JP3254727B2 - Method for forming boron nitride-containing film - 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 forming a boron nitride-containing film, and more particularly, to a field requiring abrasion resistance and sliding property, a field requiring a high thermal conductivity, or a semiconductor. The present invention relates to a method for forming a boron nitride-containing film used in a field where characteristics are required.

[0002]

2. Description of the Related Art Boron nitride (BN) has a crystal structure similar to that of hexagonal graphite (h-BN) and cubic zinc blende type (BN). c-BN) or hexagonal wurtzite type (w-BN). h-BN is C
Since it is a substance with openness in the axial direction, it is soft but has excellent slidability. Currently, artificially synthesized powders are widely used to lower the friction coefficient of various sliding parts. ing.

[0003] On the other hand, c-BN has the second highest hardness and thermal conductivity next to diamond, and is more excellent in thermal and chemical stability than diamond. It is applied to fields and materials for heat sinks. Furthermore, c-BN has a band gap larger than that of diamond, and can be applied as a semiconductor that can operate up to a temperature range that is difficult to use with conventional semiconductor devices by being doped with various impurities, or can be applied with ultraviolet light through a pn junction. It has also been reported that it also operates as a diode that emits light, and has attracted attention in terms of characteristics as a semiconductor.

However, h-BN is easily synthesized into a powder under low pressure, and various PVD methods (Physical Vapor Deposit) are used.
ion) and CVD (Chemical Vapor Deposition), it is easily formed into a film, whereas c-BN is
It can be synthesized only in bulk at high temperature and high pressure, and even if synthesized, its manufacturing cost is extremely high, and its application range is limited.

[0005] If c-BN is synthesized at a low temperature which does not require a high pressure and can be formed on a substrate with good adhesion, the above-mentioned applications can be greatly expanded. As an example of the research using the thermal CVD method, which is one of the attempts, in this method, a substrate is placed in a reaction chamber and a gas containing a boron element (B) or a source gas containing a nitrogen element (N) is used. Is introduced into a reaction chamber and heated to a temperature close to 1000 ° C., whereby the source gas is thermally decomposed to form a film on the surface of the substrate.

However, this method has a drawback that the type of the substrate is limited because the substrate requires heat resistance. For example, about 50, such as high-speed tool steel (high-speed steel)
It is not possible to use, as a base, a material that causes deterioration in hardness at a temperature of 0 ° C. or more, or a metal mold that cannot allow for dimensional accuracy due to deformation under high temperature. Furthermore, although the synthesis of h-BN has been facilitated by the CVD method, an example of synthesizing c-BN has not yet been reported, and is in a research stage.

Further, in the PVD method, a method has been attempted in which a target made of boron nitride is sputtered by, for example, irradiating a laser to form a boron nitride-containing film on a substrate surface. Synthesis of c-BN was not possible. However, in recent years, c-BN has been used under low temperature by actively using ions and plasma.
Attempts have been made to synthesize c-BN, and to a small extent, successful cases of c-BN synthesis have been reported. For example, the source gas is decomposed using plasma,
The plasma CVD method of reacting has the advantage that a boron nitride-containing film can be synthesized at a low temperature and has a high excited state of the source gas, as compared with the thermal CVD method of thermally decomposing and reacting the source gas. C-BN is synthesized at a temperature at which thermal damage to the substrate is relatively small.

[0008] c using other ions and plasma
Some examples of synthesis of -BN have been reported, and c-BN
The low-temperature synthesis of has been attracting industrial attention.
Although the use of plasma, ions and the like has opened the way to the synthesis of a boron nitride-containing film at low temperatures, the adhesion between the substrate and the film has not yet been solved for industrial practical use.

The method of synthesizing a film by applying heat to the substrate, as in the thermal CVD method, which has been attempted in the past, involves the problem of thermal damage to the substrate, but with respect to the adhesion, the film is formed at a low temperature. There was a tendency that it was superior to the method of doing. c-BN
Although low-temperature synthesis has been successful, at present, there has not yet been established a method for achieving both a film without thermal damage to the substrate and a film with good adhesion.

In order to form a BN film having good adhesion on a substrate without causing thermal damage to the substrate, the inventors of the present invention used vacuum deposition and sputtering of a substance containing a boron element by vacuum deposition and sputtering. It has been proposed to use a method of irradiating the substrate with ions containing at least nitrogen ions simultaneously, alternately, or after the film is formed on the substrate.
However, in this method, c-BN formed in the film is generally in an amorphous state or has low crystallinity, and the hardness, thermal conductivity, and semiconductor characteristics of c-BN are insufficient. There was a problem.

In order to improve the crystallinity of c-BN, for example, there is a method of irradiating inert gas ions or hydrogen ions simultaneously with nitrogen ions as a kind of irradiation ions. There is a problem in that an inert gas or a hydrogen atom is mixed in, and the density of the film is reduced to cause deterioration of the characteristics of c-BN or to deteriorate long-term stability of the film.

