JPH06116088A - Method of manufacturing thin film diamond - Google Patents

Abstract

(57) [Summary] [Purpose] The nucleation density during diamond crystal synthesis was set to 10
^A finer and more flat thin film diamond is formed with ¹⁰ / cm ² or more. [Structure] A p-type silicon (100) substrate is dipped in a solution in which alcohol is mixed with about 27% potassium hydroxide, and anisotropic etching is performed to form pyramid-shaped irregularities on the substrate surface. 2 g of diamond powder with a particle size of 0.25 μm
Dip the substrate in 100cc of ethanol
Perform ultrasonic cleaning for an hour. By doing so, fine diamond particles to the uneven portion of the substrate surface remains degree to 10 ⁹ / cm ^2, can be increased nucleation density of approximately 10 ¹⁰ / cm ^2. Therefore, a fine and flat polycrystalline thin film diamond can be formed by synthesizing a thin film diamond by a vapor phase synthesis method using the residual fine particles as nuclei.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing thin film diamond for forming polycrystalline thin film diamond.

[0002]

2. Description of the Related Art Polycrystalline diamond is the hardest material of all materials, has the highest thermal conductivity, high electrical insulation, wide transparency from ultraviolet to infrared and chemical stability, and is a good material. is there. Further, it is known as a material having a larger band gap, dielectric breakdown voltage and carrier mobility than semiconductor materials such as silicon and gallium arsenide.

Further, a semiconductor thin film layer can be formed by adding an impurity element during the vapor phase synthesis of thin film diamond or by ion implantation into diamond. By utilizing these characteristics, a high temperature resistance that can function even at a high temperature of 500 ° C. or higher can be obtained. There is a possibility that electronic devices such as a light emitting device and an ultraviolet light emitting device, which have been impossible in the past, can be realized.

In recent years, formation of a polycrystalline thin film diamond on a different type of substrate by a vapor phase method has been tried by various methods such as a hot filament CVD (chemical vapor deposition) method, a microwave plasma CVD method or a DC plasma jet CVD method. There is.

In forming a polycrystalline thin film diamond by these methods, methane (CH ₄ ), carbon monoxide (CO),
Carbon dioxide (CO ₂ ), methanol (CH ₃ OH), hydrogen (H ₂ )
The nucleation density of the synthesized diamond and the particle size of the grown diamond can be greatly affected by the type of source gas such as, the gas concentration, the gas activation method, the substrate temperature, and the substrate pretreatment method. It is being revealed.

Further, the nucleation of diamond crystals on the substrate in the non-thermal parallel state depends on the substrate material, the surface state of the substrate (pretreatment method of the substrate surface), the temperature and the supersaturation degree of the reactive species, There are various points to be solved in order to use a polycrystalline diamond thin film as a material applicable to a semiconductor substrate. For example, in the above-mentioned diamond vapor phase growth, physical sputtering and chemical erosion proceed at the same time because the CVD is performed at a high hydrogen concentration and a high substrate temperature, and the adhesion probability is further reduced. Therefore, there is a theory that the improvement of the nucleation density of diamond is limited.

By the way, as described above, the pretreatment method of the substrate, the type of the substrate and the surface condition of the substrate are major factors for the nucleation of diamond crystals on the substrate in the non-thermal equilibrium state. Therefore, a method for forming a high-quality polycrystalline thin film diamond that can be used as a semiconductor substrate on different kinds of substrates is being sought by examining such various conditions.

As a method for forming diamond crystals, FI
Using B (focused ion beam) method, EB lithography (electron beam writing apparatus) method and dry etching method, a recess having a depth and width of 50 Å to 5000 Å is formed on the substrate to form a thin film diamond. A method of synthesizing is shown (Japanese Patent Laid-Open No. 1-2032).
No. 93). This method is a method of nucleating / growing diamond crystals from the unevenness of the substrate, and in particular, a method of synthesizing a flat and dense thin film diamond that can be used as a semiconductor substrate is not shown.

Further, according to the synthesis of high quality diamond crystals, it becomes possible to form polycrystals, which are relatively close to natural diamond, by controlling the kind of gas, the substrate temperature, etc. even on different kinds of substrates. It was However, at present, the surface of the synthetic thin film has large irregularities, and the obtained polycrystalline thin film diamond has not been put to practical use as a semiconductor material. For example, microwave plasma CV
The surface roughness of the polycrystalline thin film diamond formed by vapor phase synthesis of D method is about ± 0.2 μm in a thin film with a thickness of 1 μm,
It is known that the surface roughness tends to increase as the film thickness increases. As a solution to this problem, it is necessary to increase the nucleation density to form a dense and flat film diamond as thin as possible.

As a method for improving the nucleation density of diamond on the substrate, for example, in the case of a mirror-polished silicon substrate, diamond powder (average particle size 10 μm to 40 μm) is used.
It is customary to perform a substrate pretreatment in which the substrate is submerged in an alcohol solution containing (μm) and is oscillated for an appropriate time with an ultrasonic cleaner. In this way, the diamond nucleation center can be easily created by tapping the substrate surface with the diamond powder by ultrasonic cleaning.

