JP2611521B2 - Method of forming boron nitride thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a machine tool such as a cutting tool, a mold, a magnetic head, etc.
The present invention relates to a method for forming a hard boron nitride thin film on a surface of a mechanical component or a semiconductor device.

[Conventional technology]

Boron nitride (hereinafter abbreviated as BN) is cubic zinc-blende-type boron nitride (hereinafter abbreviated as c-BN) or hexagonal graphite-type boron nitride (h-
BN), hexagonal wurtzite boron nitride (hereinafter referred to as w
-BN).

c-BN has the second highest hardness next to diamond and has excellent thermal conductivity, insulation and chemical stability, and is therefore applied as a coating thin film in a wide range of fields such as semiconductors and cutting tools. I have. In addition, it is also expected to be used for materials such as heat sink materials that make use of insulating properties and high thermal conductivity.

However, at present, in order to obtain c-BN, it has to be artificially synthesized under high temperature and high pressure, and therefore, its manufacturing cost becomes very high and the synthesized c-BN Can only obtain a granular or powdery solid, and its application range is also limited.
Therefore, research on a method for forming a thin film of c-BN under a low temperature and a low pressure has been actively conducted by a chemical vapor deposition method (CVD method) or a physical vapor deposition method (PVD method).

For example, in a chemical vapor deposition method (CVD method), a substrate on which a thin film is deposited is placed in a reaction chamber and heated to a temperature of 500 ° C. or more, and then a gas containing a boron element (B) and a nitrogen element (N)
Is introduced into the reaction chamber and subjected to a thermal decomposition reaction to form a BN thin film on the surface of the substrate.

In the physical vapor deposition (PVD) method, a target containing boron element (B) is sputtered with an ion species in a nitrogen gas atmosphere, and sputtered particles are deposited on the surface of a substrate to form a BN thin film. Law.
Further, there is an ion-plating method in which flying particles of the boron element (B) are ionized, these particles are accelerated by an electric field to several eV to several KeV, and are deposited on the surface of the substrate to form a BN thin film.

[Problems to be solved by the invention]

However, in the chemical vapor deposition method (CVD method), it is necessary to maintain the substrate at a high temperature (about 500 ° C. or higher), and the BN thin film cannot be formed because the substrate is thermally degraded. The disadvantage is that the substrate is limited. Further, the BN thin film formed by this method tends to be a thin film mainly composed of soft h-BN, and the above-mentioned properties of c-BN cannot be fully utilized.

Also, in the physical vapor deposition method (PVD method), as in the chemical vapor deposition method (CVD method), only a thin film mainly composed of h-BN can be obtained.

An object of the present invention is to provide a method for forming a boron nitride thin film that can form a BN thin film mainly composed of a c-BN structure on a surface of a substrate at a low temperature.

[Means for solving the problem]

The method for forming a boron nitride thin film of the present invention is characterized in that, at the same time as the deposition of boron on the surface of the substrate, at least one or more rare gas ions and nitrogen ions are mixed, and irradiation energy of 100 eV to 500 eV and the rare gas ions are mixed. Irradiation is performed at a dose ratio of 0.05 to 1.5 with the nitrogen ions, and a ratio of the number of particles of boron and nitrogen (B / N composition ratio) in the formed boron nitride (BN) thin film is 0.5 to 1.5. It contains crystal grains of cubic boron nitride of 3.0.

One example of a BN thin film forming apparatus of the method for forming a boron nitride thin film of the present invention will be described with reference to FIG.

In a vacuum device (not shown), a base 2 is fixed to a holder 1 that can be cooled by circulating water.
An evaporation source 3 and an ion source 5 are arranged at a position facing the base 2.

The evaporation source 3 can be heated to a high temperature by an electron beam, a laser beam, a high frequency or the like, and includes an evaporation substance 4 containing boron (B) composed of boron alone, boron oxide or boron nitride. Is inserted.

Further, the ion source 5 is of a Kauffman type, a bucket type using a cusp magnetic field for confining plasma, or the like, and a gas obtained by mixing a gas composed of at least one kind of rare gas element and a gas composed of nitrogen element. This is an apparatus that irradiates the surface of the substrate 2 with ionization into rare gas ions 6a and nitrogen ions 6b.

Further, a film thickness meter 7 and a current measuring device 8 are arranged in the vacuum device.

This film thickness meter 7 is for measuring the film thickness of the vapor deposition material 4 deposited on the surface of the substrate 2 and the number of boron particles. For example, a vibration type film thickness meter using a quartz oscillator is used. It is. The current measuring device 8 is for measuring the amount of nitrogen ions 6b of the ions irradiated on the substrate 2, and is, for example, a cup-shaped ion beam having a secondary electron suppressing electrode such as a Faraday cup. It is a current meter.

