JP6604011B2 - Method for observing ceramic dielectrics - Google Patents

Description

The present invention relates to a method for observing a ceramic dielectric, and more particularly to a method for observing a ceramic dielectric for observing a solid solution state or a dispersion state of an additive dissolved in the ceramic dielectric using an electron microscope.

  Conventionally, in the material design of ceramic dielectrics used for multilayer ceramic capacitors, it is fundamental to dissolve solid-state additives represented by rare earth elements (for example, Dy, Gd, Y, La, Ho, etc.) in the ceramic dielectric. It has become. When this type of additive is dissolved in the ceramic dielectric, the movement of oxygen vacancies is suppressed, or the resistance change of the ceramic dielectric occurs and local electric field concentration at the ceramic grain boundary is suppressed. As a result, the reliability of the multilayer ceramic capacitor can be dramatically improved.

  For this reason, when designing materials for ceramic dielectrics used in multilayer ceramic capacitors, the solid solution state and dispersion state of additives are important design indicators, and these are observed using an electron microscope. Yes.

  For example, in Japanese Patent Application Laid-Open No. 2010-24086 (Patent Document 1), a ceramic dielectric is observed using a transmission electron microscope (TEM), which is a kind of electron microscope, or in addition to the TEM. By observing the ceramic dielectric using an energy dispersive X-ray spectroscopy (EDX) apparatus attached to the ceramic, the solid solution state and dispersion state of the additive in the ceramic dielectric Confirmation has been made.

JP 2010-24086 A

  However, in order to confirm the solid solution state and dispersion state of the additive in the ceramic dielectric using TEM, the sample is thinned to a considerable extent so that a sufficient amount of electron beam is transmitted through the sample. There is a problem that it takes a lot of labor and time to make the slice thin. Therefore, development of an observation method that can more easily observe the solid solution state and dispersion state of the additive in the ceramic dielectric is required.

  Therefore, the present invention has been made to solve the above-described problems, and provides a novel method for observing a ceramic dielectric that can easily observe the solid solution state and dispersion state of the additive in the ceramic dielectric. The purpose is to do.

  The present inventor can visualize the surface distribution of electrical resistance on the observation target surface of the sample by observing the sample under a predetermined condition using a scanning electron microscope (SEM) which is a kind of electron microscope. Based on this, the inventors have conceived that the solid solution state and the dispersion state of the additive in the ceramic dielectric can be observed using the SEM, and completed the present invention.

That is, the method for observing a ceramic dielectric according to the present invention is a method for observing a solid solution state or a dispersion state of an additive dissolved in a ceramic dielectric, and exposing an observation target surface of the ceramic dielectric. And visualizing the surface distribution of electrical resistance on the observation target surface by irradiating the observation target surface with an electron beam under a condition that the penetration depth is 10 nm or less using a scanning electron microscope. A step of observing the observation target surface by obtaining a charged image .

  In the method for observing a ceramic dielectric according to the present invention, it is preferable that an acceleration voltage when irradiating the surface to be observed with the electron beam is 200 [V] or more and 700 [V] or less.

  In the ceramic dielectric observation method according to the present invention, the arithmetic average roughness Ra of the observation target surface is preferably 50 [nm] or less.

  Here, the scanning electron microscope used in the method for observing a ceramic dielectric according to the present invention does not require a sample to be thinned during observation. Therefore, the ceramic dielectric observation method according to the present invention can observe the solid solution state and dispersion state of the additive much more easily than the conventional observation method using a transmission electron microscope. .

  Therefore, according to the present invention, it is possible to easily observe the solid solution state and dispersion state of the additive in the ceramic dielectric.

It is the perspective view and sectional drawing of a common multilayer ceramic capacitor. It is a flowchart which shows the observation method of the ceramic dielectric material in embodiment of this invention. It is a schematic diagram which shows the preparatory step of the observation surface of the ceramic dielectric material shown in FIG. 2 in steps. It is a figure which shows the difference in the behavior of the primary electron in the sample surface based on the difference in the acceleration voltage at the time of using SEM, and the difference in an observation area. It is the contrast image obtained by the observation method of the ceramic dielectric material which concerns on a comparative example and an Example, and the element mapping image of the rare earth element obtained by TEM. It is a table | surface which shows the result of a 2nd verification test.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, the same or common parts are denoted by the same reference numerals in the drawings, and description thereof will not be repeated.

  First, before explaining a method for observing a ceramic dielectric in an embodiment of the present invention, the structure of a general multilayer ceramic capacitor will be described. 1A is a perspective view of a general multilayer ceramic capacitor, and FIG. 1B is a cross-sectional view taken along the line IB-IB shown in FIG. 1A.

