JPH08109069A - Aluminum nitride sintered compact - Google Patents

Abstract

PURPOSE: To obtain an aluminum nitride sintered compact developing no bled liquid phase portion on its surface and capable of forming an electrically conductive layer with high bond strength thereon. CONSTITUTION: This sintered compact is obtained by monolithically forming a porous aluminum nitride layer 2a having <90% of relative density on at least a part of the surface of aluminum nitride sintered compact body 3a. The relative density inside the body 3a is designed to stand at >=90%. Besides, it is preferable that the thickness of the layer 2a is set at 20-1000μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride sintered body used as an insulating substrate for a semiconductor device or a heat dissipation substrate part, and more particularly to an aluminum nitride sintered body capable of increasing the bonding strength with a conductive layer. Regarding the body

[0002]

2. Description of the Related Art Aluminum nitride (AlN) sintered bodies are used as heat-resistant materials because they have little strength deterioration even at high temperatures and have excellent chemical resistance, while utilizing their high thermal conductivity and high electrical insulation. Then, the heat sink material of the semiconductor device,
It is also widely used as an insulator material for circuit boards.

The above-mentioned aluminum nitride sintered body is usually formed by pressing a raw material mixture obtained by adding 1 to 7% by weight of a rare earth element compound (for example, Y ₂ O ₃ ) as a sintering aid to fine aluminum nitride powder. In a firing container made of aluminum nitride or carbon nitride sheath and lid, which is molded into a predetermined shape by a method or the like, and the resulting molded body is placed on a floor plate made of aluminum nitride or boron nitride. Housed in
1600 to 2000 ° C in a reducing atmosphere containing nitrogen gas
It is manufactured by firing at a temperature of.

The aluminum nitride sintered body produced in this manner is characterized by having a higher thermal conductivity than other ceramics sintered bodies. It is greatly affected by the amount of oxygen in impurities inside. That is, by the above firing operation, yttrium oxide (Y ₂ O ₃ ) added as a sintering aid reacts with oxygen on the surface of the aluminum nitride raw material powder and oxygen inside the powder to produce A.
A liquid phase of a yttrium-aluminum compound such as l _X Y _Y O _{3 (X + Y) / 2} is formed, and this liquid phase promotes sintering of the raw material powder.

On the other hand, oxygen dissolved in AlN at the time of sintering segregates as an oxide at the grain boundary by adding Y ₂ O ₃ . As a result, it is considered that the inside of the aluminum nitride crystal grains is highly purified to be an AlN sintered body with few lattice defects, and the thermal conductivity is improved.

Al ₅ Y ₃ remaining in the grain boundary phase
Oxides such as O ₁₂ , AlYO ₃ and Al ₂ Y ₄ O ₉ are considered to be heat conduction inhibiting substances.

Therefore, a method of using a carbon container and a lid as a firing container and firing the AlN compact in a reducing atmosphere containing carbon gas and nitrogen gas to reduce oxides in the grain boundary phase is also adopted. It That is, when firing is performed in a reducing atmosphere containing the above carbon gas and nitrogen gas, the yttria-aluminum compound remaining in the grain boundary phase is reduced by the carbon gas on the surface of the sintered body and further reacted with nitrogen gas. To produce yttrium nitride (YN). Even if such a reduction nitriding reaction proceeds only on the surface of the sintered body, material diffusion in the sintered body occurs sequentially, and the grain boundary phase can be gradually removed from the inside of the sintered body. As a result, an AlN sintered body having a higher thermal conductivity of about 260 W / m · K is also obtained.

[0008]

According to the above AlN sintered body, various characteristics such as chemical composition, thermal conductivity and density are
It is uniform in each part of the sintered body. However, since the liquid phase is exuded and solidified locally on the surface of the AlN sintered body as it is sintered, the surface of the sintered body is electrically conductive by, for example, a refractory metallization method. Even if an attempt is made to form a layer to form a circuit board, there is a drawback that the bonding strength of the conductive layer is lowered. Therefore, conventionally, a method has been adopted in which the exuded portion is scraped off in advance by lapping or honing, and then a conductive layer (metallized circuit pattern) is formed. However, even in this method, the bonding strength of the conductive layer is not sufficient, and the number of man-hours for mechanical grinding is added, so that there is a problem that it is difficult to inexpensively manufacture the circuit board.

