JP4146103B2 - Electron beam apparatus equipped with a field emission electron gun - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electron beam apparatus such as a scanning electron microscope, an electron probe microanalyzer, and an Auger spectrometer using a field emission electron gun as an electron beam source.
[0002]
[Prior art]
In a scanning electron microscope, an electron beam is finely focused on a sample, and a predetermined range on the sample is scanned with the electron beam. Secondary electrons are generated by irradiating the sample with an electron beam. This secondary electron is detected, and this detection signal is supplied to a cathode ray tube synchronized with the scanning of the primary electron beam to display a scanned image of the sample. I am doing so.
[0003]
In the electron probe microanalyzer, the sample is irradiated with an electron beam to detect characteristic X-rays generated from the sample. Further, the Auger spectrometer detects Auger electrons from the surface portion of the sample and measures the energy.
[0004]
In such various electron beam apparatuses, a field emission electron gun is recently used as an electron beam source with a wide variable range of irradiation current. In an electron beam apparatus such as a scanning electron microscope, an electron probe microanalyzer, an Auger spectrometer, etc., a variable range of the irradiation current amount requires an irradiation current in a wide range from picoampere order to several hundred nanoamperes.
[0005]
By the way, in order to efficiently collect the on-axis electron beam with a field emission electron gun having a small total emission current amount, it is desirable to install the first condenser lens above the anode electrode stop. In an electron beam apparatus equipped with a field emission electron gun, the resolution at a large irradiation current of nanoampere or more depends on the angular current density of the field emission electron source and the spherical aberration coefficient of the first condenser lens. It is known to deteriorate.
[0006]
Furthermore, the angular current density is determined by the field emission electron source. For this reason, in order to improve the resolution at the time of a large irradiation current, it is necessary to improve the spherical aberration coefficient of the first condenser lens. Therefore, in the conventional electron optical system using the two-stage condenser lens, the irradiation current amount is controlled by the first condenser lens, and the second condenser lens is controlled to match the optimum opening angle condition.
[0007]
[Problems to be solved by the invention]
If the first condenser lens is installed in the vicinity of the field emission emitter, the distance between the main surface of the first condenser lens and the object point is too short, making it difficult to use the first condenser lens in the real image mode. For this reason, in the conventional first condenser lens, the irradiation current is continuously controlled in the virtual image mode. In this case, the aberration coefficient of the first condenser lens that determines the resolution at the time of a large irradiation current cannot be considered. Further, when the first condenser lens is installed in the vicinity of the emitter and used in the virtual image mode, even if a two-stage condenser lens system is used, there is a restriction on the variable range of the irradiation current amount.
[0008]
The present invention has been made in view of these points, and an object of the present invention is to realize an electron beam apparatus including a field emission electron gun that can be used optimally without any difficulty in any irradiation current region. .
[0009]
The invention according to claim 1 includes a field emission emitter, an extraction electrode for extracting electrons from the emitter, an anode electrode for accelerating an electron beam emitted from the emitter, and a main surface above the anode electrode. , A magnetic field type first condenser lens for converting the electron beam extracted by the extraction electrode into a parallel beam or a real image mode beam that is more focused than the parallel state, and a second provided below the anode electrode a condenser lens, aperture angle control lens and comprises an electronic optical system having an objective lens for focusing the electron beam onto the sample, parallel beams with the electron beam by the first condenser lens or the real image mode The electron beam passes through the anode electrode and the amount of beam current is controlled by the second condenser lens. In a state, as opening angle on the specimen by focusing action by the angular aperture control lens is optimized, characterized in that it is focused on the sample by the opening angle control lens and the objective lens.
[0010]
According to the first aspect of the present invention, since the electron beam from the emitter is converted into a parallel beam or a real image mode beam by the first condenser lens, the resolution can be improved as compared with the conventional use in the virtual image mode.
[0011]
In the invention of claim 2, so as to be switched to a mode for stopping the operation of the mode substantially first condenser lens for the electron beam and the parallel beam or the real mode beam by the first condenser lens, minute The amount of current can be changed without losing resolution from the current use region to the large irradiation current irradiation region.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 and 2 show an example of an electron optical system of an electron beam apparatus according to the present invention. FIG. 1 shows a mode in which a sample is irradiated with a large current, and FIG. 2 shows a case in which a sample is irradiated with a minute current. Shows the mode.
[0015]
In FIG. 1 and FIG. 2, 1 is a field emission emitter, and 2 is an extraction electrode. Although not shown, an extraction voltage is applied between the emitter 1 and the extraction electrode 2. Reference numeral 3 denotes an anode electrode, and an acceleration voltage of an electron beam is applied between the emitter 1 and the anode electrode 3.
