JPH07100859B2 - Method for producing cubic boron nitride film - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention is excellent in high hardness, high insulation, etc., which are expected to be tool materials such as cutting tools and abrasion resistant tools, electronic materials such as heat sinks, and various other applications. The present invention relates to a method for producing a cubic boron nitride film having the above characteristics, and particularly to a method for producing a cubic boron nitride film in which a cubic boron nitride film is deposited on a substrate by a gas phase reaction.

Conventional technology Boron nitride usually has a crystal structure similar to graphite [hexagonal boron nitride] (hereinafter abbreviated as HBN) and is a soft and slippery substance, but graphite is transformed into diamond under high temperature and high pressure. Boron nitride is also a graphite type HB
It is known that N is transformed into cubic boron nitride having a diamond type crystal structure (hereinafter, abbreviated as CBN) to be a material excellent in hardness, insulating property, thermal conductivity and corrosion resistance. Particularly, in terms of hardness, it is used as a material for cutting tools, blades, etc. used at high temperatures because it has a hardness enough to damage each other with diamond and has corrosion resistance against high temperature iron group metals not found in diamond. Furthermore, since CBN has an insulating property similar to that of silicon oxide and has a thermal conductivity about three times that of silicon oxide in terms of thermal conductivity, CBN has a substrate such as a VLSI or an electronic device such as a heat sink. It is a material that is also attracting attention as a material.

Conventionally, in order to produce CBN having such excellent properties, an ultra-high pressure high temperature sintering method, that is, applying a pressure of 60 Kbar or more to an HBN using an ultra-high pressure generator, at a high temperature of 1500 to 2000 ° C or more. Therefore, I had to rely on the method of melting with the catalyst.

By the way, it is known that nitrogen and boron atoms form a stable SP ³ hybrid bond in the cubic crystal of CBN. In order to form such an SP ³ hybrid bond using nitrogen and boron separately as raw materials and without using the ultra-high pressure and high temperature sintering method, first, an electron of a nitrogen atom and a boron atom is formed into an SP ³ hybrid orbital by some method. It is necessary to excite each electronic excited state to make. Next, by giving the opportunity for such nitrogen atoms and boron atoms in the electronically excited state to collide with each other, it is possible to
SP ³ hybrid bonds are formed. The specific mechanism for producing such a stable SP ³ hybrid bond has not yet been clarified, and only a few theories that serve as the clue have been proposed.

Under these circumstances, in recent years, CBN and cubic close-packed boron nitride (hereinafter abbreviated as WBN), which is obtained at the same time as CBN in the ultra-high pressure high temperature sintering method, have been processed by the above-mentioned ultra high pressure high temperature sintering method. There is proposed a method of manufacturing by using physical vapor deposition and / or ion irradiation without using.

For example, (i) depositing boron on a substrate to which a negative bias voltage is applied from an evaporation source containing boron, and
There has been proposed a method for producing CBN in which an ion species containing at least nitrogen separated by a mass spectrometer is irradiated to generate CBN on the substrate [see JP-A-60-181262]. In addition, (ii) by HCD (hollow cathode deposition) method, while depositing boron with an electron beam, the N ₂ ionic species formed in the hollow anode is applied to the substrate to which a self-bias effect is applied by applying a high frequency voltage. CBN to irradiate
Manufacturing method of [Proceeding 9th Symposium
On Ion Source Ion Assisted Technology (Proceeding 9th Symposium on Ion Source Ion
Asisted Technology), 85, Tokyo, (1985)],
Furthermore, (iii) a method in which the ion deposition (ID) method used for producing a diamond-like thin film is applied to a method for producing boron nitride, that is, a boron-containing solid is irradiated with an electron beam to evaporate boron, By introducing gas and ionizing boron and nitrogen simultaneously,
Method for producing CBN [Vacuum, Vol. 28, No. 7 (1985)
[Refer] etc. are proposed.

Problems to be Solved by the Invention As described above, CBN has various excellent properties advantageous for application to cutting tool materials, electronic materials, etc. Various manufacturing techniques have been proposed.

However, the above method (i) is an extremely complicated and expensive device such as having a high kinetic energy of 5 to 100 KeV for ions, focusing an ion beam, and having a mass separation function for selecting a specific N ₂ ^+. Had the problem of needing. In addition, the method of (ii) above and (iii) above
In the method, since boron has a melting point and a boiling point close to each other, it is apt to cause bumping on the solid surface by electron beam irradiation, and there is a problem that it is difficult to control the electron beam. On the other hand, the latter has the problem that the purity of the obtained CBN is relatively low.

Therefore, the object of the present invention is simple, in the production of CBN, without requiring a complicated device such as an ion beam or an electron gun,
Moreover, it is to provide a method for producing CBN that is less likely to be contaminated with impurities and the like.

