JP2000226261A - Aluminum nitride sintered body and method of manufacturing the same - Google Patents

Abstract

(57) Abstract: An aluminum nitride sintered body to which yttrium oxide is added as a sintering aid has high mechanical strength and high thermal conductivity, and a method for producing the same. A maximum particle size of an yttrium compound generated at a grain boundary of an aluminum nitride crystal is set to 10 μm or less. As a production method, yttrium oxide powder having an average particle diameter of 1.0 μm or less or a specific surface area of 10 m ² / g or more is added, and calcined at 1800 ° C. for 2 hours.
Cool at a cooling rate of at least / min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered body of aluminum nitride (hereinafter referred to as AlN) having good mechanical strength and thermal conductivity, and a method for producing the same.

[0002]

2. Description of the Related Art In power modules such as large-capacity transistors and IGBTs, a ceramic substrate is used as a substrate for insulating and radiating heat. Conventionally, an aluminum oxide (hereinafter referred to as Al ₂ O ₃ ) plate has been widely used as a ceramic substrate because of its good insulation properties, high thermal conductivity and high strength. In recent years, an AlN sintered plate has been used as an insulating material having a higher thermal conductivity in order to improve heat dissipation for miniaturization and high performance of a power module.

[0003] It is difficult to obtain a dense sintered body at normal pressure by using AlN powder alone, and oxides or fluorides of rare earth elements such as yttrium and lanthanum, oxides of alkaline earth elements such as calcium, and fluorides. Sintering is performed by adding a sintering aid such as a compound. In particular, when yttrium oxide (hereinafter, referred to as Y ₂ O ₃ ) is used as a sintering aid, AlN is reduced to 1,800.
It is known that a sintered body that can be densified at a temperature of about ° C and has high thermal conductivity can be obtained.

[0004] This is because the sintering aid Y ₂ O ₃ during firing is
It is thought that liquid phase sintering at normal pressure is possible by liquid phase sintering because it reacts with oxides or oxynitrides existing very near the surface of AlN powder to generate a liquid phase composed of an yttrium compound. Have been.

In general, commercially available AlN powder used as a raw material contains 0.5 to 1% by weight of oxygen, but the oxygen contained in the AlN particles is reduced at the grain boundary during sintering. It is considered that high thermal conductivity can be obtained by discharging the gas to the air.

[0006] In particular, in JP-A 1-242469 discloses, not the Y ₂ O ₃ powder sold were prepared by gas phase method, the average particle diameter of 10 to 100 nm Y ₂
By using O ₃ , Al at 1500 to 1700 ° C.
It is disclosed that an N sintered body can be manufactured. In the following, the diameter of a raw material powder such as AlN or Y ₂ O ₃ will be referred to as a particle diameter, and the diameter of crystal grains of a sintered polycrystal will be referred to as a particle diameter.

[0007]

SUMMARY OF THE INVENTION Commercially available Y ₂ O
An AlN sintered plate using ₃ as a sintering aid has a four-point bending strength of 3
It is about 00 to 350 MPa. When this AlN sintered plate is used as an insulating heat radiation substrate of a power module, it may be broken by stress at the time of metal electrode bonding, may be broken by stress generated from a difference in thermal expansion with the electrode in a heat cycle after electrode bonding, or may be screwed. If it is broken when tightened, its strength is insufficient, and further reinforcement has been required.

[0008] Under such circumstances, an object of the present invention is to provide an aluminum nitride sintered body having further enhanced mechanical strength without lowering thermal conductivity, and a method for producing the same.

[0009]

According to the observation of the fractured surface of the AlN sintered body, when the AlN is composed of small crystal grains of 5 μm or less, the destruction is mainly at the grain boundary. I found that. From the relationship between the grain size of the yttrium compound crystal generated at the grain boundary of AlN and the four-point bending strength, the maximum grain size of the yttrium compound crystal at the grain boundary is 10 μm.
When m is exceeded, it was found that the fracture crack progressed remarkably and the strength rapidly decreased, and conversely, the smaller the particle size of the yttrium compound, the higher the mechanical strength.

