JPH0117100B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an X-ray microanalyzer or the like having a rectilinear crystal focusing spectrometer using a curved crystal to obtain an electron beam The present invention relates to a method of acquiring an X-ray image by scanning.

One of the analytical methods conventionally performed using this type of method is a method called area analysis. In other words, an electron beam is scanned two-dimensionally over a sample, and out of the X-rays sequentially generated from the sample, only the X-rays with wavelengths corresponding to the sample components to be analyzed are focused using a straight crystal focusing method using a curved crystal. The X-rays are selectively made to enter an X-ray detector via a spectrometer, and an output signal from the detector corresponding to the X-ray intensity is supplied as a luminance signal to a cathode ray tube that is scanned in synchronization with the scanning, and the cathode ray tube screen is A characteristic X-ray image corresponding to the concentration distribution of the sample component to be analyzed can be obtained.

FIG. 1 is a schematic diagram of an apparatus for obtaining such a characteristic X-ray image. Sample 1 is a sample, and it is assumed that sample 1 does not contain any other elements that are different from the element of interest whose concentration distribution is to be determined and that have a spectral peak near the spectral peak of the element of interest. . This sample 1 is irradiated with an electron beam 2 . M represents a spectroscopic crystal, and the spectroscopic crystal M moves on a fixed axis L forming an X-ray extraction angle α with respect to the sample surface. Different values of the angle of the crystal plane of the spectroscopic crystal M (angle with the axis L) correspond to different positions on the fixed axis L in a one-to-one correspondence, and the spectroscopic crystal M cannot be moved on the fixed axis L. The angle is changed by . Also, S is X guided through the spectroscopic crystal M.
This is the slit of the detector D that detects the line, and the point _x0 is the intersection of the sample 1 and the fixed axis L. Also, point x ₀ and M,
S is on the Rowland circle 3 of radius R, and the line segment
x ₀ M and MS are made equal. Now, when trying to obtain a detected image of a characteristic X-ray of wavelength λ using such a device, for example, the tangent g to the Rowland circle 3 of the crystal center plane of the spectroscopic crystal M is expressed by the following Bragg equation with respect to the fixed axis L. The position of the spectroscopic crystal M on the straight line L is set so that θ satisfies the electron beam 2.
It is sufficient to scan in the very vicinity of point x ₀ . Incidentally, at this time, the tangent line g also forms an angle θ with the straight line MS.

2dsinθ=nλ ……(1) However, d is the interplanar spacing of the spectroscopic crystal, and n is a natural number. However, when trying to obtain a relatively low magnification image of the sample, the electron beam scanning range on the sample becomes wide, so the electron beam 2 is moved from the x coordinate provided on the surface of the sample 1, for example, from It is necessary to scan until x=xv. If the electron beam 2 is scanned over the sample 1 while the spectroscopic crystal M is fixed at the position shown in Fig. 1, the detection signal will be Figure 2a
The signal representing the element concentration cannot be output at a point where the irradiation point of the electron beam 2 is far from the position x ₀ on the optical axis. This is because when the electron beam irradiation point, which is the X-ray generation point, moves away from x ₀ , the angle of incidence of the X-rays on the spectroscopic crystal M deviates from θ, and equation (1) no longer holds true. Incidentally, when scanning the electron beam 2 in a direction perpendicular to the plane containing the Rowland circle 3, the X-rays of the wavelength of interest are sufficiently detected even if the electron beam is scanned over a distance of about 1 mm over the sample. There is no need to consider this direction.

