JP4827061B2 - Method for producing cubic boron nitride - Google Patents

Description

  The present invention relates to a method for producing cubic boron nitride by depositing boron nitride on a substrate in a reaction vessel of a plasma apparatus.

  Trigonal boron nitride (c-BN) is a substance with properties very similar to diamond but does not exist in nature. In addition to the excellent electrical, optical and mechanical properties equivalent to diamond, compared to diamond, it has low reactivity to iron-based metals (Fe, Co, Ni, Cr), oxidation resistance at high temperatures, and greater bandwidth. Both pn-type semiconductors have the advantage of being easy to manufacture. From these characteristics, c-BN is a substance that can be a useful functional material such as tools, wear-resistant materials, optical materials, semiconductor materials, and short wavelength optoelectronic materials. The crystal grains have already been industrially synthesized under a high pressure of tens of thousands of atmospheres using an ultra-high pressure apparatus, but it is difficult to control the shape by the high pressure method, in particular, it is very difficult to make a film, For application as a functional material, a low-pressure synthesis method is required.

  For this reason, attempts have been made since the 1970s to synthesize from the gas phase at a pressure of 1 atm or less (Non-Patent Documents 1 and 2). These methods are classified into two types. One is an activated reactive vapor deposition method, bias in which boron is deposited on a substrate by electron beam heating vapor deposition or sputtering in a low pressure reaction vessel of 10 Pa or less, and simultaneously using ion bombardment of nitrogen ions and other ions. Physical vapor deposition (PVD) such as sputtering and ion beam vapor deposition.

The other type is chemical vapor deposition (CVD), which uses a reaction between gas phase species or between a gas phase species and a substrate in a vessel of a plasma apparatus, and usually uses gaseous molecular species as a raw material. As the boron source, diborane, boron trichloride and the like are used. As the nitrogen source, ammonia, nitrogen and the like are used. As the boron source containing both boron and nitrogen, aminoborane, borazine and the like are used. This CVD method is also a method for obtaining c-BN by colliding ions on a negatively biased substrate with the reaction chamber pressure being as low as 10 ⁻¹ to 10 Pa and making the gas phase in a plasma state.

  These conventional c-BN films are produced by any method (physical vapor phase synthesis (PVD), chemical vapor phase synthesis (CVD)) in which negative bias is applied to the substrate in the discharge plasma. It is formed by applying a strong ion bombardment of about 50 to 1000 eV to the substrate surface by voltage application or ion beam irradiation.

In 1999, one of the present inventors introduced boron or a gas species containing fluorine into the gas phase in the CVD method, thereby providing boron nitride with much better crystallinity and less residual stress than conventional methods. Has been developed (Patent Document 1, Non-Patent Document 3). In this method, a wide pressure range of 10 ⁻¹ Pa to 10 ⁷ Pa can be used for the reaction chamber pressure, but also in this method, in order to produce cubic boron nitride, a negative bias of 75 V to 450 V is applied to the substrate. It was necessary to use it. Furthermore, although there is a report that c-BN was produced using ECR plasma containing fluorine (Non-patent Document 4), ion bombardment of 45 to 80 V is also used in this case.
JP 2001-302218 (Japanese Patent Application No. 2000-348883) JP-A-4-228572 P. B. Mirkarimi et al, Mater. Sci. Eng. R21 (1997) 45: Review about cBN T. Yoshida, Diamond Relat. Mater. 5 (1996) 501: Review of cBN preparation methods S. Matsumoto and W.M. J. et al. Zhang, Jpn. J. et al. Appl. Phys. 39 (2000) L442: First paper to make c-BN using fluorine, using a bias of -70 to -85V C. Y. Chan, W.H. J. et al. Zhang et al, Diamond Relat. Mater. 12 (2003) 1162: ion bombardment of −45 to −80 V in consideration of plasma potential in ECR plasma K. Teii, R.A. Yamao, T .; Yamamura, S .; Matsumoto, J. et al. Appl. Phys. 101 (2007) 033031: part of the method of the present invention

In the above conventional method, due to the influence of momentum conversion due to ion bombardment, the obtained c-BN film has problems such as poor adhesion to the substrate, poor crystallinity, and small crystal size. Therefore, it was difficult to apply to hard coating and optoelectronic devices.
An object of the present invention is to provide a method for producing cubic boron nitride that can solve such problems.

