JPH0513821A - Manufacture of thermoelectric material and manufacturing device - Google Patents

Abstract

PURPOSE:To increase the Seebeck coefficient and electric conductivity of a thermoelectric material by a method wherein a process for forming a thin film containing hydrogen or oxygen in addition to Si on a substrate in a vacuum vessel and a process for making metal or metal-silicon alloy superfine particles adhere on the substrate surface formed with the thin film are simultaneously or alternately performed. CONSTITUTION:An SiO film 13 is subjected to clustering utilizing an overcooling due to an adiabatic expansion which is caused by a pressure difference in a vacuum vessel 7. Thermoions are cast on the cluster and the cluster is ionized and is turned into an ion cluster beam. At that time, Ar gas is simultaneously introduced in a vacuum vessel 8 through an inert gas introducing port 20. A tungsten board 22 is heated in an atmosphere of the Ar gas and Fe grains 23 are dissolved and evaporated. Thereby, it becomes possible to make a thermoelectric material of a structure, wherein fine particles of a mean diameter of 40 to 4000Angstrom are dispersed in an Si-O amorphous film which is an amorphous film having a preferential Si-oxygen bond.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing a thermoelectric material for converting heat into electricity, and more particularly to a method and an apparatus for producing a high performance metal-silicon alloy thermoelectric material.

[0002]

2. Description of the Related Art The thermoelectric performance of thermoelectric materials is represented by the figure of merit Z.

Z = S ² σ / λ where S is the Seebeck coefficient, σ is the electrical conductivity, and λ is the thermal conductivity. That is, the figure of merit is high when the Seebeck coefficient is large, the electrical conductivity is high, and the thermal conductivity is low. In the theory of thermoelectric phenomena of semiconductors, the Seebeck coefficient and the electric conductivity have an inverse correlation, so it was difficult to obtain a thermoelectric material having a large figure of merit in a stable and homogeneous material produced in an equilibrium state.

However, in recent years, an amorphous Fe-Si-O type thin film material produced in a non-equilibrium state has attracted attention as a thermoelectric material having high thermoelectric conversion efficiency. It has been reported that the thin film material produced by the ICB (ion cluster beam) method can significantly improve the thermoelectric performance by the preferential bonding of Si and oxygen over Fe and oxygen [Matsubara. Kakuei: Energy Conversion Technology, 1984, p12
3 to p133].

Further, the structure of this thin film material prepared by the IAD (ion assisted deposition) method at the atomic level is such that fine particles of Fe having an average particle size of about 100 Å are present in the form of islands in the Si--O system amorphous. It has been reported that there is a [K. Nagao et al.:Proc. 13th
Symp. On Ion Source and Ion assisted Tech.'90 (199
0) 245.].

As a conventional manufacturing method for manufacturing a thermoelectric material having a structure in which fine particles are present in the form of islands in the amorphous state, the IAD method is shown below with reference to FIG.

FIG. 3 is a schematic vertical sectional view of a conventional thermoelectric material manufacturing apparatus. In the vacuum vessel 1, the crucible 2 and the electron gun 3
Is installed. The ion gun 4 is the vacuum container 1
It is installed diagonally in the center of the room. A substrate 5 is held near the top of the vacuum container 1. The vacuum container 1 is connected to a vacuum pump (not shown).

In such a structure, Fe is contained in the crucible 2.
Insert the particles 6 and put SiO (not shown) in the ion gun 4.
Insert. The pressure in the container 1 is adjusted to 10 by a vacuum pump.
^-5 to 10 ^-6 Torr. The Fe particles 6 inserted into the crucible 2 are irradiated with an electron beam from the electron gun 3 to generate Fe particles 6
Evaporate. At the same time, the vaporized SiO is ionized in the ion gun 4 and irradiated toward the substrate 5. By doing so, vapor deposition of Fe and vapor deposition of SiO ions are simultaneously performed on the surface of the substrate 5.

The thin film obtained by the above method is heated to 1000 to 1200 ° C. in nitrogen gas or argon gas.
By performing the heat treatment at about a temperature, it is possible to obtain a stable structure in which fine Si particles having an average particle diameter of about 100 Å are present in an island shape in the Si—O system amorphous.

