JP2013205017A - Apparatus and method for preparing minute thin film sample for transmission electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for preparing a minute thin film for a transmission electron microscope having a reduced effect of the magnetism of a steel material without introducing ion radiation damage by focused ion beam processing.SOLUTION: In a thin film sample 3 preliminarily subjected to electrolytic polishing, a thin film sample 3a for a transmission electron microscope, which has a reduced effect of the magnetism of a steel material, is obtained by moving a thin film member 8 provided at the tip of a movable probe 9 to an observation place while observing a secondary electron image by irradiating an electron beam and processing the thin film sample 3 by a focused ion beam while shielding the focused ion beam by the thin film member 8, without introducing damage caused by ion irradiation into the observation place. The minute thin film sample 3a is fixed to a second movable probe 10 by a vapor deposition film 12 and followed by extraction.

Description

  The present invention relates to a sample preparation apparatus and a sample preparation method for producing a micro thin film sample for a transmission electron microscope of a metal material having magnetism such as a steel material by a focused ion beam.

  In order to produce a metal material having a better material, for example, a steel material, it is important to control a fine structure such as nanometer order precipitates and grain boundary segregation. In order to control such a fine structure, in order to know what the actual structure is, an analysis technique of a minute region is necessary, and observation with a transmission electron microscope (hereinafter referred to as TEM) is indispensable. ing. Among other observation techniques using a transmission electron microscope, scanning transmission electron microscopy using an electron beam as a probe is also accompanied by the development of aberration correction technology in the irradiation system, which enables observation and elemental analysis of minute regions with high resolution. This is a very important analysis technique.

  However, the ferritic steel material has magnetism, and the thin film sample for 3 mmφ TEM observation manufactured by the twin jet electropolishing method that is generally used has a magnetic property of the sample even if aberration correction is performed in advance. Due to the influence, aberrations appear during actual TEM observation, and it is difficult to exhibit the high resolution inherent in TEM.

  Therefore, Patent Document 1 discloses that a focused ion beam (hereinafter referred to as FIB) processing method is effective as a method of reducing the influence of magnetism of a sample by reducing the volume of the sample. However, since FIB processing irradiates an ion beam having a large energy, there is a problem that a damage layer such as a dislocation loop or an ion source element is formed on the surface layer of the thin film sample. Not.

  As a method of taking a damaged layer, Patent Document 2 discloses a method of performing argon ion sputtering with a low acceleration voltage in addition to the FIB processing. However, argon ion sputtering has a problem that fine irregularities are formed on the sample surface, and the contrast of fine precipitates becomes unclear in observation at a high magnification, making observation difficult.

JP 2001-289552 A Japanese Patent Laid-Open No. 2004-199969

  The present invention has been made in view of the current situation as described above, and in a metal material having magnetism, for example, a steel material, without introducing ion irradiation damage due to focused ion beam processing, transmitted electrons having a small magnetic effect. An apparatus and method for producing a micro thin film sample for a microscope are provided.

