JP2653967B2 - Analytical electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analytical electron microscope which performs an X-ray analysis using an electron microscope to simultaneously perform an electronic level structural analysis and a nanometer level elemental analysis.

[0002]

2. Description of the Related Art As a conventional analytical electron microscope, for example, there is one as shown in FIG. The configuration comprises an electron gun 11 forming a high-speed electron beam source, a multistage focusing lens system 13 for reducing and projecting the electron beam 12 onto a sample surface, an objective lens system 14 therebelow, and an upper magnetic pole 15 forming an objective lens system 14.
And a lower magnetic pole 16, an upper magnetic pole piece 17 and a lower magnetic pole piece 18, and a sample chamber 22 including a sample 21 disposed between the magnetic poles of the upper magnetic pole 15 and the lower magnetic pole 16. The sample chamber 22 is formed from the side of the lens barrel 20.
An X-ray detector 25 is provided so as to enter the inside. The vicinity of the X-ray detector 25 is shown in FIG.

The electron beam 12 generated by the electron gun 11 and passing through the focusing lens system 13 and the objective lens system 14
1, and the spot 2 where the electron beam 12 is irradiated on the sample 21 due to the interaction between the electron beam 12 and the surface of the sample 21.
3, X-rays 24 are generated radially.
Is detected by the X-ray detector 25, amplified and subjected to signal processing to know the elements contained in the sample 21 and the percentage thereof. Here, the detection unit 27 of the X-ray detector 25
Is generally disposed in a protective cylinder having a diameter of 12 to 14 mm, a pressure-resistant partition wall such as beryllium is stretched at the tip of the protective cylinder, and is placed at a position about 2 mm from the tip.
It has a surface area of 0 mm ² .

Further, the upper magnetic pole 15 and the lower magnetic pole 16 have an upper magnetic pole piece 17 and a lower magnetic pole piece 18 in the form of truncated cones. To improve the performance of the electron microscope, if the spherical aberration is to be reduced. The apex angle of this pole piece must be 50 ° or more. Further, in the analytical electron microscope, the position of the X-ray detector 25 is set on the horizontal plane including the analysis point 23 so that the X-ray generated from the analysis point (the point 23 irradiated with the electron beam spot) is easily captured by the detector. Holds a certain angle.

[0005]

SUMMARY OF THE INVENTION
In the conventional X-ray analyzer, the X-ray detector is arranged in the protective tube, and the detection section at the tip can have only a surface area of about 30 mm ² . In addition, the apex angle of the pole piece in the shape of a truncated cone of a magnetic pole has a restriction that it must be 50 ° or more in order to keep the spherical aberration coefficient described below at a limit value of about 0.4 mm.

Further, the position of the X-ray detector is set with respect to a horizontal plane including a spot (analysis point) where the sample is irradiated with an electron beam.
A certain angle must be maintained. That is, if this angle is too small, detection will be performed at a portion where the intensity of diverging X-rays is weak. If this angle is too large, it will conflict with the upper pole piece, so this angle should be about 20 °. Must be retained. Under such conditions, the distance R from the analysis point to the detection unit of the X-ray detector has a somewhat large value.

On the other hand, the scale indicating the detection efficiency of X-ray analysis is:
The detected solid angle Ω is a value obtained by dividing the surface area S of the detection unit of the X-ray detector by the square of the distance R from the analysis point to the X-ray detector. Ω = S / R It is expressed by ² steradians (1). In order for the X-ray detector to operate effectively,
It is desirable that the detected solid angle Ω is large. However, in the conventional analytical electron microscope, a detection solid angle of 0.13 steradian is realized.
When S = 30 mm ² is applied to equation (1) and calculated,
R = 15 mm. Therefore, in order to increase the detection efficiency of the X-ray detector, the distance R from the analysis point to the detection unit must be one.
There is a problem that the solid angle must be made smaller than 5 mm and the solid angle must be made larger.

The present invention has been made in view of such a conventional problem, and the conditions such as the apex angle of a frustum-shaped pole piece and the position of an X-ray detector in an analytical electron microscope are set to the above values. It is an object of the present invention to provide an analytical electron microscope capable of shortening the distance from an analysis point to a detection unit of an X-ray detector while maintaining the detection solid angle to be equal to or larger than a certain limit.

