JPH06321688A - Forming method of highly oriented diamond thin film - Google Patents

Abstract

PURPOSE:To obtain a diamond thin film of large area having little grain boundaries, high mobility of the carrier and high breakdown electric field and little leak current by applying an electric field between a hot filament and a single crystal substrate for a specified time in the initial stage of synthesis. CONSTITUTION:The highly oriented diamond thin film is formed by hot filament method. The reaction chamber 1 is evacuated with a pump 14 through a tube 15, while a specified source material gas is introduced through a mass flow controller 8, electromagnetic valve 7, and tube 11 to the reaction chamber 1. the filament 2 is heated to produce plasma in the reaction chamber 1. In the initial stage of synthesis, about 200V DC voltage is applied on a substrate 4 such as single crystal silicon at about 650-800 deg.C for 30min to produce negative electric field to form a crystal seed layer of about <=1mum thickness on the substrate 4. Then the layer is grown to form a highly oriented diamond thin film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a highly oriented diamond thin film used for electronic parts / devices such as transistors and diodes and heat sinks.

[0002]

2. Description of the Related Art Diamond is excellent in heat resistance, has a large band gap, and is usually an insulator, but if added with impurities, it becomes a semiconductor. In order to have such characteristics,
Diamond is extremely useful as a material for electronic parts and electronic devices for high temperature, high frequency, and high electric field.

In order to make the most of the above-mentioned excellent characteristics of diamond in electronic devices, it is necessary to synthesize high-quality single crystals with controlled impurities. However, single crystal diamond obtained by conventional high temperature and high pressure synthesis is limited in size and it is impossible to control impurities. As a diamond synthesizing method other than the high temperature and high pressure synthesizing method, a vapor phase synthesizing method such as a hot filament method, a microwave chemical vapor deposition method, a direct current plasma chemical vapor deposition method and a combustion method is also known. The vapor phase synthesis is not only advantageous for controlling impurities, but also obtains diamond in a thin film form, and thus is expected to be applied to diamond synthesis for electronic materials.

However, when vapor phase synthesis of diamond is carried out using a substrate other than diamond, only polycrystalline diamond containing high-density grain boundaries can be obtained. Therefore, single crystal diamond (Fujimori, T.Imai, HN
akahata, H.Shiomi, and Y.Nishibayashi, in Diamond,
Silicon Carbide and Related Wide Bandgap Semicond
uctors, (Materials Research Society symposium proc
eedings 162), edited by J, T.Glass, R.Messier, and
N, Fujimori, (Materials Research Society, Pittsburg
h, Pennsylvania, 1990), pp.23-33), single crystal cubic boron nitride (cBN) (S. Koizumi, T. Murakami, T. Inuzuka
and K. Suzuki, Applied Physics Letters, Vol.57, pp, 56
3-565 (1990)), single crystal nickel (Y, Sato, I. Yashima, H,
Fujita, T. Ando, and M. Kamo, Second International C
onference on New Diamond Science and Technology, e
dited by R, Messier, JT, Glass, JEButler and R.Ro
y, (Materials Research Society, Pittsburgh, Pennsyl
vania, 1991), pp.371-376), single crystal silicon carbide (BR Stone
er and JT Glass, Applied Physics Letters, Vol.60,
pp.698-700 (1992)) has been reported, and in this case, epitaxial growth is observed.

However, the size of single crystal diamond and cBN substrates is limited, and it is difficult to increase the area for electronic device applications. Further, when single crystal nickel and single crystal silicon carbide are used for the substrate, only island-shaped discontinuous films can be synthesized.

[0006]

As described above, a diamond polycrystalline film that is vapor-phase-synthesized generally has a low mobility of electrons (holes) and a low breakdown electric field due to the presence of grain boundaries containing many defects. , As well as increased leakage current, many problems arise in electronic device applications. Even when single crystal diamond or cBN is used for the substrate, it is not possible to obtain a sufficient and necessary area for producing an electronic device due to the limitation of the substrate size. When single crystal nickel or single crystal silicon carbide is used for the substrate, a continuous film having a sufficient film thickness cannot be obtained.

