JP2907117B2 - Structure observation method of insulating polycrystalline sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for observing the structure of an insulated polycrystalline sintered body, especially a sintered ceramic body of silicon nitride.

[0002]

2. Description of the Related Art A ceramic sintered body of silicon nitride is used for various structural materials such as automobile parts. The silicon nitride sintered body is composed of μm-level grains of silicon nitride constituting the same and a glass phase such as yttrium oxide added as a sintering aid called a grain boundary. The grain size, grain size distribution, and ratio of grain boundaries are referred to as a structure of silicon nitride. This structure is known to affect properties such as mechanical strength, wear resistance, and high-temperature strength that are important as structural materials. Controlling this organization is very important for production.

In order to observe such a fine structure, it is usually necessary to use a scanning electron microscope. The scanning electron microscope irradiates a sample with a finely focused electron beam and obtains an image with a contrast based on the amount of secondary electrons emitted from the observation sample. The amount of secondary electron emission depends on the constituent elements of the sample and its three-dimensional structure. Therefore, in order to clearly and accurately observe the structure of the silicon nitride sintered body at the μm level, as shown in FIG. 1, after the observation sample is polished smoothly, grains or grain boundaries are removed. As shown in 2,
It is an important technology to make unevenness (step).

As the method, there are a method of chemically etching with an acid (for example, hydrofluoric acid), a method of etching by irradiating with an ion beam, and a method of etching with reactive ions. Without any of these methods, the structure of the silicon nitride sintered body cannot be observed. In addition, since silicon nitride ceramics are insulators, they cannot be observed in a scanning electron microscope in which observation is performed by irradiating an electron beam, which is a charged particle, unless a process for imparting conductivity to the sample is performed. As the method, a conductive element such as gold, platinum, palladium, or carbon is thinly coated on the surface of an observation sample by a sputtering method or an evaporation method to change a fine structure.

[0005] It is known that silicon nitride ceramics change from α-type to β-type during the sintering process, which is a manufacturing process thereof. Controlling the proportion of this crystal form is also one of the factors that affect the properties such as the mechanical strength of silicon nitride ceramics in addition to the above structure. Therefore, X-ray diffraction has been used as a method for evaluating this.

[0006]

In order to develop a high mechanical strength, etc., which is a characteristic of a silicon nitride ceramics sintered body, control of the structure is important, and its evaluation method is also important. When observing the structure of a silicon nitride ceramics sintered body with a scanning electron microscope, a process for imparting conductivity is indispensable because the sample is an insulator. This treatment involves thinly coating the surface of the sample with gold or the like, but this treatment makes it difficult to observe the microstructure, as one of the factors that contributes to contrast in a scanning electron micrograph cannot be understood. It is very important to give a three-dimensional structure to. In the grain boundary etching method using an acid, which is a conventional method, it is necessary to change the type, concentration, and processing time of the acid depending on the composition of the grain boundary.

When the grain boundaries to be etched are small, the outline of the grains cannot be clearly grasped. In the method using an ion beam, since the silicon nitride ceramics are insulators, electric charges accumulate on the irradiated sample surface, and there has been a problem that etching cannot be efficiently performed due to repulsion by the electric charges. There is also a problem that the selectivity of etching between grains and grain boundaries is insufficient. If the grains and grain boundaries are simultaneously etched without selectivity, a three-dimensional structure cannot be produced, and the structure cannot be clearly observed with a scanning electron microscope. Although particles are etched by reactive ion etching, a reaction product may be formed with silicon nitride, which may be inconvenient for observation.

[0008] In the evaluation of the crystal form, which is another factor producing the characteristics of the silicon nitride ceramics sintered body, the evaluation method by X-ray diffraction has been used without any problem for the evaluation of a wide range on the millimeter level. However, if the sample or product to be evaluated was small, the distribution of the crystal form could not be evaluated. It was stated that the structure and crystal form are important factors for the characteristics of the silicon nitride ceramic sintered body.However, the structure was evaluated using a scanning electron microscope on a nanometer-level micro area, and the crystal form was evaluated using millimeters. In such a situation, evaluation must be performed by a separate method of performing a wide range of regions by X-ray diffraction, and there is a problem that the evaluation requires time and effort. Further, there is a problem that the same sample or the same portion of the sample is not accurately evaluated. In other words, the setting itself at the same place when observing would force a very laborious operation. The present invention provides a method by which a clear structure of a silicon nitride ceramic sintered body can be observed, and furthermore, an evaluation method corresponding to a crystal microscopic region, which is another factor that produces characteristics of the silicon nitride ceramic sintered body. Is to give. Another object of the present invention is to provide an analysis / evaluation method capable of simultaneously obtaining two pieces of information on the structure and crystal form of a sample by one method using a scanning electron microscope.

