JPWO2016170663A1 - Sample observation method and specimen production method using ionic liquid - Google Patents

Abstract

After irradiating plasma, ultraviolet rays, or ion beams to the ionic liquid attached in the form of droplets, the droplet shape is transformed into a film shape, and then the sample to be observed is placed on the ionic liquid that has been transformed into a film shape .

Description

  The present invention relates to a method for observing a sample fixed to a substrate using an electron microscope. The present invention also relates to a method for producing a specimen for the observation.

  Conventionally, when observing the surface of a powder or particulate sample using a scanning electron microscope, a technique of fixing the sample to a substrate using a conductive adhesive or a conductive tape has been used. The conductive adhesive is solidified by volatilization of the solvent and fixes the sample to the substrate. On the other hand, when the conductive adhesive is used for fixing a powder or particulate sample, it is necessary to mount the sample on the substrate at an optimal timing. For example, if the mounting timing is too early, the sample is buried in the conductive adhesive. On the other hand, when the mounting timing is late, the conductive adhesive is dried, and the sample cannot be bonded to the substrate. In addition, although there is no worry about drying in a conductive tape, since the adhesive layer is thick, the stability of a sample is lacking. For this reason, the conductive tape is not suitable for high-magnification observation of a sample.

  Therefore, a technique for bonding a sample to a substrate using an ionic liquid has been studied (Patent Document 1). An ionic liquid is a salt that is liquid at room temperature and has a vapor pressure of almost zero. In addition, since the ionic liquid has ionic conductivity, it is suitable for adhesion to a conductive substrate.

International Publication No. 2007/083756

  However, since the ionic liquid has a high surface tension, the ionic liquid becomes a thick droplet when applied to a substrate for use as an adhesive. When a particulate sample is mounted on a droplet-like ionic liquid, the sample is buried in the droplet, or the fine structure of the sample surface is obscured by the ionic liquid, similar to the conductive adhesive described above. It is difficult to observe the original surface structure.

  In order to solve the above-described problems, the present invention employs the configurations described in the claims. That is, the present invention employs a technique in which a droplet of an ionic liquid before mounting a sample is irradiated with plasma, ultraviolet rays, or an ion beam to deform the droplet into a film shape.

  According to the present invention, when the sample is fixed to the substrate, the sample is not buried in the ionic liquid, or the fine structure of the sample surface is not covered with the ionic liquid. Problems, configurations, and effects other than those described above will become apparent from the following description of embodiments.

The flowchart explaining a series of processes from sample production to observation. The figure which shows the image which observed the ionic liquid dripped on the silicon substrate hydrophilized by the scanning electron microscope of the acceleration of 1 keV (conventional example). The figure which shows typically the droplet shape of the ionic liquid dripped at the silicon substrate hydrophilized (conventional example). The figure which shows the image (60 degree inclination) which observed the particulate sample (toner) mounted in the ionic liquid of FIG. 1 with the scanning electron microscope of the acceleration of 1 keV. The figure which shows the image which observed the particulate sample (toner) mounted in the ionic liquid of FIG. 1 with the scanning electron microscope of the acceleration of 0.5 keV (conventional example). The figure explaining schematic structure of a plasma irradiation apparatus. The figure which shows the image which observed the ionic liquid formed into the film form on the silicon substrate by plasma irradiation with the scanning electron microscope of the acceleration of 1 keV. The schematic diagram of the ionic liquid which became a film | membrane form on the silicon substrate by plasma irradiation. The figure which shows the image (60 degree inclination) which observed the particulate sample (toner) mounted in the ionic liquid of FIG. 6A with the scanning electron microscope of the acceleration of 1 keV. The figure which shows the image which observed the particulate sample (toner) mounted in the ionic liquid of FIG. 6A with the scanning electron microscope of the acceleration of 0.5 keV. The figure explaining schematic structure of a scanning electron microscope. The figure which shows the image which observed the ionic liquid which became a film | membrane form by the ultraviolet irradiation after having apply | coated to the silicon substrate with the scanning electron microscope of the acceleration of 1 keV.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiment of the present invention is not limited to the embodiments described later, and various modifications are possible within the scope of the technical idea.

[Example 1]
[Ionic liquid]
The inventor has confirmed by experiments that the droplet shape is collapsed by irradiating the droplet of the ionic liquid (PhCH2N ⁺ Me2Et [(CF3SO2) 2N] ⁻ ) with plasma and spreads in a film shape on the substrate. The inventor has the same effect on other ionic liquids (Et ₃ N ⁺ (CH ₂ ) ₅ CH ₃ [(CF ₃ SO ₂ ) ₂ N] ⁻ ) and (C ₇ H ₁₉ NO ₄ S). Also confirmed. In this embodiment, any one of these ionic liquids is used. The contents of the following examples can be applied to both a hydrophilic ionic liquid and a hydrophobic ionic liquid.

