JPH1192229A - Production of highly heat-conductive aluminum nitride sintered product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an aluminum nitride sintered product comprising dense aluminum nitride having high heat conductivity. SOLUTION: This method for producing a highly heat-conductive aluminum nitride sintered product comprises sintering (a) a molded product or a sintered product (b) in a sintering vessel producing carbon gas or in a reducing atmosphere obtained by including a substance producing carbon gas on sintering in a sintering vessel (c) under an atmospheric pressure including a reduced pressure at 1,550-2,050 deg.C for a time exceeding 24 hr. The molded product is obtained by mixing aluminum nitride powder having an impurity oxygen content of <=7 wt. % and an average-particle diameter of 0.05-5 μm with a compound comprising (excluding fluorides) the oxides, nitrides, oxynitrides of rare earth elements in an amount of 0.01-15 wt.% converted into the weight of the rare earth elements. The sintered product has a rare earth element content of 0.01-15 wt.% and an oxygen content of 0.01-20 wt.%, and contains AIN as a main phase and further the phases of a (rare earth element)-Al-O compound and/or a (rare earth element)-O compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum nitride sintered body composed of a single phase of aluminum nitride.

[0002]

2. Description of the Related Art Aluminum nitride (AlN) is used as a heat-resistant material because its strength does not decrease to a high temperature and has excellent chemical resistance. On the other hand, a semiconductor device utilizing its high thermal conductivity and high electrical insulation is used. Is also promising as a heat sink material and an insulator material for circuit boards. Such aluminum nitride does not have a melting point under normal pressure and decomposes at a high temperature of 2500 ° C. or higher. Therefore, it is used as a sintered body except for applications such as thin films.

[0003] Such an aluminum nitride sintered body is usually obtained by molding and firing aluminum nitride powder. When an ultrafine powder (about 0.3 μm or less) of AlN powder is used, an almost dense sintered body can be obtained by itself, but oxygen in the oxide layer on the surface of the raw material powder is dissolved in the AlN lattice during sintering. Or an Al—O—N compound is generated, and as a result, the thermal conductivity of the sintered body without addition is at most about 100 W / m · K.
When AlN powder having a particle size of 0.5 μm or more is used, since the sintered compact is not good, it is difficult to obtain a dense sintered body without any addition except by hot pressing. In order to obtain a sintered body at normal pressure, rare earth oxides are used as sintering aids in order to densify the sintered body and prevent solid solution of impurity oxygen of AlN raw material powder into AlN grains. It is common to add an alkaline earth metal oxide or the like (JP-A-60-127267, JP-A-61-10071, JP-A-60-71575).
No.). These sintering aids react with the impurity oxygen of the AlN raw material powder to form a liquid phase to achieve densification of the sintered body, and fix the impurity oxygen as a grain boundary phase (oxygen trap) to provide a high thermal conductivity. Is expected to achieve

[0004] As described above, by adding a sintering aid, the sintered body is certainly densified and has a high thermal conductivity.
As a result, due to the existence of the remaining grain boundary phase (sub-phase with respect to the main phase of AlN) and the presence of oxygen and the like which could not be completely trapped, the aluminum nitride sintered body is at most 19
About 0 W / m · K, the theoretical thermal conductivity of AlN is 320 W /
It was much lower than m · K. Therefore, various attempts have been made for the purpose of improving the thermal conductivity of the aluminum nitride sintered body, but none of them have been obtained yet.

[0005]

At present, a material having a higher thermal conductivity is desired for a circuit board for mounting a semiconductor, a heat dissipation board, and the like. However, due to the presence of oxygen and other impurities, in particular, the grain boundary phase formed at the grain boundary as a result of the addition of the auxiliary agent, there has been a limit in increasing the thermal conductivity of the aluminum nitride sintered body. The present invention has been made in view of the above points, and has as its object to provide a method for manufacturing an aluminum nitride sintered body having excellent thermal conductivity.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a sintering aid added to aluminum nitride powder, sintering conditions, sintered body composition, sintered body microstructure, and the like. As a result of conducting experiments and studies on the relationship, the following new matter was discovered, and the present invention was completed.

