JP2023160934A - Diamond formation device by high-frequency plasma cvd - Google Patents

Abstract

To provide a diamond formation device by high-frequency plasma CVD so as to solve the problem that although a microwave plasma CVD device and a hot filament CVD device, etc., are developed for formation of a diamond film as a power semiconductor material, it is difficult for the former to have a larger area because of wavelength restrictions and it is also difficult for the latter to achieve high-speed film deposition because of trade-off relation between increased temperature for higher density of generation of thermal electrons and control over a substrate temperature.SOLUTION: A diamond formation device by high-frequency plasma CVD comprises a radiation heating and plasma generating electrode used in common for heating of a substrate by radiation and generation of high-frequency plasma, a DC power supply comprising a coil blocking the entry of high-frequency electric power, and a high-frequency power supply comprising a capacitor blocking the entry of DC electric power. The radiation heating and plasma generating electrode is supplied with the DC electric power from the DC power supply and with the high-frequency electric power from the high-frequency power supply so as to form diamond by making methane and hydrogen of raw material gas into plasma.SELECTED DRAWING: Figure 1

Description

The present invention relates to a diamond forming apparatus using high frequency plasma CVD. In particular, the present invention relates to a diamond forming apparatus using high frequency plasma CVD using a frequency in the VHF band (30 MHz to 300 MHz).

For example, as described in Non-Patent Literature 1 and Non-Patent Literature 2, diamond is used not only in jewelry and machining materials, but also as a wide-gap semiconductor, which is far superior to semiconductors such as Si and SiC. Because of its unique characteristics, it is attracting attention as the ultimate power semiconductor material. In order to apply this technology to power semiconductor materials, intensive research and development is being carried out on large-area diamond forming equipment that can handle 4- to 5-inch substrates.
It is known that there are two main methods for forming diamond as a power semiconductor material: microwave plasma CVD and hot filament CVD. Additionally, the following is generally known: That is, in the above CVD method, when diamond is used for the substrate, diamond is formed by homoepitaxial growth, impurities can be easily controlled, and a strain-free crystal can be formed. Further, when the substrate is made of a material other than diamond, diamond is formed by heteroepitaxial growth, which may cause distortion and reduce crystallinity.

The microwave plasma CVD method is characterized by using microwaves to heat the substrate and decompose the source gas. In other words, by using microwaves to turn a mixed gas of methane (CH ₄ ) and hydrogen (H ₂ ), which are raw material gases, into plasma, the electrons and ions generated in the plasma are essential for forming a diamond film. In addition to generating CH ₃ radicals and atomic hydrogen H, which are the main radicals of Heat. Diamond formed on a substrate uses CH ₃ radicals as its main precursor, which is chemically adsorbed onto the substrate, and hydrogen components and graphite components are removed by atomic H and the like on the substrate, and diamond crystals grow.
However, from the viewpoint of application to the formation of the ultimate power semiconductor material, the microwave plasma CVD method is generally Although the diamond growth rate is relatively high at 1 to 10 μm/h, the width of the uniform plasma generation region is limited due to the short wavelength of microwaves, and the area that can be deposited is λ/8 to λ/10. The problem is that it is difficult to increase the area, which is an essential condition for dealing with 4- to 5-inch substrates. In addition, in the case of a frequency of 2.45 GHz, the wavelength λ in high-density plasma is the wavelength λ ₀ (122 mm) in vacuum x wavelength shortening rate (for example, 0.65) = 79.3 mm, and uniform high-density plasma If the generation region is estimated to be, for example, about λ/8 to λ/10, the area where a film can be formed is about 8 to 10 mm in diameter.
The hot filament CVD method is characterized by using radiant heat to heat the substrate, and by using hot electrons, ultraviolet rays, etc. emitted from the hot filament to decompose the source gas. That is, a high-temperature filament (approximately 1,000°C to 2,400°C) is installed at a position several mm to 10 mm directly above the substrate, and source gas is heated by thermionic and ultraviolet rays emitted from the high-temperature filament. A certain mixed gas of hydrogen (H ₂ ) and methane (CH ₄ ) is decomposed to generate CH ₃ radicals, atomic hydrogen H, etc., which are the main radicals essential for forming a diamond film. Diamond uses CH ₃ radicals as its main precursor, and is chemically adsorbed onto a substrate. Hydrogen and graphite components are removed by atomic H and the like on the substrate, and diamond crystals are formed. The temperature of the substrate is generally set at about 700 to about 1,000°C.
However, from the viewpoint of application to the formation of the ultimate power semiconductor material, the hot filament CVD method generally has a film formation rate of 1 Since the speed is as low as .5 to 2.0 μm/h, the challenge is to realize high-speed film formation on the same level as microwave plasma CVD. In addition, in order to apply it to power semiconductor materials, it is necessary to increase the area so that it can be applied to 4- to 5-inch substrates.

Representative patent techniques relating to a diamond forming apparatus using hot filament CVD include, for example, Patent Documents 1 to 3.
Patent Document 1 discloses a method for depositing diamonds by introducing raw material gas heated by a heating element onto the surface of a substrate, in which two or more heating elements are arranged in multiple stages facing the gas flow. A vapor phase synthesis method is described. In addition, as specific knowledge, there is a statement with the gist shown below. That is, (a) a method in which a heating body consisting of a first filament layer and a second filament layer made of a high melting point metal such as W or Ta is arranged in two stages in front of a nozzle for ejecting raw material gas, Each filament is placed facing the gas stream from the nozzle to the jetting substrate. Therefore, the gas that has passed through the first filament becomes fully active in the second filament. (b) The greater the number of filament layers and the smaller the distance between filaments, preferably within 20 mm, the better results can be obtained. (c) In place of the filament, other shapes of heating elements, such as mesh-shaped, rod-shaped, coil-shaped, or plate-shaped heating elements, can also be used.
Patent Document 2 includes the following description regarding a diamond forming apparatus using hot filament CVD. In other words, in the conventional technology, the high-temperature heating element is composed of one heat-generating system, so the central part and the peripheral part of the high-temperature heating element are different in terms of heat escape to the reaction vessel. Low temperature areas appear and the uniformity of the catalytic cracking reaction is impaired. Therefore, there is a problem in that it is difficult to make the film formed within the plane of the substrate good and uniform in thickness. In order to make the thickness of the thin film deposited on the substrate good and uniform, it is necessary to control the amount of active species that reach the substrate surface depending on the location on the substrate. A semiconductor manufacturing apparatus that solves this problem includes a reaction chamber for processing a substrate, a gas supply means for supplying a reaction gas into the reaction chamber, and a means for supplying a reaction gas into the reaction chamber by contacting the reaction gas supplied into the reaction chamber. and a high-temperature heating element that decomposes, the high-temperature heating element is composed of units that are controlled independently or in combination, and the units are arranged in a plurality of regions that are appropriately divided within the reaction chamber. It is characterized by the presence of As an example, a configuration is described in which a plurality of filaments are arranged in two planes parallel to the plane of the substrate and at different distances from each other, and heating power supplies independent of each other are arranged.

Patent Document 3 includes the following description regarding a diamond forming apparatus using a hot filament method.
In other words, as a conventional technical problem, plasma CVD is a method of forming a film by converting the raw material gas supplied into the film forming chamber into a plasma state using microwaves, etc., so the growth rate is relatively high at 1 to 10 μm/h. However, it has the disadvantage that the structure of the device is complicated and expensive, and there is a limit to the possible film formation area due to wavelength restrictions such as microwaves.
Hot filament CVD is a film forming method that thermally decomposes the raw material gas supplied to the film forming chamber using a high temperature filament to induce a chemical reaction.It has a simple structure, is inexpensive, and can increase the film forming area. can. However, until now, this hot filament CVD has had a problem in that the growth rate of film formation is lower than that of the plasma CVD.
As a semiconductor manufacturing apparatus that solves this problem, the apparatus described in Patent Document 3 includes a film forming chamber, a substrate holder placed in the film forming chamber for placing a substrate, and a substrate heated to 2,500° C. or higher. a filament layer for discharging gas, a gas supply means for supplying raw material gas and a carrier gas into the film forming chamber, and an exhaust means for exhausting gas from the film forming chamber; The filament layers are arranged in multiple stages at intervals of ~10 mm, and each of the filament layers arranged in the multiple stages includes wires made of tantalum or its alloy with a wire diameter of 0.1 to 1.0 mm spaced at intervals of 3 to 30 mm. It is characterized by having multiple pieces arranged.
An embodiment of the apparatus described in Patent Document 3 includes the following description. (a) The wire diameter of the filament is in the range of 0.1 to 1.0 mm, preferably in the range of 0.1 to 0.3 mm. (b) The interval between filaments forming one filament layer is in the range of 3 to 30 mm, preferably 5 to 15 mm. (c) The distance between the first filament layer and the second filament layer is in the range of 1 mm to 10 cm, preferably 1 to 10 mm. (iv) Various materials can be used for the filament as long as it can withstand high temperatures of 2,400° C. or higher. For example, they are tungsten, tantalum, etc., and these may be alloys thereof or compounds such as carbides. Tantalum is preferred.
The diamond forming apparatus using hot filament CVD described in Patent Document 3 uses tantalum (Ta) as the material of the hot filament as a means to increase the amount of thermionic generation (thermionic emission amount), and It is characterized in that the temperature is heated to 2,500° C. or higher, and the hot filaments are arranged in multiple stages.

