JPH0969672A - Silicon nitride circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the radiation characteristic and mechanical strength of a high-thermal conductivity Si nitride substrate as well as its heat resistance cycle characteristic by setting the relation of the thickness of the substrate to those of metal circuit sheets to meet specified relational expression. SOLUTION: Si nitride circuit board has a high-thermal conductivity Si nitride substrate 2 having a thermal conductivity of 60W/mK or more and 3-point bending strength of 650MPa or more (at room temp.) and metal circuits 4 and 5 bonded through an oxide layer on the substrate. If the thickness of the substrate 2 is DS(<0.8mm) and those of the sheets 4 and 5 are DM, they are set so as to meet an expression DS< or =2DM or DM< or DS< or =(5/3)DM. The substrate 2 is made from a sintered Si nitride contg. an rare earth element 2.0-17.5wt.% as converted in oxide and impurity cation elements Li, Ha, K, Fe, Ca, Mg, Sr, Ba, Mn and B 0.3wt.% in total.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic circuit board used for a semiconductor device or the like, and more particularly to a silicon nitride circuit board having improved heat dissipation characteristics and mechanical strength and improved heat resistance cycle characteristics.

[0002]

2. Description of the Related Art Conventionally, a conductive metal circuit layer is integrally joined with a brazing material to the surface of a ceramic substrate having excellent insulating properties such as an alumina (Al ₂ O ₃ ) sintered body, A circuit board in which a semiconductor element is mounted at a predetermined position on a circuit layer is widely used.

On the other hand, a ceramic sintered body containing silicon nitride as a main component generally has excellent heat resistance even in a high temperature environment of 1000 ° C. or higher, and also has excellent thermal shock resistance. As a high-temperature structural material that replaces the heat-resistant superalloy described above, it has been tried to be applied to various high-strength heat-resistant parts such as gas turbine parts, engine parts, and steel-making machine parts. In addition, because of its excellent corrosion resistance to metals, it has been tried to apply molten metal as a melt-resistant material, and because of its excellent wear resistance, it can be put to practical use in sliding members such as bearings and cutting tools. ing.

Conventionally, as a composition of a silicon nitride ceramics sintered body, yttrium oxide (Y
₂ O ₃ ), cerium oxide (CeO), calcium oxide (CaO) and other rare earth elements or alkaline earth element oxides are known to be added as sintering aids. The sinterability is enhanced to achieve higher density and higher strength.

A conventional silicon nitride sintered body is formed by adding the above-mentioned sintering aid to a silicon nitride raw material powder, and molding the obtained molded body at a temperature of about 1600 to 2000 ° C. in a firing furnace. It is manufactured by a manufacturing method in which after firing for a time, the furnace is cooled, and the resulting sintered body is ground and polished.

[0006]

However, although the silicon nitride sintered body manufactured by the above-mentioned conventional method has excellent mechanical strength such as toughness, it is different from other aluminum nitrides in terms of thermal conductivity. AlN) sintered body, beryllium oxide (BeO) sintered body, silicon carbide (SiC) sintered body, etc. are significantly lower than those in electronic materials such as semiconductor circuit boards that require heat dissipation. Has not been put to practical use, and has a drawback that its application range is narrow.

On the other hand, the aluminum nitride sintered body has the characteristics of high thermal conductivity and low thermal expansion coefficient as compared with other ceramics sintered bodies, and therefore, higher speed, higher output, multi-functionality and larger size are progressing. It is widely used as a circuit board component for mounting a semiconductor element (chip) and a package material. However, since what has been sufficiently satisfied in terms of mechanical strength has not been obtained, there are problems that damage occurs in the mounting process of the circuit board or the mounting process becomes complicated and the manufacturing efficiency of the semiconductor device decreases. It was

That is, when a circuit board whose main constituent material is a ceramics substrate such as the above aluminum nitride sintered body substrate or aluminum oxide sintered body substrate is fixed to the mounting boat by screwing or the like in the assembly process, In some cases, the circuit board may be damaged by a slight deformation due to the pressing force of or and the impact at the time of handling, and the manufacturing yield of the semiconductor device may be significantly reduced. Accordingly, there is a demand for a circuit board that has both high strength characteristics to withstand external force, high toughness characteristics, and excellent heat dissipation characteristics capable of coping with high output and high heat generation.

Further, in a circuit board formed by integrally bonding a metal circuit layer and a semiconductor element on the surface of the aluminum nitride substrate as described above, the mechanical strength and toughness of the aluminum nitride substrate itself are insufficient, so that the semiconductor Due to repeated thermal cycles associated with the operation of the element, cracks are likely to occur in the aluminum nitride substrate in the vicinity of the joint portion of the metal circuit layer, and the heat cycle characteristics and reliability are low.

Further, even when a circuit board is manufactured by using a ceramic substrate having a large thermal conductivity such as aluminum nitride, an aluminum nitride substrate having a large thickness is used to secure a certain strength value and insulation resistance. Had to use. Therefore, despite the high thermal conductivity of the AlN substrate, the thermal resistance value of the circuit board as a whole increases, and there is a problem in that heat dissipation proportional to the thermal conductivity cannot be obtained.

The present invention has been made in order to meet the above-mentioned demands, and utilizes the high-strength and high-toughness characteristics originally possessed by a silicon nitride sintered body, and further has high thermal conductivity and excellent heat dissipation. Another object of the present invention is to provide a silicon nitride circuit board having significantly improved heat resistance cycle characteristics.

[0012]

In order to achieve the above object, the present inventor has researched a substrate material which does not deteriorate the heat dissipation (thermal conductivity) of a circuit board and satisfies both strength and toughness values. At the same time, we conducted extensive research into measures to prevent tightening cracks that occur during the circuit board assembly process and cracks that occur during the application of heat cycles.
As a result, regarding the substrate material, by appropriately controlling the composition and manufacturing conditions, a silicon nitride sintered body having a high thermal conductivity was obtained, using this silicon nitride sintered body as a substrate material, When a circuit layer such as a metal circuit board is integrally formed on the surface of the board and the thickness of the board and the thickness of the metal circuit board are set to a predetermined ratio to form a circuit board, or the amount of bending or bending of the circuit board When the strength value is set to a predetermined value or more, it is possible to effectively reduce the tightening cracks of the circuit board in the assembly process, to greatly improve the heat resistance cycle characteristics, and especially to reduce the thickness of the board The inventors have completed the present invention by discovering that heat dissipation can be greatly improved.

That is, with respect to the substrate material itself, the present inventors have studied the types of silicon nitride powder, the types and amounts of sintering aids and additives, and the sintering conditions which have been conventionally used. We have developed a silicon nitride sintered body that has high thermal conductivity, which is more than twice the thermal conductivity of the silicon nitride sintered body. Furthermore, when this silicon nitride sintered body is used as a substrate material and a metal circuit board having conductivity is integrally bonded to the surface of the circuit board to produce a circuit board, mechanical strength, toughness value, heat cycle characteristics It was confirmed by experiments that a silicon nitride circuit board satisfying all the heat dissipation characteristics was obtained.

Specifically, a raw material mixture obtained by adding a predetermined amount of a rare earth element oxide or the like to fine and highly pure silicon nitride powder is molded and degreased, and the obtained molded body is heated at a predetermined temperature for a certain period of time. After carrying out densification sintering while holding, it is gradually cooled at a cooling rate not higher than a predetermined value, and when the obtained sintered body is manufactured by grinding and grinding, the thermal conductivity of the conventional silicon nitride sintered body is Greatly more than doubled, specifically 60 W / mK or more, and three-point bending strength of 650 at room temperature (25 ° C)
It was found that a silicon nitride sintered body having high strength and high toughness such as MPa or more can be obtained, and a new silicon nitride material satisfying both heat dissipation characteristics and strength characteristics was developed.
It has been found that when this silicon nitride material is applied to a substrate material of a circuit board, excellent heat dissipation characteristics, durability and heat cycle characteristics can be simultaneously improved.

Li, which inhibits oxygen and high heat conductivity,
By using high-purity silicon nitride raw material powder with a reduced content of specific impurity cation elements such as Na, K, Fe, Ca, Mg, Sr, Ba, Mn, and B, and sintering under the above conditions , Can effectively suppress the formation of the glass phase (amorphous phase) in the grain boundary phase, and can reduce the crystal compound in the grain boundary phase to 2
0% by volume or more (based on the entire grain boundary phase), more preferably 5
By setting the content to 0% by volume or more, a silicon nitride sintered body having a high thermal conductivity of 60 W / m · K or more, and more preferably 80 W / m · K or more, even when only the rare earth element oxide is added to the raw material powder. We have obtained the knowledge that a substrate can be obtained.

Further, conventionally, when the heating power source of the firing furnace was turned off after the sintering operation 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 less, preferably 50 ° C. or less per hour, 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 transmission are obtained. It has been found that the thermal properties are achieved at the same time.