Further, in the conventional method for producing an aluminum nitride sintered body, since the whole compact is fired so that the reducing atmosphere acts uniformly, characteristics such as composition, thermal conductivity and density are uniform. Only a sintered body was obtained. Therefore, for example, as a substrate material for mounting a plurality of elements having different required heat transfer characteristics, it is necessary to individually prepare substrates according to the required characteristics of the element.

The present invention has been made in order to solve the above-mentioned problems, and does not cause a liquid phase bleeding portion on the surface thereof, and aluminum nitride firing capable of forming a conductive layer having high bonding strength. The purpose is to provide a union.

Further, on the surface of the sintered body and inside thereof,
Another object is to provide an aluminum nitride sintered body having different characteristics such as composition, thermal conductivity, and density in arbitrary shaped portions on the same surface of the sintered body.

[0012]

In order to achieve the above-mentioned object, the present inventor forms a sintered body by changing the firing conditions of the aluminum nitride molded body, and the respective conditions vary depending on the composition, density, etc. of the sintered body. The effects on them were compared and examined. As a result, especially by adjusting the distance between the aluminum nitride compact and the inner wall of the carbon container for firing, there is no exudation part of the liquid phase on the surface, and the density and composition are different between the surface and the inside of the sintered body. An aluminum nitride sintered body was obtained. That is, a low-density porous aluminum nitride layer made of aluminum nitride and yttrium nitride was formed on the surface of the sintered body, while an aluminum nitride sintered body having a dense aluminum nitride inside was obtained. Further, a paste containing a reducing substance such as carbon that releases a reducing gas during firing is partially applied to the surface of the molded body, or a jig containing the reducing substance is partially placed on the molded body. It was found that the porous aluminum nitride layer was formed in a film form on the site due to the reduction action of the sintering aid by the reducing substance during firing.

This film-like porous aluminum nitride layer is characterized by the presence of yttrium nitride (YN) produced by the reducing action as compared with the inside of the sintered body, and the low thermal conductivity and density. . And on the surface of the aluminum nitride sintered body through this porous aluminum nitride layer,
It was found that a circuit board having high bonding strength can be obtained when the conductive layer is formed by the metallizing method or the like.
The present invention has been completed based on the above findings.

That is, the aluminum nitride sintered body according to the present invention is characterized in that a porous aluminum nitride layer having a relative density of less than 90% is integrally formed on at least part of the surface of the aluminum nitride sintered body. To do. The relative density inside the aluminum nitride sintered body is 90% or more. Further, the thickness of the porous aluminum nitride layer is 20 to 1
It is recommended to set it to 000 μm. It is also possible to form a porous aluminum nitride layer having an arbitrary plane shape on the surface of the aluminum nitride sintered body body.

The aluminum nitride sintered body of the present invention is formed into a raw material mixture prepared by adding 1 to 7% by weight of a sintering aid to aluminum nitride raw material powder, and the obtained green body is formed into carbon. It is manufactured by firing in a reducing atmosphere in a reducing vessel at a temperature of 1700 to 2000 ° C. for 3 to 100 hours.

As the above aluminum nitride raw material powder,
Considering sinterability and thermal conductivity, the impurity oxygen content is 3
It is suppressed to less than or equal to wt% and the average particle size is 0.05 to 5μ.
m, preferably 3 μm or less of AlN raw material powder is used.

Conventionally, when a high thermal conductivity AlN sintered body having a thermal conductivity of about 260 W / m · K is produced, a reducing atmosphere containing carbon gas generated from a carbon container for firing is spread over the entire compact. A sufficient space was secured in the carbon container for firing. However, in the present application, contrary to the above-mentioned conventional method, the specific surface of the molded body is brought close to the inner wall of the carbon container, or a paste containing a reducing substance such as carbon that releases a reducing gas during firing is partially formed on the molded body surface. Of the reducing substance such as carbon gas is applied to the sintered body by applying the reducing agent or the jig containing the reducing substance partially on the molded body. A porous AlN layer is partially formed at the site.

