JPH0611467A - Depth direction spectrometric method for specimen surface with sputtering - Google Patents

Abstract

PURPOSE:To provide a depth direction analyzing method for the surface of a specimen using sputtering process. CONSTITUTION:Electron beams generated by an electron gun 1 are converged by an electromagnetic lens 2, etc., and cast onto a specimen S fixed to a stage 3. The secondary electrons including Auger electrons generated from} this part are passed through an energy analyzer 4, sensed/amplified by a secondary electron multiplier tube 5, and fed to a computer 6 to be analyzed as the energy spectrum, and at the same time, the secondary electron image obtained in two directions i.e., from a secondary electron sensor 8 and another 11 installed in different direction from it is fed to another computer 13 to determine the plane direction of the part to be analyzed as object. Into the depth, the sputtering time is converted into the depth using the relation between the previously determined plane direction and the speed of sputtering, and thereby the depth direction analysis can be performed quickly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing a sample surface in the depth direction by sputtering.

[0002]

2. Description of the Related Art Since the structure of various materials, such as the surface or the vicinity of grain boundaries, within about several thousand liters influences the characteristics of the material, investigating their composition and structure is an essential theme for material research. To investigate this, for example, Auger electron spectroscopy (hereinafter abbreviated as AES), secondary ion mass spectrometry (hereinafter abbreviated as SIMS), which is generally referred to as surface analysis method, X-ray photoelectron spectroscopy (hereinafter ESCA). Is abbreviated) and the like are used.

Among them, AES and SIMS are used as a micro-region analysis method for analyzing grain boundaries and micro-precipitates because they analyze a beam by narrowing it down. In the depth direction analysis of such a surface analysis method, it is general to utilize sputtering and convert the sputtering time into the depth to obtain the result. Where AE
S will be described in detail. Scanning AES commonly used
Then, as shown in FIG. 6, the electron beam generated by the electron gun 1 is focused by the electromagnetic lens 2 or the like and irradiated onto the sample S fixed to the sample stage 3. Secondary electrons including Auger electrons are generated from the irradiated part of the sample S, detected and amplified by the secondary electron multiplier 5 through the energy analyzer 4, and then taken into the computer 6 to obtain the energy spectrum. Is used for analysis and the result is displayed on the analysis monitor 7. Further, the signal from the secondary electron detector 8 is displayed on the monitor 9 such as a cathode ray tube in synchronization with the scanning of the electron beam, and the secondary electron image is observed to recognize the sample shape.

In order to carry out the depth direction analysis, ions such as Ar ⁺ are accelerated by applying a voltage from the ion gun 9 for sputtering to irradiate the surface of the sample S to carry out sputtering. At this time, in order to convert the sputtering time to the depth direction, in advance, at the same acceleration voltage as in the case of actual analysis, how fast the target material is dug at a certain ion current density, that is, the sputtering speed is obtained. Need to be kept.

The sputtering speed is measured by accurately measuring the ion current density with a Faraday cup, and sputtering a target material of known thickness under that condition, or directly measuring the sputtered depth with a measuring instrument such as a profile meter. Then, it is obtained from the relationship between the sputtering time and the depth. If the ion current density is measured before the actual analysis, the sputtering rate can be easily calculated from the above result, and the sputtering time can be converted into the depth.

[0006]

However, the reason why the sputtering time can be directly converted into the depth by using the previously obtained sputtering rate is that the surface to be sputtered maintains the same angle as the sample for which the sputtering rate is obtained. Only if you are. This is because when the angle changes, the irradiation angle of the ions on the surface is different from that when the sputtering rate is obtained, so the ion current density changes and the sputtering rate changes, and the so-called sputtering yield (per incident ion) This is due to the fact that the number of atoms sputtered on the metal has an angle dependence.

Therefore, in the depth direction analysis, it is possible to analyze the sputtering time by converting it to the depth so that the surface of the sample holder such as the plating layer or the thin film on the silicon substrate and the analysis surface can maintain substantially the same angle. It was limited to samples. That is, in the analysis of a portion in which the surface to be analyzed has unevenness and is oriented in a direction different from the angle at which the sputtering rate was obtained, it was not possible to convert it into the depth even if sputtering was performed.

However, analysis of grain boundaries is also required for methods such as AES and SIMS capable of surface analysis of minute portions. For example, in order to investigate the concentration of elements in the grain boundaries and the condition of the grain boundary layer of 100 Å or less, the sample is broken and the surface of the grain boundary is exposed and analyzed. In such a fractured surface, the angle of each surface to be analyzed cannot be maintained at the angle for which the sputtering rate was obtained, and therefore the depth of sputtering cannot be accurately obtained even if depth direction analysis is performed. It was not possible to evaluate the degree of element enrichment in the field.

The present invention has been made in order to solve the above-mentioned problems of the prior art. In the depth direction of the analysis surface, a constant angle cannot be maintained as in the depth direction analysis of the fracture surface. An object of the present invention is to provide a method for analyzing a depth direction of a sample surface by sputtering, which enables accurate determination of depth information in analysis.

[0010]

The present invention is a method for analyzing the distribution state of elements in the depth direction from the surface of a sample by sputtering, which is obtained by installing secondary electron detectors in at least two directions. The feature is that the surface direction of the target analysis part is determined by using multiple secondary electron images, and the depth direction analysis is performed by converting the sputtering time into the depth based on the relationship between the surface direction and the sputtering speed obtained in advance. Is a method for analyzing the depth direction of the sample surface by sputtering.

