JP2013032265A - Alumina zirconia sintered board for semiconductor device and manufacturing method therefor - Google Patents

Abstract

An alumina zirconia sintered substrate for a semiconductor device having high heat conduction characteristics and high strength characteristics, and a method capable of advantageously producing the same.
SOLUTION: ZrO ₂ : 2 to 15% by weight, Y ₂ O ₃ : 0.01 to 1% by weight and Al ₂ O ₃ obtained by firing a raw material composition to which no sintering aid is added. A sintered substrate composed of the balance, wherein the average crystal grain size of Al ₂ O ₃ is larger than 2 μm and 7 μm or less, and the Al ₂ O ₃ grain boundary length is 60% or more of the total grain boundary length. Thus, the thermal conductivity was 30 W / m · K or more and the bending strength was 500 MPa or more.
[Selection] Figure 1

Description

  TECHNICAL FIELD The present invention relates to an alumina zirconia sintered substrate for a semiconductor device and a method for manufacturing the same, and particularly, in an aluminum zirconia sintered body having excellent characteristics in which a semiconductor chip is mounted by soldering or the like in a semiconductor device such as a power transistor module. The present invention relates to a substrate and a method for producing it advantageously.

Conventionally, in a semiconductor device such as a power transistor module such as an inverter or a converter, an insulating substrate on which a semiconductor chip is mounted is an alumina (Al ₂ O ₃ ) substrate, an aluminum nitride (AlN) substrate, or silicon nitride (Si _3). Three types of ceramic substrates, N ₄ ) substrates, have been put into practical use. In addition, such a ceramic substrate also has a function as a heat dissipation substrate. For this reason, a metal plate such as a thin foil-like Cu plate or Al plate is bonded to at least one surface of the substrate. However, due to the difference in thermal expansion during heating, a large load is applied to the ceramic substrate. In particular, a substrate that can withstand the high-voltage and high-current energization of a semiconductor chip in a semiconductor device in recent years is required. Therefore, it is required to have high strength and high thermal conductivity. ing.

However, among the three types of ceramic substrates put into practical use, the AlN substrate and the Si ₃ N ₄ substrate require special management in the metal plate joining process in addition to the problem of high material costs. The problem is inherent. On the other hand, the Al ₂ O ₃ substrate has been widely used as a general-purpose product because of its low material cost. However, the strength and thermal conductivity are not sufficient, and a semiconductor device loaded with high voltage or high current is used. It was insufficient for use as a ceramic substrate.

  On the other hand, Japanese Patent Application Laid-Open No. 2000-344569 discloses a high-strength alumina sintered body containing zirconia and a method for producing the same, in which a surface of alumina powder is coated with a Zr-Al hydroxide. After preparing the quasi-raw material powder that has been deposited, this is calcined to obtain a raw material powder having tetragonal and / or cubic zirconia deposited on the surface. After being molded into a predetermined shape, firing is performed so that the average crystal particle diameter of zirconia is 0.1 to 1.0 μm, the average crystal particle diameter of alumina is 0.5 to 2.0 μm, and the sintered body has a rough surface It has been clarified that a high-strength alumina sintered body having a thickness (Ra) of 0.2 μm or less can be obtained. In addition, although an alumina sintered body having a bending strength exceeding 700 MPa is disclosed there, the alumina conductive body obtained therewith is used for sliding balls such as bearing balls and plunger rods. Since it is intended for applications such as moving members, pulverizing members, cutting / polishing tools, etc., nothing has been clarified, and no specific technical means to enhance its heat conduction characteristics are clarified. It has not been done.

  JP-A-8-195450 discloses a substrate made of a high-temperature fired body obtained by adding a certain amount of zirconia and an additive such as yttria to alumina as a main component as a substrate for a semiconductor device. It has been clarified that it has the characteristics that the bending strength is higher and the thermal conductivity is further improved as compared with a ceramic substrate made of alumina alone. Specifically, the thermal conductivity is 40 W / m · K. And it is disclosed that it has the characteristic that bending strength: 400MPa.

However, even if the substrate has high thermal conductivity, if it has a bending strength of about 400 MPa, it is only as strong as a 96% Al ₂ O ₃ substrate that is a general-purpose product. , There is no merit. In order to obtain high thermal conductivity in a high-strength substrate, it is necessary to grow Al ₂ O ₃ crystal grains to reduce the grain boundary glass layer that becomes a barrier for thermal conduction. Since the abnormal grain growth of Al ₂ O ₃ crystal grains that are easily induced by N2 is a fatal factor of strength reduction, Al ₂ O ₃ based substrates having both higher thermal conductivity and higher bending strength are still not available. For this reason, the realization of a substrate having both of these characteristics at the same time is an issue. As specific target characteristic values, the thermal conductivity is 30 W / m · K or more, and the bending strength is 500 MPa or more.

