JPH08319568A - Production of hard nitrogen-containing carbon film - Google Patents

Abstract

PURPOSE: To produce an ultrahard nitrogen-contg. carbon film by regulating a gaseous atmosphere contg. carbon and nitrogen to a specified vacuum degree and exciting it into a plasma state by using resonance between an electromagnetic wave of specified frequency and a magnetic field having specified intensity. CONSTITUTION: The atmosphere of a plasma chamber 1 is held to a vacuum degree of <=10<-2> Pa. A reactive gas 7 contg. carbon and nitrogen is fed to the plasma chamber 1. By using resonance between an electromagnetic wave 9 having >=10GHz frequency add a magnetic field having >=500G intensity generated by a coil 8, the reactive gas 7 is excited into a plasma shape. The obtd. plasma 11 of carbon ions and nitrogen ions is accelerated by a D.C. bias power source 12 of 20 to 500 electrons V and is applied to a substrate 3. As the reactive gas 7, a gas of carbon-base materials such as CH4 , C2 H6 , CH3 OH, C2 H5 OH, CO, CO2 or C2 H4 or nitrogen-base materials such as N2 , NH, or the like as simple body or that of their combination of several kinds is preferably used. An ultrahard thin film having 12,500 Knoop hardness can be formed.

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 hard nitrogen-containing carbon thin film on the surface of a substrate.

The sample obtained using the technique of the present invention is expected to be an effective hard coating material by itself, and also a starting material for synthesizing crystalline β-type C ₃ N _4. It

[0003]

2. Description of the Related Art The technique of providing a hard protective film on the surface of various substrates is intended for TiC or TiN thin films, hard carbon thin films, boron nitride thin films, etc., for enhancing the cutting ability of cutting tools and magnetic properties. Many film forming techniques have been developed for various purposes such as surface protection of recording media. Those techniques are publicly known, and examples thereof include a vapor deposition method, a sputtering method, and various CVD methods using heat and plasma.

The undeveloped crystalline substance β-type C ₃ N ₄ has recently attracted a great deal of attention as a next-generation substance for such superhard materials. This was proposed by the group of Liu et al. In 1989 from the result of computer simulation.
β-type C ₃ N ₄ has a structure in which Si of β-type Si ₃ N ₄ which is a known substance is replaced with C. They are the β-type C ₃ N ₄
It was reported that the bulk modulus was calculated using a semi-empirical model and was comparable to that of single crystal diamond. Here, the bulk modulus is known as a value that serves as a measure of the hardness of the substance, and it is considered that the numerical value changes depending on the treatment during substance synthesis.

Therefore, the β-type C ₃ N ₄ may appear as a substance harder than diamond.

At the same time, many researchers have found that the β-type C ₃
It is predicted that the electrical properties of N ₄ will be characterized by having a wide bandgap. These predictions make people expect that the β-type C ₃ N ₄ will play an important role in the coming era of diamond devices.

Based on this proposal, many researchers have attempted to artificially synthesize the β-type C ₃ N ₄ bulk body or thin film body, but as is well known, the success of the definite crystal body has been successful. Not reported.

On the other hand, in the field of thin film synthesis, attempts have been made to add nitrogen to an amorphous carbon thin film material, or to form a compound of nitrogen and carbon which does not exhibit crystallinity. For example, there have been reported examples of a sputtering method in which a sputtering gas is nitrogen with graphite as a target, and an ion beam evaporation method in which a nitrogen ion beam is irradiated during carbon deposition.

Attempts to form such an amorphous and hard nitrogen-containing carbon thin film have been made for three reasons. One is that the obtained hard nitrogen-containing carbon film sample is predicted to be very effective as a starting material for synthesizing the β-type C ₃ N ₄ .

Another reason is that the bond energy of the double and triple bond of C and N, which is expected to be formed in the film by introducing nitrogen, is the bond energy of the C—C bond (sp ³ hybrid orbital) of diamond. Sometimes it exceeds. The β
All bonds of type C ₃ N ₄ are predicted to be composed of a single bond of C and N. Therefore, this fact shows the possibility of realizing the formation of a hard nitrogen-containing carbon thin film other than the formation of the crystal structure. And, another one is that the bond length of the double bond of C and N is the above-mentioned CC bond (sp ³
It is shorter than the bond length of the hybrid orbital).

