JPH11223588A - Manufacture of thin-piece sample for transmission electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a thin-piece sample, with few crystal defects, with high accuracy and in a short time by a method wherein, in a final process in which the thin-piece sample is finished, the sample is made thin by an ion beam whose energy is at a specific level or lower. SOLUTION: In a method in which a thin-piece sample for a transmission electron microscope is manufactured by using a focused ion beam, the thin-piece sample is made thin by the ion beam whose energy is at 15 keV or lower in a final process in which the thin-piece sample is finished. In addition, it is desirable that the diameter of the ion beam is set at 0.03 μm or lower. For example, in a rough working process, a sample manufacturing operator manufactures a sample piece 17 comprising a part, to be observed, at the inside by a mechanical cutting operation, and the sample piece 17 is irradiated with an ion beam 1 at an energy of 30 keV so as to be cut. Then, in a finishing and working process, a part C and a part D in a sample 18 are shaved by the ion beam 1. The energy of the ion beam 1 which is used in the finishing and working process is set to be low so that a defect generated due to the creeping of the ion beam 1 is suppressed as far as possible.

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 (hereinafter, referred to as a TEM) using a focused ion beam to scan a massive sample.
The present invention relates to a method for processing a sample into a thin section for observation, and more particularly to a method for preparing a sample for a transmission electron microscope capable of thinning the sample by reducing artifacts.

[0002]

2. Description of the Related Art A TEM sample usually needs to be as thin as about 0.1 μm due to the necessity of electron beam transmission. Conventionally, in order to make such a thin sample, a method has been used in which a specimen is cut into small thin pieces by mechanical cutting, and the surface is then cut by electrolytic polishing or ion irradiation polishing to make an ultra-thin piece with a thickness of about 0.1 μm. I have been. With this method, it is difficult to make a sample in which the part to be observed is exactly contained in the slice.

Therefore, in recent years, a method of processing a thin sample using a focused ion beam has been adopted. That is,
A TEM with a thickness of about 0.05 μm is formed by shaving both sides of the target area of the sample with a finely focused ion beam to form a thin wall.
Finish the sample for use. According to this method, a sample including a portion to be observed with high reliability can be produced. Since an ion beam with a high energy of 30 keV to 50 keV is usually used, processing is performed at a high speed.

[0004]

However, the method using the focused ion beam also has a problem. This is because in the process of thinning with an ion beam, the ion beam penetrates into the thin wall and moves the atoms that make up the sample (hereinafter, sample atoms) to change their positions and arrange the sample atoms. That is to change the state. For this reason, if the sample is crystalline, various crystal defects such as dislocations of atoms and vacancies will occur.If this degree is severe, the penetration portion of the ion beam will have an amorphous structure. Will change.

[0005] The depth of penetration of ions into a sample can be measured, for example, in "MICROSCOPY RESEARCH AND TECHNIQUE" Vol.
According to page 0-333, an ultra-thin sample having a thickness of about 0.1 μm and a thickness of about 0.1 μm formed by a conventional focused ion beam processing method has an artifact layer of about 0.01 μm on both surfaces thereof. You may have. This artifact layer forms a background in the electron microscope image and reduces the image contrast.

An object of the present invention is to provide a method for preparing a TEM observation sample in which the thickness of an artifact layer is smaller than about 1/2 or less as compared with the prior art. It is another object of the present invention to provide a TEM sample manufacturing method capable of manufacturing a sample having few artifacts with a high accuracy with respect to a processing position and a short processing time.

[0007]

In order to reduce the penetration depth of irradiated ions, the method for preparing a thin section sample for a transmission electron microscope of the present invention employs the ion beam energy used in a conventional TEM sample preparation apparatus. The sample was finished to a final shape using a low energy ion beam of 以下 or less. Processing with a low energy ion beam increases the time required for processing. Therefore, in order to reduce the total time used for sample preparation, the entire processing from material to TEM sample processing is performed by roughing, intermediate processing, finishing processing, and ‥.
The process is divided into a plurality of processing steps such as ‥, and the processing other than the finishing processing step is performed with a high energy ion beam.

