JP2001308519A - Aluminum nitride circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum nitride circuit board the mechanical strength of which is improved as a whole by increasing the joining strength between a metallic circuit layer and an aluminum nitride substrate and which hardly causes such a defect as the peeling, blister, etc., of metallic circuit boards. SOLUTION: In this aluminum nitride circuit board 8, the metallic circuit boards 4a and 5a are directly bonded to the surface of the aluminum nitride substrate 2a carrying an aluminum oxide film 3a on its surface. The content of the α aluminum oxide constituting the oxide film 3a is adjusted to >=30 mol%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride circuit board used for a semiconductor device or the like, and more particularly, to increasing the bonding strength between a metal circuit board and an aluminum nitride board to improve the mechanical strength and reliability of the entire circuit board. An improved aluminum nitride circuit board.

[0002]

2. Description of the Related Art Conventionally, a conductive metal circuit board is formed on a surface of a ceramic substrate having excellent insulation properties, such as an alumina (Al ₂ O ₃ ) sintered body, with a brazing material, an adhesive or a metallized metal layer. 2. Description of the Related Art A ceramic circuit board integrally joined has been widely used as a substrate for a power transistor module or a substrate for a switching power supply module.

[0003] However, in the above-mentioned circuit board, since an intervening substance such as a brazing filler metal, an adhesive or a metallized layer exists between the metal circuit board and the ceramic substrate, the thermal resistance between the two becomes large, and the metal circuit board becomes large. There is a problem that it is difficult to quickly radiate heat generated by a semiconductor element or the like provided on the plate to the outside of the system.

In order to solve such problems, in recent years,
A method of directly joining a metal circuit board punched into a predetermined shape on a ceramic substrate and heating it without using the brazing material, adhesive or metallized layer has been studied. This direct joining method is a method of directly joining ceramics and a metal without interposing a joining layer such as a brazing material layer, an adhesive layer, or a metallized layer. In this direct bonding method, a eutectic liquid phase is generated between the metal and a binder (oxygen in the case of copper) present in the metal or on the surface of the metal. The members are directly joined.

FIGS. 3 to 5 are sectional views showing examples of the structure of a conventional ceramic circuit board. As the material of the ceramic substrate, an oxide ceramic sintered body such as alumina (Al ₂ O ₃ ) or ferrite (FeO) or a nitride sintered body such as aluminum nitride (AlN) is used. FIG. 3 shows a copper circuit board 4 containing no oxygen as a binder.
Shows a ceramic circuit board 1 in which is bonded directly to the surface of an Al ₂ O ₃ substrate 2. Note that a surface oxide layer (copper oxide layer) 7 having a predetermined thickness is formed in advance on the surface of the copper circuit board 4 in order to secure an oxygen component for generating a eutectic liquid phase at the time of joining.

In this ceramic circuit board 1, as shown in FIG. 3, a copper circuit board 4 as a metal circuit board is directly joined to the surface side of the Al ₂ O ₃ substrate 2, while a copper as a back copper plate is provided on the back side. Similarly, the circuit board 5 has a structure in which the circuit board 5 is directly joined, and the semiconductor element 6 is integrally joined to a predetermined position of the copper circuit board 4 on the surface side via a solder layer (not shown).

A conventional ceramic circuit board 1a shown in FIG. 4 is a copper circuit board 4a containing oxygen as a binder.
And the back copper plate 5a is directly bonded to the front and back sides of the Al ₂ O ₃ substrate 2, respectively.

The direct bonding method is applicable only to oxide ceramics such as Al ₂ O ₃ .
Aluminum nitride (AlN) substrates and silicon nitride (Si ₃
Even when applied directly to a non-oxide ceramic substrate such as a N ₄ ) substrate, sufficient bonding strength of the metal circuit board cannot be obtained because of low wettability to the substrate.

Therefore, when a non-oxide ceramic substrate is used, it is necessary to form an oxide film on the surface of the substrate in advance to increase the wettability to the substrate. FIG. 5 is a sectional view showing a structural example of a ceramic circuit board 1b using an AlN substrate 2a as a ceramic substrate. In this case, an oxide film (Al ₂ O ₃ film) 3 is formed on the entire surface of the AlN substrate 2a by heating the AlN substrate 2a in an oxidizing atmosphere before the joining operation of the metal circuit boards 4a and 5a. You.

