JP2003069172A - Simultaneously baking silicon nitride circuit board and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simultaneously baking silicon nitride circuit board which has a high thermal conductivity and excellent heat sink properties, which has a high strength and small occurrence of a fault due to a release of a conductor layer (metallized layer) and which can be formed in a small size and to provide a method for manufacturing the same. SOLUTION: The simultaneously baking silicon nitride circuit board 1a comprises a silicon nitride board 2a, and simultaneously baking metallized layers 3a, 3b integrally formed on at least a front surface of the board 2a and containing at least one type of high melting point metals of W and Mo as main components. The thermal conductivity of the board 2a is 60 W/m.K or more. An areal ratio of a crystal compound phase in a grain boundary phase of the board 2a with respect to an overall grain boundary phase is 20% or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a co-fired silicon nitride circuit substrate in which a conductor layer (metallized layer) as a circuit is integrally formed on a silicon nitride substrate by a co-firing method, and a method for manufacturing the same. The present invention relates to a co-fired silicon nitride circuit board that has heat dissipation properties, high strength, less defects due to peeling of a conductor layer, and can be formed in a small size, and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a component of an electronic device or a semiconductor device, as shown in FIGS. 1 and 2, alumina (Al ₂ O
₃ ) Various circuit boards (thick film circuit boards) 1 in which a conductor layer (metallized wiring layer) 3 to be a circuit is integrally formed on the surface of a ceramic substrate 2 such as a substrate or an aluminum nitride (AlN) substrate are widely used. There is. A circuit board in which a metal circuit board made of a conductive material such as copper (Cu) is integrally bonded to the surface of the ceramic substrate 2 by using an active metal method or a direct bonding method is also widely used.

An alumina substrate having a thermal conductivity of about 10 to 20 W / m · K is generally used as a ceramic substrate constituting the above conventional circuit board. For applications requiring higher heat dissipation, a combination of heat dissipation plates and heat sinks of various shapes with a circuit board is used. Further, there is an example in which higher heat dissipation is secured by using an aluminum nitride (AlN) substrate having a thermal conductivity of about 50 to 150 W / m · K.

In recent years, a semiconductor device using a ceramics circuit board has been rapidly increased in output, semiconductor elements have been increased in capacity and integration, and thermal stress and thermal load repeatedly applied to the ceramics circuit board have been rapidly increased. There is a tendency to increase, and ceramic circuit boards are also required to have sufficient strength and heat dissipation properties against the above thermal stress and thermal cycles.

In order to meet the above technical requirements, AlN having a high thermal conductivity of about 180 W / m · K.
Ceramic substrates have also been developed. For this AlN substrate, a raw material mixture obtained by adding a sintering aid such as yttria (Y ₂ O ₃ ) to a high-purity AlN raw material powder is molded, and the obtained molded body is kept at a high temperature for about 48 to 72 hours and a long time. It is manufactured by sintering for a period of time to achieve densification, and at the same time, a liquid phase component that becomes a thermal resistance is discharged to the surface of the substrate for high purification.

Further, in response to technical demands for miniaturization and thinning of portable electronic equipment, development of a small-sized and high-strength circuit board is underway, and an alumina substrate and an aluminum nitride, which have been widely used conventionally, are being developed. A circuit board using a higher-strength silicon nitride (Si ₃ N ₄ ) board instead of the board has also been proposed.

[0007]

However, in the above conventional silicon nitride circuit boards, a metal circuit board made of a conductive material such as copper (Cu) is integrally formed on the surface of the silicon nitride board which is a single plate. Since it has a bonded structure and the circuit is a single layer wiring, there are many restrictions due to the wiring rules that regulate the wiring width and wiring interval, it is difficult to form fine high-density wiring, and the circuit board is downsized There was a problem that became a major obstacle in doing so.

Along with the further development of the demand for miniaturization of electronic equipment, there is also a demand for equipment as a high-density wiring board with improved wiring density for circuit boards. As a means to meet such a demand, a method of stacking a plurality of silicon nitride substrates in a multilayer to form a wiring (metallized wiring layer) in place of the conventional single-layer silicon nitride substrate is also adopted. There is. In this method, each wiring layer is formed by simultaneous firing, and adjacent interlayer wirings are electrically connected by via holes filled with a conductor. By adopting this method, high-density wiring can be performed while complying with the prescribed wiring rule.

