JP3298283B2 - Method for firing aluminum nitride 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 method for firing an aluminum nitride (AlN) substrate without deformation such as warpage.

In order to rapidly process a large amount of information, a semiconductor device constituting a main body of an information processing apparatus has been increased in capacity by downsizing unit elements, and integrated circuits such as LSI and VLSI have been put into practical use. I have.

[0003] Incidentally, since these integrated circuits with significant power consumption, the substrate for mounting the integrated circuit is required to be excellent in heat resistance, initially, alumina (Al ₂ O
₃ ) Substrates have been used.

Here, the necessary conditions for the substrate on which the integrated circuit is mounted are that the thermal conductivity is large, the coefficient of thermal expansion is close to that of the semiconductor substrate (Si), and the dielectric constant is small. In this regard, AlN is focused on and Al
N substrates have been put to practical use.

That is, the thermal conductivity of Al ₂ O ₃ is 20 W
/ mK, AlN is as large as 320 W / mK, and the thermal expansion coefficient of Al ₂ O ₃ is 7.2 × 10 ⁻⁶ / ° C., whereas AlN is 4.2 × 10 ⁻⁶ / ° C. There is 3.6 × 10 ^{-6 of} Si /
Close to ° C. The dielectric constant of Al ₂ O ₃ is 10, whereas that of AlN is as low as 8.9. For these reasons, the demand for the AlN substrate is increasing as a substrate for mounting an integrated circuit.

[0006]

_2. Description of the Related Art As described above, AlN has excellent properties. However, while the melting point of Al ₂ O ₃ is 2015 ° C., the melting point of AlN is as high as 2200 ° C. Therefore, Difficult to bake the substrate. Materials having a melting point exceeding 2000 ° C are fired in a carbon furnace using an inert gas atmosphere. A graphite container or boron nitride (BN) container is suitable for firing AlN substrates. ing. However, since firing in a graphite container results in a reducing atmosphere, color unevenness and bleeding are likely to occur on the AlN substrate. Therefore, firing is generally performed using a BN container.

That is, BN has a melting point of about 3000 ° C. and exhibits considerable sublimation even below the melting point. It is used. FIG. 2 shows a conventional baking method using a BN container, in which a BN setter 2 is placed in a BN container 1, and a degreasing-treated AlN green sheet 3 and a BN correction substrate are placed thereon. The AlN substrate is fired by placing a BN cover 4 thereon, placing a BN lid 5 in a carbon furnace, and firing in an inert gas, for example, nitrogen (N ₂ ) atmosphere.

Here, the AlN green sheet is obtained by adding a small amount of a sintering aid, for example, calcium carbonate (CaCO ₃ ) to AlN powder, adding a binder, a plasticizer, and a dispersion medium (solvent) to the AlN powder, kneading the mixture well, and then mixing with a It is formed into a sheet by a blade method, dried, heated in an inert gas such as a nitrogen (N ₂ ) atmosphere to perform a degreasing treatment prior to a high-temperature baking treatment, and then subjected to 1800 in an inert gas atmosphere. The substrate is heated at a high temperature of about ℃ to cause a solid phase reaction between the AlN powder and the sintering aid to sinter the AlN powder to form a substrate.

However, shrinkage is caused by the high-temperature firing, and the surface is roughened by friction generated at this time, and if a gap is formed between the straightening substrate 4 due to warpage, the atmosphere distribution on the substrate surface becomes non-uniform. There is a problem that color unevenness occurs from the image.

[0010]

In firing the AlN substrate, the degreased AlN green sheet 3 is placed on the setter 2 in the BN container 1 as shown in FIG.
The correction substrate 4 is placed thereon, the cover 5 is closed, and the substrate is formed by heating to a high temperature of 1800 ° C. and sintering in an inert gas atmosphere such as N ₂ .

However, there is a problem that the substrate is easily deformed or colored during the firing, and it is difficult to manufacture an AlN substrate with a good yield. This problem has been solved.

[0012]

The object of the present invention is to provide a high melting point metal powder, for example, tungsten (W) powder, which reacts with BN at least at the sintering temperature of AlN and causes volume expansion in a firing vessel. The sintering of the AlN green sheet is performed by placing the sintering container in a state where the lid of the sintering container is in close contact with the correction substrate, and the sintering can be achieved by sintering the AlN substrate.

[0013]

The present invention utilizes the phenomenon that W reacts with BN at the sintering temperature of AlN to form tungsten boride (W ₂ B), which causes a volume expansion at that time, and uses this phenomenon to prevent deformation of the AlN substrate. Things.

The AlN substrate is made by heating an AlN green sheet to a high temperature of 1800 ° C. in an inert gas atmosphere such as N ₂ and sintering the same. In order to prevent it, a correction substrate made of BN is placed on top and baked. It is difficult to eliminate deformation. The reason is that AlN green sheets are degreased using a tunnel furnace or the like before performing high-temperature firing, but if this degreasing is performed completely, the formed body becomes brittle and cannot be transferred to a BN container. Therefore, the degreasing treatment is performed under the condition that most of the additives (binders, plasticizers, dispersion media) are decomposed and scattered. ing.