Assuming that the scanning area of the electron beam for determining the concentration distribution spans from point xu to xv in Figure 1,
Conventionally, the spectroscopic crystal is moved linearly in a plurality of steps along the fixed axis, and the sample is two-dimensionally scanned by an electron beam during each stop period of the spectroscopic crystal, and each scan Each time, a detection signal for one screen is acquired from the X-ray detector of the spectrometer, and the detection signals are superimposed to display a distribution image of the element. At this time, the slit is set wider than when selecting only the X-rays generated from the point _x0 . That is, the characteristic X-rays generated from point
A slit S is arranged so that the characteristic is the slit width
It is set to Sw. Therefore, in the method based on the present invention, the condensing conditions for each of the Bragg-reflected X-rays are not, strictly speaking, satisfied. However, since the distance between xu and xv is actually extremely small, the deviation from the condensing condition is slight, and even with this method, there is almost no practical problem in reducing the amount of X-rays necessary to obtain a concentration distribution image. It can be detected to the extent that it does not occur. Furthermore, since the distance between xuxv is small, the slit width Sw is actually quite narrow.

However, the angle of the spectroscopic crystal (the distance along the fixed axis L) that should be changed in steps varies depending on the spectrometer used, the element of interest (the wavelength of the characteristic X-ray of interest), etc. In this method, the amount of step change is set based on intuition, and images are taken by trial and error while examining the resulting photograph and adjusting the amount of step change. As a result, it may take an extremely long time to obtain an image by moving the spectroscopic crystal in smaller steps than necessary, or conversely, the amount of change per step of the spectroscopic crystal may be too large, resulting in poor detection sensitivity in the sample image obtained. Areas that were too low appeared in stripes, making it difficult to obtain a good image.

The present invention has been made to solve these conventional drawbacks, and will be described below with reference to the drawings.

Now, as mentioned above, there is no need to consider the direction perpendicular to the plane containing the Rowland circle of the spectrometer. Consider the case where the sample is line-scanned (along the lines). As described above, the sample does not contain any element other than the element of interest that has a spectral peak near the spectral peak of the element of interest, and the sample contains the element of interest at a uniform concentration. Further, it is assumed that the slit S is set wide as described above.

Under the above conditions, the following facts hold both experimentally and theoretically.

That is, when comparing the signals obtained during line scanning, the peak position of the output signal of the detector D differs depending on the position of the spectroscopic crystal M on the fixed axis L during line scanning, but the spectroscopic Regardless of the position of the crystal M on the fixed axis L, the peak values of the output signals of the detector D are approximately equal, and the half-value widths are also approximately equal. Furthermore, the position of each peak corresponds to the position of the spectroscopic crystal M on the fixed axis L.

Conversely, if the spectroscopic crystal M is moved stepwise along the fixed axis L by a certain distance and the line scan is performed during each stop period of the spectroscopic crystal M, the peak values of the signals and their half-widths will be different from each other. If a series of signals as shown in Fig. 2a to Fig. 2i are obtained from detector D, and the peak positions are approximately equal to each other and differ by the half width, then when these signals are superimposed, , as shown in FIG. 2j. When the electron beam is two-dimensionally scanned over the sample, if the vertical scanning range is from xu to xv along the paper in Figure 1, the superimposed signal value in this range is approximately constant as shown in Figure 2 j. Therefore, by moving the spectroscopic crystal in steps along the fixed axis L so as to obtain the signals shown in Fig. 2a to Fig. 2i, and superimposing these signals, the spectroscopic crystal can be moved the minimum number of times. By simply moving the image in steps, it is possible to obtain an elemental distribution image that does not have fringes caused by uneven sensitivity. Therefore, in order to move the spectroscopic crystal M as described above, we will consider how the spectroscopic crystal M should be moved step by step on the fixed axis L.

