JPH0826828A - Production of aluminum nitride sintered compact - Google Patents

Abstract

PURPOSE:To improve appearance and physical properties by making an absorbent containing a readily reducing substance in the vicinity of interstices present in a hermetically closed type container therein so as not to come into contact with an AlN sintered compact and baking. CONSTITUTION:This method for producing an aluminum nitride sintered compact good in appearance is to add a sintering assistant such as Y2O3 and an organic binder to AlN, knead the resultant mixture, subsequently form the kneaded mixture, provide a green sheet compact, thermally degrease the compact, then house an AlN compact to be sintered such as a degreased compact into an integral type hermetically closed container of a structure for placing an inserting lid of the same quality in a container body comprising an AlN sintered compact without containing a sintering assistant, produce gaps by the deformation of a superposed part or crystal grain growth, etc., of AlN with increasing frequency of use, thereby disable the maintenance of adhesivity in the superposed part of the lid on the container body, then arrange an absorbent such as the AlN sintered compact containing a readily reducing substance such as Y203 of a prescribed shape near the gaps to be present in the hermetically closed container so as not to come into contact with the AlN compact to be sintered, place the hermetically closed container in a carbon furnace and thermally bake the AlN compact to be sintered in an atmosphere of N2 with a carbon heater.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing an aluminum nitride sintered body. Specifically, when firing an aluminum nitride sintered body in a nitrogen atmosphere using a carbon furnace, it is possible to stably obtain an aluminum nitride sintered body even if there is a gap in the closed vessel for firing. The present invention provides a method for firing an aluminum nitride sintered body capable of

[0002]

2. Description of the Related Art In recent years, as semiconductors have become highly integrated, attention has been paid to aluminum nitride substrates, which have a thermal conductivity ten times as high as that of conventional alumina substrates, as substrates for mounting semiconductors. The aluminum nitride substrate is an aluminum nitride sintered material obtained by degreasing a green body formed by molding an aluminum nitride powder with an organic binder together with a sintering aid or a green body on which a conductor circuit of a refractory metal is formed. It is manufactured by firing the bonded body in an inert atmosphere. A high temperature is required for firing aluminum nitride, and a carbon furnace that is easy to manufacture in a large furnace and is advantageous in terms of cost, that is, a firing furnace using a heater and a heat insulating material made of carbon is generally used. In addition, cheap nitrogen gas is generally used to maintain an inert atmosphere.

However, the carbon vapor and nitrogen gas present in the furnace during firing react with the sintering aid in the aluminum nitride sintered body, so that the surface of the aluminum nitride sintered body is nitrided with the sintering aid. However, there is a problem in that a product is generated to cause a defective appearance, and in a severe case, a defective sintering occurs. For example, when yttrium oxide is used as the sintering aid, yttrium nitride is produced. The above-mentioned yttrium nitride has a low volume resistance of 93 × 10 ⁻⁶ Ωcm, and depending on the application, the deterioration of the insulating property of aluminum nitride may be a problem.

On the other hand, when an aluminum nitride substrate is used as a semiconductor mounting substrate, a homogeneous substrate free of such low resistance products on the surface is required.

Therefore, in order to prevent nitriding of the sintering aid in the aluminum nitride material to be sintered, a method of accommodating the aluminum nitride material to be sintered in a hermetically sealed container and holding the atmosphere in the container for firing is proposed. It is commonly done.

Materials such as an aluminum nitride sintered body, a boron nitride sintered body, and a composite of aluminum nitride and boron nitride are used as the closed container for firing the aluminum nitride.

However, in the case of firing an aluminum nitride sintered body having a conductor circuit of a refractory metal such as tungsten, if a hermetically sealed container made of a boron nitride sintered body or a boron nitride composite is used, it is This refractory metal is not suitable because it is borated and its properties are significantly deteriorated. Therefore, generally, an aluminum nitride sintered body that does not substantially contain a sintering aid is used. Such an aluminum nitride sintered body is air-sintered several times in an inert atmosphere at a temperature higher than the sintering temperature of the aluminum nitride sintered body, and a sintering aid or oxygen or The container is made of aluminum nitride in which impurity components are sufficiently removed, or a container made of aluminum nitride obtained by firing without adding a sintering aid.

