JPS6369972A - Production of cubic boron nitride film - Google Patents

Abstract

PURPOSE:To obtain a cubic boron nitride (CBN) film nearly free from impurities by a simple method, by projecting high frequency waves on a preheated mixture of a gas contg. B with a gas contg. N to convert the mixture into plasma and by depositing a CBN film on a heated substrate. CONSTITUTION:A gas contg. B such as B2H6 or BCl3 is mixed with a gas contg. N such as N2 or NH3 in 0.1-10 atomic ratio of B/N and the mixture is heated to >=1,000 deg.C preferably with a thermoelectron radiator. High frequency voltage is applied to the gaseous mixture preheated and pre-excited as mentioned above to convert the mixture into plasma and further excitation, dissociation and ionization are carried out. Various kinds of molecules and atoms are produced and especially chemically active free boron and nitrogen are brought into a reaction by the action of heat energy of a heated substrate to form stable SP<3> bond and to deposit and form a CBN film on the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a material with excellent hardness, high insulation properties, etc., which is expected to be used as tool materials such as cutting tools and wear-resistant tools, electronic materials such as heat sinks, and various other applications. The present invention relates to a method of manufacturing a cubic boron nitride film having such characteristics, and particularly relates to a method of manufacturing a cubic boron nitride film in which the 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 transforms into diamond under high temperature and high pressure. In this way, boron nitride also transforms from graphite-type HBN to cubic boron nitride (hereinafter abbreviated as CBN) with a diamond-type crystal structure, which improves hardness, insulation,
It is known to be a material with excellent thermal conductivity and corrosion resistance. In particular, it is hard enough to damage both diamond and diamond, and it also has corrosion resistance against high-temperature iron group metals that diamond does not have, so it is used as a material for cutting tools and blades that are used at high temperatures. Furthermore, CBN has an insulating property comparable to that of silicon oxide, and has a thermal conductivity that is about three times that of silicon oxide, so it can be used for electronic substrates such as ultra-LSIs or heat sinks. It is also a material that is attracting attention.

Conventionally, in order to produce CBN with such excellent properties, the ultra-high pressure and high temperature sintering method was used to apply HBN to a pressure of 60 Kbar or more using an ultra-high pressure generator and heat the HBN to 1,500 Kbar or more.
The first place had no choice but to rely on a method of melting together with the catalyst at a high temperature of ~2000°C or higher.

By the way, it is known that nitrogen and boron atoms form stable SP3 hybrid bonds in the cubic crystal of CBH. In order to form such an SP3 hybrid bond using nitrogen and boron separately as raw materials without using an ultra-high pressure and high temperature sintering method, first, the electrons of nitrogen atoms and boron atoms must be formed into SP' hybrid orbitals by some method. It is necessary to excite each electron to its excited state. next,
By providing opportunities for such electronically excited nitrogen and boron atoms to collide with each other, SP' hybrid bonds are formed between the nitrogen and boron atoms. The specific mechanism for producing such a stable SP3 hybrid bond has not yet been clarified, and only a few theories have been proposed to provide clues.

Under these circumstances, in recent years, CBN and cubic close-packed boron nitride (hereinafter abbreviated as WBN), which can be obtained simultaneously with CBN using the ultra-high pressure and high temperature sintering method, have been developed using the ultra-high pressure and high temperature sintering method described above. Manufacturing methods using physical vapor deposition and/or ion irradiation have been proposed.

For example, (i) boron is evaporated onto a substrate to which a negative bias voltage is applied from an evaporation source containing boron, and
CB that generates CBN on the substrate by irradiating it with ion species containing at least nitrogen separated by a mass spectrometer.
A method for producing N has been proposed [Japanese Patent Application Laid-open No. 60-1812
See Publication No. 62]. (ii) Using the HCD (hollow cathode deposition) method, while evaporating boron with an electron beam, the N2 ion species formed in the hollow anode are irradiated onto the substrate, which has been given a self-bias effect by applying a high-frequency voltage. Manufacturing method of CBN [Proceeding]
9th Symposium on Ion Source Ion-Assisted Technology (Proceeding
9th Symposium on Ion 5ou
rcetonAssisted Technology
), ・35. Tokyo, (1985)], and (iii) a method in which the ion deposition (ID) method used to produce diamond-like thin films is applied to the production of boron nitride, that is, by irradiating a boron-containing solid with an electron beam. A method for producing CBN on a substrate surface by evaporating boron, introducing a nitrogen-containing gas, and simultaneously ionizing boron and nitrogen [Vacuum, Vol. 28, No. 7 (1)
985) and the like have been proposed.

