JP2009244240A - Method for manufacturing sample for cross-sectional observation by scanning electron microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a sample for cross-section observation by a scanning electron microscope that is appropriate to smooth cross-section formation of 10-100 μm order, does not require a skilled technique of a worker, has high processing position accuracy, and accurately forms a cross section at a desired specific position. <P>SOLUTION: In this method for manufacturing the sample for cross-section observation by the scanning electron microscope, a rough cross section passing a part to be observed of the sample is formed, a transparent substrate with a thickness of a processing depth or smaller by an ion beam is fixed to the sample so as to cover the part to be observed, then the sample is installed in a sample holder of a device for irradiating the sample with the ion beam, the part to be observed and the ion beam irradiation position of the device are aligned, then the rough cross section existing on the part to be observed is processed by the ion beam irradiation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for preparing a sample for observing a cross section with a scanning electron microscope, which can form a smooth cross section with a large area with excellent processing position accuracy.

  In order to observe the internal structure of a sample, for example, to detect abnormalities or foreign matters in the vicinity of the surface of the sample, a method of observing a cross section of the sample with a scanning electron microscope is performed. As a method of forming a cross section, a method using a focused ion beam processing observation apparatus (FIB), a method of embedded polishing in which a sample is embedded in a resin or the like and polished to form a cross section of the sample, a cross section polisher (CP apparatus) is used. The method to be used is known.

  Methods using FIB are disclosed in Japanese Patent Application Laid-Open No. 2003-4667 (Patent Document 1), Japanese Patent No. 3263920 (Patent Document 2), Japanese Patent Application Laid-Open No. 4-345740 (Patent Document 3), and the like. The method described in Patent Document 1 is a method for producing a thin film sample for a scanning transmission electron microscope (STEM) using FIB. The sample is cut to form a cross section, and the inside of the sample close to the cross section is formed. In this method, a hole is formed using FIB to form a thin film, and the surface on which the hole is formed is used as an observation surface.

The method described in Patent Document 2 is a method for producing a thin-film sample for a transmission electron microscope (TEM), which uses FIB. Further, the method described in Patent Document 3 is a method of forming a concave portion by scanning the sample surface using FIB and forming an observation surface on the side surface of the concave portion. In this method, the sample is processed while scanning in a state where the shield plate positioned accurately is installed.
JP 2003-4667 A Japanese Patent No. 3263920 JP-A-4-345740

  Among the above methods, the method using FIB has excellent processing position accuracy and can perform cross-sectional processing at a desired position. However, since the beam diameter used for processing is on the nanometer order, There is a problem that it takes too much time to process a size exceeding 100 μm. For example, the observation width described in the example of Patent Document 2 is 5 μm, and this method is not suitable for observation of a wide area (on the order of 50 to 100 μm).

  The embedded polishing method has a problem that the skill of the operator is greatly affected. When the operator's skill is low, sagging and scratches occur, and skilled techniques are required to obtain a smooth processed surface at a specific position.

  On the other hand, a CP device is used for processing a size of several tens to several hundreds μm (on the order of 10 μm to 100 μm). However, since the CP device is not originally a device for processing a specific position, there is a problem that the processing position accuracy is not good.

  The present invention solves the above-mentioned problems of the prior art, is suitable for forming a smooth cross section having a size of the order of 10 μm to 100 μm, does not require the skill of an operator, has excellent processing position accuracy, and is desired. It is an object of the present invention to provide a method for producing a sample for observing a section by a scanning electron microscope, which can accurately form a section at a specific position.

  As a result of intensive studies, the present inventor can align a position while observing the observed portion from the substrate if a thin transparent substrate is fixed to the portion observed by the scanning electron microscope, that is, the observed portion of the sample. It has been found that even when a CP device is used, it is possible to easily adjust the machining position to a desired position. Then, by using a device that irradiates the sample with an ion beam such as a CP device, it was found that a cross section for observation by a scanning electron microscope can be formed smoothly over a large area with excellent processing position accuracy. Completed the invention.