Conventionally, as a multilayer silicon nitride circuit substrate having the above-mentioned co-firing metallized layer, for example, Japanese Patent Laid-Open Nos. 10-256686 and 2000-2 are known.
The configuration example is introduced in Japanese Patent No. 44121. In any of the above publications, the electric resistance of the conductor layer (metallized layer) is reduced by reducing the amount of high-resistive high-melting point metal silicide that occurs when a metallized layer made of a high-melting point metal such as W or Mo is co-fired. The purpose is to reduce the speed and speed up the signal processing.

However, according to the knowledge of the present inventors, when the refractory metal silicide is not formed to some extent during the simultaneous firing, the bonding strength (peel strength) of the metallized layer is not sufficient, and this metallized layer is formed. The heat resistance cycle characteristic (TCT characteristic) of the circuit board is insufficient, and there is a problem that the reliability and durability of the electronic device incorporating the circuit board deteriorates.

As described above, in the above-mentioned conventional ceramic circuit board, by improving the type of ceramic board and the sintering method, the strength becomes insufficient even though high thermal conductivity is obtained, and the board strength itself is As a result, the joining strength of the metallized layer becomes low even if it becomes higher, so that heat cycle resistance and bending strength are not sufficiently obtained, and there is a problem that the reliability and the product yield of the semiconductor device using the circuit board are lowered.

On the other hand, in response to higher integration and higher output of the semiconductor elements mounted on the circuit board, the thermal cycle load is also significantly increased, and thermal stress causes the board to crack, resulting in loss of the function of the circuit board. There was a problem that caused it. Also, since the bending strength of the circuit board is small and the amount of deflection is small, if you try to tighten the circuit board to the mounting board with screws during assembly, the ceramic board may be destroyed by the slight tightening force of the screws. There is also a problem that the product yield of the semiconductor device using the circuit board decreases. Furthermore, due to the thermal stress generated during use, cracks in the board,
In many cases, peeling of the metallized layer occurs, and the reliability of the semiconductor device is reduced.

The present invention has been made to solve the above problems and has a high heat conductivity and an excellent heat dissipation property.
It is an object of the present invention to provide a co-fired silicon nitride circuit board which has high strength, is less likely to cause defects due to peeling of a conductor layer (metallized layer), and can be formed in a small size, and a method for manufacturing the same.

[0014]

In order to achieve the above object, the inventors of the present invention have obtained a particularly high thermal conductivity,
Various studies have been conducted on the structure structure of the circuit board that does not cause a decrease in strength. As a result, a predetermined conductor pattern is formed on the compact of the silicon nitride raw material powder whose composition and purity are adjusted with a refractory metal paste, and the patterned compact is degreased and then heated to a temperature of 1700 in a reducing atmosphere. At least a part of the grain boundary phase is obtained by sintering at a temperature of ℃ or higher for a predetermined time, and then gradually cooling the temperature from the sintering temperature to the solidification temperature of the liquid phase (about 1500 ℃) at a cooling rate of 100 ℃ or less per hour. Was crystallized, and a co-fired silicon nitride circuit substrate having both high thermal conductivity and high strength characteristics with a thermal conductivity of 60 W / m · K or more was obtained.

Furthermore, when the above-mentioned slow cooling operation is performed, a refractory metal silicide layer is formed in a thin layer and uniformly at the bonding interface between the refractory metal metallization layer and the silicon nitride substrate. It was found that the bonding strength of the metallized layer was significantly improved by the layer, and it was found for the first time that a circuit board with less peeling of the metallized layer and excellent durability was realized. The present invention has been completed based on the above findings.

That is, a circuit board according to the present invention is integrally formed with a silicon nitride substrate and at least a surface portion of the silicon nitride substrate, and contains at least one refractory metal of W or Mo as a main component. A co-firing metallized layer, the silicon nitride substrate has a thermal conductivity of 60 W / mK or more, and the area ratio of the crystalline compound phase to the entire grain boundary phase in the grain boundary phase of the silicon nitride substrate. Is 20% or more.

In the co-firing silicon nitride circuit substrate according to the present invention, the average film thickness is 0.01 to 1 μm at the joint interface between the co-firing metallization layer and the silicon nitride substrate.
It is preferable that a refractory metal silicide layer of m is formed. By forming this silicide layer, it is possible to increase the bonding strength of the metallized layer.

When the average film thickness of the refractory metal silicide layer is less than 0.01 μm, or when the film is not uniform and the refractory metal silicide is scattered, the effect of improving the bonding strength of the metallized layer is obtained. I can't get it. On the other hand, when the average film thickness is formed to be thicker than 1 μm, the bonding strength is rather lowered, and the content of the silicide layer having a high electric resistance value is increased, so that the resistance value of the metallized layer is increased. It becomes difficult to speed up signal processing. Therefore, the average film thickness of the silicide layer is set in the range of 0.01 to 1 μm, more preferably 0.03 to 0.5 μm.

