JPH05892A - Diamond crystal and substrate for forming diamond - Google Patents

Abstract

PURPOSE:To obtain a clean diamond crystal free from unevenness and voids by deposition even in case of a small thickness by forming a diamond crystal on a substrate with a formed graphite layer. CONSTITUTION:When a diamond single crystal is selectively formed on a substrate 21, a graphite layer 22 is first formed on the substrate 21. A mask 23 of a resist, etc., is then formed on the layer 22 by beam drawing or the like and the layer 22 is etched by reactive ion etching with oxygen-contg. gas or ion beam etching with rare gas such as Ar. The mask 23 is removed and diamond formation is carried out. Diamond 24 can selectively be formed only on the graphite layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diamond crystal having excellent characteristics as an electronic material and a substrate for forming the diamond crystal.

[0002]

2. Description of the Related Art Diamond has a large band gap (5.5 eV) and a large carrier mobility (electrons 1800).
cm ² / V · S, hole 1600 cm ² / V · S), large thermal conductivity (20 W / cm · k), high hardness and excellent wear resistance, and other materials that cannot be obtained with other materials. It has the characteristics of

In recent years, the synthesis of diamond from the vapor phase has progressed, and it has become possible to form a diamond film by the chemical vapor deposition method (CVD method).

In this technique, a mirror-polished substrate is usually used.

However, in a mirror-polished silicon substrate, since the crystal nucleus formation density of diamond is low, conventionally, the substrate surface is scratched with diamond abrasive grains, or a liquid (alcohol containing diamond abrasive grains) is used. , Water, etc.) to give a film-like diamond crystal by increasing the nucleation density by subjecting the substrate surface to a scratch treatment by applying ultrasonic vibration.

[0006] In addition, selective deposition of diamond crystals is possible by separately forming a region on the substrate on which fine irregularities are formed and a region on which fine irregularities are not formed by the scratching process. For example, Japanese Patent Application Laid-Open No. 2-
According to 30697, it is possible to form a diamond crystal at an arbitrary location by combining a substrate scratching process and an etching process.

[0007]

However, in the above-described technique of scratching the surface of the substrate, since abrasives and polishing debris remain on the substrate and diamond nucleation occurs along the scratch, The diamond precipitation was likely to be uneven. In particular, when the diamond film thickness is as thin as 1 μm or less, precipitation unevenness (region where diamond is not formed) is likely to occur due to this unevenness.

[0008] In addition, the polishing agent and polishing debris remain, for example, when it is used in a semiconductor manufacturing process that requires a very clean condition, it becomes a major obstacle.

Furthermore, it has been difficult to control the crystal orientation in the technique of increasing nucleation by the scratching process.

The present invention has been made in view of the above problems, and provides a diamond crystal and a diamond-forming substrate which are clean and free from uneven deposition or precipitation even when the diamond film thickness is as thin as 1 μm or less. The purpose is to do.

A further object of the present invention is to provide a selectively deposited diamond crystal and a substrate for selective diamond formation that does not require a substrate scratching process.

Yet another object of the present invention is to provide a controlled orientation diamond crystal and a controlled orientation diamond forming substrate.

[0013]

The diamond crystal of the present invention is characterized by being formed on a substrate having a graphite layer formed thereon.

Further, the diamond crystal of the present invention is characterized in that it is formed on a substrate on which a C-axis oriented graphite layer is formed and has a {111} plane orientation.

The diamond forming substrate of the present invention is characterized in that a graphite layer having a thickness of 2 nm or more is formed.

The diamond-forming substrate of the present invention is characterized in that a C-axis oriented graphite layer having a thickness of 2 nm or more is formed.

[0017]

The present invention will be specifically described below.

The present inventors diligently studied a pretreatment method of a substrate for forming a diamond crystal in order to form a diamond crystal having high smoothness and crystal orientation, and as a result, a graphite layer is formed on the substrate. As a result, it was found that diamond nucleation was increased and a diamond film with high smoothness was formed. The present invention is based on this.

