JPH0680473A - Production of aluminum nitride substrate - Google Patents

Abstract

PURPOSE:To provide an aluminum nitride substrate having a small amount of molded article contracted during sintering and having high dimensional precision. CONSTITUTION:A mixture of aluminum nitride raw material powder, a sintering auxiliary and an organic component such as binder is molded to mold a primary molded article and the prepared primary molded article is adjusted to a given density by pressurizing. Then the prepared secondary molded article is defatted and sintered in a nonoxidizing atmosphere. When the primary molded article is pressurized, the primary molded article is heated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an aluminum nitride substrate, and more particularly to a method for manufacturing an aluminum nitride substrate having a small amount of shrinkage of a compact during sintering and having high dimensional accuracy.

[0002]

2. Description of the Related Art Silicon nitride (Si ₃ N ₄ ) and alumina (Al ₂ O ₃ ) are superior in properties such as strength, heat resistance, corrosion resistance, wear resistance, and lightness to conventional metal materials. Sintered ceramics such as aluminum and aluminum nitride (AlN) are used in semiconductors, electronic equipment materials, engine parts, high-speed cutting tool materials, nozzles, bearings, etc. Widely used as mechanical parts, functional parts, structural materials and decorative materials used below.

Conventionally, as a ceramic substrate for semiconductors, a substrate made of alumina (Al ₂ O ₃ ) is generally used. Currently, alumina (Al ₂ O ₃ ) has a raw material price of 1/20 to 20% compared to aluminum nitride (AlN).
It is cheap as 1/50, and many kinds of raw material powders having different characteristic values such as particle size distribution are prepared. Therefore, it is possible to form a high-density molded body by filling fine particles into the gaps between coarse particles, and therefore control of the shrinkage rate during sintering is relatively easy. Therefore, various sheet-shaped molded products can be obtained by the doctor blade method which is a general molding method. Further, a semiconductor package in which the above-mentioned sheet-shaped molded body is multilayered can be easily manufactured.

On the other hand, an aluminum nitride (AlN) sintered body is an insulator having a high thermal conductivity, and has a thermal expansion coefficient close to that of silicon (Si). Its use is expanding as a substrate.

Conventionally, AlN substrates are generally mass-produced by the following manufacturing method. That is, first, a sintering aid, an organic binder, and if necessary various additives and solvents, and a dispersant are added to aluminum nitride powder to prepare a raw material mixture, and the obtained raw material mixture is doctor blade. Or a roll forming method to form a thin plate-shaped or sheet-shaped molded product, or a raw material mixture is press-molded to form a thick plate-shaped or large-sized molded product. Next, the obtained molded body is heated in an air or nitrogen gas atmosphere to be degreased,
The hydrocarbon component used as the organic binder is removed and degreased from the molded body. The degreased compact is heated to a high temperature in a nitrogen gas atmosphere or the like and densified and sintered to form an aluminum nitride sintered compact.

In the above manufacturing method, when an ultrafine raw material powder having an average particle size of about 0.3 μm or less is used as the raw material AlN powder, a considerably dense sintered body can be obtained by the AlN powder alone. However, a large amount of impurities such as oxygen adhering to the surface of the raw material powder and the like are solid-solved in the AlN crystal lattice at the time of sintering, or Al-O- which hinders the propagation of lattice vibration.
As a result of producing a compound oxide such as an N compound, the thermal conductivity of the AlN sintered body that did not use a sintering aid was relatively low.

On the other hand, when an AlN powder having an average particle size of 0.5 μm or more is used as the raw material powder, the raw material powder alone does not have good sinterability. It was difficult to obtain a bound body and there was a drawback that mass productivity was low. Therefore, in order to efficiently manufacture a sintered body by the atmospheric pressure sintering method, in order to prevent the densification of the sintered body and the impurity oxygen in the AlN raw material powder from forming a solid solution in the AlN crystal grains. In addition, rare earth oxides such as yttrium oxide (Y ₂ O ₃ ) and alkaline earth metal oxides such as calcium oxide are generally added as a sintering aid.

