JPH0442861A - Preparation of highly strong aluminum nitride sintered product - Google Patents

Abstract

PURPOSE:To prepare an AlN sintered product having high thermal conductivity and high strength by adding an oxide sintering auxiliary and a prescribed amount of alpha-alumina powder of a regulated average particle diameter to an Al powder having a regulated average particle diameter, a regulated impurity oxygen content and a regulated cationic impurity content, and subsequently sintering the mixture. CONSTITUTION:Aluminum nitride powder having an average particle diameter of <=5 mum, an impurity oxygen content of <=3wt.% and a cationic impurity content of <= 0.3wt.% as a main component is mixed with a rare earth element or alkaline earth metal oxide sintered product auxiliary (e.g. Y2O3) and further with 0.6-5 wt.% of alpha-alumina powder having an average particle diameter of 5<=mum. The mixture is mixed with additives such as a binder, molded and then sintered to prepare an aluminum nitride sintered product having high thermal conductivity and high strength, which is suitably employed for highly thermal conductive insulated boards, etc., in fields requiring high heat-releasing characteristics for various semiconductors.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an aluminum nitride sintered body having high thermal conductivity and high strength. The aluminum nitride sintered body obtained by the present invention is particularly useful in the field of electronic materials.
Insulated substrates for engineering C and LSI that require high heat dissipation characteristics,
Used for HIC boards, etc.

[Background Art] In recent years, with the progress of semiconductor technology, various characteristics are now required of semiconductor substrate materials.

One of these is the improvement in the heat dissipation characteristics of substrate materials as semiconductor chips become more dense and output. Among conventional substrate materials, alumina substrates have been most commonly used due to their insulating properties, mechanical strength, and cost. However, with alumina substrates, there are limits to the improvement of heat dissipation characteristics due to the material's thermal conductivity and coefficient of thermal expansion. Until now, beryllia substrates have been used in fields that require such high heat dissipation properties, but beryllia is toxic and
Another drawback was that it was very expensive.

For this reason, there is a need for a substrate material that has material properties comparable to alumina and has high heat dissipation properties.

Therefore, aluminum nitride substrates, which have high thermal conductivity, a coefficient of thermal expansion close to that of semiconductor chips, and good insulation properties, are attracting attention. However, since aluminum nitride is a material that has strong covalent bonds and is difficult to sinter, it is difficult to densify it alone. Therefore, when creating an aluminum nitride substrate by sintering.

Perform pressure sintering (Japanese Patent Publication No. 62-22952) or add a sintering aid (for example, Japanese Patent Publication No. 47-18655,
(Japanese Patent Publication No. 63-31434, etc.), liquid phase sintering is caused and densification is achieved.

Aluminum nitride reacts easily with water and air, so the powder usually contains some oxygen. Therefore, when pressure sintering is performed, the thermal conductivity does not reach a very high value due to this impurity oxygen.Currently, there is a method of densification using a sintering aid that effectively uses this impurity oxygen as a liquid phase component. is widely practiced. In this case, Intoria or the like is used as the sintering aid. However, if the amount of impurity oxygen is large, the amount of sintering aid added will be large, or the thermal conductivity of the resulting sintered body will be low. In the process of producing a sintered body of aluminum nitride, methods have been taken to avoid increasing the amount of oxygen as much as possible.

By this method, it has now become possible to easily obtain an aluminum nitride sintered body with a power of 100 W/m- or more.

[Problems to be Solved by the Invention] However, the aluminum nitride sintered bodies produced so far have low bending strength, especially when used as thick film semiconductor ceramic substrates.
During actual operation, it cannot withstand the repeated stress caused by the difference in thermal expansion coefficient with the copper plate bonded as a thick film circuit using the active metal method, etc., resulting in cracking or breaking before the required durability time. It could not be used as a product.

[Means for Solving the Problems] The present inventors have conducted extensive research on the production of aluminum nitride sintered bodies, and have developed a sintered body with high bending strength while maintaining thermal conductivity higher than the conventional 100 W/m- Completed the manufacturing method of aluminum nitride.