The graphite used in the present invention has crystallinity. Amorphous carbon easily scatters in a diamond forming atmosphere and is not useful for diamond formation. On the other hand, crystalline graphite has a certain degree of stability in a diamond forming atmosphere and has a function of assisting diamond formation.

The method for forming graphite on the substrate used in the present invention is not particularly limited, but for example, the substrate is formed at 1 atm in an atmosphere of a gas containing a hydrocarbon such as CH ₄ as a main component. There is a method of heating to 1200 ° C. or higher, a method of spraying a hydrocarbon gas such as methane or a hydrocarbon gas and a diluent gas such as H ₂ , He, Ar, etc. to a substrate heated to 500 ° C. or higher.

Further, as a method for orienting the graphite layer in the C-axis, it is possible to form the graphite layer at a relatively high temperature.

For example, a graphite layer can be easily formed by using an ion beam vapor deposition apparatus as shown in FIG.

An example of a method for forming graphite will be described with reference to FIG.

Reference numeral 1 is a vacuum chamber, 2 is an ion beam source, 3 is a gas inlet, and a gas cylinder and a gas flow rate controller (not shown) are attached. An exhaust port 4 is connected to a turbo molecular pump and a rotary pump (not shown) and can exhaust up to 10 ⁻⁶ Torr. Reference numeral 5 is an ion beam, and 6 is a substrate heating holder, which can be heated up to 1000 ° C. by a power source and a temperature controller not shown. 7 is a base. First, the inside of the vacuum chamber 1 was evacuated to 5 × 10 ⁻⁶ Torr using an exhaust device, the substrate was heated to 600 ° C., and methane gas was introduced into the ion beam source at a pressure of 5 × 10 ⁻⁴ Torr for ionization. Do 5
The substrate is irradiated with a methane ion beam at an acceleration voltage beam current of KV of 0.5 mA / cm ² . At this time, a graphite layer of about 2000 liters is formed by irradiation for 10 minutes. The substrate is heated to 500 ° C. or higher, preferably 600 ° C. or higher, and 700 ° C. or higher, preferably 750 ° C. or higher for C-axis orientation.

At temperatures below 500 ° C., the film does not become graphite but amorphous carbon, and the effect of the present invention cannot be obtained. The conditions for forming the graphite layer are not limited to the above-mentioned conditions. For example, as a raw material gas, another hydrocarbon gas such as ethylene, acetin, benzene, etc., and an additive gas such as H ₂ , Ar, or He are introduced into the hydrocarbon gas. You may.
The acceleration voltage can be selected in the range of 0.1 KV to 50 KV.

The method for forming the graphite layer is not limited to the above method, and the present invention can be achieved by other thermal CVD method, plasma CVD method, or the like. The thickness of the graphite layer is 2 nm or more, preferably 10 nm to 1 μm, and more preferably 50 nm to 50 nm.
It is 0 nm. If the thickness is 2 nm or less, the effect of the present invention is not sufficiently obtained due to scattering in a diamond forming atmosphere, and even if the thickness is 1 μm or more, the effect of the present invention is not improved.

Examples of the diamond vapor phase synthesis method include a CVD method (chemical vapor deposition method). Of course, other methods may be used. FIG. 2 shows an example of a CVD apparatus for forming diamond. Reference numeral 11 is a quartz reaction tube, 12 is a heater, 13 is a tungsten filament, 14 is a silicon substrate having a porous surface, 15 is a gas introduction port, 16 is an exhaust port, and an exhaust device and a pressure control valve (not shown). Connected). Examples of raw material gas for forming diamond crystals include hydrocarbon gas (methane, ethane, etc.) or liquid organic compound (alcohol,
Acetone and the like) which has been heated and gasified can be used. Further, these raw material gases may be diluted with hydrogen, oxygen, etc. and introduced as necessary. Further, in order to form semiconductor diamond, a compound containing boron, phosphorus, nitrogen or the like may be added to the raw material, if necessary.
These raw material gas and additive gas are decomposed by the filament 13 heated to about 2000 ° C., and diamond is formed on the substrate. The diamond forming method of the present invention is
The method is not limited to the above-mentioned method, but may be a microwave plasma CVD method, a high frequency plasma CVD method, a direct current plasma C
The present invention can also be achieved by methods such as the VD method, the magnetic field microwave plasma CVD method, and the combustion flame method.