At that time, the mirror-polished substrate before treatment is polished to have irregularities of several nm or less, and the surface is relatively treated with ultrasonic waves having a diameter of several nm and a depth of about 10 nm. A smooth scratch is introduced. And it is reported that these subtle unevenness is the center of nucleation (Yugo: “Around diamond nucleation” “New Diamond” Vol.7,
No. 1, pp7, (1991)). There is also a report that the nucleation mechanism by the pretreatment of the substrate is not the unevenness of the surface due to the scratch itself but the ultra-fine fragments of diamond remaining on the substrate surface as seeds and the diamond grows.
(Iijima: "Observation of initial growth of diamond thin film by electron microscope""NewDiamond" Vol.7, No.3, pp9-13, (1
991)).

In any case, the nucleus generation density of diamond crystals obtained by vapor phase synthesis by the conventional method is 10
^{About 7} to 10 ⁸ pieces / cm ² are obtained. However, as the film thickness increases, the particle size tends to increase and the surface irregularities tend to increase.

On the other hand, studies have also been conducted for forming a polycrystalline thin film diamond of high quality and large grain size with few crystal grain boundaries by selectively setting nucleation positions of diamond crystals.

Specifically, 1.2 μ is formed on the surface of silicon (Si).
A silicon oxide (SiO ₂ ) layer is formed at a size of m × 1.2 μm square, height of 0.2 μm, and interval of 10 μm, and then the substrate surface is ultrasonically cleaned with diamond powder (particle diameter 40 μm). The surface is scratched by. Next, the substrate is placed in a vacuum chamber (~ 10 ^-4 Torr), and argon ions are added.
Irradiate (Ar ⁺ ) on the substrate surface at an angle of 30 degrees. And
During the vapor phase synthesis of diamond on this substrate by the plasma CDV method, the diamond crystal is selectively grown from the edge portion of the silicon oxide layer which is not irradiated with argon ions,
It is intended to form a thin film composed of diamond crystals with a particle size of 10 μm or more (Jing Sheng MA et al.
"NUCLEATION CONTROL AND SELECTIVE GROWTH OF DIAMO
ND PARTI-CLES FORMED WITH PLASMA CVD "" Journal of
Crystal Growth "99 (1990) pp1206-1210).

Although various attempts have been made to form thin film diamond in this way, the application of thin film diamond to semiconductors or optical elements utilizing the excellent thermal conductivity and wide band gap of diamond has been examined, but it has not been investigated yet. It has not been put to practical use.

[0016]

In order to use the thin film diamond for the development of various devices, it is necessary to realize a more dense and flat thin film diamond. For that,
10 ¹⁰ as the nucleus generation density during diamond crystal synthesis
It is important to establish the technology of substrate processing and synthesis method that achieves / cm ² to 10 ¹¹ pieces / cm ² or more. On the other hand, it is also important to establish a technique for easily realizing a high-quality thin film diamond composed of a large diamond crystal with few crystal grain boundaries. However, the above two technologies have not been established yet.

Therefore, an object of the present invention is to provide a method for producing a thin film diamond capable of producing a dense and flat thin film diamond by setting the nucleus generation density during diamond crystal synthesis to 10 ¹⁰ pieces / cm ² or more, and a crystal grain boundary. It is an object of the present invention to provide a method for producing a thin film diamond capable of producing a high quality thin film diamond composed of a large diamond crystal having a small amount of impurities.

[0018]

In order to achieve the above object, the method for producing a thin film diamond of the first invention is such that after the minute surface roughness is formed on the surface of the substrate to increase the surface area of the substrate, It is characterized in that the substrate on which irregularities are formed is subjected to surface scratch pretreatment with diamond particles, and thin film diamond is vapor-phase synthesized on the substrate.

A second invention is the method for manufacturing a thin film diamond according to the first invention, wherein the fine irregularities formed on the surface of the substrate are formed by anisotropic etching.
The convex portion is characterized by having a tetrahedral shape.

A third invention is the method for manufacturing a thin film diamond of the second invention, wherein the tops of the minute tetrahedral convex portions formed on the substrate surface are removed by dry etching or mechanical polishing. It is characterized by being formed into a trapezoidal convex portion.

A fourth invention is the method for producing a thin film diamond according to the first invention, wherein the fine irregularities formed on the surface of the substrate are island-shaped by a surface vapor deposition process such as a vacuum vapor deposition method or a sputter vapor deposition method. It is characterized in that it is formed of metal particles that have been grown.

Further, in the method for producing a thin film diamond of the fifth invention, an oxide film is formed on the surface of a silicon substrate, and metal particles are grown into islands by surface vapor deposition treatment such as vacuum vapor deposition or sputter vapor deposition. After removing the underlying oxide film by selective etching to form minute unevenness due to the oxide film and metal particles on the surface of the silicon substrate, the substrate surface area is increased, and then in an alcohol solution in which fine diamond powder is turbid The surface pre-treatment for surface scratching is performed, and thin film diamond is vapor-phase synthesized on the substrate.

The sixth invention is the method for producing a thin film diamond according to any one of the first to fifth inventions, wherein the fine irregularities formed on the surface of the substrate are formed on the surface of the substrate. It is characterized in that the protective film is formed only in a predetermined region patterned by a photolithography technique or the like.

Further, in the method for producing a thin film diamond of the seventh invention, the substrate surface is patterned at equal intervals by photolithography technique to form concave regions and minute concaves and convexes are formed only in the concave regions. It is characterized in that the concave region in which the minute irregularities are formed is subjected to surface scratch pretreatment with diamond particles, and thin film diamond is vapor-phase synthesized on the substrate.

