JP2001289752A - Method for preparing sample for observation of magnetic material by transmission electron microscope - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for preparing a sample for observation by a transmission electron microscope of a magnetic material, which can minimize disturbance of a magnetic field due to a sample shape and perform observation and analysis with higher accuracy. SOLUTION: In producing a sample for observation by a transmission electron microscope of a magnetic material by a focused ion beam processing method, t < ₁ is defined between a width w1 of a slice processing portion to be observed and a sample thickness t of a portion adjacent thereto. A method for preparing a sample for observation with a transmission electron microscope of a magnetic material, wherein the sample is processed so that a relationship of 3 × w ₁ is satisfied. The width w of the sliced part to be observed
It is preferable that the relationship w ₂ > 10 × w ₁ be further established between ₁ and the entire sample width w ₂ .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a sample for observation with a transmission electron microscope, and more particularly, to a method for processing a magnetic material by a focused ion beam processing method to prepare a thin sample for observation with a transmission electron microscope. About.

[0002]

2. Description of the Related Art There are various methods for manufacturing a transmission electron microscope, such as a microtome method, an electrolytic polishing method, and an argon ion sputtering method. In recent years, a focused ion beam (hereinafter abbreviated as FIB) processing method capable of thinning a target at a specific place of a material has been developed. For example, Japanese Patent Application Laid-Open No. 2-132345 discloses a thin-film sample using the same. A fabrication method is disclosed.

The FIB processing method is based on the principle of sputtering by applying a Ga ion beam almost vertically to a sample of about 2 mm length × 0.05 mm thickness × 1.5 mm height in a millimeter order. In this method, the peripheral portion of the observation target portion is scraped off, and as a result, an extremely thin portion having a thickness of about 0.2 μm or less is produced. This FI
The biggest advantage of B processing is that the secondary electron generated by Ga ion beam irradiation is imaged, and the section to be sliced is observed as a scanning ion microscope image, and the desired place is selectively sliced in micron order. This method is very popular and has attracted much attention as a method for preparing a sample for electron microscopic observation of a semiconductor device material or the like that requires processing on the order of microns and control of a laminated portion.

In particular, the development of a sample preparation method for performing elemental analysis with a transmission electron microscope with high precision has been energetically performed. For example, as disclosed in Japanese Patent Application Laid-Open No. 7-318468, FIB processing of a sample has been carried out. There is a technology that enables good energy dispersive X-ray elemental analysis in most places of a thin film by chamfering a steep wall of a portion remaining without performing a taper on a taper.

The FIB processing technique applied as a method for preparing a sample for observation of a semiconductor device material for transmission electron microscopy is described below.
When applied to magnetic materials such as iron and steel materials, unlike semiconductors such as silicon, metal materials such as steel materials have a long sputtering time with a Ga ion beam. ,
Some measures have been taken to reduce the initial thickness.

Further, since the sample is placed in a transmission electron microscope under a high magnetic field of 10,000 gauss or more, even if the sample is large or small, the portion of the steel material to be observed in the actual transmission electron microscope observation. There is a problem that it is extremely difficult to adjust the astigmatism and focus of the image. In order to perform observation with a transmission electron microscope and elemental analysis with high accuracy, a device for removing a steep wall other than a thin section which causes this has been attempted.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method for preparing a sample for observation of a magnetic material by a transmission electron microscope, which can minimize the disturbance of the magnetic field due to the shape of the sample and can observe and analyze with higher accuracy. That is the task.

[0008]

Means for Solving the Problems In order to achieve the above object, the inventors focused on disturbance of the magnetic field distribution in a transmission electron microscope and studied the shape of the sample after FIB processing. The main points of the project are as follows. (1) In preparing a transmission electron microscope observation sample of a magnetic material by the focused ion beam processing method, t <3 is set between the width w ₁ of the sliced portion to be observed and the thickness t of the peripheral portion adjacent thereto. A method for preparing a sample for observation with a transmission electron microscope of a magnetic material, wherein the sample is processed so that a relationship of xw ₁ is satisfied.

(2) The width w _{1 of the} sliced portion to be observed
And w ₂ > 10 × w ₁ between the sample width w ₂ including the peripheral portion.
The method according to (1), wherein the following relationship is further satisfied.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the case of a steel material, such as an electrolytically polished thin sample, the effect of a magnetic field was particularly strong during observation, and there was no hindrance to astigmatism or focusing.
A feature of the sample manufactured by the FIB processing method is that a thick film portion of several tens of μm easily coexists, and by paying attention to this point, the state of the sample in a transmission electron microscope is shown in FIG.
This will be described with reference to FIG.

The flaked portion to be actually observed has a thickness of usually 0.2 μm or less so that an electron beam can pass therethrough, and the peripheral portion has a thickness of 30 to 50 μm or more. Therefore, it is considered that the magnetic field is largely disturbed locally. Therefore, assuming that the thickness of the thin section is almost negligible compared to the peripheral section, the influence was examined by changing the thickness t of the peripheral section adjacent to the thin section in various ways. As a result, the width of the lamina processing unit when the w _1, when t is three times more than the thickness, making it impossible to perform astigmatism correction in a conventional electron microscope operating, the more the entire surface of the thin portion It has been found that it is more desirable that t is not more than twice the thickness of w _{1 in} order to allow stable observation.