In order to solve the above problems, the present invention employs the following configuration.

In the method for producing cubic boron nitride according to the first aspect of the present invention, the gas phase containing fluorine or a fluorine-containing gas species is activated by plasma, and the time of the substrate with respect to the conductive reaction vessel wall or the reference electrode installed in the reaction vessel is reduced. more an average potential to the potential or positively biased, and wherein the depositing the boron nitride containing the standing-cubic boron nitride. This reference electrode but it may also be grounded to the earth potential.

Invention 2 is characterized in that, in the method for producing cubic boron nitride of Invention 1, a direct current voltage or direct current + high frequency is used as a voltage applied to the substrate.

Invention 3 is characterized in that, in the method for producing cubic boron nitride of Invention 1 or 2, the time average potential of the substrate is set to the same potential as the plasma potential or a positive potential.

  In the present invention, the above-described problems can be solved by utilizing a c-BN film preparation method (the present invention) in an environment where extremely weak ion bombardment or no ion bombardment is used. That is, in the present invention, a source gas containing fluorine and high-density plasma are used, and a zero or positive bias voltage is applied to the substrate with respect to the potential of the reference electrode, or the substrate is made to have a float potential of 45 eV. The c-BN film can be produced with the following ion bombardment energy lower than that of the prior art, and also with a very low ion bombardment energy of about 0 to 3 eV.

The impact energy of ions incident on the substrate depends on the plasma potential (usually positive with respect to the reference electrode potential) -substrate bias potential. from the case of applying a positive bias 0, the ion bombardment energy is closer rather to 0 decreases from a positive value by the plasma potential. Even under the conditions of these can create a c-BN according to the method of the present invention using a gas phase species containing fluorine (invention 1).

  Even if the substrate is positively biased, the plasma potential generally rises. Therefore, the potential of the substrate is negative with respect to the plasma potential, but it can be zero or positive, and ion bombardment energy can be further reduced. . This can be achieved by reducing the surface area of the substrate relative to the area of the reference electrode, using a substrate having a large secondary electron emission ability, or selecting conditions that facilitate positive ion accumulation on the substrate surface. The area ratio varies depending on the plasma conditions such as the bias current value, but is achieved by selecting, for example, 1/7 or less, preferably 1/100 or less. Also in these cases, c-BN can be prepared by the method of the present invention using a vapor phase species containing fluorine (Invention 3).

The present invention is epoch-making in that the substrate negative bias application or ion beam irradiation, which is an essential condition in the conventional c-BN low-pressure synthesis method, is unnecessary, and the ion bombardment is extremely reduced. Since the c-BN film can be formed under conditions where ion bombardment on the substrate is very small, the generation of crystal defects, the generation of secondary nuclei, the reduction of residual stress, The adhesion, crystallinity, crystal size, etc. can be improved.
The adverse effect of ion bombardment, which has been an obstacle to the creation and application of c-BN films, is eliminated, and it is thought that this will greatly contribute to the development of research on c-BN films and the possibility of practical application.

(Plasma type)
In the synthesis method of the present invention, the plasma to be used may be either nonequilibrium plasma or equilibrium (thermal) plasma, and the power source for plasma generation may be any of direct current, low frequency alternating current, high frequency, and microwave. The coupling method to the reactor may be any of capacitive coupling, inductive coupling, antenna coupling, resonator coupling, surface wave excitation, and the like. However, high-density plasma with a plasma density of 10 ¹⁰ cm ⁻³ or more is desirable, and high-density plasma with a plasma density of 10 ¹² cm ⁻³ or more is more desirable.

