JP2569423B2 - Gas phase synthesis of boron nitride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a boron nitride film by a vapor phase synthesis method.

[0002]

2. Description of the Related Art When boron nitride is used as a sintered body from a powder, its density is at most 1.8 to 1.9 g / cm ³ , and the density of boron nitride is high. As boron, pyrolytic boron nitride (pBN) is known, and its density is about 1.99 to 2.15. Due to its high heat resistance, high temperature strength, low reactivity, etc., pBN is made of silicon or III-V.
It is used for crucibles for the production of group III semiconductor crystals.

As a method for producing this pBN, conventionally, 5 pBN is used.
At a low pressure of 0 Torr or less and a high temperature of 1800 ° C. or more, boron chloride (BCl ₃ ) and ammonia gas (NH ₃ ) (NH ₃ / BCl)
₃ > 1) is thermally decomposed and deposited on a graphite material. The reason for using this low pressure is that only a powdery or bulky precipitate can be obtained at a high gas pressure.

[0004] However, at a pressure of 1 atm of dense boron nitride,
In addition, if the synthesis can be performed at a lower temperature, the manufacturing apparatus and the manufacturing process can be simplified, and deposition can be performed on various substrates.

[0005] It is an object of the present invention to provide a method capable of synthesizing dense boron nitride under one atmosphere or at a low temperature under such circumstances.

[0006]

Means for Solving the Problems The present inventors have studied various synthetic methods to solve the above-mentioned problems, and as a result,
By using plasma, using boron trifluoride as a raw material, and performing the reaction such that the gas phase composition in the raw material gas becomes H / F <1, dense boron nitride can be obtained at a lower temperature than before. It has been found that the present invention has been completed.

That is, the present invention uses thermal plasma or non-equilibrium plasma and uses boron trifluoride as a boron source.
In a gas phase synthesis method using a nitrogen-containing compound as a raw material as a nitrogen source, the gist of the present invention is a method for synthesizing boron nitride, wherein the H / F ratio in the raw material gas is set to 1 or less.

[0008]

The present invention will be described below in detail.

The dense boron nitride referred to in the present invention has a density of 1.95 g / cm ³ or more, and is synthesized by gas-phase synthesis using thermal (equilibrium) plasma or non-equilibrium plasma. The most characteristic of the reaction is that boron trifluoride is used and the gas phase composition is H / F <1.

As a raw material, boron trifluoride is used as a boron source, and a compound containing nitrogen (nitrogen-containing compound) such as ammonia, nitrogen gas, nitrogen trifluoride, hydrazine or hydrazine tetrafluoride is used as a nitrogen source. One or several types may be used simultaneously. In addition, one of rare gases such as argon and helium or hydrogen as a diluent gas or a reactive gas is used.
Species or a mixed gas thereof may be added, but it is necessary to make the overall source gas composition satisfy H / F <1.

[0011] In this gas phase synthesis method, fluorine seems to play an important role, but its detailed action is not clear. The reason for the need for H / F <1 is also unknown, but one possibility is that the synthesis of dense boron nitride requires certain fluorine and boron containing species, increasing the amount of hydrogen. Then, it is considered that fluorine becomes HF in the gas phase, and the number of chemical species decreases.

The plasma used in the present invention may be either non-equilibrium plasma or equilibrium (thermal) plasma, and the power source for generating plasma may be any of direct current, low frequency alternating current, high frequency and microwave. The method of coupling to the reactor may be any of capacitive coupling, inductive coupling, and coupling using an antenna.

The reaction can be carried out at a pressure of 10 ^-4 to 10 ² atm. However, the reaction pressure is preferably 10 ^-3 to 10 atm in terms of deposition rate and handling of the apparatus.

The substrate on which boron nitride is deposited in the present invention can be any of a semiconductor such as silicon, an insulator such as quartz, and a metal such as tungsten carbide and molybdenum, and is not particularly limited.

The reaction temperature is not limited with respect to the temperature of the gas phase, but the temperature of the substrate on which boron nitride is deposited can be from 200 ° C. The temperature is preferably 400 ° C. or more from the viewpoint of the density and stability of the product, and the upper limit can be up to 2000 ° C.

Next, an example of a procedure for synthesizing boron nitride according to the present invention will be described with reference to examples. Embodiment 1 is an example using high-frequency thermal plasma, and Embodiment 2 is an example using microwave low-pressure plasma. However, as described above, plasma using DC discharge or low-frequency AC discharge may be used. However, it can be used.

[0017]

Embodiment 1 In the high-frequency plasma apparatus shown in FIG.
Place the silicon substrate 3 on the substrate holder 3 'and
After exhausting to Torr, Ar (15 L / min) is passed from the gas supply 6 through the valve 7 ″, Ar (0.4 L / min) is passed through the valve 7 ′, and Ar + BF ₃ + N ₂ is passed through the valve 7. (1 liter / min + 0.01 liter / min + 1 liter / min)
The plate power of 4 MHZ and 15 kW was supplied to the work coil 12 to generate plasma.

By discharging for 20 minutes at 1 atm, boron nitride having a thickness of about 20 μm was obtained on the substrate. X-ray diffraction, infrared absorption spectrum, and photoelectron spectroscopy (XPS) spectrum confirmed that boron nitride was formed,
Its density was 2.1 g / cm ³ . The H / F ratio in the source gas during the reaction is 0 in this embodiment. The substrate temperature was 450 ° C.

[0019]

Embodiment 2 In the microwave plasma apparatus shown in FIG.
After evacuation to 02 Torr, H ₂ + BF ₃ + N ₂ (0.5 ml / min + 1 ml / min + 100 ml / min) was passed from the gas supply 6 through the valve 7, and 2.45 GHz from the microwave oscillator 21. A power of 5 kW was supplied to generate plasma in the reaction tube. By discharging for 3 hours under 30 Torr, a film was obtained on the substrate. As in the case of Example 1, X-ray diffraction and infrared absorption spectrum confirmed that the substance was boron nitride, and its density was 2.0 g.
/ Cm ³ . The H / F ratio in the source gas at the time of the reaction was 1/3. The substrate temperature was 590 ° C.

[0020]

As described above, according to the present invention,
It is possible to synthesize dense boron nitride at a lower temperature than before and under a high gas pressure of 1 atm.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an apparatus for synthesizing boron nitride, in which high-frequency thermal plasma is used.

FIG. 2 is a diagram showing another example of an apparatus for synthesizing boron nitride, in which microwave plasma is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction tube 3 Substrate 3 'Substrate holder 4 Column 5 Exhaust device 6 Gas supply device 7 Valve 7' Valve 7 "Valve 11 High frequency power supply 12 Work coil 21 Microwave power supply 22 Waveguide and microwave discharge applicator

Claims (2)

(57) [Claims] In a gas phase synthesis method using thermal plasma or non-equilibrium plasma and using boron trifluoride as a boron source and a nitrogen-containing compound as a nitrogen source, the ratio of H / F in the source gas is 1 or less. A method for synthesizing boron nitride. 2. The method according to claim 1, wherein the substrate temperature is 200 ° C. or higher.
The method described in.