JPH0465367A - Production of aluminum nitride sintered compact - Google Patents

Abstract

PURPOSE:To easily and stably obtain a sintered compact having high thermal conductivity by sintering a green compact prepared by adding alkaline earth compound and rare earth compound to AlN powder under an inert atmosphere in which an AlN sintered compact where the content of oxygen as impurity is regulated to a value below a specific value and graphite as allowed to coexist. CONSTITUTION:A green compact prepared by adding alkaline earth compound and/or rate earth compound to an AlN powder is sintered under an inert atmosphere where an AlN sintered compact containing <0.5 wt.% oxygen as impurity and graphite are allowed to coexist. By this method,the above additives are changed into multiple oxides, such as alkaline earth aluminate and rare earth aluminate, and removed, at the time of the completion of sintering, from the system of a sintered compact by the action of trace amounts of carbon gas generated from the graphite. Further, the reduction in the weight of the AlN sintered compact to be obtained can be prevented owing to the coexisting AlN sintered compact, and also the reduction in thermal conductivity as well as the occurrence of irregular color in the AlN sintered compact to be obtained can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for producing an aluminum nitride sintered body (lN sintered body).

(Prior art) Af1N sintered body has higher thermal conductivity than alumina etc.
And since the coefficient of thermal expansion is similar to that of silicon (St),
It is used as a mounting board for semiconductor devices. Also,
AgN sintered bodies have characteristics such as high strength at high temperatures and poor reactivity with molten metal, so their applications in other fields are expanding. In recent years, by increasing the purity of AIJN sintered bodies, it has become possible to increase the thermal conductivity to ~270 W/m. It is well known that an A, 9N sintered body at 270 W/m- contains only several hundred ppm of impurity oxygen and cation impurities, respectively.

As is well known, aluminum oxide impurities that are inevitably included in AIJN powder react with additives during sintering to produce aluminates, and these aluminates form a liquid phase during sintering to form A, QN sintered bodies. Promote densification. Usually, the aluminate remains as a grain boundary phase at grain boundary triple points. In other words, aluminum oxide impurities are trapped in the grain boundary phase, and the AgN crystal itself is highly purified. For example, if Y2O is used as an additive, 3Y2035AiJ2
03 Y2O3AN2032 Y 203 ・Al
When a Y-Ag-0 complex oxide such as 120< is produced and CaO is used as an additive, Ca0-A1203.2Ca
o e A Ca-Aj7-0 based plate composite oxide such as AJ7203 is produced and remains in the sintered body. Such aluminate remains as a grain boundary phase at grain boundary triple points.

When the above-mentioned composite oxide is present in the grain boundary phase, the thermal conductivity of the sintered body decreases accordingly. For this reason, high purity of the negative layer, that is, high thermal conductivity, is achieved by performing long-time firing in a reducing atmosphere to remove the composite oxide from the system. It is known that the AIN sintered body that does not contain the composite oxide consists of a single phase of AIJN within the range evaluated by X-ray diffraction or SEM. Several theories have been reported regarding the mechanism by which the composite oxide is removed, but no established theory has been reached, and it is believed that the reduction-nitridation reaction and evaporation of the composite oxide are involved. The composite oxide is A1! The speed at which the N sintered body migrates out of the system depends on the firing atmosphere, and is known to be faster in an atmosphere where a small amount of carbon gas is generated from a heater or a firing container.

In the production of high thermal conductive AIIN single phase sintered bodies, the influence of the firing atmosphere is extremely large. Depending on the firing atmosphere,
The speed at which the grain boundary phase is removed and the amount of impurities remaining in the sintered body differ. As a result, the properties of the sintered body change significantly.

Conventionally, when manufacturing A, QN single phase sintered bodies, the firing atmosphere has been controlled by changing the firing container.

In addition to graphite as a carbon gas supply source, AIN sintered body, BN (boron nitride), tungsten, and the like have been used in the firing container. However, even with this method, it is difficult to consistently produce a highly thermally conductive ApN sintered body, and this problem becomes more pronounced especially when the size of the sintered body increases. .

(Problems to be Solved by the Invention) The present invention was made to solve the above conventional problems, and is a method for easily and stably manufacturing an A,ON sintered body having excellent high thermal conductivity. This is what we are trying to provide.

[Structure of the Invention (Means for Solving the Problems)] The present invention provides a method of nitriding a molded product obtained by adding an alkaline earth compound and/or a rare earth compound to aluminum nitride powder with an impurity oxygen content of less than 0.5% by weight. This is a method for producing an aluminum nitride sintered body, which is characterized by firing in an inert atmosphere in which an aluminum sintered body and graphite coexist.

