JPH05312700A - Apparatus for preparing transmission electron microscope sample - Google Patents

Abstract

PURPOSE:To make a plurality of thin samples which have been completed with dimpling into final thin pieces together by a relatively simple structured dry etching device. CONSTITUTION:When a sample is made into a thin piece by dry etching for observation of a structure/organization of a semiconductor or metal by a transmission electron microscope, reactive gas is introduced into a vacuum chamber 2 where a pair of electrodes 4, 5 are placed in parallel inside to allow reactive ion etching. A plurality of thin piece samples T are mounted in parallel in a plane on one of the electrodes 5, a sample holding part 11 formed with etching openings 16, 17, and a rotating mechanism 12 for rotating this sample holding part 11 are placed. After one face of the thin piece sample is etched, the sample holding part 11 is rotated 180 deg. by the rotating mechanism 12 to etch the other face.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission electron microscope for thinning a crystal material or the like by dry etching so that the structure or fine structure of the crystal material such as a semiconductor, an insulator or a metal can be observed with the transmission electron microscope. The present invention relates to a sample preparation device.

[0002]

2. Description of the Related Art A transmission electron microscope transmits electrons accelerated to a high voltage through a crystalline material and observes a diffracted wave due to scattering of electrons in the crystalline material as an image. It is necessary to make the crystalline material as a sample extremely thin so that the structure, surface morphology, defects, etc. of the material can be observed with high resolution. Such a transmission electron microscope sample can be basically manufactured in two steps. In the first step, the cross section to be observed (or it may be a flat surface, but here is an example of observation of the cross-sectional structure.) Is adhered, cut, rough-polished, dimpled, etc. to have an outer diameter of 3 mm and an outer peripheral portion. Is about 200
In this step, a disc-shaped sample having a thickness of about 15 μm is prepared at the central portion, and both surfaces thereof are mirror-polished.

FIG. 6 shows a thin piece sample for cross-section observation manufactured in the first step. (a) is a perspective view of the external appearance, (b) is a cross-sectional view, and (c) is an enlarged view of the central portion of the thin sample. In this figure, the thin piece sample T is such that the observation surfaces of the crystalline material 50 reinforced by the reinforcing material 51 face each other,
After bonding with an extremely thin adhesive layer 52, it is obtained by cutting out into a plate shape, polishing the surface, and denting the central portion by dimpling. However, as it is, since the crystal material is thick and the transmission image cannot be observed even when the electron beam is incident, the thinned sample is further thinned by the second step. The second step is ion milling (ion beam etching) in an Ar gas atmosphere, and the thin section sample is extremely thinned to a thickness of about 3000 angstroms at the center.

Although the crystalline material can be observed with a transmission electron microscope through the above-mentioned two steps, labor and expensive equipment are required in both the first and second steps, and it is necessary to develop an efficient sample preparation method. Regarding the second step, a dedicated apparatus for Ar ion milling is commercially available.
A tan Dual ion mill Model 600 is used. Ar ion milling is a type of dry etching, and is a method of accelerating Ar ions and applying them to the sample surface to physically sputter the atoms on the sample surface for etching. In general, since the mirror surface layer of the crystal material thinly polished by the dimpling has a processing strain, the Ar ion milling apparatus for preparing an electron microscope sample has a thickness of about 3000 angstroms while removing the processing strain. In order to prevent the formation of a damaged layer due to the Ar ion beam impact due to the ion beam process itself, the sample is rotated at 10 to 20 rpm while the incident angle of the Ar ion beam to the sample is 10 to 10 rpm. 20
Ion etching is performed by obliquely incident the light at an angle.

[0005]

However, in the Ar ion milling apparatus as described above, the structure of the apparatus itself is complicated, and since the ion beam is tilted and the sample is rotated about its axis, particularly the sample is rotated. In the case of a cross-section observation sample for thinning, it is necessary to use two high-frequency power supplies because ions are injected in two directions.
The device configuration is complicated and expensive, and requires skilled techniques for sample preparation, the throughput of sample preparation is extremely low (the number of sample preparations per day is 1-2), and the observation cost is high. There's a problem. In particular, production sites and research institutions are required to be able to feed back information obtained by electron microscope observations to R & D in a short period of time, so it is efficient to prepare a large number of samples at once in the ion etching process. Realization of an ion etching apparatus for a transmission electron microscope is strongly desired. In addition, the complicated and expensive ion milling of the second step,
There is also a method of preparing a transmission electron microscope sample in which the first step and the second step can be performed by the same apparatus instead of the step of supplying the slurry to the grinding wheel and processing (Japanese Patent Application No. 2-179587). -66840]), it is not possible to make a large number of samples at once by this method, and it is not possible to make efficient production.