[0025]

EXAMPLES The present invention will be described in detail below with reference to examples. The present invention is not limited to the following embodiments.

<First Example> In this example, the nucleus generation density is 10 ¹⁰
/ cm ² or more, and relates to a method for forming a dense and flat polycrystalline thin film diamond on a silicon substrate.

As described above, in order to enhance the generation of diamond crystal nuclei on the surface of the substrate, it is effective to increase the number of remaining diamond particles on the surface of the substrate during the pretreatment of the substrate with the diamond particles. As a result of observing the substrate surface by an atomic force microscope after performing the substrate pretreatment with a commercially available ultrasonic cleaning machine using the ordinary silicon substrate, the inventors have found that the diameter remains several angstroms to several hundred angstroms. It was confirmed that particles were present at about 10 ⁹ particles / cm ² . The number of residual particles is in good agreement with the density of growth nuclei observed at the initial stage of diamond growth.

Therefore, in order to further improve the nucleus generation density during diamond growth, minute surface irregularities are formed on the surface of the substrate to increase the apparent surface area of the substrate so that diamond particles remain during the substrate pretreatment. Make it easier. By doing so, the growth rate of the concave portion becomes higher than that of the convex portion (at the surface concave portion, diamond crystals start to grow from each side surface, and at the bottom portion of the concave portion, crystals are easily bonded to each other to form a thin film. It is considered that a denser and flatter polycrystalline thin film diamond can be formed by utilizing (1).

[First Embodiment] In this embodiment, a fine surface unevenness is formed on the surface of a silicon substrate by anisotropic etching to increase the nucleation density, thereby forming a dense and flat polycrystal on the silicon substrate. A method for forming thin film diamond. A high-resolution scanning electron microscope was used for observing the shape of the formed polycrystalline thin film diamond, a high-speed backscattered electron diffraction device was used for identification, and a Raman spectroscopic device was used for evaluation of the film quality.

The surface of the p-type silicon (100) substrate was
% Hydrofluoric acid solution to remove the natural oxide film on the surface, dip it in a solution (liquid temperature: 90 ° C to 95 ° C) in which alcohol is mixed with about 27% potassium hydroxide (KOH). Is left for 30 minutes while stirring, and then immediately transferred to a container containing pure water.

After cleaning the substrate with isopropyl alcohol (or acetone) for 5 minutes with an ultrasonic cleaner, it is dried with an infrared heater. By such anisotropic etching treatment for exposing the silicon (111) surface, a substrate surface having pyramid-shaped irregularities of about 1 μm to 2 μm is formed. By doing so, the surface area is geometrically increased to 3 ^1/3 times, and it can be expected that the diamond particles for the substrate pretreatment remain more than the flat silicon substrate.

Next, this substrate is immersed in 100 cc of ethanol in which 2 g of diamond powder having a particle diameter of 0.25 μm is dispersed, and subjected to ultrasonic cleaning treatment for 1 hour. At that time, by making the water surface in the ultrasonic cleaning machine and the liquid surface in which the diamond powder is dispersed substantially flush with each other, the residual fine particles are effectively high density (about 10 ⁹ particles / cm ² ) on the substrate surface. Order) and can be embedded uniformly.

On the other hand, p not subjected to anisotropic etching
The silicon substrate obtained by ultrasonically cleaning the mold-silicon substrate (100) with the same diamond powder solution for the same time as in the case of the p-type silicon substrate subjected to the anisotropic etching treatment is used as the reference substrate. Set on the substrate holder. Using the two types of substrates thus obtained,
Thin film diamond synthesis was performed by electron cycloton resonance microwave plasma CVD method. Hydrogen-0.5% methane mixed gas was used as the source gas, and the total flow rate was 200 sc
Synthesis was carried out at m, gas pressure of 9 Torr, substrate temperature of 800 ° C., and microwave (2.45 GHz) power of 1.5 kW. Synthesis temperature is 5 hours, 10 hours and 10 hours
There are three types of time, 0 hours. Of course, the substrate is synthesized at a position satisfying the electron cycloton resonance condition.

Each sample thus obtained has a high resolution--
It was observed with a field emission scanning electron microscope. First, when the growth time is 5 hours, the diameter of the diamond crystal particles is about 0.2 μm or less in the sample (reference sample) which is not subjected to anisotropic etching, and the nucleus generation density is ~
It is 8 × 10 ⁸ pieces / cm ² , and the polycrystalline diamond does not reach a continuous film. On the other hand, in the sample subjected to anisotropic etching, a dense continuous film was formed in the concave part, and the particle size of the diamond crystal in that part was 0.1 μm.
Below, the apparent nucleation density was equivalent to ~ 6 x 10 ⁹ / cm ² . However, polycrystalline diamond is not continuous as a thin film.

When the growth time is 10 hours, the particle size of the diamond crystal is 0.2 μm to 0.3 μm in the reference sample not subjected to anisotropic etching.
Polycrystalline diamond does not partially form a continuous film. On the other hand, in the sample subjected to anisotropic etching, the polycrystalline diamond is formed as a continuous film in the concave portion of the surface, and the polycrystalline diamond is partially continuous in the convex portion of the surface. Although the particle size of the diamond crystal had grown to about 0.2 μm, the surface irregularities of the polycrystalline thin film diamond were significantly smaller than the irregularities of the substrate itself.

