Silicon nitride sintered substrate

Abstract

Provided is a silicon nitride sintered substrate which is not polished yet after the sintering of a silicon nitride powder, and which is reduced in the occurrence of problems such as the problem of contamination with a boron nitride powder used as a mold release material or the like and a problem in bonding strength, insulation resistance and the like upon the lamination of a metal layer or the like, all of which are associated with a net-like structure formed by silicon nitride crystals on the surface of the silicon nitride sintered substrate.　The silicon nitride substrate is not polished after sintering, in which the cumulative pore volume of pores each having a pore diameter of 1 to 10 μm as measured by a mercury intrusion porosimetry method is 7.0 × 10-5 mL / cm2 or less, and it is preferred that the Ra value is 0.6 μm or less and the arithmetic mean peak curvature (Spc) value at a peak top point is 4.5 [1 / mm] or less in the surface of the silicon nitride sintered substrate.

Description

Technical Field

[0001] The present invention relates to a novel silicon nitride sintered substrate. Specifically, it provides a silicon nitride sintered substrate that, after sintering, has an extremely small pore volume of a specific size present on the surface in an unpolished state and is extremely less contaminated by a parting agent used to prevent fusion during firing.

Background Art

[0002] A silicon nitride sintered body obtained by adding various sintering aids to silicon nitride powder and sintering at a high temperature has characteristics such as being lightweight, having strong mechanical strength from room temperature to high temperature, excellent chemical resistance, and excellent electrical insulation among various ceramic sintered bodies, and is used as a wear-resistant member such as a ball bearing and a high-temperature structural member. Also, by devising the type of aid and sintering conditions, it is possible to increase the thermal conductivity, so it has come to be used as a thin and high-strength heat dissipation substrate material.

[0003] As crystal forms of silicon nitride powder, it is known that there are α-type and β-type. Among them, α-type silicon nitride powder is currently widely used because a dense and high-thermal-conductivity sintered body can be obtained by re-precipitating as β-type during the sintering process (see Non-Patent Document 1).

[0004] However, when attempting to manufacture a silicon nitride sintered substrate using α-type silicon nitride powder, although the growth of the β-type crystal is large and internal densification can be achieved, many pores are formed on the surface due to a network structure formed by the grown needle-like crystals. Generally, a silicon nitride sintered substrate, after sintering, in an unpolished state, that is, a substrate obtained by subjecting an adherend such as a parting agent present on the surface of the sintered body obtained by firing to a blasting treatment to remove it is used as it is.

[0005] Therefore, when a silicon nitride sintered substrate obtained by sintering with α - type silicon nitride powder as the main component is used for a laminated substrate for semiconductors by laminating a metal layer or the like with deposits remaining in the pores after firing, especially boron nitride generally used as a release material, there is a concern that the heat cycle resistance may decrease or malfunction of the semiconductor may occur.

[0006] In addition, it has also been reported that boron nitride exists in the reticular structure on the surface during the process of manufacturing a silicon nitride sintered substrate, which makes it easier for undulations and warping to occur in the obtained silicon nitride sintered substrate.

[0007] Furthermore, a silicon nitride substrate obtained with α - type silicon nitride powder as the main component has a porous surface due to the reticular structure when manufacturing a laminated substrate by laminating a metal layer or the like. Therefore, the surface is rough and direct bonding is difficult, and it is common to perform lamination using a brazing material or grease. In this case, although the reticular structure has the advantage of exerting an anchor effect, air bubbles tend to remain in the reticular structure on the surface, which may reduce the bonding strength and insulation resistance of the laminated substrate, and there is also a problem that an excessive amount of brazing material to fill the reticular layer is required.

[0008] On the other hand, a technique for manufacturing a sintered body with β - type silicon nitride powder as the main component has also been proposed (see Patent Document 1). For example, a green sheet (body to be fired) containing β - type silicon nitride powder with an average particle size of 0.5 μm and a sintering aid composed of ytterbium oxide and magnesium silicon nitride powder is sintered at 1900 °C for 2 to 24 hours in pressurized nitrogen at 10 atmospheres to obtain a silicon nitride sintered body.

[0009] The above - mentioned method aims to realize crystal growth during sintering while using β - type silicon nitride as the main component by performing sintering in pressurized nitrogen, and obtain a sintered body equivalent to the sintered body obtained with the α - type silicon nitride as the main component, but it does not solve the above - mentioned problems caused by the reticular structure formed on the surface due to crystal growth.

Prior Art Documents

Patent Document

[0010]

Patent Document 1

Non-Patent Document

[0011]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] Therefore, an object of the present invention is to provide a silicon nitride sintered substrate capable of reducing the occurrence of problems such as the contamination caused by the network structure formed by silicon nitride crystals on the surface and the bonding strength and insulation resistance in the lamination of a metal layer or the like in an unpolished state after sintering the silicon nitride powder.

Means for Solving the Problems

[0013] As a result of intensive studies to solve the above problems, the present inventors have found that problems such as contamination by a release agent and generation of voids by a brazing material in the lamination of a metal layer or the like are caused by pores of a specific size formed by the network structure of silicon nitride crystals in the surface portion of the sintered body. Based on such findings, as a result of further studies, by using a specific β-type silicon nitride powder and adopting specific firing conditions, by moderately suppressing crystal growth during sintering by firing, generation of the network structure of silicon nitride crystals formed in the surface portion by sintering is suppressed, and a silicon nitride sintered substrate in which pores of a specific size that cause contamination and the like are significantly reduced has been successfully obtained, and the present invention has been proposed.

[0014] That is, according to the present invention, a silicon nitride substrate in an unpolished state after sintering, wherein the cumulative pore volume of pores having a pore diameter of 1 to 10 μm measured by a mercury intrusion method is 7.0×10 -5 mL / cm2 There is provided a silicon nitride sintered substrate characterized by the following.

[0015] Due to the small number of the above - specified pores, the silicon nitride sintered substrate of the present invention has a very smooth surface property such that, for its surface, Ra is 0.6 μm or less and the value of the arithmetic mean curvature (Spc) of the peak points is 4.5 [1 / mm] or less.

[0016] Also, in the silicon nitride sintered substrate of the present invention, in a micrograph measured by taking a scanning electron micrograph of an arbitrary cross - section at a magnification of 2000 times, the maximum major axis of crystal grains observed in the visual field range 50 μm or more inside from the surface is 10.0 μm or less, the average major axis is 1.5 - 2.0 μm, and the ratio of the major axis to the minor axis (major axis / minor axis) is 1 - 5. It preferably has such an internal structure.

[0017] Furthermore, the silicon nitride sintered substrate of the present invention preferably has a thickness of 0.1 - 1.5 mm.

[0018] Furthermore, the present invention can also provide a silicon nitride sintered substrate characterized in that, due to the above - mentioned surface characteristics, the concentration of boron element measured by fluorescent X - ray analysis is less than the detection limit.

[0019] The present invention also provides a laminated substrate for semiconductors obtained by using the above - described silicon nitride sintered substrate.