In the above configuration, the evaporation source 3 is heated to deposit the evaporation substance 4 containing the boron element (B) on the surface of the substrate 2 and at least one or more rare gas ions 6a and nitrogen Irradiate with ions 6b.

At this time, the value of the irradiation energy of the rare gas ions 6a and the nitrogen ions 6b is such that damage and defects in the crystal structure are extremely small.
Irradiation energy value of 100 eV to form BN thin film
Up to 500 eV.

The lower limit of the range of the irradiation energy is 100 eV or more because the actual performance of the ion source 5 and a current density sufficient for practical use cannot be obtained, and the upper limit of the range of the irradiation energy is In order to further reduce the thermal damage to the formed BN thin film, it is set to 500 eV or less.

Further, the rare gas ions 6a and the nitrogen ions irradiated to the substrate 2
Irradiation is performed at a ratio of the amount of irradiation with 6b (in other words, the ratio of the rare gas and the nitrogen gas supplied to the ion source 5) in the range of 0.05 to 2.0. When the ratio of the irradiation amount is smaller than this range, that is, when the irradiation ratio of the rare gas ion 6a and the nitrogen ion 6b is less than 0.05, the BN in the BN thin film where the rare gas ion 6a is formed is
Excitation energy applied to the bond is insufficient, and the effect on the reaction between the boron-containing evaporant 4 and the nitrogen ion 6b is insufficient. If the ratio of the irradiation amount of the rare gas ion 6a to the irradiation amount of the nitrogen ion 6b is larger than 2.0, the irradiation amount of the nitrogen ion 6b becomes insufficient, and the reaction between the boron-containing vaporized substance 4 and the nitrogen ion 6b progresses. Insufficiently, a BN thin film mainly composed of a c-BN structure cannot be formed.

Further, the ratio of the number of particles of boron and nitrogen in the BN thin film formed on the surface of the substrate 2 (hereinafter, abbreviated as B / N composition ratio) is
The film is formed while measuring and controlling the deposition amount of the deposition material 4 and the irradiation amounts of the rare gas ions 6a and the nitrogen ions 6b by the film thickness meter 7 and the current measuring device 8 so as to be in the range of 0.5 to 3.0. If the B / N composition ratio is out of this range, if the B / N composition ratio is larger than 3.0, the amount of boron deposited on the substrate 2 becomes too large, the content of c-BN in the BN thin film decreases, and the B / N composition ratio becomes 0.5. If it is smaller, too much nitrogen cannot be chemically bonded to boron in the formed BN thin film,
This is because the desired high hardness, thermally and chemically stable BN thin film cannot be obtained.

The rare gas elements which are supplied to the ion source 5 to be rare gas ions 6a include He (helium), Ne (neon), and Ar
(Argon), Kr (krypton), and Xe (xenon) are used to supply at least one or more rare gases.

Under such conditions, the rare gas ion 6a becomes a nitrogen ion
6b reacts with boron in the evaporating substance 4 in an excited state,
It is possible to promote the formation of a BN thin film having a c-BN structure, which was conventionally formed only under high temperature and high pressure conditions.

Next, another example of the BN thin film forming apparatus will be described with reference to FIG.

In a vacuum device (not shown), a base 2 is fixed to a holder 1 which can be cooled by circulating water, and a film thickness meter 7 and a current measuring device 8 similar to those described above are arranged on both sides thereof. . The evaporation source 3 is located at a position facing the base 2.
And two ion sources 5, 5 '.

The evaporation source 3 and the ion sources 5, 5 'are similar to those of the BN thin film forming apparatus shown in FIG. 1 and described above. The evaporating substance 4 containing boron (B) consisting of, for example, is charged.

The ion source 5 ionizes a gas composed of at least one or more rare gas elements and irradiates the surface of the substrate 2 with rare gas ions 6a. The ion source 5 ′ ionizes a gas composed of a nitrogen element. Substrate 2 with nitrogen ions 6b
The surface is irradiated.

Thus, by arranging the two ion sources 5 'for irradiating the rare gas ions 6a and the nitrogen ions 6b as the ion sources, the irradiation energies of the rare gas ions 6a and the nitrogen ions 6b can be individually controlled. Thus, the irradiation amount of the rare gas ion 6a for setting the reaction conditions to the excited state and the irradiation amount of the nitrogen ion 6b reacting with boron contained in the evaporating substance 4 can be individually adjusted.

