JPWO2020090832A1 - Manufacturing method of silicon nitride substrate and silicon nitride substrate - Google Patents

Abstract

A plurality of green sheets containing silicon nitride powder and a sintering aid are laminated with a separating material interposed therebetween, sintered, and then separated to obtain a plurality of silicon nitride sintered bodies. A method for producing a silicon nitride substrate, which obtains a silicon nitride substrate from a silicon nitride sintered body, characterized in that the separating material contains silicon nitride powder. Since the obtained silicon nitride substrate does not contain boron nitride powder on its surface, it has excellent heat cycle properties when bonded to copper. The separating material has a specific surface area measured by the BET method of 1 m2 / g or more and 20 m2 / g or less, a volume-based 50% particle diameter D50 measured by the laser diffraction / scattering method of 20 μm or less, and an oxygen content. Is 0.3% by weight or more and less than 2% by weight, and by applying the separating material to the surface of the green sheet at a coating amount of 0.1 mg / cm2 or more and 3 mg / cm2 or less, the thermal conductivity is 80 W / (m) at room temperature. -K) or more, and a silicon nitride substrate having a four-point bending strength of 800 MPa or more at room temperature can be obtained.

Description

The present invention relates to a method for manufacturing a silicon nitride substrate used for an insulating substrate and a circuit board, and a silicon nitride substrate manufactured by this manufacturing method.

In recent years, various ceramic (sintered) substrates have been widely used as substrates for semiconductor modules and structural members. For example, a substrate for a semiconductor module on which a semiconductor element having a large power and a large calorific value is mounted is required to have high mechanical strength, high thermal conductivity, and high electrical insulation. Nitride sintered bodies such as aluminum nitride and silicon nitride are excellent in these characteristics, and these nitride sintered body substrates are widely used.

The nitride sintered body, which is the _{basis of the nitride substrate, is produced by sintering a green sheet containing nitride (AlN, Si 3} N _4, etc.) powder as a main component in a high-temperature nitrogen atmosphere. At this time, a general manufacturing method is to manufacture a nitride sintered body having a large area and cut out a plurality of the above-mentioned substrates having a desired size from the sintered body. This sintering is performed using an electric furnace or the like, but in order to reduce the manufacturing cost, a method of obtaining a plurality of nitride sintered bodies at the same time by laminating and sintering a plurality of green sheets is used. Be done.

At the time of this sintering, in order to prevent adhesion between the laminated nitride sintered bodies, the green sheet to be the nitride sintered body is laminated after applying a separating material on the surface. After sintering, a plurality of nitride sintered bodies can be separated by a separating material.

Since a nitride sintered body such as aluminum nitride or silicon nitride needs to be sintered at a high temperature of 1600 ° C. or higher, stable boron nitride (BN) powder at a high temperature of 1600 ° C. or higher is generated between the nitride sintered bodies. It is widely used as a separating material to improve peelability.

As described above, since the BN powder is sintered while being interposed between the nitride sintered bodies, the nitride sintered body is restrained at the time of sintering or reacts with the nitride sintered body. By doing so, it must be prevented from being deformed. Therefore, it is necessary to select the manufacturing conditions such as the properties of the BN powder to be used and the method of applying the BN powder.

Patent Document 1 describes a plate-shaped ceramic sintered body in which a plurality of green sheets are laminated with a release material made of highly heat-resistant fine particles interposed between them, and the laminated green sheet is fired while being pressed in the laminating direction. The manufacturing method is disclosed. In the present invention, it is described that warpage and cracks at the time of sintering are prevented, and the stacked sheets can be easily peeled off without sticking. However, there is no description about the silicon nitride thin plate as the ceramic sintered body, and there is no description about using the silicon nitride powder as the release material in the production of the silicon nitride thin plate.

In Patent Document 2, the separating material is a boron nitride (BN) powder having an oxygen content of 0.01 to 0.5% by weight, an average particle diameter of 4 to 20 μm, and a specific surface area of 20 m ² / g or less, and the BN powder is 0. A method for producing a silicon nitride substrate to be applied to the surface of a green sheet at a coating amount of .05 to 1.4 mg / cm ^{2 is disclosed.} The present invention describes providing a silicon nitride substrate having good peelability, high relative density, high strength, high thermal conductivity, and little deformation. However, the bending strength is 790 MPa or less, and the thermal conductivity is 93 W / mK or less.

Patent Document 3 describes a silicon nitride substrate made of silicon nitride particles and a silicon nitride sintered body containing a sintering aid composed of at least magnesium oxide, and the silicon nitride particles have a minor axis a of 0.5. When columnar crystal particles with an area ratio of ~ 5 μm and a major axis b ratio (b / a) of 2 or more to a minor axis a are contained in an area ratio of 30% or more, and the arithmetic average roughness Ra of the surface of the substrate in the first half is 0.3 to 2 μm or more. Yes, the ratio of BN and silicon nitride remaining on the substrate surface is more than ^{6.5 × 10-5 and 300 × 10-5} or less in the ratio (B / Si) of the fluorescent X-ray intensity of B and the fluorescent X-ray intensity of Si. A method for manufacturing a silicon nitride substrate, a silicon nitride substrate, and a circuit substrate using the same are disclosed. However, by setting the residual amount of boron nitride, which is a separating material remaining on the surface of the silicon nitride substrate, to an appropriate range, the heat cycle resistance when the copper plates are joined is improved, but the bending strength is 750 MPa or more and 830 MPa or less. Is.

Japanese Unexamined Patent Publication No. 1-87574 Japanese Unexamined Patent Publication No. 2011-178598 Japanese Unexamined Patent Publication No. 2011-216577 International Publication No. 2013/146713

According to these conventional techniques, by applying boron nitride, which is a separating material, to the surface of a ceramic green sheet, a plurality of green sheets are laminated and sintered, and then the peelability is good and the silicon nitride is less deformed. A silicon substrate can be obtained, but since boron nitride, which is a separating material, remains on the surface of the substrate, there is a problem in heat cycle resistance when the copper plates are joined, and it is desired to improve the heat cycle resistance.

Further, in these conventional techniques, thermal conductivity or mechanical characteristics tend to be insufficient for semiconductor modules whose heat generation amount is increasing more and more in recent years, and in particular, stable heat dissipation is ensured even in a high temperature region during operation. In the present situation where is further desired, there is also a problem that the performance is insufficient in terms of both thermal conductivity and mechanical properties.

For example, in order to improve heat cycle resistance, a method of reducing the amount of boron nitride (BN) separating material applied to the surface of the green sheet, or strengthening processing conditions such as wrapping or honing the surface of the silicon nitride sintered body. Then, by adopting a method of forcibly removing the BN separator and setting the B / Si fluorescent X-ray intensity ratio, which represents the ratio of BN and silicon nitride remaining on the substrate surface, to 5 × 10 ^-5 or less, As defects remain or damage occurs on the surface of the silicon nitride sintered body, its bending strength decreases.

In Patent Document 3, in a silicon nitride substrate made of silicon nitride particles and a silicon nitride sintered body containing a sintering aid composed of at least magnesium oxide, the silicon nitride particles have a minor axis a of 0.5 to 5 μm. In addition, columnar crystal particles having a major axis b ratio (b / a) of 2 or more to a minor axis a are contained in an area ratio of 30% or more, the arithmetic average roughness Ra of the substrate surface is 0.3 to 2 μm, and the substrate surface. The ratio of BN and silicon nitride remaining in is an appropriate range in which the ratio of fluorescent X-ray intensity of B to fluorescent X-ray intensity of Si (B / Si) ^{exceeds 6.5 × 10-5} and is 300 × ^{10-5 or less.} By doing so, the bonding strength when the copper plate is bonded to the surface of the silicon nitride substrate is increased, and the heat cycle resistance is improved. However, in the method of Patent Document 3, the separating material is formed by forming recesses having a predetermined depth on the surface of the substrate by setting the area ratio of the columnar crystal particles having a b / a ratio of 2 or more to 30% or more. Since the heat cycle resistance is improved by a method in which the BN remains in the concave portion and the BN does not exist on the outermost surface, the unevenness on the surface of the silicon nitride substrate is increased. Therefore, the bending strength of the silicon nitride sintered body remains at the level of 830 MPa or less.

By using silicon nitride powder instead of the conventional boron nitride powder as the separating material, the present inventors can solve the problem that the heat cycle property when bonded to copper is not sufficient, and have predetermined characteristics. It has been found that by using the silicon nitride powder, both the above-mentioned problem of lowering the bending strength and the problem of insufficient durability against the heat cycle can be solved at once.

That is, the present invention has been made in view of the above problems, and is a silicon nitride substrate having excellent heat cycle property when bonded to copper, a method for producing the same, and much higher strength and heat than the prior art. It is an object of the present invention to provide a silicon nitride substrate which is conductive and has little deformation and a method for producing the same.

The present inventors have conducted intensive studies to solve the above problems, and can use silicon nitride (SN) powder instead of silicon nitride (BN) powder as a separating material for producing a silicon nitride substrate. As a result, a silicon nitride substrate having excellent heat cycle resistance can be obtained, and a coating amount of silicon nitride (SN) powder having a specific specific surface area, particle size, and oxygen content and a low aluminum content as a separating material. The present invention has been made by finding that a silicon nitride substrate having good peelability, high strength, high thermal conductivity, and little deformation can be obtained by setting the production conditions such as the above to a specific range. That is, the present invention relates to the following.

[Aspect 1] A plurality of green sheets containing silicon nitride powder and a sintering aid are laminated by arranging a separating material between them, and the separating material contains silicon nitride powder.
The plurality of green sheets in the obtained laminate are sintered and
By separating from the laminate, a plurality of silicon nitride sintered bodies can be obtained.
A silicon nitride substrate is obtained from the silicon nitride sintered body.
A method for manufacturing a silicon nitride substrate, which is characterized by the above.

[Aspect 2] The method for producing a silicon nitride substrate according to Aspect 1, wherein the sintering of the plurality of green sheets is performed in a silicon nitride enclosure or a boron nitride enclosure.

[Aspect 3] The method for producing a silicon nitride substrate according to Aspect 1 or 2, wherein the plurality of green sheets are covered with silicon nitride powder to perform the sintering.

[Aspect 4] The method for producing a silicon nitride substrate according to any one of aspects 1 to 3, wherein the separating material remaining on the surface of the silicon nitride sintered body obtained after the sintering is removed. ..