As described above, since the AlN green sheet is fragile due to the degreasing treatment, the weight of the correction substrate placed on the setter of the BN container after being set on the setter of the BN container is limited. On the other hand, AlN is fired at a high temperature of about 1800 ° C. In this firing step, a liquid phase reaction proceeds between calcium carbonate (CaCO ₃ ), which is added as a sintering aid, and AlN, and the sintering of AlN occurs. Progresses to form an AlN substrate, during which the amount of shrinkage of the green sheet due to sintering of AlN is large, and it is difficult to prevent deformation only by the weight of the correcting substrate.

Therefore, in the present invention, since the deformation of the substrate due to sintering occurs in the sintering process, a material that expands at the sintering start temperature is placed under a setter, and expands during the sintering process to expand the AlN green sheet. Is applied to prevent deformation of the AlN substrate. For this purpose, prior to high-temperature baking, the correction substrate placed on the AlN green sheet must be in close contact with the lid. is there.

FIG. 1 shows an embodiment of the present invention.
When the lid 5 made of aluminum is brought into contact with the firing container 1, the lid 5 and the Al
It is necessary that the correction substrate 4 placed on the N green sheet 3 be in close contact with the substrate, and a refractory metal powder is placed under the setter 2 made of BN so as to be in this state. As the powder, W powder is most suitable. That is, W has a high melting point of 3387 ° C. and is not deformed by the heat treatment at about 1800 ° C. On the other hand, BN forming the baking container 1, the lid 5, the setter 2, the correction substrate 4 and the like is BN at high temperature.
Although steam is generated to form a vapor pressure, it reacts with the BN molecules to form W ₂ B, and the sintering of AlN proceeds as a result of expanding the volume of the reactant to about twice the original volume. As a result, mechanical pressure is applied from above and below, thereby suppressing deformation due to sintering.

[0018]

【Example】

Example 1: CaCO ₃ as a sintering aid was added to 100 parts by weight of AlN powder.
5 parts by weight, 10 parts by weight of PVB (polyvinyl butyral) as a binder, 10 parts by weight of DBP (dibutyl butyrate) as a plasticizer, and 50 parts by weight of ethanol as a dispersant.
Add the parts by weight, knead with a ball mill to make a slurry,
A green sheet was formed by a doctor blade method with a forming gap of 500 μm, and the green sheet was stamped and formed into a square of 90 mm. The six layers were laminated to prepare a sample, and ten sheets were prepared.

Next, this sample was heated at 900 ° C. for 4 hours in a stream of N ₂ using a belt furnace to degrease it, and then the W powder was spread on the bottom of a firing vessel made of BN, and BN was placed on this. A setter is placed thereon, and 10 layers of a sample made of an AlN green sheet / a correction substrate made of BN / a sample made of an AlN green sheet are laminated on the setter, and a lid made of BN is placed so as to be in close contact with the correction substrate, and N ₂ The firing was performed at 1800 ° C. for 30 hours in an air stream.

As a result, 10 AlN substrates having a thickness of about 1 mm have no color unevenness, and the warpage is 30 μm per 50 mm square area.
And the surface roughness was 3 μm or less. Comparative Example 1: A green sheet was 90 m in the same manner as in Example 1.
After punching and forming into an m-square, the six layers were laminated to prepare a sample, and ten samples were prepared. Next, this sample was degreased by heating at 900 ° C. for 4 hours in a N ₂ stream using a belt furnace.

Next, 10 layers of a sample made of AlN green sheet / a correction substrate made of BN / a sample made of AlN green sheet are laminated on a setter made of BN placed on the bottom of a firing container made of BN, with 10 layers. The substrate was placed with a gap between the substrate and the correction substrate, and baked at 1800 ° C. for 30 hours in an N ₂ stream.

As a result, color unevenness occurred on seven of the ten AlN substrates having a thickness of about 1 mm, and the warpage was less than 50 μm for three of the 50 mm square areas without color unevenness. The surface roughness was 5 μm or less, but the warpage was 90 μm or more and the surface roughness was as large as 8 μm or less for 7 sheets having uneven color.

[0023]

According to the present invention, it is possible to obtain an AlN substrate having much less warpage than the conventional one.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a firing method according to the present invention.

FIG. 2 is a cross-sectional view illustrating a conventional firing method.

[Explanation of symbols]

 Reference Signs List 1 firing container 2 setter 3 AlN green sheet 4 correction substrate 6 high melting point metal powder (W powder)

Continuation of front page (56) References JP-A-62-100479 (JP, A) JP-A-3-137058 (JP, A) JP-A-4-198806 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) C04B 35/64 C04B 35/581

Claims (2)

(57) [Claims] 1. A firing vessel (1) made of boron nitride, a setter (2) made of boron nitride, an aluminum nitride green sheet (3) having been degreased, and a correction substrate (4) made of boron nitride. And in the firing method, the firing vessel (1) is heated to a temperature equal to or higher than the sintering start temperature of aluminum nitride in an inert gas atmosphere, and the aluminum nitride is sintered to form a substrate. A high melting point metal powder (6) which reacts with boron nitride at least at the sintering temperature of aluminum nitride to cause volume expansion at least at the bottom of the firing vessel (1), and the lid (5) of the firing vessel (1) is A method for firing an aluminum nitride substrate, comprising sintering the aluminum nitride green sheet (3) while keeping it in close contact with the correction substrate (4). 2. The method for firing an aluminum nitride substrate according to claim 1, wherein said refractory metal powder (6) is tungsten powder.