According to the ceramic circuit board in which the metal circuit board is joined to the ceramic substrate by the direct joining method,
Since no brazing material or adhesive layer having high thermal resistance is interposed at the bonding interface, a circuit board having low thermal resistance between both members and excellent heat dissipation can be obtained. In addition, since it has a simple structure, it has advantages that a small size and high mounting can be achieved, and further, the work process can be shortened.

[0011]

However, in each of the conventional ceramic circuit boards formed by the direct bonding method as described above, even if a metal circuit board containing oxygen is used, or a surface oxide film is formed. Even when the formed metal circuit board is used, it has been difficult to bond the metal circuit board and the ceramic substrate with sufficient bonding strength.

In particular, in a conventional aluminum nitride circuit board in which the surface of an aluminum nitride substrate is oxidized and a metal circuit board is directly joined, when an oxide film is formed on the surface of the aluminum nitride circuit board, the film is placed in an oxidizing atmosphere, for example, in the atmosphere. Due to the influence of water vapor and the like contained therein, there was a problem that 80 mol% or more of the crystal structure of the generated oxide film was occupied by γ-alumina (activated alumina). This γ-type
Alumina has a spinel structure containing defects and has poor crystallinity, so when a metal circuit board is directly joined via such an oxide film containing a large amount of γ-alumina,
Bonding strength is reduced. Specifically, the bonding strength expressed by the peel strength of the copper circuit board is 4.5 to 5.5 kgf / cm.
There was a problem that it stayed at a low value.

Further, when the peel strength of the metal circuit board is measured after the direct bonding operation, when the bonded surface is observed, it has been found that the area ratio of the unbonded portion is large and the peel strength is reduced. I have. Further, in the obtained ceramic circuit board, peeling or swelling of the metal circuit board tends to occur starting from the unbonded portion, and in any case, the durability of the circuit board is low, and the production of a semiconductor device using this circuit board is difficult. There has been a problem that the yield and reliability are significantly reduced.

On the other hand, in order to cope with higher integration and higher output of a semiconductor element mounted on a circuit board, conventional alumina (A)
l 2 _{O 3)} high thermal conductivity compared to the ceramic substrate, such as a substrate, heat dissipation is excellent aluminum nitride (Al
N) A circuit board using a substrate is widely used as a mounting circuit board for high-output transistors, power modules, and the like. In this case, the ceramic circuit board on which high-heat-generating components such as high-output transistors are mounted is operated in a thermal cycle in which the temperature changes drastically. receive. In order for the circuit board to operate normally even under such severe conditions, a high joining strength is required at the joint between the ceramic substrate and the metal circuit board.

However, in an aluminum nitride circuit board in which a copper circuit board is directly bonded to the aluminum nitride substrate by the copper direct bonding method (DBC method), particularly, A
An unbonded portion is likely to be generated between the 1N substrate and the copper circuit board, and the bondability and the heat cycle characteristic are inferior to those of the alumina substrate. Also, there is a problem that the bonding strength of the copper circuit board to the actual AlN substrate is significantly reduced as compared with the case where the alumina substrate is used.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and in particular, it has been proposed to improve the mechanical strength of a circuit board as a whole by increasing the bonding strength between a metal circuit layer and an aluminum nitride substrate. An object of the present invention is to provide an aluminum nitride circuit board in which occurrence of defects such as peeling and swelling is small.

[0017]

Means for Solving the Problems In order to achieve the above object, the present inventors have developed a cause of peeling or swelling of a metal circuit board in a conventional aluminum nitride circuit board and an unbonded portion of the metal circuit board. We investigated the cause. As a result, it was found that when the oxide film formed on the aluminum nitride substrate surface was composed of γ-alumina, the bonding strength of the metal circuit board was reduced, and the reliability of the aluminum nitride circuit board was significantly reduced. . On the other hand, in the step of forming an oxide film on the surface of the aluminum nitride substrate, when the AlN substrate is heated to 1000 ° C. or more to form an oxide film having a α-alumina content of a predetermined amount or more, It has been found that when a metal circuit board is directly bonded to an AlN substrate, the bonding strength of the metal circuit board is improved, and the reliability of the AlN circuit board for mounting a semiconductor module can be greatly increased.

The present invention has been completed based on the above findings. That is, the aluminum nitride circuit board according to the present invention is an aluminum nitride circuit board in which a metal circuit board is directly bonded to the surface of an aluminum nitride substrate having an oxide film formed of aluminum oxide formed on the surface. Aluminum content ratio is 30mo
1% or more.