The film thickness of the refractory metal silicide layer can be measured by observing the cross section of the circuit board by EPMA. A unit area of 30 μm × 30 μm is observed at arbitrary three points, and the film thickness value is averaged. Is the average film thickness.

In the above co-fired silicon nitride circuit substrate, the peel strength of the co-fired metallization layer is 1 kN.
/ M or more is preferable. By ensuring the peel strength of 1 kN / m or more, the heat-resistant cycle characteristics (TCT characteristics) of the circuit board can be favorably maintained. The peel strength is 5 μm in the metallized layer.
It can be calculated from the tensile load when peeling occurs after Ni plating is applied and the Kovar terminal plate is joined thereto via the BAg-8 brazing material.

Further, in the above co-fired silicon nitride circuit substrate, the thickness of the co-fired metallization layer is preferably 7 μm or more. By forming the co-firing metallization layer having a thickness of 7 μm or more, a large current carrying capacity can be secured, and in particular, a functional element that operates at a high output and a high speed can be mounted.

The thickness of the co-fired metallized layer is measured by EPMA or the like, including the thickness of the refractory metal silicide layer.

The co-firing silicon nitride circuit substrate of the present invention may be formed in a single layer structure so that the co-firing metallization layer exists only on the surface of the silicon nitride substrate.
It is also possible to form a multilayer structure as described below. That is, the silicon nitride substrate has a multilayer structure in which a plurality of substrate elements are laminated, a co-firing metallization layer is formed on each substrate element, and the co-firing metallization layers adjacent to each other in the laminating direction are interlayer-connected. By forming the wiring structure with a multilayer structure, higher density wiring can be achieved.

In the method for producing a co-fired silicon nitride circuit board according to the present invention, oxygen is 1.7 wt% or less, and Al, Li, Na, K, Fe and B as impurity cation elements are used.
a, Mn, and B are contained in a total amount of 0.3% by weight or less, α-phase type silicon nitride is contained in an amount of 90% by weight or more, and an average particle diameter is 1.0 μm or less. 2.0 to 17.5% by weight, and Mg in the form of an oxide of 0.
A raw material mixture containing 3 to 3.0% by weight is molded to prepare a molded body, and a conductor paste containing a refractory metal of at least one of W and Mo is applied to the molded body to form a conductor pattern. After degreasing the molded body on which this conductor pattern is formed, it is sintered at a temperature of 1700 to 1900 ° C., and the temperature is from the sintering temperature to the temperature at which the liquid phase formed by sintering the rare earth element and MgO solidifies. The sintered body is characterized by being cooled gradually at a cooling rate of 100 ° C. or less per hour.

In the above manufacturing method, the conductor paste is applied to laminate a plurality of molded bodies having conductor patterns, and then degreasing and sintering are performed to obtain a co-fired silicon nitride circuit having a multilayer wiring structure. A substrate is obtained.

In the above manufacturing method, at least one of calcium (Ca) and strontium (Sr) is preferably added to the silicon nitride powder in an amount of 1.5% by weight or less in terms of oxide. Further, it is preferable that at least one of Ti, Zr, V, Nb, Ta, Cr, Mo, and W is added to the silicon nitride powder in an amount of 1.5 wt% or less in terms of oxide.

According to the above manufacturing method, a crystallized grain boundary phase containing a rare earth element or the like is formed in the crystal structure of silicon nitride, the porosity is 2.5% or less, and the thermal conductivity is 60 W / mK.
As described above, a silicon nitride sintered body having a three-point bending strength of 750 MPa or more at room temperature and excellent in both mechanical properties and heat conduction properties was obtained, and the bonding strength such that the metallized layer had a peel strength of 1 kN / m or more. An excellent co-fired silicon nitride circuit board is obtained.

The silicon nitride substrate constituting the co-firing silicon nitride circuit substrate according to the present invention is excellent in thermal shock resistance, heat dissipation and structural strength, especially for mounting a large capacity and high output functional element. It is preferable to use a silicon nitride substrate made of a silicon nitride sintered body that can obtain high bonding strength when the metallized layer is integrally formed.

Specifically, as described in Japanese Patent Application Laid-Open No. 2000-34172, which is a prior application filed by the present applicant, it has a high thermal conductivity of 60 W / mK or more and has a grain boundary phase. It is preferable to use a silicon nitride substrate made of a silicon nitride sintered body having at least a part thereof crystallized.