In the above-mentioned Japanese Patent Application Laid-Open No. 8-195450, a substrate having Al ₂ O ₃ as a main component and having a thermal conductivity of 30 W / m · K or more is shown. The strength is as low as about 400 MPa. However, in the case of a ceramic substrate used as a heat dissipation substrate for a semiconductor device, in a situation where a large load is applied due to a difference in thermal expansion between the metal plate and the metal plate joined thereto, particularly in a heat dissipation substrate for high output, Since the metal plate to be joined becomes thicker, if the bending strength of the substrate is less than 500 MPa, there is a problem that the substrate itself is destroyed because it cannot withstand the load during heating.

In addition, the thermal conductivity of the substrate mainly composed of Al ₂ O ₃ is 1/10 or less than the thermal conductivity of Cu, which is the material of the metal plate to be joined thereto, and the thermal resistance of the entire semiconductor component is reduced. This is the rate-determining factor, which accounts for about 50%. Therefore, improving the thermal conductivity of the ceramic substrate is the most effective solution for improving the heat dissipation of semiconductor components. However, the Al ₂ O ₃ substrate having a bending strength of 500 MPa or more that can withstand bonding to a metal plate has a low thermal conductivity of less than 30 W / m · K, but the bending strength characteristics of 500 MPa or more. If the thermal conductivity of the Al ₂ O ₃ substrate can be improved to 30 W / m · K or more while maintaining the above, the same characteristics as when using an AlN substrate or Si ₃ N ₄ substrate are obtained. It will be obtained. In the case of a substrate mainly composed of Al ₂ O ₃ having such high thermal conductivity and high bending strength at the same time, by increasing the thickness of the metal plate bonded thereto, the heat dissipation as a semiconductor component is further increased. It is possible to improve.

Japanese Patent Laid-Open No. 2000-344569 JP-A-8-195450

  Here, the present invention has been made in the background of such circumstances, and the problem to be solved is that the thermal conductivity is 30 W / m · K or higher, high thermal conductivity characteristics and bending strength is 500 MPa or more. The present invention is to provide an alumina zirconia sintered substrate for a semiconductor device having both high strength characteristics and a method for advantageously producing an alumina zirconia sintered substrate for a semiconductor device having such excellent characteristics. It is to provide.

  The present invention can be suitably implemented in various modes as listed below in order to solve the above-mentioned problems or problems grasped from the description of the entire specification and the drawings. Each aspect described in can be employed in any combination. It should be noted that the aspects or technical features of the present invention are not limited to those described below, and can be recognized based on the description of the entire specification and the inventive concept disclosed in the drawings. Should be understood.

(1) Made of a mixture of Al ₂ O ₃ powder, ZrO ₂ powder and Y ₂ O ₃ powder, or a mixture of Al ₂ O ₃ powder and ZrO ₂ —Y ₂ O ₃ powder, with sintering aid added In a sintered body comprising ZrO ₂ : 2 to 15% by weight, Y ₂ O ₃ : 0.01 to 1% by weight, and Al ₂ O ₃ : the balance obtained by firing a raw material composition that has not been fired And the average grain size of Al ₂ O ₃ is larger than 2 μm and 7 μm or less, and the grain boundary length in which Al ₂ O ₃ particles are in direct contact is 60% or more of the total grain boundary length An alumina zirconia sintered substrate for a semiconductor device, characterized in that the thermal conductivity is 30 W / m · K or more and the bending strength is 500 MPa or more.
(2) The alumina zirconia sintered substrate for a semiconductor device according to the aspect (1), wherein an average crystal particle diameter of the Al ₂ O ₃ is 2.5 to 4.5 μm.
(3) The alumina zirconia sintered substrate for a semiconductor device according to the aspect (1) or the aspect (2), wherein 80 mol% or more of ZrO _{2 in} the sintered body is a tetragonal crystal.
(4) Alumina zirconia firing for a semiconductor device according to any one of Embodiments (1) to (3), wherein an average crystal particle diameter of ZrO _{2 in} the sintered body is 0.5 to ₂ μm. Bonding board.
(5) The alumina zirconia firing for a semiconductor device according to any one of the aspects (1) to (4), wherein the sintered body has a sintered density of 3.70 g / cm ³ or more. Bonding board.
(6) The alumina zirconia sintered substrate for a semiconductor device according to any one of the aspects (1) to (5), wherein the sintered body has a surface roughness (Ra) of 0.3 μm or less.
(7) The alumina zirconia sintered substrate for a semiconductor device according to any one of the aspects (1) to (6), wherein the substrate thickness is in a range of 0.1 to 1 mm.
(8) The alumina zirconia sintered substrate for a semiconductor device according to any one of the aspects (1) to (7), wherein a copper plate or an aluminum plate is bonded to at least one surface of the substrate.
(9) Any of the above aspects (1) to (8), wherein the ZrO ₂ —Y ₂ O ₃ powder is a partially stabilized zirconia powder obtained by dissolving Y ₂ O ₃ in ZrO ₂ . The alumina zirconia sintered substrate for semiconductor devices as described in one.
(10) In the method for producing an alumina zirconia sintered substrate for a semiconductor device according to any one of the embodiments (1) to (9), an Al ₂ O ₃ powder, a ZrO ₂ powder, and a Y ₂ O are used. _In the firing of a raw material composition comprising a mixture of ₃ powders, or a mixture of Al ₂ O ₃ powder and ZrO ₂ —Y ₂ O ₃ powder, to which no sintering aid is added, from 1200 ° C. to 1600 ° C. to A method for producing an alumina zirconia sintered substrate for a semiconductor device, characterized in that a temperature rising rate in a temperature range up to a maximum temperature between 1700 ° C. is smaller than a temperature rising rate in a temperature range of 500 ° C. to 1200 ° C. .

