JP2008256560A - Thin film sample and manufacturing method thereof - Google Patents

Abstract

An object of the present invention is to provide a sample capable of simultaneously observing and measuring an index sample and a specimen sample under the same conditions.
In the method for producing a thin film sample of the present invention, a lump of an indicator sample is brought into close contact with a specimen sample and integrated, and the integrated portion is cut out to form a sample piece. Then, the sample piece is thinned with a laser. When integrating, first, carbon is vapor-deposited to protect the surface of the specimen sample, and the index sample lump is dispersed on the specimen sample. Then, a tungsten deposition process is further performed thereon to form a protective layer over the entire surface. In this state, a sample piece of a predetermined size (for example, 2 μm × 10 μm) is cut out and thinned (for example, 0.1 μm thick).
[Selection] Figure 2

Description

  The present invention relates to a thin film sample and a manufacturing method thereof, and more particularly to a sample capable of accurate EDX analysis quantification or magnification correction in a transmission electron microscope and a manufacturing method thereof.

  Recent advances in ultra-high vacuum technology and microfabrication technology have accelerated the research and development of new functional materials and advanced devices that reach the atomic order. For these research and development, it is necessary to evaluate the material, physical properties, structure, composition, etc. produced and feed back to the design process. As this evaluation means, a transmission electron microscope is widely used. Recently, an electron microscope has come to be used as a process evaluation means in production sites such as dimensional inspection and failure analysis. Against this background, there is an urgent need to increase the accuracy and speed of measurement data of electron microscopes, and sample preparation (pretreatment) is an important point that affects the quality of data.

  A conventional standard sample for EDX analysis in a transmission electron microscope is thinned separately from a specimen sample that is a measurement purpose. Moreover, the specimen sample and the standard sample for EDX analysis are individually analyzed. That is, the quantification analysis of the specimen sample is performed based on the measurement data obtained with the standard (index) sample.

  When performing EDX mapping, it is necessary to perform drift correction on the sample in order to ensure accuracy (because the sample must be stationary on the nano order), but there is an indicator in the thinned specimen sample. If there is no such structure, drift correction is not performed.

  In addition, the magnification of the electron microscope image, which is important when measuring the dimensions, is calibrated using the standard value of the apparatus as it is or using a commercially available standard sample.

  When performing standard quantification of EDX analysis in a transmission electron microscope (TEM), a standard sample is indispensable. Therefore, it was necessary to prepare a standard sample for a transmission electron microscope. Patent Document 1 discloses a TEM sample preparation method by the FIB method, and a standard sample for EDX analysis can be prepared using this method.

Japanese Patent Laid-Open No. 10-68683

  However, even if the standard sample can be prepared in Patent Document 1, since the standard sample and the specimen sample are individually measured as described above, the same conditions (thickness, shape, Measurement in background, system peak, etc. is not possible. This is because, in TEM, the results obtained are different if the standard sample and the specimen sample have different thicknesses.

  In addition, when EDX mapping is performed as described above, drift correction is necessary, but drift correction is difficult if there is no structure serving as an index in the measurement sample.

  Further, a commercially available standard sample for magnification correction uses a replica of a grating engraved at a 0.2 micron pitch for low magnification correction of about 10,000 times. For high-magnification calibration, carbon graphite powder and gold vapor-deposited particles that are easy to capture a lattice image are used. In the conventional method described above, since the standard sample is observed and photographed separately from the specimen sample, it is difficult to perform measurement under exactly the same conditions (focal length, magnification, exposure, etc.) as the specimen specimen is observed. For this reason, an exact value is not required.

  The present invention has been made in view of such circumstances, and provides a sample capable of simultaneously observing and measuring an index sample and a specimen sample under the same conditions.

  In order to solve the above problems, in the method for producing a thin film sample of the present invention, a lump of index sample is brought into close contact with a specimen sample and integrated, and the integrated portion is cut out to obtain a sample piece. Then, the sample piece is thinned with a laser. When integrating, first, carbon is vapor-deposited to protect the surface of the specimen sample, and the index sample lump is dispersed on the specimen sample. Then, a tungsten deposition process is further performed thereon to form a protective layer over the entire surface. In this state, a sample piece of a predetermined size (for example, 2 μm × 10 μm) is cut out and thinned (for example, 0.1 μm thick).

  The thin film sample thus produced includes a specimen sample layer, an indicator sample layer integrated on the specimen sample layer, a protective layer (tungsten) for protecting the specimen sample layer and the indicator sample layer, Consists of. The index sample layer may be configured with a standard sample of the specimen sample. Further, the index sample layer may be composed of a sample having a known lattice interval.