On the other hand, as seen in Patent Document 4 and Patent Document 5, for example, a diamond forming apparatus using VHF plasma CVD in which the frequency of the power source is in the VHF band (30 to 300 MHz) has been proposed.
The VHF plasma CVD diamond forming apparatus described in Patent Document 4 is characterized in that it uses power in the ultrahigh frequency range (30 to 300 MHz) when synthesizing diamond by the plasma CVD method that uses plasma for opposed electrode capacitive discharge. do.
The VHF plasma CVD diamond forming apparatus described in Patent Document 5 uses an inductively coupled plasma CVD method and a high frequency frequency of 40 to 250 MHz to form a diamond film using a carbon-containing raw material. It is characterized by decomposing gas and forming a diamond film on the substrate.
However, a VHF plasma CVD diamond forming apparatus that can control the substrate temperature to about 700 to about 1,000° C., suppress ion damage, and form high-quality diamond has not yet been developed.

JP 03-103396 JP2002-093714 Patent 7012304 Tokuho 07-042197 JP 08-027576

Osamu Ariyada, CVD equipment for diamond synthesis, Vacuum Journal, January 2023, 24-26 Hideaki Yamada, Current status and challenges of single crystal diamond synthesis by plasma CVD, J. Plasma Fusion Res. Vol.90, No.2 (2014)152-158 Toshiaki Kobayashi, About SPring8 Thermionic Electron Gun, Operator Training Materials, 2003.5.12 Guido (Susumu Yokobori, Osamu Kuga, co-translator), Basic Heat Transfer Engineering, 1960 (Maruzen), 20-222 Michio Kondo, Hiroyuki Fujiwara, Akihisa Matsuda, Current status and prospects of silicon-based thin film deposition technology, Applied Physics Vol. 71, No. 7 (2002), 823-832 Shota Nunomura, Hiroki Katayama, Isao Yoshida, Physical chemistry of hydrogen atoms in hydrogen plasma for surface treatment, AIST solar power generation research, Results report 2017 M. Murata, Y. Takeuchi, E. Sasakawa, K. Hamamoto, Inductively coupled radio plasma frequency chemical vapor deposition using a ladder-shaped antenna, Rev. Sci. Instrum.67(4), April 1996,1542-1545

As mentioned above, since the wavelength of the microwave used in a diamond forming apparatus using microwave plasma CVD is short, the plasma generation area is small (for example, about 8 to 10 mm), and the size 4 There is a problem in that it is essentially difficult to deal with substrates in the ~5-inch class.
A diamond forming apparatus using a conventional hot filament CVD method, for example, a diamond forming apparatus using a hot filament CVD method described in Patent Documents 1 to 3, when forming a diamond, changes the hot filament temperature to CH ₃ radical and atomic form. The substrate temperature is set at about 2,400 to about 2,500 degrees Celsius or higher, which is suitable for generating a large amount of H, etc. (herein referred to as device operating parameter A), and the substrate temperature is set to about 700 to about 1,000 degrees Celsius, which is suitable for diamond growth. ℃ (herein referred to as device operating parameter B).
The generation of thermionic electrons follows the Richardson-Dushman equation (the generation of thermionic electrons is proportional to the square of the hot filament temperature), as described in Non-Patent Document 3. When generating a large amount of thermoelectrons, the higher the temperature of the hot filament, the better. On the other hand, when the temperature of the hot filament is increased, the radiant energy of the hot filament reaching the substrate increases by 4 times the temperature of the hot filament according to the Stefan-Boltzmann law, as described in Non-Patent Document 4. Since it is proportional to the square of the distance between the hot filament and the substrate, if the temperature of the hot filament is increased, the temperature of the substrate will rise.
In other words, there is a relationship (trade-off relationship) in which raising the temperature of the thermal filament to an extremely high temperature (device operating parameter A) for generating a large amount of thermoelectrons and setting the appropriate value for the substrate temperature (device operating parameter B) are incompatible. be. Therefore, the device operating parameter A, which is an increase in the amount of thermionic and ultraviolet rays (higher density of thermionic electrons) that have the effect of generating a large amount of CH ₃ radicals and atomic H, which are essential for diamond formation, and the diamond growth The device operation parameter B, which is the setting of an appropriate value for the substrate temperature, which is essential for the above, is incompatible. As a result, there is a problem that it is difficult to increase the diamond film formation rate (growth rate).
A VHF plasma CVD apparatus that uses the VHF band (30 MHz to 300 MHz) as a power supply frequency has a plasma sheath voltage (difference between plasma potential V _p and wall potential V ₄ : V _p -V ₄ ) is low, and ion damage is suppressed. Furthermore, for example, as described in Non-Patent Document 6, it is possible to generate a high concentration of atomic hydrogen H, and the concentration of the atomic hydrogen H increases in proportion to the pressure. It has characteristics. That is, the VHF plasma CVD apparatus has the following characteristics: (a) it is possible to suppress ion damage, and (b) it is possible to generate high concentration atomic H, and is expected to be applied to diamond forming apparatuses.
However, diamond forming apparatuses using the VHF plasma CVD method other than those described in Patent Documents 4 and 5 have not been found. In the VHF plasma CVD method, the wavelength of the generated plasma is sufficiently longer than that of microwave plasma, so there is no problem caused by the wavelength. Therefore, the challenge is to create a diamond forming apparatus using the VHF plasma CVD method that can be put to practical use.
An object of the present invention is to provide a diamond forming apparatus using high frequency plasma CVD that can solve the above problems. That is, the object of the present invention is to provide a diamond forming apparatus using high-frequency plasma CVD that is capable of high-speed film formation and that can be applied to large-area substrates in the 4 to 5 inch class. Another object of the present invention is to provide a diamond forming apparatus using ultra-high frequency plasma CVD, which is capable of suppressing ion damage and generating CH ₃ radicals, high concentration atomic H, and the like.

