JP2742598B2 - Aluminum nitride sintered body and method for producing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride sintered body and a method for producing the same, and more particularly, to a material for electronic components such as a substrate having high thermal conductivity and heat dissipation. The present invention relates to a suitable aluminum nitride sintered body and a method for producing the same.

(Prior art)

In recent years, as information processing devices have become higher in performance and higher in speed, the density of semiconductor integrated circuits constituting the information processing devices has also increased rapidly, and the integration thereof has rapidly advanced. In order to operate the semiconductor integrated circuit device normally and stably, there is a problem how to efficiently remove the generated heat.

Therefore, conventional semiconductor packages based on alumina have low thermal conductivity and insufficient heat dissipation.
A beryllium oxide sintered body has been proposed as a ceramic material having a high thermal conductivity, but has a problem in use due to its toxicity.

Therefore, it has high mechanical strength from room temperature to high temperature, high electrical insulation, high thermal conductivity, and thermal expansion coefficient of silicon single crystal compared to alumina as a high thermal conductive substrate material replacing beryllium oxide sintered body. Attention has been paid to aluminum nitride sintered bodies having excellent properties such as closeness.

However, aluminum nitride is inherently difficult to sinter, and it was difficult to obtain a high-density sintered body having high thermal conductivity simply. Therefore, aluminum nitride raw material powder is used as a sintering aid
A sintered body is obtained by adding a compound of a group a element, for example, an alkaline earth metal such as calcium, strontium and barium, or a compound of yttrium and a rare earth element.

[Problems to be solved by the invention]

However, in the conventional method, the amount of the sintering aid component present in the grain boundary phase of the aluminum nitride sintered body is not uniform, and it is difficult to easily and stably produce a material having high thermal conductivity. Was. At the same time, due to the non-uniformity of the grain boundary phase, when used for a substrate or the like, there is a problem that the metallization property is poor and the long-term reliability is reduced.

Such a tendency is particularly remarkably observed in Y ₂ O ₃ which is generally used as a sintering aid. This is because the sintering aid reacts with the oxide phase contained in the aluminum nitride to form a grain boundary phase and promotes sintering of the aluminum nitride. As a result, in the sintered body, there occur problems such as generation of color unevenness, spots, etc., and local nonuniformity of thermal conductivity, which makes it difficult to manufacture easily and stably. Had.

Therefore, as one countermeasure, it is conceivable to reduce the grain boundary phase by reducing the amount of the sintering aid as much as possible. However, since the sintering aid is an essential element for sintering aluminum nitride, If the amount of the auxiliary agent is too small, there is a problem that a high-density sintered body cannot be obtained.

Therefore, the present invention has previously found that the evaporation rate of the sintering aid used at the sintering temperature of aluminum nitride has a large effect on the amount and non-uniformity of the residual grain boundary phase in the sintered body. Evaporation rate at 1900 ° C is 10 ^-6 as binder
10 using a metal or metal compound in the range of ^-3 g / cm ² · sec, when firing the sintering aid, is blended in an amount capable of producing sufficient liquid phase required for sintering simultaneously By volatilizing the sintering aid during the firing process, the grain boundary phase in the final sintered body is reduced as much as possible, and at the same time, the non-uniformity of the grain boundary phase is almost eliminated, and the density is increased and the heat is increased. It was found that conductivity could be achieved, but its thermal conductivity was at most 200 W / m · K.

[Object of the invention]

An object of the present invention is to solve the above-mentioned problems, and specifically, to provide a uniform aluminum nitride sintered body having high thermal conductivity and high density. An object of the present invention is to provide a method for easily and stably producing the sintered body.

[Means for solving the problem]

The present inventors have conducted studies on the above problems, and as a result,
The evaporation rate of the sintering aid used at the sintering temperature of aluminum nitride greatly affects the amount and non-uniformity of the residual grain boundary phase in the sintered body. It has been found that a metal compound may be added simultaneously. So using the evaporation rate at a temperature of 1900 ° C. as the sintering aid is 10 ^-6 ~10 ^-3 g / cm metal or metal compound is in the range of ² · sec and an alkaline earth metal or a metal compound, the sintering At the time of firing, the auxiliary is mixed in an amount capable of producing a sufficient liquid phase required for sintering, and at the same time, the sintering aid is volatilized during the firing step, thereby forming a grain boundary phase in the final sintered body. Was found to be as small as possible, and at the same time, the grain boundary phase was almost completely non-uniform, and it was possible to achieve a high density and a high thermal conductivity.

