JPH0371397B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a diamond film exhibiting n-type semiconductor characteristics used in electronic devices and the like. [Background of the Prior Art] Carbon (C) belongs to group b in the periodic table, and is thought to have the potential to be used as a semiconductor material like Si, which is in the same group. However, graphite has high conductivity and cannot be used as a semiconductor. On the other hand, since diamond is insulating, it is theoretically possible to use it as a semiconductor by adding impurities or the like. Most naturally occurring diamonds are electrically
It is an insulator with a resistance of 10 ¹¹ Ωcm or more, but there are a small number of insulators with a resistance of 10 ⁰ to
There is a type with a resistance value as low as 10 ⁴ Ωcm, and it is called type b. Detailed investigation has revealed that this b-type is a p-type semiconductor, which can be artificially produced by ultra-high pressure and high temperature synthesis. However, not only does diamond, an n-type semiconductor, not exist naturally, but there is currently no example of its production by ultra-high pressure synthesis. For the production of diamond semiconductor devices, both pn and pn type semiconductors are essential, and in order to make this possible, attempts have been made to produce n-type semiconductors by ion implantation. As a result, it has been reported that the junction between the ion-implanted layer of Sb, Ar, C, etc. and the B-implanted layer has characteristics close to rectifying action. But n
We have not yet been able to confirm the type of semiconductor. [Disclosure of the Invention] In order to solve the above-mentioned problems, the present invention provides a method for manufacturing an n-type semiconductor layer using a thin film method. A feature of the present invention is to introduce a gas that easily decomposes and releases impurities (dopants) such as P and As during vapor phase synthesis of a diamond film from a mixed gas of hydrocarbons and hydrogen. We believe that when impurities are introduced in this type of vapor phase synthesis, they are contained much more uniformly than in high-pressure synthesis, and the impurity atoms can enter into more reasonable positions than in ion implantation, making it easier to produce the effect as a dopant. . The present invention was realized based on this idea, and succeeded in synthesizing an n-type semiconductor that could not be synthesized by conventional high-pressure synthesis methods or ion implantation methods. In order to carry out the present invention, it is necessary to use a thin film dimer synthesis method, but plasma CVD or CVD can be used to form a film with good crystallinity without residual carbon.
Law is preferable. In this case, it is appropriate that the reaction gas has a molar ratio of hydrocarbon C to H ₂ of 0.001 or more and 0.02 or less. 0.001
If it is less than 0.02, the growth rate of the film will be extremely slow and uneconomical, and if it is more than 0.02, the crystallinity of the film will be poor and it will not be possible to add sufficient performance as a semiconductor layer. Further, as dopant elements, P, As, and Sb had the same effect as when converting ordinary Si to n-type. The molar ratio between the dopant element and C is 0.0001 or more
Should be 0.002. If it is less than 0.0001, it cannot provide sufficient conductivity as a semiconductor. Moreover, if it is more than 0.002, strain will occur in the film, resulting in a film with many defects, making it difficult to apply to semiconductor devices. If the film produced in this manner is formed on a diamond single crystal, it can be epitaxially grown to obtain a single crystal film, and thus can be used as a semiconductor element. Further, as a thin film forming method, either plasma CVD or CVD is possible. As a gas excitation means, any means such as high frequency, microwave, electron beam, laser, etc. will have the same effect, and it is also within the scope of the present invention to further strengthen the excitation using a magnetic field. Next, a detailed explanation will be given using examples. Example 1 CH ₄ : 0.5 using a known plasma CVD method (in which plasma is ignited using microwaves at 2.45 GHz).
A diamond film with a thickness of 0.5 μm was formed on the (111) plane of a diamond single-crystal substrate using a reaction gas containing _0.05 % residual _H2 . The electrical resistance of this film was measured to be 1×10 ³ Ωcm, and Hall effect measurements confirmed that it was an n-type semiconductor. Example 2 Using the same method as in Example 1, diamond films each having a thickness of 0.3 μm were prepared from the reaction gas having the composition shown in Table 1, and the electrical resistance and electron mobility were measured. The results are shown in Table 1.

[Table] Example 3 C/H ₂ =
0.005, C ₂ H ₆ so that As/C=0.001,
When AsH ₃ and H ₂ gases were mixed and a 0.3 μm film was formed on an artificial diamond single crystal and the electrical resistance value and Hall effect were measured, the resistance was 1.5 × 10 ² Ωcm and it was identified as n-type The mobility was 720cm ² /v.sec. Example 4 Comparisons were made in the same manner as in Example 2, with different concentrations of As and Sb added. As is _AsH3 , Sb is
It was added in gaseous state as SbCl ₅ .

[Table] An n-type semiconductor diamond film was obtained from the samples covered in the present application.

Claims (1)

[Claims] 1 A reaction gas consisting of a gas containing one or more dopant elements selected from the group consisting of P, As, or Sb, a hydrocarbon gas, and hydrogen, in which the molar ratio of carbon atoms to hydrogen molecules contained in the hydrocarbon gas is 0.001.
~0.02, and the molar ratio of the dopant atoms to the carbon atoms is 0.0001 to 0.002, thermally decomposing the reaction gas,
Alternatively, a method for producing an n-type semiconductor diamond film characterized by plasma decomposition and vapor deposition on a substrate.