JP2620252B2 - Method for producing nitrogen-containing hard carbon film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a hard carbon film coated on a surface of a base material, and more particularly, to a novel method for producing a nitrogen-containing diamond thin film. Since diamond has properties such as high hardness and chemical inertness, high thermal conductivity, and low coefficient of thermal expansion, the present invention is applied to fields where these properties are advantageous, such as cutting tool materials. When used for coating, etc., very excellent effects can be exhibited.

[Conventional technology]

As a conventional technique related to so-called diamond coating, in which diamond is deposited on the base material surface from a gas phase under reduced pressure without using an ultra-high pressure and high temperature device, so-called diamond coating, hydrocarbon molecules are placed in a high energy state in the gas phase. There is a method in which a substrate is coated with diamond or a diamond-like amorphous carbon film in a metastable state by exciting to perform decomposition.

For example, a mixed gas of hydrocarbon and hydrogen is preheated to excite and decompose, and diamond is deposited on the surface of the base material heated and maintained at 700 to 1000 ° C. 58-91100), microwave non-polar discharge (JP-A-58-1104949), plasma (JP-A-58-135117), combined use of thermal filament and plasma (JP-A-58-156594) And various other measures are taken.

Then, according to the above-mentioned conventional technique, for example, a method utilizing microwave non-polar discharge, it is possible to coat a diamond film with a very high degree of perfection on the surface of a base material such as Si, Mo and W.

[Problems to be solved by the invention]

However, with this type of conventional technology, when the Si base material is coated with diamond, and when the film thickness reaches about 20μ or more, carbon other than diamond begins to co-precipitate in the film. As a result, the integrity of the obtained diamond starts to deteriorate, and when it exceeds 30 μm, there is a problem that the film peels off from the base material.

The cause of the peeling is generally considered to be due to internal compressive stress in the diamond film synthesized from the gas phase, and it has been found that the peeling occurs regardless of the excitation means and the like.

SUMMARY OF THE INVENTION The present invention has been made for the purpose of solving a problem of a conventional diamond film synthesized by a gas phase and to provide a novel method for producing a diamond film.

[Means and actions for solving the problems]

In the present invention, nitrogen is decomposed by a metal filament at 1600 to 2800 ° C. so that nitrogen is 10 ppm or more in terms of base paper.
% Of a hard carbon film having a content of not more than 0.1% on a surface of a base material.

By using diamond coating technology from the conventional gas phase, diamond coating with a film thickness of 20 μm or more
The reason why it cannot be achieved is, as described above, the internal compressive stress inherent in vapor-phase synthetic diamond.

There are various theories as to the cause of this internal compressive stress, and the details are unknown.However, as the film thickness increases, the total stress obtained by multiplying the internal stress by the film thickness exceeds the fracture strength of the diamond film, It is considered that the film is peeled off from the base material due to the fracture.

Therefore, the present inventors have repeated research on a method of alleviating the internal compressive stress in a diamond film, and for this purpose, carbon may be replaced by an atom having an atomic radius smaller than that of carbon constituting diamond. I thought that it might be.

The atomic radius of carbon is as small as 0.77 °, and the atoms with smaller atomic radii are only hydrogen, nitrogen, oxygen and fluorine. Of these, hydrogen has an extremely small atomic radius of 0.30 °, so that even if it is contained in diamond, it is not replaced with carbon but is contained in the interstitial, which rather increases the compressive stress, which is not preferable. Although both oxygen and fluorine can be substituted with carbon, various experiments have been conducted to produce diamond actually contained therein, but they did not sufficiently substitute for carbon.

In comparison with these, nitrogen was able to substitute for carbon, and the function of relaxing the internal compressive stress of the obtained diamond film was confirmed. When the nitrogen content is less than 10 ppm (0.001%) in atomic ratio, the above effect cannot be confirmed. When the nitrogen content exceeds 2%, a diamond structure cannot be obtained, so that the atomic ratio is preferably in the range of 0.001 to 2%.

As a method for obtaining the nitrogen-containing diamond film of the present invention, the conventional technique of the vapor phase synthesis method of the diamond film may be applied as it is, and at this time, N ₂ , It is advisable to add an N-based additive gas such as NH ₃ , N ₂ O, NO NO ₂ and the like. Alternatively, CH ₃ CN, CH ₃ NH ₂
The same effect can be obtained by using a mixed gas of nitrogen-containing hydrocarbon such as hydrogen and hydrogen as a starting material. If the atomic ratio of the N source gas to the reaction system is less than 0.1% with respect to the hydrocarbon gas (C source gas), the reaction will be too slow, and if it exceeds 10%, the resulting diamond will be incomplete. Is not preferred. The hydrogen gas is preferably used in an amount of 50 to 99% in terms of atomic ratio with respect to the whole gas of the reaction system, so that good results can be obtained.

