JPH0762657B2 - Sample surface analysis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention is, for example, an electron beam microanalyzer (EPMA).
As described above, the present invention relates to a surface analysis method for exciting a sample with a charged particle beam and measuring the concentration distribution of elements on the sample surface using the generated characteristic X-rays.

(B) Conventional technology and its problems Generally, when measuring the concentration distribution of elements in the sample surface by line analysis or area analysis in EPMA, if the sample surface is not horizontal, the sample will move as the sample moves. The analysis height (the distance from the measurement point of the sample to the spectroscope) changes, and the deviation from the focus of the spectroscope causes the X-ray intensity to change.

Therefore, there are methods such as using a jig to keep the sample surface horizontal, and obtaining the amount of inclination of the sample surface in advance, and based on this, changing the analysis height sequentially and continuously while moving the sample. Has been done.

However, in any of these methods, it is premised that the sample surface is a flat surface without unevenness, and it is necessary to make it flat by polishing or the like, but when the analysis surface of the sample becomes large, for example, 10 cm × 10 cm. In many cases, it is technically and costly difficult to obtain a required flat surface by polishing. Furthermore, when elemental analysis of fracture surfaces is performed, it cannot be horizontal in nature. Therefore, there is a problem that the measurement data is affected by the unevenness of the sample surface.

The present invention has been made in view of the above points, and an object of the present invention is to provide a sample surface analysis method that improves accuracy by eliminating an error in measurement data due to unevenness of the sample surface.

(C) Means for Solving the Problems In the present invention, in order to achieve the above-mentioned object, the sample on the surface of the sample is excited based on the characteristic X-ray generated by exciting the sample with a charged particle beam. In the surface analysis method of the sample to measure the concentration distribution, etc., a coating layer containing a coating material containing a specific element is formed on the surface of the sample to be analyzed, and the change in the analysis height of the sample at any point on the surface of the sample A characteristic X-ray intensity change characteristic of the analytical element and the specific element of the coating material is measured in advance, and the characteristic X-ray intensity of the analytical element and the specific element of the coating material is measured at each point on the sample surface to be analyzed, and the coating is performed. Based on the intensity of the characteristic X-ray of the specific element of the material, the intensity of the characteristic X-ray of the analytical element with respect to the analytical height of the sample is corrected at each measurement point, and at that time. As the intensity of the characteristic X-ray of the specific element at the measurement point, an average value of the intensity of the characteristic X-ray of the specific element at the measurement point and the intensity of the characteristic X-rays of the specific element at a plurality of measurement points around the measurement point is used. Is configured to do.

(D) Action According to the above configuration, the coating layer containing the specific element is formed on the surface of the sample to be analyzed, and the intensity of the characteristic X-ray of the analytical element and the specific element with respect to the change of the analysis height of the sample at any point thereof. Change characteristic is measured in advance, and at the time of actual analysis, the intensity of the characteristic X-ray of the specific element of the coating layer is measured by measuring the intensity of the characteristic X-ray of the analysis element and the specific element at each measurement point. By knowing the amount of the analysis height, it becomes possible to correct the influence of the analysis height of the sample on the intensity of the characteristic X-ray of the analysis element.
Further, when performing the correction, the intensity of the characteristic X-ray of the specific element at the measurement point to be corrected is defined as the intensity of the characteristic X-ray of the specific element at the measurement point and the intensity of the specific element at a plurality of measurement points around the specific element. Since the average value with the characteristic X-ray intensity is used, elemental analysis is possible with high accuracy even if the surface of an unknown sample is severely uneven, such as elemental analysis of fracture surfaces. Becomes

(E) Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an EPMA used for carrying out the method of the present invention. In the figure, 1 is a sample to be analyzed, 2 is a filament part for generating an electron beam, 3 is a converging lens, 4 is an astigmatism correction coil, 5 is an objective diaphragm, and 6 is an objective lens. This EPMA is equipped with two first and second spectroscopes, 9 and 10 are dispersive crystals constituting each spectroscope, and 11 and 12 are characteristic X-rays from each spectroscope. These are the first and second detectors for detection. 13 is the sample stage
A drive control circuit for driving 14, 15 is the first and second detectors 11, 12
The X-ray measurement circuit for measuring the X-ray intensity signal obtained in step 1, 17 is a display device for converting the measurement data into an image signal and performing so-called color content mapping (color density distribution) display, and 16 is each of these circuits. It is a control circuit that controls and corrects the measured data by performing a predetermined calculation process as described later.