Problems to be Solved by the Invention As mentioned above, CBN has various excellent properties that are advantageous for application to cutting tool materials, electronic materials, etc. Many manufacturing technologies have been proposed.

However, in the method (i) above, the ion has 5 to 100 Ke.
This has the problem of requiring extremely complicated and expensive equipment, such as having a high kinetic energy of V, focusing the ion beam, and having a mass separation function to select a specific N 2+. In addition, in the method (11) and the method (iii) above, since the melting point and boiling point of boron are close to each other, bumping is likely to occur on the solid surface when irradiated with an electron beam, making it difficult to control the electron beam. In the former, the inert gas used in the reactor tends to mix into the precipitated product, while in the latter, the purity of the CBN obtained is relatively low. It also had some problems.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for manufacturing CBN that does not require complicated equipment such as an ion beam or an electron gun, is simple, and has a low possibility of contamination with impurities. It is in.

Means for Solving the Problems The present inventors have conducted extensive studies and studies in order to solve the above-mentioned problems in the CBN manufacturing methods that have been proposed in the past.
As a result of the research, by combining a series of processes of preheating and plasmaization of the reactive gas and heating of the substrate, a stable SP3 hybrid bond is generated between nitrogen atoms and boron atoms, and CBN is formed on the substrate. It has been found that it can be precipitated.

That is, the present invention provides a method for producing CBN, which includes the steps of preheating a mixture of a boron-containing gas and a nitrogen-containing gas, then applying a high frequency voltage to the mixture to turn it into plasma, and depositing CBN on a heated substrate. It is something to do.

In the method of the present invention, first, a boron-containing gas and a nitrogen-containing gas are preheated. As the raw material gas of the present invention used here, that is, the boron-containing gas, for example, B2H
6, BCl3, B2H6N3, BF3, etc.,
It is of course also possible to use mixtures of these gases.

On the other hand, examples of the nitrogen-containing gas include N2, NH3, lower alkyl group-substituted ammonia, NO, and mixtures thereof. In this step, the raw gas mixture is pre-excited.

In these reaction gases, the mixing ratio of boron-containing gas and nitrogen-containing gas is such that the ratio of boron atoms to nitrogen atoms (hereinafter abbreviated as B/N) in these gas components is 0.
．． It is preferable to set it in the range of 1 to 10.

When B/N is less than 0.1, amorphous boron nitride tends to precipitate, while when it exceeds 10, boron becomes excessive and amorphous boron tends to precipitate on the substrate, so both are preferable. do not have. The total pressure and flow rate of these reactive gases, boron-containing gas and nitrogen-containing gas, are generally governed by the discharge conditions, which are the steps after preheating.

As a means for preheating these reaction gases,
It is preferable to heat the reaction gas using a thermionic emitting material, such as a tungsten filament or a thorium-containing tungsten filament. Adjustment is preferred. If this temperature is less than 1000° C., the desired CBN cannot be deposited on the substrate, and other crystal systems will precipitate, which is not preferable.

According to the method of the present invention, the next step is to apply a high frequency voltage to the raw material gas mixture that has been preheated and preexcited as described above. This turns the raw gas mixture into plasma, which undergoes further excitation, dissociation, and ionization to form various molecular and atomic species, which react with particularly chemically active free boron and nitrogen under the action of the thermal energy of the heated substrate. It forms a stable SP3 bond and is deposited as cubic boron nitride on the substrate. In this process, the high-frequency voltage application conditions are a raw material gas pressure of 0.01 to 100T.
orr, high frequency frequency I KHz ~13.56M
It is preferable to set it as Hz. In addition, in order to achieve sufficient activation, it is advantageous to set the residence time of the raw material gas in the high frequency application region to 10-2 to IS, and the raw material gas flow rate and high frequency voltage application region Adjust the width etc.

In the substrate on which CBN is deposited, which is the object of the manufacturing method of the present invention, it is preferable to heat the substrate to a temperature of 300 to 2000°C.
Crystalline boron nitride other than BN and amorphous boron nitride are precipitated. In order to heat the substrate to the above temperature, it is usually preferable to install a heating heater under the substrate. The material of the substrate is preferably one that does not melt under the above heating conditions, such as tungsten, silicon wafer, molybdenum, etc., and ceramic materials such as A1□03, S
Examples include i3N4, SiC, etc., and cemented carbide.