[0008] These sintering aids react with impurity oxygen and Al ₂ O ₃ contained in the AlN raw material powder to form a liquid phase, achieve densification of the sintered body, and at the same time, the impurity oxygen is granulated. It is believed that it can be fixed as a phase phase and achieve high thermal conductivity.

[0009]

However, as described above, aluminum nitride has a property that the physical properties such as the thermal conductivity of the aluminum nitride substrate greatly change depending on the contents of oxygen and impurities in the raw material powder stage. In particular, the pulverization treatment causes a rapid increase in the oxygen content of the raw material powder, and the coarse AlN raw material powder also has a large amount of impurities and oxygen, resulting in a decrease in the thermal conductivity of the substrate. As described above, in order to prevent a decrease in thermal conductivity, which is a basic characteristic of the AlN sintered body, the grain size is usually 1 to 2 μm.
Therefore, it was necessary to use a fine single raw material powder by a reduction nitriding method with a narrow particle size distribution and a low oxygen content. Therefore, it is difficult to mix the raw material powders having different particle size distributions to adjust the density of the compact, and it is inevitable that the shrinkage rate during sintering becomes complicated and it is difficult to obtain an AlN substrate having high dimensional accuracy. Met.

Particularly when using a doctor blade method capable of mass-producing sheet-shaped compacts, it is practically difficult to arbitrarily increase the density of the compacts or strictly adjust it to a predetermined value, and AlN sintering is performed. There is a problem that defects such as warp are likely to occur on the body, and it is difficult to manufacture an AlN substrate having high dimensional accuracy at a high yield in any case.

The present invention has been made to solve the above problems, and in particular, an aluminum nitride substrate having a small amount of shrinkage of a compact during sintering and having high dimensional accuracy can be easily manufactured. An object is to provide a method for manufacturing an aluminum nitride substrate.

[0012]

The inventor of the present application has examined the influence of the density of the molded body on the dimensional shrinkage during sintering, and the shrinkage amount decreases as the density of the molded body approaches the theoretical density of the sintered body. We have found that it becomes smaller and a highly accurate substrate can be obtained. Then, by pressing the primary molded body formed by the doctor blade method or the like, the density of the molded body can be appropriately adjusted,
It has been found that a substrate having high dimensional accuracy can be obtained.

The present invention has been completed based on the above findings. That is, the method for producing an aluminum nitride substrate according to the present invention, a primary molded body is formed by molding a mixture of an aluminum nitride raw material powder, a sintering aid, and an organic component such as a binder. Is pressed to form a secondary molded body having a predetermined density, after which the obtained secondary molded body is degreased and sintered in a non-oxidizing atmosphere. Moreover, it is advisable to heat the primary molded body when pressing the primary molded body.

The aluminum nitride raw material (AlN) powder used in the method of the present invention, which is the main component of the sintered body, has an impurity oxygen content of 3% by weight or less in consideration of sinterability and thermal conductivity. The average particle size is 0.05-5 μm
The thickness is preferably about 3 μm or less.

As a sintering aid, rare earth elements (Y, Sc,
Ce, Dy, etc.) oxides, nitrides, oxides of alkaline earth metals (Ca), or substances that become these compounds by a sintering operation are used, particularly yttrium oxide (Y
₂ O ₃ ), cerium oxide (CeO) and calcium oxide (CaO) are preferred.

As the method for molding the primary molded body, the method of the present invention is extremely effective especially when the doctor blade method, which is difficult to control the density of the primary molded body, is used.
That is, by pressurizing the sheet-shaped primary compact having a low density prepared by the doctor blade method, a secondary compact having a higher density than the primary compact can be formed.
The pressing force depends on the composition of the raw material mixture, but is 10
0-500 kg / cm ² , more preferably 200-300 kg
The range of / cm ² is good.

