JP7264627B2 - Ceramic plates, semiconductor devices and semiconductor modules - Google Patents

Description

The present invention relates to a ceramic plate, a semiconductor device and a semiconductor module having a silicon nitride sintered body.

A semiconductor element such as a power semiconductor element is mounted on an insulating plate such as a ceramic plate and mounted on various devices as a semiconductor device. For example, a semiconductor element mounted on an insulating plate is thermally connected to a metallic radiator through the insulating plate or the like, and heat is radiated to the outside through the radiator. A semiconductor element is electrically connected to an external electric circuit through a conductive connecting member such as a lead terminal. The insulating plate on which the semiconductor element is mounted is thermally connected to a radiator such as a heat conductor including radiator fins or cooling pipes.

As the ceramic plate, a ceramic plate made of a silicon nitride sintered body has come to be used. Since the silicon nitride sintered body has relatively high mechanical strength and relatively high thermal conductivity, it can be used as a thin insulating plate with high thermal conductivity. Therefore, the weight of the semiconductor device including the insulating plate can be reduced. As a silicon nitride sintered body, for example, techniques described in Patent Documents 1 to 3 have been proposed.

JP-A-8-8772 JP-A-2001-335359 WO2005/060274

In recent years, ceramic plates are required to have not only improved thermal conductivity but also improved mechanical strength.

A ceramic plate according to an embodiment of the present invention includes a first phase containing a plurality of silicon nitride first crystals and a plurality of silicon nitride second crystals larger than the first crystals, and the plurality of second crystals are separated from each other. a second phase in contact;
A grain boundary phase exists between the first phase and the second phase, the elastic modulus of the grain boundary phase is smaller than that of the first crystal and the second crystal, and the area of the grain boundary phase in a cross-sectional view is The ratio is 5% or more and 20% or less ,
In a cross-sectional view, the ratio of the area of the first phase is 40% or more, and the ratio of the area of the second phase is 20% or more.

A semiconductor device according to an embodiment of the present invention includes the ceramic plate configured as described above and a semiconductor element arranged on the surface of the ceramic plate.

A semiconductor module according to an embodiment of the present invention includes the semiconductor device configured as described above and a radiator in contact with the semiconductor device.

Since the ceramic plate according to the embodiment of the present invention has the above structure, it is possible to have both excellent thermal conductivity and excellent mechanical strength. That is, it is possible to improve the mechanical strength mainly by the first phase and improve the thermal conductivity mainly by the second phase.

Since the semiconductor device according to the embodiment of the present invention includes the ceramic plate having the above structure, it is possible to improve the thermal conductivity between the ceramic plate and the semiconductor element or the like arranged on the surface of the ceramic plate. Become.

Since the semiconductor module according to the embodiment of the present invention includes the semiconductor device having the above configuration, it is possible to improve the thermal conductivity between the semiconductor device and a radiator or the like in contact with the semiconductor device. It is possible to improve the heat dissipation to.

It is a schematic diagram which expands and shows a part in planar view of the ceramic plate which concerns on embodiment of this invention. 1A is a cross-sectional view showing an example of a ceramic plate according to an embodiment of the present invention, and FIG. 1B is a plan view showing an example of a ceramic plate according to an embodiment of the present invention; FIG. 1 is a cross-sectional view showing an example of a semiconductor device and a semiconductor module according to an embodiment of the invention; FIG. 1 is a cross-sectional view showing an enlarged part of a ceramic plate according to an embodiment of the present invention; FIG. (a) is a cross-sectional view showing an enlarged part of a ceramic plate according to an embodiment of the present invention, and (b) is a table showing evaluation results of the ceramic plate according to the embodiment of the present invention.

A ceramic plate, a semiconductor device, and a semiconductor module according to embodiments of the present invention will be described with reference to the accompanying drawings.

