JPH06128722A - Formation of metallizing layer on aluminum nitride substrate - Google Patents

Abstract

PURPOSE:To provide a method for forming a metallizing layer on an AIN substrate by which the bonding strength of the metallizing layer to the substrate is enhanced and this bonding strength is not deteriorated even when a semiconductor chip mounted on the substrate is used at a high temp. CONSTITUTION:When a metallizing layer 15 is formed on the surface of an AlN substrate 11, an Al2O3 layer is previously formed on the surface of the substrate 11 and this Al2O3 layer is allowed to react with YAlO3 to form a Y3Al5O12 grain boundary layer 13. The metallizing layer 15 is then formed on the grain boundary layer 13. Since this layer 13 has satisfactory wettability with a metal (W, Mo or Ta) forming the metallizing layer 15, the adhesive strength is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a metallized layer on an aluminum nitride substrate having a high bonding strength between the aluminum nitride substrate and a metallized layer formed thereon.

[0002]

2. Description of the Related Art When designing the structure of a hybrid IC, which is a circuit board on which a semiconductor IC and various individual components are mounted on a wiring board, miniaturization thereof is important for reducing the storage space and the cost of materials used. On the other hand, due to miniaturization, it is necessary to generate heat due to internal loss and release the heat.
On the other hand, in designing the structure of a computer or transmission device using such a hybrid IC, it is important to reduce signal delay, distortion, and noise to achieve high speed. As described above, in order to increase the integration degree and output of the electronic circuit and realize the high speed, it is necessary that the circuit board used has a high thermal conductivity and a high withstand voltage.

In order to meet such requirements, various ceramics are used as circuit board materials from the viewpoint of excellent thermal conductivity. Generally, a circuit board made of alumina (Al ₂ O ₃ ) or beryllia (BeO) is well known. However, the thermal conductivity of the alumina substrate is as low as about 1/10 that of the beryllia substrate. On the other hand, the beryllia substrate has a high thermal conductivity of about 250 W / m · K, but it is poorly versatile because it is highly toxic. For this reason, recently, aluminum nitride substrates are increasingly used in place of these. As shown in Table 1, this aluminum nitride substrate has a thermal conductivity that is about eight times higher than that of the alumina substrate, a dielectric strength higher than that of the beryllia substrate, and almost the same value as the alumina substrate.

A semiconductor IC is mounted on the aluminum nitride substrate.
In order to increase the bonding strength between the mounted component and the substrate, a conductive metallization layer is usually formed on the aluminum nitride substrate, and the semiconductor IC or the like is mounted on the metallization layer. Soldered and joined. Prior to the formation of this metallized layer, a step of polishing the surface of the aluminum nitride substrate to adjust the center line average value (Ra) in the surface roughness measurement curve to 1 μm or less is usually performed. This step is performed only to enhance the smoothness of the substrate surface, not to expose the internal grain boundary layer.

As a method for forming such a metallized layer on an aluminum nitride substrate, a direct bond copper method or a thick film method using gold, silver, palladium, copper or the like is used. In these methods, the firing temperature of the metallized layer is as low as 1000 ° C. or lower, so that when the substrate is held at a high temperature, the bonding strength between the aluminum nitride and the metallized layer is often insufficient. For example, when mounting a metal part through a metallized layer laminated by these methods, a high temperature (800
It was difficult to perform brazing at about (° C.). Also, due to the heat generated when the semiconductor device mounted on this aluminum nitride substrate is used and the thermal cycle due to repeated use,
There is also a problem that the metallized layer peels off from the substrate.

Therefore, for example, Japanese Patent Laid-Open No. 62-19737.
In Japanese Patent Laid-Open No. 5 (1994), it is proposed that the metallization layer contains a metal of the same kind as the sintering aid for firing the aluminum nitride sintered body to increase the bonding strength between the two. However, even with such an aluminum nitride substrate, the bonding strength thereof is higher than that of the conventional substrate, but the bonding force during use is still insufficient. In addition, the composition of the metallized layer may be complicated, and the function of the metallized layer may deteriorate (for example, the resistance may increase).

[0007] Therefore, as a result of earnest studies by the present inventors, the YAlO ₃ component is present on the surface of the aluminum nitride substrate after firing. Due to this component, the wettability between the surface layer and the metallized layer is poor and the adhesion strength thereof is high. I have found that is decreasing. Therefore, by removing the YAlO ₃ component present in the surface layer of the aluminum nitride substrate after firing, the wettability with the metallized layer can be enhanced.
I got the knowledge.

Based on this finding, the inventors of the present invention grinded and removed the YAlO ₃ component existing in the surface layer in the prior application, and formed a metallized layer on the newly exposed Y ₃ Al ₅ O ₁₂ grain boundary layer. It proposes a method of forming.