In short, the present invention is suitable for Al ₂ O ₃ particles (crystals) and ZrO ₂ particles (crystals) in an alumina zirconia substrate made of a sintered body having a predetermined ratio of Al ₂ O ₃ , ZrO ₂ and Y ₂ O _3. The ZrO ₂ particles in the sintered body constituting the substrate obtained by firing under appropriate sintering conditions that suppress abnormal grain growth while ensuring a stable dispersion state are grain boundaries of Al ₂ O ₃ particles. By realizing a microstructure that is positioned at the triple point, that is, a state in which the contact area between Al ₂ O ₃ particles is large, both high thermal conductivity and high strength characteristics can be obtained simultaneously with an inexpensive Al ₂ O ₃ substrate. It was possible to give to.

  And, in such an alumina zirconia sintered substrate according to the present invention, the high thermal conductivity characteristics and high strength characteristics make it possible to reduce the thickness of the substrate on which the semiconductor chip is mounted. Therefore, it is possible to advantageously improve the heat dissipation and increase the current capacity, and accordingly, it is possible to respond advantageously to the demand for higher voltage and higher current in the semiconductor device. It is.

  Further, by using an alumina zirconia substrate having high thermal conductivity and high strength characteristics according to the present invention, a semiconductor device such as a power transistor module, in particular, an insulated gate bipolar transistor (IGBT), which generates a high temperature with a large power. ) It can be used widely for modules and the like.

It is a scanning electron microscope (SEM) photograph of the board | substrate structure | structure in an example of the alumina zirconia sintered substrate obtained according to this invention. It is a graph which shows the relationship between the heat conductivity and bending strength of the alumina zirconia sintered substrate obtained in the Example, and the addition amount of partially stabilized zirconia.

Here, the alumina zirconia sintered substrate (sintered body) according to the present invention is composed only of Al ₂ O ₃ , ZrO ₂ and Y ₂ O ₃ , and is conventionally known as an alumina zirconia substrate. Further, it does not substantially contain a sintering aid such as SiO ₂ , MgO or CaO added as a sintering aid. Here, “substantially not contained” means that the essence of the present invention is that even if a small amount of inevitable impurities that are inevitably mixed in from the raw material are included in the manufacturing process of the sintered substrate. It is not damaged. In such a sintered substrate, Y ₂ O ₃ is dissolved in ZrO ₂ and exists as partially stabilized zirconia, and most of the partially stabilized zirconia is Al ₂ as crystal particles. It exists at the O ₃ grain boundary triple point. Therefore, there is no sintering aid phase that becomes thermal resistance at the grain boundary of the sintered alumina zirconia substrate, and the Al ₂ O ₃ crystal particles are in direct contact with each other. It is.

In such an alumina zirconia sintered substrate according to the present invention, Al ₂ O ₃ is used as a main component, and in order to increase its strength, the proportion of ZrO ₂ is ₂ to 15% by weight. It is contained in. If the ZrO ₂ content is less than 2% by weight, abnormal grain growth of the Al ₂ O ₃ crystal phase during sintering cannot be suppressed, and it becomes difficult to obtain sufficient substrate strength. On the other hand, when it exceeds 15% by weight, a decrease in the thermal conductivity of the sintered substrate is caused, and in addition, a large amount of ZrO ₂ is dispersed in the Al ₂ O ₃ crystal. In addition, the problem of deteriorating the characteristics of the alumina crystal itself is caused.

