JPS62256796A - Production of diamond - Google Patents

Abstract

PURPOSE:To produce the title diamond having excellent adhesive strength to a substrate by activating a gaseous mixture of hydrogen and hydrocarbons under specified conditions, and then depositing diamond on the heated surface of the substrate. CONSTITUTION:The gaseous mixture of hydrogen and hydrocarbons is supplied from a raw gas supply port 4 into a reaction vessel 1 kept at 0.01-100Torr. Capacity coupling power is supplied between a thermion emitting material 2 and the electrode in the reaction vessel 1 or the reaction vessel 1 itself (when the vessel is conductive) or an external electrode 5 provided on the outside of the reaction vessel 1 (when the vessel is insulating) by using the thermion emitting material 2 heated at >=1,600 deg.C and a high-frequency power source 7 to generate high-frequency plasma, hence the gaseous mixture is decomposed, excited, and activated, and diamond is deposited on the surface of the substrate 3 heated at 600-1,200 deg.C by an external heater 6.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an improvement in the low-pressure gas phase synthesis method for diamond. The present invention relates to a low-pressure vapor phase synthesis method for diamond, which is a method for synthesizing a diamond film and enables mass production on an industrial scale.

[Conventional technology]

゛Conventionally, diamond synthesis was carried out under high temperature and pressure.
Although the processing cost was high, in recent years a low-pressure vapor phase synthesis method has been developed that synthesizes diamond under low pressure without using ultra-high pressure.

Methods for vapor phase synthesis of diamond include ■ High-frequency plasma CVD method and microwave plasma CVD method that use plasma ■ Ionization vapor deposition method and ion beam deposition method that use ion particles ■ Thermionic emission CVD method that uses neutral particles etc. are known.

Among these methods, it is possible to synthesize a crystalline diamond film using the methods (1) and (2), and an amorphous diamond-like carbon film has been obtained using the method (2). Crystalline diamond film has extremely high hardness, so it can be used as a surface coating for wear-resistant parts, as a surface coating for cutting tools, and because of its high thermal conductivity, it can be used as a heat sink component for semiconductor devices. Since the gap is large, doping with impurities and applying it as a semiconductor device is also being actively investigated.

[Problem that the invention seeks to solve]

■High-frequency plasma CVD and microwave plasma CVD methods that use plasma have extremely low carbon content with structures other than diamond structure, and twin crystals, etc., compared to diamond films synthesized by thermionic emitter CVD method. It is possible to synthesize diamond with excellent crystallinity, which has almost no defects, and the physical properties of the diamond film,
For example, its electrical resistance and hardness exhibit higher values, and values closer to single-crystal diamond, which contains almost no impurities. In other words, regarding the film quality of diamond, thermionic emitting material C
Better quality can be obtained than by the VD method.

However, due to the unique properties of discharge plasma, the method of decomposing and exciting raw material gas using low-temperature plasma using electrical energy is affected by the shape of the base material, resulting in differences in the discharge state and the plasma not being uniform. The disadvantage is that it is not distributed.

For example, if the substrate has sharp edges, a strong discharge will occur at the tip, resulting in uneven plasma distribution.
The disadvantage is that uniform coating is difficult. Further, even if the shape of the substrate is complex or there are large irregularities, the plasma becomes unrestricted, making uniform coating impossible.

Furthermore, the method of activating source gas and synthesizing diamond using discharge plasma alone requires high plasma intensity, and in order to realize plasma with such high energy density, the reaction is perpendicular to the generally used waveguide. Microwave plasma CVD in which microwave plasma is formed in a reaction vessel inside a waveguide by penetrating the tube.
This is possible with an RF plasma CVD device that forms plasma by applying high-power radio frequency waves using an inductively coupled power supply method. The range in which these devices can synthesize diamonds is limited to a narrow range, which poses a major obstacle when considering upsizing and mass production on an industrial scale.

■Ionization vapor deposition methods and ion beam vapor deposition methods that use ion particles tend to produce diamond-like carbon with an amorphous structure, making it difficult to obtain diamonds with good crystallinity.

■Thermionic emitting material CVD method does not use plasma and is not affected by the shape of the base material, but the quality of the diamond film synthesized by the method described in
inferior to that of

Another drawback is that the reaction region in which diamond is precipitated is narrow. This is because the life of the reactive gas, which is decomposed and excited by the thermionic emitting material and is in an activated state, is short.

