JP3157520B2 - Manufacturing method of aluminum nitride substrate - Google Patents

Description

The present invention relates to a method for manufacturing an aluminum nitride substrate used as an electronic circuit board.

[Problems to be Solved by the Prior Art and the Invention] Generally, aluminum nitride is known to have excellent thermal conductivity, and has conventionally been used as an electronic circuit board for mounting a chip having a large heat value. Have been. However, since the aluminum nitride substrate has poor wettability to metal, it has been difficult to form a circuit pattern by directly metallizing its surface with, for example, copper.

In order to solve this problem, JP-A-59-40404 discloses that aluminum nitride is heated in air, an oxide layer is formed on the surface thereof, and a tough pitch electrolytic copper plate is overlaid and heat treated. Discloses a method of manufacturing an aluminum nitride substrate in which a copper plate is bonded to an aluminum nitride substrate.

However, since the method forcibly oxidizes the aluminum nitride surface by heating in air,
The smoothness of the joint surface with the copper plate, that is, the surface of the oxide layer is reduced.
Therefore, it is difficult to overlap the oxide layer on aluminum nitride and the copper plate in a state of reliable contact during the heat bonding, and a eutectic composed of copper and copper oxide is formed at the bonding portion, and the eutectic is wetted. Even if both were joined in a state where the property was improved, the obtained bonding strength was not satisfactory.

In the above-mentioned heat bonding treatment, oxygen required for forming a eutectic of copper oxide and copper is supplied from an oxide layer on aluminum nitride. Therefore, it is necessary to form a hot oxide layer on aluminum nitride inevitably, and there is a possibility that the intrinsic properties of aluminum nitride, such as excellent thermal conductivity, may be impaired.

Further, JP-A-59-40404 discloses an aluminum nitride substrate in which a tough pitch electrolytic copper plate is superposed on aluminum nitride obtained by adding a binder of a copper plate and aluminum nitride in the form of an oxide, followed by heat treatment. Is also disclosed. However, in order to sufficiently supply oxygen involved in eutectic formation, it is necessary to add more oxide as a binder to aluminum nitride. There is a problem that the original properties of aluminum are easily damaged.

In view of the above points, the present inventors have made various studies and found that Al ₂ O ₃ , Y ₂ O ₃ and SiO ₂ are formed on the surface of the aluminum nitride base material.
Form a thin film of one oxide selected from ₂ , superimpose a copper plate on the thin film of oxide, above the eutectic temperature of copper and copper oxide,
By heating the copper plate to the aluminum nitride substrate via the thin film by heating to a temperature lower than the melting point of copper, the copper plate can be firmly bonded without impairing the original properties of the aluminum nitride base material, which is excellent in thermal conductivity and the like. It has been found that it is possible to combine.

The present invention has been made based on the above findings, and an object of the present invention is to easily and reliably bond a copper plate by improving wettability to copper without impairing the high thermal conductivity of an aluminum nitride base material. It is another object of the present invention to provide a method for manufacturing an aluminum nitride substrate that can ensure sufficient bonding strength between the two.

[Means and Actions for Solving the Problems] In order to achieve the above object, the present invention provides an aluminum nitride substrate having a surface formed of one oxide selected from Al ₂ O ₃ , Y ₂ O ₃ and SiO ₂ . Forming a thin film by plasma spraying,
A step of superimposing a copper plate on the oxide thin film, and a step of joining the copper plate to the aluminum nitride substrate via the thin film by heating to a temperature equal to or higher than the eutectic temperature of copper and copper oxide and lower than the melting point of copper. Consists of

Al ₂ O ₃ , Y ₂ O ₃ and SiO _{2 on} the surface of aluminum nitride substrate
After forming a thin film of one oxide selected from the above, by overlaying copper plates, oxygen required for eutectic formation of copper oxide and copper can be reliably supplied to the joint surface of both it can. Then, when both are heated to a temperature equal to or higher than the eutectic temperature of copper and copper oxide and lower than the melting point of copper, the 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,
Oxygen required for eutectic formation is mainly supplied from the oxide thin film, so that a eutectic is formed more efficiently than in the past, and a strong bond is secured between the two.

The oxygen thin film formed on the surface of the aluminum nitride substrate is desirably an oxide selected from Al ₂ O ₃ , Y ₂ O ₃ and SiO ₂ , and these are generally formed of an aluminum nitride substrate. This is known as a sintering aid added at the time of firing.

