JP3230861B2 - Silicon nitride metallized substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metallized silicon nitride substrate in which a metallized layer such as a circuit pattern is integrally formed on a silicon nitride substrate, and is particularly suitable for a semiconductor module requiring high heat dissipation and high bonding strength. A metallized silicon nitride substrate.

[0002]

2. Description of the Related Art Conventionally, alumina (Al ₂ O ₃ ), aluminum nitride (Al
N) and beryllium oxide (BeO) are widely used as ceramic metallized substrates in which a metallized layer is integrally formed on the surface of a ceramic sintered body.

[0003] This ceramic metallized substrate is prepared by applying a paste prepared from a metal powder of a molybdenum-manganese alloy, molybdenum, tungsten or the like to the surface of the above-mentioned sintered ceramic substrate, or applying a predetermined circuit pattern. It is manufactured by printing by screen printing or the like to form a ceramic substrate on which a circuit pattern or the like is printed, and firing at a high temperature of about 1600 to 1800 ° C. in a nitrogen gas atmosphere to form a hard conductor layer (metallized layer). ing. Further, the metallized layer may be formed by a DBC method (direct bonding copper method) in which a copper plate is directly arranged on a ceramic substrate and heated and joined, a thick film method, or a plating method.

By providing the metallized layer, the wettability to a bonding material such as solder is improved, and a semiconductor element (IC chip) or an electrode plate can be bonded to a ceramic sintered body with high bonding strength. As a result, the heat dissipation from the semiconductor element and the operation reliability of the element can be kept good. Further, by forming a metallized layer also on the back surface of the ceramic substrate, the objects of stress relaxation and prevention of warpage (thermal deformation) of the ceramic substrate can be achieved.

[0005]

[SUMMARY OF THE INVENTION However, among the ceramic metallized substrate, in the metallized substrate using the Al ₂ O ₃ substrate, good heat dissipation is obtained for the thermal conductivity of Al ₂ O ₃ is low However, there is a problem that it is not possible to sufficiently cope with heat radiation measures accompanying high-density integration and high output of semiconductor elements.

In the case where a beryllium oxide (BeO) substrate is used, BeO is a material having the highest thermal conductivity and excellent heat dissipation among oxide ceramics. And there are many difficulties in handling.

[0007] Further, when an AlN substrate is used, the heat conductivity is high and sufficient heat dissipation is obtained. However, when the metallized layer is formed by firing, the liquid phase oozes out to the joint surface,
There has been a problem that the bonding strength between the AlN substrate and the metallized layer is reduced and color unevenness is apt to occur. As a result, there has been a problem that the metallized layer is peeled off due to a thermal load that repeatedly acts during use, heat dissipation is rapidly reduced, and the operation reliability of the electronic device is reduced.

The present invention has been made to solve the above problems, and has as its object to provide a silicon nitride metallized substrate having high heat dissipation and high bonding strength and suitable as a component for a semiconductor module. And

[0009]

Means for Solving the Problems In order to achieve the above object, the present inventors formed a metallized layer on various ceramics sintered bodies to prepare a ceramic metallized substrate, dissipated the heat, and joined the metallized layer. The strength and appearance were compared and examined.

As a result, silicon nitride having excellent mechanical properties such as flexural strength and fracture toughness can be sintered with a high thermal conductivity of 60 to 180 W / m · K by optimizing the firing process conditions. It turned out to be a body. Even when the metallized layer material is printed on the surface of the silicon nitride sintered body and baked, the discoloration of the liquid phase and the discoloration and color unevenness of the substrate due to the exudation are small, and the metallized layer for the silicon nitride substrate is reduced. It was also found that the bonding strength of the steel could be maintained high. Furthermore, by using a silicon nitride substrate having a high thermal conductivity and a high mechanical strength as described above, when setting to give the same strength as a conventional Al ₂ O ₃ substrate or an AlN substrate, Can reduce the thickness of the silicon nitride substrate to about 1/2. Therefore, as the thermal resistance decreases, the conventional high thermal conductivity AlN
It was confirmed that a silicon nitride metallized substrate having the same heat radiation property as that obtained when the substrate was used was obtained. The present invention has been completed based on the above findings.

