beams that have passed through the slit are absorbed by the Faraday cup, and the shape of the beam cannot be directly observed. Adjustment of the monochromator requires adjustment of the energy filter while directly observing the beam shape, and adjustment of the position of the energy selection slit. When the conditions of the energy filter are changed, the beam current after inserting the Faraday cup is changed. It is cumbersome to measure the amount, and the operator is burdened with further operations. In addition, it takes a long time to adjust the monochromator and it is difficult to say that the device is easy to use.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a monochromator slit position control method and apparatus, and an analytical electron microscope that can adjust the monochromator in a short time. It is said.

In order to solve the above-described problems, the present invention has the following configuration.
(1) The invention according to claim 1 includes an energy filter that receives an incident charged particle beam and causes energy dispersion, and electrons having a desired energy width through an energy selection slit provided on the energy dispersion surface. In the monochromator in which a line is taken out, the current flowing through the energy selection slit is detected, and the position of the energy selection slit is controlled so that the detected current value is minimized.

  (2) The invention according to claim 2 has an energy filter that receives the incident charged particle beam and causes energy dispersion, and has electrons having a desired energy width through an energy selection slit provided on the energy dispersion surface. In a monochromator configured to take out a line, a current detection unit that detects a current flowing through the energy selection slit, and a slit that controls a position of the energy selection slit so that a current value detected by the current detection unit is minimized. And a position control means.

  (3) The invention according to claim 3 receives an electron beam transmitted through the energy selection slit and generates an optical signal corresponding to the intensity of the electron beam, and receives an output of the fluorescent plate as an electrical signal. A photoelectric conversion unit for converting, and a filter control unit that receives the output of the photoelectric conversion unit and controls the current and / or voltage of the energy filter so that the image received by the fluorescent plate becomes a perfect circle. It is characterized by that.

  (4) The invention according to claim 4 includes the energy filter according to claim 2 or 3 and an energy selection slit therein, and enables electron energy loss spectroscopy with high energy resolution by operating as a monochromator. It is characterized by doing.

The present invention has the following effects.
(1) According to the first aspect of the invention, the position of the energy selection slit is controlled so that the current flowing through the energy selection slit is minimized, that is, the current passing through the energy selection slit is maximized. The monochromator can be adjusted in a short time.

  (2) According to the second aspect of the present invention, the position of the energy selection slit is controlled so that the current flowing through the energy selection slit is minimized, that is, the current passing through the selection slit is maximized. The meter can be adjusted in a short time.

  (3) According to the invention described in claim 3, since the current and / or voltage of the energy filter is controlled so that the image received by the fluorescent screen becomes a perfect circle, the energy filter can be optimized.

  (4) According to the invention described in claim 4, electron energy loss spectroscopy with high energy resolution can be realized by including an energy filter and an energy selection slit in the inside thereof and acting as a monochromator.

It is a block diagram which shows one Example of this invention. It is a figure which shows energy distribution of an electron beam. It is explanatory drawing of energy filter optimization.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. The apparatus shown in the figure has an energy filter that receives an incident charged particle beam and causes energy dispersion, and takes out an electron beam having a desired energy width through an energy selection slit installed on the energy dispersion surface. Constitutes a monochromator.

  In the figure, 1 is a lens barrel, and 2 is a monochromator provided in the lens barrel 1. The monochromator 2 includes an energy filter 21 and an energy selection slit 22. The energy filter 21 may be of any type as long as it can perform electron beam dispersion. For example, an Ω filter or a Wien filter is used. The energy selection slit 22 is formed to be movable in a direction indicated by an arrow in the drawing. Reference numeral 3 denotes a filter power source that provides operating power to the energy filter 21, and 4 denotes a current detector that detects a current flowing through the energy selection slit 22. For example, an ammeter is used as the current detector 4.

  Reference numeral 5 denotes a slit position control means for controlling the movement of the energy selection slit so that the current flowing through the current detector 4 is minimized. Reference numeral 6 denotes a fluorescent plate that receives an electron beam passing through the slit of the energy selection slit 22 and converts it into an optical signal. Reference numeral 7 denotes a photoelectric conversion unit that converts a signal emitted from the fluorescent plate 6 into an electric signal. A monitor 8 receives the output of the photoelectric conversion unit 7 and displays an electron beam image. As the monitor 8, for example, a CRT or a liquid crystal display is used.

  A filter control unit 9 receives the output of the photoelectric conversion unit 7 and controls the energy filter 21 so that the image displayed on the monitor 8 changes from an ellipse to a perfect circle, and 10 indicates that the image displayed on the monitor 8 is It is an operation part for operating the filter control part 9 so that it may become a perfect circle. As the operation unit 10, a keyboard, a knob, or the like is used. The filter control unit 9 controls the current and / or voltage of the energy filter 21. The operation of the apparatus configured as described above will be described as follows.

