JPH075432B2 - Gas phase synthesis of diamond - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a method for synthesizing diamond by a chemical vapor deposition (CVD) method, and more specifically, to a diamond having high purity, high crystallinity, and versatility at low cost. Moreover, the present invention relates to a gas phase synthesis method capable of high-speed synthesis.

[Conventional technology]

Conventionally, artificial diamond has been synthesized in a thermodynamic equilibrium state under high temperature and high pressure, but recently, it is possible to synthesize diamond from a vapor phase.

In this vapor phase synthesis method, a hydrocarbon gas diluted with 10 times or more of hydrogen is usually used, and this gas is excited by plasma or a hot filament to form a diamond layer on the substrate in the reaction chamber.

Among the conventional methods, there is a method (Patent No. 1272728) in which a source gas is preheated and introduced into the surface of a heating substrate to thermally decompose hydrocarbons for diamond precipitation.

[Problems to be Solved by the Invention]

In the conventional diamond vapor phase synthesis method, various methods such as a heat input method for causing a chemical reaction have been considered, but both methods basically use a large amount of hydrogen, and therefore,
The raw material gas is expensive, and hydrogen is taken into the diamond to deteriorate the purity, crystallinity, etc., and the diamond synthesis conditions, synthesis rate, synthesizable area, base material, etc. are restricted. There was a problem.

As disclosed in Japanese Patent Laid-Open No. 59-30709, it has been considered to synthesize a diamond by supplying a halogen atom, a hydrogen atom and a carbon atom to a reaction system in an extremely low pressure range and an introduced power. The method is insufficient in terms of high purification, and there are problems in cost of raw material gas, synthesis rate, etc., and it is difficult to expect industrial diamond synthesis. The cause seems to be that the composition of the raw material gas is not appropriate.

The present invention aims to eliminate these problems.

[Means for Solving the Problems]

As a result of studying various gas conditions, the inventors have found that stable plasma is generated under the following conditions in which hydrogen other than hydrogen that may be contained in the compound gas is not used, and diamond with good crystallinity is obtained. It has been found that can be synthesized in a large area at high speed.

That is, the method of the present invention comprises mixing fluorine gas, chlorine gas, or both with at least one gas selected from oxygen gas, nitrogen oxides, and sulfur dioxide gas, and a compound gas containing carbon. A gas, or a mixed gas obtained by adding an inert gas to this mixed gas, is introduced into a reaction container, and plasma is generated by an electromagnetic field in the container to generate diamond on a substrate arranged in the container. According to this method, the conventional CVD (chemical vapor depositi
It has been found that a diamond of high purity and high crystallinity can be obtained uniformly at a growth rate several times higher than that of the (on) method, and in which a wide range (tens of square millimeters) does not contain hydrogen and the like.

The use of at least one of oxygen gas, nitrogen oxides, and sulfur dioxide gas effectively works for high purification.
That is, when fluorine gas (F ₂ ) or chlorine gas (Cl ₂ ) alone is used in combination with a compound gas containing carbon, fluorine and chlorine are easily mixed in the synthesized diamond, but the above-mentioned gases are used. And, depending on the synthesis conditions, oxygen gas takes out fluorine and chlorine, so high purity can be obtained.
Further, by taking it out, the adhesion of fluorine and chlorine to the wall surface of the reaction furnace is reduced, and the damage of the device is reduced.

It should be noted that the plasma generation source may use either a direct current or an alternating current electromagnetic field, but in the latter case, a high frequency having a frequency of 1 KHz or more or a microwave is preferable because of good operability. More preferably, a microwave of 300 MHz or higher is used.

In addition, the mixing ratio of the gases used is such that fluorine (F), chlorine (Cl), oxygen (O) in the raw material gas is used in order to prevent deposition of non-diamond carbon and obtain a high-purity, highly crystalline film. , The atomic ratio of carbon (C) is (F + Cl + O) / C = 5 to 0.05, more preferably 1.8 to 0.09, while when the carbon compound contains hydrogen, fluorine (F), chlorine (C
l), the atomic ratio of oxygen (O) to carbon (C), hydrogen (H) is (F + Cl + O) / (C + H) = 4 to 0.01, and more preferably 0.9 to 0.04. .

When an inert gas is used in combination, the inert gas (X) and fluorine (F), chlorine (Cl), oxygen (O), nitrogen (N), sulfur (S), carbon (C) atoms are used. The ratio is X / (F +
Cl + O + C) = 100 to 0, more preferably 20 to 0.01.

The use of an inert gas is extremely preferable because it has the effect of enabling plasma generation in a wide pressure range, further increasing the growth rate, and facilitating the coding of a large area.

Next, as the inert gas used in the present invention, one kind selected from He (helium), Ne (neon), Ar (argon), Kr (krypton), and Xe (xenon), or these A mixed gas of a plurality of types can be mentioned, but in view of mass productivity and production cost of diamond, an argon gas which is inexpensive and easy to obtain is particularly preferable.

