JPS5840527Y2 - Magnetic shielding device for X-ray microanalyzer - Google Patents

Description

[Detailed description of the invention] This invention relates to a magnetic shielding device for an X-ray microanalyzer, which reduces the influence of an external magnetic field on the electron beam flux by magnetically shielding the X-ray microanalyzer, thereby obtaining a stable electron beam flux. It is something.

X-ray microanalyzer, specifically electron loop X-ray microanalyzer (hereinafter abbreviated as EPMA)
The method focuses the electron beam from an electron gun to a diameter of 1 μm or less using an electromagnetic lens, projects it onto the surface of the sample, and collects characteristic X-rays, continuous X-rays, and backscattered electron beams emitted from minute parts of the sample. It is an analytical instrument that uses the absorbed electron beam absorbed in the sample to obtain various information such as qualitative and quantitative analysis of this minute part and the distribution state of elements.

In EPMA, the electron beam beam must be projected onto a very narrow and limited range of the sample, so the projection position of the electron beam must be affected by changes in various external conditions and In particular, the condition that it does not move due to fluctuations in the external magnetic field must be met.In particular, as analysis by EPMA is being used recently, the external environment may not be ideal. This eliminates the need to suppress the positional movement of the electron beam, that is, the deviation of the projection position, which is caused by external magnetic fluctuations caused by the presence of high-voltage transformers, high-frequency oscillators, high-voltage conductors, etc. in the vicinity, in addition to geomagnetic fluctuations. It's coming.

For example, even when there is little variation in the external magnetic field, the
．． An example has also been reported in which a deviation in the projection position of an electron beam flux of 2μ was measured.

Even if such a minute deviation of the projection position occurs, a portion of the sample other than the specified position and adjacent to the specified position will also be measured, causing an inconvenience.

As shown in Figure 1, the EPMA includes an electron gun 1, an anode 2,
Electromagnetic convergence lens 3, aperture 4, astigmatism correction coil 5.4
5° reflector 6.2 Its holding cylinder 7 indicated by a dotted chain line, curved reflectors 9 and 10 for optical observation, an optical observation system enclosed by a dotted line including an optical microscope 11, an electromagnetic deflection coil 12, and an electromagnetic objective lens 13 , an analysis sample 14, an X-ray spectroscopy crystal 15, an X-ray detector 16, a secondary electron backscattered electron detector 17, an ammeter 18 for detecting absorbed electron beams, and other electron optical systems and an X-ray spectroscopy system are precisely incorporated. ing.

In this conventional apparatus, a method is taken to prevent the influence of an external magnetic field on the electron beam flux.

That is, the reflecting mirror holding cylinder itself, which also serves as a path for the electron beam flux, is made of a soft magnetic material with high initial permeability, or it is made of the same soft magnetic material that is coaxially arranged integrally with the holding cylinder. In this method, a diaphragm cylinder is provided.

It is said that by taking such measures against fluctuations in the external magnetic field, the deviation in the projection position of the electron beam flux in the case where the fluctuation in the external magnetic field is small is corrected to about 0.06 μ.

For an electron beam that is focused to a diameter of 1 μm or less, for example, about 0.3 μm, even this corrected amount of deviation becomes a considerable amount.

There is a gap in the optical observation system surrounded by the dotted line in Figure 1, and this gap is where the electron beam is projected onto the sample 14, and the characteristic X-rays emitted from it are extracted, thereby allowing some elements to be detected. It is open for multi-channel analysis in which multiple X-ray spectroscopic systems are arranged around the sample 14 so that they can be analyzed simultaneously.
In order to improve the analytical performance of A, the X-ray extraction angle θ is set to be as large as, for example, 52.5°.

Therefore, it has conventionally been considered difficult to shield the gap with a soft magnetic material without interfering with the extraction of X-rays.

In view of the above-mentioned current situation, this invention aims to further reduce the influence of external magnetic fields on the electron beam flux, and attempts to apply a magnetic shield to the gap so as not to interfere with the extraction of X-rays. Above the electromagnetic objective lens 13, there is an outer magnetic shield made of a soft magnetic material such as permalloy having a high initial permeability, which has an inverted truncated conical shape and has a constant height along the extended surface of the mortar-shaped opening, and a curved surface. The lower end of the periphery of the reflector holder has the same shape as described above with a smaller opening angle than the shield and its height is kept to such an extent that it does not enter the objective lens magnetic field, and an inner magnetic field made of the same material as described above. X-ray shields are added to each of these, and the deviation of the projection position of the electron beam on the sample surface in conventional equipment can be further suppressed by the external magnetic shield without reducing the X-ray extraction angle.
This applies to magnetic shielding devices for line microanalyzers.

Next, an embodiment of the magnetic shielding device for an X-ray microanalyzer according to this invention will be described based on the drawings.

FIG. 2 is a partial vertical cross-sectional view of the EPMA equipped with this device, showing the upper and lower parts of the optical observation system shown in a frame surrounded by dotted lines in FIG. 1.

Parts with the same numbers in the figures as those in FIG. 1 indicate the same parts.

