JP4851376B2 - Pretreatment method of conductive substrate used for synthesis of diamond film and method of manufacturing diamond film - Google Patents

Description

The present invention relates to a pretreatment method for a conductive substrate used for synthesis of a diamond film and a method for producing the diamond film.

As the pretreatment of the substrate used for the synthesis of the diamond film, (1) the substrate is immersed in a liquid in which abrasive particles are dispersed and ultrasonic waves are applied (see Patent Documents 1 and 2), (2) the surface of the substrate is Polishing with abrasive powder (see Patent Documents 3 and 4), (3) performing electrolytic treatment (see Patent Documents 5 to 8), and the like are known. By these pretreatments, nuclei that serve as starting points for the growth of the diamond film are formed on the surface of the substrate.
JP 61-121859 A JP-A-62-226889 JP 62-108798 A JP 62-108799 A Japanese Patent No. 2616255 Japanese Patent No. 2720384 Japanese Patent No. 2766686 Japanese Patent No. 2794601

However, in the above method (1), a long period of ultrasonic treatment is required in order to form a flaw as a growth nucleus on the surface of the substrate. For example, in Patent Document 2, ultrasonic treatment for 1 hour is required. Further, when the substrate is hard, scratches that become growth nuclei are difficult to be formed. Further, since uneven polishing is likely to occur, non-uniformity occurs in the state of the diamond film formed thereafter.
The method (2) cannot be performed unless the substrate is a flat plate. Moreover, in order to make a fine flaw, it is necessary to use a fine polishing powder, so that a long time is required for polishing. Further, when large particles are mixed in the polishing powder, deep scratches are formed on the surface of the substrate, and the diamond film after film formation also reflects this shape.
In the method (3), nuclei cannot be sufficiently formed on the surface of the substrate.

  The present invention has been made in view of the above points, and provides a pretreatment method and a diamond film manufacturing method that can be easily performed and can form a good diamond film regardless of the hardness and shape of the substrate. For the purpose.

(1) The invention of claim 1
A pretreatment method of a conductive substrate used for synthesis of a diamond film,
The gist is a pretreatment method characterized by immersing the conductive substrate in an electrolyte solution in which fine particles are suspended and performing electrolytic treatment by alternating current electrolysis .

  By performing the pretreatment method of the present invention, a large number of fine scratches and pits can be formed on the surface of the conductive substrate, and a large number of fine particles can be firmly held on the surface of the conductive substrate. These scratches, pits, and fine particles function as a growth nucleus of the diamond film.

According to the pretreatment method of the present invention, a conductive substrate preferable for the growth of a diamond film can be formed very easily and in a short time. In addition, since the number of scratches, pits and fine particles that become the growth nucleus of the diamond film increases, the anchor effect is high, and the adhesion between the diamond film and the conductive substrate can be improved. Furthermore, the above effects can be achieved regardless of the hardness and shape of the conductive substrate.
The reason why the pretreatment method of the present invention has the above-mentioned effect is not clear, but one reason is presumed as follows. That is, when electrolytic treatment is performed in the pretreatment method of the present invention, an electrochemical reaction occurs on the surface of the electrode to generate hydrogen or oxygen, which are observed as fine bubbles. When the conductive substrate is an anode, the components of the conductive substrate are also eluted. Bubbles generated from the surface cause convection in the solution, and the fine particles collide with the surface of the conductive substrate along the convection. Alternatively, a large kinetic energy is generated when the bubble bursts, and the fine particles collide with the surface of the conductive substrate. Thereby, the fine particles are fixed on the surface of the conductive substrate, and further fine scratches and pits are formed on the surface of the conductive substrate.
This is supported by the following facts. That is, as in Comparative Example 1 to be described later, even if the conductive substrate is electrolyzed in NaOH that does not contain diamond fine particles, fine scratches and pits after performing the pretreatment method of the present invention are not detected. When the conductive substrate is an anode, it is dissolved so that the surface becomes smoother. This is because scratches and pits formed on the surface of the conductive substrate after the pretreatment method of the present invention are not caused only by bubbles generated by electrolysis, and the presence of fine particles is essential. Indicates that
The pretreatment refers to a treatment for making the surface of the conductive substrate suitable for the formation of the diamond film before forming the diamond film on the surface of the conductive substrate.