When the aluminum nitride sintered body is housed in the hermetically sealed container and fired, if the hermetically sealed container is incompletely sealed, carbon vapor and nitrogen gas in the furnace enter the container, The sintering aid in the aluminum nitride sintered body is nitrided, and a nitride of the sintering aid is generated on the surface of the aluminum nitride sintered body.

Therefore, in order to stably produce a good aluminum nitride sintered body, it is necessary to maintain a high hermeticity of the hermetically sealed container, but the hermeticity of the container should always be kept high. Is practically difficult and impractical.

For example, as the shape of the hermetically-sealed container, an integrated container or a combination of a plurality of sintered body parts is used, of which an integrated container (hereinafter referred to as a box setter). Is a structure that puts a sintered body of aluminum nitride in the container body and covers it, so it is easy to achieve hermeticity, and the hermeticity at the part where the container body and the lid overlap is maintained at the beginning, but with the increase in the number of times of use Deformation of the polymerization part of the container due to high temperature during firing, growth of aluminum nitride crystal grains, or sintering aid components and aluminum nitride scattered from the aluminum nitride sintered body during firing, polymerization of the container Reattachment to the part creates a gap, and the hermeticity cannot be maintained.

A container formed by combining a plurality of sintered body blocks (hereinafter referred to as an assembly setter) is a container which can cope with various sizes of the sintered body by changing the size of the sintered body. However, since the container of the above structure is not an integrated structure, the sealing property is incomplete at the joint part of each sintered body block, the frame plate is easily displaced during firing, and a gap is formed at the displaced part. It is larger and more difficult to maintain hermeticity than a box setter.

[0012] In any setter, the surface of the superposed portion of the container can be surface-processed in order to restore the hermeticity, but it is very costly, and each time the processing is performed,
There was a problem that the dimensions of the sintered body became smaller and eventually it became unusable.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to burn an aluminum nitride sintered body which does not substantially contain a sintering aid when firing an aluminum nitride sintered body in a nitrogen atmosphere in a carbon furnace. It is an object of the present invention to provide a firing method for obtaining an aluminum nitride sintered body having good appearance and physical property values even if a gap is present in a sealed container made of a bonded body.

[0014]

[Means for Solving the Problems] The present inventors have conducted extensive research to solve the above technical problems. As a result, the presence of the absorbent having an easily reducing substance as an active ingredient in the vicinity of the gap existing in the closed container causes the carbon vapor entering the container through the gap of the container to be absorbed by the easily reducing substance. , The generation of nitride of the sintering aid in the aluminum nitride sintered body that is fired in the container is effectively suppressed,
It was found that an aluminum nitride sintered body having good appearance and characteristics can be obtained, and further research was conducted to complete the present invention, which led to the proposal thereof.

That is, according to the present invention, the aluminum nitride sintered body is housed in a hermetically sealed container which is made of an aluminum nitride sintered body substantially containing no sintering aid and has a gap.
When firing in a nitrogen atmosphere using a carbon furnace,
Firing of aluminum nitride, characterized in that an absorbent containing a reducible substance is present in the closed container in the vicinity of a gap existing in the closed container and without contact with the sintered body of aluminum nitride. Is the way.

The present invention will be described in detail below. In the present invention, the composition and shape of the aluminum nitride sintered body that is housed in the closed container and fired is not particularly limited, and a green molded body obtained by molding aluminum nitride powder with an organic binder together with a sintering aid, etc. Those obtained by degreasing can be used without limitation.

To give an example of the above green molded body, a green sheet molded body obtained by a sheet molding method, a molded body in which a plurality of green sheet molded bodies are laminated, and a high melting point metal paste is printed on the green sheet molded body. Molded product with circuit formed, green sheet molded product with via hole filled with high melting point metal paste, printed with high melting point metal paste to form circuit, molded product with multiple laminated layers, obtained by spray drying method, etc. A press-molded body obtained by press-molding the obtained granules, a molded body obtained by printing a high-melting-point metal paste on the press-molded body to mold a circuit, and the like can be used.