Therefore, the crystal grain size of AlN is set to 5 μm or less, and the maximum grain size of the yttrium compound crystal existing at the grain boundary is set to 10 μm or less. Thereby, the fracture at the grain boundary is dominant, and a high-strength AlN sintered body can be obtained.

Yttrium generated at grain boundaries of AlN sintered body
To reduce the maximum particle size of compound crystals to 10 μm or less
In addition, Y added to AlN powder having an average particle diameter of about 3 μm
_TwoO _ThreeIt is necessary to highly disperse the raw material powder, and the average particle size
Is less than 1.0 μm_TwoO_ThreePowder or specific surface area 10m^Two/
Y over g_TwoO_ThreeAdd the powder and binder or about
What is necessary is just to bake at 1800 degreeC for 2 hours. Just like that
If the maximum particle size of the yttrium compound crystal is 10 μm or less
Experiments have shown that it can be made smaller.

[0012] If pre-Y ₂ O ₃ ball milling only raw material powder and a solvent, the average particle size is obtained the following Y ₂ O ₃ powder 1.0μm was confirmed experimentally.
However, if the AlN raw material powder is also added and ball milling is performed, the amount of oxygen in the sintered body increases and the strength decreases, which is not preferable. It is important that the rate of temperature decrease during firing is 10 ° C./min or more.

[0013] Even if raw material powders having the same average particle size are used,
It was also found that the particle size of the yttrium compound crystal changed with the temperature decreasing rate during firing, and it was also found that it was necessary to cool the range of 1800 ° C. to 1700 ° C. at a rate of 10 ° C./min or more.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The progress and results of experiments leading to the present invention will be described in detail below. [Experiment 1] A commercially available AlN powder having an average particle diameter of about 3 μm and containing 0.95% by weight of oxygen was prepared. The average particle diameter of the AlN powder is 0.1 to 8 μm as a sintering aid.
4 wt% of various Y ₂ O ₃ powders different from m were added, and about 10% of polyvinyl butyral (hereinafter referred to as PVB) was added as a binder. They were put into a 1000 ml polyethylene ball mill with 25 zirconia balls having a diameter of 10 mm, and xylene,
4-methyl-2-pentanol, isopropyl alcohol (I
PA) was added and mixed while rotating at a rotation speed of 10 rpm to form a slurry. The Y ₂ O ₃ powder of Sample No. 4 has the same average particle diameter as Sample No. 5, but has a flattened shape due to a different manufacturing method, so that the specific surface area is about twice as large.

A sheet is formed from the slurry by a doctor blade method, and the obtained green sheet is formed into a predetermined size.
The binder was removed in an atmosphere of 0 to 500 ° C. for 2 hours. Further, the temperature was raised to 1800 ° C. at a temperature rising rate of 5 ° C./min in a nitrogen atmosphere, followed by holding for 2 hours and firing. After that, the cooling rate was 10 ° C /
Cooled to room temperature in minutes.

The obtained AlN sintered body is processed and subjected to JIS-
A four-point bending strength test was performed according to R-1601. The size of the sample piece is 26 mm × 56 mm and the thickness is 0.63 mm. The thermal conductivity at room temperature was determined by a laser flash method. The cross section of the sample was mirror-polished, observed with a scanning electron microscope (SEM), and the maximum particle diameter of the yttrium compound was measured by image processing as a major axis diameter.

The results are shown in Table 1.

[Table 1] The maximum particle size of the yttrium compound increases as the average particle size of the Y ₂ O ₃ powder increases. And at this time,
The four-point bending strength is gradually decreasing. The thermal conductivity has hardly changed.

In the last column, the four-point bending strength which is a suitable standard for a semiconductor device substrate is 400 MPa or more and the thermal conductivity is 160 W / (m · K) or more. Those that do not are marked with a cross.

From these results, it was found that the AlN sintered body having a maximum particle size of the yttrium compound of 10 μm or less has a bending strength of 400 μm.
It is more than MPa and the thermal conductivity is more than 160 W / (m · K), which indicates that the substrate has good characteristics as a semiconductor substrate.

The maximum particle size of the yttrium compound is 1
It can be seen that the average particle diameter of the Y ₂ O ₃ powder to be added should be 1.0 μm or less or the specific surface area should be 15 m ² / g in order to make it 0 μm or less.