  The material of the conductive substrate is not particularly limited as long as it is a solid with conductivity, and may be a hard material. For example, tungsten, platinum, molybdenum, niobium, tantalum, titanium, glassy carbon, silicon (having conductivity by doping with antimony or the like), and the like can be given. The shape of the conductive substrate is not particularly limited, and examples thereof include a linear shape and a flat plate shape. In the case of a linear conductive substrate, by performing the pretreatment method of the present invention, it is possible to make the surface state suitable for forming a diamond film and sharpen the shape of its end. it can.

As the fine particles, those made of a material having high hardness (so-called super hard fine particles) are preferable, and those having a higher hardness than the conductive substrate are particularly preferable. By doing so, an effect can be obtained in which the fine particles are likely to sink into the surface of the substrate and be fixed. Examples of the fine particle material include diamond, SiC, Si ₃ N ₄ , Mo, Al ₂ O ₃ , AlN, and WC. In particular, fine particles made of diamond are preferable because the quality of the diamond film can be further improved. This is presumably because the affinity of the diamond film is improved when the fine particles held on the conductive substrate and the diamond film are the same substance. The particle diameter of the fine particles is preferably 40 μm or less. By being 40 μm or less, the fine particles do not sink in the electrolyte solution. In addition, the particle diameter here is a value measured by a method such as a dynamic light scattering method, a laser diffraction scattering method, or an image processing method.

As the electrolyte solution, any liquid having conductivity can be used without any particular limitation. The liquidity of the electrolyte solution may be any of alkaline, neutral, and acidic, but it is desirable to select appropriately in consideration of the characteristics of the conductive substrate. Specific examples of the electrolyte solution include aqueous solutions such as NaOH, Na ₂ SO ₄ , and H ₂ SO ₄ . The concentration of the electrolyte in these aqueous solutions is preferably in the range of 0.01 to 5M.

The electrolysis treatment, the use of ac electrolysis, even many particles fixed to the surface of the conductive substrate, also, it is possible to form a more many fine scratches and pits, for deposition of diamond film More preferable.
The reason is presumed as follows. That is, by alternating current in alternating current electrolysis, oxygen generation and hydrogen generation occur alternately on the surface of the conductive substrate, and the generated bubbles become very fine. The convection form is also very complicated, whereby the number of fine particles that collide with the surface of the conductive substrate increases, more fine particles are fixed, and fine scratches and pits are formed.

  In addition, when alternating current electrolysis is used, the currents are switched alternately, so there is no distinction between the anode side and the cathode side of the electrodes, and it can be considered that the same reaction occurs between the two electrodes. It can be set as a conductive substrate. Therefore, two conductive substrates can be pretreated at the same time.

  After performing the pretreatment method described above, a diamond film can be synthesized on the surface of the conductive substrate. By doing so, a dense diamond film having a good crystal structure can be easily and quickly manufactured regardless of the hardness and shape of the conductive substrate. As a method for synthesizing the diamond film, known methods can be widely used. For example, a microwave plasma CVD method, a hot filament CVD method, or the like can be used.

  The time for the electrolytic treatment is preferably in the range of 10 seconds to 10 minutes. In addition, the temperature of the electrolyte solution in which the fine particles are suspended is preferably in the range of 10 to 60 ° C. during the electrolytic treatment.

The present invention will be specifically described based on examples.
1. Configuration of Electrolytic Treatment Cell 1 As shown in FIG. 1, the electrolytic treatment cell 1 includes a power source 3 for flowing an AC or DC current, a lead wire 7 connecting the power source 3 and the substrate 5, and a pretreatment described later. It consists of a carbon crucible 9 which is a container for the liquid 13, a lead wire 11 connecting the power source 3 and the crucible 9, and a pretreatment liquid 13 accommodated in the crucible 9. In the electrolytic processing cell 1, the crucible 9 functions as a counter electrode. In addition, as a container for the pretreatment liquid 11, a container made of a non-conductive material such as a beaker may be used instead of the crucible 9, and a counter electrode may be separately inserted therein.