A part of the high thermal conductivity silicon nitride sintered body itself having a thermal conductivity of 60 W / m · K or more has already been applied for a patent by the inventor of the present invention.
The application has been disclosed in Japanese Patent No. 135771 and Japanese Patent Laid-Open No. 7-48174. The silicon nitride sintered bodies described in these patent applications contain the rare earth element in an amount of 2.0 to 7.5% by weight in terms of oxide. However, as a result of further improvement research conducted by the present inventor, when the contained rare earth element exceeds 7.5% by weight in terms of oxide, the sintered body has a higher thermal conductivity, and the sintered body has a higher thermal conductivity. 7.5% by weight due to good binding
It is preferable to use a material having a viscosity of more than. In particular, the effect is remarkable when the rare earth element is a lanthanoid series element. By the way, even when the ratio of the crystal compound phase in the grain boundary phase to the whole grain boundary phase is 60 to 70%, the sintered body can achieve a high thermal conductivity of 110 to 120 W / m · K or more.

As described above, the silicon nitride sintered body satisfying both the high strength property and the high heat transfer property is used as the substrate material, and the metal circuit board is integrally bonded to the surface of the substrate material to form the circuit board. It has been found that the toughness and thermal conductivity of the entire board can be improved, and in particular, the occurrence of tightening cracks in the circuit board assembly process and cracks due to the addition of heat cycles can be effectively prevented.

In particular, the above-mentioned silicon nitride sintered body has not only high strength characteristics and high thermal conductivity but also excellent insulation resistance. It becomes possible to form a thin film as compared with. And by reducing the board thickness, the thermal resistance of the entire circuit board can be reduced,
It was found that the heat dissipation of the circuit board can be synergistically improved due to the high thermal conductivity of the board material itself.

The present invention has been completed based on the above findings. That is, the silicon nitride circuit substrate according to the first invention of the present application has an oxide layer on a high thermal conductivity silicon nitride substrate having a thermal conductivity of 60 W / mK or more and a three-point bending strength (normal temperature) of 650 MPa or more. In a silicon nitride circuit board formed by joining a metal circuit board through the above, a relational expression D _{S is} obtained when the thickness of the high thermal conductivity silicon nitride board is D _S and the thickness of the metal circuit board is D _M. It is characterized by satisfying ≦ 2D _M.

The silicon nitride circuit board according to the second invention of the present application is a highly heat conductive silicon nitride board having a thermal conductivity of 60 W / mK or more and a three-point bending strength (normal temperature) of 650 MPa or more. A silicon nitride circuit board obtained by bonding a metal circuit board through a metal bonding layer containing at least one active metal selected from Ti, Zr, Hf and Nb, wherein the high thermal conductivity silicon nitride substrate is used. Where D _{S is} the thickness of the metal circuit board and D _M is the thickness of the metal circuit board, the relational expression D _S ≦ 2D _M
It is characterized by satisfying.

In the silicon nitride circuit boards according to the first and second aspects of the present invention, the thickness D _S of the high thermal conductivity silicon nitride substrate and the thickness D _M of the metal circuit board are related by the relational expression D _M ≤D
_It is more preferable that _S ≤ (5/3) D _M is satisfied.

The silicon nitride circuit board according to the third invention of the present application is a circuit board in which a circuit layer is integrally bonded to a high thermal conductivity silicon nitride board having a thermal conductivity of 60 W / mK or more. It is characterized in that when a load is applied to the central portion while the circuit board is held at a support interval of 50 mm, the maximum amount of deflection until the silicon nitride board breaks is 0.6 mm or more.

In another embodiment, the thermal conductivity is 60 W /
A circuit board in which a circuit layer is integrally bonded to a high thermal conductivity silicon nitride substrate of m · K or more, and when the bending test is carried out with the circuit board held at a support interval of 50 mm, the bending strength is It is characterized by being 500 MPa or more.

Further, the thickness of the silicon nitride substrate having high thermal conductivity may be set to 0.8 mm or less. Further, the circuit layer is a copper circuit board, and the copper circuit board is directly bonded to the silicon nitride substrate by a Cu—O eutectic compound.
Further, the circuit layer is a copper circuit board, and the copper circuit board is bonded to the silicon nitride substrate through an active metal brazing material layer containing at least one active metal selected from Ti, Zr, Hf and Nb. It may be configured to. The circuit layer may be composed of a refractory metallized layer containing W or Mo and at least one active metal selected from Ti, Zr, Hf and Nb.

The high-thermal-conductivity silicon nitride substrate is 2.0 to 17.5% by weight in terms of oxide of rare earth element, and Li, Na, K, Fe, Ca, as impurity cation elements.
It is characterized by being composed of a silicon nitride sintered body containing Mg, Sr, Ba, Mn and B in a total amount of 0.3% by weight or less.

Further, the high thermal conductivity silicon nitride substrate contains the rare earth element in an amount of 2.0 to 17.5% by weight in terms of oxide, and is composed of a silicon nitride crystal and a grain boundary phase and in the grain boundary phase. It may be made of a silicon nitride sintered body in which the ratio of the crystal compound phase to the entire grain boundary phase is 20% or more.

Further, the high thermal conductivity 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 whole grain boundary phase is 50% or more. More preferably,

In the silicon nitride circuit board according to the first aspect of the present invention, a bonding agent such as a brazing material is not used, and after an oxide layer is formed on the surface of the silicon nitride board, it is directly bonded to a metal circuit board, for example. If the metal circuit board is a copper circuit board, add 1 oxygen
Tough pitch electrolytic copper containing about 0 to 1000 ppm is used, and both members are directly bonded at the bonding interface by the eutectic compound of copper and copper oxide (DBC method). That is, in the DBC method, tough pitch electrolytic copper containing oxygen necessary for forming a eutectic compound is used.

On the other hand, in the silicon nitride circuit substrate according to the second aspect of the present invention, an oxide layer is not formed on the surface of the silicon nitride substrate and a metal bonding layer containing an active metal is used as a bonding agent. The silicon substrate and the metal circuit board are joined. In this case, the metal circuit board does not need to contain oxygen, and one formed of oxygen-free copper, copper phosphate or electroless copper is used.

It is particularly preferable to use a lanthanoid series element as the rare earth element in order to improve the thermal conductivity of the silicon nitride substrate.

The high-thermal-conductivity silicon nitride substrate may contain at least one of aluminum nitride and alumina in an amount of 1.0% by weight or less. Further, 1.0% by weight or less of alumina and 1.0% by weight or less of aluminum nitride may be used together.

The high thermal conductivity silicon nitride substrate used in the present invention is made of Ti, Zr, Hf, V, Nb, Ta, Cr,
It is preferable that at least one selected from the group consisting of Mo and W is contained in an amount of 0.1 to 0.3% by weight in terms of oxide. This Ti, Zr, Hf, V, Nb, Ta, C
At least one selected from the group consisting of r, Mo and W can be contained by adding it to the silicon nitride powder as an oxide, a carbide, a nitride, a silicide or a boride.

The high thermal conductivity silicon nitride substrate used in the present invention is manufactured, for example, by the following method. That is, 1.7 wt% or less of oxygen, L as an impurity cation element
i, Na, K, Fe, Ca, Mg, Sr, Ba, Mn,
0.3% by weight or less of B in total and 90% of α-phase silicon nitride
2.0 to 1 in terms of oxide of a rare earth element in a silicon nitride powder having an average particle size of 1.0 μm or less, which is contained by weight% or more.
7.5 wt% and, if necessary, at least one of alumina and aluminum nitride was added at 1.0 wt% or less to form a raw material mixture to prepare a green body, and after degreasing the obtained green body, the temperature was adjusted. Atmospheric pressure sintering at 1800 to 2100 ° C., and the cooling rate of the sintered body from the above sintering temperature to the temperature at which the liquid phase formed during sintering by the above rare earth element solidifies is set to 100 ° C. or less per hour. Slowly cool.

In addition to silicon nitride powder, Ti, Z
oxides of r, Hf, V, Nb, Ta, Cr, Mo, W,
It is preferable to add 0.1 to 3.0% by weight of at least one selected from the group consisting of carbides, nitrides, silicides and borides.

According to the above manufacturing method, a grain boundary phase containing a rare earth element or the like is formed in the silicon nitride crystal structure, the porosity is 2.5% or less, the thermal conductivity is 90 W / m · K or more, and It is possible to obtain a silicon nitride sintered body having a point bending strength of 650 MPa or more at room temperature, which is excellent in both mechanical properties and heat conduction properties.

The silicon nitride powder, which is the main component of the high thermal conductivity silicon nitride substrate used in the present invention, has an oxygen content of 1.7 wt% in consideration of sinterability, strength and thermal conductivity. % Or less, preferably 0.5 to 1.5% by weight,
Li, Na, K, Fe, Mg, Ca, Sr, Ba, M
The total content of impurity cation elements such as n and B is 0.3.
It contains 90% by weight or more, preferably 93% by weight or more, of α-phase type silicon nitride suppressed to a weight% or less, preferably 0.2% by weight or less, and has an average particle size of 1.0 μm or less, preferably 0. Fine silicon nitride powder of about 4 to 0.8 μm can be used.

