JPS63242985A - Aluminum nitride substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an aluminum nitride (AfLN) substrate, and more specifically, the present invention relates to an aluminum nitride (AfLN) substrate, and more specifically, a conductive metal lice layer is formed on the surface of the substrate with high bonding strength. Connect it to the AIN board.

(Prior Art) AfLN sintered bodies are attracting attention as substrate materials for semiconductors because they have good thermal conductivity, excellent heat dissipation, and electrical insulation properties.

This AiN sintered body is generally manufactured as follows. That is, Y 203 +3m203 in AuN powder,
A predetermined amount of a sintering aid such as CaO is blended, an acrylic resin binder is added as necessary, the whole is thoroughly mixed, and the resulting mixture is, for example, pressure molded to form a predetermined shape. After forming an AIN sintered precursor (green molded body), this is sintered at a predetermined temperature in, for example, a nitrogen atmosphere.

By the way, when using an AIN sintered board as a substrate for a semiconductor, it is necessary to form a conductive thin layer on the side on which the semiconductor is mounted. Conventionally, this thin layer was deposited on the surface of the AiN sintered plate using the DBC method (Direct Bond Cu).
Copper (Cu) formed by applying pper method) or thick film method
, gold (Au), silver-palladium (A g -P d
) conductive metallized layer.

However, this conventional substrate has the following problems.

The first problem is that the bonding strength between the formed metallized layer and the surface of the AIN 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, the temperature is approximately 800°C in a hydrogen-nitrogen mixed gas.
However, since the metallized layer baking process is usually at a low temperature of about 600 to 1000°C, this brazing is sometimes performed at a temperature of about 600 to 1000°C. This means that the joint strength will drop significantly, making brazing virtually impossible.

A similar problem also occurs in the case of high-temperature soldering.

The third problem is a problem based on the difference in coefficient of thermal expansion between the A4N 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 is mounted, such as a silicon wafer, undergoes severe thermal cycles of heating and cooling during use. As a result, at the bonding surfaces of the AfLN sintered body, metallized layer, brazing layer (or solder layer), and semiconductor element, thermal stress is generated due to the difference in the coefficient of thermal expansion of each layer, causing each layer to peel off. occurs.

In the case of the metallized layer described above, A! ;The coefficient of thermal expansion is about 2-4 times larger than that of the LN firing plate (the coefficient of thermal expansion is about 4.6 x 10-'/"0), and it is also equivalent to the brazing layer (or solder layer). Since the value is the value of the lying position and there is a large difference from AIN, micro-cracks are likely to occur at the interface between the metallized layer or brazing layer (or solder layer) and AIN during thermal cycling. These microcracks gradually develop over time, and may eventually lead to peeling of the mounted semiconductor element.

Such a problem is extremely inconvenient because it reduces 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 AfLN sintered plate at high temperatures is low, and as in the second case, the reliability during high temperature use is low.

For this reason, recently, tungsten (W), molybdenum (
Thin layers of Mo) or titanium nitride (T i N) are beginning to be applied.

(Problem to be solved by the invention) The conductive metallized layer is the above-mentioned W layer, M0 layer, Ti
In the case of N layer, the above-mentioned Cu layer, Au layer, Ag-Pd
The above-mentioned problems have been improved compared to the case of layers, and attempts have been made to improve the bonding strength with the AIN sintered body and improve reliability during use, but this is still not sufficient and further improvements are desired.

An object of the present invention is to provide an AIN substrate that has high bonding strength between an AuN sintered plate and a metallized layer, and also has high reliability during use.

[Structure of the invention] (Means/effects for solving the problem) The present inventors,
When we examined the relationship between the interface state and bonding strength between the AuN sintered plate and the W layer on an A4N substrate with a W metallized layer, we found that the substrate with high bonding strength has a yttrium aluminum garnet (YAG) layer at the interface. is formed,
On the contrary, we have found that in substrates with low bonding strength, YAG is not concentrated in this interface area and is relatively uniformly distributed throughout the AuN sintered plate. This phenomenon was similarly observed in the case of substrates in which the metallized layer was a Mo layer or a TiN layer.