2. Pretreatment Method Using Electrolytic Treatment Cell 1 As shown in FIG. 1, a lead wire 11 is connected to a base 5 and the base 5 is immersed in a pretreatment liquid 13. The material and shape of the base 5 will be described later. The pretreatment liquid 13 is obtained by suspending fine particles in an electrolyte solution containing an electrolyte at a concentration of 1 M, and the amount of fine particles is 0.25 to 0.35 g per 100 ml of the electrolyte solution. Details of the fine particles and the electrolyte solution will be described later. The temperature of the pretreatment liquid 13 is set to 30 ° C. during the entire pretreatment period.

  Next, the power source 3 is used to energize the base 5 and the crucible 9 to perform electrolytic treatment. The energization was performed in each case of alternating current and direct current. The energization conditions in the case of AC are a voltage of 10 V, a frequency of 60 Hz, and an energization time of 1 minute, and the energization conditions in the case of DC are a voltage of 12 V and an energization time of 30 seconds.

The current conditions (direct current / alternating current), the material of fine particles, the fine particle diameter, the composition of the electrolyte solution, and the shape and material of the substrate 5 are as shown in Table 1, and the pretreatments of Examples 1 , 3 to 18 and Reference Example 2 were performed. went.

In the column of the base material in Table 1, W represents tungsten having a purity of 99.95%, Pt represents platinum having a purity of 99.98%, Mo represents molybdenum having a purity of 99.95%, and Nb represents Ni represents 99.9% purity, Ta represents 99.95% purity tantalum, Ti represents 99.5% purity titanium, GC represents glassy carbon, Si represents n-type, antimony doped, resistance It represents silicon with a rate of 0.018 Ωcm or less.

  In the column of the shape of the substrate in Table 1, “line” represents a line shape having a diameter of 0.3 mm and a length of 2 cm, and “plate” represents a rectangular shape having a size of 2 cm × 0.5 cm. In addition, the particle size of the fine particles in Table 1 is a value described in the catalog.

When the surface of the substrate 5 was observed with an electron microscope after the pretreatment of Example 1, the surface morphology as shown in FIG. 2 was obtained. That is, many fine scratches and pits were formed on the surface, and diamond fine particles held on the surface were observed as white spots. The diameter of the fine particles was 100 nm or less, and the number thereof was 4.4 × 10 ⁸ particles / m ² . The number of fine particles is four times the number in Comparative Example 8 described later. A particle size of 100 nm or less is an ideal size for forming a diamond film. Furthermore, since a lot of fine scratches and pits are formed on the surface, it can be seen that the number of parts that become the core of the growth of the diamond film is considerably increased as a whole.

3. Pretreatment Method of Comparative Example As a pretreatment of Comparative Examples 1 to 7, a pretreatment was performed using an electrolyte solution containing no fine particles instead of the pretreatment liquid 13. The processing conditions are shown in Table 1 above.

  Further, as a pretreatment of Comparative Example 8, the same tungsten wire as that used in Example 1 was subjected to ultrasonic treatment for 30 minutes in an ethanol solution containing diamond fine particles. The kind of diamond fine particles and the amount of fine particles with respect to ethanol were the same as in Example 1.

When the surface of the substrate 5 was observed with an electron microscope after the pretreatment of Comparative Example 1, the surface morphology as shown in FIG. 3 was obtained. This surface form is smooth compared with the case of Example 1 (FIG. 2), and the foreign material is not hold | maintained on the surface.
Further, when the surface of the substrate 5 was observed with an electron microscope after performing the pretreatment of Comparative Example 8, a surface form as shown in FIG. 4 was obtained. That is, the surface form was smooth with no fine scratches or pits compared to the case of Example 1 (FIG. 2). Further, the number of diamond fine particles (observed as white dots) held on the surface of the substrate 5 is 1.1 × 10 ⁸ particles / m ^2, which is only about ¼ of the case of Example 1. There wasn't. Further, the diameter of the fine particles was 300 nm or less, which was much larger than that in Example 1.
As described above, in Comparative Example 8, there are no fine scratches or pits and the number of retained diamond fine particles is small because fine particles suspended in ethanol have sufficient kinetic energy in ultrasonic vibration. It is thought that this is because it has not. In other words, the kinetic energy of the object (mass) × (speed) because it is the amount determined by the ^2/2, even without being immobilized by colliding with the Never particles surface to obtain a fast enough by sonication Bounced back.

