JP2679798B2 - Manufacturing method of aluminum nitride - Google Patents

Description

The present invention relates to a method for producing aluminum nitride.

[Conventional technology]

Aluminum nitride is used as a heat dissipation plate for semiconductor devices as a ceramic having high thermal conductivity.

Conventionally, as a method for producing aluminum nitride, for example,
The Al powder is heated to 700 to 1600 ° C in a nitrogen atmosphere to synthesize an AlN raw material, and a sintering aid (for example, 3 to 5% by weight of yttria) is added and mixed into the AlN raw material to form a molded body. To
There is known a sintering method in which an AlN sintered body is formed by sintering at 1700 to 1900 ° C.

However, the AlN sintered body obtained by this method has a problem that thermal conductivity is reduced due to the presence of a sintering aid.
Further, in this method, the raw material AlN powder is oxidized by moisture in the air, etc., the oxygen concentration in AlN tends to be high, the conduction of phonons that transfer heat is poor, and this also causes a decrease in thermal conductivity. Was there.

[Problems to be solved by the invention]

Therefore, the base material is installed in the reaction furnace, the aluminum compound gas and the ammonia gas are supplied, and 600 to 1400 ° C., 0.1
A CVD method has been proposed in which AlN is deposited on the substrate by reacting under the condition of -50 kPa. (For example, Japanese Patent Application No. 61-29401).

With this method, high-purity AlN can be synthesized, and as in the case of the sintering method, a decrease in thermal conductivity due to a sintering aid or oxygen can be prevented. However, in order to further improve the thermal conductivity by this method, it is necessary to improve the sinterability of AlN, which is why AlN is heated at temperatures above 1300 ° C.
Must be synthesized. And at such a high temperature
When Al is synthesized, there is a problem that the crystal grain size increases and the strength decreases.

The present invention has been made to solve the above problems, and an object of the present invention is to propose a method capable of producing aluminum nitride having high strength and high thermal conductivity.

[Means for solving the problem]

The method for producing aluminum nitride of the present invention is to install a base material in a reaction furnace, supply an aluminum compound gas and NH ₃ gas to react at 600 to 1300 ° C., and deposit AlN on the base material. 1,500 ~ in an inert or reducing atmosphere
It is characterized by heat treatment at 2100 ° C.

In the present invention, the aluminum compound is AlC
At least one of l ₃ , AlH ₃ , and Al (CH ₃ ) ₃ is used.

In the present invention, the reaction temperature of the aluminum compound gas and the NH ₃ gas by the CVD method is set to 600 to 1300 ° C. for the following reason. That is, when the reaction temperature is lower than 600 ° C., the reaction does not proceed sufficiently, and Cl and H are easily taken in as impurities into AlN, resulting in a decrease in thermal conductivity. On the other hand, when the reaction temperature exceeds 1300 ° C., the crystal grain size of AlN becomes large and the strength is lowered. The pressure during AlN synthesis by the CVD method is preferably set to 0.1 to 50 kPa.

In the present invention, as a specific means for making the surroundings of AlN synthesized by the CVD method into an inert atmosphere or a reducing atmosphere, one of N ₂ , Ar, He, H ₂ , CO or NH ₃ or Method of supplying atmosphere gas consisting of two or more kinds, or AlN
There is a method of coating carbon with carbonaceous powder.

In the former method of supplying the atmosphere gas, in order to prevent oxygen from being taken into AlN as much as possible, the atmosphere gas containing the reducing gas (for example, H ₂ , CO, NH ₃ ) is supplied. Is desirable. The heat treatment temperature in the case of using this method is set to 1550 to 1900 ° C. The reason is that if the temperature is less than 1550 ° C, the effect of improving the crystallinity of AlN is small, the thermal conductivity cannot be improved so much, while the temperature is 1900 ° C or less. This is because the effect of improving the thermal conductivity is often saturated, and even if the temperature exceeds 1900 ° C, the heating cost only increases and the thermal conductivity cannot be improved. Note that when a simple inert gas is used instead of a gas containing a reducing gas as the heat treatment atmosphere, when the heat treatment temperature exceeds 1700 ° C., it is contained in the water or the inert gas adsorbed on the surface of AlN. The heat treatment temperature is more preferably 1550 to 1770 ° C., since a small amount of water or oxygen may diffuse into the AlN structure and cause phonon scattering, which may lower the thermal conductivity.