The present invention has been made in view of the above-described situation, and an object thereof is to simultaneously perform final thinning processing on a plurality of thin sample pieces that have been subjected to dimpling processing all together by a dry etching apparatus. It is an object of the present invention to provide a transmission electron microscope sample preparation apparatus that can realize a reduction in sample preparation time, an improvement in reproducibility, and a significant reduction in apparatus cost.

[0007]

In order to achieve the above object, the present invention has the following constitution. That is, in order to observe the structure and microstructure of a material with a transmission electron microscope, a manufacturing apparatus for obtaining a transmission electron microscope sample by thinning the material by dry etching is introduced with a pair of electrodes facing each other in parallel. A sample equipped with a vacuum chamber in which reactive ion etching is performed with a reactive gas, and a plurality of thin sample pieces mounted in parallel in the plane of the plate and detachably attached, and the front and back surfaces of the thin sample pieces can be exposed. The holding unit and a rotating mechanism that rotates the sample holding unit so that the front and back surfaces of the thin sample can be etched. As the vacuum chamber, a commercially available parallel plate type reactive ion etching device can be used, or a newly manufactured one can be used. The rotating mechanism may be a mechanism capable of collectively rotating a plurality of sample holders by 180 ° from the outside, and for example, a system using a rack, a pinion, or a push rod can be adopted.

[0008]

In the first step, a plurality of thin sample pieces subjected to the dimpling process are mounted on the sample holder, and the sample holder is installed on one electrode in the vacuum chamber. After the inside of the vacuum chamber is set to a high vacuum, reactive gas is introduced and reactive ion etching is performed. When etching of one surface of the thin sample is completed, the sample holder is rotated by 180 ° by the rotating mechanism, and reactive ion etching of the other surface is performed.
Both sides of a thin sample can be etched with a relatively simple structure. In reactive ion etching, since the etching proceeds due to the chemical reaction between the sample surface and the reactive ions at the same time that the sample is etched by ion bombardment, many techniques are required without adjusting the ion incident angle. It is possible to collectively make the final thin pieces of the thin sample.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an illustrated embodiment. FIG. 1 is an overall schematic view showing an apparatus for producing a transmission electron microscope sample of the present invention, FIG. 2 is a perspective view showing a sample mounting portion thereof, and FIG. 3 is an enlarged perspective view showing a sample holding portion of the sample mounting portion. is there. As shown in FIG. 1, the manufacturing apparatus 1 of the present invention mainly includes a vacuum chamber 2 and a sample mounting unit 3. The vacuum chamber 2 is provided with an anode 4, a water-cooled cathode 5, a reactive gas introduction part 6, a rotary pump 7, a diffusion pump 8, a leak valve 9, a high frequency power source 10, etc., and constitutes a parallel plate type reactive ion etching apparatus. To do so. In such a manufacturing apparatus 1, it is possible to substitute a commercially available reactive ion etching apparatus (for example, DEM451 manufactured by ANELVA) except for the sample mounting section 3.

The anode 4 and the cathode 5 are parallel plate type discharge electrodes arranged in parallel in the vacuum chamber 2.
The anode 4 is installed in the upper part, the cathode 5 is installed in the lower part, and the high frequency power supply 10 is connected. The rotary pump 7 and the diffusion pump 8 introduce a reactive gas such as fluorocarbon into the high-vacuum vacuum chamber 2 for reactive ion etching. Reactive ion etching is different from Ar ion beam etching, which physically sputters with an accelerated ion beam, and has the effect that ions accelerated by an electric field are perpendicularly incident on the sample to scatter the sample surface. Etching is performed by the effect of the chemical reaction between the generated reactive ions and the sample surface.