  According to the first aspect of the present invention, a sample is cut out from an object to be measured, a cross section passing through the observed portion or the vicinity thereof is formed in the cut sample, and the transparent having a thickness equal to or less than the processing depth by the ion beam After fixing a substrate so as to cover the observed portion, the sample is placed on a sample holder of a device that irradiates the sample with an ion beam, and the observed portion and the ion beam irradiation position of the device are Provided is a method for producing a sample for observing a cross section by a scanning electron microscope, characterized by performing alignment and then processing the cross section by irradiating the cross section with an ion beam.

  Here, the observed portion of the sample is a portion of the sample that is observed with a scanning electron microscope. Further, as a device for irradiating the sample with an ion beam, a device suitable for processing of several tens to several hundreds of μm size such as a CP device is preferably used. According to the method of the present invention, even if a CP apparatus is used, the processing position accuracy is excellent, so that even when the observed portion has a size of the order of 10 μm to 100 μm, a smooth cross section can be easily formed at a desired specific position. it can.

  In the method of the present invention, first, a sample having a size that can be processed by an apparatus that irradiates the sample with an ion beam is cut out from the measurement object. In order to facilitate the processing of a specific position (observed portion) on the micron order by this apparatus, it is preferable to cut in advance near the observed portion (processing position by this apparatus) of the sample. The size of the sample to be cut is usually about 10 mm or less in length and width (preferably about 10 mm or less and about 8 mm or less), and the thickness is about 2 mm or less, but is not particularly limited because it varies depending on the apparatus. If the measurement object is smaller than the size that can be processed by this apparatus, the cutting may not be necessary.

  A method and means for cutting (cutting) may be selected according to the material of the sample, the cutting size, and the like. For example, scissors, a band saw, a razor, a scalpel, etc. are mentioned.

  Preferably, after the cutout, the entire surface generated by the cutout is polished to the vicinity of a specific processing position (surface polishing may be performed only in the vicinity of the portion to be observed). Polishing to the vicinity of a specific processing position means that the cross section formed by this polishing is further processed (polished) by a device that irradiates the sample with an ion beam, such as a CP device, so that the processed surface including the observed portion can be easily obtained. This means that polishing is performed up to a position where it can be formed. Therefore, the polishing is performed so that a cross section formed by polishing passes through the observed portion or the vicinity thereof.

  The surface accuracy of the cross section formed in this way may be as rough as # 800. Therefore, the chamfering can be performed using a parallel polishing jig, a parallel polishing glass plate, and sandpaper having a roughness of about # 800 to 2,000. Hereinafter, the cross section formed in this way (the cross section after chamfering) is referred to as a rough cross section.

  The method of the present invention is characterized in that a thin transparent substrate having a thickness equal to or smaller than a processing depth by an ion beam is fixed to a sample so as to cover the observed portion. Since the transparent substrate is fixed so as to cover the observed portion, it is easy to visually recognize the observed portion of the sample from the substrate, and the irradiated portion of the device that irradiates the sample with the observed portion and the ion beam Can be adjusted while visually recognizing the part to be observed using the scope of the apparatus.

  Processing by the apparatus for irradiating the sample with an ion beam is performed by a method of irradiating an ion beam of Ar or the like from this transparent substrate, so that processing of the sample becomes difficult when the substrate is thick. Therefore, the thickness of the transparent substrate is equal to or less than the processing depth by the ion beam. When the apparatus for irradiating the sample with the ion beam is a CP apparatus, the processing depth is usually several hundred μm to Since the thickness is about 1 mm, the thickness of the transparent substrate is preferably 0.5 mm or less. Preferably, the transparent substrate has a thickness of 0.3 mm or less, more preferably 0.2 mm or less. If the thickness of the transparent substrate is made thinner, the thickness at which the sample is processed can be increased. Therefore, it is preferable to reduce the thickness of the transparent substrate as long as the mechanical strength of the transparent substrate can be maintained.

  As a material for the transparent substrate, glass excellent in strength, chemical resistance, heat resistance and the like is preferable. A glass plate that is commercially available as a cover glass has a thickness of slightly over 0.1 mm, and is inexpensive and easily available, so that it can be preferably used.

