Formation of diamond film

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention forms a diamond film on a substrate made of a metal other than Si, Si, graphite, or another conductive material when manufacturing a semiconductor having a diamond film used for a thermistor, a high-temperature semiconductor, an optical element, or the like. Regarding the method.

【0002】

[Conventional technology]

A diamond film is a method of decomposing a gas of a compound composed of hydrogen and / or hydrogen or oxygen diluted with hydrogen by generating plasma with thermal energy, microwave or arc energy in a vacuum. Is formed on the substrate by.

【0003】

First, a method of forming a diamond film on a substrate by using a single crystal Si wafer as a substrate and generating plasma in hydrogen-diluted methane gas by microwaves will be described as an example.

【0004】

First, a Si wafer substrate cut to a predetermined size is immersed in water in which diamond powder is dispersed, and ultrasonic waves are applied to cause the diamond powder to collide with the surface of the Si substrate to perform a scratching treatment. The diamond-damaged Si substrate is placed in a quartz glass tube inserted in a 2.35 GHz microwave generator. And 10 at the beginning in the glass tube^-3Create a vacuum of torr or higher, then introduce 1% methane gas diluted with hydrogen gas to change from several torr to several tens of torr, and then input power to generate plasma near the Si substrate. Is heated to form diamonds on the substrate. Recently, it has been confirmed that a diamond film is formed on the metal even when a metal such as Ni is used as the substrate.

【0005】

Further, as another known example, a method of using a ceramic sintered body as a substrate and providing a carbide as an inner layer for forming diamond is disclosed in Japanese Patent Application Laid-Open No. 61-106478.

【0006】

Further, Japanese Patent Application Laid-Open No. 63-153275 describes a method for forming a diamond by interposing a silicon carbide film between a substrate specified as an alumina substrate and a diamond layer.

【0007】

[Problems to be Solved by the Invention]

In the above method of forming diamonds on a Si substrate after damaging the Si substrate, it is necessary to control the substrate temperature when changing the particle diameter, but the power is reduced because it correlates with the power of microwaves. Then it is often admitted that it does not become a diamond.

【0008】

Further, there is a problem that the above method cannot be applied when it is not desired to perform the scratching treatment with diamond, for example, when it is desired to continuously form a SiC-SiC-diamond or a SiC-diamond semiconductor device.

【0009】

Further, in JP-A-61-106478 and JP-A-63-153275, a method for controlling the particle size of diamond formed on a SiC layer in order to use diamond as a semiconductor, a conductive material. -The method of forming a layer of SiC-diamond, the examination of the conditions for forming a diamond film and the method of forming SiC suitable for it, the method of positively utilizing the structural similarity between SiC and diamond, etc. are described. Moreover, the above-mentioned problem has hardly been examined in the past.

【0010】

[Means for solving problems]

As a result of diligent studies in view of the above problems, the present inventors have investigated a method for controlling the particle size of diamond and a method for forming diamond without damaging with diamond, and any method can be used. We have found that SiC works effectively and have completed the present invention.

【0011】

That is, in the present invention, a gas containing a silicon atom and a gas containing a carbon atom are introduced into a region where a substrate made of a conductive material heated to 1150 to 1500 ° C exists, and the substrate is thermally decomposed by the introduced gas. After forming a SiC layer on top, a method of introducing a gas containing carbon diluted with hydrogen into a region where a heated substrate having the SiC layer exists to form a diamond film under reduced pressure (hereinafter, diamond film). Method A), a gas containing silicon atoms and a gas containing carbon atoms were introduced into the region of the substrate made of a conductive material heated to 1150-1500 ° C, and the heat of the introduced gas was introduced. After forming a SiC layer on the substrate by decomposition, the surface of the SiC layer is scratched with diamond powder, and then a gas containing carbon diluted with hydrogen in the region where the heated substrate having the SiC layer exists. The present invention relates to a method of forming a diamond film under reduced pressure (hereinafter referred to as a method B of forming a diamond film).

【0012】

[Action]

In the method A for forming a diamond film of the present invention, the nucleation density of the diamond film formed on the SiC layer can be changed by changing the formation temperature of the SiC layer formed on the substrate.

【0013】

Further, in the method B of forming a diamond film by damaging the formed SiC layer with diamond powder, the particle size of the formed diamond can be controlled by changing the formation temperature of the SiC layer.

【0014】

[Example]

In the present invention, a conductive material is used as the substrate.

