JP2698011B2 - Manufacturing method of aluminum nitride sintered body - 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 producing an aluminum nitride sintered body.

[0002]

2. Description of the Related Art High integration and high power of semiconductor devices typified by ICs and the like have progressed, and accordingly, an electrical insulating material having good heat dissipation properties has been required. Among them, in particular, an insulating substrate made of an aluminum nitride sintered body has been put to practical use because it is excellent in thermal conductivity, thermal expansion, electrical insulation, and the like.

[0003] However, aluminum nitride has a covalent bond.
It is a compound having compatibility and is hardly sintered. Therefore, Sera
Use a sintering aid to obtain a mix,
Aluminum nitride of high density and high thermal conductivity
Attempts have been made to obtain sintered ceramics. Aluminum nitride
Sintering aids used to obtain sintered_TwoO
_Three(JP-A-49-111909) and CaO (JP-B-58-49510)
No.), but when using Kosara, 1800 ° C.
It is necessary to fire at the above high temperature. Sintering aid
Y _TwoO_ThreeAnd CaO in combination at a temperature of about 1700 ° C
It has been proposed to calcinate in JP-A-61-117160
No), but the thermal conductivity is not enough.

In addition, sintering additives Y ₂ O ₃ and LaB ₆
It has been proposed to use a combination of CaO and LaB ₆ as sintering aids (Japanese Patent Laid-Open No. 197366/1991). In this case, the thermal conductivity is sufficient, but a high firing temperature of 1900 ° C. is required. When the firing temperature is high, problems such as an increase in energy cost (running cost) arise.

[0005] In addition, when the firing temperature is high, there is a disadvantage that jigs and equipment such as setters required in the firing step are limited to expensive materials. On the other hand, the obtained aluminum nitride substrate is an optimal substrate for use in a power module.
Since it is preferable that the thermal conductivity is not less than / mK, the utility increases if this is possible.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a method capable of obtaining an aluminum nitride sintered body having a high thermal conductivity at a low firing temperature.

[0007]

Means for Solving the Problems To solve the above problems,
The method for producing the aluminum nitride sintered body according to the present invention
The method is to add a sintering aid to aluminum nitride powder and mold it.
By firing in a non-oxidizing atmosphere
In manufacturing method of aluminum nitride sintered body to be sintered
The specific surface area of the aluminum nitride powder is 4.0 m^Two
/ M over 8.0m ^Two/ G or less (flat surface determined from specific surface area)
(Equivalent particle size is 0.23 μm or more and 0.46 μm or less)
And the following sintering agents a and b are
Use in the form of a combination with
The firing in a non-oxidizing atmosphere is performed at a temperature of 1640 ° C. or less.
I am trying to do it.

"Sintering aid a": rare earth oxide, and
At least one member of the rare earth compound group consisting of compounds that become rare earth oxides by firing is added in a range of 0.5 to 10% by weight based on 100% by weight of the entire sintered body (rare earth oxides by firing) "Sintering aid b": at least one member of the group consisting of alkaline earth oxides and alkaline earth compounds consisting of compounds that become alkaline earth oxides upon firing. The whole sintered body 1
In the present invention, the following sintering agent c is added as a sintering aid in the range of 0.1 to 10% by weight in the range of 0.1 to 10% by weight. The form used in combination with the above sintering agents a and b in the following range of the addition amount is highly useful.

"Sintering aid c": LaB ₆ is added in the range of 0.05 to 3% by weight based on 100% by weight of the whole sintered body (a compound which becomes a rare earth oxide upon firing is converted to an oxide. Further, in the present invention, firing in a non-oxidizing atmosphere is performed at a temperature of 1625 ° C. or lower, or an aluminum nitride powder having an oxygen content of 1.8% by weight or less (hereinafter, referred to as
Use of “AlN powder”) is also highly useful.