  According to the present invention, the index sample becomes a part of the specimen sample and is uniformly thinned. Therefore, it is possible to provide a sample capable of simultaneously observing and measuring the index sample and the specimen sample under the same conditions.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be noted that this embodiment is merely an example for realizing the present invention and does not limit the present invention. In each drawing, the same reference numerals are assigned to common components.

<Configuration of apparatus used for sample preparation>
The produced sample can be observed using a transmission electron microscope in which the electrons transmitted through the sample are enlarged by an electron lens. When electrons enter the specimen sample, characteristic X-rays are emitted, and the emitted characteristic X-rays can be detected by a semiconductor detector to perform elemental analysis (EDX analysis). However, what is important here is that the specimen sample must be sufficiently thinned to allow the specimen sample to transmit electrons. In addition, when performing EDX analysis, it is desirable to reduce the film thickness uniformly in consideration of the background (sample thickness, shape, etc.). For such uniform thinning of the sample, it can be said that the FIB processing method using a Ga ion beam is most suitable among recent methods.

  FIG. 1 shows a schematic configuration of a FIB (focused ion beam) processing observation apparatus 100 as a specific example of a sample preparation apparatus according to an embodiment of the present invention.

  The FIB processing and observation apparatus 100 includes a main body unit 101 and a workstation unit 102 roughly. The mirror unit 101 includes a Ga ion source 1, an optical (lens) system 2 that focuses the Ga ion beam 5 on the specimen sample 11 and the index (standard) sample 12, and focuses the Ga ion beam 5 on the minute ion beam. A sample fine movement device (not shown), a detector 3 for detecting secondary electrons generated from the sample, a deposition function unit 4 for performing a deposition process on the sample, and a sample piece for fixing and operating A microprobe 10 and a sample chamber 6 are included. The workstation unit 102 includes a monitor (not shown), an apparatus power supply system 7, a control system (workstation) 8, and an evacuation system 9 for evacuating the sample chamber 6. In the FIB processing observation apparatus 100, secondary electrons generated by scanning on the sample surface can be acquired to observe an image of the sample, and a processing region can be set and a processing state can be confirmed.

<Details of FIB processing method>
Hereinafter, with reference to FIG. 2, a sample preparation procedure using the FIB processing according to the present embodiment will be described.
(A) First, a specimen sample to be subjected to FIB processing is formed into a size that can be accommodated in the apparatus, and carbon is vapor deposited in order to protect the sample surface. Then, a lump of index sample of 0.1 μm to several μm is placed on the thinning position (FIG. 2A). The index sample may be crushed with a mortar or the like and scattered on the surface of the specimen sample 11. However, the index sample is arbitrarily processed by the FIB processing method, and the microprobe 10 (see FIG. 1) having the same function is used as the target sample. It is also possible to carry it.
(B) Tungsten deposition is further performed on the thinned position of the specimen sample on which the lump of the index sample is placed for surface protection (FIG. 2 (b)). As shown in the drawing, the tungsten deposition is performed in a horizontally long shape.
(C) Peripheral processing is performed so that the tungsten deposition film remains. Thereafter, in order to cut off the bottom portion 15, the machining is performed with an inclination of 60 degrees. The sample piece is supported by the peripheral sample only at the connection point (FIG. 2 (c)).
(D) The tip of the microprobe 10 is brought into contact with a peripherally processed sample (sample piece) 13 and the portion is fixed by tungsten deposition. Then, after processing the sample support portion (connection point) (disconnecting the connection point), the microprobe 10 is operated and lifted (FIG. 2D). The size of the sample piece is, for example, about 2 μm in length and about 10 μm in width.
(E) The suspended sample is cut and brought into contact with the mesh 14 and fixed with tungsten deposition. Then, the microprobe 10 is cut and cut (FIG. 2 (e)).
(F) The fixed sample is thinned to a thickness of about 0.1 μm to obtain a sample for a transmission electron microscope (FIG. 2 (f)).

  FIG. 3 shows a schematic diagram of a transmission electron micrograph of the sample prepared by the steps shown in FIGS. 2 (a) to 2 (f). This figure shows a 100 nm (0.1 μm) portion of FIG.

<Specific example of standard quantitative (EDX) analysis>
A substance whose composition ratio has been clarified in advance is used as an index (standard) sample (Co ₂ Cr ₃ Pt ₅ ), and the composition ratio of an unknown substance (Co _x Cr _y Pt _z ) is obtained. As described above, the sample prepared by the sample preparation method of the present invention is formed into a thin film by integrating the specimen sample whose composition ratio is unknown and the index sample whose composition ratio is known.

