JPH04174517A - Manufacture of diamond semiconductor - Google Patents

Abstract

PURPOSE:To form N-type diamond of low resistance value at a low cost and with excellent reproducibility, in the vapor phase synthesis of diamond, by using lithium or lithium containing compound as impurities acting as donar. CONSTITUTION:The pressure inside a plasma generating chamber 4 is reduced; for example, hydrogen gas, hydrogen carbide gas, etc., are introduced while the flow rate is adjusted; the inside of the chamber 4 is kept at a specified pressure. In the chamber 4, non-polarized discharge of microwave is generated by a microwave oscillator 7; by the discharge, hydrogen carbide and hydrogen in the excited state are formed; thus diamond crystal 1 is formed on a substrate 5. A film 2 containing lithium or lithium containing compound is laminated on the formed diamond film, and further heated. As the result of solid phase- solid phase diffusion, the lithium is diffused in the diamond. Thereby N-type diamond semiconductor 3 of low resistance value can be formed, at a low cost and with excellent reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION [A Field of Application of Soil Collection] The present invention relates to a method for manufacturing a diamond semiconductor useful for electronic materials and the like.

[Prior Art] So-called diamond semiconductors doped with elements of Group IIIB or Group VB of the Periodic Table have an extremely larger band gap (about 5.4 eV) than semiconductors such as Si. It has advantages such as high hole mobility, almost the same electron mobility as sl, low dielectric constant, and high thermal conductivity.

As methods for manufacturing this diamond semiconductor, the following methods (a) to (cl) are conventionally known.

(a) A method of implanting impurity ions into a diamond crystal by bringing the impurity ions into a high energy state and irradiating the impurity ions into the diamond crystal (ion implantation method).

(b) When performing vapor phase synthesis of diamond crystals on a substrate,
A method in which a gas containing impurities (doping gas) is introduced together with the raw material gas for diamond crystals.

(C) When performing vapor phase synthesis of diamond crystals on a substrate,
II, I in the liquid organic compound of diamond crystal raw material
By dissolving a compound containing elements of groups II, V, and VT,
A method of introducing impurities.

((1) A film containing impurities is layered on a diamond crystal and heated to remove the impurities into a solid phase in the diamond crystal.
Solid phase diffusion method (Japanese Unexamined Patent Publication No. 1-308900)
.

[The invention attempts to solve i! However, in the conventional methods (a) to (d) above,
Each of them had the following issues.

First, in the method (a) of implanting ions, 20k
Because ions are implanted with high energy of eV or more,
The resulting diamond semiconductor is prone to defects due to radiation damage, and requires expensive equipment for ion implantation.

Furthermore, in any of the methods (a) to (d), a p-type semiconductor can be stably created by introducing boron, but an n-type semiconductor created by introducing nitrogen or phosphorus cannot be reproducibly produced. is poor, and the resistance value is also 103Ω・cm.
It is possible to obtain an n-type semiconductor by introducing lithium ions into diamond using the ion implantation method, but after ion implantation, it is possible to obtain a low resistance value of 102Ω・Cm or less. There are problems with productivity, such as the need for annealing.

In this way, conventionally, low-resistance n
type semiconductor diamond could not be created.

The present invention has been made in view of the problems of the prior art described above, and its object is to produce a diamond semiconductor that is inexpensive, has good reproducibility, and can produce a low-resistance n-type diamond semiconductor through diamond vapor phase synthesis. The purpose of this invention is to provide a method for manufacturing the same.

[Means for Solving Problem a] The method for manufacturing a diamond semiconductor according to the present invention includes the steps of stacking a film containing impurities that act as donors on a diamond crystal, and removing the impurities from within the film by heating. A method for producing a diamond semiconductor, which at least includes a step of solid phase-solid phase diffusion into a diamond crystal, characterized in that lithium or a lithium-containing compound is used as an impurity that acts as a donor. .

[Function] The function of the present invention will be explained below along with the detailed structure of the present invention.

In order to achieve this objective, the present inventor has conducted extensive research and has developed a process of stacking a film containing an impurity that acts as a donor on a diamond crystal, and a process to solidify the impurity from within the film into the diamond crystal by heating. In a method for manufacturing a diamond semiconductor that includes a step of phase-solid phase diffusion, by using lithium or a lithium-containing compound as an impurity that acts as a donor, it is possible to manufacture a diamond semiconductor at low cost and with good reproducibility and low resistance. I found out that it is possible.

Hereinafter, the manufacturing method of the present invention will be explained in detail.