In the present invention, the graphite layer may be formed in a pattern on a part of the substrate. As a method of forming the graphite layer only on a part of the substrate,
A method of forming a graphite layer after forming a heat-resistant mask on the substrate, and then removing the mask together with the graphite layer, and further forming a mask after forming the graphite layer on the entire surface of the substrate and performing ion etching. There is a method of removing the graphite layer by such a method.

At this time, the area of the region where the graphite layer is formed is 0.5 μm ^{2 to} 20 μm ² , preferably 1 to
It is also possible to selectively form only a single diamond single crystal on the graphite layer by setting it to 10 μm ² , and optimally ² to 5 μm ² . When it is 0.5 μm ² or less, precipitation is liable to occur and the selectivity is deteriorated. 20 μm
^When it is ² or more, a plurality of diamond nuclei are formed and polycrystallized, so that single crystal particles cannot be obtained. A process for selectively forming a diamond single crystal is shown in FIG. First, the graphite layer 22 is formed on the substrate 21 (FIG. 3 (1)), and then the mask 23 such as a resist is formed by using an optical drawing method or the like (FIG. 3 (2)).

The graphite layer is etched from this substrate by reactive ion etching using an oxygen-based gas or ion beam etching using a rare gas such as Ar (the apparatus shown in FIG. 1 can be used) (FIG. 3 (3)). )). Then, if the resist mask 23 is removed and diamond is formed, the diamond 2 is selectively formed only on the graphite layer.
4 is formed (FIG. 3 (4)).

The present invention will be described in detail below with reference to specific examples.

Example 1 First, a graphite layer was formed on a substrate by using the ion beam apparatus shown in FIG. As the base, a silicon single crystal substrate having a diameter of 25 mm and a thickness of 0.5 mm and having a {100} plane orientation was used. The formation conditions for the graphite layer are: substrate temperature 580 ° C., pressure 4 × 10 ⁻⁴ Torr.
By introducing methane gas of 50 SCCM, the acceleration voltage was 4 KV and the ion beam current density was 0.5 mA / cm ² . About 400 liters of graphite layer was formed by film formation for 2 minutes.

Next, the substrate 14 on which the graphite layer was formed was placed in the diamond synthesizing apparatus shown in FIG.
Diamond was formed by the VD method.

The details will be described below. First, the inside of the quartz reaction tube 8 was evacuated to 10 ⁻³ Torr using an exhaust device. Next, from the gas cylinder, hydrogen and methane gas were introduced into the quartz reaction tube 8 at a rate of 200 ml / min and 2 ml / min, respectively, and the pressure inside the reaction tube was adjusted to 100 by a pressure adjusting valve.
I chose Torr. Next, after heating the substrate 14 to 800 ° C. by the heater 12, the tungsten filament 13 was heated to about 2000 ° C. by a power source (not shown).
The heated filament decomposes methane and hydrogen gas to form a film-shaped diamond crystal on the substrate 14.

After forming the film for 1 hour, about 0.8 μm is formed on the substrate.
The polycrystalline diamond film of was formed on the entire surface of the substrate.

(Comparative Example 1) Diamond was formed in the same manner as in Example 1 except that the graphite layer formation treatment was not performed on the silicon substrate. As a result, 500 granular diamond particles having a particle size of about 3 μm were formed on the substrate. It was not possible to obtain a film-shaped diamond because it was only scattered about mm ² .

(Comparative Example 2) Using a lateral polishing machine,
The silicon substrate was polished for 30 minutes with 10 μm diamond abrasive grains. When diamond was formed in the same manner as in Example 1 using this substrate, a diamond film having a film thickness of about 1 μm was formed, but there was uneven deposition, and a few μm-wide precipitates (a part where no diamond was formed). Is about 200 pieces / mm
² accepted.

