JP2005001975A - Ceramic base and its producing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic base such as an AlN sintered base having extremely small surface roughness and little defects, and its efficient producing method. <P>SOLUTION: The ceramic base has a structure joining a plurality of crystalline phases having a crystallite diameter of 1-50 μm and being composed of same kinds of inorganic substances each other via a grain boundary phase composed of different kinds of inorganic substances. The arithmetic surface roughness Ra of at least a face of the ceramic base is 0.04 μm or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a metallized ceramic suitable for a heat-dissipating circuit board and the like, a ceramic substrate serving as a raw material substrate thereof, and a manufacturing method thereof.

  A ceramic body mainly composed of aluminum nitride (AlN) has excellent characteristics in terms of not only thermal conductivity but also insulation, dielectric characteristics, and thermal expansion characteristics. As it is rapidly spreading. Such a heat radiating substrate is usually manufactured by the following method.

  That is, after a green sheet containing AlN powder and a sintering aid is first formed into a plate shape, degreased and fired to obtain a sintered substrate, and then the surface of the sintered substrate is ground or polished to a certain surface. On the finished surface, the first thin film layer such as Ti, Cr, Ni—Cr, TaN, Al, Mo, W, Zr, the second thin film layer such as Ni, Pt, Co, Cu, etc. , Au, Ag, Pd and the like are manufactured by forming a third thin film layer in this order. The reason why the metal layer has the three-layer structure as described above is that the adhesion of the metal used in the third thin film layer serving as the conductive layer to the aluminum nitride is low, so that the first thin film is used as the adhesive layer. This is because a layer needs to be formed (see Patent Document 1), and a second thin film layer needs to be provided as a barrier layer in order to prevent diffusion of the material between both layers. After the metal thin film layer is formed on the surface in this way, a pattern is formed as necessary, and an electronic element (for example, a laser diode) is mounted on the metal thin film layer using a thin film solder or the like.

  By the way, in order to cope with the recent miniaturization and high integration of semiconductor elements, demands for heat dissipation substrates for mounting electronic elements such as semiconductor elements and capacitors have become stricter, and the processing accuracy required in the manufacturing process is also increased. It is high. For example, it is necessary to reduce the surface roughness of the metal layer as much as possible in order to reduce the variation in strength of the joint portion of the electronic element and improve the durability against thermal cycling. In addition, the surface roughness of the metal film formed by the thin film forming method is not only determined by the surface roughness of the AlN sintered substrate as the base, but also the surface roughness of the AlN sintered substrate as the base. When the thickness is large, the adhesion of the metal thin film layer also decreases, so that the surface of the AlN sintered substrate on which the thin film is formed needs to be highly smoothed. For this reason, the grinding or polishing process of the AlN sintered substrate is very important.

  As a method of polishing the surface of an AlN sintered substrate, polishing using free abrasive grains is known. For example, by rotating or moving left and right an end plate containing diamond abrasive grains, the surface of the substrate is polished by Ra. Has a surface roughness of 0.5 μm or less (see Patent Document 2).

Japanese Patent No. 2563809 JP 2002-173361 A

However, when polishing a ceramic sintered substrate such as an AlN sintered substrate using loose abrasive grains, the surface roughness that can be achieved by grinding within an acceptable processing time is usually Ra 0.05 μm or more. Even when further polishing takes place over a long time, a ceramic sintered substrate generally has a structure in which many crystallites are bonded via a grain boundary layer containing sintering aids having different hardnesses. Therefore, the occurrence of surface defects (usually observed as concave portions having a diameter of 1 to 50 μm) due to crystallites falling off during polishing is inevitable (around 10 within a range of 200 μm × 200 μm). Occurred).
Therefore, the present invention provides a substrate having a very small surface roughness and a small number of defects as described above in a ceramic sintered substrate such as an AlN sintered substrate, and a method for efficiently producing such a substrate. For the purpose.

  The present inventors have intensively studied to solve the above problems. As a result, when an electrolytic in-process dressing grinding (ELID grinding) processing method was applied to the polishing of a ceramic sintered substrate, grinding was performed using a conductive grindstone containing abrasive grains having a specific grain size # 2000 or more and # 30000 or less. When it was done, it was found that the intended purpose could be achieved, and the present invention was completed.