[0009]

The above-mentioned method is a very useful method because the metallized layer has a good compatibility with Y ₃ Al ₅ O _{12 and} a high adhesive force can be obtained. However,
In this method, one sample is extracted from each lot of the produced AlN substrate, the grinding amount is determined while determining the grain boundaries of the substrate surface layer by the X-ray diffraction method, and then the other A
For the 1N substrate, the same amount as this dummy sample was ground. Therefore, the process is complicated. Further, there has been a problem that the grinding amount has to be changed for each lot. In addition, the surface smoothness of the substrate was somewhat difficult.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a method for forming a metallized layer on an aluminum nitride substrate which has a sufficient bonding strength even if a mounted semiconductor device or the like is used.

[0011]

Such an object is achieved by the present invention described below. That is, the method of the present invention is
On the aluminum nitride substrate fired using yttrium oxide as a sintering aid, tungsten, molybdenum,
And a method for forming a metallized layer containing at least one metal selected from the group of tantalum, wherein a thickness of 0.01 to 100 μm is formed on the surface of the aluminum nitride substrate prior to the formation of the metallized layer. This is for forming an alumina layer. This alumina and AlN
YAlO _{3 on the} surface of the substrate causes a chemical reaction, and Y ₃ Al ₅ O
_It produces ₁₂ grain boundary layers.

[0012]

In the present invention, Y ₂ O ₃ is used as a sintering aid for the aluminum nitride substrate. In the aluminum nitride substrate using Y ₂ O ₃ as a sintering aid, a grain boundary layer containing YAlO ₃ as a main component in AlN is formed on the surface portion thereof, and more than the grain boundary layer of YAlO ₃ is formed. At the deep portion, a grain boundary layer containing Y ₃ Al ₅ O ₁₂ as a main component in AlN is formed. The conductor paste for forming the metallized layer has poor wettability with YAlO _{3 in the} surface layer portion. For this reason, the adhesion with the AlN substrate becomes insufficient. However, in the present invention, the surface of the AlN substrate is Y ₃ Al ₅
Since it is formed of the O ₁₂ grain boundary layer, strong adhesion can be obtained. This is because the conductor paste has good wettability with respect to this Y ₃ Al ₅ O ₁₂ .

Hereinafter, a specific configuration of the present invention will be described in detail with reference to FIGS. 1 and 2. The circuit board according to the present invention is an AlN board 11 fired using Y ₂ O ₃ as a sintering aid. The firing conditions, composition, component composition, etc. of the AlN substrate 11 may be in accordance with the usual firing method of the AlN substrate. Table 1 shows the physical properties of the AlN substrate compared with other ceramic substrates. Since the baking of the AlN substrate 11 is usually performed in a reducing atmosphere, the surface layer portion having a strong reducing power is not burned.
As shown in, the grain boundary layer 12 containing YAlO ₃ as a main component in AlN is formed. In addition, the AlN substrate 11
A grain boundary layer 13 containing Y ₃ Al ₅ O ₁₂ as a main component in AlN is formed inside the.

[0014]

[Table 1]

In the present invention, an Al ₂ O ₃ layer 14 is laminated on the grain boundary layer 12 containing YAlO ₃ as a main component,
The material is heated and baked under the temperature condition of 0 to 1800 ° C. By this heating, YAlO _{3 of the} grain boundary layer 12 diffuses and permeates into the Al ₂ O ₃ layer 14, and changes into Y ₃ Al ₅ O ₁₂ by a chemical reaction. At this time, the layer thickness of the laminated Al ₂ O ₃ layer 14 is 0.0
If it is 1 μm or less, the Y ₃ Al ₅ O ₁₂ conversion reaction is not sufficiently carried out, and YAlO ₃ is precipitated in the outermost layer portion. Also, 100μ
If it is more than m, the Al ₂ O ₃ layer 14 remains unreacted in the outermost surface layer portion. Therefore, the layer thickness of the Al ₂ O ₃ layer 14 is 0.01 to 100.
It is desirable that the thickness is about μm. Within this range, Al
The outermost surface layer portion of the N substrate 11 becomes the grain boundary layer 13 of Y ₃ Al ₅ O ₁₂ . As shown in FIG. 2, the metallized layer 15 containing at least one of W, Mo, and Ta as a main component is formed of YAlO ₃
The wettability is not good for the grain boundary layer 12. But Y ₃
The metallized layer 15 has good compatibility with the grain boundary layer 13 containing Al ₅ O ₁₂ . Therefore, the metallization layer 15 is set to Y
_When it is directly formed on the grain boundary layer 13 of ₃ Al ₅ O ₁₂ , a strong adhesive force is obtained and the bond strength thereof can be increased. Here, the Al ₂ O ₃ layer 14 is formed by a normal sol-gel method,
Both the sputtering method and the vapor deposition method can be used.