It should be noted that the distinction between upper and lower sides in the following description is for convenience and does not specify the upper and lower directions when a ceramic plate or the like is actually used. Further, in the following description, the first crystal and the second crystal of silicon nitride are sometimes collectively referred to simply as crystals without distinguishing them from each other. In addition, the first phase and the second phase are sometimes collectively referred to simply as crystal phases without being distinguished from each other.

<Ceramic plate>
The ceramic plate 10 according to the embodiment of the present invention includes a first phase 1A including a plurality of first crystals 1 of silicon nitride, a plurality of second crystals 2 of silicon nitride larger than the first crystals 1, and a plurality of second crystals 2 It is basically composed of the second phase 2A in which the crystals 2 are in contact with each other. The ceramic plate 10 is a silicon nitride sintered body (hereinafter simply referred to as a sintered body). The mutually contacting portions of the second crystal 2 are sintered together. In the ceramic plate 10 of the present embodiment, it can be considered that the second phases 2A are dispersed in the first phases 1A that can function as the base material (between the first phases 1A). Specifically, the second crystals 2 (second phase 2A), which are partially in contact with each other, are surrounded by the first crystals 1 (first phase 1A) existing therearound. Here, the second crystal 2 is a single crystal. Also, the first crystal 1 is polycrystalline.

The ceramic plate 10 according to the present embodiment is mainly composed of the first crystal 1 and the second crystal 2 having different sizes. It is about 1.0 μm, and the size of the second crystal 2 is, for example, about 2 to 6 μm. The first crystal 1 and the second crystal 2 have, for example, a columnar shape such as a hexagonal prism or a spheroidal shape (a spheroidal shape with the long axis as the axis of rotation). The size of the first crystal 1 and the second crystal 2 is, for example, the length of the columnar shape or the length of the long axis of the spheroid (in this specification, both are not distinguished, and the length of the long axis is also referred to as identified by These major axis lengths can be measured, for example, by observing a cross section of the ceramic plate 10 as shown in FIG. 1 using an electron microscope such as an SEM. The size ratio between the first crystal 1 and the second crystal 2 is, for example, about 1:3 to 0.2:10. The average grain size of each of the first crystals 1 and the second crystals 2 is obtained by, for example, measuring the lengths of the major axes of the plurality of first crystals 1 and the plurality of second crystals 2 as described above, and calculating the arithmetic average. It can be measured by a method of calculation.

Here, the average grain size of the plurality of second crystals 2 contained in the second phase 2A should be 3 to 50 times the average grain size of the first crystals 1 contained in the first phase 1A. In this case, the second crystals 2 having a relatively large average grain size constitute the second phase 2A, so the grain boundaries existing in the second phase 2A can be reduced. Therefore, the thermal conductivity of the second phase 2A can be effectively enhanced, and the thermal conductivity of the ceramic plate 10 can also be effectively enhanced.

That is, if the average grain size of the second crystals 2 is at least three times as large as the average grain size of the first crystals 1, it is possible to effectively obtain the effect of improving thermal conductivity by reducing the grain boundaries as described above. That is, it is effective for improving the thermal conductivity of the ceramic plate 10 . If the average grain size of the second crystals 2 is 50 times or less than the average grain size of the first crystals 1, the second crystals 2 can be efficiently surrounded by the first crystals 1 having a relatively small average grain size. can be formed, and the bonding strength between the first phase 1A and the second phase 2A can be improved. That is, it is effective in improving the mechanical strength of the ceramic plate 10 .

The ratio of the average grain size between the first crystal 1 and the second crystal 2 can be adjusted, for example, by applying a method for adjusting the size of crystals as described later. Further, the average grain size of the first crystal 1 and the second crystal 2 can also be measured and calculated by the method described later (the method of observing the cross section).