[0016]
A first condenser lens 4 is disposed between the extraction electrode 2 and the anode electrode 3, and a second condenser lens 5 is disposed below the anode electrode 3 .
[0017]
An objective lens aperture 6 is disposed below the second condenser lens 5, and an opening angle control lens 7 is disposed below the objective lens aperture 6. An objective lens 8 is provided below the opening angle control lens 7, and the sample 9 is irradiated with an electron beam focused by the objective lens 8.
[0018]
Although not shown, the scanning electron microscope includes a deflector for two-dimensionally scanning the electron beam EB on the sample 9. Further, a secondary electron detector for detecting secondary electrons generated by irradiation of the sample 9 with an electron beam is disposed in the vicinity of the sample 9. Furthermore, the electron probe microanalyzer is equipped with an X-ray spectrometer for spectroscopically analyzing characteristic X-rays generated by irradiating the sample with an electron beam. An electron spectrometer is attached.
[0019]
In the electron optical systems of FIGS. 1 and 2, electrons are emitted from the emitter 1 in accordance with the extraction voltage between the emitter 1 and the extraction electrode 2. Electrons from the emitter 1 are accelerated by the anode electrode 3 and finely focused on the sample 9 by the second condenser lens 5, the opening angle control lens 7, and the objective lens 8.
[0020]
In the scanning electron microscope, the electron beam EB is deflected by a deflector (not shown), and the electron beam on the sample 9 is scanned two-dimensionally. For example, secondary electrons generated by irradiation of the sample 9 with the electron beam are detected by a secondary electron detector. Although not shown, the detection signal of the detector is amplified by an amplifier and then supplied to a signal processing circuit to be subjected to signal processing such as contrast and luminance adjustment. The video signal from the signal processing circuit is supplied to the cathode ray tube 14. As a result, a secondary electron image of the sample is obtained in the cathode ray tube.
[0021]
In the electron probe microanalyzer, the characteristic X-ray generated by the electron beam irradiation to the sample 9 is guided to the spectroscopic crystal, and a spectrum corresponding to the wavelength of the characteristic X-ray is obtained. Further, in the Auger spectroscopic device, Auger electrons generated by irradiation of the sample 9 with the electron beam are guided to the energy analyzer, and energy analysis of the Auger electrons is performed.
[0022]
The state shown in FIG. 1 is set to a mode in which a sample is irradiated with a high-current electron beam. That is, in order to obtain a large irradiation current of the order of several hundred nanoamperes, it is necessary to collect electrons emitted from the emitter 1 as much as possible. It will be cut by the aperture.
[0023]
For this reason, in the present invention, as shown in FIG. 1B, the electron beam generated from the field emission emitter 1 is given a convergence property by the first condenser lens 4 slightly more than the parallel beam (solid line) or the parallel state. A real image mode beam (dotted line) is used. As a result, the electron beam limited by the anode electrode 3 can be minimized.
[0024]
Electron beam into a parallel beam or real mode beam passes through the aperture of the anode electrode 3, it is focused by the second condenser lens 5. The amount of beam current applied to the sample 9 is determined by the degree of focusing of the electron beam by the second condenser lens 5 and the aperture diameter of the objective lens aperture 6.
[0025]
The electron beam EB that has passed through the aperture of the objective lens aperture 6 is appropriately focused by the opening angle control lens 7 and is finely focused on the sample 9 by the objective lens 8. At this time, if the opening angle control lens 7 focuses the electron beam relatively strongly as shown by the solid line in the figure, the opening angle of the electron beam irradiated on the sample 9 becomes relatively small. On the other hand, if the electron beam is focused relatively weakly as indicated by the dotted line, the opening angle of the electron beam irradiated on the sample 9 becomes relatively large.
[0026]
As described above, in the mode shown in FIG. 1, the electron beam emitted from the emitter 1 is converted into a parallel beam or a real image mode beam by the first condenser lens 4, so that a large current can be obtained and the aberration coefficient can be kept low. be able to. When the electron beam is converted into a parallel beam or a real image mode beam by the first condenser lens 4, the amount of current varies depending on the relationship between the imaging position of the second condenser lens 5 and the aperture diameter of the objective lens aperture 6. Determined.