[0010]

However, in the case of such a manufacturing method, oxygen is combined with Fe in the process in which Fe aggregates to form fine particles, and oxygen is preferentially combined with only Si. However, there is a problem in that high performance cannot be obtained, or it is difficult to control the particle diameter and the number of particles.

It is an object of the present invention to solve the above problems and to provide a method and an apparatus for manufacturing a thermoelectric material, which can achieve an increase in Seebeck coefficient and electric conductivity and a decrease in thermal conductivity with good controllability. .

[0012]

In order to achieve the above object, the present invention provides a process of forming an amorphous thin film containing hydrogen or oxygen in Si on a substrate in a vacuum container, and a process of forming the amorphous thin film. A thermoelectric material is manufactured by simultaneously performing the process of adhering ultrafine particles of a metal or a metal-silicon alloy having an average particle size of 40 to 400Å on the surface of the substrate.

[0013]

The operation obtained by the above manufacturing method is as follows.

A process of forming an amorphous thin film containing hydrogen or oxygen on Si on a substrate in a vacuum container, and a metal or a metal having an average particle size of 40 to 400Å on the surface of the substrate on which the amorphous thin film is formed. -Since the process of adhering the ultrafine particles of the silicon-based alloy is performed at the same time, the fine particles of the metal or the metal-silicon alloy are dispersed in the Si-O-based or Si-H-based amorphous material without the heat treatment step. It becomes possible to fabricate a structure.

Further, since ultrafine particles of primary particles are used, fine particles having a particle size of 40 to 400 Å can be obtained. Furthermore, it becomes possible to more strongly achieve the bond between Si and oxygen or hydrogen, and avoid the bond between the metal or the metal-silicon alloy and oxygen or hydrogen. In addition, it is possible to easily control the particle size of fine particles and the amount of dispersion.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a longitudinal sectional view showing the construction of an embodiment of a thermoelectric material manufacturing apparatus of the present invention. The vacuum container 7 and the vacuum container 8 are connected by an ultrafine particle transfer pipe 10 having an orifice 9. In the vacuum container 7, a crucible 12 having a nozzle 11 is installed. Crucible 12
SiO13 is inserted in the inside. Around the crucible 12, a filament 14 for causing thermoelectrons to collide with the crucible 12 is installed. A filament 15 and an electron extraction grid 16 are installed on the upper part of the crucible 12.
Further, an acceleration electrode 17 is installed above it.

A substrate 18 is placed above the vacuum container 7 so as to face the ICB source. The vacuum container 8 is provided with an inert gas inlet 20 having a valve 19 and an exhaust system having a valve 21. A tungsten boat 22 is installed in the vacuum vessel 8, and Fe particles 23 are inserted in the tungsten boat 22. Vacuum container 7
And 8 are connected to a vacuum pump (not shown).

In such a structure, first, the vacuum container 7 and the vacuum container 8 are evacuated to about 10 ^-6 to 10 ^-7 Torr, and then the filament 1 heated by electric heating is used.
By making the thermoelectrons emitted from No. 4 collide with the crucible 12, the crucible 12 is heated to a high temperature. SiO13 inserted in the crucible 12 sublimes and passes through the nozzle 11, thereby utilizing the supercooling due to adiabatic expansion caused by the pressure difference between the vapor pressure inside the crucible 12 and the pressure inside the vacuum vessel 7 lower than that. , SiO13 into clusters (agglomerates of 500 to 2000 atoms or molecules). The cluster is ionized by irradiating the cluster with thermoelectrons extracted from the hot filament 15 by the grid 16 to form an ion cluster beam.

Further, a voltage is applied to the accelerating electrode 17 to accelerate the ion cluster beam. At the same time, in the vacuum container 8, the valve 21 is closed, the valve 19 is opened, and the Ar gas is introduced from the inert gas inlet 20 until the pressure in the vacuum container 8 becomes several to several tens Torr. In the atmosphere, the tungsten boat 22 is heated and the Fe particles 2
3. Dissolve and evaporate. In the case of vacuum vapor deposition, since the inside of the vacuum container has a high vacuum of 10 ⁻⁴ Torr or less, the vaporized atoms arrive at the substrate without colliding with the molecules of the residual gas on the way. In the case of, Fe grains 23
Is cooled with argon gas at room temperature, atoms are agglomerated with each other, and become Fe ultrafine particles 24. Since the pressure in the vacuum container 7 is lower than the pressure in the vacuum container 8, Ar gas in the vacuum container 8 flows into the vacuum container 7 through the orifice 9.