In order for diamond to precipitate on the base material, the reactive gas must reach the base material while maintaining its activated state.If the lifetime of the reactive gas in the activated state is short, the distance between the thermionic emitting material and the base material will increase. is inevitably limited, resulting in a narrow reaction area.

Therefore, it has been difficult to process large base materials or large quantities of base materials, which has been a major obstacle to industrial scale production.

As mentioned above, all of the current diamond coating processes have the disadvantage that it is difficult to expand the reaction area, and the diamond film quality is equivalent to or better than that produced by microwave plasma CVD, and the complex shape is formed in a wide reaction area. There has been a strong desire for a diamond coating process that can coat sharply shaped substrates with good coverage, uniform coating, and the ability to process a large amount of substrates at the same time.

[Means to solve the problem]

The present inventors carefully examined the characteristics of existing diamond coating processes, and aimed to create a diamond film with a complex shape or higher quality than that of a diamond film produced by the microwave plasma CVD method, which has the best film quality among existing processes. A new coating process that has a sharp shape that allows for good coverage of the substrate and enables uniform coating, a wide coating zone so that even large substrates can be treated, and a large amount of substrates that can be treated at the same time. In order to develop this, we conducted extensive research. As a result, in a diamond low-pressure vapor phase synthesis method in which a mixed gas of hydrogen and hydrocarbon is activated and diamond is precipitated on the surface of a substrate heated to 600°C or more and 1200°C or less, the activation of the raw material gas is
In addition to using a thermionic emitting material heated to 00°C or higher, a high-frequency power source is used to connect the thermionic emitting material to the reaction vessel (if the reaction vessel is conductive) or an external electrode placed outside the reaction vessel (if the reaction vessel is electrically conductive). In the case of a non-conductor), by performing a capacitively coupled power supply between the two and forming a high-frequency plasma between the two, activation by the thermionic emitting material and activation by forming a high-frequency plasma are combined. As a result, the diamond film, which has film quality equivalent to or better than diamond film produced by microwave plasma CVD and has excellent adhesion strength to the substrate, can be applied to large parts, complex shapes, and sharp shapes in a wide range of coating zones. It has been newly discovered that the coating has good coverage on the substrate, enables uniform coating, and can coat a large amount of substrates at the same time.

- The coating process according to the present invention can be said to be truly revolutionary as it solves the problems of the diamond coating process.

The details of why the diamond production method according to the present invention allows a diamond film with excellent crystallinity to be obtained in a wide reaction zone that contains almost no carbon with a structure other than diamond and has almost no defects such as twins is unknown. However, by using high-frequency discharge plasma in addition to the thermal decomposition of the raw material gas using a thermionic emitting material, the decomposition of the reactive gas and its activation through excitation are further promoted, and the energy possessed by the activated raw material gas is increased. It is thought that this is because the amount of gas becomes larger and the ratio of gas in the activated state increases, resulting in a longer life span.

For example, it is thought that the presence of abundant atomic hydrogen suppresses the precipitation of graphite and amorphous carbon, which have structures other than diamond.

The present invention is characterized by a method for forming high-frequency discharge plasma that is used in conjunction with the activation of source gas by a thermionic emitting material, and in that a capacitively coupled power supply method is used. The reason why a capacitively coupled power supply system is used is that, compared to an inductively coupled system, plasma can be stably formed in a significantly wider space, and a wider coating zone can be obtained.

However, in order to perform capacitively coupled power supply and form high-frequency discharge plasma in a wide space, it is necessary to
At a pressure of 100 Torr, it is difficult to start and maintain a discharge, but in the present invention, by using a thermionic emitting material in combination, the thermionic emitting material emits thermoelectrons, so even under such pressure, It is easy to start and maintain discharge, and it is possible to form discharge plasma stably. Furthermore, as in the present invention, by using the thermionic emitting material as one of two electrodes that load high frequency waves, the thermionic emitting material is subjected to a half cycle of high frequency negative potential and a half cycle of positive potential. In some cases, the current flowing into the electrodes varies significantly, and the intensity of the plasma varies greatly at minute intervals, forming what can be called a kind of intermittent plasma. Although the reason for this effect of intermittent plasma is not clear, it has the effect of crushing the precipitation of graphite and amorphous carbon, and it is thought that a high-quality diamond film can be obtained by the diamond synthesis method of the present invention.

