JP2004178980A - Electron microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve accuracy by simplifying procedures for complicated energy calibration necessary at spectral measurement by EELS (Electron Energy Loss Spectroscopy). <P>SOLUTION: By arranging in free detachment a standard matter 16 with a known composition made in a thin-film shape on a light path of electron beams transmitting a sample 9, an EELS spectrum is obtained in the form of an EELS spectrum of the sample 9 and that of the standard matter 16 overlapped. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a means for improving the analysis accuracy when performing a composition analysis of a sample using an electron energy loss spectroscopy (EELS) device attached to an electron microscope.
[0002]
[Prior art]
Generally, when an electron probe is used to irradiate a thin film sample with an electron microscope, the irradiated electrons are ionized by atoms constituting the sample (inelastic scattering). At that time, the incident electrons lose energy peculiar to the atomic species. By splitting this electron beam, an electron beam energy loss spectroscopy (EELS) spectrum is obtained in which the vertical axis represents electron intensity and the horizontal axis represents loss energy, and a peak is formed at a specific loss value of the spectrum. Qualitative analysis can be performed because the loss energy value indicated by the spectrum peak has a value specific to the atomic species. In addition, information on the bonding state can be obtained from the shape of the peak.
[0003]
[Problems to be solved by the invention]
Recently, it has been routine to narrow an electron beam with an electron microscope and measure an EELS spectrum from a sample region having a diameter of about 1 nm. Even if an EELS spectrum is obtained from a very small area of a sample, it often happens that it is difficult to calibrate the energy loss of the spectrum due to the absence of a known substance.
[0004]
Conventionally, in order to calibrate the energy of the EELS spectrum of a sample, after measuring the sample, replace the sample with a substance having a known composition, obtain an EELS spectrum, and calibrate the energy loss of the spectrum of the sample from the EELS spectrum. And complicated operations were required. The measurement conditions sometimes changed with the passage of time during that time. Further, it is necessary to calibrate the energy loss each time the dispersion of the spectrum is changed or the measurement energy range is changed.
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the related art, and has as its object to simplify a complicated energy calibration procedure required for measuring an EELS spectrum and improve the accuracy thereof.
[0005]
[Patent Document 1]
JP-A-58-178948 [Patent Document 2]
JP-A-7-21967
[Means for Solving the Problems]
In the present invention, a thin film of a standard substance having a known composition is disposed on the image plane of the lens on the optical path of the electron beam transmitted through the sample in a detachable manner, and the EELS spectrum of the sample and the spectrum of the standard substance are measured. The object is achieved by performing loss energy calibration by acquiring an EELS spectrum in a superimposed form.
[0007]
That is, the electron microscope according to the present invention comprises an electron gun for generating an electron beam, a sample stage for holding the sample, and an electron beam generated from the electron gun for focusing and deflecting the electron beam on the sample held on the sample stage. An electron microscope including an irradiation system for irradiating a desired position, an imaging system having an objective lens to form an enlarged image of the sample, and an electron beam spectrometer for measuring an energy loss spectrum of an electron beam transmitted through the sample. A thin film having a known composition is set as a standard sample on an optical path between an objective lens and an electron beam spectrometer, and electron beam energy loss spectral spectra of the sample and the standard sample are simultaneously obtained. The standard sample is preferably installed at the selected area aperture position.
[0008]
The standard sample can be installed by inserting a holder having at least one pair of holes having the same diameter and a thin film used as the standard sample in one of the holes on the optical axis. The standard sample may be held on a transmission electron microscope observation sample grid. As the standard sample, one of a plurality of standard samples arranged on the holder may be selected and used. Also, a plurality of types of thin films having known compositions may be simultaneously provided as a standard sample on the optical path between the objective lens and the electron beam spectrometer.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic longitudinal sectional view showing an example of the analytical electron microscope according to the present invention.
An electron beam 2 generated by the electron gun 1 is accelerated to a desired acceleration voltage by an acceleration voltage supplied from a high voltage power supply 4 toward an anode 3, and an irradiation lens 6 driven by an irradiation lens driving power supply 5, The light is converged by an objective lens 8 driven by an objective lens driving power supply 7 and is irradiated on a thin film sample 9 (hereinafter, sample 9). At this time, the electron beam 2 is irradiated to a desired analysis spot on the sample 9 by the electron beam deflection coil 11 driven by the electron beam deflection coil drive power supply 10.
