JPH06199596A - Method for synthesizing diamond film - Google Patents

Abstract

(57) [Abstract] [Purpose] To enable the synthesis of diamond film by plasma CVD using a source gas with high concentration of methane or carbon monoxide, and to widen the selection range of methane concentration. [Structure] When mixing oxygen in addition to methane and hydrogen, even if the methane concentration is higher than 20%, which is higher than the conventional value, the oxygen content in the source gas is x%, the methane content is y%, and the hydrogen content is z%. Then, x + y + z = 1, y> 2x-0.1, y <2x +
If adjusted to 0.05, a good quality diamond film can be obtained. 20
When a mixed gas of carbon monoxide, hydrogen, and oxygen with a high concentration of 0.1% or more is used as a raw material gas, a high quality diamond film can be obtained by suppressing the oxygen concentration to 1.5% or less. Further, the emission spectrum of plasma can also be used as a guide for determining film formation conditions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing a diamond film, which is attracting attention for application as a semiconductor device.

[0002]

2. Description of the Related Art It is well known that diamond, which is a typical gemstone, is the hardest substance, and is one of the industrially important materials such as cutting tools and abrasives. In addition to this, diamond belongs to Group IV of the periodic table like Si and Ge, and also has properties as a semiconductor. It has been previously reported that not only the energy gap is larger than that of Si, but also carrier mobility, saturation drift velocity, breakdown electric field and thermal conductivity are large. By utilizing the excellent properties of this diamond, it was expected to be applied as a material for high temperature operating devices, high power devices, blue light emitting devices, etc., but it was not possible to synthesize high quality and large area diamond films. In recent years, a technique for producing this diamond film by a vapor phase synthesis (CVD) method has been developed, and its application as a semiconductor device has been drawing attention. Actually, trial production of thermistors, Schottky diodes, FETs, light emitting elements, etc. has been actively conducted.

Although diamond is a crystal composed of carbon atoms, it is not a stable phase under normal circumstances. The CVD method is a method of synthesizing a metastable diamond. This is due to activation of a gas composed of carbon such as CH ₄ and CO and a large amount of H ₂ gas, and Si heated to a high temperature of 600 to 1200 ° C.
It is a method of forming a diamond film on a substrate such as. H
_When activated, the ₂ gas becomes highly reactive atomic hydrogen, and re-evaporates the graphite component, which is a stable phase that precipitates simultaneously with diamond. Various methods for activating these gases have been devised, which are named hot filament CVD method, μ wave plasma CVD method, direct current plasma jet CVD method and the like. The synthesized diamond becomes polycrystalline except when the substrate is made of diamond or c-BN. However, a small amount of components such as graphite remain in the diamond film, and its crystallinity is inferior to that of natural diamond. When O ₂ gas is activated to form atomic oxygen without using H ₂ gas, the atomic oxygen has a very strong action of selectively removing carbon such as graphite components other than diamond as compared with hydrogen. Has been done. It has been reported that addition of CH ₄ or CO and H ₂ as well as several% of oxygen improves the quality of diamond film and increases the growth rate of the film. In addition, Japanese Patent Laid-Open No. 4-2140
Japanese Patent No. 94 discloses that carbon compounds of CH ₄ or CO 0.1%
To 20%, O ₂ is 1 ppm to 10%, the balance H ₂ CO / O
It is described that a diamond film was synthesized using a ₂ / H ₂ system gas.

[0004]

[Problems to be Solved by the Invention] H₂CV using gas
O when synthesizing diamond film by D method₂Use gas
For example, CH_FourLarge amount of carbon produced when gas concentration is high
It is thought that it is possible to remove the minute, but CH_Four-O
₂In the gas system, the parts of the CVD equipment, such as packing and
Deterioration caused by oxidation of empty oil etc.
Become. Also, CH _FourUse raw material gas mixed with a large amount of gas
Unknown about the synthesis of diamond films
Yes. Die using raw material gas mixed with a large amount of CO gas
Nothing is known about the synthesis of Yamond films.

An object of the present invention is to solve the above problems and to provide a method for synthesizing a good quality diamond film for removing a large amount of carbon components by using a raw material gas having a high hydrocarbon concentration or carbon monoxide concentration. is there.