Hereinafter, the present invention will be described more specifically. In the method for manufacturing an aluminum nitride sintered body, it is very useful to reduce the particle size of the AlN powder in terms of obtaining a dense sintered body by firing at a low temperature, but the specific surface area is 10.0 to 14. An AlN powder of 0 m ² / g or more enables densification at a temperature of 1600 ° C. or less. However, as the particle size of the AlN powder becomes smaller, the oxygen content increases, and the specific surface area obtained by the ordinary reduction nitriding method is 10.0 m ² /
With AlN powder of g or more, the oxygen content exceeds 1.8% by weight. The specific surface area obtained by another method is 10.0
AlN powder of m ² / g or more does not have an oxygen content of about 1.5% by weight, but such an AlN powder does not have a stable oxide layer on the surface. It is easy to deteriorate to a poor storage stage, and it is difficult to maintain the initial low oxygen content until the actual sintering stage.

According to the present invention, in order to properly suppress the content of the above-described impurity oxygen, a certain degree of particle size is ensured with respect to the AlN powder. They are trying to make up for it. That is, as a result of intensive studies, the inventors found that the specific surface area was 4.0.
0.5 to 10% by weight of sintering agent a and 0.1 to 10% by weight of sintering agent b based on AlN powder of m ² / g or more and 8.0 m ² / g or less.
When used together in the range of 10% by weight, it can be densely fired at a low temperature of 1640 ° C. or
The inventors have found that an aluminum nitride sintered body having a high thermal conductivity of not less than W / mK and further 130 W / mK can be obtained, thereby completing the above invention.

If the specific surface area of the AlN powder exceeds 8.0 m ² / g, the oxygen content becomes 2.0% by weight or more, and it becomes difficult to increase the thermal conductivity by firing at a low temperature. Those having a surface area of less than 8.0 m ² / g and an oxygen content of 1.8% by weight or less are preferred. As the AlN powder, one produced by a reductive nitridation reaction method is usually used. Some are produced by a method other than the reductive nitridation reaction method and have a specific surface area of 4.0 m ² / g or more and a very small amount of oxygen content. However, they lack stability and are deteriorated during the production process. The oxygen content is about the same as the AlN powder produced by the method. In order to prevent deterioration during the manufacturing process, handling with an inert gas can be considered, but this is not practical.

The inventors have also found that a higher thermal conductivity can be achieved by using a sintering agent (lanthanum boride = LaB ₆ ) c in combination with the sintering agents a and b. The thermal conductivity increases as the amount of LaB ₆ increases, but if it exceeds 3% by weight, the sinterability tends to decrease. Therefore, the amount of LaB ₆ added is closely related to the specific surface area of the AlN powder used, that is, the oxygen content. In the case of AlN powder having a small specific surface area and relatively low sinterability but a low oxygen content and relatively good thermal conductivity, the amount of LaB ₆ added is reduced. Conversely, in the case of AlN powder having a large specific surface area and relatively good sinterability, but having a high oxygen content and not so good in terms of thermal conductivity, La is used to secure thermal conductivity.
Increasing the addition amount of B _6.

The rare earth elements in the rare earth compound of the sintering aid a include Y, La, Dy, Er, Ce, Sm, N
Examples thereof include d, Gd, Pr, Ho, and Yb, and Y and La are particularly preferable. When using the sintering aid a, a plurality of rare earth oxides are used in combination, or a plurality of compounds that become a rare earth oxide when fired are used in combination, or a rare earth oxide and a rare earth oxide become fired. You may make it use together with a compound. Compounds that become rare earth oxides upon firing include those in the form of carbonates, nitrates, hydroxides, oxalates, and the like.

Examples of the alkaline earth element in the alkaline earth compound of the sintering aid b include Mg, Ca, Sr, and Ba, with Ca being particularly preferred. When using the sintering aid b, a plurality of alkaline earth oxides may be used in combination, a plurality of compounds which become alkaline earth oxides by firing may be used in combination, or an alkaline earth oxide may be used by firing together with the alkaline earth oxides. A compound that becomes an oxide may be used in combination. Examples of the compound which becomes an alkaline earth oxide upon firing include those in the form of a carbonate, a nitrate, a hydroxide, and an oxalate.

LaB ₆ which is a sintering aid c has a purity of 9%.
It is preferably 9.9% or more, and the particle size is preferably less than 10 μm in order to uniformly disperse with the aluminum nitride powder. The calcination is performed in a temperature range of 1500 to 1640 ° C. (preferably 1625 ° C. or less) for about 3 to 6 hours. The firing atmosphere is a non-oxidizing atmosphere. Examples of the atmosphere include an inert gas atmosphere such as N ₂ and Ar, a reducing gas atmosphere such as H ₂ , and a mixed gas atmosphere of an inert gas and a reducing gas.