[Aspect 5] The separating material has a specific surface area measured by the BET method of 1 m ² / g or more and 20 m ² / g or less, and a volume-based 50% particle diameter D50 measured by the laser diffraction / scattering method is 20 μm or less. And the amount of oxygen is 0.3% by weight or more and less than 2% by weight.
The silicon nitride substrate according to any one of aspects 1 to 4, wherein the separating material is ^{applied to the surface of the green sheet at a coating amount of 0.1 mg / cm 2} or more and 3 mg / cm ^{2 or less.} Manufacturing method.

[Aspect 6] The method for producing a silicon nitride substrate according to Aspect 5, wherein the aluminum content of the separating material is less than 50 ppm.

[Aspect 7] Aspect 5 is characterized in that the sintering is carried out in a nitrogen atmosphere at a gas pressure of 0.15 MPa or more and 3 MPa or less and a sintering temperature of 1750 ° C. or more and 1910 ° C. or less for 6 hours or more and 22 hours or less. Alternatively, the method for manufacturing a silicon nitride substrate according to 6.

[Aspect 8] A silicon nitride substrate made of a silicon nitride sintered body containing silicon nitride particles and a sintering aid, having a thickness of 0.5 mm or less and having boron nitride powder on the surface of the substrate. A silicon nitride substrate characterized by not being used.

^{[Aspect 9] The ratio of boron nitride to silicon nitride on the surface of the substrate is 15 × 10 -5} or less in terms of the ratio (B / Si) of the fluorescent X-ray intensity of boron (B) to the fluorescent X-ray intensity of silicon (Si). The silicon nitride substrate according to aspect 8, wherein the silicon nitride substrate is characterized by the above.

[Aspect 10] The silicon nitride substrate according to aspect 8, wherein the substrate does not contain boron nitride (BN).

[Aspect 11] A silicon nitride substrate made of a silicon nitride sintered body containing silicon nitride particles and a sintering aid, wherein the silicon nitride particles have a minor axis a of 0.5 to 5 μm and a minor axis a with respect to the minor axis a. Columnar crystal particles having a major axis b ratio (b / a) of 2 or more have an area ratio of 35% or less on the substrate surface, and the arithmetic average surface roughness of the substrate surface is 0.03 μm or more and 0.5 μm or less. ^{The ratio of boron nitride to silicon nitride on the surface of the substrate is 15 × 10-5} or less in terms of the ratio (B / Si) of the fluorescent X-ray intensity of boron (B) to the fluorescent X-ray intensity of silicon (Si). A characteristic silicon nitride substrate.

[Aspect 12] The silicon nitride substrate according to aspect 11, wherein the surface of the substrate does not have boron nitride powder.

[Aspect 13] The silicon nitride substrate according to Aspect 11 or 12, wherein the thermal conductivity is 80 W / (m · K) or more at room temperature, and the four-point bending strength is 800 MPa or more at room temperature.

[Aspect 14] The silicon nitride substrate according to any one of aspects 11 to 13, wherein the aluminum content of the separating material is less than 50 ppm.

[Aspect 15] The silicon nitride substrate according to any one of aspects 11 to 14, characterized in that the thickness is 0.5 mm or less.

[Aspect 16] An insulating substrate and a circuit board, wherein the silicon nitride substrate according to any one of aspects 8 to 15 is used.

According to the silicon nitride substrate of the present invention, since boron nitride (BN) powder is not present on the surface of the substrate, the heat cycle resistance when the copper plates are joined is improved, and a silicon nitride substrate that can be used stably for a long period of time can be obtained. be able to.

Further, according to the present invention, when a plurality of green sheets are laminated via an SN separator and then the silicon nitride sintered body is sintered, the plurality of silicon nitride sintered bodies can be easily peeled off and have high strength. , A silicon nitride substrate having high thermal conductivity and little deformation can be obtained. In particular, the present invention is particularly effective in the case of a silicon nitride sintered body using magnesium oxide as a sintering aid.

It is a figure which shows the state which laminated the green sheet 2 in the manufacturing method of the silicon nitride substrate of this invention. It is a figure which shows the state which the green sheet 2 was laminated and packed powder 5 in the manufacturing method of the silicon nitride substrate of this invention. It is a schematic diagram which shows the fine structure of the silicon nitride particle 8 and the separating material 9 on the surface of the silicon nitride sintered body.

The method for manufacturing the silicon nitride substrate and the silicon nitride substrate of the present invention will be described in detail. The silicon nitride substrate of the present invention is suitably used as an insulating ceramic substrate.

[First aspect: use of silicon nitride powder as a separating material]
In this aspect of the invention,
"A plurality of green sheets containing silicon nitride powder and a sintering aid are laminated by arranging a separating material between them, and the separating material contains silicon nitride powder.
The plurality of green sheets in the obtained laminate are sintered and
By separating from the laminate, a plurality of silicon nitride sintered bodies can be obtained.
A silicon nitride substrate is obtained from the silicon nitride sintered body.
A method for manufacturing a silicon nitride substrate, which is characterized by this. "
"A silicon nitride substrate made of a silicon nitride sintered body containing silicon nitride particles and a sintering aid, having a thickness of 0.5 mm or less and having no boron nitride powder on the surface of the substrate. Silicon Nitride Substrate Featuring
Is provided.

Conventionally, when a plurality of green sheets containing silicon nitride powder and a sintering aid are laminated and sintered via a separating material, the sintering or reaction temperature is higher than the sintering temperature of the raw material silicon nitride powder. Boron nitride powder having the above is used as a separating material, and silicon nitride powder is not used as a separating material for sheet-shaped silicon nitride sintering. However, contrary to the expectation of the prior art, the present inventor can unexpectedly use the silicon nitride powder as a separating material for sheet-shaped silicon nitride sintering, and the boron nitride powder on the surface of the plate-shaped sintered body. It was found that it is an excellent separating material having an effect of improving the heat cycle property when copper is bonded to the obtained silicon nitride substrate because the residue does not remain. The silicon nitride powder does not react with the base material at all because the separating material does not react at all with the base material to be sintered, but rather cannot function as a separating material unless it reacts with the base material to some extent. It was confirmed that it is excellent as a separating material for plate-shaped silicon nitride sintering in that it is not excluded from its use as a material and is not a foreign substance (impurity) with respect to the base material.

In this aspect of the present invention, in the method for manufacturing a silicon nitride substrate, first, as a raw material preparation / mixing step, an organic solvent is used as a dispersion medium of ceramic powder as a sintering aid in silicon nitride powder, and a ball mill or the like is used. It is mixed and further mixed with a binder and a plasticizer to prepare a slurry.

As the silicon nitride powder, any silicon nitride powder used as a raw material for producing a silicon nitride substrate by a sheet molding method and sintering of a green sheet can be used, but a preferable silicon nitride powder has a specific surface area of 10.0 m. ^It may be 2 / g or more, the oxygen content is 1.0 wt% or more, and the aluminum content may be less than 100 ppm, more preferably the specific surface area is 13.0 m ² / g or more and the oxygen content is 1.2 wt% or more. It is 2.3 wt% or less and the aluminum content is less than 50 ppm. In one embodiment, the silicon nitride powder may have a specific surface area of 25.0 m ² / g or less and an oxygen content of 2.3 wt% or less.

As the sintering aid, any sintering aid used in the production of the silicon nitride substrate can be used, and the oxide sintering aid is preferably used without particular limitation. Examples of oxides include magnesium oxide and oxides of rare earth elements, and examples of rare earth elements include Y, La, Ce, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu. However, oxide Y ₂ O ₃ is preferable. For example, silicon dioxide may be used as the sintering aid.

For example, the amount of magnesium oxide added is in the range of 0.5% by mass to 4% by mass and the amount of rare earth element oxide added is in the range of 1.5% by mass to 15% by mass with respect to 98% by mass to 81% by mass of the silicon nitride raw material. The amount of magnesium oxide added is 1.0% by mass to 3% by mass, and the amount of rare earth element oxide added is 1 with respect to 97.5% by mass to 91% by mass of the silicon nitride raw material. It may be in the range of .5% by mass to 6% by mass.

Magnesium oxide (MgO) and an oxide of a rare earth element (RExOy) are preferable as the sintering aid in order to obtain a silicon nitride substrate having high thermal conductivity. Since magnesium oxide forms a liquid phase at a relatively low temperature, it is possible to promote the sintering of the silicon nitride sintered body, and it is difficult to dissolve in the silicon nitride particles, so that the thermal conductivity of the silicon nitride substrate is high. can do. Examples of rare earth elements include Y, La, Ce, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, etc. Among them, Y oxide Y ₂ O ₃ is silicon nitride. It is effective for increasing the density of the substrate, which is more preferable.

Next, as a molding step, the viscosity of the slurry produced by the above mixing is adjusted as necessary, and this is molded into a sheet having a predetermined thickness by a doctor blade method, an extrusion molding method, or a method similar thereto. The plate thickness of the sheet molded product at this time can be appropriately determined depending on the application such as a semiconductor power module, but it should be in the range of about 0.1 mm to 0.6 mm, and further, about 0.2 mm to 0.5 mm. Further, it is preferably in the range of about 0.2 mm to 0.40 mm. The plate thickness of the sheet molded product shall be the average value of the measured values at any ten or more points.

Next, after cutting the green sheet into a desired shape, a separating material is applied to one or both sides of the cut green sheet, and then a plurality of green sheets coated with the separating material are laminated and sintered. It is preferable to apply a separating material to the lower side of the lowermost layer and the upper side of the uppermost layer of the laminate, but it is not necessary to apply the separating material.

The separating material used in the present invention and the first aspect is a powder containing silicon nitride (SN) powder. According to the present invention and the first aspect, by using silicon nitride (SN) powder as a separating material between the green sheets of silicon nitride, boron nitride is applied to the surface of the silicon nitride sintered body after sintering as in the prior art. Since the (BN) powder does not remain and even if it does remain, it is silicon nitride (SN) powder, so that the heat cycle property when the silicon nitride substrate is bonded to copper can be excellent. Although only silicon nitride (SN) powder can be preferably used as the separating material, a part of boron nitride (BN) powder may be contained as long as the effect of using silicon nitride (SN) powder as the separating material can be obtained. .. For example, boron nitride (BN) powder may be contained in an amount of 30% by weight or less, and further 10% by weight or less. However, since only silicon nitride (SN) powder is preferably used as the separating material in the present invention, it will be described below assuming that silicon nitride (SN) powder is used as the separating material unless otherwise specified.