In the ceramic plate 10 according to the present embodiment, the first crystals 1 and the second crystals 2 are crystals such as columnar crystals. The ends of the columnar crystals should be in contact with each other. The plurality of second crystals 2 may be in contact with each other at their ends in the longitudinal direction, thereby further improving thermal conductivity. Adjacent columnar crystals are sintered between the contacting ends to form a second phase 2A continuous in the length direction of each second crystal 2 . Since the thermal conductivity within each crystal is greater than that at the grain boundary, a heat transfer path with high thermal conductivity is formed in the length direction of the second crystals 2 that are in contact with each other. Thereby, the thermal conductivity in the ceramic plate 10 can be effectively improved. The second columnar crystal 2 may have, for example, a ratio of its lengthwise dimension to its widthwise dimension (perpendicular to the lengthwise direction) of about 5:1 to 10:1. The size and shape (e.g., forming a columnar shape) of the second crystal 2 can be adjusted, for example, by applying a method for adjusting the crystal size, which will be described later.

Also, the ratio of the area of the first phase 1A to the entire ceramic plate 10 may be set in the range of 40 to 80%, for example. With such an area ratio, an arrangement in which the second phase 2A is dispersed in the first phase 1A, or an arrangement in which the second phase 2A is surrounded by the first phase 1A. can be done. If the first phase 1A is 40% or more, the mechanical strength of the ceramic plate 10 can be effectively improved. Moreover, if the first phase 1A is 80% or less (if the second phase 2A is 20% or more), the thermal conductivity of the ceramic plate 10 can be effectively improved. Here, the ratio of the first phase 1A and the second phase 2A can be calculated as an area ratio by observing a cross section as shown in FIG. 4, for example.

Also, the glass layer 5 may be present at the contact portion between the second crystals 2 . Although the glass layer 5 has lower thermal conductivity and mechanical strength than silicon nitride crystals, the presence of the glass layer 5 having a predetermined thickness at the contact portion of the silicon nitride crystals improves the overall thermal conductivity and mechanical strength. It is possible to improve the target strength.

The glass layer 5 contains rare earth elements, alkali metals, and the like.

The glass layer 5 may be present with a thickness of 5 nm or less in the central portion of the portion where the second crystals 2 are in contact with each other. Here, the glass thickness can be measured, for example, by measuring the middle point (or the point at the same distance from both ends) of the portion where the second crystals 2 are in contact with each other in a TEM photograph.

As a specific experimental result, as shown in FIG. In Nos. 1 to 5, the glass thickness is 2 to 4 nm. In 6 and 7, the glass thickness was 9 nm and 7 nm, respectively. The evaluation results were obtained for No. 1 of the example in which the thickness of the glass layer 5 was 5 nm or less. In 1 to 5, the thermal conductivity of the ceramic plate was 72 to 74 W/mK, and the bending strength was 717 to 845 MPa. On the other hand, No. 1 of the comparative example in which the thickness of the glass layer 5 is larger than 5 nm. In 6 and 7, the thermal conductivity of the ceramic plate was as low as 60-65 W/mK, and the bending strength was also as low as 666-695 MPa. In other words, it was found that when the thickness of the glass layer 5 was 5 nm or less, both excellent thermal conductivity and excellent bending strength were obtained.

Also, the glass layer 5 may be present at the contact portion between the first crystals 1 . In this case, the thickness of the glass layer 5 intervening between the contact portions between the second crystals 2 is slightly smaller than the thickness of the glass layer 5 existing in the central portion of the portion where the first crystals 1 are in contact with each other. Just do it.

Also, the glass layer 5 can be present at the contact portion between the first crystal 1 and the second crystal 2 .

In addition, the ceramic plate 10 contains components such as sintering aids in addition to silicon nitride crystals (first crystal 1, second crystal 2) and crystal phases (first phase A1, second phase A2). may Components such as sintering aids are present, for example, between silicon nitride crystals (grain boundary portions).

Moreover, the ceramic plate 10 according to the embodiment may further include a grain boundary phase 4 existing between the first phase 1A and the second phase 2A. The grain boundary phase 4 is, for example, a phase mainly containing the above-described sintering aid, and is, for example, oxides such as silicon oxide, magnesium oxide, erbium oxide and yttrium oxide. Note that the grain boundary phase 4 is not hatched in FIG. 4 in order to make the drawing easier to see.

