JPH08201317A - Method and apparatus for measuring element distribution in sample and composition analysis - Google Patents

Abstract

PURPOSE: To quickly measure the element distribution and analyze the composition with high accuracy by applying a low-accelerating voltage electron beam to the surface of a sample, detecting the backward scattering electrons generated on the surface of the sample while observing the secondary electron image, and analyzing the luminance distribution. CONSTITUTION: A low-accelerating voltage electron beam is irradiated to the surface of a sample, a backward scattering electron image is displayed on an observation monitor 8, the gain of a backward scattering electron intensity amplifier 5 is adjusted to make the backward scattering electron strength to a constant luminance distribution, then the backward scattering electron intensity is fed to a measurement/analysis calculating device 9. It is compared with the backward scattering electron intensity of a sample with the known composition stored in advance to obtain the composition of the sample, and the measured/analyzed results are displayed on a measuring/ analyzing monitor 10. When the irradiating current is changed during the measurement, an irradiating current detector 6 detects the change of the irradiating current and sends signals to a controller 2 and the backward scattering electron intensity amplifier 5 via an irradiating current side measuring device 7 to control them so that the irradiating current becomes a set value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring element distribution in a sample, a composition analysis method and an apparatus therefor, and more specifically, by detecting backscattered electrons in a scanning electron microscope and analyzing the brightness distribution thereof. The present invention relates to a method and apparatus for measuring element distribution and further analyzing composition.

[0002]

2. Description of the Related Art Elemental distribution measurement and composition analysis of minute portions in a sample using a scanning electron microscope (hereinafter abbreviated as SEM) include, for example, nickel (Ni) and chromium in steel.
(Cr), manganese (Mn), molybdenum (Mo), carbon (C)
When measuring such as, there is an energy dispersive X-ray analyzer disclosed in, for example, JP-A-3-165440.

[0003] The content is that in an energy dispersive X-ray analyzer used in combination with an electron microscope or similar device, the irradiation electron beam energy of a sample irradiation electron beam of the electron microscope or similar device is monitored and X-ray analysis is performed. It is characterized by having a function of using this for processing.

[0004]

However, in order to measure the element distribution using the apparatus disclosed in Japanese Patent Laid-Open No. 3-165440, the time required for the measurement is very long, so that the number of samples that can be measured per day is limited. In addition, there are inconveniences such as high measurement cost, and because the area where characteristic X-rays are generated is as large as about 1 μm compared to the spot size of the incident electron beam, the measurement magnification and spatial resolution are insufficient for the required accuracy. There is such a problem. Although there is a method in which the SEM is equipped with a backscattered electron detector to measure the approximate distribution of the elements, it is impossible to identify or analyze the elements by this method.

The present invention has been made to solve the above-mentioned problems of the prior art. It is possible to perform element distribution measurement and composition analysis rapidly and highly accurately while observing a minute portion in a sample. It is an object to provide a method and a device.

[0006]

In order to achieve the above object, the present invention irradiates a sample surface with a low-acceleration electron beam and simultaneously detects a secondary electron image while simultaneously detecting backscattered electrons generated on the sample surface. Then, the luminance distribution is measured, and the distribution of elements in the sample is measured and the composition is analyzed by performing calibration using the backscattered electron intensity obtained from a sample of known composition determined in advance. And the composition analysis method.

The present invention also provides a scanning electron microscope for irradiating a low-acceleration electron beam, a secondary electron detector, a backscattered electron detector, and an irradiation current measuring device which are attached to the lens barrel of the scanning electron microscope. A backscattered electron intensity amplifier for adjusting the gain to obtain a constant brightness distribution by inputting the backscattered electron intensity signal detected by the backscattered electron detector, A device for measuring element distribution in a sample and a composition analyzer, comprising: an arithmetic processing unit for calibrating a backscattered electron intensity signal input from the backscattered electron intensity amplifier according to scattered electron intensity to obtain a composition of the sample. is there.

[0008]

[Operation] The present inventors focused on the fact that the backscattered electron intensity generated on the sample surface when irradiated with an electron beam was proportional to the atomic number, and measured the distribution of the backscattered electron intensity to determine the element It was found that distribution measurement is possible. In this case, in order to avoid the influence of the generation region of the backscattered electrons, that is, the resolution of the element distribution measurement from the acceleration voltage of the electron beam, the irradiation current, and the diameter of the electron beam, the electron gun of the SEM has a directivity. A good field emission type was used, and low acceleration voltage and low irradiation current were used. Also, the irradiation current of the electron beam is constantly changing, and since this method cannot directly identify the element, the irradiation current is measured during observation and the gain of the amplifier of the backscattered electron detector is adjusted. By adjusting
A constant brightness distribution is always obtained.