By using a fine raw material powder having an average particle size of 1.0 μm or less, it is possible to form a dense sintered body having a porosity of 2.5% or less even with a small amount of a sintering aid. It is also possible to reduce the risk of the sintering aid impairing the heat conduction characteristics.

Li, Na, K, Fe, Ca, Mg,
Impurity cation elements of Sr, Ba, Mn, and B are substances that impede thermal conductivity. Therefore, in order to ensure a thermal conductivity of 60 W / m · K or more, the content of the impurity cation elements is It can be achieved by setting the total to 0.3% by weight or less. Particularly, for the same reason, the total content of the above-mentioned impurity cation elements is 0.2% by weight or less,
More preferred. The silicon nitride powder used for obtaining the usual silicon nitride sintered body is particularly Fe, C.
Since a and Mg are contained in relatively large amounts, Fe and C
The total amount of a and Mg is a measure of the total content of the above impurity cation elements.

Further, by using a silicon nitride raw material powder containing 90% by weight or more of α-phase type silicon nitride, which is superior in sinterability as compared with the 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 Ho, Er, Yb, Y,
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, but especially holmium oxide (Ho ₂ O
₃ ) and erbium oxide (Er ₂ O ₃ ) are preferred.

In particular, by using lanthanoid series elements Ho, Er and Yb as the rare earth element, the sinterability or high thermal conductivity is improved, and the firing is sufficiently dense even in the low temperature region of about 1850 ° C. A union is obtained. Therefore, the effect of reducing the equipment cost and running cost of the firing apparatus can be obtained. These sintering aids are
It reacts with the silicon nitride raw material powder to form a liquid phase and functions as a sintering accelerator.

The amount of the above-mentioned sintering aid added is in the range of 2.0 to 17.5% by weight based on the raw material powder in terms of oxide.
If the addition amount is less than 2.0% by weight, the densification of the sintered body is insufficient. Especially, when the rare earth element is an element having a large atomic weight such as a lanthanoid element, the strength is low and the thermal conductivity is low. A rate of sintered body is formed. On the other hand, the addition amount is 17.
If the amount exceeds 5% by weight, 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 4 to 15% by weight.

Further, Ti, Zr, Hf, V, Nb and T used as other selective addition components in the above manufacturing method.
The oxides, carbides, nitrides, suicides, and borides of a, Cr, Mo, and W promote the function of the above-mentioned rare earth element sintering promoter and, at the same time, function as a dispersion strengthener in the crystal structure of Si ₃ It improves the mechanical strength of the N ₄ sintered body, and a compound of Hf and Ti is particularly preferable. If the addition amount of these compounds is less than 0.1% by weight, the effect of addition is insufficient, while if it exceeds 3.0% by weight, the thermal conductivity, mechanical strength, and electrical breakdown Since the strength decreases, the addition amount is set to the range of 0.1 to 3.0% by weight. In particular, it is desirable that the content be 0.2 to 2% by weight.

The compounds of Ti, Zr, Hf and the like also function as a light-shielding agent for coloring the silicon nitride sintered body in a black system and imparting opacity. Therefore, particularly when manufacturing a circuit board on which an integrated circuit or the like is likely to malfunction due to light, it is desirable to appropriately add the compound such as Ti to obtain a silicon nitride substrate having an excellent light shielding property.

Further, in the above-mentioned manufacturing method, alumina (Al ₂ O ₃ ) as another optional additional component plays a role of promoting the function of the sintering promoter for the rare earth element, and particularly, the pressurization. It exhibits a remarkable effect when sintering is performed. When the added amount of Al ₂ O ₃ is less than 0.1% by weight, it is necessary to sinter at a higher temperature, while when the added amount exceeds 1.0% by weight, an excessive amount of grain boundary is used. A phase is generated or a solid solution begins to form a solid solution in silicon nitride and the thermal conductivity is lowered. Therefore, the addition amount is 1% by weight or less, preferably 0.1 to 0.75% by weight.
In particular, in order to secure good performances in both strength and thermal conductivity, it is desirable that the addition amount be in the range of 0.1 to 0.5% by weight.

When used in combination with AlN, which will be described later, the total addition amount is preferably 1.0% by weight or less.

Aluminum nitride (AlN) as another additional component not only suppresses evaporation of silicon nitride in the sintering process, but also promotes the function of the rare earth element as a sintering accelerator. Is.

When the amount of AlN added is less than 0.1% by weight (less than 0.05% by weight when used in combination with alumina), sintering at a higher temperature is required, while
If the amount exceeds 0% by weight, an excessive amount of grain boundary phase is generated or begins to form a solid solution in silicon nitride, and the thermal conductivity decreases, so the addition amount is 0.1 to 1.0. The range is wt%. In particular, in order to secure good performances in terms of sinterability, strength, and thermal conductivity, it is desirable that the addition amount be in the range of 0.1 to 0.5% by weight. When used in combination with Al ₂ O ₃ , the addition amount of AlN is 0.05 to 0.5% by weight.
Is preferred.

The porosity of the sintered body has a great effect on the thermal conductivity and the strength, so that the sintered body is manufactured so as to have a porosity of 2.5% or less. If the porosity exceeds 2.5%, it will hinder heat conduction,
The thermal conductivity of the sintered body decreases and the strength of the sintered body also decreases.

Further, the silicon nitride sintered body is structurally composed of silicon nitride crystals and a grain boundary phase. The proportion of the crystalline compound phase in the grain boundary phase has a great influence on the thermal conductivity of the sintered body. However, in the high thermal conductivity silicon nitride sintered body used in the present invention, it is necessary to make it 20% or more of the grain boundary phase,
More preferably, 50% or more is preferably occupied by the crystal phase. If the crystal phase is less than 20%, the thermal conductivity will be 60 W / m.
This is because it is not possible to obtain a sintered body having excellent heat dissipation characteristics of K or more and excellent high temperature strength.

Further, as described above, the porosity of the silicon nitride sintered body is set to 2.5% or less, and 20% or more of the grain boundary phase formed in the silicon nitride crystal structure is occupied by the crystal phase. A silicon nitride compact at a temperature of 1800-210.
It is important to perform pressure sintering at 0 ° C. for about 2 to 10 hours and gradually cool the sintered body immediately after the completion of the sintering operation to 100 ° C. or less per hour.

If the sintering temperature is less than 1800 ° C., the densification of the sintered body will be insufficient and the porosity will be 2.5 vol% or more, resulting in a decrease in both mechanical strength and thermal conductivity. On the other hand, if the sintering temperature exceeds 2100 ° C., the silicon nitride component itself tends to evaporate and decompose. Not especially pressure sintering,
When pressureless sintering is carried out, decomposition vaporization of silicon nitride begins at around 1800 ° C.

The cooling rate of the sintered body immediately after the completion of the above-mentioned sintering operation is an important control factor for crystallizing the grain boundary phase, and when performing the rapid cooling such that the cooling rate exceeds 100 ° C. per hour. The grain boundary phase of the sintered body structure becomes amorphous (glass phase), the liquid phase generated in the sintered body occupies less than 20% of the grain boundary phase as a crystal phase, and the strength and thermal conductivity are Both will decrease.

The temperature range in which the cooling rate should be strictly adjusted is a temperature range from a predetermined sintering temperature (1800 to 2100 ° C.) to the solidification of the liquid phase produced by the reaction of the above-mentioned sintering aid. Is enough. By the way, the liquidus freezing point when the above-mentioned sintering aid is used is approximately 1600 to 15
It is about 00 ° C. The cooling rate of the sintered body from at least the sintering temperature to the liquidus solidification temperature is set to 10 per hour.
0 ° C or lower, preferably 50 ° C or lower, more preferably 2
By controlling the temperature to 5 ° C or lower, 20% or more of the grain boundary phase,
Particularly preferably, 50% or more becomes a crystalline phase, and a silicon nitride sintered body excellent in both thermal conductivity and mechanical strength can be obtained.

The high thermal conductivity silicon nitride substrate used in the present invention is manufactured, for example, through the following process. That is, with respect to the fine silicon nitride powder having a predetermined fine particle diameter and a small amount of impurities, a predetermined amount of a sintering aid, an organic binder, and other necessary additives and, if necessary, Al ₂ O. _A raw material mixture is prepared by adding ₃ , AlN, Ti compounds and the like, and the obtained raw material mixture is then molded to obtain a molded product having a predetermined shape. As a molding 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.

Subsequent to the above 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 binder added in advance is added. Remove components thoroughly and degrease.
Next, the degreased molded body is subjected to 1800 to 210 in an inert gas atmosphere such as nitrogen gas, hydrogen gas or argon gas.
Atmosphere pressure sintering is performed at a temperature of 0 ° C. for a predetermined time.

The high thermal conductivity silicon nitride substrate manufactured by the above manufacturing method has a porosity of 2.5% or less, 60 W / m · K.
It has a thermal conductivity of (25 ° C.) or higher, further 100 W / m · K or higher, and a three-point bending strength of 650 MPa or higher at room temperature, further 800 MPa or higher, which is excellent in mechanical properties.