The compound gas containing carbon is, for example, an organic compound containing a small amount of oxygen, nitrogen, or sulfur in molecules such as gaseous methane, ethane, acetylene, propane, natural gas, carbon monoxide, carbon dioxide, and alcohol. It may be. Furthermore, compounds containing carbon are CF4, C2F6, C3F8, c-C4F8, C
It may be a compound containing halogen such as 5F12, CHF3, CBrF3, CC14, CC13F, CC12F2, CC1F3.

The preferred embodiments of the present invention including the above are summarized and shown above.

(1) When using an alternating electromagnetic field, the plasma generation source uses a high frequency or a microwave having a frequency of 1 KHz or more, and more preferably a microwave of 300 MHz or more.

(2) The compound gas containing carbon used by mixing with other gas is an aliphatic hydrocarbon, an aromatic hydrocarbon, an alcohol,
One or more gases selected from ketones and the like are used.

(3) The input power required to generate plasma is 1 w / cm ³ or more, and the pressure in the reaction chamber is 5 to 760 Torr.

(4) The flow rate of the mixed gas in the diamond formation reaction section is set to 0.1 cm / sec or more.

(5) The mixing ratio of the gases is such that the raw material ratio in the raw material gas is (F
+ Cl + O) /C=5-0.05, more preferably 1.8-0.09.

Alternatively, when hydrogen is contained in the compound gas containing carbon, (F + Cl + O) / (C + H) = 4 to 0.01, more preferably 0.9 to 0.04.

(6) When the inert gas (X) is used in combination, the atomic ratio is X / (F + Cl + O + C) = 100 to 0, more preferably 20 to
0.01.

In such a method of the present invention, the substrate temperature (120-1
(200 ° C), reaction tube pressure, mixed gas ratio, gas flow rate, and other manufacturing conditions can be easily controlled, and three-dimensional substrates that were difficult to coat with diamond can be easily coated. Furthermore, since hydrogen is not actively used, it is possible to coat even a substrate that is easily embrittled by hydrogen.

Further, by changing the manufacturing conditions, it is possible to grow large diamond particles having a diameter of several hundred μm or more at a high speed.

In the vapor phase synthesis of diamond using plasma, μ wave is the best. Further, an apparatus having a structure in which an electrode is not included in the reaction container is desirable because the plasma is stable. Further, in order to control the temperature of the base material, the base material may be cooled or a heating mechanism may be used. Normally, when such a mechanism is put in a reaction vessel, plasma or the like is disturbed, so that it can be made of an insulator.

Speaking of the base material, Si, Si ₃ N ₄ , SiC, BN, B ₄ C, A
Ceramics such as 1N, refractory metals such as Mo, W, Ta and Nb, or metals or alloys made of Cu, Al, cemented carbide or the like can be used to lower the substrate temperature. In the case of an atmosphere containing oxygen, it is necessary to control the partial pressure of H ₂ generated by division. It was also found by the emission spectroscopy analysis that the plasma generated under the conditions of the present invention has the following differences from the conventional method using hydrogen gas as the main source gas. That is, the plasma generated under the conditions of the present invention has a relatively weak H ₂ continuous band strength and a strong hydrogen atom strength such as H (α). From such a phenomenon, it is considered that the raw material gas is decomposed more efficiently under the conditions of the present invention than in the conventional method.

Further, in the conventional example, the concentration of the compound gas containing carbon is several vol% (0.8 to 2.0 vol%) with respect to hydrogen gas, which is the deposition of diamond from a state of low supersaturation. Since the deposition of diamond is several hundred times more than that of the conventional method, it is considered possible to deposit a diamond film with low defects and high quality.

〔Example〕

First, FIGS. 1 to 4 show schematic views of a diamond synthesizing apparatus used in the present invention.

Figure 1 shows a microwave plasma CVD system (hereinafter referred to as μ-P
Fig. 2 shows a high-frequency plasma CVD device (hereinafter referred to as RF).
-PCVD), Fig. 3 shows DC plasma CVD equipment (hereinafter D
FIG. 4 shows a high frequency high temperature plasma CVD apparatus (hereinafter referred to as RF-HPCVD), and any of these apparatuses may be used in the present invention. In the figure, 1 is a base material, 2 is a reaction quartz tube, 3 is a vacuum exhaust port, 4 is a source gas introduction port, 5 is plasma generated, 6 is a magnetron, 7 is a waveguide, and 8 is a plasma position adjusting plunger. , 9 is RF
Power supply, 10 DC power supply, 11 base material support, 12 insulation seal,
13 is a cathode. The quartz tube 2 shown in FIG. 4 can be cooled.

Next, specific examples and comparative examples of the present invention using the above four types of devices will be described.