If the performance parameters (particularly, the spherical aberration coefficient) of the objective lens system are degraded, the actual diameter of the electron beam probe deviates from the ideal irradiation radius, and the resolution of imaging decreases. At the same time, when the spherical aberration coefficient increases, the probe current also decreases. For example, spherical aberration coefficient C
_s1 = 0.4 mm and C _s2 = 1.2 mm2
When comparing the two cases, make the probe diameter constant,
Assuming that the respective probe currents are Ip ₁ and Ip ₂ , the result calculated or measured by a known method is Ip ₂ = Ip _1/2 . On the other hand, the yield of X-rays per unit time is proportional to the product of the probe current Ip and the detected solid angle Ω.
In order to improve the line detection efficiency, it is important to keep the spherical aberration coefficient of the objective lens system as small as possible.

The present invention has been made in view of the above-mentioned conventional problems, and it has been proposed to detect X-rays while keeping the spherical aberration coefficient affecting the performance of the objective lens of the analytical electron microscope as small as possible. It is another object of the present invention to provide an analytical electron microscope capable of improving the efficiency and increasing the yield of X-rays.

[0011]

The present invention, as means for solving the above-mentioned problems, comprises an electron source 11 for generating an electron beam 12, and a focusing lens system 13 for projecting the electron beam 12. An objective lens system 14 having an upper magnetic pole 15 having a truncated conical surface and a lower magnetic pole 16;
A lens barrel 20 having a sample chamber 22 including a sample 21 disposed between the lower pole 5 and the lower magnetic pole 16, and detecting the X-rays that enter the sample chamber 22 from the side surface of the lens barrel 20 and are generated from the sample 21. In the analytical electron microscope 10 having the X-ray detector 25, the notch 30 into which the detection unit 27 of the X-ray detector 25 is fitted is provided in the pole piece 17 of the upper magnetic pole 15 of the objective lens system 14). In addition, in the portion of the pole piece 17 other than the cutout portion 30 of the truncated conical surface 26, a built-up portion 31 is provided symmetrically with respect to the electronic axis 12.

A notch 30 of the magnetic pole piece 17 of the upper magnetic pole 15 into which the detecting portion 27 of the X-ray detector 25 is fitted.
Is provided, the notch 30 is provided at a symmetrical position with respect to the electron beam axis 12. Also, four notches 30
Are provided on the pole pieces 17 at equal angular intervals.

[0013]

Next, the operation of the present invention will be described. The upper magnetic pole 1
5 is provided with a notch 30 into which the detector 26 of the X-ray detector 25 is fitted, and a part of the pole piece 17 other than the notch 30 on the truncated conical surface 26 is provided with the electron beam axis. Since the overlay portion 31 is provided symmetrically to 12, the detection portion 27 of the X-ray detector 25 fits into the notch portion 30,
The objective lens system 14 can be installed close to the analysis point on the sample 21, the solid angle at the time of X-ray detection is increased, the efficiency of X-ray analysis is improved, and the notch 30 is provided. Can be suppressed, the resolution of the image is maintained, and the measurement accuracy is improved.

Further, since the notches 30 are provided at symmetrical positions about the electron beam axis 12 and the four notches 30 are provided at equal angular intervals, the yield of X-rays is increased, and the X-ray analysis is improved. Efficiency is further improved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.
The schematic diagram of the configuration of the electron microscope 10 of the present invention is similar to that of the prior art shown in FIG.
1. a converging lens system 13 for reducing and projecting the electron beam 12 onto a surface of a sample 21; a next objective lens system 14;
An upper magnetic pole 15 and a lower magnetic pole 16 are provided to form the upper and lower magnetic poles 4. The upper magnetic pole 15 and the lower magnetic pole 16 have an upper magnetic pole piece 17 and a lower magnetic pole piece 18 having a truncated conical surface 26. The sample 21 is placed between the upper magnetic pole 15 and the lower magnetic pole 16.

The size of the gap between the magnetic poles is 2 mm.
It is as follows. The upper magnetic pole 15 and the lower magnetic pole 16 are
The magnetic material is formed from an alloy of iron and cobalt. The sample 21 is disposed in the sample chamber 22, and the lens barrel 20 is formed by these components. The X-ray detector 25 is disposed so as to enter the sample chamber 22 from the side surface of the lens barrel 20. I have.

Then, an electron beam 12 generated by the electron gun 11 and passing through a lens system is radiated from a spot 23 irradiated on a sample 21 to generate an X-ray 24 radially. This is called X-ray detector 2
5 to perform signal processing by detecting the elements contained in the sample 21 and the percentage thereof, and have a configuration substantially similar to that of the conventional technology up to this point.
The same members are denoted by the same reference numerals.

