JP2523052B2 - Gas phase synthesis of diamond - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for vapor phase synthesis of diamond, and more particularly to a new method for uniformly synthesizing a diamond film on both surfaces of a flat substrate or a substrate having a complicated shape.

(Prior Art) In recent years, a vapor phase synthesis technique of diamond has progressed, and various synthesis methods have been proposed. Of these, the methods for synthesizing diamond having the same hardness and crystallinity as natural diamond from the vapor phase are classified as follows, characterized by the method of exciting the raw material gas.

Journal of Crystal Growth, 2 has been used for a long time as a method of exciting raw material gas for diamond synthesis without using discharge.
(1968) p386, there is a method in which a container containing graphite and a substrate is filled with hydrogen gas and the hydrogen gas is excited by a thermal means to chemically transport diamond to the substrate. On the other hand, as a further advanced method, for example, as shown in JP-A-58-91100, a hot filament excites a mixed gas of hydrocarbon gas and hydrogen gas, and a substrate placed in the vicinity of the hot filament. There is a method of synthesizing diamond in the above, or a method of synthesizing diamond in a combustion flame of a mixed gas of hydrocarbon and oxygen, as shown in the magazine "New Diamond", Vol.4, No.3 (1983) p34. can give.

As a method of exciting a raw material gas for diamond synthesis by using an electric discharge, the oldest method has been Journal of Crystal Growth, 52.
(1981) p219, but the method of discharge has not been clarified. Discharge method is disclosed, for example, as shown in JP-A-60-221395, a method of exciting by performing direct current discharge between a hot filament as a cathode and an anode, or JP-A-60-118693. As shown in JP-A-58-135117, a method of exciting a raw material gas by passing an arc discharge between cold cathodes as shown in FIG. As disclosed in JP-A-58-110494, there is a method of exciting by microwave discharge.

Also, magazine "New Diamond", Vol.4, No.2
(1988) p30, a plasma torch is used to excite a gas by a high-current DC discharge, and a method of synthesizing diamond in a jet-like plasma flow is also used. Can be given as an example.

(Problems to be Solved by the Invention) All of the above methods (1) to (3) are characterized by the method of exciting the raw material gas for synthesizing diamond. However, all of them uniformly coat a wide area substrate or a complex shaped substrate with diamond. Difficult to do. On the other hand, recently, as shown in p3 of the 2nd Diamond Symposium Lecture Collection (1987) p3, it has been attempted to expand the diamond synthesis region. If the shape is complicated, it becomes difficult to secure a wide diamond synthesis space.

In addition, there is a strong directivity in the flow of the excited gas or the discharge current. Therefore, for example, a thick diamond film is formed on the upstream side of the gas flow and a thin diamond film is formed on the downstream side. Further, for example, when the substrate is placed on the anode by the above-mentioned method and plasma is generated by direct current discharge to synthesize diamond, the thickness of the synthesized diamond film becomes thicker in the portion close to the cathode side of the substrate, The phenomenon of thinning occurs near the side.

(Means for Solving the Problem) The gist of the present invention is to solve the above problems and to provide a method for uniformly coating both front and back surfaces of a complex substrate with diamond. 2 or 3 electrodes made of thermionic emission material that can be heated by
It is installed in a place, and each electrode is heated by an alternating current of a commercial frequency, and by applying an alternating electric field of a commercial frequency between the electrodes, the direction of the electron current emitted from the heated electrodes becomes the direction of the alternating electric field. A discharge plasma that changes from time to time is generated in the raw material gas for diamond synthesis introduced into the vacuum chamber, and diamond is uniformly synthesized on the surface of the substrate placed at the intermediate position of the electrode.

Preferably, the raw material gas for synthesizing diamond is introduced into the vacuum chamber through the introduction ports provided at two or more locations while alternately switching the introduction paths and changing the gas flow direction with time.

The AC electric field referred to here is a single-phase AC electric field when the electrodes are installed at two locations and a three-phase AC electric field when the electrodes are installed at three locations.

(Operation) When discharge is performed in the raw material gas for diamond synthesis, atoms or molecules in the gas are ionized to generate plasma. The gas is highly excited in this plasma and diamond is synthesized by placing the substrate therein. Factors that make the thickness of the diamond film on the substrate non-uniform are (a) the flow of electrons and ions is different on the cathode side and the anode side of the substrate, (b) the flow of the source gas is directional ( c) The temperature of the substrate greatly differs depending on the position.