【0015】

Examples of the conductive material include graphite, silicon, tungsten, molybdenum and the like.

【0016】

When graphite is used as the conductive material of the substrate, its shape is preferably plate-like.

【0017】

When Si is used as the conductive material, since the melting point of silicon is 1414 ° C, SiC must be formed at 1400 ° C or less.

【0018】

In order to form a SiC layer on the substrate by thermal decomposition, a gas containing silicon atoms and a gas containing carbon atoms are introduced into the region where the substrate exists.

【0019】

The gas containing a silicon atom used as a raw material for forming the SiC layer in the present invention is, for example, a Si compound that is easily decomposed at a high temperature or a Si compound diluted with a gas.

【0020】

Examples of the Si compound include silicon tetrachloride, silane, trimethylsilane and the like, and examples of the diluting gas include hydrogen and argon.

【0021】

Similarly, the gas containing a carbon atom used as a raw material is a carbon compound that is easily decomposed at a high temperature or the carbon compound diluted with a gas.

【0022】

Examples of the carbon compound include methane, propane, ethylene and acetylene, and examples of the diluting gas include hydrogen and argon.

【0023】

Next, the gas containing silicon atoms and the gas containing carbon atoms are mixed, but the mixing ratio is 0.7 to 1.3 for Si / C (atomic ratio), and 0.9 to 1.1 is close to the chemical equivalent ratio. Is preferable. The total content of the Si compound and the carbon compound as the reaction raw materials in the diluted gas is preferably 5 to 30 vol%, more preferably 10 to 20 vol% in order to obtain an appropriate adhesion rate.

【0024】

The dilution gas may not be mixed in advance, but may be mixed and diluted when the Si compound and the carbon compound are mixed and introduced into the container.

【0025】

The pressure of the mixed gas introduced onto the substrate is preferably 1 to 20 Torr, more preferably 5 to 15 Torr, and the temperature is preferably 1150 to 1500 ° C.

【0026】

If the temperature of the substrate is less than 1150 ° C, SiC is not formed. Further, if the temperature of the substrate exceeds 1500 ° C, the irregularities on the formed SiC surface become peeled off, which is not preferable.

【0027】

It was found by X-ray diffraction analysis that the temperature of the substrate and the orientation of the crystals of the SiC layer formed had a certain tendency as follows.

【0028】

That is, for example, when graphite is used as the substrate, as shown by in FIG. 2, when the temperature of the substrate is in the range of 1150 to 1500 ° C and the substrate temperature is around 1150 to 1250 ° C, the crystal axis is [ 111] Cubic SiC oriented in the axial direction is likely to be formed, but as the temperature gradually rises, cubic SiC oriented in the [220] axis direction is likely to be formed, and X is formed near 1250 to 1300 ° C. When examined by line diffraction, the intensity of the peak corresponding to the [111] axis and the peak corresponding to [220] are the same. As the substrate temperature rises, the amount of crystals oriented on the [220] axis increases, and at temperatures around 1350 to 1400 ° C, the intensity ratio of the peak corresponding to the [220] axis ((220) / { (220) + (111)}) is the highest value of 0.7 to 0.9.

【0029】

However, when the temperature is further increased, the peak corresponding to the [111] axis increases again, and the peak intensity ratio becomes about 0.5 at around 1500 ° C.

【0030】

In this way, the SiC layer is formed on the conductive material, and the orientation of the SiC layer described above has a great influence on the formation of the diamond film described later.

【0031】

Next, the substrate on which the SiC layer is formed is heated, and a gas containing carbon diluted with hydrogen is introduced to form a diamond film under reduced pressure.

【0032】

Examples of the hydrogen-diluted carbon-containing gas used for forming the diamond film include a gas obtained by diluting a carbon compound such as carbon monoxide, methane, and methyl alcohol with hydrogen.

【0033】

The content of carbon monoxide diluted with hydrogen is preferably 0.5 to 10 vol%, more preferably around 5%. (It differs between carbon monoxide and methane. The cause is SP³Bond and H₂And O₂It is considered that this is because it becomes a competition for the etching effect due to the above. ) When the gas containing carbon is introduced onto the substrate on which the SiC layer is formed, the pressure is preferably several Torr to 100 Torr, further 5 to 50 Torr, and the temperature is preferably 900 to 980 ° C.