Specific examples of the composition of the green sheet molded product and the press molded product are aluminum nitride 1
Generally, 0.01 to 10 parts by weight of a compound consisting of yttrium and a lanthanide element as a sintering aid and 0.1 to 30 parts by weight of an organic binder are generally used with respect to 00 parts by weight.

Degreasing of the green compact is carried out by oxidizing gas such as oxygen and air, reducing gas such as hydrogen and carbon monoxide, inert gas such as nitrogen, and a mixed gas of these gases or a humidifying gas. The method is generally performed by heat treatment in an atmosphere. The degreasing temperature is 300 ° C to 12
The degreasing time is 00 ° C., and the degreasing time is in the range of 1 minute to 500 minutes, and may be appropriately selected according to the green molded body and the degreasing method.

In the present invention, the aluminum nitride sintered body is housed in a closed container made of an aluminum nitride sintered body containing substantially no sintering aid, and fired in a nitrogen atmosphere using a carbon furnace. To be done.

The carbon furnace for carrying out the above firing is a muffle,
All furnaces in which at least some of the internal parts such as heaters and heat insulating materials are made of carbon material are targeted.

In the present invention, as the aluminum nitride sintered body used in the closed container, any aluminum nitride sintered body can be used as long as it does not substantially contain a sintering aid. For example, an aluminum nitride sintered body is fired. A sintered body of aluminum nitride in which the sintering aid is sufficiently removed by pre-firing several times at a temperature sufficiently higher than the above temperature, or a sintered body of aluminum nitride without addition of the sintering aid can be preferably used.

As the shape of the closed container, any known shape can be used. For example, FIG. 1 and FIG. 2 exemplify typical aspects of a hermetically sealed container used in the present invention, but the shape of the container is not limited thereto.

The closed container shown in FIG. 1 is a box setter, which is composed of a container body 1 and a lid 2, and is usually used by stacking it in a plurality of stages. In the above-mentioned container, there is no gap in the initial stage, but a gap of 0.05 mm or more is visually observed in the polymerized portion as the number of times of use increases.

The form of the hermetically sealed container shown in FIG. 2 is a setter, which is a square bottom plate 3 made of an aluminum nitride sintered body and four frame plates 4 (aluminum nitride sintered body block).
It is usually used by stacking several stages, but like the box setter, a gap is generated on the overlapping surface. Further, the assembled setter maintains the airtightness inside the container by combining the bottom plate and the frame plate, but there is a gap in the portion where the frame plates are combined.

In the present invention, known conditions can be adopted without particular limitation as long as the firing of the aluminum nitride sintered body is carried out in a nitrogen atmosphere. The general firing conditions are shown below. The firing temperature is 1400 ° C to 2100 ° C, preferably 1650 ° C to 1900 ° C. The rate of temperature rise to such a temperature is 1 ° C./min to 40 ° C./min. The holding time of the above temperature is 1 minute to 20 hours.

In the present invention, the absorbent containing the easily reducing substance (hereinafter referred to as "absorbent"), which is present in the vicinity of the gap of the closed container, is easily reduced by carbon vapor at the firing temperature, that is, A substance that has a function of absorbing carbon vapor and that does not decompose under firing conditions is used without limitation, and a substance that does not deteriorate the aluminum nitride sintered body or inhibits its sintering is particularly preferably used.

The easily reducing substance contained in the absorbent is not particularly limited as long as it is reduced by carbon vapor to produce a reduced substance, but is reduced by carbon vapor and nitrided by coexisting nitrogen. It is preferable that the substance has a high carbon absorption rate and the like and can sufficiently exhibit the effects of the present invention.

