JP2003192445A - Silicon nitride substrate, method of producing the same and silicon nitride substrate having thin film obtained by using the substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon nitride substrate in which a silicon nitride sintered compact has an intrinsic high strength, and especially, the sintered compact constituting the substrate is substantially free from pores, which has small surface roughness, from which particles hardly drop off when it is processed, and which is capable of effectively suppressing the quantity of leak current. <P>SOLUTION: In the silicon nitride substrate formed from the silicon nitride sintered compact containing a sintering aid, the silicon nitride substrate is characterized in that the silicon nitride sintered compact is substantially free from pores. It is preferable that the surface roughness Ra of the silicon nitride substrate is ≤0.5 μm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride substrate, a method for manufacturing the same, and a thin film silicon nitride substrate using the substrate, and more particularly to substantially pores in a sintered body constituting the substrate. Since it is not formed and the surface roughness is small, grain removal is unlikely to occur during processing, and moreover, the generation of leak current is effective when various power modules and circuit boards are constructed using this thin silicon nitride substrate. It is possible to suppress, and even when a thin film is formed on the substrate surface, it is possible to prevent swelling and peeling of the thin film, and even when used in electronic devices with large power consumption and large capacity, its insulating property,
The present invention relates to a silicon nitride substrate capable of greatly improving durability and operation reliability, a method for manufacturing the same, and a silicon nitride substrate with a thin film using the same.

[0002]

2. Description of the Related Art A ceramic sintered body containing silicon nitride as a main component has excellent heat resistance even in a high temperature environment of 1000 ° C. or more, and also has excellent thermal shock resistance due to its low coefficient of thermal expansion. Because of its various characteristics, it has been attempted to be applied to various high-strength heat-resistant parts such as gas turbine parts, engine parts, and steel-making machine parts as high-temperature structural materials replacing conventional heat-resistant superalloys. In addition, since it has excellent corrosion resistance to metals, it has been tried to apply it as a melt-resistant material of molten metal, and because it has excellent wear resistance, it can be put to practical use in sliding members such as bearings and cutting tools. ing.

Conventionally, as a sintering composition of a silicon nitride ceramics sintered body, silicon nitride-yttrium oxide-aluminum oxide system, silicon nitride-yttrium oxide-aluminum oxide-aluminum nitride system, silicon nitride-yttrium oxide- Aluminum oxide-titanium, magnesium, or zirconium oxide systems are known.

Oxides of rare earth elements such as yttrium oxide (Y ₂ O ₃ ) in the above-mentioned sintering composition have been generally used as a sintering aid from the past, and enhance the sinterability to densify the sintered body. It is added to increase the strength.

In recent years, attention has been paid to the high-strength characteristics and insulating properties of silicon nitride sintered bodies, and they have been used as circuit boards for mounting semiconductor elements and the like, especially as substrates for various power modules for large power and large capacity. Attempts are being made to do so.

In the conventional silicon nitride sintered body, a raw material mixture obtained by adding the above-mentioned sintering aid as an additive to silicon nitride powder is press-molded at a pressure of 80 to 100 MPa, or an extrusion molding method is used. Or using the doctor blade method,
The obtained molded body is mass-produced by a manufacturing method in which it is subjected to atmospheric pressure sintering for a long time in a firing furnace at a high temperature of about 1600 to 1900 ° C. and then the furnace is naturally cooled.

[0007]

However, as described above, even when the atmospheric pressure sintering method or the like is adopted in order to increase the density of the sintered body, the pores generated in the sintered body. It was difficult to completely eliminate (Pore).

Therefore, the pores formed in the sintered body increase the dielectric loss, and when used as a circuit board, a leak current is apt to occur and the insulating property deteriorates.
When the sintered body has a thin film on the surface, swelling or peeling of the thin film occurs when the thin film is formed on the surface of the sintered product, and the durability and operation reliability of electronic devices are significantly reduced. There was a problem that caused it.

That is, various power modules are manufactured by using a silicon nitride sintered body manufactured by a conventional manufacturing method as a ceramic substrate, bonding a metal circuit layer to the surface of the silicon nitride substrate, and mounting a semiconductor element. If formed, the insulation of the silicon nitride substrate is low,
Due to the large dielectric loss, it has been difficult to obtain a highly reliable power module. This tendency has become more prominent with the recent progress in higher output and higher integration of semiconductor elements.

Specifically, when various power modules for large power and large capacity are formed by using the above silicon nitride substrate, the insulation between the front and back of the silicon nitride substrate is lowered and leak current is reduced. It tends to occur. When the leak current value exceeds a predetermined value, the current flowing through the metal circuit board passes through the silicon nitride substrate and leaks to another metal circuit (leakage).
Resulting in. Therefore, even though it is not electrically connected, it leaks to other metal circuit boards.
Therefore, there is a problem in that the semiconductor device malfunctions and the components of various power modules are damaged.

Further, although the silicon nitride sintered body manufactured by the above-mentioned conventional method has excellent mechanical strength such as toughness value, in view of heat conduction characteristics, other aluminum nitride (AlN) sintered bodies and oxidized ones can be used. Beryllium (BeO) sintered body,
Since it was insufficient as compared with a silicon carbide (SiC) sintered body or the like, it has not been put into practical use as an electronic material such as a ceramics substrate for semiconductors that particularly requires heat dissipation,
There was a problem that the application range was narrow.

On the other hand, the aluminum nitride sintered body is characterized by having a high thermal conductivity and a low coefficient of thermal expansion as compared with other ceramics sintered bodies, and therefore has a high speed and a high output.
Although it is widely used as a semiconductor circuit board material and a package material, which are becoming more multifunctional and larger in size, a material that is sufficiently satisfactory in terms of mechanical strength has not been obtained. Therefore, there is a demand for the development of a ceramics sintered body having high strength, high insulation and high thermal conductivity.

In order to meet the above demand, the present inventors have
For example, JP-A-9-69594 and JP-A-2000-3
As disclosed in Japanese Patent No. 4172, a silicon nitride sintered body having excellent mechanical strength and thermal conductivity has been developed by improving the composition, structure, etc. of the sintered body. However, in the conventional silicon nitride sintered body, the size of the pores existing in the crystal grain boundary phase is liable to increase to about 1 μm in diameter, and it is difficult to completely eliminate the pores. Then, when voltage is applied, there is a problem in that current leakage easily occurs through the pores. Therefore, in such a sintered body, there is a problem that it cannot be said to be sufficient as a substrate for a semiconductor because the insulating property is deteriorated.