A first aspect of the present invention for solving the above-mentioned problems includes a reaction vessel equipped with a raw material gas supply system and an exhaust system containing at least methane gas (CH ₄ ) and hydrogen gas (H ₂ ); A substrate holding table having a main surface disposed inside to hold a substrate, a plasma generation electrode for both radiant heating and generating high-frequency plasma and generating radiant energy for heating the substrate, and the plasma generation electrode for radiant heating and other functions. a high-frequency power supply that supplies high-frequency power to the radiation heating and plasma generation electrode via an impedance matching device; and a first electrically ungrounded current introduction terminal for the vacuum device; A diamond forming apparatus using high frequency plasma CVD, comprising a grounded second current introduction terminal for a vacuum apparatus,
The radiation heating and plasma generation electrode includes a power feeding area to which the DC power and the high frequency power are fed, and a grounding area to be grounded,
The output terminal of the DC power source is connected to the first vacuum device current introduction terminal via a coil that blocks intrusion of the high frequency power generated by the high frequency power source,
The output terminal of the impedance matching device is connected to the first vacuum device current introduction terminal via a capacitor that blocks the intrusion of the DC power generated by the DC power supply,
The power supply region of the radiation heating plasma generation electrode and the first vacuum device current introduction terminal are connected,
The grounding region of the radiation heating plasma generation electrode and the grounded second vacuum device current introduction terminal are connected, and
The radiation heating and plasma generation electrode is arranged directly above the substrate holding table,
the substrate is placed on the substrate holder,
The DC power is supplied from the DC power supply to the radiant heating/plasma generation electrode to raise the temperature of the radiant heating/plasma generation electrode, and the substrate is heated by the radiant energy emitted by the radiant heating/plasma generation electrode. ,
The high frequency power is supplied from the high frequency power source to the radiation heating plasma generation electrode via the impedance matching device, and the raw material gas supplied from the raw material gas supply system is turned into plasma, thereby forming diamonds on the substrate. It is characterized by the formation of
A second invention is based on the first invention, wherein the radiation heating and plasma generating electrode includes one thin wire made of tungsten (W), tantalum (Ta), or an alloy containing tantalum; The thin wire is provided with a plurality of bent portions and is arranged parallel to the main surface of the substrate holder, and one end of the single thin wire is provided with a first power feeding area, and is connected to the first power feeding area. The first vacuum device current introducing terminal is connected, the other end of the one thin wire is provided with a first grounding region, and the first grounding region and the second vacuum device current introducing terminal are connected. The present invention is characterized in that when the terminals are connected, tension is applied to the one thin wire by tension applying means provided at the plurality of bent portions.
A third invention is based on the first invention, wherein the radiation heating and plasma generating electrode is made of first to nth strips made of n pieces made of tungsten (W), tantalum (Ta), or an alloy containing tantalum. the first to nth strip-shaped thin plates are arranged parallel to each other at equal intervals;
One end of the first strip-shaped thin plate and one end of the second strip-shaped thin plate are connected by a first metal fixing rod, and the other end of the second strip-shaped thin plate is connected. and one end of the third strip-shaped thin plate are connected by a second metal fixing rod, and one end of the n-1th strip-shaped thin plate and the n-th strip-shaped thin plate are sequentially connected. one end of which is connected with the n-1th metal fixing rod,
A second power supply region is provided at the other end of the first thin strip, and the second power supply region and the first vacuum device current introduction terminal are connected,
A second grounding region is provided at the other end of the n-th strip-shaped thin plate, and the second grounding region and the second vacuum device current introducing terminal are connected,
Tension is applied to the first to n-th strip-shaped thin plates by tension applying means provided in the first to n-1 metal fixing rods.
A fourth invention is characterized in that in the first invention or the second invention, the radiation heating and plasma generation electrode has a circular cross-sectional shape with a diameter of approximately 0.1 mm to 1.0 mm.
A fifth invention is based on the first invention or the third invention, wherein the radiation heating and plasma generating electrode has a cross-sectional shape with a thickness of approximately 0.05 mm to 0.5 mm and a width of approximately 0.5 mm to 10 mm. It is characterized by its rectangular shape.
A sixth invention is characterized in that in any one of the first to fifth inventions, the frequency of the high frequency power source is in the VHF band (30 MHz to 300 MHz).
A seventh invention is the invention according to any one of the first invention to the sixth invention, wherein the substrate holder is made of tantalum (Ta) and includes a cooling means using a refrigerant. do.

The diamond forming apparatus using high-frequency plasma CVD of the present invention configured as described above supplies DC power from a DC power source equipped with a coil for blocking the penetration of high-frequency power to the radiation heating plasma generation electrode to generate radiant heat. In addition, by generating thermoelectrons, ultraviolet rays, etc., and supplying high frequency power from a high frequency power source equipped with a capacitor that blocks the intrusion of the DC power, the raw material gas (mixed gas of methane and hydrogen) is turned into plasma. It becomes possible to generate a high concentration of CH ₃ radicals and a high concentration of atomic H, which are precursors for the formation of . The plasma generation of the raw material gas is achieved by effectively synergizing the three effects of the radiation heating and plasma generation electrode: the effect of generating radiant heat, the effect of generating thermoelectrons, and the effect of generating high-density plasma by VHF. This makes it possible to generate a high concentration of CH ₃ radicals and a high concentration of atomic H. As a result, it becomes possible to grow diamonds in a large area at high speed and with high quality, thereby achieving the effect that the above-mentioned problems can be solved.

FIG. 1 is a schematic cross-sectional view showing the configuration of a diamond forming apparatus using high frequency plasma CVD according to a first embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing the configuration of a first radiation heating and plasma generation electrode which is a component of the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention. FIG. 3 shows the principle of radiant energy, thermoelectrons, and plasma emitted from the first radiant heating and plasma generating electrode, which is a component of the diamond forming apparatus by high-frequency plasma CVD according to the first embodiment of the present invention. This is a schematic diagram. FIG. 4 is a schematic diagram showing the principle of decomposition of raw material gas (mixed gas of methane CH ₄ and hydrogen H ₂ ) by plasma in the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention. FIG. 5 is a schematic diagram illustrating the principle of the growth process of diamond formed using the high-frequency plasma CVD diamond forming apparatus according to the first embodiment of the present invention. FIG. 6 is a schematic configuration diagram showing the configuration of a second radiation heating plasma generating electrode which is a component of a diamond forming apparatus using high frequency plasma CVD according to a second embodiment of the present invention.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In each figure, similar members are given the same reference numerals, and overlapping explanations will be omitted.
Note that the present invention is not limited to the following description, and can be modified as appropriate without departing from the gist of the present invention. Further, in the drawings shown below, for convenience of explanation, the scale of each member may be different from the actual scale. Furthermore, the scales of the drawings may differ from the actual scale.

(First embodiment)
First, the configuration of a diamond forming apparatus using high frequency plasma CVD according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 5.
FIG. 1 is a schematic cross-sectional view showing the configuration of a diamond forming apparatus using high frequency plasma CVD according to a first embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing the configuration of a first radiation heating and plasma generation electrode which is a component of the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention. FIG. 3 shows the principle of radiant energy, thermoelectrons, and plasma emitted from the first radiant heating and plasma generating electrode, which is a component of the diamond forming apparatus by high-frequency plasma CVD according to the first embodiment of the present invention. This is a schematic diagram. FIG. 4 is a schematic diagram showing the principle of decomposition of raw material gas (mixed gas of methane CH ₄ and hydrogen H ₂ ) by plasma in the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention. FIG. 5 is a schematic diagram illustrating the principle of the growth process of diamond formed using the high-frequency plasma CVD diamond forming apparatus according to the first embodiment of the present invention.

As shown in FIGS. 1 and 2, a diamond forming apparatus using high-frequency plasma CVD according to the first embodiment of the present invention includes a reaction vessel 1 having an exhaust system, a raw material gas supply system (not shown) (the raw material gas is (containing at least methane gas _CH4 and hydrogen gas _H2 ), a substrate holding table 6 having a main surface 6a disposed inside the reaction vessel 1 and holding the substrate 9, and generating radiant energy for heating the substrate 9. and a first radiant heating plasma generating electrode 2 that generates high-frequency plasma, a DC power source 8 that supplies DC power to the first radiant heating plasma generating electrode 2, and the first radiant heating plasma generating electrode 2. A high-frequency power source 10 that supplies high-frequency power to the generating electrode via an impedance matching device 11, an electrically ungrounded first current introduction terminal 12a for the vacuum device, and a grounded second current introduction terminal for the vacuum device. 12b.
The reaction vessel 1 is a cylindrical box-shaped or rectangular box-shaped reaction vessel. Inside the reaction vessel 1, a first radiation heating/plasma generation electrode 2, a substrate holding table 6 having a main surface 6a for holding a substrate 9, and a raw material gas supply box 13 are arranged. The substrate holding table 6, the first radiation heating/plasma generation electrode 2, and the source gas supply box 13 are arranged in this order.
The reaction vessel 1 is equipped with exhaust ports 17a and 17b connected to a vacuum pump (not shown). By operating the exhaust ports 17a and 17b in combination with a vacuum pump (not shown), it is possible to adjust the inside of the reaction vessel 1 to a predetermined pressure and maintain this pressure. Furthermore, it is possible to evacuate the inside of the reaction vessel 1 to a high degree of vacuum.
The reaction container 1 is equipped with a working flange (not shown) for assembling and installing each component inside the reaction container 1.

The substrate holding stand 6 has a main surface 6a, and the main surface 6a contacts and holds the substrate 9. The temperature of the substrate 9 is heated by the radiant heat emitted by the first radiant heating/plasma generation electrode 2, and is brought to a predetermined temperature in cooperation with a cooling means using a refrigerant (not shown) provided inside the substrate holder 6. controlled. The temperature of the substrate 9 is set at about 700 to about 1,200°C, for example 1,000°C. Note that the temperature of the substrate 6 is measured using a radiation thermometer 19, which will be described later.
The cross-sectional shape of the substrate holder 6 is similar to the shape of the substrate 9. For example, if the size of the substrate 9 is a disk shape with a diameter of 5 inches, the size is one size larger than that, for example, 153 mm in diameter. For example, when the size of the substrate 9 is a rectangular plate measuring 5 inches x 5 inches, the size is slightly larger than that, for example, 153 mm x 153 mm.
By opening and closing a substrate loading/unloading valve (not shown), the substrate 9 is loaded and placed on the main surface 6a of the substrate holding table 6 from the atmosphere side, and after the intended plasma processing is performed, it is carried out to the atmosphere side. be done.
Here, the substrate 9 is, for example, a single crystal Si wafer with a diameter of 5 inches. The size of the main surface 6a of the substrate holding table 6 is, for example, 153 mm in diameter. Note that the substrate 9 is not limited to a single-crystal Si wafer; for example, a plurality of small-sized diamonds manufactured by a high-temperature, high-pressure method may be placed thereon.