【0034】

Examples of the method for forming the diamond film include a method of forming by generating plasma by microwaves, a thermal filament method, an electrocyclotron resonance (ECR) method, a gas burner method, a plasma spraying method, and the like, and a gas containing carbon. Any of the above methods may be used as long as is activated.

【0035】

In the method of generating plasma by microwaves, 2.35 GHz is usually used as microwaves.

【0036】

When the diamond film is formed by the above method, the particle size and nucleation density of the formed diamond are greatly affected by the orientation state of the SiC layer as the substrate when the diamond film is formed. That is, as described above, when the SiC layer is formed on the conductive material, the orientation of the SiC layer formed on the substrate differs depending on the temperature of the substrate. It was found that there is a correlation between the orientation direction of the crystal axis of the above and the nucleation density of the formed diamond particles, for example, as shown in FIG. 2 of the example. That is, for example, when graphite is used as a substrate, the nucleation density of diamond is approximately proportional to the amount of crystals oriented in the [220] axis. From this, by changing the temperature when forming the SiC layer on the substrate in the range of 1150 to 1500 ° C, the nucleation density when forming diamond is usually 2 × 10.⁵~2×10⁸Pieces / cm²Can be controlled within the range of.

【0037】

By forming a diamond on the SiC layer to be formed without damaging the formed SiC layer as in the above-mentioned method A for forming a diamond film, for example, three types of semiconductors of SiC-SiC-diamond or two types of SiC-diamond. Heterostructure devices made of semiconductors can be configured, and the devices can be used for thermistas, high-temperature semiconductors, optical elements, and the like.

【0038】

In the above-mentioned method, a diamond film is formed without any treatment on the SiC layer formed on the conductive material. However, after the surface of the SiC layer is scratched with diamond powder, diamond is formed on the SiC layer. A film may be formed.

【0039】

Examples of the method of performing the scratching treatment include a method of immersing the diamond powder in dispersed water and applying ultrasonic waves to cause the diamond powder to collide with the surface of the SiC layer for the scratching treatment, a method of polishing with a diamond paste, and the like. ..

【0040】

It is not clear what the effect of the scratch treatment is, but it is not that the scratches are as large as those seen under a microscope, and it is thought that lattice distortion, lattice defects, and micro cracks have occurred.

【0041】

Even when a diamond film is formed on the SiC layer after the scratching treatment is performed on the surface of the SiC layer, the particle size of the formed diamond is affected by the physical properties of the SiC layer as the substrate on which the diamond is formed.

【0042】

That is, as shown in FIG. 1, as the temperature at which the SiC layer is formed rises, the particle size of the diamonds formed becomes smaller in proportion to the temperature, and the diamonds that precipitate without changing the diamond forming conditions. The diameter of the particles can be changed. In this way, the particle size of the diamond to be formed can be controlled in the range of 0.5 to 2 μm by the formation temperature of the SiC layer formed on the substrate. In this case, the thickness of the diamond film formed becomes 2 μm in 3 hours. By controlling the particle size of the diamond film formed in this way, it is possible to control the characteristics of parts such as a thermistor, a high-temperature semiconductor using polycrystals, and an optical element.

【0043】

Hereinafter, the present invention will be described based on specific examples.

【0044】

[Examples 1 and 2] 20 mm × 20 mm graphite (substrate) is heated to 1200 ° C in a vacuum furnace, and hydrogen gas is placed in the furnace at 300 cc / min, silicon carbide and 80 cc / min at 80 cc / min. When methane gas was mixed and introduced at 10 torr, taken out after 60 minutes, and examined by X-ray diffraction, it was found that cubic SiC having a crystal axis oriented in the [111] direction was precipitated. The thickness of the SiC layer was 3.5 μm.

【0045】

This was immersed in water in which diamond powder was suspended, and ultrasonic waves were applied to cause the diamond powder to collide with the SiC surface, resulting in damage treatment with diamond. After that, it was placed in a quartz glass tube placed in a microwave waveguide and evacuated. Then, hydrogen-diluted 5% CO gas was introduced to make it 30 torr, plasma was generated by microwaves having a frequency of 2.35 GHz, the substrate temperature was set to 950 ° C, and a diamond film was formed on the SiC layer. By performing the above treatment for 3 hours, a diamond having a diameter of about 2 μm was formed to a thickness of about 2 μm (Example 1).

