JP6863139B2 - Method of preparing a cross-section sample and method of measuring a cross-section sample - Google Patents

Description

The present invention belongs to a method for producing a cross-sectional sample and a method for measuring a cross-sectional sample.

Scanning probe microscope (SPM) is a general term for microscopes that scan a sample while bringing the probe close to or in contact with the sample to capture changes in the physical quantity acting on the probe. In SPM, since different probes are used depending on the physical quantity to be captured, there are various types.

Among SPMs, scanning scanning microscopes (SSRMs) and scanning capacitance microscopes (SCMs) are used for in-plane distribution information (for example, in-plane resistance values) of electrical characteristics in a minute region. Since mapping) can be obtained, it has become an indispensable tool for observing the carrier concentration distribution of devices in the semiconductor field, which has been miniaturized in recent years. Further, since the electrical characteristics in a minute region can be obtained as two-dimensional information, it has begun to be applied not only to semiconductor materials but also to various materials. Hereinafter, SSRM will be described as an example.

[Scanning electron microscope]
The SSRM consists of a sample stage, a conductive probe, and a logarithmic amplifier that detects the current flowing through the conductive probe.
The conductive probe mentioned here has a configuration in which a probe is provided at the tip of a cantilever (cantilever), and the probe is mainly coated with conductive diamond.
Further, by using SSRM, a bias voltage is applied to the sample through the sample stage, and when the conductive probe is brought into contact with the sample, the current flowing from the sample through the conductive probe is detected and the sample surface is scanned. The spread resistance distribution of the sample can be obtained by measuring while measuring. Since the bias voltage applied here is rapidly attenuated directly under the probe, the carriers that can flow into the probe are limited to those existing in the immediate vicinity of the probe, and this is detected as the resistance value. Such a local resistance is called a spreading resistance.
The SSRM is a combination of SPM and spread resistance measurement technology, and it is possible to obtain resistance distribution information in a minute region with high resolution.

[Conductive probe]
The configuration of the conductive probe described above is such that a cantilever equipped with a probe at the tip is connected to a substrate called a substrate. The probe has a pyramid or conical shape, and the tip portion that comes into contact with the sample has a sharp shape, and the surface thereof is coated with a conductive substance.
Since SSRM is measured by applying a high load in order to reduce contact resistance, wear resistance is important in addition to conductivity. Therefore, the standard probe has a conductive diamond coated on the surface of the Si probe, which has high conductivity and abrasion resistance, and can stably perform high-resolution electrical resistance measurement. It has become.

[Preparation for measurement using SSRM]
By the way, in SSRM, if the measurement surface of the sample has irregularities, the contact resistance and contact area between the sample and the probe change, and the measurement result becomes unstable. Therefore, Patent Document 1 describes a technique for preparing a sample for measurement using SSRM. Patent Document 1 describes a technique in which a semiconductor substrate is used as a measurement target, the semiconductor substrate is diced, and the cut surface is mirror-processed.

Japanese Unexamined Patent Publication No. 2003-322599

The following findings were obtained by the present inventor as findings when preparing a sample not only for SSRM but also for a scanning probe microscope.

First, it is assumed that a powder sample is selected as a measurement target by a scanning probe microscope. A powder sample is a powder composed of a plurality of fine particles. Since each particle is fine, it is relatively difficult to handle when measuring. Therefore, in order to facilitate the measurement, a method of pre-embedding and curing an appropriate amount of powder sample with resin can be considered.

However, with this method, there are the following points to consider. That is, since the resin generally used for embedding is an insulator such as an epoxy resin or an acrylic resin, electrical conduction between the sample and the sample stage cannot be obtained, and a scanning probe microscope (particularly SSRM) is used. Measurement) cannot be performed effectively.

A method to eliminate the above concerns is to mix a powder sample with a conductive powder such as fine carbon particles so that electrical continuity can be ensured when the powder sample is embedded and cured with a resin. Is embedded in a resin and cured.

