JPH049472A - Method for synthesizing cubic boron nitride - Google Patents

Abstract

PURPOSE:To form cubic BN having a regular composition on a substrate in good yield at the time of forming the BN from a gas contg. B atom and a gas contg. N atom by CVD method by exciting the gas contg. B atom with UV and the gas contg. N atom with plasma. CONSTITUTION:Gaseous N2 1 is supplied from the top of a vertical reaction tube 20 in which an Si wafer substrate 3 is arranged, passed through electrodeless discharge plasma produced in a microwave cavity 5 by a microwave oscillator 7 and further through a strong magnetic field generated by a coil 5 below the cavity, excited and supplied on the substrate 3. Meanwhile, gaseous BCl3 2 is generated by an excimer laser 8, excited by excimer laser light from a quartz window 9 and then supplied on the substrate 3 in the tube 20. Extremely hard cubic BN (c-BN) is deposited on the substrate 3 as a thin film.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for synthesizing cubic boron nitride (c-BN), and in particular to a method for synthesizing cubic boron nitride (c-BN), in particular, using a boron atom-containing gas and a nitride atom-containing gas as raw material gases. , c-BN by vapor phase chemical vapor deposition (CVD) method
Concerning how to synthesize.

[Prior Art] Conventionally, as a method for synthesizing c-BN using a boron atom-containing gas and a nitride atom-containing gas, there is a method disclosed in JP-A-63-134662.
As disclosed in the publication, excimer laser-CV
A synthesis method using a combination of D method and plasma CVD method has been known.

That is, as shown in FIG. 4 or FIG. 5, a boron atom-containing gas supply device 41 and a nitrogen atom-containing gas supply device 42
A mixed gas of a boron atom-containing gas and a nitrogen atom-containing gas supplied into the chamber 44 is first decomposed by an excimer laser 46 to bring it into an excited state, and then passed through a high-frequency plasma generated by a high-frequency coil 50. ,3
It was introduced onto the surface of a substrate 47 heated to 00 to 2000° C. to precipitate cubic boron nitride. In this case, the ratio B/N between the number of boron atoms in the boron atom-containing gas and the number of nitride atoms in the nitride atom-containing gas is in the range of B/N = 0.1 to 10, and the raw material gas contains boron Only atom-containing gas and nitride atom-containing gas were used, and no mixture of gases such as hydrogen was used.

In addition, in FIGS. 4 and 5, excimer laser 4
6 is generated by an excimer laser generator 43 and passes through an excimer laser guide 45 to the chamber 4.
4, and the high frequency was supplied to the high frequency coil 50 from the high frequency power supply 51. Heater 49 is used to heat the substrate.
(in the case of Figure 4) or high frequency plasma (in the case of Figure 5)
It was carried out by The gas after the reaction is supplied to the cock 52,
The air was exhausted through an exhaust device 53 and an exhaust port 54.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, a mixed gas of a boron atom-containing gas and a nitride atom-containing gas is introduced into a chamber at once, and these mixed gases are excited by light and plasma. Was. In such a method, the energy required for dissociation and ionization is large between the boron atom-containing gas and the nitride atom-containing gas (if they are different, dissociation and ionization will not occur even if a certain power output is input to the plasma or light). The reactive gas that is more easily excited is excited, and its active species concentration becomes higher than the other.As a result, the composition of the synthesized boron nitride film, that is, the B/N ratio, also deviates from 1 and becomes uneven. It had the disadvantage of being stored away.

In this case, the B/N ratio was controlled by controlling the flow rate ratio of the boron atom-containing gas and the nitrogen atom-containing gas, but it is not possible to obtain a boron nitride film with an accurate film composition by controlling the flow rate ratio alone. That was difficult.

In addition, conventionally, not only nitrogen atom-containing gases but also
Since the boron atom-containing gas was also introduced into the plasma at the same time, both radical and ion active species were generated for both gases. The presence of nitride-based ionic active species such as N2 is important because it removes boron nitride (h-BN) and selectively grows cBN, but boron-based ionic active species exist. Then, side reactions proceed, so
Generation of c-BN was inhibited, and as a result, the film formation rate became low.

The present invention was made in view of such conventional problems, and an object of the present invention is to provide a c-BH synthesis method that can efficiently generate c-BN having a desired composition ratio.

[Means for solving the problem] In order to achieve the above object, the invention according to claim 1 provides c.
In synthesizing -BN, a boron atom-containing gas excited by ultraviolet light and a nitride atom-containing gas excited by at least plasma are introduced onto the substrate surface to precipitate boron nitride on the substrate surface.

Further, the invention according to claim 2 provides that, in synthesizing c-BN, a boron atom-containing gas excited by ultraviolet light;
At least a nitrogen atom-containing gas excited by plasma after being mixed in advance with hydrogen gas or an inert gas is introduced onto the substrate surface to deposit boron nitride on the substrate surface.

