JPS624818B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a scanning electron microscope (hereinafter referred to as SEM) with an X-ray analyzer, and an X-ray microanalyzer (hereinafter referred to as SEM).
XMA), transmission electron microscope with X-ray analyzer (hereinafter referred to as
The present invention relates to an electron beam application device such as a TEM (TEM) in which an electron probe is formed and used for analysis, and particularly relates to an aperture plate in such an electron beam application device.

In conventional electron beam application equipment, an electron beam passage hole with a diameter of about 20 μm to 400 μm (depending on the equipment and purpose of use) is provided in the aperture plate (recently often made of molybdenum) attached to the aperture holder, and the spherical surface of the electron lens is The function is to minimize the amount of blurring of the electron probe due to aberration (δ = 1/2C _s・ α ³ : C _s is the spherical aberration coefficient, α is the aperture angle), and it is also called self-cleaning, and the plate is used to reduce heat conduction. The thickness was about 10 to 20 μm, and the function was to heat and sublimate contamination attached around the electron beam passage hole by electron beam irradiation.

In addition, when contamination still adheres even after self-cleaning, the diaphragm can be switched from outside the vacuum and used as a clean diaphragm each time, without having to introduce air into the vacuum container each time. Conventionally, a plurality of aperture plates are attached to an aperture holder to provide a plurality of electron beam passage holes in the mirror body.

FIG. 1 is a schematic explanatory diagram of an SEM equipped with an energy dispersive X-ray analyzer (EDX). Electrons emitted from the electron gun 1 are accelerated by the anode 2 and form an electron beam 3. This radiation source normally has a cross section with a diameter of about 30 μm, and in order to narrow it down to a diameter of several 10 Å to several 100 Å, the first focusing lens 4
and second focusing lens 5 and objective lens 7 are used.

Further, for secondary electron image observation, the deflection coil 6 is configured to scan the surface of the sample 8 in two dimensions of XY. Note that the secondary electron image observation system is not shown because it is not directly related to the present invention.
The sample 8 is placed on the sample stage 9,
Fine movement knob 23 provided outside the vacuum case 13
It can be moved by.

From the sample 8, X-rays (continuous X-rays and characteristic X-rays) are generated by the impact of the electron probe 11 that passes through the electron beam passage hole of the aperture plate 12A, but this is detected by X-ray detection. Container 10 (EDX in this example)
The output is supplied to the analyzer 14 and analyzed. Note that 12 is an aperture holder that holds the aperture plate 12A, and 24 is a refrigerant tank (such as a juicer bottle) for cooling the detector 10.

FIG. 2 is a schematic explanatory diagram of a TEM equipped with an X-ray analyzer, and the same reference numerals as in FIG. 1 represent the same or equivalent parts. 15 is an aperture plate moving mechanism, 16 is an intermediate lens, 17 is a projection lens, 18 is a fluorescent plate, 19
is photographic film, 20 is film cassette, 21
2 is a TEM aperture section, and 22 is an aperture plate moving mechanism.

When performing X-ray analysis of the sample 8, the aperture holder 12 and the aperture plate 12A are inserted and set in the illustrated positions, and an electron probe 11 is formed from the electron beam 3 and is made to impact the sample 8. By this,
As in the case of FIG. 1, X-rays are emitted from the sample 8 and detected.

As described above, in an electron beam application device equipped with an X-ray analyzer that uses an electron probe to impact a sample to emit X-rays and detect the X-rays,
The main surface of the lens that forms the electron probe in front of the sample position (objective lens for SEM, final focusing lens for TEM) is designed to prevent scattered electrons from reaching the sample, and is the most important lens. An aperture plate is provided to reduce blurring of the electron probe due to spherical aberration.

FIG. 3 shows this state, and shows an enlarged cross-sectional view of the corresponding portion of FIG. 1 as an example.
In such a case, in a normal device, in order to extend the cleaning cycle, a plurality of electron beam passing holes 12B are provided in the diaphragm plate 12A as shown in the figure, and full-scale cleaning is not performed until all of them are dirty. It is made unnecessary. The thickness of the aperture plate is made relatively thin, about 10 to 20 μm, so that the heat generated by electron irradiation around the electron beam passage hole of the aperture plate is difficult to escape, and therefore the aperture plate is sufficiently heated. , it is designed so that attached dirt can be easily sublimated. (Even in this case, dirt accumulates over a long period of time, causing astigmatism.) By the way, the problem caused by the thinness of the aperture plate is that The X-rays 30 generated by the scattered electron beam are transmitted through the diaphragm plate 12A, and the transmitted X-rays are irradiated onto the sample 8 to generate secondary X-rays (fluorescent X-rays).
rays) are generated, which are incident on the detector 10 and reduce the accuracy of the analysis.

