JPH0788266B2 - Aluminum nitride substrate and manufacturing method thereof - Google Patents

Description

The present invention relates to an aluminum nitride (AlN) substrate and a method for producing the same, and more specifically, a conductive metallized layer having high bonding strength on the surface thereof. The present invention relates to a formed AlN substrate and a method for manufacturing the same.

(Prior Art) An AlN sintered body is attracting attention as a substrate material for semiconductors because it has good thermal conductivity, excellent heat dissipation, and electrical insulation.

This AlN sintered body is generally manufactured as follows. In other words, the AlN powder _{Y 2 O 3, Sm 2 O} 3, the sintering aid such as CaO predetermined amount, thoroughly mixed the whole was added to an acrylic resin binder, if necessary, The obtained mixture is, for example, pressure-molded to obtain an AlN sintering precursor (green compact) having a predetermined shape, and then this is sintered at a predetermined temperature in, for example, a nitrogen atmosphere.

By the way, when an AlN sintered plate is used as a semiconductor substrate, it is necessary to form a conductive thin layer on the surface on which the semiconductor is mounted. Conventionally, this thin layer is copper (Cu), gold (Au), silver-palladium (Ag-Pd) formed by applying the DBC method (Direct Bond Copper method) or the thick film method to the surface of the AlN sintered plate. Is a conductive metallization layer.

However, this conventional substrate has the following problems.

The first is that the bond strength between the formed metallized layer and the surface of the AlN sintered plate is low, and a peeling phenomenon often occurs between the two, resulting in low reliability of the substrate.

The second problem is a problem that occurs when a predetermined semiconductor element or wire is brazed or high temperature soldered to the formed metallized layer. That is, for example, in the case of brazing, it is carried out in a hydrogen-nitrogen mixed gas at a temperature of about 800 ° C. However, since the temperature at the time of the metallizing layer baking treatment is usually a low temperature of about 600 to 1000 ° C., This means that the bonding strength between the metallized layer and the surface of the AlN sintered plate is significantly reduced during this brazing, making brazing practically impossible. In addition, the same problem occurs in high temperature soldering.

The third problem is a problem based on the difference in thermal expansion coefficient between the AlN sintered plate and the metallized layer. That is, as in the case of brazing and high-temperature soldering, a substrate on which a semiconductor element such as a silicon wafer is mounted undergoes a severe heat-cooling thermal cycle during its use. as a result,
AlN sintered body-metallized layer-brazing layer (or solder layer)
-At each bonding surface of the semiconductor element, thermal stress is generated based on the difference in the coefficient of thermal expansion of each layer, and an action of separating each layer occurs.

In the case of the above-mentioned metallized layer, its value is about 2 to 4 times larger than that of the AlN sintered plate (coefficient of thermal expansion is about 4.6 × 10 ⁻⁶ / ° C.), and the brazing layer (or solder layer) From the value equivalent to 1 /
Since it is the second highest value and has a large difference from AlN, it does not adhere to the metallization layer or brazing layer (or solder layer) during heat cycle.
Microcracks easily occur at the N interface. The microcracks gradually develop as the heat cycle is applied, and may eventually cause peeling of the mounted semiconductor element.

Such a problem is extremely inconvenient because it lowers the reliability of a device mounted with a substrate on which a semiconductor element is mounted.

The fourth problem is that the bonding strength between the metallized layer and the AlN sintered plate at high temperature is small, and the reliability at high temperature is low as in the second case.

For this reason, recently, a thin layer of tungsten (W), molybdenum (Mo) or titanium nitride (TiN) has begun to be applied as a metallization layer instead of the above-mentioned thin layer.

(Problems to be Solved by the Invention) In the case where the conductive metallized layer is the above-mentioned W layer, Mo layer, or TiN layer, the above-mentioned problems are more serious than in the case of the Cu layer, Au layer, or Ag-Pd layer described above. Although it is attempted to improve the bonding strength with the AlN sintered body and the reliability during use, it is not yet sufficient, and further improvement is desired.

It is an object of the present invention to provide an AlN substrate having high bonding strength between an AlN sintered plate and a metallized layer and high reliability during use, and a method for manufacturing the same.

[Structure of the Invention] (Means / Action for Solving Problems) The present inventors have found the relationship between the interface state between the AlN sintered plate and the W layer and the bonding strength for an AlN substrate in which the metallized layer is the W layer. As a result of examination, a substrate with high bonding strength has an yttrium aluminum garnet (YAG) layer formed on the interface portion, and conversely, a substrate with low bonding strength has YA on this interface portion.
We found that G was not concentrated and was distributed relatively uniformly throughout the AlN sintered plate. Then, this phenomenon was similarly observed in the case where the metallized layer was a Mo layer or a TiN layer.