When the primary molded body is pressed, the primary molded body is crushed by 3 times.
By heating to about 0 to 150 ° C., the density of the molded product can be increased in a shorter time, and the time required for the molding process can be further shortened.

Further, by forming through holes (conduction holes) and scribe lines (split grooves) at the stage of the high-density secondary molded body prepared as described above, through holes and scribes having high positional accuracy and dimensional accuracy are obtained. It is also possible to form a multilayer aluminum nitride substrate in which lines are formed and operation reliability is high.

Subsequent to the above secondary molding operation, the secondary molded body is heated in air or in a non-oxidizing atmosphere, for example, in a nitrogen gas atmosphere to a temperature of 400 to 800 ° C. to add the organic binder added in advance. Remove enough.

Next, the degreased sheet-shaped secondary compacts are stacked in multiple stages in the firing furnace through the interstitial powder made of sintered ceramic powder such as AlN or BN. The plurality of secondary compacts are collectively sintered at a predetermined temperature. For the sintering operation, the molded body is heated to a temperature of 1700 to 2000 ° C. for 2 to 10 in a non-oxidizing atmosphere such as nitrogen gas.
It is carried out by heating for about an hour. The sintering atmosphere is nitrogen gas or a reducing atmosphere containing nitrogen gas. H ₂ gas or CO gas may be used as the reducing gas.
Sintering is performed under vacuum (including a slight reducing atmosphere), reduced pressure,
You may perform in the atmosphere containing pressurization and normal pressure. When sintered at a low temperature of 1700 ° C. or lower, it depends on the particle size of the raw material powder and the amount of oxygen contained, but it is difficult to obtain a dense sintered body. Since the vapor pressure of AlN itself becomes high and densification may become difficult, the sintering temperature is set within the above range.

[0021]

According to the method of manufacturing an aluminum nitride substrate having the above-described structure, since the low-density primary compact is further pressed into a high-density secondary compact, a high dimension with less warpage or shrinkage during sintering is obtained. It is possible to obtain a precision aluminum nitride substrate.

Further, by heating the primary compact when pressing the primary compact, it becomes possible to form a high-density secondary compact in a shorter molding time. Further, by forming the through holes and the like at the stage of the high-density secondary molded body, the positional shape accuracy of the through holes and the like is improved, and a substrate having higher operation reliability can be obtained.

[0023]

EXAMPLES The effects of the method for manufacturing an aluminum nitride substrate according to the present invention will be described more specifically with reference to the following examples.

Example 1 An aluminum nitride (AlN) powder having a purity of 99.0% or more and an average particle size of 1.5 μm was prepared, and a predetermined amount of a sintering aid, an organic solvent and an acrylic binder were added thereto, and then the mixture was placed in a ball mill. And mixed for 30 minutes to prepare a uniform raw material slurry. Next, after adjusting the viscosity of the obtained raw material slurry, a doctor blade device was used to make AlN having a thickness of 0.8 mm.
A large number of sheet-shaped primary moldings were prepared. The density of the obtained primary molded product was 1.80 g / cm ³ .

Then, the obtained primary compact was heated and maintained at a temperature of 50 ° C. and pressed at a pressure of 200 kgf / cm ² for 20 minutes to form a secondary compact having a density of 1.95 g / cm ³ . .

Next, the secondary molded body thus obtained is pressed and punched using a die press to form a through hole having a diameter of 0.5 mm, and the outer shape is cut into a square shape of 50 mm length × 50 mm width to form a substrate. I made it a body.

Next, the obtained molded substrate was degreased in air at a temperature of 500 ° C. for 1 hour and then sintered in a nitrogen gas atmosphere at a temperature of 1800 ° C. for 5 hours to produce an AlN substrate according to Example 1. did.