However, if a gas containing reducing gas is supplied as the atmosphere gas as described above, there is a danger of explosion if outside air enters the reaction furnace. Measures are needed. Also, in the case of an atmosphere gas containing H ₂ and NH _3, at the processing temperature exceeding 1800 ° C, AlN
There is a possibility that a part of the gas will be eroded (etched) by the reducing gas.

Therefore, by using the latter method of coating AlN synthesized by the CVD method with carbonaceous powder, it is possible to solve the problem that occurs when an atmosphere gas containing a reducing gas is used. That is, if AlN is coated with carbonaceous powder, it is not necessary to use a reducing gas, so there is no danger of explosion even if outside air enters the reaction furnace. Moreover, even if air enters, the carbonaceous powder is only oxidized and does not affect AlN. In this method, HIP treatment (1000kg / cm
It is also possible to apply high temperature treatment under high pressure of ² or more). When using this method, the heat treatment temperature is 1500 to 2100 ℃
The reason is that if the temperature is less than 1500 ° C, the effect of improving the crystallinity of AlN is small, so that the thermal conductivity cannot be improved so much, while at 2100 ° C or less, the effect of improving the thermal conductivity is often saturated. The reason is that even if the temperature exceeds 2100 ° C, the heating cost only increases and the thermal conductivity cannot be improved. If the HIP treatment is not performed and the heat treatment temperature exceeds 1900 ° C, a part of the surface of AlN may be decomposed. On the other hand, HIP treatment does not decompose AlN even at a high temperature of 1900 to 2100 ℃.

According to the method of the present invention as described above, since the synthesis temperature by the CVD method is relatively low at 600 to 1300 ° C., the crystal grain size is small, and even in the subsequent heat treatment, the crystal growth does not occur without causing crystal grain growth. The crystallinity can be improved and phonon scattering is reduced. Therefore, AlN having high strength and high thermal conductivity can be manufactured.

〔Example〕

 Hereinafter, embodiments of the present invention will be described.

A carbon substrate (made by Mechanical Carbon Co.,
MC4402) is installed and the reaction temperature is 700 as shown in Table 1.
AlCl ₃ (purity 95% or higher) and NH ₃ (purity 99.9% or higher) were supplied at a ratio of about 1: 1 at a temperature of up to 1500 ° C to form an AlN film with a thickness of about 3 mm on the carbon substrate. . AlN generated even when the reaction gas supply ratio is changed in the range of 1: 0.8 to 1.4
There was no effect on the membrane. Table 1 shows the results of measuring the density, bending strength, crystal grain size, oxygen concentration and thermal conductivity after separating each of the obtained AlN films from the carbon substrate.

Next, the obtained AlN film was heat-treated by the apparatus shown in FIG. 1, the apparatus shown in FIG. 2, or the HIP apparatus shown in FIG.

In FIG. 1, both ends of a quartz tube 1 are sealed with lids 2 and 3, and the lid 2 has a supply pipe 4 and a glass window 5 for temperature measurement.
However, an exhaust pipe 6 is attached to the lid body 3. A high frequency induction coil 7 is arranged on the outer circumference of the quartz tube 1, and a carbon heater 9 is provided inside the quartz tube 1 with a heat insulating material 8 interposed therebetween. AlN on the surface of this carbon heater 9
The carbon base material 10 on which the film 11 is formed is placed. Then, the inside of the furnace is set to a predetermined temperature, and, for example, N ₂ gas or N ₂ + H ₂ gas is supplied from the supply pipe 4 to heat-treat the AlN film 11.

2 is different from FIG. 1 in that a carbon crucible 12 is placed on a carbon heater 9, and an AlN film 11 is formed on the surface of the inside of the carbon base material 10. It is only to be in a state of being coated with (Crecussphere A-200). Also in this case, the inside of the furnace is set to a predetermined temperature, and, for example, N ₂ gas is supplied from the supply pipe 4 to heat-treat the AlN film 11.

