JP2772580B2 - Method for producing aluminum nitride sintered body - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an aluminum nitride sintered body having high thermal conductivity, and more particularly, to an aluminum nitride sintered body which can be fired at a low temperature and has excellent mass productivity. About the body.

(Prior art) In recent years, as information processing apparatuses have become higher in performance and higher in speed, semiconductor integrated circuits constituting the information processing apparatuses have been rapidly becoming denser and more highly integrated. The problem is how to efficiently remove the heat generated to operate the semiconductor integrated circuit device normally.

In recent years, such a substrate has been replaced with a substrate made of alumina or a substrate made of beryllium oxide, which has long been known as a high thermal conductive substrate. Aluminum nitride-based sintered bodies having high properties, high thermal conductivity, and excellent properties such as a coefficient of thermal expansion closer to that of silicon single crystal as compared with alumina are attracting attention.

However, aluminum nitride is inherently difficult to sinter,
Since a high-density sintered body having high thermal conductivity cannot be obtained simply, rare-earth element oxides such as Y ₂ O ₃ as sintering aids,
Alternatively, a method of adding an alkaline earth element oxide such as CaO to increase the density has been adopted.

(Problems to be Solved by the Invention) However, in the conventional method, in order to obtain a high-density aluminum nitride sintered body, it is necessary to fire at a high temperature of 1700 ° C. or more, and sometimes 1900 ° C. or more. Was. When the sintering temperature is high, for example, when sintering is performed simultaneously with the metal conductor pattern formed on the substrate, there is a problem that the bonding strength between the conductor and the substrate is reduced due to the metal conductor grain growth, and The structure of the firing furnace itself also requires heat resistance, so that there is a problem that the cost of production equipment and the like becomes high, and the cost of the substrate itself becomes extremely high.

Therefore, a method of simultaneously adding a rare earth element oxide and an alkaline earth element oxide to achieve low-temperature calcination is described in JP-A-61-117160, but the calcination temperature is at most 1700 ° C. At a firing temperature of about 1600 ° C., densification has not been achieved. Further, a method of lowering the sintering temperature by adding a fluoride of a rare earth element to aluminum nitride is described in JP-A-61-209959, but the fluoride itself is very expensive, and fluorinated oxidation occurs during sintering. It is not suitable for mass production because the furnace is corroded due to the volatilization of materials.

(Object of the Invention) The object of the present invention is to solve the above-mentioned problems, and more specifically, it has a thermal conductivity of 40 W / m · K or more and a relative temperature of 1700 ° C. or less. An object of the present invention is to provide a method for producing an aluminum nitride sintered body that achieves a density of 90% or more.

(Means for Solving the Problems) As a result of repeated studies on the above problems, the present inventors have found that elements of Group IIIa and II of the Periodic Table as sintering aids.
It was found that by simultaneously adding lithium oxide together with the oxide of the group (a) element, an aluminum nitride sintered body having a high relative density and a high thermal conductivity can be obtained even by firing at a low temperature of 1700 ° C. or less, The present invention has been reached.

That is, the method for producing an aluminum nitride-based sintered body of the present invention comprises the steps of: converting an aluminum nitride powder into an oxide of Group IIa of the periodic table or a compound capable of changing to the oxide by firing;
And Group IIIa oxides of the Periodic Table or compounds that can be converted to the oxides by calcination
0.01 to 20% by weight, lithium oxide or a compound which can be converted to its oxide by firing is 0.001 to 10
After the mixture added at a ratio of 1% by weight is molded, the mixture is fired at a temperature of 1500 to 1700 ° C. in a non-oxidizing atmosphere containing nitrogen to have a relative density of 90% or more and an impurity oxygen amount of 0.2 to 6%.
What is claimed is: 1. A method for producing an aluminum nitride-based sintered body, comprising obtaining a sintered body by weight.

 Hereinafter, the present invention will be described in detail.

A major feature of the present invention resides in that an oxide of at least one element selected from Group IIIa and Group IIa of the periodic table and a compound containing lithium are added as a sintering aid.