Therefore, according to the present invention, a back-scattered electron generated on the sample surface is simultaneously irradiated with a low acceleration voltage electron beam by irradiating the sample surface with a field emission type electron gun and observing a secondary electron image. Is detected and its luminance distribution is analyzed, so that a constant luminance distribution is always obtained, and it is possible to automatically perform the identification and distribution analysis of the elements in the sample, and further the quantitative analysis.

Further, according to the present invention, the intensity distribution of the backscattered electrons is measured instead of measuring the intensity distribution of the characteristic X-ray, so that the element distribution measurement and the quantitative analysis can be performed quickly, It is possible to reduce the time required for measurement and analysis and save energy. For example, conventional ED
In the two-dimensional mapping of S, the resolution was about 1 μm when the analysis time was 30 minutes or more, but it was about 54 seconds for the backscattered electron of the present invention, and the resolution was also about 10 nm.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a measurement / analysis apparatus according to the present invention. In this figure, 1 is an S equipped with an electron gun chamber, a sample chamber for storing a sample, an observation chamber, etc.
EM lens barrel portion, 2 is a control unit of the lens barrel portion 1, 3 is a backscattering electron detector attached to the lens barrel portion 1, 4 is a secondary electron detector attached to the lens barrel portion 1, and 5 is backscattering A backscattered electron intensity amplifier for inputting the backscattered electron intensity signal of the sample surface detected by the electron detector 3 to adjust the gain in order to obtain a constant brightness distribution, 6 is an irradiation current detection attached to the lens barrel portion 1. Measuring instrument 7, an irradiation current measuring device, 8 an observation monitor, 9 a backscattered electron intensity of a sample having a known composition, and a calculation / analysis operation for comparison calculation with the backscattered electron intensity signal from the backscattered electron detector 3. The device, 10 is a measurement / analysis monitor.

The sample is set in the sample chamber of the lens barrel portion 1 of the SEM, and the examiner makes adjustments while looking at the observation monitor 8 so that a normal electron microscope image can be obtained. Therefore, the backscattered electron image is displayed on the observation monitor 8, the gain of the backscattered electron intensity is adjusted by the backscattered electron intensity amplifier 5 to obtain a constant luminance distribution, and then the measurement / analysis calculation device 9 imports it. The composition of the sample is obtained by performing a comparison operation with the backscattered electron intensity of the sample of known composition stored in advance, and then the measurement / analysis result is displayed on the measurement / analysis monitor 10. If the irradiation current changes during measurement, the irradiation current detector 6 detects the change in the irradiation current and sends a signal to the control unit 2 and the backscattered electron intensity amplifier 5 via the irradiation current measuring device 7. , The irradiation current is controlled to reach the set value.

In order to confirm the performance of the device of the present invention thus constructed, Fe; 37.31 wt%, Cu; 50.75 wt%, C; 1
The investigation was carried out using a ternary sample consisting of 1.94 wt%. At this time, the acceleration voltage was 5 kV and the probe current was 0.5 nA.
FIG. 2 is a micrograph of the element distribution state measured at a magnification of 500 times. In this figure, the white area is Cu and the gray area is
The Fe and black regions respectively indicate C, but as is clear from this figure, it is understood that good measurement results can be obtained because the element distribution can be detected with high sensitivity.

Further, since the backscattered electron intensity is quantized with respect to the atomic number Z as shown in FIG. 3, the element can be identified and its area occupancy (%) can be calculated. Gives the elemental concentration (atomic%). Therefore, the result of measuring the element concentration by changing the field of view of the SEM to a low magnification of 30 times is shown in FIG. As a result, C; 40.20 atom
ic%, Fe; 27.51 atomic%, Cu; 30.77 atomic% were measured. Therefore, the lower limit of detection in the present invention is 0.01 at.
It is omic%.

Next, Cr steels having different Cr concentrations (Cr content ratio;
The relationship between the average atomic number and the backscattered electron intensity was investigated by using 13 to 60 mass%, average atomic number; 24.8 to 25.74) as a sample, and accelerating voltage; 15 kV, probe current; 0.3 nA. At this time, the backscattered electron intensity was measured three times in the same visual field, and was measured in three visual fields. The result is shown in FIG. In the figure, error bars indicate variations in the measurement of three visual fields, and squares indicate the average value thereof. Although the measurement results were different for each visual field, by averaging them, a calibration curve having a good correlation between the average atomic number and the backscattered electron intensity was obtained.