As shown in FIG. 2, the sample mounting section 3 comprises a plurality of sample holding sections 11 on which a plurality of thin sample T are mounted, and a rotation mechanism 12 for rotating these sample holding sections 11.
It is placed on the lower cathode 5. The sample holder 11 is shown in FIG.
As shown in FIG. 3, the plate member is a rectangular plate member in plan view on which a plurality of disk-shaped thin sample T that has been subjected to the dimpling process are mounted, and includes a substrate 13 and a holder plate 14. The substrate 13 has
A plurality of mounting holes 15 having an inner diameter slightly larger than the outer diameter of the thin piece sample T are provided at intervals in the longitudinal direction.
A thin piece sample T is inserted into. Further, a circular opening (etching window) 16 having an inner diameter slightly smaller than the outer diameter of the thin sample T is bored concentrically in the mounting hole 15, and the thin sample T
The surface of the can be etched. The holder plate 14 is a lid member that is attached to the substrate 13 with screws or the like and holds the thin sample T so that it does not drop. A circular opening 17 having the same diameter as the circular opening 16 corresponds to the position of the circular opening 16. Have been drilled. In addition, stainless steel is used for these members.

The rotating mechanism 12 is a mechanism for simultaneously rotating a plurality of sample holders 11, and includes a pinion 18, a pair of rack guides 19, a drive rack 20, and a push rod 21.
Etc. A rotary shaft 22 is provided on both end surfaces of the substrate 13 in the longitudinal direction so as to coincide with the central axis of the sample holder 11, and the pinion 18 is attached to the rotary shaft 22. The rack guide 19 is a member on the upper surface of which a rack that meshes with the pinion 18 is formed, and is a member that guides and supports the sample holding unit 11 in a rotatable manner, and is arranged on the cathode 5 at a predetermined interval. This rack guide 19 is for the cathode 5
It may be formed integrally with the. The drive rack 20 is
A pair of rack portions 20a facing the rack guide 19
And a connecting portion 20b connecting these rack portions in a U shape in a plan view, the rack at the lower portion of the rack portion 20a is arranged so as to mesh with the pinion 18, and is sandwiched from above and below by the lower rack guide 19. Is a member for rotating and driving the pinion 18. The drive rack 20 has a rack portion 20a slidably guided and supported by a guide rail or the like (not shown).

The push rod 21 is a member whose tip abuts on the connecting portion 20b of the drive rack and pushes and moves the drive rack 20, and by manually projecting the base end from the outside of the vacuum chamber 2 from the outside. Alternatively, it can be operated by a driving device. Further, an O-ring or the like is provided between the push rod 21 and the side wall of the vacuum chamber 2 so that airtightness is maintained. Outside the vacuum chamber 2, a plurality of thin sample T is mounted on the sample holder 11, the pinion 18 of the sample holder 11 is placed on the rack guide 19, and the drive rack 20 is moved.
The sample holder 11 is held horizontally by sandwiching the pinion 18 from above and below by the rack guide 19 and the drive rack 20.
When the etching of one surface of the thin sample is completed, the push rod 21 is pushed to move the drive rack 20 and rotate the sample holder 11 by 180 °. With such a structure, it is possible to simultaneously rotate the plurality of sample holders 11 with a planar structure and a simple structure. Further, it goes without saying that this rotation mechanism is not limited to this, and a rotation mechanism having another configuration that can be operated from the outside and that can simultaneously rotate a plurality of sample holding units can be used.

A process of producing a transmission electron microscope sample using the production apparatus 1 having the above-described structure will be described. (1) A plurality of thin-section samples (external diameter 3 mm, thickness about 200 μm) that have been dimpled in the first step described in the section of the prior art.
m, the thinnest piece layer is about 15 μm) on the substrate 1 of the sample holding unit 11.
The holder plate 14 is fixed to the substrate 13 by inserting the holder plate 14 into the mounting hole 15 of No. 3. (2) The sample holding unit 11 is placed on the rack guide 19 and held horizontally so that the sample surface to be etched faces up. (3) The vacuum chamber 2 is evacuated by the rotary pump 7, and then the diffusion pump 8 is evacuated to a high vacuum. (4) CF from the reactive gas introduction part 6 into the vacuum chamber 2
₄ is introduced at a flow rate of 30 cc / min, high-frequency power of 150 W (13.56 MHz) is applied under a pressure of about 3 Pa, and reactive ion etching is performed. (5) After the etching time of about 1 hour has passed, the push rod 21 is pushed from the outside of the vacuum chamber 2 to push the sample holder 1
1 is rotated 180 °, and the back surface of the thin sample T is subjected to reactive ion etching. (6) After etching for about 1 hour, air is introduced into the vacuum chamber 2 and the thin sample is taken out. Through the above steps, a transmission electron microscope sample could be produced.