That is, in the metallized silicon nitride substrate according to the present invention, a metallized film comprising at least one of molybdenum and tungsten and an active metal nitride is formed on a surface of a silicon nitride substrate having a thermal conductivity of 60 to 180 W / m · K. It is characterized in that the layers are integrally formed.

Further, the weight ratio of the active metal nitride to at least one of molybdenum and tungsten is set to 1.5 to 1.5.
2.5 is set.

Further, it is preferable that a plating layer made of nickel or a nickel alloy is integrally formed on the surface of the metallized layer.

The silicon nitride substrate having a thermal conductivity of 60 to 180 W / m · K used for the metallized silicon nitride substrate according to the present invention is manufactured by optimizing the composition and process conditions as described below. That is, 1.7% by weight of oxygen
Hereinafter, a silicon nitride powder containing 0.3% by weight or less of impurity cation elements such as Fe, Ca, and Mg and 90% by weight or more of α-phase type silicon nitride and having an average particle size of 0.8 μm or less,
A molded body is formed by molding a raw material mixture in which a rare earth element is added in an oxide amount of 2 to 7.5% by weight and aluminum is added in an amount of 0.5 to 2% by weight in terms of alumina. After degreasing, sintering is performed under atmospheric pressure at a temperature of 1800 to 2000 ° C., and the cooling rate of the sintered body from the sintering temperature to a temperature at which a liquid phase formed at the time of sintering by the rare earth element solidifies is set to an hourly rate. It is manufactured at a temperature of 100 ° C. or lower.

According to the above manufacturing method, a grain boundary phase containing a rare earth element or the like is formed in the crystal structure of the silicon nitride substrate, the porosity is 1.5% or less, and the thermal conductivity is 60 W / m · K or more. ,
A silicon nitride substrate having a three-point bending strength of 80 kg / mm ² or more at room temperature and excellent in both mechanical properties and heat conduction properties can be obtained.

The silicon nitride powder used as a main component of the substrate in the above-mentioned manufacturing method has an oxygen content of 1.7% by weight in consideration of sinterability, strength and thermal conductivity.
Below, preferably 0.5 to 1.5% by weight, Fe, Mg,
The content of impurity cation elements such as Ce is suppressed to 0.3% by weight or less, preferably 0.2% by weight or less, and α-phase silicon nitride having excellent sinterability is 90% by weight or more, preferably 93% by weight or more. It is preferable to use fine silicon nitride powder containing at least 0.8% by weight and having an average particle diameter of 0.8 μm or less, preferably about 0.4 to 0.6 μm.

By using fine raw material powder having an average particle size of 0.8 μm or less, a dense sintered body substrate having a porosity of 1.5% or less can be formed even with a small amount of sintering aid. And the likelihood of the sintering aid interfering with the heat transfer properties is reduced. In addition, impurity cation elements such as Fe, Mg, and Ca also become substances that inhibit thermal conductivity.
In order to ensure a thermal conductivity of W / m · K or more, the content of the impurity cation element is set to 0.3% by weight or less. In particular, by using a silicon nitride raw material powder containing 90% by weight or more of α-phase type silicon nitride having excellent sinterability as compared with β-phase type, it is possible to manufacture a high-density sintered body substrate. it can.

The rare earth elements to be added to the silicon nitride raw material powder as a sintering aid include Y, La, Sc, Pr, C
Oxides such as e, Nd, Dy, and Gd, or substances that become these oxides by the sintering operation may include a single substance or a combination of two or more types of oxides. Particularly, yttrium oxide (Y ₂ O ₃ ) is preferred. These sintering aids react with the silicon nitride raw material powder to generate a liquid phase and function as sintering accelerators.