  As a method of fixing the transparent substrate so as to cover the observed portion, a method of bonding the substrate and the sample with an adhesive is preferable. An appropriate adhesive is selected from the viewpoints of transparency, heat resistance, familiarity with the sample (affinity), and curing speed. Furthermore, since the temperature of the workpiece is raised during processing by the CP device, it is preferable to consider durability against thermal damage of the adhesive.

  Specifically, a cyanoacrylate adhesive (for example, Aron Alpha manufactured by Toa Gosei Co., Ltd.) is preferable because it is quick-drying and easy to handle.

  The transparent substrate and the sample may be fixed before the rough cross section is formed. In this case, a transparent substrate is also polished at the same time.

  When a CP apparatus is used as an apparatus for irradiating a sample with an ion beam, the sample manufactured as described above is placed on a sample holder of the CP apparatus. The CP apparatus has the sample holder and an ion gun, and irradiates an ion beam from the ion gun to a processing position (observed part) of the sample placed on the sample holder to process the sample (cross-section polishing, etc.) )I do. Therefore, the sample is placed on the sample holder so that the transparent substrate is on the ion gun side.

  The sample holder and / or the ion gun are provided so as to be movable in the horizontal position, and the horizontal position is adjusted so that the ion beam is irradiated to the desired position of the sample, that is, the cross section of the sample in the observed portion. Is called. The CP device usually has a scope for visually recognizing the sample surface in order to facilitate the adjustment of the horizontal position. With this scope, the position is adjusted so that processing by an ion beam can be performed at an accurate position while visually recognizing the portion to be observed on the sample surface.

  In order to prevent damage caused by irradiation of the ion beam other than the processed portion of the sample during processing by the apparatus that irradiates the sample with an ion beam such as a CP device, the processed portion and the portions other than the vicinity thereof are usually shield plates. Covered with. That is, in the present invention, a shielding plate is provided on a transparent substrate. The shielding plate only needs to be a material that is not damaged by a temperature rise during a processing time of several hours. From the viewpoint of cost, durability, workability, and the like, a metal material is often used. A metal plate or the like whose surface is nickel-plated is used. As a device for irradiating the sample with an ion beam, a commercially available normal CP device can be used. Examples of the ion beam include an Ar ion beam.

  The invention according to claim 4 is characterized in that the outer periphery of the sample is covered with a heat conductive resin, and the sample, the transparent substrate and the sample holder are fixed to each other by the heat conductive resin. A method for producing a cross-sectional observation sample by a scanning electron microscope according to any one of claims 1 to 3.

  When processing with a device that irradiates the sample with an ion beam, the processing position of the sample may shift due to temperature rise, etc. To prevent this, the sample end, transparent substrate, and sample holder are fixed with resin or the like. It is preferable. This fixing allows the sample to be more securely attached to the sample holder.

  As the resin used for fixing, it is possible to use a thermosetting resin, for example, a thermosetting paste, but by using a heat conductive resin so as to cover the outer periphery of the sample, a heat escape path can be obtained. It is preferable because it can efficiently remove heat and reduce thermal damage due to temperature rise during irradiation processing. In particular, when the heat conductive resin is conductive, SEM observation can be performed with the sample attached to the sample holder, and SEM observation is facilitated. Therefore, a conductive resin having thermal conductivity is preferably used. It is done.

  Here, what is called a conductive paste is often used as the conductive resin having thermal conductivity. This is a mixture of a binder resin and a conductive filler, and carbon powder or a metal filler is used as the conductive filler. Specific examples include carbon paste and silver paste. Similarly, the heat conductive resin is obtained by blending a heat conductive filler with a binder resin, and aluminum nitride, bengara, or the like is used as the heat conductive filler. For this application, a paste-like material is easy to use, and a method of applying a necessary amount to a thin needle-like jig and applying it to a necessary portion is preferable because it is easy to work.

  In the case of using a thermosetting resin (such as a thermosetting paste), a resin having a low curing temperature is preferable because damage to the sample due to heat during curing is small. Accordingly, room temperature cured products are preferably used.