In order to achieve the above object, the gist of the present invention is as follows.
(1) A micro thin film sample manufacturing apparatus for a transmission electron microscope having a sample chamber evacuated to a vacuum, a sample stage on which a thin film sample can be placed and moved in the sample chamber, and a sample stage placed on the sample stage A focused ion beam irradiation optical system for irradiating the thin film sample with a focused ion beam, an electron beam irradiation optical system for irradiating the thin film sample placed on the sample stage with an electron beam, and the focused ion beam and electron beam irradiation A secondary electron detector for detecting secondary electrons generated by the secondary electron detector, an image display device for displaying a secondary electron image from the secondary electron intensity detected by the secondary electron detector, and a part of the thin film sample. A first movable probe provided with a thin film member for shielding from irradiation of the focused ion beam, and a microscopic sample cut out by irradiating the thin film sample placed on the sample stage with the focused ion beam. A second movable probe for transferring a small thin film sample, a gas deposition mechanism for supplying a source gas for fixing the second movable probe and the small thin film sample when cutting out the small thin film sample, An apparatus for preparing a micro thin film sample for a transmission electron microscope.
(2) A method for preparing a micro thin film sample for a transmission electron microscope using the micro thin film sample manufacturing apparatus for a transmission electron microscope according to (1), wherein a thin film sample subjected to electrolytic polishing in advance is placed on the sample stage. A thin film sample placing step of irradiating the thin film sample with an electron beam and observing the thin film sample in a secondary electron image; and observing the thin film sample in the thin film sample placing step, A first thin film member moving step of moving a first movable probe provided with a thin film member for shielding a part and avoiding irradiation of a focused ion beam above a cut-out portion of a minute thin film sample; The focused ion beam is irradiated to a partial region of the thin film sample including the first and second regions to observe the partial region of the thin film sample. Irradiate the beam above A cutting process step for cutting a thin film sample, and irradiating the electron beam or the focused ion beam to observe the micro thin film sample with the cut position set in a secondary electron image, and a part of the cut position A movable probe fixing processing step in which the tip of the second movable probe is applied to the first movable probe, and the focused ion beam is irradiated to fix the contact portion between the cutting position and the second movable probe with a deposition film; A micro thin film sample cutting process for cutting out the micro thin film sample by irradiating the focused ion beam to a position; an extracting process for extracting and transporting the cut micro thin film sample using a second movable probe; and the micro thin film sample A supporting body placing step for placing a supporting body for supporting the sample on a sample stage, and irradiating the electron beam, The transfer step of transferring the micro thin film sample to the support while observing the support with a secondary electron image, and the micro thin film sample transferred to the support by irradiating the electron beam and the support A second thin film member moving step of moving the first movable probe provided with the thin film member above the minute thin film sample, and irradiating the focused ion beam, A contact step between the micro thin film sample transferred to the support and the support is observed with a secondary electron image and the micro thin film sample and the support are fixed by a deposition film; and the focused ions A cutting step of cutting the second movable probe from the micro thin film sample fixed to the support by irradiating a beam, and producing a micro thin film sample for a transmission electron microscope.

  According to the TEM micro thin film sample preparation apparatus and method according to the present invention, a sample can be prepared without irradiating a high-energy focused ion beam to a TEM observation portion of a micro thin film sample in FIB processing, so that a damage layer is formed. Never do. By reducing the volume of the sample, no aberration appears due to the influence of the magnetism of the sample. Further, according to the manufacturing method of the present invention, a sufficiently thin region can be obtained by pre-processing by electropolishing, so that a TEM micro thin film sample can be obtained without additional processing after FIB processing.

It is a schematic block diagram which shows the micro thin film sample preparation apparatus for transmission electron microscopes of this invention. It is explanatory drawing which shows a mode that the focused ion beam is shielded using a thin film member, (a) shows a mode that a micro thin film sample is extracted from a thin film sample, (b) transfers a micro thin film sample to a support body. Show the state. It is a figure which shows the outline | summary of the procedure of the sample preparation method of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a configuration example of a focused ion beam processing apparatus as a micro thin film sample manufacturing apparatus for a transmission electron microscope of the present invention will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration example of a focused ion beam processing apparatus. The focused ion beam processing apparatus focuses a sample stage 2 placed in a sample chamber 1 evacuated to a vacuum and a thin film sample 3 placed on the sample stage 2 with a focused ion beam using gallium as a radiation source. An ion beam irradiation optical system 4, an electron beam irradiation optical system 5 for irradiating an electron beam, a secondary electron detector 6 for detecting secondary electrons generated from a focused ion beam and electron beam irradiation unit, and detected secondary electron intensity A first movable probe 9 having a thin film member 8 for shielding irradiation of a focused ion beam onto a part of the thin film sample 3, and a small thin film sample extracted from the thin film sample 3. The second movable probe 10 to perform the gas deposition mechanism for supplying the source gas for fixing the second movable probe 10 and the minute thin film sample when extracting the minute thin film sample Equipped with a 1. The sample stage 2 is movable in the sample chamber 1 in accordance with the irradiation position and direction of the focused ion beam while the thin film sample 3 is placed thereon.