The addition amount of the sintering aid is set in the range of 2 to 7.5% by weight based on the raw material powder in terms of oxide.
If the amount is less than 2% by weight, the sintered substrate is not densified and a low-strength, low-thermal-conductivity sintered substrate is formed. On the other hand, if the added amount exceeds 7.5% by weight, an excessive amount of the grain boundary phase is generated, and the heat conductivity and strength begin to decrease. It is particularly desirable to set the content to 3 to 6% by weight.

Further, alumina (Al ₂ O ₃ ) as another additive component in the above-mentioned substrate manufacturing method plays a role of promoting the function of the rare earth element sintering accelerator, and particularly performs pressure sintering. It has a remarkable effect in some cases. When the addition amount of Al ₂ O ₃ as an aluminum source is less than 0.5% by weight, the densification is insufficient, while when the addition amount exceeds 2% by weight, an excessive amount of grain boundary phase is generated. , Or begin to form a solid solution with silicon nitride, resulting in a decrease in heat conduction. Therefore, the amount of addition is set in the range of 0.5 to 2% by weight. In particular, in order to ensure good performance in both strength and thermal conductivity, it is desirable to set the addition amount in the range of 0.7 to 1.5% by weight.

The porosity of the sintered body substrate is set to 1.5% or less because it greatly affects the thermal conductivity and strength of the metallized substrate. If the porosity exceeds 1.5%, heat conduction will be hindered, and the thermal conductivity of the sintered body substrate will decrease and strength will decrease.

Since the grain boundary phase formed in the silicon nitride crystal structure greatly affects the thermal conductivity of the sintered substrate, the silicon nitride substrate used in the present invention has a grain boundary phase of 20%.
% Or more is set so as to occupy the crystal phase. Crystal phase 2
If it is less than 0%, it is not possible to obtain a sintered body having excellent heat radiation properties such that the thermal conductivity is 60 W / m · K or more and having excellent high-temperature strength.

Further, as described above, the porosity of the silicon nitride substrate is set to 1.5% or less, and the crystal phase occupies 20% or more of the grain boundary phase formed in the silicon nitride crystal structure. Has a temperature of 1800 to 2000
It is necessary to perform pressure sintering at 0.5 ° C. for about 0.5 to 10 hours and adjust and control the cooling rate of the sintered body immediately after completion of the sintering operation to 100 ° C. or less per hour.

When the sintering temperature is set to less than 1800 ° C., the densification of the sintered body is insufficient, the porosity becomes 1.5 vol% or more, and both the mechanical strength and the thermal conductivity decrease. . On the other hand, when the sintering temperature exceeds 2000 ° C., the silicon nitride component itself is liable to be vaporized and decomposed. Especially not pressure sintering,
When normal-pressure sintering is performed, decomposition and evaporation of silicon nitride starts at about 1800 ° C.

The cooling rate of the sintered body immediately after the completion of the sintering operation is an important control factor for crystallizing the grain boundary phase, and when the rapid cooling is performed such that the cooling rate exceeds 100 ° C./hour. Is that the grain boundary phase of the sintered body structure becomes non-crystalline (glass phase), the area ratio of the liquid phase formed in the sintered body as a crystal phase to the grain boundary phase is less than 20%, and the strength and thermal conductivity are reduced. Decrease together.

The temperature range in which the cooling rate should be strictly adjusted is a temperature range from a predetermined sintering temperature (1800 to 2000 ° C.) to a temperature at which a liquid phase produced by the reaction of the sintering aid solidifies. Is enough. Incidentally, the liquidus freezing point when using the sintering aid as described above is approximately 1600 to 15
It is about 00 ° C. By controlling the cooling rate of the sintered body substrate at least from the sintering temperature to the above-mentioned liquid phase solidification temperature to 100 ° C. or less, preferably 50 ° C. or less, most of the grain boundary phase becomes a crystalline phase. Thus, a sintered substrate excellent in both thermal conductivity and mechanical strength can be obtained.