On the other hand, highly oriented crystal grains with uniform plane orientation formed by the effect of applying an electric field by BR Stoner or the like use the microwave chemical vapor deposition method to synthesize diamond. ) The synthesis area is limited to 5 cm or less depending on the size of plasma, and (2) there is a problem that the deposition rate must be reduced to synthesize a high quality film, which is not economical.

The present invention has been made in view of the above problems, and forms a large area diamond thin film with few crystal grain boundaries, high carrier mobility and high breakdown electric field, and low leakage current with high efficiency. It is an object of the present invention to provide a method for forming a highly oriented diamond thin film that can be used.

[0009]

The method for forming a highly oriented diamond thin film according to the present invention is a method for forming a highly oriented diamond thin film in which a diamond thin film is synthesized on a single crystal substrate by a hot filament method. In the step, an electric field that makes the single crystal substrate negative is applied between the hot filament and the single crystal substrate for a predetermined time to form an oriented crystal nucleus layer on the single crystal substrate, and then this crystal nucleus layer It is characterized in that a highly oriented diamond thin film is synthesized by growing the diamond.

[0010]

In the present invention, an electric field is applied to the hot filament so that the substrate is negative for a certain period of time during the nucleation process, which is the initial stage in the vapor phase synthesis of the diamond thin film by the hot filament method. In this case, the effective area for the substrate is expanded by expanding the effective area for the substrate by making the hot filament spiral or crossing a plurality of hot filaments in a net shape. It is possible to easily increase the area, which is difficult by the method.

For the substrate, in addition to the single crystal silicon carbide substrate, various carbides and silicides and materials such as silicon, titanium or tungsten that form them are useful.
Further, single crystal nickel and single crystal copper having a lattice constant close to that of diamond and alloys thereof can be used as the substrate. According to the present invention, oriented crystal nuclei are formed on the substrate before the step of vapor phase synthesizing an ordinary diamond thin film. As a result, a continuous highly oriented diamond thin film can be formed on the non-diamond substrate. By devising the shape of the hot filament and expanding the effective area for the substrate, a high surface area with a uniform surface orientation of 20 cm ² or more, which was difficult with the electric field application method in the conventional microwave chemical vapor deposition method. An oriented diamond thin film can be obtained. Then, an electronic component or electronic device can be easily manufactured at low cost using this highly oriented diamond thin film.

As described above, the present invention is advantageous in terms of large area and economy, as compared with the case of using the conventional single crystal diamond or single crystal cBN substrate. Further, the present invention is advantageous in terms of easiness of increasing the area and accelerating the synthesis speed, as compared with the conventional microwave chemical vapor deposition method using the effect of applying an electric field.

The present invention is to synthesize a highly oriented diamond thin film as a pseudo single crystal on various substrates by a hot filament method using an electric field application effect. Examples of this substrate include single crystal silicon, single crystal titanium, single crystal tungsten, and single crystal tantalum.
It is also possible to use those obtained by forming various carbides such as silicon carbide, titanium carbide, tungsten carbide and tantalum carbide, and various silicides such as titanium silicide, tungsten silicide and tantalum silicide on these substrates. Further, any one of single crystal nickel, single crystal copper, and nickel-copper alloy having a lattice constant close to that of diamond can be used as the substrate.

The hot filament method used in the present invention is widely known as one of vapor phase synthesis methods for diamond thin films, and an attempt to apply an electric field between a substrate and a filament has been reported so far (YH Lee, GHMa, KJBachmann,
JT, Glass. In Daimond, Silicon Carbide and Related
Wide Bandgap Semiconductors, (Materials Research
Society symposium proceedings 162), edited by JT
Glass, R, Messier, and N, Fujimori, (Materials Resea
rch Society, Pittsburgh, Pennsylvania, 1990), pp, 1
19-125.). However, the present invention is different from the above-mentioned conventional hot filament method in that an electric field is applied only for a certain period of time in the initial stage of thin film synthesis, whereby a highly oriented diamond thin film can be formed on a non-diamond substrate. it can.

Diamond can also be epitaxially grown using this highly oriented diamond thin film as a substrate. Furthermore, it is easy to remove the non-diamond substrate and use the highly oriented diamond thin film as a simple substance, unlike the conventional case.

[0016]

Embodiments of the present invention will be specifically described below with reference to the accompanying drawings.