It should be noted that a silicon nitride sintered body obtained by adding SiC or the like having a high thermal conductivity to silicon nitride having a low thermal conductivity so that the thermal conductivity of the whole sintered body is 60 W / m · K or more is the present invention. Not included in the range. However, the thermal conductivity is 60W
/ M · K or higher silicon nitride sintered body with high thermal conductivity S
Needless to say, a silicon nitride-based sintered body in which iC or the like is compounded is included in the scope of the present invention as long as the thermal conductivity of the silicon nitride sintered body itself is 60 W / m · K or more. .

The thickness D _S of the high-thermal-conductivity silicon nitride substrate is set to various thicknesses according to the required characteristics when it is used as a circuit board. In the present invention, the thickness of the metal circuit board is set. Is _defined as D _M , the relational expression D _S ≦ 2D _M is satisfied. That is, the thickness D _S of the high thermal conductivity silicon nitride substrate is not more than twice the thickness of the metal circuit board. By making the thickness D _{S of the} silicon nitride substrate less than or equal to twice the thickness D _M of the metal circuit board, the thermal resistance of the silicon nitride substrate having a specific thermal conductivity can be reduced, and by extension, the entire circuit substrate The thermal resistance can be reduced. The thickness D _{S of the} high-thermal-conductivity silicon nitride substrate and the thickness D _M of the metal circuit board satisfy the relational expression D _M ≦ D _S ≦ (5/3) D _M to obtain a ceramic circuit board. Since it is possible to simultaneously satisfy the strength characteristics and the heat dissipation property, it is more preferable.

The specific thickness of the high thermal conductivity silicon nitride substrate in this case is in the range of 0.25 to 0.8 mm. In particular, by setting the thickness of this silicon nitride substrate to 0.5 mm or less, preferably 0.4 mm or less, the thickness of the entire circuit board can be reduced and the thermal resistance between the upper and lower surfaces of the circuit board can be reduced. It is possible to reduce the difference more effectively,
The heat dissipation of the entire circuit board can be further improved.
However, in order to secure the strength characteristics of the substrate, it is desirable that the thickness D _S of the high-thermal-conductivity silicon nitride substrate be equal to or greater than the thickness D _M of the metal circuit board.

The silicon nitride circuit board according to the present invention has the high thermal conductivity silicon nitride substrate manufactured as described above,
It is manufactured by integrally forming a circuit layer such as a metal circuit board having conductivity with a semiconductor element and mounting the semiconductor element on the metal circuit board.

The method of forming or joining the circuit layer such as the metal circuit board is not particularly limited, and a direct joining method, an active metal method, a metallizing method, or the like described below can be applied.

In the direct bonding method, an oxide layer having a thickness of about 0.5 to 10 μm is formed on the surface of a high thermal conductivity silicon nitride substrate, and a metal circuit board to be a circuit layer is formed through this oxide layer. This is a method of directly bonding to the silicon nitride substrate. Here, the metal circuit board is directly and integrally bonded to the surface of the silicon nitride substrate without using a bonding agent such as a brazing material. That is, for example, when the metal circuit board is a copper circuit board, oxygen is added in several tens.
A copper material containing 0 ppm is used, and both members are directly bonded by a eutectic compound of copper and copper oxide.

This direct bonding method can be applied only to oxide-based ceramics such as Al ₂ O ₃ , and even if it is directly applied to a silicon nitride substrate, the wettability with respect to the substrate is low. Cannot obtain good bonding strength.

Therefore, it is necessary to previously form an oxide layer on the surface of the silicon nitride substrate to enhance the wettability with respect to the substrate. This oxide layer is formed on the silicon nitride substrate having high thermal conductivity at a temperature of about 1000 to 1400 ° C. in an oxidizing atmosphere such as air.
Formed by heating for ~ 15 hours. When the thickness of the oxide layer is less than 0.5 μm, the effect of improving the wettability is small, but even when the oxide layer is formed to be thicker than 10 μm, the improving effect is saturated and the thermal conductivity is rather lowered. Therefore, the thickness of the oxide layer is set in the range of 0.5 to 10 μm, more preferably 1 to 5 μm.

The above oxide layer is initially composed only of SiO ₂ which is an oxide of the Si ₃ N ₄ substrate component, but during the bonding operation of the metal circuit board by heating, the Si ₃ N ₄ substrate has a sintering aid. As a result of the rare earth element oxide added as the agent diffusing and moving toward the oxide layer, the rare earth oxide is concentrated in the oxide layer. For example, as a sintering aid, Y ₂
When O ₃ is used, the oxide layer after the heat bonding operation is Y
Comes to be composed of SiO ₂ -Y ₂ O ₃ compound such yttria silicate containing about a ₂ O ₃ 1 to 20% by weight.

As a metal constituting the above-mentioned metal circuit board, a eutectic compound with a substrate component such as a simple substance of copper, aluminum, iron, nickel, chromium, silver, molybdenum, cobalt, or an alloy thereof is formed and directly contacted. There is no particular limitation as long as it is a metal to which legality can be applied, but copper, aluminum or an alloy thereof is particularly preferable from the viewpoint of conductivity and cost.

The thickness of the metal circuit board is determined in consideration of the current-carrying capacity and the like, but the thickness of the silicon nitride substrate is 0.25 to 0.25.
The thickness of the metal circuit board is set to 0.1 mm while the range is set to 1.2 mm.
If they are set in the range of about 0.5 mm and they are combined, the influence of deformation due to a difference in thermal expansion becomes less likely.

When the metal circuit board is a copper circuit board, the joining operation is carried out as follows. That is, a copper circuit board is placed in contact with a predetermined position on the surface of a silicon nitride substrate having a high thermal conductivity on which an oxide layer is formed, and is pressed toward the substrate at a temperature lower than the melting point (1083 ° C.) of copper and −
The copper circuit board is directly bonded to the surface of the high thermal conductivity silicon nitride substrate by heating it to a temperature higher than the eutectic temperature of copper oxide (1065 ° C.) and using the generated Cu—O eutectic compound liquid phase as a bonding agent. This direct bonding method is a so-called copper direct bonding method (DBC: Dire
ct Bonding Copper method). Further, a semiconductor element (Si chip) is soldered and mounted at a predetermined position on the directly bonded copper circuit board, whereby the Si ₃ N ₄ circuit board according to the present invention is manufactured.

On the other hand, when the metal circuit board is an aluminum circuit board, the Al circuit board is heated to a temperature higher than the eutectic temperature of aluminum-silicon while the Al circuit board is pressed against the surface of the Si ₃ N ₄ substrate, and the generated Al- Al using Si eutectic compound as a bonding agent
The circuit board is bonded directly to the Si ₃ N ₄ substrate surface. Then, the semiconductor element is solder-bonded and mounted on a predetermined position of the directly bonded Al circuit board, whereby the Si ₃ N ₄ of the present invention is mounted.
A circuit board is manufactured.

As described above, the metal circuit board is directly bonded to the surface of the Si ₃ N ₄ substrate by using the direct bonding method, and further the semiconductor element is mounted on the metal circuit board to form the Si according to the present invention.
According to the ₃ N ₄ circuit board, since there is no inclusion such as an adhesive or a brazing material between the metal circuit board and the Si ₃ N ₄ board, the thermal resistance between the two is small, and It is possible to quickly dissipate the heat generated by the semiconductor element provided in the outside of the system.

Next, a method for joining metal circuit boards by the active metal method will be described.

In the active metal method, an Ag-Cu-Ti-based brazing material containing at least one active metal selected from Ti, Zr, Hf and Nb and having an appropriate composition ratio is used to form a silicon nitride substrate surface. An active metal brazing material layer (metal bonding layer) having a thickness of about 20 μm is formed, and a metal circuit board such as a copper circuit board is bonded via the metal bonding layer. The active metal has an effect of improving the wettability of the brazing material with respect to the substrate and increasing the bonding strength. Specific examples of the active metal brazing material include 1 to 10% by weight of the active metal and 15 to 15% of Cu.
A brazing filler metal composition having 35% and the balance being substantially Ag is preferable. The metal bonding layer is formed by a method such as screen-printing a bonding composition paste prepared by dispersing the brazing material composition in an organic solvent on the surface of the silicon nitride substrate.

Then, in a state where a metal circuit board to be a circuit layer is placed in contact with the screen-printed metal bonding layer, in a vacuum or in an inert gas atmosphere, for example, at an Ag-Cu eutectic temperature (780 ° C.) or higher. By heating the metal circuit board to a temperature equal to or lower than the melting point (1083 ° C. in the case of copper) of the metal circuit board, the metal circuit board is integrally bonded to the silicon nitride substrate via the metal bonding layer.