The thin film needs to be formed by plasma spraying. This method can easily and reliably form a thin film at a low temperature. Further, the aluminum nitride substrate itself is not exposed to a high temperature, so that it is not decomposed. Other methods such as sputtering, chemical plating and paste application can ultimately obtain the desired bond between the copper plate and aluminum nitride, but a more uniform and smooth oxide thin film is obtained, Plasma spraying is preferred because high temperatures are not required during formation.

It is preferable that the thickness of the oxide thin film is 0.3 to 3.0 μm.

When the thickness of the oxide thin film is 0.3 μm or less,
Oxygen required for bonding cannot be supplied from the thin film.
On the other hand, when it exceeds 3.0 μm, the formed thin film is liable to peel off.

It is desirable that the copper plate has been subjected to an oxidation treatment in advance. This oxidation treatment is desirably performed in air at about 300 ° C. for 10 minutes. If the copper plate is treated under these conditions, a copper oxide layer having excellent wettability to aluminum nitride is 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 processing temperature is higher than 300 ° C. and the processing time is longer than 10 minutes, not only the effect on wetting is not remarkable, but also the inherent properties of copper such as good electrical conductivity are lost.

It is desirable that the copper plate contains oxygen of 100 to 2000 ppm. As a material satisfying the above conditions, for example, tough pitch electrolytic copper containing oxygen is preferable.

In this case, if the oxygen concentration is less than 100 ppm, sufficient oxygen cannot be supplied to form a strong bond. 2000ppm
Is not preferable because not only does the bonding strength not greatly differ, but the significance of using copper having good electrical conductivity is lost.

The temperature above the eutectic temperature and less than the melting point of copper is 1068 ° C to 10 ° C.
It is desirable to be in the range of 75 ° C. That is, it is necessary to control most of the copper plate to a solid state even at the highest temperature.

When the temperature is lower than 1068 ° C., eutectic formation containing copper, copper oxide, oxide, and aluminum nitride at the joint between the aluminum nitride base material and the copper plate is not sufficient, so that the bonding between them is weakened. If it exceeds 1075 ° C., that is, the melting point of copper is approached, and the copper plate begins to melt, so that no eutectic containing copper, copper oxide, oxide and aluminum nitride is formed at the interface.

The bonding treatment of the copper plate is desirably performed in an inert gas atmosphere containing 100 ppm or less of oxygen, and nitrogen, argon, helium, or the like is preferably used as the inert gas.

If the bonding process is performed in an inert gas atmosphere containing oxygen exceeding 100 ppm, the copper plate is excessively oxidized and expands, and a smooth surface is not formed. However, according to this condition, the copper plate as a whole is not oxidized even after the bonding process, copper oxide can be formed only at the bonding portion, and the smoothness of the copper plate surface is maintained.

On the other hand, if the above-mentioned bonding treatment is performed in a reactive atmosphere, a step of removing an oxide film formed on the surface of the copper plate is required, which is not preferable.

It is preferable that the surface of the aluminum nitride base material has been subjected to boiling treatment, oxygen plasma treatment, ultraviolet ozone treatment, or the like before the formation of the oxide thin film. Thereby, the impurities attached to the surface layer of the aluminum nitride base material are removed, and the thin film is more reliably formed.

Embodiment 1 Next, an embodiment in which the present invention is embodied in an electronic circuit board will be described with reference to the drawings.

First, as shown in FIG. 1 (a), an Al ₂ O ₃ thin film 2 was coated on the surface of an aluminum nitride substrate 1 by plasma spraying for about 1 hour.
It is formed to a thickness of about μm.

In this case, before the formation of the Al ₂ O ₃ thin film 2, the surface of the aluminum nitride substrate 1 is cleaned by boiling. Next, the copper plate 3 is oxidized at about 300 ° C. for 10 minutes in the air to form a copper oxide layer 4 on one surface. Subsequently, the Al ₂ O ₃ thin film 2 on the aluminum nitride substrate 1 is brought into contact with the copper oxide layer 4 side of the copper plate 3 and heated to 1072 ° C. in a nitrogen gas atmosphere (FIG. 1 (b)).

After these series of treatments, they were cooled to almost room temperature and the bonding state was examined.