Example 2 A 0.8 mm-thick sheet-shaped primary molded article made of AlN prepared by using the doctor blade method in Example 1 was heated to 1 ° C.
20 at a pressure of 200 kgf / cm ² while heating and holding at 00 ℃
By pressurizing for a minute, a secondary molded body having a density of 2.00 g / cm ³ was formed.

Next, the through hole of the obtained secondary compact was formed by a die press in the same manner as in Example 1, the outer shape was cut into a square shape, and the obtained substrate compact was degreased and baked under the same conditions. Then, a large number of AlN substrates according to Example 2 were manufactured.

Comparative Example 1 The AlN sheet-form primary molded article having a thickness of 0.8 mm prepared in Example 1 was directly subjected to Example 1 without heating and pressing.
In the same manner as above, through holes were punched, the outer shape was cut, and degreasing and sintering were performed to manufacture a large number of AlN substrates of Comparative Example 1 by the conventional manufacturing method.

In order to evaluate the finished dimension accuracy of the AlN substrates according to Examples 1 and 2 and Comparative Example 1 thus obtained, the outer dimension finished dimension of each AlN substrate and the finished dimension of the through hole were measured, respectively, and their standards The magnitudes of variations from the values were compared and the results shown in Table 1 below were obtained.

[0032]

[Table 1]

As is clear from the results shown in Table 1, in the substrate obtained by sintering the AlN compacts of Examples 1 and 2 in which the primary compact was pressed under a predetermined temperature condition to adjust the density, the density was adjusted. As compared with the case of Comparative Example 1 in which the above-described procedure is not performed, the variation in the through-hole diameter and the outer dimension is 1/2 to 1 /
AlN, which has been greatly reduced to about 5 and has high dimensional accuracy
It was demonstrated that a substrate was obtained.

As described above, according to the manufacturing method of this embodiment, a substrate having a high dimensional accuracy can be obtained, and the density of the molded body can be adjusted according to the mold so that A of a predetermined dimensional standard can be obtained.
It was possible to manufacture the 1N substrate with a high yield.

[0035]

As described above, according to the method for manufacturing an aluminum nitride substrate of the present invention, since the low-density primary compact is further pressed to form the high-density secondary compact, warpage during sintering It is possible to obtain an aluminum nitride substrate having high dimensional accuracy with less shrinkage.

Further, by heating the primary compact when pressing the primary compact, it is possible to form a high-density secondary compact in a shorter molding time. Further, by forming the through holes and the like at the stage of the high-density secondary molded body, the positional shape accuracy of the through holes and the like is improved, and a substrate having higher operation reliability can be obtained.

[Procedure amendment]

[Submission date] October 7, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction content]

Example 1 An aluminum nitride (AlN) powder having a purity of 99.0% or more and an average particle size of 1.5 μm was prepared, and a predetermined amount of a sintering aid, an organic solvent and an acrylic binder were added thereto, and then the mixture was placed in a ball mill. And mixed for 24 hours to prepare a uniform raw material slurry. Next, after adjusting the viscosity of the obtained raw material slurry, a doctor blade device was used to make AlN having a thickness of 0.8 mm.
A large number of sheet-shaped primary moldings were prepared. The density of the obtained primary molded product was 1.80 g / cm ³ .

Claims (4)

[Claims] 1. A primary compact is formed by molding a mixture of aluminum nitride raw material powder, a sintering aid and an organic component such as a binder, and the obtained primary compact is pressed to a predetermined density. A method for producing an aluminum nitride substrate, which comprises forming an adjusted secondary molded body, degreasing the obtained secondary molded body, and sintering in a non-oxidizing atmosphere. 2. The method for producing an aluminum nitride substrate according to claim 1, wherein the primary compact is formed by using a doctor blade method. 3. The method for producing an aluminum nitride substrate according to claim 1, wherein the primary compact is heated when the primary compact is pressed. 4. The method for manufacturing an aluminum nitride substrate according to claim 1, wherein at least one of a through hole and a scrub line is formed in the secondary molded body adjusted to have a predetermined density.