That is, when an yttrium compound is added to an AlN powder as a sintering aid and calcined for a long time in a reducing atmosphere containing nitrogen, the amount of a grain boundary phase (Y-Al-O-based compound phase, etc.) is reduced. It was found that the amount was reduced as compared with the conventional aluminum nitride sintered body. And when it is sintered for a sufficiently long time, there is substantially no subphase and it consists of AlN single phase,
It has been found that an aluminum nitride sintered body having a very high thermal conductivity can be obtained as a polycrystal. This increase in thermal conductivity was similarly observed for other rare earth elements.

Based on this fact, the present invention is based on the results of various studies on the optimum conditions for achieving high thermal conductivity. A) The content of impurity oxygen is 7% by weight or less and the average particle size is 0.05 to 5 μm. A) a mixture of aluminum nitride powder as described above and 0.01 to 15% by weight, in terms of weight of rare earth element, of a compound of rare earth element oxide, nitride, and oxynitride; A baking vessel for generating gas or a reducing atmosphere obtained by including a substance that generates carbon gas during baking in a baking vessel; c) an atmosphere containing reduced pressure at 1550 to 2050 ° C. for more than 24 hours. Baking under the heat conductivity of 220W
/ M · K is a method for producing a highly thermally conductive aluminum nitride sintered body.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The aluminum nitride sintered body obtained by such a method has a very high polycrystalline body of 220 W
/ K, and only the AlN crystal grains are observed when the sintered body is observed for its constituent phases by X-ray diffraction and electron microscopy, and no other phases are observed. Further, when the component analysis was performed, Al and N were the main components, and the rare earth element 0.0
It was a novel aluminum nitride sintered body containing 1 to 8000 ppm, less than 2,000 ppm of impurity oxygen, and 1000 ppm or less of other impurity ion elements. From the viewpoint of improving the thermal conductivity, the rare earth element is 0.01 to 1000 p
pm and impurity oxygen are preferably 1000 ppm or less. From a practical viewpoint, the rare earth element is preferably 10 to 3000 ppm. Since this rare earth element is not observed at the crystal grain boundary, it is considered that it is dissolved in AlN crystal grains. The same applies to the oxygen element. In the sintered body of the present invention, the amount of impurity oxygen is desirably as small as possible, and the amount of impurity cations caused by the raw material powder is also desirably as small as possible because it causes a decrease in thermal conductivity.

The density of the AlN sintered body of the present invention is 3.120.
~ 3.285 g / cm ³ is preferred. If the density is low, the densification is not sufficient, and if the density is high, the impurity component is large. Preferably it is 3.259-3.264 / cm < ³ >.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The outline of an embodiment of the method for producing a highly thermally conductive aluminum nitride sintered body of the present invention will be described. The production method of the present invention is mainly based on the purity and average particle size of the aluminum nitride raw material powder, sintering aid, sintering vessel, firing time and firing atmosphere.

The aluminum nitride raw material powder, which is the main component, contains 7% by weight or less of oxygen in consideration of sinterability and thermal conductivity, practically 0.01 to 7% by weight, and has an average particle diameter of 0%. It is used in the range of 0.05 to 5 μm.

As an additive, a rare earth element compound (Y, S
c, Ce and Dy are preferred, and an yttrium compound is particularly preferred). The compound of the rare earth elements, acid <br/> product, nitride, oxynitride, or is optimal materials comprising these compounds by firing. Above, for example by calcination
Examples of the material that becomes the rare earth oxide include carbonates, nitrates, oxalates, and hydroxides of these elements.

The rare earth element compound is added in the range of 0.01 to 15% by weight in terms of the weight of the rare earth element. When the amount is less than 0.01% by weight, the effect of the additive is not sufficiently exhibited, and the sintered body is not densified,
Oxygen is dissolved in the AlN crystal and a sintered body having high thermal conductivity cannot be obtained. If the addition amount is excessively large, the grain boundary phase remains in the sintered body, or the volume of the grain boundary phase removed by the heat treatment is large, so that pores remain in the sintered body, and the shrinkage rate decreases. It becomes very large and has disadvantages such as the shape being distorted. Preferably, it is 0.1 to 15% by weight, more preferably 0.5 to 10% by weight.

In the method of the present invention, such a compact in which the AlN powder and the rare earth element compound are mixed may be sintered under the conditions described below, or a conventional method (for example, Japanese Patent Application Laid-Open No.
-17160), the rare earth element content is 0.01
Sintering with a main phase of AlN and a (rare earth element) -Al-O compound phase and / or a (rare earth element) -O compound phase A body may be manufactured and used in place of the compact.