【0046】

When diamonds are formed on the SiC surface under the same conditions as in Example 1 without performing the diamond scratching treatment, the nucleation density of diamonds is 2 × 10.⁵Pieces / cm²It was very small, and only a very small amount of diamond was formed (Example 2).

【0047】

[Examples 3 to 4] The same graphite used in Example 1 was heated to 1300 ° C in a vacuum furnace, and hydrogen gas was placed in the furnace at 300 cc / min, and silicon carbide was used at 80 cc / min. Methane gas was mixed and introduced at 80 cc / min, and the mixture was made into 10 torr and taken out after 60 minutes. When examined by X-ray diffraction, cubic SiC having crystal axes [111] and [220] at almost the same height was found. Was found to be precipitated. The thickness of the SiC layer was 25 μm.

【0048】

This was immersed in water in which diamond powder was suspended in the same manner as in Example 1, and ultrasonic waves were applied to cause the diamond powder to collide with the SiC surface for damage treatment. After that, it was placed in a quartz glass tube placed in a microwave waveguide and evacuated. Then, hydrogen-diluted 5% CO gas was introduced to make 30 torr, and plasma was generated by microwaves in the same manner as in Example 1 to form diamonds on SiC. By performing the above treatment for 3 hours, a diamond having a diameter of about 1.5 μm was formed with a thickness of about 2 μm (Example 3).

【0049】

On the other hand, when diamonds were formed under the same conditions as in Example 3 without damaging the diamonds, diamonds were formed, but the nucleation density was 7 × 10.⁶Pieces / cm²It was sparse (Example 4).

【0050】

[Example 5] When graphite was heated to 1400 ° C in a vacuum furnace to form cubic SiC by the same method as in Example 1 and examined by X-ray diffraction, the crystal axis was oriented to [220]. It was found that it was precipitated. As in Example 1, plasma was generated by microwaves to form diamonds on SiC without damaging the diamonds. By performing the above treatment for 3 hours, diamonds having a diameter of about 6 μm were formed to the extent that some gaps were left. The nucleation density at this time is 7 × 10.⁷Pieces / cm²Met.

【0051】

Figure 1 shows the relationship between the cubic SiC formation temperature and the approximate diameter of diamond particles when the surface of cubic SiC is scratched with diamond.

【0052】

As can be seen from this relationship, the diameter of diamond particles can be controlled by the SiC formation temperature without changing the diamond formation conditions. However, SiC was not formed when the SiC formation temperature was 1100 ° C or lower. Further, when the SiC formation temperature exceeds 1500 ° C, the surface irregularities become peeled off under the SiC formation conditions. Therefore, the SiC formation temperature is preferably 1150 to 1500 ° C.

【0053】

The reason why the diamond particle size can be controlled by the SiC formation temperature is 4.377A when the SiC lattice constant is 1200 ° C and 4.358A when it is formed at 1500 ° C. During this period, the lattice constant decreases continuously as the formation temperature rises and approaches the diamond lattice constant (3.567A), which may be related to the lattice constant.

【0054】

In addition, Fig. 2 shows the peak intensity ratio of the crystal plane of cubic SiC measured by X-ray diffraction as a function of the formation temperature, and at the same time shows the nucleation density when the diamond damage treatment is not performed.

【0055】

[Effect of the invention]

As described above, in the method B of forming a diamond film by scratching the SiC layer formed on the substrate of the present invention, the grain size of the diamond can be changed depending on the SiC formation temperature, so that the thermistor and polycrystal can be used. It has the effect of being able to control the characteristics of parts such as high-temperature semiconductors and optical elements using.

【0056】

In the method A of forming a diamond film without damaging the SiC layer with diamonds of the present invention, the nucleation density of diamonds can be controlled. Therefore, the particles can be formed by covering the entire surface of the substrate with diamond particles for a longer period of time. It can be a diamond device with a large diameter.

【0057】

Further, by not performing the scratching treatment of the SiC layer with diamonds in this way, diamonds can be formed in continuous vacuum following the formation of the SiC layer. Therefore, three types of SiC-SiC-diamonds or two types of SiC-diamonds can be formed. It has the effect of being able to construct a heterostructured device using the above semiconductors.

[Simple explanation of drawings]

[Figure 1]

It is a graph which shows the relationship between the formation temperature of the SiC layer in this invention, and the particle size of diamond.

[Figure 2]

It is a graph which shows the relationship between the formation temperature of the SiC layer in this invention, the peak intensity ratio of X-ray diffraction, and the nucleation density.