[Observation procedure]
The newly developed observation procedure will be described with reference to FIG.
Step 101
A hydrophilic treatment is performed on the conductive substrate. A known method is used for the hydrophilic treatment. For example, the substrate can be hydrophilized by plasma irradiation. The substrate preferably has conductivity in consideration of observation with an electron microscope. The material of the substrate is arbitrary as long as it is flat to some extent. For example, a silicon substrate, a glass substrate, an aluminum substrate, or a resin substrate may be used. In addition, even if it does not hydrophilize a board | substrate, an ionic liquid can be changed to a film | membrane form by the process mentioned later. However, by making the substrate hydrophilic, it becomes easier to form a film of an ionic liquid by a process described later.

Step 102
A solution in which the ionic liquid is diluted is dropped on the substrate. For diluting the ionic liquid, for example, water or ethanol is used. In this example, a solution in which the concentration of the ionic liquid was diluted to 2% was used. However, the concentration of the ionic liquid is not limited to this value and may be any percentage. For example, a solution diluted to 1% may be used, or an ionic liquid having a concentration of 100% (not diluted) may be used.

Step 103
To expedite drying, excess ionic liquid is removed. For example, a filter paper is placed on the substrate surface, and excess ionic liquid is adsorbed on the filter paper side. However, a blower or a micropipette may be used to remove the excess of the ionic liquid. Note that the step of removing the excess of the ionic liquid is not essential.

Step 104
In this embodiment, the substrate after the processing up to the previous step is placed in a plasma irradiation apparatus, and the ionic liquid is irradiated with plasma. The plasma generation conditions will be described later. Due to the plasma irradiation, the ionic liquid droplets changed into a film. The optimum film thickness varies depending on the sample to be observed. In general, the longer the plasma irradiation time or the stronger the irradiation intensity (the higher the irradiation energy), the thinner the film thickness. In any case, the ionic liquid after film formation only needs to have a sufficient thickness for adhesion of the sample.

Step 105
A sample is placed on the surface of the ionic liquid changed into a film shape. In this embodiment, a particulate sample is placed, but a powder sample may be used. The sample may be a porous material, an insulator, a conductive material, or a material that is generally difficult to fix. The production of the specimen is completed up to this step.

Step 106
The specimen is placed in a scanning electron microscope (SEM) and the sample surface is observed. In this example, observation is made at an acceleration voltage of 5 keV or less. However, 5 keV is an example, and is not intended to exclude acceleration voltages exceeding 5 keV.

[Observation using ionic liquid by conventional method]
2A and 2B show a state immediately after the ionic liquid solution (2% ethanol solution) is dropped onto the silicon substrate 2 whose substrate surface has been made hydrophilic.

  As shown in FIGS. 2A and 2B, the ionic liquid 1 dropped on the silicon substrate 2 is in the form of droplets due to its high surface tension. In FIG. 2B, the height of the droplet is about the same as the size of the contact surface. FIG. 3 and FIG. 4 show an electron microscope image when the particulate sample (toner) 3 is mounted on the surface of such an ionic liquid 1 and observed. In FIG. 3, the particulate sample (toner) 3 is buried in the ionic liquid 1. In FIG. 4, the film 4 of the ionic liquid 1 covers the surface structure of the particulate sample (toner) 3.

[Observation using ionic liquid by the method of the example]
FIG. 5 shows a schematic diagram of the plasma irradiation apparatus used in step 104. In this embodiment, oxygen plasma is generated by the discharge electrode 6 disposed in the decompression vessel 5 and is irradiated to the ionic liquid 1 dropped on the silicon substrate 2. In the figure, the silicon substrate 2 is placed on a sample stage 8. Further, the inside of the decompression vessel 5 is decompressed to an atmospheric pressure or less by an exhaust pump 9.

  Plasma generation conditions such as the pressure in the decompression vessel 5 and the type of plasma are not particularly limited. For example, plasma may be generated and irradiated to the ionic liquid 1 in an argon gas atmosphere, or plasma may be generated and irradiated to the ionic liquid 1 in a mixed atmosphere of argon gas and oxygen gas. The atmospheric pressure may be atmospheric pressure as long as plasma is generated.