Advantages of the Invention

[0020] In the silicon nitride sintered substrate of the present invention, after sintering silicon nitride powder, in the unpolished state, since the number of the above - specified pores is extremely small, the contamination of the substrate by boron powder used as a release material is extremely small. Thereby, the reduction of heat cycle resistance and the occurrence of malfunction of the semiconductor are suppressed, and it can be suitably used also in semiconductor applications. Moreover, it is also an advantage that a flat sintered substrate without the occurrence of undulation or warpage can be obtained.

[0021] In addition, it is possible to effectively prevent a decrease in bonding strength and insulation resistance due to the generation of air bubbles during the application of a brazing material in the lamination of a metal layer or the like. Moreover, the amount of the brazing material used can be dramatically reduced, and a laminate with good adhesion can be formed. Furthermore, since the surface is smooth, it is also possible to directly form a metal layer on the lamination surface without using a brazing material.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0023] [Silicon Nitride Sintered Substrate] The silicon nitride sintered substrate of the present invention is a silicon nitride substrate in an unpolished state after sintering, and the cumulative pore volume of pores having a pore diameter of 1 to 10 μm measured by the mercury intrusion method is 7.0×10 -5 mL / cm 2 Hereinafter, preferably, 4.0×10 -5 mL / cm 2 or less, and is characterized by the following.

[0024] Hereinafter, the pores having a pore diameter of 1 to 10 μm measured by the mercury intrusion method may also be referred to as "specific pores".

[0025] In the present invention, the cumulative pore volume is obtained by the measurement method shown in the examples described later.

[0026] In the present invention, "in an unpolished state after sintering" means a state in which a polishing process for smoothing the surface of the silicon nitride sintered substrate obtained by sintering silicon nitride powder has not been performed.

[0027] However, it is preferable that after sintering, a blasting process for removing foreign matters such as release materials adhering to the surface, which has been generally carried out conventionally, is performed. For the above blasting process, a known processing method to the extent of removing the foreign matters is adopted without particular limitation. For example, it is performed by colliding a fluid containing abrasive grains with the surface of the sintered silicon nitride sintered substrate in a wet or dry manner. Specifically, in the case of dry, an air flow containing abrasive grains having a hardness of about alumina and an average particle size of 400 to 800 μm is generally collided with the surface of the silicon nitride sintered substrate at a collision pressure of about 0.2 to 0.4 MPa for processing.

[0028] In the blasting process for removing the above foreign matters, it has been confirmed by the experiments of the present inventors that the specific pores are hardly affected before and after the process.

[0029] When the present inventors investigated commercially available silicon nitride sintered substrates, it was found that in the unsurfaced state after sintering, the integrated volume of the specific pores was one digit larger than that of the silicon nitride sintered substrate of the present invention. From this, the silicon nitride sintered substrate of the present invention exhibits a characteristic surface property that the integrated volume of such specific pores is extremely small.

[0030] And due to such surface property, it has become possible to provide a so-called "boron-free" silicon nitride sintered substrate in which the release material used during sintering, specifically boron nitride powder, does not remain in the pores.

[0031] In addition, the silicon nitride sintered substrate of the present invention having an extremely small integrated volume of specific pores also makes it possible to manufacture a laminated substrate with high insulation resistance in which bubbles hardly remain in the network structure even in the manufacture of a laminated substrate using a brazing material.

[0032] In the present invention, the integrated pore volume existing other than the specific pores is not particularly limited. For example, the integrated pore volume of 1 to 100 μm is 2.0×10 -4 mL / cm 2 ~8.0×10 -4 mL / cm 2can take the range of, and while having such a pore volume, the specific pore volume satisfies the above range. On the other hand, for commercially available silicon nitride sintered substrates, even if the cumulative pore volume of pores of 1 to 100 μm falls within the above range, the cumulative volume of specific pores shows a value much smaller than the range of the present invention. From this, it can be seen that the cumulative volume of specific pores is not proportional to the cumulative volume of other pores.

[0033] The silicon nitride sintered substrate of the present invention can be obtained by the method described later. The surface of such a substrate has a small surface roughness and an extremely smooth surface property as a characteristic due to the extremely small size of the specific pores, or together with such a characteristic. Such a property exhibits an effect of improving the adhesion of the bonding surface when laminating a metal layer or the like using the above brazing material or when directly laminating a metal layer.

[0034] That is, in the present invention, for the silicon nitride sintered substrate, regarding the surface, it is preferable that Ra is 0.6 μm or less, particularly 0.5 μm or less, and the value of the arithmetic mean curvature (Spc) of the peak points is 4.5 [1 / mm] or less, particularly 4.2 [1 / mm] or less.

[0035] The value of Ra indicating the above surface roughness and the value of Spc indicating the state of the convex portions of the surface are specifically shown in the examples described later, and are values obtained using a non-contact three-dimensional measuring device (manufactured by Keyence Corporation, product name: VR-5000).

[0036] Here, Spc will be explained. The arithmetic mean curvature Spc of the peak points represents the average of the principal curvatures of the peak points on the surface. The following formula 1 is the calculation formula for the arithmetic mean curvature Spc of the peak points. In formula 1, z means the height direction component in the x and y coordinates, n indicates the number of peak points, and the arithmetic mean curvature Spc of the peak points represents the average value of the reciprocals of the radii of the approximate circles of the peak points of the surface uneven shape. The smaller this value, the more rounded the peak of the mountain and the wider the shape.

[0037]

Equation

[0038] The silicon nitride sintered substrate of the present invention has the small Ra value and shows an extremely small value of the Spc value on the surface of 4.5 [1 / mm] or less. As a result, it has a smoother surface texture compared to conventional silicon nitride sintered substrates whose Spc values generally exceed 5 [1 / mm].

[0039] In addition, in the crystal grains constituting the sintered body of the silicon nitride sintered substrate of the present invention, in a micrograph measured by taking a scanning electron micrograph of an arbitrary cross-section at a magnification of 2000 times, the maximum major axis of the crystal grains observed in the visual field range 50 μm or more inside from the surface is 10.0 μm or less, particularly 4.0 to 7.0 μm, the average major axis is 1.5 to 2.0 μm, and the ratio of the major axis to the minor axis (major axis / minor axis) is 1 to 5, particularly preferably 3 to 5.

[0040] The properties of the crystal grains inside the substrate also affect the state of the substrate surface. Therefore, a silicon nitride sintered substrate in which the crystal grains inside the substrate are within the above range is suitable. That is, when the maximum major axis, average major axis, and the ratio of the major axis to the minor axis exceed the above range, the integrated volume of specific pores tends to increase. Also, when the average major axis and the ratio of the major axis to the minor axis are smaller than the above range, the strength of the silicon nitride sintered substrate tends to decrease.