  As shown in FIGS. 1A and 1B, the multilayer ceramic capacitor 10 has a substantially rectangular parallelepiped shape as a whole, and includes an element body 11 and a pair of external electrodes 14. The element body 11 has a rectangular parallelepiped shape, and includes ceramic dielectric layers 12 and internal electrode layers 13 that are alternately stacked along the thickness direction T. The pair of external electrodes 14 are located at both ends of the element body 11 in the length direction L of the length direction L and the width direction W orthogonal to the thickness direction T.

The ceramic dielectric layer 12 is formed of, for example, a ceramic material mainly composed of BaTiO ₃ , CaTiO ₃ , SrTiO ₃ , CaZrO _{3, and the} like, and the ceramic dielectric layer 12 includes a rare earth element (as an additive) For example, Dy, Gd, Y, La, Ho, etc.) are in solid solution. Further, the ceramic dielectric layer 12 may contain an Mn compound, Mg compound, Si compound, Co compound, Ni compound, V compound, or the like as an additive.

  The internal electrode layer 13 is formed of, for example, a metal material typified by Ni, Cu, Ag, Pd, an Ag—Pd alloy, Au, or the like.

  The external electrode 14 is composed of a laminated film of a sintered metal layer and a plating layer, for example. A sintered metal layer is formed by baking pastes, such as Cu, Ni, Ag, Pd, an Ag-Pd alloy, Au, for example. A plating layer is comprised by the Ni plating layer and the Sn plating layer which covers this, for example. Instead of this, the plated layer may be a Cu plated layer or an Au plated layer. Moreover, the external electrode 14 may be comprised only by the plating layer. Further, a conductive resin paste can be used as the external electrode 14.

  Here, the element body 11 prepares a plurality of material sheets in which a conductive paste that becomes the internal electrode layer 13 is printed on the surface of a ceramic sheet (so-called green sheet) that becomes the ceramic dielectric layer 12, and the plurality of material sheets are prepared. The pair of external electrodes 14 are formed by laminating and pressing and firing, and the pair of external electrodes 14 are formed so as to cover the outer surfaces of both end portions of the element body 11 manufactured through the above-described steps.

  As shown in FIG. 1B, one of a pair of internal electrode layers 13 adjacent to each other with the ceramic dielectric layer 12 sandwiched along the thickness direction T is a pair of external electrodes 14 inside the multilayer ceramic capacitor 10. The other of the pair of internal electrode layers 13 adjacent to each other across the ceramic dielectric layer 12 along the thickness direction T is paired inside the multilayer ceramic capacitor 10. It is electrically connected to the other of the external electrodes 14. Thus, a plurality of capacitor elements are electrically connected in parallel between the pair of external electrodes 14.

  FIG. 2 is a flowchart showing a method for observing a ceramic dielectric according to an embodiment of the present invention, and FIGS. 3A and 3B show the preparation of the observation target surface of the ceramic dielectric shown in FIG. It is a schematic diagram which shows a step in steps. Hereinafter, a method for observing a ceramic dielectric in the present embodiment will be described with reference to FIGS.

  As shown in FIG. 2, in the ceramic dielectric observation method according to the present embodiment, after an observation target surface of the ceramic dielectric is prepared in step ST1, a scanning electron microscope (SEM) is used in step ST2. The surface to be observed of the ceramic dielectric is observed.

  In step ST1 of preparing the observation target surface of the ceramic dielectric, first, the sample is sealed with a sealing resin (step ST11), and then the sample is polished (step ST12).

  Samples include not only general multilayer ceramic capacitors as described above, but also various objects (particularly electronic components) having a ceramic dielectric containing an additive. In the following description, a case where a general multilayer ceramic capacitor as described above is used as a sample will be described.

  As shown in FIG. 3A, in step ST11 in which the sample is sealed with the sealing resin, the multilayer ceramic capacitor 10 is sealed resin so that the multilayer ceramic capacitor 10 as the sample is embedded therein. 100 is sealed. The material and shape of the sealing resin 100 are not particularly limited.

  As shown in FIG. 3B, in step ST12 in which the sample is polished, the multilayer ceramic capacitor 10 as the sample is polished together with the sealing resin 100. The polishing is performed until the cross section of the multilayer ceramic capacitor 10 to be observed is exposed as the observation target surface S. Various types of polishing apparatuses can be used for polishing, but it is preferable to reduce the surface roughness of the polishing surface to be the observation target surface S by decreasing the size of the abrasive grains in order. Here, the surface roughness of the observation target surface S after polishing preferably has an arithmetic average roughness Ra of 100 [μm] or less, and more preferably 50 [μm] or less.