That is, the first aspect of the present invention includes a structure in which a plurality of crystal phases having an average crystallite diameter of 1 to 50 μm composed of the same kind of inorganic material are joined via a grain boundary phase composed of different inorganic materials. A ceramic substrate characterized in that an arithmetic surface roughness Ra of at least one surface thereof is 0.04 μm or less, particularly a surface having the arithmetic surface roughness Ra of 0.04 μm or less. The ceramic substrate is characterized in that the average number of defects having a diameter of 0.3 to 50 μm is 1.25 × 10 ⁻⁴ pieces / μm ² or less.

  Since the ceramic substrate of the present invention has a highly smooth surface that cannot be obtained by a conventional polishing method using loose abrasive grains, it adheres to the metal thin film when a metal thin film is formed on the surface. It has the characteristic that it has high property. Further, the Vickers hardness is Hv 1800 to 2200, the friction coefficient with alumina is 0.4 to 0.7, and oxygen is detected as a substance other than the main component up to a depth of 10 μm from the surface. .

  The second aspect of the present invention is a powder composed of a single component and sintered with a sintering aid using a powder composed of inorganic particles containing a crystal phase having an average crystallite diameter of 0.3 to 50 μm. The method for producing a ceramic substrate according to the present invention is characterized in that the sintered ceramic substrate obtained by the above process is processed by electrolytic in-process dressing grinding using a conductive grindstone containing abrasive grains having a grain size of # 2000 to # 30000. .

  According to the production method of the present invention, it is possible to efficiently produce a novel ceramic substrate of the present invention. As shown in the experimental results to be described later, when processing is performed by ELID grinding using a conductive grindstone containing abrasive grains of # 2000 to # 30000, ductility mode grinding occurs, and excellent smoothness as described above. It has become possible to obtain. Note that ELID grinding is a method of grinding a workpiece while concentrating a conductive grindstone with electrolytic dressing, and is known as an efficient mirror grinding method for silicon, quartz, alloys and the like. However, there are not so many examples in which ELID grinding is applied to grinding of ceramic sintered substrates in which layers having greatly different hardness are mixed, and ELID grinding is applied to grinding of ceramic sintered substrates. This is the first time that the properties of the resulting grinding surface have been examined in detail. In general, in a sliding system of a hard material such as ceramic, grinding in a ductile mode is unlikely to occur unless the temperature is extremely high, and it is difficult to obtain such a high temperature only by cutting energy. It has also been confirmed for the first time that ductile mode grinding is possible for ceramic sintered substrates, especially AlN sintered substrates.

According to a third aspect of the present invention, there is provided a metallized ceramic substrate comprising a metal thin film layer bonded to a surface having an arithmetic surface roughness Ra of 0.003 to 0.04 μm. It is. In the metallized ceramic substrate of the present invention, not only the adhesion between the ceramic substrate and the metal thin film layer is very high, eg, 3 Kgmm ⁻² or more, but also the arithmetic surface roughness Ra of the metal thin film layer is 0.1 μm or less, which is very smooth. Therefore, when an electronic device such as a laser diode or a capacitor is mounted, the strength variation of the joint portion of the electronic device is small, and the durability against thermal cycling is high. As a result, the yield when the electronic element is mounted on the surface is also increased to about 70% to 100%.

  The metallized ceramic substrate of the present invention has a high level of surface smoothness that is not found in conventional substrates as a ceramic sintered substrate, and is obtained when a metal thin film layer is formed on the surface of the metallized ceramic substrate. The metal thin film layer surface of the metallized substrate of the invention can be made not only highly smooth, but also can be made extremely high in adhesion strength. Furthermore, the metallized ceramic substrate of the present invention has a high hardness, a low friction coefficient, and oxygen is detected as a substance other than the main component from the surface to a deep position. Further, since the metallized substrate of the present invention has such excellent characteristics, not only the yield when the electronic device is mounted on the surface is high, but also the quality of the obtained device mounting substrate is excellent. Furthermore, according to the manufacturing method of the present invention, it is possible to efficiently manufacture the excellent ceramic substrate of the present invention as described above.