The silicon nitride substrate is manufactured, for example, through the following process. That is, a predetermined amount of the sintering aid, a necessary additive such as an organic binder, etc. are added to the fine silicon nitride powder having the predetermined particle size and impurity content to prepare a raw material mixture. The obtained raw material mixture is molded to obtain a molded body having a predetermined shape. As a forming method of the raw material mixture, a general-purpose mold 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 600 ° C.
By heating at 800 ° C. for 1 to 2 hours, the organic binder added in advance is sufficiently removed and degreased. Next, the degreased molded body is subjected to atmospheric pressure sintering at a temperature of 1800 to 2000 ° C. for a predetermined time in an inert gas atmosphere such as nitrogen gas, hydrogen gas or argon gas.

The silicon nitride substrate manufactured by the above-described method has a porosity of 1.5% or less and a porosity of 60 to 180 W / m · K.
(25 ° C.) and has excellent three-point bending strength of 80 kg / mm ² or more at room temperature.

The metallized layer integrally formed on the surface of the silicon nitride substrate comprises Mo and W as conductive materials.
And an active metal nitride such as Ti, Zr, Hf, or Nb. The nitride (for example, TiN) of an active metal such as Ti contained in this metallized layer
It has the function of densifying conductive materials such as o and W, forming TiN, Ti silicide, and Ti-Si-N compounds on the surface of the silicon nitride substrate during firing, and firmly joining the metallized layer to the substrate surface. .

The weight ratio of the active metal nitride to the conductive material such as Mo or W is set in the range of 1.5 to 2.5. When the weight ratio is less than 1.5, the function of increasing the bonding strength of the metallized layer to the silicon nitride substrate is insufficient. On the other hand, when the weight ratio exceeds 2.5, the bonding strength of the metallized layer is reduced. In addition, since the adhesion when forming the plating layer is deteriorated, the peel strength of the metallized layer takes the maximum value in the above range of the weight ratio.

The metallized silicon nitride substrate according to the present invention is manufactured, for example, by the following procedure. That is, the raw material powder of Mo or W as the conductive material and the active metal nitride powder are weighed and mixed so as to have a predetermined weight ratio,
A binder such as ethyl cellulose in the obtained mixture,
A metallized paste is prepared by adding a solvent such as butyl acetate and stirring, and the metallized paste is printed on a surface of a high thermal conductive silicon nitride substrate prepared by the above-described manufacturing method by a screen printing method or the like to obtain a predetermined metallized paste. A conductor layer (circuit) pattern is formed. Next, the silicon nitride substrate on which the semiconductor layer pattern is printed is dried and then fired at a temperature of 1600 to 1800 ° C. in a non-oxidizing atmosphere such as nitrogen gas.

Further, in order to protect the metallized layer and to improve wettability with a bonding material such as solder used for bonding a semiconductor element or an electrode material to the metallized layer, nickel (Ni) or Ni- A plating layer made of a nickel alloy such as P, Ni-Ag may be formed.
The thickness of this plating layer is set to about 1 to 6 μm, and is formed using a general-purpose electrolytic plating method or an electroless plating method.

[0033]

According to the silicon nitride metallized substrate having the above-mentioned structure, when the metallized layer is formed by sintering, a high thermal conductive silicon nitride substrate with a small liquid phase exudation is used. It is possible to obtain a silicon nitride metallized substrate having high durability and excellent heat dissipation and bonding strength with less deterioration of the metallized layer due to bleeding over time. Also, uneven color of the substrate due to liquid phase seepage,
Discoloration is also reduced, and the product yield of metallized substrates can be greatly improved.

In particular, since a silicon nitride substrate having extremely high mechanical strength is used as compared with the conventional AlN substrate and Al ₂ O ₃ substrate, the silicon nitride substrate is set to the same strength as the conventional one. Thickness can be reduced to about 1/2, and higher-density mounting is possible. In addition, the thermal resistance is reduced in proportion to the decrease in thickness, and the heat dissipation is equivalent to that of the conventional AlN substrate. You can also get.