Furthermore, in the present invention, activation of the raw material gas is performed by using both activation using a thermoelectric preforming C-φ member and activation using high-frequency discharge plasma. Compared to diamond synthesis methods such as plasma CVD and RF plasma CVD, the intensity of the plasma can be lowered by using thermionic emitting material, so it is possible to reduce the intensity of the plasma on the base material surface, which can be a problem when generating strong plasma. Non-uniformity caused by the shape of the base material of the generated plasma can be reduced, and even base materials with complex or sharp shapes can be coated uniformly.

In the present invention, the base material may be electrically connected to either of the two electrodes that apply high frequency, or it may be insulated from the two electrodes, but either of these cases is acceptable. do not have.

In the present invention, a diamond film of excellent film quality can be coated over a wide range of areas such as large parts, complex shapes, and sharp parts by using a combination of activation of the raw material gas using a thermionic emission material and activation by the formation of high-frequency discharge plasma. Although it is possible to uniformly coat a substrate having a shape, it is also possible to coat a substrate with
DC)? It has surprisingly been found that by applying a bias potential to the substrate using a tt source, the adhesion strength between the diamond film and the substrate is significantly improved.

Although the details are unknown as to why the adhesive strength between the diamond film and the substrate is significantly improved by applying a bias potential to the substrate using a DC (direct current) power source,
This is thought to be due to the formation of high-frequency discharge plasma, which ionizes the raw material gas, and the ions are preferentially attracted to the surface of the base material.

It is also believed that this is due to changes in the form of discharge plasma generated on the surface of the base material.

When applying a bias potential to a base material using a DC (direct current) power source, there are two cases in which the base material is electrically connected to one of the two electrodes that apply high frequency, and the other is insulated from the two electrodes. However, either case is acceptable.

;'t'':T □,''P However, when using a direct current (DC) power supply in order to apply a bias potential to the high frequency and the sample, a high frequency cutoff filter should be installed in the middle to prevent the high frequency from flowing into the DC power supply. must be entered.

In the present invention, the hydrocarbons that are the raw material gas include all hydrocarbons such as paraffin hydrocarbons such as methane, ethane, and propane, olefin hydrocarbons, acetylene hydrocarbons, diolefin hydrocarbons, and aromatic hydrocarbons. Applicable.

The ratio of N7 to the number of carbon atoms in the hydrocarbon is 0.0
If it is 1% or more and 20% or less, if it is less than 0.01%, the growth rate of diamond will be extremely low and it will be difficult to use it in practice, and if it is more than 20%, carbon will have a structure other than diamond. Precipitation of diamond increases, making it impossible to form a diamond film. In addition, the gases introduced into the reaction vessel are gases other than hydrogen and hydrocarbons that do not participate in the reaction and have low thermal conductivity such as Ar, r, Xe, and R.
LN2 may be mixed as a cooling gas. Regarding the material of thermionic emitting material, it has excellent thermionic emission ability,
Since it is required to have a low vapor pressure and a high melting point at high temperatures, high melting point metals such as W, Ta, Mo, La5g, graphite, etc. are preferable. Thermionic emitting material is 1
Use by heating to 600°C or higher. When the temperature is lower than this, precipitation of graphite and 111 regular carbon becomes dominant.

Diamond will not precipitate unless the surface temperature of the base material is 600°C or more and 1200°C or less. The pressure inside the reaction vessel is preferably 0.05 Torr or more and 100 Torr or less.

If it deviates from this range, it will be difficult to form diamonds, which is not preferable.

Also, the high frequency that is injected into the plasma formation space? The output of the Ii source is such that its power density is greater than 0.01w/c++1. Ow/
It is desirable that it be less than or equal to cffl.

In the plasma CVD method, the intensity of plasma depends on the gas atmosphere, the discharge type, the shape and structure of the discharge electrode, and the output of the plasma excitation power source. Among these, it is convenient to adjust the plasma intensity by changing the output of the excitation power source because it is easy to change the output of the excitation power source and the plasma intensity can be varied over a wide range. Since the plasma intensity varies depending on the device and the shape and structure of the discharge electrode differs even when the same output is applied, it is preferable to express the plasma intensity in terms of the power input from the excitation power source per unit volume of the plasma formation space. Power density is 0
．． This is because if it is smaller than O1w/cnl, the effect of improving the film quality of the coating film y· by the combined use of high frequency plasma according to the present invention will be small.