The above Al)N powder has an impurity oxygen content of 0.1 to 2.
．． 5% by weight, more preferably 0.3-2.0% by weight,
Moreover, it is desirable to use particles having an average hourly particle size of 1.5 μm or less, more preferably 0.1 to 1.2 μm.

The above alkaline earth compounds and/or rare earth compounds change into composite oxides such as alkaline earth aluminates, rare earth aluminates, alkaline earth rare earth aluminates, etc. during firing, and at the end of firing, the sintered body is removed outside.

Such alkaline earth compounds include, for example, Ca, Ba
%Sr oxide, carbide, fluoride, carbonate, oxalate, nitrate, or alkoxide.

Examples of rare earth compounds include Y and La.

Ce, Nd, Dy5Pr oxides, carbides, fluorides,
Carbonates, oxalates, nitrates, alkoxides, etc. can be mentioned, especially Y and La.

Compounds of Ce are preferred.

The amount of the alkaline earth compound and/or rare earth compound added is 30% by weight or less, more preferably 0.1% or less, A/(A+B), where A is the elemental equivalent of these compounds and B is the amount of AgN powder. It is desirable that the content be in the range of ~20% by weight. The reason for this is that when the amount of the compounds exceeds 30% by weight, the elements of those compounds remain at the ION grain boundaries, resulting in AΩ
There is a possibility that the high thermal conductivity of the N sintered body will be inhibited.

The A, QN sintered body containing impurity oxygen can be made to coexist in a reducing atmosphere, for example, in the form of a bottom plate of the molded body or a block placed adjacent to the molded body. Such A
The reason why the amount of impurity oxygen in the ρN sintered body is limited is that if the amount is 0.5% by weight or more, the thermal conductivity of the A11N sintered body decreases and color unevenness occurs in the sintered body. A more preferable amount of impurity oxygen is 0.4% by weight or less.

The graphite acts as a source of a trace amount of carbon gas, and is coexisting in the atmosphere in the form of, for example, a graphite heater of a firing furnace or a graphite container. As the inert gas, for example, N2, Ar5He, etc. can be used.

It is desirable that the above-mentioned firing be performed at a temperature range of 1800 to 2000°C. The reason for this is that if the temperature is lower than 1800°C, the sinterability will deteriorate, but the elements of the alkaline earth compound and/or rare earth compound as a sintering aid will
, 9N does not escape from the grain boundaries and remains, and if the temperature exceeds 2000° C., there is a risk that not only will A and QN sublimate, but also react with carbon gas in the atmosphere to form carbide. In addition, Gagaru firing is performed on the low temperature side (1800'
In C), it is desirable to carry out the heating for 6 hours or more, and on the high temperature side (2000°C), it is desirable to carry out the heating for 4 hours or more.

In addition to the above-mentioned compact, the object to be fired in the method of the present invention contains AIH as a main component, and the grain boundary phase is an alkaline earth element aluminum oxide, a rare earth element aluminum oxide, and an alkaline earth element rare earth element aluminum oxide. A sintered body containing at least one selected from the following may be used.

(Function) The method of the present invention produces a molded body obtained by adding an alkaline earth compound and/or rare earth compound to A47N powder, in which an A, QN sintered body with an impurity oxygen content of less than 0.5% by weight and graphite coexist. Calcinate in an inert atmosphere. In this firing process, the additives are changed into composite oxides such as alkaline earth aluminates, rare earth aluminates, alkaline earth rare earth aluminates, etc., and are fired by the action of a trace amount of carbon gas generated from the graphite. At the end of the process, it is removed from the sintered body. In other words, the additive is AIH
After contributing to the densification of aluminum oxide and the trapping of impurity aluminum oxide, it is removed from the system. Moreover, the A, 9N sintered body coexisting in the atmosphere can prevent weight loss of the A, QN sintered body to be obtained.

Moreover, by specifying the impurity oxygen in the AgN sintered body coexisting in the atmosphere to less than 0.5% by weight, it is possible to prevent color unevenness and decrease in thermal conductivity of the AgN sintered body to be obtained. . As a result, it is possible to easily and stably produce an A, QN single-phase sintered body having high thermal conductivity (thermal conductivity of 240 W/m*K or more) due to highly purified AIH.

(Example) Examples of the present invention will be described in detail below.

