JPS6250648A - Method for analyzing noticed element in sample by electron ray irradiation - Google Patents

Abstract

PURPOSE:To non-destructively analyze the concn. distribution of a noticed element in the depth direction in a short period by determining the concn. distribution of the noticed element at the specified depth in accordance with the differential signal between an X-ray detection signal when an electron ray is irradiated to the analytical point of a sample and an X-ray detection signal obtd. by changing the diameter of an electron beam. CONSTITUTION:The electron beam 2 emitted from an electron gun 1 is accelerated by the high voltage from a high-voltage power source 16 and is converted by a convergent lens 3 and an objective lens 4. The converged beam irradiates the sample 5, from which the characteristic X-ray 6 is generated. The X-ray 6 is detected by an X-ray detector 8 by increasing the acceleration voltage each slightly. The detection signal is fed to a measuring circuit 9 by which the X-ray intensity is counted. The beam diameter of the X-ray beam 2 decreases gradually in this stage and the region where the X-ray is generated increases in the depth direction. A control circuit 10 stores the count value in a storage circuit 11 and stores the difference in the count values before and after the increase of the acceleration voltage by one step into the storage circuit 11. The concn. distribution of the noticed element at the specific point in the depth direction of the element is calculated in an arithmetic circuit 12 in accordance with the stored value thereof and is displayed on a display device 13.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention irradiates a sample with an electron beam, detects characteristic X-rays,
The present invention relates to a method for analyzing the concentration of an element of interest contained in a sample based on the detection of these X-rays.

[Prior art] When using an analytical electron microscope or the like to focus on a certain element and analyze how that element is distributed in the depth direction of a sample, conventionally, the analysis point is removed by etching or the like. The electron beam was irradiated and analyzed while gradually increasing the depth.

[Problems to be solved by the invention] Therefore, with such conventional methods, analysis cannot be performed without destroying the sample, and etching the surface takes time, making it difficult to perform analysis in a short time. could not.

The downside is that it takes a particularly long time to analyze the concentration distribution of the element of interest in the depth direction between two points on the sample, or the two-dimensional distribution of the element of interest at a certain depth. Because of the large number of cases, it was a big problem that needed to be solved.

The present invention aims to eliminate the above-mentioned drawbacks and analyze the depthwise distribution of an element of interest in a sample in a short time and non-destructively.

[Means for solving the problem] In order to solve this problem, the present invention irradiates a sample with an electron beam, detects characteristic X-rays generated from the sample by the irradiation with the electron beam, and detects the characteristic In a method of analyzing a sample based on detection, an analysis point on the sample is irradiated with an electron beam to obtain a first X-ray detection signal, and the accelerating voltage of the electron beam is increased (or decreased); The diameter of the electron beam is decreased (or increased) and the analysis point is irradiated with the electron beam, a second X-ray detection signal is obtained by the irradiation, and the first. The present invention is characterized in that the difference between the second X-ray detection signals is determined, and the concentration distribution of the element of interest at a certain depth from the surface of the analysis point is determined based on the difference signal.

[Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an example of an apparatus for carrying out the present invention. In FIG. 1, an electron beam 2 is emitted from an electron gun 1, which is converged by a converging lens 3, further converged by an objective lens 4, and irradiated onto a sample 5. Characteristic X-rays 6 generated from the irradiated portion of the sample 5 are guided to an X-ray detector 8 through an X-ray spectroscopy crystal 7, and a detection signal is obtained. This detection signal is sent to a measurement circuit 9 that counts the X-ray intensity, and only the X-ray detection signal with a predetermined energy is extracted and measured. The count value from the measurement circuit 9 is stored in the memory circuit 11 connected to the control circuit 10.
is memorized. Reference numeral 12 denotes a numbing circuit that determines the presence or absence of characteristic X-rays and performs various calculations based on the data from the storage circuit 11. The calculation results from the calculation circuit 12 are displayed on the display device 13. 14 is a scanning coil for two-dimensionally scanning the electron beam 2; 15 is a scanning power supply for supplying a scanning signal to the scanning coil 14; 16 is a high-voltage power supply for accelerating the electron beam 2; It is controlled by a high voltage control circuit 17. 18 is a converging lens 3. An electron optical system control circuit for controlling each lens current of the objective lens 4, and these scanning power supplies 15. High voltage control circuit 17. Each of the electron optical system control circuits 18 and 10
controlled by. Reference numeral 19 denotes a sample stage on which the sample 5 is placed, and the sample stage 19 is driven by a stage drive circuit 20 controlled by a control port M10.

In such a configuration, the electron beam 2 emitted from the electron gun 1 is accelerated by the high voltage from the high voltage power supply 17,
Convergent lens 3. The sample 5 is narrowed down by the objective lens 4.
The sample 5 irradiated with the electron beam 2 generates characteristic X-rays 6 unique to each element.

By the way, when a sample is irradiated with an electron beam, the area where X-rays are generated from the electron beam irradiated part of the sample is as shown in Figures 2 (a) and (b), assuming the electron beam diameter φ is constant. It is known that the higher the accelerating voltage ■, the deeper the beam becomes, as well as wider in the lateral direction (direction perpendicular to the incident direction of the electron beam).

As shown in FIG. 3, in a sample that is normally analyzed, the element e of interest is not only present on the surface, but also often exists deep within the sample.

