JP2017187387A - Method for preparing thin film sample - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing a thin film sample with a focused ion beam device, which is capable of preparing a sufficiently thin and strainless straight thin film sample even in the case of a sample containing a soft material such as a rubber composition.SOLUTION: The method for preparing a thin film sample containing a rubber composition with a focused ion beam device comprises: a protective film formation step of forming a carbon or metal protective film on a sample surface on a target site by a focused ion beam; a cutting-out step of cutting out a micro sample including the target site by the focused ion beam; a fixing step of fixing the micro sample on sample table; a reinforcing film formation step of forming two or more continuous carbon or metal reinforcing films approximately in parallel on each of a front surface, a top surface and a rear surface of the micro sample by the focused ion beam; and a thin film making step of making the target site into a thin film by the focused ion beam.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a method for preparing a thin film sample containing a rubber composition by a focused ion beam apparatus.

  Conventionally, when TEM observation is performed on a soft sample such as a rubber composition or a thermoplastic elastomer, a cryomicrotome method of cutting a frozen sample is generally used as a method for preparing a thin film sample. However, if the sample to be observed is a composite material of a rubber composition and a hard material that cannot be processed by a cryomicrotome method such as metal, a thin film sample cannot be prepared by this method.

  On the other hand, the microsampling method is used for sample preparation for observation of an electron microscope of hard materials such as integrated circuit chips, semiconductor wafers, and metals. The microsampling method is a technique that can cut out and extract a sample (microsample) in an arbitrary direction and shape, and a focused ion beam (FIB) method using a focused ion beam is known. . The FIB method is a processing technique in which accelerated gallium (Ga) ions are irradiated while scanning the sample surface, and the sample is etched by the sputtering effect (for example, Patent Documents 1 and 2).

  For a transmission electron microscope (TEM) observation sample, a part of the microsample of the integrated circuit chip or semiconductor wafer obtained by the microsampling method can be further thinned by FIB, and this thinned portion can be observed by TEM. Are known.

  As a sample preparation method for TEM observation of a hard material by the FIB method, for example, a step of cutting a microsample including an observation site by irradiating the FIB from at least two different angular directions with respect to the sample surface, the microsample on a TEM sample stage There is a method including a step of transporting and a step of thinning a part of a microsample on a TEM sample stage by FIB.

JP 2005-100995 A Japanese Patent Laid-Open No. 2005-12208

  Even when a composite material of a rubber composition and a metal is used as a sample, a FIB apparatus can be used for a sample containing a rubber composition because a thin film sample can be prepared and a sample can be cut into an arbitrary position, direction and shape. Attempts have been made to prepare a thin film sample using sapphire.

  In the case of a hard material such as an integrated circuit chip, a semiconductor wafer, or a metal, even when a thin film sample of 100 nm or less is prepared by an FIB apparatus, distortion occurs because the thin film portion has sufficient hardness. Absent. On the other hand, in the case of a soft material such as a rubber composition, when the sample is thinned by the FIB apparatus, the thin sample is distorted due to the softness of the sample, and a sufficiently thin and straight thin film sample is prepared. There is a problem that is difficult.

  The present invention prepares a thin film sample by a focused ion beam apparatus capable of preparing a thin film sample that is sufficiently thin and has a small amount of distortion even when the sample includes a soft sample such as a rubber composition. It aims to provide a method.

  The present invention is a method for preparing a thin film sample containing a rubber composition by a focused ion beam apparatus, a protective film forming step of providing a carbon or metal protective film on a sample surface on a target site by a focused ion beam, a focused ion beam Cutting out the microsample including the target site by the step, fixing step of fixing the microsample to the sample stage, two or more continuous carbon or metal reinforcing films on the front surface, top surface and rear surface of the microsample by the focused ion beam. The present invention relates to a method including a reinforcing film forming step to be provided and a thinning step of thinning a target portion with a focused ion beam.

  The thin film sample is preferably a thin film sample for observation with a transmission electron microscope.