[0011] In general hard carbon thin film (so-called diamond-like carbon: DLC film) on one of the causes compressive stress within the film is accumulated, the carbon bond during the growth reaction of the film, sp ³ from sp ² hybrid orbital It has been pointed out that the bond length increases when changing to a hybrid orbit. Based on this example, it is highly likely that introducing nitrogen into the DLC thin film is very effective when a thin film having low internal stress and high hardness is to be formed.

Until now, many researchers who have been involved in research on DLC thin films have manufactured such hard amorphous carbon thin films by a plasma CVD method or a sputtering method using a radio frequency of 13.56 MHz. Are trying. As a result, we reported that the introduction of nitrogen reduced the internal stress. However, no successful case has been reported regarding the effect of hardening. Therefore, in order to realize the increase in hardness based on the addition of nitrogen, it is necessary to introduce a manufacturing means based on a concept different from the conventional one.

The inventors of the present invention have hitherto developed an industrial frequency of 2.4.
An attempt was made to synthesize a DLC thin film using so-called ECR plasma CVD that utilizes the resonance phenomenon between a microwave of 5 GHz and a magnetic field of intensity 875 G, and a carbon ion was applied to the substrate surface by applying a bias voltage between the plasma and the substrate. It has been confirmed that irradiating with is effective for hardening the film and improving the growth rate.

By applying the combination of the ECR plasma CVD apparatus and the bias voltage application technique, it was possible to manufacture a hard carbon film containing nitrogen, and an experiment was tried. It was revealed that an ultra-hard thin film containing nitrogen and having a film hardness of 10,000 or more can be obtained by a Knoop indenter, and the present invention was completed. Needless to say, the above nitrogen concentration is much lower than that of a hypothetical β-type C ₃ N ₄ crystal.

[0015]

The gist of the present invention will be described with reference to the accompanying drawings.

In a gas atmosphere containing carbon and nitrogen, 1
On the surface of a substrate installed in a vacuum container maintained at a vacuum degree of 0 ^-2 Pa or less, a gas atmosphere is brought into a plasma state by using resonance of electromagnetic waves with a frequency of 10 GHz or more and a magnetic field of 500 G or more. A hard nitrogen containing a carbon thin film containing nitrogen on the surface of the substrate to form a carbon thin film having a high hardness by accelerating and irradiating a carbon ion and a nitrogen ion obtained by excitation in the direction of the substrate by an electric field. The present invention relates to a method for manufacturing a carbon film containing carbon.

The electric field for accelerating carbon ions and nitrogen ions according to claim 1 is 20 to 500 electron V, and relates to a method for producing a hard nitrogen-containing carbon film.

The gas atmosphere containing carbon and nitrogen according to claim 1 is CH ₄ , C ₂ H ₆ , CH ₃ OH, C ₂ H ₅ O.
A carbon-based raw material typified by H, CO, CO ₂ or C ₂ H ₄ and a nitrogen-based raw material typified by N ₂ or NH ₃ are formed by a single gas or a combination of several gases. The present invention relates to a method for producing a hard nitrogen-containing carbon film.

The gas atmosphere containing carbon and nitrogen according to claim 1 is CH ₃ NH ₂ , (CH ₃ ) ₃ N or CH.
_{The present} invention relates to a method for producing a hard nitrogen-containing carbon film, characterized in that a nitrogen-containing organic compound typified by ₃ CN or the like is used alone or in combination as a gas.

[0020]

EXAMPLES Examples of the present invention will be described in detail below.

In this example, the method of the present invention was used to produce Si.
An attempt was made to form a hard nitrogen-containing carbon thin film on the (100) surface of a single crystal substrate. FIG. 1 shows a schematic diagram of the ECR plasma CVD apparatus used for production in this example. In the reaction chamber 2 below the plasma chamber 1, the sample substrate 3 is set on the sample stage 4, and after the reaction chamber 2 is closed, the rotary chamber 5 and the turbo molecular pump 6 are used to set the reaction chamber 2 and the plasma chamber 1 to 10
^-6 Evacuate to a high vacuum degree on a Torr table.