  In FIG. 1, the focused ion beam irradiation optical system 4 is drawn in the vertical direction with respect to the sample stage 2 so that the sample stage surface and the focused ion beam irradiation optical system 4 face each other without tilting the sample stage 2. Although drawn, the focused ion beam irradiation optical system 4 may not be in the vertical direction.

  The thin film member 8 may be manufactured by processing the tip of the first movable probe 9 into an arbitrary shape. Alternatively, a thin film made of a material such as molybdenum or tungsten that is hard to be sputtered more easily than iron is placed on the sample stage 2, and a thin film member 8 obtained by processing the thin film into an arbitrary shape is gas deposited on the first movable probe 9. It may be fixed by a vapor deposition film.

A method for producing a micro thin film sample for a transmission electron microscope using the above-described micro thin film sample producing apparatus for a transmission electron microscope includes the following steps.
Thin film sample placement step: The thin film sample 3 that has been subjected to electropolishing in advance is placed on the sample stage 2, the thin film sample 3 is irradiated with an electron beam, and a thin film is displayed on the secondary electron image displayed on the image display device 7. Sample 3 is observed.
First thin film member moving step: While observing the thin film sample 3 in the thin film sample placing step, a thin film member 8 for shielding a part of the thin film sample 3 and avoiding the portion from irradiation with the focused ion beam is provided. The provided first movable probe 9 is moved above the cut-out portion of the minute thin film sample 3a.
Cutting process step: A part of the thin film sample 3 including the thin film member 8 is irradiated with a focused ion beam, and a part of the thin film sample 3 is observed with a secondary electron image, and the thin film sample 3a The thin film sample 3 is cut by irradiating with a focused ion beam.
Movable probe fixing processing step: irradiating an electron beam or a focused ion beam, observing the cut-out position of the minute thin film sample 3a with a secondary electron image, and the tip of the second movable probe 10 at a part of the cut-out position Then, the focused ion beam is irradiated, and the contact portion between the cut-out position and the second movable probe 10 is fixed by the deposited film 12 by deposition.
Micro thin film sample cutting process: A focused ion beam is irradiated to the cutting position to cut out the small thin film sample 3a.
Extraction step: The cut out thin film sample 3 a is extracted and transferred using the second movable probe 10.
Support body placing step: The support body 13 that supports the small thin film sample 3 a is placed on the sample stage 2.
Transfer step: The micro thin film sample 3a is transferred to the support 13 while irradiating an electron beam and observing the micro thin film sample 3a and the support 13 with secondary electron images.
Second thin film member moving step: a first movable member provided with the thin film member 8 while observing the micro thin film sample 3a transferred to the support 13 and the support 13 with a secondary electron image by irradiating an electron beam. The probe 9 is moved above the small thin film sample 3a.
Fixing step: A contact portion between the thin film sample 3a transferred to the support 13 and the support 13 by irradiation with a focused ion beam is observed with a secondary electron image, and the deposited thin film sample 14 is deposited by deposition. 3a and the support 13 are fixed.
Excision step: The second movable probe 10 is excised from the small thin film sample 3a fixed to the support 13 by irradiation with a focused ion beam.