Y added to aluminum nitride raw material powder
_A sintering aid such as ₂ O ₃ has a great influence on the densification of AlN crystal grains, and if the amount of the sintering aid is small, the densification of the sintered body is hindered. However, in the firing method of the present invention, the AlN molded body is brought close to the inner wall of the carbon container for firing, or a paste or a jig containing a reducing substance is applied to or placed on the molded body so that the initial firing is performed. In the above, Y ₂ O ₃ as a sintering aid existing on the surface of the molded body is reduced by carbon gas or the like, and at the same time, nitrided by nitrogen gas in the atmosphere to become yttrium nitride (YN). That is, the sintering aid becomes deficient only in the surface portion of the AlN molded body that is close to the inner wall of the carbon container, or in the portion where the paste is applied or the portion where the jig is placed, and the sintering aid is not densified even after firing.
On the other hand, a sufficient amount of the sintering aid remains on the surface of the AlN compact other than the above, the normal sintering progresses, and further the densification and high purification of the sintered compact progress. In this way, a porous aluminum nitride layer in which densification does not proceed is formed only on the surface and yttrium nitride (YN) remains, while a dense AlN sintered body body is formed inside.

The porous AlN layer thus formed has characteristics such as relatively low thermal conductivity and density as compared with the inside of the AlN sintered body.

Further, the relative density of the porous AlN layer is as follows when a circuit board is manufactured by forming a conductive layer on the porous AlN layer.
Affects the bonding strength of the conductive layer. When the relative density of the porous AlN layer is 90% or more, the bonding strength with the conductive layer decreases, so the relative density of the porous AlN layer is set to less than 90%. Furthermore, the thickness of the porous AlN layer is 20 to 10
It is set in the range of 00 μm. When the thickness is less than 20 μm, the effect of improving the bonding strength of the conductive layer is small, while when the thickness exceeds 1000 μm, the structural strength of the entire AlN sintered body decreases, and further, the high thermal conductivity inherent to AlN. Is damaged.

Further, a portion other than the porous AlN layer in the surface layer portion,
That is, the relative density of the internal AlN sintered body is 90% or more, preferably 93% or more, in order to maintain the structural strength of the entire sintered body.

In order to form the porous AlN layer having the above-mentioned predetermined thickness, the distance between the AlN compact and the inner wall of the carbon-made baking container at the time of baking is set to 3 to 20 mm, and the baking is performed.

As a method for forming a porous AlN layer, in the above-mentioned manufacturing method, an AlN compact is used as a starting element, but AlN once manufactured by a normal sintering method.
The sintered body is housed in a firing container made of carbon, and the firing is performed by setting the distance between the AlN sintered body and the inner wall of the carbon container within the above range, or by firing or paste containing a reducing substance. It is also possible to use a method in which the tool is applied to or placed on a sintered body and then fired again to form the tool.

[0024]

According to the aluminum nitride sintered body having the above structure, since the liquid phase component is reduced to form the porous aluminum nitride layer, the exuded portion of the liquid phase is not formed,
When the conductive layer is formed as it is, the conductive layer component wraps around the pores of the porous aluminum nitride layer and solidifies, so that the bonding strength of the conductive layer can be significantly increased and a highly reliable circuit board, etc. Can be provided at low cost.

Further, by partially forming the above porous aluminum nitride layer, a sintered body having different characteristics such as density and thermal conductivity can be obtained, and a plurality of element parts having different required characteristics can be formed as a single piece. It becomes possible to assemble it on the aluminum nitride sintered body, and it becomes possible to manufacture the element mounting substrate and the like at low cost.

[0026]

Embodiments of the present invention will now be described more specifically with reference to the accompanying drawings.

Examples 1 to 5 Average particle size 1.0 μm containing 0.7% by weight of impurity oxygen
5% by weight of yttrium oxide (Y ₂ O ₃ ) as a sintering aid was added to the aluminum nitride raw material powder of m, and a binder was further added and mixed, and a sheet was formed by a doctor blade method. The obtained sheet-shaped molded body is thermocompression-bonded to form a laminated molded body. The laminated molded body is degreased at a temperature of 500 ° C. in a nitrogen gas atmosphere, and then the degreased body is placed on an aluminum nitride laying plate. The floor plate on which the degreased body was placed was housed in a carbon baking container. Then, as shown in Table 1, the distance between the degreased body and the inner wall of the baking container is 3 to 15 mm.
Set in the range of mm and contain carbon gas 9
After holding at a temperature of 1800 ° C. for 2 hours in a nitrogen gas atmosphere at atmospheric pressure, the NiN sintered body according to Examples 1 to 5 is fired at a temperature of 1850 ° C. for 24 hours with the nitrogen gas pressure lowered to 1 atmosphere. Was prepared.