[0011]

[Operation] First, a case where the configuration of the present invention is applied to a scanning AES will be described. As shown in FIG. 1, another method for obtaining a stereo secondary electron image in a direction different from that of the secondary electron detector 8 will be described. A secondary electron detector 11 is provided. Then, the secondary electron image picked up by the secondary electron detector 11 is sent to the computer 13 for arithmetic processing through the monitor 12, and the secondary electron image from the conventional secondary electron detector 8 and the analysis surface are displayed. Processing for determining the angle of is performed.

The procedure of processing in the computer 13 will be described below with reference to FIG. Input two secondary electronic images. Determine the analytical surface. Calculate the angle between the analysis plane and the ion gun. Correct the sputtering rate. Convert the sputtering time to depth.

There are two methods for determining the analysis plane in the step. That is, a three-dimensional image is constructed by image processing using secondary electron beam images from two directions as a stereo image, and the angle of the analysis surface and the angle of the ion gun are obtained from the spatial coordinates of three points on the analysis surface. The second method is to calculate the azimuth of the plane on which the four points exist, from the positional relationship between the corresponding four points of the two stereo images and the positional relationship of the secondary electron detector. Of these, the first method requires time because image processing is used, but three-dimensional coordinates can be obtained over the entire range in which the secondary electronic image can be captured, and the second method is quick in calculation. When a sample tilting mechanism is provided, the sample is tilted while the angle of the analysis surface is obtained, and the sample is tilted to the desired angle for depth direction analysis.

The first method will be described in more detail. Using two secondary electron images, a three-dimensional image is constructed by image processing based on a preset angle of the secondary electron detector, and an observation field of view is obtained. Find the spatial coordinates of each point. Next, by selecting three points from the target surface and picking up the coordinates, the normal vector of that surface is obtained.
By previously obtaining the direction of the ion gun in the space coordinates, the angle between the ion gun and the analysis plane can be determined from the normal vector described above.

Specifically, the coordinates of three points on the analysis plane in the constructed three-dimensional coordinates are (x ₁ , y ₁ , z ₁ )
(X ₂ , y ₂ , z ₂ ) (x ₃ , y ₃ , z ₃ )
The analysis surface is expressed by the following equation 1,

[0016]

[Equation 1]

The normal vector to this surface is expressed by the following equation 2
Is.

[0018]

[Equation 2]

A unit vector parallel to this normal vector can be easily calculated, and it can be calculated as A (ax, ay, a
z) and the direction of the ion gun is I (ix, iy, iz), the angle θ formed by these two vectors is expressed by Equation 3, so that the angle θ between the analysis surface normal and the ion gun can be obtained. .

[0020]

[Equation 3]

Therefore, it is possible to calculate the correction coefficient from the relationship between the sputtering speed and the angle obtained in advance, correct the sputtering speed, and convert the sputtering time into the depth. Further, in the case of the second method, four or more points from the analysis surface such as the fracture surface shown in FIG. 3 are designated, and corresponding points between two secondary electron images are designated to determine the analysis surface from the positional relationship of the points. Since it is possible to obtain the angle of (the hatched portion defined by the points a, b, c, and d), the angle between the analysis surface normal and the ion gun can be obtained.

[0022]

[Example] In order to observe the concentration of elements in the grain boundaries of Mn-Zn ferrite, the grain boundaries are exposed by fracture and analyzed, and the concentration of the enriched elements in the grain boundaries toward the grain is determined. Scanning AES to which the method of the present invention is applied when analyzing whether it shows a change
When the angle dependence of the sputtering rate was experimentally obtained using, the results shown in FIG. 4 were obtained. From this result and the result of obtaining the angle of the analysis surface, an accurate sputtering rate can be applied to the analysis surface.

Further, FIG. 5 shows Mn burned by changing the amount of Ca added.
This is an analysis example of Ca concentrated in the grain boundary of a -Zn ferrite sample, and the amount of Ca added to sample A is about twice that of sample B. As is clear from this figure, in the case of sample A, not only the amount of concentration at grain boundaries is large but also the spread into grains is larger than in sample B. As described above, by using the method of the present invention, the spread can be converted into a specific numerical value and quantitatively evaluated.

[0024]

As described above, according to the present invention, the sputtered distance can be accurately obtained even for a sample in which the plane direction of the analysis surface is not constant, so that, for example, the element concentration at the grain boundary is broken. When the evaluation is performed in the depth direction of the surface, the size of the concentrated region can be quantitatively expressed, which can be useful for material evaluation.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of application of the present invention to a scanning AES.

FIG. 2 is a flowchart showing a processing procedure of the method of the present invention.

FIG. 3 is a schematic view of a fractured surface of an analysis sample.

FIG. 4 is a characteristic diagram showing a relationship between an incident angle and a sputtering speed ratio.

FIG. 5 is a characteristic diagram showing the relationship between AES peak intensity and depth.

FIG. 6 is a configuration diagram showing a conventional example of a scanning AES.

[Explanation of symbols] 1 electron gun 2 electromagnetic lens 3 sample stage 4 energy analyzer 5 secondary electron multiplier 6 computer 7 analysis monitor 8 secondary electron detector 9 monitor 10 ion gun 11 monitor 12 secondary electron detector 13 Computer S sample

Claims (1)

[Claims] 1. A method for analyzing a distribution state of elements in the depth direction from a sample surface by sputtering, wherein secondary electron detectors are installed in at least two directions, and a plurality of secondary electron images obtained are used. The depth direction of the sample surface by sputtering is characterized by determining the surface direction of the target analysis part and converting the sputtering time to the depth based on the relationship between the surface direction and the sputtering speed obtained in advance. Direction analysis method.