Moreover, if it is larger than 1. Ow/c++t, the ion sputtering phenomenon will adversely affect the coating process, and a high-output power source capable of inputting such a power density will be expensive, which is undesirable from an industrial standpoint.

Furthermore, it is desirable that the absolute value of the negative potential applied to the base material by the DC power source is 1ooov or less.

This is because if the absolute value of the negative potential is greater than 1000 V, abnormal discharge occurs locally and stable discharge cannot be maintained.

Next, the present invention provides a first example of a preferred apparatus for carrying out the invention.
Figures (a) and (b) and Figures 2 (a) and (a).

FIGS. 1(a) and 2(a) are top views, and FIGS. 1(a) and 2(b) are front views. Figure 1 (a), (b)
is equipped with a reaction vessel (insulator) and a cylindrical electrode 5 on the outside,
A capacitively coupled high frequency power supply is performed between the internal thermionic radiation material 2 and plasma is formed.

In addition, in FIGS. 2(a) and (b), the
Similarly, high-frequency plasma is formed between the cylindrical electrode 9 and the thermionic radiation material 2.

Furthermore, the shaft 11 is rotated by external power, and this power causes the base material 10 to rotate around its axis by the base material rotation mechanism 12. According to the present invention, in addition to activation of the raw material gas by the thermionic emitting material, high-frequency plasma is formed over a wide range by capacitively coupled power supply, so the diamond film has excellent coverage, but it is not suitable for the thermionic emitting material. Since the diamond coating is not uniform on the opposite side, for example, for a base material such as a drill, it is possible to uniformly apply diamond coating by rotating the sample around its axis.

The surfaces of the base material 3 and the base material 10 are heated to 600 °C by the ion bombardment effect by the thermionic radiation material 2 heated to 1600 °C or higher, the external heater 6, and high-frequency plasma.
It is heated to a temperature of 1200°C or higher.

The inside of the reaction vessel 1 is evacuated by a vacuum exhaust device through an exhaust port 8 attached to the reaction vessel to a temperature of 0. The pressure is maintained at not less than ITorr and not more than 100Torr.

A mixed gas of hydrogen and hydrocarbon is supplied from the raw material gas supply port 4 toward the thermionic emitting material, and the thermionic emitting material 2 and the thermionic emitting material and the reaction vessel 1, or the reaction vessel external electrode 5, or the reaction vessel internal electrode. The diamond is decomposed and excited by the high-frequency plasma formed between the substrate 9 and becomes activated, and diamond is deposited on the surface of the base material.

Examples will be described in detail below.

Example 1 ,-“,・(Commercially available IS OK-10 cemented carbide type @
SPG 422 was used as a base material, and a diamond coating was applied using the apparatus shown in FIG.

First, after evacuating the inside of the reaction vessel to 10-'Torr or less,
CI the raw material gases C114 and H2! , /H2=
Gas mixed at a ratio of 1/100 is 500+++1/
min. into the reaction vessel, and the pressure inside the reaction vessel was increased to 2.
It was maintained at 5 Torr. Further, a W-filament was used as the thermionic emitting material, heated to 2000°C, and used in an external heating furnace to bring the surface temperature of the base material to 900°C.

A 13.56 MHz RF power source was used as a high frequency power source, and RF was applied to the plasma formation space at a power density of 0.0811/cut.

A diamond thin film of about 6 μm was formed by coating for 4 hours. This base material is designated as A.

For comparison, we also tried a case where no RF load was applied.

In this case, no RF load was applied, and all other conditions were the same. Similarly, it took 5 hours to obtain a diamond thin film of approximately 6 μm.

This base material is designated as B.