The presence of the grain boundary phase 4 containing such an oxide increases the sintering strength between the first crystal 1 of the first phase 1A and the second crystal 2 of the second phase 2A having different grain sizes. Therefore, the mechanical strength of the ceramic plate 10 can be enhanced. In addition, the presence of the grain boundary phase 4, which has a relatively small elastic modulus compared to silicon nitride crystals (the first crystal 1 and the second crystal 2), can improve the toughness of the ceramic plate 10 as well. Therefore, the possibility of mechanical destruction such as cracks in the ceramic plate 10 can be reduced. In other words, the ceramic plate 10 can be effectively improved in reliability.

If the grain boundary phase 4 exists in approximately 5 to 20% of the entire ceramic plate 10 in a cross-sectional view as shown in FIG. 4, the above effect can be sufficiently obtained. Also, the thermal conductivity of the ceramic plate 10 can be ensured to be as high as when the grain boundary phase 4 is not included.

The ceramic plate 10 may contain other members (not shown) such as a glass coating layer adhered to the outer surface such as the upper surface or the lower surface, in addition to the silicon nitride crystals and crystal phases.

As described above, the ceramic plate 10 according to the present embodiment contains silicon nitride crystals and is a silicon nitride sintered body. The first phase 1A in the silicon nitride sintered body mainly has the function of ensuring the mechanical strength of the sintered body (also referred to as bending strength in this specification). In other words, the first phase 1A is the part that basically constitutes the ceramic plate 10 . In the first phase 1A, silicon nitride first crystals 1 having relatively small grain sizes are mutually sintered to form a sintered body having high mechanical strength. Moreover, the second phase 2A mainly has the function of increasing the thermal conductivity of the ceramic plate 10 . That is, the second phase 2A constitutes a heat transfer path having a relatively high thermal conductivity in the thickness direction of the ceramic plate 10 or the like. In the second phase 2A, portions of the second silicon nitride crystals 2 having a relatively large grain size are in contact with each other and sintered to form a heat transfer path. Since the individual crystals of the second crystal 2 are relatively large, there are few grain boundaries, and the influence of a decrease in thermal conductivity at the grain boundaries (interfaces where crystals are connected to each other) is relatively small. Therefore, the thermal conductivity of the ceramic plate 10 can be effectively increased by the second phase 2A. The mechanical strength of the ceramic plate 10 does not depend only on the first phase 1A, but the second phase 2A also has the function of ensuring the mechanical strength of the ceramic plate 10. FIG. Moreover, the thermal conductivity of the ceramic plate 10 does not depend only on the second phase 2A, but the first phase 1A also has the function of ensuring the thermal conductivity of the ceramic plate 10. FIG. As described above, according to the ceramic plate 10 according to the present embodiment, by including the first phase 1A and the second phase 2A, it is possible to achieve both excellent thermal conductivity and excellent mechanical strength. .

Further, the ceramic plate 10 according to the present embodiment has a flat plate shape as shown in FIG. 2, and has a rectangular shape or a rectangular shape such as a square shape in plan view. The ceramic plate 10 has a surface 2 comprising upper and lower surfaces located opposite each other.

Since the ceramic plate 10 has such a structure, when the semiconductor element 11 is arranged on the surface 2 as described later, the heat generated by the operation of the semiconductor element 11 is efficiently dissipated, and the semiconductor element 11 is arranged. It can be conducted to a location away from the location where it is located. For example, if the semiconductor element 11 is arranged in the central portion of the upper surface of the ceramic plate 10, the heat can be smoothly transferred to the lower surface side and the outer peripheral portion side of the ceramic plate 10, and can be radiated to the outside. . Therefore, the ceramic plate 10 can easily improve heat dissipation to the outside when the semiconductor element 11 is mounted.

