JPH09315890A - Synthesizing method of semiconductor diamond - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize impurities in a diamond thin film by laser ablation and to dope in good control by exciting a gaseous starting material and simultaneously to applying a laser to an impurity source. SOLUTION: Power is supplied to a filament 3 arranged in a diamond deposition tank 1 and having 0.01-1mm diameter to heat it to 1800-2800 deg.C, then the gaseous starting material is supplied to a gas introducing pipe 2 in 200-2000sccm flow rate to allow the gas to contact with the heated filament 3 to excite, and the gas is allowed to arrive a substrate 5 supported by a substrate holder 6 to deposit the diamond thin film. Simultaneously, the impurities are evaporated and gasified by applying the laser to the impurity source 10 set in a vicinity of the filament 3 from a laser irradiation device 4 to dope the impurities on the 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 p-type semiconductor which is well controlled and stable in impurities when a semiconductor diamond, which is attracting attention as a semiconductor material for electronic devices and power electronics operating at high temperatures, is produced, and which is simple and easy. It is a method for providing a semiconductor or an n-type semiconductor.

[0002]

2. Description of the Related Art A technique for forming a diamond film from a mixed gas of hydrocarbon and hydrogen is disclosed in JP-A-58-9110.
No. 0, the hot filament CVD method described in JP-A-59-
The microwave plasma CVD method described in 3098 is a well-known representative technique. These excite and decompose the raw material gas with high heat or electromagnetic wave energy to synthesize a diamond film on the substrate. Although it has been attempted to dope various impurities into a diamond thin film synthesized by these methods, a method of adding a compound containing an impurity to be added to a raw material gas is usually used. For example, when producing p-type diamond by B doping, a method of mixing and introducing B ₂ H ₆ as a boron source with a source gas has been attempted. Also, B as a boron source
(CH _{3) 3} the microwave plasma CVD method (hereinafter, "MW
A method of adding by "CVD method") is also proposed. A method of dissolving boric acid in a mixed solution of acetone and methanol and bubbling it with hydrogen gas has also been reported. Recently, diamond thin films have been p-doped by ion implantation.
-Type or n-type diamond has been attempted, and ¹¹ B ⁺ and ³¹ P ⁺ have been used as the implantation species, and doping has been performed on diamond produced by the low pressure vapor phase synthesis method.

[0003]

Ion implantation into diamond has long been considered to be a powerful means. However, the most problematic point in diamond ion implantation is crystal damage that occurs during ion implantation. In silicon, damage can be recovered by annealing at 500 to 900 ° C., but in diamond, the “C-
Due to the strength of the bond between C's, a long time annealing at a higher temperature is required, and the annealing also has many technical problems such as phase transition to graphite in the defect dense region.

On the other hand, although diborane (B ₂ H ₆ ) is often used for synthesizing p-type diamond, diborane is strictly regulated legally, is highly toxic, has a strong ignitability, and has various handling risks. Further, it is difficult to control the boron concentration in the method of dissolving boric acid in alcohol as a boron source and the method of dissolving boron oxide in a mixed solution of acetone and alcohol and introducing it into the reactor, and it is difficult to obtain a predetermined impurity concentration. difficult. Also, trimethylboron is used as a boron source in MWC.
The method of adding by the VD method is not legally regulated and has a low risk, but it has a problem that it is difficult to be incorporated into crystals. As described above, according to the conventional technique, it is difficult to dope a diamond thin film with a predetermined impurity concentration. An object of the present invention is to develop a simple method for doping a semiconductor diamond thin film with good controllability and stability.