[0009]

After the surface of the insulated polycrystalline sintered body on which the mask is placed is subjected to a process for imparting conductivity, the mask is removed and the portion not subjected to the conductivity process is scanned. In the method of observing the structure of the insulating polycrystalline sintered body under a microscope, the surface of the insulating polycrystalline sintered body on which a mask is to be placed is irradiated with a neutral molecular beam on the surface of the insulating polycrystalline sintered body that has been polished in advance. The grain boundaries are removed with an acid, or the surface of the insulated polycrystalline sintered body that has been polished in advance is etched at the grain boundaries with an acid and then irradiated with a neutral molecular beam at an angle of 45 ° to 90 ° with the surface. Is what you do.

[0010] The treatment for imparting conductivity is to coat the conductive layer by ion sputtering or vapor deposition. The insulating polycrystalline sintered body is a silicon nitride sintered body,
The size of the mask is not more than 0.25 mm ^{2 and not} less than 0.01 mm ² . The acid is a mixed solution of hydrochloric acid and aqueous hydrogen peroxide, and the observation of the structure of the insulated polycrystalline sintered body is performed by calculating the area ratio by controlling the density in the image of the electron scanning microscope in binary. It is.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to clearly observe the structure of a silicon nitride ceramic sintered body with a scanning electron microscope, it is necessary to efficiently form a three-dimensional structure. As means for this purpose, the grain boundaries of the sintered body are removed by using an acid, or the grain boundaries of the sintered body are selectively etched using a neutral molecular beam having no charge. When this neutral molecular beam is used, the angle between the beam and the sample surface is set to 45 ° or more and 90 ° or less. Further, if the grain boundaries composed of oxides are etched in advance with an acid before the use of the neutral molecular beam, the effect is dramatically increased. Surprisingly, by using a combination of hydrochloric acid and aqueous hydrogen peroxide as the acid, etching is efficiently performed regardless of the composition of the grain boundary.

When observing the structure of the silicon nitride ceramics sintered body with a scanning electron microscope, since the object to be observed is an insulator, a treatment for imparting conductivity is performed. no longer can Do observe, in order to be a mask is small and difficult to handle, is practically gold sample from the place the mask is 0.25 mm ² or less 0.01 mm ² or more, platinum, platinum palladium,
A treatment for imparting conductivity by coating a conductive layer such as silver or aluminum is applied. By removing the mask and observing the part that has not been subjected to the conductive treatment, a fine contrast depending on the type of crystal appears in the grains. Thereby, the crystal form can be evaluated even in a nanometer-level minute region that can be observed with a scanning electron microscope. According to the present invention, as described above, both the structure and the crystal form that determine the characteristics of a silicon nitride ceramics sintered body can be simultaneously evaluated from exactly the same sample by one analysis method.

[0013]

EXAMPLE In the present invention, a neutral molecular beam having no charge was used in order to efficiently etch a silicon nitride ceramic sintered body which is an insulator. As this molecular species, a rare gas atom such as argon or krypton, or an inert gas such as nitrogen is desirable. Conventional etching by reactive ions had a problem of reacting with silicon nitride, but as will be understood from this, even neutral molecule beams react with active molecular species such as halogens. As a result, the tissue could not be given a sharp outline. Although the incident energy was examined at 1 to 10 keV, the effect was observed at any of the energies. Further, the processing time was also examined, but it was found that the optimal time was between 10 minutes and 30 minutes. Even more surprisingly, it has been found that when the incident angle of the neutral molecular beam with respect to the sample surface of the sintered body is reduced, the grains themselves are etched, and when the angle is increased, the grain boundaries are etched. Although it was pointed out that it was difficult to selectively etch grains and grain boundaries by ion beam etching, the incidence angle of neutral molecular beams varied from 45 ° to 90 °, especially from the sample surface. This allows selective etching.

It has been found that an effect is further enhanced if an acid treatment is performed before the treatment with the neutral molecular beam. As a result of studying the kind of the acid, the combination of hydrochloric acid and hydrogen peroxide solution was most effective, and the grain boundary could be efficiently etched even when the composition of the grain boundary was different.
The concentration is 1 to 5 mol / l for hydrochloric acid and 0.1 to 1 for hydrogen peroxide solution.
It was confirmed that the range of mol / l was good, and that the treatment time could be shortened by heating to 50 to 80 ° C without boiling.

