JPH07110993B2 - Method for producing hard boron nitride and synthesizer used therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention has extremely high hardness next to diamond,
The present invention also relates to a novel method for producing cubic boron nitride having excellent thermal conductivity and a synthesis apparatus used for the method.

(Prior Art) Cubic boron nitride has a Vwitzkerth hardness of 4500, which is the second highest hardness after diamond on the earth, and is as excellent in thermal conductivity as diamond.

Further, it is excellent in oxidation resistance as compared with diamond, and has a property of hardly reacting with an iron group metal at a high temperature, so that it is very excellent as a cutting tool material or a wear resistant tool material.

Further, in addition to being excellent in heat conductivity, it is also applied to a heat dissipation base material for semiconductor devices and the like that it is also excellent in electric insulation.

Conventionally, cubic boron nitride was synthesized using an ultra-high pressure ultra-high temperature generator similar to diamond, but in the same way as in the case of diamond in recent years, on a substrate heated from the gas phase without using ultra-high pressure ultra-high temperature. A vapor-phase synthesis method of precipitating into the atmosphere is being developed.

Currently attempted methods include an ion plating method using metal boron as a boron source, an ionization deposition method, and an IVD method. Hexagonal boron nitride or metal boron is used as a target, and sputtering using Ar or N ₂ is sputtered. There is a law.

Further, a plasma CVD in which a boron source and a nitrogen source utilize a gas body, and an electric power such as high frequency or microwave is externally applied to the raw material gas to excite it into a plasma state to synthesize boron nitride on a heated and held substrate. The law is known.

(Problems to be Solved by the Invention) With the above-described existing method for producing hard boron nitride, it is extremely difficult to synthesize single-phase cubic boron nitride as in the vapor phase synthesis method of diamond, and cubic nitride In addition to boron, there is a problem that hexagonal boron nitride and amorphous boron nitride easily coexist. In addition, it has been reported that cubic boron nitride close to a single phase can be formed, and hexagonal boron nitride is hardly detected in the infrared absorption spectrum. As described above, the synthesis of a cubic boron nitride single phase having an extremely high degree of perfection has not been made yet.

In view of the problems of the conventional method, the present inventors have earnestly studied to synthesize cubic boron nitride excellent in crystallinity and not containing amorphous boron nitride or cubic boron nitride from the vapor phase. As a result of stacking, the present invention was completed.

(Means for Solving the Problems) That is, the method for producing hard boron nitride according to the present invention is a method for synthesizing hard boron nitride in a vapor phase, which comprises a nitrogen (N) source and a boron (N) source. B) Each of the sources is independently activated, and the activated B source and N source are mixed on a substrate kept at 400 ° C or more and 1200 ° C or less to form hard boron nitride on the substrate. The source gas, which is the B source, is activated by microwave plasma, and the N source forms DC plasma between the source gas introduction nozzle and the thermionic emission material placed in front of it and heated to a high temperature of 1400 ° C or higher. It is characterized in that thermal activation of the source gas of the B source and the N source by the thermoelectron emitting material activated by the above and heated at a high temperature is used in addition to the plasma activation.

The synthesis apparatus used in the method for producing hard boron nitride of the present invention (see FIG. 1 described later) is a base material support in which a base material (7) for forming boron nitride is installed in a reaction tank (4). Table (8)
And a thermionic emission material (5) located in front of the base support, and a nitrogen source opened near the base support and the thermionic emission material and introduced into the reaction tank through the opening. A nitrogen source gas nozzle (6) for forming a DC plasma for activating the gas with the thermionic emission material is provided, and on the other hand, on the wall side of the reaction tank (4), in front of the base material support table. Microwave plasma for activating a boron source gas which is provided with a boron source gas introduction port (3) and is vertically penetrated outside the reaction vessel by the reaction vessel and introduced into the reaction vessel through the gas introduction port. It is characterized in that a microwave waveguide (1) for forming the is provided.

The present invention will be described in detail below.

The present invention is a method of independently activating raw material gases to be a B source and an N source, and mixing the activated B source and N source on a substrate whose surface temperature is maintained at 400 ° C. or higher and 1200 ° C. or lower. Then, the activation of the B source is performed by a microwave non-polar discharge and by forming a microwave plasma, while N
The source is provided by forming a DC plasma between a gas introduction nozzle and a high temperature heated thermionic emission material placed in front of it. Also, due to thermionic emission heated at high temperature, B
By also activating the heat source and the N source, cubic boron nitride which does not contain amorphous boron nitride or hexagonal boron nitride at all on the surface of the base material and which has excellent crystallinity and which has an extremely high degree of perfection. We newly discovered that it can be synthesized from the gas phase.