Therefore, in the present invention, the sample is analyzed in the depth direction by utilizing the properties of X-ray generation when the sample is irradiated with an electron beam, and the acceleration voltage The characteristic X-rays 6 generated from the sample 5 are counted by increasing V11, V2 and V3 little by little.

In this case, by increasing the accelerating voltage of the electron beam 2, the X-ray generation area expands in the horizontal direction, so the beam diameter φ of the electron beam 2 to be irradiated is changed from φ1° in the first scan to beam diameter φ1° in the second scan. φ2... and beam diameter φ
is linked to the accelerating voltage to generate X-rays f!4VL
is increased only in the depth direction without expanding in the lateral direction.

FIG. 4 is a bar graph showing the count values at each acceleration voltage V+, V2, Vs at positions tiA, B, ...E on the sample when the sample 5 is scanned by the electron beam 2 using this method. This is shown in .

By comparing FIG. 3 and FIG. 4, the following points become clear. That is, the acceleration voltage of the electron beam is increased by one step for each scanning frame, and the beam diameter φ is increased by one step.
If the step is made smaller, the X-ray generation area increases only in the depth direction as described above, so the characteristic If they are the same, the element of interest e is hardly distributed in a region deeper than depth 1, and if the count value is increasing at a constant rate as at point C in Figure 3, This means that the element of interest e is distributed at depths 2 and 3 at the same concentration as on the surface.

Therefore, the control circuit 10 sends the count values from each analysis point at the initial acceleration voltage to the storage circuit 11 to be stored therein, and when the count value signal after increasing the acceleration voltage by one step is sent, this memory circuit Read the value and
For each analysis point, the count value before raising the acceleration voltage is subtracted from the count value after raising the acceleration voltage, and the difference signal is stored in the storage circuit 11. Therefore, the memory circuit 11 stores the difference between the count value when the acceleration voltage is Vo+iΔV and the count value when the acceleration voltage is Vo+(i+1)Δ■.
0.1.2. ... and is stored for each analysis point.

Therefore, when the operator specifies a specific analysis point based on a control signal from the control circuit 10, the control circuit 10 reads out the stored value of the storage circuit 11 for this analysis point, and based on this stored value, the operator specifies a specific analysis point. The concentration distribution of elements in the depth direction can be displayed.

5(a) shows an example of the distribution of elements in the depth direction at point C in FIG. 3 displayed on the display device 13 in this way, and FIG. 5(b) shows the depth distribution at point E. This shows an example of element distribution in the horizontal direction.

Furthermore, if the operator indicates a specific depth of the sample,
The control circuit 10 reads only the difference signal corresponding to a specific depth stored in the memory circuit 11, and based on this read value, also determines the two-dimensional concentration distribution of the element of interest at this specific depth. can be displayed.

FIG. 5(C) illustrates the element concentration distribution at depth 3 in FIG. 3 displayed in this way.

The embodiments described above are merely representative examples of the present invention, and the present invention may be implemented in many other forms.

For example, in the embodiment described above, the acceleration voltage was gradually increased and the diameter of the electron beam was gradually decreased.
The diameter of the electron beam may be gradually increased while decreasing the accelerating voltage gradually.

Furthermore, in the embodiments described above, the X-ray attenuation effect, which increases as the X-ray generation region deepens, is ignored, but this effect can also be corrected for more accurate analysis.

[Effects of the Invention] As described in detail above, according to the present invention, the elemental distribution in the depth direction of a sample can be analyzed non-destructively and in a short time.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of an analytical electron microscope for carrying out the method of analyzing elements of interest in a sample based on the present invention, and Figures 2 (a) and (b) are X-rays in the sample by electron beam irradiation. Figure 3 is a diagram to explain the occurrence region, Figure 3 is a diagram to explain the presence of the element of interest e in the sample and the irradiation state of the electron beam 2, Figure 4 is a bar graph showing the count values obtained for each scan. FIG. 5 is a diagram showing an example of the display on the display device 13. 1: Electron gun, 2: Electron beam, 3: Convergent lens, 4: Objective lens, 5: Sample, 6: Characteristic X-ray, 7: X-ray spectrometer crystal, 8: X-ray detector, 9: Measurement circuit, 10 :Control circuit, 1
1: Memory circuit, 12: Arithmetic circuit, 13: Display device, 14
: Scanning coil, 15: Scanning power supply, 16: High voltage power supply, 17
: High voltage control circuit, 18: Electron optical system control circuit, 19: Sample stage, 20: Stage drive circuit.

Claims (1)

[Claims] A method in which a sample is irradiated with an electron beam, characteristic X-rays generated from the sample are detected by the irradiation with the electron beam, and the sample is analyzed based on the detection of the X-rays. irradiating the electron beam to obtain a first X-ray detection signal, increasing (or decreasing) the accelerating voltage of the electron beam, decreasing (or increasing) the diameter of the electron beam, and irradiating the analysis point with the electron beam. Then, a second X-ray detection signal is obtained by the irradiation, the difference between the first and second X-ray detection signals is determined, and the target element is detected at a certain depth from the surface of the analysis point based on the difference signal. A method for analyzing elements of interest in a sample using electron beam irradiation to determine the concentration distribution.