At the time of observation with a scanning electron microscope, a mask formed of a 400 μm-thick silicon wafer chip cut into a 0.5 mm square (cross section: 0.25 mm ² ) was etched by etching with an acid and a neutral molecular beam. Gold was applied on the surface of the silicon ceramic sintered body by about 30 nm by ion sputtering. Then, the chip is removed with, for example, tweezers or the back of the sample is patted lightly, so that the mask falls off very easily, exposing the portion not coated with gold, and the surface is clearly observed with a scanning electron microscope. A fine tissue could be observed. In the silicon nitride ceramics sintered body structure observed by this method, grains having a slightly gray contrast inside were observed. The area ratio is obtained by binarizing and controlling the ratio of the area of the grain having the gray contrast to the entire area of the scanning electron micrograph to be spherical, which is a feature of the α-type crystal form. When,
It was found that there was a proportional relationship with the ratio of the α-type crystal form by the conventional X-ray diffraction method, and it was found that the silicon nitride grains of the α-type crystal were observed as shown in FIG. As a result, it was found that the crystal form can be evaluated with the resolution of the scanning electron microscope.

When the gray-grayed grains were observed with an atomic force microscope, a similar pattern was observed. When the step was measured, it was found that the recess had a nanometer-level step. This is presumed to be due to the fact that the etching rate by the neutral molecular beam differs due to the difference between the α-type and β-type crystals. This effect was discovered by observing the region not coated by the conductive treatment using a mask with a scanning electron microscope. In fact, when the gold coating was applied to the sample where the gray contrasted grains were observed, the gray contrast was no longer observable. This is because the steric effect, which is one of the causes of generating the contrast of the scanning electron microscope image, disappears due to the coating of gold or platinum, which has a high probability of secondary electron emission, and the contrast disappears.

[0017]

[Table 1]

In Examples 1 to 2, 5 and Comparative Examples 2 to 6, the difference in etching was investigated by changing the type and concentration of the acid. After the treatment was performed under the conditions shown in Table 1, the structure was examined with a scanning electron microscope, and whether or not a clear outline could be confirmed in the scanning electron micrograph was evaluated by ／/ ×.
As a result, depending on the composition and time and temperature in Table 1,
With phosphoric acid, hydrochloric acid and aqueous hydrogen peroxide, grain boundaries were etched and the structure could be observed, but with other methods the etching of the grain boundaries was insufficient and satisfactory structure observation was not possible. Etching cannot be performed unless the acid concentration is also higher than 1 mol / l. In the case of hydrochloric acid + hydrogen peroxide solution, it was confirmed that etching was performed if the hydrogen peroxide solution was 0.1 mol / l or more.

In Examples 3 and 4, and Comparative Examples 7 to 10, the difference in etching depending on the irradiation condition of the neutral molecular beam was investigated. As a result, the energy is 1 to 10 keV and the time is 10
~ 30 minutes is optimal. Conversely, when the irradiation time was long, it was found that the damage of the whole sample was large and the outline of the grains was unclear, and it was difficult to observe the structure. Comparison between Example 5 and Comparative Example 6 reveals that even when the acid etching is insufficient, the structure can be observed by irradiation with a neutral molecular beam. further,
By comparing Examples 3 and 10, it was found that when both the conditions of the acid etching and the irradiation of the neutral molecular beam were optimized, the structure could be more clearly observed.

FIGS. 4 to 8 are photographs of a sample which was etched under the conditions of Example 7 and which was observed with a scanning electron microscope without applying a conductive coat. The crystal structure was clearly observed. . In addition, although these five photographs have different α crystal abundance ratios, the ratio of grains having a light and deep contrast is increasing in connection with this. This relationship is shown in FIG. FIG. 3 is a graph in which the abscissa is used to measure the abundance ratio of α-crystals at three arbitrary points in the sample measured by X-ray analysis using the structure observation method of the present invention, and the average is obtained. As a result, it is recognized that the α ratio (existence ratio) can be evaluated by observing the tissue.

[0021]

[Table 2]

In this neutral molecular beam irradiation, the effect of changing the incident angle was investigated. When the irradiation with the surface was made at a shallow angle of about 30 °, the particles were etched,
It is understood that when the angle is 45 ° or more and 90 ° or less, the grain boundary is etched.

[0023]

According to the present invention, the structure of a silicon nitride ceramic sintered body can be observed with good reproducibility up to the nanometer level. Thereby, the correlation between the tissue and the structure can be examined. In addition, it provides a means for evaluating microscopic regions in the crystal form, which is another important factor. In addition, since two properties of a material can be evaluated by a single observation with a scanning electron microscope, it means that the evaluation time can be reduced and two pieces of information can be obtained from the same place of the same material. This means that, even in a silicon nitride ceramic sintered body having a complicated shape, the structure can be observed for each part, the crystal form can be evaluated, and the strength for each part can be predicted. The structure and crystal form of a silicon nitride ceramic sintered body are greatly affected by the sintering temperature and time during production. However, according to the present invention, the process can be indirectly evaluated, and a stable production environment and its accompanying This has the effect of improving the yield.