[0017]

According to the present invention, the sinterability of AlN powder having a specific surface area of not less than 4.0 m ² / g and not more than 8.0 m ² / g and having a low oxygen content can be adjusted by sintering agents a and b in appropriate amounts. By supplementing them together, it becomes possible to obtain a dense aluminum nitride sintered body having a high thermal conductivity of 120 W / mK or more by firing at a low temperature of 1640 ° C. or less and further at a temperature of 1625 ° C. or less.

When LaB ₆ was added, a reaction product was formed between certain aluminum oxides present on the surface layer of the AlN powder and rare earth oxides and alkaline earth oxides of the sintering aid, LaB ₆ . Certain low-melting substances among composite oxides (although the details of the compound that forms the liquid phase are unknown) have the effect of promoting sintering and trap impurity oxygen that has a negative effect on the thermal conductivity of the system. It is considered that this has the effect of removing from the grain boundary phase that acts as a barrier for thermal conductivity.

In addition to the sintering aid, AlN
By setting the specific surface area of the powder to 4.0 m ² / g or more, Al
The activation due to the increase in the surface energy of the N powder acts synergistically to promote densification at a temperature lower than the conventional sintering temperature, and at the same time, to achieve high thermal conductivity. When LaB ₆ is used in combination with the sintering aid, it becomes easier to obtain an aluminum nitride sintered body having high thermal conductivity.

The low-temperature firing at 1640 ° C. or lower not only reduces the energy cost, but also enables a longer life of the expensive h-BN setter required in the firing step, and a low cost alternative to h-BN. Oxide (eg, alumina) -based materials can be used, and the structure of the firing furnace (such as the material of the heat insulating material) can be changed to inexpensive materials. A large reduction can be achieved. These reduction effects are remarkable when the firing temperature is 1625 ° C. or lower.

The oxygen content of the aluminum nitride powder is 1.
When the content is 8% by weight or less, it becomes easy to obtain an aluminum nitride sintered body having a high thermal conductivity.

[0022]

Embodiments of the present invention will be described below. The present invention is not limited to the following embodiments. Example 1 The following sintering aid was added to AlN powder having a specific surface area of 5.0 m ² / g and an oxygen content of 1.25% by weight, and mixed with a ball mill using isopropyl alcohol as a solvent.

“Sintering aid a”: Y ₂ O ₃ , addition amount of 2.0% by weight “Sintering aid b”: CaCO ₃ , (in terms of CaO) 0.5
Wt% of the added amount "sintering aid c": LaB _6, after the mixed powder obtained amount of 0.1 wt%, was molded to a diameter 20 mm, disc-shaped height 10 mm, 1.5 ton / The rubber was pressed at a pressure of ² cm ² , stored in a BN container, and fired under normal pressure at a temperature of 1600 ° C. for 4 hours in a non-oxidizing atmosphere containing nitrogen.
An aluminum nitride sintered body was obtained.

Example 2 An aluminum nitride sintered body was obtained in the same manner as in Example 1, except that the addition amount of LaB _{6 as} the sintering aid c was 0.20% by weight. Example 3 An aluminum nitride sintered body was obtained in the same manner as in Example 1, except that the amount of LaB ₆ added to the sintering aid c was 0.30% by weight.

Example 4 An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that the amount of LaB ₆ added to the sintering aid c was 0.40% by weight. Example 5 Example 1 was repeated except that the amount of LaB ₆ added to the sintering aid c was 0.50% by weight and the firing temperature was 1620 ° C.
In the same manner as in the above, an aluminum nitride sintered body was obtained.

Example 6 The specific surface area of the AlN powder was 4.5 m ² / g, the oxygen content was 1.10% by weight, and LaB of the sintering aid c was used.
An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that ₆ was not added. -Example 7- The specific surface area of the AlN powder is 6.5 m ² / g, the oxygen content is 1.40% by weight, and the following sintering aids a to
An aluminum nitride sintered body was obtained in the same manner as in Example 1, except that c was added and normal pressure firing was performed at a temperature of 1580 ° C. for 4 hours.