The specific surface area of the separating material is preferably such that the specific surface area measured by the BET method is 1 m ² / g or more and 20 m ² / g or less. The specific surface area of the separating material is selected in consideration of the adhesion of the separating material to the surface of the green sheet. If the specific surface area is too small and the adhesion is insufficient, it will be easy to peel off during handling, while if the specific surface area is too large, it will react significantly with the sintering aid in the green sheet during sintering, and the sintered body will react through the separating material. There is a risk that they will stick to each other and cannot be peeled off. The specific surface area is ^{more preferably 1 m 2} / g or more and 12 m ² / g or less, 2 m ² / g or more and 7 m ² / g or less.

As the average particle size of the separating material, it is preferable that the volume-based 50% particle size (D50) measured by the laser diffraction / scattering method is 20 μm or less. If the D50 of the separating material is too large, the adhesion of the separating material to the green sheet deteriorates and it is easy to peel off during handling. D50 is more preferably 10 μm or less, 5 μm or less, 3 μm or less, and 2 μm or less. D50 may be 1 μm or less. The lower limit of D50 is not limited, but D50 may be 0.3 μm or more. The volume-based 50% particle size (D50) means a particle size in which the cumulative value of the volume-based particle size is 50% of the total cumulative value.

The oxygen content of the separating material is preferably 0.1% by mass or more and less than 2.0% by mass. The amount of oxygen in the separating material is such that the separating material reacts appropriately with the sintering aid component of the silicon nitride sintered body during sintering and is present on the surface of the silicon nitride sintered body, and the adjacent silicon nitride sintered body is present. It is desirable to select a range that can prevent the silicon nitride sintered body from being deformed while preventing the bodies from adhering to each other and improving the peelability. If the amount of oxygen is too large, it reacts remarkably with the sintering aid in the green sheet at the time of sintering, and the sintered bodies stick to each other via the separating material and cannot be peeled off. In particular, this phenomenon is likely to occur when magnesium oxide is used as the sintering aid, and becomes remarkable when the thickness of the silicon nitride substrate is 0.1 to 0.6 mm. On the other hand, if the amount of oxygen is too small, the reaction between the separating material and the silicon nitride sintered body hardly occurs during sintering, so the separating material may move on the substrate surface due to sintering shrinkage, and is applied to the surface of the green sheet. The uniformity of the separated material is impaired, a place where the abundance ratio of the separating material is low is generated, and the adjacent silicon nitride sintered bodies are adhered to each other, and the peelability is impaired. From the above viewpoint, the oxygen content of the separating material is more preferably 0.3 to less than 2.0% by mass and more preferably 0.3 to 1.2% by mass.

The aluminum content of the separating material is preferably less than 100 ppm. If the aluminum content is too high, the amount of aluminum that dissolves inside the β-type silicon nitride particles after sintering increases. Phonon scattering by solid-melted aluminum ions causes a decrease in thermal conductivity, which is not preferable because the thermal conductivity of the obtained silicon nitride substrate is reduced. The preferable range of the aluminum content is 50 ppm or less, more preferably 40 ppm or less.

The amount of the separating material applied to the surface of the green sheet ^{is preferably 0.1 mg / cm 2} or more and 4.0 mg / cm ² or less. If the amount of the separating material applied is too large, a large amount of separating material easily enters between the silicon nitride particles on the surface of the silicon nitride sintered body during the sintering process and hinders shrinkage, so that the density of the silicon nitride sintered body decreases. However, the strength is also reduced. On the other hand, if the amount of the separating material applied is too small, there will be places where the separating material is insufficient, and due to the reaction between the adjacent silicon nitride sintered bodies, the silicon nitride sintered bodies will adhere to each other and can be peeled off. It disappears. From the above viewpoint, the preferable coating amount of the separating material is 0.1 mg / cm ² or more and 3 mg / cm ² or less, and more preferably 0.2 mg / cm ² or more and 1 mg / cm ² or less.

As a method of applying the separating material, in order to apply it uniformly to the surface of the green sheet, after preparing a slurry in which the separating material is dispersed in an organic solvent, it is atomized by a spray-type coating machine and applied to one or both sides. Alternatively, the separating material may be applied directly to one side or both sides with a brush. Here, when producing the slurry, it is preferable to mix the separating material and the organic solvent using silicon nitride balls. The reason why the slurry is prepared by using an organic solvent is that when the slurry is prepared by using water, the amount of oxygen in the separating material increases in the presence of water and the peelability deteriorates. The ratio of the separating material to the organic solvent is appropriately in the range of about 1/10 to 1/2 of the separating material / organic solvent in terms of weight ratio. Further, the reason for mixing using the silicon nitride balls is to crush the agglomeration of the separating material and uniformly disperse it.

A slurry in which the separating material is dispersed in an organic solvent is applied, and several to several tens of dried green sheets are stacked and laminated, and then degreasing is performed to remove organic components such as binders in the green sheet. .. The degreasing is preferably performed in the air at 900 ° C. or lower, or in an inert atmosphere such as nitrogen or argon. The number of green sheets to be laminated is preferably 5 to 50.

After the degreasing step, the green sheet is sintered (sintering step). FIG. 1 is a cross-sectional view showing an example of a state in which a plurality of green sheets 2 are laminated with a separating material 1 interposed therebetween, placed on a setter 3, surrounded by a spacer 4, and further pressed by the setter 3. The upper and lower setters 3 and the surrounding spacers 4 form a surrounding body of a plurality of laminated bodies of the green sheets 2. The laminate of the plurality of green sheets 2 surrounded by the setter 3 and the surrounding spacer 4 is arranged in a heating furnace and heated to a predetermined temperature. In the present invention, the setter 3 and the spacer 4 may be made of boron nitride, but are preferably made of silicon nitride. If the setter 3 and the spacer 4 are made of boron nitride, boron nitride diffuses from the setter 3 and the spacer 4 into the sintered body at the time of sintering. Therefore, it is preferable to use the setter 3 and the spacer 4 made of silicon nitride. The silicon nitride setter 3 and spacer 4 may be made of a silicon nitride sintered body, but the temperature is higher than the maximum sintering temperature of the green sheet 2 in order to suppress evaporation of a sintering aid and the like from the silicon nitride sintered body. Those fired at a temperature may be used. Further, referring to FIG. 2, even when the boron nitride setter 3 and the spacer 4 are used, the silicon nitride powder can be wrapped around the laminate of the plurality of green sheets 2 with the stuffing powder 5 to nitrid the mixture. It is preferable because it is possible to prevent the vapor diffusion of boron nitride from the boron-made setter 3 and the spacer 4 to the sintered body. Further, a silicon nitride setter 3 and a spacer 4 may be used, and the silicon nitride powder may be covered with the filling powder 5. In the present invention, the apparatus for heat-treating a laminate of a plurality of green sheets 2 having silicon nitride powder as a separating material is not limited to the embodiments shown in FIGS. 1 and 2.

The laminate of green sheets with the separating material interposed is degreased and sintered. The laminated body of the green sheet with the separating material interposed therebetween may be placed on the heat-resistant setter, the side surface may be surrounded by the heat-resistant spacer, and then the top surface may be heated while being pressed by the heat-resistant setter. The setter and the spacer (in the present specification, the setter and the spacer are collectively referred to as a surrounding body) are made of conventional boron nitride (BN) or, according to the present invention, preferably made of silicon nitride (SN). Can be done. Even if the enclosure is made of boron nitride (BN), if silicon nitride (SN) powder is used as the separating material, the boron nitride (BN) powder does not remain on the surface of the silicon nitride substrate after sintering, so that the obtained nitridation can be obtained. The silicon substrate can be excellent in heat resistance and heat cycle property when bonded to copper. Further, since the boron nitride (BN) powder is not used, the content of BN contained on the surface of the silicon nitride substrate can be remarkably reduced. Further, if the surrounding body is made of silicon nitride (SN), contamination due to vapor diffusion of BN can be completely prevented. Further, by packing silicon nitride (SN) powder around the laminated body of the green sheet and sintering it, it is possible to prevent BN from being mixed.

The degreased green sheet may be vacuumed at 10 Pa or less to remove residual gas, and then sintered in a vacuum or in an inert atmosphere such as a rare gas, but preferably in an atmosphere substituted with nitrogen.

The nitrogen atmospheric pressure may be, for example, a high pressure of 10 MPa or less, but preferably a low pressure of 0.15 MPa or more and 3 MPa or less. High pressure is costly, while if the atmospheric gas pressure is too low, it becomes difficult to raise the maximum holding temperature during sintering to a suitable firing temperature.

The sintering temperature may be, for example, 1600 ° C. or higher and 1950 ° C. or lower, but more preferably 1750 ° C. or higher and 1900 ° C. or lower, and for example, 1790 ° C. or higher and 1880 ° C. or lower. If the maximum holding temperature at the time of sintering is low, the progress rate of sintering is slow, and it is difficult to obtain a dense silicon nitride substrate. Alternatively, even if a dense silicon nitride substrate can be obtained at a low maximum holding temperature, the growth of columnar β-type silicon nitride particles is insufficient, so that only a silicon nitride substrate having a low thermal conductivity can be obtained. It is difficult to increase the conductivity. If the maximum holding temperature is too high, the growth of columnar β-type silicon nitride particles becomes extremely fast, the surface irregularities of the silicon nitride substrate become large, and the reaction between adjacent silicon nitride sintered bodies causes the silicon nitride sintered bodies to grow together. Will adhere, making peeling difficult.

The holding time at the sintering temperature, particularly the maximum holding temperature, may be generally 4 hours or more and 30 hours or less, but is preferably about 6 hours or more and 22 hours or less, and changes depending on the profile of the firing temperature and the like. You can do it.

