JP3450400B2 - Aluminum nitride sintered body and aluminum nitride multilayer circuit board - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride sintered body and an aluminum nitride multilayer circuit board, and particularly to aluminum nitride which has a high thermal conductivity even if it contains a certain amount of impurities and can be manufactured at low cost. The present invention relates to a sintered body and an aluminum nitride multilayer circuit board using the sintered body.

[0002]

BACKGROUND OF THE INVENTION Aluminum nitride (AlN) sintered body has low strength decreases to a high temperature, chemically resistant to <br/> Me also was that excellent, while used as the heat-resistant material, its high thermal conductivity,
It has been widely used as a heat sink material for semiconductor devices and an insulator material for circuit boards by utilizing its high electrical insulation.

In particular, in response to high integration and high density mounting of semiconductor elements and high speed and high output of semiconductor devices, the applications of aluminum nitride sintered bodies having particularly high thermal conductivity are expanding, and higher. Development of an aluminum nitride sintered body having thermal conductivity is desired.

In response to the above technical requirements, the conventional high thermal conductivity aluminum nitride sintered body uses a raw material powder containing as little impurities as possible, and the oxygen content and cations in the AlN sintered body are used. It was manufactured by a method that reduces the amount of impurities as much as possible. That is, a compact is placed in a carbon baking container to form a strong reducing atmosphere.
High thermal conductivity was ensured by performing a firing operation for a long time of about 100 hours.

By this firing operation, the impurity oxygen in the AlN crystal grains is trapped in the grain boundary phase (Al-O-Y phase), and the grain boundary phase near the surface of the sintered body is changed by C and CO in the atmosphere. reduced, Al-O, are excluded from the sintered body as a Y-N (when using Y ₂ O ₃ aid) volatilization substance such as, with the sintered body near the surface is highly purified by this volatilization As a result, the grain boundary phase inside moves to the surface, and the inside of the sintered body is highly purified. Further, by removing the surface phase by grinding or the like, an aluminum nitride sintered body having high purity and high thermal conductivity as a whole can be obtained.

[0006]

However, in the conventional method for producing a high thermal conductivity AlN sintered body, the raw material powder having a small content of impurities such as oxygen is expensive, and inevitably causes an increase in production cost. It was Further, since it is burned for a long time in a strong reducing atmosphere to achieve high purity, there is a problem that manufacturing efficiency is significantly reduced and product cost is significantly increased.

In particular, when a plurality of substrate elements each having a wiring conductor pattern formed on the surface of an AlN molded body are laminated and co-fired to manufacture an AlN multilayer wiring board, the conductor is carbonized and the difference in shrinkage ratio is increased. Since the wiring resistance is likely to increase and disconnection is likely to occur, there is a drawback that the long-time simultaneous firing method in the strongly reducing atmosphere cannot be applied in the manufacturing process of the AlN multilayer circuit board including the conductor in the inner layer.

Further, the highly purified AlN sintered body has high thermal conductivity, but also has a slight light transmitting property. Therefore, the semiconductor element mounted on the AlN sintered body substrate transmits through the substrate. However, there is a problem that malfunctions are likely to be caused by the ultraviolet rays and the like, and in any case, a multilayer circuit board having excellent operation reliability cannot be obtained.

The present invention has been made in order to solve the above-mentioned problems, and has high thermal conductivity even when an impurity such as a transition metal compound is contained to provide a light-shielding property, and the manufacturing cost is low. It is an object of the present invention to provide an aluminum nitride sintered body which can be manufactured and an aluminum nitride multilayer circuit board using the sintered body.

[0010]

In order to achieve the above object, the inventors of the present invention have found the purity of the AlN raw material powder used for producing the AlN sintered body, the sintering aid and the additives. The effect of these condition elements on the microstructure and properties of the AlN sintered body as the final product was confirmed by experiments by changing the types of the above, the sintering conditions, and the like.

As a result, by properly setting the atmosphere during sintering and the cooling rate of the sintered body after sintering,
As the sintering of aluminum nitride progresses, the aluminum nitride
The cation impurities and oxygen contained in the raw material powder and sintering aid can be concentrated as a grain boundary phase, and a compound in which only the grain boundary phase is agglomerated in a lump form is formed in the sintered body structure. It was found that this massive compound was formed to a size comparable to or larger than the primary particles after aluminum nitride sintering. Therefore, in the AlN sintered body structure, the area in which the aluminum nitride crystal grains are in direct contact with each other is significantly increased, and the proportion of the structure in which the AlN crystal grains having high thermal conductivity are continuous is increased, while the thermal conductivity is improved. It was found that compounds containing interfering impurities aggregate locally. As a result, it was found that an AlN sintered body having a high thermal conductivity as the whole sintered body can be obtained.
In addition, it was possible to impart a light-shielding property to the sintered body by adding a transition metal compound such as WO ₃ as a sintered body component. The present invention has been completed based on the above findings.