[0005]

As a result of diligent efforts to solve the above problems, the present inventor has found that in a method of synthesizing semiconductor diamond by a vapor phase method, a source gas is excited and an impurity source is formed at the same time. The inventors have found a method for synthesizing semiconductor diamond, which is characterized by irradiating a laser, and a method for synthesizing semiconductor diamond, which is characterized by irradiating a source gas with a laser. The point is that the impurity source set in the CVD diamond synthesizer is irradiated with a laser to evaporate and vaporize the impurity source to dope the impurities diffused in the reaction container into the produced diamond. The present invention introduces a raw material gas containing a carbon compound and / or hydrogen into a space excited by a hot filament, microwave, high frequency, etc., and at the same time, irradiates a laser on an impurity source to generate an impurity and control the diamond film to be a well-controlled impurity. Is a method of doping.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention will be specifically described below with reference to FIG. FIG. 1 is a schematic diagram showing an example of an apparatus used in the method of the present invention. In the figure, 1 is a diamond precipitation tank, 2 is a source gas introduction pipe, and the introduction pipe is arranged in the precipitation tank 1. The hot filament 3 is installed in front of the introduction tube, and the substrate holder-6 is further provided in front of it.
The substrate 5 is supported by. Reference numeral 4 denotes a laser irradiation device, in which the laser is an impurity source support 9 and an impurity source 1.
It is installed to irradiate 0. The inside of the deposition tank is depressurized by a vacuum pump 7 to a predetermined degree of vacuum. 8 is a viewing window.

In this case, the raw material gas supplied from the gas introduction pipe is brought into contact with the hot filament, which is the excitation source, to be radicalized, and then directly sent to the substrate to reach the substrate.
There, a diamond film is deposited on the substrate. At the same time, the laser is irradiated to the impurity source set near the hot filament, and the evaporated and vaporized impurities are taken into the diamond film. The amount of dopant added to the diamond film is uniquely controlled by the laser irradiation conditions.

As the raw material gas, a carbon compound and / or hydrogen and, if necessary, other gas, for example, a mixed gas containing oxygen and the like is used. Here, the carbon compound may be any compound as long as it contains carbon at room temperature and atmospheric pressure. Linear hydrocarbons such as methane, ethane, propane, ethylene and propylene, hydrocarbons containing benzene rings,
It also includes alcohols such as methanol and ethanol, ketones typified by acetone, and inorganic gases such as carbon monoxide. From the viewpoint of reducing impurities mixed in the diamond film to be synthesized, a compound composed of only carbon and hydrogen is desirable. The mixing ratio of the carbon compound and hydrogen is preferably 5 vol% or less of the carbon compound and 95 vol% or more of hydrogen because the non-diamond-like carbon is less mixed in the diamond film.

When the carbon compound molecule contains a plurality of carbon atoms, the substantial concentration of carbon atoms increases due to the decomposition, so it is necessary to set the concentration in consideration of that amount. Generally, the lower the ratio of carbon compound to hydrogen, the lower the film formation rate, but the higher the quality of the synthesized diamond film.

The flow rate of the gas varies depending on the size of the filament and the base material, and when these are large, it is preferable to use a plurality of filaments and gas introduction pipes. The preferable range of the gas flow rate is 200 to 2000 sccm, and the more preferable range is 400 to 1500 sccm. If the flow rate is less than 200 sccm, the amount of active species effective for film formation reaches the substrate is small, and the deposition rate becomes slow.
Exceeding 0 sccm is not preferable because excitation of the raw material gas in the filament becomes insufficient. If the pressure in the diamond deposition tank is too high, the laser attenuation also increases, so approximately 100 Torr or less is desirable.

The gas that has passed through the introduction tube comes into contact with the hot filament, undergoes thermal decomposition and excitation, and then reaches the substrate. In this case, the excitation source is not limited to the hot filament, and microwaves, high frequencies, DC voltage application, arcs, etc. may be used.
Also, these excitation sources may be superposed. The filament is preferably a heat-resistant metal such as tungsten or tantalum or a carbide thereof, but carbon or the like can be used.
A filament having a diameter of about 0.01 to 1 mm is suitable. The filament is generally heated by energization, and the temperature is suitably 1800 to 2800 ° C. When a filament is used as the excitation source, the substrate is preferably one that can withstand 900 ° C. in a reducing atmosphere, and particularly diamond, silicon, silicon carbide, tungsten carbide, etc. are excellent.