[0041] The thickness of the silicon nitride sintered substrate of the present invention is not particularly limited, but the range of 0.1 to 1.5 mm is common. As described later, the silicon nitride sintered substrate of the present invention is preferably obtained using silicon nitride powder that does not substantially contain or contains no aluminum as a raw material. Therefore, the total aluminum concentration in the sintered substrate is 0.1% by mass or less, particularly 800 ppm or less. Although boron nitride powder is generally used as a parting agent, the surface boron concentration of the silicon nitride sintered substrate of the present invention after removing foreign matter by the blasting treatment is less than the detection limit as measured by fluorescent X-ray analysis. And due to such characteristics, when the laminated substrate for a semiconductor is configured, a decrease in heat cycle resistance and the occurrence of malfunction of the semiconductor can be effectively suppressed.

[0042] [Method for manufacturing silicon nitride sintered body] The method for manufacturing the silicon nitride sintered substrate of the present invention is not particularly limited. However, if a typical method is exemplified, a green sheet containing silicon nitride powder with a β-phase ratio of 90% or more, a specific surface area of 7 to 20 m 2 / g, and a crystal strain of 4.0×10 -4 or more, and a sintering aid, and having the total content of aluminum element adjusted to 800 ppm or less, is heated to a temperature of 1200 to 1800 °C under an inert gas atmosphere and a pressure of 0.1 MPa·G or more and less than 0.5 MPa·G to sinter silicon nitride.

[0043] According to the above method, by using silicon nitride powder having a high β-phase ratio, a high specific surface area obtained by a specific pulverization described later, and a high crystal strain, dense sintering can be performed at low pressure and low temperature. As a result, it is possible to suppress the growth of acicular crystals on the surface of the silicon nitride sintered substrate, and to obtain a silicon nitride sintered substrate with excellent properties while suppressing the formation of pores with a size of 1 to 10 μm on the substrate surface.

[0044] [Method for manufacturing silicon nitride sintered body using continuous firing furnace] Furthermore, it is preferable to use a continuous firing furnace in the method for manufacturing the silicon nitride sintered body of the present invention. Specifically, a green sheet having a β-phase ratio of 80% or more, a specific surface area of 7 to 20 m 2A firing jig containing silicon nitride powder of / g and a sintering aid and accommodating a green sheet with the total aluminum element content adjusted to 800 ppm or less is supplied to a continuous firing furnace equipped with a sealed firing container having a supply opening / closing door and a discharge opening / closing door at its ends, a heating mechanism provided on the outer periphery of the body of the firing container, a transfer mechanism for feeding and discharging the firing jig into and out of the firing container, and a gas supply mechanism for supplying an inert gas into the firing container, and heated to a temperature of 1200 to 1800 °C under an inert gas atmosphere and a pressure of 0 MPa·G or more and less than 0.1 MPa·G (hereinafter, such a slightly pressurized range may also be referred to as "normal pressure"). Silicon nitride is sintered.

[0045] Regarding the advantages when using a continuous firing furnace, when firing under pressure in the conventional case, it was necessary to use a pressure-resistant container during manufacturing. Therefore, the manufacturing method had equipment constraints and could only be carried out by a batch method, and there was a problem that the manufacturing cost was high due to the need to repeat the temperature increase and cooling for each batch. However, since the present invention adopts conditions for sintering at normal pressure or substantially normal pressure without the need to use a pressure-resistant container, by using the above continuous firing furnace, continuous firing can be performed from the supply of the sintering raw material to the firing furnace to the removal of the sintered body after firing, eliminating the need to raise the temperature of the furnace from room temperature to the firing temperature for each batch, enabling sintering with extremely low energy, and being able to manufacture a silicon nitride sintered body with good productivity, so it is effective for reducing the manufacturing cost.

[0046] 〔Green sheet〕 In the method for manufacturing a silicon nitride sintered substrate of the present invention, the green sheet contains specific silicon nitride powder and a sintering aid described below.

[0047] <Silicon nitride powder> (β conversion rate) The β-phase conversion rate of the silicon nitride powder contained in the green sheet is 80% or more. Since silicon nitride powder with a β-phase conversion rate of 80% or more can be obtained without setting strict manufacturing conditions, it can be manufactured at a relatively low cost. Therefore, by using silicon nitride powder with a high β-phase conversion rate, the overall manufacturing cost of the silicon nitride sintered body can be suppressed. In addition, by setting a high β-phase conversion rate, the amount of oxygen taken in when α-type silicon nitride particles transform into β-type silicon nitride particles during firing can be further reduced. Here, the β-phase conversion rate of the silicon nitride powder is preferably 85% or more, more preferably 90% or more.

[0048] Note that the β-phase conversion rate of the silicon nitride powder means the peak intensity ratio of the β-phase to the total of the α-phase and β-phase in the silicon nitride powder [100×(peak intensity of the β-phase) / (peak intensity of the α-phase + peak intensity of the β-phase)], and is determined by powder X-ray diffraction (XRD) measurement using CuKα rays. More specifically, it is determined by calculating the weight ratio of the α-phase and β-phase of the silicon nitride powder by the method described in C.P. Gazzara and D.R. Messier: Ceram. Bull., 56(1977), 777-780.

[0049] (Specific surface area) The specific surface area of the silicon nitride powder is 7 to 20 m 2 / g. When the specific surface area of the silicon nitride powder exceeds 20 m 2 / g, it becomes difficult to lower the amount of dissolved oxygen, and when the specific surface area is less than 7 m 2 / g, it becomes difficult to obtain a high-density and high-strength silicon nitride sintered body. The specific surface area of the silicon nitride powder is preferably 12 to 15 m 2 / g.

[0050] Note that in the present invention, the specific surface area means the BET specific surface area measured using the BET one-point method by nitrogen gas adsorption.

[0051] (Crystal strain) In the production of the silicon nitride sintered substrate of the present invention, the silicon nitride powder, together with the above characteristics, has a crystal strain of 4.0×10 -4The above-described materials are used. Although it is not clear how the formation of the network structure on the surface of the silicon nitride sintered substrate, i.e., the generation of pores, is affected by such crystal distortion, according to the experiments of the present inventors, it was confirmed that the integrated volume of the specific pores can be reduced by changing the crystal distortion of the silicon nitride powder to the larger side.

[0052] Note that the crystal distortion was measured by the method shown in the examples.

[0053] (Other physical properties) Other physical properties of the silicon nitride powder are not particularly limited. For example, from the viewpoint of obtaining a silicon nitride sintered body with high thermal conductivity, the amount of dissolved oxygen is preferably 0.2% by mass or less, more preferably 0.1% by mass or less.

[0054] Here, the amount of dissolved oxygen means oxygen dissolved inside the particles of the silicon nitride powder (hereinafter also referred to as internal oxygen), and does not include oxygen derived from oxides such as SiO2 inevitably present on the particle surface (hereinafter also referred to as external oxygen).

[0055] The amount of dissolved oxygen can be measured by the method described in the examples.