(Example 2) Diamond crystals were formed in the same manner as in Example 1 except that the C-axis oriented graphite layer was formed at a substrate temperature of 750 ° C during formation of the graphite layer, and the {111} orientation was obtained. A polycrystalline diamond film having properties was formed on the entire surface of the substrate (here, the orientation was measured by the X-ray diffraction method).

(Embodiment 3) As in Embodiment 1, a φ2 μm PMMA-based resist mask of 10 μm was formed on a substrate having a graphite layer formed thereon by optical drawing (photolithography).
The graphite layer was formed at m pitches, Ar ⁺ ion beam etching was performed, and the graphite layer was etched. At that time, the acceleration voltage of the Ar ⁺ ion beam was 0.5 KV and the etching time was 5 minutes.

Next, the resist was removed using acetone, and diamond was formed on the Si substrate by the microwave plasma CVD method. The diamond synthesizing conditions at that time were as follows: microwave power of 500 W, methane and hydrogen flow rates of 1 SCCM and 200 SCCM, respectively, and a substrate temperature of 8
The temperature was 50 ° C. and the pressure was 60 Torr.

By the above diamond formation, diamond single crystal grains were selectively formed in the mask forming portion (graphite remaining portion). The single crystal particles did not show orientation and the orientation was random.

(Embodiment 4) Similar to Embodiment 2, Embodiment 3 is carried out on a Si substrate on which a C-axis oriented graphite layer is formed.
When the mask formation, the etching treatment, and the diamond formation were performed under the same conditions as in (1), diamond single crystal particles were selectively formed in the remaining portion of the graphite layer. The diamond crystals obtained by the X-ray diffraction method are {111}
It was found that they showed plane orientation.

(Examples 5 to 14, Comparative Examples 3 to 5) Using the same apparatus as in Example 1, a graphite layer was formed at various temperatures and thicknesses to form diamond crystals under the same conditions as in Example 1. . In Examples 5 to 8 and Comparative Example 3, a graphite layer was formed on the entire substrate. Further, in Examples 9 to 14 and Comparative Examples 4 to 5, graphite layer patterns having various pattern diameters were formed in the same manner as in Example 3.

Table 1 shows the results of the diamond film uniformity and the diamond single crystal selectivity depending on the graphite forming conditions, the pattern diameter size (in the film uniformity, X indicates that it is worse than the result of Comparative Example 2).

In these examples, the Si substrate was used as the substrate for forming the graphite layer, but as the substrate for forming the graphite layer, in addition to the Si substrate, oxides such as quartz glass, sapphire and spinel, molybdenum, tungsten, Metals such as iron and nickel can be used.

[0046]

[Table 1]

[0047]

As described above, the diamond crystal of the present invention is free from uneven deposition and has excellent flatness and excellent characteristics.

Further, the diamond crystal of the present invention has excellent characteristics with controlled orientation.

The diamond-forming substrate of the present invention is useful for forming good quality crystalline diamond.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an ion beam vapor deposition apparatus that can be used for forming a graphite layer.

FIG. 2 is a schematic view showing an example of a diamond forming apparatus.

FIG. 3 is a schematic view showing a selective diamond forming step.

Claims (7)

[Claims] 1. A diamond crystal formed on a substrate on which a graphite layer is formed. 2. A {111} plane-oriented diamond crystal formed on a substrate on which a C-axis oriented graphite layer is formed. 3. The diamond crystal according to claim 1, wherein the graphite layer or the C-axis oriented graphite layer has a thickness of 2 nm or more. 4. The diamond crystal according to claim 1 or 2, wherein the graphite layer is formed in a pattern, and the pattern area is in the range of 0.5 to 20 μm ² . 5. A diamond-forming substrate on which a graphite layer having a thickness of 2 nm or more is formed. 6. A diamond-forming substrate on which a C-axis oriented graphite layer having a thickness of 2 nm or more is formed. 7. The diamond-forming substrate according to claim 5, wherein the graphite layer is formed in a pattern and the pattern area is in the range of 0.5 to 20 μm ² .