In FIG. 3, a carbon crucible 12 is placed on a support base 22 in a high-pressure vessel 21, and an AlN film 11 is provided on the surface inside the crucible 12.
The carbon base material 10 on which is formed is installed in a state in which the periphery is covered with the carbonaceous powder 13. A heater 23 is provided around the carbon crucible 12. Also, the high-pressure container 12
A supply pipe 24 is connected to the bottom of the gas cylinder 25 and the compressor.
Connected to 26. Then, the inside of the high-pressure container 21 is set to a predetermined temperature, and high-pressure N ₂ gas is supplied from the supply pipe 24 to supply the AlN film 1
Perform the heat treatment of 1.

First, using the apparatus shown in FIG. 1, 900 ° C, 1000 ° C, 120 ° C
Each AlN film synthesized at 0 ℃ and 1300 ℃, 1600 ℃ in N ₂ atmosphere
4 and 5 show the relationship between the processing time and the thermal conductivity and the relationship between the processing time and the bending strength in the case of the heat treatment in FIG.
Shown in the figure. As can be seen from FIG. 4, the thermal conductivity sharply improves from the start of the heat treatment to about 1 hour and then gradually increases with the treatment time, but the change in the thermal conductivity is small even if the heat treatment is performed for 2 hours or more. Further, as can be seen from FIG. 5, the bending strength hardly changes regardless of the processing time. Although not shown, the atmosphere (however, Ar, He,
Even when the heat treatment temperature is different from the above, at least one of H ₂ , CO, and NH ₃ ), the same tendency as in FIGS. 4 and 5 was observed. Therefore, in each of the following experiments, the heat treatment time was set to 2 hours.

Next, the synthesized AlN film was heat-treated under various heat-treatment conditions. Table 2 shows the heat treatment conditions and the properties of the AlN film. In Table 2, the heat treatment atmosphere is No2, 12 to 1
4, 31, 39 are N ₂ : H ₂ = (2: 1) reducing mixed gas atmosphere, No1
0, 11, 36, and 37 are N ₂ : H ₂ = (1: 1) reducing mixed gas atmospheres, and Nos. 15, 16, 17, 28, and 29 are N ₂ gas atmospheres containing 0.1% O ₂ gas ( Atmosphere assuming that air has entered from the outside).

6 to 13 show the relationship between the processing temperature and the thermal conductivity of the AlN film, and the relationship between the processing temperature and the bending strength of the AlN film. 6 and 7 show the case where N ₂ gas at 1 atm is supplied using the apparatus shown in FIG. 1, and FIGS. 8 and 9 show N at 1 atmosphere using the apparatus shown in FIG. _{When 2} : H ₂ = (1: 1) mixed gas is supplied, when 1 atm N ₂ : H ₂ (2: 1) mixed gas is supplied using the apparatus shown in FIGS. 10 and 11, First
12 and 13 show the results when N ₂ gas at 1 atm was supplied in a state where the AlN film was covered with carbonaceous powder using the apparatus shown in FIG.

As can be seen from FIG. 6, when the atmospheric gas is N ₂ , the thermal conductivity is improved after the heat treatment temperature is around 1550 ° C, but the heat conductivity is slightly lowered when the heat treatment temperature exceeds about 1700 ° C. There is a tendency (however, the thermal conductivity is higher than that of the untreated case). Also, FIGS. 8, 10 and 12
As can be seen from the figure, in the case of N ₂ : H ₂ (1: 1) reducing mixed gas atmosphere, in the case of N ₂ : H ₂ (2: 1) reducing mixed gas atmosphere,
Alternatively, in the N ₂ gas atmosphere covered with the carbonaceous powder, the thermal conductivity continues to improve up to 1800 ° C. in most cases, and the thermal conductivity is maintained even at 2000 ° C.

Further, as is clear from FIGS. 7, 9, 11 and 13, the bending strength does not deteriorate even if the heat treatment is performed in any of the above atmospheres after the AlN film is formed by the CVD method. I understand. This is a sufficiently expected result because the crystal grains did not grow even after the heat treatment as shown in Table 2.

As described above, in order to investigate the cause of the difference in the effect of improving the thermal conductivity due to the difference in the atmosphere, the results of examining the relationship between the heat treatment temperature and the oxygen concentration in the AlN sample for a part of the AlN sample FIG. 14 shows the relationship between the heat treatment temperature and the full width at half maximum of the AlN (002) peak by X-ray diffraction, and FIG. 15 shows the results.

