JPH04175295A - Production of semiconductive diamond - Google Patents

Abstract

PURPOSE:To accomplish the vapor phase synthesis of n-type semiconductive diamond with a resistance value at low cost in good reproducibility by mixing a feedstock gas with a gas produced by heating and evaporating Li or its compound. CONSTITUTION:A feedstock gas for diamond crystal production is mixed with a gas produced by heating and evaporating metallic Li or its compound such as LiCl or Li2O at the element ratio (Li/C) of 10<-2>-10<-6>, thus obtaining the objective semiconductive diamond containing the Li as doner through vapor phase synthesis.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing semiconductor diamond containing lithium as a donor.

[Prior Art] Conventionally, so-called diamond semiconductors doped with elements of group IIIB or group VB of the periodic table have an extremely larger band gap (approximately 5.4 eV) than semiconductors such as Si. High hole mobility,
It has advantages such as having almost the same electron mobility as Si, a low dielectric constant, and high thermal conductivity.

As methods for manufacturing this diamond semiconductor, the following methods (a) to (C) 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, II in the liquid organic compound of diamond crystal raw material
A method of introducing impurities by dissolving a compound containing elements of Groups I, V, and ■.

Problems to be Solved by Invention C] However, the conventional methods (a) to (C) above have the following problems:
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 (C), 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 not possible to obtain a low resistance value of 102Ω・0m or less. Furthermore, although it is possible to obtain an n-type semiconductor by introducing lithium ions into diamond using the ion implantation method, there are problems in productivity, such as the need for annealing at a temperature of several hundred degrees Celsius after ion implantation.

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, and its object is to produce semiconductor diamond that can be produced inexpensively, with good reproducibility, and with low resistance in the vapor phase synthesis of diamond. The purpose is to provide a manufacturing method.

[Means for Solving the Problems] The method for producing semiconductor diamond of the present invention includes heating and evaporating lithium or a compound containing lithium to mix it into a diamond crystal raw material gas.
It is characterized by producing semiconductor diamond containing lithium as a toner by vapor phase synthesis.

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

According to the present invention, by heating and evaporating lithium or a compound containing lithium and mixing it into a raw material gas for diamond crystal, a toner containing lithium can be produced.
This made it possible to manufacture diamond-shaped semiconductor diamonds.

As a result of extensive studies, the inventors of the present invention have discovered that compared to conventional n-type semiconductors formed by adding nitrogen or phosphorus, lithium or lithium-containing compounds are heated and evaporated and mixed into the raw material gas to produce lithium. It has been found that an n-type semiconductor formed by adding 20% of the total number of nanotubes has excellent reproducibility and can obtain a low resistance value.

The manufacturing method of the present invention will be explained in detail below.

The lithium or lithium-containing compound used in the present invention includes lithium car bodies, lithium oxide (Li2O
), lithium hydroxide (LiOH), lithium chloride (Li
Examples include C1), but any material containing Li may be used. Furthermore, the Li source is not limited to a solid one, and may be a Li-containing organic compound liquid.

The lithium vehicle body and the method of introducing the lithium-containing compound into the raw material gas will be described with reference to FIG. In addition,
The method of introducing lithium or a lithium-containing compound of the present invention is not limited to the method shown in this figure.

Figure 1 shows hot filament CVD (chemical vapor deposition)
This figure schematically shows a method of adding lithium as an impurity to diamond in the process of diamond formation.

In the figure, 1 is a quartz reaction tube, 2 is an electric furnace for heating raw material gas for diamond crystal, 3 is a tungsten filament, 4 is a substrate, 5 is an electric furnace for heating a lithium source, and 6 is a lithium source (lithium or lithium (compounds containing), 7
is a carrier gas or raw material gas inlet, which is connected to a gas cylinder and a gas flow meter (not shown). Reference numeral 8 denotes a raw material waste inlet port, which is connected to a gas cylinder and a gas flow meter (not shown). Reference numeral 9 denotes an exhaust port, which is connected to a pressure regulating valve and an exhaust system (not shown). In this hot filament CVD method, a carbon-containing gas (1 to 1000 Torr, preferably 1
0-400T o r r, optimally 20-100To
rr), and this gas is decomposed by the filament 3 heated to about 1,600 to 2,800° C., thereby forming diamond on the substrate 4. As the filament, for example, tungsten, tantalum, simple platinum, an alloy thereof, or a carbide thereof can be used. In this embodiment, tantalum is used, which has been previously baked out in a hydrogen-methane atmosphere (~2000°C) and then carbonized for use in diamond formation. At this time, without flowing the carrier gas or raw material gas from the gas inlet 7, the lithium source 6 containing lithium or a lithium-containing compound is heated and evaporated, and introduced into the quartz reaction tube 1 together with the carrier gas or raw material gas to cause precipitation. Lithium is added to the diamond.

Here, as the raw material gas for diamond crystals, hydrocarbon gases such as methane, ethane, and propane, and organic compounds such as methanol, ethanol, and acetone can be used. It can also be used diluted with gas. Hydrogen, rare gas, etc. can be used as the carrier gas.