Since the surface of the silicon nitride sintered body does not contain boron nitride powder, it may be used as it is as a silicon nitride substrate, but it is preferable to perform surface treatment such as blasting. In the blasting process, for example, by injecting 10 to 100 μm SiC abrasive particles onto the surface of the silicon nitride substrate, the silicon nitride particles protruding from the surface are scraped off, the surface roughness is reduced, and the bondability with the metal plate is improved. To carry out. The surface depth (thickness) of the silicon nitride substrate removed by blasting or wrapping may be, for example, 30 μm or less, but preferably 20 μm or less, further 10 μm or less, and particularly 5 μm or less. It may be there. According to the first aspect of the present invention, it is possible to remove the separating material and realize excellent surface properties with a minimum of blasting.

By adopting the above-mentioned method for manufacturing a silicon nitride substrate, a plurality of silicon nitride sintered bodies can be easily peeled off, and the unevenness on the surface of the sintered body is controlled to an appropriate level, so that the silicon nitride has high strength. Moreover, it is possible to obtain a silicon nitride substrate with less deformation. In addition, since BN powder is not present on the surface of the silicon nitride substrate, and because the substrate does not contain BN or contains only a very small amount, the heat cycle resistance when the copper plates are joined is improved and stable for a long period of time. Can be used.

According to this aspect, by using SN powder instead of the conventional BN powder as the separating material, a silicon nitride substrate in which BN powder does not remain on the surface of the substrate can be obtained. In this aspect, the BN on the surface of the substrate can be analyzed by fluorescent X-ray analysis, but the silicon nitride substrate is obtained by the ratio (B / Si) of the fluorescent X-ray intensity of boron (B) to the fluorescent X-ray intensity of silicon (Si). It may be 15 × ^10-5 or less, 12 × ^10-5 or less, 10 × ^10-5 or less, 8 × ^10-5 or less, and further ^{less than 6.5 × 10-5 and} less than 5 × ^10-5 . There can be. In particular, at the time of sintering, the green sheet laminate is installed in a silicon nitride enclosure (setter), or the green sheet laminate is covered with silicon nitride powder and sintered to BN on the substrate surface. A silicon nitride substrate containing no BN in the powder and the main body can be obtained. The silicon nitride substrate on this side can have an arbitrarily low BN content, and boron (B) can be set to be below the detection limit by fluorescent X-ray analysis and can be free of BN. The fact that the silicon nitride substrate does not contain BN means that boron (B) is below the detection limit by fluorescent X-ray analysis. However, in the present invention, silicon nitride is used for both the separating material and the enclosure. The silicon nitride substrate may be completely BN-free.

The silicon nitride substrate on this side surface is preferably applied to a silicon nitride substrate manufactured by using a separating material, and a silicon nitride substrate having a thickness of, for example, 0.5 mm or less. Further, the thickness may be 0.45 mm or less, 0.4 mm or less, and 0.35 mm or less. Further, the thickness may be 0.1 mm or more and 0.15 mm or more. The silicon nitride substrate obtained through sheet molding on this side surface is made of β-type silicon nitride (101) obtained by irradiating a surface polished to an arithmetic average roughness Ra of 0.03 μm or more and 0.5 μm or less with X-rays. ) The ratio I (101) / I (210) of the diffraction intensity I (101) of the surface to the diffraction intensity I (210) of the surface (210) may be 0.62 or more and 0.95 or less.

The method for producing the silicon nitride substrate and the preferred embodiment of the silicon nitride substrate on this side surface include the method for producing the silicon nitride substrate on the second side surface and each aspect of the silicon nitride group described below.
In this aspect, a silicon nitride substrate having a thermal conductivity of 80 W / (m · K) or more at room temperature, further 90 W / (m · K) or more, and a four-point bending strength of 800 MPa or more at room temperature, and further 900 MPa or more is used. It is possible to obtain. The silicon nitride substrate of the present invention is obtained by sintering a thin green sheet obtained by sheet molding, and is essentially a bulk sintered body obtained by CIP molding, die press molding and sintering. different.

[Second aspect: Silicon nitride substrate with high strength and high thermal conductivity]
In the second aspect of the present invention, silicon nitride (SN) powder having a specific specific surface area, particle size, and oxygen content and a low aluminum content is used as a separating material, and production conditions such as a coating amount are set within a specific range. As a result, it has been found that a silicon nitride substrate having good peelability, high strength, high thermal conductivity, and little deformation can be obtained. Further, the silicon nitride substrate obtained on this side surface may contain columnar crystal particles in a specific area ratio. The second aspect of the present invention has an aspect of an embodiment suitable for the first aspect of the present invention, and the matters described in the first aspect are, apart from further limiting points, in principle. As, this aspect can also be applied.

According to this aspect, "a plurality of green sheets containing silicon nitride powder and a sintering aid are laminated with a separating material placed between them.
The plurality of green sheets in the obtained laminate are sintered and
By separating from the laminate, a plurality of silicon nitride sintered bodies can be obtained.
A method for manufacturing a silicon nitride substrate, which obtains a silicon nitride substrate from the silicon nitride sintered body.
The separating material contains silicon nitride powder, has a specific surface area of 1 m ² / g or more and 20 m ² / g or less measured by the BET method, and has a 50% particle diameter based on the volume measured by the laser diffraction / scattering method of D50. The D50 is 20 μm or less, and the amount of oxygen is 0.3% by weight or more and less than 2% by weight.
A method for producing a silicon nitride substrate, characterized in that the separating material is applied to the surface of the green sheet at a coating amount of 0.1 mg / cm ² or more and 3 mg / cm ^{2 or less ”is provided.}
Further, "a silicon nitride substrate made of a silicon nitride sintered body containing silicon nitride particles and a sintering aid, wherein the silicon nitride particles have a minor axis a of 0.5 to 5 μm and a major axis with respect to the minor axis a. Columnar crystal particles having a ratio of b (b / a) of 2 or more have an area ratio of 35% or less on the substrate surface, and the arithmetic average surface roughness of the substrate surface is 0.03 μm or more and 0.5 μm or less. ^{The ratio of boron nitride to silicon nitride on the surface of the substrate is 15 × 10-5} or less in terms of the ratio (B / Si) of the fluorescent X-ray intensity of boron (B) to the fluorescent X-ray intensity of silicon (Si). "Silicon nitride substrate" is provided.

In the method for producing a silicon nitride substrate on the second aspect of the present invention, first, as a raw material preparation / mixing step, a ball mill is used in which a ceramic powder as a sintering aid is used as a dispersion medium for the silicon nitride powder. Etc., and further mixed with a binder and a plasticizing agent to prepare a slurry.

In the second aspect, as the raw material silicon nitride powder, any of the silicon nitride powders usually used for producing a silicon nitride substrate can be used as in the first aspect, and the specific surface area is preferably 10. 0 m ² / g or more, oxygen content 1.0 wt% or more, aluminum content less than 100 ppm, more preferably specific surface area 13.0 m ² / g or more, oxygen content 1.2 wt% or more 2.3 wt It may be a silicon nitride powder having an aluminum content of less than 50 ppm. In one embodiment, the silicon nitride powder may have a specific surface area of 25.0 m ² / g or less and an oxygen content of 2.3 wt% or less.

Further, the raw material silicon nitride powder has a specific surface area of 5 to 30 m ² / g, and the content ratio of oxygen existing from the particle surface to 3 nm directly below the particle surface is FSO (mass%), and the content ratio is FSO (mass%), and the inside is from 3 nm directly below the particle surface. When the content ratio of oxygen present in is FIO (mass%) and the specific surface area is FS (m ² / g), FS / FSO is 8 to 25 and FS / FIO is 22 or more. It may be a powder, and this silicon nitride powder can be produced by the production method disclosed in Patent Document 4.

Magnesium oxide (MgO) and an oxide of a rare earth element (RExOy) are preferable as the sintering aid in order to obtain a silicon nitride substrate having high thermal conductivity. Since magnesium oxide forms a liquid phase at a relatively low temperature, it is possible to promote the sintering of the silicon nitride sintered body, and it is difficult to dissolve in the silicon nitride particles, so that the thermal conductivity of the silicon nitride substrate is high. can do. Examples of rare earth elements include Y, La, Ce, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, etc. Among them, Y oxide Y ₂ O ₃ is silicon nitride. It is effective for increasing the density of the substrate, which is more preferable. Further, for example, silicon dioxide may be used as the sintering aid.

The amount of magnesium oxide added is preferably in the range of 0.5% by mass to 4.0% by mass with respect to 98% by mass to 81% by mass of the silicon nitride raw material, and the amount of oxide of a rare earth element added is 1. It is preferably in the range of .5% by mass to 15% by mass. More preferably, the amount of magnesium oxide added is 1.0% by mass to 3% by mass, and the amount of rare earth element oxide added is 1. It may be in the range of 5% by mass to 6% by mass. When an additional oxide such as silicon dioxide is added, it may be added in the range of 0.3% by mass to 1.5% by mass separately from magnesium oxide.

Next, as a molding step, the viscosity of the slurry produced by the above mixing is adjusted as necessary, and this is molded into a sheet having a predetermined thickness by a doctor blade method, an extrusion molding method, or a method similar thereto. The plate thickness of the sheet molded product at this time can be appropriately determined depending on the semiconductor power module, but is preferably in the range of about 0.2 mm to 0.6 mm. The plate thickness of the sheet molded product is the average value of the measured values at any ten or more points.

Next, after cutting the green sheet into a desired shape, a separating material is applied to one or both sides of the cut green sheet, and then a plurality of green sheets coated with the separating material are laminated and sintered.

The separating material contains silicon nitride (SN) powder, has a specific surface area of 1 m ² / g or more and 20 m ² / g or less measured by the BET method, and has a 50% particle size D50 based on the volume measured by the laser diffraction scattering method. The oxygen content is 20 μm or less, the oxygen content is 0.3% by mass or more and less than 2% by mass, the aluminum content is less than 50 ppm, and the coating amount is 0.1 mg / cm ² or more and 3 mg / cm ² or less. More preferably, D50 is 10 μm or less, 5 μm or less, oxygen content is 0.3% by mass or more and 1.2% by mass or less, aluminum content is 40 ppm or less, and coating amount is 0.2 mg / cm ² or more and 1 mg / cm ² or less. May be. The separating material is preferably composed of only silicon nitride (SN) powder, and the separating material SN powder will be described below. However, as long as the effect of using the SN powder can be obtained, a part of the separating material may be boron nitride (BN) powder. good.

