JP2002265296A - Diamond thin film and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a diamond thin film deposited very thin in a wide surface area and having a flat surface free from pin holes, high adhesion to a substrate and excellent heat conductivity and permeability, and to provide a manufacturing method therefor. SOLUTION: The diamond thin film is deposited by a microwave plasma CVD method, in which, when a charged microwave power is expressed by M (unit: kw, M>3 kw) and the pressure in a plasma chamber is expressed by P, the ratio P/M of the pressure to the microwave power is kept to 359-439 and the surface temperature in the synthesis is kept to <=500 deg.C. As a result, the diamond thin film, in which when the surface area is expressed by (a) and the film thickness is expressed by (t), the ratio t/a of the film thickness to the surface area is <=3×10<-5> (m<-1> ), is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial diamond thin film applied to optical transmission / reflection windows, optical parts, semiconductor packages, chemical resistant coatings, wear resistant coatings, decorative coatings and the like.

[0002]

2. Description of the Related Art Diamond is a semiconductor or insulator having excellent heat resistance and a large forbidden band width of 5.5 eV. Utilizing the fact that the thermal conductivity is large and the specific heat is small, diamond is used as a heat dissipation substrate material, and the hardest property among materials is used to apply to wear-resistant members and tool coatings, Utilizing high light transmittance and refractive index, it is applied to optical materials and the like.

In order to apply diamond to various fields, it is important to form it into a thin film. Diamond thin films are prepared by microwave chemical vapor deposition (microwave CV).
D) Method (for example, Japanese Patent Publication No. 59-27754 and Japanese Patent Publication No. Sho 6-6)
1-33) and the like. This vapor phase synthesis method is suitable for obtaining a large-area thin film diamond at low cost.

[0004]

However, the diamond thin films which have been artificially prepared so far have the following problems with respect to their shapes: (1) the area that can be formed is limited; and (2) a certain amount or more for forming a continuous film. However, there is a limitation that the film thickness is required. In practical use of diamond having excellent chemical stability and light transmittance, there are many application fields of thin continuous films having a large area, and it is desirable that the continuous film be thin and have no pinholes and have a large area. Although the area that can be formed is limited due to the problem of an apparatus used for film formation, it has been difficult to form a continuous film having a large area and a thin film using a conventional apparatus. This is because diamond has a large surface energy and grows almost isotropically after nucleation, so that a film thickness of about 1 μm is usually required to obtain a continuous film. Accordingly, the surface flatness is also deteriorated at the same time as the film is thickened, and the unevenness becomes remarkable, which causes light scattering, which causes a problem that the optical characteristics are reduced. In order to flatten the surface, polishing may be performed, but it is technically difficult and causes a significant increase in cost.

[0005] In order to avoid such problems, there is a method of forming a diamond thin film by a sputtering method or the like capable of coating a large area with diamond. However, in the sputtering method and the like, diamond-like carbon which is non-diamond-based carbon is used. Carbon (DLC) precipitates. This diamond-like carbon has a problem that its chemical and optical properties are inferior to those of the diamond, and there are other technical problems such as deterioration of adhesion and the like, so that its use is limited.

The present invention has been made in view of the above problems, and has a wide area and an extremely thin thickness, a flat surface, no pinholes, high adhesion to a substrate, excellent heat conductivity and excellent heat conductivity. An object of the present invention is to provide a diamond thin film having transparency and a method for manufacturing the same.

[0007]

In the diamond thin film according to the present invention, when the surface area is a and the film thickness is t, the ratio of the film thickness to the surface area t / a is 3 × 10 ⁻⁵ (m ⁻¹ ) or less. There is a feature.

In the present invention, since the ratio of the film thickness to the surface area, t / a, is 3 × 10 ⁻⁵ (m ⁻¹ ) or less, it has a large area and is extremely thin, and is applied to optical windows and protective films. can do.

[0009] It may be doped with one kind of material selected from the group consisting of boron, nitrogen and phosphorus.

Further, it can be formed on a substrate made of a material having heat resistance of 500 ° C. or more, such as silicon, germanium, silicon-germanium, sapphire, silicon carbide, gallium nitride, quartz or glass.

In the method for producing a diamond thin film according to the present invention, the microwave power to be applied is M (unit: kW, M ≧ 3 kW) and the pressure in the plasma chamber is P (unit: Pa) by microwave plasma CVD. , The ratio P / M of pressure to microwave power is 360 to 4
The diamond thin film according to any one of claims 1 to 3, wherein the diamond thin film is formed while maintaining the surface temperature during synthesis at 500 ° C or lower while maintaining the temperature at 40 ° C.