The present invention has been made in order to meet the above-mentioned demands, and in addition to the high-strength characteristics originally possessed by a silicon nitride sintered body, in particular, it is substantially contained in the sintered body forming the substrate. Since no pores are formed in the surface and the surface roughness is small, grain removal does not occur easily during processing, and even when various power modules and circuit boards are constructed using this thin silicon nitride substrate, the amount of leakage current is small. Can be effectively suppressed, and even when a thin film is formed on the substrate surface, swelling and peeling of the thin film can be prevented, and even when used in electronic equipment, its insulation, durability and operational reliability. It is an object of the present invention to provide a silicon nitride substrate capable of significantly improving the temperature, a method of manufacturing the same, and a silicon nitride substrate with a thin film using the same.

[0015]

In order to achieve the above object, the inventors of the present invention have clarified the cause of leakage current in a module using a conventional silicon nitride ceramic substrate and obtained the following findings. It was

That is, since the surface of a conventional silicon nitride substrate has poor sinterability of the silicon nitride sintered body constituting the substrate, microcracks with a width of 1 μm or more and a width of 1 μm or more are present.
If many cracks such as submicron cracks of less than m are easily formed and these cracks propagate in the thickness direction of the substrate, the thickness of the ceramic substrate decreases by an amount corresponding to the length of the cracks. Since the substantial thickness of the ceramic substrate as an insulator is reduced, the insulating property is lowered, and a leak current is likely to occur when a module is formed. The cracks are likely to occur even when polishing a silicon nitride sintered body having pores to a predetermined thickness. It was also found that shedding is likely to occur in the pores and the surface roughness of the polished surface becomes large.

Further, since silicon nitride crystal grains are originally insulators, no current flows, but in an actual silicon nitride substrate, a glass phase made of a composite oxide of a sintering aid component serves as a grain boundary phase. It was found that the glass phase formed in the grain boundary phase is one of the causes of the current leakage phenomenon.

Further, it has been found that the above-mentioned glass phase has a large thermal resistance, so that the thermal conductivity of the silicon nitride substrate is likely to be lowered, and that if the glass phase is large, cracks are likely to occur. The grain boundary phase is necessary for keeping the strength of the silicon nitride substrate high to some extent. However, when the width (maximum diameter) of the grain boundary phase becomes large, the structure tends to generate a leak current as described above. Therefore, in a preferred embodiment of the present invention, the maximum diameter of the grain boundary phase is defined so that a leak current is unlikely to occur and the grain boundary phase having high thermal conductivity is formed.

Specifically, the maximum diameter of the grain boundary phase is 1.5 μm.
By setting the ratio below or crystallizing at least a part of the grain boundary phase, the ratio of the glass phase having a high thermal resistance is reduced to reduce the thermal conductivity of the silicon nitride substrate to 50 W / m.
The leakage current is effectively prevented at the same time as it is increased above K.

Further, by adding a predetermined amount of Hf oxide, it is possible to suppress the generation of the above-mentioned glass phase, the crystallization of the grain boundary phase is likely to proceed, the high thermal conductivity of the substrate and the leakage current increase. It was also found to be effective in terms of both suppression.

Further, since carbon has conductivity,
It was also found that carbon remaining on the silicon nitride substrate after sintering is one of the causes of the leak current. As a countermeasure against this, it has been found that the leakage current value of the silicon nitride substrate can be effectively reduced by limiting the residual carbon amount of the molded body after molding and degreasing the raw material mixture to a predetermined value or less.

Further, when manufacturing a conventional silicon nitride sintered body, the kind of silicon nitride powder generally used,
The production conditions such as the type and amount of sintering aids and additives, and the sintering conditions were variously changed, and the effects of these elements on the properties of the sintered body as the final product were confirmed by experiments.

As a result, by carrying out hot isostatic pressing (HIP) treatment after sintering, in particular, for a molded product having a predetermined composition, pores are substantially formed in the sintered product forming the substrate. Therefore, it was found that a sintered body that is dense and has few cracks can be obtained, and that the generation of leak current can be effectively reduced. In addition, since a substrate with a small surface roughness and good surface properties can be obtained, graining is less likely to occur during processing, and even when a thin film is formed on the surface of the substrate, the thin film is less swollen and peeled off, and thus a highly reliable thin film. We have obtained the finding that a silicon nitride substrate with a substrate can be obtained.

In a preferred embodiment, a raw material mixture obtained by adding a predetermined amount of a rare earth element to fine and highly pure silicon nitride powder is molded and degreased, densified and sintered, and then at a predetermined cooling rate. It was found that when gradually cooled, the pores became smaller, the thermal conductivity was greatly improved, and a silicon nitride sintered body having high strength was obtained.

By using a high-purity silicon nitride raw material powder having a reduced content of oxygen and impurity cation elements, and setting a small thickness of the silicon nitride compact to sinter,
Generation of a glass phase (amorphous phase) in the grain boundary phase can be effectively prevented, and silicon nitride firing having a high thermal conductivity of 50 W / mK or more even when only rare earth element oxide is added to the raw material powder. We obtained the finding that a conjunctiva was obtained.

Further, conventionally, when the heating power source of the firing furnace was turned off after the sintering operation was finished and the sintered body was cooled in the furnace, the cooling rate was as rapid as 400 to 800 ° C./hour. According to the experiments by the inventor, the cooling rate is 10
By controlling the temperature slowly to 0 ° C or lower, the grain boundary phase of the silicon nitride sintered body structure changes from an amorphous state to a phase containing a crystalline phase, and high strength characteristics and high heat transfer characteristics are simultaneously achieved. It turned out that

However, as a result of further improvement research by the present inventor, the sinterability was improved when 0.3 to 3.0% by weight of Mg was added as an oxide in addition to the rare earth element. It was found that the strength of the silicon nitride sintered body can be increased because of the improvement. By the way, 150 raw material compacts
Even when a silicon nitride substrate is sintered in the temperature range of 0 to 1900 ° C., the leak current value when applying an alternating voltage of 1.5 kV-100 Hz is 800 to 1300 nA.
A silicon nitride substrate having a dielectric loss of 0.001 or less when an alternating voltage of 1 MHz is applied can be obtained. Also, this silicon nitride substrate is 500M
A bending strength of Pa or more and a high thermal conductivity of 50 W / m · K or more can be achieved.

Further, fine silicon nitride raw material powder is added to a rare earth oxide, and if necessary, a compound of magnesia (MgO) and Hf, and compounds of Ti, Zr, W, Mo, Ta, Nb, V and Cr in predetermined amounts. After performing degreasing of the added raw material mixture and performing main sintering, the cooling rate of the sintered body from the sintering temperature to the temperature at which the liquid phase formed during sintering by the rare earth element solidifies When annealed at 100 ° C. or less per hour, in addition to high strength and high thermal conductivity, especially when hot isostatic pressing (HIP) treatment is adopted as part of the sintering process, it occurs when voltage is applied. It was found for the first time that a silicon nitride substrate having a high insulating property capable of suppressing leakage current was obtained.