[0056] The method for adjusting the amount of dissolved oxygen in the silicon nitride powder is not particularly limited. For example, when producing the silicon nitride powder, it is preferable to use high-purity raw materials. For example, when producing the silicon nitride powder by the direct nitridation method, it is preferable to use silicon powder that has no factor for oxygen to be dissolved inside as the raw material to be used. Specifically, it is preferable to use silicon powder derived from semiconductor-grade silicon, for example, silicon powder typified by the cutting powder generated when the above silicon is processed such as cutting. The above semiconductor-grade silicon is typically polycrystalline silicon obtained by the so-called "Siemens method" in which high-purity trichlorosilane and hydrogen are reacted in a Bell jar type reaction vessel. Also, the average particle size D of the silicon nitride powder 50is preferably 0.5 to 3 μm, more preferably 0.7 to 1.7 μm. When using silicon nitride powder with such an average particle size, sintering is more likely to proceed. The average particle size D 50 is the value based on 50% volume measured by the laser diffraction scattering method.

[0057] The proportion of particles with a particle size of 0.5 μm or less in the silicon nitride powder is preferably 20 to 50% by mass, more preferably 20 to 40% by mass. Also, the proportion of particles with a particle size of 1 μm or more in the silicon nitride powder is preferably 20 to 50% by mass, more preferably 20 to 40% by mass. When using silicon nitride powder having such a particle size distribution, it is easy to obtain a dense silicon nitride sintered body with high thermal conductivity.

[0058] The reason for this is not clear, but unlike α-type silicon nitride particles, β-type silicon nitride particles are less likely to undergo dissolution and reprecipitation during firing, and by adjusting fine particles and coarse particles to a certain balance at the initial stage of firing, it is considered possible to obtain a denser sintered body. Furthermore, the total oxygen content of the silicon nitride powder is preferably 1% by mass or more. The total oxygen content is the sum of the above-mentioned solid-solution oxygen (internal oxygen) content and the external oxygen content. When the total oxygen content is equal to or higher than these lower limit values, for example, the effect that sintering is easily promoted by silicon oxide on the particle surface is exhibited.

[0059] Even if the total oxygen content of the silicon nitride powder is 1% by mass or more, as long as the solid-solution oxygen content is below a certain value as described above, the thermal conductivity of the sintered body can be increased.

[0060] The total oxygen content of the silicon nitride powder can be measured by the method described in the examples.

[0061] The amount of silicon nitride powder in the green sheet is preferably 70% by mass or more, more preferably 80% by mass or more, based on the total amount of the green sheet.

[0062] <Manufacture of Silicon Nitride Powder> The method for producing silicon nitride powder is not particularly limited as long as it can obtain silicon nitride powder having the above-described characteristics. Examples of the method for producing silicon nitride powder include a reduction nitridation method in which silica powder is used as a raw material and nitrogen gas is passed through in the presence of carbon powder to produce silicon nitride, a direct nitridation method in which silicon powder and nitrogen are reacted at a high temperature, and an imide decomposition method in which silicon halide and ammonia are reacted. However, from the viewpoint of easily producing silicon nitride powder having the above-described characteristics, the direct nitridation method is preferable, and among them, the direct nitridation method (combustion synthesis method) using the self-combustion method is more preferable.

[0063] The combustion synthesis method is a method in which silicon powder is used as a raw material, a part of the raw material powder is forced to ignite in a nitrogen atmosphere, and silicon nitride is synthesized by the self-exotherm of the raw material compound. The combustion synthesis method is a known method, and for example, reference can be made to JP-A-2000-264608, WO 2019 / 167879, etc.

[0064] In addition, although the crystal strain obtained by the above combustion synthesis method has a certain degree of large crystal strain, the crystal strain can be further increased by further pulverization. As the above pulverization method, pulverization by a vibration ball mill is preferable, and it is preferable to perform such pulverization for 5 to 15 hours.

[0065] <Sintering aid> In the green sheet used for producing the silicon nitride sintered substrate of the present invention, known sintering aids can be used without particular limitation, but it is preferable to use a sintering aid containing a compound having no oxygen bond because it can prevent a decrease in the thermal conductivity of the obtained silicon nitride sintered substrate.

[0066] As the compound having no oxygen bond, a carbonitride-based compound containing a rare earth element or a magnesium element (hereinafter, also referred to as a specific carbonitride-based compound) and a nitride-based compound (hereinafter, also referred to as a specific nitride-based compound) are preferable. By using such a specific carbonitride-based compound and a specific nitride-based compound, it becomes easier to obtain a silicon nitride sintered body having a higher thermal conductivity more effectively. The above specific carbonitride-based compound functions as a getter agent that adsorbs oxygen contained in the silicon nitride powder, and in the specific nitride-based compound, the total oxygen amount of the silicon nitride sintered body is reduced, and as a result, a silicon nitride sintered body having a high thermal conductivity can be obtained.

[0067] In the carbonitride-based compound containing a rare earth element, as the rare earth element, Y (yttrium), La (lanthanum), Sm (samarium), Ce (cerium), Yb (ytterbium), etc. are preferable.

[0068] Examples of the carbonitride-based compound containing a rare earth element include Y2Si4N6C, Yb2Si4N6C, Ce2Si4N6C, etc. Among these, from the viewpoint of easily obtaining a silicon nitride sintered body having a high thermal conductivity, Y2Si4N6C and Yb2Si4N6C are preferable.

[0069] Examples of the carbonitride-based compound containing a magnesium element include MgSi4N6C, etc. Examples of the specific nitride-based compound containing a magnesium element include MgSiN2, etc.

[0070] These specific carbonitride-based compounds and specific nitride-based compounds may be used alone or in combination of two or more.

[0071] Among the above-described carbonitride-based compounds containing a rare earth element or a magnesium element, particularly preferable compounds and specific nitride-based compounds are Y2Si4N6C, MgSi4N6C, and MgSiN2.

[0072] In addition to the compound having no oxygen bond, the sintering aid can further contain a metal oxide. By containing a metal oxide in the sintering aid, the sintering of the silicon nitride powder is facilitated, and it becomes easier to obtain a denser and higher-strength sintered body.

[0073] Examples of the metal oxide include yttria (Y2O3), magnesia (MgO), ceria (CeO), etc. Among these, yttria is preferred. The metal oxide may be used alone or in combination of two or more.

[0074] The mass ratio (compound having no oxygen / metal oxide) of the compound having no oxygen represented by the specific carbonitride-based compound contained in the sintering aid to the metal oxide is preferably 0.2 to 4, more preferably 0.6 to 2. In such a range, it becomes easier to obtain a dense silicon nitride sintered body with high thermal conductivity.

[0075] Also, the content of the sintering aid in the green sheet is preferably 5 to 20 parts by mass, more preferably 7 to 10 parts by mass with respect to 100 parts by mass of the silicon nitride powder.

[0076] <Binder> The green sheet can be formed using a binder. In this case, the green sheet is formed by forming the following molding composition into a sheet shape, drying it as necessary, and removing the binder by degreasing under known conditions to be subjected to firing.

[0077] The binder is not particularly limited, and examples thereof include polyvinyl alcohol, polyvinyl butyral, methyl cellulose, alginic acid, polyethylene glycol, carboxymethyl cellulose, ethyl cellulose, acrylic resin, etc.