When the growth time is 100 hours, in the reference sample not subjected to anisotropic etching,
The unevenness of the surface of the polycrystalline thin film diamond is larger than that of the film grown for 10 hours, the film thickness is 2 μm, and the unevenness of the polycrystalline thin film diamond is increased to ± 0.35 μm. On the other hand, in the sample subjected to anisotropic etching, the particle size of the diamond crystal is around 0.2 μm, and the surface irregularity of the polycrystalline thin film diamond is ± 0.1.
It became less than 5 μm. However, the flatness of the polycrystalline thin film diamond formed on the sample subjected to anisotropic etching is not strictly flat because it is affected by the unevenness of the substrate when viewed macroscopically.

As described above, in the above embodiment, the natural oxide film on the surface of the silicon (100) substrate was removed, and a liquid temperature of 90% was obtained by mixing alcohol with about 27% potassium hydroxide.
By immersing in a solution of ℃ ~ 95 ℃, anisotropic etching,
Pyramid of about 1 μm to 2 μm on the substrate surface ((111)
The texture of the shape is formed. Next, the above substrate is immersed in 100 cc of ethanol in which 2 g of diamond powder having a particle diameter of 0.25 μm is dispersed, and surface pretreatment is performed for 1 hour with an ultrasonic cleaner.

By doing so, about 10 ⁹ particles / cm ^{2 of} fine diamond particles remain on the irregularities on the surface of the substrate, and the apparent density of residual fine diamond particles is increased as compared with the case of a substrate having a flat surface. . Therefore, if thin film synthesis is carried out by the conventional vapor phase synthesis method using these residual fine particles as nuclei, a dense and flat polycrystalline thin film diamond can be formed.

[Second Embodiment] This embodiment relates to a method for forming a denser and flatter polycrystalline thin film diamond by improving a part of the substrate processing step in the first embodiment.

Anisotropic etching is performed on the p-type silicon (100) substrate as in the first embodiment. Then, a low-viscosity polyimide film with a slight amount of ultrafine particles (silicon oxide particles) added thereto so as to have a dry etching rate similar to that of silicon is applied to the surface, and dry etching is performed. Then, by this dry etching, the tops of the convex portions of the microtetrahedron are removed and a silicon substrate having trapezoidal irregularities is formed. After that, the polyimide film is removed.

The sample thus formed is subjected to ultrasonic treatment with diamond powder in the same manner as in the first embodiment to form a substrate in which residual fine particles of diamond powder are uniformly embedded. Then, using this substrate, the first
Thin film diamond synthesis is performed under the same conditions as in the example. The growth time is 40 hours. As a result, the grain size of the polycrystalline thin film diamond grown on the trapezoidal texture surface is 0.
The thickness was about 2 μm, the film thickness was about 0.8 μm, and the surface irregularities were ± 0.07 μm or less, and a dense and flat polycrystalline thin film diamond was formed.

As described above, in this embodiment, by forming the trapezoidal texture on the surface of the substrate, a denser and flatter polycrystalline thin film diamond can be formed.

[Third Embodiment] This embodiment relates to a method for producing a polycrystalline thin film diamond only in a necessary region of a substrate.

A silicon oxide film having a thickness of about 0.1 μm is formed on the entire surface of a p-type silicon (100) substrate. After patterning with photoresist on the substrate, the portion where the polycrystalline thin film diamond is to be formed is etched with a 10% hydrofluoric acid solution to remove the silicon oxide film.

Next, anisotropic etching is performed with the same alkaline solution as in the first embodiment to form irregularities on the substrate surface. This substrate is subjected to ultrasonic treatment for 1 hour in an alcohol solution containing diamond powder having a particle diameter of 0.25 μm. Then, the photoresist is removed to obtain a substrate for forming a thin film diamond. A substrate that does not pass the anisotropic etching step is also prepared as a reference sample.

The vapor phase synthesis of thin film diamond was performed by the hot filament CVD method. Hydrogen as source gas
Using 1.0% methane mixed gas, gas flow rate is 300sccm
The gas pressure was 20 Torr, the filament temperature was about 2000 ° C., and the substrate temperature was 800 ° C. Growth times are two different times: 0.5 hours and 3 hours.

As a result, when the growth time is 0.5 hours, the particle size of the diamond crystal of the sample subjected to anisotropic etching is about 0.5 μm, and the nucleus generation density is
It was 4 × 10 ⁸ pieces / cm ² . On the other hand, the particle size of the diamond crystal of the reference sample is 2 μm to 3 μm
Before and after, the nucleus generation density was ˜2 × 10 ⁷ pieces / cm ² . Neither sample is continuous.

When the growth time reaches 3 hours, in the anisotropically etched sample, the diamond thin film has a particle diameter of about 0.5 μm to 1 μm, and the polycrystalline thin film diamond has a continuous film thickness of about 3 μm. Roughness is approximately ± 0.3μ
It is within the range of m. On the other hand, the reference sample has a diamond crystal particle size of 4 μm to 5 μm and a film thickness of about 4 μm.
μm, surface irregularities are ± 1.5 μm. Therefore, the substrate processing effect of anisotropic etching was confirmed. Both samples can be patterned on the polycrystalline thin film diamond.