A specific example of the manufacturing apparatus used in the present invention is shown in FIG. This device mainly consists of a reaction gas control system that supplies a reaction gas mixture of nitrogen-containing gas and boron-containing gas to a reaction vessel and simultaneously adjusts the internal pressure of the reaction vessel, and a reaction gas control system that excites, dissociates, and reacts the reaction gas. and a CBN reaction system that deposits CBN on the substrate. In a reaction vessel 1 that can maintain airtightness, a thermionic emitting material 3 is arranged near an inlet 2 for a reaction gas inside the reaction vessel, and an outlet provided on an inner wall facing from the inlet 2 is further provided. 4
A high-frequency irradiation coil 5 is arranged near the outer periphery of the side surface of the reaction vessel.

Furthermore, a substrate 6 for depositing CBN and its support stand 7 are installed at the bottom of the inner wall of the portion of the reaction vessel 1 covered by the high-frequency coil 5.

Furthermore, the reaction vessel 1 is connected to reaction gas supply devices 9 and 10 via a reaction gas inlet 2 and an inlet pipe 8, and on the other hand, the reaction gas It is connected to the exhaust device 12. Moreover, a high frequency power source 13 for a high frequency irradiation coil and a power source 14 for a thermionic radiation material are provided outside the reaction vessel 1. In this device, heating of the substrate is adjusted to a predetermined temperature by the plasma output by placing the substrate in plasma.

On the other hand, FIG. 2 shows another example of the manufacturing apparatus used in the present invention. Basically, the configuration is the same as that shown in FIG. 1, and the various steps of the present invention can be carried out. However, the difference from the device shown in FIG. 2, and is installed parallel to the inner wall where the inlet is located, and the substrate 6 and its support stand 7 are installed on the inner wall where the outlet 4 is located, facing the thermionic emitting material. ing. In the case of this apparatus, unlike the case of FIG. 1, the substrate 6 is slightly separated from the high frequency coil 5 that generates plasma, so a heater 15 is installed under the substrate as means for heating the substrate.

C by operating the manufacturing equipment used in the present invention as described above.
In order to obtain one BN, first, the reaction chamber is equipped with an exhaust system 12,
For example, after exhausting with an oil diffusion pump or the like, the boron-containing gas and nitrogen-containing gas are evacuated using the boron-containing gas and nitrogen-containing gas supply devices 9. The containing gas is supplied, and the mixed gas is heated with the thermionic emitting material 3 so that the temperature of the mixed gas reaches a predetermined temperature. Further, a high frequency voltage is applied to generate high frequency plasma. Furthermore, the substrate 6 is heated using a heater or plasma so that a predetermined temperature is obtained.

After performing such operations, CBN is deposited on the substrate by continuing to operate the apparatus.

Working CBN has a diamond-shaped crystal structure in which nitrogen atoms and boron atoms form stable SP3 hybrid bonds within the cubic crystal.

In order to form this SP3 hybrid bond, it is necessary to excite each nitrogen atom and boron atom to an excited state in some way to create an SP3 hybrid orbital, and furthermore, by giving them an opportunity to collide with each other, the SP3 Forms molecular orbitals that become hybrid bonds. By placing the electrons of each excited atom in the molecular orbitals forming SP3 hybrid bonds, a large amount of stabilizing energy is obtained, and the system is stabilized, resulting in the excellent properties described above. We have it.

Thus, in order to produce CBN, it is important to find conditions that facilitate the formation of SP3 hybrid bonds from B and N sources. In this regard, according to the present invention, a series of energy supply processes are performed, such as heating the raw material mixed gas in advance with a thermionic emitting material to pre-excite it, applying a high frequency voltage to turn it into plasma, and heating the substrate. According to the above S
It became possible to generate P3 hybrid bonds, and CBN could be deposited on the substrate. Here, the preheating temperature is
The substrate temperature and plasma generation conditions are important in the present invention, and it is preferable to set the conditions within the ranges described above in order to obtain CBN.

According to the present invention, a high-quality CBN thin film can be obtained with relatively simple operations and inexpensive equipment, so it is economically advantageous, and is therefore useful as various tools and electronic materials as described above.

EXAMPLES Hereinafter, the present invention will be specifically explained 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 the substrate, and the boron-containing gas as the raw material gas was B2.
NH3 was used as Ha and nitrogen-containing gas, 4 cc each.
/min, and 1 Qcc/min into the reaction chamber. In addition, the temperature inside the reaction vessel was adjusted to 2000°C using a tungsten filament, and a high frequency voltage was applied so that the output of high frequency plasma was IKW.
With the above gas flowing, the pressure inside the reaction chamber was adjusted to 5'l'orr using an exhaust system, and the operation was continued in this state for 4 hours, and a boron nitride film with a thickness of about 8 μm was obtained. Ta.