According to the present invention, since a conductive film is formed by ion sputtering or vapor deposition with a mask placed on the surface, the surface of the sintered body can be tapped with tweezers or the like, and can be knocked down from behind the sintered body. The exposed surface can be easily formed, and the size of the mask is 0.25 mm ² or less and 0.01 mm ² or more, which is easy to handle. It can be easily imaged. Further, the surface to be observed by a scanning electron microscope can be easily formed by using a neutral molecular beam alone or in combination with an acid. Furthermore, since the insulating polycrystalline sintered body is a silicon nitride sintered body, the characteristics and strength of the silicon nitride sintered body can be evaluated. In addition, the observation surface can be easily formed by etching the grain boundary with the mixed solution of hydrochloric acid and hydrogen peroxide solution on the exposed surface which becomes the observation symmetry. Further, since the structure of the insulating polycrystalline sintered body is observed by calculating the area ratio by controlling the density of the image of the electron scanning microscope in a binary manner, the α structure can be grasped numerically.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a silicon nitride ceramic sintered body before etching a grain boundary.

FIG. 2 is a schematic cross-sectional view of a silicon nitride ceramic sintered body after removing a grain boundary by etching.

FIG. 3 shows an area ratio of a dark contrast portion in an SEM photograph and a ratio of an α-type crystal by an X-ray diffraction method.

FIG. 4 is a photomicrograph of a metallographic structure instead of a drawing showing the metallographic structure of the silicon nitride ceramic sintered body when the α ratio is 0%.

FIG. 5 is a photomicrograph of a metallographic structure instead of a drawing showing the metallographic structure of the silicon nitride ceramic sintered body when the α ratio is 7%.

FIG. 6 is a photomicrograph of a metallographic structure instead of a drawing showing the metallographic structure of the silicon nitride ceramic sintered body when the α ratio is 22%.

FIG. 7 is a photomicrograph of a metallographic structure instead of a drawing showing the metallographic structure of the silicon nitride ceramic sintered body when the α ratio is 33%.

FIG. 8 is a photomicrograph of a metallographic structure instead of a drawing showing the metallographic structure of the silicon nitride ceramics sintered body when the α ratio is 43%.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Takehisa Yamamoto 1-1-1, Koyo-Kita-Kita, Itami-shi, Hyogo Prefecture Itami Works, Sumitomo Electric Industries, Ltd. Chome 1-1, Itami Works, Sumitomo Electric Industries, Ltd. (56) References JP-A-5-45265 (JP, A) JP-A-1-221637 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 1/28 G01N 1/32

Claims (9)

(57) [Claims] 1. A process for imparting conductivity to the surface of an insulating polycrystalline sintered body on which a mask is placed, and then removing the mask and observing a portion that has not been subjected to the conductivity treatment with a scanning electron microscope. A method for observing the structure of an insulating polycrystalline sintered body, characterized by comprising the following: 2. The surface of the insulating polycrystalline sintered body on which the mask is to be placed is subjected to a neutral molecular beam irradiation treatment for removing grain boundaries on the surface of the insulating polycrystalline sintered body which has been polished in advance, or the surface of the grain is treated with an acid. The method for observing the structure of an insulated polycrystalline sintered body according to claim 1, wherein the structure is removed. 3. The surface of the insulating polycrystalline sintered body on which the mask is to be placed is subjected to a neutral molecular beam irradiation treatment after the surface of the insulating polycrystalline sintered body which has been polished and finished in advance is etched with an acid. The method for observing the structure of an insulated polycrystalline sintered body according to claim 1, wherein the structure is removed. 4. The insulating polycrystalline sintered body according to claim 2, wherein the irradiation with the neutral molecular beam is performed at an angle of 90 ° or less and 45 ° or more with the surface of the insulating polycrystalline sintered body. Tissue observation method. 5. The method for observing the structure of an insulated polycrystalline sintered body according to claim 1, wherein the treatment for imparting conductivity comprises coating the conductive layer by ion sputtering or vapor deposition. . 6. The method for observing the structure of an insulating polycrystalline sintered body according to claim 1, wherein the insulating polycrystalline sintered body is a silicon nitride sintered body. 7. The method for observing the structure of an insulating polycrystalline sintered body according to claim 1, wherein the size of the mask is not more than 0.25 mm ^{2 and not} less than 0.01 mm ² . 8. The method for observing the structure of an insulating polycrystalline sintered body according to claim 3, wherein the acid is a mixed solution of hydrochloric acid and aqueous hydrogen peroxide. 9. The observation of the structure of the insulating polycrystalline sintered body is performed by calculating the area ratio by binarizing and controlling the shading in the image of the electron scanning microscope. 2. The method for observing the structure of an insulating polycrystalline sintered body according to item 1.