In addition, Y ₂ O ₃ contained together with such ZrO ₂ functions as a partial stabilizer of ZrO ₂ , contributes to increasing the strength of the alumina zirconia sintered substrate, and provides a sintered body that gives such a substrate. It is a component that can improve the sinterability, and its content is in the range of 0.01 to 1 wt%. If the content of Y ₂ O ₃ is less than 0.01% by weight, ZrO ₂ may not be sufficiently stabilized, which may cause a reduction in the strength of the substrate and may cause sintering. Causes problems such as deteriorating sex. On the other hand, when the content of Y ₂ O ₃ exceeds 1% by weight, ZrO ₂ is completely stabilized, which may cause a decrease in substrate strength, and promotes abnormal grain growth of Al ₂ O _3. This also causes a problem that the strength of the substrate is lowered.

And, in the present invention, when sintering ZrO ₂ and Y ₂ O _{3 in the} proportions as described above and the remaining Al ₂ O ₃ , in the absence of a normal sintering aid, By controlling the grain growth of the Al ₂ O ₃ crystal grains, it was possible to effectively suppress the generation of the sintering aid phase and pores that become thermal resistance, and to achieve high strength. Here, high strength can be obtained without the use of a sintering aid because of the decrease in the low strength sintering aid phase present at the grain boundaries and the abnormalities in Al ₂ O ₃ particles due to the absence of the sintering aid. This is because the change from the intragranular fracture to the grain boundary fracture occurs due to the suppression of grain growth. On the other hand, when a sintering aid is added, the crystal particle diameter of Al ₂ O ₃ increases, the shape of the crystal particles becomes irregular, and high strength cannot be obtained. The generation of the agent phase and pores may cause a decrease in thermal conductivity. In addition, since the sintering aid added to the conventionally known alumina zirconia substrate has a very low thermal conductivity, when interposed in the Al ₂ O ₃ grain boundary, the thermal conductivity of the alumina zirconia substrate is reduced. This will cause a significant drop.

Therefore, in the present invention, the Al ₂ O ₃ crystal particles in the sintered body giving the alumina zirconia sintered substrate contribute to the increase in strength and thermal conductivity of the substrate by its homogeneous dispersion. The average crystal particle size is controlled to be larger than 2 μm and 7 μm or less, and in particular, adjusted to be in the range of 2.5 to 4.5 μm. When the average crystal particle diameter of Al ₂ O ₃ is 2 μm or less, the sintered body becomes insufficiently densified, leading to a decrease in strength and a decrease in thermal conductivity. If the particle diameter is larger than 7 μm, the variation of the crystal particle diameter becomes large, and the homogeneity cannot be maintained, which causes problems such as a decrease in strength.

Further, in the alumina zirconia sintered substrate according to the present invention as described above, as apparent from FIG. 1 showing an example of a scanning electron microscope (SEM) photograph of the crystal structure of the sintered body to give the grain boundary, As, ZrO ₂ grain boundary 1 in which Al ₂ O ₃ crystal grains and ZrO ₂ crystal grains are in contact, Al ₂ O ₃ grain boundary 2 in which Al ₂ O ₃ crystal grains are in direct contact, and Al _A first pore grain boundary 3 in which ₂ O ₃ crystal grains and pores existing in the grain boundary are in contact; a second pore grain boundary 4 in which ZrO ₂ crystal grains and pores existing in the grain boundary are in contact; Will exist. Therefore, they total length of the four grain boundary (grain boundary total length) Al ₂ O ₃ grain boundary length ratio to become Al ₂ O ₃ grain boundary relative lengths of the 2 to 2 for the inclusion of ZrO ₂ It depends on the amount and the sintered density. That is, if the content of ZrO ₂ is large, the relative length of the Al ₂ O ₃ grain boundary 2 decreases, and much of ZrO ₂ is present at the grain boundary triple point or is burned. If there are few pores inside the aggregate, the relative length of the Al ₂ O ₃ grain boundary 2 will increase.

In the present invention, the length of the Al ₂ O ₃ grain boundary 2, in other words, the grain boundary length in which Al ₂ O ₃ crystal grains are in direct contact with each other is 60 to the total grain boundary length. By adjusting the ratio to be at least%, the strength and thermal conductivity of the substrate are increased by homogenous dispersion of ZrO ₂ crystal particles. On the other hand, when the length of the Al ₂ O ₃ grain boundary 2 is less than 60% of the total grain boundary length, the length of the ZrO ₂ grain boundary 1 and the length of the first pore grain boundary 3, Since the length of the 2nd pore grain boundary 4 becomes large, it will become difficult to implement | achieve the target bending strength and heat conductivity.