  The ceramic substrate of the present invention comprises a structure in which a plurality of crystal phases having an average crystallite diameter of 1 to 50 μm composed of the same kind of inorganic substance are joined via a grain boundary phase composed of different kinds of inorganic substances. It consists of a ceramic substrate. Such a structure can be easily confirmed by observing the cross section of the ceramic substrate with a scanning electron microscope (SEM).

  In general, a ceramic sintered substrate obtained by sintering a crystalline ceramic powder using a sintering aid has a grain boundary phase in which a plurality of crystallites originate from the sintering aid (generally, this grain boundary layer). Is made of a material obtained by a reaction between a ceramic material and a sintering aid during sintering, is made of a material different from the ceramic constituting the crystallite, and its hardness is greatly different from that of the ceramic constituting the crystallite). It is a well known fact to have a bonded structure. Therefore, the ceramic substrate of the present invention has a surface of a sintered ceramic substrate (raw material ceramic sintered substrate) obtained by sintering a powder composed of single-component crystalline inorganic particles using a sintering aid. It can be said that it was processed so as to have a specific smoothness.

  The raw material ceramic sintered substrate is made of, for example, a ceramic powder composed of single-component crystalline inorganic particles, a slurry containing a sintering aid, an organic binder, a plasticizer and a solvent into a thin sheet by a doctor blade method or the like. It can be suitably obtained by degreasing and sintering the processed product (green sheet), or press molding, degreasing and firing the above raw material powder and the like. The shape of the raw ceramic sintered substrate is not particularly limited, but the thickness is preferably 50 μm to 5 cm, particularly preferably 100 μm to 2 cm from the viewpoint of easy shape processing.

  The above method is not particularly different from the usual method of obtaining a ceramic sintered substrate using a green sheet, and various materials used, the amount used, degreasing conditions, firing conditions, etc. are not particularly different from conventional methods. . For example, the ceramic powder is not particularly limited as long as the particles constituting the powder contain a crystal phase, and those made of a known ceramic material can be used. Examples of ceramic materials that can be suitably used include aluminum nitride, aluminum oxide, silicon nitride, boron nitride, silicon carbide, and silicon dioxide. Among these, when used as a heat dissipation substrate, it is particularly preferable to use aluminum nitride having high thermal conductivity (100 W / mK to 320 W / mK) and high mechanical strength (bending strength to 800 MPa). . In general, the crystallites contained in the raw material powder grow in the firing process during substrate production, and most of them are crystallites having an average crystallite diameter of about 0.3 μm to 50 μm, more specifically about 0.5 to 10 μm. Become. Thus, the average crystallite diameter of 0.3 to 50 μm is not special as the size of the crystallite contained in the crystalline ceramic sintered substrate, and is a commercially available ceramic sintered substrate. Many contain crystallites of this size. For example, about 70% to 98% of the crystallite size measured by measuring the particle size distribution in all crystallites contained in a commercially available representative aluminum nitride sintered substrate (for example, SH-15 manufactured by Tokuyama Corporation). The range is 0.5 to 10 μm.

  Moreover, as a sintering aid, what is known to be usable as a sintering aid depending on the material of the ceramic powder can be used without any limitation. For example, when aluminum nitride powder is used as the ceramic powder (in the case of an AlN sintered substrate), calcium oxide, calcium aluminate, tricalcium phosphate, yttrium oxide, lanthanum oxide, cerium oxide, or the like is used. These sintering aids can be used alone or in a mixture of different kinds. The amount of these sintering aids is within the range normally used depending on the material of the ceramic powder. For example, in the case of an AlN sintered substrate, 0.1 to 10 parts by weight with respect to 100 parts by weight of the aluminum nitride powder. 1-7 parts by weight are preferably used.

  Although the ceramic substrate of the present invention has the above-described structure, it has a feature that the arithmetic surface roughness Ra of at least one surface thereof is 0.04 μm or less. Such surface roughness cannot be obtained when a ceramic sintered substrate is ground by a conventional grinding method using loose abrasive grains. By having such excellent surface smoothness, when a metal thin film is formed on the surface, not only the adhesion to the metal thin film can be made high, but also the arithmetic operation of the formed metal thin film The surface roughness itself can be reduced. From the viewpoint of such effects, the arithmetic surface roughness of at least one surface of the ceramic substrate of the present invention is preferably 0.003 to 0.04 μm, particularly 0.005 to 0.01 μm.