Further, the coefficient of thermal expansion of the silicon nitride substrate is S
The thermal expansion coefficient of the semiconductor element whose main component is i is close to that of the semiconductor element. Even when the semiconductor elements are integrally joined and subjected to repeated thermal shock, the generation of stress due to the difference in thermal expansion is small, and defects such as cracks are generated. There is an advantage that hardly occurs.

[0036]

Next, the present invention will be specifically described with reference to the following examples.

Examples 1 to 5 An average particle diameter of 0.55 μm containing 1.3% by weight of oxygen, 0.15% by weight of cation impurities and 97% of α-phase silicon nitride
m 2 of silicon nitride raw material powder, Y ₂ O ₃ (yttrium oxide) powder 5 having an average particle size of 0.7 μm as a sintering aid.
Al ₂ O ₃ (alumina) with a weight% of 0.5 μm in average particle size
Add 1.5% by weight of powder and add 24% in ethyl alcohol.
After wet-mixing for hours, the mixture was dried to prepare a raw material powder mixture. Next, a predetermined amount of an organic binder is added to the obtained raw material powder mixture, and the mixture is uniformly mixed. Then, the mixture is press-molded at a molding pressure of 1000 kg / cm ² to have a length of 50 mm × a width of 50 mm × a thickness of 5 mm.
Many mm compacts were manufactured. Next, the obtained molded body was
After degreased in an atmosphere gas at 0 ° C. for 2 hours, the degreased body was maintained at 1900 ° C. for 6 hours at 7.5 atm in a nitrogen gas atmosphere, and after performing densification sintering, it was attached to a sintering furnace. By controlling the amount of electricity to the heating device, the sintering furnace temperature becomes 1
The sintered body was cooled by adjusting the cooling rate of the sintered body until it dropped to 500 ° C. so as to be 50 ° C./hr,
Many silicon nitride substrates for Examples 1 to 5 were prepared.

On the other hand, Mo powder and W as conductor materials
Powder, TiN powder and Nb as active metal nitride
N powder was weighed and mixed so as to have a weight ratio shown in Table 1 to prepare five kinds of mixtures, and further, ethyl cellulose as a binder and butyl acetate as a solvent were added and stirred, and the five kinds of uniform substances were stirred. A metallized paste was prepared.

Each of the following metallized pastes was screen-printed on the surface of the high thermal conductive silicon nitride substrate prepared by the above-mentioned method, dried, and then dried at a temperature of 1700 to 1 in a nitriding atmosphere.
By firing at 800 ° C., a circuit pattern as a metallized layer was integrally formed.

In order to further improve the wettability with respect to a bonding material such as solder, a thickness 2 having a composition as shown in Table 1 is used.
A μm plating layer was formed by an electroless plating method to manufacture silicon nitride metallized substrates according to Examples 1 to 5, respectively.

Comparative Examples 1 to 3 On the other hand, as a ceramic substrate, an Al ₂ O ₃ sintered substrate (for Comparative Example 1) and an AlN sintered substrate (Comparative Example 2) were used, respectively.
Using a BeO sintered body substrate (for Comparative Example 3),
Metallized layers and plated layers having the compositions shown in Table 1 were formed on the surface of each sintered body substrate under the same conditions as in Examples 1 to 5, and a number of various ceramic metallized substrates according to Comparative Examples 1 to 3 were prepared.

Each of the ceramic substrates according to Examples 1 to 5 and Comparative Examples 1 to 3 thus prepared was subjected to room temperature (2
At 5 ° C.), characteristic values such as thermal conductivity, three-point bending strength, metallized layer bonding strength, and solderability were measured, and the appearance defect rate such as color unevenness was measured. The bonding strength was measured as the peel strength of the metallized layer after performing a thermal shock test (TCT) in which each sample metallized substrate was subjected to a heat cycle under the following conditions 100 times. The heat cycle was performed by cooling at −50 ° C. for 30 minutes and room temperature for 10 minutes.
Hold at + 150 ° C. for 30 minutes and at room temperature for 10 minutes.
The heating and cooling operation for holding for one minute was one cycle.