[0010]
The transmitted electrons 12 transmitted through the sample 9 are enlarged by the objective lens 8, and an enlarged image 13 is formed between the first projection lens 15 driven by the imaging lens driving power supply 14 and the objective lens 8. Usually, a selected area stop is placed at a position where the enlarged image 13 is formed. An electron diffraction image having information on the entire area irradiated by the electron beam 2 is formed between the sample 9 and the enlarged image 13. When the electron beam is allowed to pass, it is possible to extract an electron beam diffraction image of the area of the enlarged image selected by the selected area stop from the electron beam diffraction image having information on the entire electron beam irradiation area.
[0011]
When the electron beam 2 passes through the sample 9, energy loss occurs due to atoms constituting the sample 9, and the electron beam 12 having lost a specific energy also participates in the formation of the enlarged image 13. The enlarged image 13 of the objective lens 8 and the object plane of the first projection lens 15 match, and the enlarged image 13 of the objective lens 8 is further enlarged by the first projection lens 15. A standard sample 16 made of an amorphous carbon thin film is loaded and inserted into the standard sample holder 17 on the image plane on which the enlarged image 13 is formed.
[0012]
2A and 2B are schematic views showing an example of the shape of the tip of the standard sample holder. FIG. 2A is a plan view, and FIG. The tip of the sample holder 17 is made of a Mo plate having a thickness of about 100 μm, and four holes having a diameter of 3 mm, 1 mm, 0.3 mm, and 0.1 mm are provided in two rows. A hole of one row is covered with an amorphous carbon film having a thickness of about 100 nm, and this amorphous carbon film becomes the standard sample 16. Each of the four types of holes or the standard sample 16 provided at the tip of the sample holder 17 also has a role of a selected area stop, and a hole diameter to be selected is selected depending on which region of the EELS spectrum is to be acquired. You. In the sample holder 17 shown in FIG. 2, the four holes having different hole diameters are provided so that the hole diameter can be selected according to the size of the region on the sample to be measured. Is not limited to four types, and may be more or less than four types.
[0013]
The standard sample holder 17 is movable in the horizontal direction with respect to the optical axis, and can be moved in and out of the optical axis from outside the vacuum. By inserting the standard sample 16 at the image plane position of the enlarged image 13, the electron beam 12 forming the enlarged image 13 including the electron beam that has lost the energy in the sample 9 further passes through the standard sample 16. Energy loss occurs again because of the excitation of the amorphous carbon. In other words, according to this arrangement, the actual installation positions of the sample 9 and the standard sample 16 are different, but the values are the same as those in which both are installed at the same position in terms of electron optics.
[0014]
The electron beam transmitted through the standard sample 16 is adjusted by an imaging lens 18 and enters an electron beam spectroscope 19. The trajectory of the transmission electron beam 12 is bent by 90 ° by the magnetic field of the sector coil 21 driven by the sector drive power supply 20 of the electron beam spectroscope 19. Among the transmitted electrons 12, the electron beam 22 that has been elastically scattered and did not lose energy during transmission through the sample 9 and the standard sample 16 retains the energy of the accelerating voltage as it is, so that it is the outermost in the electron beam spectrometer 19 And enters the phosphor detector 23 through the orbit. Since the trajectory of the electron beam 24 whose energy has been lost due to inelastic scattering is smaller than that of the elastic scattered electrons, the image is formed inside the electron beam spectroscope 19, so that the EELS as shown in FIG. The spectrum is formed on the phosphor detector 23. The EELS spectrum is converted into an electric signal by a photodiode array 25 disposed on the back side of the phosphor detector 23, amplified by an amplifier 26, sent to an EELS control unit 27, and displayed on a CRT 28.
[0015]
FIG. 4 is a schematic diagram of an EELS spectrum measured by the analytical electron microscope shown in FIG. When the position of the standard sample holder 17 having the tip shown in FIG. 2 is adjusted so that the electron beam passes through the hole on which the amorphous carbon thin film is stuck, the EELS spectrum a shown in FIG. 4 is obtained. Using the fact that the energy loss value of the carbon peak appearing in the EELS spectrum a is 284 eV, the loss energy values of other peaks on the same EELS spectrum are calibrated. When acquiring the EELS spectrum of the sample alone for some reason, immediately after acquiring the EELS spectrum a, the position of the standard sample holder 17 is adjusted under the same measurement conditions, and the electron beam is irradiated with the amorphous carbon of the standard sample holder 17. The thin film is allowed to pass through the holes that are not stretched. Thus, the EELS spectrum b shown in FIG. 4 is obtained.