The diamond crystal used in the method of the present invention includes, for example, diamond single crystal, Si, and Ta.

These include diamond polycrystals formed by a vapor phase method on substrates such as MO, S i 02 , AA203, etc., and diamond epitaxial crystals formed by a vapor phase method on a diamond single crystal substrate.

Note that the shape of the diamond crystal used is not limited to a film shape.

Examples of lithium or lithium-containing compounds used in the present invention include simple lithium (L i )
, lithium oxide (L i20 ), lithium hydroxide (LiOH), lithium chloride (LiCλ), etc., but any material containing Li may be used.

In the method of the present invention, first, a film containing impurities as described above is laminated on a diamond crystal.

One embodiment of the layer formation method includes, for example, a method in which a liquid in which impurities are dispersed is applied onto a diamond crystal, and the coating film is solidified by an appropriate method.

The coating method is not particularly limited as long as it is possible to form a suitably uniform film; for example, a spin code method can be used.

Further, the dispersion liquid to be applied is not particularly limited as long as it has suitably good film-forming properties, and an appropriate solvent may be used depending on the type of impurity.

Furthermore, for the purpose of maintaining the dispersibility of impurities, a suitable organic binder or the like may be added to prepare a dispersion liquid.

For example, when metallic lithium is used as an impurity, metallic lithium can be dissolved in an alcohol-based solvent and the solution can be applied onto the diamond crystal.

Moreover, the above-mentioned impurities can be added to a silicon-based compound represented by the structural formula Rn Si (OH) 4-n to form a dispersion.

Furthermore, the impurities described above can be added to a suitable metal hydroxide colloid, metal acid ester, metal alcoholate, etc. to prepare a dispersion.

Examples of metal alcoholates include ethylene silicate and silicon tetraethoxide.

In addition, as another method for forming a layer, lithium or a lithium-containing compound is deposited in a vacuum (10-'Torr or more),
Examples of methods include forming the diamond film on a diamond film using a resistance heating method or an electron gun evaporation method.

The impurity concentration in the film is preferably 1 to 10'ppm, more preferably 10 to 10''ppm, and 20 to 10''ppm.
500 ppm is optimal.

In addition, the film thickness is preferably 0.1 to 10 μm, and 1 to 10 μm.
5 μm is more preferable.

In the method of the present invention, after the above-described film stacking is formed, impurities are solid-phase-solid-phase diffused from within the film into the diamond crystal by heating.

The heating conditions may be set so that the impurities undergo solid phase-solid phase diffusion to obtain a diamond semiconductor exhibiting the desired electrical conductivity. It is necessary to set the temperature appropriately depending on the temperature, etc., and it is not particularly limited.
000℃.

The heating time needs to be set appropriately depending on the desired electrical conductivity of the diamond semiconductor, and is not particularly limited, but may be performed for, for example, about 30 minutes to 100 hours, preferably about 1 hour to 10 hours. .

In addition, the heating can be performed using, for example, N, gas, rare gas, etc. in the reaction chamber.
This may be carried out while introducing 02 gas or the like. The pressure of the gas is
For example, 100 to 1000 Torr, the flow rate is iIL/
Introduce about min.

If it is necessary to remove the impurity-containing film after the desired diamond semiconductor is formed by diffusing impurities as described above, the impurity-containing film can be removed, for example, by etching. The film can be easily removed by using various acids and alkalis, such as HF solution and KOH solution, as an etching agent.

The manufacturing apparatus that can be used in the method of the present invention may be any apparatus as long as it has means for heating to enable solid phase-solid phase diffusion of impurities as described above.

In addition, methods for forming diamond thin films on various substrates by vapor phase methods include, for example, hot filament CVD.
(chemical vapor deposition) method, microwave plasma CVD
method, high frequency plasma CVD method, direct current plasma CVD method, etc., and is not particularly limited.

FIG. 2 shows an example of a diamond forming apparatus that can be used in the present invention.

This apparatus is a microwave plasma CVD apparatus conventionally used for forming diamond thin films and the like.

- This device includes a means for placing a substrate 5 inside the plasma generation chamber 4, a system 6 for supplying a reactive gas to the plasma generation chamber 4, and a waveguide for introducing microwaves from a microwave oscillator 7. It has a configuration including a pipe 8 and an exhaust system 9.

When forming a diamond crystal film using this apparatus, first, the pressure inside the plasma generation chamber 4 is reduced, and hydrogen gas, hydrocarbon gas, etc. are introduced through the reaction gas supply system 6 while adjusting the flow rate, and the plasma is generated. The inside of the plasma generation chamber 4 is maintained at a predetermined pressure, and the microwave oscillator 7 generates a microwave non-polar discharge in the plasma generation chamber 4, and this discharge generates hydrocarbons and hydrogen in an excited state, which are then deposited on the substrate 5. Generate diamonds.