[Specific Example] Molecular beam epitaxy (M
The germanium (Ge) is deposited on the silicon (Si) substrate (111) at a substrate temperature of 500 ° C. by the BE method.
In order to observe the state of the growth interface between the Si substrate and the Ge thin film in the sample grown by angstrom, the sample for cross-section observation was prepared by the above-described manufacturing process using the manufacturing apparatus 1 of the present invention, and the acceleration voltage of 400 KV was applied. It was observed with a transmission electron microscope. The photograph of FIG. 4 is an example (cross-sectional TEM image) of observing the growth interface of Ge on the Si substrate, and the observation magnification is 200,000 times. From this photograph, it can be seen that Ge is not layer-grown on the substrate but island-shaped, and the size of Ge island is about 700 angstrom and its height is about 60 angstrom. Note that this photograph was further magnified 10 times or more, and a lattice image of the interface between Si and Ge could be observed (not shown).

The photograph of FIG. 5 shows a G on a Si substrate under the above-mentioned conditions.
For the sample in which e was grown, G grown on the Si substrate
In order to observe the surface of e, the Si substrate side is mirror-finished into a thin piece by dimpling, and then the manufacturing apparatus 1 of the present invention is used.
2 shows a sample for plane observation that has been subjected to reactive ion etching using. FIG. 5A is a surface micrograph of the Si (111) substrate after the reactive ion etching is completed. A small hole (diameter about 140 μm) is partially formed in the central part of the sample by reactive ion etching, and an extremely thin Si substrate is formed in the peripheral part of the small hole so that interference fringes can be observed. I understand. FIG. 5B shows the thin Si substrate portion observed with a transmission electron microscope, and the magnification is 200,000 times. About 7 on a part of Si substrate surface
It can be seen that island-shaped Ge having a size of 00 angstrom is growing. Moire fringes are observed on the island Ge, and the reason for this is that moiré fringes are formed due to a slight difference (about 4%) in lattice constant between Si and Ge. From the observation examples of the photographs in FIGS. 4 and 5 (b), it was observed that the Ge crystals grown on the Si substrate were island-shaped.
ranski-Krastanov mode (SK mode) growth, G
e exceeds the critical film thickness (9.8 Å),
It can be seen that the lamellar growth changed to island growth.

Comparing the observation sample by the manufacturing apparatus of the present invention with the observation sample formed by the conventional Ar ion beam etching, the present invention was able to clearly observe the lattice image. This is because the Ar ion beam etching formed an amorphous layer on the surface layer as weak damage due to ion bombardment. On the other hand, in the reactive ion etching of the present invention, simultaneously with the etching of the sample by the ion bombardment, the etching proceeds due to the chemical reaction between the reactive ions colliding with the silicon surface, and the surface scattering of the electron beam incident during observation is observed. Since the influence was small, the electron diffraction image became extremely clear and a grid image with high resolution was obtained. Further, as an advantage in producing a transmission electron microscope sample by the producing apparatus of the present invention,
First, by installing the sample holder 11, it is possible to simultaneously mount a plurality of small samples (about 3 mm in diameter) on a flat surface, and at the time of exhaust operation from atmosphere to vacuum or from vacuum to atmosphere. That is, the small sample does not scatter. Secondly, unlike reactive ion etching in the silicon LSI process, in the preparation of ordinary transmission electron microscope samples, the cross-section / planar structure to be observed differs from sample to sample even if they have the same appearance and size. And
Although it is not possible to distinguish between a plurality of samples simply by glancing at the observation part, the provision of the sample holding part 11 allows the plurality of samples to be classified into addresses.