The Group IIIa and Group IIa elements in the sintered body are 0.01 to 20% by weight as an oxide, particularly 0.1 to 15% by weight,
Lithium oxide (Li ₂ O) as 0.001 to 10 wt%, it is important that in particular 0.01 to 5.0 wt%.

The reason why the amount of the sintering aid is limited to the above range is as follows.
1700 when the group IIIa and group IIa elements are less than 0.01% by weight
This is because a relative density of 90% or more cannot be achieved by calcination at a temperature of not more than 20 ° C., and if it exceeds 20% by weight, the thermal conductivity is lower than 40 W / m · K. On the other hand, even when the amount of lithium exceeds 10% by weight, the thermal conductivity becomes 40 W / m · K or less, and when the amount is 0.001% by weight or less, the effect of low-temperature sintering is hardly obtained.

According to the present invention, as a sintering aid component, three components of Group IIa element of the periodic table, Group IIIa element of the periodic table, and lithium are added in combination. In this case, Periodic Table IIa
Group elements and Group IIIa elements were all converted to oxides at 0.
By setting the content to 01% by weight or more, the densification by low-temperature firing can be performed more stably.

According to the present invention, the amount of impurity oxygen in the sintered body containing the sintering aid is 0.2 to 6% by weight, particularly 0.4 to 3.0%.
It is also important that the percentage is by weight. The impurity oxygen amount is an oxygen amount excluding the oxygen in the oxide mixed as the sintering aid from the total oxygen amount in the sintered body, and mainly includes oxygen as an unavoidable impurity in the aluminum nitride raw material powder. Equivalent to. This impurity oxygen also greatly contributes to the sinterability of the entire system. If the amount is less than 0.2% by weight, high density by low-temperature sintering cannot be achieved, and if it exceeds 6% by weight, the thermal conductivity decreases.

Further, according to the present invention, it is desirable that the average crystal grain size of aluminum nitride in the sintered body is 0.8 μm or more, particularly 1.2 μm or more. The crystal grain size greatly contributes to the thermal conductivity of the sintered body, and the larger the grain size, the higher the thermal conductivity. That is, when the particle size is smaller than 0.8 μm, the volume (area) occupied by the grain boundaries between the crystal grains is large, so that the grain boundaries become obstacles for phonon conduction, and the thermal conductivity is reduced.

Next, a method for manufacturing such an aluminum nitride sintered body will be described.

First, the aluminum nitride raw material powder is manufactured by a known method such as a direct nitriding method, an alumina reducing method,
Powders with an average particle size of 2 μm or less with an oxygen content of 1.5% by weight or less, a carbon content of 0.2% by weight or less, a cationic impurity content of 0.1% by weight or less excluding aluminum, and particularly a Si content and a Fe content of 100ppm or less. It is preferably used.

The sintering aid component is a compound that can be converted into an oxide by firing, in addition to using an oxide powder, such as carbonate, chloride, and water. It can also be added as a compound such as an oxide.

The mixed powder obtained by adding the sintering aid component to the aluminum nitride raw material powder is mixed in an organic solvent if desired. At this time, the amount of water contained in the organic solvent is set to 0.4% by weight or less. Thereby, the dispersibility of the aluminum nitride powder can be improved, and oxidation of the surface of the aluminum nitride particles due to the reaction with moisture can be prevented.

The obtained mixed powder is formed into a desired shape by a known molding method, for example, press molding using a mold or hydrostatic pressure, sheet molding, extrusion molding, or the like, and then is transferred to firing.

Firing is performed in a non-oxidizing atmosphere containing nitrogen gas, and as the firing means, normal pressure firing, hot press firing, nitrogen gas pressure firing, or the like is employed.
By setting the firing temperature at this time to 1500 ° C. or higher, the density can be increased to a relative density of 90% or higher, and the average crystal grain size of aluminum nitride rapidly increases from the primary particles in the raw material.