In order to reliably produce a thin sample having a thickness of about 0.1 μm, it is necessary to use an ion beam having a thickness of about 30% or less of the thin wall, that is, a diameter of 0.03 μm or less. With a beam having a thickness of 0.05 μm, the flakes often break during fabrication. However, as a feature of the ion beam, a low-energy ion beam to be used for finishing is thinner and harder to draw than a high-energy ion beam. Therefore, in order to perform high-precision processing even with a low-energy ion beam, the method of focusing the beam is different between a low-energy ion beam for finish processing and a high-energy ion beam for other processing.

That is, the present invention relates to a method for producing a slice sample for a transmission electron microscope using a focused ion beam, wherein the final step of finishing the slice sample is a step of thinning with an ion beam having an energy of 15 keV or less. There is a feature. The ion beam having an energy of 15 keV or less used in the last step preferably has a diameter of 0.03 μm or less.

Further, according to the present invention, in a method of producing a thin sample for a transmission electron microscope using a focused ion beam, the step of processing a bulk material into a thin sample includes a plurality of processing steps using ion beams having different energies. Characterized by comprising the steps of: The ion beam used in the final finishing step for finishing the flake sample is an ion beam having lower energy than the ion beam used in other steps. By differentiating the beam focusing method of the ion beam used in the final finishing step, that is, the focal length of the objective lens, or the operation mode of the objective lens from the beam focusing method of the ion beam used in other steps, another finishing step is performed. A narrow beam can be generated with lower energy in the process.

In the method for preparing a thin section sample for a transmission electron microscope using a focused ion beam according to the present invention, the conditions of the beam focusing method of the ion beam used in each step are stored in advance, and the sample preparation for a plurality of steps is performed. As the operation progresses, it can be performed using an ion beam processing apparatus provided with a control device that instructs the apparatus to form an ion beam with the stored focusing conditions.

According to the present invention, there is provided an apparatus for preparing a thin sample for a transmission electron microscope, comprising an ion source, an accelerating voltage power supply connected to the ion source, an objective lens for focusing an ion beam generated from the ion source, and an objective lens. An objective lens power supply for applying voltage, a sample stage on which a sample is mounted, a stage drive power supply for driving the sample stage, a control device for controlling an acceleration voltage power supply, an objective lens power supply, and a stage drive power supply, and storing an ion beam focusing condition. A controller that controls an acceleration voltage power supply, an objective lens power supply, and a stage drive power supply according to the ion beam focusing conditions stored in the storage device, and uses a plurality of ion beams focused under different beam focusing conditions. The method is characterized in that a sample is sliced by a process.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. First, in a TEM sample preparation process using a focused ion beam, the manner in which ions irradiating the sample cut the sample and a part of the ions enter the sample will be described with reference to FIG.

FIG. 1 illustrates a state in which a thin rectangular wall 2 is being formed by irradiating an ion beam 1 to a small rectangular parallelepiped piece as shown by a dashed line while controlling its position. When the ion beam 1 irradiates a small piece, the sample atoms 3 in the irradiated portion are repelled into a vacuum and the sample is shaved. On the other hand, the irradiation ions 4 which ejected the sample atoms 3
Even when the sample atoms 3 are repelled, a large amount of energy remains at the same level as at the time of irradiation, so that they enter the inside of the thin wall by following the trajectory drawn by an arrow, for example. The energy is lost by moving the sample atoms, and when the energy becomes zero, it stops in the sample as shown in FIG.
That is, the ions that have entered the sample move the sample atoms along the path and change their positions. Therefore, if the sample is made of crystal, crystal defects such as transfer and substitution of sample atoms and vacancies occur in the portion of the irradiation ion invasion region 5. The size (depth of the layer) of the irradiation ion penetration region 5 is, for example, about 0.01 μm as described in the related art when processing a silicon material with a gallium ion beam of 30 keV.

The binding energy of silicon is about 4.7 eV
Note that it is small. In other words, of the energy of 30 keV at the time of irradiation, only a small part of the energy used to repel sample atoms near the sample surface is consumed, and most of the energy is consumed by moving the sample atoms inside the sample. I have. Considering this fact, it is estimated that the number of defects generated in the sample due to the penetration of ions changes almost in proportion to the energy possessed during irradiation. Therefore, if the energy at the time of irradiation is 15 ke
If thinning is performed using an ion beam of V or less, it is considered that the thickness of the defect layer can be suppressed to 0.005 μm or less.