This method is carried out at 1500 to 1700 ° C.
Cannot be sintered at low temperature and requires heat treatment at about 1800 ° C
Was adjusted by a gas phase method having an average particle diameter of 10 to 100 nm.
Y_TwoO_ThreeJP-A-1-242469 using fine powder
Compared with the method of the gazette, a commercially available Y _TwoO_ThreeI can make it with powder
Therefore, there is an advantage that it can be easily implemented. Also, about 1800 ° C
Is sufficient for sintering, the thermal conductivity is
Approximately 120 W / (mK) by the method of JP-A-242469
Compared to 160W / (m ・ K)
There are also features. [Experiment 2] In Experiment 1, Y_TwoO_ThreeAverage particle size of powder
Is set to 1.0 μm or less, a tough AlN substrate can be obtained.
I understand. Therefore, Y as a sintering aid_TwoO_Threepowder
Experiments to establish appropriate processing conditions
Was.

The average particle diameter was prepared Y ₂ O ₃ powder of 8 [mu] m, zirconia balls having a diameter of 10mm in a polyethylene pot 1000ml into 25 placed ball mill, Y ₂ O
Only ₃ powders and IPA were weighed and charged, and pulverized at 120 rpm for 1 to 20 hours.

Thereafter, AlN powder, polyvinyl butyral (PVB), xylene, and 4-methyl-2-pentanol were added. Further, a slurry was prepared by mixing with a ball mill in the same manner as in Example 1, and a sample was prepared and evaluated in the same manner. Also,
From the beginning, in addition to the Y ₂ O ₃ powder and IPA, an AlN raw material powder and one charged into a ball mill were similarly prepared (Sample No. 13).

In the same manner as in Experiment 1, the obtained AlN sintered body was evaluated for the four-point bending strength, the thermal conductivity at room temperature, and the maximum particle size of the yttrium compound.

The results are shown in Table 2. In the last column, the four-point bending strength, which is a suitable standard for a semiconductor device substrate, is 40.
A mark of 0 MPa or more and a heat conductivity of 160 W / (m · K) or more was marked with a circle, and those not satisfying either were marked with a cross.

[0026]

[Table 2] Sample No. 7 has a ball mill crushing time of 0 and is data of Sample No. 7 of Experiment 1.

From Table 2, it can be seen that the longer the ball milling time, the higher the four-point bending strength. However, there is no significant change in the thermal conductivity. That is, it is understood that the strength of the sintered body can be enhanced by ball milling the Y ₂ O ₃ powder.

In this experiment, a ball mill having a bending strength of 400 MPa or more was obtained with a ball milling time of 10 hours or more. Also, the thermal conductivity at that time was 160 W / (m · K) or more, showing good characteristics. This is because, in consideration of the results of Experiment 1, the maximum particle size of the yttrium compound in the sintered body became 10 μm or less by pulverizing the Y ₂ O ₃ powder with a ball mill to obtain fine powder. is there. After pulverization for 10 hours or more, the Y ₂ O ₃ powder had an average particle diameter of 1 μm or less.

The ball mill has a pot capacity, a ball material,
The crushing effect changes greatly depending on the ball diameter and the number of revolutions. Therefore, it cannot be said that the pulverization time should be generally 10 hours or more.

Sample No. 13, which was pulverized from the beginning with the AlN raw material powder, had a particle size of the yttrium compound of 8.5 μm in the sintered body, but did not have sufficient four-point bending strength. This is considered to be because the AlN powder was further pulverized and the surface area increased, so that the amount of oxygen in the sintered body increased and the strength decreased.

[0031] This method, since a commercially available Y ₂ O ₃ powder is only pulverized in a ball mill and adjusted by a gas phase method Y ₂
O ₃ can advantageously be readily implemented as compared with JP-A 1-242469 discloses a method of using a fine powder.

[Experiment 3] Of the firing conditions described in Experiment 1, the maximum temperature and the holding time are extremely important. 180
If the temperature is lower than 0 ° C., the sintering is insufficient.