(Example)
The ceramic plate 10 according to this embodiment has a thermal conductivity of about 70 to 75 W/mK and a bending strength of about 800 W/mK when the first crystal 1 and the second crystal 2 have the sizes described above. ~850 MPa. Here, in this specification, thermal conductivity and bending strength may be measured by the following methods, for example. The thermal conductivity of the ceramic plate 10 can be measured, for example, by a laser flash method. Also, the bending strength of the ceramic plate 10 can be measured, for example, by a three-point bending test method (based on JIS-K7171).

(Comparative example 1)
On the other hand, in the case of a ceramic plate made of a silicon nitride sintered body having a crystal major axis length of about 4 to 20 μm, the thermal conductivity can be as high as about 75 W/mK, but the bending strength is about Relatively small at 650 MPa. In other words, it is difficult to reduce the thickness of the ceramic plate (reduction in thickness) when it is necessary to ensure mechanical strength. Therefore, in such a ceramic plate, it is difficult to shorten the heat transfer path from the semiconductor element mounted on the upper surface to the radiator connected to the lower surface, which will be described later, and it is difficult to improve the heat dissipation.

(Comparative example 2)
In addition, in the case of a ceramic plate made of a silicon nitride sintered body having a crystal major axis length of about 1 to 7 μm, the bending strength can be increased to about 850 to 900 MPa, but the thermal conductivity is about 60 W/ mK and relatively small. In other words, even if the ceramic plate can be made thinner, it is difficult to improve the thermal conductivity. Therefore, even if the heat transfer path from the semiconductor element mounted on the upper surface to the radiator connected to the lower surface can be shortened by, for example, thinning the ceramic plate, the thermal conductivity itself is relatively small. It is difficult to improve heat dissipation.

(Evaluation results)
As a specific example, the ceramic plate 10 according to the present embodiment, which has an outer dimension of 60 mm×35 mm in plan view and a thickness of about 0.35 mm, has a semiconductor element 11 having a heat generation amount of 300 W. When mounted, 214 W of heat transfer to the underside is possible. On the other hand, in the case of the ceramic plate of Comparative Example 1, it is difficult to make the thickness of the ceramic plate smaller than about 0.46 mm. Therefore, when the other conditions are the same as the ceramic plate 10 according to the present embodiment, the heat conduction to the lower surface side of the ceramic plate of Comparative Example 1 remains at about 163W. In addition, in the case of the ceramic plate of Comparative Example 2, although the thickness can be reduced to the same extent as the ceramic plate 10 according to the present embodiment, other conditions are the same as those of the ceramic plate 10 according to the present embodiment. , the heat conduction to the lower surface side remains at about 171 W.

<Ceramic plate manufacturing method>
The ceramic plate 10 according to the embodiment described above can be manufactured, for example, by the following steps.

First, raw material powders such as silicon nitride, silica (silicon oxide), magnesium oxide, erbium oxide and yttrium oxide, an organic solvent, and a binder are pulverized by pulverizing means such as a mill to produce raw material powders. At this time, the materials are mixed to a particle size corresponding to each material to prepare a slurry. Here, silica (silicon oxide), magnesium oxide, erbium oxide, yttrium oxide, etc. are additives such as sintering aids.

Next, the prepared slurry is formed into a sheet by a method such as a doctor blade method to produce a strip-shaped ceramic green sheet. The produced ceramic green sheet is cut into a suitable size and shape to produce a plurality of sheets.

Thereafter, a plurality of these sheets are superimposed one on top of the other as required, and then fired at a temperature of about 1400 to 1900.degree. In this step, the silicon nitride is held at 1500 to 1700° C. for 1 to 3 hours under nitrogen pressure to transform the silicon nitride from α-type to β-type to precipitate crystals. Thus, the ceramic plate 10 having the first phase 1A containing the first crystals 1 and the second phase 2A containing the second crystals 2 can be manufactured.