Based on these findings, the present inventors believe that if the YAG layer is concentrated at the interface between the A-N substrate and the metallized layer,
Having the idea that the bonding strength of the substrate could be improved, we experimentally confirmed the validity of the idea and developed the AIN substrate of the present invention.

That is, the A-shaped N substrate of the present invention is composed of an A4N sintered plate and the A-shaped N substrate.
It is characterized in that a YAG layer exists near the interface of the conductive metallized layer formed on the surface of the uN sintered plate.

The A or N sintered plate used in the substrate of the present invention is preferably one having a thermal conductivity of 50 W/mIIK or more. Such an AIN sintered plate has a predetermined grain size (7)A, for example.
i N powder, Y 203! Y F 3 rSm
203, a sintering aid such as CacO3 and a binder component such as a wax type or plastic type are mixed in a predetermined ratio, and this mixture is formed into a sheet shape by pressure molding or a doctor blade at room temperature. The green molded body is then produced by sintering the green molded body.

At this time, the particle size of the AIN powder and sintering aid powder.

AI obtained by appropriately selecting the conditions in each process such as the mixing ratio of both, molding pressure, sintering temperature, and sintering time.
The properties of the N sintered plate can be determined.

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

Specifically, a layer composed of individual components of W, Mo, and TiN; W and Mo, and W and TiN.
, a layer composed of two components such as Mo and TiN; furthermore, a layer composed of three components such as W, Mo and TiN.

In the case of a metallized layer composed of multiple components, the proportion of each component present is not particularly limited.

The main feature of the substrate of the present invention is that a YAG layer is present near the interface between the above-described AfLN sintered plate and the metallized layer.

YAG is produced when Y2O3, which is generally blended as a sintering aid, reacts with A or 203, which is an impurity in AIN, during the sintering process.
In this case, G is concentrated in the vicinity of the interface between the AfLN 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 thought to be that YAG has diffused into both the AIN substrate and the metallized layer.

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

First, according to the usual method, the prescribed properties, especially the thermal conductivity, are 5.
An A4N sintered plate with a power output of 0 W/m11 or more is manufactured. Next, a paste containing components for forming the desired metallized layer is applied to the surface of this AIN sintered plate. As a coating method, well-known methods such as screen printing, brush coating, spin roller coating, etc. may be used.

The paste is composed of components that form the metallized layer and a medium that disperses them. That is, W, Mo
, Ti, TiN layer 7) One type or an appropriate combination of two
For example, if the metallized layer is a TiN layer, which is formed by dispersing more than one type of powder in a medium, Ti powder or TiN powder may be used as the paste component.

Examples of the medium used include mixtures of ethylcellulose and nitrocellulose with their solvents such as terpineol, tetralin, and butylcarpitol.

The amount of the above components to be dispersed in the medium is determined as appropriate in relation to the viscosity of the resulting paste. If the former is in an excessive amount, the resulting paste will become highly viscous, making it difficult to uniformly apply it to the iN sintered board. Also, in the opposite case, the paste viscosity will be low and the applied paste will be A! ; It flows down from the surface of the LN sintered plate. Usually 1.0X105~2.
The former may be dispersed into the latter so that the number of voices becomes 5×105.

After applying the paste, the entire structure is heated to form a metallized layer. During this heat treatment, it is necessary that the atmosphere be a nitrogen gas atmosphere and the temperature be 1600 to 1900°C.

If the temperature is lower than 1600°C, the formation of a high-quality metallized layer is insufficient, and at the same time the YAG layer near the interface
There is also little diffusion and permeation of the layer, and the improvement in bonding strength is insufficient. Further, if the temperature is higher than 1900° C., Mo, W, etc. in the metallized layer start to melt, which is disadvantageous. Preferably it is 1700-1800°C.

In this heating process, A!N exists between the grains of A! ;L'
It is thought that the YAG crystals uniformly distributed in the N sintered plate enter a liquid phase state and move to the interface with the metallized layer.