[0027]
For this reason, when the electron beam is converted into a parallel beam or a real image mode beam by the first condenser lens 4, the variable range of the current amount of the electron beam applied to the sample 9 is the angular current density of the emitter 1, the emitter 1 and the first It is determined by the distance between the first condenser lens 4 and the distance between the second condenser lens 5 and the objective lens aperture 6. In addition, the one where the distance between the emitter 1 and the 1st condenser lens 4 is short becomes easy to obtain large irradiation current amount. Further, the shorter the distance between the second condenser lens 5 and the objective lens stop 6 is, the stronger it is against disturbances.
[0028]
By the way, when the distance between the second condenser lens 5 and the objective lens diaphragm 6 is short, the second condenser lens is most excited when the distance between the second condenser lens 5 and the objective lens diaphragm 6 is short. Even so, it is impossible to obtain a weak current of picoampere order. That is, as shown in FIG. 1, when an electron beam converted into a parallel beam or a real image mode beam by the first condenser lens 4 is controlled only by the second condenser lens 5, the second condenser lens 5 is controlled. The lens 5 requires a very large magnetomotive force, which is not realistic. Further, if the distance between the second condenser lens 5 and the objective aperture 6 is increased, the height of the lens barrel increases, and it becomes easy to be affected by disturbance.
[0029]
However, since the primary cause of determining the resolution in the weak current region is the aberration of the objective lens, the resolution is not affected even if the aberration coefficient of the first condenser lens 4 is increased.
[0030]
For the above reasons, in the present invention, in the weak current region, as shown in FIG. 2, the excitation of the first condenser lens 4 is turned off, and the irradiation current is controlled only by the second condenser lens 5. ing. By such control, it is possible to always provide an optimum resolution from a weak irradiation current region of picoampere order to a large irradiation current region of several hundred nanoamperes. In FIG. 2, the excitation of the first condenser lens 4 is completely turned off, but it may be in a certain weak excitation state proportional to the acceleration voltage.
[0031]
3 and 4 are diagrams showing another embodiment of the present invention. In this embodiment, the first condenser lens 4 is disposed below the anode electrode 3. FIG. 3 is a ray diagram at the time of irradiation with a large current, and FIG. 4 is a ray diagram at the time of irradiation with a minute current. 1 and 2, the main surface of the first condenser lens 4 is provided on the anode electrode 3. However, various restrictions such as the structure and heat resistance of the first condenser lens are required for this purpose. Although this occurs, such a restriction is alleviated in the structure of FIGS.
[0032]
【The invention's effect】
As described above, in the electron beam apparatus provided with a field emission electron gun based on the first aspect of the invention, the first condenser lens, because the electron beam from the emitter into parallel beams or real mode beam, conventional The resolution can be improved compared to the use in the virtual image mode.
[0033]
In the invention of claim 2, the first condenser lens can be switched between a mode in which the electron beam is a parallel beam or a real image mode beam and a mode in which the operation of the first condenser lens is substantially stopped. The amount of current can be varied without impairing the resolution from the region where the minute current is used to the region where the large irradiation current is irradiated.
[Brief description of the drawings]
FIG. 1 is a diagram showing a ray diagram when an electron beam apparatus according to the present invention is irradiated with a large current.
FIG. 2 is a diagram showing a light ray diagram of the electron beam apparatus according to the present invention when a minute current is irradiated.
FIG. 3 is a diagram showing a light ray diagram when an electron beam apparatus according to the present invention is irradiated with a large current.
FIG. 4 is a view showing a light ray diagram when an electron beam apparatus according to the present invention is irradiated with a minute current.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Emitter 2 Extraction electrode 3 Anode electrode 4 1st condenser lens 5 2nd condenser lens 6 Objective lens diaphragm 7 Opening angle control lens 8 Objective lens 9 Sample

Claims (2)

A field emission emitter; an extraction electrode for extracting electrons from the emitter; an anode electrode for accelerating an electron beam emitted from the emitter; and an electron extracted by the extraction electrode with a main surface located above the anode electrode Magnetic field type first condenser lens for converting the beam into a parallel beam or a real image mode beam that is more focused than a parallel state, a second condenser lens provided below the anode electrode, and opening angle control a lens provided with an electronic optical system having an objective lens for focusing the electron beam on the sample, is the first condenser lens such that the electron beam and the parallel beam or the real mode beam, the electron beam passes through the anode electrode, the second condenser lens in a state where the amount of beam current is controlled, the opening angle control As opening angle on the specimen is optimal by focusing action by lens, the electron beam apparatus provided with a field emission electron gun, characterized in that it is focused on the sample by the opening angle control lens and the objective lens.   2. A mode in which an electron beam is converted into a parallel beam or a real image mode beam and a mode in which the operation of the first condenser lens is substantially stopped can be switched by the first condenser lens. An electron beam apparatus comprising the field emission electron gun described.

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