Method for synthesizing n-type diamond having low resistance

Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With a step of measuring – testing – or sensing

Reexamination Certificate

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C117S104000, C117S068000, C117S930000, C423S446000

Reexamination Certificate

active

06340393

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a method for synthesizing an artificial diamond, and more specifically, to a method for synthesizing a transparent n-type diamond having low resistance in manufacturing a diamond by a vapor-phase growth method, a sputtering method, a high-temperature and high-pressure synthesis method, or the like.
TECHNICAL BACKGROUND
As a method for synthesizing a diamond, a method for artificially synthesizing a diamond from a graphite carbon by using a catalyst under high-temperature and high-pressure (50 kbr, 1500 k or more), and a method for synthesizing a diamond thin film on a substrate by a CVD method from a mixed gas of a hydrocarbon and a hydrogen under low pressure (<1 Torr) and high temperature (>800° C.), or the like, are known. Japanese Patent Unexamined Laid-open Publication No. S62(1987)-70295 discloses a method for manufacturing an n-type semiconductor diamond thin film. According to the method, a reaction gas comprising a gas including P, As or Sb as a dopant element, a hydrocarbon gas and hydrogen is decomposed by heat or decomposed by plasma to be evaporated on a substrate by a microwave plasma CVD method or a thermal decomposing CVD method, to thereby manufacture an n-type semiconductor diamond thin film.
The above-mentioned plasma CVD method and thermal decomposing CVD method have drawbacks such that it is troublesome to execute the method due to the high-temperature processing, the obtained film is easily broken due to the residual stress maintained in the film, and it is difficult to control an amount of dopant. As a method for solving these problems, Japanese Patent Unexamined Laid-open Publication No. H5(1993)-345696 discloses a method for manufacturing a diamond thin film, which is excellent in hardness, corrosion resistance, heat resistance, and the like, and is possible to be applied to a high temperature electric equipment. In the method, a dopant ion beam is simultaneously introduced when a film is growing at low temperature by sputtering an ion beam.
Furthermore, a method for forming a p-type or n-type diamond is also known (Japanese Patent Unexamined Laid-open Publication Nos. H5(1993)-117088 and H5(1993)-117089). In the method, an electron beam or excimer laser is irradiated toward a surface of a single crystal diamond to activate a dopant disposed on the single crystal diamond, so that the dopant is diffused therein. Also known is an n-type semiconductor diamond in which nitrogen atom of 1×10
19
cm
−3
or more is doped (Japanese Patent Unexamined Laid-open Publication No. H7(1995)-69794). Furthermore, it is also known that, in forming an n-type diamond single crystal by a vapor-phase growth method, in order to prevent a reaction of gases due to corrosion thereof before reaching a substrate, each gas is directly supplied in a molecular flow state to the substrate (Japanese Patent Unexamined Laid-open Publication No. H10(1998)-149986).
Furthermore, the inventor invented a method for obtaining a single crystal diamond excellent in crystallization (Japanese Patent Unexamined Laid-open Publication No. H9(1997) -20593). In the method, an amorphous carbon hydride is formed by adding a hydrogen to a carbon, rapidly cooling a decomposed carbon gas hydride on a substrate, or sputtering a graphite by hydrogen atom, and atoms are rearranged into a crystal diamond under low temperature by forming atomic holes and interstitial atom pairs in the amorphous carbon hydride, to thereby effectively cause a movement of the interstitial atom. The single crystal diamond obtained by this method meets characteristics required by various semiconductor materials and optical semiconductor materials requiring a highly controlled crystallization.
(Problems to be Solved by the Invention)
A p-type diamond thin film having low resistance can be easily manufactured by a conventional technique. Although an n-type diamond having high resistance can be manufactured, it is difficult to manufacture an n-type diamond thin film having low resistance because it is impossible to activate at room temperature (300° K) due to the self-compensation effect and the deep donor level (500 meV).
If an n-type diamond having low resistance can be synthesized as a single crystal diamond thin film, by combining it with a p-type diamond having low resistance, which is already realized by doping impurities, it is possible to manufacture a high power and high speed semiconductor device using a diamond operable at high temperature and an ultraviolet semiconductor laser diode made of diamond, which is essential for a high density recording and a vast information transmittance.
It is also possible to manufacture a transparent n-type single crystal protective film utilizing high hardness of a diamond, which is excellent in electric conductivity and thermal conductivity. Furthermore, by utilizing the negative electron affinity energy of a diamond, it is possible to manufacture a display having a large surface area made by highly efficient electron beam materials of an n-type diamond having low resistance.
To form an n-type diamond having low resistance means to delete the deep donor level due to N in a synthesized diamond and change the deep level to a shallow level, whereby an absorption of natural light (sun light) is prevented, to thereby extinguish the color caused by the deep level of the single N in the synthetic diamond. This is the same as in forming a transparent synthesized diamond by forming an n-type diamond having low resistance. In synthesizing a diamond by a high-temperature and high-pressure synthetic technique utilizing nickel catalyst or the like, it becomes possible to manufacture a transparent diamond valuable as a jewel.
(Means for Solving the Problems)
The inventor has found the facts that, in order to solve the aforementioned problems, in forming a single crystal diamond thin film on a substrate by a vapor-phase growth method or a sputtering method, by simultaneously doping a p-type dopant and an n-type dopant, it becomes possible to stabilize an n-type dopant in a high densitys, lower an impurity level and greatly increase the number of carriers, to thereby synthesize a high quality single crystal diamond thin film having low resistance.
The inventor has also found the following fact. That is, in synthesizing an artificial diamond by a conventional high-temperature and high-pressure synthesizing method utilizing nickel catalyst or the like, by mixing H as a p-type dopant and N, P or As as an n-type dopant at the atomic density ratio of 1:2 to 1:3 before synthesizing, a donor-acceptor compound, such as a P—H—P pair, an N—H—N pair or a As—H—As pair, is formed in a crystal, to lower the impurity level as compared to a single doping to thereby form an n-type diamond having low resistance. This results in a transparent artificial diamond, wherein a conventional artificial diamond made by a conventional method had color because the natural light is absorbed by the deep impurity level of N.
In other words, the method according to the present invention is based on a principle that, regardless of a method for synthesizing a diamond, by simultaneously doping H as an acceptor and P, N, or As as a donor at the atomic density ratio of 1:2 to 1:3, an acceptor-donor complex (compound) is formed, resulting in a decreased donor level. According to this principle, a diamond in a metallic state (0.001 &OHgr;cm) can also be made.
As shown in
FIG. 1
, by forming a P—H—P pair, an N—H—N pair or a As—H—As pair (complex) by a simultaneous doping, electron scattering due to an n-type carrier dopant is decreased, and the movement of the electron is greatly increased. This lowers the donor level to thereby increase the carrier density in a diamond crystal, which increases the activation rate by 10 to 1000 times, resulting in an n-type diamond having lower resistance.
In the diamond crystal, H as an acceptor and N, P, or As as a donor take a structural position (an impurity complex) forming the crystal model shown in FIG.
2
. The positioning of the accepto

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