JP3008466B2 - Selective growth method of diamond thin film using diamond fine powder - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for selectively forming a diamond thin film.

(Problems to be Solved by the Prior Art and the Invention) Diamond has the highest hardness and thermal conductivity among all materials, and is widely used industrially such as 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 and high-temperature method has various difficulties as a diamond manufacturing method, such as a complicated manufacturing method, a large-sized manufacturing apparatus, and uneconomical. On the other hand, the synthesis of diamond by the recently developed low-pressure gas phase method is simple in its production method,
This is an economical diamond production method. 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.

One of the difficulties of forming a diamond thin film by the low-pressure gas 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 smooth film may be formed. It is considered that the reason for this is that the pretreatment causes "flaws" on the substrate surface and increases the density of crystal growth nuclei by five orders of magnitude. However, this conventional method lacks reproducibility and does not always form a smooth film.

An object of the present invention is to provide a method for selectively forming a uniform diamond thin film having a smooth surface with good reproducibility.

(Means for Solving the Problems) In the selective growth method of the present invention, diamond powder is formed as a seed crystal on a substrate surface, and then a diamond thin film is selectively formed. A diamond fine powder having a particle size of several tens of nm or less is used as a seed crystal, which is buried at a high density on the substrate surface, and a homogenous thin film having a smooth surface can be formed by using this as a growth nucleus. As a method for selectively forming a diamond thin film, first, a diamond fine powder seed crystal is implanted on the entire surface of a substrate, and a pattern is formed according to a usual lithography technique. Next, the diamond fine powder on the substrate surface not covered with the protective film for pattern formation is reacted in an oxygen plasma atmosphere, and the diamond fine powder is etched away. Next, the protective film is removed to expose the diamond fine powder on the substrate, and diamond is selectively grown on the portion of the substrate where the diamond fine powder remains, in accordance with ordinary low-pressure vapor deposition of diamond. Let it.

In order to remove the diamond fine powder, a method of destroying the diamond fine powder by a physical method such as ion irradiation, ion sputtering, or electron beam irradiation is effective other than utilizing a chemical reaction by oxygen plasma. The substrate material for forming the diamond thin film is not particularly limited as long as diamond can be grown in a vapor phase, and examples thereof include oxides, nitrides, semiconductors, metals, and metalloids. In the low pressure gas phase method, any method for forming diamond may be used as long as it is a diamond manufacturing method such as a thermal gas phase method, a plasma gas phase method, and an electron impact gas phase method.

Before the fine powder is implanted, SiO ₂ , Si ₃ N ₄
A method may be used in which a pattern of a protective film such as that described above is formed, fine powder is then implanted, the protective film is removed by etching or the like, and the fine powder is left only in portions where the protective film was not formed. . Further, after the fine powder is implanted on the entire surface, a focused ion beam or a focused electron beam is irradiated to a desired portion to destroy the fine powder in that portion, and then a thin film is grown, whereby a thin film can be selectively formed.

The point that the method of the present invention differs from the conventional diamond thin film selective formation technique is that prior to the formation of the diamond thin film,
By artificially forming a diamond fine powder having a particle size of several tens of nanometers on the substrate surface and using it as a seed crystal, a uniform and smooth diamond thin film surface can be produced with good reproducibility. In the above-mentioned conventional method, although the main focus has been on increasing the number of crystal growth nuclei by generating some flaws on the substrate surface due to the pretreatment of the substrate, the substance of the crystal growth nucleus was unknown. The inventor of the present invention did not form a smooth diamond thin film not only because of the flaws on the substrate, but also part of the diamond powder with a particle size of several microns It was discovered that it was planted in. Conventionally, diamond powder was used to scratch the substrate, so that "planting" did not always occur and reproducibility was poor.

The apparatus of the present invention using such a method will be described. The apparatus comprises an apparatus for forming diamond fine powder on a substrate, an apparatus for removing diamond fine powder, and an apparatus for forming a diamond thin film. The latter is
A heating furnace capable of reducing the pressure inside the furnace, a supply system for supplying a mixed gas of hydrocarbon gas and hydrogen gas into the heating furnace, a system for supporting a substrate in the heating furnace, a hydrocarbon gas and hydrogen It consists of a system that converts gas into reactive gas.

