JP2638275B2 - Production method of vapor phase diamond thin film using diamond fine powder as seed crystal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a diamond thin film.

(Prior Art and Problems to be Solved by the Invention) Diamond has the highest hardness and thermal conductivity among all materials, and is widely used industrially, such as in abrasives and cutters. A method for producing diamond by a high-temperature and high-pressure method is widely known. The diamond synthesis method by the high-pressure high-temperature method has various difficulties as a diamond manufacturing method, such as a complicated manufacturing method, a large-sized manufacturing apparatus is not economical, and a manufacturing process is not simple. On the other hand, a recently developed low pressure phase method for synthesizing diamond is a simple and economical method for producing diamond. Diamond synthesis by the vapor phase method is characterized by the synthesis of thin film diamond. Diamond thin films are attracting attention as electronic materials such as semiconductor lasers, heat sinks for LSI devices, and high-temperature semiconductors, and are being studied. The diamond thin film is grown on a substrate surface such as silicon or tungsten.

One of the difficulties of forming a diamond thin film by the low pressure phase method is that it is difficult to obtain a uniform thin film. When diamond is grown using silicon or tungsten as a substrate, massive diamond particles grow, the surface becomes rough, and a smooth film cannot be obtained. As a solution to this problem, it has been proposed to pretreat the substrate before forming the diamond thin film. For example, when a substrate is immersed in a suspension of diamond powder having a particle diameter of about several microns and stirred for a certain period of time by ultrasonic waves, the growth of a diamond thin film is promoted, and a film having a smooth surface may be formed. It is believed that this pretreatment causes "cracks" on the substrate surface and increases the density of crystal growth nuclei by as much as five orders of magnitude. However, this method lacks reproducibility and does not always provide a film having a smooth surface.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for producing a uniform diamond thin film having a smooth surface and good reproducibility, and an apparatus therefor.

(Means for Solving the Problems) The present invention is to maintain a diamond powder suspension layer having a particle diameter of submicron or more between a substrate surface on which a diamond thin film is to be formed and a vibrating plate vibrated by ultrasonic waves. And pulverize the diamond powder to fill the substrate surface with diamond fine powder having a particle size of several tens of nm or less, and use this as a crystal nucleus to form a diamond thin film by a vapor phase method. The embedded diamond fine powder is a powder composed of diamond fine particles having a particle diameter of several tens nm or less. Since the diamond powder before being pulverized has a particle size of submicron or more (usually several microns or more), it is smaller by one to two orders of magnitude. The diamond powder is brought into contact with the substrate by ultrasonic waves, and the chip is chipped and the fine powder is embedded in the substrate. As a result, the nuclei are uniformly dispersed and form high-density diamond crystal nuclei.

In addition, a gas for forming a diamond thin film is arranged between a vibration plate vibrating by ultrasonic waves and a plate opposed thereto, and a diamond powder suspension or a diamond powder paste having a particle size of submicron or more is put between the two plates, Ultrasonic waves may be used to pulverize the diamond powder to bury diamond fine powder having a particle size of several tens of nm or less on the surface of the substrate.

Efficiency is improved by adding hard particles having a particle size of several hundred μm to the suspension layer or paste in addition to diamond powder having a particle size of submicron or more.

The diamond thin film is formed by converting a mixed gas of hydrocarbon gas and hydrogen gas into a reactive gas by heating or ionizing. This reaction gas grows homoepitaxially, using diamond fine powder uniformly dispersed on the substrate surface as a seed crystal, and has high adhesion to the substrate, smooth surface,
Grow into a homogeneous diamond thin film. The substrate material for forming the diamond thin film is not particularly limited as long as diamond is homoepitaxial vapor phase growth, and examples thereof include oxides, nitrides, semiconductors, metals,
Semimetals.

The method of forming diamond by the low pressure gas phase method is a diamond manufacturing method such as thermal vapor phase, plasma vapor phase method, electron impact gas phase method, etc., and the reactive gas flow is viscous and there is no direction in gas transport. is important. The thickness of the diamond thin film produced by the low-pressure gas phase method depends on the pressure of the mixed gas of hydrocarbon gas and hydrogen gas, the mixing ratio, the temperature of the reactor,
By adjusting the reaction time and the like, it is possible to grow to a desired thickness.

This method is different from the conventional method of pretreating a substrate for forming a diamond thin film in that diamond fine powder having a particle size of several nm is embedded in the substrate surface prior to film formation. Conventional methods have focused on creating some kind of flaw on the crystal surface. However, the present inventor believes that the formation of a smooth diamond thin film on the substrate is not due to the flaws formed on the substrate, but a part of the diamond powder having a particle diameter of about several μm used for flaws becomes a fine powder and becomes ultrafine. It was found for the first time that it was implanted on the substrate surface by sound waves. In the past, diamond powder was used to scratch the substrate, so that part of the powder was not always implanted in the substrate, and the reproducibility was poor.