That is, the aluminum nitride sintered body according to the present invention contains 0.8% by weight or more of oxygen and 0.16% by weight.
An aluminum nitride crystal structure containing at least one of the above cation impurities, a lump compound containing the oxygen and the cation impurities is formed in the crystal structure, and the average particle size of the lump compound is an aluminum nitride crystal grain. It is characterized by having an average particle size or more. The thermal conductivity is 2
It is an AlN sintered body having a high thermal conductivity of 00 W / m · K or more.

Further, in the aluminum nitride multilayer circuit board according to the present invention, a plurality of board elements each having a wiring conductor formed on the surface of an AlN compact are laminated and co-fired so that the grain boundary phase in the AlN sintered body becomes a lump. You can get it.

Originally, both oxygen and cation impurities combine with an Al component or the like to form a compound that inhibits the thermal conductivity, which lowers the thermal conductivity of the AlN sintered body. In such an AlN sintered body, oxygen and cation impurities are agglomerated at the grain boundaries, so that thermal conductivity is less likely to be hindered.

In order for the oxygen content to be less than 0.8% by weight or the cationic impurity content to be less than 0.16% by weight, it takes a considerable time for sintering to discharge the grain boundary phase. This increases the manufacturing cost. On the other hand, when the oxygen content exceeds 1.5% or the cation impurity content exceeds 1% by weight, an oxide phase which also impairs thermal conductivity is uniformly formed at the grain boundaries. Since it becomes easier and the thermal conductivity of the AlN sintered body decreases, the content of oxygen is
The content of cationic impurities is set in the range of 0.8 to 1.5% by weight and the range of 0.16 to 1% by weight. The total content of oxygen and cationic impurities is more preferably set to 2.0% by weight or less.

The aluminum nitride sintered body according to the present invention is
For example, it is manufactured by the following steps. Against Sunawa Chi nitrided aluminum raw material powder, molding the Y ₂ O ₃ raw material mixture obtained by adding 3 to 8% by weight and a predetermined amount of binder sintering aid, such as, the obtained molded body After degreasing, 2 to 15 in a temperature range of 1600 to 1900 ° C in a non-oxidizing atmosphere such as nitrogen
Sintering is carried out for an hour, and the cooling rate from the above sintering temperature to 1400 to 1750 ° C. is set to 5 to 10 ° C. per hour and gradually cooled to manufacture. During the slow cooling, the sintering atmosphere was changed to 200 to 300 To.
When the pressure is reduced to rr, the thermal conductivity of the AlN sintered body can be further increased.

According to the above-mentioned aluminum nitride sintered body, the oxygen contained in the raw material, the cation impurities and the raw material components such as Al undergo an agglomeration reaction to form a massive compound phase at the grain boundary portion, and Since the average grain size of this compound is equal to or larger than that of the aluminum nitride crystal grains, the proportion of the structure in which high-purity AlN particles having high thermal conductivity are continuously in contact with each other is increased, while inhibiting the thermal conductivity. The compound containing impurities is locally aggregated and formed. Therefore, it is possible to obtain an AlN sintered body that has a high thermal conductivity as a whole as a whole and that has a light transmissive property suppressed by the above compound.

Oxygen and cation impurities are agglomerated locally in the sintered body to the extent that they do not hinder the thermal conductivity, so that it is not necessary to positively remove these impurities.
Therefore, it becomes possible to use an inexpensive raw material having a large amount of impurities including oxygen inevitably attached, and the raw material cost can be significantly reduced. In particular, in order to achieve high thermal conductivity in the past, in order to remove the above impurities,
Although a high-purification baking treatment was required for a long time in a reducing atmosphere, according to the present invention, the thermal conductivity was 200 W / m.multidot. Due to the sintering operation in a non-oxidizing atmosphere such as nitrogen gas.
When it is K or more, an AlN sintered body having excellent thermal conductivity can be manufactured at low cost.