Comparative Examples 1 to 3 On the other hand, in Examples 1 to 5, except that the interval between the degreased body and the inner wall of the carbon burning container was set to a wide range of 30, 50 and 70 mm. Similarly, molding, degreasing and firing were performed to prepare AlN sintered bodies according to Comparative Examples 1 to 3, respectively.

In the AlN sintered bodies of Examples 1 to 5 thus prepared, the surface portion was reduced and the porous AlN layer was formed, so that no exudation portion of the liquid phase was observed. Further, in order to investigate the structures in the vicinity of the surface of the AlN sintered bodies of Examples 1 to 5, the cross section in the thickness direction of each sample was observed with a scanning electron microscope (SEM), and as shown in FIGS. 1 and 2. I got good results.

As shown in FIGS. 1 and 2, A of Examples 1 to 5
In the 1N sintered body, the thickness from the surface 1 is 50 to 800 μm.
A porous AlN layer 2 is formed over a range of m, and a dense AlN sintered body body 3 is formed inside the porous AlN layer 2, and the texture is completely different between the surface layer and the inside of the sintered body. You can see that Further, when the dense AlN sintered body main body 3 was further enlarged and observed by SEM, aluminum nitride crystal grains and yttrium-aluminum compound in the grain boundary portion were observed.

On the other hand, from the sintered bodies of Examples 1 to 5, the porous A
As a result of crushing only the 1N layer portion and subjecting the obtained powder to an X-ray diffractometer (XRD) to investigate its constituent components, FIG.
The XRD profile as shown in was obtained. That is, it was found that the porous AlN layer was composed of AlN crystal particles and yttrium nitride (YN) produced by reducing the auxiliary component and the like.

On the other hand, in the AlN sintered bodies according to Comparative Examples 1 to 3, since the distance between the compact and the carbon container is set to be wide as before, the reductive nitriding reaction on the surface portion does not proceed greatly. The formation of the porous AlN layer was not confirmed, and the structure was uniform in the thickness direction.

The above Examples 1 to 5 and Comparative Examples 1 to 3
Conductive layers were formed on the surfaces of the AlN sintered bodies according to the above-mentioned items by a high melting point metallizing method, and the bonding strength of the conductive layers was measured. That is, after applying the Mo-Mn paste on the surface of the AlN sintered body, it was fired at a temperature of 1700 ° C. for 20 minutes in a heating furnace filled with nitrogen gas to form a conductive layer of Mo-Mn having a thickness of 20 μm. The pins were soldered and fixed on the upper surface of each conductive layer, and the maximum pull strength when the pins were pulled upward to separate the conductive layer was measured as the bonding strength, and the results shown in Table 1 below were obtained.

[0034]

[Table 1]

As is clear from the results shown in Table 1, Examples 1 to 5 in which a porous AlN layer was formed by firing with a small distance between the AlN compact and the inner wall of the carbon firing vessel during firing In the AlN sintered body according to Example 1, A according to Comparative Examples 1 to 3 in which a porous AlN layer is not formed.
It was found that, as compared with the 1N sintered body, the conductive layer has a high bonding strength and can be used as a circuit board having excellent durability.

The reason why the bonding strength of the conductive layer is increased as described above is that, as shown in FIG. 4, the conductive layer is formed in the pores of the porous AlN layer 2a formed on the surface of the AlN sintered body 3a. Porous AlN layer 2
It is considered that this is because the junction area due to the catching between a and the conductive layer 4 increases.

Further, since the exuded portion of the liquid phase is not formed on the surface of the AlN sintered bodies according to Examples 1 to 5, lapping processing or honing processing for removing the exuded portion is not required, After the bonding, the circuit board can be formed by forming the conductive layer as it is. Therefore, it is possible to inexpensively manufacture a circuit board on which a conductive layer having high bonding strength is formed.