  The sample containing the rubber composition is preferably a sample composed of a rubber composition and a metal.

  The thickness of the protective film is preferably 1.0 μm or more.

  The thickness of the reinforcing film is preferably 0.6 μm or more.

  According to the method for preparing a thin film sample of the present invention with a focused ion beam apparatus, even if the sample includes a soft sample such as a rubber composition, a thin film sample that is sufficiently thin and has a straight line with little distortion is obtained. Can be prepared.

It is the schematic which shows the fixing process of this invention. It is the schematic which shows the fixing process of this invention. It is the schematic which shows the reinforcement film | membrane formation process of this invention. It is the schematic which shows the reinforcement film | membrane formation process of this invention. It is the schematic which shows the thin film formation process of this invention. It is the schematic which shows the thin film formation process of this invention. It is a scanning electron microscope observation image of the thin film sample of an Example. It is a scanning electron microscope observation image of the thin film sample of a comparative example.

  The method of preparing a thin film sample containing the rubber composition of the present invention with a focused ion beam (FIB) apparatus includes a protective film forming step of providing a protective film on the surface of the sample, a cutting step of cutting out the microsample, and fixing the microsample to the sample stage. A fixing step, a reinforcing film forming step of providing a predetermined reinforcing film, and a thinning step of thinning.

Sample The thin film sample according to the present invention is a thin film sample prepared by cutting out a part of a sample containing a rubber composition. The sample may be a composite sample of a rubber composition and another material, or may be a rubber composition sample consisting only of a rubber composition. Other materials are not particularly limited as long as they can be processed by FIB. For example, various metals, wood, carbon fiber reinforced plastics, synthetic resins such as thermosetting resins and thermoplastic resins, semiconductors, glass, ceramics, Examples include elastomers other than rubber compositions. Especially, it is preferable from the reason that the effect of this invention can be exhibited more that it is a sample which contains the metal which cannot be cut with a cryomicrotome, a semiconductor, glass, and ceramics as another material.

  Specific examples of composite samples of rubber compositions and other materials include composite samples of rubber compositions and metal cords or textile cords constituting tires, vibration-proof rubbers and sealant rubbers, and resin and metal automobile parts. And composite materials. In particular, since the adhesion interface with the metal in the rubber composition is affected by the metal, the influence from the metal can be analyzed by observing the interface with a transmission microscope.

  The rubber composition is not particularly limited, and can be a rubber composition appropriately containing a rubber component, a filler, a vulcanizing agent, and other compounding agents. In addition, content of various compounding agents is not specifically limited unless the effect of this invention is impaired, It can be set as content in the conventional rubber composition.

  The rubber component is not particularly limited, and rubber components generally used in the rubber industry, such as chloroprene rubber (CR), natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), ethylene propylene diene rubber (EPDM), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, etc. These rubber components may be used alone or in combination of two or more.

  Examples of the filler include, but are not limited to, fillers generally used in the rubber industry, such as carbon black and white fillers such as silica, and may contain one or more of these fillers. Good.

  Examples of the vulcanizing agent include sulfur such as powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur. Examples of the other compounding agents include, but are not particularly limited to, compounding agents generally used in the production of rubber compositions, such as zinc oxide, anti-aging agents, oils, softeners, and waxes.

  The sample containing the rubber composition is preferably treated so that microsampling of the target site to be observed is facilitated before the protective film forming step described later is performed. That is, it is preferable to prepare a sample piece in which the target site exists near the sample surface. For example, in the case of a composite sample including a tire rubber composition constituting a tire and a bead cord, the tire is first disassembled and the vicinity of the bead is cut out, and further a sample piece in which the rubber composition remains thinly on the bead cord with a knife or the like. It is preferable to prepare and use this sample piece for the subsequent steps.