Further, in the present invention, since it is important to accurately control the surface temperature of the substrate, it is desirable to carry out heating or forced cooling of the support, microwave plasma intensity, DC plasma intensity, thermionic emission material temperature. In addition, the surface temperature can be accurately controlled independently of the positional relationship between the thermionic emission material and the base material. Therefore, we succeeded in synthesizing single-phase cubic boron nitride having high crystallinity for the first time because the substrate surface temperature and other conditions could be separated.

FIG. 1 is a schematic sectional view showing a synthesizing apparatus according to an embodiment of the present invention. A substrate support base (8) is housed in the reaction tank (4). A base material (7) for forming boron nitride thereon is installed on the upper surface of the base material support base (8).
Further, a thermoelectron emitting material (5) is placed in front of the base material support (8) (upper side in this embodiment) at a predetermined distance. The thermoelectron emitting material (5) and the nitrogen source introducing gas nozzle. DC plasma is formed between (6) and N source gas is activated.

On the other hand, the boron source gas is introduced into the reaction tank (4) through the gas introduction port (3), and microwaves are fed by the microwave waveguide (1) vertically penetrated by the reaction tank to supply microwaves in the reaction tank. A wave non-polar discharge is generated, the boron source gas is activated by the formation of microwave plasma, and the activated boron source gas is supplied to the lower substrate in the figure.

Further, since the thermoelectron emitting material is heated at a high temperature, it also has a thermal activation effect on the nitrogen source gas and the boron source gas, and at the same time heats the surface of the base material.

The substrate support base (8) can be heated by a heater or cooled by introducing a cooling medium, if necessary, and the surface temperature of the substrate can be maintained at a predetermined temperature.

With this device, a boron source activated by microwave plasma and a nitrogen source activated by DC plasma (and both of them are also thermally activated at the same time) are mixed on the substrate,
Cubic boron nitride having high purity and high crystallinity is synthesized on the surface of the base material. Depending on the conditions, it is possible to synthesize wurtzite hard boron nitride.

In the above, the boron source is preferably diborane or boron trichloride, and the nitrogen source is preferably nitrogen or ammonia, but it is also possible to use borazine containing a boron source and a nitrogen source at the same time. In addition, the gas introduced into the reaction tank is other than the above gases.
H ₂ , Ar, Kr, Xe, Rn may be mixed and used.

These non-H ₂ in the gas can be used as a cooling gas low for substrate thermal conductivity and these gases, including of H ₂ is also a function of adjusting the intensity of the plasma.

The ratio of boron atoms to nitrogen atoms in the reaction gas is 0.
01% or more and 100% or less is desirable, and if it deviates from this range, it becomes difficult to form hard boron nitride having a stoichiometric composition.

Regarding the material of the thermionic emission material, it is required that the vapor pressure is low at a high temperature and that it has a high melting point, and that it is also required to have excellent thermionic emission, so that the high melting point of W, Ta, Mo, etc. It is preferable to use metal, LaB ₆ or the like. The thermionic emissive material should be heated to 1400 ℃ or higher before use. When the temperature is lower than this temperature, precipitation of hexagonal boron nitride and amorphous boron nitride becomes dominant.

Hard boron nitride does not precipitate unless the surface temperature of the substrate is 400 ° C or higher and 1200 ° C or lower.

The pressure in the reaction tank is stable within a very wide range of 1 × 10 ^-5 Torr to 4 × 10 ² Torr, and it is possible to deposit hard boron nitride, but it is possible to deposit on the low pressure side. Since the speed becomes extremely small and conversely the hexagonal boron nitride is mixed on the high side, 1 × 10 ⁻³ Torr to 1 × 10 ² Torr is more preferable.

(Operation) One of the features of the present invention is that the B source and the N source are independently activated and mixed on the surface of the substrate. The reason for using such a method is that if the B source and the N source are mixed and activated at the same time, since both are rich in reactivity, amorphous boron nitride is likely to be formed, and a definite crystalline boron nitride is generated. Even if it is obtained, there is a problem that stable phase hexagonal boron nitride is easily generated. On the other hand, by independently activating the boron source and the nitrogen source independently and mixing them on the surface of the base material, it was possible to obtain only the non-equilibrium hexagonal boron nitride.