However, diligent research by the present inventor has revealed that accurate measurement results cannot be obtained by the above method. Details will be described in Comparative Example 2 described later, but as a measurement result when SSRM is used, a histogram as shown in FIG. 4 (horizontal axis: resistance value (logarithm), vertical axis: the entire portion where the measurement was performed, The ratio of the portion showing the resistance value shown on the horizontal axis) was obtained. In FIG. 4, the low resistance portion corresponds to the conductive powder, the high resistance portion corresponds to the resin, and the resistance value provided by the powder sample should be obtained in the meantime, but between low resistance and high resistance. , There is no protruding bar graph part. This is because the powder sample is relatively high because the particles constituting the powder sample have not been able to ensure conduction well, although there should be a bar graph portion that protrudes at a predetermined resistance value between low resistance and high resistance. It is presumed that the resistance value is shown and a gentle histogram is to be obtained.

Factors that bring about this include that the blending ratio of the conductive powder and the resin cannot be adjusted appropriately, and that the mixed state of the powder sample and the conductive powder is non-uniform. In particular, in the case of a scanning probe microscope, the amount of sample required is extremely small, so it is extremely difficult to adjust the compounding ratio and to make the mixed state uniform in the first place.

If measurement is performed using a scanning probe microscope in such a state, the measurement results will vary or the measurement will be impossible. In that case, it is necessary to perform the work of embedding the powder sample with the resin and curing it again, which requires a considerable amount of time. Even if a seemingly normal measurement result is obtained, it is not clear whether it is the result of ensuring continuity in the particles and showing the correct result of the powder sample.

In addition to the sample for the scanning probe microscope (details will be described later, for example, a sample for a scanning electron microscope (SEM) and a sample for electron backscatter diffraction analysis (EBSD)), the cross section of the sample is also used. We have also newly obtained the finding that the above problems occur when observing.

In view of the findings obtained through the diligent study of the present inventor as described above, the present invention provides a technique for obtaining stable and accurate measurement results even when the measurement target is a powder sample. The purpose.

In order to solve the above problems, the present inventor has conducted diligent studies.

First, when the powder sample is embedded and cured with a resin, the powder sample is embedded and cured with a resin instead of the above-mentioned method of embedding and curing a mixture of the conductive powder and the powder sample with the resin. A method of coating a conductive material (hereinafter referred to as a sample-containing cured resin) with a conductive film was examined. However, with this method, the conductive film is present only on the surface of the sample-containing cured resin, and if mirror polishing as described in Patent Document 1 is performed in order to perform measurement using SSRM, the conductive film is formed. All of them are polished, and in the end, continuity cannot be ensured.

Therefore, the present inventor has created an unprecedented technical idea of coating a conductive film on the powder sample itself. Then, he created a method of embedding and curing a powder sample coated with a conductive film with a resin.

Aspects of the present invention made based on the above findings are as follows.
The first aspect of the present invention is
A curing step of curing a resin containing a powder sample coated with a conductive film to obtain a sample-containing cured resin,
A smoothing step of smoothing the sample-containing cured resin to reveal a cross section of the sample-containing cured resin.
It is a method of preparing a cross-sectional sample having.

A second aspect of the present invention is the aspect described in the first aspect.
Prior to the curing step, the powder sample placed in the container is coated with a conductive film through the opening of the container.

A third aspect of the present invention is the aspect described in the second aspect.
Sputtering or vapor deposition is used in the coating step.

A fourth aspect of the present invention is the aspect described in the second or third aspect.
Prior to the coating step, there is a filling step of putting the powder sample into the container through the opening of the container used in the curing step and filling the inside of the container with the powder sample.

A fifth aspect of the present invention is the aspect according to any one of the first to fourth aspects.
In the smoothing step, the surface on the opening side of the container used in the curing step is smoothed together with the container.

A sixth aspect of the present invention is the aspect according to any one of the second to fifth aspects.
The maximum width of the opening is less than 1 mm.

A seventh aspect of the present invention is the aspect according to any one of the first to sixth aspects.
The resin is an acrylic resin.

The eighth aspect of the present invention is the aspect according to any one of the first to seventh aspects.
The conductive film is at least one of a carbon film and a metal film.

A ninth aspect of the present invention is the aspect according to any one of the first to eighth aspects.
Defoaming is performed in the curing step.

A tenth aspect of the present invention is the aspect according to any one of the first to ninth aspects.
The cross-section sample is a sample for a scanning probe microscope.

The eleventh aspect of the present invention is a method for measuring a cross-sectional sample in which a sample produced by the method according to any one of the first to tenth aspects is measured using a scanning probe microscope.