[Fourth Embodiment] In this embodiment, nucleation density is increased by forming metal particles having a size of several nm in an island shape to form fine surface irregularities on the surface of the silicon substrate. A method for forming a dense and flat polycrystalline thin film diamond on top. The denseness of the formed polycrystalline thin film diamond was evaluated by forming electrodes on the front surface and the rear surface of the substrate of the synthesized thin film diamond so that there was no leak current. Further, as in the above, a high-resolution scanning electron microscope was used for shape observation, a high-speed backscattered electron diffraction apparatus was used for identification, and a Raman spectroscopic apparatus was used for evaluation of the film quality.

The natural oxide film on the surface of the p-type silicon (100) substrate which has been mirror-polished is removed with a hydrofluoric acid solution and dried, and then the substrate is set in an ion sputtering deposition apparatus. At that time, platinum (Pt) -20 wt% palladium (Pd) was used as the target of the ion sputtering deposition apparatus.
Using an alloy, the target metal was sputtered at a film thickness setting of 5 nm to deposit island-shaped platinum-palladium alloy particles on the surface of the substrate. As a result, an island-shaped platinum-palladium alloy particle layer having a particle diameter of 2 nm to 5 nm (particle irregularities of 1 nm to 3 nm) was formed. Furthermore, in order to improve the adhesion between the platinum-palladium alloy particles and the silicon substrate, heat treatment was performed in air at 350 ° C. for 30 minutes.

Next, this substrate is immersed in a 100 cc ethanol solution in which 2 g of diamond powder having a particle diameter of 0.25 μm or less is dispersed, and ultrasonic cleaning treatment is carried out for 1 hour. At that time, by making the water surface in the ultrasonic cleaning machine and the liquid surface in which the diamond powder is dispersed substantially flush with each other, a high density of residual diamond particles of about 5 nm (~ 10 ¹⁰ particles /
(order of cm ² ) and can be embedded uniformly.

On the other hand, a silicon substrate obtained by removing the natural oxide film of the p-type silicon substrate (100) and ultrasonically cleaning it with the same diamond powder solution for the same time as described above is used as a reference substrate.

The two types of substrates thus obtained were set in the same substrate holder, and thin film diamond synthesis was carried out by the electron cycloton resonance microwave plasma CVD method. Hydrogen-0.5% methane mixed gas was used as the source gas, the total flow rate was 200 sccm, and the gas pressure was 9
Torr, substrate temperature 700 ° C., microwave (2.
The synthesis was carried out with a power of 45 GHz) of 1.5 kW. There are two types of synthesis temperatures, 5 hours and 10 hours. Of course, the substrate is synthesized at a position satisfying the electron cycloton resonance condition.

Each sample obtained as described above was observed by a high resolution field emission scanning electron microscope. First,
When the growth time is 5 hours, the diameter of the diamond crystal particles is about 0.2 μm or less in the sample (reference sample) in which the unevenness of platinum-palladium alloy particles is not formed on the silicon surface by the surface vapor deposition treatment, The generation density is ˜8 × 10 ⁸ pieces / cm ² , and the polycrystalline diamond does not partially reach a continuous film. On the other hand, in the sample subjected to the surface vapor deposition treatment, a dense continuous film is formed, and the diamond crystal grain size is 0.1 μm or less,
The nucleation density corresponded to ˜1.5 × 10 ¹⁰ nuclei / cm ² . In this case, the thickness of the obtained polycrystalline thin film diamond is 0.2
The surface roughness measurement result of the polycrystalline thin film diamond with an atomic force microscope was ± 0.05 μm or less, and a flat diamond film was formed.

When the growth time is 10 hours, the diamond sample has a particle diameter of 0.2 μm to 0.3 μm in the reference sample not subjected to the surface vapor deposition treatment, and the polycrystalline diamond is a continuous film. . On the other hand, in the sample subjected to the surface vapor deposition treatment, the thickness of the polycrystalline thin film diamond is 0.35 μm, the polycrystalline diamond is formed as a continuous film in the concave portion of the surface of the substrate, and the polycrystalline diamond is formed in the convex portion of the surface. Diamond continuity is partial. The particle size of the diamond crystal is 0.2 μm or less, and the surface irregularities of the polycrystalline thin film diamond are almost the same as those of the substrate itself.

As described above, in order to measure the denseness of the polycrystalline thin film diamond obtained by carrying out the surface vapor deposition treatment, aluminum was applied to both sides of the sample.
(Al) electrode is formed to a thickness of 0.2 μm, and nitrogen gas at 400 ° C
Annealed in (N ₂ ) for 30 minutes. Thus, the structure of the aluminum electrode (diameter 2 mm) / thin film diamond / silicon substrate / aluminum electrode (entire surface) was formed and the leak characteristics were examined. As a result, electrical leakage does not occur only in the sample substrate subjected to the surface vapor deposition treatment and having a high nucleus generation density. As a result, the nucleus generation density is 10 ¹⁰ / c
It was found that the thin film in which diamond crystals were grown on the order of m ² was composed of dense diamond crystals.

As described above, in the above embodiment, the natural oxide film on the surface of the silicon (100) substrate was removed, and platinum-palladium alloy particles were formed by the surface vapor deposition treatment by the sputter vapor deposition method to form the platinum-palladium alloy particles on the substrate surface. Asperities with a size of several nm are formed. Next, the above substrate is immersed in 100 cc of ethanol in which 2 g of diamond powder having a particle diameter of 0.25 μm is dispersed, and surface pretreatment is performed for 1 hour with an ultrasonic cleaner.