The grain boundary lengths of the ZrO ₂ grain boundary 1, Al ₂ O ₃ grain boundary 2, first pore grain boundary 3 and second pore grain boundary 4 described above are the surface of the sintered substrate (sintered body). After mirror polishing, the grain boundaries are exposed by thermal etching at 1500 ° C., and then any three points on the exposed surface are each photographed with a scanning electron microscope at a magnification of 5000 times. The three secondary electron images in the 20 μm × 25 μm region can be obtained by actually measuring with the image analysis software WinROOF. Then, Al ₂ O ₃ grain boundary ratio is the ratio of the length of the Al ₂ O ₃ grain boundary 2 to intergranular total length is being calculated from them measured-obtained grain boundary length. That is, the Al ₂ O ₃ grain boundary ratio is the total length of the Al ₂ O ₃ grain boundary 2, the total length of the ZrO ₂ grain boundary 1, and the first pore grain boundary 3 respectively present in the aforementioned 20 μm × 25 μm region. This is the relative value of the total length of the Al ₂ O ₃ grain boundary 2 with respect to the sum of the total length and the total length of the second pore grain boundary 4, and is the minimum value among the three results obtained by the above three-point measurement. Thus, the Al ₂ O ₃ grain boundary ratio of the substrate is obtained.

As described above, in an alumina zirconia sintered substrate made of a sintered body containing Al ₂ O ₃ as a main component and containing ZrO ₂ and Y ₂ O ₃ in a predetermined ratio, the average crystal particle diameter of Al ₂ O ₃ is The grain boundary length is adjusted to be larger than 2 μm and equal to or smaller than 7 μm, and the grain boundary length in which the Al ₂ O ₃ crystal particles are in direct contact with each other is 60% or more of the total grain boundary length. Thus, the characteristics that the thermal conductivity is 30 W / m · K or more and the bending strength is 500 MPa or more can be advantageously realized. That is, by imparting a thermal conductivity of 30 W / m · K or more to the substrate, the heat dissipation characteristics of the substrate can be improved, and thus the heat dissipation of the module in which it is incorporated can be improved. In addition, since the bending strength of the substrate is 500 MPa or more, the substrate can be thinned, and the strength of the module can withstand the stress at the time of joining the metal plates. This can greatly contribute to the improvement of the above. If the thermal conductivity is less than 30 W / m · K, it cannot be used as a power module with a high load. If the bending strength is less than 500 MPa, the substrate is destroyed when the metal plates are joined. This will cause problems.

Incidentally, as to above, in the alumina zirconia sintered substrate according to the present invention (sintered body), with respect to the crystalline form of ZrO _2, less than 80 mol% of ZrO ₂ are, Shi desirable is tetragonal arbitrariness . Tetragonal ZrO ₂ phase-transforms to monoclinic ZrO ₂ due to external stress and absorbs fracture energy, thereby advantageously suppressing substrate breakdown. When tetragonal ZrO ₂ is less than 80 mol%, it is difficult to advantageously absorb external stress, and high strength may not be obtained.

In addition, the average crystal particle diameter of ZrO _{2 in} the sintered body is preferably in the range of 0.5 to ₂ μm in order to increase the strength of the substrate by homogenous dispersion. In order for the average crystal particle diameter of ZrO ₂ to be less than 0.5 μm, it is necessary to make the raw material powder finer, and there is a problem that sheet formability deteriorates, and it exceeds 2 μm. As a result, it becomes difficult to maintain the homogeneity of ZrO _{2 in} the sintered body, the characteristics of the sintered body itself are easily deteriorated, and it may be difficult to obtain high strength.

Further, it is desirable that the sintered body constituting the alumina zirconia sintered substrate is appropriately sintered and densified, and generally has a sintered density of 3.70 g / cm ³ or more. Configured to be. If this sintered density is too low, the sintered body will be insufficiently densified, and many pores will be present in the sintered body. It becomes easy to induce. The upper limit of the sintered density is generally 4.15 g / cm ³ , since when densification is promoted to further increase the sintered density, abnormal grain growth of Al ₂ O ₃ crystal grains is caused. It is desirable to set the degree.

In addition, even when the surface roughness (Ra) of the alumina zirconia substrate (sintered body) is as described above, it is preferably 0.3 μm or less in order to advantageously avoid the breakage due to concentration of external stress. When abnormal grain growth of Al ₂ O ₃ particles is induced, this surface roughness (Ra) becomes larger than 0.3 μm, and there is a possibility that strength is lowered.