[0016]
FIG. 5 is a schematic plan view showing another example of the tip of the standard sample holder according to the present invention. In the standard sample holder of this example, three holes each having a different diameter are provided at the tip of the holder, an amorphous carbon thin film is attached to one hole for each diameter, and the other hole is attached to another hole. Is a film in which an amorphous silicon nitride thin film is adhered, and the other one hole is left as it is without being attached. When the standard sample holder shown in FIG. 5 is used, another standard sample can be used only by selecting a hole without exchanging a tip portion. Even when 284 eV of carbon is required as a standard sample, it can be used as a standard sample. Further, it can cope with a case where 402 eV of nitrogen having a high loss energy is required.
[0017]
FIG. 6 is a schematic plan view showing another example of the tip of the standard sample holder according to the present invention. The tip of the standard sample holder of this example is one in which two types of standard sample thin films are adhered to one hole, and the energy loss peaks of the two standard samples can be obtained simultaneously. For example, when an amorphous carbon film and a manganese oxide thin film are used as a standard sample, energy loss peaks of 284 eV of carbon and 640 eV of manganese are simultaneously obtained in the EELS spectrum as shown in FIG. Therefore, by utilizing the fact that the loss energy values of the two peaks of carbon and manganese are known, the energy calibration of the measurement spectrum can be performed, and the loss energy value of the unknown peak on the EELS spectrum of the measurement sample can be corrected. .
[0018]
Still another example of the standard sample holder according to the present invention will be described with reference to FIGS. FIG. 8 is a schematic diagram of a mesh attaching portion at the tip of the standard sample holder, and FIG. 9 is a schematic diagram showing a state where a mesh is attached to the mesh attaching portion.
When an existing transmission electron microscope sample having a known composition is used as a standard sample, it is not necessary to prepare a standard sample for loss energy calibration. Therefore, a standard sample holder having a tip as shown in FIG. 8 is used. A typical mesh for a transmission electron microscope sample has a diameter of 3 mm and a thickness of 20 to 50 μm. A counterbore with a diameter of about 3.2 mm and a depth of about 100 μm is placed at the tip of the standard sample holder so that the mesh can be inserted. A mesh carrying a transmission electron microscope sample used as a standard sample is placed in the counterbore, and the end of the mesh is adhered and fixed to the tip of the standard sample holder with a carbon paste as shown in FIG. 9, and measured by the method described above. I do. According to this embodiment, it is not necessary to prepare a standard sample by using an existing transmission electron microscope sample as the standard sample.
[0019]
FIG. 10 is a schematic longitudinal sectional view showing another example of the analytical electron microscope according to the present invention. An electron beam 2 generated by the electron gun 1 is accelerated to a desired acceleration voltage by an acceleration voltage supplied from a high voltage power supply 4 toward an anode 3, and an irradiation lens 6 driven by an irradiation lens driving power supply 5, The light is converged by an objective lens 8 driven by an objective lens driving power supply 7 and is irradiated on a thin film sample 9 (hereinafter, sample 9). At this time, the electron beam 2 is irradiated to a desired analysis spot on the sample 9 by the electron beam deflection coil 11 driven by the electron beam deflection coil drive power supply 10. The transmitted electrons 12 transmitted through the sample 9 are enlarged by the objective lens 8, and an enlarged image 13 is formed between the first projection lens 15 driven by the imaging lens driving power supply 14 and the objective lens 8. When the electron beam 2 passes through the sample 9, energy loss occurs due to atoms constituting the sample 9, and the electron beam 12 having lost a specific energy also participates in the formation of the enlarged image 13. The enlarged image 13 of the objective lens 8 and the image plane of the first projection lens 15 coincide with each other, and the enlarged image 13 of the objective lens 8 is further enlarged by the first projection lens 15. An enlarged image 30 by the first projection lens 15 is similarly formed between the second projection lens 29 and the second projection lens 29.