In the present invention, the ratio P / M of the pressure in the plasma chamber to the microwave power is maintained at 360 to 440, and the surface temperature at the time of synthesis is 500 ° C.
If it is maintained below, the most common microwave CVD method for the vapor phase synthesis of diamond has no pinholes, has high adhesion to the substrate, has a large area, is extremely thin, and has a flat surface. A diamond thin film can be formed.

In the vapor phase synthesis of diamond, in addition to the above-mentioned microwave CVD method, hot filament CVD is used.
Method, a DC plasma CVD method, a plasma jet method, a thermal CVD method, or the like can also be used.

Further, as a raw material gas at the time of vapor phase synthesis,
Hydrogen diluted methane can be used, but other hydrocarbons may be used. Further, a gas containing an oxygen component such as carbon monoxide, carbon dioxide, ethanol, and acetone may be used.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. When a diamond thin film is formed by microwave plasma CVD, if the pressure in the chamber is reduced with respect to the microwave input power (microwave power),
It is conventionally known that plasma spreads and a diamond thin film can be synthesized over a large area. However, when the pressure in the chamber is excessively lowered, the substrate temperature decreases, and the film forming speed extremely decreases. In general, if the surface temperature of the sample is set to 500 ° C. or lower during diamond film formation, the film formation rate is reduced, so that productivity is low and non-diamond-based carbon may be deposited. Further, if the pressure in the chamber is excessively lowered, the inner wall of the vacuum vessel interacts with the plasma, which is a constraint.

The inventors of the present invention have conducted intensive experiments and researches under conditions not conventionally used due to such restrictions. As a result, the input microwave power is M (kW) and the pressure in the plasma chamber is P. (Pa), the pressure P in the plasma chamber with respect to the microwave power M
Even if P / M is kept in a range of 360 to 440, a diamond thin film having excellent properties can be synthesized over a wide area without depositing non-diamond carbon as in the conventional case. I found Further, since the film is formed by vapor phase synthesis, the adhesion to the substrate is high. However, since it is necessary to decompose the source gas by plasma to generate a precursor for diamond film formation, the absolute value of the microwave power M needs to be M ≧ 3 kW.

Further, the inventors of the present invention have reduced the power density of the plasma so that the surface temperature at the time of forming the diamond thin film is 500 ° C. or less, which is much lower than the normal film forming temperature (700 to 1100 ° C.). Then, on the contrary, they found that there is an advantage that the nucleation of diamond is promoted and abnormal growth of diamond is suppressed. Therefore,
An extremely thin diamond thin film that is flat and has no pinholes can be formed.

However, if the temperature is too low, the diamond growth rate becomes extremely low at less than 0.05 μm / hour,
The range of 450 to 480 ° C. is preferable because it is not practical.

In addition, due to the lowering of the surface temperature at the time of film formation, a diamond thin film is used for materials having a heat resistance of 500 ° C. or more, such as glass and plastic, which could not be coated with diamond in the past from the viewpoint of heat resistance. Can be formed, and the choice of the substrate material can be expanded.

Further, a source gas containing an oxygen component such as carbon monoxide, carbon dioxide, ethanol and acetone has conventionally been used to improve the quality of diamond obtained by preferentially removing non-diamond components by etching. The present inventors have also found that these gases contribute to the growth of diamond at relatively low temperatures.

The resulting diamond thin film has a diameter of 100
It has a thickness of 0.1 to 1 μm in an area of 1 to 300 mm. In order to apply the diamond thin film to various technologies, it is preferable that the diamond thin film has a large area and is a thin film. Therefore, it is preferable that the area of the substrate is 100 mm or more in diameter and 1 μm or less in film thickness. On the other hand, in order to increase the area of the substrate, it is necessary to reduce the pressure in the chamber. It is preferable that Further, in order to form a diamond thin film uniformly on one surface, the film thickness needs to be about 0.1 μm. Therefore, assuming that the surface area of the diamond thin film is a and the film thickness is t, the ratio of the film thickness to the surface area t / a is 3 × 10 ⁻⁵ (m ⁻¹ ) or less.

When the plasma interacts with the inner wall of the vacuum vessel, carbon adheres to the inner wall of the vacuum vessel.
Problems such as the inner wall of the vacuum vessel being heated and decomposed by the plasma to break the vessel, and the inner wall of the vacuum vessel being heated and decomposed by the plasma to be mixed as impurities into the diamond film occur.