〔Example〕

Example 1 In the apparatus described with reference to FIG. 1, a holder 2 was prepared by setting a cut surface [100] of a substrate made of a silicon single crystal wafer to face an evaporation source 3 and an ion source 5.
After fixation, boron (purity 99.7% or more) is evaporated
And the inside of the vacuum device is set to 2 × 10
A high vacuum of ^-6 [Torr] or less was maintained. And evaporation source 3
Is heated by an electron beam to vaporize the evaporating substance 4 on the surface of the substrate 2, and at the same time, a mixed gas composed of a rare gas composed of Ar (argon) gas and a nitrogen gas is supplied to the bucket type ion source 5. The surface of the substrate 2 was irradiated with rare gas ions 6a and nitrogen ions 6b (argon).

At this time, the irradiation energy of the rare gas ion 6a and the nitrogen ion 6b is set to 300 eV, and the rare gas ion 6a and the nitrogen ion 6b are irradiated.
Of the BN thin film formed by controlling the current density of the rare gas ions 6a and the nitrogen ions 6b to 0.15 [A / cm ² ] and the boron deposition rate to 1 [Å / sec] with the irradiation dose ratio of 0.1 The B / N composition ratio is set to 1, and the number of particles of the evaporating substance 4 composed of boron and the number of particles of nitrogen reaching the substrate 2 are measured by the film thickness meter 7 and the current measuring device 8 while measuring 5000 [Å]. BN thin film was formed.

The supply amounts of the rare gas and the nitrogen gas composed of Ar (argon) to be mixed and supplied to the evaporation source 5 are precisely controlled and supplied by a mass flow controller. Also,
During the formation of the BN thin film, the holder 2 is constantly cooled with water, so that the substrate 2 is kept at room temperature (RT = 23 ° C.).

Example 2 Substrate 2, evaporant 4, rare gas ion of the same material as in Example 1
At the same time as the evaporation of the evaporating substance 4 using the nitrogen ions 6a and the nitrogen ions 6b, the irradiation ratio of the rare gas ions 6a and the nitrogen ions 6b is set to 0.
Except for the formation condition of 8, the conditions were controlled so as to be the same as those in Example 1, and the surface of the substrate 2 had a BN of 5000 [Å].
A thin film was formed.

Example 3 Substrate 2, evaporant 4, rare gas ion of the same material as in Example 1
At the same time as the evaporation of the evaporating substance 4 using 6a and the nitrogen ions 6b, the irradiation ratio of the rare gas ions 6a and the nitrogen ions 6b is set to 1.
The formation conditions other than 5 were controlled so that the same conditions as in Example 1 were applied to the surface of the base 2 so that BN of 5000 [Å] was applied.
A thin film was formed.

Comparative Example Substrate 2, evaporant 4, rare gas ion of the same material as in Example 1
Simultaneous with the deposition of the evaporating substance 4 using the 6a and the nitrogen ions 6b, the formation conditions other than supplying only the nitrogen gas without supplying the rare gas to the ion source 5 and irradiating the substrate 2 with only the nitrogen ions 6b are as follows. Each condition was controlled so that the same conditions as in Example 1 were obtained, and a 5000 [薄膜] BN thin film was formed on the surface of the substrate 2.

Of each of Examples 1 to 3 and Comparative Example formed under the above conditions.
In order to confirm the structure and properties of the BN thin film, CuK α ray (λ
= 1.5406 °) and Knoop hardness (Hk) were measured.

As a result, regarding the X-ray diffraction, the diffraction angle 2θ = 43.3 showing the c-BN structure in all the BN thin films of each of Examples and Comparative Examples.
Diffraction peaks are observed, and any BN containing c-BN structure
Although it was confirmed that the BN thin film was a thin film, the BN thin film of Example 2 showed about 5 times the diffraction strength as compared with the BN thin film of the comparative example. Was confirmed to be excellent in crystallinity.

For the Knoop hardness (Hk), Ar (argon)
Hardness (H) with respect to the ratio of the irradiation amount of rare gas ions 6a and nitrogen ions 6b (hereinafter abbreviated as Ar / N ion ratio)
As shown in FIG. 3, the Knoop hardness (Hk) of the BN thin film of the comparative example formed by irradiating the substrate 2 with only the nitrogen ions 6b (Ar / N ion ratio = 0) as the value of k) is 1200 [ kg / mm ² ], the Knoop hardness (Hk) of each of the BN thin films of Examples 1 to 3 having an Ar / N ion ratio of 0.1, 0.8 and 1.5 is 3100, 4200, 30
It has a Knoop hardness (Hk) of about 2.5 to 3.5 times as high as 00 [kg / mm ² ], and formation of a hard BN thin film having a c-BN structure is recognized.