In the examples, the sample is silicon. However, it is not limited to silicon, and it is possible to collectively process a wide range of crystal materials such as semiconductors such as gallium arsenide and indium phosphide and silicon oxides and metals. There is no end. Further, in the examples, the preparation of the sample for observing the cross-sectional structure and the planar morphology of the sample has been described, but it is also possible to simultaneously prepare the cross-sectional and planar observation sample.

[0019]

As described above, according to the present invention, a parallel plate type reactive ion etching type apparatus is used in a vacuum chamber for dry etching a material, and a plurality of thin sample holders are mounted in the vacuum chamber. Since the parts are rotatably arranged by the rotating mechanism, the following effects are obtained. (1) It is possible to collectively make 10 to 20 thin-piece samples for which the dimpling process has been completed at the same time into the final thin pieces. Skills such as adjusting the ion incident angle are not required, and the sample preparation time can be greatly shortened, so that the throughput can be greatly improved and the observation time can be shortened, which greatly contributes to R & D and other industries. Therefore, the observation cost can be significantly reduced. (2) Since it is reactive ion etching, damage to the sample does not occur, and a large number of thin slice samples with extremely clear electron diffraction images can be prepared at one time. (3) Since the sample holder is installed in a parallel plate shape, the device can have a simple structure, can be easily miniaturized, and the device price can be significantly increased compared to the conventional ion beam type. The cost can be reduced. (4) The sample holder allows many samples to be mounted on a flat surface at the same time, and small samples do not scatter during evacuation. (5) With the sample holder, it is possible to distinguish a plurality of samples having the same external appearance by assigning addresses.

[Brief description of drawings]

FIG. 1 is an overall schematic view showing an apparatus for producing a transmission electron microscope sample of the present invention.

FIG. 2 is a perspective view showing a sample mounting portion of FIG.

FIG. 3 is an enlarged perspective view showing a sample holding portion in the sample mounting portion of FIG.

FIG. 4 is an island-shaped Ge / Si (111) produced by the present invention.
2 is a photomicrograph of a cross-section observed with a transmission electron microscope (observation magnification is 200,000 times).

FIG. 5: Island Ge / Si (111) produced by the present invention
3A and 3B are micrographs of the surface observed with a transmission electron microscope, where (a) is the appearance of the observed sample and (b) is the surface with an observation magnification of 200,000 times.

6A and 6B show a thin piece sample after the dimpling step, where FIG. 6A is a perspective view, FIG. 6B is a sectional view, and FIG. 6C is an enlarged plan view of the center.

[Explanation of symbols]

 1 Transmission Electron Microscope Sample Preparation Device 2 Vacuum Chamber 3 Sample Mounting Section 4 Anode 5 Cathode with Water Cooling 6 Reactive Gas Introducing Section 7 Rotary Pump 8 Diffusion Pump 9 Leak Valve 10 High Frequency Power Supply 11 Material Mounting Section 12 Rotation Mechanism 13 Substrate 14 Holder Plate 15 Mounting hole 16 Opening 17 Opening 18 Pinion 19 Rack guide 20 Drive rack 21 Push rod

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[Procedure amendment]

[Submission date] March 5, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

FIG. 4 is an island-shaped Ge / Si (111) produced by the present invention.
2 is a photomicrograph of the crystal structure of which a cross section was observed with a transmission electron microscope (observation magnification: 200,000 times).

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

FIG. 5: Island Ge / Si (111) produced by the present invention
3A and 3B are micrographs of the crystal structure of the surface of which was observed with a transmission electron microscope. FIG.

Claims (1)

[Claims] 1. A manufacturing apparatus for obtaining a transmission electron microscope sample by thinning a material by dry etching so that a structure and a fine structure of the material can be observed by a transmission electron microscope, wherein a pair of electrodes face each other in parallel. A vacuum chamber that is placed and is used for reactive ion etching by the introduced reactive gas, and a plurality of thin-plate samples that are mounted in parallel in the plane of the flat plate and are detachably mounted, and the front and back surfaces of the thin-plate samples can be exposed. An apparatus for producing a transmission electron microscope sample, comprising: a sample holder having a section; and a rotation mechanism that rotates the sample holder so that the front and back surfaces of a thin sample can be etched.