When Raman spectroscopic analysis was carried out to evaluate the physical properties of the diamond films of substrates A and B, substrate B had a sharp Raman peak at 1333 cm-' and 155 cm, which is attributed to diamond.
A broad peak attributed to carbon other than diamond was observed near 0c+n-', but in base material A, 1333(
Only a sharp Raman peak of J-' was observed, and no broad peak was present. Further, when the microstructure was observed using a scanning electron microscope, many twins were observed in the base material B, but none were found in the base material A. That is, it has been confirmed that, according to the method of the present invention, a diamond film containing almost no carbon other than diamond can be obtained, and a crystalline diamond film with extremely few defects such as twins can be obtained.

A cutting test was conducted under the following conditions using substrate A, substrate B, and substrate C which was not subjected to coating treatment.

Work material: AC4C Cutting speed: 1200m/min Feed: 0.1mm/rev Depth of cut: 1. Omm Holder: F PIIR-44A Δ had flank wear of 0.02 mm after cutting for 45 minutes, whereas diamond film peeled off from B after cutting for 15 minutes. On the other hand, base material C that was not coated with diamond
After cutting for 2 minutes, flank wear was 0.50 mm.

Example 2 One of the effects of the present invention is that a large amount of substrates can be treated at one time.

Commercially available IS OK-10 cemented carbide type @ S P
Using G 422 as a base material, diamond coating was performed using the apparatus shown in FIG. 1, in which the reaction vessel was made of an alloy and no external electrode was used. With the rake face facing the thermionic emitting material,
30 pieces are placed in a concentric circle and 20 pieces are arranged vertically.
A total of 600 coatings/batch were applied.

The coating conditions are that the raw material gas is CH4/H, = 1/10
Gases mixed at a ratio of 1000 m 12 /old n were introduced into the reaction vessel, and the pressure inside the reaction vessel was maintained at 20 Torr.

In addition, W-filament was used as the thermionic emitting material, and 2
The surface temperature of the rake face was brought to 930°C using an external heating furnace. 13.56 MHz RF
Using a Ti source, O, 01lW/C is added to the plasma formation space.
[RF loaded at a power density of I+.

After 4 hours of coating treatment, TΔ placed on the same stage
The film thickness on the rake face varied by less than 5% against the target of 6μ, and the variation between the upper and lower stages of 20 stages was less than 10%.

Compared to normal industrial-scale CVD coating equipment,
The present invention showed excellent values, and the film quality was comparable to that of a small batch.

That is, it was confirmed that even human substrates can be coated uniformly according to the present invention.

Furthermore, since the coating equipment used in this test is a small test equipment, it is easy to further expand the throughput. Next, as an example of a base material having a large surface to be treated, 150 (width) x 3Q (1 (length) x 3 (1 (thickness) mm)
The base material was coated with diamond.

Using the above-mentioned coating apparatus, the substrate support jig was replaced and the substrate was set.

The coating conditions were as described above, but the surface temperature of MO was 900°C.

After 6.5 tlr coating treatment, a diamond film with an average thickness of 10μ was obtained on the side facing the thermionic emitting material, and the variation in film thickness was less than 10%, making it possible to uniformly coat even large substrates with diamonds. .

Example 3 Commercially available small-diameter drill made of ultra-fine cemented carbide (drill diameter 0, 08
mm) was coated with diamond using the apparatus shown in FIG. First, the inside of the reaction vessel was heated to 10"' Tor.
After exhausting to below r, the raw material gases CH4 and H2 are converted to C
A gas mixed at a ratio of H,/H,=0.5/1000 was introduced into the reaction vessel at a rate of 300 mj2/min, and the pressure inside the reaction vessel was maintained at 40 Torr.

Using W-filament as the thermionic emitting material, 205
The substrate was heated to 0°C and the external heating furnace was adjusted so that the surface temperature of the substrate was 880°C. RF was applied to the plasma formation space using a 13.56 MHz RF power source at a power density of 0.07 W/cffl. Furthermore, the base material rotation mechanism gave the base material rotation and revolution motion. By the coating treatment of 2.511r, a diamond thin film of about 3μ was uniformly formed. This base material is designated as D.

A cutting test was carried out under the following conditions using this base material and base material E which had not been coated.

Work material: Quartz fiber cloth board Drill speed: 60. OOOrpm feed
: f = Q, Q5mm/rev The flank wear width of the cutting edge after 150,000 hits was 0.07mm. Base material E was so worn after about 6,000 hits that it became unusable.