The method of the present invention has an average particle size of 5 μm or less, an impurity oxygen content of 3 wt% or less, and a cation impurity content of 0°3 wt%.
In order to produce a highly thermally conductive aluminum nitride sintered body containing the following aluminum nitride powder as a main component and adding a rare earth or alkaline earth metal oxide sintering agent, α-alumina with an average particle size of 5 μm or less is used. Powder 0.6-5wt%
This is a method for producing a high-strength aluminum nitride sintered body with high thermal conductivity, characterized by adding the above-mentioned aluminum nitride powder to the mixture of aluminum nitride powder.

That is, the main component is aluminum nitride powder, a rare earth or alkaline earth metal oxide sintering aid such as ittria, and 0.6 to 5 wt% of α-alumina powder with an average particle size of 5 μm or less. to these mixed powders.

After adding binder, deflocculant, plasticizer, solvent, etc. as appropriate and mixing uniformly to create a slurry, it is molded using the usual ceramic molding method, and the molded body is molded in air, vacuum, or nitrogen atmosphere. , removing volatile components at a temperature of approximately 400 to 1000° C., in a nitrogen atmosphere or an inert atmosphere containing nitrogen.

The present invention relates to a method for producing a high-strength aluminum nitride sintered body that is sintered at a temperature of 1600 to 2000°C.

The present invention will be explained in detail below.

The aluminum nitride powder used in the present invention may be a powder manufactured by a direct nitriding method of metal aluminum or a powder manufactured by an alumina reduction nitriding method, but it has an average a diameter of 5 μm or less and an impurity oxygen content of 3 wt. % or less, the amount of cation impurities is 0. It must be less than 3 wt% aluminum nitride powder. The reason why the average particle size of aluminum nitride is limited to 5 μm is that it is difficult to densify powder with a particle size exceeding this by sintering. Note that the average particle size of the powder here refers to the average value of the primary particle size of the particles observed by SEM, etc., and therefore, the shape of the particles is one that can be easily loosened by a deflocculant, or one that is light. It may be an aggregate, as long as it becomes a powder that can be loosened by pulverization and has the above particle size. The amount of impurity oxygen refers to the oxygen that is considered to be dissolved in the surface of the aluminum nitride powder, and is the amount of oxygen that does not appear as an alumina peak in X-ray diffraction of the powder. Even when the above range is exceeded, densification can be achieved by adding an appropriate amount of sintering aid, but the result is a sintered body with low thermal conductivity. The reason why the amount of cationic impurities is limited as described above is that powders exceeding this range similarly make it difficult to maintain high thermal conductivity, which is a major feature of aluminum nitride.

As the sintering aid, rare earth metal oxides such as yttria or alkaline earth metal oxides such as calcia can be used. The amount of this sintering aid added varies depending on the characteristics of the aluminum nitride powder used, but it is approximately 0.
．． The amount added is 1 to 20 wt%, more preferably 1 to 7 wt%.

When adding α-alumina powder, which is a feature of the present invention, the alumina purity of the powder is preferably 80 wt% or more, and α-alumina powder with an alumina purity of 99 wt% or more is more suitable. A final groove purity of 80 wt% is not preferable because it causes a decrease in the thermal conductivity of the sintered body. In addition, the average particle size of the α-alumina powder is preferably 5 μm or less. This is because particle sizes exceeding 5 μm cannot contribute to the strength, which is a feature of the present invention, and the denseness of the sintered body is reduced. This is because it hinders the development of The amount of α-alumina powder added is 0.6 to 5 wt%.

If the amount added is less than this range, it will not be possible to sufficiently increase the strength of the aluminum nitride sintered body, which is the objective of the present invention, and if the amount added exceeds this range, the high thermal conductivity, which is a characteristic of aluminum nitride, will not be achieved. cannot be achieved.

In addition, in the present invention, α-alumina can be added to aluminum nitride powder in the form of powder as described above.
Alternatively, a method may be used in which alumina balls are used as grinding media to intentionally cause alumina contamination and then added.