[0020]
The standard sample 16 made of an amorphous carbon thin film is loaded and inserted into the standard sample holder 31 on the image plane on which the enlarged image 30 is formed. The standard sample holder 31 is rotatable about an axis perpendicular to the optical axis, and is inserted into the optical axis or retracted off-axis by being operated and rotated from outside the vacuum.
[0021]
By inserting the standard sample 16 at this position, when the electron beam 12 forming the magnified image 30 including the electron beam that has lost energy in the sample 9 further transmits the standard sample 16, amorphous carbon is removed. Due to the excitation, energy loss occurs again. This means that the positions where the sample 9 and the standard sample 16 are actually placed are different from each other, but that the values are the same as those placed at the same position in terms of electron optics. Thereafter, these electron beams are adjusted by the imaging lens 18 and are incident on the electron beam spectroscope 19, and the EELS spectrum is obtained in the same manner as in the above-described embodiment.
[0022]
【The invention's effect】
According to the present invention, there is no need to replace the measurement sample and the standard sample, and complicated energy loss calibration is simplified. Further, since the spectrum of the standard sample completely overlaps the EELS spectrum of the measurement sample, the calibration accuracy is improved.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view showing an example of an analytical electron microscope according to the present invention.
FIG. 2 is a schematic view showing an example of the shape of the tip of a standard sample holder.
FIG. 3 is a schematic diagram of an EELS spectrum.
FIG. 4 is a schematic diagram of an EELS spectrum measured by the analytical electron microscope of the present invention.
FIG. 5 is a schematic plan view showing another example of the tip of the standard sample holder according to the present invention.
FIG. 6 is a schematic plan view showing another example of the tip of the standard sample holder according to the present invention.
FIG. 7 is a schematic view of another example of the EELS spectrum measured by the analytical electron microscope of the present invention.
FIG. 8 is a schematic view of a mesh attachment portion of a standard sample holder.
FIG. 9 is a view showing a state where a mesh is attached to a standard sample holder.
FIG. 10 is a schematic longitudinal sectional view showing another example of the analytical electron microscope according to the present invention.
[Explanation of symbols]
1: electron gun, 2: electron beam, 3: anode, 4: high voltage power supply, 5: irradiation system lens driving power supply, 6: irradiation system lens, 7: objective lens driving power supply, 8: objective lens, 9: thin film sample, 10: electron beam deflection coil drive power supply, 11: electron beam deflection coil, 12: transmitted electron, 13: enlarged image, 14: imaging lens drive power supply, 15: first projection lens, 16: standard sample (amorphous Carbon thin film), 17: standard sample holder, 18: imaging lens, 19: electron beam spectrometer, 20: sector drive power supply, 21: sector, 22: elastic scattered electron, 23: phosphor detector, 24: non-conductive Elastic scattering electrons, 25: photodiode array, 26 amplifier, 27: EELS control unit, 28: CRT, 29: second projection lens, 30: enlarged image, 31: standard sample holder

Claims (6)

An electron gun for generating an electron beam, a sample stage for holding a sample, and an irradiation system for converging and deflecting the electron beam generated from the electron gun to irradiate a desired position on the sample held by the sample stage And, in an electron microscope equipped with an imaging system having an objective lens and forming an enlarged image of the sample, and an electron beam spectrometer for measuring the energy loss spectrum of the electron beam transmitted through the sample,
An electron, wherein a thin film having a known composition is set as a standard sample on an optical path between the objective lens and the electron beam spectrometer, and electron beam energy loss spectral spectra of the sample and the standard sample are simultaneously obtained. microscope. 2. The electron microscope according to claim 1, wherein the standard sample is set at a selected area stop position. 3. The electron microscope according to claim 1, wherein a holder having at least one pair of holes having the same diameter and a thin film used as the standard sample adhered to one of the holes is inserted on the optical axis. Electron microscope. 3. The electron microscope according to claim 1, wherein the standard sample is held on a transmission electron microscope observation sample grid. 3. The electron microscope according to claim 1, wherein one of a plurality of standard samples arranged on a holder is selected and used as the standard sample. 3. The electron microscope according to claim 1, wherein a plurality of thin films of known compositions are simultaneously installed as a standard sample on an optical path between the objective lens and the electron beam spectrometer.

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