  Here, the arithmetic surface roughness is an average roughness that is calculated arithmetically of the unevenness of the sample surface, and is a value determined by measurement using a contact-type or non-contact-type surface roughness measuring device. .

In addition, the ceramic substrate of the present invention is a more preferable embodiment from the viewpoint of the above-described effects. An average number of 1.25 × 10 ⁻⁴ pieces / μm ² or less (corresponding to 5 pieces in the range of 200 μm × 200 μm), preferably 0.5 × 10 ⁻⁴ pieces / μm ² or less Contains. In general, a sintered ceramic substrate has a structural feature in which a crystallite phase and a grain boundary layer having different hardnesses are mixed, and therefore, a grinding surface obtained in grinding is likely to become a brittle mode removal surface in which grain boundary fracture is the mainstream. Therefore, on the ground surface obtained by the conventional grinding method, the average number of defects having a maximum diameter of 0.3 to 50 μm caused by crystallite dropping is 2.5 × 10 ⁻⁴ / μm ² (200 μm × 200 μm). In the range of 10). In contrast, the number of defects in the ceramic substrate of the present invention is less than half.

  Here, the number (average) of defects having an aperture of 0.3 to 50 μm is, for example, observed with a metallographic microscope at five arbitrary fields of view on the ground surface, and an aperture of 0.3 to 50 μm included in the range of 200 × 200 μm. The number of defects can be counted and the average value can be obtained. Usually, the observed defect is not a perfect circle but a polygon. In such a case, the length in the major axis direction is the defect aperture.

  The method for producing the ceramic substrate of the present invention is not particularly limited, but the raw ceramic sintered substrate is processed by electrolytic in-process dressing grinding (ELID grinding) using a conductive grindstone containing abrasive grains having a grain size of # 2000 to # 30000. It can manufacture suitably. Even when the ELID grinding method is applied, when a conductive grindstone containing abrasive grains of # 325 to # 1200 is used, grain boundary fracture becomes a mainstream brittle mode removal surface, and the ceramic substrate of the present invention cannot be obtained. .

  Here, the ELID grinding method is a method of grinding a workpiece while eluting the bond material by electrolysis using a conductive grindstone (metal bond grindstone) in which abrasive grains are dispersed and fixed in a conductive bond material such as iron. For example, a precision horizontal ELID rotary surface grinder as shown in FIG. 1 can be used. FIG. 1 is a configuration diagram of a typical precision horizontal ELID rotary surface grinder, which includes a conductive grindstone 2 for grinding a workpiece 1 (ceramic substrate), an electrode 3 positioned at a distance from a processing surface of the grindstone, A grinding fluid supply means 5 for flowing the conductive grinding fluid 4 and an ELID power source 6 for applying a voltage between the grindstone and the electrode and controlling the current flowing between them to a predetermined range are included. The surface grinding machine to which the conductive grindstone 2 is fixed has an air bearing on the rotating shaft, and has a structure capable of positioning with high resolution (for example, 0.1 μm) by full-closed scale feedback. The workpiece 1 is fixed to a rotatable workpiece fixing table facing the surface grinding machine by a vacuum chuck or the like. In grinding, the surface grinder and the work fixing base are rotated at different rotational speeds in the same rotational direction, and the ground surface of the conductive grindstone 2 is brought into contact with the work surface of the work 1 and the contact surface is electrically conductive. A voltage is applied between the conductive grindstone 2 and the electrode 3 while supplying the conductive grinding fluid 4 intermittently or continuously. By doing so, it becomes possible to elute the bond material during grinding and make the abrasive grains on the surface of the conductive grindstone 2 always protrude, and grinding can be performed efficiently.

  The conductive grindstone used in the production method of the present invention is not particularly limited as long as the grain size of the abrasive grains contained therein is # 2000 to # 30000, and the abrasive grains include diamond, SiC, alumina, BN, etc. As the bond material, a material composed of a conductive material such as iron, cast iron, or carbon can be used. However, it is preferable to use a material in which the abrasive is diamond and the bond material is cast iron because it can be efficiently ground. .