Through the steps described above, the ceramic plate 10 according to the present embodiment can be manufactured.
In the process of manufacturing the ceramic plate 10, conditions such as the particle size of the raw material powder of silicon nitride, the type and amount of sintering aid to be added, the temperature during firing and the keeping time are adjusted as appropriate. By adjusting, the grain size of the first crystal 1 and the second crystal 2 can be adjusted. Specific examples are as follows. The ratio of the time at a temperature (1600 to 1700° C.) for converting silicon nitride from α-type to β-type and crystal precipitation and the time at a temperature (1800 to 1900° C.) for crystal growth determines the first crystal 1. The ratio of the first phase 1A containing and the second phase 2A containing the second crystal 2 can be adjusted. In addition, if the keeping time during firing is lengthened, the grain size of the crystal can be increased by grain growth, and if the amount of the sintering aid is increased, the grain size of the crystal can be decreased as a whole. .

<Semiconductor device, semiconductor module>
As shown in FIGS. 2 and 3, a semiconductor device 20 according to an embodiment of the present invention is composed of a ceramic plate 10 having the above configuration and a semiconductor element 11 arranged in a mounting area 3 on the upper surface of the ceramic plate 10. ing. The ceramic plate 10 and the semiconductor element 11 can be connected using a bonding material (no reference numeral) such as brazing material. In the example of FIG. 2, the semiconductor element 11 and the ceramic plate 10 are shown separately. Note that the ceramic plate 10 functions as a base material for positioning and fixing the semiconductor element 11 .

According to such a semiconductor device 20, the heat generated by the operation of the semiconductor element 11 can be efficiently conducted through the ceramic plate 10 to a position away from the position where the semiconductor element 11 is arranged. For example, if the semiconductor element 11 is arranged in the central portion of the upper surface of the ceramic plate 10, the above heat can be smoothly transferred to the lower surface side and the outer peripheral portion side of the ceramic plate 10. FIG. Also, heat can be effectively dissipated from the lower surface and outer peripheral portion of the ceramic plate 10 .

The semiconductor element 11 in this example is mounted on the mounting area 3 located in the center of the top surface of the ceramic plate 10 . The semiconductor element 11 is bonded and fixed to the ceramic plate 10 by, for example, a bonding material 12 or the like. As the joining material 12, for example, a low-melting-point brazing material such as a gold-tin brazing material can be used. Further, the bonding material may be a tin-silver based brazing material or the like, or may be an adhesive containing an anisotropic conductive adhesive or the like.

For example, the semiconductor element 11 can be bonded to the ceramic plate 10 by aligning the semiconductor element 11 with the mounting region 3 via a preform of gold-tin brazing material and heating them to a predetermined temperature. . Through this process, the semiconductor device 20 according to the embodiment as shown in FIG. 3 can be manufactured.

The ceramic plate 10 and the semiconductor element 11 mounted thereon are basic units for transmitting/receiving electric signals to/from the outside and radiating heat to the outside. Various electric signals from an external electric circuit (not shown) are received by the semiconductor element 11, and various operations such as calculation are performed in the semiconductor element 11. FIG. The result of this operation is transmitted to the external electric circuit, and the device including the external electric circuit is controlled. Examples of such devices include computers, communication devices, and control devices for controlling automobile engines and the like.

The semiconductor module 30 according to the embodiment of the present invention includes the semiconductor device 20 configured as described above, the external connection conductor 22 electrically connected to the semiconductor element 11, and the radiator 21 thermally connected to the semiconductor element 11. It is composed by In the semiconductor module 30, the external connection conductors 22 for electrically connecting the semiconductor element 11 to the outside are not essential and may be arranged. Since the semiconductor module 30 includes the semiconductor device 20 configured as described above, the thermal conductivity between the ceramic plate 10 and the radiator 21 or the like thermally connected to the ceramic plate 10 is improved. It is easy, and it becomes easy to improve heat dissipation to the outside. The ceramic plate 10 in the semiconductor module 30 also has a function of conducting heat generated by the semiconductor element 11 to the radiator 21 and radiating it to the outside.