Next, a method of forming a circuit layer by the metallizing method will be described. In the metallization method, for example, molybdenum (M
o) or a refractory metal such as tungsten (W) and a metallized composition mainly containing Ti or a compound thereof are baked on the surface of the silicon nitride substrate to form a refractory metal metallized layer as a circuit layer having a thickness of about 15 μm. Is a method of forming.

When the circuit layer is formed by this metallizing method, it is preferable to further form a metal plating layer of Ni or Au having a thickness of about 3 to 5 μm on the surface of the metallizing layer. By forming this metal plating layer,
The surface smoothness of the metallized layer is improved, the adhesion with the semiconductor element is further improved, and the solder wettability is improved, so that the bonding strength of the semiconductor element using solder can be further increased.

The maximum amount of deflection of the silicon nitride circuit board manufactured as described above is a factor that has a great influence on the rate of occurrence of tightening cracks in the assembly process of the circuit board. It is preferably set to 0.8 mm or more. The maximum deflection is 0.6
If it is less than mm, tightening cracks of the circuit board in the assembly process rapidly increase, and the manufacturing yield of the semiconductor device using the circuit board sharply decreases.

The flexural strength of the circuit board is a factor that affects the rate of occurrence of the above-mentioned tightening cracks and controls whether or not the silicon nitride board can be thinned.
It is regulated to 0 MPa or more. This bending strength is 500MP
If it is less than a, tightening cracks on the circuit board increase.
Further, it becomes difficult to make the thickness thinner than other conventional ceramics substrates, and it becomes difficult to synergistically reduce the thermal resistance value of the entire circuit board accompanying the reduction in thickness. Therefore, the bending strength of the circuit board is set to 500 MPa or more, but it is more preferable to set it to 600 MPa or more.

According to the silicon nitride circuit board having the above-described structure, in addition to the high strength and high toughness characteristics inherent in the silicon nitride sintered body, especially the high thermal conductivity silicon nitride board in which the thermal conductivity is greatly improved. It is formed by integrally joining a metal circuit board to the surface. Therefore, since the toughness value of the circuit board is high,
It is possible to secure a large maximum deflection of 0.6 mm or more. In addition, it is possible to make the silicon nitride substrate thinner than before, and even in that case, the bending strength of the circuit substrate is 500M.
It becomes Pa or more. For this reason, the circuit board does not suffer from cracking in the assembly process, and semiconductor devices using the circuit board can be mass-produced with a high manufacturing yield.

Since the toughness value of the silicon nitride substrate is high,
It is possible to provide a semiconductor device in which cracks are less likely to occur in a substrate due to heat cycle, heat cycle characteristics are remarkably improved, and durability and reliability are excellent.

Furthermore, since a silicon nitride substrate having a high thermal conductivity, which has not been achieved in the past, is used, the thermal resistance characteristics of the semiconductor device can be improved even when a semiconductor element for high output and high integration is mounted. Shows excellent heat dissipation with little deterioration.

In particular, since the silicon nitride substrate itself is excellent in mechanical strength, when the required mechanical strength characteristics are kept constant, the substrate thickness is made larger than that when other ceramic substrates are used. It becomes possible to reduce. Since the substrate thickness can be reduced, the thermal resistance value can be synergistically reduced, and the heat dissipation characteristics can be further improved. Further, since it is possible to sufficiently meet the required mechanical characteristics even with a substrate thinner than before, it is possible to mount the circuit board at a high density and further downsize the semiconductor device.

[0084]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be specifically described with reference to the following examples.

Examples 1 to 3 1.3 wt% oxygen, Li as the impurity cation element,
Containing 0.15 wt% of Na, K, Fe, Ca, Mg, Sr, Ba, Mn and B in total, and 97% of α-phase type silicon nitride
With respect to the average particle size silicon nitride material powder of 0.55μm comprising, an average particle size of 0.7μm as a sintering aid Y ₂ O
₃ (yttrium oxide) powder 5% by weight, average particle size 0.5
1.0 wt% of Al ₂ O ₃ (alumina) powder of μm was added, wet-mixed in ethyl alcohol for 24 hours, and then dried to prepare a raw material powder mixture.

Next, a predetermined amount of an organic binder was added to the obtained raw material powder mixture and the mixture was uniformly mixed.
A large number of compacts were produced by press molding with a compacting pressure of cm ² . Next, after degreasing the obtained molded body in an atmospheric gas at 700 ° C. for 2 hours, the degreased body was held at 1900 ° C. for 6 hours at 9 atm in a nitrogen gas atmosphere, and after performing densification sintering, Control the amount of electricity to the heating device attached to the sintering furnace and adjust the cooling rate of the sintered body to 100 ° C / hr until the temperature inside the sintering furnace drops to 1500 ° C. The sintered body was cooled, and the obtained sintered body was subjected to polishing to obtain a thermal conductivity k of 70 W / m · K and thicknesses of 0.25 mm, 0.4 mm and 0.6 mm, respectively. A silicon nitride substrate having a length of 29 mm and a width of 63 mm for Examples 1 to 3 was prepared. The volume fraction of the crystal phase in the grain boundary phase of the silicon nitride substrate was 30%, and the porosity of the substrate was 0.2%.

Next, as shown in FIG. 1, each silicon nitride substrate 2
30 wt% Ag-65% Cu-5% Ti brazing filler metal is screen-printed on the portion where the front surface circuit layer is formed and the rear portion where the copper plate is joined, and the active metal brazing filler metal layers 7 a and 7 b having a thickness of 20 μm are dried. Was formed. At a predetermined position on the active metal brazing material layers 7a and 7b, a thickness of oxygen-free copper of 0.3
The copper circuit board 4 having a thickness of 0.25 mm and the back copper plate 5 having a thickness of 0.25 mm were placed in contact with each other, and were held in vacuum at a temperature of 850 ° C. for 10 minutes to form a bonded body. Next, a predetermined circuit pattern (circuit layer) was formed by etching each bonded body. Further, a 16 mm square × 0.5 mm thick semiconductor element (output: 300 W) 6 was soldered to the central portion of the copper circuit board 4 to manufacture a large number of silicon nitride circuit boards 1 according to Examples 1 to 3.

Example 4 Thickness 0.3 mm and 0.25 used in Example 3
Except for using a 0.5 mm thick copper circuit board on the front side and a 0.3 mm thick back copper plate on the back side instead of the mm copper circuit board,
The same treatment as in Example 3 was carried out to prepare a Si ₃ N ₄ circuit board according to Example 4.

Example 5 Instead of the high thermal conductivity silicon nitride substrate having a thermal conductivity of 70 W / mK used in Example 2, the cooling rate after completion of sintering was adjusted to obtain a thermal conductivity of 100 W / mK. A Si ₃ N ₄ circuit board according to Example 5 was prepared in the same manner as in Example 2 except that the K silicon nitride substrate was used.

Comparative Example 1 In place of the silicon nitride substrate having a thickness of 0.6 mm used in Example 3, the thermal conductivity k was 170 W / m · K and the thickness was 0.
A circuit board according to Comparative Example 1 was manufactured by integrally bonding a copper circuit board and a back copper plate to the surface of the board by the active metal method in the same manner as in Example 3 except that an 8 mm aluminum nitride (AlN) board was used.

Comparative Example 2 An active metal was prepared in the same manner as in Example 3 except that a silicon nitride substrate having a thickness of 0.8 mm was used in place of the silicon nitride substrate having a thickness of 0.6 mm used in Example 3. A circuit board according to Comparative Example 2 was manufactured by integrally bonding a copper circuit board and a back copper plate to the surface of the board by the method.

The maximum deflection amount and bending strength of the circuit boards according to Examples 1 to 5 and Comparative Examples 1 and 2 thus prepared were measured, and the silicon nitride circuit board 1 according to Examples 1 to 5 was measured. Was found to have a maximum deflection amount and a bending strength twice or more as compared with the circuit board of Comparative Example 1 using the conventional aluminum nitride substrate. It was also confirmed that as the thickness of the silicon nitride substrate was reduced, the amount of deflection and the bending strength were further improved.

Further, a heat dissipation evaluation test was conducted on each circuit board. In the heat dissipation evaluation test, as shown in FIG. 3, the circuit board 1 on which the semiconductor element 6 having an output of 300 W is mounted is
The surface temperature Ti of the semiconductor element 6 was measured while energizing the semiconductor element 6 while being bonded to the copper heat sink 8 having a heat dissipation capacity of 9000 W / m ² · K. Then, the outside air temperature (T = 30
The difference (ΔTi = Ti−T) from 0 K) was calculated, and the quality of heat dissipation was evaluated by the size of the temperature rise width (ΔTi) of the semiconductor element 6. Table 1 shows the measured values of the temperature rise width (ΔTi).

As is clear from the results shown in Table 1, according to the circuit boards of the respective examples, the Si ₃ N ₄ substrate whose thermal conductivity is smaller than that of the conventional AlN substrate (Comparative Example 1) is used. Nevertheless, since the thickness of the Si ₃ N ₄ substrate can be reduced, the thermal resistance of the entire circuit board can be reduced. Therefore, it was found that the temperature rise width ΔTi of the semiconductor element is almost the same as that of the conventional AlN circuit board, and exhibits excellent heat dissipation. Further, it was also confirmed that the thermal resistance is reduced by reducing the thickness of the Si ₃ N ₄ substrate, so that the heat dissipation characteristics of the entire circuit substrate can be further improved.