  Using this grindstone, processing is performed step by step from rough grinding to intermediate grinding to finish grinding. In addition, the grindstone particle size used in each process is # 325 to # 600 for rough grinding, # 1200 to # 2000 for intermediate grinding, and # 4000 to # 30000 for finishing grinding, and is appropriately selected according to the required surface quality. To do. The peripheral speed of the grindstone is about 800 to 1200 m / min, and the coolant is preferably a weakly conductive water-soluble grinding fluid.

Since the ceramic substrate of the present invention manufactured by the method as described above has a highly smooth surface, a metallized substrate (metallized substrate of the present invention) in which a metal thin film is formed on the smooth surface by a thin film forming method is a ceramic substrate. The adhesion between the substrate and the metal thin film is high, and the arithmetic surface roughness Ra of the metal thin film surface is small. For this reason, when it is used as a substrate for mounting an electronic element such as a semiconductor element or a capacitor, not only the yield at the time of mounting the electronic element is increased, but also the substrate on which the electronic element is mounted has a high strength of the junction of the semiconductor element. It will be of high quality with little variation and high durability against thermal cycling. In addition, with regard to the adhesion to the metal thin film, the ceramic substrate of the present invention manufactured by the above method using ELID grinding is the adhesion strength of the metal thin film when the metal thin film is formed on the ground surface. Exceeds the adhesion strength expected from the smoothness of the underlying surface. For example, when a Ti thin film layer (thickness 0.1 μm) is formed on the ground surface by sputtering, the adhesion force of the Ti thin film layer is as high as 3.5 kg / mm ² or more. This is probably because the surface of the ceramic substrate has undergone some modification due to ELID grinding and has changed to a state of high adhesion to metal. At present, it is unclear what kind of modification has been made by ELID grinding, but the ceramic substrate of the present invention obtained by ELID grinding has a Ti thin film layer (thickness of 0.1 μm) formed by sputtering. It can be said that the Ti thin film layer has a special smooth surface with an adhesion of 3.5 kg / mm ² or more.

  The manufacturing method of the metallized substrate of the present invention is not particularly different from the metallized method using the conventional film forming method except that the ceramic substrate of the present invention is used as the ceramic substrate. Although either a thin film formation method or a thick film formation method can be adopted as a film formation method, the thin film formation method is adopted when used as a substrate for mounting a semiconductor element that requires miniaturization and high integration. It is preferable to do this. In particular, the vapor deposition method, the sputtering method, and the chemical vapor deposition (CVD) method can form a high-purity metal thin film (metallized film) with high thickness accuracy. Therefore, it is particularly preferable to employ these methods.

  For example, in order to form a metal thin film layer (metallized layer) by a sputtering method, a sputtering target made of the same kind of substance as the substance to be formed is formed, and the desired material is sputtered on the ceramic substrate. A metallized film of material can be formed. At this time, it is possible to accurately manage the deposited film thickness by measuring the film thickness of the vapor deposition material with a film thickness monitor using a crystal resonator. When sputtering is performed, the ceramic substrate is not heated and may be heated at room temperature. Further, when the metallized film can be formed from a gaseous raw material by the CVD method, the CVD method can be suitably employed.

Further, when the metallized film is formed by the CVD (chemical vapor deposition) method, it can be suitably performed using an organic metal CVD apparatus. In this method, a raw material gas such as Ta (OC ₂ H ₅ ) ₅ is introduced into a evacuated reaction vessel after being diluted with a diluent gas such as nitrogen and thermally decomposed in the reaction vessel onto a heated ceramic substrate. A metallized film is formed. The ceramic substrate is generally heated to about 50 ° C. to 1000 ° C., although it varies depending on the film growth conditions. In addition, by measuring the film forming speed for each forming condition in advance, the film forming time can be controlled to accurately estimate the film thickness. In addition to nitrogen, non-deposition gas such as helium, argon, xenon, neon, krypton can be used as a diluent gas. In these methods, the shape can be arbitrarily changed by masking the ceramic substrate during film formation. It is also possible to change the film shape by etching after film formation.