  The alumina zirconia sintered substrate as described above is generally set to a substrate thickness within the range of 0.1 to 1.0 mm in order to reduce the thermal resistance by reducing the thickness of the substrate and improve the heat dissipation of the module. It is desirable. If the thickness of the substrate is less than 0.1 mm, it cannot withstand external stress and easily breaks, leading to a decrease in reliability. If the thickness is greater than 1.0 mm, the thermal resistance increases. As a result, there is a risk that the heat dissipation performance is lowered.

By the way, in manufacturing the alumina zirconia sintered substrate according to the present invention as described above, first, a mixture of Al ₂ O ₃ powder, ZrO ₂ powder and Y ₂ O ₃ powder, or Al ₂ O ₃ powder and ZrO ₂ —Y. _A raw material composition consisting of a mixture with ₂ O ₃ powder and not added with a sintering aid is prepared. Here, the ZrO ₂ —Y ₂ O ₃ powder is a powder obtained by pulverizing a fired product obtained by firing a mixture of a ZrO ₂ powder and a Y ₂ O ₃ powder in advance. ZrO ₂ powder obtained by dissolving Y ₂ O _{3 in 2} and partially stabilized with Y ₂ O ₃ is advantageously used. In addition, an appropriate amount of a surfactant as a dispersant and an organic solvent as a dispersion medium is blended in such a powder mixture, and the average particle diameter of the entire ceramic component (powder) is 0.5 μm to The mixture is pulverized and mixed so as to be about 2 μm. Further, after that, a binder, a plasticizer, and an organic solvent are added and mixed by stirring to prepare a slurry for sheet forming.

  Next, a green sheet is formed using the obtained slurry in accordance with a known sheet forming method such as a doctor blade method. Then, the green sheet is punched into a predetermined shape by press working to obtain a plate-like green molded product (substrate precursor).

Thereafter, by using the green molded product thus obtained and firing it, the intended alumina zirconia sintered substrate is formed. By this firing operation, the average crystal of Al ₂ O ₃ Since the particle diameter and the grain boundary length in which the Al ₂ O ₃ particles are in direct contact with each other are determined, the following firing operation is advantageously employed in the present invention. It will be.

That is, after heating the green molded product according to a conventional method and slowly raising the temperature to a temperature of about 500 ° C., the solvent, binder and plasticizer in the green molded product are removed, and then the temperature is 1200 ° C. The temperature is increased at a temperature increase rate of about 200 to 250 ° C./hour, and the temperature increase rate in the temperature range from 1200 ° C. to the maximum temperature between 1600 ° C. and 1700 ° C. is set to 500 ° C. to 1200 ° C. The temperature rise rate is lower than the temperature rise rate in the temperature range of ° C, and the temperature rises slowly, preferably 150 ° C / hour or less, more preferably 120 ° C / hour or less, particularly preferably 80 to 100 ° C / hour. Thus, by allowing the green molded product to proceed with the sintering, the average crystal particle diameter of Al ₂ O ₃ defined in the present invention and the Al ₂ O ₃ particles are in direct contact with each other. Therefore, the grain boundary length can be advantageously realized. And by holding at the highest temperature for a predetermined time, generally about 1 to 3 hours, densification of the sintered substrate obtained from the green molded product is promoted, and Al defined in the present invention _{The 2} O ₃ grain boundary will be realized in a better state. In addition, the temperature lowering operation after holding at such maximum temperature for a predetermined time, as in the past, slowly cools down to a temperature range where the substrate does not deform, and then slowly cools down to room temperature so that the substrate does not break down. You will be harassed.

In addition, as mentioned above, the maximum temperature reached in the firing operation of the green molded product is in the range of 1600 ° C. to 1700 ° C., but is preferably in the range of about 1620 to 1680 ° C. It will be. When the maximum temperature reached is lower than 1600 ° C., the sinterability becomes insufficient, so that the substrate is not sufficiently densified and it is difficult to obtain high strength. In general, firing is performed so that the sintered density is 3.70 g / cm ³ or more. In addition, when the maximum temperature reached in the firing operation is higher than 1700 ° C., the growth of Al ₂ O ₃ grains is promoted, causing a problem that the surface of the substrate (sintered body) becomes rough. Since the roughness of the substrate surface may concentrate external stress and become a substrate destruction source, even if the sintered density of the substrate is high, high strength is not always obtained. Therefore, it is desirable that the surface roughness (Ra) of the substrate be 0.3 μm or less.

  The alumina zirconia sintered substrate according to the present invention obtained by such a firing operation is generally formed as a plate having a thickness of 0.1 to 1.0 mm. The foil-like thin copper plate or aluminum plate is bonded to the at least one surface in accordance with a conventional method and used as a substrate for a semiconductor device. By sticking such a copper plate or an aluminum plate, the thermal conductivity or heat dissipation can be advantageously improved.