There is no particular limitation on the type of the sample substrate 3 installed inside. As described above, in this embodiment, S which is widely distributed in the field of semiconductors is used.
An i single crystal (100) plane substrate having a thickness of 0.5 to 0.7 mm was used. In addition, a material used in the field of hard materials such as a WC sintered body, a sintered body of silicon nitride or silicon carbide may be used. Further, an intermediate layer may be provided on the surface for film formation. In the case of a carbon-based thin film material like the present invention,
It is also effective to provide a crystalline or amorphous carbon film.
Further, a nitrided base material thin film, here, a crystalline or amorphous SiN thin film may be provided.

At this time, the sample is heated by an electric heater provided on the back surface of the sample stage 4. The heating temperature can be set widely depending on the gas flow rate and reaction pressure. However, in this example, an electric heater with a maximum setting of 400 ° C. was used, and the setting was 200 ° C.

When the degree of vacuum reaches a predetermined value, the reaction gas 7
Is introduced into the plasma chamber 1.

In this embodiment, the reaction gas is CH ₄ , H ₂ , N ₂
Were mixed at flow rates of 30 cc / min, 30 cc / min, and 20 cc / min, respectively. A wide range of raw materials containing carbon and nitrogen can be selected as the raw material gas.

The addition of H _{2 in} this example is expected from the results of the DLC film synthesizing experiments by the present inventors up to the effect of etching away the fragile bond. .

It is known that the addition of Ar or the like also has the effect of exciting other gases in plasma, and is considered to be an effective method.

With respect to the source gases other than H ₂ , if carbon and nitrogen are contained, no particular limitation is imposed. For example, as an example other than the examples, C
₂ H ₆ , CH ₃ OH, C ₂ H ₅ OH, CO, CO ₂ or C
A carbon-based raw material represented by ₂ H ₄ or the like and a nitrogen-based raw material represented by NH ₃ or the like can be used alone or in combination.

Further, nitrogen-containing organic compounds represented by CH ₃ NH ₂ , (CH ₃ ) ₃ N, CH ₃ CN, etc. may be used alone or in combination as a gas.

The reaction chamber 2 into which the reaction gas 7 is introduced is 6.
The pressure is increased to 2 × 10 ^-4 Torr. For this pressure increase, there are a method of adjusting the conductance on the exhaust side and a method of adjusting the total flow rate of the reaction gas. The pressure in the reaction chamber 2 that has been increased at this time is maintained even at the time of the film formation reaction.

The set value of the reaction pressure is determined by the size of the reaction chamber 2 and the like. The reaction pressure changes the so-called mean free path. The mean free path is the distance that molecules and / or active species can move without collision in the space. For example, it is said that the mean free path of nitrogen molecules at the set pressure of this embodiment is about 50 cm. On the other hand, when the pressure is increased to the level of 10 ^-3 Torr, the value is about 5
down to cm. In the apparatus of this embodiment, the distance between the plasma chamber 1 and the sample stage 4 is about 30 cm, and theoretically, the active species in the plasma can reach the surfaces of the sample stage 4 and the sample substrate 3 without collision. Therefore, if the sample substrate 3 and the plasma chamber 1 are closer to each other in the positional relationship, the film can be formed at a higher pressure.

When the predetermined pressure is reached, a magnetic field of 875 G is applied from the coil 8 installed around the plasma chamber 1, and a microwave 9 of 2.45 GHz is introduced from the upper part of the plasma chamber 1. The required effective electric power of the microwave varies depending on the dissociation energy and the excitation energy of the raw material used, and therefore cannot be clearly defined in this specification. For example, in the case of this embodiment, a power supply device having a maximum output of 600 W was used and the input power was 200 W.

When a stable discharge can be confirmed inside the plasma chamber 1, the shutter 10 provided between the plasma chamber 1 and the reaction chamber 2 is opened and the surface of the sample substrate 3 is irradiated with the plasma 11. Immediately after the irradiation is started, a DC bias power supply 12 applies a bias voltage for accelerating ions between the sample stage 4 and the plasma 11. In the present embodiment, this was not taken into consideration in order to form a relatively thin film, but since the formed thin film has an insulating property, the bias to be applied is a radio wave (for example, an industrial frequency of 13.56 MHz). It is very effective.