Note that 19, which is not shown in FIG. 1, is an electron beam scanning coil.

In FIG. 2, 5 is an astigmatism correction coil, and the holding part 5
7 is a reflecting mirror holding cylinder, and at its lower end there is a reflecting mirror that is inclined at 45 degrees with respect to the direction in which the electron beam is projected and has a small hole in the center for the electron beam to pass through. 6 is provided.

12 is an electromagnetic deflection coil for manipulating the electron beam flux, 13 is an electromagnetic objective lens, 14 is a sample as a target, and 9 and 10 are curved reflecting mirrors for optical observation.

Reference numeral 15 denotes an X-ray spectroscopy crystal that separates characteristic X-rays from the sample 14. Although not shown in the figure, the crystal mounting is moved by the wavelength feed axis via a plate guide; It is shown in a position quite close to.

Reference numeral 20 denotes an outer magnetic shield, which is made of a soft magnetic material such as permalloy with high initial permeability and has an inverted truncated conical shape and an appropriate height above the electromagnetic objective lens 13 along the extended surface of the mortar-shaped opening. It is completely formed.

21 is the other inner magnetic shield, which has a lower opening angle than the shield surface 20 at the lower end of the peripheral edge of the outer periphery holding portion 9' of the curved reflecting mirror 9, and whose height is set within the magnetic field of the electromagnetic objective lens 13. It has the same shape as the above, to a limited extent, and is made of the same material as the above.

And an outer magnetic shield 20 and an inner magnetic seal 21
The overlap between the two is increased.

Since the electromagnetic objective lens 13 forms a strong magnetic field around it, fluctuations in the external magnetic field have little effect on the electron beam flux within that magnetic field. Just to the extent that it does not enter the magnetic field of the lens 13.

Further, the holding part 9' of the curved reflector 9, the holding part 5' of the astigmatism correction coil 5, and the shielding cylindrical part 19' around the scanning coil 19 are each made of permalloy, which is a material with high initial magnetic permeability. , magnetically shielded.

Next, the operation of this device will be explained.

Above the cavity of the optical observation system described above, there are a curved reflecting mirror 9 and a holding section 9' for the astigmatism correction coil 5, respectively.
5' and the shielding cylinder 19' of the scanning coil 19 are both made of permalloy and form a good magnetic shield, so even if the external magnetic field fluctuates, the electron beam flux is hardly affected. For the part, the electron beam flux is prevented from shifting due to fluctuations in the external magnetic field by both the outer magnetic shield 20 and the inner magnetic shield 21 made of permalloy, or by only the inner magnetic shield 21.

Since the inner magnetic shield 21 is prevented from entering the magnetic field of the electromagnetic objective lens 13, it cannot cause astigmatism, and the outer magnetic shield 20 is separated from the pole piece 13' of the electromagnetic objective lens 13. In addition, the overlapping parts of the magnetic shields 21 and 20 on both the inner and outer sides are made to be large, and the opening angles of each are made to be different, so that the space between them widens. Since the X-ray spectroscopy crystal 1 is formed between
5 can be moved and driven, and even though there is an X-ray extraction opening, the same shielding effect as when magnetically shielding the entire outer periphery can be achieved using less shielding material.

Since the magnetic shielding device for the X-ray analyzer according to this invention is constructed as described above, this device has almost the same effect as the magnetic shielding for stabilizing the electron beam of the conventional X-ray analyzer. The upper part of the observation system can be raised to the upper part of the observation system, and the lower cavity, that is, the magnetic shield that was left unused for the This is made possible by adding a magnetic shield, making it possible to further reduce the deviation of the projection position of the electron beam on the sample surface due to fluctuations in the external magnetic field.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing the configuration of the main parts of an X-ray microanalyzer, and FIG. 2 is a partial vertical sectional view of the X-ray microanalyzer to which a shielding device according to the invention is added. 1: Electron gun, 2: Anode, 3: Electromagnetic focusing lens, 4: Aperture, 5: Astigmatism correction coil, 5': Astigmatism correction coil holding part (magnetic shield), 6: 45' reflector, 7: Reflector holding cylinder, 9, 10: Curved reflector for optical observation, 9'
: Curved reflector holding part (magnetic shield), 11: Optical microscope, 12: Electromagnetic deflection coil, 13: Electromagnetic objective lens, 1
3': pole piece, 14: sample, 15: X-ray spectrometer crystal, 16: -X-ray detector, 19: scanning coil, 19': shielding cylinder (magnetic shield), 20: outer magnetic shield, 2
1: Inner magnetic shield.

Claims (1)

[Scope of utility model registration request] Above the electromagnetic objective lens, there is an outer magnetic shield made of a material with high initial magnetic permeability and having a constant height in the shape of an inverted truncated conical surface along the extended surface of the aperture of the objective lens; The lower edge of the periphery of the holding portion of the curved reflecting mirror has a shape similar to that described above, with an opening angle smaller than that of the magnetic shield, and its height is kept to such an extent that it does not enter the magnetic field of the electromagnetic objective lens, and A magnetic shielding device for an X-ray microanalyzer that includes an inner magnetic shield made of the same material.