The heating temperature of lithium or a lithium-containing compound varies depending on the substance, but the elemental ratio of lithium and carbon in the raw material gas for diamond crystals after mixing (L i / C
) is about 10-2 to 10-', preferably 10-3 to 1
It is desirable to adjust the vapor pressure of the material to be 0-7, more preferably 10-4 to 10-6, optimally 5xto-' to 5xlO-'. When (Li/C) is 10-8 or more, the specific resistance value of the diamond semiconductor film becomes lower, and when it is 10-2 or less, the crystallinity becomes better.

For example, when the methane partial pressure is 100 Torr, lithium or a lithium-containing compound may be heated so that the vapor pressure of Li changes from 10-'Torr to ITorr. For example, in the case of Li metal, 10-'Torr at 306°C,
The vapor pressure is ITorr at 744°C.

In addition, elements other than lithium contained in lithium-containing compounds (for example, C1 for LiCj, 0 for Li2O) have a larger atomic radius than Li, and the amount that can fit into the diamond lattice is Very little compared to Ll,
The effect of deteriorating the electrical characteristics as an n-type semiconductor is small. Therefore, Li compounds other than Li metal alone can also be used as doping sources.

The material of the substrate on which the diamond is to be formed is not particularly limited and may be, for example, Si, SiO2, or SiC.

A substrate made of a semiconductor such as AIL203, GaAs, or W, an insulator, or a metal can be used.

In addition, the method for forming diamond semiconductor crystals is not limited to the above-mentioned hot filament CVD method, but also microwave plasma CVD method.
Any method such as the D method, high frequency plasma CVD method, or direct current plasma CVD method may be used.

[Example] Next, examples of the present invention will be shown.

(Example 1) A diamond semiconductor was formed using the apparatus shown in FIG.

First, a single crystal silicon substrate (φ25 mm, thickness 0.5 m
m) was placed in a quartz reaction tube 1 as a substrate 4. Further, as a lithium source 6, lithium metal was placed in a platinum boat and placed in the quartz reaction tube 1.

The inside of the quartz reaction tube was heated to 10-'To
After evacuation to rr, hydrogen gas was pumped to 100 mj2/
Hydrogen gas and methane gas were introduced into the quartz reaction tube at a rate of 2 mλ/min and 100 mu/min, respectively, from the gas inlet 8.

Thereafter, the pressure inside the reaction tube was set to 100 Torr using a pressure regulating valve (not shown), and then the silicon substrate was heated to 800° C. using the electric furnace 2 and the lithium source 6 was heated to 402° C. using the electric furnace 5. At this time, the vapor pressure of lithium was about 10-' Torr, and the ratio of lithium to carbon (Li/C) in the raw material gas was 1100 pp (=10-').

Next, the filament 3 was energized by a power supply (not shown) and heated to about 2200° C., thereby forming a diamond on the silicon substrate.

A diamond thin film of about 3 μm was formed after 6 hours of reaction.

The diamond semiconductor obtained as described above had a specific resistance at room temperature of 20 Ω·cm, and was an n-type semiconductor. Also,
The Raman spectrum of this diamond semiconductor is 133
A peak was observed around 3 cm-', and it was confirmed that it was a diamond crystal.

(Example 2) The vapor pressure of lithium is f 0-5Torr ((L
A diamond thin film was formed in the same manner as in Example 1, except that the electric furnace 2 was adjusted to 350°C so that i/C) was 10 ppm (=1 o-5), and the obtained diamond semiconductor was as follows. n with a specific resistance of 100Ω・cm at room temperature
It was a type semiconductor.

Further, in the Raman spectrum of this diamond semiconductor, a peak was observed near 1333 cm-', and it was confirmed that it was a diamond crystal.

(Example 3) Lithium in the lithium source 6 was replaced with lithium fluoride (LiF). In addition, hydrogen and methane gas are used as raw material gases.
The water was introduced at a rate of 100 mJl/min and a pressure of 100 Torr. Furthermore, the vapor pressure of lithium fluoride is set to 1O-5Torr ((Li/C) is 50p
The electric furnace 2 is
Diamond was formed in the same manner as in Example 1 except that the temperature was adjusted to 56°C, and the resulting diamond semiconductor had a specific resistance of 5.
It was an n-type semiconductor with a resistance of about 0Ω·cm.

The Raman spectrum of this diamond semiconductor is 13
A peak was observed around 33 cm-', and it was confirmed that it was a diamond crystal.

[Effects of the Invention] As explained above, according to the present invention, diamond with a low resistance value can be formed with good reproducibility.

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

[Brief explanation of drawings]

FIG. 341 is a schematic diagram showing an example of a diamond forming apparatus used in carrying out the present invention. (Explanation of symbols) 1... Quartz reaction tube, 2.5... Electric furnace, 3... Hot filament, 4... Substrate, 6... Lithium source, 7
．． 8...Gas inlet, 9...Gas exhaust port. Figure 1

Claims (2)

[Claims] (1) A semiconductor diamond characterized in that a semiconductor diamond containing lithium as a donor is produced by vapor phase synthesis by heating and evaporating lithium or a compound containing lithium and mixing it into a raw material gas for diamond crystals. manufacturing method. (2) The elemental ratio of lithium and carbon (Li/C) in the raw material gas for diamond crystal is 10^-^2 to 10^-
8. The method for producing semiconductor diamond according to claim 1, wherein: ^8.