As can be seen from FIG. 14, N ₂ : H ₂ (1: 1) reducing mixed gas atmosphere, N ₂ : H ₂ (2: 1) reducing mixed gas atmosphere, and N in the state coated with carbonaceous powder _{In the 2} gas atmosphere, the oxygen concentration does not change much, but in the N ₂ gas atmosphere,
Oxygen concentration rises from around 1700 ℃.

Further, as can be seen from FIG. 15, in the N ₂ : H ₂ (1: 1) reducing mixed gas atmosphere, the half-value width decreases and the crystallinity improves as the heat treatment temperature increases. In the case of N ₂ gas atmosphere, the half-value width is reduced up to around 1700 ° C and the crystallinity is improved, but when it exceeds 1700 ° C, the half-value width tends to increase again and the crystallinity tends to deteriorate. is there.

The following can be seen from FIGS. 6 to 15. That is,
When heat-treated in N ₂ gas, at temperatures above 1700 ° C, the thermal conductivity is improved compared to the untreated case, but Al
Moisture adsorbed on the surface of N and a small amount of water and oxygen contained in N ₂ diffuse into the AlN structure, and the oxygen concentration in AlN increases and the crystallinity deteriorates, causing phonon scattering. The thermal conductivity decreases. On the other hand, in the case of N ₂ : H ₂ (1: 1) reducing mixed gas atmosphere, N ₂ : H ₂ (2: 1) reducing mixed gas atmosphere, and N ₂ gas atmosphere coated with carbonaceous powder Since oxygen is reduced and removed from H _{2 at} a high temperature, the cause of phonon scattering disappears, and the thermal conductivity improves as the heat treatment temperature rises.

In the case of an atmosphere containing H ₂ , there is a danger of explosion if air from the outside enters, so it is necessary to take safety measures against the intrusion of air, such as using a double sealed structure of the furnace. This is also the case with an atmosphere containing NH ₃ . Also, as can be seen from No. 15 and 16 in Table 2 (atmosphere assuming that air has entered), the effect of improving the thermal conductivity is extremely reduced, whereas AlN is coated with carbonaceous powder. In this case, the atmosphere containing the reducing gas does not have to be used, so that no special safety measure is required. And the second
As is clear from Nos. 28 and 29 in the table, even if air enters, the carbonaceous powder is only oxidized and does not affect AlN, so that the thermal conductivity can be sufficiently improved.

Further, as can be seen from Table ₂ , in an atmosphere containing H _2, at a heat treatment temperature of 1800 ° C. or higher, a part of the surface of AlN is corroded (etched) due to the strong reducing property of H ₂ gas, and therefore the weight is reduced. is decreasing. On the other hand, when coated with carbonaceous powder, there is no reduction in weight even at 1900 ° C.
However, even when coated with carbonaceous powder, the weight is slightly reduced at 2000 ° C.

Further, as can be seen from Nos. 4, 24 to 27, 33, and 41 in Table 2, the AlN film was coated with carbonaceous powder, and H was applied at a pressure of 1500 kg / cm ^2.
When IP treatment is performed, AlN is produced even at a high temperature of 1900 to 2100 ° C.
No decomposition occurs and the thermal conductivity is improved.

In the above example, N ₂ gas or N ₂ was used as the atmosphere gas.
Although the case where the -H ₂ mixed gas is used has been described, it has been confirmed that the same tendency as described above is exhibited when another gas is used as the atmosphere gas.

〔The invention's effect〕

As described in detail above, according to the method of the present invention, it is possible to produce aluminum nitride having high strength and high thermal conductivity, and its industrial value is extremely large.