4). Formation of Diamond Film After the pretreatment of each example and each comparative example, the substrate 5 was taken out from the electrolytic processing cell 1 and introduced into a microwave plasma CVD apparatus, and a diamond film was formed under the following conditions.

Microwave frequency: 2.45 GHz
Microwave output: 8kW
Pressure in the chamber: 90 Torr
Gas flow rate: 500sccm
4. Diamond film formation time: 2 hours Evaluation of Diamond Film After the completion of the diamond film formation, the surface state of the diamond film formed on the substrate 5 was observed with an electron microscope. The diamond film was evaluated according to the following criteria.

◎: Very dense film without pinholes ○: Very dense, but partially (1% or less of the total area) pinholes △: Pinholes to some extent (1-20% of the total area) Film with x: Diamond does not form a film but exists as particles or hardly grows. The results are shown in Table 1 above.

As is clear from Table 1, the evaluation results for each of the examples that were pretreated in each Example were Δ to ◎. In particular, the surface condition of the diamond film was better in the case where the electrolytic condition was alternating current (Example 1) than in the case where the electrolytic condition was direct current ( Reference Example 2). In addition, the material of the base 5 made of W, Nb, and Ta (Examples 1, 5, and 6) is a diamond film than the material of the base 5 made of other materials (Examples 3 to 4, and 7). The surface condition was even better. In addition, when the material of the fine particles is diamond (Example 1), the material of the fine particles is SiC, Mo, AlO _3.
The surface condition of the diamond film was better than those of AlN and WC (Examples 10 to 14). Further, regarding the particle size of the fine particles, the surface condition of the diamond film was good in any case of 0.5 μm or less, 0.5 to 1 μm, and 30 to 40 μm (Examples 1, 15 to 16). It was. Moreover, the type of the electrolyte solution is an aqueous solution of NaOH and Na ₂ SO ₄ (Examples 1 and 17), and the case where the electrolyte solution is an aqueous solution of H ₂ SO ₄ (Example 18) is higher than that of the diamond film. The surface condition was even better.

Moreover, as is clear from Table 1, all of the samples subjected to the pretreatment in Comparative Examples 1 to 5 were x.
In Examples 8 to 9 and Comparative Examples 6 to 7, the film could not be formed by the microwave plasma CVD method due to the problem of the material of the substrate 5 itself. It has been reported that the hot filament CVD method can form a film on the substrate 5 made of these materials.

  The surface state of the diamond film formed after the pretreatment of Example 1 is shown in FIG. As can be seen from FIG. 5, a very good film is formed. On the other hand, the surface state of the diamond film formed after the pretreatment of Comparative Example 1 is shown in FIG. As is apparent from FIG. 6, no diamond film is formed.

2 is an explanatory diagram showing a configuration of an electrolytic treatment cell 1. FIG. It is an electron micrograph showing the surface form of substrate 5 after pretreatment. It is an electron micrograph showing the surface form of substrate 5 after pretreatment. It is an electron micrograph showing the surface form of substrate 5 after pretreatment. It is an electron micrograph showing the surface form of a diamond film. It is an electron micrograph showing the surface form of a diamond film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolytic processing cell 3 ... Power supply 5 ... Base | substrate 7, 11 ... Lead wire 9 ... Crucible 13 ... Pre-processing liquid

Claims (5)

A pretreatment method of a conductive substrate used for synthesis of a diamond film,
A pretreatment method comprising immersing the conductive substrate in an electrolyte solution in which fine particles are suspended and performing electrolytic treatment by alternating current electrolysis .   The pretreatment method according to claim 1, wherein the hardness of the fine particles is higher than the hardness of the conductive substrate.   The pretreatment method according to claim 1, wherein a particle diameter of the fine particles is 40 μm or less.   The pretreatment method according to claim 1, wherein the fine particles are made of diamond. The method according to the performing pre-processing method according to any one of Items 1-4, the diamond film to synthesize a diamond film on the surface of the conductive substrate.