  FIG. 2 shows a state in which the thin film member 8 shields irradiation of a focused ion beam onto a region (hereinafter referred to as an observation region) 15 to be extracted and observed as a TEM observation micro thin film sample. FIG. 2A shows a state in which the small thin film sample 3a is extracted from the thin film sample 3 (micro thin film sample cutting process step). When extracting the micro thin film sample 3a, the outer periphery of the micro thin film sample 3a cut out from the thin film sample 3 is cut, and processing with a focused ion beam to create a gap between the thin film sample 3 and the micro thin film sample 3a; The vapor deposition film 12 by gas deposition is required for fixing the movable probe 10 of 2 to the minute thin film sample 3a. At this time, if the focused ion beam is irradiated to the observation region 15, problems such as implantation of gallium ions, introduction of dislocations, and the observation region 15 may not be removed occur. The observation area 15 is prevented from being irradiated with the focused ion beam. The timing at which the second movable probe 10 is fixed to the minute thin film sample 3a by the vapor deposition film 12 is the second movable probe of the outer peripheral portion of the thin film member 8 when the thin film sample 3 is processed by irradiating the focused ion beam. It may be any time after the processing near the position where the probe 10 is fixed until the micro thin film sample 3a is completely separated. However, more preferably, when the second movable probe 10 is in contact with the region where the minute thin film sample 3a is to be extracted, the possibility that the region of the minute thin film sample 3a to be extracted is bent or bent is reduced. Therefore, after finishing the vicinity of the position where the second movable probe 10 is fixed, it is preferable to fix the second movable probe 10 before processing other portions.

  FIG. 2B shows a state in which the small thin film sample 3a is transferred to the support 13 (fixing step). At the time of transfer, it is necessary to produce the vapor deposition film 14 by gas deposition for fixing the small thin film sample 3 a and the support 13 and to cut off the second movable probe 10. At this time, as described above, a problem occurs when the observation region 15 is irradiated with the focused ion beam. Therefore, the observation region 15 is covered with the thin film member 8 so that the observation region 15 is not irradiated with the focused ion beam. ing.

  As an example of the present invention, a TEM observation micro thin film sample was fabricated from a 1.2 mm thick steel sheet having a ferrite single phase structure by the fabrication apparatus and fabrication method of the present invention. As preparation for FIB processing, a 3 mmφ electropolished sample was prepared by a twin jet electropolishing method. First, a 10 mm × 15 mm × 1.2 mmt sample was cut out from a steel plate with a precision cutting machine, and a 3 mmφ disk was punched out using a disk punch device from a sample that had been thinned to about 60 μm by mechanical polishing. It was. Using a 3 mmφ disk with an electrolytic solution in which acetic anhydride is mixed at 90% by volume and perchloric acid at a rate of 10% by volume, under conditions of an electrolytic solution temperature of 14 ° C. and an applied voltage of 70V, a twin jet electropolishing method is used. A thin film sample having a sample thickness of about 30 nm was obtained at the observation location. In the example of the present invention, the twin jet electropolishing method is used as a method for producing the electropolished thin film sample, but the thin film sample may be produced by other electropolishing methods such as a window opening method.

The procedure of the sample preparation method of the present invention example using the focused ion beam of FIG. 1 will be described with reference to FIG.
FIG. 3A: While observing the secondary electron image obtained by irradiating the electron beam, the first movable probe 9 is formed at the position where the thin film sample is removed at the edge of the hole opened by the electrolytic polishing of the thin film sample 3. The thin film member 8 at the tip of was moved. The size of the thin film member 8 was about 10 μm × about 10 μm × about 3 μmt.
FIG. 3B: A position 2 μm away from one side of the thin film member 8 that shields the observation region 15 was processed by a focused ion beam. The focused ion beam had an acceleration voltage of 40 kV and a beam current amount of 0.4 nA. The reason why the position 2 μm away from one side of the thin film member 8 is processed is that the second movable probe 10 for microsampling is secured to the thin film sample 3 by gas deposition (FIG. 3C). It is to do. In this embodiment, the interval is set to 2 μm, but may be adjusted according to the size of the tip of the second movable probe 10.
FIG. 3C: After the second movable probe 10 is brought into contact with the region between the observation region 15 and the processing location shown in FIG. 3B, the second movable probe 10 and the thin film sample 3 are attached by gas deposition. The vapor deposition film 12 was fixed.
FIG. 3D: The periphery of the remaining two sides of the observation region 15 is processed with a focused ion beam, cut into a size of about 12 μm × about 11 μm, and the small thin film sample 3 a is cut off to form the second movable probe 10. Thus, a small thin film sample 3a was extracted.
FIG. 3E: While observing the secondary electron image obtained by irradiating the electron beam, the second movable probe 10 to which the minute thin film sample 3a is fixed is moved, and the minute thin film sample 3a is brought into contact with the support 13. Then, the first movable probe 9 was moved, and the thin film member 8 was moved above the small thin film sample 3a so as to block the focused ion beam from the focused ion beam irradiation optical system 4.
FIG. 3 (f): A thin ion sample 3a and a support 13 are fixed by a vapor deposition film 14 by gas deposition by irradiating a focused ion beam, and then the second movable probe 10 is separated by a focused ion beam. It was.