Therefore, in the present invention, as a result of studying to solve the above problems, the inventors have come to the knowledge that these problems can be solved by the following method. Regarding the problem of the above (a), electrodes are installed at two or three places and each electrode is heated by an alternating current of a commercial frequency, and
When the electrodes are installed in two places, a single-phase AC electric field of commercial frequency is applied, and when the electrodes are installed in three places, a three-phase AC electric field of commercial frequency is applied between the electrodes, so that the period of the commercial frequency is changed. Since the potential of each electrode changes sinusoidally and with a phase shift for each electrode, electrons and ions do not flow in only one direction in the plasma generated as in the case of DC discharge. By making the position of the substrate placed in the generated plasma the intermediate position of the electrode, the flow of electrons and ions around the substrate becomes uniform, so that the activated gas component can be generated at any position on the substrate surface. Since it becomes uniform, it is possible to reduce the non-uniformity of the film thickness of the diamond coating generated on the substrate surface due to the uneven flow of electrons and ions in the plasma. . Further, regarding the problem of the directionality of the flow of the raw material gas in the above (b), a plurality of gas introduction ports are provided so that the gas flow does not flow only from one direction of the substrate, and the gas is alternately supplied from each introduction port. It can be solved by pouring. Regarding the problem of (c), it is not easy to solve the problem because the method of holding the substrate is complicatedly related, but a large discharge plasma space is created by the discharge plasma generating method of the present invention, and the substrate is placed in the plasma space. It is improved to a certain extent by putting it on.

When plasma is generated by electric discharge, the use of a thermoelectron emitting material lowers the discharge voltage and enables stable electric discharge. Examples of thermionic emission materials suitable for the purpose of the present invention include known materials such as lanthanum boride, tungsten, thoria-containing tungsten, tantalum, and zirconium carbide.
These materials emit thermoelectrons while keeping the materials at a high temperature by resistance heating or self-heating due to discharge or their synergistic effect. When the thermoelectron emitting material is heated to a high temperature by being energized as in the present invention, a linear, winding, foil or net material is used as the electrode material.

The present invention will be described in detail below with reference to examples.

(Example) Example 1 FIG. 1 shows a schematic view of an apparatus used in a first example of the present invention. That is, two opposing filaments 1 connected to an AC power source via a filament support tool 2 are installed in a vacuum chamber (not shown), and a width of 12 mm placed on the substrate support base 4 in the middle of these filaments. , Length 60mm, thickness 1m
A substrate 3 made of a silicon plate of m was placed. The diamond synthesis raw material gas is introduced into the vacuum chamber in a direction orthogonal to the line connecting the two filaments so that the introduced gas is blown to the center of the portion of the substrate where the diamond is desired to be coated. It is carried out via the two gas introduction ports 5 thus formed. FIG. 2 is a configuration diagram of an AC power supply for generating discharge plasma used in the first embodiment. Each filament 1 is heated by an AC power supply 6 of a commercial frequency capable of voltage adjustment via an insulation transformer, and an AC power supply 7 of a commercial frequency capable of output adjustment via an insulation transformer is provided between both filaments. AC voltage is applied.

As a diamond synthesis procedure, first set the vacuum chamber to 10 ^-3.
Evacuate to Pa, and then use 3 ml / min of carbon monoxide, 3 ml / min of carbon monoxide, and 300 ml / min of hydrogen as a raw material gas for diamond synthesis through a gas inlet into the vacuum chamber, and then the vacuum chamber. After maintaining the internal pressure at 1200 Pa, the two filaments were heated to about 2000 ° C. by energization, and an AC voltage was applied between both filaments to generate discharge plasma. The substrate, which is between the two filaments and is surrounded by the plasma, is heated by the radiation heat from the filament and the heat from the plasma. The temperature of the substrate is desired to synthesize diamond by adjusting the discharge current. The temperature of the part was adjusted to be in the range of 850 to 900 ° C.
As a result of performing the coating treatment for 10 hours, diamond having a thickness of 8 μm was uniformly synthesized on the surface of the silicon substrate excluding the portion clamped to the substrate support.
Further, since the diamond film was equally synthesized on both sides of the substrate, the substrate did not warp after the treatment.

The following tests were performed as an example of the conventional method outside the present invention. That is, the apparatus of the present invention shown in FIG. 1 was used, and the treatment conditions were the same as the method of the present invention for 10 hours except that the current was not applied to one filament. as a result,
The diamond film was thick on the side of the substrate heated by electric current and thin on the opposite side, and the substrate was curved. This is because when only one of the filaments is energized, the electron current in the plasma has many components that flow from the energized filament side to the non-energized filament side, so that anisotropy appears in the flow of electrons and ions, so that energization is performed. This is because there was a difference in the thickness of the synthesized diamond between the filament side and the filament side that was not energized.

Example 2 As a second example, diameter 12 mm, blade length 26 mm, total length 75 mm,
A diamond film was coated on the surface of a cemented carbide end mill having four blades as a substrate. In the case of the conventional method, since the flow of gas and the flow of electrons or ions have directivity, it is difficult to uniformly synthesize diamond over the entire blade portion of a complicated substrate such as an end mill. FIG. 3 shows a schematic view of the apparatus used in this example.
As shown in the figure, three filaments 1 are arranged in a vacuum chamber so as to keep equal distances from each other, and a substrate 3 is provided between them.
I put it. A tantalum wire having a diameter of 0.2 mm was used as the filament material. In the figure, 2 is a filament support,
Reference numeral 4 indicates a base support. Each gas inlet 5 is 120 °
It was installed at three positions with an angle of, and the source gas was installed so as to be blown to the central portion of the portion of the substrate where the diamond is to be synthesized.