Examples of the substances that are reduced by the above carbon vapor and nitrided by coexisting nitrogen include yttrium, lanthanoid elements, aluminum,
Scandium and titanium are preferably used. In particular, a compound used as a sintering aid component in the aluminum nitride sintered body, that is, a lanthanoid element such as erbium or dysprosium, yttrium in that it does not deteriorate the quality of the aluminum nitride sintered body or inhibits its sintering. At least one compound selected from the compounds consisting of is preferably used. Specifically, yttrium oxide, erbium oxide, dysprosium oxide and the like are preferably used.

The easily reducing substance may be used alone or in combination with another substance to form an absorbent material. A concrete example of the case where a sintering aid component is used will be described as an example of such a composite mode. A green molded body (degreased) composed of the above-mentioned sintering aid and an organic binder, the green molded body. Or a sintered body obtained by firing the same degreased body as the aluminum nitride sintered body containing the sintering aid component or the aluminum nitride sintered body containing the sintering aid component. It is preferably used. Further, if the above composition is more specifically shown, a green molded body (degreased) or a sintered body of 0.1 to 100 parts by weight of an organic binder, 100 parts by weight of aluminum nitride, relative to 100 parts by weight of yttrium oxide On the other hand, it is a degreased body or a sintered body containing 0.1 part by weight or more of a sintering aid.

As the shape of the absorbent material, any shape can be adopted as long as it can be placed in the vicinity of the gap of the hermetically sealed container without coming into contact with the material to be sintered, but it is easy to handle and easy to reuse. In view of the above, a block-shaped, thin-plate-shaped molded body is preferably used rather than a powdered molded body.

Further, the use of the degreased body or sintered body of aluminum nitride containing the above-mentioned sintering aid as the absorbing material means that aluminum nitride was discarded as a residual material or a waste material in the manufacturing process of the aluminum nitride sintered body. The degreased body or sintered body can be used, which is preferable.

In the present invention, the absorbent is placed near the gap existing in the closed container. This is necessary for the carbon vapor to come into contact with the absorbent before it is absorbed before the carbon vapor entering through the gap diffuses into the hermetically sealed container and prior to the aluminum nitride sintered body. Is. Incidentally, the aspect of arranging the absorbent material in the vicinity of the gap includes an aspect of arranging the absorber material with a slight gap from the gap and an aspect of arranging the absorber material in contact with the gap portion,
The optimum position may be appropriately determined depending on the structure of the closed container, the shape of the absorbent material, and the like.

Further, in this case, it is important that the absorber is arranged without contacting the sintered body of aluminum nitride. That is, if the absorbent material and the aluminum nitride sintered body come into contact with each other during firing, there is a risk of fusion with the absorbent material at the contact portion.

The mode of arranging the absorbent material in the vicinity of the gap existing in the closed container is not particularly limited as long as it satisfies the above conditions.

FIG. 3 shows a mode in which the plate-shaped absorbent material 5 is placed upright along the inner wall of the container body so as to be located near the gap between the container body and the lid in the box setter. Further, in the above embodiment, FIG. 6 shows a state in which the aluminum nitride sintered body is housed in a hermetically-sealed container, and the sintered body is polymerized in a plurality of stages.

FIG. 4 shows an assembled setter in which a triangular prism-shaped absorber 5 having a height slightly lower than the upper surface of the frame plates is arranged in the vicinity of the gap between the portions where the frame plates meet each other. Further, FIG. 5 shows a state in which the aluminum nitride sintered body is housed in the container and is polymerized in a plurality of stages.

[0038] In general, when the absorbent is used for firing, a nitride is formed on the surface thereof, the amount of the generated nitride increases as the number of times of use increases, and the effect of absorbing gas entering from the outside of the container gradually decreases. Come on.

Therefore, in order to maintain the effect sufficiently, it is preferable to appropriately replace the absorbent material in such a state. Further, when the aluminum nitride sintered body is used as the absorbent material, the nitride formed on the surface can be removed by a means such as washing with water and dried to be used again as the absorbent material.