In the present invention, the slurry is created from the above-mentioned powder mixture by directly using the method used in ordinary ceramic molding, in which binders, deflocculants, plasticizers, solvents, etc. are added as appropriate and mixed uniformly. can. However, since aluminum nitride is highly reactive with water, an organic solvent-based slurry creation method is applied, and a suitable binder and
Deflocculants and plasticizers are used. Ball mill mixing is typically used to create the slurry. Ball mill mixing in the present invention is usually performed wet, but dry mixing may be performed before wet ball mill mixing. At this time, pots and balls made of resin, aluminum nitride, alumina, etc., which have low reactivity with solvents and are hard to wear, are used.

Methods for forming aluminum nitride powder compacts using this slurry include 1 sheet forming method using a doctor blade, which is a normal ceramic forming method, slurry casting,
Applicable methods include producing granules using a spray dryer and then producing a molded body using a press molding method.

When sintering the molded body produced by this method, it was added before sintering to give the molded body appropriate strength and flexibility. Volatile components such as binders and plasticizers must be removed. In this step of removing volatile components, a method of removing them by heating, which is a method of a normal ceramic sintering step, is used. The atmosphere at this time may be air, vacuum, or nitrogen atmosphere. However, in the case of air, the amount of moisture contained in the air and the flow rate of the air must be appropriately controlled in order not to excessively increase the amount of impurity oxygen in aluminum nitride.

The heating temperature in this binder removal process is as follows.

A suitable temperature between 400 and 1000°C can be selected. However, when debinding is performed in the atmosphere,
Since decomposition of aluminum nitride occurs, it is preferable to carry out the process at a temperature below 650°C.

The molded body from which the binder has been removed is sintered in a nitrogen atmosphere or an inert atmosphere containing nitrogen.

The temperature at this time is in the range of 1600 to 2000°C, more preferably in the range of 1750 to 1950°C. At temperatures lower than this, the sintered body is insufficiently densified;
Furthermore, at temperatures exceeding this range, sublimation of aluminum nitride becomes non-negligible and uneven sintering of the sintered body tends to occur.

[Effects] The aluminum nitride sintered body produced by the above method is
The sintered body has a bending strength of 35 kg/m m2 or more, a thermal conductivity of 100 W/m-2 or more, and is used as a thick film semiconductor ceramic substrate. It can withstand repeated stress caused by the difference in thermal expansion coefficient between the aluminum nitride and the bonded copper plate due to the temperature difference that occurs during actual operation, and can be fully used as a product without causing cranking or destruction. Although this effect is not clear, it is thought to be due to the following mechanism.

That is, when the aluminum nitride molded body according to the present invention is sintered, the state immediately before the molded body begins to shrink is such that the surface of each aluminum nitride particle contains alumina generated from oxygen dissolved in solid solution on the surface. It is thought that it exists. The added sintering aid particles react with alumina on the surface of the nearby aluminum nitride particles to generate a complex oxide liquid phase, and the resulting liquid phase reacts repeatedly with the alumina on the surface of one particle, causing nitridation. It is generally believed that aluminum nitride begins to shrink at the same time as it spreads over the aluminum particle surface one after another.

At the same time, the sintering aid particles, with the expansion of the surrounding liquid phase,
By expelling the components into the liquid phase, they become smaller and eventually disappear. As the shrinkage progresses, grain growth of the aluminum nitride particles will occur and the particle surfaces will be covered with a liquid phase.

At the same time, the added alumina particles, which are present between the aluminum nitride particles, react with the liquid phase formed on the surface of the aluminum nitride particles, and the particles themselves begin to change into a liquid phase. , begins to collect its liquid phase into particles. Naturally, the sintering aid particles will eventually become a complex oxide-based liquid phase, but the mobility between the alumina particles and the liquid phase on the aluminum nitride surface is in the solid phase, or the alumina particles are close to the solid phase. It is assumed that there should be fewer particles, and that the effect of collecting the liquid phase as an alumina source would be greater than flowing out into the liquid phase.

Due to the action of collecting the liquid phase of this alumina particles.

Although the alumina particles eventually change to the liquid phase.