  The type of metal thin film to be formed on the ceramic substrate and the film structure of the metal thin film (for example, whether it is a single layer or a structure in which a plurality of layers are laminated) are appropriately determined according to the material of the ceramic substrate to be used. That's fine. For example, when an aluminum nitride sintered substrate is used as the ceramic substrate, the three-layer structure as described above is preferable.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

25 mm x 25 mm plate shape from 1.5 mm thick aluminum nitride sintered substrate obtained by degreasing and firing a green sheet containing 5 parts by weight of yttrium oxide as a sintering aid for 100 parts by weight of aluminum nitride powder Four bodies were cut out and used as samples. When the surface of the sample was observed by SEM, it was confirmed that the aluminum nitride sintered substrate had a structure in which crystallites having an average particle diameter of 2 to 6 μm were bonded to each other through a grain boundary phase.
The sample was set on a precision horizontal ELID rotary surface grinder having the structure shown in FIG. 1, and the surface was ground under the following conditions. Table 1 shows the grinding experimental system.

[Grinding conditions]
Grinding was performed using the cast iron bond wheels 2 of # 325, # 600, # 1200, # 2000, # 4000, # 8000, and # 30000. Each wheel was trued and subjected to the conditions shown in Table 2 after initial electrolytic dressing. .

  After grinding, after washing with water and drying, arithmetic surface roughness Ra of the ground surface was measured using a surface roughness measuring device. When a # 30000 grindstone was used, processing was about 30 minutes. In time, Ra = 0.008 μm. Table 3 shows the measurement results of the surface roughness for each wheel. The result that the surface roughness improved as the wheel became finer was obtained. In particular, with a # 4000 wheel, a very good machined surface roughness that can be called a mirror surface with a machined surface roughness of 0.1240 μmRy and 0.0176 μmRa was obtained. In addition, a sharp improvement in machined surface roughness was observed between the # 600 and # 2000 wheels. It seems that there was a change in the removal mechanism during this period.

  FIG. 2 shows the electrolytic current value during grinding with the # 4000 wheel and the grindstone shaft load. In both cases, no significant fluctuation was observed, indicating that stable machining could be achieved from beginning to end. Similar results were confirmed for the other wheels.

  FIG. 3 shows an SEM image of the processed surface with # 325 to # 30000 wheels. The processed surface by # 325 and # 600 wheels shows a rough processed surface state due to grain boundary fracture. Further, the processed surface by the # 1200 wheel is a brittle mode removing processed surface in which grain boundary fracture is the mainstream, as in the case of the # 325 wheel, although slight removal other than the grain boundary fracture is slightly confirmed.

  On the other hand, the processed surfaces with # 2000, # 4000, # 8000, and # 30000 wheels show smooth processed surface states in which almost no grain boundary fracture is observed. From this SEM result, it was confirmed that a brittle-ductile transition point of aluminum nitride exists between # 1200 and # 2000 wheels. In order to create a high-quality machined surface, it was found that the use of a fine abrasive wheel of # 2000 or higher was indispensable.

  In addition, the ground surface was observed with a metallurgical microscope at five arbitrary fields of view (magnification: 200 times), the number of defects having a diameter of 0.3 to 50 μm included in the range of 200 × 200 μm was counted, and the average When the value was calculated | required, the number (average value) was two pieces. Table 4 shows the measurement results.

Next, a Ti thin film layer (thickness 0.1 μm), a Pt thin film layer (thickness 0.3 μm), and an Au thin film layer (thickness 0) are formed on the ground surface of one sample after grinding by sputtering. .7 μm) were sequentially formed to obtain a metallized ceramic substrate. When the arithmetic surface roughness of the metallized layer of the obtained metallized substrate was measured, Ra = 0.01 μm. After that, after nickel-plated pins (tips with a flat tip diameter of 0.5 mm, made of 42 alloy) were soldered vertically on one metallized substrate, the surface of the metallized layer was soldered, and then the Toyo Seiki Seisakusho Co., Ltd. The pin was set on the graph M2 and the pin was pulled in the vertical direction at a pulling speed of 10 mm / min, and the breaking strength was measured. As a result, the breaking strength was 10 kg / mm ² . Further, when the peeling mode was examined by observing the interface after the test with a real microscope, a metal microscope, or an X-ray microanalyzer, the peeling mode was a base material (AlN) breakdown (Table 4).