As for the thermal connection between the semiconductor element 11 and the radiator 21, the surface of the ceramic plate 10 of the semiconductor device 20 and the radiator 21 are connected to each other via a connecting material. That is, the semiconductor device 20 and the radiator 21 are mechanically and thermally connected to each other via, for example, a connecting material. Here, the thermal connection between the semiconductor element 11 and the radiator 21 refers to a state in which the thermal conductivity between the two is approximately 20 W/mK or more. In this case, the semiconductor element 11 and the radiator 21 may be in direct contact with each other, or may be connected and fixed to each other via a connecting material as described above. The connecting material includes, for example, a connecting material containing a viscous material.

In the example shown in FIG. 3, the semiconductor device 20, the radiator 21, and the external connection conductor 22 are shown separately. In this example, the semiconductor device 20, radiator 21 and external connection conductor 22 may be integrally covered with a sealing resin (not shown). This effectively suppresses oxidation and corrosion of the semiconductor element 11 and the like due to the external environment (oxygen, moisture, etc.).

The connection and fixation of the semiconductor device 20 and the radiator 21 can be performed, for example, by bonding them together via a viscous material (not shown) such as grease. Filler particles may be added to the viscous material to enhance its thermal conductivity. It is a base material for holding the heat transfer particles 25 . A viscous material is interposed between the ceramic plate 10 and the radiator 21 to mechanically connect the two, thereby thermally connecting the two. The material forming the filler particles may be, for example, a material having a thermal conductivity of about 50 W/mK or higher. Specific examples of the filler particles include ceramic materials such as aluminum oxide and zinc oxide, and good thermally conductive materials such as inorganic materials such as carbon.

Reference Signs List 1 First crystal 1A First phase 2 Second crystal 2A Second phase 3 Mounting region 4 Grain boundary phase 5 Glass layer 10 *Ceramic plate 11...Semiconductor element 12...Joining material 20...Semiconductor device 21...Radiator 22...External connection conductor

Claims (11)

a first phase containing a plurality of silicon nitride first crystals;
a second phase including a plurality of second crystals of silicon nitride larger than the first crystals, wherein the plurality of second crystals are in contact with each other;
A grain boundary phase exists between the first phase and the second phase, the elastic modulus of the grain boundary phase is smaller than that of the first crystal and the second crystal, and the area of the grain boundary phase in a cross-sectional view is The ratio is 5% or more and 20% or less ,
A ceramic plate , wherein the area ratio of the first phase is 40% or more and the area ratio of the second phase is 20% or more in a cross-sectional view. 2. The ceramic plate according to claim 1, wherein said first crystal has a major axis length of 0.1-1.0 μm, and said second crystal has a major axis length of 2-6 μm. 3. The ceramic plate according to claim 1, wherein said second crystal is a single crystal. The ceramic plate according to any one of claims 1 to 3 , wherein said first phase is polycrystalline. 5. The ceramic plate according to claim 1, wherein the average grain size of said second crystals is 3 to 50 times the average grain size of said first crystals. 6. The ceramic plate according to claim 1, wherein said plurality of second crystals are columnar, and said second crystals are in contact with each other. 7. The ceramic plate according to any one of claims 1 to 6 , wherein a glass layer having a thickness of 5 nm or less is present in the central portion of the portions where the second crystals are in contact with each other. 8. The glass layer of claim 7, wherein the glass layer interposed in the contact portion between the second crystals is thinner than the glass layer present in the central portion of the portion where the first crystals are in contact with each other. Ceramic plate as described. a ceramic plate according to any one of claims 1 to 8 ;
and a semiconductor element arranged on the surface of the ceramic plate. a semiconductor device according to claim 9 ;
and a radiator in contact with the semiconductor element. 11. The semiconductor module according to claim 10 , further comprising an external connection conductor electrically connected to said semiconductor element.

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