In the above-mentioned aluminum nitride circuit board, the metal circuit board is preferably a copper circuit board. Further, the content of γ-type aluminum oxide in the oxide film is preferably in the range of 10 to 70 mol%. The thickness of the oxide film is preferably in the range of 1 to 5 μm, and more preferably in the range of 2 to 3 μm.

The ceramic substrate constituting the circuit board of the present invention preferably has a thermal conductivity of 70 to 20 in order to secure a high heat radiation required for mounting a high output element.
An aluminum nitride (AlN) substrate of about 0 W / m · K is used. The AlN substrate may contain a sintering aid such as yttrium oxide.

The oxide film formed on the surface of the AlN substrate is indispensable for enhancing the wettability of the AlN substrate and enabling direct joining of the metal circuit board. Particularly, the oxide film in the present invention constitutes the oxide film. The content ratio of α-type aluminum oxide (α-alumina) is 30 mol% or more.

The α-alumina is made of corundum or the like, has a crystal structure close to a hexagonal close-packed lattice, and has a small lattice constant of 5.14 angstroms. And has a stable crystal structure. Therefore, when the metal circuit board is directly bonded to the AlN substrate via the oxide film containing a predetermined amount of α-alumina, the bonding strength (peeling strength) of the metal circuit board can be increased.

If the content of the α-alumina constituting the oxide film is too small, less than 30 mol%, the effect of improving the bonding strength of the metal circuit board is small. Therefore, α
The content of the mold-alumina is in a range of 30 mol% or more, and more preferably in a range of 50 mol% or more.

The content of γ-alumina in the oxide film is preferably in the range of 10 to 70 mol%. Γ-alumina mainly composed of activated alumina is slightly softer than hard α-alumina and contains some fine bubbles, so it is easy to inhibit heat conduction,
It is also a component that can exhibit a buffering effect that can reduce impact.
Therefore, a predetermined amount of α-alumina and a predetermined amount of γ-
By coexisting alumina and the oxide film, a synergistic effect of increasing the bonding strength of the metal circuit board and increasing the mechanical characteristics of the circuit board can be obtained.

Further, since the impact can be reduced, the stress at the time of bonding the aluminum nitride substrate and the metal circuit board can also be reduced, thereby reducing bonding defects such as substrate cracking and metal circuit board distortion generated at the time of bonding. Is also possible.

That is, while the bonding strength of the metal circuit board is increased by the action of α-alumina, the thermal stress and deformation caused by the difference in thermal expansion between the AlN substrate and the metal circuit board are reduced.
The metal circuit board is less likely to peel off due to thermal cycling because it is absorbed by the soft γ-alumina bubbles. If the content of the γ-alumina is less than 10 mol%, the buffer effect is insufficient.
On the other hand, if the content exceeds 70 mol%, good thermal conductivity of the AlN substrate is impaired. Therefore, the content ratio of γ-type alumina in the oxide film is 10 to 7
The range is 0 mol%, but the range of 20 to 50 mol% is more preferable.

The metal constituting the metal circuit board includes:
Although it is not particularly limited as long as it is a metal that can form a eutectic compound with a substrate component and can be directly bonded, such as a simple substance of copper, aluminum, iron, nickel, chromium, silver, molybdenum, and cobalt, or an alloy thereof, Copper, aluminum or an alloy thereof is preferred from the viewpoints of properties and cost.

The thickness of the metal circuit board is determined in consideration of the current carrying capacity and the like.
If the thickness of the metal circuit board is set in the range of 0.1 to 0.5 mm while the thickness is set in the range of 5 to 1.5 mm and the two are combined, the metal circuit board is less susceptible to deformation or the like due to a difference in thermal expansion.

In particular, when a copper circuit board is used as a metal circuit board, a copper circuit board made of tough pitch electrolytic copper containing 100 to 1000 ppm of oxygen is used. By forming the copper oxide layer in advance, the amount of Cu—O eutectic generated at the time of direct bonding can be increased, and the bonding strength between the substrate and the copper circuit board can be further improved.