Means for Solving the Problems The inventors of the present invention have made extensive studies and researches in order to solve the above-mentioned problems in the conventionally-proposed CBN manufacturing method, and as a result, a reaction of preheating and plasmaization. By combining a series of steps of treating the gas and heating the substrate, it is possible to stabilize the stable operation between nitrogen and boron atoms.
It was found that CBN can be deposited on the substrate by forming SP ³ hybrid bond.

That is, the present invention provides a method for producing CBN, which comprises preheating a mixture of a boron-containing gas and a nitrogen-containing gas, applying a high frequency voltage to the mixture to generate plasma, and depositing CBN on the heated substrate. To do.

In the method of the present invention, first, the boron-containing gas and the nitrogen-containing gas are preheated. The raw material gas of the present invention used here, that is, the boron-containing gas, for example, B ₂ H ₆ , BC
l ₃ , B ₃ H ₆ N ₃ , BF _{3 and the} like can be mentioned, and of course, a mixture of these gases can be used. On the other hand, examples of the nitrogen-containing gas include N ₂ , NH ₃ , lower alkyl group-substituted ammonia, NO and the like, or a mixture thereof. In this step, the source gas mixture is pre-excited.

In these reaction gases, the mixing ratio of the boron-containing gas and the nitrogen-containing gas is such that the ratio of boron atoms to nitrogen atoms in these gas components (hereinafter, abbreviated as B / N) is 0.1 to
It is preferable to determine it within the range of 10. B / N is 0.1
When it is less than less than 100%, amorphous boron nitride tends to precipitate,
On the other hand, when it exceeds 10, boron becomes excessive and amorphous boron is easily deposited on the substrate, which is not preferable. The total pressure and flow rate of these reactive gases, the boron-containing gas and the nitrogen-containing gas, are generally governed by the discharge conditions that are the steps after preheating.

Preliminary heating of these reaction gases is performed using a thermionic emission material. Examples of the thermoelectron emitting material include a tungsten filament and a thorium-containing tungsten filament.
Adjust within the range of 00 ℃ or higher. The preheating by the thermionic emission plate is different from the usual thermal activation and efficiently decomposes and activates the raw material gas by the emission of thermions. If this temperature is lower than 1000 ° C., the target CBN cannot be deposited on the substrate, and another crystal system is deposited, which is not preferable.

According to the method of the present invention, as a next step, a high frequency voltage is applied to the raw material gas mixture preheated and preexcited as described above. As a result, the raw material gas mixture is turned into plasma and further excited, decomposed, and ionized to become various molecular species and atomic species, and free chemical boron and nitrogen, which are chemically active, are generated by the action of the thermal energy of the heated substrate. It reacts to form stable SP ³ bonds and is deposited on the substrate as cubic boron nitride. In this step, it is preferable that the source gas pressure is 0.01 to 100 Torr and the high frequency is 1 KHz to 13.56 MHz as the high frequency voltage application condition. Further, in order to achieve sufficient activation, it is advantageous that the residence time of the raw material gas in the high frequency application region is 10 ^{-2 to 1} S, and the raw material gas flow rate and the high frequency voltage application region are set so as to satisfy this condition. Adjust the width, etc.

In the substrate for depositing CBN which is the object of the production method of the present invention, it is preferable to heat the temperature of the substrate to 300 to 2000 ° C., and if it is outside this temperature range, nitriding of a crystal system other than CBN is performed on the substrate. Boron and amorphous boron nitride are deposited. In order to heat the substrate to the above temperature, it is usually preferable to install a heater for heating under the substrate. The material of the substrate is preferably one that does not melt under the above heating conditions, for example, tungsten, silicon wafer, molybdenum and the like and ceramic materials such as Al ₂ O ₃ , Si ₃ N ₄ , SiC and the like, and cemented carbide. Can be mentioned.

A specific example of the manufacturing apparatus used in the present invention is shown in FIG. This apparatus mainly comprises a reaction gas control system that supplies a mixture of a nitrogen-containing gas and a boron-containing gas, which are reaction gases, to the reaction vessel and at the same time adjusts the internal pressure of the reaction vessel, and excites, dissociates and reacts the reaction gas. And a CBN reaction system for depositing CBN on the substrate. In a reaction vessel 1 capable of maintaining airtightness, a thermoelectron emitting material 3 is arranged near a reaction gas introduction port 2 inside the reaction vessel, and a discharge port provided on the inner wall facing the introduction port 2 4, a high frequency irradiation coil 5 is arranged on the outer periphery which is the side surface of the reaction container. Further, a substrate 6 for depositing CBN and a supporting base 7 thereof are installed at the bottom of the inner wall of the portion of the reaction vessel 1 covered with the high frequency coil 5. Further, the reaction container 1 is connected to the reaction gas supply devices 9 and 10 through the reaction gas inlet 2 and the inlet pipe 8, while the reaction gas outlet 4 and the exhaust pipe 11 are connected.
It is connected to the reaction gas exhaust device 12 via. Further, outside the reaction vessel 1, a high frequency power source 13 for a high frequency irradiation coil and a power source 14 for a thermoelectron emitting material are provided. In this apparatus, the heating of the substrate is such that the substrate is placed in the plasma and adjusted to a predetermined temperature by the output of the plasma.