Next, the method for surface analysis of the sample of the present invention by applying the EPMA having the above structure will be described. First, the sample surface to be analyzed is coated with a coating material containing a specific element. For example, a coating layer containing Au containing a coating layer having a thickness of several hundred angstroms is formed on the surface of the sample for analyzing the distribution of Si by a method such as sputtering.
This coating layer is formed to have a uniform thickness along the irregularities on the sample surface, and does not fill the irregularities on the sample surface to flatten the surface. Next, for any point of this sample, the Si
The change characteristics of the characteristic X-ray intensity of Au and Au are measured in advance as follows.

The sample is set on the sample stage 14 and the electron beam generated in the filament part 2 is converged by the converging lens 3, the objective diaphragm 5,
It is guided by the objective lens 6 to irradiate the reference sample. Among the characteristic X-rays generated from the reference sample by the irradiation of the electron beam, the characteristic X-rays of Si are detected by the first detector 11 and the characteristic X-rays of Au are detected by the second detector 12. The X-ray intensity signals from the detectors 11 and 12 are given to the X-ray measurement circuit 15, and further,
It is given to the control circuit 16. Here, when the height of the sample stage 14 is sequentially changed and the X-ray measurement of Au and Si is performed, the control circuit 1
Data for the change in the intensity (I / Imax) of the characteristic X-rays of Si and Au with respect to the change in the analysis height (Z) of the sample shown in FIG. 2 will be given to 6. These data are stored in the internal memory of the control circuit 16. In FIG. 2, Z ₀ is the analysis height that coincides with the focus of the X-ray spectrometer, Im
ax indicates the strength at that time.

The size (depth) of the X-ray generation area from the sample surface
Is about 1 μm, whereas the thickness of the coating layer is several hundred angstroms (100 angstroms = 0.0
1 μm), the difference in analysis height between the coating layer and the sample surface can be ignored. Next, the intensity distribution of the characteristic X-rays of Si and Au is measured at each point of the sample.
That is, the sample on which the coating layer is formed is moved using the sample stage 14 to start measurement at each point. The electron beam generated in the filament section 2 is guided by the converging lens 3, the objective diaphragm 5, and the objective lens 6 and is applied to the sample 1. At that time, the drive control circuit 13 drives the sample stage 14 to two-dimensionally scan the sample surface with the electron beam.

Among the characteristic X-rays generated from the sample surface due to the irradiation of the electron beam, the characteristic X-rays of Si are detected by the first detector 11 by the Au detector.
The characteristic X-rays of 1 are detected by the second detector 12 and given to the X-ray measuring circuit 15. Each intensity data from the X-ray measuring circuit 15 is given to the control circuit 16.

In the control circuit 16, based on the measured intensity of the characteristic X-rays of Si and Au and the intensity of the characteristic X-rays of Si and Au related to the previously measured analysis height, the Si for each analyzed point is measured.
The analytical height of the sample is corrected with respect to the intensity of the characteristic X-ray of each measurement point. That is, the control circuit 16 calculates the true intensity I _X of the characteristic X-ray of Si at each measurement point according to the following equation.

Ix = I ₁ / {F (z) × I ₂ a / I ₂ max} (1) where I ₁ is the intensity of the characteristic X-ray of Si at each measurement point,
I ₂ a is a value obtained by taking a weighted average of the characteristic X-ray intensity I ₂ of Au at each measurement point and the characteristic X-ray intensity of Au at a plurality of measurement points around it, and F (z) is the measurement value. Analysis height of point z
Intensity ratio of characteristic X-rays of Si and Au in
(Z) = I ₁ (z) / I ₂ (z), and the analysis height z of this measurement point corresponds to the measurement value of I ₂ a / I ₂ max and is the second for each measurement point. It is determined from the pre-measured data shown in the figure. In addition, I ₂ max is the intensity of the characteristic X-ray of Au at the focus position, and is the value measured at the position Z ₀ previously.