  Further, a thin film capacitor was produced on the metallized layer of the remaining one metallized substrate. A thin film capacitor is an element in which tantalum oxide is sandwiched between gold electrodes to a thickness of 0.3 μm. Tantalum oxide was produced by sputtering. Thereafter, the element was evaluated by dropping the probe onto a gold electrode sandwiching tantalum oxide and measuring the capacitance (the defective product is short-circuited in this case). As a result of producing 100 elements, no short circuit occurred and the product was 100% non-defective (Table 4: No. 5).

Comparative Example 1
First, roughing is performed with a # 700 grindstone (60 rpm): 10 minutes (Ra: 0.8) with a lapping apparatus using loose abrasive grains, and then flattening is performed with a # 600 grindstone (60 rpm). ): 30 minutes (Ra: 0.6), and finally finished to a mirror surface by polishing using 6 micron abrasive grains (100 rpm): 1 hour (Ra: 0.1).
Except for polishing the surface of the aluminum nitride sintered substrate under the above conditions, the sample after grinding was evaluated, the metallized substrate was prepared and evaluated, and the thin film capacitor was prepared and evaluated. The results are shown in Table 4 (No. 1). The adhesion was 2.5 Kg / mm ² , the number of defects was 30, and the device yield was 0%.

  The sample after grinding and grinding was performed in the same manner as in Example 1 except that the grinding time with a # 2000 wheel was changed under ELID grinding conditions to produce processed surfaces having surface roughness of 0.04 μm and 0.02 μm. Evaluation, creation and evaluation of a metallized substrate, and creation and evaluation of a thin film capacitor were performed. The results are shown in Table 4 (No. 3, 4).

Comparative Example 2
Grinding and grinding in the same manner as in Example 1 except that a lapping apparatus using loose abrasive grains is used to change the polishing time to produce a processed surface having a surface roughness of 0.07 μm (processing time 4 hours). Evaluation of the sample after processing, preparation and evaluation of a metallized substrate, and preparation and evaluation of a thin film capacitor were performed. The results are shown in Table 4 (No. 2).

  As shown in Table 4, the ceramic substrate of the present invention obtained by using the production method of the present invention has a remarkable reduction in surface roughness as compared with a substrate obtained by polishing using conventional loose abrasive grains. As well as a feature that significantly reduces the number of defects present on the surface. Furthermore, in the metallized substrate in which the metal thin film is formed on the ceramic substrate obtained in the present invention, the adhesion between the ceramic surface and the metal thin film can be improved. Furthermore, the yield of the electronic elements formed on the ceramic substrate obtained by the present invention can be remarkably improved.

Prepare a ceramic substrate of the present invention (hereinafter referred to as an ELID processed material) manufactured using a # 30000 wheel and a conventional ceramic substrate manufactured by polishing (hereinafter referred to as an abrasive processed material). Measurement was performed using a small hardness tester (NHT) and an atomic force microscope (AFM). The measurement conditions were as follows.
Indenter shape: Triangular pyramid Vertical load: 300mN
Indentation depth: 20-30 μm

FIG. 4 is a comparative view of the obtained surface hardness. In this figure, FIG. 4 (A) shows the distribution of data of 10 points, respectively, and FIG. 4 (B) shows the average value. From this figure, the ceramic substrate (ELID processed material) according to the present invention has a Vickers hardness in the range of Hv 1800 to 2200, which is significantly harder than the Vickers hardness of the conventional abrasive processed material: Hv 1400 to 1750. I understand that.
Incidentally, in the bulk hardness evaluation, about Hv1000 is obtained, but in the present method of detecting the extreme surface with an ultra-micro hardness tester, about Hv1800 is obtained even with a conventional polished product. This difference in value is a difference in measurement depth, and the reason for the outermost surface does not reflect the bulk physical properties although the reason is unknown. Some reforming effect seems to exist. In this invention, it turns out that the difference appeared in the Vickers hardness in the outermost surface by surface modification.

Using the ceramic substrate (ELID processed material) of the present invention prepared in Example 3 and a conventional ceramic substrate (polished material), a tribological test was performed using a reciprocating sliding frictional wear tester (HEIDEN). The test conditions were as follows.
Load: 200g
Counterpart material (alumina ball) diameter: 3.175 mm
Sliding distance: 10mm
Test speed: 5 mm / s Number of tests: 100 times

  FIG. 5 is a comparison diagram of the obtained friction coefficients. In this figure, each data is an average value of arbitrary five places. From this figure, the ceramic substrate according to the present invention has a friction coefficient in the range of 0.4 to 0.7 at the number of sliding times of 30 times or more, and the friction coefficient of the conventional abrasive: 0.75 to 0.00. As can be seen from FIG.