[0078] The content of the binder used in the production of the green sheet is preferably 1 to 30 parts by mass with respect to 100 parts by mass of the silicon nitride powder, and the ratio may be appropriately determined according to the molding method.

[0079] <Total content of aluminum element> The total content (by mass) of aluminum element in the green sheet is 800 ppm or less. That is, the green sheet used in the present invention has a very small amount of aluminum element, and thus it is possible to obtain a silicon nitride sintered body having a high thermal conductivity. The total content of aluminum element in the green sheet is preferably 700 ppm or less, and more preferably 600 ppm or less.

[0080] 〔Manufacture of green sheet〕 The method for manufacturing the green sheet used in the present invention is not particularly limited. For example, there is a method of molding a molding composition containing at least silicon nitride powder and a sintering aid by known molding means. Examples of known molding means include, for example, press molding method, extrusion molding method, injection molding method, doctor blade method, etc. In particular, the doctor blade method is preferable.

[0081] In addition, from the viewpoints of ease of handling and ease of molding, the molding composition may contain a solvent. The solvent is not particularly limited, and examples thereof include organic solvents such as alcohols and hydrocarbons, and water. In the present invention, it is preferable to use water. That is, it is preferable to mold a molding composition containing silicon nitride powder, a sintering aid, and water to obtain a green sheet. When water is used as the solvent, the environmental load is reduced as compared with the case of using an organic solvent, which is preferable.

[0082] 〔Sintering method〕 In the method for manufacturing the silicon nitride sintered body of the present invention, the above-mentioned green sheet is degreased if necessary and then fired under certain conditions to sinter silicon nitride. In the above firing, it is common to apply a parting material made of boron nitride powder to the green sheet in advance. Hereinafter, the conditions for firing will be described.

[0083] The firing is carried out in an inert gas atmosphere. The inert gas atmosphere means, for example, a nitrogen atmosphere or an argon atmosphere.

[0084] Also, in such an inert gas atmosphere, firing is carried out under a pressure of 0 MPa·G or more and less than 0.1 MPa·G. The pressure is preferably 0 MPa·G or more and 0.05 MPa·G or less. Here, the G at the end of the pressure unit MPa·G means gauge pressure.

[0085] Since firing does not require high pressure, it can be carried out in a batch furnace such as a muffle furnace or a tubular furnace, or it is also possible to carry out in a continuous furnace such as a pusher furnace.

[0086] The green sheet is heated to a temperature of 1200 to 1800 °C for firing. If the temperature is less than 1200 °C, the sintering of silicon nitride becomes difficult to progress, and if it exceeds 1800 °C, silicon nitride is likely to decompose. From such a viewpoint, the heating temperature during firing is preferably 1600 to 1800 °C.

[0087] Also, the firing time is not particularly limited, but it is preferably about 3 to 20 hours.

[0088] When a binder is used for the formation of the green sheet, it is preferable to carry out the removal of organic components such as the binder by providing a degreasing step. The above degreasing conditions are not particularly limited, but for example, it may be carried out by heating the green sheet to 450 to 650 °C in air or in an inert atmosphere such as nitrogen or argon.

[0089] By carrying out the above firing, a silicon nitride sintered substrate having the above characteristic properties can be obtained.

[0090] 〔Sintering method using a continuous firing furnace〕 Furthermore, in the method for producing a silicon nitride sintered body of the present invention, continuous firing can be carried out using a continuous firing furnace.

[0091] FIG. 1 is a schematic view showing one embodiment of a continuous firing furnace used for continuous firing of the present invention.

[0092] As shown in FIG. 1, a firing jig 2 containing a green sheet 1 is supplied to a continuous firing furnace equipped with a sealed firing container 5 having a supply opening / closing door 3 and a discharge opening / closing door 4 for the firing jig at its ends, a heating mechanism 6 provided on the outer periphery of the body of the firing container, a transfer mechanism for feeding and discharging the firing jig into and out of the firing container, and a gas supply mechanism for supplying an inert gas into the firing container, and the green sheet is fired to produce a silicon nitride sintered body.

[0093] Hereinafter, the above firing method will be described for an embodiment in which the sintered body having the shape of the green sheet 1 is plate-shaped and used as a substrate for a semiconductor device. It is efficient to stack a plurality of plate-shaped objects to be fired, accommodate them in a firing jig, and supply and discharge them to and from a continuous firing furnace. When the green sheet is formed using a binder, it is preferable to stack and handle them from before degreasing as described above. Further, it is preferable to interpose boron nitride powder as a mold release material between the layers in the above stacking. Further, as shown in the enlarged view of FIG. 1, the firing jig 2 is preferably a box-shaped container having side walls. Although not shown, it is preferable to arrange, for example, plate-shaped sintered bodies of silicon nitride at the upper and lower ends of the stacked green sheets.

[0094] In the continuous firing furnace, the firing container 5 for firing in an inert gas atmosphere only needs to have a structure that can withstand the pressure of normal pressure, and a high-pressure resistant structure is not required. For example, a casing made of stainless steel or the like with a heat-resistant member, specifically, a carbon member lined inside is suitable.

[0095] The above-mentioned inert gas atmosphere is formed by supplying an inert gas such as nitrogen gas or argon gas (hereinafter, nitrogen is described as an example) to the firing container 5. The pressure inside the firing container is preferably adjusted to 0 MPa·G or more and less than 0.1 MPa·G. More preferably, the pressure is 0 MPa·G or more and 0.05 MPa·G or less. Here, the G at the end of the pressure unit MPa·G means gauge pressure.

[0096] Generally, at such a pressure in the normal pressure or substantially normal pressure range, since silicon nitride is easily decomposed, the temperature for firing cannot be set to exceed, for example, 1800 °C. Therefore, it has been difficult to obtain a dense silicon nitride sintered body with high thermal conductivity. On the other hand, in the manufacturing method of the present invention, since the green sheet using the specific raw material as described above is used, it is possible to fire at a temperature that can prevent the decomposition of silicon nitride within the above pressure range, and a silicon nitride sintered body with high thermal conductivity can be obtained.

[0097] The green sheet is heated and fired at a temperature of 1200 to 1800 °C. When the firing temperature is less than 1200 °C, the sintering of silicon nitride hardly proceeds, and when it exceeds 1800 °C, silicon nitride is easily decomposed. From such a viewpoint, the heating temperature for firing is preferably 1600 to 1800 °C.

[0098] A heating mechanism 6 for adjusting the inside of the container to the temperature for the firing is provided in the body of the firing container 5. As the heating mechanism 6, a carbon heater is common. Further, in order to adjust the heating rate to the temperature for firing in the firing container 5, the maintenance of the above temperature, and the temperature profile from the above temperature to cooling, it is preferably divided into a plurality of zones in the advancing direction of the green sheet and independently temperature controllable. In the drawing, the heating mechanism 6 is shown in a three-divided mode, but in order to perform a finer temperature setting, it can be divided into four or more parts and provided so that each heating temperature can be independently adjusted. The ratio of the heating time in each zone can be changed by adjusting the division ratio of the heating mechanism 6.

