JP6944699B2 - Method for manufacturing hexagonal boron nitride film - Google Patents

Description

The present invention relates to a method for producing a hexagonal boron nitride film by microwave-excited surface wave plasma CVD.

Hexagonal boron nitride is an insulator having a large bandgap close to about 6 eV. Since its electronic properties are close to those of GaN and it may be applied to electronic devices as a functional material by semiconductorization, it has attracted a great deal of attention. Since it is convenient to make a thin film when it is used for an electronic device or the like, research on thinning the film is underway. Non-Patent Document 1 below discloses a hexagonal boron nitride film thinned by a thermal CVD method. The hexagonal boron nitride thin film produced by the thermal CVD method has good crystallinity.

Further, in Patent Document 1 below, an intermediate layer made of SiON is epitaxially grown on a SiC substrate, and a gate insulating film made of a hexagonal boron nitride layer is laminated on the intermediate layer by a thermal CVD method at a temperature of 1000 ° C. The MOSFET that has been made is disclosed. Then, it is disclosed that plasma CVD may be used in addition to thermal CVD, and that a compound containing both boron atoms and nitrogen atoms such as borazin and ammonia borane may be used as a raw material gas. There is.

Further, Patent Document 2 below discloses that cubic boron nitride is formed by surface wave excitation plasma using a nitrogen boron compound such as aminoborane and borazine as a raw material.

Japanese Unexamined Patent Publication No. 2017-41503 Japanese Unexamined Patent Publication No. 2008-222488

Surface Technology, Vol.58, No12, 2007, p121-124

However, the thermal CVD method requires a high temperature of 1000 ° C. or higher. Therefore, for example, if a hexagonal boron nitride thin film is formed by a thermal CVD method after manufacturing a circuit element on a Si substrate, the characteristics of the circuit element deteriorate due to the high temperature. When a film is formed by the PE-CVD method, which can form a film at a relatively low temperature and does not deteriorate the circuit element, it becomes a thin film having many defects due to ionic impact and has poor crystallinity, and cannot be used as an electronic device.
The technique disclosed in Patent Document 1 is a method of forming a hexagonal boron nitride film on a SiON film optically grown on the surface of a SiC substrate by a thermal CVD method at 1000 ° C. However, Patent Document 1 does not suggest that a hexagonal boron nitride film can be formed at a low temperature by surface wave excitation plasma CVD.
Further, the technique of Patent Document 2 is a method of forming a cubic boron nitride film on a substrate by applying a positive bias voltage to the substrate by a plasma CVD method, and a hexagonal boron nitride film is formed. It does not suggest that. It is also suggested that surface wave excitation plasma may be used, but this is related to the formation of a cubic boron nitride film, and the hexagonal boron nitride film is a cubic boron nitride film. It does not suggest that it is formed using surface wave excited plasma with high purity without boron mixture.

The present invention has been created in view of the above problems, and an object of the present invention is to form a high-purity hexagonal boron nitride that can be formed at a low temperature, has good crystallinity, and is not mixed with cubic boron nitride. The purpose is to provide a method for producing a thin film.

The present invention is a method of producing a hexagonal boron nitride film on a substrate by plasma-decomposing a raw material gas, in which a solid of ammonia borane (NH ₃ BH ₃ ) is provided in a plasma generation chamber and the solid is heated. The raw material gas is generated by vaporization, the raw material gas is passed on the substrate placed in the plasma generation chamber, the surface wave plasma of the raw material gas is generated by microwave excitation on the substrate, and hexagonal boron nitride is generated on the substrate. It is a method for producing a hexagonal boron nitride film, which comprises producing a film.

In the present invention, the raw material gas is generated by providing a solid of ammonia borane in the plasma generation chamber and heating and vaporizing this solid . Further, although it is not the present invention, it is also possible to vaporize the solid ammonia borane and supply the ammonia borane gas to the plasma generation chamber in a chamber separate from the plasma generation chamber .

It is desirable that the temperature of the substrate at the time of forming the hexagonal boron nitride film is 400 ° C. or higher and 600 ° C. or lower. In this temperature range, a hexagonal boron nitride film having high crystallinity and purity can be formed. High purity means that the mixing ratio of the cubic boron nitride film is absent or small.
The substrate on which the hexagonal boron nitride film is formed is not particularly limited, but a Si substrate can be used. Further, a Si substrate coated with Cu may be used as a catalyst. Further, iron, cobalt, nickel, alloys thereof or compounds thereof, platinum or other noble metals may be formed on at least the entire surface of the substrate.