The surface oxide layer such as the above-mentioned copper oxide layer is formed, for example, by performing a surface oxidation treatment in which a metal circuit board is heated in the atmosphere at a temperature of 150 to 360 ° C. for 20 to 120 seconds. Here, if the thickness of the copper oxide layer is less than 1 μm, the amount of Cu—O eutectic generated is small, so the unbonded portion between the substrate and the copper circuit board increases, and sufficient bonding strength can be obtained. Absent. On the other hand, when the thickness of the copper oxide layer is 10
Even if the thickness exceeds μm, the effect of improving the bonding strength is small and the conductive characteristics of the copper circuit board are rather hindered. Therefore, the thickness of the copper oxide layer formed on the surface of the copper circuit board is preferably in the range of 1 to 10 μm. And for the same reason, the range of 2 to 5 μm is more desirable.

Also, the bonding strength tends to be higher when the aluminum nitride substrate has a rough surface than when the surface is smooth. Note that in the oxidation treatment, the surface roughness of the aluminum nitride substrate can be increased by increasing the heating temperature or increasing the treatment time. The surface roughness of the aluminum nitride substrate after the surface oxidation treatment is preferably such that the center line average roughness (Ra) is in the range of 5 to 10 μm. If necessary, the surface roughness may be adjusted by honing the surface of the aluminum nitride substrate.

The direct bonding method can be applied only to an oxide-based ceramic substrate such as Al ₂ O _3. Even if the direct bonding method is applied to a non-oxide-based ceramic substrate such as aluminum nitride or silicon nitride as it is, the direct bonding method can be applied to the substrate. Owing to the low bonding strength, sufficient bonding strength of the metal circuit board cannot be obtained.

Therefore, when an aluminum nitride (AlN) substrate is used as the ceramic substrate as in the present invention, it is necessary to form an oxide film on the surface of the AlN substrate in advance to increase the wettability to the substrate. This oxide film is formed on the AlN substrate in an oxidizing atmosphere such as air at a temperature of 100.
5 hours or more at about 0 to 1250 ° C., preferably 10 to 2 hours
It is formed by heating for 5 hours. The thickness of this oxide film is 1 μm
If less than, the effect of improving the wettability is small,
Since the improvement effect is saturated even if the oxide layer is formed thicker than 5 μm, the thickness of the oxide layer needs to be in the range of 1 to 5 μm, and more preferably in the range of 2 to 3 μm.

The heating time is less than 5 hours, for example,
In about 2 hours, the content of α-type aluminum oxide is 30 m
% or less, that is, the amount of γ-type aluminum oxide is 70 m
Only an aluminum oxide film with many defects exceeding ol% can be obtained. On the other hand, a long-time oxidation treatment exceeding 25 hours is not preferable because the thickness of the aluminum oxide film easily exceeds 5 μm.

Further, by setting the heating time to 5 hours or more, even in a normal atmosphere containing a small amount of water vapor (for example, 3 vol% or less) or a nitrogen atmosphere containing 15 to 30 vol% of oxygen, good results can be obtained. An aluminum oxide film is obtained. Therefore, for example, it is not necessary to always perform a special treatment for preparing dry air.

The aluminum nitride circuit board according to the present invention is manufactured by directly bonding the metal circuit board to the surface of the AlN substrate on which the oxide film has been formed as described above.

Here, the metal circuit board is directly and integrally bonded to the AlN substrate surface without using a bonding agent such as a brazing material. That is, a eutectic compound (eutectic melt) of a component of a metal circuit board and a substrate component is generated by heating, and the two members are joined using the eutectic compound as a joining agent, that is, a so-called direct joining method is used. Is done.

When the metal circuit board is a copper circuit board, the joining operation is performed as follows. That is, in a state where a copper circuit board is in contact with a predetermined position on the surface of an AlN substrate on which an oxide film is formed and pressed toward the substrate, the eutectic temperature of copper-copper oxide (1065 ° C.)
° C) or higher, and the copper circuit board is directly bonded to the AlN substrate surface using the generated Cu-O eutectic compound liquid phase (eutectic melt) as a bonding agent. This direct bonding method is a so-called copper direct bonding method (DBC: Direct Bonding).
Copper method).

On the other hand, when the metal circuit board is an aluminum circuit board, Si is selected as a binder, and the aluminum circuit board is heated to a temperature higher than the eutectic temperature of aluminum-silicon while pressing the Al circuit board against the AlN substrate surface. The Al circuit board is directly bonded to the surface of the ceramic substrate using the formed Al-Si eutectic compound liquid phase (eutectic melt) as a bonding agent.
An N circuit board is manufactured.