Hereinafter, the diamond thin film according to the embodiment of the present invention will be described in more detail. FIG. 1A and FIG.
(B) shows a scanning electron microscope (Scanning Elect) showing a surface and a cross section, respectively, of the diamond thin film according to the embodiment of the present invention.
ron Microscope (SEM) photograph. The diamond thin film shown in FIG. 1 has a thickness t of 0.25 μm (250 n
m), the substrate diameter is 100 mm, and the surface area a is 7.85 × 10
⁻³ m ² and t / a are 3.2 × 10 ⁻⁵ (m ⁻¹ ).

As shown in FIG. 1 (a), a polycrystalline diamond thin film 1 is formed on one surface of a substrate (not shown), and as shown in FIG. A small and flat diamond thin film 1 is formed. Also,
The surface area a of the diamond thin film is the same as the size of the substrate used.

In this embodiment, the ratio of the thickness t to the surface area a, t / a, of the diamond thin film is 2.7 to 3.3 × 10 ^−5, which is extremely thin, has a large area, and has a large surface area. Since the roughness is small and there is no need to polish, it takes advantage of the inherent properties of diamond such as chemical stability, light transmittance, high refractive index, high hardness and low dielectric loss, and at low cost optical transmission and reflection windows, It can be applied to optical parts, semiconductor packages, chemical resistant coatings, abrasion resistant coatings and decorative article coatings.

Next, the method for producing a diamond thin film according to an embodiment of the present invention will be described in more detail. As a substrate for forming a diamond thin film, for example, (0
A single crystal silicon having a (01) crystal plane or a (111) crystal plane is used, and a diamond thin film is vapor-phase synthesized on the substrate by a microwave CVD method.

As a method of vapor phase synthesis of a diamond thin film, in addition to a microwave CVD method, a hot filament CVD method, a DC plasma CVD method, a plasma jet method, and a thermal CV method which are conventionally known as a vapor phase synthesis method of diamond.
Method D or the like can also be used. For example, the conditions for forming a diamond film by the hot filament CVD method include a filament temperature of, for example, 2200 ° C., a gas pressure of, for example, 3.99 kPa to 19.95 kPa, and a sample surface temperature of, for example, 450 to 500 ° C. As the raw material gas, for example, a mixed gas composed of hydrogen gas, methane gas and carbon dioxide gas can be used, and the flow rate of hydrogen gas is, for example, 1 to 10 liter / min, and the flow rate of methane gas is, for example, 0.2 to 1 liter / The carbon dioxide gas flow rate is, for example, 0.2 to 1 liter / minute.

Next, a method of forming a diamond thin film by a microwave CVD method will be described in more detail.
FIG. 2 is a schematic diagram showing a microwave CVD apparatus for diamond vapor phase synthesis. An opening 12 for introducing microwaves into the vacuum container 11 is provided on the bottom surface of the vacuum container (chamber) 11.
2, a waveguide is connected. In the vacuum vessel 11 and on the bottom surface thereof, there is provided a cylindrical quartz-made microwave window 13 for introducing microwaves onto a substrate 14 in the vacuum vessel 11.
Is provided. The substrate 14 is placed on the microwave window 13.
A substrate support 15 for supporting the substrate is held. Outside the microwave window 13 on the bottom surface of the vacuum vessel 11, a pipe 16 is connected to exhaust the raw material gas supplied into the vacuum vessel 11, and this pipe 16 is connected to the exhaust valve 1.
7 is connected. At the upper part of the vacuum vessel 11, a source gas pipe 18a is provided with its tip inserted into the vacuum vessel 11, thereby forming a source gas supply unit 18 for introducing a plurality of types of source gases. . The raw material gas supply unit 18 is provided with a flow controller (not shown) and the like.
The source gas supplied into the vacuum chamber 11 can be controlled. A pipe 19 for flowing cooling water is provided on the substrate support 15, and the pipe 19 extends to the inside of the substrate support 15, thereby cooling the substrate support 15 with water.

In such an apparatus, first, the substrate used for the vapor phase synthesis is cleaned with alcohol before diamond phase is vapor-phase synthesized, and a diamond powder or a diamond paste is used. Damage treatment is performed by treatment or ultrasonic treatment. afterwards,
The inside of the vacuum container 11 is evacuated. Next, the vacuum container 11
The source gas is supplied from the upper source gas supply unit 18 to the vacuum vessel 11.
After the mixing ratio of the raw material gas and the pressure in the vacuum chamber 11 become constant, the microwave (frequency 915 MH)
z) a quartz microwave window 13 from the bottom of the vacuum vessel 11
To generate a plasma 21 above the substrate 14 placed on the substrate support 15. The source gas is decomposed by the plasma 21, a part of the source gas is vapor-deposited on the substrate 14 as diamond, and the remainder is exhausted through the pipe 16 by the exhaust valve 17. The pressure in the chamber 11 depends on the supply amount of the raw material gas and the chamber 11.
It can be controlled by the amount of exhaust inside. The substrate 14 is cooled from the back by cooling the substrate support 15 with water, but is kept at a constant temperature during the vapor phase synthesis of the diamond thin film due to the balance with the microwave power. That is, the substrate surface temperature is above the vacuum vessel 11,
Monitoring is performed by a radiation thermometer (not shown), and the microwave power is controlled so that the substrate surface temperature is kept constant.