On the other hand, in Comparative Example 2 using the 0.8 mm thick Si ₃ N ₄ substrate which is more than twice the thickness of the metal circuit board, the temperature rise ΔTi of the semiconductor element is large and the heat dissipation characteristics are relatively high. Turned out to be low.

When the circuit board of each of the above-mentioned embodiments was mounted on the board in the assembly process, tightening cracks did not occur, and the semiconductor device using the circuit board could be mass-produced with a high manufacturing yield.

Each circuit board is heated from −45 ° C. to room temperature (RT), then heated from room temperature to + 125 ° C., and then cooled to −45 ° C. after passing through room temperature as one cycle. A cycle was repeatedly added, and a heat resistance cycle test was conducted to measure the number of cycles until a crack or the like was generated in the substrate part. With the circuit boards of Examples 1 to 5, even after 1000 cycles, Si ₃ N ₄ Board cracks and metal circuit boards (Cu circuit boards)
It was found that no peeling was observed and the excellent heat cycle characteristics were exhibited. On the other hand, in the AlN circuit board of Comparative Example 1, it was confirmed that cracks occurred at 100 cycles and the durability was low.

Examples 6 to 10 The metal circuit board was integrally bonded to the Si ₃ N ₄ substrate by the copper direct bonding method (DBC method) instead of the active metal method, and Example 1 was used.
Si _{3 according to} Examples 6 to 10 of the same size corresponding to
The N ₄ substrate was manufactured as follows.

That is, the Si ₃ N ₄ substrate prepared in Examples 1 to 5 has a thermal conductivity k of 70 W / m · K or 100 W / m · K and a thickness of 0.25 mm,
By heating each 0.4 mm, 0.6 mm, and 0.8 mm Si ₃ N ₄ substrate in an oxidation furnace at a temperature of 1300 ° C. for 12 hours, the entire surface of the substrate is oxidized to form an oxide layer having a thickness of 2 μm. Formed. The oxide layer is formed of a SiO ₂ film.

Next, as shown in Table 1, a thickness of 0.3 mm or 0.5 was formed on the surface of each Si ₃ N ₄ substrate on which an oxide layer was formed.
While a copper circuit board made of tough pitch electrolytic copper of mm is placed in contact, a copper circuit board made of tough pitch electrolytic copper of 0.25 mm or 0.3 mm in thickness is placed in contact as a backing material to form a laminated body on the back side. This laminated body is inserted into a heating furnace adjusted to a nitrogen gas atmosphere at a temperature of 1075 ° C. and heated for 1 minute to directly bond copper circuit boards to both sides of each Si ₃ N ₄ substrate, and further solder bond semiconductor elements. Examples 6 to 1
No. 0 Si ₃ N ₄ circuit boards were prepared.

[0102] Each Si ₃ N ₄ circuit board 1a is oxidized layer 3 made of SiO ₂ is formed on the entire surface the Si ₃ N ₄ substrate 2 as shown in FIG. 2, Si ₃ N ₄ surface of the substrate 2 While the copper circuit board 4 as a metal circuit board is directly joined to the side,
Similarly, a copper circuit board 5 as a back copper plate is directly joined to the back side, and further, semiconductor elements 6 are integrally joined to predetermined positions of the copper circuit board 4 on the front side via a solder layer (not shown). . When the copper circuit boards 4 and 5 are bonded to both surfaces of the Si ₃ N ₄ substrate 2, the copper circuit board 5 as the back copper plate contributes to promotion of heat dissipation and prevention of warpage, which is effective.

The maximum deflection of the Si ₃ N ₄ circuit boards according to Examples 6 to 10 in which the circuit layers were formed by the direct bonding method as described above was in the range of 0.8 to 1.6 mm, and the bending strength was Is in the range of 550 to 900 MPa, and
As in the case of No. 5, the characteristic value equivalent to that when the circuit layer was formed by the active metal method was obtained. In the heat resistance cycle test, 10
Even after the lapse of 00 cycles, there was no cracking of the Si ₃ N ₄ substrate or peeling of the metal circuit board, and excellent heat cycle characteristics were exhibited.

Comparative Example 3 An aluminum nitride (AlN) substrate having a thermal conductivity k of 170 W / m · K and a thickness of 0.8 mm was used instead of the silicon nitride substrate used in Example 8. A circuit board according to Comparative Example 3 was manufactured by integrally bonding a copper circuit board and a back copper plate to the surface of the board by the direct copper bonding method as in Example 8.

Comparative Example 4 The same method as in Example 8 was repeated except that a silicon nitride substrate having a thickness of 0.8 mm was used instead of the silicon nitride substrate having a thickness of 0.6 mm used in Example 8. A circuit board according to Comparative Example 4 was manufactured by integrally bonding a copper circuit board and a back copper plate to the surface of the board by a bonding method.

Regarding the circuit boards according to Examples 6 to 10 and Comparative Examples 3 to 4 manufactured as described above, Examples 1 to 5 were used.
And the heat dissipation evaluation test shown in FIG. 3 was carried out in the same manner as in Comparative Examples 1 and 2, and the temperature rise width ΔTi due to the heat generation of the semiconductor device with an output of 300 W was measured to obtain the results shown in Table 1 below. 4 is a graph showing the relationship between the thickness of a ceramic substrate such as a silicon nitride substrate and the temperature rise ΔTi of the semiconductor element.

[0106]

[Table 1]

As is clear from the results shown in Table 1 and FIG. 4, as the thickness of the silicon nitride substrate is reduced, the thermal resistance of the entire circuit substrate is reduced and the temperature rise ΔTi of the semiconductor element is temporarily increased. It was confirmed that the heat dissipation was reduced and the heat dissipation was improved. In particular, Example 6 (circle) and Example 10 (▽
(Mark) and Comparative Example 3 (mark), as is clear from the comparison,
Si _{3 with} thermal conductivity of 70 W / mK and thickness of 0.25 mm
By forming a circuit board by using an N ₄ substrate or a Si ₃ N ₄ substrate having a thermal conductivity of 100 W / m · K and a thickness of 0.4 mm, the thermal conductivity is 170 W / m · K. It was possible to secure heat dissipation equivalent to that of a circuit board formed by using an AlN substrate having a thickness of 0.8 mm. Further, the substrate thickness can be reduced to 1/2 or less as compared with the conventional one, and the substrate manufacturing cost can be reduced.

It was also found that each Si ₃ N ₄ substrate had a good insulation resistance even when formed thin, and could maintain a dielectric breakdown resistance equal to or higher than the conventional one. On the other hand, in Comparative Example 4 using the 0.8 mm thick Si ₃ N ₄ substrate that is more than twice the thickness of the metal circuit board, the temperature rise ΔTi of the semiconductor element is large and the heat dissipation characteristic is relatively low. found.

Next, the influence of the thickness of the silicon nitride substrate used in the present invention on the deflection amount and bending strength of the circuit substrate will be described with reference to the following examples.

Examples 11 to 13 Nitrogen containing 1.3% by weight of oxygen, 0.15% by weight of the impurity cation elements in total, and 97% of α-phase type silicon nitride, and having an average particle diameter of 0.55 μm. For silicon raw material powder,
5% by weight of Y ₂ O ₃ (yttrium oxide) powder having an average particle size of 0.7 μm as a sintering aid and Al having an average particle size of 0.5 μm
1.5 wt% of ₂ O ₃ (alumina) powder was added, wet-mixed in ethyl alcohol for 24 hours, and then dried to prepare a raw material powder mixture.

Next, a predetermined amount of an organic binder was added to the obtained raw material powder mixture and the mixture was uniformly mixed.
Press-formed with a forming pressure of cm ² , length 80 mm × width 50 mm
× Many molded products having a thickness of 1 to 5 mm were manufactured. Next, the obtained molded body was degreased in an atmosphere gas at 700 ° C. for 2 hours, and then the degreased body was subjected to a nitrogen gas atmosphere at 9 atmospheric pressure for 19 hours.
After carrying out densification sintering by holding at 00 ° C for 6 hours, the amount of electricity supplied to the heating device attached to the sintering furnace is controlled to perform sintering until the temperature inside the sintering furnace drops to 1500 ° C. The cooling rate of each body was adjusted to 100 ° C./hr, the sintered body was cooled, and each obtained sintered body was ground to obtain a thermal conductivity k of 70 W / m · K. Examples 11 to 1 having thicknesses of 0.4 mm, 0.6 mm and 0.8 mm
A silicon nitride substrate for 3 was prepared.