Example 4 Using a 10 mm x 5 mm W plate, Figure 2 (a)
, Diamond coating was applied using the apparatus shown in (b). The W plate used was finished by grinding with a 220# diamond whetstone. The inside of the reaction vessel is 1O-3 Torr.
After preheating in an external heating furnace, a mixture of CI-1, H2 and CH, /H2 at a ratio of 2/100 was introduced into the reaction vessel at 500 mA/min. The internal pressure was maintained at 30 Torr.

A filament of Ta was used as the thermionic emitting material. It was carbonized in advance to form TaC and used at 2150°C.

RF was applied to the plasma formation space by a 13.56 MHz RF':4 source at a power density of 0.08 W/c+d. Also, connect the DC power supply to the device shown in Figure 2 and
It was maintained at 300 ■. The base material surface temperature after generation of plasma was 970°C. After 2 hours of coating treatment, a diamond thin film of about 8 μm was formed.

Let this base material be L. For comparison, without applying a DC bias, the surface temperature of the substrate was adjusted to 970° C. by adjusting an external heating furnace, and coating was performed to form a diamond thin film of about 8 μm. The coating time required at this time was 4 hours. This base material is designated as M. When the diamond thin film of the base material and M was evaluated by Raman spectroscopy,
The base material M is 1333CID-, which belongs to diamond.
In addition to a sharp Raman beak at 2550 cm-', a broad peak attributed to carbon other than diamond was observed in the base material, but only a sharp Raman beak at 2333 au-' was observed in the substrate, and microstructure observation using a scanning electron microscope showed that In the case of the base material, almost no defects such as twins were observed, whereas in the case of M, many defects were observed. That is, even by applying a positive bias to the substrate, a high-quality diamond film containing almost no carbon other than diamond, such as amorphous carbon, was obtained, and an improvement in the deposition rate was observed.

[Brief explanation of drawings]

Figure 1 (a), Figure 1 et al.), Figure 2 (a), Figure 2 et al.)
is a schematic configuration diagram showing one embodiment of the invention, and FIG.
) and FIG. 2(a) are top views, FIG.
Figure (b) is a front view. In the figure, l is a reaction vessel, 2 is a thermionic emitting material, 3 is a base material, and 4
1 is a raw material gas supply nozzle, 5 is an external cylindrical electrode, 6 is an external heating heater, 7 is a high frequency power source, 8 is a gas exhaust port, 9 is an internal cylindrical electrode, 10 is a base material, 11 is a rotating shaft, 12
is the base material rotation mechanism. Agent Patent Attorney Tetsuji Udai - Summer Figure 1 Figure 2 Supplementary Procedure Device 20 Name of Invention Method for Manufacturing Diamonds 3 Relationship with the Amendment Person Case Patent Application Appointment Office
5-15 Kitahama, Higashi-ku, Osaka Name (213)
President of Sumitomo Electric Industries, Ltd. Tetsube 4, Agent Address: Within Sumitomo Electric Industries, Ltd., 1-1-3 Shimaya, Konohana-ku, Osaka (Telephone: 06-461-1031) Name (7881) Patent Attorney Tetsu Tsukasa 5
, date 6 of the amendment order, detailed description of the invention in the specification subject to amendment. 7. Contents of amendment (1) In the specification, page 14, line 18, “negative potential” has been changed to “
Correct to "bias potential". (2) In the same book, "negative potential" on the bottom line of the same page has been corrected to "bias potential."

Claims (3)

[Claims] (1) Activate a mixed gas of hydrogen and hydrocarbons and heat to 600℃
In the low-pressure vapor phase synthesis method for diamond in which diamond is precipitated on the surface of a substrate heated to 1200°C or lower, the raw material gas is activated by a thermionic emitter heated to 1600°C or higher, and a high-frequency power source is used. High-frequency plasma is generated by capacitively coupled power supply between the thermionic emitting material and the electrode inside the reaction vessel, the reaction vessel itself (if it is conductive), or the external electrode placed outside the reaction vessel (if it is an insulator). 1. A method for producing diamond, characterized in that activation is performed by a thermionic emitter and activation by formation of high-frequency plasma. (2) A method for manufacturing diamond according to claim (1), characterized in that a bias potential is applied to the base material using a DC (direct current) power source. (3) The method for producing diamond according to claim (1), characterized in that the base material has a mechanism for rotating, revolving, or rotating around its axis.