As shown in FIG. 2, the first radiation heating plasma generation electrode 2 includes one thin wire 2a made of tungsten (W), tantalum (Ta), or an alloy containing tantalum. The thin wire 2a is provided with a plurality of bent portions 2aa, and is arranged parallel to the main surface 6a of the substrate holding table 6, and one end of the single thin wire 2a is provided with a first power feeding area 2b, and the The first power supply region 2b and the first vacuum device current introduction terminal 12a are connected via the first power supply rod 5a, and the other end of the single thin wire 2a is connected to the first ground region 2c. The first grounding region 2c and the second vacuum device current introduction terminal 12b are connected via the second power supply rod 5b, and the one thin wire 2a is connected to the plurality of bent portions 2aa. It has a configuration in which tension is applied by a tension applying means 3 provided for.
Note that the tension applying means 3 provided at the plurality of bent portions 2aa is fixed to the wall of the reaction vessel 1 via an insulating material 4. Further, the tension applying means 3 is not limited to the coil spring type tension applying means shown in FIG. 2, but may be a plate spring type or a torsion rod type tension applying means. Further, the material of the tension applying means 3 that pulls the plurality of bent portions 2aa is a metal material with a high melting point, for example, tungsten, tantalum, or a tantalum alloy.
The reason why tungsten (W), tantalum (Ta), or an alloy containing tantalum is selected as the material for the single thin wire 2a is as follows.
That is, from the viewpoint of thermoelectron generation, tungsten (W, φ=4.5 eV), tantalum (Ta, φ=4.2 eV), or an alloy containing tantalum, which is a material with a low work function φ, is selected. The cross-sectional shape of the single thin wire 2a is circular or rectangular in consideration of electrical resistance and surface area. In addition, when the cross-sectional shape of the single thin wire 2a is circular, there is an advantage that the wire used as the material is inexpensive and easily available. Moreover, when the cross-sectional shape of the single thin wire 2a is rectangular, there is an advantage that the amount of thermoelectrons generated can be easily increased because the surface area is large.
In the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention, a circular shape is selected. For example, from a diameter of 0.1 mm to 1.0 mm, for example, a diameter of 0.3 mm is selected.
The reason for selecting a diameter of 0.1 mm to 1.0 mm is that it has a proven track record as a hot filament CVD apparatus, as described in Patent Documents 1 to 3, and is valid as general knowledge. It is. This is because, also from the viewpoint of plasma generation, the above size can be relatively easily applied as a component of a plasma generation electrode, as described in Non-Patent Document 7, for example.
The length of the single thin wire 2a is the length necessary for the area surrounded by the dotted line 2d shown in FIG. 500 mm, for example, 1,300 mm.

When the single thin wire 2a is made of tantalum, the electric resistance of the single thin wire 2a (tantalum wire) approximately has the following value. Incidentally, the resistivity of tantalum wire is 61.5x10 ^-6 Ωcm at 1,200°C.
Resistance value R of the single thin wire 2a (tantalum wire) (diameter: 0.3 mm, length 130 cm)
= Resistivity (Ω・cm) x Length (cm)/Cross-sectional area (cm ² )
= ^61.5x10-6 (Ωcm)x130(cm) ^/0.7x10-3 ( ^cm2 )
=11.4Ω...(1)
The distance between the single thin wire 2a and the substrate 9 is determined in consideration of plasma generation conditions and substrate temperature setting conditions. Here, the substrate temperature is set at about 700 to about 1,200° C., for example, 1,000° C., and the temperature of the one thin wire 2a is maximized to increase the generation of thermoelectrons, which will be described later. In order to satisfy the condition that the generated plasma is in a glow discharge region, the distance between the single thin wire 2a and the substrate 9 is selected to be in the range of about 4 mm to about 40 mm. For example, let it be 5 mm.

As shown in FIG. 1, the raw material gas supply box 13 includes a raw material gas supply port 7, a raw material gas ejection hole 13a, and a temperature measuring quartz window 19a. Note that the quartz window 19a has a property of transmitting infrared rays and part of visible light, so that the substrate 9 can be seen from outside the reaction vessel 1.
The temperature measuring quartz window 19a is used in conjunction with the radiation thermometer 19 to measure the substrate temperature. The diameter of the raw material gas ejection hole 13a is, for example, approximately 0.4 mm to approximately 1 mm, and the aperture ratio is, for example, approximately 30% to approximately 80%. By setting the diameter of the hole to 0.4 mm to 1 mm, the raw material gas can be ejected uniformly. Furthermore, by setting the aperture ratio to 30% to 80%, the surface of the substrate can be seen through the quartz window 19a for temperature measurement, so the temperature of the substrate 9 can be measured with the radiation thermometer 19 via the quartz window 19a. . Note that the radiation thermometer 19 can measure not only the temperature of the substrate 9 but also the temperature of the single thin wire 2a.

As shown in FIGS. 1 and 2, the DC power supply means for supplying DC power to the first radiation heating plasma generation electrode 2 includes a DC power supply 8, an ungrounded DC power supply line 8a, and a grounded DC power supply line 8a. It includes a DC power supply line 8b, an electrically ungrounded first vacuum current introduction terminal 12a, a grounded second vacuum current introduction terminal 12b, and a coil 16 that cuts off high frequency power. Note that the DC power supply 8 is a DC power supply of a constant power control type, and can be controlled so that constant power always flows even if the load condition changes.
The first vacuum current introduction terminal 12a is connected to the first power supply area 2b via the first power supply rod 5a. The second vacuum current introducing terminal 12b is connected to the first grounding area 2c via the second power supply rod 5b.
The ungrounded output terminal of the DC power supply 8 is connected to the first vacuum current introduction terminal 12a via the ungrounded DC power supply line 8a and the coil 16. A grounded output terminal of the DC power supply 8 is connected to a second vacuum current introduction terminal 12b via a grounded DC power supply line 8b.
That is, the DC power supply circuit of the DC power supply 8 includes, in order from the output terminal of the DC power supply 8, an ungrounded DC power supply line 8a, a coil 16, a first vacuum current introduction terminal 12a, and a first power supply rod 5a. , the first power supply area 2b, one thin wire 2a, the first grounding area 2c, the second power supply rod 5b, the second vacuum current introduction terminal 12b, the grounded DC power supply line 8b, and the DC power supply It is formed by a loop connecting eight grounded output terminals.
The DC power supply 8 is of a constant power control type, and controls the temperature of the single thin wire 2a of the component of the first radiant heating/plasma generation electrode 2 to about 1,000 to about 2,500°C, for example. It is heated to 2,400°C and can be controlled to a constant temperature. The DC power supply 8 uses a commercially available device, for example, a constant power control type DC power supply with an output current: maximum 50 A, output voltage: maximum 1 kV, and output power: maximum 50 kW.
The coil 16 has an inductance that blocks high-frequency power generated by a high-frequency power supply 10 (described later) from entering the DC power supply 8. Note that the inductance that matches the frequency of the high-frequency power can be adjusted by adjusting the number of turns of the coil, and the high-frequency power can be cut off.