The silicon nitride powder used in the method of the present invention, which is the main component of the sintered body constituting the silicon nitride substrate, has an oxygen content in consideration of sinterability, strength and thermal conductivity. 1.7% by weight or less, preferably 0.5 to 1.5
% By weight, Al, Li, Na, K, Fe, Ba, Mn, B
Impurity cation element content such as total 0.3% by weight
The content of α-phase type silicon nitride, which is suppressed to 0.2% by weight or less, is preferably 90% by weight or more, preferably 93% by weight or more, and the average particle size is 1.0 μm or less, preferably 0.1.
It is preferable to use fine silicon nitride powder having a size of about 4 to 0.8 μm.

By using a fine raw material powder having an average particle size of 1.0 μm or less, a dense sintered body having a porosity of 2.5% or less can be formed 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.

Al, Li, Na, K, Fe, Ba,
Since the impurity cation elements of Mn and B are also substances that impede the thermal conductivity, the total content of the above impurity cation elements is not more than 0.1 in order to secure a thermal conductivity of 60 W / m · K or more. It can be achieved by setting the content to 3% by weight or less. Particularly, for the same reason, it is more preferable that the total content of the impurity cation elements is 0.2% by weight 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 weight or more of α-phase type silicon nitride, which is excellent 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 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 weight based on the raw material powder in terms of oxide.
If the addition amount is 2.0% by weight or less, the densification or high thermal conductivity 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, 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 weight, an excessive amount of grain boundary phase is generated, and the thermal conductivity and the 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 weight.

The magnesium (Mg) oxide (MgO) used as an additive component in the present invention promotes the function of the above-mentioned rare earth element sintering accelerator, enables densification at low temperature, and has a crystal structure. In the above, the grain growth is controlled, and the mechanical strength of the Si ₃ N ₄ sintered body is improved. The addition amount of this MgO is 0.
When the amount is less than 3% by weight, the effect of addition is insufficient, while when the amount exceeds 3.0% by weight, the thermal conductivity decreases, so the amount added is 0.3 to 3.0% by weight. %
The range is. In particular, it is desirable to set it to 0.5 to 2% by weight.

In the present invention, Hf may be added as a selective addition component in a predetermined amount. This Hf is an oxide,
These compounds are added as carbides, nitrides, suicides, and borides. These compounds have the function of promoting the function of the above-mentioned rare earth element as a sintering promoter and also of crystallization of the grain boundary phase, and Si ₃ It is intended to improve the thermal conductivity and mechanical strength of the N ₄ sintered body. If the amount of Hf added is less than 0.3% by weight in terms of oxide, the effect of addition is insufficient, while if it exceeds 3.0% by weight, thermal conductivity and mechanical strength and Since the electric breakdown strength is lowered, the addition amount is set in the range of 0.1 to 3.0% by weight.

Further, in the present invention, a predetermined amount of oxides of Ca and Sr (CaO, SrO) may be added as another optional additive component. These oxides play a role of promoting the function of the above-mentioned rare earth element as a sintering accelerator, and exhibit a remarkable effect particularly when performing atmospheric pressure sintering. When the total addition amount of CaO and SrO is less than 0.1% by weight, it is necessary to sinter at a higher temperature, while when the total addition amount exceeds 1.5% by weight, an excessive amount of grain boundaries is required. The addition amount is 1.5% by weight or less, preferably 0.1 to 0.1%, because a phase is generated and heat conduction is reduced.
The range is 1.0% by weight. In particular, in order to secure good performances in both strength and thermal conductivity, the addition amount is 0.1 to 0.75.
It is desirable to set it in the range of wt%.

In the present invention, Ti, Zr, V, Nb, Ta, Cr, Mo and W are used as other optional additive components.
May be added in a predetermined amount. These elements are added as oxides, carbides, nitrides, suicides, and borides, and these compounds promote the function of the above rare earth elements as a sintering promoter and the function of dispersion strengthening in the crystal structure. In order to improve the mechanical strength of the Si ₃ N ₄ sintered body, a compound of Ti and Mo is particularly preferable. If the addition amount of these compounds is less than 0.1% by weight in terms of oxide, the effect of addition is insufficient, while if it exceeds 1.5% by weight, thermal conductivity and mechanical strength are increased. Since the electric breakdown strength decreases, the addition amount is set to the range of 0.1 to 1.5% by weight. Especially 0.2-1.
It is preferably 0% by weight.

Further, the compounds such as Ti and Mo also function as a light-shielding agent for coloring the silicon nitride sintered body in a black system to impart opacity. Therefore, when a 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 obtain a silicon nitride substrate excellent in light shielding property. It is desirable to do.

The porosity of the sintered body has a great influence on the thermal conductivity and the strength, so that the sintered body is manufactured so as to be 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.