[0099] In the continuous firing furnace, as the transport mechanism for transporting the firing jig 2 containing the green sheet 1, a structure adopted in a known continuous heating furnace can be adopted without particular limitation. FIG. 1 shows a pusher-type transport mechanism that sequentially pushes the firing jig 2 forward from the inlet side of the firing container 5 within the firing container 5. Specifically, it includes a guide plate 8 for sliding the fired jig 2 pushed in from the inlet side and moving it inside the furnace, and a roller 9 (not shown) having a drive unit for independently removing the fired jig 2 from the furnace near the outlet of the firing container 5.

[0100] The firing time at the heating temperature is not particularly limited, but it is preferably about 3 to 20 hours at the temperature for firing, and such time is set by adjusting the transport speed by the above transport means, the length of the firing container, etc.

[0101] For loading and unloading the firing jig 2 into and out of the firing container 5 of the continuous firing furnace, a supply opening / closing door 3 and a discharge opening / closing door 4 that can be opened and closed are provided at the inlet and outlet, respectively. The supply opening / closing door 3 and the discharge opening / closing door 4 open and close in conjunction with the operation of the transport mechanism when supplying or removing the firing jig 2 into the firing container 5. As the supply opening / closing door 3 and the discharge opening / closing door 4, those having a known structure capable of ensuring the airtightness inside the firing container can be used without particular limitation.

[0102] The continuous firing furnace used in the present invention is provided with a supply chamber 11 partitioned from the firing container 5 by a supply opening / closing door 3 and equipped with a facility for nitrogen replacement of the internal space on the inlet side of the firing container 5. In the supply chamber, the loading door (not shown) is opened to load the firing jig, the internal space is nitrogen-replaced, and after the pressure is adjusted to match that inside the firing container 5, the supply opening / closing door 3 is opened and the firing jig 2 is pushed into the firing container for supply. For the above operation, a piston cylinder 10 can be provided in the supply chamber 11. Incidentally, it is preferable that the supply chamber 11 is provided with a guide plate 7 having the same height as the transport surface of the firing container to smoothly supply the firing container to the transport means.

[0103] On one hand, on the outlet side of the firing container 5, there is provided a take-out chamber 13 which is partitioned from the firing container 5 by an opening / closing door 4 for discharge and is equipped with a facility for nitrogen replacement of the internal space. When taking out the firing jig from the firing container 5, the internal space of the take-out chamber 13 is nitrogen-replaced, the pressure is adjusted to match that inside the firing container 5, and then the opening / closing door 4 for discharge is opened, and an operation of taking out the firing jig 2 into the take-out chamber 13 is performed. Then, the opening / closing door 4 for discharge is closed, the take-out door 12 is opened, and the silicon nitride sintered body is taken out together with the firing jig from the take-out chamber 13. It is preferable that the supply and discharge of the firing jig 2 to / from the firing container 5 are carried out in conjunction so that the number of firing jigs 2 inside the firing container is constant.

[0104] Thus, the silicon nitride sintered body can be continuously fired by a continuous firing furnace.

[0105] In addition, the silicon nitride substrate of the present invention is made into a product by removing deposits such as a release material made of boron nitride powder attached by performing the blasting treatment after firing.

Example

[0106] Hereinafter, examples are shown to more specifically explain the present invention, but the present invention is not limited to these examples.

[0107] In the examples, the measurement of various physical properties was carried out by the following methods.

[0108] (1) β-phase ratio of silicon nitride powder The β-phase ratio of the silicon nitride powder was determined by powder X-ray diffraction (XRD) measurement using CuKα rays. Specifically, according to the method described in C.P. Gazzara and D.R. Messier: Ceram. Bull., 56(1977), 777-780, the weight ratios of the α-phase and β-phase of the silicon nitride powder were calculated to obtain the β-phase ratio.

[0109] (2) Specific surface area of silicon nitride powder The specific surface area of the silicon nitride powder was measured using the BET one-point method by nitrogen gas adsorption with a BET specific surface area measuring device (Macsorb HM model-1201) manufactured by Mountech Co., Ltd.

[0110] Before performing the above-mentioned specific surface area measurement, the silicon nitride powder to be measured was heat-treated in air at 600 °C for 30 minutes in advance to remove the organic substances adsorbed on the powder surface.

[0111] (3) Crystal strain of silicon nitride powder It was calculated by the following procedure using powder X-ray diffraction (XRD) with CuKα rays. From the X-ray diffraction pattern obtained by scanning the X-ray detector in steps of 0.02° in the range of 2θ from 15° to 80°, the integral widths of the (101), (110), (200), (201) and (210) planes of the β phase were calculated, and the integral widths were substituted into the Williamson-Hall equation of Equation 2 below. Plotting "2sinθ / λ" on the X-axis and "βcosθ / λ" on the Y-axis in Equation 2 below, the crystal strain (η) was calculated from the slope of the straight line obtained by the least squares method. βcosθ / λ = η×(2sinθ / λ)+(1 / Dc) (2) (β: integral width (rad), θ: Bragg angle (rad), η: crystal strain, λ: X-ray wavelength, Dc: crystal diameter (nm))

[0112] (4) Particle size of silicon nitride powder (i) Pretreatment of sample As a pretreatment for the silicon nitride powder of the sample, the silicon nitride powder was calcined in air at a temperature of about 500 °C for 2 hours. In the above calcination treatment, in particle size measurement, there may be cases where the amount of surface oxygen of the silicon nitride powder is small, or the particle surface is covered with a hydrophobic substance by a grinding aid or the like during grinding, and the particles themselves exhibit hydrophobicity. In such cases, the dispersion in water becomes insufficient, and it may be difficult to perform reproducible particle size measurement. Therefore, by calcining the silicon nitride powder of the sample in air at a temperature of about 200 °C to 500 °C for several hours, hydrophilicity is imparted to the silicon nitride powder, making it easier to disperse in an aqueous solvent and enabling highly reproducible particle size measurement. At this time, it has been confirmed that calcining in air has almost no effect on the measured particle size.

[0113] (ii) Measurement of particle size Into a beaker (inner diameter 60 mmφ, height 70 mm) with a scale line of up to 100 mL, 90 mL of water and 5 mL of sodium pyrophosphate with a concentration of 5 mass% were added and stirred well. Then, about a spoonful of the silicon nitride powder of the sample was added, and the silicon nitride powder was dispersed for 2 minutes at an AMPLITUDE (amplitude) of 50% (about 2 amperes) using an ultrasonic homogenizer (US-300E manufactured by Nippon Seiki Co., Ltd., chip diameter 26 mm).

[0114] Note that the tip of the above chip was inserted up to the position of the 20 mL scale line of the beaker for dispersion.

[0115] Next, for the obtained dispersion of the silicon nitride powder, the particle size distribution was measured using a laser diffraction / scattering particle size distribution measuring device (Microtrac MT3300EXII manufactured by Microtrac Bell Co., Ltd.). The measurement conditions were as follows: the solvent was water (refractive index 1.33), the particle characteristics were a refractive index of 2.01, the particle permeability was transmission, and the particle shape was non-spherical. The particle size at which the cumulative curve of the particle size distribution measured by the above particle size distribution measurement reaches 50% is defined as the average particle size (average particle diameter D50).