That is, according to the present invention, AlN powder is added at 84 to 97% by weight,
Containing 3 to 15% by weight of erbium (Er) or a metal compound powder thereof as a rare earth metal having an evaporation rate in the range of 10 ^-6 to 10 ^-3 g / cm ² · sec, and an alkaline earth metal After forming a mixture containing 0.01% to 0.2% by weight of calcium (Ca) or its metal compound powder, the mixture is fired at a temperature of 1700 to 2000 ° C. in a non-oxidizing atmosphere containing 1 Torr or more of nitrogen gas. By volatilizing the erbium or its metal compound until the content in the sintered body becomes 0.1% by weight or less in terms of metal and calcium or its metal compound becomes 0.01% by weight or less in terms of metal, density 3.2~3.3g / cm ^2, the thermal conductivity of 200 W / m
-It is possible to obtain an aluminum nitride sintered body of K or more.

 Hereinafter, the present invention will be described in detail.

A major feature of the present invention is that the sintering aid has an evaporation rate at 1900 ° C. of 10 ⁻⁶ to 10 ⁻³ g / cm ^2.
Sec, in particular, a rare earth metal or its metal compound and an alkaline earth metal or its metal compound in the range of 10 ^-5 to 10 ^-4 g / cm ² · sec. The metal compound includes Er ₂ O ₃ , and the alkaline earth metal compound includes CaO. The evaporation rate is data obtained from a sintered body of a substance in a vacuum as described in Balkevich et al. (Inorg. Mat. 11 (7), 12 (1)). According to the literature evaporation rate at 1900 ° C. is the Er ₂ O ₃ 1.2
× 10 ^-5 g / cm to which the a _² · sec, Y ² O ₃ usually used
Shows a small value of 8.0 × 10 ⁻⁸ g / cm ² · sec.

On the other hand, the aluminum nitride powder used in the present invention is manufactured by a known method such as a direct nitriding method or an alumina reduction method, and has an oxygen content of 1.5% by weight or less and a carbon content of 0.1% or less.
It is a powder having an average particle diameter of 2 μm or less in which the content of cationic impurities excluding aluminum is 0.1% by weight or less, particularly the content of both Si and Fe is 100 ppm or less.

The aluminum nitride powder and the sintering aid are mixed in such an amount that the sintering aid can sufficiently form a liquid phase in firing, and the aluminum nitride powder is 84 to 97% by weight, the rare earth metal or its metal Cl content 3 To 15% by weight, and an alkaline earth metal or its metal compound powder in a ratio of 0.01 to 0.2% by weight.

The compounded 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. As a result, the dispersibility of the AlN powder is improved, and the reaction with water in the solvent
Oxidation of the AlN particle surface can be prevented.

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

The firing is performed at a firing temperature of 1700 to 2000 ° C. in a non-oxidizing atmosphere containing nitrogen gas at 1 Torr or more, particularly 760 Torr or more. Examples of firing means include normal pressure firing and nitrogen gas pressure firing, and the rare earth metal or its metal compound in the sintered body obtained by these firings is 0.1% by weight or less in terms of metal, Ca metal Alternatively, the densification can be promoted by hot isostatic firing of a sintered body containing the compound in an amount of 0.01% by weight or less in terms of metal.

According to the present invention, in the firing step, the rate of temperature increase from 1200 ° C. to the firing temperature is set to an average of 40 ° C./min or less, and the sintering aid and the nitriding It is desirable to uniformly generate aluminate as a liquid phase component by reaction with oxygen on the surface of the aluminum powder, and if the temperature rise rate exceeds an average of 40 ° C./min, the aluminate that is a liquid phase component is not generated sufficiently. As it reaches the firing temperature,
The sintering aid volatilizes, and sufficient sintering does not proceed, so that a high-density sintered body cannot be obtained.

