JPH0196094A - Method for manufacturing P-type semiconductor diamond film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of introducing impurities into artificial diamonds,
In particular, it relates to methods of introducing impurities during low-pressure synthesis of artificial diamonds.

[Prior art]

Diamond has the same crystal structure as silicon and germanium, and is also an element in the same group II of the periodic table. Therefore, research on adding impurities that can act as donors or acceptors to diamond and using it as a semiconductor material has recently been attracting attention.

The low-pressure synthesis method for diamond involves introducing a raw material gas such as methane and hydrogen gas into a reaction chamber, decomposing the raw material gas by heating or applying plasma under a pressure close to normal pressure, and then depositing it on the substrate. Various CVD (chemical vapor deposition) methods are known for depositing thin films of diamond. The first method of introducing impurities into diamond is to introduce diborane (s*H-) or phosphine (PH3) into the raw material gas.
), and this mixed gas is mixed with C.
It is known to obtain a diamond thin film into which impurities such as boric acid (B) and phosphorus (P) are introduced by decomposing it using the VD method.

A second method is an ion implantation method in which ionized impurity atoms are directly implanted into the diamond.

[Problem to be solved by the invention]

However, there is a problem in that the diborane gas and phosphine gas used in the first method are highly toxic and extremely dangerous, and sufficient equipment is required as a safety measure.

In addition, in the second method, ion implantation method, damage caused when impurity atom ions are implanted into diamond,
The principle of forming acceptors and donors by ion implantation is not clear, and furthermore, the annealing process has not been determined, and it is not yet clear whether the impurity-containing diamond produced can still be used as a semiconductor material. Furthermore, a device for generating ions is required, which inevitably increases the size of the equipment.

The present invention has been made in view of the problems of the prior art,
The purpose is to provide a method for safely and easily introducing impurities during low-pressure synthesis of diamond.

[Means for solving problems]

Raw materials used to synthesize diamond include hydrocarbon gases such as methane or organic compounds such as methanol. However, many organic compounds are in liquid form, and the difference is that the liquid must first be vaporized to become a gas before being introduced into the CVD reaction chamber. However, the inventors focused on the fact that diamond raw materials are liquid, and because they are liquid, they can easily mix other substances by dissolving various substances, such as liquid liquid, liquid + solid, etc. I came up with the idea of taking advantage of this fact.

The present invention has been made from this point of view, and the method for introducing impurities in low-pressure diamond synthesis according to the present invention is to combine a diamond raw material gas and an impurity element-containing gas by CVD.
When a diamond thin film containing impurity elements is formed by decomposition using the D method, compounds containing impurity elements that can serve as donors or acceptors are added to the liquid organic compound that is the diamond raw material (compounds containing impurity elements that can serve as donors or acceptors (of the periodic table n, The method is characterized in that a compound containing at least one element is dissolved, this solution is vaporized, and a mixed gas of a diamond raw material gas and an impurity element-containing gas is introduced into a CVD reaction chamber.

The diamond raw material used in the present invention is a liquid organic compound such as acetone, methanol, ethanol, or acetaldehyde, which is usually obtained by liquefying a hydrocarbon-based diamond raw material gas used when synthesizing artificial diamonds at low pressure. It is something.

Compounds containing impurity elements that dissolve in the liquid organic compound that is the raw material for diamond include those in the periodic table n, m, V, and V.
A compound containing an element that falls under I valence.

Compounds other than nitrogen compounds, regardless of whether they are liquid or solid. Although nitrogen is a valent element, it does not function as a donor, so only nitrogen compounds are excluded.

CVD methods include thermal filament CVD, microwave plasma CVD, and electron impact CVD (EACVD).
method), DC plasma method, etc., and any method may be used.

[Effect]

The diamond raw material used in the present invention is a liquid organic compound, and can easily dissolve compounds containing impurity elements that can serve as donors or acceptors. This diamond raw material solution in which the impurity element-containing compound is dissolved is vaporized and introduced into a reaction chamber, where a diamond thin film to which donors or acceptors are added is formed by the CVD method.

Therefore, it is safe because it does not use toxic gas unlike the conventional example.

〔Example〕

The present invention will now be described in detail.

FIG. 1 shows an embodiment of an apparatus for carrying out the method of the invention.

In this figure, this device is a hot filament CVD device, and the diamond raw material in the raw material receiving container 2 is processed by CVD.
It has a structure in which the raw material gas is introduced into the reaction chamber 4, where it is thermally decomposed to synthesize diamond.

A raw material storage container 2 contains a diamond raw material solution 3 in which a compound containing an impurity element that can serve as a donor or an acceptor is dissolved, and a gas introduction pipe 6 extends from the container 2 to the reaction chamber 4 .

Reference numeral 8 is a carrier gas supply device, from which a gas supply pipe 9 is connected.
a is connected to the gas introduction pipe 6, and another gas supply pipe 9b is branched in the middle of this gas supply pipe 9a and extends to near the bottom of the raw material storage container 2. Hydrogen is generally used as the carrier gas, and the hydrogen gas is bubbled through the raw material solution 3 to vaporize it, and the raw material gas is introduced into the reaction chamber 6.

A tungsten filament 10 is arranged in the reaction chamber 4, a holder 12 is provided below it, and this holder 12
A substrate 14 for depositing diamond is placed thereon. The material of this substrate 14 is generally silicon (
Si) is used, but molybdenum (Mo), silicon carbide (S i C), and diamond may also be used. Note that the reference numeral 16 is a thermocouple for measuring the temperature of the substrate 14;
8 is an electric furnace for heating the inside of the reaction chamber 4, and 20 is an exhaust port for exhausting unreacted gas.