On the other hand, the apex angle of the truncated conical upper pole piece 17 must be 50 ° or more in order to reduce the spherical aberration C _S, and the position of the X-ray detector 25 is
1 must maintain an angle of 20 ° with respect to the horizontal plane including the spot 23 (analysis point) irradiated with the electron beam, and the distance R from the analysis point 23 to the X-ray detector 25 under this condition. As shown in FIG. 1, the pole piece 17 of the upper magnetic pole 15 of the objective lens 14 is
Is provided with a cutout portion 30 into which the detection portion 27 at the tip of the X-ray detector 25 is fitted.

Notch 30 is formed in pole piece 17 of upper magnetic pole 15.
Is provided, the spherical aberration coefficient C _S of the objective lens system 14
Increases, with an increase of the spherical aberration coefficient C _S, the probe current of the X-ray detector 25 is reduced. This interrupts the yield per unit time of the X-rays in the X-ray detector 25 is reduced, it is necessary to minimize the spherical aberration coefficient C _S.

Therefore, the X-ray detector 25 is positioned symmetrically about the electron beam axis 12 on the frusto-conical surface of the upper pole piece 17.
The notches 30 are not provided, and four notches 30 are provided at symmetrical positions at regular intervals of 90 °. Further, a build-up portion 31 is provided symmetrically with respect to the electron beam axis 12 in a portion other than the cutout portion 30 on the side surface of the upper magnetic pole piece 17. FIG.
FIG. 3 is a perspective view of a cutout portion 30 and a built-up portion 31 of the upper magnetic pole piece 17.

On the side surface of the upper pole piece 17 having a truncated cone shape, X
Notch 3 into which detector 27 at the tip of line detector 25 is fitted
0, the notch 30 has an X-ray detector 25
The detection unit 27 at the tip of the X-ray detector is fitted, and the X-ray detector 25 can be installed close to the analysis point 23 on the sample 21, the distance R from the analysis point to the X-ray detector decreases, and X The solid angle at the time of line detection increases, and the efficiency of X-ray analysis improves.

By providing the notch 30,
Since the spherical aberration C _S of the objective lens system 14 increases, it must be kept as small as possible. And the objective lens must have the perfection of both sides: to focus the electron beam on the sample without any defect, and to execute the imaging of the sample with an atomic resolution.
However, when only one cutout portion 30 is provided, defects such as an increase in secondary and tertiary astigmatism of the objective lens system and an appearance of coma aberration occur.

Therefore, in order to prevent the disturbance of the magnetic flux due to the notch portion 30 from damaging the optical axis of the lens and increasing astigmatism, the notch portion into which the detection portion 27 at the tip of the X-ray detector 25 fits. It is conceivable to provide a dummy notch 30 at a symmetrical position of the pole piece 17 about the electron beam axis 12 of the pole piece 17. When two notches 30 are provided at symmetrical positions, a secondary astigmatism corrector is used. When three notches 30 are provided at symmetrical positions, a tertiary astigmatism corrector is used. Must be provided separately from the astigmatism corrector. Therefore, the four notches 30 are arranged at 90 ° intervals to form the pole pieces 17.
Are provided at equal intervals on the truncated conical surface 26 of FIG.

Further, in the portion other than the notch 30 of the conical surface 26 on the side surface of the upper pole piece 17 having a truncated conical shape, a built-up portion 31 is provided symmetrically with respect to the electron beam axis 12. The resulting loss of cross-sectional area in this part of the magnetic circuit is compensated for. Thereby, an increase in the spherical aberration coefficient C _S due to the provision of the notch 30 can be suppressed.

Further, in order to compensate for the loss of the magnetomotive force of the objective lens 14 caused by providing the notch 30 in the pole piece 17, the exciting current of the objective lens 14 is increased. Furthermore, by providing the notch 30 in the pole piece 17, a sub-lens is formed by the action of the leakage magnetic flux, and the C / O point of the objective lens 14 moves. Further, since the C / O point also moves due to the exciting current, it is necessary to move the position of the sample 21 upward in consideration of these. However, as the surface of the sample 21 is shifted upward, the size of the probe diameter changes, and as a result, the spherical aberration coefficient generally increases.
Determine by trial and error by calculation or actual measurement.

The effect of improving the performance of the analytical electron microscope obtained by the above embodiment is shown as experimental data. When the electron accelerating voltage is 200 kV, the structure of the present invention allows
Realize an objective lens with a spherical aberration coefficient of 0.5 mm,
In this case, the distance R from the analysis point is 10 mm, the increase in the exciting current is 5%, the increase in the sample position is 2.5% of the pole gap length, and the increase in the spherical aberration coefficient is 2%. The spherical aberration coefficient was almost within the range of the error, and one having no influence on the X-ray yield was obtained.