The apparatus used and other manufacturing conditions are as shown in Table 1 and Table 2, respectively. In addition, the base material used was a 2-inch (φ50.8 mm) Si single crystal wafer that was finally polished with # 5000 diamond powder in both the examples and comparative examples. This substrate was held in the reaction quartz tube 2 shown in the figure, and the raw material gas was first introduced into the tube 2. Plasma was generated by the plasma generation source at a pressure of 1 Torr, and the pressure inside the tube was quickly raised to obtain the results shown in Table 1. The diamond was grown and synthesized on the base material for the time shown in the table while maintaining the tube pressure shown in. The surface temperature of the base material was measured by an optical pyrometer by instantaneously interrupting the plasma.

Then, the diamond obtained under the conditions of each sample No. was subjected to surface observation by a scanning electron microscope, film thickness measurement, X-ray diffraction, and Raman scattering spectroscopy to evaluate crystallinity.
The results are also shown in Tables 1 and 2. In Table 1, the example of the present invention is sample No. 4 to which NO gas was added.

In Tables 1 and 2, "Dia" is diamond and "g".
“R” indicates graphite, and “ac” indicates amorphous carbon. F is fluorine, Cl is chlorine, O is oxygen, and C
Represents carbon and X represents one or more inert gases. In addition, the Raman spectrum of the sample No. 2 sample in Table 1,
The transmission spectra in the ultraviolet and visible regions are shown in Figs. 5 and 6, respectively, and the fact that the diamond film has much better crystallinity than in Fig. 5 shows that it has an absorption edge of 225 nm from Fig. 6 in the ultraviolet to infrared region. It can be seen that it has high translucency. It is also considered to be a very effective method for application to window materials. Further, when Ti / Mo / Aμ electrodes were vapor-deposited and the electrical resistivity was measured, it was found that the characteristic was that it showed a value of 10 ¹² Ωcm or more and was stable and extremely high resistance even after diamond vapor deposition.

[Effect] According to the present invention described above, unlike the conventional method, the plasma
For the diamond synthesis by the CVD method, a gas obtained by adding a compound gas containing carbon to halogen-based fluorine gas, chlorine gas, and at least one of oxygen gas, nitrogen oxide, and sulfur dioxide gas is used. The following effects can be obtained.

(1) Since hydrogen is not used other than hydrogen atoms that may be contained in the compound gas, diamond coating is possible even on a substrate such as titanium that is easily embrittled by hydrogen.

(2) A highly pure and highly crystalline diamond film containing no hydrogen can be obtained.

(3) Depending on the manufacturing conditions, it can be grown selectively in a film or granular form at a high speed of 100 μm / H or more.

(4) Diamond can be coated on a base material having a complicated shape, and growth to a large area is possible.

(5) In the method of using an inert gas together, plasma can be generated in a wide pressure range, so that the growth rate can be further improved and the diamond area can be further increased.

(6) Oxygen atoms have the effect of removing fluorine and chlorine, and the purity of the synthesized diamond is further increased, and the pain of the synthesizer is reduced.

(7) Oxygen gas, nitrogen oxides, and sulfur dioxide gas are inexpensive, so the cost of raw material gas is reduced, which is economically advantageous.

In addition, due to the above effects, it can be used for diamond heat sinks, diamond abrasive grains, etc., which were conventionally produced by the high-pressure method, and also has high thermal conductivity, constant induction, high translucency, high specific elasticity, high strength, and wear resistance. A few μm to the required field
It is possible to provide not only the following thin film but also a substrate having a thickness of several tens of μm or more.

In addition, the apparatus to be used may be a conventional apparatus, and even if the conventional apparatus is used, the manufacturing process for manufacturing does not particularly change or increase, so that it is excellent in terms of stable operation and equipment cost.

[Brief description of drawings]

1 to 4 are all schematic views of a plasma CVD apparatus usable in the method of the present invention. 5 and 6 and FIG. 1 are graphs showing Raman spectroscopic spectra of Sample No. 2 in Table 1 and transmission spectra in the ultraviolet and visible regions. 1 ... Substrate, 2 ... Quartz tube, 3 ... Vacuum exhaust port, 4 ... Raw material gas inlet port, 5 ... Generated plasma, 6 ... Magnetron, 7 ... Waveguide, 8 ... Plunger , 9 ... RF power supply, 10 ... DC power supply, 11 ... Base material support, 12 ... Insulation seal, 13 ... Cathode, 14 ... Cooling water.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-59-30709 (JP, A) JP-A-61-36200 (JP, A) JP-A-62-265198 (JP, A)

Claims (2)

[Claims] 1. A fluorine gas, a chlorine gas, or both, at least one gas selected from oxygen gas, nitrogen oxides, and sulfur dioxide gas, and a compound gas containing carbon are introduced into a reaction vessel. A method for vapor phase synthesis of diamond, characterized in that plasma is generated in the container by an electromagnetic field of direct current or alternating current to generate diamond on a substrate held in the container. 2. A reaction of fluorine gas or chlorine gas or both with at least one gas selected from oxygen gas, nitrogen oxides and sulfur dioxide gas, an inert gas and a compound gas containing carbon. A method for vapor phase synthesis of diamond, which comprises introducing into a container and generating plasma in the container by an electromagnetic field of direct current or alternating current to generate diamond on a substrate held in the container.