Protective film forming step The protective film forming step is a step of forming a carbon or metal protective film on the surface of the sample on the target site by FIB. This protective film functions to protect the portion left as a thin film in the thinning process described later from sputtering by FIB, and to suppress distortion of the thin film sample by a reinforcing effect when the protective film forms the upper end of the thin film sample. Have

  As a method of forming the protective film, a conventional film forming function using a focused ion beam can be used. That is, it can be formed by locally irradiating the FIB while supplying a compound gas containing phenanthrene, platinum, carbon, tungsten or the like from a gas injection nozzle mounted on the FIB apparatus.

  The protective film is a film provided by attaching carbon or metal by FIB. Platinum or tungsten can be suitably used as the metal. A protective film other than carbon is preferable for the purpose of clarifying the distinction between a rubber composition and a protective film when analyzing a thin film sample, but it is appropriate depending on the angle of the gas injection nozzle attached to the FIB apparatus to be used. Just choose.

  The thickness of the protective film is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 2.0 μm or more, because the part to be left as a thin film in the thinning step is protected from sputtering by FIB.

  The FIB irradiation conditions in the protective film formation step are not particularly limited, and can be performed under conditions according to the material of the sample. For example, it can be performed under conditions such as an acceleration voltage of 30 kV and an irradiation current of 0.1 to 1.0 nA.

Cutting-out process The cutting-out process is a process of cutting out a microsample including a target site from a sample piece by FIB. A microsampling method or the like by the FIB method can be applied to the cutting process. That is, the sample surface is irradiated with FIB and processed by the sputtering effect of FIB to cut out a microsample including the target portion and having the protective film as the upper end surface.

  The shape of the microsample to be cut out is not particularly limited, but a substantially rectangular parallelepiped shape is preferable from the viewpoint of ease of handling in a subsequent process. Depending on the FIB apparatus, it may be difficult to cut out the bottom surface of the microsample, that is, the surface opposite to the top surface on which the protective film is formed, in parallel with the top surface. It is not particularly limited as long as it can be fixed to the sample stage.

  The FIB irradiation conditions in the cutting process are not particularly limited, and can be performed under conditions according to the material of the sample. For example, rough processing can be performed under conditions such as an acceleration voltage of 30 kV and an irradiation current of 7 to 65 nA, and fine processing can be performed under conditions of an acceleration voltage of 30 kV and an irradiation current of 0.5 to 5 nA.

  It is preferable that the microsample cut out in the cutting step is supported by the probe because the microsample can be easily transferred to the sample stage for observation. As the probe, a general probe used in a microsampling method can be used. In addition, it is preferable to make this probe contact before a micro sample is cut | disconnected from a sample piece in a cutting-out process.

  The fixing process, the reinforcing film forming process, and the thinning process will be described with reference to the accompanying drawings, but are not limited to these forms.

Fixing process The fixing process is a process of fixing the microsample obtained in the cutting process after placing it on the sample stage for observation. The fixing step is a step of fixing the microsample by attaching the carbon or metal to the contact portion or gap between the microsample and the sample table or the lower part of the side surface of the microsample by FIB after the microsample is set on the sample table. Is preferred.

  In FIG. 1, a microsample A cut out from a sample in which a protective film 2 is formed on the upper surface of a composite sample 1 composed of a rubber composition 11 and a metal cord 12 is operated, and a probe B connected to the upper surface of the microsample A is operated. Then, the state of being placed on the sample stage C is schematically shown. FIG. 2 shows the gap between the microsample A and the sample stage C and the microsample while supplying a compound gas containing phenanthrene, platinum, carbon, tungsten, or the like from a gas injection nozzle attached to the FIB apparatus. The micro sample A fixed to the sample stage B is schematically shown by irradiating the lower part of the side surface of A and providing the fixed layer 3 formed by adhering carbon or metal.

  The amount of carbon or metal deposited in the fixing step is not particularly limited as long as the microsample is fixed to the sample stage to the extent that there is no problem when performing the post-process or observation of the present invention. It may be adjusted as appropriate according to the conditions.