A twelfth aspect of the present invention is the aspect described in the eleventh aspect.
The scanning probe microscope is a scanning spread resistance microscope.

According to the present invention, stable and accurate measurement results can be obtained even when the measurement target using the scanning probe microscope is a powder sample.

It is a figure which shows the outline of the method of making a sample for a scanning probe microscope in this embodiment. It is a histogram for each resistance value in each particle constituting a powder sample obtained from the measurement result obtained by using the scanning spread resistance microscope with respect to the sample prepared in Example 1. FIG. It is a histogram for each resistance value in each particle constituting a powder sample obtained from the measurement result obtained by using the scanning spread resistance microscope with respect to the sample prepared in Example 2. FIG. It is a histogram for each resistance value in each particle constituting a powder sample obtained from the measurement result obtained by using the scanning spread resistance microscope with respect to the sample prepared in Comparative Example 2.

Hereinafter, embodiments of the present invention will be described in the following order.
1. 1. Method for preparing cross-section sample for scanning probe microscope 1-1. Preparation process 1-2. Filling process 1-3. Coating process 1-4. Curing process 1-5. Smoothing process 2. Measurement method of cross-section sample 3. Modifications, etc. In this specification, “~” refers to a value equal to or greater than a predetermined value and less than or equal to a predetermined value.

<1. Method for preparing cross-section sample for scanning probe microscope>
In this embodiment, the following steps are mainly performed. Hereinafter, each step will be described. At that time, FIG. 1 showing an outline of a method for preparing a cross-sectional sample for a scanning probe microscope in the present embodiment is used. Reference numeral 1 is a powder sample, reference numeral 2 is a container, reference numeral 3 is a conductive film, and reference numeral 4 is a resin. For convenience of explanation, the reference numerals will be omitted below.

1-1. Preparation step In this step, preparations are made for a method for preparing a cross-sectional sample for a scanning probe microscope. Specifically, preparation of a scanning probe microscope, preparation of a powder sample to be measured using a scanning probe microscope, preparation of a container for containing the powder sample, preparation of a device for coating a conductive film, and smoothing. In this step, preparation of a polishing device for conversion is performed.

In the present embodiment, the scanning probe microscope is not particularly limited, but a scanning spread resistance microscope (SSRM) is exemplified. The specific configuration of a scanning probe microscope such as a conductive probe is as described above. Further, known devices (devices for coating a conductive film, polishing devices for smoothing) used in the present embodiment may be adopted.

The powder sample in this embodiment is not particularly limited, and for example, as described in the item of Examples, a powder such that a resistance value as particles can be obtained between low resistance (conductive film) and high resistance (resin). If it is a sample, there is no particular problem. The particle size and shape of each particle constituting the powder sample are not particularly limited, but in the present embodiment, since the powder sample is put into the container through an opening having a maximum width of less than 1 mm, for example, the average particle size is 100 μm or less. Is preferable.

The container for containing the powder sample preferably has an opening having a maximum width of less than 1 mm. In the first place, in the measurement using a scanning probe microscope, a very small amount of sample is required, but if the width of the opening is reduced in this way, the sample powder will scatter when the coating step described later is performed. Can be effectively suppressed. The shape of this opening is not particularly limited, but in the present embodiment, a circular opening in a plan view is exemplified. That is, in this case, the diameter of the opening is preferably less than 1 mm (more preferably 0.5 mm or less).
The depth of the opening of the container is such that the sample-containing cured resin (described later) remains even after polishing in the smoothing step described later, more specifically, the sample powder in which the conductive film is formed in the coating step. The depth may be such that the particles remain, and is preferably in the range of 0.5 to 2 mm, for example.
The opening of the container may be a through hole or a non-through hole, but in the case of a through hole, one of the openings on both sides of the through hole must be closed, so that the non-through hole is used. The amount of work is smaller if there is one.
The material of the container is not particularly limited as long as it can be polished together with the sample-containing cured resin in the smoothing step, but in the present embodiment, aluminum is exemplified.

1-2. Filling step In this step, a powder sample is placed in the container through the opening of the container and the inside of the container is filled with the powder sample (FIG. 1 (a)). Here, filling means, for example, a state in which a powder sample is put into a container having a non-through hole formed through the opening, and the powder sample is worn out at the opening while the powder sample overflows from the opening.