On the other hand, the higher the energy at the time of irradiation, the higher the speed at which the sample atoms are repelled, that is, the processing speed.
Needless to say, it is desirable to prepare a sample in as short a time as possible. Therefore, the preparation time of the TEM sample is as short as possible.
In addition, in order to finish the defect layer of the completed sample as thin as possible, it is considered that the step of ion beam processing may be divided into a plurality of steps having different irradiation energies. That is, the processing of the portion away from the target portion may be performed at a high speed by irradiating a high-energy ion beam because a defect may be generated. That is, in order to cut a portion 10 nm or more away from the target portion, processing is performed using a high-energy ion beam as in the related art, and processing is performed using an ion beam of 15 keV or less in the final step of completing a TEM sample. If it is not necessary to reduce the time for preparing the TEM sample, it goes without saying that the entire process of preparing the sample may be processed with a low energy ion beam.

FIG. 2 is a schematic view showing an example of a focused ion beam processing apparatus used for carrying out the method for preparing a TEM sample of the present invention. The ion beam 1 emitted from the ion source 6 passes through the deflector 7 and enters the objective lens 8.
The objective lens 8 is composed of three electrodes as shown, and a voltage is applied to a central electrode (hereinafter, referred to as a lens voltage).
Is applied, the ion beam 1 can be focused. The ion beam 1 narrowed down by the objective lens 8 irradiates the sample 9 and excavates the irradiated portion of the sample 9. FIG. 2 shows a state in which the irradiation position of the ion beam 1 is controlled by using the deflector 7 so that the sample 9 is originally being processed from a rectangular parallelepiped small piece to a thin-walled TEM sample. The sample 9 is placed on a sample stage 10 that can be moved up and down by a stage drive power supply 11.

Control of each part of the focused ion beam processing apparatus necessary for processing the sample 9 is performed by the overall controller 12. That is, the general controller 12 applies predetermined ion beam energy and predetermined ion beam scanning to the ion beam 1 via the acceleration voltage power supply 14 and the deflector power supply 15 in accordance with a procedure programmed in the personal computer 13 in advance. , A predetermined sample-lens distance (hereinafter, referred to as
The stage driving power supply 11 is driven and adjusted so that the sample 9 is positioned at a working distance. A lens voltage is applied to the objective lens 8 from an objective lens power supply 16 controlled by the general controller 12.

Using the ion beam processing apparatus shown in FIG.
FIG. 3 shows an example of a method for producing a TEM slice sample according to the present invention. The TEM sample manufacturing process described here includes a roughing process and a finishing process. Apparatus control parameters required for performing the method of the present invention include ion beam energy E (keV), lens voltage V (kV),
The working distance W (mm), the ion beam diameter D (μm), and the ion beam current value I (nA).

First, as shown in FIG. 3A, a TEM sample maker prepares an approximately 2 × 0.3
A specimen 17 of × 0.7 mm was produced by mechanical cutting,
It is loaded on the sample stage 10 of the ion beam processing apparatus of FIG. The ion beam 1 supplied with energy of 30 keV by the accelerating voltage power supply 14 irradiates the sample piece 17 having a working distance W of 18 mm, and excavates the portions A and B in FIG.

The ion beam 1 used at this time is shown in FIG.
Beam diameter D obtained by applying a voltage of lens voltage V = −32.18 kV to the objective lens 8 of FIG.
Is an ion beam of about 0.2 μm. The current value I is 9 nA, which is 45 times larger than the current value at the time of finishing described below. When processing is performed for about 1.5 hours with the high current beam, a sample 18 having a thin wall with a thickness of about 1 μm is obtained. In this processing step, the processing place is about 0.4
This is a step of high-speed machining using a high-current ion beam on a portion which is not affected by the occurrence of defects and which is apart by μm or more. The rough processing step is a step of excavating a large volume of about 20 × 20 × 300 μm ³ as shown in FIG. 3, and it is essential to use a high-current ion beam for processing in as short a time as possible. .

Next, as shown in FIG. 3 (2), the thin wall formed by the rough processing is thinned to a thickness of about 0.05 μm including a desired portion to be observed.
In order to finish to a thin wall of m, finishing processing is performed. That is, in FIG. 3, portions C and D on both sides of the wall of the sample 18 are cut by the ion beam 1. The necessary conditions of the ion beam 1 used for finishing are (1) use of an ion beam of low energy in order to suppress defects caused by penetration of the ion beam as much as possible, and (2) about 0.05 μm.
The use of a narrow beam is necessary to make a sample as thin as m. 10 k in the finish processing of this embodiment
An ion beam of eV energy and 0.02 μmφ is used. That is, in the present embodiment, an ion beam of 30 keV and 0.2 μmφ is used for rough processing, and an ion beam of 10 keV and 0.02 μmφ is used for finish processing.