(Example) FIG. 2 shows an example of an apparatus for forming a diamond fine powder on a substrate surface. The apparatus includes a metal disk (2) connected to an ultrasonic generator (1) and a metal disk (2). It consists of an installed substrate (3). The substrate is fixed by a micrometer (4) to a gantry (5) movable vertically to the 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. The metal disk (2), the substrate (3), and the pedestal (5) of the substrate were prepared by suspending an ordinary diamond powder having a particle diameter of about 10 microns used in an abrasive, a cutter, or the like in a solution of water, alcohol, acetone, or the like. It is immersed in a container (8) containing the liquid. 300μ gap between metal disk (2) and substrate (3)
m, stirred by an ultrasonic generator (1) for about 10 minutes, taken out of the substrate, washed, and dried. As a result, diamond powders of 10 μm collide with each other and pulverize, and diamond fine powders having a particle size of several tens nm or less are embedded at high density on the substrate surface. That is, the powder is brought into contact with the substrate by the ultrasonic wave, and the fine powder is buried by the chipping.

FIG. 1 shows an example of a pattern forming step on a substrate prepared by the method of FIG. A protective film for forming a pattern, for example, a photoresist film (12) is applied to a silicon substrate (3) having a diamond fine powder (9) formed on the entire surface (FIG. 7A). On this film, a pattern (12) having a line width of 0.5 μm is formed by a usual lithography technique, and the diamond fine powder (9) not covered with the protective film is exposed to oxygen plasma (pressure 4 × 10 ^-2 Pa) for 10 times. Then, it is exposed for a minute, etched and removed (FIG. 7B). Next, the substrate (3) from which the diamond fine powder has been removed is immersed in a suitable solvent such as acetone to remove the protective film (FIG. (C)). Before the fine powder is implanted, SiO ₂ , Si ₃ N
_A method may be used in which a pattern of a protective film such as ₄ is formed, fine powder is implanted thereafter, the protective film is removed by etching or the like, and the fine powder is left only in a portion where the protective film was not formed. . This silicon substrate was transferred to a diamond thin film forming apparatus, and heat-treated for 60 minutes in a mixed gas (pressure 5 × 10 ³ Pa) atmosphere having a sample mixing temperature of 850 ° C. and a hydrocarbon gas / hydrogen gas volume ratio of 1%. As a result, it was confirmed that a diamond thin film pattern 14 having both a thickness and a width of 0.5 μm was formed on the diamond fine powder 9 ((d)).
Figure). Although the steps shown in FIGS. 1A to 1D were performed several times, the same thin film pattern was always obtained, and it was confirmed that reproducibility was obtained.

(Effect of the Invention) According to the present invention, selective growth of a diamond thin film on a substrate can be performed with good reproducibility.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a selective growth method according to an embodiment of the present invention, and FIG. 2 is a schematic diagram showing an apparatus for embedding diamond fine powder on a substrate. The numbers following the numbers in the figure are shown. 1 ... Ultrasonic generator, 2 ... Metal disk, 3 ... Substrate sample, 4 ... Micrometer, 5 ... Substrate support, 6 ...
... Chuck, 7 ... Rotary motor, 8 ... Container, 9 ...
Diamond fine powder, 10 ... Photoresist film, 11 ...
Diamond thin film.

Claims (2)

(57) [Claims] A substrate is immersed in a solution in which diamond powder of several tens of microns is suspended, and ultrasonic waves are generated to pulverize the diamond powder of several tens of microns into diamond fine powder of several tens of nm. And selectively forming diamond using the diamond fine powder of several tens of nm or less embedded as a seed crystal. 2. The method for selectively growing a diamond thin film according to claim 1, wherein a base for generating ultrasonic waves and a surface of the substrate on which diamond is selectively grown face each other.