  In order for the monochromator to operate normally, it is necessary that the energy filter 21 is optimized and the position of the energy selection slit 22 is optimized. The energy selection slit 22 is installed on the optical axis 11. The ammeter 4 is connected between the energy selection slit 22 and the ground, and detects the current flowing through the energy selection slit 22.

  In order for the monochromator 2 to measure the dispersion of the electron beam in an optimum state, the electron beam needs to pass through the slit of the energy selection slit 22 with the maximum current value. FIG. 2 is a diagram showing the energy distribution of the electron beam. The horizontal axis is energy, and the vertical axis is electron beam intensity. ΔE in the figure is a half width, for example, about 0.7 to 1.0 eV. In order for the monochromator 2 to measure the optimum energy dispersion, the apex partial region ΔE ′ of the electron beam energy needs to pass through the slit.

  When the center region ΔE ′ of the electron beam passes through the energy selection slit 22, the maximum current passes, and when the skirt of FIG. 2 passes through the energy selection slit 22, the current becomes smaller and energy The current flowing through the selection slit 22 increases. In order for the monochromator 2 to operate in the optimum state, the electron beam needs to pass through the slit portion of the energy selection slit 22 at the maximum value.

  Therefore, the slit position control means 5 drives a slit position moving device for the energy selection slit 22 (not shown) so that the current value of the ammeter 4 is minimized. The slit position control means 5 drives the slit position moving device and stops the operation when the current value of the ammeter 4 becomes minimum. With this configuration, the position of the energy selection slit 22 is controlled so that the current flowing through the energy selection slit 22 is minimized, that is, the current passing through the selection slit is maximized. Can be performed in a short time. The current flowing through the ammeter 4 may be displayed on the monitor 8.

  Next, optimization of the energy filter 21 will be described. In a normal state, the waveform observed on the monitor 8 is elliptical as shown in FIG. When the energy filter 21 is optimized, the waveform observed by the monitor 8 becomes a perfect circle as shown in FIG. Therefore, the operator adjusts the knob of the operation unit 10 so that the elliptical waveform becomes a perfect circular waveform while observing the waveform shown on the monitor 8.

  When the knob of the operation unit 10 is adjusted, the adjustment signal is given to the filter control unit 9. The filter control unit 9 controls the voltage and / or current in the energy filter 21 according to the adjustment signal from the operation unit 10. As a result, the waveform displayed on the monitor 8 becomes a perfect circle. Thus, according to the present invention, since the current and / or voltage of the energy filter is controlled so that the image received by the fluorescent plate becomes a perfect circle, the energy filter can be optimized.

  An analysis electron microscope that enables electron energy loss spectroscopy with high energy resolution can be realized by including the energy filter and the energy selection slit configured as described above and acting as a monochromator.

  As described above, according to the present invention, it is possible to provide a monochromator slit position control method and apparatus, and an analytical electron microscope capable of adjusting the monochromator in a short time.

DESCRIPTION OF SYMBOLS 1 Lens tube 2 Monochromator 3 Filter power supply 4 Ammeter 5 Slit position control means 6 Fluorescent screen 7 Photoelectric return part 8 Monitor 9 Filter control part 10 Operation part 11 Optical axis 21 Energy filter 22 Energy selection slit

Claims (4)

In a monochromator that has an energy filter that receives an incident charged particle beam and causes energy dispersion, and takes out an electron beam having a desired energy width through an energy selection slit installed on the energy dispersion surface.
Detecting a current flowing through the energy selection slit;
Controlling the position of the energy selection slit so that the detected current value is minimized,
A method for controlling the slit position of a monochromator characterized by the above. In a monochromator that has an energy filter that receives an incident charged particle beam and causes energy dispersion, and takes out an electron beam having a desired energy width through an energy selection slit installed on the energy dispersion surface.
Current detection means for detecting a current flowing through the energy selection slit;
Slit position control means for controlling the position of the energy selection slit so that the current value detected by the current detection means is minimized;
A slit position control device for a monochromator. A fluorescent screen that receives an electron beam transmitted through the energy selection slit and generates an optical signal corresponding to the intensity of the electron beam;
A photoelectric conversion unit that receives the output of the fluorescent plate and converts it into an electrical signal;
Filter control means for receiving the output of the photoelectric conversion unit and controlling the current and / or voltage of the energy filter so that the image received by the fluorescent screen becomes a perfect circle;
The slit position control device for a monochromator according to claim 2, further comprising:   4. An analytical electron microscope comprising the energy filter according to claim 2 or 3 and an energy selection slit therein, and allowing electron energy loss spectroscopy with high energy resolution by functioning as a monochromator.

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