JPH04209767A - Production of aluminum nitride substrate - Google Patents

Abstract

PURPOSE:To improve the bonding strength between an aluminum nitride substrate and a copper plate by forming the thin film of an oxide selected from Al2O3, Y2O3 and Sin. on the surface of the aluminum nitride substrate, superposing a copper plate on the formed thin film, and subsequently heating at a prescribed temperature. CONSTITUTION:The thin film (having a thickness of 0.3-3.0mum) 2 of an oxide selected from Al2O3, Y2O3 and SiO2 is formed on the surface of an aluminum nitride substrate 1 preliminarily boiling-washed. The thin film 2 is subjected to an oxidation treatment at approximately 300 deg.C for 10min in air, and brought into contact with a copper plate 3 having a copper oxide layer 4 formed on a surface thereof, and heated at a temperature of from the eutectic temperature between both the copper and the copper oxide to 1068-1075 deg.C which are below the melting point of the copper to form an eutectic layer 5 between the substrate 1 and the copper plate 3, thereby both the substrate 1 and the copper plate 3 are strongly combined with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing an aluminum nitride substrate used as an electronic circuit board.

[Prior art and problems to be solved by the invention] Generally,
Aluminum nitride is known to have excellent thermal conductivity, and has conventionally been used for electronic circuit boards and the like on which chips that generate a large amount of heat are mounted. However, since aluminum nitride substrates have poor wettability with metals, it has been difficult to form circuit patterns by directly metallizing the surface with copper, for example.

In order to solve this problem, Japanese Patent Application Laid-Open No. 59-40404 discloses that aluminum nitride is heated in air to form an oxide layer on its surface, and then tough pitch electrolytic copper plates are stacked on top of each other and heat treated. discloses a method for manufacturing an aluminum nitride substrate in which a copper plate is bonded to an aluminum nitride substrate.

However, since the method described above forcibly oxidizes the aluminum nitride surface by heating in air, the smoothness of the bonding surface with the copper plate, that is, the surface of the oxide layer is reduced. Therefore, during thermal bonding, it is difficult to overlay the oxide layer on aluminum nitride and the copper plate in reliable contact with each other, and a eutectic consisting of copper and copper oxide is formed at the bonding area to prevent wetness. Even if the two are joined together with improved sex,
The bond strength obtained was not satisfactory.

Further, the above-mentioned thermal bonding treatment attempts to supply oxygen required for forming a eutectic between copper oxide and copper from the oxide layer on the aluminum nitride. Therefore, it is inevitably necessary to form a thick oxide layer on aluminum nitride, and there is a risk that the original properties of aluminum nitride, such as excellent thermal conductivity, may be impaired.

Furthermore, JP-A No. 59-40404 discloses an aluminum nitride substrate in which a tough pitch electrolytic copper plate is superimposed on aluminum nitride containing a copper plate and aluminum nitride with a binder added in the form of an oxide, and then heat treated. A method of manufacturing is also disclosed.

However, in order to supply sufficient oxygen involved in eutectic formation, it is necessary to add more oxide (a binder) to aluminum nitride. There was a problem in that the original properties of aluminum nitride were easily impaired.

In view of the above points, the present inventors have conducted various studies, and as a result,
AIt on the surface of the aluminum nitride base material.

By forming a thin film of one oxide selected from $, YtOs, and 5ift, overlaying a copper plate on the oxide thin film, and heating it to a temperature above the eutectic temperature of copper and copper oxide and below the melting point of copper. discovered that by bonding a copper plate to an aluminum nitride base material through the thin film described above, it is possible to firmly bond the copper plate without impairing the original properties of the aluminum nitride base material, such as excellent thermal conductivity. Ta.

The present invention was made based on the above findings, and
The purpose of this is to improve the wettability of the aluminum nitride base material to copper without impairing its thermophilic conductivity, thereby making it possible to bond copper plates easily and reliably, and to maintain sufficient bonding strength between the two. It is an object of the present invention to provide a method for manufacturing an aluminum nitride substrate that can secure the aluminum nitride substrate.

[Means and effects for solving the problem] In order to achieve the above object, the present invention provides an aluminum nitride base material with A
l t Os , Yt O3 and Sin! a step of forming a thin film of one oxide selected from the above, a step of superimposing a copper plate on the oxide thin film, and a step of heating to a temperature above the eutectic temperature of copper and copper oxide and below the melting point of copper. It consists of a step of joining a copper plate to an aluminum nitride base material through a thin film.