The present invention has been completed based on the above findings.

That is, the silicon nitride substrate according to the present invention is a silicon nitride substrate made of a silicon nitride sintered body containing a sintering aid, and substantially no pores are present in the silicon nitride sintered body. It is characterized by

In the above silicon nitride substrate, the surface roughness Ra is preferably 0.5 μm or less. In particular, since hot isostatic pressing (HIP) is performed after sintering, pores in the silicon nitride substrate are prevented from substantially existing and the surface roughness Ra of the substrate is 0.5.
It is easy to reduce the thickness to less than μm. By realizing good surface properties in this way, even when a thin film is bonded to the substrate surface to form a thin film-coated silicon nitride substrate, swelling or peeling of the thin film is less likely to occur due to heat cycles, and reliability is improved. An excellent silicon nitride substrate with a thin film can be obtained. Further, the surface roughness Ra of the silicon nitride substrate is 0.0
It is more preferably 5 μm or less.

Further, the maximum diameter of the grain boundary phase containing the sintering aid component present on the surface of the silicon nitride substrate is 1.5 μm.
The following is preferable.

Further, in the above-mentioned silicon nitride substrate, the current leakage value when an alternating voltage of 1.5 Kv-100 Hz was applied between the front and back of the silicon nitride sintered body under the conditions of temperature of 25 ° C. and humidity of 70%. It is preferably 100 nA or less.

The thickness of the silicon nitride substrate according to the present invention is not particularly limited, but it can be made as thin as 0.4 mm or less. Since the silicon nitride substrate of the present invention is densely formed so as to have substantially no pores, it has high mechanical strength and leaks even when formed to a thin thickness of 0.1 to 0.4 mm. Shows excellent insulation with low current. In addition, since it can be formed thin, it has low thermal resistance,
Combined with the high thermal conductivity of the substrate itself, the heat dissipation of the silicon nitride substrate can be synergistically improved.

Furthermore, the silicon nitride substrate with a thin film according to the present invention is characterized in that a metal thin film is provided on the silicon nitride substrate prepared as described above.

The fracture toughness value of the silicon nitride substrate is preferably 6.5 MPa · m ^1/2 or more.

Further, it is preferable that the silicon nitride substrate is composed of a silicon nitride crystal and a grain boundary phase, and the ratio of the crystal compound phase in the grain boundary phase to the entire grain boundary phase is 20% or more. In the silicon nitride ceramic substrate, the rare earth elements are converted into oxides of 2.0 to 17.
It is preferable to contain 5% by mass.

The thermal conductivity of the silicon nitride substrate is 9
It is also possible to configure it to be 0 W / m · k or more.

Further, in the silicon nitride substrate, Mg is used as M
It is preferable to contain 0.3 to 3.0 mass% in terms of gO.

Further, in the above silicon nitride sintered body, at least one of Hf and Mg is converted into an oxide of 0.3 to.
It is preferable to contain 3.0 mass% and 0.5 mass% or less of Al, Li, Na, K, Fe, Ba, Mn, and B as impurity cation elements in total.

The residual carbon content in the silicon nitride substrate is preferably 500 ppm or less. The residual carbon content (or residual carbon content) in the silicon nitride substrate of the present invention indicates the content of carbon simple substance remaining in the ceramic substrate, and does not include the content of metal carbide. Absent.

In the above silicon nitride substrate, the porosity is below the detection limit and the volume ratio is 0.01%.
It is preferably less than (substantially 0.009% or less) and the total oxygen content is 3.5% by mass or less. Also Ti,
At least one selected from the group consisting of Zr, W, Mo, Ta, Nb, V and Cr is 2% by mass in terms of oxide.
It is preferable to contain the following.

In the method for manufacturing a silicon nitride substrate according to the present invention, oxygen is 1.5 mass% or less and Al, Li, Na, K, Fe, Ba, Mn and B as impurity cation elements are added in total. 0.5% by mass or less, α-phase silicon nitride 75 to 9
Silicon nitride powder containing 7% by mass or more and having an average particle size of 1.0 μm or less has a 2-1 value obtained by converting a rare earth element into an oxide.
The raw material mixture added with 7.5% by mass is molded to prepare a molded body, and the obtained molded body is degreased and then the temperature is set to 1700 to 190.
Sintering was performed at 0 ° C., and the obtained sintered body was heated at a temperature of 1550 to 170.
Hot isostatic pressure (HIP) at 0 ° C and pressure of 50 to 250 MPa
It is characterized by processing.

Further, in the above method for manufacturing a silicon nitride substrate, after the sintering, the cooling rate of the sintered body from the sintering temperature to a temperature at which a liquid phase formed by sintering the rare earth element solidifies. It is preferable to gradually cool to 100 ° C. or less per hour.

Further, the silicon nitride powder contains oxygen of 1.5% by mass or less and Al, Li, N as impurity cation elements.
a, K, Fe, Ba, Mn, B in a total amount of 0.5 mass% or less and α-phase silicon nitride in an amount of 75 to 97 mass% or more,
The average particle diameter is preferably 1.0 μm or less.

In the above manufacturing method, it is preferable that at least one of Hf and Mg is added to the silicon nitride powder in an amount of 0.3 to 3.0 mass% in terms of oxide. In addition, the silicon nitride powder, Ti, Zr, W, Mo, Ta,
At least one selected from the group consisting of Nb, V, and Cr
It is preferable to add 2% by weight or less in terms of oxides.

Further, it is preferable that the raw material mixture is molded at a molding pressure of 120 MPa or more to prepare a molded body. Further, the molding pressure is preferably in the range of 120 to 200 MPa. The residual carbon content of the sintered body after sintering is preferably 500 ppm or less.

According to the above manufacturing method, since the sintered body is subjected to hot isostatic pressing (HIP) under a predetermined condition after sintering, the porosity is less than 0.01%, which is below the detection limit. A silicon nitride substrate is obtained in which substantially no pores are formed in the sintered body that constitutes the substrate. Further, the surface roughness Ra is preferably as small as 0.5 μm or less and the surface properties are excellent, and a grain boundary phase containing a rare earth element or the like is formed in the silicon nitride crystal structure, and the maximum diameter of the grain boundary phase is 1. A silicon nitride substrate having a thickness of 5 μm or less is obtained. More preferably, the leak current value when an alternating voltage of 1.5 kV-100 Hz is applied under the condition of a temperature of 25 ° C. and a humidity of 70% is 100 nA or less, and preferably the total oxygen amount is 3.5 mass. %, The thermal conductivity is 50 W / mK or more, and the three-point bending strength is 50 at room temperature.
0 MPa or more and a fracture toughness value of 6.5 MPa · m
^A silicon nitride substrate having excellent insulating properties, mechanical properties, and heat conduction properties can be obtained as it is ^½ or more.