As means for exciting and decomposing the raw material gas, a hot filament is used at a temperature of 1600 to 2800 ° C.

The present invention will be described in detail in the following embodiments with reference to the drawings.

〔Example〕

REFERENCE EXAMPLE 1 As shown in FIG. 1, a 2.45 GHz microwave plasma CVD apparatus comprising a quartz reaction tube 1, an oscillation device 2, a waveguide 3, and an electrode 4 was used as a reference example of the present invention. Lumber 5
Was coated with a nitrogen-containing diamond coating by a plasma CVD method. H ₂ ^{99 CC} / min, CH ₄ ^{1 CC} / min,
N ₂ , O _2, or CF ₂ was introduced at 0.01 cc / min, plasma was generated at a microwave output of 300 W while maintaining the inside of the reaction tube 1 at 40 Torr, and coating was performed for 4 hours using a 10 mmφ Si wafer as a base material. Got it. Thereafter, the samples were removed, using an ion micro Mana riser, where the analysis of the components other than carbon in the coated film formed was row summer, when the addition of N ₂ is nitrogen of 1080ppm in the film O ₂ and F detected
_{Even when 2} was added, all components other than nitrogen were detected at only 10 ppm or less. From the above experiment, it was confirmed that nitrogen could be successfully replaced with carbon.

Reference Example 2 A 10 mmφ Si wafer was set in the same microwave plasma CVD apparatus of FIG. 1 as in Reference Example 1, and H ₂ 99 c.c./min, CH ₄
0.99cc / min, the N ₂ 0.01 cc / min was introduced into the apparatus,
The inside of the apparatus was maintained at 80 Torr, plasma was generated at a microwave output of 500 W, and a coating was deposited on the surface of the Si wafer. After coating was continued for 100 hours in this state, a sample was taken out.

When the sample was examined by X-ray diffraction and Raman spectroscopy, it could be identified as diamond with extremely high perfection. Examination with a scanning electron microscope revealed that the diamond film with good self-shape was uniformly coated on the Si wafer with a thickness of about 250 μm. Next, this sample was analyzed with an ion microanalyzer.
% Nitrogen was confirmed to be contained.

Reference Example 3 In Reference Example 1, diamond coating was performed under the same conditions except that H _{2 was} 99 c.c./min and CH _{4 1} c.c./min. The coating was stopped because large peeling was observed in the film.

Examination of the obtained sample by X-ray diffraction and Raman spectroscopy revealed that a large amount of carbon other than diamond was contained in the film, and that the crystallinity was extremely poor. In addition, it was found that the coating film was completely peeled off from the base material when viewed with a scanning microscope.

Example 1 Diamond coating was performed according to the present invention by using a thermal CVD apparatus provided with a metal filament 6 such as Ta or W as shown in FIG. A 10 mmφ Si wafer is set as a base material 5 in a thermal CVD apparatus using a Ta filament as a metal filament 6, and the surface temperature is set to 950.
° C, while using H ₂ , CH ₄ , NH ₃ gas as the source gas
H ₂ / CH ₄ = 94/3 and total gas flow rate 1000c.c./min 10
Introduced into the apparatus at Torr, the Ta filament was heated to 2200 ° C.
Up to time, a coating was formed on the Si wafer surface.

Table 1 shows the nitrogen content in the obtained film and the coating time until the film was separated.

The results in Table 1 show that the nitrogen content in diamond is preferably in the range of 0.001% (10 ppm) or more and 2% or less in the present invention.

〔The invention's effect〕

The nitrogen-containing hard carbon film according to the present invention is a diamond film containing nitrogen, whereby the internal compressive stress in the film can be relieved, and is produced as a coating film deposited from the gas phase on the substrate surface. In doing so, there is an effect that a film thicker than before can be coated without peeling.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a first embodiment of the present invention, showing a microwave plasma method. FIG. 2 is a schematic view for explaining an embodiment of the present invention, showing a thermal CVD method.

Claims (1)

(57) [Claims] (1) Decomposing a raw material gas with a metal filament at 1600 to 2800 ° C. so that nitrogen is at least 10 ppm by atomic ratio.
% By depositing a hard carbon film having a content of not more than 0.1% on the surface of the base material and coating the same.