The firing is performed in a reducing atmosphere, particularly in a reducing atmosphere containing nitrogen gas. The reducing atmosphere can be created by the presence of one or more of CO, H ₂ gas and C (gas and solid phase).

Regarding the firing container, aluminum nitride,
Alumina, Mo, etc. are also possible (Japanese Patent Laid-Open No. 61-14 / 1986).
No. 6769). However, in the case of using these containers, the (rare earth element) -Al-O compound phase or the like remains in the sintered body, and high thermal conductivity cannot be obtained. In the present invention, it is preferable to use a container that creates a carbon gas atmosphere during firing. As such a firing container, an AlN plate, a BN plate, a W plate, or the like is laid on a place where a sample is to be set, and a container made of aluminum nitride and a top cover made of carbon is used. be able to. The carbon gas atmosphere referred to in the present invention is 1
The vapor pressure is 1 × 10 in the sintering temperature range of 550-2050 ° C.
^{-6 to} 5 × 10 ^-2 Pa refers to gas generated. This carbon gas has an effect of reducing AlN during firing, and more specifically, has an effect of removing a grain boundary phase such as a (rare earth element) -Al-O ternary compound from the sintered body. In operation, the aluminum nitride sintered body becomes an AlN single phase and changes to a sintered body having high thermal conductivity.

The internal volume of this container is preferably 1.1 × 10 ⁰ to 1 × 10 ^{7, in} which the ratio of the internal volume to the volume of the aluminum nitride molded product (the internal volume / the volume of the molded product) is good. When a larger volume is used, the carbon vapor pressure in the vicinity of the sample is low, and the effect of carbon to remove the grain boundary phase is reduced. The volume ratio is preferably 5 × 10 ⁰ to 1 × 10 ⁵ .

The sintering time is conventionally as short as 1 to 3 hours using various auxiliaries. However, in such a time, even if the sintering is performed in the above-mentioned sintering vessel, the aluminum nitride sintered body may be used. Although it is possible to densify and fix the oxygen on the surface of the raw material powder to the grain boundary phase, a grain boundary phase exists at the ridges and triple points between AlN grains, and a sintered body of AlN single phase is obtained. Absent. When the carbon gas atmosphere as described above cannot be obtained, the effect of removing the grain boundary phase does not appear even by firing for a long time. In order to form an AlN single phase, a time exceeding 24 hours is required, depending on the sintering temperature and the amount of the additive.

Regarding the firing temperature, 1550-2050
Although it is about C, it is preferably 1700-2050C. When firing at a low temperature, a dense sintered body is difficult to obtain, depending on the particle size and oxygen content of the raw material powder, and the generation of carbon gas is reduced, leaving a grain boundary phase. Further, when firing at a temperature higher than 2050 ° C., the vapor pressure of AlN itself increases, making it difficult to densify, and there is a possibility that a reaction between aluminum and carbon produces aluminum carbide (Al ₄ C ₃ ). The (rare earth element) -O compound is reduced and nitrided to produce a phase presumed to be a nitride. The firing temperature is more preferably 1800 to 2000 ° C. Furthermore, 1800-1950 degreeC is preferable.

When calcined in an oxidizing atmosphere, not only does the effect of purifying the carbon grain boundaries not work, but also high thermal conductivity cannot be obtained due to solid solution of oxygen and formation of a different phase. The sintering is performed in an atmosphere including vacuum (including a slight reducing atmosphere), reduced pressure, increased pressure, and normal pressure.

Next, an example of the method for producing the aluminum nitride sintered body of the present invention will be described below. First, a predetermined amount of a rare earth element compound as a sintering additive is added to AlN powder, and then mixed using a ball mill or the like. A normal pressure sintering method is used for sintering. In this case, a binder is added to the mixed powder, kneading, granulation, and sizing are performed, followed by molding. As the molding, a mold press, an isostatic press, a sheet molding, or the like can be applied. Subsequently, the molded body is heated in a non-oxidizing atmosphere, for example, in a nitrogen gas stream to remove the binder, and then sintered at normal pressure. The firing container used at this time creates a carbon gas atmosphere during firing, for example, a carbon container,
The ratio between the volume in the container and the volume of the compact is 1.1 × 10 ⁰ to 1 ×
Use 10 ⁷ materials. Sintering temperature is 1550-205
At 0 ° C., the sintering time is set to a time exceeding 24 hours.
The sintered body of the present invention can be obtained by such a method.