The specific surface area of the separating material of this aspect of the present invention measured by the BET method is 1 m ² / g or more and 20 m ² / g or less. When the specific surface area is 1 m ² / g or more, the adhesion of the separating material to the surface of the green sheet is improved and it becomes difficult to peel off during handling. When the specific surface area is 20 m ² / g or less, the amount of oxygen in the separating material can be reduced so as not to exceed 2% by mass, and the separating material reacts with the sintering aid in the green sheet during sintering. , It is possible to prevent the sintered bodies from sticking to each other via the separating material and becoming unable to be peeled off. From the above viewpoint, the specific surface area of the separating material ^{is preferably 1 m 2} / g or more and 12 m ² / g or less, and ^{more preferably 2 m 2} / g or more and 7 m ² / g or less.

The D50 of the separating material on this side of the present invention is 20 μm or less. When D50 is 20 μm or less, the separating material has good adhesion to the green sheet and is difficult to peel off during handling. D50 is more preferably 5 μm or less, 3 μm or less, and 2 μm or less. D50 may be 1 μm or less. The lower limit of D50 is not limited, but D50 may be 0.3 μm or more.

The amount of oxygen in the separating material of this aspect of the present invention is 0.3% by mass or more and less than 2% by mass. If the amount of oxygen in the separating material is within this range, the separating material powder reacts appropriately with the sintering aid component of the silicon nitride sintered body during sintering and is present on the surface of the silicon nitride sintered body. It is possible to prevent adhesion between adjacent silicon nitride sintered bodies, improve peelability, and prevent deformation of the silicon nitride sintered body. When the amount of oxygen is less than 2% by mass, it is possible to prevent the sintered bodies from sticking to each other via the separating material and becoming unable to be peeled off due to a significant reaction with the sintering aid in the green sheet during sintering. This reaction and phenomenon are likely to occur when magnesium oxide is used as the sintering aid, and become remarkable when the thickness of the silicon nitride substrate is 0.2 to 0.6 mm. .. On the other hand, when the amount of oxygen is 0.3% by mass or more, the reaction between the separating material and the silicon nitride sintered body is likely to occur at the time of sintering, so that the separating material does not move on the substrate surface due to the sintering shrinkage. The uniformity of the separating material applied to the surface of the green sheet is maintained, a place where the abundance ratio of the separating material is small does not occur, and it is prevented that the adjacent silicon nitride sintered bodies adhere to each other and the peelability is impaired. The amount of oxygen in the separating material is more preferably 0.3 to 1.2% by mass from the above viewpoint.

The aluminum content of the separator on this side of the invention is preferably less than 50 ppm. At 50 ppm or more, the amount of aluminum that dissolves inside the β-type silicon nitride particles after sintering increases. Phonon scattering by solid-melted aluminum ions causes a decrease in thermal conductivity, and the thermal conductivity of the obtained silicon nitride substrate is reduced to less than 90 W / (m · K) and further to less than 80 W / (m · K). It is not preferable because there is. The preferred range of aluminum content is 40 ppm or less.

The amount of the separating material on this side surface of the present invention applied to the surface of the green sheet is 0.1 mg / cm ² or more and 3 mg / cm ² or less. When the coating amount of the separating material is 3 mg / cm ² or less, a large amount of the separating material does not easily enter between the silicon nitride particles on the surface of the silicon nitride sintered body during the sintering process and does not hinder shrinkage. The density of the sintered body is improved, and the strength is also improved. On the other hand, when the coating amount of the separating material is 0.1 mg / cm ² or more, the separating material is sufficiently present, so that the silicon nitride sintered bodies adhere to each other due to the reaction between the adjacent silicon nitride sintered bodies. , It is possible to prevent the peeling from becoming impossible. From the above viewpoint, the preferable coating amount of the separating material is 0.2 mg / cm ² or more and 1 mg / cm ² or less.

As a method of applying the separating material, in order to apply it uniformly to the surface of the green sheet, after preparing a slurry in which the separating material is dispersed in an organic solvent, it is atomized by a spray-type coating machine and applied to one or both sides. Alternatively, the separating material may be applied directly to one side or both sides with a brush. Here, when producing the slurry, it is preferable to mix the separating material and the organic solvent using silicon nitride balls. The reason why the slurry is prepared by using an organic solvent is that when the slurry is prepared by using water, the amount of oxygen in the separating material increases in the presence of water and the peelability deteriorates. The ratio of the separating material to the organic solvent is appropriately in the range of about 1/10 to 1/2 of the separating material / organic solvent in terms of weight ratio. Further, the reason for mixing using the silicon nitride balls is to crush the agglomeration of the separating material and uniformly disperse it.

A slurry in which the separating material is dispersed in an organic solvent is applied, and several to several tens of dried green sheets are stacked and laminated, and then degreasing is performed to remove organic components such as binders in the green sheet. .. The degreasing is preferably performed in the air at 900 ° C. or lower, or in an inert atmosphere such as nitrogen or argon. The number of green sheets to be laminated is preferably 5 to 50.

The laminate of green sheets with the separating material interposed is degreased and sintered. The laminated body of the green sheet may be installed on a heat-resistant setter, the side surface may be surrounded by a heat-resistant spacer, and then the top surface may be pressed by the heat-resistant setter and sintered (defatted and). The spacer (also referred to as an enclosure in the present specification) can be preferably made of silicon nitride (SN) in addition to the conventional boron nitride (BN) according to the present invention. Even if the enclosure is made of boron nitride (BN), if silicon nitride (SN) powder is used as the separating material, the boron nitride (BN) powder does not remain on the surface of the silicon nitride substrate after sintering, so that the obtained nitridation can be obtained. The silicon substrate can be excellent in heat resistance when copper is bonded. Further, if the surrounding body is made of silicon nitride (SN), it is possible to completely prevent the mixing of BN due to vapor diffusion. As the silicon nitride enclosure, one fired at a high temperature may be used. Further, by packing silicon nitride (SN) powder around the laminated body of the green sheet and sintering it, it is possible to prevent BN from being mixed.

After degreasing, the green sheet is preferably vacuumed at 10 Pa or less to remove residual gas, and then sintered in an atmosphere replaced with nitrogen. It is preferable to hold the sinter at a pressure of 0.15 MPa or more and 3 MPa or less, a sintering temperature of 1750 ° C. or more and 1910 ° C. or less, more preferably 1790 ° C. or more and 1880 ° C. or less for 6 hours or more and 22 hours or less in a nitrogen atmosphere.

When the nitrogen gas pressure is 0.15 MPa or more, the maximum holding temperature at the time of sintering can be raised to 1750 ° C. or higher, and further to 1790 ° C. or higher. When the maximum holding temperature is 1750 ° C. or higher, further 1790 ° C. or higher, the sintering progress rate is high, and a dense silicon nitride substrate can be obtained. Alternatively, when a dense silicon nitride substrate is obtained at a maximum holding temperature of 1750 ° C. or higher, further 1790 ° C. or higher, columnar β-type silicon nitride particles grow sufficiently, and a silicon nitride substrate having high thermal conductivity can be obtained. Therefore, the thermal conductivity can be 80 W / (m · K) or more, and further 90 W / (m · K) or more. When the maximum holding temperature is 1910 ° C. or lower, and further 1880 ° C. or lower, the growth of the columnar β-type silicon nitride particles is at an appropriate rate, the unevenness on the surface of the silicon nitride substrate does not increase, and the adjacent silicon nitride sintered. It is prevented that the silicon nitride sintered bodies adhere to each other due to the reaction between the bodies and cannot be peeled off.

The silicon nitride sintered body has an excellent substrate surface condition, and in particular, BN powder does not remain on the substrate surface and the BN content is extremely low. Therefore, the silicon nitride sintered body may be used as it is as a silicon nitride substrate, but it may be blasted or the like. It is preferable to perform the surface treatment according to. In the blasting process, for example, by injecting 10 to 100 μm SiC abrasive particles onto the surface of the silicon nitride substrate, the silicon nitride particles protruding from the surface are scraped off, the surface roughness is reduced, and the bondability with the metal plate is improved. To carry out. The surface depth (thickness) of the silicon nitride substrate removed by blasting or wrapping may be, for example, 30 μm or less, but preferably 20 μm or less, further 10 μm or less, and particularly 5 μm or less. It may be there. In the second aspect of the present invention, it is possible to remove the separating material and realize excellent surface properties with a minimum of blasting.

By adopting the above-mentioned method for manufacturing a silicon nitride substrate, a plurality of silicon nitride sintered bodies can be easily peeled off, and the columnar silicon nitride particles constituting the silicon nitride sintered body have an appropriate size and are baked. Since the unevenness of the surface of the body is also controlled to an appropriate level, it is possible to obtain a silicon nitride substrate having high strength, high thermal conductivity, and little deformation. Further, since BN powder is not present on the surface of the substrate, the heat cycle resistance when the copper plates are joined is improved, and the copper plates can be used stably for a long period of time. Specifically, it is a silicon nitride substrate made of silicon nitride particles and a silicon nitride sintered body containing a sintering aid composed of at least magnesium oxide, and the silicon nitride particles have a minor axis a of 0.5 to 0.5 to. Columnar crystal particles having an area ratio of 5 μm and a major axis b ratio (b / a) of 2 or more to a minor axis a are 35% or less, further 30% or less, 25% or less in terms of area ratio, and the arithmetic average surface of the substrate surface. A silicon nitride substrate having a roughness of 0.03 μm or more and 0.5 μm or less can be obtained.

Further, according to this aspect, by using SN powder instead of the conventional BN powder as the separating material, it is possible to obtain a silicon nitride substrate in which BN powder does not remain on the surface of the substrate. In this aspect, the BN on the surface of the substrate can be analyzed by fluorescent X-ray analysis, but the silicon nitride substrate is obtained by the ratio (B / Si) of the fluorescent X-ray intensity of boron (B) to the fluorescent X-ray intensity of silicon (Si). It may be 15 × ^10-5 or less, 12 × ^10-5 or less, 10 × ^10-5 or less, 8 × ^10-5 or less, and further ^{less than 6.5 × 10-5} and 5 × ^10-5 or less. There can be. In particular, at the time of sintering, the green sheet laminate is installed in a silicon nitride enclosure (setter), or the green sheet laminate is covered with silicon nitride powder and sintered to form the substrate surface and the main body. A silicon nitride substrate containing no BN can be obtained. The silicon nitride substrate on this side can have an arbitrarily low BN content, and boron (B) can be below the detection limit by fluorescent X-ray analysis and can be free of BN.