A method of exciting the B source and the N source is also important, and the B source uses microwave plasma which has a high electron density and can obtain high activity, while the N source can be said to be a low energy ion source. DC between the electronic discharge source and the gas ejection nozzle
A hollow anode type DC plasma that produces plasma is used. This is because when a high energy N ion source is used, the coating film may be damaged by ion bombardment.

In the present invention, there is also an effect of thermal activation of the raw material gas by the high temperature heated thermionic emission material that becomes a hot cathode that causes DC plasma, and it is considered that the activation of the raw material gas is promoted as compared with the conventional plasma CVD method. To be

The surface temperature of the base material is determined by multiple factors such as microwave power, DC power, the temperature of thermionic emission material, gas pressure, and the position of the base material. For example, since the surface temperature can be set independently of the above-mentioned coating conditions, the degree of freedom in selecting the coating conditions is large.

(Examples) Examples of the present invention will be described below.

Example 1: FIG. 1 shows a schematic cross-sectional view of a synthesis apparatus according to an embodiment of the present invention. Using this apparatus, cubic boron nitride was synthesized. A Si wafer (size: 10mm x 10mm x
0.3 mm) was used as the base material (7).

Reaction vessel (4) in the 1 × 10 ^-6 Torr was evacuated below inlet port (3) from H ₂ 100SCM, the H ₂ 20SCM from the nozzle (6) is introduced into the reaction vessel, to maintain the pressure in 3Torr , W filament was used as the thermionic emission material (5) which doubles as a hot cathode.
After heating to ℃, microwave is fed into the reaction tank through the waveguide (1) to generate microwave non-polar discharge,
At the same time, a DC power source is used to generate DC plasma between the nozzle (6) and the thermionic emission material (5). At this time, the microwave power was 200W and the DC power was 30W.

Then, by flowing a cooling gas through the base material support base (8), the base material support base was cooled to keep the surface temperature of the base material (7) at 850 ° C. After that, B ₂ H ₆ diluted with hydrogen was introduced from the inlet (3).
(B ₂ H ₆ 1% + H ₂ 99%) 5 SCM, NH ₃ from nozzle (6) 10 SC
M introduced at the same time.

After coating for about 3 hours, a coating film was formed. When this film was examined by X-ray diffraction and infrared absorption spectroscopy, a unique diffraction peak of cubic boron nitride and infrared absorption were detected, and diffraction peaks due to other crystal structures such as hexagonal crystal were detected. No infrared absorption was detected. In the structure observation by SEM, a polycrystalline aggregate having a clear ridge of 0.5 to 1 μm was observed. The value of 5200 Hv was obtained as the result of the hardness measurement with the Micro Vickers. Further, the film thickness of the coating film was 4.5 μm from the observation of the fracture surface.

Example 2: A commercially available ISO P-30 cemented carbide model number SPU422 was used as a substrate (7), and cubic boron nitride was coated using the same apparatus as in Example 1.

The distance between the thermionic emission material (5), which also serves as a hot cathode, and the upper surface (rake surface) of the cemented carbide is maintained at 25 mm, and the inside of the reaction tank is 1 ×.
After evacuating to 10 ^-6 Torr or less, coating was performed with the raw material gas having the composition shown in Table 1, the flow rate, the pressure, the microwave power, the DC power, the filament temperature, and the substrate surface temperature.

First, only H ₂ is introduced from the inlet (3) and the nozzle (6), the filament is heated to a predetermined temperature, and then microwave power and DC power are input to form microwave plasma and DC plasma, Heat the base material support so that the base material surface temperature reaches the specified temperature. Alternatively, after cooling, the B source and the N source are caused to flow at the same time, and the pressure is finely adjusted to a predetermined pressure to start the reaction.

The results of X-ray diffraction of the obtained coating film after coating for about 3 hours are shown in Table 1.

Of the No. 1 to No. 14 samples, it is considered that No. 1 obtained hexagonal BN because the substrate surface temperature was high. On the contrary, in No. 4, it is considered that amorphous BN was obtained because the substrate surface temperature was low. Furthermore, in No. 8, the filament temperature was too low, so it is considered that amorphous BN was obtained. Other than that, cubic BN was synthesized.

Using these coating chips, a cutting test was conducted under the following conditions.