The requirement that the finishing process requires lower energy and a much thinner ion beam than the roughing process is actually a reciprocal problem from the viewpoint of generating a focused ion beam. This is because the limit of narrowing down the ion beam is limited by the chromatic aberration of the objective lens, so that a low energy ion beam is narrower and harder to stop down than a high energy ion beam.

In the present invention, 30 keV used for roughing is used.
This problem is addressed by making the focal length of the lens different between the beam and the 10 keV beam used for finishing. That is, in the embodiment shown in FIG. 3, the working distance W is changed from 18 mm to 3 mm in the rough processing and the finishing processing. In the finishing processing, the objective lens operates so as to narrow the beam under a short focal length lens condition. This is just the case when using an optical microscope, when switching from low-magnification wide-field observation to high-magnification high-resolution observation, change the lens from a long focal length objective lens to a short focal length objective lens and observe. Is similar to how you do it. Of course, even in rough processing, it is better if the working distance W can be reduced to 3 mm and a beam of 30 keV can be generated under a short focal length lens operating condition. However, in the case of an electrostatic lens, it is necessary to provide a predetermined focal length. Has a property that the applied voltage is proportional to the beam energy, and in the case of the present embodiment, there is a problem in practical use of the device. That is, 30
If a keV beam is focused on a sample having a working distance W = 3 mm, it is necessary to apply a high voltage of -90.3 kV to the objective lens, and the lens is damaged.

In this embodiment, a method of changing the working distance W to change the focal length as a means for changing the convergence method of the rough processing beam and the finishing processing beam is adopted. However, the working distance W is set to a short focal length of 3 mm. Side, the beam for roughing of 30 keV and 10
Even by a method of changing the operation mode of the objective lens between the keV finishing beam and the rough machining beam, a thin finishing beam can be generated with lower energy than the rough machining beam.

FIG. 4 is an explanatory diagram of another embodiment of the present invention. In this embodiment, the operation mode of the objective lens is changed, which is different from the embodiment described in FIG. 3 in the following two points. (1) In rough processing, the lens is driven with the same short focal length as in the finishing processing. (2) The ion beam used for the roughing and the ion beam used for the finishing are generated by applying voltages of different polarities to the objective lens.

As shown in FIG. 4, in the roughing,
Ion beam energy E = 30 keV, working distance W = 3 mm, lens voltage V of the objective lens = 2
Under the condition of 1.68 kV, the ion beam diameter D is about 0.3.
An ion beam having a μm current value I of 10 nA is generated.
Using the large current beam, the portions A and B of the small piece 17 shown in FIG. 3 are excavated to prepare a sample having a wall having a thickness of about 2 μm. In the next intermediate processing, the ion beam energy E =
An ion beam having an ion beam diameter D of about 0.04 μm and an ion beam current value 1 nA is generated under the conditions of 30 keV, working distance W = 3 mm, and lens voltage V of the objective lens = 23.03 kV. Using this ion beam, both sides of the sample thin wall made by rough processing are shaved,
A sample having a thin wall with a thickness of 0.2 μm is prepared. In the final finishing process, the ion beam energy E = 1
Under the conditions of 0 keV, working distance W = 3 mm, and lens voltage V of the objective lens = −30.12 kV, an ion beam having an ion beam diameter D of about 0.02 μm and an ion beam current value I of 0.02 nA is generated. Using this ion beam, both surfaces of the sample thin wall produced by the intermediate processing are shaved to complete a sample for TEM observation having a thin wall of 0.08 μm.

As is well known, even if a positive voltage is applied to the objective lens constituted by an electrostatic lens,
Focusing occurs even when a negative voltage is applied. The former focusing method is referred to as deceleration mode focusing, and the latter is referred to as acceleration mode focusing. Working distance W = 3 with 30 keV ion beam for rough machining, short focal length in acceleration mode
If we try to focus on a mm sample,
An extremely high lens voltage of 90.3 kV is required, but if this is to be converged in the deceleration mode, +21.
A voltage of 7 kV may be applied to the objective lens.