It is also conceivable to increase the crystallinity by heating the substrate during film formation, but in this case, there is a problem that it is inappropriate from the viewpoint of low-temperature growth. The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for forming a boron nitride-containing film in which hardness, thermal conductivity, semiconductor characteristics, and the like are improved and long-term stability is ensured.

[0013]

According to the present invention, vacuum deposition or sputtering of a substance containing boron element and irradiation of ions containing at least nitrogen ions are used in a vacuum vessel in combination with a substrate. This provides a method for forming a cubic boron nitride-containing film, wherein the cubic boron nitride-containing film is formed while irradiating ultraviolet light when forming the cubic boron nitride-containing film.

A film forming apparatus for carrying out the present invention includes an evaporation source, an ion source, and the like. For example, a film forming apparatus as shown in FIG. 1 can be used. In FIG. 1, 1 is a substrate, 2 is a substrate holder, 3 is an evaporation source, 4 is an ion source, which are housed in a vacuum vessel 5. The vacuum vessel 5 is evacuated to a predetermined degree of vacuum by an exhaust device 9 and held. The evaporation source 3 is for heating the boron-containing substance to vaporize it by an electron beam, resistance or high frequency, and may use any other method such as sputtering. However, when the evaporation rate is not stable in the method in which the boron-containing substance is heated and vaporized with a sublimable substance, it is preferable to use the sputtering method. The type of the ion source 4 is not particularly limited, either.
A Kauffman type or bucket type can be used as appropriate. A film thickness monitor 6 is provided near the substrate holder 2 for monitoring the amount of vapor deposited atoms on the substrate 1.
However, an ion current measuring device 7 capable of monitoring the amount of irradiation of the substrate 1 with ions is provided. The methods of the film thickness monitor 6 and the ion current measuring device 7 are not particularly limited. For example, a film oscillator using a crystal oscillator is used as the film thickness monitor 6, and a Faraday cup or the like is appropriately used as the ion current measuring device 7. Can be used. In addition, for example, an ultraviolet irradiation lamp 8 is provided at a position facing the base 1 to irradiate an electromagnetic wave. In addition, as the ultraviolet irradiation lamp 8 for irradiating an electromagnetic wave, a lamp using a mercury arc can be used, and in addition, light from an X-ray from an X-ray source or a lamp using a deuterium lamp is also used. be able to.

In practicing the present invention, the substrate is placed on a substrate holder and placed in a vacuum vessel, for example, 1 ×
After evacuating to a degree of vacuum of 10 ⁻⁶ torr or less, the boron-containing substance is heated from an evaporation source and vaporized to be deposited on the substrate. As the boron-containing substance vaporized from the evaporation source, a simple substance of boron, an oxide, a nitride, a carbide, or the like can be used. Then, simultaneously with, alternately with, or after the deposition of the substance, an ion source is irradiated with ions containing at least a nitrogen element. At this time, it is effective to use nitrogen ions as the ions to be irradiated. However, in order to increase the crystallinity of the film, particularly in order to form a film having high hardness, nitrogen ions and an inert gas element are used. An ion or hydrogen ion-containing material can be used. These can be obtained, for example, by introducing only nitrogen gas or nitrogen gas and an inert gas or hydrogen gas to the ion source. In this case,
The inert gas ions and the hydrogen ions cause the vapor-deposited boron atoms to be in a further highly excited state, so that the degree of crystallinity of the film is improved, and as a result, a film having particularly high hardness is obtained. The angle of incidence of ions on the substrate at this time is not particularly limited, and the film may be formed while rotating the substrate in order to make the thickness of the film formed on the substrate uniform.

In the present invention, the ion acceleration energy for forming a film is preferably about 40 keV or less. If the ion acceleration energy exceeds 40 KeV, excessive defects are generated in the film, and the hardness and chemical stability of the film are undesirably deteriorated. Further, the number ratio (B / N transport ratio) of boron atoms and nitrogen ions that reach the substrate when forming the film is preferably about 0.5 to 60. When the B / N transport ratio is smaller than 0.5, the sputtering by the irradiation ions of the vapor-deposited boron becomes excessive, which also generates excessive defects in the film, and deteriorates the hardness and the chemical stability of the film. It is not preferable. When the B / N transport ratio is more than 60, the amount of BN contained in the film becomes small, and the characteristics of the BN are not sufficiently brought out, which is not preferable. The adjustment of the transport ratio can be performed using a film thickness monitor and an ion current measurement monitor in the film forming apparatus.

Further, in the present invention, the substrate is irradiated with electromagnetic waves simultaneously with the formation of the boron nitride-containing film. The energy at that time is preferably about 10 ^-2 eV to 10 ⁶ eV. The method of irradiating this electromagnetic wave is not particularly limited, but when the irradiation energy is smaller than 10 ⁻² eV,
If the excited state of the boron atom is poor and is higher than 10 ⁶ eV, damage to the film due to irradiation cannot be ignored, which is not preferable.

In the present invention, when using a substrate in which thermal damage must be extremely avoided, it is preferable to form a film while cooling the substrate holder by water cooling.