[0006]

In order to achieve the above object, a method for synthesizing a diamond film according to the present invention comprises:
In a method of activating a source gas in which oxygen and hydrogen are mixed by plasma discharge to synthesize a diamond film on a substrate in a vapor phase, the concentration of methane is 20% or more, the oxygen content in the source gas is x%, and the methane content is y. %, When the hydrogen content is z%,
If x + y + z = 1, it is effective that y> 2x-0.1. It is also effective that y <2x + 0.05. Alternatively, in a method of activating a raw material gas in which carbon monoxide, oxygen and hydrogen are mixed by plasma discharge to synthesize a diamond film on a substrate in a vapor phase, the carbon monoxide concentration in the raw material gas is 20% or more and the hydrogen concentration is The oxygen concentration is 5% or more and the oxygen concentration is 1.5% or less. When the carbon monoxide content in the source gas is p%, the oxygen content is q%, and the hydrogen content is r%, it is effective that if p + q + r = 1, then p> 0.4q + 0.3. In either method, it is effective to form the film under the plasma conditions in which no peak appears at the wavelength of 618 nm in the plasma emission spectrum.

[0007]

[Function] When a diamond film is vapor-phase synthesized using a raw material gas containing a high concentration of hydrocarbons, if the oxygen gas concentration in the raw material gas is increased, a high quality CH ₄ gas can be obtained according to a predetermined rule. The diamond film can be synthesized. When carbon monoxide, hydrogen, or oxygen is used as a source gas, if the oxygen gas concentration is suppressed to 1.5% or less, a film can be formed even when carbon monoxide is contained at a high concentration of 5% or more. It is possible to synthesize a high quality diamond film by removing a large amount of the carbon component. Also in this case, if the oxygen gas concentration in the raw material gas is increased within the above range, a good quality film can be synthesized even if the CO gas concentration is increased accordingly.

[0008]

EXAMPLE A mixed gas of CH ₄ , O ₂ and H ₂ was used as a raw material gas, the mixing ratio was changed, and a microwave plasma CVD method was performed under the following conditions. A diamond film was synthesized on the scratch-treated silicon plate. Raw material gas flow rate 100 sccm Reaction pressure 30 Torr μ Wave power Approx. 250 W Substrate temperature Approx. 850 ° C. Synthesis time 3 hours The presence of diamond in the film synthesized on the substrate was determined by X-ray diffraction and scanning electron microscopy (SEM). I confirmed it. Fig. 1 shows the results, using x% O ₂ gas, y% CH ₄ gas, and the remaining H ₂ gas as raw materials, □ indicates a good diamond film, ○ indicates a diamond-containing film, and ● indicates. Indicates that a film containing no diamond was synthesized, and + indicates that the film was not synthesized. As is clear from the figure,
When the O ₂ gas concentration x is 0, that is, the source gas is CH ₄
And H ₂ only, the CH ₄ gas concentration y is 5%.
A high-quality diamond film could not be synthesized unless it was controlled. On the other hand, 60% by mixing O ₂ gas
Even with the above CH ₄ gas concentration, a good quality diamond film can be synthesized. Line 1 in the figure is y = 2x-0.1, line 2 is y = 2x
+0.05, line 30 is x + y = 1, ie no H ₂ gas.

From this, it is necessary that y> 2x-0.1 in order to obtain a film containing diamond, and a good quality diamond film confirmed to have a clear automorphism by SEM observation is obtained. , It is necessary to add a condition of y <2x + 0.05. FIG. 2 shows a CH ₄ gas concentration of 40% in a plasma emission spectrum obtained by using a high-speed spectrum analyzer in which a window of a reaction vessel and an optical fiber spectroscope are connected during film formation by the μ-wave plasma CVD method.
In the case of the above case, as the value of x becomes higher, a peak appearing to be associated with OH at a wavelength of 618 nm appears. It is considered that this is because when O ₂ gas is excessive, it reacts with H ₂ to form OH. When such a peak appears, the film is not synthesized as shown in FIG. Since a good quality diamond film can be obtained when the O ₂ gas concentration is slightly lower than that, observing this plasma emission spectrum
_{2 A} good quality diamond film can be synthesized by adjusting the gas concentration.

In another embodiment, the source gas is CO,
A diamond film was synthesized by a microwave plasma CVD method on a scratch-treated silicon plate under the same conditions as above, using a mixed gas of O ₂ and H ₂ and changing the mixing ratio. The film synthesized on the substrate as described above was confirmed to be diamond by X-ray diffraction, Raman spectroscopy and SEM observation. FIG. 3 is a summary of the results. The asterisk (*) represents the conditions under which the film could not be synthesized, and the films synthesized under the conditions of ● and ◯ were found to be a diamond-free film and a diamond-containing film by X-ray diffraction. Further, the films marked with Δ and □ in the area surrounded by the line 3 are diamond films having better quality than those obtained by X-ray diffraction and Raman spectroscopy, and films with or without diamond self-formation by SEM observation. .