Further, according to this aspect, it is possible to obtain a silicon nitride substrate having a thermal conductivity of 80 W / (m · K) or more at room temperature and a four-point bending strength of 800 MPa or more at room temperature. Thermal conductivity is 85 W / (m · K) or more, 90 W / (m · K) or more, 95 W / (m · K) or more, 97 W / (m · K) or more, 100 W / (m · K) at room temperature. The four-point bending strength may be 840 MPa or more, 900 MPa or more, 930 MPa or more, 960 MPa or more, and 1000 MPa or more at room temperature. The silicon nitride substrate of the present invention is obtained by sintering a thin green sheet obtained by sheet molding, and is essentially a bulk sintered body obtained by CIP molding, die press molding and sintering. different.

The silicon nitride substrate on this side surface is preferably applied to a silicon nitride substrate having a thickness of 0.5 mm or less manufactured by using a separating material. Further, the thickness may be 0.45 mm or less, 0.4 mm or less, and 0.35 mm or less. Further, the thickness may be 0.1 mm or more and 0.15 mm or more. The silicon nitride substrate obtained through sheet molding on this side surface is made of β-type silicon nitride (101) obtained by irradiating a surface polished to an arithmetic average roughness Ra of 0.03 μm or more and 0.5 μm or less with X-rays. The ratio I (101) / I (210) of the diffraction intensity I (101) on the surface () and the diffraction intensity I (210) on the surface (210) is 0.62 or more and 0.95 or less.

A silicon nitride substrate made of a silicon nitride sintered body containing a sintering aid made of at least magnesium oxide, wherein the silicon nitride particles have a minor axis a of 0.5 to 5 μm and a major axis b with respect to the minor axis a. Columnar crystal particles with a ratio (b / a) of 2 or more were set to 35% or less in area ratio, and further to 30% or less, especially 25% or less. It is possible to prevent the separating material having a D50 of 20 μm or less from segregating into the recess formed by the columnar crystal particles to form a part without the separating material, and the adjacent substrates can react and peel off at the part without the separating material. This is because it is possible to prevent defects from remaining on the surface of the silicon nitride sintered body by being forcibly peeled off or disappearing, so that the bending strength can be improved.

FIG. 3 shows a schematic view of the microstructure of the surface of the silicon nitride sintered body. FIG. 3 shows how a separating material 9 made of silicon nitride (SN) powder is embedded between the columnar crystal particles of the silicon nitride particles 8 in the region where the silicon nitride particles 8 which are columnar crystal particles are present. Has been done.

The arithmetic average surface roughness of the silicon nitride substrate surface is set to 0.03 μm or more and 0.5 μm or less because when it is 0.03 μm or more, it is possible to prevent a decrease in bending strength of the silicon nitride substrate due to residual stress during processing. be. This is because if the thickness is 0.5 μm or less, joining with a metal plate for forming a circuit becomes easy. The arithmetic mean surface roughness of the substrate surface may be 0.4 μm or less and 0.3 μm or less.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to those examples. The physical properties of the SN powder used as the separating material and the raw material of the present invention and the evaluation method of the silicon nitride substrate of the present invention were carried out by the following methods.

(Measuring method of specific surface area of SN powder)
The specific surface area of the SN powder was determined by measuring with a BET 1-point method by adsorbing nitrogen gas using a Macsorb manufactured by Mountech.

(Measuring method of D50 of SN powder)
The particle size distribution of the separating material SN powder was measured by the laser diffraction / scattering method as follows. The powder was put into a 0.2 mass% aqueous solution of sodium hexametaphosphate and dispersed for 6 minutes at an output of 300 W using an ultrasonic homogenizer equipped with a stainless steel center cone having a diameter of 26 mm to prepare a dilute solution. , As a measurement sample. The particle size distribution of the measurement sample was measured using a laser diffraction / scattering type particle size distribution measuring device (Microtrac MT3000 manufactured by Nikkiso Co., Ltd.), and a volume-based particle size distribution curve and its data were obtained. D50 was calculated from the obtained particle size distribution curve and its data.

(Measuring method of oxygen content of SN powder)
The total oxygen content FTO and the surface oxygen content FSO of the SN powder were measured by the following methods. First, the silicon nitride powder is weighed, and the total oxygen content FTO, which is the sum of the surface oxygen and the internal oxygen of the silicon nitride powder, is determined by the inert gas melting-carbon dioxide infrared absorption method based on the method for quantifying JIS R1603-10 oxygen. It was measured with a TC-136 type manufactured by LECO. Next, the weighed silicon nitride powder was mixed with the silicon nitride powder and the hydrofluoric acid aqueous solution so that hydrogen fluoride was 5 parts by mass with respect to 1 part by mass of the silicon nitride powder, and the mixture was stirred at room temperature for 3 hours. This was suction-filtered, and the obtained solid was vacuum-dried at 120 ° C. for 1 hour, and then the weight and oxygen content of the hydrofluoric acid-treated powder were measured. This value was defined as FIO (% by mass with respect to hydrofluoric acid-treated powder) before correction. The internal oxygen amount FIO (mass% with respect to the silicon nitride powder) was calculated from the following formula (1), and the surface oxygen amount FSO (mass% with respect to the silicon nitride powder) was calculated from the following formula (2). The fact that the amount of surface oxygen thus determined is due to the oxygen existing in the range of 3 nm below the particle surface from the particle surface is due to the depth profile of the X-ray photoelectron spectrum of the silicon nitride powder before and after the hydrofluoric acid treatment and the depth profile of the X-ray photoelectron spectrum. It was confirmed from the change in powder weight before and after the treatment.
FIO (mass%) = ((hydrofluoric acid-treated powder) (g)) / (silicon nitride powder weight (g)) × FIO before correction (mass%) ... (1)
FSO (mass%) = FTO (mass%) -FIO (mass%) ... (2)

(Method of measuring Al content of SN powder)
The Al content of the separating material SN powder was measured as follows. The above powder is put into a container containing a liquid containing a mixture of hydrofluoric acid and nitric acid, sealed tightly, and the container is heated by irradiating with microwaves to completely decompose silicon nitride, and the obtained decomposition liquid is used. The volume was adjusted with ultrapure water to prepare a test solution. Using ICP-AES (SPS5100 type) manufactured by SII Nanotechnology, the metal impurities of Al in the test solution were quantified from the detected wavelength and its emission intensity, and the Al content was calculated.

(Evaluation method of peelability of silicon nitride substrate)
The peelability of the silicon nitride substrate is evaluated when the silicon nitride substrate can be easily peeled off without cracking or cracking (○), and when the silicon nitride substrate is peeled off by applying an impact with a wooden hammer, the silicon nitride substrate cracks or cracks. When there was even one substrate on which cracks occurred, it was determined to be (Δ).

(Method for measuring the area ratio of columnar crystal particles having a minor axis a of 0.5 to 5 μm and a ratio (b / a) of the major axis b to the minor axis a of 2 or more)
For the area ratio of columnar crystal particles having a minor axis a of 0.5 to 5 μm and a ratio of the major axis b to the minor axis a (b / a) of 2 or more, the minor axis a and the major axis b are measured by the following method. It was calculated by. After polishing an arbitrary cross section of the silicon nitride substrate, etching is performed to elute the sintering aid component, and then a scanning electron microscope (SEM) is used to take an SEM photograph at an observation magnification of 5000 times for image analysis. The minor axis a and the major axis b are measured by the device. From these measurement results, select silicon nitride particles having a minor axis a of 0.5 to 5 μm, and determine the total area of columnar crystal particles having a ratio (b / a) of major axis b to minor axis a of 2 or more. .. The area ratio (area ratio) of the total area of the columnar crystal particles to the measured area was calculated.

(Measurement method of arithmetic mean surface roughness of silicon nitride substrate surface)
The arithmetic mean surface roughness of the surface of the silicon nitride substrate was measured as follows. The arithmetic mean roughness Ra of the surface of the obtained silicon nitride substrate was measured according to JIS B 0601-2001 (ISO4287-197). Using a stylus type surface roughness meter, apply a stylus with a stylus tip radius of 2 μm to the surface of the silicon nitride sintered body that has been surface-treated by blasting after sintering to measure the measurement length. The surface roughness was measured by setting the scanning speed of the stylus to 5 mm and 0.5 mm / sec, and the average value of the five points obtained by this measurement was taken as the value of the arithmetic mean roughness Ra.

(Measuring method of bending strength of silicon nitride substrate)
The bending strength of the silicon nitride substrate was measured as follows. A bending test piece having a width of 4.0 mm, a thickness of 0.35 mm, and a length of 40 mm was used for measuring the bending strength of the obtained silicon nitride substrate. Room temperature using a 4-point bending test jig with an inner span of 10 mm and an outer span of 30 mm by a method compliant with JIS R1601 except that the thickness (0.35 mmt) of the test piece is different using an Instron universal material tester. The 4-point bending strength was measured.

(Measurement method of thermal conductivity of silicon nitride substrate)
In the measurement of thermal conductivity of a silicon nitride substrate, a disk-shaped test piece having a diameter of 10 mmφ and a thickness of 1 mmt is prepared, and the disk-shaped test piece is used to measure the thermal conductivity by a flash method conforming to JIS R1611. Measured at room temperature.

(Measurement method of B / Si fluorescent X-ray intensity ratio on the surface of silicon nitride substrate)
The B / Si X-ray fluorescence intensity ratio on the surface of the silicon nitride substrate is determined by using XRF (X-ray Fluorescence Analysis), in particular, the composition of boron (B) and silicon (Si) on the surface of the silicon nitride substrate. The analysis was performed, and the B / Si fluorescent X-ray intensity ratio was obtained from the measurement result of XRF. Here, as the fluorescent X-rays, B Kα rays (energy 0.183 keV) and Si Kα rays (energy 1.74 keV) are targeted, and these intensity ratios are B / Si fluorescent X-ray intensity ratios. In the table of Examples, "not detected" in the "B / Si" column means that element B was not detected in the fluorescent X-ray analysis.

(Example 1)
Magnesium oxide (MgO) powder (specific surface area 3 m ² / g, manufactured by High Purity Chemical Laboratory) and yttrium oxide (Y ₂ O ₃ ) powder (specific surface area 3 m ² / g, manufactured by Shin-Etsu Chemical Industry Co., Ltd.) are used as sintering aids. I prepared it.