As shown in FIGS. 1 and 2, the high-frequency power supply means for supplying high-frequency power to the first radiation heating plasma generation electrode 2 includes a high-frequency power supply 10, a coaxial cable 10a, an impedance matching box 11, It includes one high frequency power line 11a, a capacitor 15, a second high frequency power line 11b, a first vacuum current introduction terminal 12a, and a second vacuum current introduction terminal 12b. Note that the second vacuum current introduction terminal 12b is grounded.
The frequency of the generated power of the high frequency power source 10 is selected from 30 MHz to 300 MHz in the VHF band. For example, a 60 MHz power source is used. Note that the DC power supply 10 and the impedance matching device 11 to be described later are commercially available devices, for example, a high frequency power supply with a frequency of 60 MHz and a maximum output of 1 kW.
In plasma generation using a frequency in the VHF band, the direction of the electric field formed by the first radiation heating plasma generation electrode 2 changes from positive to negative in an extremely short period of time, so that electrons in the plasma This has the effect of increasing the electron density by being captured by the region. As a result, high-density plasma can be generated, and plasma with low electron temperature can be generated.
The non-grounded output terminal of the high frequency power supply 10 is connected to the first vacuum current introduction terminal 12a via the coaxial cable 10a, the impedance matching device 11, the first high frequency power line 11a, the capacitor 15, and the second high frequency power line 11b. Connected. The impedance matching device 11 is designed to minimize the strength of the reflected wave of the high frequency power supplied from the high frequency power supply 10 reflected from the first vacuum current introduction terminal 12a side to the upstream side and returned. The impedance adjustment means built in the impedance matching device 11 is adjusted. Further, the capacitor 15 has a capacitance that blocks the DC power generated by the DC power source 8 from entering the high frequency power source 10 . Note that a capacitance suitable for supplying high-frequency power and cutting off DC power can be achieved by using a variable capacitor, and it is possible to transmit high-frequency power and cut off the DC power that is the output of the DC power supply 8. .
That is, the high-frequency power supply circuit of the high-frequency power supply 10 includes, in order from the output terminal of the high-frequency power supply 10, a coaxial cable 10a, an impedance matching device 11, a first high-frequency power line 11a, a capacitor 15, a second high-frequency power line 11b, and a first high-frequency power line 11a. Vacuum current introduction terminal 12a, first power supply rod 5a, first power supply area 2b, one thin wire 2a, first grounding area 2c, second power supply rod 5b, second vacuum current introduction terminal 12b, formed by a loop connecting the grounded output terminals of the high frequency power source 10.
A band-shaped conductor plate or a coaxial cable is used for the first high-frequency power line 11a and the second high-frequency power line 11b. Here, a strip-shaped conductor plate with low impedance is used.

Next, the form of radiant heat and thermoelectrons generated when DC power is supplied from the above-mentioned DC power supply means to the first radiant heating/plasma generation electrode 2 will be explained below.
In FIG. 1, the output of the DC power supply 8 is, for example, 500 W to 10 kW, for example, 3 kW, and is supplied to the first radiation heating plasma generating electrode 2. Then, the one thin wire 2a of the component of the first radiation heating plasma generation electrode 2 becomes red hot, and as shown in FIG. 3, radiant energy (infrared rays, visible light, Radiant heat (including ultraviolet rays, etc.) 100 is emitted, and the substrate 9 is heated. In FIG. 3, reference numeral 100 indicates radiant energy (radiant heat including infrared rays, visible light, ultraviolet rays, etc.) radiated from the single thin wire 2a.
The radiant energy (radiant heat including infrared rays, visible light, ultraviolet rays, etc.) 100 emitted from the single thin wire 2a is expressed by the Stefan-Boltzmann law, for example, as described in Non-Patent Document 4. . That is, the radiant energy Es emitted from the single thin wire 2a is expressed by the following equation (2).
Es ∝ ε・σ・T ⁴ (w/cm ² ) ... (2)
Here, ε is the emissivity, σ is the Stefan-Boltzmann constant, and T is the absolute temperature of the single thin wire 2a.
The radiant energy Q incident on the substrate 9 is expressed by the following equation (3), for example, as described in Non-Patent Document 4.
Q ∝ Es・Ss・cosθ/d ² ...(3)
Here, Es is the radiant energy radiated from the one thin wire 2a, Ss is the surface area of the one thin wire 2a, and θ is the radiant energy radiated from the one thin wire 2a with respect to the normal to the substrate 9 as shown in FIG. The angle (elevation angle) at which the thin wire 2a is looked up, and d is the distance between the one thin wire 2a and the substrate 9.
Furthermore, exchange of radiant energy occurs between two adjacent high-temperature objects. For example, if the temperature of a first high-temperature object placed next to each other is _T1 and the temperature of a second high-temperature object is _T2 , the net energy exchange amount ΔE per unit area is expressed by the following equation (4). be done.
ΔE ∝ ε・σ・(T ₁ - T ₂ ) ⁴ ...(4)
This indicates that, if the temperatures are the same, no net energy exchange occurs between the single thin wires 2a arranged next to each other. That is, since the temperatures of the single thin wires 2a arranged next to each other are almost the same, there is no net energy exchange between them.
The surface temperature of the substrate 9 is determined by the distance d between the adjacent thin wires 2a and the distance d between the thin wire 2a and the substrate 9, as expressed by the above formulas (2) to (4). Since it depends on the output of the DC power supply 8, while measuring the surface temperature of the substrate 9 with the radiation thermometer 19, the surface temperature of the substrate 9 is made to be almost uniform over the front surface of the substrate 9. Data regarding the distance between the adjacent thin wires 2a, the distance d between the thin wire 2a and the substrate 9, and the optimal values of the output of the DC power source 8 are determined in advance through experiments.
Here, the surface temperature of the substrate 9 is determined based on the data regarding the distance between the two thin wires 2a, the distance between the one thin wire 2a and the substrate 9, and the optimum value of the output of the DC power source 8, which has been grasped in advance. is set at about 700 to about 1,200°C, for example, 1,000°C, and maintained and controlled.

On the other hand, when the single thin wire 2a is heated to a high temperature, thermoelectrons are generated. The generation situation of thermoelectrons is schematically shown in FIG. In addition, in FIG. 3, the reference numeral 101 is a thermoelectron emitted from the single thin wire 2a.
When the single thin wire 2a is at a high temperature, it generates thermoelectrons according to the Richardson-Dushman equation, for example, as described in Non-Patent Document 3.
That is, the number Ne of thermoelectrons generated by one thin wire 2a is expressed by the following equation (5).
Ne ∝ T ²・exp {-φ/kT} (Unit: A/m ² ) ...(5)
However, T is the absolute temperature of the one thin wire 2a, φ is the work function of the one thin wire 2a, and k is the Boltzmann constant.
Therefore, the higher the temperature of the single thin wire 2a and the lower the work function, the greater the number of emitted thermoelectrons. For example, according to Non-Patent Document 3, the work function φ of tungsten (W) is 4.5 eV, and the work function φ of tantalum (Ta) is 4.2 eV. For tantalum Ta (melting point: 2,850 °C), 0.01 A/cm ² at 2,000 °C and 1 A/cm ² at 2,400 °C are obtained; for tantalum Ta (melting point: 2,850 °C) at 1,400 °C, At 0.01 A/cm ² and 1,800°C, 1 A/cm ² has been obtained.
That is, the above equation (5) and the data described in Non-Patent Document 3 indicate that the higher the temperature of the single thin wire 2a, the more thermoelectrons are generated. Furthermore, when compared in terms of their ability to generate thermoelectrons, it can be seen that tantalum is superior to tungsten.
Here, in order to maximize the amount of thermoelectrons generated, the temperature of the single thin wire 2a is set to be below the melting point, and is selected to be the highest possible temperature. For example, while maintaining the surface temperature of the substrate 9 at a required value, the temperature of the single thin wire 2a is set to as high as possible, for example, 2,400°C. However, if the temperature of the single thin wire 2a rises, the temperature of the substrate 9 also rises, so the surface temperature of the substrate 9 is controlled to about 1,000°C using the cooling means built into the substrate holding table 6. do.