The leak current value is measured as follows. That is, metal electrodes are bonded between the front and back surfaces of a silicon nitride substrate, and 1.5 kV-100 Hz is applied between these electrodes.
The current value of the leak current flowing between the metal electrodes when the AC voltage is applied can be measured using a curve tracer or the like.

If the leakage current value exceeds 100 nA, the insulating property of the substrate itself is insufficient and it becomes unsuitable as a ceramic substrate material for a power module, which has a particularly high output and a high integration and a high capacity. Preferably 50n
It is A or less.

In specifying the leak current value, in the present invention, the measurement conditions are unified to a temperature of 25 ° C. and a humidity of 70%. The leak current value is a value that fluctuates somewhat depending on temperature and humidity, so the measurement conditions were specified. Further, since the present invention only specifies the measurement conditions of the leak current value, it goes without saying that the silicon nitride substrate of the present invention can be used under conditions other than these conditions.

Furthermore, the silicon nitride substrate of the present invention can reduce the leak current value to 100 nA or less even in an environment in which the humidity is 70% and electric leakage is likely to occur.

The silicon nitride powder used in the method of the present invention, which is the main component of the sintered body constituting the substrate, has an oxygen content of 1.5 in view of sinterability, strength and thermal conductivity. Mass% or less, preferably 0.5 to 1.2 mass%,
Α-phase silicon nitride in which the content of impurity cation elements such as Al, Li, Na, K, Fe, Ba, Mn, and B is suppressed to 0.5 mass% or less, preferably 0.3 mass% or less. 75 to 97% by mass, preferably 80 to 95% by mass, and having an average particle size of 1.0 μm or less, preferably 0.4 to
It is preferable to use fine silicon nitride powder of about 0.8 μm.

Although α-phase type and β-phase type powders of silicon nitride raw material are known, the strength of α-phase type silicon nitride raw material powder is small when it is made into a sintered body. On the other hand, the β-phase type silicon nitride raw material powder tends to be insufficient, but high temperature firing is required, but a high strength sintered body with a high aspect ratio and complicated fibrous silicon nitride is obtained. To be Therefore, in the present invention, it is preferable that the α-phase type raw material powder is fired at a high temperature to obtain a β-phase type sintered body as the silicon nitride sintered body.

In the present invention, the reason why the blending amount of the α-phase type silicon nitride powder is limited to the range of 75 to 97 mass% is 7
This is because the bending strength, thermal conductivity and insulating property of the sintered body are remarkably improved in the range of 5 mass% or more, and the excellent properties of silicon nitride become remarkable. On the other hand, considering the sinterability, 97
The range is up to mass%. Preferably 80 to 95% by mass
It is preferable to set it as the range.

The starting material powder of silicon nitride has an oxygen content of 1.5% by mass or less, preferably 0.5 to 1 in consideration of sinterability, bending strength, thermal conductivity and insulation. 2% by mass, containing 90% by mass or more of α-phase silicon nitride,
The average particle size is 1.0 μm or less, preferably 0.4 to 0.8
It is preferable to use fine silicon nitride powder having a size of about μm.

By using a fine raw material powder having an average particle size of 1.0 μm or less, the triple point between silicon nitride powders can be made small, so that even if a small amount of sintering aid is used, the porosity is substantially reduced. It is possible to form a dense sintered body that is difficult to form, and the risk of the sintering aid impeding the heat conduction characteristics is reduced.

The total amount of oxygen contained in the silicon nitride substrate according to the present invention is preferably 3.5% by mass or less. If the total oxygen content of this substrate exceeds 3.5% by mass, the maximum pore diameter in the grain boundary phase becomes large, and the current leak value in particular becomes large, so that the insulating property of the sintered body deteriorates.

Al, Li, Na, K, Fe, Ba,
Since the impurity cation elements of Mn and B are substances that hinder the thermal conductivity, the total content of the above impurity cation elements is 0. 0 in order to secure a thermal conductivity of 50 W / mK or more. It can be achieved by setting the content to 5% by mass or less. Particularly, for the same reason, it is more preferable that the total content of the impurity cation elements is 0.3% by mass or less. Since the silicon nitride powder used to obtain a usual silicon nitride sintered body contains a relatively large amount of Fe and Al, the total amount of Fe and Al is the above-mentioned impurity cation element. It is a guideline for the total content of.

Further, by using a silicon nitride raw material powder containing 90% by mass or more of α-phase type silicon nitride, which has excellent sinterability as compared with β-phase type, a high density sintered body is manufactured. can do.

The rare earth elements added to the silicon nitride raw material powder as a sintering aid include Y, Ho, Er, Yb,
Depending on the oxide such as La, Sc, Pr, Ce, Nd, Dy, Sm, Gd or the sintering operation, these oxide substances may be used alone or in combination of two or more kinds. Good. These sintering aids react with the silicon nitride raw material powder to generate a liquid phase, and function as a sintering accelerator.

The amount of the above-mentioned sintering aid added is in the range of 2.0 to 17.5% by mass based on the raw material powder in terms of oxide.
If the addition amount is less than 2.0% by mass, the densification or high thermal conductivity of the sintered body is insufficient. Especially, when the rare earth element is an element with a large atomic weight such as a lanthanoid element, comparison is made. A sintered body having a relatively low strength and a relatively low thermal conductivity is formed. On the other hand, if the addition amount exceeds 17.5% by mass, an excessive amount of grain boundary phase is generated, and thermal conductivity and strength start to decrease, so the above range is set. Particularly, for the same reason, it is desirable that the amount is 3 to 15% by mass.

Further, magnesium (Mg) oxide (MgO) used as a selective additive component in the present invention.
Has the function of controlling the grain growth in the crystal structure while facilitating the function of the above-mentioned rare earth element sintering promoter and enabling densification at low temperature, and also the mechanical strength of the Si ₃ N ₄ sintered body. Is to improve. If the added amount of MgO is less than 0.3 mass% in terms of oxide, the effect of addition is insufficient, while if it exceeds 3.0 mass%, the thermal conductivity decreases. , The addition amount is 0.3 ~
The range is 3.0% by mass. It is particularly desirable to set the content to 0.5 to 2% by mass.

There is also a Hf compound as a component exhibiting the same effect as MgO. Hf compounds are added as oxides, carbides, nitrides, silicides, borides,
The composite addition together with MgO can further promote the sintering and reduce the glass phase more effectively. The amount added is 0.3 to 3% by mass, preferably 1.0 to
It is 2.5% by mass. Since MgO and the Hf compound show similar effects, it is possible to obtain a synergistic effect by adding both MgO and the Hf compound.