  If the sample is processed using the CP apparatus in the method for producing the sample for cross-sectional observation by the scanning electron microscope of the present invention, the processing of the order of 10 μm to 100 μm can be performed without the skill of the operator. In addition, it can be performed easily and efficiently. For example, a person having no skill can easily form a cross-section including a foreign substance or an irregular portion having a size of the order of 10 μm to 100 μm. In addition, since processing is performed using an ion beam, there is no occurrence of sagging or scratches that are problematic in the case of embedding polishing, etc., and anyone can obtain a smooth and clean cross section, greatly reducing production failures. it can.

  Furthermore, the position of the sample can be adjusted while visually recognizing the processing position, and the positioning is easy, so the processing position accuracy is excellent. In particular, when the sample, transparent substrate, and sample holder are fixed to each other with resin, the sample and sample holder can be firmly fixed, preventing misalignment during processing and improving processing position accuracy. And reduce failures.

  Therefore, the present invention can be applied to the cross-section preparation of a sample where failure is not allowed, and directly leads to the improvement of the yield in the preparation of the sample, for example, for observing a foreign substance or an abnormal part having a size of several tens to several hundred μm. This is a very effective method for obtaining a smooth cross section.

  The present invention further provides a sample for cross-sectional observation using a scanning electron microscope, which is produced by the method for producing a sample for cross-sectional observation using a scanning electron microscope according to any one of claims 1 to 4. Claim 5).

  According to the method for producing a sample for observing a section by a scanning electron microscope of the present invention, a smooth section having a size of the order of 10 μm to 100 μm is required for the sample for observing the section, and the skill of the operator is required. It is possible to carry out with excellent machining position accuracy.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to this mode.

  FIG. 1 is a schematic cross-sectional view showing a state in the vicinity of a portion irradiated with an ion beam before processing by a CP apparatus, as an example of a cross-sectional observation sample using a scanning electron microscope. In the figure, reference numeral 1 denotes a sample whose cross section is observed by a scanning electron microscope, and reference numeral 5 (a portion surrounded by a dotted line) denotes an irradiated portion to which an ion beam is irradiated by a CP apparatus. The irradiated part 5 in the sample 1 is an observed part processed by the CP device.

  In the figure, 2 is a cover glass which is a transparent substrate, and 3 is an adhesive. As shown in this figure, the sample 1 and the cover glass 2 are fixed to each other with an adhesive 3, and the observed portion of the sample 1 is covered with the cover glass 2.

  4 in the figure is a conductive resin having high thermal conductivity, and as shown in this figure, the outer periphery (and the exposed part of the adhesive 3) of the end part (part close to the cover glass) of the sample 1 is It is covered with a conductive resin 4 (conductive paste) having high thermal conductivity, and the sample 1 and the cover glass 2 are also fixed by the conductive resin 4.

  Next, a method for manufacturing a sample is described.

  FIG. 2 is a schematic perspective view showing a state in which a sample to be processed by the CP device is cut out from the measurement object. A state in which a sample (sample for sample preparation) having a size of 10 × 8 × 2 mm or less is cut out from the measurement object is shown, but one of the cut out cross sections (cross section A in the figure) Cutout is performed so as to pass through the observed portion.

  The sample and cover glass (transparent substrate) cut out in this way are bonded together by an adhesive and fixed to each other, and further fixed by the conductive resin 4 as described above. The cover glass is bonded so as to cover the observed portion of the sample, but the other part of the cover glass is bonded to the sample holder of the CP device, and the sample, the cover glass, and the sample holder are fixed. Bonding of the cover glass and the sample holder can be performed with the conductive resin 4 (conductive paste).

  FIG. 3 and FIG. 4 are a perspective view and a cross-sectional view, respectively, showing how the sample (sample and cover glass) fixed to the sample holder in this way is processed by the CP device. As shown in these figures, the sample is fixed to the cover glass by an adhesive and a conductive resin having high thermal conductivity, and the other part of the cover glass is fixed to the sample holder by the conductive resin having high thermal conductivity. (In FIG. 3, illustration of a conductive resin having high thermal conductivity is omitted.) In this way, fixing the sample, cover glass, and sample holder with a conductive paste can more reliably prevent misalignment during processing, and heat generated during processing by the conductive paste having high thermal conductivity. Is dissipated and damage to the sample due to heat can be reduced.