According to the present invention, a raw material gas obtained by heating and vaporizing solid ammonia boron nitride placed in a plasma generation chamber is allowed to flow on a substrate placed in the plasma generation chamber, and a surface wave of the raw material gas is applied onto the substrate by microwave excitation. Since plasma is generated to produce a hexagonal boron nitride film on the substrate, low-temperature growth is possible, and a hexagonal boron nitride film having high crystallinity and purity can be formed.
According to the present invention, since a hexagonal boron nitride film can be directly formed on a substrate (for example, Si, GaN, etc.) without using a catalyst, a gate insulating film in FET, a protective insulating film of an element, and inter-element insulation can be formed. It can be used as a separation membrane or the like.

The block diagram which shows the manufacturing apparatus of the hexagonal boron nitride film used in the manufacturing method of an Example in this invention. The measurement figure of the infrared absorption spectrum of the hexagonal boron nitride film manufactured by the manufacturing method of an Example. FIG. 3 is a measurement diagram of B1s by X-ray photoelectron analysis of a hexagonal boron nitride film produced by the production method of the example. The measurement figure of N1s by X-ray photoelectron analysis of the hexagonal boron nitride film manufactured by the manufacturing method of an Example.

Hereinafter, the present invention will be described based on examples, but the present invention is not limited to the following examples.

In this example, a gas _{obtained from ammonia borane (NH 3} BH ₃ ) was used as the raw material gas. Ammonia borane has a melting point of 104 ° C. and a boiling point of 196 ° C., and is solid at room temperature (25 ° C.).

FIG. 1 is a configuration diagram showing a configuration of a hexagonal boron nitride film manufacturing apparatus 100 according to the present invention. As shown in FIG. 1, the manufacturing apparatus 100 has a CVD reaction vessel 1 which is a plasma generation chamber, and a waveguide 2 arranged above the CVD reaction vessel 1. A plasma excitation plate 3 made of quartz is provided between the CVD reaction vessel 1 and the waveguide 2. A large number of minute recesses 30 are formed on the surface of the plasma excitation plate 3 facing the CVD reaction vessel 1 side. By concentrating the electric field in the recess 30, the recess 30 becomes the starting point for plasma generation, and plasma can be easily generated at low power. Further, a slot antenna 4 is provided below the waveguide 2 in order to excite the inside of the CVD reaction vessel 1 and the plasma excitation plate 3 with microwaves. 2.45 GHz microwaves are supplied to the waveguide 2, and electromagnetic waves are supplied to the inside of the CVD reaction vessel 1 and the plasma excitation plate 3 via the slot antenna 4.

Inside the CVD reaction vessel 1, a susceptor 6 on which a substrate 5 for growing a hexagonal boron nitride film is installed and a heating device 7 for heating the substrate 5 are provided. On the left side of the CVD reaction vessel 1, _{an introduction port 1L for introducing argon (Ar) and hydrogen (H 2} ) as carrier gas is provided, and on the right side, a discharge port 1R for discharging argon gas and hydrogen to the outside is provided. Has been done. The inside of the CVD reaction vessel 1 is depressurized to about ^{4.1 × 10 -4 Pa by a vacuum pump (not shown).} The pressure inside the CVD reaction vessel 1 is in ^{the range of 1 × 10 -6} Pa to 1 × 10 Pa, and a hexagonal boron nitride film can be formed. Further, the hexagonal boron nitride film can be formed in a temperature range of 400 ° C. or higher and 600 ° C. or lower, preferably 450 ° C. or higher and 550 ° C. or lower. In this example, the film is formed at 500 ° C. An appropriate amount of ammonia borane 11 as a raw material gas for producing a hexagonal boron nitride film is arranged on a boat provided on the susceptor 6 in the CVD reaction vessel 1. In this example, it is 3 mg.

Next, a method of manufacturing a hexagonal boron nitride film on the substrate 5 will be described. Two types of substrates 5 were used: a Si substrate and a Si substrate coated with Cu. The surface of the substrate 5 was washed with acetone, ethanol, and pure and then dried, the substrate 5 being placed on the susceptor 6.