From these findings, the present inventors have the idea that if the YAG layer is concentratedly present at the interface between the AlN substrate and the metallized layer, the bonding strength of the substrate can be improved, and experimentally After confirming the correctness of the idea, the inventors have developed the AlN substrate of the present invention.

That is, the YAG layer is present in the vicinity of the interface between the AlN sintered plate of the present invention and the metallized layer containing at least one of W, Mo and TiN formed on the surface of the AlN sintered plate. .

Further, the manufacturing method of the AlN substrate of the present invention is
A metallized layer is formed by applying a paste containing at least one of W, Mo, and TiN on the surface of the sintered plate, and heating it to form YAG near the interface between the sintered plate and the metallized layer. It is characterized by being unevenly distributed.

The AlN sintered plate in the substrate of the present invention is preferably one having a thermal conductivity of 50 W / m · K or more. Such an AlN sintered plate, for example, AlN powder of a predetermined grain size, Y ₂ O ₃ , Y
A sintering aid such as F ₃ , Sm ₂ O ₃ or CaCO ₃ and a binder component such as a wax type or a plastic type are mixed in a predetermined amount ratio, and this mixture is subjected to pressure molding or doctor blade at room temperature. Is molded into a sheet to give a green molded body, and then the green molded body is sintered.

At this time, the characteristics of the AlN sintered plate obtained by appropriately selecting the conditions in each process such as the particle size of AlN powder and sintering aid powder, the mixing ratio of the two, molding pressure, sintering temperature, and sintering time. Can be determined.

The conductive metallized layer formed on the surface of this AlN sintered plate is a conductive layer containing at least one of W, Mo and TiN.

Specifically, a layer composed of W, Mo, and TiN respectively, a layer composed of W and Mo, W and TiN, a layer composed of two components such as Mo and TiN, and further W, Mo, and TiN. It is a layer composed of three components. In the case of a metallized layer composed of multiple components,
The abundance ratio of each component is not particularly limited.

The greatest feature of the substrate of the present invention is that the YAG layer exists near the interface between the AlN sintered plate and the metallized layer.

YAG is produced by reacting Y ₂ O ₃ which is generally added as a sintering aid with Al ₂ O ₃ which is an impurity in AlN during the sintering process. In the present invention, the YAG is concentrated in the vicinity of the interface between the AlN sintered plate and the metallized layer and exists in the form of a layer.

The reason why the bonding strength is improved when this YAG layer is formed is that Y
It is considered that this is because AG diffuses and penetrates into both the AlN substrate and the metallized layer.

The AlN substrate of the present invention can be manufactured as follows.

First, according to the usual method, the specified characteristics, especially the thermal conductivity of 50
Manufacture AlN sintered plate with W / m · K or higher. Then, a paste containing a component forming a target metallized layer is applied to the surface of the AlN sintered plate. As a coating method, for example, a known method such as screen printing, brush coating, spin roller coating may be applied.

The paste is composed of a component forming the metallized layer and a medium in which the metallized layer is dispersed. That is, W, Mo, Ti, Ti
It is constituted by dispersing one kind of N or two or more kinds of powders appropriately combined in a medium. After that, the metallization layer is TiN
When used as a layer, as a paste component, Ti powder or Ti
N powder may be used.

Examples of media used include ethyl cellulose and nitrocellulose, and terpineol as a solvent for them,
A mixture with tetralin and butyl carbitol can be mentioned.

The amount of the above components dispersed in the medium is appropriately determined in relation to the viscosity of the obtained paste. If the former is too much, the obtained paste becomes highly viscous and it becomes difficult to apply it uniformly to the AlN sintered plate. On the other hand, in the opposite case, the paste viscosity becomes low and the applied paste is fluidized from the surface of the AlN sintered plate. Usually, the former may be dispersed in the latter so as to obtain 1.0 × 10 ^{5 to} 2.5 × 10 ⁵ poise.

After applying the paste, the whole is heated to form a metallized layer. At the time of this heat treatment, it is necessary that the atmosphere is a nitrogen gas atmosphere and the temperature is 1600 to 1900 ° C.

When the temperature is lower than 1600 ° C, the formation of a good quality metallized layer is insufficient, and at the same time, the diffusion and penetration of the YAG layer in the vicinity of the interface is small and the improvement of the bonding strength is insufficient. On the other hand, if the temperature is higher than 1900 ° C, melting of Mo, W, etc. in the metallized layer will start, which is inconvenient. Preferably 1700-1800
℃.

It is considered that during this heating process, the YAG crystals existing between the AlN crystal grains and uniformly distributed in the AlN sintered plate become in a liquid phase state and move to the interface with the metallized layer.