A method for synthesizing impurity-doped artificial diamond using the apparatus shown in FIG. 1 will be explained.

First, as shown in FIG. 2(a) or FIG. 2(b), a compound 3b containing a predetermined impurity element is dissolved in a liquid diamond raw material 3a, and this is placed in a container 3.

Figure 2(a) shows the case where the compound to be dissolved is powder;
Figure (b) shows the case of liquid. Then,
On the holder 12, for example, silicon (Si) II! Board 1
Set 4. Then, the electric furnace 18 is operated to bring the interior of the reaction chamber 4 to a predetermined temperature, and the filament 10 is heated to a predetermined temperature, after which the cock 9c of the gas supply device 8 is opened. As a result, the carrier gas (H2) is introduced into the container 2 via the supply pipe 9b, and the raw material solution 3 is introduced into the carrier gas (H2) through the supply pipe 9b.
H2) is bubbled and vaporized, and the CV is passed through the gas introduction pipe 6 by the carrier gas supplied from the supply pipe 9a.
D is guided into the reaction chamber 4.

In the reaction chamber 4, a raw material gas mixture of a diamond raw material and an impurity compound is thermally decomposed by a tungsten filament 10 heated to a high temperature, and a diamond thin film containing impurity elements is formed on a substrate 14 placed directly below the filament 10. It is formed. Note that this thermal decomposition reaction, for example, when acetone is used as the diamond raw material,
CH.

C0CH, +CH, +C0CH, (7) It is decomposed into two. This methyl group (CH3) is extremely reactive, and hydrogen atoms (H) are liberated and carbon atoms (C) are bonded one after another, and at this time, impurity atoms are also bonded, forming a diamond crystal structure containing impurities. It seems that. The formation process of this diamond is not clear, but the methyl group (CH
)) and hydrogen atoms (I()) are thought to have great significance in the growth of diamond.As for hydrogen, the CVD reaction is carried out in a hydrogen atmosphere, and this hydrogen atom is extremely active. Atoms are highly reactive and easily break down double bonds to form graphite structures, other than diamond crystals.

For example, it works to prevent the formation of graphite and amorphous carbon□.

The concentration of impurities actually doped into the synthesized diamond is thought to be different from the concentration of impurities in the raw material solution, but the concentration of impurities doped is proportional to the concentration of impurities in this raw material solution. can also be increased or decreased, thereby changing the resistance of the synthesized diamond.

As described above, according to this embodiment, a diamond containing a donor or an acceptor can be synthesized safely and easily.

In the above embodiment, the raw material solution 3 is vaporized using a carrier gas and introduced into the reaction chamber 4, but the container 2 is heated to vaporize the raw material solution 3 and the raw material solution 3 is vaporized in the reaction chamber 4 under a hydrogen atmosphere. It may also be possible to guide the

Further, in the above embodiments, only low pressure synthesis using the hot filament CVD method was explained, but it goes without saying that the present invention can be applied to other CVD low pressure synthesis methods.

[Experimental Example 1] Powdered boric acid (B 20 a ) was mixed with methanol (CH30
H) and this solution was dissolved in acetone (CH,C0CH
, ) to dilute it several times to several thousand times, and attempted to synthesize diamond using the hot filament CVD method. filament 1
The temperature of 0 is 2000 to 2300°C, and the temperature of substrate 14 is 6
The reaction was carried out under conditions of 50 to 900°C, gas flow rate of 50 to 2005 CCM, and reaction pressure cuff of 60 Torr. However, silicon (Si) was used for the substrate 14, and hydrogen (H2) was used for the carrier gas. As a result, a diamond exhibiting P' type semiconductor properties was synthesized.

The diamond thin film obtained in this way was evaluated using inspection methods such as X-ray diffraction, reflection high-energy electron diffraction (RIIEED), and Raman spectroscopy, and it was found that the content of graphite and amorphous carbon was extremely low. It was confirmed that the diamond was of high purity. It was also confirmed that the diamond obtained by this method exhibits a stable resistance value even at high temperatures, and is particularly useful as a low-resistance semiconductor material.

[Experimental Example 2] Phosphoric acid (H3PO4) was mixed with diethyl ether (C2H50
diluted several times to several thousand times with C2H, ), and using this solution, filament CVD was performed under the same conditions as in [Experimental Example 1].
When attempting to synthesize diamond using this method, a diamond exhibiting N-type semiconductor properties was synthesized.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, impurities can be safely and easily introduced into diamond.

And the diamond obtained by this invention is heated to 500℃.
The resistance characteristics remain unchanged even under high temperature conditions, and it can be used in a wide range of fields as an element with enhanced environmental resistance.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an embodiment of an apparatus for carrying out the method according to the present invention, and Figures 2 (a) and (b) are explanatory diagrams of states in which a compound containing an impurity element is dissolved in a diamond raw material, respectively. It is. 2... Diamond raw material storage container, 3... Diamond raw material solution in which a compound containing an impurity element is dissolved, 3a... Liquid diamond raw material, 3b... Compound containing an impurity element, 4... CVD reaction chamber, 8...carrier gas supply device;

Claims (1)

[Claims] The method is characterized by dissolving a compound containing an impurity element that can serve as a donor or acceptor in a liquid organic compound that is a raw material for diamond, vaporizing this solution, and decomposing it using the CVD method to form a thin film of diamond containing the impurity element. A method for introducing impurities in the low-pressure synthesis of diamond.