[Function] In the c-BN synthesis method of the present invention having the above configuration, the boron atom-containing gas is excited in advance by ultraviolet light and introduced into the chamber as active species mainly consisting of radicals. On the other hand, since the nitrogen atom-containing gas is excited in advance by at least plasma, it is introduced into the chamber mainly as active species of radicals and ions. On the other hand, since the nitrogen atom-containing gas is excited in advance by at least plasma, it is introduced into the chamber mainly as active species of radicals and ions. The two gaseous active species described above are mixed in the chamber, and an active reaction occurs on or near the substrate surface, and highly crystalline c-BN is deposited on the substrate surface.

The c-BN structure is produced by a competitive process of deposition and etching. The main process in the film formation reaction is a radical reaction, as in the normal CVD process, so in order to perform film formation efficiently, active species of radicals must be generated for both the boron atom-containing gas and the nitrogen atom-containing gas. It is necessary to On the other hand, the etching reaction is performed using N2
The main process is an etching reaction by nitrogen-based ionic active species such as No. 4. Since a relatively long-lived metastable state exists in the excited state of nitrogen, the ionization efficiency can be increased by nitrogen-based ions. This is because ionization occurs when molecules in an excited state collide with molecules in a ground state, and the longer the lifetime of molecules in an excited state, the more likely they are to collide, and the more efficiently ionization proceeds. .

Due to the presence of nitrogen-based ionic active species such as N and +, hexagonal boron nitride (h-BN) is selectively etched away from the deposited boron nitride (BN), and c-
Since BN is grown selectively, nitrogen-based ionic active species play an important role in the generation of the c-BN structure. On the other hand, when boron-based ionic active species exist in the reaction system, side reactions proceed and the production of c-BN is inhibited. Therefore, in order to efficiently generate c-BN, both radical and ionic active species must exist in nitrogen atom-containing gases, and only radically active species must exist in boron atom-containing gases, while ionic active species must exist in boron atom-containing gases. It is preferable that there is no.

In the present invention, since the boron atom-containing gas is excited by ultraviolet light, radical active species are generated, and the nitrogen atom-containing gas is excited by plasma, so not only radical active species but also nitrogen-based ionic active species are generated. also occurs. Therefore, according to the present invention, c-BN can be efficiently generated.

As described above, the present invention provides c-
This is a method of selectively producing effective active species involved in the production of BN and advantageously promoting the production of c-BN.

Further, according to the present invention, even when the energy required for dissociation and ionization is significantly different between a boron atom-containing gas and a nitrogen atom-containing gas, c-
BN can be easily obtained. That is, in the present invention, since the boron atom-containing gas and the nitrogen atom-containing gas are excited using different excitation methods, the amount of produced excited species of each gas can be adjusted by adjusting the power of each power source or light source. can be controlled individually. Therefore, by combining the conventional method of controlling the amount of excited species generated by controlling the flow rate ratio of each raw material gas using a mass flow controller, it is now possible to precisely set the optimal conditions for film formation. It becomes possible to produce c-BN having a composition of (BZN ratio).

Furthermore, in the c-BN synthesis method according to claim 2,
Since the nitrogen atom-containing gas mixed with hydrogen gas or inert gas is excited by the plasma, active species can be generated more efficiently than when only the nitrogen atom-containing gas is excited by the plasma. ,c-
BN can be generated more efficiently.

As for the boron atom-containing gas, it is preferable that only radical active species exist and no ionic active species exist, so it is preferable that the boron atom-containing gas does not pass through the plasma after being excited by ultraviolet light. On the other hand, for nitrogen atom-containing gas, it is sufficient to generate both radical active species and ionic active species, so it may be excited by plasma alone, or it may be excited by plasma and then further excited by ultraviolet light. . That is, a boron atom-containing gas and a nitride atom-containing gas may be excited separately in advance by ultraviolet light and plasma, and then the excited gases may be mixed.
First, a nitrogen atom-containing gas is excited with plasma, and then
The nitrogen atom-containing gas excited by the plasma and the boron atom-containing gas before excitation may be mixed in advance, and this mixed gas may be excited with ultraviolet light.

Further, by installing a magnetic field downstream of the region where plasma is generated, ions to be generated by the plasma are accelerated by the magnetic field and collide with the substrate.

The ultraviolet light source is preferably an excimer laser or a deuterium lamp, and the plasma is preferably generated by microwave electrodeless discharge. The substrate on which c-BN is being grown is preferably heated to 300 to 1300° C., and a rare gas such as He is preferably used as the inert gas mixed with the nitrogen atom-containing gas in advance.

[Example 1 (First Example) A c-BN film was formed using a vertical vapor phase apparatus shown in FIG. N2 and BC (23) were used as raw material gases, and a Si wafer was used as the substrate 3.N2 gas 1 was supplied from the top of the vertical reaction tube 20, and was introduced into the microwave cavity 5 by a 2450MH1 microwave oscillator 7. 875 Gau passed through the generated electrodeless discharge plasma and was further generated by the coil 6 installed below.
After passing through the sS magnetic field, it was supplied onto the substrate 3 placed on the susceptor 4. On the other hand, B(13 gas 2 is generated from excimer laser 8 and excited by excimer laser light irradiated through quartz window 9,
0 and supplied onto the substrate 3.