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

Example 2 The manufacturing apparatus shown in FIG. 2 was used, a molybdenum substrate was used as the substrate, and the boron-containing gas as the raw material gas was BCIs,
NH3 is used as the nitrogen-containing gas, 5 cc/+n each.
in, and introduced into the reaction chamber at a flow rate of 5 cc/min.

In addition, the temperature inside the reaction vessel was adjusted to 2200°C using a tungsten filament, and the output of the high-frequency plasma was adjusted to 2. Apply a high frequency voltage so that it becomes OKW,
With the above gas flowing, the pressure inside the reaction chamber was adjusted to 8 TOrr using an exhaust device. After setting the substrate temperature to 900℃, continuous operation was continued for 4 hours in this state, and 1
A boron nitride film with a thickness of about 2 μm was obtained.

When the obtained boron nitride film was crushed and subjected to X-ray diffraction, a sharp peak peculiar to CBN was observed around 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
A boron nitride film with a thickness of about 10 μm was obtained in the same manner as in Example 1 except that the film-forming time was 5 hours.

When the obtained boron nitride film was crushed and subjected to X-ray diffraction, a sharp peak peculiar to HBN was found around 2θ=26.7° and a peak position peculiar to CBN at 2θ=43.2
A gentle peak was observed around 0.degree., and it became clear that this boron nitride film was a polycrystalline system of HBN and CBN, and moreover, HBN was contained in a larger amount.

Cutting test using boron nitride film Using the manufacturing conditions of Examples 1 to 2 and Comparative Example 1, a chip, which is a substrate, was coated with a film thickness of 3 μm, and the cutting conditions shown in Table 1, that is, the work material, cutting A cutting test was conducted under different speeds, depths of cut, and feed, and the time required to reach a relief wear width of 0.1 mm under each condition was measured. The results obtained are shown in Table 2.

In addition, similar cutting tests were conducted using TNMG432, a wc-based cemented carbide, as the tip, without coating and with TiN coating using the reactive ion blating method, and the results were reported. It is shown in Table 2.

From Table 1 and 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. A mixture of crystal systems of boron nitride other than CBN (Comparative Example 1) shows wear resistance comparable to that of the case coated with TiN.

In addition, FIG. 3 shows the C
Cutting tests were conducted on BN-coated chips, TIN-coated chips, and uncoated chips, and the results are shown as a relationship between cutting speed and chip life. Figure 4 shows that 5NG435 was used as the tip, FC30 was used as the work material, and the cutting speed was 250 m/+.
Cutting tests were conducted on the CBN-coated chips, TiC-coated chips, and uncoated chips obtained in Example 2 at the time of nin, and the relationship between the fracture resistance and the number of impacts was shown. From FIGS. 3 and 4, it can be seen that the tip coated with CBN has wear resistance about 1.5 times that of the tip coated with other materials.

As described in detail, the manufacturing method of the present invention is a gas phase reaction method that does not use the conventional ultra-high pressure and high temperature sintering method, and moreover, it does not require complicated and expensive equipment such as ion beams and electron guns. This is a simple CBN manufacturing method that does not require Furthermore, the CBN of the present invention! ! ! According to the production method, it is possible to produce excellent CBN with less contamination of impurities and other crystalline boron nitrides, and its industrial value is extremely high.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams of a manufacturing apparatus used in the present invention. FIG. 3 is a graph plotting the relationship between cutting speed and chip life for CBN-coated chips and other chips. FIG. 4 is a graph showing the fracture resistance of CBN coated tips and other tips in cutting cast iron. (Main reference numbers) 1. Reaction vessel, 2. Reaction gas inlet, 3. Thermionic emission material, 4. Reaction gas outlet, 5. High frequency coil, 6. Substrate, 7. Substrate support stand, 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 source, 14...Power source for thermionic radiation material, 15
··heater

Claims (4)

[Claims] (1) A cubic system comprising the steps of preheating a mixture of a boron-containing gas and a nitrogen-containing gas, then irradiating the mixture with high frequency to turn it into plasma, and depositing a cubic boron nitride film on the heated substrate. A method for manufacturing a crystalline boron nitride film. (2) The method for manufacturing a cubic boron nitride film according to claim 1, wherein the preheating is performed using a thermionic emitting material heated to 1000° C. or higher. (3) The method for manufacturing a cubic boron nitride film according to claim 1, wherein the temperature of the heated substrate is 300 to 2000°C. (4) Production of the cubic boron nitride film according to claim 1, wherein in the mixture of the boron-containing gas and the nitrogen-containing gas, the ratio B/N of boron atoms to nitrogen atoms is 0.1 to 10. Method.