In the present invention, the metallized layer 15 formed on the AlN substrate 11 is coated with a raw material paste containing at least one metal selected from the group consisting of W, Mo and Ta by a method such as screen printing. By doing so, they are laminated. The metallized layer 15 may be formed under normal conditions. For example, a normal conductor paste prepared by adding the above metal to a medium such as ethyl cellulose or nitrocellulose and dissolving it in an organic solvent such as butyl carbitol, acetone or tetralyl may be used. Further, the atmospheric gas, heating temperature, time, etc. are not particularly limited and may be in accordance with known examples.

Further, the metallized layer 15 thus formed is plated with Ni 16 and a semiconductor chip or the like is mounted thereon. The attaching method is a usual method such as soldering or brazing. Note that YAlO contained in the AlN substrate 11 during the Ni plating 16
Conventionally, there was a phenomenon in which ₃ diffuses and exudes to the surface of the metallized layer 15, and the adhesion of the Ni plating 16 decreases. However, such a problem is solved as a side effect of the present invention.

[0018]

EXAMPLE 95 parts by weight of AlN powder and 5 parts by weight of Y ₂ O ₃
After mixing the powder and using polyvinyl butyral (PVB) as a binder to form a green sheet, 60 mm × 6
Cut into 0 mm x 0.70 mm and 1 in N ₂ gas atmosphere
It was fired at 800 ° C. for 3 hours. This AlN sintered body was ground to obtain an AlN substrate having dimensions of 50 mm × 50 mm × 0.65 mm.

On the other hand, Al was added to 1000 ml of a solution prepared by dissolving 1 wt% aluminum butoxide in n-butanol.
After dipping the N substrate for 1 minute, pulling it up, 300
It was dried at ℃ for 1 h. An Al ₂ O ₃ layer is formed on an AlN substrate. In this example, the firing of the Al ₂ O ₃ layer was omitted. The layer thickness of the Al ₂ O ₃ layer is 0.1 μm.
And

Next, 97 parts by weight of W and 3 parts by weight of Al
100 parts by weight of N-mixed powder was dispersed in 5 parts by weight of ethyl cellulose and 15 parts by weight of butyl carbitol to prepare a metallized layer forming paste.

Then, the paste was printed on the alumina layer through a 325 mesh screen, and the conductor layer was further heated in a N ₂ gas stream at 1700 ° C. for 3 hours. As a result, a metallized layer having a layer thickness of 10 μm is formed on the AlN substrate. In addition, Al
When the surface layer of the N substrate was judged by the X-ray diffraction method, it was YAl
50% of O ₃ was changed to Y ₃ Al ₅ O ₁₂ .

The bonding strength between the AlN substrate thus obtained and the metallized layer was measured. Bonding strength is measured by C of φ 0.9 mm in the 2 mm x 2 mm metallized part.
The u wire was soldered and peeled off in the 90 ° direction. The results are shown in Table 2. Further, the same AlN substrate was not formed with the alumina layer but only the metallized layer was formed, and the same measurement as that of the comparative sample was performed. The results are also shown in Table 2. From the above results, AlN produced by the method of the present invention
It is clear that the substrate has a high bonding strength. Table 3
The manufacturing conditions, component composition, and the like of the AlN substrate of this example will be described in the order of steps.

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

According to the present invention, it is possible to obtain an aluminum nitride substrate having a high bonding strength with the metallized layer even when used at high temperatures. In this case, the process of forming the metallized layer can be simplified. Further, the surface of the metallized layer can be kept smooth.

[Brief description of drawings]

FIG. 1 is a sectional view showing a grain boundary distribution before firing of an Al ₂ O ₃ layer of a surface layer of an aluminum nitride substrate in the method of the present invention.

FIG. 2 is a sectional view showing an AlN substrate structure in which a metallized layer is formed after the disappearance of an Al ₂ O ₃ layer according to the method of the present invention.

[Explanation of symbols]

11: Aluminum Nitride Substrate 12: YAlO ₃ Grain Boundary Layer 13: Y ₃ Al ₅ O ₁₂ Grain Boundary Layer 14: Al ₂ O ₃ Layer 15: Metallized Layer

Claims (1)

[Claims] 1. A metallized layer containing at least one metal selected from the group consisting of tungsten, molybdenum, and tantalum is formed on an aluminum nitride substrate that has been baked using yttrium oxide as a sintering aid. A method for forming a metallized layer on an aluminum nitride substrate, which comprises forming an alumina layer having a thickness of 0.01 to 100 μm on the surface of the aluminum nitride substrate prior to forming the metallized layer.