The aluminum nitride sintered body fired by the firing method of the present invention does not generate nitride as an auxiliary component on the surface or cause insufficient sintering due to the influence of carbon vapor. It has a good appearance without discoloration, uneven color, or deformation. Further, the thermal conductivity, the density of the sintered body, the other physical properties of the sintered body, the physical properties of the refractory metal formed on the surface of and inside the sintered body, and the electrical properties are also good.

[0041]

According to the present invention, in a method of firing an aluminum nitride sintered body in a nitrogen atmosphere in a carbon furnace, a hermetically sealed aluminum nitride sintered body containing substantially no sintering additive is used. Even if there is a gap in the mold container, the influence of carbon vapor generated in the carbon furnace is caused by allowing the absorbent containing the easily reducing substance to exist in the vicinity of the gap so as not to come into contact with the aluminum nitride sintered body. It is possible to obtain an aluminum nitride sintered body that is excellent in appearance and physical properties without undergoing damage.

[0042]

EXAMPLES Examples will be shown below for specifically explaining the method of the present invention, but the present invention is not limited to these examples. In the examples and comparative examples, the appearance of the fired aluminum nitride was evaluated according to the following criteria.

Rank A: Good, no yttrium nitride was formed on the surface of the sintered body, and there was no insufficient sintering. Rank B: Yttrium nitride is slightly generated on the surface of the sintered body, but there is no insufficient sintering. Rank C: Yttrium nitride is produced on the surface of the sintered body, and there is also a portion where sintering is insufficient.

Example 1 A green body of aluminum nitride containing 5 wt% of yttrium oxide as a sintering aid (165 mm square (hereinafter referred to as "<<<<
"mm square" means a square with one side <<<< mm), thickness 3m
m) was degreased by a conventional method. Next, as shown in FIG. 5, the degreased body 7 was placed on a bottom plate 3 of 186 mm square made of aluminum nitride, and a pressing plate 8 made of aluminum nitride was placed thereon. Then, along the four sides on the bottom plate, length 18
A frame plate 4 of 0 mm, a width of 30 mm, and a wall thickness of 6 mm made of aluminum nitride was arranged. Then, the absorber 5 made of an aluminum nitride sintered body containing 5 parts by weight of yttrium oxide as a sintering aid component and having a shape of a triangular prism having a right-angled triangle having two sides of 15 mm and a height of 25 mm is attached to the frame plates. Placed just inside the part. Next, another bottom plate 3 was placed on the upper surface of the frame plate to seal the inside of the assembled setter. This setter is further put in a carbon muffle, and while flowing 2 liters of nitrogen gas per minute in a firing furnace having a carbon heater,
Firing was performed at 1830 ° C. for 5 hours. The assembled setter used here was air-fired several times at a temperature higher than 1830 ° C. and then ground, and was used 10 times or more for firing the aluminum nitride fired body, so that there was a visually visible gap in the part where the bottom plate and the frame plate meet. I used one. In the assembled setter after firing, the frame plates were slightly misaligned, and a gap was formed in the part where the frame plates were joined together. Yttrium nitride was formed on the surface of the absorbent material, but the obtained aluminum nitride sintered body had a uniform good appearance and was A rank. The thermal conductivity was 180 W / mK or more.

Example 2 The same degreased aluminum nitride compact as in Example 1 was used.
It was housed in the same setter as in Example 1. As the absorbent material, a degreased body of the same material as the sintered body of aluminum nitride and the same shape as in Example 1 was used. Next, as in Example 1, the muffle was placed in a carbon muffle and fired under the same conditions. The obtained aluminum nitride sintered body,
Appearance is uniformly good and A rank. Thermal conductivity is 180
It was W / mK or more.

Example 3 A green sheet of aluminum nitride containing 5% by weight of yttrium oxide as a sintering aid was provided with a via hole having a diameter of 0.2 mm in (165 mm square, 0.4 mm thick), and tungsten was the main component. Then, a circuit was formed on the both surfaces of the green sheet by screen printing with a paste containing tungsten as a main component. Six sheets were laminated by hot pressing and then degreased by a conventional method. Then, firing was performed under the same method and conditions as in Example 1. The obtained sintered body has a uniformly good appearance and is A
It was ranked and the thermal conductivity was 180 W / mK or more. Further, the surface and internal wiring resistance and the via wiring resistance were sufficiently low.