The ratio of the intensity of the Raman scattering peak from diamond appearing at 1333 cm ^-1 to the intensity of the broad Raman scattering peak of non-diamond carbon appearing at about 1500 cm ^-1 is used for the evaluation of the diamond film quality. . FIG. 4 shows the oxygen concentration dependence of this Raman scattering peak intensity ratio in lines 4 and 5 for CO of 5% and 60%, respectively. As the oxygen concentration increases, the proportion of diamond scattering increases, and the film quality improves. Even when the CO concentration is as high as 60%, when oxygen is added, the characteristics exceeding the case of 5% CO are obtained.

From the above, it is understood that when the carbon monoxide gas concentration in the source gas is 20% or more and the hydrogen concentration is 5% or more and the oxygen gas concentration is 1.5% or less, the diamond film can be synthesized. Also, the carbon monoxide concentration in the source gas is p
%, Oxygen concentration is q%, hydrogen concentration is r%, p + q +
If r = 1, p> 0.4 q + 0.3 and a good quality diamond film could be synthesized.

FIG. 5 shows that the CO gas concentration p of the plasma emission spectrum obtained by connecting a high-speed spectrum analyzer comprising a spectroscope and an optical fiber to the window of the reaction vessel during film formation by the μ-wave plasma CVD method. This is an example of 60%. As the oxygen concentration increases, as shown in Fig. 5, the wavelength is 618 nm.
The OH peak appears in. When such a peak appears, the film is not synthesized as can be seen from FIG. Since a good quality diamond film is obtained when the oxygen gas concentration is slightly lower than that, a good quality diamond film can be synthesized by observing the plasma emission spectrum and adjusting the oxygen gas concentration. Although an OH peak appears at wavelengths other than 618 nm, it overlaps with the CO peak, etc., so this peak is suitable for observation.

[0014]

According to the present invention, when oxygen is added to the source gas used in the CVD method in addition to hydrocarbons and hydrogen, by keeping the relationship between the oxygen concentration and the hydrocarbon concentration within a predetermined range, A good quality diamond film could be obtained.
As a result, the degree of freedom in the film forming conditions for obtaining a high quality diamond film is increased, and since the oxygen and hydrogen are both contained in the source gas, the life of the CVD apparatus member can be extended. Further, according to the present invention, the oxygen gas concentration
By controlling the content to 1.5% or less, the concentration of carbon monoxide was increased, and it became possible to synthesize diamond with a mixed gas of hydrogen. As a result, the degree of freedom in the film forming conditions for obtaining a high quality diamond film is increased. In addition, by using the plasma emission spectrum, it is possible to judge whether or not the film can be formed, and it is possible to control the film quality, which facilitates management of the film forming operation.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the O ₂ gas and CH ₄ gas concentrations in the raw material gas and the properties of the synthesized film.

FIG. 2 is a plasma emission spectrum diagram with a CH ₄ gas concentration of 40% and an O ₂ gas concentration as a parameter.

FIG. 3 is a diagram showing the relationship between the O ₂ gas and H ₂ gas concentrations in the raw material gas and the properties of the synthesized film.

FIG. 4 is a diagram showing the relationship between the ratio of the Raman scattering peak intensity of diamond to the Raman scattering peak intensity of non-diamond carbon and the oxygen gas concentration with CO gas concentration as a parameter.

FIG. 5: Plasma emission spectrum diagram with CO gas concentration of 60% and O ₂ gas concentration as a parameter

Claims (5)

[Claims] 1. A method for activating a raw material gas, which is a mixture of methane, oxygen and hydrogen, by plasma discharge to synthesize a diamond film on a substrate in a vapor phase, wherein the raw material gas contains x% oxygen and y% methane. , When the hydrogen content is z%, x + y
A method of synthesizing a diamond film in which y> 2x-0.1 when + z = 1. 2. The method for synthesizing a diamond film according to claim 1, wherein y <2x + 0.05. 3. A method of activating a raw material gas, which is a mixture of carbon monoxide, oxygen and hydrogen, by plasma discharge to synthesize a diode film on a substrate in a vapor phase, wherein the carbon monoxide concentration in the raw material gas is 20% or more, A method for synthesizing a diamond film, wherein a hydrogen concentration is 5% or more and an oxygen concentration is 1.5% or less. 4. When the carbon monoxide content in the source gas is p%, the oxygen content is q%, and the hydrogen content is r%, if p + q + r = 1, then p>
The method for synthesizing a diamond film according to claim 3, wherein the value is 0.4q + 0.3. 5. The film formation is performed under plasma conditions in which a peak does not appear at a wavelength of 618 nm in the plasma emission spectrum.
5. The method for synthesizing a diamond film according to any one of 4 to 4.