  As described above, a work in a state where the observation target surface S of the multilayer ceramic capacitor 10 as a sample is exposed is obtained, whereby the preparation of the ceramic dielectric observation target surface (ST1) is completed.

  Referring to FIG. 2, in step ST2 in which the observation target surface of the ceramic dielectric is observed using SEM, the work prepared through step ST1 described above is set on the SEM stage.

  Next, an electron beam as primary electrons is irradiated from the electron gun provided in the SEM toward the observation target surface S of the workpiece. Accordingly, secondary electrons are emitted from the observation surface S, and the secondary electrons are detected using a detector provided in the SEM. Here, the acceleration voltage of the electron beam to be irradiated is preferably 200 [V] or more and 700 [V] or less.

  Thereby, in the SEM, a charged image in which the surface distribution of the electrical resistance on the observation target surface S is visualized can be obtained, and the solid solution state and the dispersed state of the additive can be confirmed by observing the charged image. become. Here, in the obtained charged image, the surface distribution of electric resistance is expressed by the difference in contrast, and the portion of the observation target surface S where the electric resistance of the surface is high appears in a darker color, A portion of the observation target surface S where the surface electrical resistance is low appears in a lighter color. Therefore, the portion containing the additive is expressed in a darker color, and based on this, the solid solution state and the dispersed state of the additive can be grasped.

  In the ceramic dielectric observation method according to the present embodiment described above, the sample is not required to be thinned when observing as described above. Therefore, the ceramic dielectric observation method according to the present embodiment is employed. By doing so, the solid solution state and the dispersion state of the additive can be observed much more easily than the conventional observation method using TEM.

  Here, in step ST2 of observing the observation surface of the ceramic dielectric using the SEM described above, in order to visualize the surface distribution of the electrical resistance on the observation surface S as a charged image, primary conditions are set as SEM. It is necessary to set the penetration length of the electron beam as an electron into the observation target surface S to be 10 [nm] or less. The following is a discussion of the reason.

  FIG. 4A and FIG. 4B are diagrams showing a difference in behavior of primary electrons on the sample surface and a difference in observation area based on the difference in acceleration voltage when SEM is used.

  As shown in FIG. 4A, the penetration length of the primary electrons irradiated on the observation target surface S depends on the acceleration voltage of the primary electrons, and the penetration length becomes shorter as the acceleration voltage becomes smaller. That is, referring to the figure, according to the analysis result by simulation, when the acceleration voltage is 5 [kV], the penetration length of the primary electrons is 450 [nm] or more, whereas the acceleration voltage is In the case of 1 [kV], the penetration length of the primary electrons is suppressed to about 50 [nm].

  Therefore, as shown in FIG. 4B, when the acceleration voltage is 5 [kV], as secondary electrons emitted from the observation target surface S due to primary electrons irradiated to a certain point, Secondary electrons generated in a very wide range such as the region R1 shown in the figure can be included. On the other hand, when the acceleration voltage is 1 [kV], the primary electrons irradiated to a certain point are As a result, secondary electrons emitted from the observation target surface S can include only secondary electrons generated in a very narrow range such as a region R2 shown in the drawing.

  Therefore, by suppressing the acceleration voltage of the irradiated electron beam sufficiently low, it becomes possible to acquire information only on the surface layer portion of the observation target surface S (that is, the magnitude of the electrical resistance of the sample surface), thereby It is presumed that the solid solution state and the dispersion state of the additive can be grasped by employing the ceramic dielectric observation method in the present embodiment described above.

  Here, when the acceleration voltage of the electron beam to be irradiated is actually changed, the solid solution state and the dispersion state of the additive are grasped within the acceleration voltage range of 200 [V] to 700 [V]. It has been confirmed by the present inventors that a charged image that can be satisfactorily performed is obtained (see verification tests 1 and 2 described later), and the penetration length of an electron beam as a primary electron in that case is 10 [nm]. The following are also confirmed by simulation. Note that the setting conditions of the SEM in which the penetration length of the electron beam is 10 [nm] or less are those of the electron beam in the setting condition of about 1 [kV] to about 5 [kV] set in normal object observation using the SEM. It is much smaller than the penetration depth, and can be said to be a unique setting condition in that sense.