Work Material: SCM415 (HR _C = 60), Cutting Speed: 150m / min, Feed:
0.1 mm / rev, Holder: FR21R-44A, Cutting time: 15 min The flank wear after cutting test is 0.08 mm for No. 2 and 0.12 for No. 3.
mm, No. 5 is 0.09 mm, No. 6 is 0.11 mm, No. 7 is 0.15 mm, No. 9
Is 0.12 mm, No. 11 is 0.11 mm, No. 12 is 0.13 mm, No. 13 is 0.1
3mm, No.14 was 0.09mm. The coating film peeled off probably because No. 10 had a large film thickness.

On the other hand, the uncoated cemented carbide for comparison had a life of only 1 minute.

(Effects of the Invention) As described above, according to the manufacturing method of the present invention, the boron source gas is activated by the formation of microwave plasma, the nitrogen source gas is activated by the DC plasma, and both of them simultaneously serve as the fuel cathode. By thermally activating it with a thermionic emission material heated at high temperature and mixing it on the surface of the base material, a cubic boron nitride containing almost no amorphous phase or hexagonal boron nitride and having excellent crystallinity is formed. It was possible to synthesize.

Further, according to the synthesizing apparatus of the present invention, the manufacturing method of the present invention can be carried out simply and reliably.

[Brief description of drawings]

FIG. 1 is a front view showing an example of an apparatus used for carrying out the method of the present invention. (1) …… Microwave waveguide, (2) …… For example 2.45GH
Microwave oscillator of z, (3) ... B source gas inlet, (4) ... reaction tank such as transparent quartz reaction tube, (5) ...
… Thermionic emission material, (6) …… N source material gas introduction nozzle,
(7) ... Substrate, (8) ... Substrate support, (9) ... Coolant flow pipe (or heater heating wire for support),
(10) …… Vacuum exhaust port, (11) …… Insulation seal, (12)
...... Thermionic emission material heating power supply (AC), (13) …… DC power supply

Claims (5)

[Claims] 1. A method for synthesizing hard boron nitride from a gas phase, comprising: activating a nitrogen source and a boron source independently and maintaining the temperature at 400 ° C. to 1200 ° C. A hard boron nitride is produced on a substrate by mixing a boron source and a nitrogen source activated by the above. A raw material gas as a boron source is activated by microwave plasma, and the nitrogen source is a raw material gas introduction nozzle. The source gas of the boron source and the nitrogen source is activated by forming DC plasma between the high temperature heated thermionic emission material heated to 1400 ° C. or higher and the high temperature heated thermionic emission material placed in front of it and the high temperature heated thermionic emission material. A method for producing hard boron nitride, characterized in that thermal activation of is used together with plasma activation. 2. The surface temperature of the substrate is independent of the intensity of microwave plasma, the intensity of DC plasma, the temperature and size of the thermionic emission material, and the positional relationship between the thermionic emission material and the substrate. The method for producing hard boron nitride according to claim (1), wherein the substrate support can be heated or cooled so that the surface temperature can be determined. 3. A base material support (8) in which a base material (7) for forming boron nitride is installed in a reaction tank (4), and thermoelectrons located in front of the base material support base. The radiation material (5) and a DC plasma for activating the nitrogen source gas which is opened near the base material support and the thermionic emission material and which is introduced into the reaction tank through the opening are thermionic emission material. And a nitrogen source gas nozzle (6) formed between the reaction vessel (4) and the reaction vessel (4), the boron source gas inlet (3) is provided in front of the base material support on the wall side and outside the reaction vessel. A microwave waveguide (1) for forming a microwave plasma for activating a boron source gas which is vertically penetrated by the reaction tank and introduced into the reaction tank through the gas introduction port. A synthetic apparatus for use in a method for producing hard boron nitride, characterized in that. 4. A base material support base (8) depends on the intensity of microwave plasma, the intensity of DC plasma, the temperature and size of the thermionic emission material, and the positional relationship between the thermionic emission material and the substrate. A synthesizing apparatus used in the method for producing hard boron nitride according to claim (3), which is provided with a heater so that the surface temperature can be independently determined. 5. A base material support base (8) depends on the intensity of microwave plasma, the intensity of DC plasma, the temperature and size of the thermionic emission material, and the positional relationship between the thermionic emission material and the substrate. A synthesizing apparatus for use in the method for producing hard boron nitride according to claim (3), wherein a cooling medium is introduced so that the surface temperature can be independently determined.