  Hereinafter, some examples of the present invention will be shown and the present invention will be more specifically clarified, but the present invention is not limited by the description of such examples. It goes without saying. In addition to the following examples, the present invention includes various changes and modifications based on the knowledge of those skilled in the art without departing from the spirit of the present invention, in addition to the specific description described above. It should be understood that improvements can be made.

First, as a ceramic raw material powder, an Al ₂ O ₃ powder having an average particle diameter (D ₅₀ , hereinafter the same) is 1.7 μm and 5% by weight of Y ₂ O ₃ were dissolved in ZrO ₂ . ZrO ₂ —Y ₂ O ₃ powder having an average particle diameter of 0.5 μm was prepared. As a sintering aid, a mixed powder having an overall average particle size of 2.4 μm, obtained by mixing and pulverizing magnesite, kaolin, and glass was prepared. And the raw material powder of Examples 1-4 and the raw material powder of Reference Examples 1-7 were comprised by using 2 or 3 types in those 3 types of powder in the ratio shown by following Table 1. FIG.

  Then, together with the combination of two or three kinds of raw material powders shown in Table 1, with respect to 100 parts by weight of the combination, 0.5 part by weight of a surfactant as a dispersant, xylene as a solvent, and 20 parts by weight of a mixed solution with isopropyl alcohol was put into a ball mill and pulverized and mixed so that the total average particle size was 1.18 to 1.52 μm. Further, polyvinyl butyral as a binder was further mixed. 5 parts by weight, 3 parts by weight of dioctyl adipate as a plasticizer, and 20 parts by weight of a mixed solution of xylene and isopropyl alcohol as a solvent were further added, and pulverization and mixing were continued for about 12 hours. Various slurries having an overall average particle size of 1.18 to 1.40 μm were prepared.

  Then, after forming a green sheet from each slurry according to a conventional method by a doctor blade method, a green molded product having a predetermined shape is obtained by punching the various green sheets obtained into a predetermined shape by pressing. Was made.

  And the alumina zirconia sintered substrate which concerns on a corresponding Example and a reference example was obtained by performing baking operation with respect to the obtained various green molded products, respectively. In addition, the baking operation with respect to the green molded article produced in Examples 1-4 is heating up slowly to the temperature to 500 degreeC, and after removing a binder and a plasticizer with a solvent completely, the temperature of 1200 degreeC Until the temperature is raised at a heating rate of about 200 to 250 ° C./hour and heated, and further heated to a temperature of 1650 ° C. at a heating rate of about 100 ° C./hour, Sintering is carried out slowly, and further, the obtained substrate is deformed after being promoted to be densified by holding it at 1650 ° C., which is the highest temperature, for 2 hours. Then, according to the method of slowly lowering the temperature so as not to break or break, the intended sintered substrates according to Examples 1 to 4 were obtained. Moreover, the firing operation of the green molded products according to Reference Examples 1 to 3 is performed in the same manner as the firing operation for the green molded products according to Examples 1 to 4 described above. Further, the green molded products according to Reference Examples 4 to 7 are performed. Are heated at a heating rate of 1200 ° C. to about 100 ° C./hour and sintered, respectively, except that the maximum temperature reached 1550 ° C. The same firing conditions as in No. 4 were adopted.

For the various alumina zirconia sintered substrates thus obtained, their sintered density, thermal conductivity, bending strength, Al ₂ O ₃ average crystal particle diameter, and Al ₂ O ₃ grain boundary ratio were measured, respectively. The results are also shown in Table 2 below. FIG. 2 plots and shows the relationship between the thermal conductivity and bending strength of each substrate according to Examples 1 to 4 and Reference Examples 1 to 3, and the partially stabilized zirconia content in each substrate. It was.

In measuring each characteristic, the sintered density was measured based on JIS R 1634: 1998 (measuring method of sintered ceramic density of fine ceramics), and the thermal conductivity was measured according to JIS R 1611: 2010 (fine (Measurement method of thermal conductivity by ceramic flash method), and bending strength was measured based on JIS R 1601: 2008 (Fine ceramics room temperature bending strength test method). In addition, the average crystal particle size of each substrate (sintered body) was obtained by performing a scanning electron microscope (SEM) observation after mirror-polishing the sintered body and performing thermal etching. It was calculated from the photograph by the intercept method. The Al ₂ O ₃ grain boundary ratio is measured according to the method described above.