Next, the effect of improving the thermal conductivity of the aluminum nitride sintered body of the present invention and the action of purifying the aluminum nitride sintered body by removing the grain boundaries of the (rare earth element) -Al-O compound phase and the like will be described. The exact mechanism has not been completely elucidated at present, but according to the study of the present inventors, it is estimated as follows as a factor for increasing the thermal conductivity.

First, the effect of trapping impurity oxygen in the AlN raw material powder by adding a rare earth element will be described. That is, by adding a rare earth element compound as a sintering aid, impurity oxygen can be converted into a (rare earth element) -Al-O compound or the like by A
Since it is fixed to the ridge and triple point of the 1N grain boundary, the solid solution of oxygen in the AlN lattice is prevented, and the oxynitride of AlN (Al
ON), and the generation of the AlN polytype (27R type) is prevented. According to the research results of the inventors, it is known that the sintered bodies in which AlON and 27R type are formed have low thermal conductivity. Suppressing the cause of such a low thermal conductivity can be cited as one of the causes of the high thermal conductivity.

When Y is selected as the rare earth element, the impurity oxygen in the raw material powder is 3Y ₂ O ₃ .5Al ₂ O ₃ ,
Y ₂ O ₃ · Al ₂ O ₃ , 2Y ₂ O ₃ · Al
Trapped as compounds such as ₂ O ₃ and Y ₂ O ₃ . This condition occurs in the period Shoyuihatsu, thermal conductivity is the highest 1
It reaches about 90 W / m · K.

In the subsequent sintering process, the (rare earth element) -O compound and / or (rare earth element)-
Al—O compound (for example, 2Y ₂ O ₃ .Al ₂ O
₃ ) is reduced and nitrided by a substance having a reducing action such as a nitrogen gas and a carbon gas and / or a CO gas existing in the atmosphere, and is changed into a (rare earth element) -N compound (for example, YN) and / or AlN.

The reductive nitridation reaction on the surface of the sintered body causes a concentration gradient of the (rare earth element) -O compound and / or the (rare earth element) -Al-O compound in the sintered body, which becomes a driving force. Sub-phases other than AlN move to the surface of the sintered body via the grain boundaries. And finally, the sintered body does not substantially contain other phases. It becomes an AlN single phase, and the thermal conductivity greatly increases. This is because the grain boundary phase having low thermal conductivity and acting as thermal resistance is removed. In addition, the particles of the sintered body grow by firing for a long time. When the AlN particles grow, it means that the number of grain boundaries that become the thermal resistance eventually decreases, resulting in a sintered body with small phonon scattering.

For the above reasons, the high thermal conductivity (22
(Value exceeding 0 W / m · K) An aluminum nitride sintered body can be obtained. Further, by setting the conditions of the present invention in an appropriate range, an AlN sintered body having translucency in near ultraviolet light can be obtained.

That is, as the aluminum nitride raw material powder, the crystal lattice constant of the hexagonal c-axis is 498.00 p
using an aluminum nitride powder is 498.20pm from m, yttrium of compound was added as a sintering aid,
70 Torr to 760 Torr in a nitrogen gas in which gaseous carbon exists at 1 × 10 ⁻⁶ Pa or more and 5 × 10 ⁻⁴ Pa or less.
r at 1850 ° C to 1950 ° C in an atmosphere of nitrogen pressure not higher than r
Was fired over a 24-hour time, the resulting polycrystalline material, the amount of different phase in the grain boundary is not only smaller than the conventional aluminum nitride polycrystal, grain itself physically,
The present inventors have found that a polycrystalline aluminum nitride having high transparency to light in a near ultraviolet region of at least 300 nm or more and a visible region of 850 nm can be obtained because of its high purity and denseness.

Based on this fact, various conditions necessary for achieving the transmissivity of the AlN sintered body to near-ultraviolet light were examined. As a result, it was found that the polycrystalline body was composed of hexagonal aluminum nitride crystal grains. The crystal lattice constant of the body is 497.98 pm or more and 498.20 p in the c-axis direction of the hexagonal system
m or less, and the amount of the heterophase existing in the crystal grain boundary is 2% by weight.
Or less, the porosity is 1% or less, and the density of the polycrystal is 3.2.
55Gcm ^-3 or more 3.275Gcm ^-3 or less and oxygen content VIIa on the following Periodic Table 0.2 wt%, a transition metal element belonging to VIII (Mn, Tc, Re, Fe, Co, Ni, R
u, Rh, Pd, Os, Ir, Pt) is 0.1% by weight or less, and the aluminum nitride sintered body was found to be translucent.