In the present invention, Ti, Zr, V, Nb, Ta, Cr, Mo and W are used as other optional additive components.
May be added as an oxide, a carbide, a nitride, a silicide, or a boride. These compounds promote the function of the above-mentioned rare earth element as a sintering accelerator, and at the same time serve as a dispersion strengthening function in the crystal structure to improve the mechanical strength of the Si ₃ N ₄ sintered body. , Ti, Mo compounds are preferred. If the addition amount of these compounds is less than 0.1% by mass in terms of oxide, the effect of addition is insufficient, while if it exceeds 2% by mass, the thermal conductivity, mechanical strength, and electrical properties are low. Since the dielectric breakdown strength lowers, the addition amount is set in the range of 0.1 to 2 mass%. In particular, it is desirable that the content be 0.2 to 1.0% by mass.

The compounds such as Ti and Mo also function as a light-shielding agent that imparts opacity to the silicon nitride substrate by coloring it in black. Therefore, when a ceramics circuit board on which an integrated circuit or the like is apt to malfunction due to light is manufactured from the sintered body, a compound such as Ti is appropriately added to the silicon nitride substrate excellent in light-shielding property. Is desirable.

Further, since the porosity of the sintered body has a great influence on the surface properties (surface roughness), the amount of leak current generated, the thermal conductivity and the strength, it is manufactured so as to reach the detection limit (less than 0.01%). . When the porosity is 0.01% or more, the leak current rapidly increases and the heat conduction is hindered, the insulating property and the thermal conductivity of the sintered body decrease, and the strength of the sintered body decreases. The porosity is measured by the Archimedes method.

The silicon nitride substrate is structurally composed of a silicon nitride crystal and a grain boundary phase. The proportion of the crystalline compound phase in the grain boundary phase depends on the amount of leakage current generated in the sintered body and the amount of heat generated. In the sintered body that constitutes the substrate according to the present invention, the conductivity is greatly affected, and it is preferable that the grain boundary phase accounts for 20% or more, and more preferably 50% or more of the crystal phase. If the crystal phase is less than 20%, the thermal conductivity will be 50 W / mK
This is because it is not possible to obtain a sintered body having excellent heat dissipation characteristics, a small leak current, and excellent mechanical strength as described above. In particular, since the silicon nitride crystal grains themselves of the silicon nitride sintered body are insulators, the state of the grain boundary phase greatly affects the leak current value of the silicon nitride sintered body.

Further, as described above, the porosity of the silicon nitride sintered body is set as the detection limit (less than 0.01%), and the maximum diameter of the grain boundary phase formed in the silicon nitride crystal structure is 1.5 μm or less. In order to obtain a silicon nitride sintered body having a thermal conductivity of 50 W / mK or more, a total oxygen content of 3.5% by mass or less and a current leakage value of 100 nA or less, After degreasing the prepared silicon nitride compact, a temperature of 170
After pressureless sintering or pressure sintering at 0 to 1900 ° C. for about 2 to 10 hours, the obtained sintered body is heated at a temperature of 1550 to 17
Hot isostatic pressure (HI
P) It is necessary to process. As a pressure sintering method,
Various pressure sintering methods such as atmospheric pressure sintering and hot pressing are used.

When the sintered body is slowly cooled to a temperature at which the liquid phase is solidified after sintering at a cooling rate of 100 ° C. or less per hour, crystallization of the grain boundary phase is promoted, causing porosity. Since the proportion of the glass phase that tends to be reduced is reduced, it is possible to obtain a sintered body in which current leakage is suppressed and insulation is improved.

In the present invention, the hot isostatic pressing (HIP) is applied to the silicon nitride sintered body in which the ratio of the glass phase of the grain boundary phase is reduced.
By carrying out, it is possible to obtain a silicon nitride substrate which is substantially free of pores and which is excellent in thermal conductivity and mechanical strength.

If the sintering temperature is lower than 1700 ° C., the densification of the sintered body is insufficient and the porosity is 0.01 vol.
%, The insulating property, the mechanical strength and the thermal conductivity are deteriorated. On the other hand, when the sintering temperature exceeds 1900 ° C., the silicon nitride component itself tends to evaporate and decompose. In particular, when normal pressure sintering is performed instead of pressure sintering, 1800
Decomposition and evaporation of silicon nitride begins at around ℃.

The cooling rate of the sintered body immediately after the completion of the above-mentioned sintering operation is an effective control factor for crystallizing the grain boundary phase, and when rapid cooling is performed such that the cooling rate exceeds 100 ° C./hour. In addition, the grain boundary phase of the sintered body structure becomes amorphous (glass phase), the liquid phase generated in the sintered body accounts for less than 20% of the grain boundary phase as a crystal phase, and the leak current increases. On the other hand, the thermal conductivity is not particularly improved.

The temperature range in which the cooling rate should be adjusted is sufficient from the predetermined sintering temperature (1700 to 1900 ° C.) to the solidification of the liquid phase produced by the reaction of the above-mentioned sintering aid. is there. By the way, the liquidus freezing point when the above-mentioned sintering aid is used is approximately 1600 to 1500 ° C.
It is a degree. By controlling the cooling rate of the sintered body from at least the sintering temperature to the liquidus solidification temperature at 100 ° C. or less per hour, preferably 50 ° C. or less, and more preferably 25 ° C. or less, the whole of the sintered body is controlled. The amount of oxygen is 3.5% by mass or less, the maximum diameter of the grain boundary phase is 1.5 μm or less, the porosity is below the detection limit, and the grain boundary phase 2
0% or more, particularly preferably 50% or more becomes a crystalline phase,
A silicon nitride sintered body having excellent thermal conductivity and mechanical strength and a low leak current can be obtained.

A slower cooling rate of the above sintered body is more effective for crystallization of the grain boundary phase, but if it is too slow, the manufacturing time becomes long, and therefore the lower limit of the cooling rate is 10 per hour from the viewpoint of manufacturability. C. or higher is preferable.

The "total amount of oxygen in the sintered body" defined in the present invention means the total amount of oxygen constituting the silicon nitride sintered body in mass%. Therefore, when oxygen exists as a metal oxide or an oxynitride in the silicon nitride sintered body, not the amount of the metal oxide (and the oxynitride) but the metal oxide (and the oxynitride). ) Is focused on the amount of oxygen.