At the same time, the Fe ultrafine particles 24 already produced are also carried along with the flow of Ar gas through the orifice 9 into the vacuum container 7 along the ultrafine particle carrying pipe 10. Since the tip of the ultrafine particle carrying pipe 10 is fixed near the substrate 18, the Fe ultrafine particles 24 are
The ICB source adheres to the surface of the Si—O based amorphous thin film that is being deposited and is taken into the amorphous thin film. At this time, the Fe ultrafine particles 24 are primary particles, that is, the bonds between the molecules remain, and the average particle diameter is 40 to 400Å. (If the Fe ultrafine particles 24 are taken out into the atmosphere outside the vacuum container 8, the primary particles are secondarily aggregated to become secondary particles, and the average particle size grows to ˜1000Å. Oxidation proceeds rapidly when touched, and the original characteristics of the Fe ultrafine particles 24 deteriorate.) By using the above-described manufacturing method and manufacturing apparatus, an amorphous material having a preferential bond between Si and oxygen is obtained. It is possible to produce a thermoelectric material having a structure in which fine particles having an average diameter of 40 to 400 Å are dispersed in a film Si—O type amorphous.

In the structure of this Fe-Si-O-based thin film, Fe having a large electric conductivity and a small Seebeck coefficient is used.
However, since they are fine particles (40 to 400 Å), scattering due to lattice defects and phonons does not matter within the particles (that is, they are in the same state as in the single crystal), so the electrical conductivity becomes higher. The electrons and holes are in the activated state at the cage interface.

Further, since the fine particles are dispersed in the Si--O type amorphous material having a large Seebeck coefficient and a small electric conductivity, electron and hole conduction such as tunnel conduction and hopping conduction is possible between the particles. . That is, since such a structure is achieved, this thermoelectric material has a large Seebeck coefficient and a large electric conductivity.

Further, such a dispersed state of fine particles is advantageous for movement of fine carriers such as electron and hole conduction, but scattering occurs everywhere in collective phonon diffusion such as heat. The thermal conductivity is reduced. That is, it is possible to obtain a thermoelectric element having excellent thermoelectric characteristics, in which the Seebeck coefficient and the electric conductivity are improved and the thermal conductivity is reduced. Furthermore, changing the conditions for producing ultrafine particles,
By controlling the average particle size and amount of the ultrafine particles to be dispersed, the Seebeck coefficient and electric conductivity can be easily controlled.

The ultrafine metal particles are not limited to Fe, and 3d transition metals such as Cr, Mn, Co and Ni, Fe-Si, Cr-Si, Mn-Si and Co-Si.
It goes without saying that alloy materials such as can be used.

(Embodiment 2) FIG. 2 is a schematic vertical sectional view of another embodiment of the thermoelectric material manufacturing apparatus according to the present invention. The vacuum container 25 and the vacuum container 26 are connected by an ultrafine particle loading pipe 28 having an orifice 27. Vacuum container 2
In FIG. 5, an inlet 30 having a valve 29 for introducing the organometallic gas is installed. An RF electrode 31, a substrate holder 32, and a substrate 33 for causing glow discharge are installed in the vacuum container 25. Vacuum container 26
An inert gas introduction port 35 having a valve 34 and an exhaust system having a valve 36 are installed therein. Vacuum container 26
A tungsten boat 37 is installed therein, and Fe particles 38 are inserted in the tungsten boat 37. The vacuum container 25 and the vacuum container 26 are connected to a vacuum pump (not shown).