When the aluminum nitride multilayer circuit board according to the present invention is manufactured by the co-firing method, the following steps are followed. That is, a raw material slurry is prepared by adding a solvent to an aluminum nitride mixed powder containing a predetermined amount of oxygen, cationic impurities, a sintering aid, a binder, and the like.
This raw material slurry is used to form a sheet-shaped molded body by using a molding method such as a doctor blade method, and a wiring conductor pattern is formed on the surface of the sheet-shaped molded body with a conductive paste containing a conductive metal such as W. , A plurality of sheet-shaped compacts each having a wiring conductor pattern formed thereon are laminated by thermocompression bonding to form a laminate, and after degreasing the obtained laminate, a temperature range of 1600 to 1900 ° C. in a non-oxidizing atmosphere such as nitrogen. It is manufactured by co-firing for 2 to 15 hours, gradually cooling from the above firing temperature to 1400 to 1750 ° C. at a cooling rate of 5 to 10 ° C. per hour. In addition, the sintering atmosphere is set to 200 to 300 Tor during slow cooling.
When the pressure is reduced to r, the thermal conductivity of the AlN sintered body can be further increased.

According to the aluminum nitride multi-layer circuit board having the above structure, impurities such as oxygen are locally aggregated to form a compound on the board of each layer on which the wiring conductor is formed, so that the thermal conductivity is high and high. A large proportion of pure AlN particles is continuous. Therefore, the multilayer circuit board as a whole has a high thermal conductivity, and the presence of the above compound also imparts a light-shielding property.

Particularly in the manufacturing process, it is not necessary to carry out a high-purification baking treatment in a strong reducing atmosphere (containing carbon gas) for a long time in order to completely remove impurities such as oxygen, and an inert gas such as nitrogen gas is used. Since the firing operation can be carried out in the atmosphere, there is no damage or disconnection due to carbonization of the wiring conductor during firing, so that a highly reliable multilayer circuit board can be produced with a high yield.

[0022]

EXAMPLES The present invention will be described in more detail based on the following examples.

Example 1 and Comparative Example 1 5% by weight of Y ₂ O ₃ (yttrium oxide) as a sintering aid, and 5% by weight of a binder were added to aluminum nitride raw material powder having an oxygen content of 0.8% by weight. A mixed liquid of alcoholic and aromatic hydrocarbon solvents was added to a mixed powder containing 8% by weight of PVB resin, and mixed for 24 hours in a ball mill to prepare a raw material slurry.

Next, using the doctor blade method, the above-mentioned raw material slurry is formed into a sheet shape, eight sheet-like formed bodies are laminated and then thermocompression bonded to form a laminated body, and the laminated body is nitrided. It was degreased in gas at 450 ° C. for 1 hour.

Next, the degreased laminate was sintered by holding it in a nitrogen gas atmosphere at a temperature of 1850 ° C. for 10 hours, and then 1 hour / hour.
Gradually cool to 1750 ° C at 0 ° C cooling rate, then 120
A large number of AlN sintered bodies according to Example 1 were manufactured by cooling to 0 ° C. at 300 ° C./hour and then cooling to room temperature in a furnace.

On the other hand, as Comparative Example 1, 1 at a temperature of 1850 ° C.
After holding for 0 hours to sinter, 200 hours per hour as in the conventional method
A large number of AlN sintered bodies according to Comparative Example 1 were manufactured by using the same raw materials and processing method as in Example 1 except that they were rapidly cooled at a cooling rate of ° C.

Example 1 and Comparative Example 1 thus obtained
A sample piece having a diameter of 10 mm and a thickness of 3 mm was cut out from the AlN sintered body according to, and its thermal conductivity was measured based on the laser flash method, and the oxygen content and the yttrium (Y) content were quantitatively analyzed. The results shown in Table 1 were obtained.

[0028]

[Table 1]

As is clear from the results shown in Table 1, the amount of oxygen and the yttria (Y
_The amount of yttrium due to ₂ O ₃ ) is almost the same in Example 1 and Comparative Example 1, but the thermal conductivity of the AlN sintered body according to Example 1 is higher due to the difference in crystal structure morphology. It turned out to have a rate.

Further, in order to confirm the above-mentioned difference in crystal structure morphology, the fracture surface of each sample piece was examined with a scanning electron microscope (SE).
M) and observed in FIG. 1 (Example 1) and FIG. 2 respectively.
The results shown in (Comparative Example 1) were obtained.