Example 1 First, the amount of impurity oxygen was 1.0% by weight, and the average particle size was 0.
．． As an additive to 6 μm AIN powder, an average particle size of 0.1.
czm, 99.9% pure Y2O, 3 parts by weight powder, (Y
2.38% by weight) was added and mixed in a ball mill to prepare a raw material powder. Subsequently, 5% by weight of an acrylic binder was added to this raw material powder and granulated, and then 12 g of this granulated powder was molded under uniaxial pressure of 500 kg/cm2 to form a compact of about 30 x 30 x 7 mm. Subsequently, this green compact was heated to 700° C. in a nitrogen gas atmosphere to remove the acrylic binder. Next, the green compact was placed on a base plate with a diameter of 901111% and a thickness of 11 m, which was made of an A, QN sintered body containing impurity oxygen ff10.21% by weight, and the inner dimensions of this were 10011110% in diameter and 11 m in height.
00III in a graphite container, and heated in a graphite heater furnace in a nitrogen gas atmosphere of 1 atm.
An AfiN sintered body was manufactured by firing at 900° C. for 24 hours.

Comparative Example 1 As a base plate on which the green compact is placed, impurity oxygen amount], 5% by weight
A and QN sintered bodies were manufactured in the same manner as in Example 1 except that AgN sintered bodies were used.

Comparative Example 2 A bed plate on which the compact is placed is 75 mm square and 0.05 mm thick.
An AgN sintered body was manufactured in the same manner as in Example 1, except that a tungsten sheet made of a man-made tungsten sheet was used.

Comparative Example 3 A 9N sintered body was produced in the same manner as in Example 1, except that the green compact was directly set in a Craphite container without using a tungsten sheet.

When the constituent phases of the obtained A, 17N sintered bodies of Example 1 and Comparative Examples 1 to 3 were examined by X-ray diffraction, they were found to consist of a single IcIN phase. However, the sintered body of Comparative Example 3 emits a strange odor when crushed,
It is presumed that some kind of trace impurity is mixed in. Furthermore, the density, thermal conductivity, and appearance of these AJN sintered bodies were investigated. These results are shown in Table 1 below.

Note that (1) density and (2) thermal conductivity were measured by the methods shown below.

■Density The density of the ApN sintered body was measured by the Archimedes method.

■Thermal conductivity from each A111N sintered body Diameter IDll ID1% Thickness 3
Cut out the disk of ■, 21. Thermal conductivity was measured by the laser flash method at room temperature of 'C±2°C.

Examples 2 to 6 As the bottom plate on which the powder compact is placed, a plate made of AρN sintered body having an amount of impurity oxygen shown in Table 2 below was used.
Five types of A47N sintered bodies were manufactured by the same method as in Example 1.

The density and thermal conductivity of the obtained Al)N sintered bodies of Examples 2 to 6 were examined in the same manner as in Example 1 described above. The results are also listed in Table 2.

Examples 7 to 13 Seven types of Afi N sintered bodies were manufactured in the same manner as in Example 1, except that raw material powders consisting of AIN powder and additives shown in Table 3 below were used.

Regarding the obtained A, QN sintered bodies of Examples 7 to 13,
Density and thermal conductivity were evaluated by the same method as in Example 1 described above, and electrical resistance, dielectric breakdown voltage, and dielectric constant were also examined. The results are also listed in Table 3. The electrical resistance, dielectric breakdown voltage, and dielectric constant were all measured at room temperature in accordance with JIS.

Examples 14 to 18 Five types of A and QN sintering were performed in the same manner as in Example 1, except that the IN powder had the composition shown in Table 4 below, and the sintering was performed under the conditions shown in Table 4. A body was produced.

However, in Example 1B, 6 g of granulated powder was press-molded and used for production.

Regarding the obtained AIN sintered bodies of Examples 14 to 18,
Density, thermal conductivity, electrical resistance, dielectric breakdown voltage, and dielectric constant were investigated using the same methods as described above.

The results are also listed in Table 4.

[Effects of the Invention] As detailed above, according to the present invention, there is no color unevenness and
AgN sintered bodies having a high thermal conductivity of 0 W/mK or more can be easily and stably produced, which has remarkable effects such as improving yield and reducing costs.

Claims (1)

[Claims] A molded body made by adding an alkaline earth compound and/or a rare earth compound to aluminum nitride powder has an impurity oxygen content of 0.
A method for producing an aluminum nitride sintered body, which comprises firing in an inert atmosphere in which less than 5% by weight of an aluminum nitride sintered body and graphite coexist.