Further, according to each of the above embodiments, a sintered body having various characteristics such as density, thermal conductivity and composition on the surface and the inside can be obtained, so that a plurality of element parts having different required characteristics can be obtained. It can be assembled on the surface of one sintered body. Therefore, it is possible to manufacture the element-mounted component and the like at low cost and at low cost, as compared with the case where the substrate is individually prepared for each required characteristic.

Further, according to the AlN sintered body of this embodiment, the heat transfer direction and the light transmission direction can be arbitrarily set by forming the porous AlN layer having a small thermal conductivity and a low light transmission property at a predetermined position. Can be set to. That is, FIG.
As shown in, porous Al is formed on the back surface of the AlN sintered body 3b.
When the N layer 2b is formed, it is possible to form a substrate that does not transfer heat in the rear surface direction but transfers heat only in the front surface and side surface directions as indicated by the arrow. On the other hand, as shown in FIG. 6, only the side surface of the columnar AlN sintered body 3c has the porosity A.
When the 1N layer 2c is formed, as shown by the arrow, A
Heat can be transmitted and light can be transmitted only in the height direction of the 1N sintered body.

Example 6 Average particle size 1.0 μm containing 0.7% by weight of impurity oxygen
5% by weight of yttrium oxide (Y ₂ O ₃ ) as a sintering aid was added to the aluminum nitride raw material powder of m, and a binder was further added and mixed, and a sheet was formed by a doctor blade method. The obtained sheet-shaped compact was thermocompression-bonded to obtain a laminated compact. Next, as shown in FIG. 7, a carbon (graphite) paste is screen-printed on the surface of the laminated molded body 5 to form a paste layer 6a having a predetermined shape.
6b was formed. Next, after degreasing the laminated molded body 5 in a nitrogen gas atmosphere at a temperature of 500 ° C., the degreased body is placed on a floor plate made of aluminum nitride, and the floor plate on which the degreased body is placed is placed in a carbon baking container. Accommodated. Then, the firing container containing the degreased body was held in a nitrogen gas atmosphere containing carbon gas at 9 atm at a temperature of 1800 ° C. for 2 hours to be fired, and then the temperature of the nitrogen gas was lowered to 1 atm at a temperature of 1850 ° C. Then, the AlN sintered body according to Example 6 was prepared by holding it for 24 hours and performing heat treatment.

In the AlN sintered body according to Example 6 described above, as shown in FIG. 8, the porous AlN layers 2d and 2e having a planar shape corresponding to the shape printed with the carbon paste are formed, while the printing is performed. In the non-performed portion, the aluminum nitride sintered body had the usual properties of high density and high thermal conductivity.

The porous AlN layer 2 of the above AlN sintered body is also used.
After applying the Mo-Mn paste on the upper surfaces of d and 2e,
It is fired at a temperature of 1700 ° C. for 20 minutes in a heating furnace filled with nitrogen gas, and as shown in FIG. 9, a thickness of Mo—Mn is formed on the upper surface of an AlN sintered body body 3d with porous AlN layers 2d and 2e interposed therebetween. The conductive layers 4a and 4b having a thickness of 15 μm were formed. Then, when the maximum pull strengths of the conductive layers 4a and 4b were measured in the same manner, a high value was obtained as in the case of Examples 1 to 5.

Example 7 Average particle size 1.0 μ containing 0.7% by weight of impurity oxygen
5% by weight of yttrium oxide (Y ₂ O ₃ ) as a sintering aid was added to the aluminum nitride raw material powder of m, and a binder was further added and mixed, and a sheet was formed by a doctor blade method. The obtained sheet-shaped molded body is thermocompression-bonded to form a laminated molded body. The laminated molded body is degreased at a temperature of 500 ° C. in a nitrogen gas atmosphere, and then the degreased body is placed on an aluminum nitride laying plate. The floor plate on which the degreased body was placed was housed in a baking container made of aluminum nitride. Then, the firing container containing the degreased body was held in a nitrogen gas atmosphere of 1 atm at a temperature of 1800 ° C. for 2 hours to perform firing to prepare an AlN sintered body body having a thermal conductivity of 170 W / m · K.
Next, a carbon jig having a predetermined shape was placed on the obtained AlN sintered body main body, and the AlN sintered body main body on which the jig was placed was stored in a carbon firing container at 1 atm. The AlN sintered body according to Example 7 was prepared by heat-treating at a temperature of 1850 ° C. for 24 hours in the nitrogen gas atmosphere.