As shown in FIG. 1, AlN according to Example 1
In the sintered body, a lumpy compound 2 containing oxygen and a cation impurity is formed in the structure where the AlN crystal particles 1 are continuous, as shown by the hatched portion. This compound 2
Is an oxide such as Al ₂ Y ₄ O ₉ or Y ₂ O ₃ ,
It is locally formed in the tissue with a grain size similar to that of the 1N crystal grain 1. As described above, while the compound 2 which inhibits the thermal conductivity is locally aggregated, the high-purity AlN crystal particles 1 having high thermal conductivity have a structure morphology that is continuously formed. An AlN sintered body having excellent light-shielding properties due to the inclusion of Compound 2 was obtained.

On the other hand, in the AlN sintered body of Comparative Example 1 prepared by quenching after sintering as shown in FIG. 2, oxygen and Ru compounds Na from a cation impurities and Al (oxide)
2a is thin and widely distributed along the grain boundaries of the AlN crystal structure as shown by the shaded area, and high purity AlN crystal particles 1
It was found that the light-shielding property is sufficient because the proportion of direct contact between the two is small, but the thermal resistance is large and the thermal conductivity of the entire sintered body is reduced.

According to this embodiment, an AlN sintered body having a high thermal conductivity can be provided at a low cost even when the cation element added as a sintering aid and oxygen inevitably mixed remain in the sintered body. can do.

Example 2 and Comparative Examples 2 to ₃ 5% by weight of Y ₂ O ₃ (yttrium oxide) as a sintering aid was added to a raw material powder of aluminum nitride having an oxygen content of 0.8% by weight, and a binder. A mixed liquid of an alcoholic hydrocarbon solvent and an aromatic hydrocarbon solvent was added to a mixed powder containing 8% by weight of a PVB resin as described above and mixed for 24 hours in a ball mill to prepare a raw material slurry.

Next, using the doctor blade method, the above-mentioned raw material slurry was formed into a sheet, and a through hole was formed at a predetermined position of each sheet with a drill. Then W
After filling the above through holes with a conductor paste containing, and printing a wiring conductor pattern of a predetermined shape on the surface of each sheet, the sheets are laminated and thermocompression bonded to each other.
A molded body for an IN multilayer circuit board was prepared.

Next, the molded body thus obtained was degreased in a nitrogen-hydrogen mixed gas (N ₂ + H ₂ + H ₂ O) atmosphere containing water vapor at a temperature of 900 ° C., and then in a nitrogen gas atmosphere at a temperature of 18 ° C.
By holding at 50 ° C. for 6 hours, each sheet constituting the molded body and the wiring conductor pattern are simultaneously fired, and thereafter 5 ° C./hour
After cooling to 1750 ° C. at a cooling rate of 1 and then furnace cooling, an AlN multilayer circuit board according to Example 2 was prepared.

On the other hand, as Comparative Example 2, the degreased molded body was filled in a carbon baking vessel (sheath) and continuously formed at a temperature of 1900 ° C. for 48 hours in a state of forming a strongly reducing atmosphere. Then, the AlN multilayer circuit board according to Comparative Example 2 was prepared by treating with the same raw materials and treating conditions as in Example 2, except that the firing was performed at the same time.

Further, as Comparative Example 3, the degreased molded body was held in a nitrogen gas atmosphere at a temperature of 1850 ° C. for 4 hours and simultaneously fired, and then heated up to 1200 ° C. at a rate of 30 per hour as in the conventional method.
AlN according to Comparative Example 3 under the same conditions as in Example 2 except that the cooling rate was 0 ° C. and the furnace was cooled from 1200 ° C.
A multilayer circuit board was prepared.

Example 2 and Comparative Example 2 thus prepared
In order to evaluate the AlN multilayer circuit boards according to 3 to 3, the oxygen content, the cation impurity content, the wiring resistance at a fixed wiring length, the substrate density and the thermal conductivity of each sample were measured, and the results are shown in Table 2 below. The results shown were obtained. The substrate density, thermal conductivity, oxygen content, and anodic ionic impurity amount were measured only for the portion of the AlN sintered body substrate of the multilayer substrate.

[0040]

[Table 2]

As is clear from the results shown in Table 2, the AlN multilayer circuit board according to Example 2 has a high thermal conductivity despite the high oxygen and cation impurity contents.