Next, the form of plasma generated when high frequency power is supplied from the above-mentioned high frequency power supply means to the first radiant heating plasma generation electrode 2 will be described below.
A mixed gas of methane (CH ₄ ) and hydrogen (H ₂ ) is ejected from the raw material gas ejection hole 13a, the pressure is set to a predetermined value, and the high frequency power generated by the high frequency power source 10 is transmitted to the coaxial cable 10a and the impedance matching device. 11. Supply to the first radiation heating plasma generation electrode 2 via the first high frequency power line 11a, the capacitor 15, the second high frequency power line 11b, and the first vacuum current introduction terminal 12a. Then, as shown in FIG. 3, plasma 102 is generated.
Since the plasma 102 is generated using the first radiant heating plasma generating electrode 2 and the high frequency power supply 10 whose frequency is in the VHF band (30 MHz to 300 MHz), it has the following characteristics.
(a) The first radiation heating and plasma generating electrode 2 generates thermoelectrons according to the Richardson-Dushman equation. Thermionic electrons 101 generated by the first radiant heating and plasma generation electrode 2 undergo α action (an action in which electrons collide with gas molecules to ionize them and generate new electrons) in a general plasma generation space, β In the same way as electrons generated by the action (the action in which ions collide with gas molecules and generate electrons) and the gamma action (the action in which positive ions collide with the cathode and release electrons), the ionization action of gas molecules and Has a dissociative effect.
(b) Plasma is generated by the electric field formed by the high-frequency power of the high-frequency power supply 10 applied to the first radiant heating plasma generation electrode 2, but due to the presence of thermionic electrons 101 (Edison effect) in (a) above, , compared to general plasma generation conditions, high-frequency plasma is easily generated. That is, the hot electrons 101 in (a) above are accelerated by an ultra-high frequency electric field, and VHF plasma is generated due to the above α effect and β effect. In general plasma generation, it depends on Paschen's law (the discharge starting voltage Vs takes a minimum value when the product of the pressure p and the distance d between the electrodes: pd = 1 to 10 Pa・m), and under high pressure conditions It is difficult to generate a glow discharge. However, in the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention shown in FIGS. Since the first radiation heating and plasma generating electrode 2 contains hot electrons generated, the Edison effect and ultra-high frequency electric field application effect (because the direction of the electric field changes between positive and negative directions in an extremely short period of time, the electron is captured in the spatial region, increasing the electron density), making it possible to generate plasma under high pressure conditions. As a result, ultra-high frequency glow discharge plasma can be generated when the distance d between the electrodes is, for example, 3 mm to 10 mm and, for example, at several kPa to about 10 kPa.
(c) Since the frequency of the high-frequency power source 10 is in the VHF band (30MHz to 300MHz), there is an electron capture effect in the plasma space (electric field generation space), ion damage is suppressed, and high-density plasma is generated. , maintained. Generation of high-density plasma with suppressed ion damage effectively promotes ionization and dissociation of gas molecules.
(d) When the plasma 102 is generated, a large amount of CH ₃ radicals (an electrically neutral chemically active species), which are the main precursors in diamond formation, and a large amount of atomic H are generated. The CH ₃ radicals, as the main precursors for diamond formation, are chemically adsorbed onto the substrate surface and undergo a surface chemical reaction on the substrate surface to form a large number of C--C bonds. A large amount of atomic H is incident on the CH ₃ radicals chemically adsorbed on the substrate surface and the CC bonds formed by the CH ₃ radicals, and hydrogen components and By extracting weakly bonded carbon components, a C--C bond with a regular tetrahedral structure (diamond structure) is efficiently formed and grown.

By the way, the transport (movement) of CH ₃ radicals in the gas phase follows Fick's law, which states that "the amount of diffusion of a substance per unit area and unit time is proportional to the concentration gradient." That is, this is expressed by the following equation (6). Note that the normal direction of the substrate surface is the coordinate x-axis, and the substrate surface is set to x=0. The amount of CH ₃ radicals flowing into the substrate surface per unit area and unit time J ₁ (CH ₃ ): (cm ⁻² · s ⁻¹ ) is determined by the diffusion coefficient of CH ₃ radicals being D(CH ₃ ).
J ₁ (CH ₃ )∝ D (CH ₃ )・{d[CH ₃ ]/dx} _x=0 ...(6)
However, {d[CH ₃ ]/dx} _x=0 is the CH ₃ concentration gradient (cm ⁻⁴ ) near the substrate surface.
The transport (movement) of atomic H follows Fick's law similarly to the transport (migration) of the CH ₃ radical described above. That is, the amount J ₂ (H) of atomic H flowing into the substrate surface is expressed by the following equation (7), where D(H) is the diffusion coefficient of atomic H.
J ₂ (H)∝ D(H)・{d[H]/dx} _x=0 ...(7)
However, {d[H]/dx} _x=0 is the H concentration gradient (cm ⁻⁴ ) near the substrate surface.
Equations (6) and (7) above indicate that the transport amount of CH ₃ radicals and atomic H near the substrate surface increases as their respective concentrations increase.
Furthermore, in order to increase {d[CH ₃ ]/dx} _x=0 in the above formula (6), it is effective to increase the density of electrons in the plasma that generates CH ₃ radicals. are doing.
Furthermore, in order to increase {d[H]/dx} _x=0 in the above equation (7), it is effective to increase the density of electrons in the plasma that generates atomic H. ing.

In the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention having the above characteristics (a) to (d), as shown in FIGS. 4 and 5, CH ₃ radicals and atomic H are mainly formed. Diamond is formed by a transport phenomenon caused by the diffusion of radicals, a chemical reaction phenomenon on the substrate surface, and a large amount of atomic H that pulls out hydrogen components and weakly bonded carbon components in the diamond formation precursor. Conceivable.
That is, in FIGS. 4 and 5, the highly concentrated CH ₃ radicals and atomic H generated in the region between the first radiation heating plasma generation electrode 2 and the substrate 9 move to the surface of the substrate 9 due to a diffusion phenomenon. do. A portion of the high concentration CH ₃ radicals is chemically adsorbed onto the surface of the substrate 9 . A portion of the CH ₃ radicals chemically adsorbed on the substrate surface are bonded in the form of CC due to a surface chemical reaction. A portion of the high concentration atomic H extracts the H component and the weakly bonded carbon component from the film surface and in the film. The extracted C and H components become gases such as CH ₄ and H ₂ and are discharged. In the substrate 9, C--C bonds are formed in a regular tetrahedral structure, and diamond is formed and grown.

Next, the operating procedure of the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention will be explained with reference to FIGS. 1 to 5.
First, a substrate loading/unloading valve (not shown) of the reaction vessel 1 is opened, and the substrate 9 is placed on the main surface 6a of the substrate holding table 6. Next, after closing the substrate loading/unloading valve, the inside of the reaction vessel 1 is brought to a predetermined degree of vacuum via the exhaust port 17a and the exhaust port 7b using a vacuum pump (not shown).
Next, the output of the DC power supply 8 is supplied to the radiation heating plasma generating electrode 2, and the surface temperature of the substrate 9 is set to, for example, 1,000° C. based on previously known data.
Next, while the surface of the substrate 9 is heated to the above temperature, the surface of the substrate 9 is cleaned using hydrogen plasma. Only hydrogen gas is introduced as the raw material gas from a raw material gas supply source (not shown), and the output of the high frequency power source 10 is supplied to the radiation heating plasma generating electrode 2 to generate hydrogen plasma. Note that the surface of the substrate 9 is cleaned using hydrogen plasma using a known method. The cleaning time of the surface of the substrate 9 with hydrogen plasma may be within several minutes. Here, the surface of the substrate 9 is cleaned using hydrogen plasma for 1 minute, for example.
Next, the output of the high frequency power supply 10 is temporarily returned to zero.
Next, methane gas and hydrogen are selected as raw material gases from a raw material gas supply source (not shown). The gas supply conditions include, for example, a flow rate ratio of hydrogen flow rate/methane gas flow rate = 100/3. Thereafter, methane gas and hydrogen gas whose predetermined flow rates are controlled by methane gas and hydrogen gas mass flow controllers (not shown) are supplied from a methane gas source (not shown) and a hydrogen gas source (not shown) to the raw material gas ejection hole via the raw material gas supply port 7. It is ejected from 13a.
Next, the degree of opening and closing of the exhaust valve (not shown) is controlled by an exhaust valve control device (not shown), and the internal pressure of the reaction vessel 1 is maintained at approximately 1 kPa to approximately 10 kPa. Here, for example, it is set and maintained at 4 kPa.

Next, the frequency of the high frequency power source 10 is set to VHF band (30 MHz to 300 MHz), for example, 60 MHz, and the output is set to, for example, 200 W to 1 KW, here 500 W.
Then, as shown in FIG. 3, between the first radiant heating plasma generating electrode 2 and the substrate holding table 6, and between the first radiant heating plasma generating electrode 2 and the source gas supply box 13, Plasma 102 is generated. The plasma 102 ionizes, dissociates, and excites the raw material gases methane (CH ₄ ) and hydrogen (H ₂ ). As a result, CH ₄ and H ₂ dissociate to generate CH ₃ radicals, atomic H, etc., which are precursors of diamond formation. CH ₃ radicals, atomic H, etc. diffuse and reach the surface of the substrate 9 .

Next, since the thickness of the diamond film is proportional to the duration of generation of the plasma 102, when a predetermined time has elapsed from the start of output from the high-frequency power source 10, the output thereof is reduced to zero. Also, the output of the DC power supply 8 is reduced to zero. The film forming time is determined based on data acquired in advance. Here, the duration is, for example, 30 minutes to 60 minutes, for example 60 minutes.
Note that the film forming time is related to the relationship between the distance between the first radiation heating plasma generating electrode 2 and the main surface 6a of the substrate holding table 6, the substrate temperature, the flow rate of methane gas, the flow rate of hydrogen gas, pressure, electric power, etc. Data can be grasped in advance and decisions can be made based on that data.
After the formation of the desired diamond film is completed, the supply of the methane gas and hydrogen gas is stopped, and the inside of the reaction vessel 1 is once evacuated to a high degree of vacuum. Thereafter, the reaction vessel 1 is returned to atmospheric conditions. After the reaction container 1 is returned to atmospheric conditions and the temperature of the substrate 9 reaches room temperature, a substrate loading/unloading valve (not shown) is opened and the substrate 9 is taken out. It is confirmed that a uniform diamond film is formed on the substrate 9 taken out from the reaction vessel 1.