Next, as shown in FIG. 5, each silicon nitride substrate 2
30 wt% Ag-65% Cu-5% Ti brazing filler metal is screen-printed on the portion where the front surface circuit layer is formed and the rear portion where the copper plate is joined, and the active metal brazing filler metal layers 7 a and 7 b having a thickness of 20 μm are dried. Was formed. A copper circuit board 4 made of tough pitch electrolytic copper and having a thickness of 0.3 mm and a back copper plate 5 having a thickness of 0.25 mm are provided at predetermined positions of the active metal brazing material layers 7a and 7b.
10 and 10 are placed in contact with each other in vacuum at a temperature of 850 ° C.
It was held for a minute to form a joined body. Next, a predetermined circuit pattern was formed by etching each bonded body. Further, the semiconductor element 6 was soldered to the central portion of the copper circuit board 4 to manufacture a large number of silicon nitride circuit boards 1b according to Examples 11 to 13.

Comparative Example 5 Instead of the silicon nitride substrate used in Examples 11 to 13,
A copper circuit board and a back surface were formed on the substrate surface by the active metal method in the same manner as in Examples 11 to 13 except that an aluminum nitride (AlN) substrate having a thermal conductivity k of 70 W / m · K and a thickness of 0.8 mm was used. A circuit board according to Comparative Example 5 was manufactured by integrally joining copper plates.

Examples 11 to 13 thus prepared
The maximum deflection amount and the bending strength of the circuit board according to Comparative Example 5 were measured, and the results shown in FIGS. 6 and 7 were obtained. Here, the maximum deflection amount was measured as the maximum deflection height until the Si ₃ N ₄ substrate or the AlN substrate was broken by applying a load to the central portion while supporting each circuit substrate with a supporting span of 50 mm. The bending strength was calculated from the load at break and the substrate cross-sectional area.

As is clear from the results shown in FIGS. 6 and 7, the silicon nitride circuit board 1b according to Examples 11 to 13 is obtained.
Was found to have a maximum deflection amount and a bending strength that are at least twice as high as the circuit board of Comparative Example 5 using the conventional aluminum nitride substrate. It was also confirmed that as the thickness of the silicon nitride substrate was reduced, the amount of deflection and the bending strength were further improved. Further, it was confirmed that the thermal resistance is reduced due to the reduction of the board thickness, so that the heat dissipation characteristics of the entire circuit board can be further improved.

When the above circuit board was mounted on the board in the assembly process, tightening cracks did not occur, and semiconductor devices using the circuit board could be mass-produced with a high manufacturing yield.

Each circuit board is heated from −45 ° C. to room temperature (RT), then heated from room temperature to + 125 ° C., and then cooled again to −45 ° C. through room temperature, which is one cycle. A cycle was repeatedly added, and a heat resistance cycle test was conducted to measure the number of cycles until a crack or the like was generated in the substrate part. The circuit boards of Examples 11 to 13 showed Si ₃ N ₄ even after 1000 cycles. It was found that there was no cracking of the substrate or peeling of the metal circuit board (Cu circuit board), and that it showed excellent heat cycle characteristics. On the other hand, in the circuit board of Comparative Example 5, cracking occurred after 100 cycles, and it was confirmed that the durability was low.

Example 14 The Si ₃ N ₄ substrate prepared in Examples 11 to 13 having a thermal conductivity k of 70 W / m · K and a thickness of 0.4 respectively.
By heating each Si ₃ N ₄ substrate having a size of 0.6 mm, 0.6 mm, and 0.8 mm in an oxidation furnace at a temperature of 1300 ° C. for 12 hours,
The entire surface of the substrate was oxidized to form an oxide layer having a thickness of 2 μm.

Next, a copper circuit board made of tough pitch electrolytic copper having a thickness of 0.3 mm is placed in contact with the surface side of each Si ₃ N ₄ substrate on which an oxide layer has been formed, while a tough pitch of 0.25 mm thickness is provided on the back side. As shown in FIG. 8, a copper circuit board made of copper is placed as a backing material in contact with each other to form a laminated body, which is inserted into a heating furnace adjusted to a nitrogen gas atmosphere at a temperature of 1075 ° C. and heated for 1 minute. as the Si ₃ N ₄ circuit board directly bonded copper circuit board on both sides of the Si ₃ N ₄ substrate 2 were prepared.

In each Si ₃ N ₄ circuit board 1c, an oxide layer 3 is formed on the entire surface of the Si ₃ N ₄ board 2 as shown in FIG. 8, and a metal circuit is formed on the surface side of the Si ₃ N ₄ board 2. While the copper circuit board 4 as a board is directly joined, the copper circuit board 5 as a back copper board is similarly directly joined to the back side, and a solder layer (not shown) is further provided at a predetermined position of the front side copper circuit board 4. Thus, the semiconductor element 6 is integrally joined. Si
_When copper circuit boards 4 and 5 are bonded to both sides of ₃ N ₄ substrate 2,
The copper circuit board 5 as the back copper plate is effective because it contributes to promotion of heat dissipation and prevention of warpage.

The maximum deflection of the Si ₃ N ₄ circuit board according to Example 4 in which the circuit layer was formed by the direct bonding method as described above was in the range of 0.8 to 1.6 mm, and the bending strength was 550. In the range of up to 900 MPa, Examples 11 to 13
As described above, the characteristic value equivalent to that when the circuit layer was formed by the active metal method was obtained. In the heat resistance cycle test, 100
Even after 0 cycles, there was no cracking of the Si ₃ N ₄ substrate or peeling of the metal circuit board, and excellent heat cycle characteristics were exhibited.

Example 15 As shown in FIG. 9, the Si ₃ N ₄ substrate prepared in Examples 11 to 13 has a thermal conductivity k of 70 W / m · K,
S whose thickness is 0.4mm, 0.6mm and 0.8mm respectively
On the surface of the i ₃ N ₄ substrate 2, a mixed powder of molybdenum (Mo) and titanium oxide (TiO ₂ ) added with an appropriate amount of a binder and a solvent to form a paste was screen-printed,
It was heated and baked to form a refractory metal materize layer 10 having a thickness of 15 μm. Further, a Ni plating layer 9 having a thickness of 3 μm is formed on the metallized layer 10 by an electroless plating method,
The circuit layer has a predetermined pattern. Next, the semiconductor element 6 was joined onto the circuit layer by soldering to manufacture a large number of silicon nitride circuit boards 1d according to Example 15.

The maximum deflection amount of the Si ₃ N ₄ circuit board according to Example 15 in which the circuit layer was formed by the metallizing method as described above was in the range of 1.0 to 1.8 mm, and the bending strength was 650 to 650. The range is 950 MPa, and
As shown in No. 13, characteristic values equivalent to those when the circuit layer was formed by the active metal method were obtained. In the heat cycle test, 1
Even after 000 cycles, there was no cracking of the Si ₃ N ₄ substrate or peeling of the metal circuit board, and the circuit board subjected to the plating treatment also exhibited excellent heat resistance cycle characteristics.

Next, an embodiment of a circuit board using another silicon nitride substrate having various compositions and characteristic values will be specifically described with reference to Example 16 shown below.

Example 16 First, various silicon nitride substrates which are constituent materials of a circuit board were manufactured by the following procedure.

That is, a silicon nitride raw material powder having an average particle diameter of 0.55 μm, containing 1.3% by weight of oxygen, 0.15% by weight of the impurity cation elements in total, and 97% of α-phase type silicon nitride. On the other hand, as shown in Tables 2 to 4, rare earth oxides such as Y ₂ O ₃ and Ho ₂ O ₃ as sintering aids,
If necessary, Ti, Hf compound, Al ₂ O ₃ powder, Al
N powder was added, and the mixture was wet-mixed in ethyl alcohol for 72 hours using a silicon nitride ball and then dried to prepare raw material powder mixtures. Next, a predetermined amount of an organic binder was added to each of the obtained raw material powder mixtures and uniformly mixed, followed by press molding at a molding pressure of 1000 kg / cm ² .
Many molded articles having various compositions were manufactured.

Next, each molded body obtained was degreased for 2 hours in an atmosphere gas at 700 ° C.
After carrying out the densification sintering under the sintering conditions shown in to 4, the amount of electricity supplied to the heating device attached to the sintering furnace is controlled to perform the sintering until the temperature inside the sintering furnace drops to 1500 ° C. The sintered bodies were cooled by adjusting the cooling rates of the bodies to the values shown in Tables 2 to 4, respectively, to prepare silicon nitride sintered bodies of Samples 1 to 51, respectively.

With respect to each of the silicon nitride sintered bodies according to Samples 1 to 51 thus obtained, the average value of porosity, thermal conductivity (25 ° C.) and three-point bending strength at room temperature was measured. Furthermore, the ratio (area ratio) of the crystal phase in the grain boundary phase was measured for each sintered body by the X-ray diffraction method, and the results shown in Tables 2 to 4 below were obtained.