As the firing temperature is further increased above 1500 ° C, the sinterability improves and the average crystal grain size of aluminum nitride gradually increases.However, when the temperature exceeds 1700 ° C, the heat resistance of the firing furnace is required, so The structure becomes large-scale. Therefore, in consideration of mass productivity, it is preferable that the firing temperature is set to 1700 ° C. or lower, particularly 1650 ° C. or lower, and firing at normal pressure is performed, whereby a continuous furnace or the like can be used.

In addition, the lithium compound may be partially volatilized during firing, but from the viewpoint of sinterability, high sinterability can be obtained by allowing the lithium compound to be present in the above-described predetermined amount when mixing the raw materials.

(Action) It is not clear why the firing temperature can be significantly reduced by adding an oxide of a group IIa element and a group IIIa element and a lithium compound to aluminum nitride in a complex manner. It is considered that a low melting point composite oxide is formed between the Group IIa oxide and the lithium compound, or between the Group IIIa oxide and the lithium compound, and furthermore, the Group IIa element oxide and the Group IIIa element oxide At the same time as adding a Group IIa oxide and a Group IIIa oxide.
It is presumed that the liquid-phase sintering of aluminum nitride progresses due to the formation of a composite oxide having a lower melting point between the group a oxides.

 Hereinafter, the present invention will be described with reference to the following examples.

(Example 1) Aluminum nitride raw material powder, average particle size (BET specific surface area) 3.3 m ² / g, impurity oxygen amount 1.1 wt%, carbon content
Based on a commercially available aluminum nitride raw material powder having a 0.05% by weight or less and a cationic impurity content other than aluminum of 0.1% by weight or less, a Yb ₂ O ₃ powder having an average particle diameter of 0.9 μm is 9.1% by weight and an average particle diameter is 1.5%. μm CaCO ₃ powder was added and mixed at 5.2% by weight in terms of CaO, and the amount added was fixed at 1% by weight.
Various oxides shown in the table were added. Then add this at room temperature for 10
Press molding was performed at a pressure of 00 kg / cm ² . 1500 for this compact
At 1 ° C, 1550 ° C, and 1650 ° C under 1 atmosphere of nitrogen gas
Fired for hours. For each sintered body after firing, the relative density was calculated based on the Archimedes method, and for the product fired at 1650 ° C, the thermal conductivity was measured by the laser flash method, and the appearance was further observed to determine the presence or absence of spots. .

 The results are shown in Table 1.

Sample No. 1 in which the sintering aid consisted of only addition of Yb ₂ O ₃ and CaO
At 1650 ° C. to 1700 ° C., a sintered body having a relative density of 90% or more was obtained, but densification could not be performed at a temperature lower than 1650 ° C. shown in Table 1.

Thus, comparing the effects of adding various oxides from Table 1, the addition of lithium oxide clearly reduced the firing temperature, and achieved a relative density of 90% or more at 1500 ° C. It was also confirmed that lithium oxide had an effect of improving the appearance of the sintered body, and it was found that addition of about 1% by weight did not affect the thermal conductivity.

In addition, low-temperature baking was difficult with other oxides, and the surface was stained, which was not preferable.

(Example 2) Based on the results of Example 1, using exactly the same raw materials as used in Example 1, 9.1% by weight of Yb ₂ O _{3 and} 5.2% by weight of CaCO ₃ (in terms of CaO) were added to aluminum nitride powder. The composition containing 1% by weight of Li ₂ CO ₃ in terms of Li ₂ O was calcined at normal temperature in a nitrogen gas atmosphere at the temperature shown in Table 2 for 3 hours, and the relative density, The thermal conductivity and the average crystal grain size of the aluminum nitride of the sintered body were measured.

 The results are shown in Table 2.

According to Table 2, the sample to which lithium was added was 1500 ° C.
With the above, a relative density of 90% is achieved and the thermal conductivity is also 40 W / m · K
Beyond. Further, as the temperature is further increased, the thermal conductivity also sharply increases. This is considered to be because the crystal grain size increases.

(Example 3) Next, Yb ₂ O ₃ and CaCO ₃ content is set to the same as in Example 2, was added by changing the Li ₂ CO ₃ (Li ₂ O equivalent amount), respectively 15
It was calcined at 00 ° C., 1550 ° C., and 1650 ° C. in nitrogen at normal pressure for 3 hours.