As described above, a film containing lithium or a lithium-containing compound is laminated on the diamond film thus formed, and then heated, so that lithium is in the solid phase.
It diffuses into diamond by solid-phase diffusion to obtain n-type semiconductor diamond.

[Example] Next, an example of the present invention will be shown. (Example 1) First, using the apparatus shown in FIG. 2, Si (
100) Substrate (15mm x 15mm, thickness 0.5mm)
) was formed with a diamond polycrystalline film having a thickness of about 3 μm.

Raw material gas: CO gas 5SCCM H2 gas 11005CC Gas pressure: 20 Torr Microwave: 2.45 GHz Discharge power, aoow' Substrate temperature: 880° C. It was confirmed by Raman spectroscopy that this film was a diamond crystal.

Next, 2.0 g/1 of metallic lithium was added to ethyl alcohol.
00ml/1l, and further dissolved in methyl cellosolve solvent. This solution was applied onto the diamond film of the substrate using a spinner at a rotation speed of 250 rpm for 15 minutes.
Applied for seconds. Furthermore, this substrate was placed in the atmosphere for 1
Baking was performed at 50°C for 20 minutes.

Next, this substrate was subjected to solid phase-solid phase diffusion at 900° C. for 1 hour under normal pressure in a diffusion furnace while introducing N2 gas at a flow rate of 1:1.

Next, the coating film on the diamond film was removed using an HF solution to create a diamond semiconductor.

The diamond semiconductor obtained as described above was an n-type semiconductor with a specific resistance I x about 10 2 Ω·cm.

(Example 2) First, in the same manner as in Example 1, a diamond thin film was deposited on Si.
formed on a substrate.

Next, add 1.5% lithium carbonate (Li2CO3) to pure water.
g/100 mj2, and further dissolved in a methyl cellosolve solution. This solution was applied onto the diamond film on the Si substrate using a spinner at a rotation speed of 2000 rpm for 15 seconds.

Furthermore, this substrate was baked at 150° C. for 20 minutes in the atmosphere.

Next, this substrate was subjected to solid phase treatment at 950°C for 2 hours in a diffusion furnace under normal pressure while introducing N gas at a flow rate of 1j2.
Solid phase diffusion was performed.

Next, the coating film on the diamond film was removed using an HF solution to create a diamond semiconductor.

The diamond semiconductor obtained as described above was an n-type semiconductor with a specific resistance of about 10 Ω·cm.

(Example 3) First, in the same manner as in Example 1, a diamond thin film was deposited on Si.
formed on a substrate.

Next, lithium fluoride (LiF) was vacuum evaporated on the diamond film on the Si substrate (resistance heating method, pressure 1xlO-'
Torr) was used to form a film with a thickness of about 2,000 layers.

Next, this substrate was heated in a solid phase at 800°C for 2 hours in a diffusion furnace under normal pressure while introducing N2 gas at a flow rate of IIL.
Solid phase diffusion was performed.

Next, the coating film on the diamond film was removed using an HF solution to create a diamond semiconductor.

The diamond semiconductor obtained as described above was an n-type semiconductor with a specific resistance of about 50 Ω·am.

[Effects of the Invention] As explained above, according to the present invention, it has become possible to form an n-type semiconductor diamond with a low resistance value.

The n-type semiconductor diamond obtained by the present invention can be used in a wide range of fields such as high-pressure semiconductors and semiconductors that can be used at high temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1(a) to 1(c) are schematic diagrams schematically showing steps in the manufacturing method of the present invention. FIG. 2 is a schematic diagram showing an example of an apparatus that can be used for diamond formation. (Explanation of symbols) 1... Diamond crystal, 2... Impurity-containing film, 2
a... Impurity, 3... Diamond semiconductor, 4...
- Plasma generation chamber, 5... Substrate, 6... Reaction gas supply system, 7... Microwave oscillator, 8... Waveguide, 9
...Exhaust system. Figure 1

Claims (1)

[Claims] A diamond semiconductor comprising at least a step of laminating a film containing an impurity acting as a donor on a diamond crystal, and a step of solid-phase-solid-phase diffusing the impurity from the film into the diamond crystal by heating. A manufacturing method, wherein the impurity serving as the donor includes:
A method for producing a diamond semiconductor, characterized by using lithium or a compound containing lithium.