As shown in the above description, the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention includes a first radiation heating plasma generation electrode 2, a high frequency power source 10 with a frequency of 60 MHz, and a direct current By providing the power supply 8 and the like, it is possible to handle large-area substrates, which is difficult with conventional devices.
That is, the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention has the following characteristics.
(b) In the device configuration, a first radiant heating plasma made of tantalum, an alloy containing tantalum, or tungsten that emits radiant energy (radiant heat), generates thermoelectrons, and forms an ultra-high frequency electric field. The main components are a generating electrode 2, a DC power source 8 equipped with a coil that blocks the intrusion of high-frequency power, and a high-frequency power source 10 equipped with a capacitor that blocks the intrusion of DC power.
(b) The first radiation heating plasma generation electrode 2 is made of tantalum or an alloy containing tantalum, or tungsten (φ=4.2 eV for tantalum, φ=4.5 eV for tungsten), which has a small work function φ. Therefore, it has the effect of being able to effectively generate thermoelectrons as the temperature rises. Further, the first radiation heating plasma generation electrode 2 can effectively generate high-density plasma by an ultra-high frequency electric field by applying an ultra-high frequency voltage in the VHF band (30 MHz to 300 MHz), and Due to the synergistic effect with this effect, it has the ability to form ultra-high density plasma. Further, the first radiation heating and plasma generating electrode 2 has the function of uniformly heating the substrate temperature to an arbitrary temperature selected from the range of about 800° C. to about 1,200° C.
(c) With the above (b), it is possible to turn the mixed gas of methane and hydrogen, which is the raw material gas, into plasma at high density and generate a large amount of CH ₃ radicals and atomic hydrogen H, etc., and it is possible to control the temperature at a high temperature. This has the effect that diamond can be efficiently formed on a substrate. Since the wavelength of the high-frequency power that excites the high-density plasma is as long as a meter, it is necessary to control the generation of CH ₃ radicals and increase the It is possible to control the generation of atomic hydrogen H at a high concentration, and the problems faced by conventional diamond forming apparatuses can be solved.

(Second embodiment)
A diamond forming apparatus using high frequency plasma CVD according to a second embodiment of the present invention will be described with reference to FIG. Reference is also made to FIGS. 1-5.
In addition, in the diamond forming apparatus using high frequency plasma CVD according to the second embodiment of the present invention, the first radiant heating and plasma generating electrode in the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention described above is used. 2, a second radiant heating and plasma generating electrode 22 is used.
FIG. 6 is a schematic configuration diagram showing the configuration of a second radiation heating plasma generating electrode which is a component of a diamond forming apparatus using high frequency plasma CVD according to a second embodiment of the present invention.
In FIG. 6, reference numeral 22 denotes a second radiant heating/plasma generation electrode. The second radiation heating electrode 22 is made of n rectangular thin plates 23a, 23b, 23c, 23n-1, and 23n made of tungsten (W), tantalum (Ta), or an alloy containing tantalum. The surfaces of the strip-shaped thin plates 23a, 23b, 23c, 23n-1, and 23n face the main surface 6a of the substrate holding table 6, and are arranged parallel to each other at equal intervals, and the first strip-shaped thin plate 23a and one end of the second strip-shaped thin plate 23b are connected by a first metal fixing rod 30a, and the other end of the second strip-shaped thin plate 23b is connected to one end of the second strip-shaped thin plate 23b. and one end of the third strip-shaped thin plate 23c are connected by a second metal fixing rod 30b, and one end of the n-1th strip-shaped thin plate 23n-1 is connected in sequence. and one end of the n-th strip-shaped thin plate 23n are connected by a 30n-1 metal fixing rod 30n-1, and the other end of the first strip-shaped thin plate 23a is connected to the 2 power supply areas 26a are provided, the second power supply area 26a and the first vacuum device current introduction terminal 12a are connected via the first power supply rod 5a, and the n-th thin strip 23n A second grounding region 26b is provided at the other end of the vacuum device, and the second grounding region 26b and the second vacuum device current introduction terminal 12b are connected via a second power supply rod 5b, Tension is applied to the first to n-th strip-shaped thin plates 23a to 23n by the tension applying means 3 provided in the first to n-1 metal fixing rods 30a to 30n-1. It has the following configuration.
The first to 30n-1 metal fixing rods 30a to 30n-1 are fixed to the wall of the reaction vessel 1 via the insulating material 4 by the tension applying means 3. Although the tension applying means 3 uses a coil spring type here, a plate spring type or a torsion rod type tension applying means may also be used. Further, the first to n-1th metal fixing rods 30a to 30n-1 are made of a metal with a high melting point, such as tungsten (W), tantalum (Ta), or an alloy containing tantalum. As for its dimensions, select a square bar with appropriate rigidity, for example, a square bar with cross-sectional dimensions of about 1 mm to 5 mm x 1 mm to 5 mm, or a round bar with a diameter of about 1 mm to 5 mm. Here, for example, a round bar with a diameter of 2 mm is selected.

The n strip-shaped thin plates 23a, 23b, 23c, 23n-1, and 23n are made of tungsten (W, φ=4.5 eV), tantalum (Ta, φ=4.2eV) or an alloy containing tantalum. Its dimensions are, for example, 0.1 mm thick x 1.0 mm wide from 0.05 mm to 0.5 mm thick x 1 to 5 mm wide.
The distance between the n strip-shaped thin plates 23a, 23b, 23c, 23n-1, and 23n and the main surface 6a of the substrate holder 6 is determined in consideration of plasma generation conditions and substrate temperature setting conditions. Here, the substrate temperature is set to about 700 to about 1,200° C., for example, 1,000° C., and the n strip-shaped thin plates 23a, which are conditions for increasing the generation of thermoelectrons, In order to maximize the temperature of 23b, 23c, 23n-1, 23n and to satisfy the condition that the generated plasma is a glow discharge region, the n strip-shaped thin plates 23a, 23b, 23c, 23n-1, 23n are The distance between the main surface 6a of the substrate holder 6 and the main surface 6a of the substrate holding table 6 is selected to be in the range of about 4 mm to about 40 mm. For example, let it be 7 mm.
The interval between the n strip-shaped thin plates 23a, 23b, 23c, 23n-1, and 23n is set, for example, in the range of 2 mm to 10 mm. Here, for example, it is assumed to be 5 mm.

Here, the second radiant heating plasma generation electrode used in the diamond forming apparatus by high frequency plasma CVD according to the second embodiment of the present invention, and the diamond forming electrode by high frequency plasma CVD according to the first embodiment of the present invention. The ability of the first radiant heating/plasma generation electrode used in the device to generate thermionic electrons will be compared.
The number Ne of thermoelectrons generated by the first and second radiation heating plasma generating electrodes 2 and 22 is determined by the Richardson-Dushman equation. That is, it is expressed by the following formula.
Ne ∝ T ²・exp {-φ/kT} (Unit: A/m ² ) ...(5)
Here, T is the absolute temperature of the first and second radiation heating plasma generation electrodes 2, 22, φ is the work function of the first and second radiation heating plasma generation electrodes 2, 22, and k is Boltzmann's constant. .
Since the above formula (5) is the number Ne of thermoelectrons generated per unit area, the number of thermoelectrons generated by the first and second radiation heating plasma generating electrodes 2 and 22 is calculated as follows. Become.
The number of thermoelectrons generated by the first radiant heating plasma generating electrode 2 is determined by the surface area of the single thin wire 2a of the first radiant heating plasma generating electrode 2, that is, the circumference of the diameter of 0.3 mm = The number is proportional to the product of 0.0942 cm and length 130 cm.
The number of thermoelectrons generated by the second radiation heating and plasma generation electrode 22 is determined by the number of thermionic electrons generated by the n strip-shaped thin plates 23a, 23b, 23c, 23n-1, and 23n of the second radiation heating and plasma generation electrode 22. The number is proportional to the surface area, that is, the product of the circumferential length of a thickness of 0.1 mm x width of 1.0 mm = 0.22 cm and length of 432 cm.
That is, from the viewpoint of the number of thermoelectrons generated, it can be seen that the second radiation heating and plasma generation electrode 22 is overwhelmingly superior to the first radiation heating and plasma generation electrode 2.
Therefore, the diamond forming apparatus using high frequency plasma CVD according to the second embodiment of the present invention increases the amount of thermoelectrons generated compared to the diamond forming apparatus using high frequency plasma CVD according to the first embodiment of the present invention. Since it strengthens the effect of increasing plasma density, it is possible to turn a mixed gas of methane and hydrogen, which is a raw material gas, into plasma at high density and generate a large amount of CH ₃ radicals and atomic hydrogen H, etc. This results in the effect that diamond can be efficiently formed on the substrate.