With respect to the obtained sintered body, the amount of lithium was quantified by ICP analysis, and the amount in terms of oxide is shown in Table 3. In addition, the relative density of the sintered body was measured, and the presence or absence of a stain was determined by observing the thermal conductivity and appearance of the sintered product at 1650 ° C.

 The results are shown in Table 3.

According to the results in Table 3, when the Li ₂ O content is less than 0.001% by weight, spots are observed on the surface of the sintered body, and at a temperature of 1550 ° C. or lower, a relative density of 90% cannot be achieved. In addition, the amount of Li ₂ O is 10
If it exceeds 10% by weight, the thermal conductivity is greatly reduced. Therefore,
It has been confirmed that stable sintering can be performed when the Li ₂ O content is 0.001 to 10% by weight, particularly 0.01 to 5.0% by weight.

(Example 4) Next, oxides of Table 4 were used as Group IIIa element oxides of the periodic table, and CaO, BaO, and SrO were used as carbonates of Group IIa element oxides of the periodic table, respectively. They were added at the ratios shown in Table 4 and fired at temperatures of 1500 ° C., 1550 ° C., and 1650 ° C., and the relative densities and thermal conductivity of the fired products at 1650 ° C. were measured.

The impurity oxygen content of the sintered body was calculated by subtracting the oxygen content of the oxide added as a sintering aid from the total oxygen content of the sintered body.

 The results are shown in Table 4.

According to Table 4, in Sample Nos. 58 (IIIa only) and 59 (IIa only) to which no lithium compound was added, and in Sample No. 1 (IIIa + IIa only) in Table 1 above, all were 165.
At a temperature of 0 ° C. or less, a sintered body with a relative density of 90% or more cannot be obtained.
In sample No. 56, in which the total amount of the oxides of the group II elements and the oxides of the group IIa elements exceeded 20% by weight, the thermal conductivity was low,
Sample No. 60 having less than 1% by weight had low relative density and low thermal conductivity.

Further, in Sample No. 57 in which the impurity oxygen content of the sintered body was less than 0.2% by weight, a relative density of 90% or more was not achieved below 1600 ° C., and in Sample No. 47 exceeding 6% by weight, the relative density was high. Thermal conductivity dropped significantly.

For these comparative examples, the samples of the present invention were all 1650.
A relative density of 97% or more was achieved at a sintering temperature of 150 ° C., and even at 1500 ° C., the relative density could be increased to 90 ° C. or more, and a thermal conductivity of 40 W / m · K or more was achieved. Among them, those obtained by adding a Ca compound as a Group IIa element compound and a Yb ₂ O ₃ as a Group IIIa element compound in combination with a lithium compound are the most excellent in terms of sinterability and stability of properties. Was.

(Effect of the Invention) As described in detail above, according to the present invention, the periodic table IIIa
The sinterability can be improved by adding a predetermined amount of a lithium compound to the oxides of the Group II elements and Group IIa elements, and the relative density is 90% even at a firing temperature of 1700 ° C or less.
A sintered body having the above high thermal conductivity can be obtained. This eliminates the need for a special heat-resistant structure as a sintering furnace for manufacturing a highly thermally conductive aluminum nitride sintered body, thereby reducing manufacturing costs and the like. Body can be provided.

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Claims (1)

(57) [Claims] 1. An aluminum nitride powder is added to the periodic table IIa
Group oxides or compounds that can be converted to their oxides by firing, and Group IIIa oxides or compounds that can be converted to their oxides by firing, in a total of 0.01 to 20% by weight in terms of oxides, lithium oxide Alternatively, a compound that can be converted to its oxide by firing is converted to an oxide equivalent of 0.
After molding the mixture added at a ratio of 001 to 10% by weight, in a non-oxidizing atmosphere containing nitrogen at 1500 to 1700 ° C
Baking at a temperature of more than 90%, the relative density is more than 90%, the amount of impurity oxygen is
A method for producing an aluminum nitride-based sintered body, comprising obtaining a sintered body of 0.2 to 6% by weight.