At this time, the depth indicated by D in FIG. 1 was considered to be one parameter. However, in the case of a normal electron microscope sample, it is often mounted on a sample stage of 3 mmφ, and the depth D is about 1 mm. is there. Although various changes were made in the range of about 1 to 1.7 mm, it was found that the effect of the depth had almost no effect at this level, and the thickness t of the peripheral portion adjacent to the sliced portion was the most important parameter. Was. That is, as shown in FIG. 2, it is sufficient to pay attention to the two-dimensional cross-sectional shape, and the condition of t <3 × w ₁ has been found.

When manufacturing by the focused ion beam processing method, the width w ₁ of the processed thin section cannot be so large, and is usually about 5 μm to 10 μm.
Therefore, the thickness t of the peripheral portion is 15 to 30 microns or less. If such is the fine size, sample width w ₂ including a peripheral portion also possible to increase it is practically impossible. w ₂ is also of the order of at most several tens of microns. As a means for processing a sample of such a size,
In the focused ion beam processing method, one of the manufacturing methods is to use a micro sampling method. However, when handling small pulverized samples, sample processing on the order of several tens of microns is possible from the beginning without using the microsampling method.

Next, a case where the sample size is on the order of millimeters was examined because the FIB sample often deals with a larger size. At this time,
The size of the sample in the depth direction indicated by D in FIG. 1 is not so important, and it is understood that the thickness t of the peripheral portion adjacent to the sliced portion is important in the cross-sectional shape shown in FIG. Was.

Further, by further defining the sample width w ₂ including a portion of the thickness t of the peripheral portion adjacent to the lamina processing unit was found to be easier to further observation. That is,
The w ₂ by a thickness of more than 10 times the w _1, it was found that further facilitates the astigmatism correction in the electron microscope.
In this case, the case where the thickness t is increased stepwise and the case as shown in FIG. 4 is also examined, but essentially, the thickness t of the peripheral portion adjacent to the flaked portion and the width w including the thickness t are included. The length of ₂ turned out to be an important parameter.

In order to fabricate a sample having such a shape by FIB processing, processing for a long time of 5 hours or more is required.
After pre-processed for rough machining of only securing the width w ₂ of approximately 00 microns, the sample prepared was possible by performing the usual finishing procedures.

[0017]

The present invention will be described in more detail with reference to the following examples. (Example 1) A commonly used carbon steel plate was used as a thick plate, and a sample for observation with a transmission electron microscope having a size of several tens of microns was prepared therefrom by using a microsampling device attached to an FIB device. The transmission electron microscope used for observation was an electron microscope HF-2 manufactured by Hitachi with an accelerating voltage of 200 kV.
000. When test pieces of various sizes were prepared, and the astigmatism correction mechanism of the electron microscope could correct astigmatism,
The case where it was not possible was evaluated as x, and it was confirmed whether or not the ferromagnetism of the sample adversely affected the observation. Table 1 shows the results.

[0018]

[Table 1]

(Example 2) A carbon steel commonly used as a thick plate is used, and a sample for observation with a transmission electron microscope of several tens of microns in size is obtained from the steel by using a micro-sampling device attached to an FIB device. Was prepared. The transmission electron microscope used for observation was an electron microscope HF-2000 manufactured by Hitachi.
It is. When test pieces of various sizes were prepared and the astigmatism was corrected by the astigmatism correction mechanism of this electron microscope, the result was evaluated as ○. confirmed. Table 2 shows the results.

[0020]

[Table 2]

[0021]

According to the present invention, astigmatism can be corrected as usual in a transmission electron microscope even for a ferromagnetic material such as a steel material by the focused ion beam processing method, and sufficient observation and A sample that can withstand the analysis can be provided.

[Brief description of the drawings]

FIG. 1 schematically shows a steep magnetic field change at a sample position when a sample having a shape characteristic of a focused ion beam processing method is installed in a transmission electron microscope. .

FIG. 2 schematically shows an example of a sample shape according to the present invention.

FIG. 3 schematically shows an example of a sample shape of the present invention.

FIG. 4 schematically shows an example of a sample shape according to the present invention.

[Explanation of symbols]

1 ... sample containing width w ₂ ... peripheral portion of the depth w ₁ ... lamina processing unit thickness D ... specimen periphery adjacent to the electromagnet 2 ... magnetic material A ... corner t ... lamina processing unit of the objective lens pole piece Width w ₃ … Whole width of sample

Claims (2)

[Claims] In producing a transmission electron microscope observation sample of a magnetic material by a focused ion beam processing method, a distance t between a width w ₁ of a flake processing portion to be observed and a thickness t of a peripheral portion adjacent thereto is set. A method for preparing a sample for observation with a transmission electron microscope of a magnetic material, wherein the sample is processed so that a relationship of 3 × w ₁ is satisfied. 2. A width w of a thinned portion to be observed.₁And Zhou
Sample width w including sides _TwoBetween, w_Two> 10 × w₁Become
2. The method according to claim 1, wherein the relationship is further established.
A method for preparing a sample for observation of a magnetic material using a transmission electron microscope.