1-3. Coating step Following the filling step described above, one of the features of the present embodiment is that the coating step, which is the main step, is performed on the powder sample instead of the curing step described later. In this step, the powder sample placed in the container is coated with a conductive film through the opening of the container (FIG. 1 (b)).

As described above, the powder sample is put through the opening in the filling step of the present embodiment. Therefore, the powder sample is exposed to the outside world at the opening. Then, in this step, the exposed portion is coated with a conductive film. As a result, as shown in FIG. 1B, the conductive film is coated not only on the outermost surface of the exposed portion of the powder sample but also on the particles behind the exposed portion to some extent.

Incidentally, the type of the conductive film is not particularly limited as long as it can obtain stable and accurate results when the measurement using a scanning probe microscope (for example, SSRM) is used later. However, from the viewpoint of obtaining stable and accurate results, it is preferable to use at least one of a carbon film and a predetermined metal film as the conductive film, and a carbon film is formed on the conductive film. It may be coated as follows.

The specific coating method is not particularly limited, and a known method may be adopted. However, from the viewpoint of usability, it is preferable to coat the conductive film by sputtering (Example 1 described later) or thin film deposition (Example 2 described later).

1-4. Curing Step In this step, a resin is placed in a container and cured while containing a powder sample to obtain a sample-containing cured resin in which the powder sample is embedded and cured in the resin (FIG. 1 (c)).

As the resin used here, it is preferable to use a resin having a hardness such that the cured resin is not deformed when the probe comes into contact with the resin after it has been cured in the measurement using a scanning probe microscope. By doing so, stable and accurate measurement results can be obtained more reliably. Examples of such a resin include acrylic resin.
In this embodiment, the resin is impregnated through the above opening. Since the above-mentioned opening is preferably an extremely small width of less than 1 mm in maximum width, it is preferable that the viscosity of the resin is low.
Incidentally, a known method may be adopted as a method for curing the resin. The resin may be a photocurable resin or a thermosetting resin.

It is preferable to perform defoaming in the curing step. What is produced in this embodiment is a cross-sectional sample for a scanning probe microscope. As shown above, it is preferable that the opening of the container has an extremely small width of less than 1 mm, and even a small amount of air bubbles in the resin may have a large effect on the measurement of the cross-sectional sample. I can't deny it. Therefore, it is preferable to perform defoaming in the curing step. The specific method is not particularly limited. For example, a through hole is provided at the bottom or side wall of the container shown in FIG. 1 (c) while providing a filter for preventing resin from leaking, and the container is provided. An example is a method of evacuating by fitting an exhaust pipe so as to cover it.

1-5. Smoothing step In this step, the sample-containing cured resin is smoothed to reveal the cross section of the sample-containing cured resin (that is, the cross section of the powder sample coated with the conductive film). This method is not particularly limited, but for example, the surface on the opening side of the container is smoothed together with the container to expose the cross section of the sample-containing cured resin (FIG. 1 (d)). By smoothing the surface of the container on the opening side as in this step, the cross section of the particles coated with the conductive film can be exposed. By performing measurement using a scanning probe microscope in this state, it is possible to sufficiently secure continuity with respect to the particles (FIG. 1 (e)).
Incidentally, as a specific method of this step, a known polishing method may be adopted, and for example, a method such as mirror polishing or ion milling may be used.

The above steps are carried out to prepare a cross-sectional sample for a scanning probe microscope. The cross-sectional sample in the present specification refers to a sample having a predetermined three-dimensional shape and having a cut end cut along an arbitrary line (plane). Further, in the present specification, the sample whose cross section is expressed by the smoothing step is also referred to as a cross section sample. For steps other than the above, known steps may be appropriately adopted.

<2. Cross-section sample measurement method>
The polished surface of the cross-sectional sample for the scanning probe microscope prepared as described above is measured with the scanning probe microscope. As for the measurement method, a known method may be used by using a known device. However, as shown in Examples described later, when SSRM is used as the scanning probe microscope, stable and accurate measurement results can be obtained. The reason is assumed that when the conductive powder and the powder sample are mixed, the mixing ratio of the conductive powder and the resin cannot be adjusted appropriately, and the mixed state of the powder sample and the conductive powder becomes non-uniform. However, in the present embodiment, such a risk can be eliminated. As a result, the risk of failure in preparing a cross-sectional sample for a scanning probe microscope can be reduced, the time required to obtain a measurement result can be shortened, and the accuracy of the measurement result can be improved.