The flow rate of N2 gas 1 is 50cc/rr+in, and BC
ff, the flow rate of gas 2 was lcc/min. The inside of the reaction system is kept at a reduced pressure by the exhaust system 10, and the pressure during film formation is 2.
It was Torr. Further, the temperature of the substrate 3 was 800°C.

When the reaction was carried out under these conditions for 2 hours, a 2 μm thick boron nitride film was formed on the surface of the substrate 3. When this film was examined by Fourier transform infrared spectroscopy (FT-IR), it was found that 1051
Remarkable absorption was observed at 05O', and formation of a c-BN film was confirmed.

(Second Example) Using a horizontal vapor phase growth apparatus shown in FIG. 2, c-BN was formed. N2 and B (12 m) were used as source gases, and a Si wafer was used as the substrate 3. N2 gas 1
was mixed with He gas 11 in advance, passed through the electrodeless discharge plasma generated in the microwave cavity 5 by the 2450 MH2 microwave oscillator 7, and was supplied into the horizontal reaction tube 21. At this time, the flow rate of N2 gas 1 is 10
cc/min, and the flow rate of He gas 11 is 50
It was cc/min. On the other hand, the BC9a gas 2 was supplied into the reaction tube 21 after being irradiated with light from the deuterium lamp 12 . B (123 The flow rate of gas 2 is 0.5 cc/m
It was in. The pressure inside the reaction system is reduced to 1.0 by the exhaust system 10.
The temperature of the substrate 3 was maintained at 5 Torr and 800°C.

When the reaction was carried out under these conditions for 1 hour, boron nitride with a thickness of 1 μm was deposited on the surface of the substrate 3. This film was subjected to FT-IR
When examined, significant absorption was observed at 105105O', confirming the formation of a c-BN film.

(Third Example) A C-BN film was formed using a vertical vapor phase growth apparatus shown in FIG. In the first example described above, the boron atom-containing gas was excited in advance by an excimer laser and then introduced into the reaction tube, but in this example, the boron atom-containing gas was first excited in the reaction tube without being excited in advance. After mixing with nitrogen atom-containing gas excited by plasma, this mixed gas was excited by an excimer laser.

That is, N2 and BCε3 were used as source gases, and a Si wafer was used as the substrate 3. N2 gas 1 is supplied from the upper part of the vertical reaction tube 20, passes through the electrodeless discharge plasma generated in the microwave cavity 5 by the 2450 MH microwave oscillator 7, and then passes through the coil 6 installed below. After passing through a magnetic field of 875 Gauss generated by B(13), it was mixed with gas 2. This mixed gas was then excited by an excimer laser 8 and then supplied onto the substrate 3.

The flow rate of N2 gas 1 was 30 cc/min, and the flow rate of BCl23 gas 2 was lcc/min. The pressure inside the reaction system was maintained at 1.5 Torr by the exhaust system 10, and the temperature of the substrate 3 was 750°C.

When the reaction was carried out under these conditions for 2 hours, boron nitride with a thickness of 2 um was deposited on the surface of the substrate 3. When this film was examined by FT-IR, it showed remarkable absorption at 105105O'.
Formation of a c-BN film was confirmed.

Note that the same effect can be obtained by using B2H gas instead of BCρ3 gas 2.

[Effects of the Invention] As described above, according to the method for synthesizing c-BN according to the first aspect, c-BN having a desired composition ratio can be efficiently produced by vapor phase growth.

Furthermore, according to the c-BN synthesis method described in claim 2, c-BN can be produced even more efficiently by vapor phase growth.

Therefore, with the present invention, c
-It becomes possible to artificially synthesize thin films of BN using inexpensive equipment and materials. C-BN has hardness and thermal conductivity second only to diamond, and is extremely chemically stable even with iron group alloys, so it can be used to improve the durability of cutting tools, molds, etc., or to improve the durability of semiconductor devices. , and can be used in a wide range of applications such as light emitting devices.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the device used in the first embodiment of the present invention, FIG. 2 is a schematic diagram of the device used in the second embodiment of the present invention, and FIG. 3 is a schematic diagram of the device used in the second embodiment of the present invention. A schematic diagram of the apparatus used in the example, and FIGS. 4 and 5 are schematic diagrams of the apparatus used in the conventional method, respectively. 1...N2 gas 2...BCβ3 gas 3...Substrate 5...Microwave cavity 8...Excimer laser

Claims (2)

[Claims] (1) A boron atom-containing gas excited by ultraviolet light,
1. A method for synthesizing cubic boron nitride, which comprises introducing at least a nitride atom-containing gas excited by plasma onto a substrate surface to precipitate boron nitride on the substrate surface. (2) a boron atom-containing gas excited by ultraviolet light;
Synthesis of cubic boron nitride, characterized in that boron nitride is deposited on the substrate surface by introducing at least a nitrogen atom-containing gas excited by plasma after being mixed with hydrogen gas or an inert gas into the substrate surface. Law.