In the AlN sintered body according to Example 7, the porous A having a planar shape corresponding to the shape of the placed jig was used.
While the 1N layer was formed, in the area where the jig was not placed, the aluminum nitride sintered body had the usual properties of high density and high thermal conductivity.

Further, a conductive layer was formed on the upper surface of the porous AlN layer of the AlN sintered body in the same manner as in Example 6, and the maximum pull strength thereof was measured in the same manner as in Examples 1 to 5 above. High values were obtained as well.

According to Examples 6 to 7, porous aluminum nitride having a desired shape can be integrally formed on the surface of ordinary dense aluminum nitride, and the porous portion reduces the liquid phase component and becomes porous. A high quality aluminum nitride layer is formed. Therefore, the exuded portion of the liquid phase is not formed, and when the conductive layer is formed on the surface of the porous aluminum nitride layer as it is, the conductive layer component wraps around the void portion of the porous aluminum nitride layer and solidifies. Therefore, the bonding strength of the conductive layer could be significantly increased. On the other hand, since the properties of ordinary aluminum nitride can be obtained in the portion where the conductive layer is not formed, a circuit board or the like having high heat dissipation and high reliability could be provided at low cost.

[0047]

As described above, according to the aluminum nitride sintered body of the present invention, since the liquid phase component is reduced to form the porous aluminum nitride layer on the surface, the exuded portion of the liquid phase When the conductive layer is formed as it is without forming the metal etc., the conductive layer component wraps around the pores of the porous aluminum nitride layer and solidifies, so that the bonding strength of the conductive layer can be greatly increased and the reliability is improved. It is possible to provide a circuit board or the like having high properties at low cost.

Further, by partially forming the porous aluminum nitride layer, a sintered body having different characteristics such as density and thermal conductivity can be obtained, and a plurality of element parts having different required characteristics can be formed as one element. It becomes possible to assemble it on the aluminum nitride sintered body, and it becomes possible to manufacture the element mounting substrate and the like at low cost.

[Brief description of drawings]

FIG. 1 is a scanning electron microscope (SEM) photograph showing the crystal structure of an aluminum nitride sintered body according to the present invention.

FIG. 2 is a sectional view schematically showing the crystal structure shown in FIG.

FIG. 3 is a graph showing an XRD profile of a porous AlN layer portion.

FIG. 4 is a sectional view schematically showing an AlN sintered body on which a conductive layer is formed.

FIG. 5 is a sectional view showing a heat transfer direction of the aluminum nitride sintered body of the example.

FIG. 6 is a cross-sectional view showing a heat transfer direction and a light transmission direction in the aluminum nitride sintered body of the example.

FIG. 7 is a perspective view showing a state in which a paste layer is screen-printed on the surface of the aluminum nitride laminated body.

8 is a sectional view taken along the line VIII-VIII in FIG. 7 after firing the laminated molded body shown in FIG. 7.

9 is a cross-sectional view of an aluminum nitride sintered body having a conductive layer formed on the surface of the porous AlN layer shown in FIG.

[Explanation of symbols]

1 AlN Sintered Body Surface 2, 2a, 2b, 2c, 2d, 2e Porous AlN Layer 3, 3a, 3b, 3c, 3d AlN Sintered Body Main Body (Inside) 4, 4a, 4b Conductive Layer 5 AlN Laminated Formed Body 6a, 6b paste layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C04B 35/64 C04B 35/64 A

Claims (4)

[Claims] 1. An aluminum nitride sintered body, wherein a porous aluminum nitride layer having a relative density of less than 90% is integrally formed on at least a part of the surface of the aluminum nitride sintered body. 2. The aluminum nitride sintered body according to claim 1, wherein the relative density inside the aluminum nitride sintered body is 90% or more. 3. The porous aluminum nitride layer has a thickness of 20.
The aluminum nitride sintered body according to claim 1, wherein the aluminum nitride sintered body has a thickness of about 1000 μm. 4. The aluminum nitride sintered body according to claim 1, wherein a porous aluminum nitride layer having an arbitrary plane shape is formed on the surface of the aluminum nitride sintered body body.