As described above, by making the unevenness of the substrate surface several nm in size, it is possible to uniformly fill the uneven portion of the substrate surface with fine diamond particles of about 5 nm at 10 ¹⁰ particles / cm ² and The density of apparent residual fine diamond particles is increased as compared with the case of a flat substrate. Therefore, if thin film synthesis is carried out by the conventional vapor phase synthesis method using these residual fine particles as nuclei, a dense and flat polycrystalline thin film diamond can be formed.

[Fifth Embodiment] When the substrate on which the polycrystalline thin film diamond is formed according to the fourth embodiment is broken and its cross section is observed by a scanning electron microscope, it is partially observed between the diamond film and the silicon substrate. It is observed that it has peeled off. The present example is an example in which peeling between the diamond film and the silicon substrate is eliminated.

The native oxide film on the surface of the mirror-polished p-type silicon (100) substrate is removed with a hydrofluoric acid solution and dried, and then a silicon oxide film having a thickness of about 50 nm is formed. Then, the same surface vapor deposition treatment as in the fourth example was performed to deposit platinum-palladium alloy particles of several nm size in an island shape, and heat treatment was performed in nitrogen gas at 350 ° C. for 30 minutes to obtain platinum-palladium alloy particles. And improve the adhesion between the silicon substrate and the silicon substrate. Then, the underlying silicon oxide film is removed with a solution of hydrofluoric acid: water = 1: 1 using the platinum-palladium alloy particles as a masking material. Thus, minute surface irregularities of about 50 nm are formed on the surface of the silicon substrate.

Next, three kinds of commercially available diamond powders having a particle size of 250 nm or less, 100 nm or less and 5 nm are prepared, and 2 g of each is prepared in a solution of 100 cc of alcohol to prepare a diamond powder solution. And this 3
The substrate is subjected to ultrasonic cleaning treatment under the same conditions as in the fourth embodiment by using diamond powder solutions of various types, and surface scratch pretreatment is performed.

As a result of observing the surface unevenness of each substrate subjected to the surface scratch pretreatment with the three types of diamond powder solutions by an atomic force microscope, residual diamond particles having a particle diameter of about 5 nm adhered to each substrate. I found out that The residual diamond particle density shows the largest value in the substrate surface-pretreated with a diamond powder solution having a particle diameter of 5 nm, and the value is about 6 × 10 ¹⁰ particles / cm ² . Further, in the substrate surface-scratched by the diamond powder solution having a particle size of 50 nm or less and 100 nm or less, non-uniform distribution of residual diamond particles was observed. This means that the particle diameter of the diamond powder of the diamond powder solution for performing the surface scratch pretreatment on the substrate surface irregularities of several pick-up nm is 50 nm or less and 100 nm or less is too large to easily remain. Conceivable.

As described above, electron cyclotron resonance microwave plasma CVD was performed under the same conditions as in the fourth embodiment, using the substrate pre-treated with the diamond powder solution having a high residual diamond particle density and having a particle diameter of 5 nm.
Thin film diamond synthesis is performed by the method. As a result, a polycrystalline thin film diamond having a film thickness substantially the same as that of the fourth embodiment can be obtained. At that time, no electrical leak is observed in the substrate on which the polycrystalline thin film diamond is formed. Also,
As a result of observing the cross section of the substrate on which the polycrystalline thin film diamond was formed by breaking it with a scanning electron microscope, no peeling was observed between the silicon substrate and the diamond film.

As a reference sample, a flat silicon substrate which was not subjected to the oxide film formation and surface vapor deposition treatment was subjected to surface scratch pretreatment with a diamond powder solution having a particle diameter of 5 nm. The density of residual diamond particles in this reference sample is on the order of 10 ⁹ particles / cm ² , and the nucleation density of thin film diamond synthesized using this substrate is about the same. From this, it can be seen that a substrate having surface irregularities of several nm size has a high density (10 ¹⁰ particles / cm ² ) of residual diamond particles adhered by a surface scratch pretreatment with a diamond powder solution having a particle size of 5 nm. It was revealed that a polycrystalline thin film diamond that is dense, flat, and has good adhesion can be obtained.

As described above, in this embodiment, the silicon oxide film is formed by the surface vapor deposition method prior to forming the platinum-palladium alloy particles on the surface of the silicon substrate.
Increase the surface roughness by the thickness of the silicon oxide film. 5
Surface roughness of 0 nm can be obtained. Therefore, a few nm
The apparent surface area of the silicon substrate is larger than that of the silicon substrate having surface irregularities, and a crystalline thin film diamond having high adhesion strength can be obtained.

[Sixth Embodiment] In this embodiment, the film thickness dependence of the oxide film in the fourth embodiment will be examined. Five kinds of silicon oxide films having a thickness of 0 nm, 20 nm, 50 nm, 100 nm and 200 nm were formed after removing the native oxide film on the surface of the p-type silicon (100) substrate mirror-polished with a hydrofluoric acid solution and drying. Prepare the substrate. Then, a platinum-palladium alloy is vapor-deposited in an island shape with a set film thickness of 5 nm, and then the underlying silicon oxide film is removed using the platinum-palladium alloy particles as a masking material.