  Using the ceramic substrate (ELID processed material) of the present invention prepared in Example 3 and a conventional ceramic substrate (polished material), surface XPS analysis (elemental analysis) was performed.

FIG. 6 shows the result of elemental analysis of the product of the present invention (ELID processed material), and FIG. 7 shows the result of elemental analysis of the conventional product (polished material). Each figure shows the content ratio of C, N, O, and Al from the left side, and the higher the peak, the higher the content ratio. In addition, the depth from the surface is shown from the front to the back. The depth scale is about 1 μm at the maximum in this figure.
From the comparison between FIG. 6 and FIG. 7, it can be seen that in the conventional product, the oxygen ratio is high in the vicinity of the surface but immediately decreases, and oxygen diffusion is small. On the other hand, in the product of the present invention, it can be seen that the oxygen ratio is high from the surface to the deep region, and oxygen diffusion is advanced.
Moreover, although the ratio of aluminum (Al) is comparable, it can be seen that the peak position is closer to the oxygen side in the product of the present invention, indicating that the formation of aluminum oxide (alumina) is progressing. Since the formation of alumina has the effect of improving the adhesion in sputtering of metallization, it can be seen that the ceramic substrate according to the present invention is excellent also in this respect.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention.

It is a block diagram of the precision horizontal type ELID rotary surface grinder used in the experiment. It is a relationship figure of the electrolytic current value during grinding with # 4000 wheel, and a grindstone axis load. It is a SEM image of the processing surface by # 325- # 30000 wheel. It is a comparison figure of surface hardness. It is a comparison figure of a friction coefficient. It is an elemental analysis result of this invention goods (ELID processed material). It is an elemental analysis result of a conventional product (abrasive material).

Explanation of symbols

1 Workpiece (ceramic substrate)
2 Conductive grinding wheel 3 Electrode 4 Conductive grinding fluid 5 Grinding fluid supply means 6 ELID power supply

Claims (10)

A ceramic substrate comprising a structure in which a plurality of crystal phases having an average crystallite diameter of 1 to 50 μm composed of the same kind of inorganic substance are joined via a grain boundary phase composed of different kinds of inorganic substances, A ceramic substrate having an arithmetic surface roughness Ra of at least one surface of 0.04 μm or less. The number of defects having a diameter of 0.3 to 50 μm existing on the surface having the arithmetic surface roughness Ra of 0.04 μm or less is 1.25 × 10 ⁻⁴ pieces / μm ² or less on average. Item 10. A ceramic substrate according to Item 1. 3. The ceramic substrate according to claim 1, wherein the ceramic substrate is a sintered ceramic substrate obtained by sintering powder composed of single-component crystalline inorganic particles using a sintering aid. The ceramic substrate according to any one of claims 1 to 3, comprising aluminum nitride as a main component. 5. The ceramic substrate according to claim 1, wherein the Vickers hardness is Hv 1800 to 2200. The ceramic substrate according to any one of claims 1 to 4, wherein a coefficient of friction with alumina is 0.4 to 0.7. 5. The ceramic substrate according to claim 1, wherein oxygen is detected as a substance other than the main component from a surface to a depth of 10 μm. A ceramic substrate having a Vickers hardness of Hv 1800 to 2200, wherein oxygen is detected as a substance other than a main component from a surface to a depth of 10 μm. A sintered ceramic substrate obtained by sintering a powder comprising a single component and comprising inorganic particles containing a crystal phase having an average crystallite diameter of 0.3 to 50 μm using a sintering aid. The method for producing a ceramic substrate according to any one of claims 1 to 8, wherein the ceramic substrate is processed by electrolytic in-process dressing grinding using a conductive grindstone containing abrasive grains having a grain size of # 2000 to # 30000. A metallized ceramic substrate comprising a metal thin film layer bonded to a surface having an arithmetic surface roughness Ra of 0.003 to 0.04 μm.

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