[Brief description of the drawings]

1 is a sectional view of a heat treatment furnace for carrying out the method of the present invention, FIG. 2 is a sectional view of another heat treatment furnace for carrying out the method of the present invention, and FIG. 3 is a sectional view of the heat processing furnace for carrying out the method of the present invention. FIG. 4 is a cross-sectional view of the HIP device, and FIG. 4 is a characteristic diagram showing the relationship between processing time and thermal conductivity when an AlN film synthesized by the CVD method according to the present invention is heat-treated at 1600 ° C. in an N ₂ atmosphere. FIG. 5 is a characteristic diagram showing the relationship between the treatment time and the bending strength when the AlN film synthesized by the CVD method according to the present invention is heat-treated at 1600 ° C. in an N ₂ atmosphere, and FIG. Fig. 7 is a characteristic diagram showing the relationship between the processing temperature and the thermal conductivity when the AlN film synthesized by the method is heat-treated in an N ₂ atmosphere for 2 hours. Fig. 7 shows the AlN film synthesized by the CVD method according to the method of the present invention.
Fig. 8 is a characteristic diagram showing the relationship between the treatment temperature and the bending strength when heat-treated in an N ₂ atmosphere for 2 hours. Fig. 8 shows CV according to the method of the present invention.
Fig. 9 is a characteristic diagram showing the relationship between processing temperature and thermal conductivity when an AlN film synthesized by the D method is heat-treated for 2 hours in a N ₂ : H ₂ (1: 1) reducing mixed gas atmosphere. CV according to the method of the invention
A characteristic diagram showing the relationship between treatment temperature and bending strength when an AlN film synthesized by the D method is heat-treated for 2 hours in a N ₂ : H ₂ (1: 1) reducing mixed gas atmosphere. CV according to the method of invention
Fig. 11 is a characteristic diagram showing the relationship between the processing temperature and the thermal conductivity when the AlN film synthesized by the D method is heat-treated for 2 hours in a N ₂ : H ₂ (2: 1) reducing mixed gas atmosphere. CV according to the method of the invention
A characteristic diagram showing the relationship between treatment temperature and bending strength when an AlN film synthesized by the D method is heat-treated for 2 hours in an N ₂ : H ₂ (2: 1) reducing mixed gas atmosphere. CV according to the method of invention
FIG. 13 is a characteristic diagram showing the relationship between the processing temperature and the thermal conductivity when the AlN film synthesized by the D method is coated with carbonaceous powder and heat-treated in an N ₂ gas atmosphere for 2 hours.
Fig. 14 is a characteristic diagram showing the relationship between the treatment temperature and bending strength when an AlN film synthesized by the method is coated with carbonaceous powder and heat-treated in an N ₂ gas atmosphere for 2 hours.
Fig. 15 is a characteristic diagram showing the relationship between the treatment temperature and the oxygen concentration in AlN when the AlN film synthesized by the method is heat-treated in various atmospheres for 2 hours. Fig. 15 is synthesized by the CVD method according to the method of the present invention. Characteristic diagram showing the relationship between the processing temperature and the half-width of AlN (002) by X-ray diffraction when the AlN film is heat-treated for 2 hours in N ₂ atmosphere and N ₂ : H ₂ (1: 1) mixed gas atmosphere Is. 1 ... Quartz tube, 2, 3 ... Lid, 4 ... Supply tube, 5 ...
Glass window for temperature measurement, 6 ... Exhaust pipe, 7 ... High frequency induction coil, 8 ... Heat insulating material, 9 ... Carbon heater, 10 ... Carbon base material, 11 ... AlN film, 12 ... Carbon crucible, 13
...... Carbonaceous powder, 21 ...... High-pressure container, 22 ...... Support base, 23 ...
… Heater, 24 …… Supply pipe, 25 …… Gas cylinder, 26 ……
Compressor.

Claims (3)

(57) [Claims] 1. A base material is placed in a reaction furnace, an aluminum compound gas and an NH ₃ gas are supplied and reacted at 600 to 1300 ° C., AlN is deposited on the base material, and then an inert atmosphere or A method for producing aluminum nitride, which comprises heat-treating at 1500 to 2100 ° C in a reducing atmosphere. 2. An atmosphere gas consisting of one or more of N ₂ , Ar, He, H ₂ , CO or NH ₃ is supplied to make the atmosphere of AlN an inert atmosphere or a reducing atmosphere. The method for producing aluminum nitride according to claim 1, wherein the heat treatment is performed at 1900 ° C. 3. The method for producing aluminum nitride according to claim 1, wherein the heat treatment is performed at 1500 to 2100 ° C. by coating the AlN with a carbonaceous powder to make the periphery of the AlN a reducing atmosphere.