Of the five types of substrates thus formed,
There is no masking effect of platinum-palladium alloy particles on a substrate on which a silicon oxide film having a film thickness of 200 nm is formed,
The expected surface roughness cannot be obtained. In addition, 0nm, 20nm, 5
Residual diamond particles on a substrate with a silicon oxide film thickness of 50 nm when 5 types of substrates with a silicon oxide film thickness of 0 nm and 100 nm were subjected to surface scratch pretreatment with a diamond powder solution with a particle diameter of 5 nm. The highest density was followed by the silicon oxide film thickness of 100 nm and then 20 nm.

Furthermore, the set film thickness of the platinum-palladium alloy was also examined. As a result, the set film thickness is 2 nm to 10
The island-shaped grown particles are formed at a thickness of nm, and the set film thickness of around 5 nm is the best. The optimum set film thickness is considered to be somewhat different depending on the material of the substrate and the metal deposited by the surface deposition method. <Second Example> This example relates to a method for forming a high-quality polycrystalline thin film diamond composed of large diamond crystals with few crystal grain boundaries.

Fine recesses are periodically formed by anisotropic etching on the surface of the substrate in advance, and pretreatment for surface scratching with diamond particles is performed only on the recesses to form residual fine particles only on the recesses. Diamond crystals can be grown. By doing so, only one diamond crystal grows selectively in the recess, and these crystals continue to grow three-dimensionally and are synthesized until they come into contact with the adjacent crystals to form a thin film. At that time, by optimizing the distance between the two-dimensional concave portions on the substrate surface,
It is possible to obtain a high-quality polycrystalline thin film diamond with small surface irregularities and few crystal grain boundaries. The details will be described below.

[Seventh Embodiment] A silicon oxide film having a film thickness of 0.1 μm is formed on a p-type silicon (100) substrate, and a photoresist is applied to the surface thereof. Next, the photoresist is two-dimensionally removed in a size of 1 μm × 1 μm square and at intervals of 5 μm, the silicon oxide film is removed with a 10% hydrofluoric acid solution, and the silicon substrate is anisotropically etched. And the third
After performing the same ultrasonic treatment as in the example, the photoresist is removed.

As a result, residual fine particles are present only in the above-mentioned recesses, and the other portions are silicon oxide films. Depending on the application, the silicon oxide film may be removed with an acid.

The vapor phase synthesis of diamond was performed by the hot filament CVD method. The source gas at that time is hydrogen-
Using 0.5% methane mixed gas, the gas flow rate is 300sccm
The gas pressure was 30 Torr, the filament temperature was about 2000 ° C., and the substrate temperature was 800 ° C. The growth time is 5 hours. As a result, the particle size is 5 μm,
A polycrystalline thin film diamond having a film thickness of about 5 μm was formed.

At that time, a large number of diamond crystals grow in the recesses at the initial stage of growth, but when the diamond crystal size is several μm or more, only one diamond crystal is selectively selected among the diamond crystals. To grow up. After that, when the diamond crystal is continuously synthesized, the diamond crystal comes into contact with the adjacent diamond crystal. In this way, the synthesis is stopped when the gap between the crystals disappears.

The thin film thus obtained was evaluated by a Raman spectroscope, and as a result, only a sharp diamond peak was observed near 1333 cm ⁻¹ , which had a lower background than that formed by the electron cycloton resonance microwave plasma CVD method. It was found that thin film diamond with excellent film quality was formed.

As described above, in the above embodiment, the silicon oxide film is formed on the silicon (100) substrate, and 1 μm is formed.
The silicon oxide film is two-dimensionally removed in a size of m × 1 μm square and at intervals of 5 μm to form concave regions, and the concave silicon substrate is anisotropically etched to form irregularities on the substrate surface. After that, diamond powder having a particle diameter of 0.25 μm is dispersed and subjected to ultrasonic treatment in an alcohol solution to form residual fine particles only in the concave portions.

As a result, the diamond grows from the recess during the synthesis of the thin film diamond by vapor phase synthesis. When the diamond crystal grows to a crystal of several μm or more, only one diamond crystal is selectively formed in the recess. Will grow up. Therefore, as the growth continues, a high-quality thin film diamond composed of a large diamond crystal with few crystal grain boundaries can be obtained in contact with the adjacent diamond crystal.

In the third embodiment described above, minute surface irregularities are formed by anisotropic etching in a predetermined region patterned by the photolithography technique. However, the method for forming surface irregularities in the present invention is not limited to this. For example, you may form by the surface vapor deposition process of the metal particle as shown in 4th Example and 5th Example. In addition, in the fourth and fifth embodiments, the metal particles are grown on the substrate by the sputter deposition method, but they may be grown by the vacuum deposition method or another method.

[0078]

As is apparent from the above, in the method for producing a thin film diamond of the first aspect of the invention, a substrate on which fine irregularities are formed is subjected to a surface scratch pretreatment with diamond particles, and the thin film diamond is formed on the substrate. Since the vapor phase synthesis is performed, the number of fine diamond particles remaining during the pretreatment for surface scratching increases, and the nucleus generation density during the vapor phase synthesis of diamond can be increased to 6 × 10 ⁹ pieces / cm ² . Therefore, according to the present invention, it is possible to form a more dense and flat thin film diamond by setting the nucleus generation density at the time of diamond crystal synthesis to about 10 ¹⁰ / cm ² .