Example 4 Green body of aluminum nitride containing 5 wt% of yttrium oxide as a sintering aid (63 mm square, thickness 1 mm)
Was degreased by a conventional method. Then, as shown in FIG.
The degreased body 7 is placed on a laying plate 9 made of aluminum nitride and having a size of 70 mm, and then the degreased body is housed in a box setter container body 1 made of aluminum nitride and having an inner size of 72 mm square and a depth of 10 mm. Press plate with the same shape as the floor plate 8
I put it. Length 70 made of aluminum nitride as absorber
A plate-shaped absorber 5 having a size of 8 mm, a width of 8 mm, and a thickness of 0.6 mm was leaned against the inner wall of the box setter and arranged. Then, the container body was sealed with a lid 2 made of aluminum nitride, put in a muffle made of carbon, and baked at 1815 ° C. for 5 hours while flowing 2 liters of nitrogen gas per minute in a baking furnace having a carbon heater. Was done. The box setter has been used for firing the aluminum nitride fired body 20 times or more, and a gap 6 exists in the portion where the main body container and the lid are fitted together. The obtained sintered body had a uniformly good appearance and was of A rank. The thermal conductivity was 180 W / mK or more.

Example 5 Aluminum nitride granule press body containing 15% by weight of yttrium oxide as a sintering aid (15 mm square, thickness 1.0 m)
Circuits were formed on both surfaces of m) by screen printing with a paste containing tungsten as a main component, and the circuits were degreased by a conventional method. Nine of the degreased bodies were placed side by side on the same floor plate as in Example 4, and then fired under the same method and conditions as in Example 4. The obtained sintered body had a uniformly good appearance, was A rank, and had a thermal conductivity of 180 W / mK or more.

Comparative Example 1 The aluminum nitride degreased body of Example 1 was placed in the assembled setter of Example 1 without using an absorbent. This was put into a carbon muffle and fired under the same conditions. In the assembled setter after firing, the frame plates were slightly misaligned, and a gap was formed in the part where the frame plates were joined together. In the obtained sintered body, yttrium nitride was formed on the surface of the sintered body in the vicinity of the gap, and at the same time, deformation due to insufficient sintering also occurred. The evaluation was C rank.

Comparative Example 2 The degreased aluminum nitride product of Example 4 was placed in the box setter of Example 4 without using an absorbent. This was placed in a carbon muffle and fired under the same conditions as in Example 4. In the obtained sintered body, yttrium nitride was generated on the outer peripheral portion. The evaluation was B rank.

[Brief description of drawings]

FIG. 1 is a perspective view of a typical box setter used in the present invention.

FIG. 2 is a perspective view of a representative setter used in the present invention.

FIG. 3 is a perspective view of a mode in which an absorbent material is arranged in the box setter.

FIG. 4 is a perspective view of an embodiment in which an absorber is arranged on a set setter.

FIG. 5 is a front perspective view when the degreased body and the absorbent are set in a setter and polymerized.

FIG. 6 is a front perspective view when a degreased body and an absorbent are set in a box setter and polymerized.

[Explanation of symbols]

 1 Container Main Body 2 Lid 3 Bottom Plate 4 Frame Plate 5 Absorbing Material 6 Gap 7 Degreasing Body 8 Holding Plate 9 Laying Plate

Claims (1)

[Claims] 1. An aluminum nitride sintered body is housed in a hermetically-sealed container made of an aluminum nitride sintered body which does not substantially contain a sintering aid and has a gap, and a carbon furnace is used in a nitrogen atmosphere. In the case of firing in, the absorbent containing the easily reducing substance in the closed container was made to exist in the vicinity of the gap existing in the closed container and without contact with the aluminum nitride sintered body, A method for firing aluminum nitride.