(material)
In the synthesis method of the present invention, boron as a raw material may be brought into the gas phase from a gas species containing boron or from a solid containing boron by evaporation, sputtering, or gas etching. As the gas species containing boron, one or several of boron hydrides such as diborane and decaborane, and boron halides such as boron trichloride and boron trifluoride are used at the same time. As the solid containing boron, solid boron, B ₄ C, boron nitride sintered body, borohydride compound such as sodium borohydride, borofluoride such as ammonium borofluoride, organic boron compound such as triethoxyboron, etc. are used. It is done.

  As the nitrogen source, one or several kinds of nitrogen-containing compounds such as nitrogen gas, ammonia, hydrazine and other nitrogen hydrides, nitrogen fluoride such as nitrogen trifluoride, and the like are used simultaneously. Instead of supplying nitrogen and boron as separate chemical species, a single chemical species such as amine borane, borazine, aminoborane, and dimethylaminoborane can also be supplied.

  A reaction between the boron source gas and the nitrogen source gas is performed to precipitate boron nitride, which is selected so that fluorine is always included. When fluorine is not contained in the source gas or solid source, in addition to the above compound, fluorine gas, hydrogen fluoride, halogen fluoride, rare gas fluoride or the like is added, or organic fluorine such as tetrafluoromethane The compound, sulfur fluoride, silicon fluoride, fluorine fluoride, or fluorine compound such as tungsten fluoride or fluorine obtained by decomposition of metal fluoride can be added.

  Furthermore, an inert gas such as argon or helium, or hydrogen gas can be added as appropriate for the purpose of controlling plasma or controlling the action of fluorine gas. The optimum flow rates of these raw materials and additive gases vary greatly depending on the type of plasma, the plasma generation method, the size of the synthesis apparatus, the synthesis pressure, etc., and the range is quite wide.

(Reaction pressure)
In the synthesis method of the present invention, a gas phase pressure of 10 ⁻⁶ to 10 ² atm is used, and 10 ⁻⁵ to 1 atm is desirable in terms of reaction rate and handling.

(Substrate, substrate, substrate)
In the synthesis method of the present invention, the substrate on which boron nitride is deposited can be any of a semiconductor such as silicon, an insulator such as quartz, a semimetal such as tungsten carbide, a metal such as molybdenum, or an alloy, and is not particularly limited. Absent.

(Substrate temperature)
In the synthesis method of the present invention, since activation by plasma is used, a substrate temperature in a wide range from room temperature to 1400 ° C. can be used. However, for the synthesis of c-BN having particularly good crystallinity, the substrate temperature is 500. A substrate temperature of ˜1300 ° C. is desirable.

In the high frequency induction plasma apparatus using a high frequency of 13.56 MHz shown in FIG. 1, the silicon substrate 1 is placed on the substrate holder 2, the reaction chamber 3 is exhausted to 10 ⁻⁴ Pa by the exhaust pump 5, and then from the gas supplier 7. He 20 sccm, N ₂ 1 sccm, and H ₂ 5 sccm are passed through the valve 8, and a high frequency of 1.5 kW from the high frequency power supply 9 is supplied to the work coil 10 to generate plasma. 10% BF ₃ / He 30 sccm is flowed through the valve 8 ′, a DC bias of +30 V is applied to the substrate 1 through the substrate holder 2 by the DC bias power supply 11, and synthesis is performed at a substrate temperature of 1000 ° C. for 30 minutes under 20 Pa. A boron nitride film was obtained on the substrate 1.
FIG. 2 shows an X-ray diffraction pattern of boron nitride obtained by this method. In FIG. 2, 111, 200, 220, and 311 reflections of c-BN appear. Further, although 001 reflection of hexagonal boron nitride 002 and disordered structure boron nitride is also observed, reflection of hexagonal boron nitride 100, 101, 004, etc. is not strong.
The infrared absorption spectrum is shown in FIG. From FIG. 3, the absorption of the residual line of c-BN appears strongly in the vicinity of 1100 cm ^−1, and hexagonal boron nitride and turbostratic boron nitride in the vicinity of 1360 to 1400 cm ⁻¹ and 800 cm ⁻¹ Absorption by crystalline boron nitride (represented by sp ² -BN in all three) appears, but is not as strong as that of c-BN. From these, it can be seen that the obtained boron nitride film is a dominant boron nitride film of c-BN.