After forming a thin film of one oxide selected from AIt03, YtOs, and Sing on the surface of the aluminum nitride base material, a copper plate is placed on top of the other to remove the oxygen required for eutectic formation between copper oxide and copper. , can be reliably supplied to the joint surfaces of both. Then, when both are heated to a temperature above the eutectic temperature of copper and copper oxide and below the melting point of copper, a eutectic containing copper, copper oxide, oxide, and aluminum nitride is formed at the joint between the aluminum nitride base material and the copper plate. is formed.

In this case, since the oxygen required for eutectic formation is mainly supplied from the thin film of the oxide, the eutectic is formed more efficiently than in the past, and a strong bond is therefore ensured between the two.

The oxide thin film formed on the surface of the aluminum nitride base material is preferably one oxide selected from Al t Oa, YtOs, and SiO2, and these are generally used when firing the aluminum nitride base material. This is a known sintering aid that is added.

The thin film is preferably formed by plasma spraying.

This method is a commonly used method and can easily and reliably form a thin film at low temperatures. Further, since the aluminum nitride substrate itself is not exposed to high temperatures, it is not decomposed. Other methods such as sputtering, chemical plating, and paste coating can also be used.
Although it is possible to ultimately obtain the desired bond between the copper plate and aluminum nitride, plasma spraying is preferable because a more uniform and smooth oxide thin film can be obtained and high temperatures are not required during formation.

The thickness of the oxide thin film is preferably 0.3 to 3.0 μm.

When the thickness of the oxide thin film is 0.3 μm or less, oxygen necessary for bonding cannot be supplied from the thin film. On the other hand, if the thickness exceeds 3.0 μm, the formed thin film is likely to peel off.

It is desirable that the copper plate has been subjected to an oxidation treatment in advance. This oxidation treatment is carried out in air at approximately 300°C for 10
It is desirable that the treatment be carried out for a minute, and if the copper plate is treated under these conditions, a copper oxide layer with excellent wettability to aluminum nitride will be formed on the surface of the copper plate.

When the processing temperature is lower than 300° C. and when the processing time is shorter than 10 minutes, oxygen for bonding cannot be supplied because the copper plate is not sufficiently oxidized. On the other hand, even if the treatment temperature is higher than 300° C. and the treatment temperature is longer than 10 minutes, not only the effect on wetting is not significant but also the inherent property of copper, which is good conductivity, is lost due to warping.

The copper plate preferably contains 100 to 20,001) pm of oxygen.

As a material that satisfies the above conditions, for example, tough pitch electrolytic copper containing oxygen is preferable.

In this case, if the oxygen concentration is less than 1100 pp, sufficient oxygen will not be supplied to form a strong bond. Also, 20
Even if it contains more than 0.00 ppm of oxygen, it is not preferable because not only will there be no significant difference in bonding strength, but the significance of using copper, which has good electrical conductivity, will be lost.

The temperature/degree above the eutectic temperature and below the melting point of copper is 1068°C
It is desirable that the temperature is in the range of ~1075°C.

That is, it is necessary to control most of the copper plate to be in a solid state even at the highest temperature.

If the temperature is lower than 1068°C, the formation of eutectic containing copper, copper oxide, oxide, and aluminum nitride at the joint portion between the aluminum nitride base material and the copper plate is insufficient, so that the bond between the two becomes weak. When the temperature exceeds 1075℃, that is, it approaches the melting point of copper, and the copper plate begins to melt, causing copper, copper oxide, and copper to form at the interface.
A eutectic containing oxide and aluminum nitride is not formed.

The bonding process of the copper plates is preferably performed in an inert gas atmosphere containing 1100 pp or less of oxygen, and it is preferable to use nitrogen, argon, helium, or the like as the inert gas.

If the above bonding process is performed in an inert gas atmosphere containing more than LOOppm of oxygen, the copper plate will be excessively oxidized and swell, and a smooth surface will not be formed. However, if this condition is followed, the entire copper plate will not be oxidized even after the bonding process, and copper oxide can be formed only on the bonded portion, and the smoothness of the surface of the copper plate will be maintained.

On the other hand, if the above bonding treatment is performed in a reactive atmosphere, this is not preferable because it requires an additional step of removing the oxide film formed on the surface of the copper plate.

It is preferable that the surface of the aluminum nitride base material is previously subjected to boiling treatment, oxygen plasma treatment, ultraviolet ozone treatment, etc. prior to the formation of the oxide thin film. As a result, impurities adhering to the surface layer of the aluminum nitride base material are removed, and the thin film is formed more reliably.

[Example 1] Next, an example in which the present invention is embodied in an electronic circuit board will be described based on the drawings.

First, as shown in FIG. 1(a), an Al1Os thin film 2 of about 1 μm thickness is formed on the surface of an aluminum nitride base material 1 by plasma spraying.