“Sintering aid a”: Y ₂ O ₃ , addition amount of 2.0% by weight “Sintering aid b”: CaCO ₃ , (in terms of CaO) 0.4
Wt% of the added amount "sintering aid c": LaB _6, 0.6 wt% of the added amount - a specific surface area of 8.0 m ² / g of Example 8- AlN powder, oxygen content 1 .75% by weight and the following sintering aids a to
An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that c was added and baking was carried out at 1570 ° C. under normal pressure for 4 hours.

“Sintering aid a”: Y ₂ O ₃ , 3.0 wt% added amount “Sintering aid b”: CaCO ₃ , (in terms of CaO) 0.5
Wt% of the added amount "sintering aid c": LaB _6, the addition amount of 0.5 wt% - a specific surface area in Example 9-AlN powder 4.0 m ² / g, oxygen content 1 0.0% by weight, and the following sintering aids ac:
An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that was added.

“Sintering aid a”: Y ₂ O ₃ , 3.0 wt% added amount “Sintering aid b”: CaCO ₃ , (in terms of CaO) 2.0
Wt% of the added amount "sintering aid c": LaB _6, 0.1 wt% of the added amount - a specific surface area of Example 10- AlN powder 5.5 m ² / g, oxygen content 1 .32% by weight and the following sintering aids a to
An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that c was added.

“Sintering aid a”: Y ₂ O ₃ , addition amount of 5.0% by weight “Sintering aid b”: CaCO ₃ , (in terms of CaO) 1.0
Wt% of the added amount "sintering aid c": LaB _6, 0.8 wt% of the added amount - a specific surface area of Example 11- AlN powder 7.5 m ² / g, oxygen content 1 60% by weight, and the following sintering aids a to c
An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that was added.

“Sintering aid a”: Y ₂ O ₃ , addition amount of 7.0% by weight “Sintering aid b”: CaCO ₃ , (in terms of CaO) 1.0
Wt% of the added amount "sintering aid c": LaB _6, 1.0 wt% of the added amount - a specific surface area of Example 12-AlN powder 4.8 m ² / g, oxygen content 1 Sintering aids a and b
An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that was added.

“Sintering aid a”: Y ₂ O ₃ , addition amount of 1.0% by weight “Sintering aid b”: CaCO ₃ , (in terms of CaO) 1.0
Wt% of the added amount - a specific surface area of Example 13-AlN powder 4.6 m ² / g, 1.15% by weight oxygen content, a to c sintering aid below
An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that was added.

“Sintering aid a”: Y ₂ O ₃ , 3.0 wt% added amount “Sintering aid b”: CaCO ₃ , (in terms of CaO) 2.0
Wt% of the added amount "sintering aid c": LaB _6, addition of 0.5% by weight - a specific surface area of 6.0 m ² / g in Example 14- AlN powder, oxygen content 1 0.3% by weight, and the following sintering aids a to c
And sintered at normal temperature for 4 hours at a temperature of 1620 ° C. for 4 hours to obtain an aluminum nitride sintered body in the same manner as in Example 1.

“Sintering aid a”: Y ₂ O ₃ , 2.0 wt% added amount “Sintering aid a”: La ₂ O ₃ , 1.0 wt% added amount “Sintering aid a” b ": CaCO ₃ , 0.5 (in terms of CaO)
Wt% of the added amount "sintering aid c": LaB _6, 2.0 wt% of the added amount - a specific surface area of Comparative Example 1-AlN powder 3.3 m ² / g, oxygen content 0 0.8% by weight and the following sintering aids a and b
And sintered at normal temperature for 4 hours at a temperature of 1620 ° C. for 4 hours to obtain an aluminum nitride sintered body in the same manner as in Example 1.

“Sintering aid a”: Y ₂ O ₃ , addition amount of 2.0% by weight “Sintering aid b”: CaCO ₃ , 0.5 (in terms of CaO)
Comparative Example 2 The specific surface area of the AlN powder was 3.5 m ² / g, the oxygen content was 1.0 wt%, and the following sintering aids a to c
An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that was added.