In the apparatus shown in FIG. 1, He 80 sccm, N ₂ 10 sccm, and H ₂ 9 sccm are flowed, and a high frequency of 1 kW from the high frequency power supply 9 is supplied to the work coil 10 to generate plasma. Boron nitride is formed on silicon substrate 1 by synthesizing 30% under 20 Pa at a substrate temperature of 700 ° C. by flowing 10% BF ₃ / He16 sccm through valve 8 ′, setting the reaction vessel, the reference electrode, and the substrate to ground potential. A membrane was obtained.
FIG. 4 is an infrared absorption spectrum of this film. FIG. 4 shows that boron nitride containing c-BN is generated.

In the apparatus shown in FIG. 1, He 80 sccm, N ₂ 10 sccm, and H ₂ 10 sccm are flowed, and a high frequency of 1 kW from the high frequency power supply 9 is supplied to the work coil 10 to generate plasma. 10% BF ₃ / He18 sccm is allowed to flow through the valve 8 ′, a DC bias of +100 V is applied to the substrate 1 through the substrate holder 2 by the DC bias power supply 11, and silicon is synthesized by synthesis for 20 minutes under 40 Pa at a substrate temperature of 1000 ° C. A boron nitride film was obtained on the substrate 1.
FIG. 5 is an infrared absorption spectrum of this film. FIG. 5 shows that boron nitride containing c-BN is generated.
When the plasma potential of the plasma under the same conditions as this creation condition was measured with an emissive probe, +100 V was the same as the substrate applied voltage, and the substrate incident ion energy was estimated to be approximately 0 eV.

  Since c-BN can be produced in a state with little ion bombardment, a cutting tool or the like using low reactivity with an iron group metal due to a decrease in residual stress and an improvement in adhesion to the substrate. The potential for application to heat-resistant and wear-resistant coatings has increased. Since most of the ferrous materials are used in the field of machining, high-precision machining and labor saving can be achieved over a wide area. In addition, it can be applied to a wide range of coatings on molds and the like utilizing the wear resistance, low friction, heat resistance, oxidation resistance, chemical resistance, and low wettability to other substances of c-BN. Further, by improving the crystallinity, the high-bandwidth, high carrier mobility, high thermal conductivity, and heat resistance of c-BN are utilized, high-temperature, high-frequency, high-power semiconductors, short-wavelength photoelectric devices, optical materials, field electron emission. A wide range of applications are expected, and it contributes to the improvement of the convenience of life and energy saving through the solidification of electronic and optical devices.

FIG. 1 is a schematic side view of an apparatus using high-frequency induction plasma in the method for synthesizing a film containing c-BN of the present invention. FIG. 2 is an X-ray diffraction diagram by CuKα rays of the boron nitride film obtained in Example 1 of the present invention. FIG. 3 is an infrared absorption spectrum diagram of the boron nitride film obtained in Example 1 of the present invention. FIG. 4 is an infrared absorption spectrum diagram of the boron nitride film obtained in Example 2 of the present invention. FIG. 5 is an infrared absorption spectrum diagram of the boron nitride film obtained in Example 3 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Substrate holder 3 Reaction chamber 4 Reactor 5 Vacuum pump 6 Viewing window 7 Gas supply 8, 8 'valve 9 High frequency power supply 10 Work coil 11 Bias power supply 12 Reference electrode

Claims (3)

A method of producing cubic boron nitride by depositing boron nitride on a substrate in a reaction vessel of a plasma apparatus, wherein a gas phase containing fluorine or a gas species containing fluorine is activated by plasma, and the reaction vessel wall Alternatively to the reference electrode was placed in a reaction vessel, cubic boron nitride, characterized in that more to the time average the same potential or positive biasing of the potential of the substrate, depositing a boron nitride containing standing-cubic boron nitride Manufacturing method.   The method for producing cubic boron nitride according to claim 1, wherein a direct current voltage or a direct current + high frequency is used as a voltage applied to the substrate.   3. The method for producing cubic boron nitride according to claim 1, wherein the time average potential of the substrate is set to the same potential as the plasma potential or a positive potential.