As a result, as shown in FIG. 1 (c), a eutectic layer 5 is formed between the aluminum nitride substrate 1 and the joined copper plate 3, and the eutectic layer 5 Was found to be strongly bonded. Further, the bonding strength of the aluminum nitride substrate of this example was 10 kgf / mm ² , and the thermal conductivity was 180 w / mk, which was very excellent.

Embodiment 2 Next, another embodiment in which the present invention is embodied in an electronic circuit board will be described.

In the present embodiment, the process of forming the Al ₂ O ₃ thin film 2 on the surface of the aluminum nitride base material 1 by plasma spraying is the same as in the first embodiment.

In the second embodiment, as shown in FIG. 2, the tough pitch electrolytic copper plate 6 is brought into contact with the Al ₂ O ₃ thin film 2 on the aluminum nitride substrate 1 and heated to 1072 ° C. in a nitrogen gas atmosphere. After these series of treatments, they were cooled to almost room temperature and the bonding state was examined.

As a result, a eutectic layer is formed between the aluminum nitride base material 1 and the tough pitch electrolytic copper plate 6 in the same manner as in Example 1, and both are firmly joined by the interposition of the eutectic layer. found. Further, the bonding strength of the aluminum nitride substrate of this example was 10 kgf / mm ² , and the thermal conductivity was 180 w / mk, which was very excellent.

It should be noted that the present invention is not limited to the above embodiment, and the following embodiments can be made without departing from the spirit of the invention.

(A) Instead of the oxidation treatment of the copper plate 3 by heating in air performed in the first embodiment, the copper oxide layer 4 may be chemically formed using an oxidizing compound other than oxygen.

(B) In Example 1, the oxidation treatment is performed only on the contact surface with the aluminum nitride base material 1. However, if it is easier to oxidize both surfaces, the oxidation treatment may be performed by that method. Absent.

(C) In Examples 1 and 2, Al was used as the oxide thin film.
_{Although 2} O ₃ is used, for example, an oxide such as barium, strontium, yttrium, calcium, or silicon may be used. Further, two or more of these oxides may be used in combination.

(D) In the first and second embodiments, the Al ₂ O ₃ thin film 2 is formed on the surface of the aluminum nitride substrate 1. If possible, the Al ₂ O ₃ thin film 2 is formed on the copper plate 3 side or the tough pitch electrolytic copper plate 6 side. Is also good.

[Effects of the Invention] As described above in detail, according to the method for manufacturing an aluminum nitride substrate of the present invention, the copper plate is improved by improving the wettability to copper without impairing the high thermal conductivity and the like of the aluminum nitride substrate. Can be easily and reliably bonded, and a method for manufacturing an aluminum nitride substrate capable of securing a sufficient bonding strength between the two can be provided.

[Brief description of the drawings]

1 (a) to 1 (c) are schematic diagrams showing a manufacturing process of an aluminum nitride substrate in Example 1, and FIG. 2 is a schematic diagram showing one manufacturing process of an aluminum nitride substrate in Example 2. 1 ...... aluminum nitride substrate material, 2 ...... Al ₂ O ₃ thin film, 3 ...
... copper plate, 4 ... copper oxide layer, 6 ... tough pitch electrolytic copper plate.

──────────────────────────────────────────────────の Continuing on the front page (51) Int.Cl. ⁷ identification code FI H05K 3/38 H01L 23/14 C (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 37/02 C04B 41 / 90

Claims (4)

(57) [Claims] 1. The method according to claim 1, wherein Al ₂ O ₃ , Y ₂ O
Forming a thin film of one oxide selected from ₃ and SiO ₂ by plasma spraying; laminating a copper plate on the thin film of oxide; and a temperature higher than the eutectic temperature of copper and copper oxide and lower than the melting point of copper. Bonding the copper plate to the aluminum nitride base material through the thin film by heating to a temperature. 2. The method according to claim 2, wherein the copper plate has been previously oxidized.
The method for producing an aluminum nitride substrate according to claim 1, wherein the method contains 100 to 2000 ppm of oxygen. 3. The temperature not lower than the eutectic temperature and lower than the melting point of copper is
The method for producing an aluminum nitride substrate according to claim 1, wherein the temperature is in a range of 1068 ° C to 1075 ° C. 4. The method according to claim 1, wherein the bonding of the copper plate is performed in an inert gas atmosphere containing 100 ppm or less of oxygen.