3. The above-mentioned yttrium oxide as a sintering aid was added to 94.5 parts by mass of the raw material SN powder having ^{a specific surface area of 18.5 m 2} / g and an oxygen content of 1.77% by mass produced by the method disclosed in Patent Document 4. Made of resin for ball mills together with a toluene-isopropanol-xylene solvent in which 5 parts by mass and 2 parts by mass of the above-mentioned magnesium oxide are blended and an amine-based dispersant is dissolved in powder in 2 parts by mass, and a silicon nitride ball as a pulverizing medium. It was put into a pot and wet-mixed for 24 hours. The obtained slurry was passed through a sieve having a mesh size of 44 μm, and then 16 parts by mass of a PVB-based resin binder and 4 parts by mass of a plasticizer (dimethyl phthalate) were dissolved in 100 parts by mass of the mixed powder in the resin pot. -Isopropanol-xylene solvent was added and wet-mixed for another 24 hours to obtain a sheet-forming slurry. After adjusting the amount of solvent by vacuum defoaming so that the viscosity of this molding slurry becomes about 50 poise, the obtained mixed powder slurry is cast on a carrier film to a predetermined thickness using a doctor blade device. , A sheet-molded green sheet was obtained. Further, the obtained green sheet was laminated and crimped at a temperature of 120 ° C. and a predetermined pressure to prepare a sheet having a baked size of about 0.35 mm. Then, this was cut into 60 mm × 70 mm to obtain a green sheet.

The separating material SN powder and ethanol shown in Table 1 are separated from the separating material SN powder / ethanol = 1/5 with a silicon nitride ball having a diameter of 10 mm and a batch type vibration mill at a frequency of 1200 cpm and an amplitude of 8 mm. ^{After mixing for 5 minutes to prepare a separating material SN powder slurry, 0.6 mg / cm 2} was applied to one surface of the green sheet (the bottom green sheet is on both sides) using a spray-type coating machine. It was applied with the amount of application of. The green sheet coated with the separating material was dried in the air at 25 ° C. for 5 minutes. The coating amount of the separating material SN powder was calculated by measuring the weight of the sheet before and after the coating / drying step and dividing the difference in weight by the area of the coated surface of the sheet.

The green sheet 2 coated with the separating material SN powder 1 is laminated on the BN setter 3 with the coated side facing the upper surface, and is placed on the side of the laminated green sheet 2 on the BN setter 3. A BN spacer 4 was arranged, and a BN setter 3 was placed on the spacer 4 (FIG. 1). By heating in air at 400 to 600 ° C. for 2 to 5 hours, the organic binder component and the like added in advance were sufficiently degreased (removed). Next, the degreased body was heated to 1850 ° C. under a nitrogen atmosphere of 0.8 MPa, and further held at 1850 ° C. for 10 hours for sintering. The mixture was cooled to room temperature to obtain a silicon nitride sintered body in which 10 silicon nitride sintered bodies were laminated. Then, each silicon nitride sintered body was separated, and it was confirmed whether or not the silicon nitride sintered bodies could be separated from each other. The 10 silicon nitride sintered bodies could be easily peeled off without cracks or cracks. The separated silicon nitride sintered body was blast-polished to obtain the silicon nitride substrate of Example 1. The thickness removed by the blast polishing process was 10 μm or less on average.

Table 1 shows the physical property values and coating amount of the SN powder (raw material SN powder) used for the raw material powder and the SN powder (separation material SN powder) used for the separating material in Example 1, and the sintering conditions. Table 2 shows the peelability and the characteristics of the silicon nitride substrate. The "area ratio" in Table 2 is the area ratio of columnar crystal particles having a minor axis a of 0.5 to 5 μm and a ratio of the major axis b to the minor axis a (b / a) of 2 or more.

(Examples 2 to 7)
A silicon nitride substrate was produced by the same method as in Example 1 except that the SN powder used for the separation material (separation material SN powder) was changed to the conditions shown in Table 1, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 8)
A silicon nitride substrate was produced by the same method as in Example 1 except that the SN powder used as the raw material (raw material SN powder) was changed to the conditions shown in Table 1, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Examples 9 to 13)
A silicon nitride substrate was produced by the same method as in Example 1 except that the coating amount of the separating material SN powder was changed to the conditions shown in Table 1, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Examples 14 and 15)
A silicon nitride substrate was produced by the same method as in Example 1 except that the maximum temperature at the time of sintering was changed to the conditions shown in Table 1, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Examples 16 to 18)
A silicon nitride substrate was produced by the same method as in Example 1 except that the holding time at the maximum temperature during sintering was changed to the conditions shown in Table 1, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 19)
A silicon nitride substrate was produced by the same method as in Example 1 except that the nitrogen gas pressure at the time of sintering was changed to the conditions shown in Table 1, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 20)
A silicon nitride substrate was produced by the same method as in Example 1 except that the nitrogen gas pressure at the time of sintering and the holding time at the maximum temperature were changed to the conditions shown in Table 1, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 21)
A silicon nitride substrate was produced by the same method as in Example 1 except that the wrap polishing process was performed after the blast polishing, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 22)
A silicon nitride substrate was manufactured by the same method as in Example 1 except that the degree of blast polishing in the surface polishing process was adjusted so that the Ra of the obtained silicon nitride substrate was 0.48 μm, and the same evaluation was performed. .. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 23)
A silicon nitride substrate was manufactured by the same method as in Example 1 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 24)
A silicon nitride substrate was produced by the same method as in Example 1 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 25)
A silicon nitride substrate was produced by the same method as in Example 2 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 26)
A silicon nitride substrate was produced by the same method as in Example 3 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 27)
A silicon nitride substrate was produced by the same method as in Example 4 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 28)
A silicon nitride substrate was produced by the same method as in Example 5 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 29)
A silicon nitride substrate was produced by the same method as in Example 6 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 30)
A silicon nitride substrate was produced by the same method as in Example 7 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 31)
A silicon nitride substrate was produced by the same method as in Example 9 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 32)
A silicon nitride substrate was produced by the same method as in Example 10 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 33)
A silicon nitride substrate was produced by the same method as in Example 11 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 34)
A silicon nitride substrate was produced by the same method as in Example 12 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 35)
A silicon nitride substrate was manufactured by the same method as in Example 2 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 36)
A silicon nitride substrate was manufactured by the same method as in Example 3 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 37)
A silicon nitride substrate was manufactured by the same method as in Example 4 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 38)
A silicon nitride substrate was manufactured by the same method as in Example 5 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 39)
A silicon nitride substrate was manufactured by the same method as in Example 6 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 40)
A silicon nitride substrate was manufactured by the same method as in Example 7 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 41)
A silicon nitride substrate was manufactured by the same method as in Example 9 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 42)
A silicon nitride substrate was manufactured by the same method as in Example 10 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 43)
A silicon nitride substrate was manufactured by the same method as in Example 11 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 44)
A silicon nitride substrate was manufactured by the same method as in Example 12 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Examples 51 to 53)
A silicon nitride substrate was produced by the same method as in Example 1 except that the SN powder of the separating material was changed to the conditions shown in Table 1, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Examples 54 and 55)
A silicon nitride substrate was produced by the same method as in Example 1 except that the coating amount of the SN powder of the separating material was changed to the conditions shown in Table 1, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Examples 56 to 58)
A silicon nitride substrate was produced by the same method as in Example 1 except that the firing conditions at the time of sintering were changed to the conditions shown in Table 1, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 59)
A silicon nitride substrate was produced by the same method as in Example 1 except that the sintering conditions were changed to the conditions shown in Table 1 and lap polishing was performed until Ra became 0.02 μm after blast polishing. A similar evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Examples 61-66)
In Examples 61 to 66, the specific surface area of 11. Silicon nitride substrates were produced by the same methods as in Examples 1 to 6 except that the raw material SN powder was changed to 5 m ^{2 / g and an oxygen content of 1.35% by weight, and the same evaluation was performed.} Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 67)
A silicon nitride substrate was produced by the same method as in Example 61 except that silicon nitride (SN) powder was packed around the green sheet 2 laminated on the BN setter 3, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 68)
A silicon nitride substrate was manufactured by the same method as in Example 61 except that the BN setter 3 was changed to a silicon nitride (SN) setter, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 69)
A silicon nitride substrate was produced by the same method as in Example 61 except that the holding time at the maximum temperature during sintering was changed to 22 hours, and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 70)
A silicon nitride substrate was produced by the same method as in Example 61 except that the maximum temperature at the time of sintering was changed to 1900 ° C., and the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 71)
A silicon nitride substrate was produced by the same method as in Example 61 except that the amounts of SiO _{2 shown in Table 1 were added as a sintering aid, and the same evaluation was performed.} Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 72)
A silicon nitride substrate was manufactured by the same method as in Example 61, except that the amounts of SiO _{2 shown} in Table 1 were added to the sintering aid and the holding time at the maximum temperature during sintering was changed to 22 hours. Then, the same evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

(Example 73)
A silicon nitride substrate was produced by the same method as in Example 61 except that the amount of SiO _{2 shown in Table 1 was added as a sintering aid and the maximum temperature at the time of sintering was changed to 1900 ° C.} Evaluation was performed. Table 2 shows the peelability and the characteristics of the silicon nitride substrate.

In the above embodiment, by using the SN powder as the separating material, the BN powder does not remain on the surface of the silicon nitride substrate, so that the heat cycle resistance when copper is bonded to the silicon nitride substrate is excellent. can. Further, the amount of BN remaining on the surface after removing the separating material from the surface of the silicon nitride substrate is the fluorescent X-ray intensity of boron (B) and the fluorescent X of silicon (Si) even when a BN setter is used. The linear strength ratio (B / Si) ^{is extremely small, 12 × 10-5} or less, and it not only has excellent heat cycle resistance when copper is bonded to a silicon nitride substrate, but also uses an SN setter or uses SN powder. When stuffing was performed, no BN was detected on the surface of the silicon nitride substrate.