The silicon nitride sintered body 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 has a great influence on the thermal conductivity of the sintered body. However, in the silicon nitride sintered body used in the present invention, the grain boundary phase 2
It is necessary to be 0% or more, and more preferably 50%.
It is desirable that the crystal phase occupy at least%. 20 crystalline phases
If it is less than%, it is not possible to obtain a sintered body having excellent heat dissipation properties such as a thermal conductivity of 60 W / m · K or more and excellent mechanical strength.

Further, as described above, the porosity of the silicon nitride sintered body is 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 1700-190.
Pressureless sintering or pressure sintering at 0 ° C. for about 2 to 10 hours,
Moreover, it is important to gradually cool the sintered body at a cooling rate of 100 ° C. or less immediately after the completion of the sintering operation.

When the sintering temperature is less than 1700 ° C., the densification of the sintered body is insufficient and the porosity is 2.5 vol%.
As a result, both mechanical strength and thermal conductivity are reduced. On the other hand, when the sintering temperature exceeds 1900 ° C., the silicon nitride component itself tends to evaporate and decompose. In particular, when pressureless sintering is performed instead of pressure sintering, decomposition vaporization of silicon nitride starts 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 above cooling rate should be strictly adjusted is the temperature from the predetermined sintering temperature (1700 to 1900 ° C.) to the solidification of the liquid phase produced by the reaction between the sintering aid and MgO. The range is sufficient. By the way, when the above-mentioned sintering aid is used, the liquidus freezing point is approximately 1
It is about 600 to 1500 ° C. 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, more preferably 25 ° C. or less (but 10 ° C. or more). 20% or more of the grain boundary phase, particularly preferably 50%
The above becomes a crystalline phase, and a sintered body excellent in both thermal conductivity and mechanical strength can be obtained.

The slower the cooling rate is, the more the effect of increasing the crystallization rate of the grain boundary phase is obtained. However, if it is too slow, the cooling time becomes long and the productivity is not necessarily good. It is preferably 10 ° C./hr or more.

By performing such slow cooling treatment, it is possible to obtain the effect of making the film thickness of the refractory metal silicide layer formed when the refractory metal metallization layer is simultaneously fired uniform.

The co-firing silicon nitride circuit board according to the present invention is manufactured, for example, through the following processes. That is, with respect to fine silicon nitride powder having a predetermined fine particle diameter and a low impurity content, a predetermined amount of a sintering aid, a necessary additive such as an organic binder and, if necessary, CaO or SrO. And a compound such as Ti are added to prepare a raw material mixture, and then the obtained raw material mixture is 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 manufacturing a co-fired silicon nitride circuit board having a multilayer structure, a plurality of via holes for interlayer connection are formed in advance at predetermined positions of each sheet forming body to be laminated. As a method for forming the via hole, a mechanical method using a punch, a die, a punching machine, laser processing, or the like can be adopted.

Next, a conductive paste is prepared by adding a binder and a solvent to a powder of tungsten (W) or molybdenum (Mo) and kneading, and then the conductive paste is formed into the silicon nitride green sheet formed in the above step. A predetermined pattern is printed on at least one surface by a screen printing method or the like. In this way, a conductor layer having a predetermined pattern composed of fine signal lines and power lines is formed on the green sheet.

The metallized layer of the present invention is not limited to a conductor layer used for a wiring pattern such as a signal line or a power supply line, and after plating, a semiconductor element is mounted by brazing. It shall include a metallization layer.

As the binder used in the preparation of the above-mentioned conductor paste, for example, cellulosic binder, acrylic binder, etc. are used, and as the solvent, for example, terpineol, toluene, ethanol, etc. are used. When printing this conductor paste, the via holes are simultaneously filled with the conductor paste.

When manufacturing a silicon nitride circuit board having a multi-layered structure, a plurality of green sheets printed with a conductor paste are laminated after the positions of via holes formed in the respective green sheets are accurately aligned. And thermocompression-bonded to prepare a laminate.

Then, following the above molding operation, the laminate or the patterned single-layer molded body is heated at a temperature of 600 to 800 ° C. in a non-oxidizing atmosphere or at a temperature of 40 ° C. in air.
By heating at 0 to 500 ° C. for 1 to 2 hours, the previously added organic binder component is sufficiently removed and degreased. Next, the degreased molded body is subjected to normal pressure sintering, pressure sintering or atmospheric pressure sintering at a temperature of 1700 to 1900 ° C. for a predetermined time in an atmosphere of an inert gas such as nitrogen gas, hydrogen gas or argon gas. Is carried out, and the silicon nitride formed body and the conductor pattern are simultaneously fired.