[0019]

According to the present invention, boron nitride is formed by simultaneously using vacuum deposition or sputtering of a substance containing boron and irradiation of ions containing at least nitrogen ions on a substrate in a vacuum vessel of a film forming apparatus. When forming the containing film,
Since the boron nitride-containing film is formed while irradiating the electromagnetic wave, the photon irradiated from the electromagnetic wave irradiation source collides with the deposited boron atom, or the boron atom absorbs the energy of the photon, and the electron between the bands. Transfer occurs, and the boron atom becomes a highly excited state, and a pseudo high-temperature, high-pressure state is created under non-thermal equilibrium. As a result, boron atoms tend to become c-BN, which is a high-temperature and high-pressure phase, and c-BN in the film is removed.
As the BN content increases, the crystallinity of c-BN improves.

[0020]

An embodiment of the method for forming a boron nitride-containing film according to the present invention will be described. Example 1 Using the apparatus shown in FIG. 1, a substrate 1 made of silicon (100) was placed on a substrate holder 2, and a vacuum vessel 5 was held at a degree of vacuum of 5 × 10 ⁻⁷ torr. Thereafter, an evaporating substance made of boron having a purity of 99.7% is vaporized by using the electron beam evaporation source 4 to form a boron film on the substrate 1 and, at the same time, a nitrogen gas having a purity of 5N is supplied to the ion source 4 in the vacuum vessel 5. × 10
^-5 torr was introduced, ionized in the ion source 4, and the substrate 1 was irradiated at an acceleration energy of 1 KeV at an angle of 0 ° with respect to the normal to the substrate 1. B /
The transport ratio of N was 1. The ion source 4 was a bucket type ion source using a cusp magnetic field. Then, at the same time when the BN film was formed on the base 1, the base 1 was irradiated with ultraviolet rays from a lamp 8 using a mercury arc. In this way,
A 1 μm BN film was formed on the substrate.

Comparative Example 1 The same substrate 1 as in Example 1 was used.
After maintaining the vacuum vessel 5 at a vacuum degree of 0 ^-7 torr, the purity was 99.7.
% Of boron is vaporized using the electron beam evaporation source 4 to form a boron film on the substrate 1 and, at the same time, nitrogen gas having a purity of 5N is supplied to the ion source 4 in the vacuum vessel 5 at 8 × 10 ^−5. The substrate 1 was ionized in the ion source 4, and the substrate 1 was irradiated with an acceleration energy of 2 keV at an angle of 0 ° with respect to a normal to the substrate 1. At this time, the transport ratio of B / N was 1. The ion source 4 was a bucket type ion source using a cusp magnetic field. However, unlike Example 1, the substrate 1 was not irradiated with ultraviolet rays. Thus, a 1 μm BN film was formed on the substrate 1.

FIGS. 2 and 3 show the results of the crystal structure of the BN film formed in Example 1 and Comparative Example 1 identified by X-ray diffraction using Cu-Kα rays. Each of the diffraction lines obtained from the BN film was at a position of 43.3 °, which was due to c-BN, and it was found that c-BN was formed in the BN film. The BN film formed in Example 1 had a higher diffraction intensity than that of Comparative Example 1, indicating that the BN film was excellent in crystallization state.

Further, the hardness of the BN film was measured by a Vickers hardness tester with a load of 10 g.
Although the value was 500, the value of the comparative example was 3000, and the result of the example was that the crystallization of c-BN was excellent, so that the hardness was greatly improved.

[0024]

According to the method for forming a boron nitride-containing film according to the present invention, a substrate is formed on a substrate in a vacuum chamber of a film forming apparatus.
Vacuum deposition or sputtering of a substance containing elemental boron,
When the boron nitride-containing film is formed by using irradiation of ions containing at least nitrogen ions, the boron nitride-containing film is formed while irradiating electromagnetic waves, so that the deposited boron atoms are in a highly excited state. As a result, the boron atom is liable to become c-BN, the c-BN content in the film can be increased, and the crystallinity of c-BN can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a main part of a film forming apparatus used when forming a boron nitride-containing film of the present invention.

FIG. 2 is a diagram showing X-ray diffraction of a boron nitride-containing film formed according to an example of the present invention.

FIG. 3 is a diagram showing X-ray diffraction of a boron nitride-containing film formed according to a comparative example.

[Explanation of symbols]

 1 Substrate 5 Vacuum container

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Naoto Kuratani 47, Takanecho Umezu, Ukyo-ku, Kyoto Nishidenki Co., Ltd. (56) References JP-A-3-97848 (JP, A) JP-A-61 −84379 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 14/00-14/58 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A cubic boron nitride-containing film is formed on a substrate in a vacuum vessel by using both vacuum deposition or sputtering of a substance containing a boron element and irradiation of ions containing at least nitrogen ions. Forming the cubic boron nitride-containing film while irradiating the film with ultraviolet light. 2. The method according to claim 1, wherein the acceleration energy of the ions during the ion irradiation is 40 keV or less, and the number ratio of boron atoms to nitrogen ions reaching the substrate is 0.5 to 60.