First, when analyzing the index sample Co ₂ Cr ₃ Pt ₅ , if the spectrum peak count is obtained as Co = 20, Cr = 35, Pt = 45, the composition ratio of the standard sample is Co: Cr: Pt = Since it is 2: 3: 5, the following equation holds.
Co: Cr: Pt = 2: 3: 5 = k1 × 20: k2 × 35: k3 × 45
Therefore, k1 = 1, k2 = 30/35, and k3 = 50/45 are obtained.

Next, an unknown substance (Co _x Cr _y Pt _z ) is analyzed. If the spectrum peak count is Co = 30, Cr = 70, and Pt = 135, the composition ratio of the unknown substance is as follows.
_{Co x Cr y Pt z = k1} × 30: k2 × 70: k3 × 135 = 30: 60: 150
Therefore, a _{Co x Cr y Pt z = Co} 1 Cr 2 Pt 15.

In the case of standardless quantitative analysis, since there is no k factor, it becomes Co _x6 Cr _y14 Pt _z27 .

  As described above, according to the sample preparation method according to the embodiment of the present invention, the background of the specimen sample and the index sample can be set to the same condition. Therefore, the k factor obtained from the index sample can also be used for the specimen sample. become able to.

<Magnification correction when a known sample is used as an index sample>
When a known sample is used as the index sample, the magnification correction of the specimen sample can be performed accurately.
For example, when an Si sample is used as the index sample, an image as shown in FIG. 4 is obtained when high resolution (high magnification) observation is performed with a transmission electron microscope. The lattice-like lines in FIG. 4 are called lattice images, and the intervals are determined by the substance. In the case of Si, it is 3.14 mm. Accurate magnification correction can be performed for the specimen sample based on this value.

<Summary>
In the present embodiment, when the sample for the transmission electron microscope is thinned by the FIB method, the lump of the index sample is brought into close contact with the specimen sample in advance. As a result, observation and EDX measurement can be performed simultaneously with the specimen sample and the index sample under the same conditions. For this reason, extremely accurate standard quantification is possible.
In addition, by using the standard sample of the specimen sample as the lump of the index sample, accurate standard quantification can be performed.
Further, by setting the index sample mass within the range of 0.1 μm to several μm, drift correction (of the sample) can be performed during EDX mapping. In other words, even if the specimen sample does not have a structure that serves as a mark for drift correction, the index sample can be used for correction.
In addition, by using a sample having a known lattice interval as an index sample lump, the specimen sample can be accurately corrected for magnification. That is, it is possible to observe exactly the same conditions between the index sample and the specimen sample, and precise magnification correction can be performed.

It is a figure which shows schematic structure of a FIB process observation apparatus. It is explanatory drawing which showed the sample preparation procedure by this method. It is a schematic diagram of the transmission electron micrograph obtained as a result of producing a sample by this method. It is a figure for demonstrating magnification correction at the time of using a known sample for an index | exponent sample.

Explanation of symbols

1: Ga ion source, 2: Ion optical system, 3: Detector, 4: Deposition function unit, 5: Ga ion beam, 6: Sample chamber, 7: Apparatus power supply system, 8: Works station, 9: Vacuum exhaust System: 10: Microprobe, 11: Specimen sample, 12: Index sample, 13: Tungsten deposition, 14: Cutting mesh

Claims (8)

A method for producing a thin film sample for a transmission electron microscope,
A step of bringing the sample sample into close contact with the specimen sample and integrating them,
Cutting the integrated part into a sample piece;
Thinning the sample piece with a laser;
A method for producing a thin film sample, comprising:   2. The method for producing a thin film sample according to claim 1, wherein a standard sample sample is used for the index sample lump.   The method for producing a thin film sample according to claim 1 or 2, wherein the lump of the index sample is in a range of 0.1 µm to several µm.   The method for producing a thin film sample according to claim 1, wherein a sample having a known lattice interval is used for the index sample lump. A thin film sample for a transmission electron microscope,
A thin film sample comprising: a specimen sample layer; an indicator sample layer integrated on the specimen sample layer; and a protective layer for protecting the specimen sample layer and the indicator sample layer.   The thin film sample according to claim 5, wherein the index sample layer is composed of a standard sample of a specimen sample.   The thin film sample according to claim 5 or 6, wherein the index sample layer is composed of a lump within a range of 0.1 µm to several µm.   The thin film sample according to claim 5, wherein the index sample layer is composed of a sample having a known lattice interval.

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