“Sintering aid a”: Y ₂ O ₃ , addition amount of 2.0% by weight “Sintering aid b”: CaCO ₃ , (in terms of CaO) 1.0
Wt% of the added amount "sintering aid c": LaB _6, 1.0 wt% of the added amount - the specific surface area of Comparative Example 3- AlN powder is a 3.3 m ² / g, oxygen content 0 0.8% by weight and the following sintering aids ac:
An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that was added.

“Sintering aid a”: Y ₂ O ₃ , addition amount of 1.0% by weight “Sintering aid b”: CaCO ₃ , (in terms of CaO) 2.0
Addition amount by weight “Sintering aid c”: LaB ₆ , addition amount by 0.2% by weight Comparative Example 4 AlN powder having a specific surface area of 9.0 m ² / g and an oxygen content of 2 0.1% by weight, and the following sintering aids a to c
And sintered at normal pressure for 4 hours at a temperature of 1570 ° C. for 4 hours to obtain an aluminum nitride sintered body in the same manner as in Example 1.

“Sintering aid a”: Y ₂ O ₃ , addition amount of 2.0% by weight “Sintering aid b”: CaCO ₃ , (in terms of CaO) 0.4
Addition amount of weight% “Sintering aid c”: LaB ₆ , addition amount of 0.8% by weight Each of the aluminum nitride sintered bodies obtained in Examples and Comparative Examples was reduced to a size of 10 mm in diameter and 3 mm in thickness. After polishing, the relative density was measured, and the thermal conductivity was measured by a laser flash method. Manufacturing conditions and measurement results
The results are shown in Tables 1 and 2.

[0039]

[Table 1]

[0040]

[Table 2]

By comparing the data on the sintered bodies of the examples and comparative examples, the present invention shows that the specific surface area is 4.0 m ² /
g of 8.0 m ² / g or less and sintering aids a and b and c. /
It can be seen that high thermal conductivity aluminum nitride of mK or more can be obtained. In the embodiment,
When using an alumina setter as the setter,
It was also confirmed that the setter could be performed with little loss.

[0042]

In the method for producing an aluminum nitride sintered body according to the present invention, an aluminum nitride powder having an appropriate particle size and an appropriate type of sintering aid such as a rare earth compound and an alkaline earth compound are appropriately added. 1
By firing at a low temperature of 640 ° C. or lower, a dense and high-quality aluminum nitride sintered body having high thermal conductivity can be obtained at low cost, and therefore, the present invention is very useful.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yasufumi Tanaka 1048 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works, Ltd. (56) References JP-A-63-134570 (JP, A) JP-A-63-319265 ( JP, A)

Claims (4)

(57) [Claims] 1. A method for producing an aluminum nitride sintered body, comprising sintering a molded body formed by adding a sintering aid to aluminum nitride powder and firing the molded body in a non-oxidizing atmosphere. Has a specific surface area of 4.
0 m ² / g or more and 8.0 m ² / g or less, and the following sintering agents a and b are used in combination with the following sintering agents in the following ranges of addition amounts and A method for producing an aluminum nitride sintered body, characterized in that firing in an oxidizing atmosphere is performed at a temperature of 1640 ° C. or lower. "Sintering aid a": at least one selected from the group consisting of a rare earth oxide and a compound which becomes a rare earth oxide by the above-mentioned calcination is added to 0.5% of 100% by weight of the whole sintered body. (A compound which becomes a rare earth oxide upon firing is converted to an oxide) "Sintering aid b": an alkaline earth oxide and an alkaline earth oxide upon firing At least one of the alkaline earth compound group consisting of
Add in the range of 0.1 to 10% by weight of 00% by weight (compounds that become alkaline earth oxides by firing are converted to oxides) 2. The method for producing an aluminum nitride sintered body according to claim 1, wherein the following sintering agent c is used in combination with the sintering agents a and b in the following addition amounts as sintering aids. . "Sintering aid c": the LaB _6, the sintered body the entire 100% by weight
Of which are added in the range of 0.05 to 3% by weight (compounds that become rare earth oxides by firing are converted to oxides) 3. The method for producing an aluminum nitride sintered body according to claim 1, wherein firing in a non-oxidizing atmosphere is performed at a temperature of 1625 ° C. or less. 4. The oxygen content of the aluminum nitride powder is as follows:
The method for producing an aluminum nitride sintered body according to any one of claims 1 to 3, wherein the content is 1.8% by weight or less.