The solderability was measured to evaluate the wettability of the metallized layer with respect to solder, and was measured by the following method. That is, when a 5 mm-diameter spherical solder mass is placed on the surface of the metallized layer and then melted, the rate of decrease in height from the height of the original solder mass (5 mm) to the height of the molten solder rises (%) Was used to evaluate the solderability.

The results of the above measurements are shown in Table 1 below.

[0045]

[Table 1]

As is evident from the results shown in Table 1, according to the silicon nitride metallized substrates according to Examples 1 to 5, when the metallized layer is formed by firing, the liquid phase exudes little. Even after the heat cycle test, there was little decrease in the bonding strength of the metallized layer over time, and a silicon nitride metallized substrate excellent in durability and appearance was obtained. In particular, when the ceramic substrate is prepared with the same thickness, the thermal conductivity is lower than when the AlN substrate shown in Comparative Example 2 is used.
When the thickness of the i ₃ N ₄ substrate is set, the thickness becomes 1 of the AlN substrate.
/ 2. Therefore, by using a Si ₃ N ₄ substrate having a high thermal conductivity of 60 to 180 W / m · K, a metallized substrate having the same heat radiation as that obtained by using an AlN substrate was obtained. Further, since the substrate thickness can be reduced, a semiconductor module in which semiconductor elements are mounted at a higher density has been realized.

On the other hand, according to the Al ₂ O ₃ metallized substrate according to Comparative Example 1, the thermal conductivity is low and it is not possible to cope with high output of the semiconductor module, and the AlN metallized substrate according to Comparative Example 2 has high thermal conductivity. However, when the metallized layer was formed, the exudation of the liquid phase became remarkable, the bonding strength was reduced, the color unevenness was increased, and the product yield was reduced. Further, in the BeO metallized substrate of Comparative Example 3, the thermal conductivity was high, but the bending strength was small, and it was difficult to reduce the thickness.

[0048]

As described above, the silicon nitride metallized substrate according to the present invention uses a high thermal conductive silicon nitride substrate with little liquid phase exudation when the metallized layer is formed by firing. In addition, a metal nitride layer which has less deterioration with time in the bonding strength of the metallized layer due to the exudation of the liquid phase, has high heat dissipation and excellent bonding strength, and has excellent durability can be obtained. In addition, uneven color and discoloration of the substrate due to the exudation of the liquid phase are reduced, and the product yield of the metallized substrate can be greatly improved.

In particular, since a silicon nitride substrate having extremely high mechanical strength is used as compared with the conventional AlN substrate and Al ₂ O ₃ substrate, when the same strength as the conventional one is set, the silicon nitride substrate is used. Thickness can be reduced to about 1/2, and higher-density mounting is possible. In addition, the thermal resistance is reduced in proportion to the decrease in thickness, and the heat dissipation is equivalent to that of the conventional AlN substrate. You can also get.

Further, the coefficient of thermal expansion of the silicon nitride substrate is S
It is similar to the thermal expansion coefficient of the semiconductor element containing i as the main component, and even when the semiconductor elements are integrally joined and subjected to repeated thermal shock, the generation of stress due to the difference in thermal expansion is small, and defects such as cracks are reduced. There is an advantage that is hard to occur.

Claims (3)

(57) [Claims] 1. A metallized layer comprising at least one of molybdenum and tungsten and an active metal nitride is integrally formed on a surface of a silicon nitride substrate having a thermal conductivity of 60 to 180 W / m · K. Silicon nitride metallized substrate. 2. The weight ratio of active metal nitride to at least one of molybdenum and tungsten is from 1.5 to 1.5.
2. The metallized silicon nitride substrate according to claim 1, wherein said substrate is set to 2.5. 3. The metallized silicon nitride substrate according to claim 1, wherein a plating layer made of nickel or a nickel alloy is integrally formed on the surface of the metallized layer.