The gas composition, reactive gas species, gas flow rate,
The combination of the substrate material, the substrate temperature, the gas pressure, the filament-substrate distance, the filament temperature, the applied voltage, the electric field application time, etc. is arbitrary, and the present invention can be obtained even if the synthesis is tried under conditions other than those shown in the following examples. The effect of does not change.

Example 1 First, an apparatus for synthesizing diamond by applying an electric field between a filament and a substrate will be described. FIG. 1 is a schematic view showing a highly oriented diamond thin film synthesizing apparatus of this embodiment. A substrate holder 5 and a hot filament 2 are installed in the reactor 1, and the hot filament 2 has a power source 3
Power is supplied from. Further, the substrate 4 is placed on the substrate holder 5, and the electric field applying power source 6 is connected to the substrate holder 5, whereby an electric field that makes the substrate 4 negative is applied to the substrate 4. Is applied.

An exhaust pump 14 is connected to the reactor 1 via a pipe 15. The reactor 1 and the exhaust pump 14 are connected to each other.
The solenoid valve 7 and the pressure control valve 1 are connected to the pipe 15 that connects
3 are installed. A reaction gas introduction pipe 11 is connected to the reactor 1, and the reaction gas introduction pipe 11 is connected to the gas supply source 9 via branch pipes 11a to 11c. The introduction pipe 11 is provided with a solenoid valve 7, and the branch pipes 11a to 11c are provided with a solenoid valve 7 and a mass flow controller 8. These mass flow controllers 8 are controlled by the controller 10. Further, all solenoid valves 7 are on / off controlled by a solenoid valve power source 12.

In the synthesizer thus constructed, the exhaust pump 14 exhausts the inside of the reactor 1 while supplying a predetermined source gas from the gas supply source 9 into the reactor 1. Then, by supplying power to the hot filament 2 to heat it, plasma is generated in the reaction vessel 1,
A diamond thin film is deposited on the substrate 4. In this case, in the initial step of the diamond thin film synthesis step,
A negative electric field can be applied to the substrate 4.

Using the apparatus thus constructed, a highly oriented diamond thin film was synthesized under the following conditions.

Reaction gas: CH ₄ / H ₂ (5% ratio) Gas flow rate: 200 sccm Substrate: Single crystal silicon (100) plane Substrate temperature: 650 ° C. (when electric field is applied) / 800 ° C.
(After application of electric field) Gas pressure: 30 Torr filament; 2100 ° C. Filament-to-substrate distance; 8 mm Applied voltage; 200 V (direct current) Electric field application time: 30 minutes Total formation time: 6 hours.

The resulting diamond thin film has a thickness of about 2
It was a highly oriented diamond thin film having a thickness of 0 μm and 95% of the surface of which was covered with a (100) crystal plane. Further, it was found from the cross-sectional photograph of the thin film that the height difference between the crystal planes was 0.3 μm or less. Further, analysis of the cross-sectional photograph confirmed that silicon carbide was formed between the substrate and the diamond thin film, silicon carbide was epitaxially grown on the substrate, and diamond thin film was epitaxially grown on the silicon carbide.

Example 2 Using the apparatus shown in FIG. 1 as in Example 1, a highly oriented diamond thin film was synthesized under the following conditions.

Reaction gas: CO / H ₂ (5% ratio) Gas flow rate: 300 sccm Substrate: Single crystal nickel (111) surface Substrate temperature: 650 ° C. (when electric field is applied) / 800 ° C.
(After application of electric field) Gas pressure; 30 Torr filament; 2100 ° C. filament-substrate distance; 8 mn applied voltage; 200 Vdc electric field application time; 30 minutes total formation time; 6 hours.

The obtained diamond thin film has a thickness of about 2
It was a highly oriented diamond thin film having a thickness of 5 μm and 95% of the surface of which was covered with a (111) crystal face. Further, it was found from the cross-sectional photograph of the thin film that the height difference between the crystal planes was 0.3 μm or less.

Example 3 Reaction gas: CH ₄ / H ₂ (5% ratio), B ₂ H ₆ 1pp
m additional gas flow rate; 200 sccm substrate temperature; 800 ° C. gas pressure; 30 Torr filament temperature; 2100 ° C. filament substrate distance; 8 mn synthesis time; 4 hours.