Now, when the electron beam irradiation point is x = xi in Figure 1, the spectroscopic crystal M moves on the fixed axis L at a very small distance from the initial position l ₀ so that the X-rays generated from this point are incident at a Bragg angle θ. The position indicated by M' moves by Δl and becomes l _i on the l coordinate (at this time, the angle on the display increases from θ by a small angle Δθ to θ + Δθ, the slit S becomes S′, and the detector D D′, Roland circle 3
becomes 3'). Straight line from point x ₀
Dropping the perpendicular x ₀ T to x _i M′, we get ₀ = (x ₁ − x ₀ ) sin α = (l ₀ + Δl) sin Δθ = (l ₀ + Δl) Δθ≒l ₀ Δθ ……(2) (∵Δθ is very small Therefore, <x ₀ x _i T≒α, sinΔθ≒
Δθ) Also, using the geometric conditions regarding the Rowland circle 3', sin(θ+Δθ)=l ₀ +Δl/2R...(3) By the way, sin(θ+Δθ)=sinθcosθ+cosθsinθ ≒sinθ+Δθcosθ...(4) Also, the Rowland circle From the geometrical conditions regarding 3, sinθ=l ₀ /2R (5) Using equations (4) and (5), equation (3) can be rewritten as follows.

From equations (2) and (6), In equation (7), R is the Rowland radius, α is X
Both of the line extraction angles are determined by the actual equipment, and _l0 is also determined by the interplanar spacing of the spectroscopic crystal, the wavelength input of the element of interest, etc. in addition to R, α, etc. From this derived equation, it can be seen that the spectrometer positions corresponding to the signals shown in FIGS. Furthermore, scanning the position of the spectroscopic crystal while fixing the generation point of the X-rays and scanning the electron beam irradiation point, which is the generation point of the X-rays, with the position of the spectroscopic crystal fixed are the It is completely equivalent to scan the incident angle of To move the spectroscopic crystal, under the conditions where the slit is set wide as described above, the spectroscopic crystal is fixed and the electron beam is moved over the sample by the half-width value of the signal peak shown in Figure 2. It turns out that it is equivalent to

As described above, the present invention uses a straight crystal condensing spectrometer that performs wavelength sweeping by moving a curved spectroscopic crystal straight along a fixed axis. The spectroscopic crystal is moved in a straight line, the sample is two-dimensionally scanned with an electron beam during each stop period of the spectroscopic crystal, and the X-ray detector of the spectrometer receives a detection signal for one screen for each scan. In the method of displaying the distribution image of the element by superimposing the detected signal, the X-rays generated from the sample by electron beam irradiation are transmitted to the spectroscopic crystal in order to determine the certain distance. changing the incident angle at a constant speed; determining a distance on the fixed axis corresponding to the half width of the peak of the output signal of the X-ray detector as the incident angle changes; and determining the fixed distance. The present invention is characterized by comprising a step of setting the determined distance, and a step of automatically moving the spectroscopic crystal in a straight line.

An embodiment of the present invention using such a principle will be described in detail below with reference to the drawings.

FIG. 3 shows an example of an apparatus for carrying out the present invention, in which numeral 4 represents an electron gun;
The twisted electron beam 2 is converged by a converging lens 5. The electron beam 2 converged by the converging lens 5 is deflected by the deflection coil 6 in the X direction and the Y direction. 7 is an objective lens, and the electron beam 2 is irradiated onto the sample 1 by the objective lens 7. Reference numeral 8 denotes a scanning signal generating circuit, and the scanning signal generating circuit 8 generates horizontal and vertical scanning signals according to instructions from an electronic computer 9. The scanning signal from the scanning signal generation circuit 8 is sent to the deflection coil 6 via the magnification control circuit 10.
It is also supplied directly to the deflection coil 12 of the cathode ray tube 11. The magnification control circuit 10 changes the amplitude of the signal from the scanning signal generation circuit 8 in accordance with a magnification control signal from the electronic computer 9 and supplies it to the deflection coil 6. Of the X-rays generated from the sample 1 by irradiating the sample 1 with an electron beam, only the X-rays of a specific wavelength selected by the spectroscopic crystal 13 that moves on the fixed axis L while changing the angle are detected by the detector 14. be guided by The signal detected by the detector 14 is amplified by the amplifier 15 and then sent to the cathode ray tube 11.
is supplied to the grid G, and the electronic computer 9
Also supplied. Reference numeral 16 denotes a driving mechanism for the spectroscopic crystal 13, and the driving mechanism 16 intermittently drives the spectroscopic crystal 13 at predetermined distances along the fixed axis L based on a control signal from the electronic computer 9. 17 is cathode ray tube 1
The camera device 17 is controlled by a control circuit 18 that performs control based on command signals from the computer 9. A keyboard 19 is used to input various information into the computer 9.