According to the aluminum nitride circuit board of the present invention formed by directly joining the metal circuit board to the AlN substrate surface using the direct joining method, the metal circuit board and the A
Since there is no inclusion such as an adhesive or a brazing material between the substrate and the 1N substrate, the thermal resistance between the two is small, and the heat generated by the semiconductor elements provided on the metal circuit board is quickly dissipated out of the system. It is possible to do.

According to the aluminum nitride circuit board of the present invention, since the content of α-type aluminum oxide in the oxide film formed on the surface of the aluminum nitride substrate is 30 mol% or more, the bonding property between the substrate and the metal circuit board is improved. Is improved. That is, the unjoined portion between the aluminum nitride substrate and the metal circuit board is reduced, and the joining strength between the two members can be greatly increased. Further, peeling and swelling of the metal circuit board due to the unjoined portion can be effectively prevented, and it becomes possible to mass-produce a semiconductor device using this circuit board with a high production yield.

Further, since the bonding strength of the metal circuit board is high,
It is possible to provide a semiconductor device in which a circuit layer is less likely to be peeled off or cracks are not generated in a substrate due to a heat cycle, heat resistance cycle characteristics are remarkably improved, and durability and reliability are excellent.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be specifically described with reference to the following examples.

Examples 1 to 9 and Comparative Examples 1 to 3 With respect to aluminum nitride powder having an average particle diameter of 1 μm, 3% by weight of yttrium oxide (Y ₂ O ₃ ) as a sintering aid was used.
And 5% by weight of an organic binder, 0.4% by weight of a dispersant and ethanol as a solvent, and uniformly mixed to prepare a raw material mixture. Next, the raw material mixture was subjected to a doctor blade method. The resultant is heated at 700 ° C. for 2 hours and degreased, and then heated in a nitrogen / reducing atmosphere at a temperature of 1800 ° C. for 3 hours to have a thermal conductivity of 170 W / m.・ It is K, length 55mm ×
37 mm wide x 0.8 mm thick aluminum nitride (Al
N) Many substrates were prepared. Next, by heating each AlN substrate in a heating furnace in an air atmosphere at the temperature and time shown in Table 1, the entire surface of the substrate was oxidized, and an oxide film (Al ₂ O ₃ film) having a thickness shown in Table 1 was obtained. Was formed respectively.

For each oxide film formed as described above, X
The crystal structure was identified by the X-ray diffraction (XRD) method, and the ratio of each aluminum oxide constituting the oxide film was measured. The results shown in Table 1 were obtained.

On the other hand, a number of copper circuit boards made of tough pitch electrolytic copper having a thickness of 0.3 mm and 0.25 mm containing 407 ppm of oxygen were prepared.

Next, a copper circuit board made of tough pitch electrolytic copper having a thickness of 0.3 mm is placed in contact with the surface side of each AlN substrate on which an oxide film is formed, while a copper circuit board made of tough pitch copper having a thickness of 0.25 mm is formed on the back side. The copper circuit board thus formed is placed in contact with a backing material to form a laminate, and the laminate is inserted into a heating furnace set at a temperature of 1075 ° C. adjusted to a nitrogen gas atmosphere and heated for 1 minute, whereby each AlN substrate Aluminum nitride circuit boards according to Examples and Comparative Examples in which copper circuit boards were directly bonded to both surfaces were prepared. In the circuit board of Comparative Example 3, the atmosphere of the oxidation treatment was dry air substantially free of water vapor, and the oxidation treatment was performed thereafter.

Each aluminum nitride circuit board 8 is shown in FIGS.
As shown in FIG. 2, an oxide film 3a is formed on the entire surface of the AlN substrate 2a, and a copper circuit board 4a as a metal circuit board is directly bonded to the front side of the AlN substrate 2a, while a back copper plate is formed on the back side. Similarly, the copper circuit board 5a is directly joined, and further, the semiconductor element is integrally joined at a predetermined position on the surface side copper circuit board 4a via a solder layer (not shown). When the copper circuit boards 4a and 5a are joined to both sides of the AlN substrate 2a, the copper circuit board 5a as the back copper plate is effective because it contributes to promoting heat radiation and preventing warpage.