This AlN sintered body can be manufactured as follows. a) The crystal lattice constant of hexagonal aluminum nitride is 498.00 pm 498.20 pm in the c-axis direction of the hexagonal system
B) a partial pressure of gaseous carbon, which is composed of the following aluminum nitride powder as a main component and an additive composed of a rare earth element compound added thereto in an amount of 0.01 to 15% by weight in terms of the weight of each element; Is 1 × 10 ⁻⁶ Pa or more and 5 × 1
0 ^-4 Pa exists below the pressure of the nitrogen gas in the following atmosphere 760Torr than 70 Torr, c) time exceeds 1850 ℃ ~1950 ℃ 24 hours to 7
It is obtained by firing for 20 hours.

The aluminum nitride polycrystal obtained by such a method has high translucency, and particularly exhibits translucency even in the near ultraviolet region. The light transmittance of this aluminum nitride polycrystal is shown in FIG. 8 as the wavelength dependence of the total light transmittance of the polycrystal (thickness: 0.2 mm). When the apparent absorption coefficient is calculated by the following Lambert equation,
70 cm ^-1 or less for light having a wavelength of 330 nm, and 5
For light having a wavelength of 00 nm, it is 50 cm ^-1 or less. I = I ₀ e ^-a1 I ₀ : intensity of incident light I: intensity of transmitted light I: thickness of polycrystal a: apparent absorption coefficient This aluminum nitride polycrystal can be used for light ranging from near ultraviolet to infrared. On the other hand, it has a remarkably high translucency as compared with a conventionally known aluminum nitride sintered body. Especially 300n
It has the characteristic of showing translucency to near ultraviolet light of m to 400 nm. Conventionally, aluminum nitride having a light-transmitting property from the visible part to the infrared part is known, but in the present invention, an aluminum nitride polycrystal that is light-transmitting also to near ultraviolet light is obtained. The reason why an aluminum nitride sintered body having high transmissivity in the energy region of light including near-ultraviolet light can be obtained is as follows. 1. Use a raw material powder having extremely few oxygen and cation impurities dissolved in aluminum nitride crystal grains in the raw material powder. Oxygen and cation impurities do not form a solid solution in aluminum nitride crystal grains during sintering, and furthermore, a sintering method obtained by inventing a sintering method that removes the dissolved cation impurities out of the polycrystalline body is obtained. The physical and chemical purity of the crystal grains of the crystal, that is, the amount of impurities and the amount of lattice defects are extremely small, so that the lattice constant of the polycrystal is 60,000 c of aluminum nitride.
497.95 pm to 498.20 pm in the axial direction
The lattice constant of perfect aluminum nitride is 498.1.
Because a dense polycrystal very close to 6 pm was obtained,
Absorption and scattering of light in the crystal grains of the polycrystal, especially in the region from near-ultraviolet light to infrared light due to extremely low absorption due to dissolved oxygen in the crystal grains present in the ultraviolet and resulting lattice defects. It is considered that a polycrystal having high translucency was obtained. Further, it cross-phase existing in the grain boundary is small substantially less <br/> rather porosity contributes to the improvement of transparency.

The aluminum nitride polycrystal having a high light-transmitting property as described above can be obtained only when fired under various conditions as described above, and particularly satisfy the transmittance for near-ultraviolet light. For this purpose, various conditions as described above, in particular, a lattice constant of 497.9 for the c-axis of 60,000 crystals
Most importantly, it is at least 5 pm and at most 498.20 pm, and is achieved only for polycrystals having a total oxygen content of at least 0.7% by weight and a porosity of at least 1%.