In such a configuration, the operator inputs the name of the element to be surface analyzed, the spectrometer number (channel number), the type of spectroscopic crystal, and the observation magnification using the keyboard 1.
9, the information is input to the electronic computer 9. Then, when the operator starts the apparatus, the drive mechanism is activated by a signal from the electronic computer 9, and the spectroscopic crystal 13 sweeps on the fixed axis L at a predetermined speed while changing the angle. Since the electron beam 2 that has proceeded along the optical axis without being deflected is projected onto the sample 1, the spectroscopic crystal 1
3, a signal as shown in FIG. 4 is detected by the detector 14 and supplied to the computer 9. The electronic computer 9 calculates the half-value width W of the peak of the supplied signal expressed by the l coordinate. Furthermore, the electronic computer 9 uses the set observation magnification information to
It is calculated from which position on the fixed axis L the spectroscopic crystal 13 should be moved by how many steps in each half width W. When such calculation is completed, the electronic computer 9
moves the spectroscopic crystal 13 to the calculated initial position on the L axis and opens the shutter of the camera device 17 via the control circuit 18. Therefore, the computer 9 further sends a command signal to the scanning signal generating circuit 8 to cause the electron beam 2 to scan the sample 1 for one field. At this time, an area of a predetermined size of the sample 1 is scanned by a magnification control signal from the electronic computer 9. As a result of this scanning, characteristic X-rays generated from an area approximately indicated by S1 in the imaging area A of the sample are detected by the detector 14 through the spectroscopic crystal 13 as shown in FIG. displayed at the display position. Next, the electronic computer 9 causes the driving mechanism 16 to move the spectroscopic crystal 13 by the width W on the fixed axis L, and then causes the electron beam 2 to scan one field over the sample 1. As a result, characteristic X-rays generated from the area approximately indicated by S2 in the imaging area A in FIG. 5 are displayed on the cathode ray tube 11. In this way, the spectroscopic crystal 13 is automatically moved intermittently by the number of steps calculated by the width W based on the instructions from the electronic computer 9, and each time the movement is completed, the sample 1 is moved one field by the electron beam 2. scanned one by one. In this way, X-rays generated from areas S3, S4, ..., S9 in the imaging area A are displayed on the cathode ray tube 11, and the camera device 1
7 photographs an image in which these nine images are superimposed.
When such photographing is completed, the shutter of the camera device 17 is automatically closed, and an image representing the elemental distribution of the sample 1 can be obtained using the photographic film.

As described above, according to the present invention, even when the observation magnification is low, a high-quality X-ray image can be easily obtained by electron beam scanning in a very short time.

Note that the aforementioned width W differs depending on the type of spectroscopic crystal and the element to be measured, but once the width W is determined when the spectroscopic crystal and the measured element are changed and stored in the computer, it can be used every time an image is taken. There is no need to scan the spectrometer along a fixed axis L to determine the width W.

Furthermore, in the embodiments described above, an example was explained in which the present invention is applied to a device in which the angle of the spectrometer is indirectly displayed by the coordinate l provided along the fixed axis L. It is therefore equally applicable to devices in which the angle of the spectrometer is expressed by λ, expressed as λ=l/Rd.

Furthermore, in the embodiment described above, S1, S2,
..., a photographic film was used to superimpose the images of the S9 area into a single image, but the detector signals were stored in a memory location provided for each pixel and electrically superimposed. Also good.