Since the deceleration mode operation has a disadvantage that the beam is difficult to stop down because the aberration is large as compared with the acceleration mode operation, the working distance W is increased and the objective lens is stopped down in the acceleration mode in the embodiment shown in FIG. However, in the embodiment shown in FIG. 4, the working distance W is set at a short focal length of 3 mm, and the method of narrowing the ion beam is shown. Since the working distance W is small, the diameter can be reduced to about 0.3 μm even in the deceleration mode. Of course, since the finishing beam has a low energy of 10 keV, the beam is focused in the negative acceleration mode under the same conditions as in the embodiment shown in FIG. The embodiment shown in FIG. 4 has the advantage that the sample position does not need to be changed between the rough processing and the finishing processing, but requires a lens power supply that generates high voltages of two positive and negative polarities.

[0030]

According to the present invention, a sample for a transmission electron microscope in which the number of crystal defects is reduced to half or less as compared with a sample for a transmission electron microscope manufactured using a conventional ion beam processing apparatus is provided. Can be made.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a sample processing method for ion beam applied TEM.

FIG. 2 is a schematic diagram showing an example of an ion beam processing apparatus used in the method of the present invention.

FIG. 3 is an explanatory view showing an example of a method for producing a TEM slice sample according to the present invention.

FIG. 4 is an explanatory view showing another example of a method for producing a TEM slice sample according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ion beam, 2 ... Thin wall, 3 ... Sample atom, 4 ... Irradiation ion, 5 ... Irradiation ion penetration area, 6 ... Ion source, 7 ...
Deflector, 8: Objective lens, 9: Sample, 10: Sample stage, 11: Stage drive power supply, 12: Overall controller, 13
... personal computer, 14 ... accelerating voltage power supply, 15
... Deflector power supply, 16 ... Objective lens power supply, 17 ... Sample piece,
18: a sample having a thin wall obtained by rough processing, 19: TE
Sample for M observation

Claims (7)

[Claims] 1. A method for producing a slice sample for a transmission electron microscope using a focused ion beam, wherein the last step of finishing the slice sample is a step of thinning with an ion beam having an energy of 15 keV or less. A method for preparing a lamella sample for a transmission electron microscope. 2. The method according to claim 1, wherein the ion beam having an energy of 15 keV or less has a diameter of 0.03 μm or less. Production method. 3. A method for producing a slice sample for a transmission electron microscope using a focused ion beam, wherein the step of processing a lump sample from a lump material comprises a plurality of steps of processing with ion beams having different energies. A method for preparing a lamella sample for a transmission electron microscope. 4. The method for preparing a thin section sample for a transmission electron microscope according to claim 3, wherein the ion beam used in the final finishing step of finishing the thin section sample has lower energy than the ion beam used in other steps. A method for preparing a lamella sample for a transmission electron microscope, which is a beam. 5. The method for preparing a thin section sample for a transmission electron microscope according to claim 4, wherein the beam focusing method of the ion beam used in the final finishing step is a beam focusing method of the ion beam used in another step. A method for preparing a slice sample for a transmission electron microscope, which is different from the above. 6. The method for preparing a thin section sample for a transmission electron microscope according to claim 5, wherein conditions of a beam focusing method of an ion beam used in each step are stored in advance, and the progress of the sample preparation operation over a plurality of steps is performed. A thin sample for a transmission electron microscope, characterized in that a thin sample is prepared using an ion beam processing device having a control device for instructing the device to form an ion beam under the stored focusing conditions. Production method. 7. An ion source, an acceleration voltage power supply connected to the ion source, an objective lens for focusing an ion beam generated from the ion source, and an objective lens power supply for applying a voltage to the objective lens. A sample stage on which a sample is placed, a stage drive power source for driving the sample stage,
A control device for controlling the acceleration voltage power supply, the objective lens power supply, and the stage drive power supply; and a storage device for storing an ion beam focusing condition, wherein the control device performs the acceleration according to the ion beam focusing condition stored in the storage device. A thin-film sample preparation apparatus for a transmission electron microscope, characterized in that a voltage power source, an objective lens power source, and a stage drive power source are controlled, and the sample is thinned by a plurality of processes using ion beams focused under different beam focusing conditions.