  In this embodiment, the ionic liquid 1 is irradiated with plasma with a discharge current of 7 mA for 30 seconds. This numerical value is an example, and if the discharge current is small, the irradiation time may be lengthened. If the discharge current is large (for example, 10 mA), the irradiation time may be shortened. The plasma may be generated with an intensity of about 10W. In any case, the generation conditions may be determined so that the ionic liquid 1 is formed into a thickness suitable for adhesion of the particulate sample (toner) 3.

  6A and 6B show the state of the ionic liquid 1 after plasma irradiation. FIG. 6A is a scanning electron microscope image captured at an acceleration of 1 keV. It can be seen that the scanning electron microscope image of FIG. 6A is flattened with no gradation change observed in the ionic liquid 1 as compared to the scanning electron microscope image of FIG. 2A taken under the same conditions. This is because the ionic liquid 1 spreads along the surface of the silicon substrate 1 by the plasma irradiation as shown in FIG. 6B.

  FIGS. 7 and 8 show electron microscope images in the case where the particulate sample (toner) 3 is mounted and observed on the surface of the ionic liquid 1 formed into a film by plasma irradiation. As shown in FIG. 7, the particulate sample 3 is bonded to the silicon substrate 2 with the ionic liquid 1 only on the lower surface thereof. For this reason, as shown in FIG. 8, the particulate sample (toner 3) can be observed in a state where the entire surface is exposed (without the surface structure of the sample being buried in the ionic liquid 1).

[Configuration of scanning electron microscope]
FIG. 9 shows a schematic diagram of a scanning electron microscope used in step 106. In the present embodiment, the electron beam 11 taken out from the electron gun 10 is accelerated at 5 keV or less, and then converged by the condenser lens 12 and the objective lens 13 and fixed on the surface of the silicon substrate 2 through the ionic liquid 1 ( The surface of the toner 3 is irradiated and the generated signal is detected by the secondary electron detector 15. In this embodiment, secondary electrons are detected and a secondary electron image is observed, but a reflected electron image may be observed. It can also be used for EDX (Energy dispersive X-ray spectrometry) analysis in which characteristic X-rays are detected and spectrally separated by energy.

[Summary]
As described in the present embodiment, the ionic liquid 1 dropped on the silicon substrate 2 is irradiated with plasma to form a thin film, and then the particulate sample (toner) 3 is placed on the observation surface of the particulate sample 3. Can be fixed to the silicon substrate 2 in a state where the entire structure is exposed. That is, the particulate sample 3 is not buried in the ionic liquid 1 or its surface structure is not covered with the ionic liquid 1. Therefore, it is particularly suitable for observing the original surface structure of the sample with a low acceleration voltage SEM.

  When a conductive adhesive such as a carbon paste is used for fixing the particulate sample 3 as in the conventional method, if the particulate sample 3 is carbon-based, the carbon paste may interfere with observation. However, if the ionic liquid 1 is used as a fixing material as in the present embodiment, there are no restrictions as in the conventional method, so that variations of samples to be observed can be further increased.

  In addition, when the ionic liquid 1 having a thin film as in this embodiment is used as a fixing material, a sample having a size that is difficult to fix with a conductive adhesive such as a carbon paste conventionally used can be easily fixed.

  In addition, conductive adhesives such as carbon paste are dry at the time of observation, and often only the conductive filler remains. However, in this state, the particulate sample 3 and the conductive filler are in contact with each other at a plurality of points. However, as in this embodiment, the ionic liquid 1 is in a liquid state even in a vacuum. For this reason, the contact between the ionic liquid 1 and the particulate sample 3 is a surface contact, and the charge-up suppressing effect during observation is higher than that of the conventional method.

[Example 2]
Here, a modification to the first embodiment will be described. In Example 1, plasma was irradiated to form the ionic liquid 1 into a film (flattening), but the same effect can be obtained by irradiating the droplets of the ionic liquid 1 applied on the silicon substrate 2 with ultraviolet rays. The inventor confirmed that. In this example, the ionic liquid 1 was formed into a film (flattened) by irradiating the ionic liquid 1 with ultraviolet rays including wavelengths of 185 nm and 254 nm for 5 minutes. FIG. 10 shows a state after the ionic liquid solution is applied to the silicon substrate 2 and then irradiated with ultraviolet rays. Also in FIG. 10, it can be seen that the ionic liquid 1 spreads in a film shape.