In the present invention, when correcting each measurement point, the average value I ₂ a obtained by weighting the intensities of the point and a plurality of measurement points around the point is used for correction as described above. For example, as shown in FIG. 3, when the measurement point p ₅ is corrected, this p ₅
As the intensity I ₂ of the characteristic X-ray of Au, the intensity I ₂ and the intensity I ₂ of the characteristic X-ray of Au at each of the seven measuring points p _{1 to} p ₄ and p _{6 to} p _{9 around it.}
An average value weighted with p _{1 to} Ip ₄ and Ip _{6 to} Ip ₉ is calculated by the control circuit 16 according to the following equation, and correction is performed.

I ₂ a = {3 × I ₂ ＋ 2 × (1p ₂ ＋ Ip ₄ ＋ Ip ₆ ＋ Ip ₈ ) + (Ip ₁ ＋ Ip ₃ ＋ Ip ₇ ＋ Ip ₉ )} ÷ 15 …… (2) In this second formula, the measurement for correction and intensity of the point p _5, and the intensity of the vertical and horizontal measurement point _{Ip 2, Ip 4, Ip 6} , Ip 8, the intensity of the oblique vertical direction of the measuring points _{Ip 1, Ip 3, Ip 7} , Ip 9 weighting The ratio is 3: 2: 1.

As described above, the intensity of the characteristic X-ray of Au at each measurement point is corrected by using the value obtained by averaging the intensity of the characteristic X-rays of Au of a plurality of measurement values around the surface of the unknown sample. Even when the coating layer is not evenly formed due to the severe unevenness of, the correction can be accurately performed.

For example, if the analysis height changes by 100 μm (= 0.1 mm),
X-ray intensity is halved. That is, if the sample surface having irregularities of about 0.1 mm is simply analyzed, the X-ray intensity changes by about twice due to the irregularities, and the correct intensity distribution in the horizontal direction cannot be obtained. By correcting the analysis height, the correct intensity distribution can be obtained.

In the control circuit 16, the intensity data measured by changing the height of the sample in advance in this manner and the intensity data at each point are corrected and output to the display device 17 at each measurement point. Display is performed on the display device 17 based on the corrected true measurement data.

(F) Effects As described above, according to the present invention, a coating layer containing a specific element is formed on the surface of an analysis sample, and the analysis element and the characteristic X-ray of the specific element with respect to the change in the analysis height of the sample are changed. The intensity of characteristic X-rays of the analysis element and the specific element is measured at each point to measure the intensity of the characteristic X-rays, and the intensity of the characteristic X-rays is measured in advance. It is possible to correct the analysis height of the sample with respect to the intensity of the characteristic X-ray of the analysis element at each point. Furthermore, when performing the correction,
As the intensity of the characteristic X-ray of the specific element at the measurement point to be corrected, the average value of the intensity of the characteristic X-ray of the specific element at the measurement point and the intensity of the characteristic X-rays of the specific element at a plurality of surrounding measurement points Since it is performed by using the method, the correction is performed with high accuracy even when the unevenness of the surface of the analysis sample is severe as in the case of elemental analysis of the fracture surface, and the measurement accuracy is improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an EPMA used for carrying out one embodiment of the present invention, FIG. 2 is a characteristic diagram showing the relationship between analytical height and strength,
FIG. 3 is a diagram for explaining the correction method. 1 ... Sample, 9, 10 ... Spectroscopic crystal, 16 ... Control circuit.

Claims (1)

[Claims] 1. A surface analysis method for a sample, which comprises exciting a sample with a charged particle beam and measuring the concentration distribution of elements on the surface of the sample based on characteristic X-rays generated from the sample. And forming a coating layer of a coating material containing a specific element on the surface of the sample, the change characteristics of the characteristic X-ray intensity of the analysis element and the specific element of the coating material with respect to the change of the analysis height of the sample at any point. The characteristic X-ray intensity of the analysis element and the specific element of the coating material is measured at each point on the sample surface to be measured in advance and analyzed, and the analysis height of the sample is determined based on the intensity of the characteristic X-ray of the specific element of the coating material. The characteristic X-ray intensity of the analytical element is corrected for each measurement point, and the characteristic X-ray intensity of the specific element at the measurement point to be corrected is used as the characteristic of the measurement point. Surface sample analysis method, which comprises using the mean value of the intensity of an element of the characteristic X-ray and the intensity of the characteristic X-ray of a specific element of the plurality of measurement points around.