Therefore, an object of the present invention is to solve the problems of the conventional apparatus by preventing X-rays generated on the electron gun side of the aperture plate from passing through the aperture plate.

For this reason, in the present invention, the thickness of the aperture plate around the electron beam passage hole used during image observation, where astigmatism due to contamination is a problem, is made sufficiently thin, and the thickness of the aperture plate used during X-ray analysis is made sufficiently thin. The thickness of the aperture plate around the electron beam passage hole is made sufficiently large to reduce the X-ray transmittance.

FIG. 4 is a plan view and a side sectional view of one embodiment of the present invention, where 12A is a diaphragm plate and 12B is an electron beam passage hole bored therein. In this example, four electron beam passing holes 12B are formed in the aperture plate 12A, and the thickness of the portion R where the two right electron beam passing holes 12B are located is the same as the thickness of the portion R where the two left electron beam passing holes are located. It is configured to be thicker than the thickness of L.

In this way, by partially varying the thickness of one aperture plate 12A, the thinner part L of the aperture plate can be used when astigmatism due to dirt is a problem for image observation. During X-ray analysis, the thick portion R of the aperture plate 12A can be used to eliminate the adverse effects caused by the transmission of scattered X-rays.

Since the thick part R has good thermal conductivity, the temperature does not rise and dirt is more likely to adhere to it than the thin part L, but compared to the strictness of image observation, the influence of astigmatism is small, so there is no problem in practice. . Note that in the figure, the thin part and the thick part are integrated, but the effect is the same even if this is divided into two parts.

FIG. 5 is a graph showing the X-ray transmittance versus X-ray wavelength when a molybdenum plate is used and the thickness is taken as a parameter. Curve A shows the case when the thickness is 10 μm, and curve 13 shows the case when the thickness is 100 μm.

As you can see from this figure, molybdenum aperture plate 1
The X-ray transmittance according to 2 is, for example, Cu-Kα ray (λ = 1.542 Å, ε = 8.04 KeV) and the aperture plate thickness is 10
When the thickness is 100 μm (curve A), it is 20.4%, but when the thickness is 100 μm (curve B), it is 0.0%, which is no problem. Even for Fe-Kα rays (λ = 0.937 Å, ε = 6.4 KeV), the transmittance is about 4.6% at a thickness of 10 μm, but it becomes 0.0% at a thickness of 100 μm.

In most cases, the materials of this type of equipment are iron,
These materials are brass, phosphor bronze, and stainless steel, and since these materials exhibit almost the same transmittance, there is almost no need to consider X-rays with a wavelength of 1 Å or less.

It should be noted that the thickness of the aperture plate described above is merely an example, and is not limited to this. It is a matter of course that the aperture plate with the optimum thickness can be used depending on the purpose of use, and it is possible to do so. The best effect can be achieved by doing so.

As explained in detail above, according to the present invention,
Aperture plates with partially different thicknesses or multiple aperture plates with different thicknesses are supported in the same holder and can be selectively controlled from outside the vacuum case, allowing the electron beam passage hole to be used to be switched according to image observation and X-ray analysis. By doing so, it is possible to perform the optimal throttling action on both of them, and the following effects can also be achieved.

(1) Since the thick part of the aperture plate is made of a single piece of material, X-rays generated above the aperture and on the side of the electron source from the aperture can be completely and efficiently absorbed.

(2) Since no cover etc. is attached to the aperture of the thin film part, it is possible to maintain a state of low heat conduction, and the heating sublimation function of contamination attached to the surrounding area is not deteriorated.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the SEM with EDX, Figure 2 is
A schematic explanatory diagram of a TEM with EDX, Fig. 3 is an enlarged view of the vicinity of the objective lens and a diagram showing the path of X-rays, Fig. 4 is an enlarged plan view and cross-sectional view of the aperture plate used in the present invention,
FIG. 5 is a graph showing the transmittance of X-rays. DESCRIPTION OF SYMBOLS 1... Electron gun, 4, 5... Focusing lens, 7... Objective lens, 8... Sample, 10... X-ray detector, 11... Electron probe, 12... Aperture holder, 12A... Aperture plate,
13...Vacuum case, 14...Analyzer.

Claims (1)

[Scope of Claims] 1. In an electron beam application device that can irradiate a sample with an electron beam and perform X-ray analysis such as observation of transmission and secondary electron images and qualitative and quantitative analysis, In this case, an aperture plate inserted into a lens for forming an electron probe has a plurality of electron beam passing holes, and the electron beam passing holes are selectively switched from outside the vacuum vessel, and some of the electron beam passing holes are selectively switched from outside the vacuum vessel. The holes are formed in a thin diaphragm plate whose temperature easily rises due to electron beam irradiation, and the other electron beam passage holes are formed in a thick diaphragm plate made of a single piece of material that has an X-ray absorption function. Electron beam applied equipment.