For each of the circuit boards according to the examples and the comparative examples prepared as described above, the Al
The bending strength of the N substrate was measured, and the results shown in Table 1 were obtained.
In addition, to evaluate the strength characteristics of each circuit board, the average value of the peel strength of each copper circuit board was measured, and a photograph of the peeled surface of the copper circuit board after this peel strength measurement was taken.
The area ratio of the joined portion excluding the unjoined portion remaining as a white portion on the photograph was measured by image analysis. Table 1 below shows the measurement results.
Shown in

[0050]

[Table 1]

As is clear from the results shown in Table 1 above,
According to each embodiment, after adjusting the content ratio of α-type alumina in the oxide film formed on the AlN substrate surface to 30 mol% or more to increase the α-rate, the copper circuit board is directly joined to the AlN substrate surface. According to the aluminum nitride circuit board, the above α
Compared with the circuit boards of Comparative Examples 1 to 3 having a low conversion ratio, the area ratio of the joint between the copper circuit board and the aluminum nitride substrate is large, the joining strength can be improved, and the peel strength can be increased by about 10%. It could be confirmed.

Next, the aluminum nitride circuit boards of Examples 1 to 9 and Comparative Examples 1 to 3 were treated at -40 ° C. for 30 minutes.
A thermal cycle test (TCT test) in which a thermal cycle of room temperature × 10 minutes → 125 ° C. × 30 minutes → room temperature × 10 minutes was repeated was performed.

In the circuit board of the embodiment, the number of cycles until a crack (crack) is confirmed on the aluminum nitride substrate is eight.
0 to 100, whereas in Comparative Examples,
~ 60 was inferior. The reason for this is that in Comparative Examples 1 and 2, the oxide film is too thin or too thick, and furthermore, the peel strength is low. It is considered that Comparative Example 3 has a high peel strength but a small amount of γ-type aluminum oxide in the aluminum oxide film, so that the effect of relaxing the thermal stress is small.

[0054]

As described above, according to the aluminum nitride circuit board of the present invention, the content of the α-type aluminum oxide in the oxide film formed on the surface of the aluminum nitride substrate is 30 mol% or more. The bondability with the metal circuit board is improved. That is, the unjoined portion between the aluminum nitride substrate and the metal circuit board is reduced, and the joining strength between the two members can be greatly increased. Further, peeling and swelling of the metal circuit board due to the unjoined portion can be effectively prevented, and it becomes possible to mass-produce a semiconductor device using this circuit board with a high production yield.

Also, since the bonding strength of the metal circuit board is high,
It is possible to provide a semiconductor device in which a circuit layer is less likely to be peeled off or cracks are not generated in a substrate due to a heat cycle, heat resistance cycle characteristics are remarkably improved, and durability and reliability are excellent.

[Brief description of the drawings]

FIG. 1 is a plan view showing one embodiment of an AlN circuit board according to the present invention.

FIG. 2 is a sectional view of the AlN circuit board shown in FIG.

FIG. 3 is a cross-sectional view illustrating a structural example of a conventional ceramic circuit board.

FIG. 4 is a sectional view showing a structural example of a conventional ceramic circuit board.

FIG. 5 is a sectional view showing another example of the structure of a conventional ceramic circuit board.

[Explanation of symbols]

1, 1a, 1b Ceramic circuit board 2, 2a Ceramic substrate (Al ₂ O ₃ substrate, AlN
Substrate) 3,3a Oxide film (Al ₂ O ₃ film) 4,4a Metal circuit board (copper circuit board) 5,5a Copper circuit board (copper board) 6 Semiconductor element 7 Surface oxide layer (copper oxide layer) 8 AlN circuit substrate

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H01L 25/18

Claims (5)

[Claims] 1. An aluminum nitride circuit board in which a metal circuit board is directly bonded to the surface of an aluminum nitride substrate having an oxide film made of aluminum oxide formed on the surface, the content ratio of the α-type aluminum oxide forming the oxide film is 3
An aluminum nitride circuit board characterized by being at least 0 mol%. 2. The aluminum nitride circuit board according to claim 1, wherein the metal circuit board is a copper circuit board. 3. The aluminum nitride circuit board according to claim 1, wherein the content of γ-type aluminum oxide in the oxide film is in the range of 10 to 70 mol%. 4. The aluminum nitride circuit board according to claim 1, wherein the thickness of the oxide film is in a range of 1 to 5 μm. 5. The aluminum nitride circuit board according to claim 1, wherein the thickness of the oxide film is in the range of 2 to 3 μm.