<Verification test 1>
In the verification test 1, the method for observing a ceramic dielectric in the embodiment of the present invention described above is employed, the ceramic dielectric layer actually provided in the multilayer ceramic capacitor is observed, and the observation based on the observation is performed. It was verified whether the results were valid.

Here, as a sample, a multilayer ceramic provided with a ceramic dielectric having a material composition in which a rare earth element (Dy, Gd, Y, La, Ho) as an additive is solid-dissolved in a ceramic powder mainly composed of BaTiO _3. A capacitor was used. The size of the multilayer ceramic capacitor is 1.6 [mm] in the length direction L and 0.8 [mm] in the width direction W and the thickness direction T, respectively. Is 10 [μF]. The thickness of each ceramic dielectric layer sandwiched between the pair of internal electrode layers in the thickness direction T is 1.1 [μm] as a design value, and the number of stacked layers is 350 layers. The internal electrode layer is made of Ni, and its thickness is 1.0 [μm] as a design value.

  First, the multilayer ceramic capacitor was sealed with a sealing resin and then polished. In the polishing process, polishing was performed until the LT section at the center position in the width direction W of the multilayer ceramic capacitor was exposed. Here, the polishing process was performed in stages.

  In the first rough polishing, wet polishing was performed while supplying water at room temperature to the polishing surface using # 200, # 500, and # 1000 polishing boards. Note that # 200, # 500, and # 1000 indicate the granularity of JIS R 6010, respectively.

  In the final finish polishing performed after the rough polishing, diamond abrasive grains were dispersed as a polishing agent on a polishing board made of urethane sponge, and polishing was performed using this. As diamond abrasive grains, those having a particle diameter of 3 [μm] were initially used, and those having a particle diameter of 1 [μm] were used in the final finishing. Here, diamond abrasive grains are used for finishing, but colloidal silica may be used.

  After the above polishing process was completed, the surface roughness of the exposed observation target surface of the multilayer ceramic capacitor was measured with an atomic force microscope (AFM), and the arithmetic average roughness Ra was 10 [nm. It was confirmed that

  Next, the workpiece after the above polishing process is completed is set on the SEM stage, and the central portion of the exposed LT cross section of the multilayer ceramic capacitor as the observation target surface (the portion represented by CP in FIG. 1). Observation was carried out by irradiating with an electron beam. At that time, the acceleration voltage of the irradiated electron beam was set to a range of 100 [V] to 1.5 [kV].

  In the state where the acceleration voltage was 100 [V], a contrast image appeared, but a clear contrast image was not obtained. However, in the process of increasing the acceleration voltage, a clear contrast image is obtained when it reaches 200 [V], and this clear contrast image is always obtained until the acceleration voltage is raised to 700 [V]. It was. When the acceleration voltage exceeded 700 [V], the contrast image that was gradually clear changed to an unclear one, and eventually the image itself disappeared.

  Here, FIG. 5A is a contrast image obtained by the ceramic dielectric observation method according to the comparative example, and FIG. 5B is obtained by the ceramic dielectric observation method according to the example. It is a contrast image. The contrast image obtained by the ceramic dielectric observation method according to the comparative example shown in FIG. 5A was obtained when the acceleration voltage was set to 5 [kV] in this verification test. The contrast image obtained by the ceramic dielectric observation method according to the example shown in (B) was obtained when the acceleration voltage was set to 300 [V] in this verification test.

  From the comparison between FIG. 5A and FIG. 5B, the contrast image obtained by the ceramic dielectric observation method according to the example can clearly distinguish the ceramic grain boundaries included in the ceramic dielectric layer. It can be understood that. In addition, in the contrast image obtained by the method for observing a ceramic dielectric according to the example, it can be understood that clear contrast (that is, color shading) appears in the ceramic dielectric layer.

  Subsequently, by removing the workpiece from the SEM, further thinning it and analyzing it by TEM, the contrast image obtained by the method for observing a ceramic dielectric according to the above example is in a solid solution state of the additive. And whether it was caused by the dispersion state.

  FIG. 5C is an element mapping image of rare earth elements obtained by TEM. In the element mapping image, the portion where the rare earth element as an additive is present is shown in white, and the portion where the rare earth element is not present is shown in black. It is an image. Note that the observation target position and scale of the image shown in FIG. 5C and the observation target position and scale of the contrast image shown in FIG.

  From the comparison of FIG. 5B and FIG. 5C, the dark portion of the contrast image obtained by the ceramic dielectric observation method according to the example and the white portion of the element mapping image. And the light-colored portion of the contrast image obtained by the ceramic dielectric observation method according to the example and the black portion of the element mapping image are almost identical. I can understand what I do.