FIG. 4 shows a configuration diagram of a power source for generating discharge plasma used in the second embodiment, in which 6 is an AC power source of a commercial frequency for filament heating, and 7 is a three-phase AC voltage between three filaments. It is an AC power supply of commercial frequency for applying.

As a diamond synthesis procedure, first set the vacuum chamber to 10 ^-3.
After evacuating to Pa, methane in this vacuum chamber is 3 ml per minute
And hydrogen were continuously flowed through the gas inlet at a flow rate of 300 ml / min, and the pressure was set to 1000 Pa. Next, the three filaments are heated electrically, and the temperature is set to about 2000 ° C.
A three-phase AC voltage was applied between the filaments of the book. The base is heated by the plasma generated between the three filaments and the radiant heat from the filaments. The temperature of the base is adjusted to 800 by adjusting the output of the three-phase AC power supply.
Maintained at ~ 900 ° C. During the diamond synthesis process, the gas introduction path was sequentially switched every 10 minutes to substantially make the gas flow isotropic. As a result, diamond could be uniformly coated over the entire edge of the end mill. Also, using this, an aluminum alloy containing 18% silicon was rotated at 2000 rpm.
When cutting under conditions of 0 rpm, feed rate 1600 mm / min, and depth of cut 20 mm, the cutting edge was sound even after 400 m cutting.
On the other hand, in the case of a cemented carbide end mill that does not cover diamond, the cutting edge was worn out at the time of cutting 39 m under the same cutting conditions, and the life was reached.

(Effect of the invention) According to the method of the present invention, thermionic emission materials are used for all electrodes, and by applying an alternating electric field between each electrode, the flow of electrons and ions in the plasma is eliminated,
Further, since the position of the substrate placed in the generated plasma is set to the intermediate position of the electrode, the flow of electrons and ions around the substrate becomes uniform, and the activated gas component is thereby transferred to the substrate surface. It becomes uniform at any position, and as a result, it becomes possible to reduce the unevenness of the film thickness of the diamond coating formed on the surface of the substrate.

As a result, it has become possible to uniformly synthesize diamond on both surfaces of a flat substrate which has been difficult in the past, or on the surface of a substrate having a complicated surface typified by an end mill.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for explaining the first embodiment of the present invention, and FIG. 2 is a configuration diagram of a discharge plasma generating power source used in the first embodiment. Further, FIG. 3 is a schematic diagram of an apparatus for explaining the second embodiment of the present invention, and FIG. 4 is a configuration diagram of the discharge plasma generating power source used in the second embodiment. In the figure, 1 is a filament, 2 is a filament support, 3 is a substrate, 4 is a substrate support, 5 is a gas inlet, 6 is an AC power supply for filament heating, and 7 is an AC power supply for discharge.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Kenichiro Yamagishi 20 Ishigane, Toyama City, Toyama Prefecture Fuji Echiuchi Co., Ltd. (56) Reference JP-A-62-256796 (JP, A)

Claims (3)

(57) [Claims] 1. An electrode made of a thermoelectron emitting material capable of being heated by energizing is installed in two places in a vacuum chamber, each electrode is heated by an alternating current of a commercial frequency, and a commercial frequency is applied between the electrodes. By applying a single-phase AC electric field, the direction of the electron current emitted from the heated electrode changes occasionally with the direction of the single-phase AC electric field, and a discharge plasma is introduced into the vacuum chamber. A method for vapor phase synthesis of diamond, characterized in that diamond is synthesized on the surface of a substrate which is generated in the middle of the two electrodes. 2. An electrode made of a thermoelectron emitting material capable of being heated by energization is installed in three places in a vacuum chamber so that the intervals between the electrodes are equal, and each electrode is heated by an alternating current of commercial frequency. At the same time, by applying a three-phase AC electric field having a commercial frequency between the electrodes, a discharge plasma whose direction of the electron current emitted from the heated electrode changes with the direction of the three-phase AC electric field is generated in the vacuum chamber. A method for vapor phase synthesis of diamond, characterized in that the diamond is generated in a raw material gas for synthesizing diamond introduced into, and diamond is synthesized on a surface of a substrate placed at an intermediate position of the three electrodes. 3. A diamond synthesizing source gas introduction port is provided at two or more places in a vacuum chamber, and the gas introduction positions are alternately switched to change the gas flow direction with time. Item 3. A vapor phase diamond synthesis method according to Item 1 or 2.