Hereinafter, specific embodiments of the present invention will be described. Example 1 AlN powder containing 1.0% by weight of oxygen as an impurity and having an average particle diameter of 0.6 μm was added to an AlN powder having an average particle diameter of 0.1 μm as an additive.
9 μm of Y ₂ O ₃ was added at 4% by weight in terms of the weight of yttrium element, and the mixture was mixed using a ball mill to prepare a raw material. Next, add 4 organic binders to this raw material.
After adding the powder by weight and granulating, it was press-molded under a pressure of 500 kg / cm ² to obtain a green compact of 38 × 38 × 10 mm. The green compact was heated to 700 ° C. in a nitrogen gas atmosphere to remove the binder. Further, the degreased body was accommodated in a carbon container (sintering container A) using an AlN plate coated with BN powder as a bottom plate. At this time, the shape and size of the container A are 12 cmφ × 6.4 cm and the inner volume is 720 c.
m ³ . That is, the inner volume of this container A and Al
The volume ratio of the N molded body is about 5 × 10 ¹ . Using this container in a nitrogen gas atmosphere (1 atm) 190
Sintering was performed under normal pressure at 0 ° C. for 96 hours. The obtained AlN
The density and grain size of the sintered body were measured. Also, from the sintered body,
A disk having a diameter of 10 mm and a thickness of 3.3 mm was ground and used as a test piece to measure the thermal conductivity by a laser flash method (using TC-3000 manufactured by Vacuum Riko). The measured temperature is 25 ° C.

Further, the sintered body was analyzed. Yttrium is manufactured by ICP emission spectroscopy (S
PS-1200A), the analysis of cationic impurities was performed by chemical analysis, and the analysis of impurity oxygen was performed by fast neutron activation analysis (NAT-200-I manufactured by Toshiba).
C). Table 1 shows the sintering conditions and the obtained sintering characteristics.

[0036]

[Table 1]

The sintered body was subjected to X-ray diffraction (Rotorflex RU-200 manufactured by Rigaku Corporation, goniometer CN21).
73D5, using a source of Cu 50 kV, 100 mA). FIG. 1 shows the results, and FIG.
It was shown to.

Examples 2 to 4 An AlN sintered body was manufactured in the same manner as in Example 1 except that the amount of the sintering additive was changed variously, and each was similarly evaluated.

Examples 5 to 6 In the same manner as in Example 1 except that the sintering temperature was changed variously,
An N sintered body was manufactured. The same evaluation was performed for each.

Examples 7 and 8 AlN sintered bodies were manufactured in the same manner as in Example 1 except that the sintering time was changed, and the same evaluation was performed for each.

Example 9 The steps up to degreasing were performed in the same manner as in Example 1 above. Then, sintering was performed in a sintering container having an inner diameter of 700φ × 380 mm in a reduced pressure atmosphere of nitrogen gas (0.1 atm) at 1900 ° C. for 192 hours, and the same evaluation was performed.

Example 10 The size of the molded product was 15 φ × 6 mm, and the inner size was 700 mm.
An AlN sintered body was manufactured and evaluated in the same manner as in Example 9 except that the sintering vessel A having a diameter of 380 mm was used and the sintering temperature was changed.

Example 11 An AlN sintered body was manufactured and evaluated in the same manner as in Example 1 except that a carbon container (fired container B) in which a BN plate was used as a bottom plate was used. Done.

Tables 2 to 8 show the results of examining the characteristics of Examples 13 to 89 and those obtained by changing various other conditions. However, in Example 45.83, a container made entirely of carbon (sintering container C) was used.

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

[Table 5]

[0049]

[Table 6]

[0050]

[Table 7]

[0051]

[Table 8]

Example 90 The lattice constant of the hexagonal system in the c-axis direction was 498.07 pm,
AlN powder containing 1.7% by weight of oxygen as an impurity and having an average particle diameter of 1.9 μm was added to an AlN powder having an average particle diameter of 0.1 μm as an additive.
The 9μm of Y ₂ O ₃ was added 7 by weight% by weight is to prepare a raw material subjected to mixing using a ball mill. Next, 4 wt% of an organic binder was added to the raw material, and the mixture was granulated and pressed at a pressure of 1000 kg / cm ² to obtain a compact of 38 × 10 mm. The green compact was heated to 700 ° C. in a nitrogen gas atmosphere to remove the binder. Further, the degreased body was housed in a carbon container (baking container A) ground with AlN coated with BN powder as a bottom plate. At this time, the shape and size of the container A are 12 cm
It is φ × 6.4 cm and the inner volume is about 720 cm ³ .
That is, the ratio of the volume of the container A to the volume of the AlN compact is about 5 × 10 ¹ . This container was fired at 1870 ° C. for 100 hours in a nitrogen gas atmosphere (700 Torr) under normal pressure. The density and grain size of the obtained AlN polycrystal were measured. Also, from the polycrystal, a diameter of 1
A disk having a thickness of 0 mm and a thickness of 3.0 mm was ground, and the thermal conductivity was measured by a laser flash method using this as a test piece (using TC-3000 manufactured by Vacuum Riko). Measurement temperature is 25 ° C
It is.