In this embodiment, the bias voltage is 0 to 400.
V and varied. To show that the method of the present invention is effective in forming ultra-hard thin film materials, the effect of bias voltage on film hardness was investigated.

In this embodiment, the hardness of 0.8 to 0.8 is measured for hardness measurement.
A film thickness of 1 μm is required. Preliminary experiments were conducted and it was found that the growth rate of the film varied depending on the bias voltage, so the film formation time was set to 1 to 3 hours. After the required time has passed, the bias voltage is set to 0 V and the shutter 10
Then, microwave input was stopped immediately and the magnetic field application was stopped. After closing all the introduced gas lines, the plasma chamber 1 and the reaction chamber 2 were initially vacuumed at 10 ⁻⁶ To.
The pressure was reduced to the rr level. The substrate heating is stopped here, and 100
After waiting for the substrate stage to cool to ˜150 ° C., the reaction chamber 2 was opened and the sample substrate 3 was taken out.

The Knoop hardness of the surface of the obtained thin film was measured. Fig. 2 is a graph showing the change in hardness depending on the bias voltage.
Shown in For comparison, the hardness of the hard carbon film (so-called DLC) measured by the inventors is also shown. Clearly D
Hardness significantly higher than LC was obtained, and among them, the sample obtained at a bias voltage of 300 V had a Knoop hardness of 125.
It was found to be a super-hard thin film of 00.

[0037]

As described above, the present invention has an effect of facilitating the formation of an ultra-hard thin film, which has never been seen before, such as a Knoop hardness of 12,500 which greatly exceeds DLC.

According to the present invention, it is highly expected that the surface treatment technology for various protective films and tool materials will be further developed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an ECR plasma CVD apparatus of this embodiment.

FIG. 2 is a graph showing a change in hardness according to a bias voltage of this example.

[Explanation of symbols]

 1 plasma chamber 2 reaction chamber 3 sample substrate 4 sample stage 5 rotary pump 6 turbo molecular pump 7 reaction gas 8 coil 9 microwave 10 shutter 11 plasma 12 DC bias power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Inoue 6-817 Shimoyama, Nagaoka City, Niigata Prefecture 102 Kaai Heights 102 (72) Inventor Fujio Shioya 7-15-5 Ginza, Chuo-ku, Tokyo Tokki Corporation ( 72) Inventor Yuji Yanagi Tokki Co., Ltd. 7-15-5 Ginza, Chuo-ku, Tokyo

Claims (4)

[Claims] 1. In a gas atmosphere containing carbon and nitrogen,
On the surface of a substrate installed in a vacuum container maintained at a vacuum degree of 10 ^-2 Pa or less, a gas atmosphere is made into a plasma state by using resonance of electromagnetic waves with a frequency of 10 GHz or more and a magnetic field of 500 G or more. A hard nitrogen containing a carbon thin film containing nitrogen on the surface of the substrate to form a carbon thin film having a high hardness by accelerating and irradiating a carbon ion and a nitrogen ion obtained by excitation in the direction of the substrate by an electric field. Method for producing carbon film containing carbon. 2. A method for producing a hard nitrogen-containing carbon film, wherein the electric field for accelerating the carbon ions and the nitrogen ions according to claim 1 is 20 to 500 electrons V. 3. The gas atmosphere containing carbon and nitrogen according to claim 1 is CH ₄ , C ₂ H ₆ , CH ₃ OH, C ₂ H ₅ OH, C.
A hard material characterized by being formed by a gas in which a carbon-based raw material typified by O, CO ₂ or C ₂ H ₄ and a nitrogen-based raw material typified by N ₂ or NH ₃ or the like are used individually or in combination. Method for producing nitrogen-containing carbon film. 4. The gas atmosphere containing carbon and nitrogen according to claim 1 is CH ₃ NH ₂ , (CH ₃ ) ₃ N or CH ₃ C.
A method for producing a hard nitrogen-containing carbon film, characterized in that a nitrogen-containing organic compound represented by N or the like is used alone or in combination as a gas.