In such a structure, first, the inside of the vacuum container 25 and the vacuum container 26 is set to 10 ⁻⁶ to 10 ⁻⁷ Torr.
After exhausting the gas to a certain degree, the valve 29 is opened and SiH ₄ gas is introduced into the vacuum chamber 25, and an RF potential is applied to the RF electrode 31 to cause glow discharge, decompose the SiH ₄ gas, and form an amorphous film on the substrate 33. Deposit Si: H thin film. At the same time, in the vacuum container 26, the ultrafine particles 3
9 is manufactured.

The ultrafine particles 39 already generated are also carried into the vacuum container 25 through the orifice 27 by riding on the flow of Ar gas flowing from the vacuum container 26 into the vacuum container 25. Since the tip of the ultrafine particle loading pipe 28 is fixed near the substrate 33, the ultrafine particles 39 adhere to the surface of the amorphous Si: H thin film as they are being deposited on the substrate 33 and are taken into the amorphous thin film. Since the ultrafine particles 39 at this time are primary particles, the average particle diameter is 40 to 400Å.

By using the manufacturing method and the manufacturing apparatus as described above, the average diameter is 4 in the amorphous Si: H.
It is possible to produce a thermoelectric material having a structure in which fine particles of 0 to 400 Å are dispersed.

Also in the thermoelectric material obtained in this example, the same effects as those described in Example 1 can be obtained.

The SiH ₄ gas may be diluted with Ar gas or H ₂ gas.

[0032]

As described above, the method for producing a thermoelectric material according to the present invention comprises the steps of forming an amorphous thin film containing hydrogen or oxygen in Si on a substrate in a vacuum container, and forming the amorphous thin film. The average particle size is 4 on the surface of the substrate.
Since the method for producing a thermoelectric material is used in which the process of adhering ultrafine particles of a metal or a metal-silicon alloy of 0 to 400Å is performed at the same time, the Seebeck coefficient and the electrical conductivity are increased, and the thermal conductivity is reduced. A high-performance metal-silicon alloy thermoelectric material can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts showing the configuration of an embodiment of a thermoelectric material manufacturing apparatus of the present invention.

FIG. 2 is a cross-sectional view of essential parts showing the configuration of another embodiment of the thermoelectric material manufacturing apparatus of the present invention.

FIG. 3 is a cross-sectional view of essential parts of a conventional thermoelectric material manufacturing apparatus.

[Explanation of symbols]

9, 27 orifice 10, 28 Ultra fine particle loading pipe 13 SiO 18 substrates 22,37 Tungsten boat 23, 38 Fe grains 24, 39 Fe ultrafine particles

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kuro Gyoten             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd.

Claims (7)

[Claims] 1. A process of forming a thin film containing hydrogen or oxygen on Si on a substrate in a vacuum container, and ultrafine particles of metal or metal-silicon alloy on the surface of the substrate on which the thin film is formed. A method for producing a thermoelectric material, which comprises simultaneously or alternately performing the process of adhering. 2. The method for producing a thermoelectric material according to claim 1, wherein the thin film containing hydrogen or oxygen in Si is amorphous. 3. The method for producing a thermoelectric material according to claim 1, wherein the average particle size of the ultrafine particles is 40 to 400Å. 4. The method for producing a thermoelectric material according to claim 1, wherein ultrafine particles of a transition metal such as Fe, Cr or Mn or a transition metal-silicon alloy is used. 5. A mechanism for producing Si molecules, ions or radicals having a bond with oxygen or hydrogen and the Si.
With a substrate to which the molecules or radicals of
Vacuum container for producing a thin film for a thin film, a vacuum container for producing an ultrafine particle having a metal or alloy evaporation source and an inert gas inlet, and an ultrafine particle produced in the vacuum container for producing an ultrafine particle for producing a Si thin film An apparatus for producing a thermoelectric material, which comprises a connecting pipe having an orifice to be introduced into a vacuum container. 6. The apparatus for producing a thermoelectric material according to claim 5, wherein a vacuum container for producing a Si-based thin film is used, which comprises an ion cluster beam generation source that ionizes Si in a state having a bond with oxygen and a substrate. 7. A vacuum container for producing a Si-based thin film, comprising a glow discharge generating electrode for ionizing and radicalizing Si while having a bond with hydrogen, an organosilicon gas inlet and a substrate. Manufacturing equipment for thermoelectric materials.