[0116] (5) Integrated volume of pores in the silicon nitride sintered substrate by mercury intrusion method As samples, 20 samples each with a size of 2×2×(0.04) cm were arbitrarily cut out from a silicon nitride sintered substrate. For each sample, to eliminate the influence of indentation from the side surface, the side surface of the sample was dipped into a high-viscosity resin (epoxy resin) that does not penetrate into the pores so that the peripheral edge of the plane is recessed by 0.1 mm, and the side surface was sealed.

[0117] For the samples obtained in this way, a pore size distribution curve was obtained using a mercury porosimeter (manufactured by Micromeritics, product name: AutoPore IV9520). From this, the integrated volume in a predetermined range was determined and shown as the average value of the samples.

[0118] (6) Ra and Spc of the silicon nitride sintered substrate Values determined by the international standard ISO 25178 surface texture (surface roughness measurement) are used. That is, Ra and Spc are values obtained by measuring an evaluation area in an arbitrary range of 1000 μm×1000 μm of the silicon nitride sintered substrate using a non-contact three-dimensional measuring device (manufactured by Keyence, product name: VR-5000). Specifically, an area in an arbitrary range of 2 cm×2 cm was determined, and the evaluation areas of 1000 μm×1000 μm were measured at least 20 locations within the area of the arbitrary range, and shown as the average value of the obtained values.

[0119] (7) Measurement of the major axis and minor axis of the crystal grains of the silicon nitride sintered substrate In the micrographs measured by taking scanning electron micrographs at a magnification of 2000 times of five arbitrarily selected cross-sections of the silicon nitride sintered substrate, the major axis and minor axis of the crystal grains observed in the visual field range 50 μm or more inside from the surface were measured, and the maximum major axis, average major axis, and major axis / minor axis ratio were determined.

[0120] (8) Thermal conductivity of the silicon nitride sintered substrate The thermal conductivity of the silicon nitride sintered body was measured by the laser flash method using an LFA-502 manufactured by Kyoto Electronics Industry Co., Ltd. The thermal conductivity is obtained by multiplying the thermal diffusivity, the sintered body density, and the specific heat of the sintered body. Incidentally, a value of 0.68 (J / g·K) was adopted for the specific heat of the silicon nitride sintered body. The sintered body density was measured using an automatic specific gravity meter (manufactured by Shin-Ko Electronics Co., Ltd.: DMA-220H type).

[0121] In addition, the measurement of the thermal conductivity was carried out after the surface of the silicon nitride sintered body was blasted and then Au-coated and carbon-coated on the surface.

[0122] (9) Dielectric breakdown voltage of the silicon nitride sintered substrate In accordance with JIS C2110, the dielectric breakdown voltage was measured. Specifically, a voltage was applied to the silicon nitride sintered substrate using a dielectric withstand voltage measuring device (「TK-O-20K」manufactured by Measurement Technology Research Institute), and the voltage at which dielectric breakdown occurred was measured.

[0123] (10) Total content of aluminum element in the silicon nitride sintered substrate The total content of aluminum element in the silicon nitride sintered substrate was measured using an inductively coupled plasma optical emission spectrometer (「iCAP 6500 DUO」manufactured by Thermo Fisher Scientific).

[0124] (11) Content of boron element on the surface of the silicon nitride sintered substrate The content of boron element on the surface of the silicon nitride sintered substrate was measured using a fluorescent X-ray analyzer (ZSX PrimusIV manufactured by Rigaku). Incidentally, in the above measurement, the detection limit of the boron element is 0.7 mass%.

[0125] (12) Evaluation of metallization characteristics A copper plate was joined to the silicon nitride sintered substrate, and the metallization characteristics were evaluated. As the metallization methods, metallized substrates were respectively fabricated using the AMB (Active Metal Brazing) method and the DBC (Direct Bonded Copper) method. For the metallized substrate using AMB, a brazing material (Ag-Cu-Ti 75:21:4 (mass ratio)) containing an active metal was screen-printed on both sides of the silicon nitride substrate, a 0.3 mm thick copper plate was placed, and it was heated at 850 °C for 20 minutes in a vacuum. Thereafter, in order to form a pattern, it was immersed in an aqueous solution of ferric chloride for etching. Further, in order to remove the remaining composite material, the copper plate portion was etched in an aqueous solution of ammonium fluoride and acid, and then washed with water to fabricate a metallized substrate. For the metallized substrate using DBC, copper plates (thickness 0.3 mm) were set on both sides of the silicon nitride substrate, and it was held in an inert atmosphere at 1070 °C for 10 minutes or more above the eutectic temperature to perform bonding through a eutectic compound. Thereafter, in order to form a pattern, it was immersed in an aqueous solution of ferric chloride for etching. Further, in order to remove the remaining composite material, the copper plate portion was etched in an aqueous solution of ammonium fluoride and acid, and then washed with water to fabricate a metallized substrate. Next, the metallized substrates obtained by each method were subjected to a heat cycle test (-40 to 200 °C). A heat cycle test was performed using 10 samples, and the following visual evaluation was performed. ○; None of the 10 samples had cracks or delamination. △; 1 to 9 samples had cracks or delamination. ×; All 10 samples had delamination.

[0126] In each of the examples and comparative examples, the following raw materials were used.

[0127] <Silicon nitride powder> Silicon nitride powders A and B shown in Table 1 were prepared. These were manufactured by the following method.

[0128] (Manufacture of silicon nitride powder A) Silicon powder (semiconductor grade, average particle size 5 μm) and silicon nitride powder (average particle size 1.5 μm) as a diluent were mixed to obtain raw material powder (Si: 80% by mass, Si3N4: 20% by mass). The raw material powder was filled into a reaction vessel to form a raw material powder layer. Next, the reaction vessel was placed in a pressure-resistant sealed reactor having an ignition device and a gas supply and exhaust mechanism. After evacuating the inside of the reactor to remove air, nitrogen gas was supplied for nitrogen substitution. Then, nitrogen gas was gradually supplied to increase the pressure to 0.7 MPa. The bulk density of the raw material powder at the time when the predetermined pressure was reached (ignition time) was 0.5 g / cm 3 was obtained.

[0129] Thereafter, the end of the raw material powder in the reaction vessel was ignited to carry out a combustion synthesis reaction, and a massive product made of silicon nitride was obtained. The obtained massive product was crushed by rubbing against each other, and then an appropriate amount was put into a vibration ball mill for fine pulverization for 6 hours. In addition, for the above pulverization, as a measure to prevent heavy metal contamination, the inside of the pulverizer was lined with urethane, and balls mainly made of silicon nitride were used as the pulverization media. Also, 1% by mass of ethanol was added as a pulverization aid immediately before the start of fine pulverization, and the pulverizer was kept in a sealed state and fine pulverization was carried out until the crystal strain shown in Table 1 was obtained, and silicon nitride powder was obtained. The measurement results of the obtained silicon nitride powder are shown in Table 1.