On the other hand, FIG. 2 shows another example of the manufacturing apparatus used in the present invention. Although it has basically the same configuration as that of FIG. 1 and can carry out the steps of the present invention, the difference from the apparatus of FIG. 1 is that the thermoelectron emitting material 3 for heating is a reaction gas inlet port. 2 and is installed parallel to the inner wall having the inlet, and the substrate 6 and its supporting base 7 are installed on the inner wall having the outlet 4 facing the thermoelectron emitting material. ing.
In the case of this apparatus, unlike the case of FIG. 1, since the substrate 6 is slightly apart from the high frequency coil 5 for generating plasma, a heater 15 is installed below the substrate as a substrate heating means.

The CB is operated by operating the manufacturing apparatus used in the present invention as described above.
In order to obtain N, first, the reaction chamber is evacuated by an exhaust device 12, for example, an oil diffusion pump, and then a predetermined mixing ratio by the boron-containing gas and nitrogen-containing gas supply devices 9 and 10 and the exhaust device 12, the reaction vessel. The boron-containing gas and the nitrogen-containing gas are supplied so as to have the internal pressure and the moving speed of the reaction gas, and the mixed gas is heated by the thermoelectron emitting material 3 so as to have a predetermined temperature. Further, a high frequency voltage is applied so that high frequency plasma is generated. Further, the substrate 6 is heated via a heater or plasma so as to obtain a predetermined temperature. After such an operation, CBN is deposited on the substrate by continuing the operation of this device.

Action CBN has a diamond-type crystal structure in which nitrogen and boron atoms form a stable SP ³ hybrid bond in a cubic crystal.

In order to form this SP ³ hybrid bond, it is necessary to excite each nitrogen atom and boron atom to an excited state in order to create an SP ³ hybrid orbital, and furthermore, to give them an opportunity to collide with each other. , SP ³ form a molecular orbital that becomes a hybrid bond. By placing the electrons that each excited atom had in the molecular orbital that becomes such a SP ³ hybrid bond, a large amount of stabilization energy is obtained, and the system is stabilized, resulting in the excellent properties described above. Have.

Thus, in order to produce CBN, SP ³ from B source and N source is used.
It is important to find conditions under which hybrid bonds are easily formed.
In this respect, according to the present invention, a series of energy supply treatments such as heating the raw material mixed gas in advance by thermionic emission material to pre-excite it, then applying a high frequency voltage to turn it into plasma, and heating the substrate are performed. As a result, it became possible to cause the above SP ³ hybrid bond, and CBN could be deposited on the substrate. Here, the preheating temperature, the substrate temperature and the plasmaization conditions are important in the present invention, and it is preferable to set the range conditions as described above in order to obtain CBN.

According to the present invention, a high-quality CBN thin film can be obtained with a relatively simple operation and an inexpensive device, which is economically advantageous and therefore useful as the above-mentioned various tools and electronic materials.

Examples Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

Example 1 The manufacturing apparatus shown in FIG. 1 was used, a silicon wafer was used as a substrate, B ₂ H ₆ was used as a source gas, and NH ₃ was used as a nitrogen-containing gas, and 4 cc / min and 10 cc, respectively. It was introduced into the reaction chamber at a flow rate of / min. In addition, the temperature inside the reaction vessel was adjusted to 2000 ° C using a tungsten filament, a high-frequency voltage was applied so that the output of the high-frequency plasma was 1 KW, and the exhaust gas was used in the reaction chamber while the gas was flowing. When the pressure was adjusted to 5 Torr and continuous operation was continued for 4 hours in this state, a boron nitride film having a thickness of about 8 μm was obtained.

When the obtained boron nitride film was pulverized and subjected to X-ray diffraction, a sharp peak peculiar to CBN was observed near 2θ = 43.2 °, and it was identified as CBN.

Example 2 Using the manufacturing apparatus shown in FIG. 2, a molybdenum substrate was used as a substrate, BCl ₃ was used as a raw material gas, and BCl ₃ was used as a nitrogen-containing gas, and 5 cc / min and 5 cc / min were used respectively. Was introduced into the reaction chamber at a flow rate of. In addition, the temperature inside the reaction vessel was adjusted to 2200 ° C with a tungsten filament, a high-frequency voltage was applied so that the output of the high-frequency plasma was 2.0 kW, and the reaction was performed using an exhaust device with the above gas flowing. The pressure in the room was adjusted to 8 Torr. Substrate temperature is 900 ℃
After that, when the continuous operation was continued for 4 hours in this state, a boron nitride film having a film thickness of about 12 μm was obtained.