In addition, in the explanation so far, the case where an AIN sintered plate is used when manufacturing the A-N substrate of the present invention has been described, but the manufacture of the AfLN substrate of the present invention is not limited to this method, and for example, Alternatively, the above-described paste may be applied to the surface of the green molded body, and the entire green molded body may be subjected to a heat treatment.

In this case, the metallization layering of the paste progresses simultaneously with the sintering of the green molded body.

(Embodiments of the invention) Example 1 50 parts by weight of MO powder with a particle size of 1 to 2 and T with a particle size of 1 to 2-
Mixed powder 1 obtained by mixing with 50 parts by weight of N powder
A paste with a viscosity of 1.5×10s voids was prepared by dispersing 00 parts by weight in 7 parts by weight of ethyl cellulose.

This paste was applied with a roller to a thickness of 15 μm on one side of an AJIN substrate containing 5% by weight of Y2O3 as a sintering aid.

This substrate was sintered at a temperature of 1700° C. for about 1 hour in a dry nitrogen stream.

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

Then, I got an A! ; LN substrate metallized layer and AI
EPMA line analysis was conducted near the interface with the N sintered plate, and the results are shown in FIG.

As is clear from the figure, concentrated uneven distribution of Y is observed on the AL;LN sintered plate side of the interface, suggesting the presence of a YAG layer.

A scanning electron micrograph of the vicinity of this interface is shown in FIG. 2. As is clear from FIG. 2, the YAG crystals (white part in the figure) are not uniformly dispersed within the A-N sintered plate (the right part in the figure) but are concentrated at the interface.

Next, a Ni plating layer having a thickness of about 3 to 5 JiIR was formed on the metallized layer of this AuN substrate by electroless plating. Then, after sintering the plating layer in a homing gas at 800°C, a Kovar wire with a wire diameter Q of 5++m and a tensile strength of 55 kg/mm2 was brazed thereto using silver solder. The brazing temperature was 800° C. and the atmosphere was a mixed gas atmosphere of 50 Vol 1% hydrogen and 50 Vol 1% nitrogen.

Thereafter, the A/N substrate was fixed, a Kovar wire was pulled at room temperature (20° C.), and the peeling state of the metallized layer was observed.

When the tensile strength was 5 kg/mm2, the metallized layer and the soldered portion of the Kovar wire were torn off. In other words, A.I.
It was found that the bonding strength between the N substrate and the metallized layer was 5 kg/2 or more.

For comparison, an AJIN 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 AuN substrate are shown in FIG. 3, and the scanning electron micrograph is shown in FIG. 4.

As is clear from FIG. 3, Y is not concentrated near the interface. This is clear from the fact that YAG crystals (white portions in the figures) are uniformly scattered within the AIN sintered plate in FIGS. 1 and 4.

Note that the metallized layer and AfLN in this A4N substrate
The bonding strength with the sintered plate was measured using the same method as in the example.
kg/mad2 or less.

[Effects of the Invention] As is clear from the above explanation, the AuN substrate of the present invention has the following effects:
Since the YAG layer is intensively formed near the interface between the metallized layer and the A4N sintered plate, the bonding strength between the metallized layer and the AIN sintered plate is high. Therefore, the AfLN substrate of the present invention has high reliability when put into practical use, and has great industrial value.

[Brief explanation of drawings]

Figure 1 shows the metallized layer and A of the AuN substrate of the present invention.
FIG. 2 is a diagram showing the results of EPMA line analysis near the interface with the IN sintered plate, and FIG. 2 is a scanning electron micrograph showing the metal structure near the interface. Figure 3 shows the EPM near the interface between the metallized layer and the A-N sintered plate in the AuN substrate of the comparative example.
FIG. 4 is a diagram showing the results of A-line analysis, and FIG. 4 is a scanning electron micrograph showing the metal structure near the interface. Figure 1° 21. ;

Claims (1)

[Claims] An aluminum nitride substrate characterized in that a yttrium gallium gannet layer is present near the interface between a sintered aluminum nitride plate and a metallized layer formed on the surface of the sintered aluminum nitride plate.