  The cross section A formed by the above cutting is polished with sandpaper or the like to form a rough cross section that passes through the observed portion (surface processing of the CP processed portion). It is preferable to set it in a holder because the sample holder and the polished surface are easily parallel. Therefore, preferably, as described above, after the sample, the cover glass, and the sample holder of the CP apparatus are fixed to each other, the surface of the CP processed portion is chamfered.

  The sample on which the CP processed portion is surfaced in this way is subjected to polishing (processing) of the observed portion of the rough cross section by the CP apparatus, and a sample for cross section observation using a scanning electron microscope is produced.

  As shown in the perspective view of FIG. 3 and the cross-sectional view of FIG. 4, the sample fixed on the sample holder is covered with a shielding plate in order to prevent damage caused by ion beam irradiation. The portion of the CP device that is not covered with the sample shielding plate (the portion protruding from the sample shielding plate) is irradiated with Ar ions, and the sample is processed. The processing position (irradiation position) is the observed part through which one section (section A) of the sample passes, but the upper part of the sample is covered with a cover glass, which is a transparent substrate, so the scope of the CP device (not shown) The horizontal position of the sample can be adjusted while visually recognizing this portion, so that excellent machining position accuracy is achieved.

  As a CP device (device for irradiating a sample with an ion beam), a general-purpose CP device can be used, and general-purpose conditions can also be adopted. As Ar gas, a grade B of 99.9999% or more is used, but a grade S of 99.9999% or more is recommended.

  FIG. 5 is a schematic perspective view showing the shape of the sample processed as described above. The processed surface in the figure is a portion irradiated with the ion beam of the CP apparatus. The processed surface is formed in the cross section A in FIG. 2, and thus is formed in the observed portion. Since the processing is performed by the CP apparatus, a smooth processed surface having a size of about several tens to several hundreds of μm can be formed. In the figure, a of the sample is about 10 mm, b is about 8 mm, and c is about 2 mm. Further, in this figure, the structure of the sample and the cover glass fixed to the sample is omitted, and only the integrated sample is shown.

It is a schematic cross section which shows the state before a process by CP apparatus of an example of the sample for cross-section observation by a scanning electron microscope. It is a model perspective view which shows an example of the cutout of a sample. It is a perspective view which shows the mode of a process by CP apparatus. It is sectional drawing which shows the mode of a process by CP apparatus. It is a model perspective view which shows the shape of the sample processed with CP apparatus.

Explanation of symbols

1. Sample 2. Cover glass Adhesive 4. 4. Conductive resin Irradiated part

Claims (5)

  A sample is cut out from the object to be measured, and a cross section passing through the observed portion or the vicinity thereof is formed in the cut sample, and a transparent substrate having a thickness equal to or smaller than the processing depth by the ion beam is covered with the observed portion. After fixing the sample, the sample is placed on a sample holder of an apparatus that irradiates the sample with an ion beam, and the portion to be observed is aligned with the ion beam irradiation position of the apparatus. A method for producing a sample for observing a section by a scanning electron microscope, wherein the section is processed by irradiating an ion beam.   The method for producing a sample for cross-sectional observation with a scanning electron microscope according to claim 1, wherein the transparent substrate has a thickness of 0.5 mm or less.   The method for producing a sample for cross-sectional observation with a scanning electron microscope according to claim 1 or 2, wherein the transparent substrate is made of glass.   The outer periphery of the sample is covered with a heat conductive resin, and the sample, the transparent substrate, and the sample holder are fixed to each other with the heat conductive resin. A method for producing a sample for cross-sectional observation by a scanning electron microscope according to any one of the above items.   A sample for cross-sectional observation using a scanning electron microscope, which is produced by the method for producing a sample for cross-sectional observation using a scanning electron microscope according to any one of claims 1 to 4.

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