The aluminum nitride raw material powder and the aluminum nitride polycrystal have a lattice constant of 10 to 20% by weight of Si powder (NB
SSRM640 standard sample) mixed with Rigaku Corporation rotorflex Ru-200, goniometer CN2173D5
Using 6 diffraction peaks of hexagonal aluminum nitride in the range of 100 ° <2θ <126 ° measured with a radiation source Cu K _a1 50 kV 150 mA using
The accuracy was corrected by the values of two diffraction peaks of Si in the range of θ <126 °, and then the values were obtained by the least square method. The room temperature at the time of measurement was 25 ° C. ± 1 ° C. It is known that the obtained value of the lattice constant contains an error of ± 0.05 pm. The amount of oxygen in the polycrystal was measured by fast neutron activation analysis (using NAT-200-IC manufactured by Toshiba). Further, elemental analysis of this polycrystal was performed by ICP emission spectroscopy (using SPS-1200A manufactured by Seiko Denshi Kogyo) and wet chemical analysis. The porosity and particle size of the polycrystal were obtained from the SEM photograph of the polished polycrystal (JEOL J
SM-T20 used). The light transmittance was measured using a polycrystalline body (outer diameter: 20 mmφ to 12 mmφ) having a thickness of 0.1 to 0.5 mm cut out from the polycrystalline body and optically polished.
The measurement was performed by installing an integrating sphere on an ary17 self-recording spectrophotometer (FIG. 8).

The density of the polycrystal was measured as apparent density by determining buoyancy from the weight in air and the weight in pure water. Table 9 shows the production conditions of the polycrystal, and Table 10 shows the characteristics of the polycrystal.

[0055]

[Table 9]

[0056]

[Table 10]

Table 9 also shows various other conditions.
And Table 10. Reference Examples 1 to 4 AlN degreased bodies obtained in the same manner as in Example 90 were set in a sintering container A and an AlN container D, and
It was sintered under normal pressure in N ₂ at 21950 ° C. for _{2 to} 200 hours to obtain a sintered body. Table 9 shows the production conditions of these polycrystals.
Table 10 shows the characteristics. FIG. 9 shows the measurement results of the transmittance of the polycrystal of Reference Example 1. The value of the lattice constant is as small as 497.85 pm or less with respect to the c-axis of the hexagonal system. As a result, the light transmittance is poor and the thermal conductivity is 195 W / m · K.
The following low values.

In order to obtain an AlN sintered body having such high translucency, the lattice constant of the aluminum nitride raw material powder is at least 498.00 pm with respect to the hexagonal c-axis.
20 pm or less and Y _{2 in a} carbon reducing atmosphere.
Long time after adding O ₃ auxiliary (time exceeding 24 hours)
It turns out that sintering is necessary.

Comparative Examples 1 to 3 The degreased AlN bodies obtained in the same manner as in Example 1 were variously set in sintering vessels A, B and C.
The resultant was sintered at normal pressure in an N ₂ stream of hr to obtain a sintered body. Table 11 shows the characteristics of these sintered bodies.

[0060]

[Table 11]

Further, the result of X-ray diffraction using the sintered body of Comparative Example 1 is shown in FIG. 3, and the crystal structure of the fracture surface of the sintered body is schematically shown in FIG. From these results and the result of the same evaluation, a compound containing yttrium was observed as a subphase, and it was found that the compound was not an AlN single phase. As a result, the thermal conductivity was a low value of 170 W / m · K or less.

In the case where the sintering time is as short as 24 hours or less , it is found that the removal of the grain boundary phase by using a carbon container is not sufficient, and AlN having a high thermal conductivity is obtained.
Long time to obtain a sintered body (time exceeding 24 hours )
It is understood that sintering is necessary.