Describing a thin film growth apparatus, this apparatus includes an apparatus for partially embedding diamond fine powder and an apparatus for forming a diamond thin film. The latter includes a heating furnace capable of reducing the vacuum inside, a supply system for supplying a mixed gas of hydrocarbon gas and hydrogen gas into the heating furnace, a system for supporting the substrate in the heating furnace, and a hydrocarbon. It consists of a system that converts gas and hydrogen gas into reactive gas.

(Embodiment) FIG. 1 shows an example of an apparatus for partially embedding the diamond fine powder of the present invention in the surface of a substrate, comprising a metal disk (2) connected to an ultrasonic generator (1). It consists of a substrate (3) placed in parallel with this. The substrate is fixed to a gantry (5) movable vertically to the micrometer (4) metal plate. The gantry is attached to a rotating motor (7) by a chuck (6) and continuously rotates around an axis perpendicular to the substrate surface. A metal disk (2), a substrate (3), and a base (5) of a substrate are made of a suspension of diamond powder having a particle diameter of about 10 microns, which is generally used in a solution of water, alcohol, acetone, or the like with an abrasive or a cutter. Immersed in a container (8) containing Make the gap between the metal disk (2) and the substrate (3) 30
The substrate is brought close to 0 μm, stirred for 1 minute by the ultrasonic generator (1), the substrate (3) is taken out, washed, and dried. As a result, diamond fine powder having a particle size of several tens nm or less is partially embedded in the substrate surface.

FIG. 2 shows an example of an apparatus for forming a diamond thin film, in which a mixed gas of a hydrocarbon gas and a hydrogen gas is converted into a reactive mixed gas by a thermal vapor phase method. A diamond or a silicon substrate or a tungsten substrate (3) in which diamond powder is partially embedded is placed on a sample stand (9) and placed in the center of an easy vacuum (10). The inside of the container is evacuated by the evacuation system (11). At a stage where a predetermined pressure, for example, about 10 ⁻⁵ Torr is confirmed by a vacuum gauge (12), the gas supply system hydrocarbon gas and the hydrogen gas are respectively supplied to the supply system (1).
Supplied from 3) and (14). The pressure is measured by a vacuum gauge (12), and at a predetermined pressure, a heater (15) provided on the sample stand is energized from a conductive terminal (16) and heated. The substrate temperature is measured and controlled by a thermocouple (18) installed on the sample mount. A heating wire (19) of a tungsten wire or a tungsten net is provided on the upper part of the sample stand, and electricity is supplied from the conductive terminal (17) to heat.

When the surface of a silicon substrate is treated using the apparatus shown in FIG. 1, diamond fine powder having a particle size of several tens nm or less is embedded. When the silicon substrate surface is heat-treated for 10 minutes in a mixed gas (pressure 20 Torr) with a sample temperature of 850 ° C. and a hydrocarbon gas / hydrogen gas volume mixing ratio of 1% using the apparatus of FIG. As shown in the electron micrograph of the above, fine diamond particles having a crystallographic habit of several tens of nm were formed on the silicon surface. When heat treatment is continued for about 1 hour in this atmosphere, a uniform polycrystalline diamond thin film having a smooth and amorphous portion is formed from the surface having a thickness of 0.5 μm. When the above-described thin film manufacturing process was performed several times, smooth and uniform thin films were all obtained, and it was found that sufficient reproducibility was obtained.

The formation of the diamond thin film by the vapor phase method described in this embodiment was performed by adjusting the mixing ratio of hydrocarbon gas and hydrogen gas to 3% and 5%.
%, And the other conditions were the same. As a result, fine diamond particles having a larger particle size were formed on the surface of the silicon substrate. Crystal growth nucleus density is 10 ¹⁰ cm ^-2
Met. When heat treatment was continued for about 1 hour in this atmosphere, a homogeneous polycrystalline diamond thin film having a smooth surface and no amorphous portions was obtained with good reproducibility, as is clear from the electron micrograph of FIG.