The silicon nitride substrate according to the present invention is manufactured through the following processes, for example. That is, with respect to the fine silicon nitride powder having the above-mentioned predetermined fine particle diameter and a low impurity content, a predetermined amount of a sintering aid, necessary additives such as an organic binder and, if necessary, Ti and the like are added. A raw material mixture is prepared by adding a compound, and the obtained raw material mixture is then molded to obtain a molded product having a predetermined shape. As a forming method of the raw material mixture, a general-purpose die pressing method, a sheet forming method such as a doctor blade method, or the like can be applied.

In the case of forming a compact by the die pressing method described above, the forming pressure of the raw material mixture is set to 1 in order to form a grain boundary phase in which a leak current is unlikely to occur particularly after sintering.
It is preferably set to 20 MPa or more. When the molding pressure is less than 120 MPa, a location where the rare earth element compound, which is a component that mainly constitutes the grain boundary phase, is agglomerated is likely to be formed, and a sufficiently dense molded article cannot be obtained.
Only silicon nitride substrates with many cracks can be obtained.
A current easily flows through the agglomerated portion of the grain boundary phase, which increases the leak current value. Further, even if a compact that is insufficiently consolidated is sintered, cracks are likely to occur, and the leak current due to the cracks in the substrate increases. On the other hand, if the molding pressure is excessively high to exceed 200 MPa, the durability of the molding die will be reduced.

If the molding pressure is excessively high, the molded body becomes harder than necessary, and bubbles (pores) are generated inside the molded body.
Is difficult to discharge to the outside during the manufacturing process. Therefore, the molding pressure is preferably in the range of 120 to 200 MPa.

On the other hand, in manufacturing a silicon nitride substrate having a predetermined thickness, when the thickness of the sintered body is adjusted by polishing, the impact force applied during the polishing causes cracks on the substrate surface. easy. In particular, in the case of a silicon nitride substrate having pores, grain removal is likely to occur during processing, and the grain surface of the sintered body is likely to deteriorate due to grain removal marks. Therefore, the thickness of the silicon nitride substrate is 1.5 mm or less, preferably 0.
A method in which a thin molded body is formed so as to have a thickness of 4 mm or less in the molding step and polishing processing after sintering is not performed is also effective from the viewpoint of preventing the occurrence of cracks.

Specifically, a thin sheet-shaped compact is prepared by using an extrusion forming method or a doctor blade method, and the sheet-shaped compact is simply degreased and sintered to obtain a silicon nitride sintered body having a predetermined thickness. You may form. Even in this case,
A slight honing process may be performed to remove the spread powder and the like attached to the sheet-shaped sintered body. However, it is better not to adopt a polishing method with a high impact force that causes cracks. Further, as the mild honing process, the condition that the abrasive grain injection pressure is 0.5 MPa or less can be mentioned.

Subsequent to the above-mentioned molding operation, the molded body is heated in a non-oxidizing atmosphere at a temperature of 600 to 800 ° C. or in air at a temperature of 400 to 500 ° C. for 1 to 2 hours, and the organic matter added in advance is added. Sufficiently remove the binder component and degrease it.

Here, in order to form a grain boundary phase in which a leak current is unlikely to occur, degreasing treatment is performed so that the amount of carbon remaining due to the organic binder used in forming the molded body is 500 ppm or less. It is effective to sufficiently remove the carbon component.

Generally, carbon has conductivity, and the residual carbon amount in the sintered silicon nitride sintered body is 500 ppm.
If it exceeds, the leak current value tends to increase. for that reason,
Ideally, the carbon component should not be contained from the beginning, but in reality, unless the raw material mixture is blended with a certain amount of organic matter (organic binder), the shape retention and handleability of the molded product will deteriorate. Therefore, the degreasing step is provided to reduce the amount of residual carbon.

However, it is difficult to completely remove the carbon component unless the molded body is subjected to a special treatment, and the residual carbon is combined with additives such as silicon nitride and a sintering aid during sintering. Therefore, it is difficult to completely eliminate the stable carbides. However, the residual carbon amount in the silicon nitride substrate after sintering is 50%.
By sufficiently performing the degreasing treatment so as to be 0 ppm or less, the generation of the leak current can be effectively prevented.

In particular, the substrate thickness is 1 mm or less, more preferably 0.
On a substrate as thin as 4 mm or less, it is preferable to control the residual carbon amount because a large amount of residual carbon tends to adversely affect the leak current value.

Next, the degreased molded body was subjected to 1700 to 1 in an atmosphere of an inert gas such as nitrogen gas or argon gas.
Normal pressure sintering or atmospheric pressure sintering is performed at a temperature of 900 ° C. for a predetermined time. Further, if necessary, it is preferable to perform gradual cooling after sintering.

Further, the obtained sintered body is heated at a temperature of 1550 to
By hot isostatic pressing (HIP) treatment at 1700 ° C. and a pressure of 50 to 250 MPa for 1 to 8 hours, the densification of the sintered body is further promoted, the generation of pores (pores) is prevented, and the sintering is performed. The surface roughness of the body can be reduced.

When the heating temperature and pressure in the hot isostatic pressing (HIP) treatment are less than the lower limit values described above, the densification of the silicon nitride substrate does not proceed sufficiently and the pores (pores) are substantially formed. It is not possible to obtain a substrate that does not exist. On the other hand, even if the value is set higher than the upper limit value, it is difficult to obtain a further densification effect, and the HIP equipment cost and the manufacturing cost increase sharply.

The silicon nitride sintered body produced by the above production method has a total oxygen content of 3.5% by mass or less, a porosity of less than the detection limit, a maximum grain boundary phase diameter of 1.5 μm or less, and 50 W / m ·
It has a thermal conductivity of K (25 ° C.) or higher and a three-point bending strength of 500 MPa or higher at room temperature, which is excellent in mechanical properties.

It is also possible to obtain a highly heat-conductive silicon nitride sintered body having a thermal conductivity of 90 W / m · K or more.

Further, according to the molding method as described above, a silicon nitride substrate which is dense from the stage of molding and has few cracks can be obtained. In this way, the width of the substrate surface made of the silicon nitride sintered body having improved formability and sinterability is 1
No microcracks of μm or more are generated and the width is 1μ.
The generation amount of submicron cracks of less than m can also be significantly reduced. Specifically, when the unit area is 10 μm × 10 μm, the number of submicron cracks generated in the substrate surface texture is 2 or less.

According to the silicon nitride substrate and the method of manufacturing the same according to the present invention, since the sintered body is formed by hot isostatic pressing (HIP) under predetermined conditions after the sintering step, the sintered body is formed. Densification is further promoted, pores (pores) are substantially eliminated, and the surface roughness of the sintered body is reduced.
Further, the grain boundary phase of the sintered body becomes narrower, and the maximum diameter thereof is extremely miniaturized, so that a silicon nitride substrate having a high insulating property with less leakage current is obtained.