  The FIB irradiation conditions for attaching carbon or metal in the fixing step are not particularly limited, and can be performed under conditions according to the material of the sample. For example, it can be performed under conditions such as an acceleration voltage of 30 kV and an irradiation current of 0.1 to 1.0 nA.

Reinforcing film forming process The reinforcing film forming process is a process in which two or more continuous carbon or metal reinforcing films are provided substantially in parallel on the front surface, upper surface, and rear surface of the microsample by a focused ion beam. The present invention is characterized in that after the reinforcement film is provided, the region sandwiched between the reinforcement films is thinned. Invention that succeeded in preparing a sufficiently thin and straight thin film sample without distortion caused by thinning, even if the sample includes a soft sample such as a rubber composition by providing a reinforcing film It is. FIG. 3 schematically shows a micro sample A provided with reinforcing films 4 at both ends.

  The upper surface of the microsample refers to a surface provided with a protective film. In addition, the front surface and the rear surface when the microsample is substantially a cube indicate two surfaces that are not adjacent to each other and are paired out of the four side surfaces other than the top surface and the bottom surface.

  It is preferable to provide three or more reinforcing films substantially in parallel because two or more regions sandwiched between the reinforcing films, that is, regions that can be thinned are formed. By providing two or more regions that can be thinned, it is possible to create thin film regions with different conditions such as film thickness on the same sample, so that observation and analysis work can be made more efficient. FIG. 4 schematically shows a microsample A in which reinforcing films 4 are provided at both ends and in the center.

  The distance between the reinforcing membrane and the reinforcing membrane when two or more reinforcing membranes are provided substantially in parallel is preferably 10 μm or more for the reason that sufficient observation or analysis is possible and the effect of the present invention can be more exerted. 15 μm or more is more preferable, and 20 μm or more is more preferable. Further, the distance between the reinforcing film and the reinforcing film is preferably 100 μm or less, more preferably 50 μm or less, because the effect of the present invention that the distortion is small even when the film is thinned is more exhibited.

  The reinforcing film is a film provided by attaching carbon or metal by FIB, and is provided continuously on the front surface, the upper surface, and the rear surface of the microsample. The Platinum or tungsten can be suitably used as the metal, and may be appropriately selected depending on the angle of the gas injection nozzle mounted on the FIB apparatus to be used. As shown in FIGS. 3 and 4, it is preferable that the reinforcing film 4 is extended to the surface of the sample table C because a stronger reinforcing effect can be obtained.

  The thickness of the reinforcing film is preferably 0.6 μm or more, more preferably 1.0 μm or more, and even more preferably 2.0 μm or more, because the effect of the present invention that the distortion is small even when the thickness is reduced is more exhibited. . Moreover, the upper limit of the film thickness of a reinforcement film is not specifically limited.

  The FIB irradiation conditions in the reinforcing film forming step are not particularly limited, and can be performed under conditions according to the material of the sample. For example, it can be performed under conditions such as an acceleration voltage of 30 kV and an irradiation current of 0.1 to 1.0 nA.

Thinning process The thinning process is a process for thinning a target portion with a focused ion beam. The thinning step is a step of processing a region sandwiched between the reinforcing films into a thin film portion including a target site for observation or analysis and extending from the reinforcing film to the reinforcing film by the sputtering effect of FIB. FIG. 5 schematically shows a thin film sample in which a thin film portion having a thickness of X nm is provided on a micro sample A (see FIG. 3) provided with reinforcing films 4 at both ends. FIG. 6 schematically shows a thin film sample in which a thin film portion having a thickness of Ynm and a thin film portion having a thickness of Znm are provided on a microsample A (see FIG. 4) provided with reinforcing films 4 at both ends and in the center.

  The film thickness of the thin film portion is preferably 200 nm or less, preferably 150 nm or less, because it is suitable for a thin film sample for observation with a transmission electron microscope, and because the effect of the present invention that distortion does not occur even when the film is thinned is more exhibited. More preferred is 100 nm or less. Moreover, the lower limit of the film thickness of the thin film portion is not particularly limited, and may be a lower limit of the film thickness according to observation and analysis performed on the thin film sample.