As a condition that is relatively easy to control, the 1
The cooling rate in the range from 800 ° C to 1700 ° C is from 1 ° C / min.
A sintered body was produced by changing the temperature to 20 ° C./min. 1700
The temperature was lowered at a rate of 10 ° C./min. Average particle size is 1.0
μm, specific surface area is 8m^Two/ g Y _TwoO_ThreeUsing powder, other crops
The manufacturing conditions and the evaluation method are the same as in the first embodiment.

In the same manner as in Experiment 1, the obtained AlN sintered body was evaluated for the four-point bending strength, the thermal conductivity at room temperature, and the maximum particle size of the yttrium compound. Table 3 shows the results.

In the last column, if the four-point bending strength, which is a suitable standard for a semiconductor device substrate, is 400 MPa or more and the thermal conductivity is 160 W / (m · K) or more, a circle is satisfied. Those that do not are marked with a cross.

[0036]

[Table 3] The lower the cooling rate, the lower the four-point bending strength. At 8 ° C./min or less, the bending strength is less than 400 MPa. However, thermal conductivity is large. Conversely, when the temperature was lowered at a rate of 10 ° C./min or more, a material having a bending strength of 400 MPa or more was obtained. Also, the thermal conductivity at that time was 160 W / (m · K) or more, showing good characteristics.

When the cooling rate is 8 ° C./min or less, the maximum particle size of the yttrium compound in the sintered body exceeds 10 μm, and when the cooling rate is 10 ° C./min or more, the maximum particle size is 10 μm or less. This tendency that the strength decreases as the particle size increases,
This is consistent with the result of Experiment 1.

That is, by changing the cooling rate, the particle size of the yttrium compound in the sintered body changes, and at a cooling rate of 10 ° C./min or less, the grain growth proceeds during the cooling and the yttrium in the sintered body increases. It is considered that the maximum particle size of the compound becomes 10 μm or more and the bending strength becomes 400 MPa or less.
Therefore, it is very important that the temperature drop rate be 10 ° C./min or more in the range of 1700 ° C. or more where crystal grain growth occurs.

[0039]

As described above, according to the present invention, in an AlN sintered body to which Y ₂ O ₃ is added as a sintering aid,
The average particle size of the yttrium compound generated at the grain boundary is 10 μm
AlN with excellent strength and thermal conductivity
It can be a sintered body.

[0040] As a method for producing such AlN sintered body, if the average particle diameter is added to the following Y ₂ O ₃ powder 1.0 .mu.m, or specific surface area is added to Y ₂ O ₃ powder of 10 m ² / g 170 ° C after firing at 1800 ° C for 2 hours.
The rate of temperature decrease to 0 ° C. may be 10 ° C./min or more.

The AlN sintered body having good mechanical strength and thermal conductivity according to the present invention is suitable for a substrate or a package for a semiconductor device which is resistant to a heat cycle, and particularly contributes to the development of a power device.

Claims (5)

[Claims] An aluminum nitride sintered body to which an yttrium oxide has been added and fired has an average crystal grain size of aluminum nitride of 5 μm or less and a maximum grain size of an yttrium compound present at a grain boundary of 10 μm or less. An aluminum nitride sintered body characterized in that: 2. An aluminum nitride powder having an average particle diameter of about 3 μm, a yttrium oxide powder having an average particle diameter of not more than 1.0 μm and a binder are added, and the mixture is calcined at about 1800 ° C. for 2 hours. Maximum particle size is 1
A method for producing an aluminum nitride sintered body having a size of 0 μm or less. 3. A maximum particle size of an yttrium compound, characterized by adding an yttrium oxide powder having a specific surface area of at least 10 m ² / g to an aluminum nitride powder having an average particle size of about 3 μm and firing at about 1800 ° C. for 2 hours. A method for producing an aluminum nitride sintered body having a particle size of 10 μm or less. 4. The method for producing an aluminum nitride sintered body according to claim 2, wherein the ball mill is performed in advance using only a raw material powder of yttrium oxide and a solvent. 5. The production of an aluminum nitride sintered body according to claim 2, wherein a temperature decreasing rate in a range of about 1800 ° C. to 1700 ° C. during firing is 10 ° C./min or more. Method.