Note that the present invention is applicable not only to the case where the vertical scanning direction when two-dimensionally scanning an electron beam on a sample is along the plane containing the Rowland circle of the spectrometer, but also to the case where the direction of vertical scanning is along the plane containing the Rowland circle of the spectrometer. This can be applied to cases in which the spectroscopic crystal is in the same direction as the above-mentioned width W, and even in that case, it is sufficient to move the spectroscopic crystal by the same distance as the width W.

Furthermore, in the embodiment described above, the spectroscopic crystal is moved at a constant speed along the fixed axis L while the electron beam is fixedly irradiated, and the peak of the signal from the X-ray detector obtained with this movement is The distance on the fixed axis L corresponding to the half-width is determined and this distance is set as the unit movement amount when moving the spectroscopic crystal in steps. , the sample is line-scanned with an electron beam so that the incident angle of the characteristic X-rays of the element of interest to the spectroscopic crystal changes, and a fixed line scan is performed that corresponds to the peak half-width of the signal from the X-ray detector obtained as a result of this scanning. Alternatively, the distance on the axis L may be determined, and this distance may be set as the unit movement amount during step movement of the spectroscopic crystal.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the relationship between the spectroscope and the electron beam irradiation point during low-magnification imaging, and Fig. 2 is a diagram for showing the detection signal when the spectrometer is ideally moved. Fig. 3 shows an example of a device for carrying out the present invention, Fig. 4 shows detection signals when the spectrometer is swept on the fixed axis L, and Fig. 5 shows the detection signals of the cathode ray tube at different positions of the spectrometer. FIG. 6 is a diagram showing each area on the sample to be displayed. 1: Sample, 2: Electron beam, 3, 3': Roland circle, 4: Electron gun, 5: Converging lens, 6, 12: Deflection coil, 7: Objective lens, 8: Scanning signal generation circuit, 9: Electronic computer , 10: magnification control circuit, 1
1: Cathode ray tube, M, M', 13: Spectroscopic crystal, D,
D', 14: X-ray detector, 15: amplifier, 16:
Drive mechanism, 17: Camera device, 18: Control circuit,
19: Keyboard, S, S': Slit, L: Fixed axis.

Claims (1)

[Scope of Claims] 1. Using a crystal rectilinear condensing spectrometer that performs wavelength sweeping by moving a curved spectroscopic crystal straight along a fixed axis, the above-mentioned light beam is divided into a plurality of steps at fixed distances along the fixed axis. The spectroscopic crystal is moved straight, and the sample is two-dimensionally scanned with an electron beam during each stop period of the spectroscopic crystal, and one screen worth of detection signals are obtained from the X-ray detector of the spectrometer for each scan. In the method of displaying the distribution image of the element by superimposing the detection signal, in order to determine the certain distance, X-rays generated from the sample by electron beam irradiation are incident on the spectroscopic crystal. changing the angle at a constant speed; determining a distance on the fixed axis corresponding to the half width of the peak of the output signal of the X-ray detector as the incident angle changes; A method for acquiring an X-ray image by electron beam scanning, comprising the steps of setting the determined distance and automatically moving the spectroscopic crystal in a straight line. 2. The step of changing the angle of incidence of X-rays generated from the sample onto the spectroscopic crystal at a constant speed in order to obtain the constant distance includes irradiating the electron beam to a certain point on the sample. 2. The method of acquiring an X-ray image by electron beam scanning according to claim 1, further comprising the step of moving the spectroscopic crystal at a constant speed along the fixed axis in the above-mentioned state. 3. The step of changing the incident angle of X-rays generated from the sample by electron beam irradiation onto the spectrometer crystal at a constant speed in order to find the constant distance is to move the spectrometer crystal to a certain position on the fixed axis. 2. The method of acquiring an X-ray image by electron beam scanning according to claim 1, further comprising the step of performing line scanning over the sample with the electron beam while the sample is fixed to the sample.