The conditions for forming the diamond thin film according to the present embodiment are as follows.
W, the pressure in the plasma chamber is, for example, 66.5 to 10.6 kPa, and the surface temperature is, for example, 450 to 500.
° C. The source gas supplied from the source gas supply unit may be, for example, a mixed gas composed of hydrogen gas, methane gas, and carbon dioxide gas. For example, the hydrogen gas flow rate is 1 to 5 liter / min, and the methane gas flow rate is 0.02 to 0.1 l / min and the carbon dioxide flow rate is 0.02 to 0.1 l / min.

The substrate is made of a simple substance such as silicon and germanium, a compound such as silicon-germanium, sapphire, silicon carbide and gallium nitride, a laminated body or a mixed crystal, a glass such as quartz, or a plastic resin or the like having a heat resistance of 500 ° C. or more. A substrate made of a material having properties can be used. Then, depending on the size of these substrates, a diamond thin film having a film thickness of 0.1 to 0.3 μm / hour and a thickness of 0.1 to 1 μm can be obtained in an area having a diameter of 100 to 300 mm.

According to the present embodiment, the surface temperature is maintained at 500 ° C. or less by the microwave CVD method, and the pressure P in the chamber with respect to the microwave power M (kW).
By keeping the ratio M / P of (Pa) in the range of 360 to 440, the film thickness t / surface area a becomes 3.5 × 10
^A diamond thin film having a large area and a small film thickness of not more than ⁻⁵ (m ⁻¹ ) can be obtained. Further, the diamond thin film thus obtained has high adhesion between the substrate and the diamond thin film, and has no pinholes (pinhole-free) and high quality even if it is thinner than before. Further, since the surface roughness is small, there is no need to polish after film formation. Also, in order to maintain the surface temperature during film formation at 500 ° C. or less,
Any material having a heat resistance of 500 ° C. or higher can be used as a substrate.

[0033]

As described in detail above, according to the present invention,
While maintaining the surface temperature at 500 ° C. or less, the ratio P / M of the pressure P (kW) in the chamber to the microwave power M (Pa) is set to 360 to 440, so that the surface area is a and the film thickness is t. When t / a is 3 × 10
^An extremely thin and wide diamond thin film having a size of ⁻⁵ (m ⁻¹ ) or less can be formed without defects such as pinholes. Further, since the adhesion between the substrate and the diamond thin film is high and the substrate temperature during film formation is low, the selection range of the substrate material can be widened. Thus, utilizing the inherent properties of diamond such as chemical stability, light transmittance, high refractive index, high hardness and low dielectric loss, optical transmission and reflection windows, optical related components, semiconductor packages, chemical resistant coatings, Applicable to wear-resistant coatings and decorative coatings. Further, the diamond thin film of the present invention has a very large advantage that the surface roughness is small and polishing is not required.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are photographs substituted for drawings of the surface and cross section, respectively, of a diamond thin film according to an example of the present invention.

FIG. 2 is a schematic sectional view showing a plasma CVD apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 11; vacuum container 13; microwave window 14; substrate 15; substrate support base 16, 19, 20; pipe 17; exhaust valve 18;

Claims (4)

[Claims] 1. A diamond thin film characterized in that a ratio t / a of a film thickness to a surface area is 3 × 10 ⁻⁵ (m ⁻¹ ) or less, where a is a surface area and t is a film thickness. 2. The diamond thin film according to claim 1, wherein the diamond thin film is doped with one material selected from the group consisting of boron, nitrogen, and phosphorus. 3. The method according to claim 1, wherein the substrate is formed on a substrate made of one material selected from the group consisting of silicon, germanium, silicon-germanium, sapphire, silicon carbide, gallium nitride, quartz and glass. Item 2. The diamond thin film according to item 1. 4. The microwave power to be applied is M (unit: kW, M ≧ 3 k) by a microwave plasma CVD method.
W) When the pressure in the plasma chamber is P (unit: Pa), the ratio P / M of the pressure to the microwave power is maintained at 360 to 440, and the surface temperature during synthesis is maintained at 500 ° C. or less. Any one of claims 1 to 3
13. A method for producing a diamond thin film, comprising forming the diamond thin film according to the above item.