The operating procedure of the high frequency plasma CVD diamond forming apparatus according to the second embodiment of the present invention is the same as that of the high frequency plasma CVD diamond forming apparatus according to the first embodiment of the present invention.
As shown in the above description, the diamond forming apparatus using high frequency plasma CVD according to the second embodiment of the present invention includes the second radiant heating electrode 22, the high frequency power source 10 with a frequency of 60 MHz, and the DC power source 8. By providing the above, it is possible to handle large-area substrates, which is difficult to do with conventional devices.
That is, the diamond forming apparatus using high frequency plasma CVD according to the second embodiment of the present invention has the following features.
(b) In the device configuration, a second radiation heating electrode made of tantalum, an alloy containing tantalum, or tungsten that emits radiant energy (radiant heat), generates thermoelectrons, and forms an ultra-high frequency electric field. 22, a DC power source 8 equipped with a coil 16 that blocks the intrusion of high-frequency power, and a high-frequency power source 10 equipped with a capacitor 15 that blocks the intrusion of DC power.
(b) The second radiation heating electrode 22 is made of tantalum or an alloy containing tantalum, or tungsten (φ = 4.2 eV for tantalum, φ = 4.5 eV for tungsten), which has a small work function φ. , has the effect of being able to effectively generate thermoelectrons as the temperature rises. In addition, the second radiation heating electrode 22 can effectively generate high-density plasma due to an ultra-high frequency electric field by supplying an ultra-high frequency voltage in the VHF band (30 MHz to 300 MHz), and can also reduce the Edison effect of the thermoelectrons. Due to the synergistic effect with this, it has the ability to form ultra-high density plasma. Further, the second radiation heating electrode 22 has the function of uniformly heating the substrate temperature to an arbitrary temperature selected from the range of about 800° C. to about 1,200° C.
(c) With the above (b), it is possible to turn the mixed gas of methane and hydrogen, which is the raw material gas, into plasma at high density and generate a large amount of CH ₃ radicals and atomic hydrogen H, etc., and it is possible to control the temperature at a high temperature. This has the effect that diamond can be efficiently formed on a substrate. Since the wavelength of the high-frequency power that excites the high-density plasma is long, on the order of meters, it is necessary to control the generation of CH ₃ radicals, which are essential for the formation of large-area diamonds on 4-inch to 5-inch substrates, and to achieve high concentration. It is possible to control the generation of atomic hydrogen H, and the problems faced by conventional diamond forming apparatuses can be solved.

1... reaction container,
2...first radiation heating plasma generating electrode,
2a... one thin wire made of tungsten (W) or tantalum (Ta) or an alloy containing tantalum,
2aa... multiple folds,
2b... first power feeding area,
2c...first grounding area,
3... Tension applying means,
4... Attachment jig to the reaction vessel wall made of insulating material,
5a, 5b... first and second power supply rods,
6... Board holding stand,
6a...Main surface of substrate holding stand,
7... Raw material gas supply port,
8...DC power supply,
9...Substrate,
10...High frequency power supply,
11... Impedance matching box,
12a, 12b...first and second vacuum current introduction terminals,
13... Raw material gas supply box,
13a... Raw material gas ejection hole,
15... Capacitor,
16...Coil,
19... Radiation thermometer,
19a...Quartz window for temperature measurement,
22...Second radiation heating and plasma generation electrode.

Claims (7)

a reaction vessel equipped with a source gas supply system and an exhaust system containing at least methane gas (CH ₄ ) and hydrogen gas (H ₂ ); and a substrate holding stand disposed inside the reaction vessel and having a main surface for holding a substrate. , a radiant heating and plasma generation electrode that generates radiant energy to heat the substrate and generates high-frequency plasma, a DC power supply that supplies DC power to the radiant heating and plasma generation electrode, and the radiant heating and plasma generation electrode. A high-frequency power source that supplies high-frequency power to the vacuum device via an impedance matching device, a first electrically ungrounded current introduction terminal for the vacuum device, and a grounded second current introduction terminal for the vacuum device. A diamond forming apparatus using high frequency plasma CVD,
The radiation heating and plasma generation electrode includes a power feeding area to which the DC power and the high frequency power are fed, and a grounding area to be grounded,
The output terminal of the DC power source is connected to the first vacuum device current introduction terminal via a coil that blocks intrusion of the high frequency power generated by the high frequency power source,
The output terminal of the impedance matching device is connected to the first vacuum device current introduction terminal via a capacitor that blocks the intrusion of the DC power generated by the DC power supply,
The power supply region of the radiation heating plasma generation electrode and the first vacuum device current introduction terminal are connected,
The grounding region of the radiation heating plasma generation electrode and the grounded second vacuum device current introduction terminal are connected, and
The radiation heating and plasma generation electrode is arranged directly above the substrate holding table,
the substrate is placed on the substrate holder,
The DC power is supplied from the DC power supply to the radiant heating/plasma generation electrode to raise the temperature of the radiant heating/plasma generation electrode, and the substrate is heated by the radiant energy emitted by the radiant heating/plasma generation electrode. ,
The high frequency power is supplied from the high frequency power source to the radiation heating plasma generation electrode via the impedance matching device, and the raw material gas supplied from the raw material gas supply system is turned into plasma, thereby forming diamonds on the substrate. A diamond forming apparatus using high frequency plasma CVD, which is characterized by forming. The radiation heating and plasma generation electrode includes a single thin wire made of tungsten (W), tantalum (Ta), or an alloy containing tantalum, the single thin wire is provided with a plurality of bent portions, and the single thin wire is provided with a plurality of bent portions, and Arranged parallel to the main surface of the holding table, one end of the one thin wire is provided with a first power supply region, and the first power supply region and the first vacuum device current introduction terminal are connected. a first grounding region is provided at the other end of the one thin wire, and the first grounding region and the second vacuum device current introduction terminal are connected,
2. The diamond forming apparatus using high-frequency plasma CVD according to claim 1, wherein tension is applied to said one thin wire by tension applying means provided in said plurality of bent portions. The radiation heating and plasma generation electrode includes first to nth strip-shaped thin plates made of n pieces made of tungsten (W), tantalum (Ta), or an alloy containing tantalum, and the surface of each strip-shaped thin plate is faces the main surface of the substrate holder, and each of the first to nth strip-shaped thin plates are arranged parallel to each other at equal intervals,
One end of the first strip-shaped thin plate and one end of the second strip-shaped thin plate are connected by a first metal fixing rod, and the other end of the second strip-shaped thin plate is connected. and one end of the third strip-shaped thin plate are connected by a second metal fixing rod, and one end of the n-1th strip-shaped thin plate and the n-th strip-shaped thin plate are sequentially connected. one end of which is connected with the n-1th metal fixing rod,
A second power supply region is provided at the other end of the first thin strip, and the second power supply region and the first vacuum device current introduction terminal are connected,
A second grounding region is provided at the other end of the n-th strip-shaped thin plate, and the second grounding region and the second vacuum device current introducing terminal are connected,
The high-frequency plasma according to claim 1, wherein tension is applied to the first to n-th strip-shaped thin plates by tension applying means provided in the first to n-1 metal fixing rods. Diamond forming equipment using CVD. 3. The diamond forming apparatus by high-frequency plasma CVD according to claim 1 or 2, wherein the radiation heating and plasma generating electrode has a circular cross-sectional shape with a diameter of approximately 0.1 mm to 1.0 mm. According to claim 1 or claim 3, the radiation heating and plasma generation electrode has a rectangular cross-sectional shape with a thickness of approximately 0.05 mm to 0.5 mm and a width of approximately 0.5 mm to 10 mm. A diamond forming apparatus using high frequency plasma CVD as described above. The diamond forming apparatus using high frequency plasma CVD according to any one of claims 1 to 5, wherein the frequency of the high frequency power source is in the VHF band (30 MHz to 300 MHz). The diamond forming apparatus by high frequency plasma CVD according to any one of claims 1 to 6, wherein the substrate holding table is made of tantalum (Ta) and includes a cooling means using a coolant. .

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