The co-fired silicon nitride circuit substrate manufactured by the above manufacturing method has a porosity of 2.5% or less, 60 W / m.multidot.
It has a thermal conductivity of K (25 ° C.) or higher and a three-point bending strength of 750 MPa or higher at room temperature, which is excellent in mechanical properties. The peel strength of the metallized layer is 1 kN / m.

[0057]

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

Examples 1 to 6 1.3% by weight of oxygen, Al as an impurity cation element,
Li, Na, K, Fe, Ba, Mn, B total 0.1
0% by weight of silicon nitride raw material powder having an average particle diameter of 0.40 μm and containing 97% of α-phase type silicon nitride, Y ₂ O ₃ (oxidation of an average particle diameter of 0.7 μm as a sintering aid was used). 5% by weight of yttrium) powder and 1.5% by weight of MgO (magnesium oxide) powder having an average particle size of 0.5 μm were added, wet-mixed in ethyl alcohol for 72 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.
By press molding with a molding pressure of 0 MPa, a large number of sheet-shaped compacts (green sheets) having a length of 50 mm, a width of 50 mm and a thickness of 0.6 mm were manufactured.

On the other hand, an organic binder was added to tungsten powder or molybdenum powder having an average particle size of 0.8 μm,
Two types of conductor pastes were prepared by thoroughly mixing and crushing with a ball mill dispersed in an organic solvent.

Then, the conductor paste was screen-printed on both sides of the green sheet to form a conductor layer having a thickness of 12 μm. Next, after degreasing the obtained molded body in an air stream of 500 ° C. for 2 hours, the degreased body was densified and sintered in a nitrogen gas atmosphere at the atmospheric pressure, temperature, and time shown in Table 1, and molded. After co-firing the body and conductor layers,
The amount of electricity supplied to the heating device attached to the sintering furnace is controlled so that the cooling rate of the sintered body until the temperature inside the sintering furnace drops to 1500 ° C is adjusted to the values shown in Table 1, respectively. The sintered body was gradually cooled to prepare co-fired silicon nitride circuit boards according to Examples 1 to 6 each having a refractory metallized layer.

Comparative Example 1 On the other hand, immediately after the completion of the densification and sintering, the heating apparatus power supply was turned off, and the sintered body was cooled at the conventional furnace cooling rate (about 600 ° C./hr). A co-firing silicon nitride circuit substrate according to Comparative Example 1 was prepared by performing a sintering treatment under the same conditions as in.

Comparative Example 2 The cooling rate of the sintered body after completion of the densification sintering was 2 ° C./h.
A co-fired silicon nitride circuit substrate according to Comparative Example 2 was prepared by treating under the same conditions as in Example 1 except that r was adjusted.

Each of the co-fired silicon nitride circuit substrates 1 prepared as described above was made of Si _{3 as} shown in FIGS. 1 and 2.
A predetermined conductor layer (metallized layer) 3 is integrally joined to both surfaces of the N ₄ substrate 2.

Examples 1 to 6 and Comparative Example 1 thus obtained
The thermal conductivity (25 ° C.), the average thickness of the refractory metal silicide layer, and the peel strength of the refractory metal layer (metallized layer) were measured for the co-fired silicon nitride circuit substrates according to Nos.

Here, the average thickness of the refractory metal silicide layer is 3 obtained by EPMA analysis of the cross section of the circuit board.
The peel strength of the refractory metal layer is measured as the average value of the silicide layer thicknesses at three points (unit area 30 μm × 30 μm is measured at three points).
The plating was applied, and the Kovar terminal plate was joined thereto via the BAg-8 brazing material. Further, the ratio (area ratio) of the crystal phase in the grain boundary phase of each sintered body was measured by the X-ray diffraction method.

Further, in order to evaluate the durability and reliability of each circuit board, the following thermal shock test (heat cycle test: TCT) was carried out to measure the rate of peeling or swelling of the metallized layer.

The above heat cycle test was conducted at -40 ° C for 3 hours.
Hold for 0 minutes, then heat up and hold at room temperature (25 ° C) for 10 minutes, then heat and hold at 125 ° C for 30 minutes, then return to room temperature and hold for 10 minutes as one cycle Temperature rising / falling temperature Repeat 100 cycles, 100
After the cycle was completed, the rate of peeling or swelling of the metallized layer was measured. The measurement results are shown in Table 1 below.