Here, in order to examine the accuracy of the obtained calibration curve, σ _d obtained by the following formula was calculated. σ _d = √ {Σ (Xreal−Xcal) ² / (n−1)} where σ _{d is} the accuracy of the calibration curve, Xreal is the atomic number of the solid line, Xcal is the atomic number obtained from the calibration curve, and n: It is a measurement point.

As a result, σ _d was 0.026. Therefore, it was found that the atomic number can be estimated with an accuracy of about 0.09 by taking 3σ _d . Therefore, it can be said that this 0.09 is atomic number resolution. Next, the main components of the observed sample are C: 1.94 mass%, Mo: 2.33 mass%, Cr: 6.64 mass%,
V: 5.90mass%, W: 3.80mass%, Ni: 4.48mass%, using a high-speed steel roll, high-purity Al as a standard sample,
Using Cu and Fe, they were embedded in the same wood metal and polished. Next, acceleration voltage; 5kV, incident current; 0.5n
As A, images of the observation sample and the standard sample were captured. The backward scattered electron image is shown in FIG. Furthermore, when a calibration curve was created from the relationship between the brightness of the standard sample and the atomic number, the calibration curve of FIG. 7 was obtained.

Then, as a result of measuring the luminance of the element or compound by paying attention to the elongated granular material indicated by the arrow in FIG. 6, the backscattered electron intensity is 1.18, and using this value, the calibration of FIG. The average atomic number was calculated from the line 31.5
Met. The roll material of this observation sample is already SE
It has been observed by M and TEM (abbreviation of transmission electron microscope), it contains various carbides, the type of the carbides can be identified from the shape, and Mo was detected from the analysis result of the EDS image. It is known that the above-mentioned granular material is Mo ₇ C ₃ (average atomic number; 31.2), which is a kind of carbide. Therefore, it can be seen that the average atomic number measured in this experiment is almost the same as that of Mo ₇ C ₃ .

From the results shown in FIG. 7 above, it was confirmed that the carbides also fit on the calibration curve, so it was found that the element identification based on the backscattered electron intensity may be applicable to non-conductive materials.

[0020]

As described above, according to the present invention,
Irradiate the sample surface with a low accelerating voltage electron beam using a field emission type electron gun, while observing the secondary electron image, simultaneously detect backscattered electrons generated on the sample surface and analyze the brightness distribution. Therefore, the element distribution measurement and the composition analysis of the elements in the sample can be performed with high accuracy, which contributes to the improvement of the efficiency of the element distribution measurement and the composition analysis of the minute portion in the sample.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a measurement / analysis apparatus according to the present invention.

[Fig. 2] Fe; 37.31 mass%, Cu; 50.75 mass%, C; 1
It is a microscope picture which shows the metal structure of a ternary system sample which consists of 1.94 mass%.

FIG. 3 is a characteristic diagram showing the relationship between atomic number and backscattered electron intensity.

FIG. 4 is a characteristic diagram showing a relationship between an element in a sample and its content rate.

FIG. 5 is a characteristic diagram showing the relationship between the average atomic number of Cr steel and the backscattered electron intensity.

FIG. 6 is a micrograph showing the metal structure of high-speed steel rolls.

FIG. 7 is a characteristic diagram showing the relationship between the average element number of high-speed steel rolls and backscattered electron intensity.

[Explanation of symbols]

 1 SEM (scanning electron microscope) lens barrel 2 Control unit 3 Backscattered electron detector 4 Secondary electron detector 5 Backscattered electron intensity amplifier 6 Irradiation current detector 7 Irradiation current measuring device 8 Observation monitor 9 Measurement / Analytical calculation device 10 Measurement / analysis monitor

Claims (2)

[Claims] 1. A sample surface is irradiated with a low-acceleration electron beam,
While observing the secondary electron image, the backscattered electrons that occur on the sample surface are detected at the same time, the luminance distribution is measured, and the intensity of the backscattered electrons from the sample whose composition is known in advance is used to calibrate the A method for measuring element distribution in a sample and analyzing the composition, which comprises measuring the distribution and analyzing the composition. 2. A scanning electron microscope for irradiating a low-acceleration electron beam, a secondary electron detector, a backscattered electron detector, an irradiation current measuring device attached to the lens barrel of the scanning electron microscope, and the rear side. The backscattered electron intensity amplifier that inputs the backscattered electron intensity signal detected by the scattered electron detector and adjusts the gain to obtain a constant brightness distribution, and the backscattered electron intensity of the sample of known composition stored in advance A device for measuring element distribution in a sample and a composition analyzer, which comprises an arithmetic processing means for calibrating a backscattered electron intensity signal input from the backscattered electron intensity amplifier to obtain a composition of the sample.