Further, in the method for producing a thin film diamond of the second invention, since the minute irregularities whose projections form a tetrahedron shape are formed on the substrate surface by anisotropic etching, during diamond vapor phase synthesis. Nucleation density of 10 ¹⁰
It is possible to easily form irregularities on the substrate surface to increase the number to about 1 / cm ² .

Further, in the method for manufacturing a thin film diamond of the third invention, the tops of the minute tetrahedral convex portions formed on the substrate surface are scraped off by dry etching or mechanical polishing to form trapezoidal convex portions. Since it is formed, a flatter thin film diamond can be formed.

Further, in the method for producing a thin film diamond of the fourth invention, fine irregularities are formed on the substrate surface by the metal particles grown in an island shape by the surface vapor deposition treatment such as the vacuum vapor deposition method and the sputter vapor deposition method. As a result, the substrate surface irregularities for increasing the nucleation density during diamond vapor phase synthesis to approximately 10 ¹⁰ / cm ² can be formed even finer. Therefore, the number of remaining diamond fine particles when the surface scratch pretreatment with the diamond particles is performed later is further increased, and the nucleus generation density during diamond vapor phase synthesis is increased to 10 ¹⁰
Can be increased to pieces / cm ² . Therefore, according to the present invention,
10 ¹⁰ nucleation density during diamond crystal synthesis
A finer and flatter thin film diamond can be formed on the order of / cm ² .

Further, in the method for producing a thin film diamond of the fifth invention, an oxide film is formed on the surface of a silicon substrate, and metal particles are grown in an island shape by a surface vapor deposition treatment such as vacuum vapor deposition or sputter vapor deposition, and then a base layer is formed. Oxide film is selectively removed by etching to form fine irregularities on the surface of the silicon substrate, and pretreatment for surface scratching is performed in an alcohol solution in which fine diamond powder is turbid. Since the diamond is vapor-synthesized, the nucleation density during the diamond vapor-phase synthesis can be easily adjusted to 10 to 10.
^The number can be increased to ¹⁰ pieces / cm ² , and peeling between the obtained thin film diamond and the silicon substrate can be prevented. Therefore,
According to the present invention, the density of nuclei generated during the synthesis of diamond crystals is set to be 10 ¹⁰ / cm ² , and it is possible to form a more dense, flat, and thin film diamond having good adhesion.

Further, in the method for producing a thin film diamond of the sixth invention, the nucleation density at the time of diamond vapor phase synthesis is set only in a predetermined region where the protective film formed on the surface of the substrate is patterned by the photolithography technique or the like. Roughly 10
^Since the minute unevenness for increasing the number to about ¹⁰ pieces / cm ² is formed, a dense and flat thin film diamond can be formed only in a necessary area of the substrate.

Further, in the method for manufacturing a thin film diamond of the seventh invention, minute unevenness is formed only in the concave regions formed by patterning the substrate surface at equal intervals by the photolithography technique or the like, and the minute unevenness is formed. Performed surface scratch pretreatment with diamond particles to the recessed area,
Since the thin film diamond is vapor-phase-synthesized on the substrate, only one diamond crystal selectively grows from the concave region during diamond crystal synthesis. Therefore, according to the present invention, it is possible to form a high-quality thin film diamond composed of large diamond crystals with few crystal grain boundaries.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masayoshi Kiba 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (7)

[Claims] 1. A substrate is provided with fine irregularities to increase the surface area of the substrate, and then the substrate having the fine irregularities is subjected to surface scratch pretreatment with fine diamond particles. A method for producing a thin film diamond, which comprises vapor-synthesizing a thin film diamond. 2. The method for producing a thin film diamond according to claim 1, wherein the minute irregularities formed on the surface of the substrate are formed by anisotropic etching, and the protrusions have a tetrahedral shape. Method for manufacturing thin film diamond. 3. The method for producing a thin film diamond according to claim 2, wherein the tops of the minute tetrahedral convex portions formed on the substrate surface are scraped off by dry etching or mechanical polishing.
A method for producing a thin film diamond, which is characterized in that it is formed in a trapezoidal convex portion. 4. The method for producing a thin film diamond according to claim 1, wherein the minute irregularities formed on the surface of the substrate are metal grown in an island shape by a surface vapor deposition process such as a vacuum vapor deposition method or a sputter vapor deposition method. A method for producing a thin film diamond, which comprises forming particles. 5. An oxide film is formed on the surface of a silicon substrate, metal particles are grown into islands by a surface vapor deposition process such as a vacuum vapor deposition method or a sputter vapor deposition method, and then the underlying oxide film is removed by selective etching. After increasing the surface area of the substrate by forming minute irregularities due to the oxide film and metal particles on the surface of the silicon substrate, a surface scratch pretreatment is performed in an alcohol solution in which fine diamond powder is turbid, A method for producing a thin film diamond, characterized in that a thin film diamond is vapor-phase synthesized thereon. 6. The method of manufacturing a thin film diamond according to claim 1, wherein the fine irregularities formed on the substrate surface are formed by a protective film formed on the substrate surface. A method for producing a thin film diamond, which is characterized in that the thin film diamond is formed only in a predetermined region patterned by a photolithography technique or the like. 7. The substrate surface is patterned at equal intervals by a photolithography technique to form concave regions, and minute concaves and convexes are formed only in the concave regions, and then the concave regions are formed in the minute concave and convex regions. A method for producing a thin film diamond, which comprises performing a surface scratch pretreatment with diamond particles and vapor-synthesizing the thin film diamond on the substrate.