[0068]

[Table 1]

As is clear from the results shown in Table 1, in the co-fired silicon nitride circuit substrates according to Examples 1 to 6,
As compared with Comparative Example 1, the cooling rate of the sintered body immediately after the completion of the densification sintering is set to be lower than the conventional one. Therefore, the higher the proportion of the crystal phase in the grain boundary phase, the higher the thermal conductivity. A high-strength circuit board having high heat dissipation and high heat dissipation was obtained.

In addition, since the circuit boards of the respective examples are manufactured through the above-described slow cooling operation, the thickness is 0.01
A thin layered refractory metal silicide layer having a thickness of up to 1.0 μm is uniformly formed at the joint interface, and the peel strength of the refractory metal layer (metallized layer) is 1.0 kN / m or more, which provides excellent joint strength. Have. Therefore, there is no peeling or swelling of the metallized layer even after TCT,
It was confirmed that excellent durability was exhibited.

On the other hand, when the cooling rate of the sintered body was set high as in Comparative Example 1 and was rapidly cooled, the proportion of the crystal phase in the grain boundary phase was as small as 8% or less, and the thermal conductivity decreased. In Comparative Example 1, the metallization layer and Si
_A uniform silicide layer was not formed at the bonding interface with the ₃ N ₄ substrate, and silicide pieces having a thickness of less than 0.01 μm were scattered, and the W metallized layer was not sufficiently fixed. Moreover, because the joining strength was so low that peeling occurred when trying to join the terminal plate for peel strength measurement,
No heat cycle test (TCT) was performed.

On the other hand, in the circuit board according to Comparative Example 2 manufactured by slowly cooling for a long time with the cooling rate after sintering being excessively low, the thickness of the refractory metal silicide layer was excessive, so that peeling occurred. It was found that the strength dropped sharply and durability could not be expected.

Examples 7 to 9 and Reference Example 1 In the method for manufacturing a co-fired silicon nitride circuit substrate according to Example 1, the silicon nitride green sheet is used so that the metallized layer has the thickness shown in Table 2. Except that the printing amount of the W conductor paste was adjusted, the same treatments as in Example 1 were carried out to prepare co-fired silicon nitride circuit boards according to Examples and Reference Examples, respectively.

With respect to each of the prepared circuit boards, the peel strength of the W metallized layer was measured in the same manner as in Example 1, and a thermal cycle test (TCT) was carried out to confirm the peeling and swelling of the W metallized layer after TCT. The incidence was measured and the results shown in Table 2 below were obtained.

[0075]

[Table 2]

As is clear from the results shown in Table 2 above,
Examples 7 to 9 in which the thickness of the W metallized layer is 7 μm or more
It was found that in the circuit board of No. 1, no peeling occurred after TCT, excellent durability was obtained, and the current-carrying capacity could be set to a large value, which was extremely effective.

On the other hand, it was confirmed that the circuit board of Reference Example 1 in which the W metallization layer had a thin thickness of 3 μm was susceptible to the thermal expansion due to the heat cycle, and thus peeling was likely to occur.

Examples 10 to 12 A plurality of via holes for interlayer connection are formed by using a punching machine at predetermined positions of a plurality of green sheets prepared in the method for manufacturing a co-firing silicon nitride circuit board according to Example 1. did. Next, the W conductor paste was printed on the surface of each green sheet, and at the same time, each via hole was filled with the conductor paste.

Next, after aligning the via holes formed in each of the plurality of green sheets on which these conductor pastes are printed, the laminated sheets shown in Table 3 are laminated and thermocompression-bonded. A structured silicon nitride laminate was prepared.

Hereinafter, the above laminated body was degreased and co-fired under the same conditions as in Example 1, and then gradually cooled to produce co-fired silicon nitride circuit substrates according to Examples 10 to 12 having a multilayer structure.

As shown in FIG. 3, the co-fired silicon nitride circuit substrate 1a according to each embodiment has a multilayer structure in which a plurality of substrate elements 4 are laminated on a silicon nitride substrate 2a. The co-firing metallization layers 3a and 3b are formed and are adjacent to each other in the stacking direction.
b is configured to have a multi-layer wiring path interconnected via the via hole 5. The co-firing metallization layer 3a constitutes a surface wiring layer, while the co-firing metallization layer 3b constitutes an internal wiring layer.

A heat cycle test (TC) was conducted under the same conditions as in Example 1 for the co-fired silicon nitride circuit board 1a having a multilayer structure according to each Example prepared as described above.
After 100 cycles of T), the occurrence rate of conduction failure between the metallized layers 3a and 3b formed between the layers was measured, and the results shown in Table 3 below were obtained.

[0083]

[Table 3]

As is clear from the results shown in Table 3 above,
It was confirmed that even in the case of a circuit board having a multi-layered structure, no conduction failure occurred after TCT, and excellent TCT characteristics were exhibited.