<3. Modification example>
The technical scope of the present invention is not limited to the above-described embodiment, but also includes a form in which various changes and improvements are made to the extent that a specific effect obtained by the constituent requirements of the invention and the combination thereof can be derived.

For example, one feature of the present invention is that, as described above, a coating step is performed on a powder sample, and then a curing step with a resin is performed. Therefore, other steps can be omitted as appropriate. For example, the above characteristics may be applied to a container containing a powder sample in which the filling step has been performed in advance.

Further, in the present embodiment, the coating step is performed on the powder sample placed in the container, but the powder sample coated with the conductive film in advance may be placed in the container and then cured with a resin. That is, the curing step may be performed on the powder sample for which the coating step has already been performed. However, it is preferable to coat the conductive film with the powder sample in a container rather than coating the entire powder sample with the conductive film because the work can be simplified.

Further, although the cross-section sample for the scanning probe microscope is illustrated in the present embodiment, the technical idea of the present embodiment can be applied to the cross-section sample for the scanning probe microscope. For example, when measuring the cross section of a sample using a scanning electron microscope (SEM), if the sample itself has poor conductivity, a carbon film is provided on the cross section to suppress charge-up while ensuring conductivity (in some cases). A metal film is provided, and a carbon film is further provided on the cross section). Similar measures are taken for samples for electron backscatter diffraction analysis (EBSD).
On the other hand, in recent years, in SEM, a method of observing the outermost surface of a sample as precisely as possible with a low acceleration voltage has been used. Further, in EBSD, the result of the portion having a depth of about 1 to 10 nm from the outermost surface of the sample can be obtained. Whether it is SEM or EBSD, if the carbon film is provided as in the conventional case, there is a concern that the carbon film on the outermost surface of the cross-sectional sample has a great influence on the measurement result.
However, by curing a powder sample coated with a conductive film as in the present embodiment with a resin and exposing the cross section thereof, it is possible to impart conductivity to the sample without separately providing a conductive film. It becomes. In that case, it is not necessary to separately provide a conductive film on the cross section of the sample, and it is not necessary to provide a carbon film as well. As a result, it is possible to obtain normal results in both SEM and EBSD.

Hereinafter, this embodiment will be described. The technical scope of the present invention is not limited to the following examples. Further, Comparative Example 2 described later is not necessarily a conventional technique, but is referred to as a Comparative Example for convenience of explanation.

(Example 1)
First, the container is a rotatable aluminum perforated cylindrical holder (outer diameter 3.0 mm, height 3.) that can be installed in an ion milling device (JEOL Cross Section Polisher SM-09010). 0 mm, central hole diameter 0.5 mm, hole depth 1.0 mm) were prepared.

Then, while tapping (swinging up and down) the holder, a powder sample (average particle size 5 μm) to be measured is placed in the hole, and the powder sample is ground so that it is approximately the same height as the edge of the opening of the holder. The inside of the hole was filled with a powder sample.

Then, using a precision etching and coating device (Model 682 manufactured by GATAN), the surface of the powder sample exposed at the opening of the hole was coated with a carbon film as a conductive film so as to have a thickness of about 10 nm.

Subsequently, an instant adhesive (Toagosei Aron Alpha (registered trademark)) was dropped from the opening of the hole as an embedding resin, the instant adhesive was allowed to permeate into the voids of the powder sample, and the resin remaining on the surface was wiped off. The resin was cured by allowing it to stand for 30 minutes to obtain a sample-containing cured resin.

Subsequently, a holder in which the sample-containing cured resin is present in the hole is set in the above ion milling device, and the sample-containing cured resin is subjected to ion milling processing together with the holder to smooth the surface of the sample-containing cured resin. The cross section was exposed. In this way, a cross-sectional sample for SSRM was prepared.