As shown in Examples 1 to 44 of Tables 1 and 2 above, the specific surface area of the separating material is 1 m ² / g or more and 20 m ² / g or less, D50 is 20 μm or less, and the amount of oxygen is 0.3% by mass or more 2 When silicon nitride (SN) powder having a specific surface area of less than% by weight and an aluminum content of less than 50 ppm is used and the amount of the SN powder applied to the surface of the green sheet is 0.1 mg / cm ² or more and 3 mg / cm ² or less, Examples 1-44 In all of the above, the peelability after sintering is good, and a silicon nitride substrate having a bending strength of 900 MPa or more, a thermal conductivity of 90 W / (m · K) or more, and a high silicon nitride substrate of 95 W / (m · K) or more can be obtained. I confirmed that it was possible.

In Example 51, when the specific surface area of the separating material SN powder was 0.4 m ² / g, the peelability after sintering was inferior to that of Example 1, and the bending strength was 850 MPa.

In Example 52, when the specific surface area of the separating material SN powder was 23.2 m ² / g, the peelability after sintering was inferior to that of Example 1, and the bending strength was 800 MPa.

In Example 53, when the aluminum content of the separating material SN powder was 70 ppm, the peelability was good, but the thermal conductivity was 80 W / (m · K).

In Examples 54 and 55, when the coating amounts of the separating material SN powder were 0.07 and 3.5 mg / cm ² , the peelability after sintering was inferior to that of Example 1, and the bending strength was 830 and 800 MPa. Met.

In Example 56, when the maximum temperature at the time of sintering was 1900 ° C., the area ratio of the columnar crystal particles of the obtained silicon nitride substrate was as high as 43%, and the peelability after sintering was the same as that of Example 1. It was inferior to the comparison, and the bending strength was 780 MPa.

In Example 57, when the maximum temperature holding time at the time of sintering was set to 30 hours, the area ratio of the columnar crystal particles of the obtained silicon nitride substrate was as high as 53%, and the peelability after sintering was Example. It was inferior to No. 1 and showed a bending strength of 730 MPa.

In Example 58, when the gas pressure at the time of sintering was 4 MPa, the area ratio of the obtained silicon nitride substrate was as high as 37%, the peelability after sintering was inferior to that of Example 1, and the bending strength. Showed 840 MPa.

In Example 59, when the maximum temperature at the time of sintering was 1780 ° C., the area ratio was 12% and the peelability was good, but the bending strength was 860 MPa and the thermal conductivity was 80 W / (m · K). ..

In Examples 51 to 59, the bending strength and thermal conductivity of the silicon nitride substrate are inferior to those of Examples 1 to 44, but are equal to or higher than those of the prior art. Further, no BN powder remains on the surface of the silicon nitride substrate, and the ratio of the fluorescent X-ray intensity of boron (B) to the fluorescent X-ray intensity of silicon (Si) despite the use of a BN setter. The (B / Si) value is as ^{small as 16 × 10-5} or less, and the heat cycle resistance when copper is bonded to the silicon nitride substrate can be excellent.

In Examples 61 to 66, when the specific surface area of the raw material SN powder is 11.5 m ² / g and the total oxygen content is 1.35%, the bending strength of the silicon nitride substrate is 830 to 880 MPa and the thermal conductivity is 86 to 87 W. / (M · K) was shown.

In Example 67, when the specific surface area of the raw material SN powder was 11.5 m ² / g, the total oxygen content was 1.35%, and the green sheet was covered with silicon nitride (SN) powder, the silicon nitride substrate was coated with boron. (B) was not detected, and the bending strength of the silicon nitride substrate was 890 MPa, and the thermal conductivity was 87 W / (m · K).

In Example 68, when the specific surface area of the raw material SN powder was 11.5 m ² / g, the total oxygen content was 1.35%, and a silicon nitride (SN) setter was used, boron (B) was present on the silicon nitride substrate. It was not detected, and the bending strength of the silicon nitride substrate was 870 MPa, and the thermal conductivity was 86 W / (m · K).

In Example 69, when the specific surface area of the raw material SN powder was 11.5 m ² / g, the total oxygen content was 1.35%, and the holding time at the maximum temperature during sintering was 22 hours, the silicon nitride substrate was formed. The bending strength was 830 MPa, and the thermal conductivity was 90 W / (m · K).

In Example 70, when the specific surface area of the raw material SN powder was 11.5 m ² / g, the total oxygen content was 1.35%, and the maximum temperature during sintering was 1900 ° C., the bending strength of the silicon nitride substrate was 820 MPa. , The thermal conductivity was 92 W / (m · K).

In Example 71, the specific surface area of the raw material SN powder was 11.5 m ² / g, the total oxygen content was 1.35%, and 0.8% by mass of SiO ₂ was added as a sintering aid to perform sintering. When the maximum temperature was 1900 ° C., the bending strength of the silicon nitride substrate was 850 MPa, and the thermal conductivity was 88 W / (m · K).

In Example 72, the specific surface area of the raw material SN powder was 11.5 m ² / g, the total oxygen content was 1.35%, and 0.8% by mass of SiO ₂ was added as a sintering aid during sintering. When the holding time at the maximum temperature was 22 hours, the bending strength of the silicon nitride substrate was 830 MPa, and the thermal conductivity was 93 W / (m · K).

In Example 73, the specific surface area of the raw material SN powder was 11.5 m ² / g, the total oxygen content was 1.35%, and 0.8% by mass of SiO ₂ was added as a sintering aid during sintering. When the holding time at the maximum temperature was 22 hours, the bending strength of the silicon nitride substrate was 810 MPa, and the thermal conductivity was 95 W / (m · K).

In Examples 61 to 73, the bending strength and thermal conductivity of the silicon nitride substrate are inferior to those of Examples 1 to 44, but are equal to or higher than those of the prior art. Further, even when a BN setter is used, by using SN powder as a separating material, BN powder does not remain on the surface of the silicon nitride substrate, and the fluorescent X-ray intensity of boron (B) on the silicon nitride substrate is increased. The ratio of fluorescent X-ray intensity of silicon (Si) (B / Si) is 14.5 × ^10-5 or less, which is extremely small. Further, when the green sheet was covered with SN powder or an SN setter was used, the fluorescent X-ray intensity of boron (B) was not detected on the silicon nitride substrate. Therefore, the silicon nitride substrates of Examples 61 to 73 can be excellent in heat cycle resistance when copper is bonded.

A silicon nitride substrate obtained by laminating a plurality of green sheets, sintering them, and then separating them according to the method for manufacturing a silicon nitride substrate of the present invention, which has excellent heat cycle resistance when copper is bonded. A silicon nitride substrate is provided, and further, a silicon nitride substrate having good peelability, high bending strength and high thermal conductivity, and less deformation can be obtained. This silicon nitride substrate can be used as a substrate for a power element module or the like.

1 Separator (SN powder)
2 Green sheet 3 Setter 4 Spacer 5 Stuffing powder (SN powder)
8 Silicon nitride particles (columnar crystal particles)
9 Separator (SN powder)

Claims (16)

A plurality of green sheets containing silicon nitride powder and a sintering aid were laminated by arranging a separating material between them, and the separating material contained silicon nitride powder.
The plurality of green sheets in the obtained laminate are sintered and
By separating from the laminate, a plurality of silicon nitride sintered bodies can be obtained.
A method for manufacturing a silicon nitride substrate, which comprises obtaining a silicon nitride substrate from the silicon nitride sintered body. The method for producing a silicon nitride substrate according to claim 1, wherein the sintering of the plurality of green sheets is performed in a silicon nitride enclosure or a boron nitride enclosure. The method for producing a silicon nitride substrate according to claim 1 or 2, wherein the plurality of green sheets are covered with silicon nitride powder to perform the sintering. The method for producing a silicon nitride substrate according to any one of claims 1 to 3, wherein the separating material remaining on the surface of the silicon nitride sintered body obtained after the sintering is removed. The separating material has a specific surface area measured by the BET method of 1 m ² / g or more and 20 m ² / g or less, a volume-based 50% particle diameter D50 measured by the laser diffraction / scattering method of 20 μm or less, and , The amount of oxygen is 0.3% by weight or more and less than 2% by weight,
The silicon nitride according to any one of claims 1 to 4, wherein the separating material is applied to the surface of the green sheet at a coating amount of ^{0.1 mg / cm 2} or more and 3 mg / cm ^{2 or less.} Substrate manufacturing method. The method for producing a silicon nitride substrate according to claim 5, wherein the aluminum content of the separating material is less than 50 ppm. 5. The method for manufacturing a silicon nitride substrate according to the above method. A silicon nitride substrate made of a silicon nitride sintered body containing silicon nitride particles and a sintering aid, having a thickness of 0.5 mm or less and having no boron nitride powder on the surface of the substrate. A characteristic silicon nitride substrate. ^{The ratio of boron nitride to silicon nitride on the surface of the substrate is 15 × 10-5} or less in terms of the ratio (B / Si) of the fluorescent X-ray intensity of boron (B) to the fluorescent X-ray intensity of silicon (Si). The silicon nitride substrate according to claim 8, wherein the silicon nitride substrate is characterized. The silicon nitride substrate according to claim 8, wherein the substrate does not contain boron nitride (BN). A silicon nitride substrate made of a silicon nitride sintered body containing silicon nitride particles and a sintering aid, wherein the silicon nitride particles have a minor axis a of 0.5 to 5 μm and a ratio of a major axis b to a minor axis a. Columnar crystal particles having (b / a) of 2 or more have an area ratio of 35% or less on the substrate surface, and the arithmetic average surface roughness of the substrate surface is 0.03 μm or more and 0.5 μm or less, and the substrate surface. ^{The ratio of boron nitride to silicon nitride in the above is 15 × 10 -5} or less in the ratio (B / Si) of the fluorescent X-ray intensity of boron (B) to the fluorescent X-ray intensity of silicon (Si). Silicon substrate. The silicon nitride substrate according to claim 11, wherein the surface of the substrate does not have boron nitride powder. The silicon nitride substrate according to claim 11 or 12, wherein the silicon nitride substrate has a thermal conductivity of 80 W / (m · K) or more at room temperature and a four-point bending strength of 800 MPa or more at room temperature. The silicon nitride substrate according to any one of claims 11 to 13, wherein the aluminum content of the separating material is less than 50 ppm. The silicon nitride substrate according to any one of claims 11 to 14, wherein the silicon nitride substrate has a thickness of 0.5 mm or less. An insulating substrate or a circuit board using the silicon nitride substrate according to any one of claims 8 to 15.

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