[0085]

As described above, according to the co-firing silicon nitride circuit board and the method of manufacturing the same according to the present invention, the grain boundary phase is produced because the co-firing silicon nitride circuit board and the method for producing the same are slowly cooled at a predetermined cooling rate after sintering. Crystallization is accelerated, and the silicon nitride substrate is 60 W / m
Since it has a thermal conductivity of K or more and is excellent in heat dissipation, it is possible to effectively suppress the temperature rise during the operation of the semiconductor element as compared with the conventional circuit board. Further, it becomes possible to mount a semiconductor device of higher output, and it becomes possible to sufficiently cope with higher output and higher integration of the semiconductor device. In addition, since it is slowly cooled, a refractory metal silicide layer is uniformly formed at the bonding interface between the metallization layer and the silicon nitride substrate. As a result, the bonding strength of the metallization layer is improved and peeling is reduced and durability is excellent. A circuit board is obtained.

[Brief description of drawings]

FIG. 1 is a plan view schematically showing the configuration of a circuit board.

FIG. 2 is a sectional view of the circuit board shown in FIG.

FIG. 3 is a cross-sectional view showing an embodiment of a co-firing silicon nitride circuit board according to the present invention.

[Explanation of symbols]

1, 1a circuit board (thick film circuit board) 2, 2a ceramics board (Al ₂ O ₃ board, AlN
Substrate, Si ₃ N ₄ substrate) 3,3a Conductor layer (metallized wiring layer) 4 Substrate element 5 Via hole

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05K 3/46 H01L 23/12 DN (72) Inventor Takayuki Nanami 300 Ubo, Taiko-cho, Hyogo Prefecture Toshiba Himeji Co., Ltd. F term in semiconductor factory (reference) 5E343 AA02 AA24 AA39 BB39 BB40 BB72 DD01 ER39 ER42 GG02 5E346 AA12 AA15 BB01 CC19 CC35 CC36 DD02 DD34 EE24 EE27 EE28 EE29 GG09 HH11 HH17

Claims (8)

[Claims] 1. A silicon nitride substrate, and a co-fired metallization layer which is integrally formed on at least a surface portion of the silicon nitride substrate and has at least one refractory metal of W and Mo as a main component. The thermal conductivity of the silicon nitride substrate is 60 W / mK or more, and the area ratio of the crystal compound phase in the grain boundary phase of the silicon nitride substrate to the entire grain boundary phase is 20% or more. Characteristic co-fired silicon nitride circuit board. 2. A refractory metal silicide layer having an average film thickness of 0.01 to 1 μm is formed at a bonding interface between the co-fired metallized layer and the silicon nitride substrate. Co-fired silicon nitride circuit board. 3. The co-fired silicon nitride circuit board according to claim 1, wherein the peel strength of the co-fired metallized layer is 1 kN / m or more. 4. The co-fired metallization layer has a thickness of 7 μm.
The co-firing silicon nitride circuit board according to claim 1, wherein the co-firing silicon nitride circuit board is m or more. 5. The co-firing silicon nitride circuit board according to claim 1, wherein the co-firing metallization layer is present only on the surface of the silicon nitride substrate. 6. The silicon nitride substrate has a multi-layer structure in which a plurality of substrate elements are laminated, a co-firing metallization layer is formed on each substrate element, and the co-firing metallization layers adjacent in the laminating direction are interlayer-connected. The co-fired silicon nitride circuit board according to claim 1, wherein the co-fired silicon nitride circuit board has a multilayer wiring path formed therein. 7. Oxygen of 1.7% by weight or less, Al, Li, Na, K, Fe, Ba, M as impurity cation elements.
n and B are contained in a total amount of 0.3% by weight or less, α-phase type silicon nitride is contained in an amount of 90% by weight or more, and a rare earth element is converted into an oxide in a silicon nitride powder having an average particle size of 1.0 μm or less. 2.0-
17.5 wt%, 0.3 to 3.
A raw material mixture added with 0% by weight is molded to prepare a molded body, and a conductor paste containing a refractory metal of at least one of W and Mo is applied to the molded body to form a conductor pattern. After degreasing the molded body having formed the above, it is sintered at a temperature of 1700 to 1900 ° C. A method for producing a co-fired silicon nitride circuit board, which comprises gradually cooling at a cooling rate of 100 ° C. or less per hour. 8. The method for producing a co-firing silicon nitride circuit board according to claim 7, wherein degreasing and sintering are performed after stacking a plurality of compacts having the conductor pattern formed thereon by applying the conductor paste. Method.