At the same time, the liquid phase at the aluminum nitride grain boundaries disappears. It is presumed that this effect increases the strength between the crystal grains of the aluminum nitride sintered body, thereby improving the strength of the sintered body.

[Example] An example of the present invention will be specifically shown below, but the technical scope of the present invention is not limited thereto unless it departs from the spirit of the present invention.

Actual JL Example - 3 w of ittria as a sintering aid to commercially available aluminum nitride powder (average particle size 0.8 μm) produced by the reduction nitriding method.
t%, and the alumina purity is 99.9wt% and the average particle size is 0. A binder and a plasticizer are added to a mixed powder containing 1 wt% of 6 μm alumina particles.

A dispersant and a solvent were added, and ball mill mixing was performed for 96 hours to prepare a slurry.

After discharging the slurry produced by this method, the viscosity was adjusted and the slurry was spray-dried in a nitrogen stream at 120°C to produce granules. The granules were then dry pressed using a mold under a pressure of 1000 kgf/cm2 for 1 minute to produce a 60 mm square aluminum nitride green molded body.

This molded body was then heated to 800° C. in vacuum to degrease it. This degreased aluminum nitride molded body was sintered at a temperature of 1800° C. for 4 hours in a nitrogen atmosphere.

Ten aluminum nitride sintered bodies were produced by the above method. The size of this sintered body is 50 mm square and 8 mm thick.
It was a beige, homogeneous, dense sintered body of mm.

Using this sintered body, 4 mm x 3 mm x 40
A transverse strength test piece with a diameter of 10 mm and a thickness of 2 mm
A test piece for thermal conductivity measurement of mm was processed. The measurement results using this test piece show that the bending strength is 42 kg f/
mm2. +Thermal conductivity was 165 W/m·k.

The thermal conductivity value at this time was determined by the laser flash method.

Next J1 Child L2 - In Example 1, the amounts of binder and plasticizer were changed to prepare a slurry. After adjusting the viscosity of this slurry,
Tape molding is performed using the doctor blade method, and the thickness is 0.
．． A 9 mm aluminum nitride green sheet was produced.

The above green sheet is 60mm x 60m
After punching with a die to a size of m, six of the green sheets were stacked and heated to 100 kg f/m at 120°C.
The green sheet was thermocompression bonded by holding it under a pressure of m 2 for 30 minutes. This was degreased and sintered in the same manner as in Example 1.

A test piece was prepared from this sintered body in the same manner as in Example 1, and the bending strength and thermal conductivity of the sintered body were measured. As a result, the bending strength was 39 kgf/mm2, and the thermal conductivity was 169 W/m-.

- An aluminum nitride sintered body was produced in the same manner as in Example 1, except that the amount and type of sintering aid and alumina added were changed. The results are shown in Table 1.

1. In Example 1, an aluminum nitride sintered body was produced in the same manner as in Example 1 without adding alumina. At this time, the bending strength of the sintered body was 27 kgf/mm2, and the thermal conductivity was 173 W.
/m-.

In Example 2 of Tomoshibori Toyoyu, an aluminum nitride sintered body was produced in the same manner without adding alumina. At this time, the sintered body had a bending strength of 30 kgf/mm2 and a thermal conductivity of 167 w/m-.

[Effects of the Invention] As is clear from the examples described above, the present invention has made it possible to produce an aluminum nitride sintered body with high thermal conductivity and high strength.

The present invention can be applied to thick film copper bonded substrates,
This will greatly contribute to the use of aluminum nitride substrates as highly thermally conductive insulating substrates in fields that require high heat dissipation characteristics for various semiconductors.

Claims (1)

[Claims] (1) Average particle size is 5 μm or less, impurity oxygen content is 3 wt%
Below, we will explain how to produce a highly thermally conductive aluminum nitride sintered body using aluminum nitride powder as the main component with a cationic impurity content of 0.3 wt% or less and adding a rare earth or alkaline earth oxide sintering aid. A method for producing a high-strength aluminum nitride sintered body with high thermal conductivity, characterized by adding 0.6 to 5 wt% of α-alumina powder having an average particle size of 5 μm or less to the above-mentioned mixture of aluminum nitride powder.