As is apparent from the results of Table 2 and FIG. 2, partially stabilized zirconia, which is a solid solution of ZrO ₂ and Y ₂ O ₃ , is added to Al ₂ O ₃ without adding a sintering aid. In the alumina zirconia sintered substrate contained at a predetermined ratio, the average crystal particle diameter of Al ₂ O ₃ is larger than 2 μm and 7 μm or less as in Examples 1 to 4, and the grain boundary of Al ₂ O ₃ By configuring the ratio to be 60% or more, an alumina zirconia substrate having both high thermal conductivity and high bending strength can be obtained.

Further, as apparent from FIG. 2, the thermal conductivity shows a high value as the ZrO ₂ content decreases, but the substrate has a low bending strength. In addition, it is thought that the reason why the thermal conductivity of the substrate according to Reference Example 1 is low is that the sintering aid phase that becomes thermal resistance exists in the crystal structure because the content of the sintering aid is large. It is done. The reason why the bending strengths of Reference Examples 2 and 3 are low is that the crystal grain size of Al ₂ O ₃ increases due to the inclusion of the sintering aid, and the ratio of the ZrO ₂ grain boundary length to the pore grain boundary length is relative. This is probably because the Al ₂ O ₃ grain boundary ratio was less than 60%.

Furthermore, in the alumina zirconia sintered substrates according to Reference Examples 4 to 7, although the sintering aid is not contained, since the sintering is not sufficiently performed in the firing step, Al ₂ O _{3 has} an average crystal grain size of 2 μm or less, and the Al ₂ O ₃ grain boundary ratio is lower than 60%, and thus it is recognized that the substrate has a low thermal conductivity. It is done.

1 ZrO ₂ grain boundary 2 Al ₂ O ₃ grain boundary 3 First pore grain boundary 4 Second pore grain boundary

Claims (10)

Raw material comprising a mixture of Al ₂ O ₃ powder, ZrO ₂ powder and Y ₂ O ₃ powder, or a mixture of Al ₂ O ₃ powder and ZrO ₂ —Y ₂ O ₃ powder, to which no sintering aid is added The composition is composed of a sintered body obtained by firing, ZrO ₂ : 2 to 15% by weight, Y ₂ O ₃ : 0.01 to 1% by weight, and Al ₂ O ₃ : the balance,
The average crystal particle diameter of Al ₂ O ₃ is larger than 2 μm and 7 μm or less, and the grain boundary length where the Al ₂ O ₃ particles are in direct contact is 60% or more of the total grain boundary length. An alumina zirconia sintered substrate for a semiconductor device, characterized by having a thermal conductivity of 30 W / m · K or more and a bending strength of 500 MPa or more. _{2. The} alumina zirconia sintered substrate for a semiconductor device according to claim 1, wherein an average crystal particle diameter of the Al ₂ O ₃ is 2.5 to 4.5 μm. 3. The alumina zirconia sintered substrate for a semiconductor device according to claim 1, wherein 80 mol% or more of ZrO ₂ in the sintered body is a tetragonal crystal. 4. The alumina zirconia sintered substrate for a semiconductor device according to claim 1, wherein an average crystal particle diameter of ZrO ₂ in the sintered body is 0.5 to ₂ μm. The alumina zirconia sintered substrate for a semiconductor device according to any one of claims 1 to 4, wherein the sintered body has a sintered density of 3.70 g / cm ³ or more.   6. The alumina zirconia sintered substrate for a semiconductor device according to claim 1, wherein the sintered body has a surface roughness (Ra) of 0.3 μm or less.   The alumina zirconia sintered substrate for a semiconductor device according to any one of claims 1 to 6, wherein the substrate thickness is in a range of 0.1 to 1 mm.   The alumina zirconia sintered substrate for a semiconductor device according to any one of claims 1 to 7, wherein a copper plate or an aluminum plate is bonded to at least one surface of the substrate. 9. The semiconductor device according to claim 1, wherein the ZrO ₂ —Y ₂ O ₃ powder is a partially stabilized zirconia powder obtained by dissolving Y ₂ O ₃ in ZrO _2. Alumina zirconia sintered substrate. A method for producing an alumina zirconia sintered substrate for a semiconductor device according to any one of claims 1 to 9,
Raw material comprising a mixture of Al ₂ O ₃ powder, ZrO ₂ powder and Y ₂ O ₃ powder, or a mixture of Al ₂ O ₃ powder and ZrO ₂ —Y ₂ O ₃ powder, to which no sintering aid is added During firing of the composition, the temperature increase rate in the temperature range from 1200 ° C. to the highest temperature between 1600 ° C. and 1700 ° C. is made smaller than the temperature increase rate in the temperature range of 500 ° C. to 1200 ° C. A method for producing an alumina zirconia sintered substrate for a semiconductor device.