Then, in order to confirm that the conductivity of each particle constituting the powder sample in the cross-sectional sample is sufficient, a new conductive probe ( A Bruker AXS DDESP) was attached, and the surface of the processed sample in the contact mode was measured in a range of 30 μm × 30 μm at a resolution of 512 points × 512 points at a scan speed of 0.5 Hz. A histogram of the resistance value of the sample particle portion obtained from the spread resistance distribution obtained by the measurement is shown in FIG. 2 (horizontal axis: resistance value (log), vertical axis: resistance value shown on the horizontal axis in the entire measured portion. The ratio of the part shown in. The same applies hereinafter.).

(Example 2)
In the coating of the conductive film, except that a vapor deposition apparatus (VE-2012 manufactured by Vacuum Device) was used to coat the surface of the powder sample exposed at the opening of the hole with carbon so as to have a thickness of about 50 nm. A cross-sectional sample was prepared and measured in the same manner as in 1.
FIG. 3 shows a histogram of the resistance value of the sample particle portion obtained from the spread resistance distribution obtained by the measurement.

(Comparative Example 1)
A cross-sectional sample was prepared and measured in the same manner as in Example 1 except that the conductive film was not coated.
As a result of the measurement, the entire measurement area showed a resistance value exceeding the upper limit of the detector, and no data could be obtained.

(Comparative Example 2)
In Example 1, the conductive film was coated, but in this example, the conductive film was not coated. Instead, in addition to the powder sample, a mixture of carbon black (average particle size 35 nm) as a conductive powder so as to have a volume ratio of powder sample: carbon black = 1: 1 is filled in the hole of the holder. It was.
Except for the above contents, a cross-section sample was prepared and measured in the same manner as in Example 1. FIG. 4 shows a histogram of the resistance value of the sample particle portion obtained from the spread resistance distribution obtained by the measurement.

(Evaluation)
Comparing the results of Example 1 and the results of Example 2, the resistance values and resistance distributions of the particle portions constituting the powder sample are the same, and both have the resistance values corresponding to the powder sample, that is, low resistance to high resistance. It can be seen that there is a bar graph portion that protrudes at a predetermined resistance value between them.
On the other hand, in Comparative Example 1, conductivity was not obtained in the first place, and measurement results could not be obtained. Further, in Comparative Example 2, there are particles showing the same resistance value as in Examples 1 and 2, but it is shown that there are many particles having high resistance. It is considered that this is because the contact state between the particles constituting the powder sample and the particles constituting the conductive powder becomes non-uniform, and there are particles having insufficient conduction.

(Summary)
As a result of the above, it was found that in this example, stable and accurate measurement results can be obtained even when the measurement target using the scanning probe microscope is a powder sample.

1 …… Powder sample 2 …… Container 3 …… Conductive film 4 …… Resin

Claims (12)

A curing step of curing a resin containing a powder sample coated with a conductive film to obtain a sample-containing cured resin,
A smoothing step of smoothing the sample-containing cured resin to reveal a cross section of the sample-containing cured resin.
A method for producing a cross-sectional sample. The method for producing a cross-sectional sample according to claim 1, further comprising a coating step of coating a conductive film on a powder sample placed in a container through the opening of the container before the curing step. The method for producing a cross-sectional sample according to claim 2, wherein sputtering or thin film deposition is used in the coating step. The method for producing a cross-sectional sample according to claim 2 or 3, further comprising a filling step of inserting the powder sample through the opening of the container and filling the inside of the container with the powder sample before the coating step. The method for producing a cross-sectional sample according to any one of claims 1 to 4, wherein in the smoothing step, the surface on the opening side of the container used in the curing step is smoothed together with the container. The method for producing a cross-sectional sample according to any one of claims 2 to 5, wherein the maximum width of the opening is less than 1 mm. The method for producing a cross-sectional sample according to any one of claims 1 to 6, wherein the resin is an acrylic resin. The method for producing a cross-sectional sample according to any one of claims 1 to 7, wherein the conductive film is at least one of a carbon film and a metal film. The method for producing a cross-sectional sample according to any one of claims 1 to 8, wherein defoaming is performed in the curing step. The method for producing a cross-section sample according to any one of claims 1 to 9, wherein the cross-section sample is a sample for a scanning probe microscope. A method for measuring a cross-sectional sample, wherein a measurement is performed using a scanning probe microscope on a sample prepared by the method according to any one of claims 1 to 10. The method for measuring a cross-sectional sample according to claim 11, wherein the scanning probe microscope is a scanning spread resistance microscope.

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