Next, 3 mg of ammonia borane 11 was provided on a boat provided on the susceptor 6 in the CVD reaction vessel 1. Next, argon (Ar) was supplied to the inside of the CVD reaction vessel 1 at _{a constant flow rate of 100 sccm and hydrogen (H 2} ) at a constant flow rate of 5 sccm. The pressure inside the CVD reaction vessel 1 was set to ^{4.1 × 10 -4 Pa.} Then, the substrate 5 was heated by the heating device 7, and the temperature of the substrate 5 at the time of film formation was set to 500 ° C. In this state, the vaporized ammonia borane is transported onto the substrate 5 by a stream of argon and hydrogen. Next, microwaves having a power of 1000 W and 2.45 GHz were supplied to the waveguide 2, and plasma of a raw material gas of ammonia borane, an argon gas, and a hydrogen gas was generated inside the CVD reaction vessel 1. The microwave power can be in the range of 500W to 2000W. In particular, surface wave plasmas of these gases were generated on the surface of the substrate 5. As a result, the ammonia borane was thermally decomposed on the substrate 5, and a hexagonal boron nitride film composed of B atoms and N atoms was formed on the substrate 5. After the hexagonal boron nitride film was grown on the substrate 5 for a predetermined time (3 minutes), the energization of the heating device 7 was stopped, and the temperature of the substrate 5 was lowered to room temperature (25 ° C.). In this way, a substrate on which a hexagonal boron nitride film was directly formed on a Si substrate and a substrate on which a hexagonal boron nitride film was formed on a Si substrate whose surface was coated with Cu were obtained.
The temperature of the substrate 5 can be any temperature in the range of 400 to 600 ° C.

Next, the infrared absorption spectrum (FTIR) of the hexagonal boron nitride film formed at 500 ° C. was measured directly on the Si substrate. The result is shown in FIG. For comparison, the FTIR of the Si substrate on which the hexagonal boron nitride film was not formed was measured, and the results are shown in FIG. A sharp absorption peak is seen at wavenumber 1385 cm ^-1. This indicates that the film is hexagonal boron nitride. The FTIR of cubic boron nitride ^{has an absorption peak at 1000 cm -1} but does not appear according to FIG. Therefore, it is understood that a high-purity hexagonal boron nitride film was obtained. As far as the FTIR spectrum is seen, it is considered that a 100% hexagonal boron nitride film is obtained. Even if there is a mixture, the proportion of cubic boron nitride is less than 1%, that is, the purity of hexagonal boron nitride seems to be 99% or more.
Similar results were obtained for the FTIR spectrum of a hexagonal boron nitride film formed on a Si substrate coated with Cu.

Next, X-ray photoelectron analysis (XPS) was performed on two types of hexagonal boron nitride films formed directly on the Si substrate and on the Si coated Si substrate. The measurement result is shown in Fig. 3. B1s peak. The N1s peak is shown in A in FIG. Shown in B. The B1s peak for the hexagonal boron nitride film formed directly on the Si substrate was 191.8 eV, and the N1s peak was 399.4 eV. The B1s peak of the hexagonal boron nitride film formed on the Si substrate coated with Cu was 191.1 eV, and the N1s peak was 398. It was 4 eV. The difference in peaks due to the difference in substrates is considered to be due to the level of impurities in the film. It can be seen that the spectra of B and N atoms are observed. In addition, no spectra other than C, O, B, and N atoms were observed.

The surface flatness of the formed hexagonal boron nitride film was observed with an optical microscope and SEM, and it was confirmed that the crystal grains were submicron size. In addition, the AFM image was measured on the cross section of the hexagonal boron nitride film formed, and 20 layers of hexagonal boron nitride film were observed. The surface roughness was about submicron.

Further, since a Si substrate having a diameter of 3 inches is used as the substrate, at least 20 layers of a highly flat and high-purity hexagonal boron nitride film having a diameter of at least 3 inches can be obtained by the above method. You can see that there is.

According to the present invention, by obtaining a flat, large-area, and high-purity hexagonal boron nitride film, it can be used as an insulating film for an electronic device or the like.

1: CVD reaction vessel 3: Excitation plate 5: Substrate 6: Suceptor 7: Heating device 11: Ammonia borane 30: Recess

Claims (3)

In a method of plasma-decomposing a raw material gas to produce a hexagonal boron nitride film on a substrate,
A solid of ammonia borane (NH ₃ BH ₃ ) is provided in the plasma generation chamber, and this solid is heated and vaporized to generate the raw material gas.
The raw material gas is flowed on a substrate placed in a plasma generation chamber, and a surface wave plasma of the raw material gas is generated on the substrate by microwave excitation.
A method for producing a hexagonal boron nitride film, which comprises producing a hexagonal boron nitride film on the substrate. The method for producing a hexagonal boron nitride film according to claim 1, wherein the temperature of the substrate at the time of forming the hexagonal boron nitride film is 400 ° C. or higher and 600 ° C. or lower. The method for producing a hexagonal boron nitride film according to claim 1 or 2, wherein the substrate is Si whose surface is coated with Si or Cu.

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