  Therefore, from the results, it was confirmed that the contrast image obtained by the ceramic dielectric observation method according to the example was caused by the solid solution state or the dispersion state of the additive. Therefore, it was confirmed that the solid solution state and the dispersion state of the additive can be easily observed by using the ceramic dielectric observation method in the above-described embodiment.

<Verification test 2>
In the verification test 2, as a condition for obtaining a clearer contrast image, verification was performed as to how the surface roughness of the observation target surface affects. In the present verification test, three multilayer ceramic capacitors having the same specifications as the multilayer ceramic capacitor used in the verification test 1 described above are prepared, and the surface roughness of the observation target surface is different by changing the polishing conditions. Three works were prepared.

  The workpiece according to Verification Example 1 was polished under the same polishing conditions as in Verification Test 1 described above. When the surface roughness of the observation target surface of the workpiece according to the verification example 1 was measured by AFM, the arithmetic average roughness Ra was 10 [nm].

  In the workpiece according to the verification example 2, among the polishing conditions described in the verification test 1 described above, the final polishing is performed using diamond abrasive grains having a particle size of 3 [μm], and diamond having a particle size of 1 [μm]. Implementation of finish polishing using abrasive grains was omitted. When the surface roughness of the observation target surface of the workpiece according to the verification example 2 was measured with an AFM, the arithmetic average roughness Ra was 50 [nm].

  In the workpiece according to the verification example 3, only the rough polishing was performed among the polishing conditions described in the verification test 1 described above, and the finish polishing using diamond abrasive grains was omitted. When the surface roughness of the observation target surface of the workpiece according to the verification example 3 was measured with an AFM, the arithmetic average roughness Ra was 100 [nm].

  In this verification test, the workpieces according to these verification examples 1 to 3 were set on the SEM stage, respectively, and the central portion of the exposed LT section of the multilayer ceramic capacitor as the observation target surface (represented by CP in FIG. 1). The portion was irradiated with an electron beam and observed. At that time, the acceleration voltage of the irradiated electron beam was set to a range of 100 [V] to 1000 [V].

  FIG. 6 is a table showing the results of this verification test. In the table shown in FIG. 6, a condition where a sufficiently clear contrast image is obtained is denoted as “good”, a condition where a somewhat clear contrast image is obtained is denoted as “good”, and a clear contrast image is obtained. Conditions that were not obtained are indicated as “impossible”.

  As shown in FIG. 6, in the verification examples 1 and 2, a sufficiently clear contrast image is obtained when the acceleration voltage of the electron beam to be irradiated is in the range of 200 [V] to 700 [V]. In contrast, a somewhat clear contrast image was obtained when the accelerating voltage of the irradiated electron beam was in the range of 200 [V] to 700 [V].

  From the above results, in order to obtain a clear contrast image (that is, a charged image), the surface roughness of the observation target surface is preferably smaller, and the surface roughness is 50 [nm] or less in terms of arithmetic average roughness Ra. In this case, it was confirmed that a particularly good charged image was obtained. Therefore, when observing the solid solution state or dispersed state of the additive using the ceramic dielectric observation method in the above-described embodiment, a more precise polishing process of the surface to be observed can be performed prior to the observation. It can be said that it is preferable.

  In the embodiment of the present invention described above, the case where the present invention is applied to the observation of the ceramic dielectric layer including the additive provided in the multilayer ceramic capacitor has been described as an example. The method for observing a ceramic dielectric can be applied to the observation of any object provided that it has a ceramic dielectric containing an additive.

  Thus, the above-described embodiment disclosed herein is illustrative in all respects and is not restrictive. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  10 multilayer ceramic capacitor, 11 element body, 12 ceramic dielectric layer, 13 internal electrode layer, 14 external electrode, 100 sealing resin, S surface to be observed.

Claims (3)

A method for observing a ceramic dielectric for observing a solid solution state or a dispersion state of an additive dissolved in the ceramic dielectric,
Exposing an observation target surface of the ceramic dielectric;
A charged image obtained by visualizing the surface distribution of electrical resistance on the observation target surface by irradiating the observation target surface with an electron beam using a scanning electron microscope under the condition that the penetration depth is 10 nm or less. And a step of observing the surface to be observed.   The method for observing a ceramic dielectric according to claim 1, wherein an acceleration voltage when irradiating the surface to be observed with the electron beam is 200 [V] or more and 700 [V] or less.   The method for observing a ceramic dielectric according to claim 1 or 2, wherein an arithmetic average roughness Ra of the surface to be observed is 50 [nm] or less.