In the above description, the case of using an AlN sintered plate during the production of the AlN substrate of the present invention has been described, but the production of the AlN substrate of the present invention is not limited to this method, for example, green. You may apply the above-mentioned paste on the surface of a molded object, and heat-process it as a whole.
In this case, the metallization layer formation of the paste will proceed simultaneously with the sintering of the green compact.

(Examples of the invention) Example 1 50 parts by weight of Mo powder having a particle size of 1 to 2 μm and Ti having a particle size of 1 to 20 μm
n Powder 50 parts by weight is mixed, and 100 parts by weight of the obtained mixed powder is dispersed in 7 parts by weight of ethyl cellulose to give a viscosity of 1.5 × 10 ⁵
A poise paste was prepared.

This paste was roller-coated with a thickness of 15 μm on one surface of an AlN substrate containing 5% by weight of Y ₂ O ₃ as a sintering aid.

This substrate was placed in a dry nitrogen stream at a temperature of 1700 ° C for approximately 1
Sintered for hours.

A metallized layer was formed on the surface of the obtained AlN sintered body sheet. It was confirmed by X-ray diffraction that the constituent phases of this metallized layer were Mo and TiN.

Then, an EPMA line analysis was performed in the vicinity of the interface between the metallized layer of the obtained AlN substrate and the AlN sintered plate, and the results are shown in FIG.

As is clear from the figure, a concentrated uneven distribution of Y was observed on the AlN sintered plate side of the interface, suggesting the existence of a YAG layer.

A scanning electron micrograph of the vicinity of this interface is shown in FIG. As is clear from FIG. 2, the YAG crystal (white part in the drawing) is not uniformly dispersed in the AlN sintered plate (the right part in the drawing), but is concentrated at the interface part.

Next, a Ni plating layer having a thickness of about 3 to 5 μm was formed on the metallized layer of this AlN substrate by an electroless plating method.
Then, after the plating layer was sintered in a homing gas at 800 ° C., a Kovar wire having a wire diameter of 0.5 mm and a tensile strength of 55 kg / mm ² was brazed thereto with silver brazing. The brazing temperature was 800 ° C, and the atmosphere was a mixed gas atmosphere of 50 Vol% hydrogen and 50 Vol% nitrogen.

Then, the AlN substrate was fixed and the Kovar wire was pulled at room temperature (20 ° C.) to observe the peeled state of the metallized layer.

When the tensile strength was 5 kg / mm ² , the metallized layer and the brazed portion of the Kovar wire were torn off. That is, it was found that the bonding strength between the AlN substrate and the metallized layer was 5 kg / mm ² or more.

For comparison, an AlN substrate was manufactured in the same manner as in the example except that the sintering temperature was 1600 ° C.

The results of EPMA line analysis near the interface of this AlN substrate are shown in FIG. 3, and the scanning electron micrographs are shown in FIG.

As is clear from FIG. 3, Y is not concentrated near the interface. This is also clear from the fact that YAG crystals (white portions in the figure) in FIG. 4 are uniformly scattered in the AlN sintered plate.

The bonding strength between the metallized layer and the AlN sintered plate in this AlN substrate was 1 kg / mm ² or less when measured by the same method as in the example.

[Effects of the Invention] As is clear from the above description, in the AlN substrate of the present invention, the YAG layer is intensively formed in the vicinity of the interface between the metallized layer and the AlN sintered plate. The joint strength with the plate is high. Therefore, the AlN substrate of the present invention has high reliability when put to practical use, and its industrial value is great.

[Brief description of drawings]

FIG. 1 is a diagram showing a result of EPMA line analysis in the vicinity of an interface between a metallized layer and an AlN sintered plate in an AlN substrate of the present invention,
FIG. 2 is a scanning electron micrograph showing a metal structure near the interface. FIG. 3 is a diagram showing a result of EPMA line analysis in the vicinity of the interface between the metallized layer and the AlN sintered plate in the AlN substrate of the comparative example, and FIG. 4 is a scanning electron micrograph showing a metal structure in the vicinity of the interface. .

Claims (2)

[Claims] 1. A yttrium aluminum garnet layer is present in the vicinity of an interface between an aluminum nitride sintered plate and a metallized layer containing at least one of W, Mo and TiN formed on the surface of the aluminum nitride sintered plate. Aluminum nitride substrate characterized by. 2. A surface of an aluminum nitride sintered plate containing yttrium aluminum garnet is coated with a paste containing at least one of W, Mo, and TiN, and heated to form a metallized layer and burn the metalized layer. A method for manufacturing an aluminum nitride substrate, characterized in that yttrium aluminum garnet is unevenly distributed in the vicinity of an interface between a tie plate and the metallized layer.