As a result, a P-type semiconductor diamond thin film layer having a thickness of 3 μm and having the same surface morphology as the underlying highly oriented film was laminated. The hole mobility of this semiconductor diamond layer was measured to obtain 100 cm ² / V · s. This value is the hole mobility of a normal polycrystalline diamond thin film (about 1 cm
² / V · s) is about 100 times.

Example 4 A diamond thin film was further laminated on the highly oriented diamond thin film obtained in Example 1 by the microwave plasma CVD method under the following conditions. Then, synthesis was continued for 80 hours at 0.5% methane, 99.4% hydrogen, 0.1% oxygen, gas pressure 30 Torr, gas flow rate 300 cc / min, and substrate temperature 800 ° C.

Reaction gas: CH ₄ / H ₂ (5% ratio),
O ₂ 0.1% additive gas flow rate; 300 sccm substrate temperature; 800 ° C. gas pressure; 50 Torr synthesis time; 80 hours.

As a result, the laminated diamond thin film has a thickness of about 100 μm and 98% of the surface is (100)
It was a highly oriented diamond thin film covered with crystal planes. In addition, the height difference between the crystal planes is 0.
It was found to be 1 μm or less.

[0032]

As described above, according to the present invention,
A large-area pseudo single crystal highly oriented diamond thin film is obtained on the substrate. Further, since the hot filament and the substrate can be electrically isolated and controlled from other parts of the reactor, the limitation of the electric field application method due to the shape of the device is eliminated.
That is, in the conventional method, since the reactor itself including plasma is grounded and a negative voltage is applied to the substrate, it is limited to a unitary electric field effect in which positive charges (plasma negative charges from the substrate) move from the plasma to the substrate. . On the other hand, in the present invention, for example, the filament is set to a negative voltage with respect to the reactor,
Since a larger negative voltage is applied to the substrate, in addition to the electric field effect similar to the conventional one, the negative charge is also transferred from the filament to the reactor. This flow of negative charges (electrons) is effective for forming a high quality film such as generation of atomic hydrogen and control of graphite precipitation.

As described above, according to the present invention, a large-area and high-quality highly oriented diamond thin film can be formed with high efficiency, and the present invention is extremely useful for the development and production of diamond electronic devices.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a hot filament type highly oriented diamond thin film synthesizing apparatus.

[Explanation of symbols]

 1; Reactor 2; Hot Filament 3; Hot Filament Power Supply 4; Substrate 5; Substrate Holder 6; Power Supply for Voltage Application 7; Solenoid Valve 8; Mass Flow Controller 9; Gas Supply Source 10; Controller 14; Exhaust Pump

Claims (7)

[Claims] 1. A method for forming a highly oriented diamond thin film, which comprises synthesizing a diamond thin film on a single crystal substrate by a hot filament method, wherein the single crystal is kept for a predetermined time between the hot filament and the single crystal substrate at an initial stage of synthesis. A high orientation diamond thin film is synthesized by forming an oriented crystal nucleus layer on the single crystal substrate by applying an electric field which makes the substrate negative and then growing this crystal nucleus layer. Method for forming highly oriented diamond thin film. 2. The method for forming a highly oriented diamond thin film according to claim 1, wherein the crystal nucleus layer has a thickness of 1 μm or less, preferably 0.002 to 0.1 μm. 3. The method for forming a highly oriented diamond thin film according to claim 1, wherein the single crystal substrate is a single crystal silicon substrate. 4. The single crystal substrate is formed of a material selected from the group consisting of single crystal titanium, single crystal tungsten and single crystal tantalum, and tungsten carbide and tantalum carbide are formed on the single crystal substrate. The method for forming a highly oriented diamond thin film according to claim 1, wherein a carbide or silicide layer of the substrate constituent material, which is made of titanium, titanium silicide, tungsten silicide, or tantalum silicide, is formed. 5. The highly oriented diamond thin film according to claim 1, wherein the single crystal substrate is made of a material selected from the group consisting of single crystal nickel, single crystal copper and nickel-copper alloy. Forming method. 6. The method for forming a highly oriented diamond thin film according to claim 4, wherein a part or all of the carbide formed on the single crystal substrate has an epitaxial relationship with the single crystal substrate. . 7. The method for forming a highly oriented diamond thin film according to claim 6, wherein the highly oriented diamond thin film has an epitaxial relationship with the carbide layer formed on the single crystal substrate.