  The FIB irradiation conditions in the thinning process are not particularly limited, and can be performed under conditions according to the material of the sample. For example, it can be performed under conditions such as an acceleration voltage of 30 kV and an irradiation current of 0.05 to 5 nA.

Thin film sample The thin film sample prepared by the method of the present invention is a thin film sample that is sufficiently thin and straight with little distortion even when the sample includes a soft sample such as a rubber composition. It is preferable to use a thin film sample for observation with a transmission electron microscope.

  The height of the thin film portion of the thin film sample (distance from the bottom surface to the top surface) is preferably 50 μm or less at the highest point because preparation is difficult. The height of the soft sample such as the rubber composition in the thin film portion is preferably 2 μm or more at the widest point from the viewpoint of securing the observation region or the analysis region, and more preferably 10 μm or more.

  The present invention will be described based on examples, but the present invention is not limited to the examples.

Example A pneumatic tire is disassembled, a composite sample of the rubber composition and the metal cord is cut out from the rubber composition, the metal cord, and the bonded portion, and further the rubber composition is cut off with a knife to form a rubber composition on the surface of the metal cord. A thin sample piece was prepared. This sample piece was set in an FIB apparatus (SCIOS manufactured by FEI), and a platinum protective film having a film thickness of 1.0 μm was formed on the surface of the sample piece on the target site by FIB (30 kV, 0.5 nA). A microsample (width: approx. 30 μm) with the platinum protective film on the top is cut out by the microsampling method using the FIB method, placed on a specimen table for TEM observation, and fixed by attaching platinum to the lower part of the side surface of the microsample using the FIB. did. A carbon reinforcing film having a thickness of 1.0 μm and a width of 2.5 μm was formed on both ends of the fixed microsample by FIB (30 kV, 0.5 nA) (see FIG. 3). And the thin film sample was prepared by forming a thin film part by sputtering by the area | region (width: about 25 micrometers) FIB (30 kV, 0.1-3 nA) pinched | interposed into the reinforcement film of both ends (refer FIG. 5). . FIG. 7 shows a scanning electron microscope (SEM) observation image of the prepared thin film sample from above the upper surface on which the protective film is formed.

Comparative Example A thin film sample was prepared in the same manner as in Example except that the width of the micro sample was about 15 μm and the reinforcing film was not formed. FIG. 8 shows an SEM observation image of the prepared thin film sample from above the upper surface on which the protective film is formed.

  It can be seen that the thin film sample of the example in which the thinning process was performed after the formation of the reinforcing film is a thin film sample having a film thickness of 100 nm or less and having a small distortion. On the other hand, in the comparative example in which the thinning process was performed without forming the reinforcing film, it was found that a large strain was generated before thinning to a film thickness of 100 nm and it was difficult to prepare a straight thin film sample.

A Micro sample B Probe C Sample stage 1 Composite sample 11 Rubber composition 12 Metal cord 2 Protective film 3 Fixed layer 4 Reinforcing film

Claims (5)

A thin film sample containing a rubber composition is prepared by a focused ion beam device,
A protective film forming process in which a carbon or metal protective film is formed on the sample surface on the target site by a focused ion beam;
A cutting-out process of cutting out a microsample including a target portion with a focused ion beam;
Fixing process for fixing the micro sample to the sample stage
A method comprising a reinforcing film forming step in which two or more continuous carbon or metal reinforcing films are provided substantially in parallel on the front surface, top surface, and rear surface of a microsample by a focused ion beam, and a thinning step in which a target site is thinned by a focused ion beam . The method according to claim 1, wherein the thin film sample is a thin film sample for observation with a transmission electron microscope. The method according to claim 1 or 2, wherein the sample containing the rubber composition is a sample comprising a rubber composition and a metal. The method according to claim 1, wherein the protective film has a thickness of 1.0 μm or more. The method according to claim 1, wherein the reinforcing film has a thickness of 0.6 μm or more.