On the other hand, in Comparative Example 2, high-purity firing of the AlN sintered body was carried out for a long time (48 hours) in a reducing atmosphere.
Since it is continuously carried out, the amount of oxygen and the amount of cations are significantly reduced as compared with the other examples, and higher thermal conductivity than that of Example 2 is obtained. However, since baking takes a long time, the cost of manufacturing the substrate is significantly increased, and mass productivity and economical efficiency are low. Moreover, since the wiring conductor was carbonized for a long time in a strong reducing atmosphere of carbon gas, the wiring resistance was significantly increased.

Further, in Comparative Example 3, since the material was rapidly cooled after co-firing, fine oxides containing oxygen and cationic impurities were formed in the same manner as in Comparative Example 1 shown in FIG.
It is formed thinly along the AlN crystal grain boundary and widely dispersed. Therefore, the thermal resistance was large and high thermal conductivity could not be obtained.

[0044]

As described above, according to the aluminum nitride sintered body of the present invention, the oxygen contained in the raw material, the cation impurities and the raw material components such as Al undergo an agglomeration reaction to form a grain boundary portion. Since a massive compound phase is formed and the average grain size of this compound is equal to or greater than that of the aluminum nitride crystal grains, the proportion of the structure in which high-purity AlN particles having high thermal conductivity are continuously in contact with each other is increased. On the other hand, a compound containing an impurity that impairs thermal conductivity is locally aggregated and formed. Therefore, it is possible to obtain an AlN sintered body having a high thermal conductivity as a whole as a whole and having the translucency sufficiently suppressed by the above compound.

Oxygen and cation impurities are agglomerated locally in the sintered body to the extent that they do not impair the thermal conductivity, so that it is not necessary to actively remove these impurities.
Therefore, it becomes possible to use an inexpensive raw material containing a large amount of impurities including oxygen which is inevitably attached, and the raw material cost can be reduced. In particular, conventionally, in order to achieve the high thermal conductivity, it was necessary to perform a high-purification firing treatment on the sintered body for a long time in a reducing atmosphere in order to remove the impurities. Thermal conductivity of 200 W / mK by sintering in non-oxidizing atmosphere such as gas
From the above, an AlN sintered body having excellent thermal conductivity can be manufactured at low cost.

Further, according to the aluminum nitride multilayer circuit board of the present invention, since impurities such as oxygen are locally aggregated to form a compound in the board of each layer on which the wiring conductor is formed, the thermal conductivity is high. There are many continuous high-purity AlN particles. Therefore, the thermal conductivity of the entire multilayer circuit board is high.

Particularly in the manufacturing process, it is not necessary to carry out the high-purification baking treatment in a strong reducing atmosphere for a long time in order to completely remove impurities such as oxygen, and the baking operation is performed in an inert gas atmosphere such as nitrogen gas. Because it can be implemented
Since there is no damage or disconnection due to carbonization of the wiring conductor during firing, it is possible to produce a highly reliable multilayer circuit board with high yield and manufacturing efficiency.

[Brief description of drawings]

FIG. 1 is a structural diagram schematically showing a crystal structure of a fracture surface of an aluminum nitride sintered body according to Example 1.

FIG. 2 is a structural diagram schematically showing a crystal structure of a fracture surface of an aluminum nitride sintered body according to Comparative Example 1.

[Explanation of symbols]

1 AlN crystal particles 2 Bulk compound (oxide phase) 2a compound (oxide)

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-1-126286 (JP, A) JP-A-5-105527 (JP, A) JP-A-5-17236 (JP, A) Special Table 8- 508461 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C04B 35/581

Claims (3)

(57) [Claims] 1. 0.8% by weight or more of oxygen and 0.16
An aluminium nitride crystal structure containing at least one of the cation impurities in an amount of at least% by weight, and a lump compound containing the oxygen and the cation impurities is formed in the crystal structure, and the lump compound has an average particle diameter of aluminum nitride crystal. An aluminum nitride sintered body characterized by having an average grain size or more. 2. The aluminum nitride sintered body according to claim 1, which has a thermal conductivity of 200 W / m · K or more. 3. Oxygen of 0.8% by weight or more and 0.16
An aluminium nitride crystal structure containing at least one of the cation impurities in an amount of at least% by weight, and a lump compound containing the oxygen and the cation impurities is formed in the crystal structure, and the lump compound has an average particle diameter of aluminum nitride crystal. An aluminum nitride multilayer circuit board, characterized in that an aluminum nitride sintered body having an average grain size or more and a wiring conductor are simultaneously sintered.