By molding the raw material mixture at a molding pressure of 120 MPa or more to prepare a molded body, it is possible to significantly reduce cracks generated in the substrate.
It is possible to obtain a silicon nitride substrate having a high insulating property with less leakage current.

Therefore, when a power module is prepared using this silicon nitride substrate, it is possible to form a power module having high insulation and operational reliability even if the output and the capacity are increased.

When the above silicon nitride substrate is used as a submount material such as a laser diode, a power module or a circuit board, a thin film or a metal circuit board is integrally bonded on the silicon nitride substrate to form a nitride film with a thin film. It will be used as a silicon substrate or a silicon nitride circuit substrate. As the thin film, a metal thin film such as Ti is used. The thickness of this metal thin film is preferably in the range of 3 μm or less.

In particular, since the silicon nitride substrate of the present invention has substantially no pores (less than the detection limit), when a thin metal thin film having a thickness of 3 μm or less is provided, a thermal cycle (TCT) test is performed. Even if it is applied, the reliability of the metal thin film is significantly improved because it is difficult for the generation of bubbles causing the swelling of the metal thin film and the thermal expansion of the grain boundary phase to occur. In other words, it is particularly effective as a silicon nitride substrate provided with a metal thin film.

Further, as the metal circuit board, it is preferable to use a metal or an alloy having high electric conductivity such as copper, aluminum or an alloy thereof (copper alloy, Al alloy).
As for the method of joining the metal circuit boards, various methods such as the direct joining method and the active metal method can be applied.

[0099]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a silicon nitride substrate according to the present invention will be specifically described with reference to the following examples.

Examples 1 to 7 In Examples 1 to 7, the amount of oxygen was 1.1% by mass, and the impurity cation elements were Al, Li, Na, K, Fe, Ba and M.
A sintering aid for Si ₃ N ₄ (silicon nitride) raw material powder containing 0.10 mass% of n and B in total and containing 97% of α-phase type silicon nitride and having an average particle diameter of 0.55 μm. As Y ₂ O ₃ (yttrium oxide) powder having an average particle size of 0.9 μm, Er ₂ O ₃ (erbium oxide) powder having an average particle size of 0.5 μm, and TiO ₂ (titanium oxide) having an average particle size of 1.0 μm Powder and MgO (magnesium oxide) with an average particle size of 0.5 μm
Powder and a substrate composition shown in Table 1 were added, and the mixture was wet-mixed in ethyl alcohol using a silicon nitride ball as a grinding medium for 96 hours and then dried to prepare a raw material mixture.

Next, a predetermined amount of an organic binder was added to the obtained raw material powder mixture to prepare a mixed granulated powder, and then 130 MPa
A large number of molded bodies were manufactured by press molding with the molding pressure of. Next, after degreasing the obtained molded body in an air stream at 450 ° C. for 4 hours, after sintering under the sintering conditions shown in Table 1, cooling rates until the temperature drops to 1500 ° C. are shown in Table 1, respectively. The value was set and the sintered body was cooled. Furthermore, each substrate was further densified by subjecting the sintered body to hot isostatic pressing under the HIP conditions shown in Table 1. Further, surface treatment was performed on each substrate to adjust the thickness and surface roughness shown in Table 1 to prepare silicon nitride substrates according to Examples 1 to 7, respectively. The size of each board is 50 mm long.
The width is unified to 40 mm.

Comparative Example 1 As Comparative Example 1, hot isostatic pressing (HIP) after sintering was carried out.
A silicon nitride substrate according to Comparative Example 1 was prepared by treating under the same conditions as in Example 1 except that no treatment was performed.

The surface roughness, the maximum diameter of the grain boundary phase, the porosity, the presence / absence of pores, and the leakage current value of each of the silicon nitride substrates obtained in Examples 1 to 7 and Comparative Example 1 thus obtained were measured. The results shown in Table 1 were obtained.

The surface roughness (Ra) is JIS B0.
It measured based on the standard of 601. The maximum diameter of the grain boundary phase was measured by the following method. That is, an enlarged photograph of the surface of the silicon nitride substrate is taken, and the diagonal length of the grain boundary phase having the longest diagonal in the unit area area of 50 μm × 50 μm is measured. This measurement operation is performed in at least three unit area regions,
The longest diagonal length was defined as the maximum grain boundary phase diameter.

The porosity was measured by the Archimedes method. Also, the presence or absence of pores is confirmed when the presence or absence of pores is confirmed within an arbitrary unit area area of 200 μm × 200 μm of the enlarged micrograph of the substrate structure, and the pore area cannot be confirmed even if three or more arbitrary unit areas are measured. Was displayed as "no pore". Specifically, since the pores are present in the grain boundary phase, the presence or absence of pores in the grain boundary phase can be measured by confirming with a microstructure magnified photograph at a magnification of 2000 or more. For example, when measuring the cut surface, it is possible that the silicon nitride crystal grains are shed and apparently have a morphology in which pores are present in the grain boundary phase. The area without shattering marks shall be selected and measured. If the unit area cannot be projected at one time in the enlarged photograph, it may be projected in a divided manner.

Further, the current leakage value was measured as follows. That is, both sides of each plate-shaped silicon nitride substrate are ground with a diamond grindstone, and the thickness thereof is set to 0.
It was set to 6 mm. Leak current flowing between the front and back of the substrate when an AC voltage of 1.5 Kv (100 Hz) is applied between the front and back of each plate formed in a plate in a chamber adjusted to a temperature of 25 ° C. and a humidity of 70%. The value of was measured with a curve tracer measuring device. The results of each measurement are shown in Table 1 below.

[0107]

[Table 1]

As is clear from the results shown in Table 1 above, in the silicon nitride substrate according to each of the examples, since the HIP was formed by performing the HIP under the predetermined condition after the sintering process, the generation of pores in the substrate. However, since the grain boundary phase was densified and the maximum diameter thereof was miniaturized, a high-strength silicon nitride substrate with little leakage current was obtained.

Further, in the silicon nitride substrates according to the respective examples, since the maximum diameter (width) of the grain boundary phase is miniaturized,
It was found that even when the surface roughness Ra was smoothed to about 0.01 to 0.05 μm, the formation of pores on the substrate surface was extremely small.

Furthermore, since the grain boundary phase is densified,
Even if the substrate was subjected to polishing processing, almost no shedding occurred, and a silicon nitride substrate having good surface roughness was obtained.

On the other hand, in the substrate of Comparative Example 1 not subjected to the HIP treatment after the sintering step, the grain boundary phase was not sufficiently densified, so that many pores remained and the leak current value increased.