  As Comparative Example 1, an 8 mm × 8 mm × 1.2 mmt sample was cut out from a 1.2 mm-thick steel plate having a ferrite single-phase structure with a precision cutting machine, and one side was mirror-polished and then about 10 μm with a focused ion beam processing apparatus. A cross-sectional observation sample having a size of about 10 μm × about 0.15 μm was prepared. In the focused ion beam processing, the ion source was liquid gallium, and first, tungsten was vapor-deposited by gas deposition as a protective film at the location where the cross-sectional observation sample was extracted. Next, rough processing was performed around the sample extraction site under the conditions of an acceleration voltage of 40 kV and a beam current amount of 31 nA, and finishing processing was performed around the sample extraction site under the conditions of the acceleration voltage of 40 kV and the beam current amount of 6 nA. Subsequently, the cross-section observation sample was cut into a size of about 10 μm × about 10 μm × about 2 μmt with a focused ion beam, extracted with a movable probe, and fixed to the support with a vapor deposition film of tungsten. In order to further reduce the thickness of the cross-sectional observation sample, after processing to a thickness of about 1 μm under conditions of an acceleration voltage of 40 kV and a beam current of 1.4 nA, a condition of an acceleration voltage of 40 kV and a beam current of 0.4 nA To a thickness of about 0.15 μm. Further, argon ion milling was performed to remove the damaged layer. The milling conditions were an acceleration voltage of 1 kV and a beam current of 10 mA for 1 minute, and further milling was performed until the sample thickness reached about 30 nm at an acceleration voltage of 0.6 kV and a beam current of 10 mA.

  As Comparative Example 2, a 10 mm × 15 mm × 1.2 mmt sample was cut out from a 1.2 mm thick steel plate having a ferrite single-phase structure with a precision cutting machine, and the thickness was reduced to about 60 μm by mechanical polishing. After punching out a 3 mmφ disk using a punching device, an electrolytic solution in which acetic anhydride was mixed at a rate of 90% by volume and perchloric acid at a rate of 10% by volume was used at an electrolytic solution temperature of 14 ° C. and an applied voltage of 70V. A TEM thin film sample having a specimen thickness of about 30 nm was obtained by a twin jet electropolishing method.

  As described above, in the transmission electron microscope with the acceleration voltage of 300 kV in which the three samples prepared in the present invention example, comparative example 1 and comparative example 2 were subjected to the aberration correction of the irradiation system, whether or not there is an influence of magnetism on the aberration. If the convergence half-angle of the region having the same phase of the Ronchigram is 20 mrad or more, it was judged that the influence of magnetism can be almost ignored. Further, the influence of the unevenness of the sample was observed with a high-angle annular dark field scanning transmission electron microscope with a detection angle of 61 mrad, and an image observed at a magnification of 3 million times from a random incident direction other than the zone axis incidence. If the ratio of the maximum intensity to the minimum intensity is less than 1.1, it was judged that the influence of the sample irregularities can be ignored. These results are shown in Table 1.

  The circles in the table indicate that when the effects of magnetism and surface irregularities of the sample were evaluated by the above method, the effects of magnetism or surface irregularities of the sample were almost negligible, and x was magnetic or surface irregularities of the sample. This indicates that the influence of could not be ignored. The microscopic thin film sample for TEM observation produced by the production apparatus and production method of the present invention did not show the influence of magnetism, and did not show the influence of surface irregularities, and obtained good results. On the other hand, in the sample that was subjected to argon ion milling after microsampling by focused ion beam processing, there was no influence of magnetism such as the appearance of aberration that could not be corrected by the aberration corrector due to the magnetism of the sample, but argon ion milling A change in image intensity on the order of nanometers was observed due to uneven polishing (Comparative Example 1). Moreover, although the influence by surface unevenness | corrugation was not seen in the electropolishing sample of 3 mm (phi), the convergence half angle of the area | region where the phase of the Ronchigram was aligned by the influence of magnetism was smaller than 20 mrad (comparative example 2).