FIG. 5 shows another example of embedding diamond fine powder on the surface of an object. Sample (51) contains a suspension obtained by mixing diamond powder and stainless metal beads having a particle diameter of several hundred μm. Immerse in the container (52) and fix it to the sample stand (53). The suspension has a metal disk (55) connected to an ultrasonic generator (54). The ultrasonic generator (54) is operated for an appropriate period of time to stir, and a diamond fine powder having a particle size of several tens nm or less is partially embedded in the sample surface. The substrate is taken out, washed, dried, and a diamond film is formed on the sample surface by a normal low-pressure gas phase method. Using this device,
Using a suspension of acetone mixed with diamond powder having a particle diameter of 30 μm and stainless beads having a particle diameter of 500 μm, a silica glass rod having a diameter of 5 mm and a length of 5 cm was subjected to a surface treatment for 10 minutes. Using a device as shown in FIG. 2, this sample was heat-treated by a hot filament method at a sample temperature of 850 ° C. in an atmosphere of a mixed gas (pressure: 20 Torr) of 2% by volume of hydrocarbon gas and hydrogen gas at a pressure of 20 Torr. Was done. The distance between the sample and the filament was 10 mm, and it was rotated around the axis of the silica glass rod during the reaction. Observation of the cross section of the silica glass rod showed that a polycrystalline diamond film having a thickness of 2 μm was formed uniformly, the surface of the film was smooth, and the reproducibility was sufficient. As in this example, the substrate on which the thin film is to be formed is not limited to a flat substrate, but may have various shapes such as an uneven surface or a curved surface. Instead of stainless beads, diamond particles or tungsten particles having a particle diameter of several hundred μm may be used.

FIG. 6 shows a pressure pump (67) attached to a container (66) containing a suspension in which diamond powder having a particle size of about 10 μm and stainless metal beads having a particle size of several hundred μm are mixed.
The suspension through the tube (68) through the nozzle (69)
Or at high speed, spray the suspension on the surface of sample 61,
At the same time, it is a device for embedding diamond fine powder on the sample surface. Even with this apparatus, a diamond coating can be obtained with good reproducibility.

In all of the above examples, a suspension containing at least diamond powder was used, but diamond powder or a paste containing hard particles such as stainless steel may be used instead.

Even better results can be obtained by mixing diamond fine powder having a particle size of several tens of nm into the diamond paste. Diamond fine powder is obtained as follows.

For example, in an apparatus shown in FIG. 7, an ethyl alcohol suspension containing diamond powder having a particle size of about 10 μm is placed in a container 71, and the distance between the metal plates 72 and 73 is 300 μm with a micrometer 74.
m, ultrasonic waves are applied from an ultrasonic generator 75 to vibrate the metal plate 73 perpendicular to the surface, and the powders are crushed by collision of the powders to produce a diamond fine powder having a particle size of several tens nm or less. Generate in liquid. During the application of the ultrasonic waves, the suspension is circulated through a tube 77 by a pump 76 and returned between the metal plates 73 and 72 by an inner tube 78 passing through the metal plate 73. After this pulverizing treatment, the suspension is transferred to a sedimentation vessel, and a powder having a large particle diameter is sedimented and separated, thereby obtaining only the fine powder described above.

(Effects of the Invention) According to the present invention, a uniform diamond film having a smooth surface can be formed with good reproducibility.

[Brief description of the drawings]

FIG. 1, FIG. 5, and FIG. 6 are schematic views for embedding diamond fine powder in a substrate. FIG. 2 is a schematic diagram of a diamond thin film forming apparatus. FIG. 3 is an electron micrograph showing the particle structure of the fine diamond powder embedded in the silicon substrate surface. FIG. 4 is an electron micrograph showing the particle structure of diamond fine particles grown using diamond fine powder embedded in the silicon substrate surface as a seed crystal. FIG. 7 is a schematic view of an apparatus for obtaining fine diamond powder. The numbers in the figure indicate the following. 1 ... Ultrasonic generator, 2 ... Metal disk, 3 ... Substrate sample, 4 ... Micrometer, 5 ... Substrate support, 6 ...
... Chuck, 7 ... Rotary motor, 8 ... Container, 9 ... Sample stand, 10 ... Empty container, 11 ... Evacuation system, 12 ... Vacuum gauge, 13, 14 ... Gas supply valve, 15 ... ... heater, 16,
17 Conductive terminal, 18 Thermocouple, 19 Heat generating filament.

Claims (3)

(57) [Claims] A diamond powder suspension layer having a particle diameter of submicron or more is maintained between a substrate surface on which a diamond thin film is to be formed and a vibrating plate vibrated by ultrasonic waves. A diamond fine powder having a particle size of several tens of nm or less is embedded in a substrate surface, and the diamond nucleus is used as a crystal nucleus to form a diamond thin film by a vapor phase method. 2. A diamond powder suspension or diamond powder paste having a submicron particle size or more between a vibrating plate vibrated by ultrasonic waves and a plate opposed thereto, on which a diamond thin film is to be formed. And then apply ultrasonic waves to pulverize the diamond powder to embed diamond fine powder with a particle size of several tens of nanometers or less on the surface of the substrate, and use this as a crystal to form a diamond thin film by a vapor phase method. Manufacturing method. 3. The method for producing a diamond thin film according to claim 1, wherein hard particles having a particle size of several hundred μm are added to the suspension layer or the paste in addition to the diamond powder having a particle size of submicron or more. Law.