In this case, prior to forming the Alx0a thin film 2, the surface of the aluminum nitride base material 1 is cleaned by boiling in advance. Next, the copper plate 3 is oxidized in air at about 300° C. for 10 minutes to form a copper oxide layer 4 on the surface. Subsequently, A1101 thin film 2 on aluminum nitride base material 1 and copper plate 3
in contact with the copper oxide layer 4 side in a nitrogen gas atmosphere.
Heat to 72°C (Figure 1(b)).

After a series of these treatments, the specimen was cooled to room temperature and the bonded state was investigated.

As a result, as shown in FIG. 1(C), a eutectic layer 5 is formed between the aluminum nitride base material 1 and the bonded copper plate 3, and due to the presence of this eutectic layer 5, both It was found that they were strongly bonded. In addition, the bonding strength of the aluminum nitride substrate in this example is 10 kgf/mm'',
The thermal conductivity coefficient was very excellent at 180 w/mk.

[Example 2] Next, another example in which the present invention is embodied in an electronic circuit board will be described.

In this example, Al! is applied to the surface of the aluminum nitride base material 1 by plasma spraying. The process of forming the 03 thin film 2 is the same as in Example 1.

In the second embodiment, as shown in FIG. 2, a tough pitch electrolytic copper plate 6 is placed on an aluminum nitride base material 1! 03 thin film 2
and heated to 1072° C. in a nitrogen gas atmosphere. After a series of these treatments, the specimen was cooled to room temperature and the bonded state was investigated.

As a result, a eutectic layer is formed between the aluminum nitride base material l and the tough pitch electrolytic copper plate 6, as in Example 1,
It was found that the two were firmly bonded due to the presence of this eutectic layer. In addition, the bonding strength of the aluminum nitride substrate in this example is 10 kgf/mm'', and the thermal conductivity coefficient is 1.
It was very excellent at 80 w/mk.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but may be modified in the following manner without departing from the spirit of the invention.

(a) Instead of the oxidation treatment of the copper plate 3 by heating in air, which was performed in Example 1, the copper oxide layer 4 may be formed chemically using an oxidizing compound other than oxygen.

(b) In Example 1, only the surface in contact with the aluminum nitride base material 1 is oxidized, but if it is easier to oxidize both sides, it is acceptable to perform the oxidation treatment using that method. do not have.

(c) In Examples 1 and 2, Al was used as the oxide thin film.
Although zOs is used, other oxides such as barium, strontium, yttrium, calcium, and silicon may also be used. Furthermore, two or more of these oxides may be used in combination.

(d) In Examples 1 and 2, the Altos thin film 2 is formed on the surface of the aluminum nitride base material 1, but it may be formed on the copper plate 3 side or the tough pitch electrolytic copper plate 6 side if possible.

[Effects of the Invention] As detailed above, according to the method for manufacturing an aluminum nitride substrate of the present invention, by improving the wettability to copper without impairing the thermophilic conductivity etc. of the aluminum nitride base material, It is possible to provide a method for manufacturing an aluminum nitride substrate, which allows copper plates to be easily and reliably bonded, and which can ensure sufficient bonding strength between the two.

[Brief explanation of the drawing]

1(a) to (C) are schematic diagrams showing a manufacturing process of an aluminum nitride substrate in Example 1, and FIG. 2 is a schematic diagram showing a manufacturing process of an aluminum nitride substrate in Example 2. ■... Aluminum nitride base material, 2... Al5Os thin film, 3... copper plate, 4... copper oxide layer, 6... tough pitch electrolytic copper plate. Patent applicant IBIDEN Co., Ltd.

Claims (4)

[Claims] 1. Al_2O_3, Y on the surface of the aluminum nitride base material
A step of forming a thin film of one oxide selected from _2O_3 and SiO_2, A step of superimposing a copper plate on the oxide thin film, and Heating to a temperature above the eutectic temperature of copper and copper oxide and below the melting point of copper. A method for manufacturing an aluminum nitride substrate comprising the step of bonding a copper plate to an aluminum nitride base material via the thin film. 2. The copper plate may be oxidized in advance, or
The method for manufacturing an aluminum nitride substrate according to claim 1, wherein the aluminum nitride substrate contains 00 to 2000 ppm of oxygen. 3. The temperature above the eutectic temperature and below the melting point of copper is 1068
The method for manufacturing an aluminum nitride substrate according to claim 1, wherein the temperature is in the range of 1075°C. 4. The method for manufacturing an aluminum nitride substrate according to claim 1, wherein the copper plate bonding process is performed in an inert gas atmosphere containing 100 ppm or less of oxygen.