[0129]

[Table 2]

[0130]

[Table 3]

[0131]

[Table 4]

As is clear from the results shown in Tables 2 to 4, in the silicon nitride sintered bodies according to Samples 1 to 51, the raw material composition was properly controlled, and immediately after the densification and sintering was completed as compared with the conventional example. Since the cooling rate of the sintered body is set lower than before, the higher the ratio of the crystal phase in the grain boundary phase and the higher the proportion of the crystal phase, the higher the heat dissipation and the high strength silicon nitride sintered body with high heat dissipation. was gotten.

On the other hand, 1.3 to 1.5% by weight of oxygen and 0.13 to 0.1% by weight of the above impurity cation elements are included.
A silicon nitride raw material powder containing 6% by weight and containing 93% of α-phase type silicon nitride and having an average particle size of 0.60 μm was used, and 3% of Y ₂ O ₃ (yttrium oxide) powder was added to the silicon nitride powder. ~ 6 wt% and 1.3-1.6 wt% alumina powder
The added raw material powder is molded and degreased, then sintered at 1900 ° C. for 6 hours and cooled in a furnace (cooling rate: 400 ° C./hour). The thermal conductivity was close to that of the silicon nitride sintered body manufactured by the conventional general manufacturing method.

Then, each of the obtained silicon nitride sintered bodies according to Samples 1 to 51 was subjected to polishing to obtain Examples 11 to 1
In the same manner as in No. 3, silicon nitride substrates having thicknesses of 0.4 mm, 0.6 mm and 0.8 mm were prepared. Next, according to Example 16 as shown in FIG. 5, a copper circuit board or the like was integrally bonded to the surface of each silicon nitride substrate prepared using the active metal method as in Examples 11 to 13. Each silicon nitride circuit board was prepared.

In addition, Example 1 was formed on the surface of each silicon nitride substrate.
As in Example 4, the DBC method was used to directly bond the copper circuit board and the like to prepare the silicon nitride circuit boards according to Example 16 as shown in FIG.

Further, by forming a circuit layer on the surface of each silicon nitride substrate by using the metallizing method as in the case of Example 15, a silicon nitride circuit substrate according to Example 16 as shown in FIG. 9 is obtained. Each was prepared.

The maximum deflection amount and bending strength of each Si ₃ N ₄ circuit board according to Example 16 in which the circuit layer was formed by the active metal method, the DBC method and the metallization method as described above are the same as those in Examples 11 to 15. As described above, in the heat resistance cycle test, there was no cracking of the Si ₃ N ₄ substrate or peeling of the circuit layer even after 1000 cycles, and excellent heat resistance cycle characteristics were obtained.

[0138]

As described above, according to the silicon nitride circuit board of the present invention, in addition to the high strength and high toughness characteristic inherent to the silicon nitride sintered body, the thermal conductivity is greatly improved. It is formed by integrally joining a metal circuit board to the surface of a silicon nitride substrate having high thermal conductivity. Therefore, since the toughness value of the circuit board is high, it is possible to secure a large maximum deflection amount and a large bending strength. For this reason, the circuit board does not suffer from cracking in the assembly process, and semiconductor devices using the circuit board can be mass-produced with a high manufacturing yield.

Since the toughness value of the silicon nitride substrate is high,
It is possible to provide a semiconductor device in which cracks are less likely to occur in a substrate due to heat cycle, heat cycle characteristics are remarkably improved, and durability and reliability are excellent.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a silicon nitride circuit board according to the present invention.

FIG. 2 is a sectional view showing another embodiment of the silicon nitride circuit board according to the present invention.

FIG. 3 is a cross-sectional view showing a heat dissipation evaluation test procedure of a circuit board.

FIG. 4 is a graph showing a relationship between a ceramic substrate thickness and a temperature rise of a semiconductor element in a heat dissipation evaluation test.

FIG. 5 is a cross-sectional view showing a configuration example of a silicon nitride circuit board according to the present invention.

FIG. 6 is a graph showing the relationship between the substrate thickness and the maximum deflection amount.

FIG. 7 is a graph showing the relationship between substrate thickness and bending strength.

FIG. 8 is a sectional view of a circuit board on which a circuit layer is formed by a copper direct bonding method.

FIG. 9 is a cross-sectional view of a circuit board on which a circuit layer is formed by a metallizing method.

[Explanation of symbols]

1, 1a, 1b, 1c, 1d Silicon nitride circuit board (S
i ₃ N ₄ circuit board) 2 Silicon nitride (Si ₃ N ₄ ) substrate 3 Oxide layer (SiO ₂ film) 4 Metal circuit board (Cu circuit board), circuit layer 5 Metal circuit board (back copper plate) 6 Semiconductor element ( Chip) 7a, 7b Active metal layer (metal bonding layer) 8 Heat sink 9 Metal plating layer (Ni plating layer) 10 Refractory metal metallization layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location // C04B 35/584 C04B 35/58 102C 102K 102T (72) Inventor Yu Komorida Tsurumi, Yokohama, Kanagawa Prefecture 2-4, Suehiro-cho, Tokyo Incorporated Toshiba Keihin Office (72) Inventor Kotoshi Sato 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock Company Toshiba Yokohama Office

Claims (13)

[Claims] 1. A metal circuit board is bonded via an oxide layer on a high thermal conductivity silicon nitride substrate having a thermal conductivity of 60 W / m · K or more and a three-point bending strength (normal temperature) of 650 MPa or more. In the silicon nitride circuit substrate, the relational expression D _S ≦ 2D _M is satisfied, where D _{S is} the thickness of the high thermal conductivity silicon nitride substrate and D _M is the thickness of the metal circuit board. Silicon circuit board. 2. The thickness D _{S of the} high thermal conductivity silicon nitride substrate and the thickness D _M of the metal circuit board are expressed by the relational expression D _M ≦ D _S ≦ (5 /
3) The silicon nitride circuit board according to claim 1, wherein D _M is satisfied. 3. At least one selected from Ti, Zr, Hf and Nb on a high thermal conductivity silicon nitride substrate having a thermal conductivity of 60 W / m · K or more and a three-point bending strength (normal temperature) of 650 MPa or more. In a silicon nitride circuit board obtained by bonding metal circuit boards through a metal bonding layer containing a kind of active metal, the thickness of the high thermal conductivity silicon nitride board is D _S , and the thickness of the metal circuit board is When D _M , the relational expression D _S
A silicon nitride circuit board characterized by satisfying ≦ 2D _M. 4. The high thermal conductivity silicon nitride substrate thickness D _S and the metal circuit board thickness D _M are related by the relational expression D _M ≦ D _S ≦ (5 /
3) The silicon nitride circuit board according to claim 3, which satisfies D _M. 5. A circuit board in which a circuit layer is integrally bonded to a high-thermal-conductivity silicon nitride substrate having a thermal conductivity of 60 W / m · K or more, and the circuit board is centrally held at a support interval of 50 mm. A silicon nitride circuit board having a maximum deflection of 0.6 mm or more before the silicon nitride board is broken when a load is applied to the portion. 6. A circuit board in which a circuit layer is integrally bonded to a high thermal conductivity silicon nitride substrate having a thermal conductivity of 60 W / m · K or more, and the circuit board is held at a support interval of 50 mm so as to be resistant. Folding strength is 500 MPa when folding test is performed
A silicon nitride circuit board characterized by the above. 7. The high thermal conductivity silicon nitride substrate has a thickness of 0.
7. The silicon nitride circuit board according to claim 5, which has a thickness of 8 mm or less. 8. The silicon nitride circuit according to claim 5, wherein the circuit layer is a copper circuit board, and the copper circuit board is directly bonded to the silicon nitride substrate by a Cu—O eutectic compound. substrate. 9. The circuit layer is a copper circuit board, and Ti, Zr,
The silicon nitride circuit according to claim 5, wherein the copper circuit board is bonded to the silicon nitride substrate through an active metal layer containing at least one active metal selected from Hf and Nb. substrate. 10. The circuit layer is composed of W or Mo and Ti, Z.
6. The silicon nitride circuit board according to claim 5, comprising a refractory metal metallization layer containing at least one active metal selected from r, Hf and Nb. 11. The high-thermal-conductivity silicon nitride substrate is 2.0 to 17.5% by weight in terms of oxide of rare earth element, and Li, Na, K, Fe, Ca, as impurity cation elements.
4. The silicon nitride circuit board according to claim 1, which is made of a silicon nitride sintered body containing Mg, Sr, Ba, Mn, and B in a total amount of 0.3% by weight or less. 12. The high thermal conductivity silicon nitride substrate contains a rare earth element in an amount of 2.0 to 17.5 wt% in terms of oxide, and is composed of a silicon nitride crystal and a grain boundary phase and in the grain boundary phase. 4. The silicon nitride circuit board according to claim 1 or 3, comprising a silicon nitride sintered body in which the ratio of the crystalline compound phase to the entire grain boundary phase is 20% or more. 13. A high-thermal-conductivity silicon nitride substrate is composed of silicon nitride crystals and a grain boundary phase, and the ratio of the crystal compound phase in the grain boundary phase to the whole grain boundary phase is 50% or more. The silicon nitride circuit board according to claim 1 or 3, wherein the silicon nitride circuit board comprises a body.