The distance between the raw material gas introduction pipe and the filament is 1
It is desirable to separate it to 0 to 20 mm. If the distance is shorter than this, the introduction tube is heated, and the carbon film is likely to adhere.
However, when the excitation source is microwave, high frequency, or direct current application, it is sufficient that the source gas reaches the excitation space, and the position of the introduction tube is not particularly limited. If the reactor does not have a mechanism for cooling the substrate, if the distance between the filament and the substrate is too short, the substrate will be heated to the diamond precipitation temperature or higher, so it must be separated by at least several mm. When the excitation source is microwave, high frequency, or direct current application, the substrate may be placed in the excitation space.

The impurity source 10 on the support base 9 may be attached to the side surface of the filament 3 or, in the case of another excitation source, in the vicinity of the excitation space, the laser irradiated on the impurity source 10 has an irradiation angle and a wavelength. There is no particular limitation, and an excimer laser, an infrared laser, or the like can be used, and the type of laser is not limited. The energy required for releasing impurities from the target is preferably 10 W / cm ² or more, more preferably 80 W / cm ² or more. Further, the wavelength and intensity of the laser may be selected so that the raw material gas efficiently absorbs the laser light, and the laser may be irradiated. The laser light can be used not only for emitting impurities, but also for exciting the source gas. In this case, it is possible to omit exciting the raw material gas with a hot filament, microwave, high frequency, or the like.

[0014]

EXAMPLES The present invention will be described in detail with reference to the following examples, which should not be construed as limiting the invention. (Example 1) Using the apparatus shown in FIG. 1 (precipitation tank internal volume: 20 liters), methane 2 vol% and hydrogen 98 as raw material gas
Using a mixed gas of vol%, it was jetted from a 1/4 inch diameter pore and heated to about 2200 ° C., 0.4 mm diameter,
A diamond film was synthesized on a silicon nitride substrate (5 × 5 × 3 mm) by bringing it into contact with a Ta filament having a length of 40 mm to excite the mixed gas. The distance between the tip of the pore and the filament is 20 mm, and the distance between the filament and the substrate is 3-8.
mm.

The gas supply amount at this time is 1000 sccm
(Cc / min in standard condition), pressure in the deposition tank is 90To
rr. At the same time, infrared laser (wavelength 10.6 μm,
A boron source was supplied by irradiating a boron target as an impurity source with a beam diameter of 17 mm) at an output (continuous oscillation) of 300 W perpendicularly. After reacting for 4 hours, a thin film of about 50 μm was formed on the surface of the base material, and when the electrical resistivity was measured by the four-terminal method, a conductive diamond film on the order of several tens of Ω · cm was obtained. Also, SIMS analysis confirmed that the synthesized film was doped with boron. Furthermore, when the laser output is 500 W, it is in the range of 10 ^-1 Ω · cm,
In the case of 700 W, a diamond film of 10 ^-2 Ω · cm level was obtained, and it was confirmed that the amount of impurities can be controlled by the laser output.

(Embodiment 2) In Embodiment 1, the laser irradiation pattern was intermittently used to synthesize the diamond film. When the depth direction analysis by SIMS was performed, it was confirmed that a multilayer film in which an insulating layer having a good interface controllability and a p-type conductive layer were stacked was obtained.

[0017]

According to the present invention, when a semiconductor diamond is synthesized by a vapor phase method, impurities are stabilized in a diamond thin film produced by laser ablation,
It becomes possible to dope with good control by a simple method, which is extremely effective for development of semiconductor devices and power electronics having various impurity levels.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an apparatus used in the method of the present invention.

[Explanation of symbols]

 1 Diamond Deposition Tank 2 Raw Material Gas Introducing Tube 3 Filament 4 Laser Irradiation Device 5 Substrate 6 Substrate Holder-7 Vacuum Pump 8 Peep Window 9 Impurity Source Support 10 Impurity Source

Claims (2)

[Claims] 1. A method for synthesizing semiconductor diamond by a vapor phase method, which comprises exciting a source gas and irradiating a laser on an impurity source at the same time. 2. The method for synthesizing semiconductor diamond according to claim 1, wherein the raw material gas is also irradiated with a laser.