At a low accelerating voltage, the exciting current of the objective lens can be set low, so that an increase in the exciting current, an increase in the sample position, and an increase in the spherical aberration coefficient due to the present configuration can be reduced. For example, an acceleration voltage of 60 kV
Then, the increment of each of the above values can be made zero.

Further, with this configuration, the solid angle of detection Ω = 0.28 steradian The take-out angle θ = 20 ° was simultaneously achieved, and the X-ray yield was quadrupled as compared with the conventional example of FIG. Compared with the well-known conventional spherical aberration coefficient C _S = 1.2 mm and the detected solid angle = 0.13 steradians, the detection efficiency is 2.2 times, the probe current is twice, and the X-ray detection is performed. The yield was 4.4 times.

In the above embodiment, four notches 3
Although 0s are provided at equal intervals of 90 °, two or three notches may be provided. In this case, since a stigmator must be provided, the manufacturing cost increases and the operation is increased. Although it is complicated, it has similar functions and effects.

In the above embodiment, the acceleration voltage is 200 k
Although the case of V has been described, the present invention can be applied to an electron microscope of 200 kV or more by using a well-known similarity rule of electron optics. Further, in the above embodiment, the notch is provided in the pole piece of the upper magnetic pole. However, when the sample can transmit an electron beam, the detection unit of the X-ray detector fits into the magnetic pole piece of the lower magnetic pole. By providing the notch, the detection unit of the X-ray detector can be brought closer to the analysis point, the solid angle detected can be increased, and the yield of X-rays can be increased.

[0031]

As described above, according to the present invention, the notch of the X-ray detector is provided in the pole piece of the upper magnetic pole, and the notch of the frusto-conical surface of the pole piece is provided. In other parts than the part, since the build-up part was provided symmetrically to the electron beam axis,
The detection section at the tip of the X-ray detector is fitted into the notch 30 so that the X-ray detector can be installed close to the analysis point on the sample, and the solid angle at the time of X-ray detection increases. In addition, the efficiency of X-ray analysis is improved, and the overlaid portion can suppress the increase in spherical aberration of the objective lens system due to the provision of the notch portion, thereby maintaining the resolution of the image and improving the measurement accuracy. It has the effect of doing.

Also, four notches into which the detecting portions of the X-ray detector are fitted are provided at equal angle intervals at symmetrical positions about the electron beam axis of the pole piece of the upper magnetic pole.
This has the effect of increasing the yield of X-rays, further improving the efficiency of X-ray analysis, and improving measurement accuracy.

[Brief description of the drawings]

FIG. 1 is a view of an objective lens and an X-ray detector of an analytical electron microscope showing a configuration of the present invention, wherein FIG. 1 (a) is a plan view and FIG. 1 (b) is an AOB sectional view of FIG. 1 (a). is there.

FIG. 2 is a perspective view of the upper magnetic pole of the objective lens of FIG.

FIG. 3 is a sectional view of a conventional analytical electron microscope.

FIG. 4 is a sectional view of an objective lens and an X-ray detector of a conventional analytical electron microscope.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Electron gun 12 Electron beam 13 Focusing lens system 14 Objective lens system 15 Upper magnetic pole 15 16 Lower magnetic pole 16 17 Upper magnetic pole piece 18 Lower magnetic pole piece 21 Sample 22 Sample chamber 25 X-ray detector 30 Notch 31 Overlay

Claims (3)

(57) [Claims] An electron source (11) for generating an electron beam (12).
And a focusing lens system (13) for projecting the electron beam (12).
An objective lens system (14) having an upper magnetic pole (15) having a truncated conical surface and a lower magnetic pole (16), and disposed between the upper magnetic pole (15) and the lower magnetic pole (16). (20) having a sample chamber (22) containing a sample (21)
And an X-ray detector (25) that enters the sample chamber (22) from the side of the lens barrel (20) and detects X-rays generated from the sample (21). the detection unit (27) notch in which is fitted a pole piece (17) in the X-ray detector (25) of the upper magnetic pole (15) of the objective lens system (14) provided with a (30), said pole pieces (17) The truncated conical surface (26)
In the portion other than the notch (30), the electron beam axis (12)
An analytical electron microscope characterized by symmetrically providing a built-up portion (31) . 2. The upper magnetic pole according to claim 1, wherein:
An analytical electron microscope characterized in that a notch (30) identical to the notch (30) is provided at a symmetric position of the pole piece (17) about the electron beam axis (12). 3. The upper magnetic pole according to claim 2, wherein:
Wherein the the symmetrical positions with the center electron beam axis (12), analytical electron microscope, characterized by comprising four said notch (30) at equal angular intervals of the magnetic pole piece (17).