Comparative Examples 4 to 6 An AlN degreased body obtained by the same method as in Example 1 was used. In Comparative Example 4, the inside of the container was entirely made of AlN (calcination container D).
In Comparative Example 5, the whole inner container was made of alumina (sintering container E), and in Comparative Example 6, the inner whole container was made of tungsten (sintering container F) at 1900 ° C., 96 hours, N _2.
It was sintered under normal pressure in an air stream to obtain a sintered body. Table 1 shows the characteristics of these sintered bodies. Further, using the sintered body of Comparative Example 4, X
FIG. 5 shows the result of the line diffraction, and FIG. 6 is a schematic diagram showing the crystal structure of the fracture surface of the sintered body. These results, and
From the evaluation results, a compound containing yttrium was observed as a subphase, and it was found that the compound was not an AlN single phase. As a result, the thermal conductivity is also a relatively low value of 168 W / m · K or less. As described above, at least a part of the inside has high thermal conductivity even when a firing container made of carbon is not used.
No N sintered body was obtained, indicating the effectiveness of the carbon atmosphere.

Comparative Example 7 The AlN powder used in Example 1 was 500 kg / cm ²
Into a green compact of 30 × 30 × 10 mm, put this green compact in a carbon mold, hot press for 1 hour at a temperature of 1900 ° C. under a pressure of 400 kg / cm ^{2 in} a nitrogen gas atmosphere. It was sintered to obtain a sintered body. Table 1 shows the characteristics of the sintered body. FIG. 7 shows the result of further X-ray diffraction. From this result, Al-O-N
A system compound was observed, indicating that it was not an AlN single phase. As a result, the thermal conductivity was as low as 80 W / m · K.

As described above, when no rare earth element compound is added, A
Since AlN reacts with impurity oxygen on the surface of the 1N raw material powder to produce an Al-ON compound that hinders the thermal conductivity, the effectiveness of the addition of the rare-earth element compound is understood.

[0066]

As described above, the aluminum nitride sintered body of the present invention is substantially composed of an AlN single phase and has excellent properties such as high purity and high thermal conductivity. Its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a view schematically showing a crystal structure of an AlN sintered body obtained by the present invention.

FIG. 3 is a diagram showing results of X-ray diffraction of Comparative Examples 1 to 3.

FIG. 4 is a view schematically showing a crystal structure of an AlN sintered body of a comparative example.

FIG. 5 is a diagram showing the results of X-ray diffraction of Comparative Examples 4 to 6.

FIG. 6 is a view schematically showing a crystal structure of an AlN sintered body of a comparative example.

FIG. 7 is a view showing a result of performing X-ray diffraction of Comparative Example 7.

FIG. 8 is a diagram showing the wavelength dependence of the total light transmittance in the present invention.

FIG. 9 is a diagram showing the wavelength dependence of the total transmittance of light in a reference example.

[Explanation of symbols]

 1 ... Diffraction peak of AlN 2 ... Diffraction peak of Y-Al-O compound 3 ... Peak of Al-ON compound 4 ... AlN grains 5 ... Y-Al-O compound (grain boundary phase)

Continued on the front page (72) Inventor Yoshiko Sato 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki City, Kanagawa Prefecture Inside Toshiba Research Institute (72) Inventor Akihiko Tsuge 1 Komukai Toshiba-cho, Kochi-ku, Kawasaki City, Kanagawa Prefecture Co., Ltd. Inside Toshiba Research Institute (72) Inventor Hiroshi Endo 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside Toshiba Research Institute (72) Inventor Masaru Hayashi 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Stock Company Within Toshiba Research Institute (72) Inventor Kazuo Shinozaki 1 Toshiba Research Institute, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa

Claims (2)

[Claims] 1. a) an aluminum nitride powder having an impurity oxygen content of 7% by weight or less and an average particle size of 0.05 to 5 μm, and a rare earth element of 0.01 to 15% by weight in terms of weight of the rare earth element Molded product obtained by mixing with a compound (excluding fluoride) consisting of an oxide, a nitride, and an oxynitride, or a rare earth element content of 0.01 to 15% by weight
With an oxygen content of 0.01 to 20% by weight and AlN
And a (rare earth element) -Al-O compound and / or
Or b) a sintered body containing a (rare earth element) -O compound phase, b) in a firing vessel for generating carbon gas or in a reducing atmosphere obtained by including a substance that generates carbon gas during firing in a firing vessel; ) At 1550-2050 ° C for more than 24 hours;
A method for producing a highly thermally conductive aluminum nitride sintered body, characterized by firing under an atmosphere pressure including a reduced pressure. 2. The high thermal conductive aluminum nitride sintered body according to claim 1, wherein the firing atmosphere contains nitrogen and at least one selected from hydrogen, carbon monoxide, carbon gas and carbon solid phase. Manufacturing method.