At the same time as sintering proceeds while aluminate is sufficiently generated, volatilization of the sintering aid gradually proceeds. At this time,
In order to keep the liquid phase component until sintering proceeds sufficiently, for example, by installing the same auxiliary powder as the sintering aid in the molded body in a firing furnace, After the surroundings are made almost the same as the vapor pressure of the auxiliaries, and the sintering has sufficiently proceeded, the gas in the sintering furnace is forcibly replaced to keep the surroundings of the molded body lower than the above-mentioned pressure of the auxiliaries. Volatilization can be promoted.

However, in the volatilization control based on the vapor pressure, the volatilization speed is slow, so that it is necessary to lengthen the calcination time. Therefore, the volatilization can be further promoted by preferably containing carbon in the atmosphere.

In the firing step, the amount of the firing aid is finally 0.1% by weight or less in terms of Er metal, preferably 0.07% by weight or less, more preferably 0.04% by weight or less, and 0.01% by weight or less in terms of Ca metal, It is preferably volatilized to 0.005% by weight or less, more preferably 0.003% by weight or less.

After firing, average 40 ° C / m from firing temperature to 1200 ° C
It is desirable to lower the temperature at a rate of not more than in, thereby eliminating any non-uniform layer on the surface of the sintered body and achieving uniformity.

By such a manufacturing method, in the final sintered body,
Density 3.2~3.3g / cm ^3, in particular 3.24~3.27g / cm ^3, the thermal conductivity 20
0 W / mK or more is achieved.

However, when calcination is performed to suppress volatilization in calcination even if an auxiliary agent having a high evaporation rate is used, the density is close to the apparent theoretical density (a value calculated from the density and the mixing ratio of each raw material powder of the sintered body). Value, and there are many residual assistants in the sintered body, and the thermal conductivity does not increase.

In addition, the amount of the auxiliary agent remaining in the sintered body is 0.
The reason for limiting the content to 1% by weight or less and 0.01% by weight or less in terms of Ca metal is that the amount of the residual auxiliary exceeds 0.1% by weight in terms of Er metal and C
aWhen the metal content exceeds 0.01% by weight, the thermal conductivity is 200W / m ・ K
Is not achieved, and the sintered body becomes non-uniform. Further, those having a density of less than 3.2 g / cm ³ have many vacancies, and those having a density of more than 3.3 / cm ³ mean that there are many grain boundary phases.

Further, in the above configuration of the present invention, the sintering aid 1900
If the evaporation rate at 10 ° C is lower than 10 ^-6 g / cm ² · sec, it remains as a grain boundary phase in the sintered body even after sintering has progressed, resulting in uneven color, spots, and local unevenness in thermal conductivity. It becomes a factor. Also 10 ^-3 g /
If it exceeds cm ² · sec, the auxiliary component will evaporate before sintering of aluminum nitride sufficiently proceeds, and densification will not be performed.

Further, the amount of the sintering aid was limited to 3 to 15% by weight of the Er metal or its metal compound powder and to 0.01 to 0.2% by weight of the Ca metal or its metal compound powder. %, The sintered body cannot be sufficiently densified even if the amount of the Ca metal compound is increased. If the amount exceeds 15% by weight, volatilization of the auxiliary agent becomes difficult, and a large amount of the grain boundary phase remains. This is because the thermal conductivity decreases, resulting in a non-uniform sintered body.If the amount of the Ca metal compound is less than 0.01, the thermal conductivity becomes 200 W / m.
-If it is lower than K and exceeds 0.2% by weight, no improvement in thermal conductivity is observed.

When the sintering aid is added, in addition to Er ₂ O ₃ and CaO, it may be added in the form of carbonate or nitrate which can be converted into these oxides by firing.