Although not shown in the table, the thermal conductivity of Example 1 and Comparative Example 1 in which annealing is not performed after sintering is 55 W / m · K in Example 1 and that in Comparative Example 1. 48W / m
-In contrast to K, in Examples 2 to 7, the thermal conductivity was 7
It was 0 to 120 W / mK. The three-point bending strength was 500 MPa or more in all cases.

Next, an example of a silicon nitride substrate with a thin film in which a metal thin film is formed on the silicon nitride substrate prepared as described above will be described.

Examples 8 to 14 and Comparative Example 2 Metal thin films having the materials and thicknesses shown in Table 2 using the sputtering method on the surface of the silicon nitride substrates prepared in Examples 1 to 7 and Comparative Example 1. Were integrally formed to prepare submount materials as silicon nitride substrates with thin films according to Examples 8 to 14 and Comparative Example 2, respectively.

Then, in order to evaluate the durability and reliability of the silicon nitride substrate with a thin film according to each of the examples and comparative examples prepared as described above, the following heat cycle test (heat cycle test: TCT) was conducted. It was carried out and the presence or absence of swelling or peeling of the metal thin film on the substrate was measured. In the heat resistance cycle test, after the substrate was kept at -40 ° C for 30 minutes, it was kept at room temperature (25 ° C) for 10 minutes and then heated.
After holding at 25 ° C. for 30 minutes, cooling to room temperature (25 ° C.) and holding for 10 minutes are repeated in a cycle of increasing temperature and decreasing temperature.

In this example, 100 of the heat cycle was used.
The presence or absence of defects such as swelling and peeling of the metal thin film was measured after 0 cycle and after 2000 cycles, and the results are shown in Table 2 below.
The results shown in are obtained.

[0117]

[Table 2]

As is clear from the results shown in Table 2 above,
In the silicon nitride substrate with a thin film according to each example, since the silicon nitride substrate formed by performing HIP under a predetermined condition after the sintering process is used, the surface roughness is small and extremely smooth. It was confirmed that the adhesion strength between the substrate and the metal thin film was high, there was no problem such as swelling or peeling of the metal thin film even after 1000 cycles, and that it had excellent heat resistance cycle characteristics. In the silicon nitride substrate with a thin film according to Example 8 in which the maximum grain boundary phase diameter and surface roughness are relatively large and the thermal conductivity is low, the substrate and the metal thin film were Has a relatively low adhesiveness, and since the heat dissipation of the silicon nitride substrate is poor, the substrate itself becomes a thermal resistor, so that the metal thin film swells slightly after 2000 cycles. did.

From the above results, when used as a silicon nitride substrate with a thin film, the surface roughness (Ra) was 0.1 μm.
Hereinafter, it can be said that it is preferable to use a silicon nitride substrate having a thermal conductivity of 70 W / mK or more.

On the other hand, in the silicon nitride substrate with a thin film according to Comparative Example 2 which uses the silicon nitride substrate of Comparative Example 1 in which the HIP treatment after the sintering step is not performed, the densification of the grain boundary phase is insufficient. Therefore, it was confirmed that many pores remained, and after 1000 cycles, many defects such as swelling and peeling of the metal thin film occurred, and the heat resistance cycle characteristics deteriorate.

[0121]

As described above, according to the silicon nitride substrate, the method for manufacturing the same and the silicon nitride substrate with a thin film using the substrate according to the present invention, the sintered body forming the substrate is substantially Since no pores are formed and the surface roughness is small, it is possible to obtain a silicon nitride substrate which is less likely to be shed during processing. Furthermore, even when various power modules and circuit boards are formed by forming a thin silicon nitride substrate,
The generation of leak current can be effectively suppressed. Furthermore, even when a thin film is formed on the substrate surface, it is possible to prevent swelling and peeling of the thin film, and even when used in electronic devices with high power consumption and large capacity, its insulation, durability and operational reliability are greatly improved. Can be improved.

In particular, since the substrate is formed by performing the predetermined hot isostatic pressing process after the sintering step, the grain boundary phase of the sintered body is effectively densified and the generation of pores is suppressed. It is possible to make the pore size extremely small below the measurement limit,
It is possible to obtain a silicon nitride substrate having a high insulating property with less leakage current. Therefore, when a power module is prepared by using this silicon nitride substrate as a ceramic substrate, it is possible to form a power module having high insulation, durability and operational reliability even if the output and the capacity are increased. it can.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mitsuyasu Komatsu             8th Shinsugita Town, Isogo Ward, Yokohama City, Kanagawa Prefecture             Ceremony company Toshiba Yokohama office F-term (reference) 4G001 BA08 BA09 BA32 BB08 BB09                       BB32 BB71 BC13 BC43 BC51                       BC52 BC72 BD21 BD38 BE02                       BE26 BE32 BE35

Claims (8)

[Claims] 1. A silicon nitride substrate made of a silicon nitride sintered body containing a sintering aid, wherein the silicon nitride sintered body has substantially no pores. 2. The silicon nitride substrate according to claim 1, wherein the surface roughness Ra is 0.5 μm or less. 3. The silicon nitride according to claim 1, wherein the maximum diameter of the grain boundary phase containing the sintering aid component present on the surface of the silicon nitride substrate is 1.5 μm or less. substrate. 4. A current leakage value is 100 nA or less when an alternating voltage of 1.5 Kv-100 Hz is applied between the front and back of the silicon nitride sintered body under the conditions of a temperature of 25 ° C. and a humidity of 70%. The silicon nitride substrate according to any one of claims 1 to 3. 5. The silicon nitride substrate has a thickness of 0.4 mm.
The silicon nitride substrate according to any one of claims 1 to 4, wherein: 6. A silicon nitride substrate with a thin film, wherein a metal thin film is provided on the silicon nitride substrate according to any one of claims 1 to 5. 7. Oxygen of 1.5 mass% or less, Al, Li, Na, K, Fe, Ba, M as impurity cation elements.
n and B in a total amount of 0.5 mass% or less, α-phase silicon nitride in an amount of 75 to 97 mass% or more, and a silicon nitride powder having an average particle diameter of 1.0 μm or less, and a rare earth element as an oxide. A raw material mixture added by conversion of 2 to 17.5% by mass is molded to prepare a molded body, and after degreasing the obtained molded body, a temperature of 1700
Sintered at ~ 1900 ° C, the obtained sintered body is heated at a temperature of 1550.
A method for producing a silicon nitride substrate, which comprises performing a hot isostatic pressing (HIP) process at ˜1700 ° C. and a pressure of 50 to 250 MP. 8. After the sintering, the cooling rate of the sintered body from the sintering temperature to the temperature at which the liquid phase formed by the rare earth element during the sintering is solidified is gradually cooled to 100 ° C. or less per hour. 8. The method for manufacturing a silicon nitride substrate according to claim 7, wherein.