When the obtained boron nitride film was pulverized and subjected to X-ray diffraction, a sharp peak peculiar to CBN was observed near 2θ = 43.2 °, and it was identified as CBN.

Comparative Example 1 In Example 1, the tungsten filament was not used, the pressure in the reaction chamber was 3 Torr, and the high frequency output was 1.5 kw.
In the same manner as in Example 1 except that the film formation time was 5 hours,
A boron nitride film having a thickness of about 10 μm was obtained. The obtained boron nitride film was crushed and subjected to X-ray diffraction.
A sharp peak peculiar to HBN near θ = 26.7 ° and a gentle peak near 2θ = 43.2 °, which is the peak position peculiar to CBN, are observed. This boron nitride film is a polycrystal system of HBN and CBN, and HBN It was revealed that the above was contained in a large amount.

Cutting Test with Boron Nitride Film Using the manufacturing conditions of Examples 1 and 2 and Comparative Example 1, a chip that is a substrate was coated with a film thickness of 3 μm, and the cutting conditions shown in Table 1, namely the work material and the cutting A cutting test was carried out under speed, cutting and feeding, and the time to reach a relief wear width of 0.1 mm was measured under each condition. The results obtained are shown in Table 2. In addition, when the coating was not performed and when TiN was coated using the reactive ion plating method, the same cutting test was performed using the WC-based cemented carbide TNMG432, and the results were obtained. It is shown in Table 2.

From Table 2, it is clear that the chips coated with pure CBN obtained in Examples 1 and 2 are the most excellent in terms of wear resistance. Mixing of boron nitride crystal systems other than CBN (Comparative Example 1) shows the same level of wear resistance as when TiN is coated.

Further, in FIG. 3, using TNG322 as the tip and SCM435 as the work material, the CBN-coated tip, the TiN-coated tip and the uncoated tip obtained in Example 1 were each subjected to a cutting test, The results are shown as the relationship between cutting speed and chip life. In Figure 4,
SNG435 is used as the tip, FC30 is used as the work material,
CBN obtained in Example 2 at a cutting speed of 250 m / min
A cutting test was performed on coated chips, TiC-coated chips and uncoated chips to show the relationship between fracture resistance and the number of impacts. It can be seen from FIGS. 3 and 4 that the chip coated with CBN has about 1.5 times as much wear resistance as the chip coated with other materials.

EFFECTS OF THE INVENTION As described above, the manufacturing method of the present invention is a vapor phase reaction method that does not use the conventional ultrahigh pressure and high temperature sintering method, and is a complicated and expensive apparatus such as an ion beam and an electron gun. This is a simple CBN manufacturing method that does not require. Furthermore, C of the present invention
According to the BN manufacturing method, it is possible to manufacture an excellent CBN in which impurities and other crystalline boron nitride are not mixed, and its industrial value is extremely high.

[Brief description of drawings]

1 and 2 are schematic views of a manufacturing apparatus used in the present invention. FIG. 3 is a graph plotting the relationship between the cutting speed and the life of the chips for CBN-coated chips and other chips. FIG. 4 is a graph showing the fracture resistance of CBN-coated chips and other chips in cutting cast iron. (Main reference numbers) 1 ... Reactor container, 2 ... Reactant gas inlet, 3 ... Thermoelectron emitting material, 4 ... Reactant gas outlet, 5 ... High frequency coil, 6 ... Substrate, 7 ... Substrate support, 8 ... Reaction Gas introduction pipe, 9 ... Boron-containing gas supply device, 10 ... Nitrogen-containing gas supply device, 11 ... Gas exhaust port, 12 ... Gas exhaust device, 13 ... High frequency power supply, 14 ... Thermionic emission material power supply, 15 ... Heater

Claims (3)

[Claims] 1. A mixture of a boron-containing gas and a nitrogen-containing gas is preheated by using a thermoelectron emitting material heated to 1000 ° C. or higher, and then the mixture is irradiated with high frequency to generate plasma, and then heated on a substrate. 1. A method for producing a cubic boron nitride film, comprising the steps of depositing a cubic boron nitride film on. 2. The method for producing a cubic boron nitride film according to claim 1, wherein the temperature of the heated substrate is 300 to 2000 ° C. 3. A ratio of boron atoms to nitrogen atoms in the mixture of the boron-containing gas and the nitrogen-containing gas B /
The method for producing a cubic boron nitride film according to claim 1, wherein N is 0.1 to 10.