DESCRIPTION OF SYMBOLS 1 Sample chamber 2 Sample stage 3 Thin film sample 3a Minute thin film sample 4 Focused ion beam irradiation optical system 5 Electron beam irradiation optical system 6 Secondary electron detector 7 Image display device 8 Thin film member 9 First movable probe 10 Second movable Probe 11 Gas deposition mechanism 12 Deposition film 13 Support 14 Deposition film

Claims (2)

A thin film sample preparation apparatus for a transmission electron microscope having a sample chamber evacuated to vacuum,
A sample stage on which a thin film sample can be placed and moved in the sample chamber;
A focused ion beam irradiation optical system for irradiating a thin film sample placed on the sample stage with a focused ion beam;
An electron beam irradiation optical system for irradiating the thin film sample placed on the sample stage with an electron beam;
A secondary electron detector for detecting secondary electrons generated by irradiation of the focused ion beam and electron beam;
An image display device that displays a secondary electron image from the secondary electron intensity detected by the secondary electron detector;
A first movable probe comprising a thin film member for shielding a part of the thin film sample from irradiation of a focused ion beam;
A second movable probe for transferring a thin film sample cut out by irradiating a focused ion beam to the thin film sample placed on the sample stage;
A gas deposition mechanism for supplying a source gas for fixing the second movable probe and the micro thin film sample when cutting the micro thin film sample;
An apparatus for preparing a micro thin film sample for a transmission electron microscope. A method for producing a thin film sample for a transmission electron microscope using the apparatus for producing a thin film sample for a transmission electron microscope according to claim 1,
A thin film sample placing step of placing a thin film sample subjected to electropolishing in advance on the sample stage, irradiating the thin film sample with an electron beam and observing the thin film sample in a secondary electron image;
While observing the thin film sample in the thin film sample mounting step, the first movable probe provided with a thin film member for shielding a part of the thin film sample and avoiding irradiation with the focused ion beam is used as a micro thin film sample. A first thin film member moving step of moving above the cutout portion of
Irradiating the focused ion beam to a partial area of the thin film sample including the thin film member, observing a partial area of the thin film sample with a secondary electron image, setting a cutting position of the micro thin film sample, An incision processing step of irradiating the focused ion beam and incising the thin film sample;
Irradiating the electron beam or the focused ion beam, observing the cut-out position in a secondary electron image, applying the tip of a second movable probe to a part of the cut-out position, and irradiating the focused ion beam A movable probe fixing process for fixing a contact portion between the cut-out position and the second movable probe by a deposition film;
Irradiating the cut-out position with the focused ion beam to cut out a micro-thin film sample;
An extraction step of extracting and transferring the cut out thin film sample using a second movable probe;
A support placing step of placing a support that supports the micro thin film sample on a sample stage;
A transfer step of transferring the micro thin film sample to the support while irradiating the electron beam and observing the micro thin film sample and the support in a secondary electron image;
While irradiating the electron beam and observing the micro thin film sample transferred to the support and the support in a secondary electron image, the first movable probe provided with the thin film member is positioned above the micro thin film sample. A second thin film member moving step to be moved to
The focused thin film is irradiated with the focused ion beam, the contact portion between the micro thin film sample transferred to the support and the support is observed with a secondary electron image, and the micro thin film sample and the support are separated by a deposition film. A fixing step for fixing;
An excision step of excising the second movable probe from the minute thin film sample fixed to the support by irradiating the focused ion beam;
A method for producing a micro thin film sample for a transmission electron microscope, comprising:

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