[0130] (Silicon nitride powder B) As the silicon nitride powder B, a commercially available α-type silicon nitride powder having the characteristics shown in Table 1 was used.

[0131]

Table 1

[0132] <Sintering aid> ·Y2Si4N6C powder: Yttria (manufactured by Shin-Etsu Chemical Co., Ltd.), the silicon nitride powder and carbon powder (manufactured by Mitsubishi Chemical) obtained by the above method were subjected to heat synthesis using the following reaction formula.

[0133] 8Si3N4 + 6Y2O3 + 15C + 2N2 → 6Y2Si4N6C + 9CO2 · MgSiN2 powder: Magnesium powder (Yamatake Metal Co., Ltd.), silicon nitride powder and metallic silicon powder (owned by the company itself) obtained by the above method were subjected to heat synthesis using the following reaction formula to produce it.

[0134] Si3N4 + Si + 4Mg + 2N2 → 4MgSiN2 · Yttria (Y2O3) powder: Manufactured by Shin-Etsu Chemical Co., Ltd. <Binder> Polyvinyl alcohol resin (Nippon Vinyl Acetate - Poval Co., Ltd.) was used as the binder.

[0135] [Example 1] 100 parts by mass of silicon nitride powder A, 2 parts by mass of compound Y2Si4N6C powder containing no oxygen bond, 5 parts by mass of MgSiN2 powder, and 3 parts by mass of yttria powder were weighed, and using a resin pot and silicon nitride balls with water as the dispersion medium, ball milling was carried out for 24 hours for pulverization and mixing. Note that water was weighed in advance so that the concentration of the slurry was 60 wt% and put into the resin pot. After pulverization and mixing, 22 parts by mass of the binder was added, and mixing was further carried out for 12 hours to obtain a slurry - shaped molding composition. Next, the viscosity of the molding composition was adjusted using a vacuum degassing machine (manufactured by Saya - ma Riken) to prepare a coating slurry. Then, the viscosity - adjusted molding composition was sheet - formed by the doctor - blade method to obtain a green sheet with a width of 75 cm and a thickness of 0.42 mm. The physical properties of the obtained green sheet are shown in Table 2.

[0136] The green sheet obtained as described above was placed in a firing container using boron nitride powder as a release material, and degreasing treatment was carried out at a temperature of 550 °C in dry air to obtain a sheet - shaped degreased body.

[0137] After that, a square cylindrical body made of carbon was attached to the carbon - made plate - shaped jig on which the above degreased body was placed, and it was set so as to surround the periphery as shown in the enlarged view of Figure 1.

[0138] The jig in which the above - mentioned fired body was accommodated was sequentially manufactured, and this was supplied to the continuous firing furnace shown in Figure 1 to carry out continuous firing.

[0139] For the continuous firing furnace, one equipped with a heating mechanism 6 divided into four parts on the body of the firing container 5 was used, and the temperature setting for each zone was programmed according to the conveying speed so as to obtain the firing profile shown in Fig. 2. Nitrogen was supplied into the firing container 5, and the pressure was adjusted to 0.02 MPa·G. On the other hand, the object to be fired was placed on the firing jig 2, the loading door (not shown) of the supply chamber 11 was opened to carry it into the supply chamber, after closing the loading door, the internal space was replaced with nitrogen, and after making the pressure the same as that inside the firing container 5, the supply opening and closing door 3 was opened, and the firing jig 2 was supplied by pushing it into the firing container 5 by the piston cylinder 10.

[0140] By repeating the above operations, the firing jig sequentially advanced inside the firing container 5. During this period, the length of the firing container 5, the number of divisions of the heating mechanism 6, and the length of each zone were set, and by controlling the temperature of each zone, heating was performed so as to obtain the temperature profile (total required time: 24 hours) shown in Fig. 2. Here, firing was performed at 1780 °C for 9 hours.

[0141] After the firing of the firing jig 2 was completed, the internal space of the extraction chamber 13 was replaced with nitrogen, and after making the pressure the same as that inside the firing container 5, the discharge opening and closing door 4 was opened, and the firing jig 2 was taken out into the extraction chamber 13. Then, the discharge opening and closing door 4 was closed, the extraction door 12 was opened, and the silicon nitride sintered body was taken out together with the firing jig from the extraction chamber 13.

[0142] For the obtained silicon nitride sintered substrate, after removing foreign substances on the surface by blasting with alumina abrasive grains having an average particle size of 500 μm at a pressure of 0.3 MPa by an air flow, each physical property was measured. The results are shown together in Table 2.

[0143] Also, for the above silicon nitride sintered substrate, an evaluation test of the metallization characteristics was carried out by the above method. The results are shown in Table 3.

[0144] [Comparative Example 1] Instead of the green sheet used in Example 1, a green sheet having the composition shown in Table 2 was used, and a silicon nitride sintered substrate was obtained in the same manner as in Example 1 except that the firing conditions were changed as shown in Table 2. The physical properties of the sintered body are shown in Table 2. Also, the results of the evaluation test of the metallization characteristics are shown in Table 3.

[0145]

Table 2

[0146]

Table 3

[0147] As understood from the above results, in Comparative Example 1, since the surface undulations are large, in the AMB method, the undulated portions cannot be filled with the brazing material and pores are generated. Also, in the DBC method, the undulations remain as pores as they are. On the other hand, in Example 1, in AMB, since the undulations are gentle, the brazing material is easily filled and pores are hardly generated, and similarly in DBC, pores are hardly generated compared to the comparative products. In this test, in Comparative Example 1, peeling of the copper plate end was visually observed at 50 cycles, but in the silicon nitride sintered substrate of Example 1, no cracks occurred even after 3000 cycles and good results were shown.

Claims

1. A silicon nitride substrate in an unpolished state after sintering, wherein the cumulative pore volume of pores having a pore diameter of 1 to 10 μm measured by mercury intrusion porosimetry is 7.0×10 －５ mL / cm ２ or less, characterized in that it is a silicon nitride sintered substrate.

2. The silicon nitride sintered substrate according to claim 1, wherein, for the surface, Ra is 0.6 μm or less and the value of the arithmetic mean curvature (Spc) of the peak points is 4.5 [1 / mm] or less.

3. In a micrograph measured by taking a scanning electron micrograph of an arbitrary cross-section at a magnification of 2000 times, the maximum major axis of the crystal grains observed in the field of view 50 μm or more inside from the surface is 10.0 μm or less, the average major axis is 1.5 to 2.0 μm, and the ratio of the major axis to the minor axis (major axis / minor axis) is 1 to 5. The silicon nitride sintered substrate according to claim 1 or 2.

4. The silicon nitride sintered substrate according to any one of claims 1 to 3, having a thickness of 0.1 to 1.5 mm.

5. A laminated substrate for a semiconductor, comprising the silicon nitride sintered substrate according to any one of claims 1 to 4.

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