  In addition, as long as the inventor's knowledge, there is no restriction | limiting in particular about the wavelength of an ultraviolet-ray. In this embodiment, ultraviolet rays including a plurality of wavelengths are used. However, the ionic liquid 1 may be irradiated with ultraviolet rays having a wavelength of only 185 nm or only having a wavelength of 254 nm. Of course, you may irradiate the ionic liquid 1 with the ultraviolet-ray containing another wavelength. In this embodiment, the ultraviolet irradiation time is set to 5 minutes. However, this time is an example, and it may be 3 minutes or 7 minutes. As in the case of plasma irradiation, the longer the irradiation time of ultraviolet rays (the greater the energy applied), the thinner the film thickness. In any case, it suffices to have a thickness sufficient for bonding the sample.

[Summary]
In the case of the present embodiment, as in the case of the first embodiment, the particulate sample 3 is not buried in the ionic liquid 1 or its surface structure is not covered with the ionic liquid 1, so The surface structure of can be easily observed.

[Other embodiments]
The present invention is not limited to the above-described embodiments, and includes various modifications. For example, instead of plasma or ultraviolet rays, Ar ion beam or Ga ion beam may be irradiated to the ionic liquid 1 at an acceleration of about 1.2 kV to form the ionic liquid 1 into a film (flattened). In the above-described embodiment, the hydrophilic treatment is performed before the ionic liquid 1 is dropped or applied on the surface of the silicon substrate 2. However, the surface of the substrate on which the ionic liquid 1 is dropped or applied may be hydrophobic. . Further, the above-described embodiment is an aspect of the present invention, and it is not necessary to include all the components of each embodiment. Also, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. In addition, it is possible to add, delete, or replace another configuration for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Ionic liquid 2 Silicon substrate 3 Particulate sample 4 Ionic liquid film | membrane 5 which covers the sample surface 5 Depressurization container 6 Discharge electrode 8 Sample stage 9 Exhaust pump 10 Electron gun 11 Electron beam 12 Condenser lens 13 Objective lens 15 Secondary electron detector

Claims (18)

A process for producing an ionic liquid film by performing a process of changing the liquid droplets into a film by supplying energy to the liquid droplets containing the ionic liquid;
A sample mounting step of mounting a sample on the ionic liquid film and preparing a specimen;
An observation step of observing the specimen using a scanning electron microscope. The observation method according to claim 1,
An observation method in which the sample is powdery. The observation method according to claim 2,
An observing method in which an accelerating voltage of the scanning electron microscope at the time of the observation is 5 keV or less. The observation method according to claim 3,
The observation method, wherein supplying the energy is irradiating the droplet with plasma. The observation method according to claim 4,
Further, a hydrophilic treatment is performed on the conductive substrate to produce a hydrophilic substrate,
The observation method, wherein the processing step of producing the ionic liquid film includes supplying the droplets to the hydrophilic substrate. The observation method according to claim 1,
An observing method in which an accelerating voltage of the scanning electron microscope at the time of the observation is 5 keV or less. The observation method according to claim 1,
The observation method, wherein supplying the energy is irradiating the droplet with plasma. The observation method according to claim 1,
Further, a hydrophilic treatment is performed on the conductive substrate to produce a hydrophilic substrate,
The observation method, wherein the processing step of producing the ionic liquid film includes supplying the droplets to the hydrophilic substrate. The observation method according to claim 1,
The observation method, wherein supplying the energy is irradiating the droplet with ultraviolet rays. The observation method according to claim 1,
The observation method, wherein supplying the energy is irradiating the droplet with an ion beam. A process for producing an ionic liquid film by performing a process of changing the liquid droplets into a film by supplying energy to the liquid droplets containing the ionic liquid;
A sample mounting step of mounting a sample on the ionic liquid film and preparing the sample. The method of claim 11, wherein
The method for producing a specimen, wherein the sample is powdery. The method of claim 12, wherein
A method for producing a specimen, wherein supplying the energy is irradiating the droplet with plasma. The method of claim 13, wherein
Further, a hydrophilic treatment is performed on the conductive substrate to produce a hydrophilic substrate,
The method for producing a specimen, wherein the processing step of producing the ionic liquid film includes supplying the droplets to the hydrophilized substrate. The method of claim 11, wherein
A method for producing a specimen, wherein supplying the energy is irradiating the droplet with plasma. The method of claim 11, wherein
Further, a hydrophilic treatment is performed on the conductive substrate to produce a hydrophilic substrate,
The method for producing a specimen, wherein the processing step of producing the ionic liquid film includes supplying the droplets to the hydrophilized substrate. The method of claim 11, wherein
A method for producing a specimen, wherein supplying the energy is irradiating the droplet with ultraviolet rays. The method of claim 11, wherein
A method for producing a specimen, wherein supplying the energy is irradiating the droplet with an ion beam.

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