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

〔Example〕

First, the oxygen content is 1.5% by weight or less, the carbon content is 0.15% by weight or less, and the content of cationic impurities excluding aluminum is 0.1%.
1% by weight or less of a commercially available aluminum nitride raw material powder, Er ₂
O ₃ and CaCO ₃ were mixed in the proportions shown in Table 1 while changing the amount of addition. Next, a pressure of 1000 kg / cm ² was applied to this mixed powder at room temperature to obtain a molded body. This compact was sintered under a normal pressure at 1900 ° C. in a nitrogen gas atmosphere containing carbon. In the firing, the temperature was increased from 1200 ° C. to each firing degree at a rate of 20 ° C./min.

At this heating rate, it was confirmed that a reaction product (aluminate) with Al ₂ O ₃ was generated in each sample. After reaching the firing temperature, the firing was always performed with the nitrogen gas replaced. In addition, the rate of cooling down to 1200 ° C is 20 ° C / m
set to in. However, No. 16 was fired without containing carbon in the atmosphere in the firing furnace. The density and the thermal conductivity of the obtained aluminum nitride sintered body were measured and sorted by the Archimedes method, the thermal conductivity was measured by the laser flash method, and the occurrence rate of color unevenness and spots was visually observed with a binocular microscope. The results are shown in Table 1.

In addition, the amount of the assistant (metal equivalent) in the sintered body was measured by ICP emission spectroscopy. The results are shown in Table 1.

As is clear from the results in Table 1, the evaporation rate at 1900 ° C was 10
No. 17 and No. 18 samples using Y ₂ O ₃ below ^-6 g / cm ² · sec had high density, but the auxiliary remained at 2.0% by weight or more. The generation is severe and the thermal conductivity is low. In the sample of No. 1 in which the addition amount of the Er ₂ O ₃ metal oxide was less than 3% by weight, the sintering was insufficient and high thermal conductivity was not achieved. In addition, in the sample of No. 7 in which the addition amount exceeds 15% by weight, the remaining amount of the auxiliary agent is large,
There were spots. Even when the addition amount was in the range of 3 to 15% by weight, in the sample of No. 16 in which volatilization was suppressed, the remaining amount of the auxiliary exceeded 0.1% by weight, and high thermal conductivity was not obtained.

High thermal conductivity was not achieved in the samples Nos. 8 and 9 in which the amount of CaCO ₃ added was less than 0.01% by weight. Further, in the sample of No. 15 in which the addition amount exceeded 0.2% by weight, no improvement in the thermal conductivity was observed.

In contrast, Samples Nos. 2 to ⁶ , 10 to 14 of the present invention all had an apparent density of 3.2 to 3.3 g / cm ³ and a thermal conductivity of 20 W / mK or more.
No color unevenness or spotting occurred.

(Effects of the Invention) As described above in detail, the aluminum nitride sintered body of the present invention has a high density, is excellent in heat conductor, has good thermal properties, electrical properties, and mechanical properties, and has a low raw material cost. Since it can be manufactured easily and stably without the characteristic unevenness in the material, it has many advantages as an electronic component material such as an insulating substrate on which the electronic component is mounted.

Claims (3)

(57) [Claims] An erbium (Er) metal or a compound thereof and a calcium (Ca) metal or a compound thereof as main components of AlN and a sintering aid, wherein the Er metal or the compound is 0.1% by weight in terms of metal. An aluminum nitride sintered body having a density of 3.2 to 3.3 g / cm ³ and a thermal conductivity of 200 W / m · K or more containing Ca metal or a compound thereof in a proportion of 0.01% by weight or less in terms of metal. 2. An AlN powder of 84 to 97% by weight and an Er ₂ O ₃ powder of 3%.
After molding a mixture containing CaO powder at a rate of 0.01 to 0.2% by weight and containing nitrogen gas at a rate of
In a non-oxidizing atmosphere containing 1 Torr or more, sintering is performed at a temperature of 1700 to 2000 ° C., and the content of Er metal or a compound thereof in a sintered body is 0.1% by weight or less in terms of metal, Ca metal or a compound thereof. Characterized in that it is evaporated to 0.01% by weight or less in terms of metal. 3. The method according to claim 2, wherein carbon is contained in a non-oxidizing atmosphere.