In the formation conditions of Example 2 and Comparative Example, the boron deposition rate was increased to 3,5 [Å / sec], and the B / N composition ratio was changed from 1 to 3,5. FIG. 4 shows the results obtained by forming a BN thin film under the same conditions as in Example 2 and Comparative Example and measuring the Knoop hardness (Hk) as the Knoop hardness (Hk) with respect to the B / N composition ratio together with the values of Example 2 and Comparative Example. Show.

As a result, the B / N composition ratio was 1 with the Ar / N ion ratio being 0.8.
(Example 2) In each of the BN thin films changed to 3, 5, the Knoop hardness (Hk) decreases as the B / N composition ratio increases.
In the region where the B / N composition ratio is larger than 3, the difference in the Knoop hardness (Hk) from the comparative example is small, and the value of the Knoop hardness (Hk) when the B / N composition ratio in the comparative example is changed to 3,5. (1450, 2450 [kg / mm
² )), the Knoop hardness (Hk) is reversed around the boundary of the B / N composition ratio of about 4.6.

Thus, simultaneously with the deposition of the boron-containing deposition material 4 on the surface of the substrate 2, the rare gas ions 6a and nitrogen ions 6b composed of Ar (argon) ions are irradiated at an irradiation energy of 300 eV to obtain a B / N composition. When a BN thin film having a ratio of 1 was formed, the Ar / N ion ratio was set to 0.1 in Example 1, set to 0.8 in Example 2, and set to 1.5 in Example 3, so that the formed BN thin film was formed.
The crystal structure of the thin film is mainly a c-BN structure, and a BN thin film having a high Knoop hardness (Hk) can be formed.

〔The invention's effect〕

The method for forming a boron nitride thin film of the present invention is characterized in that, at the same time as the deposition of boron on the surface of the substrate, at least one or more rare gas ions and nitrogen ions are mixed, and irradiation energy of 100 eV to 500 eV and the rare gas ions are mixed. Irradiation is performed at a dose ratio of 0.05 to 1.5 with the nitrogen ions, and a ratio of the number of particles of boron and nitrogen (B / N composition ratio) in the formed boron nitride (BN) thin film is 0.5 to 1.5. Since it contains cubic boron nitride crystal grains of 3.0, c-
A high hardness boron nitride (BN) thin film mainly composed of a BN structure can be formed.

Also, under the numerical conditions as described above, nitrogen ions and rare gas ions are mixed and irradiated simultaneously with the deposition of boron, so that compared with the case of irradiating only nitrogen ions simultaneously with the deposition of boron, Excellent crystallinity of the c-BN structure, and it is possible to obtain boron nitride of high hardness c-BN, and the irradiation energy of ions is considerably low as 100 eV to 500 eV, so that the irradiated substrate does not thermally deteriorate. The present invention is not limited thereto. For example, a semiconductor substrate can be used, and damage and defects inside the formed boron nitride thin film can be extremely reduced. Further, since the irradiation energy is low, a power supply device and an insulating structure for ion irradiation can be simplified, and the cost can be reduced.

In addition, the gas supplied to the ion source and irradiated as ions is only a rare gas and a nitrogen gas, and does not use another gas (hydrogen gas or the like) having an activity conventionally used.
A boron nitride (BN) thin film having more excellent crystallinity and adhesion to the substrate can be formed.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a thin film forming apparatus of the method for forming a boron nitride thin film of the present invention, FIG. 2 is a conceptual diagram of another thin film forming apparatus, and FIG. 3 is an Ar / N ion ratio of each of Examples and Comparative Examples. FIG. 4 is a graph of the Knoop hardness (Hk) with respect to the B / N composition ratio of Example 2 and the comparative example. 2 ... substrate, 3 ... evaporation source, 4 ... evaporation material, 5,5 '...
... Ion source, 6a ... Rare gas ion, 6b ... Nitrogen ion,
7 ... Thickness gauge, 8 ... Current measuring device

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kiyoshi Ogata 47, Umezu Takaune-cho, Ukyo-ku, Kyoto, Kyoto Prefecture Inside Nissin Electric Co., Ltd. JP-A-60-63372 (JP, A) JP-A-62-161952 (JP, A) JP-A-62-93366 (JP, A) JP-A-2-149661 (JP) , A)

Claims (1)

(57) [Claims] At least one kind of rare gas ions and nitrogen ions are mixed at the same time as the deposition of boron on the surface of a substrate to irradiate the rare gas ions and the nitrogen ions with irradiation energy of 100 eV to 500 eV. Irradiation at a volume ratio of 0.05 to 1.5, and cubic nitriding with a boron / nitrogen particle ratio (B / N composition ratio) of 0.5 to 3.0 in the formed boron nitride (BN) thin film A method for forming a boron nitride thin film containing boron crystal grains.