JPH05102535A - Thermoelectric material and its manufacturing method - Google Patents

Abstract

PURPOSE:To obtain metal-silicon based alloy thermoelectric material of especially high quality and its manufacturing method. CONSTITUTION:By a manufacturing method using a process wherein, after columnar ultrafine particles 10 of metal or metal-silicon based alloy are formed on an organic film substrate 7 surface on which fine protrusions 8 are formed in a vacuum equipment, and further an Si based thin film 11 is formed, the organic film substrate 7 is eliminated, and an Si based thin film is again formed, a structure wherein the columnar metal ultrafine particles independently exist in the Si based thin film, so as to put the long axis directions in order and not to come into contact with one another is formed. Thereby metal-silicon based alloy thermoelectric material excellent in thermoelectric characteristics that Seebeck coefficient and electric conductivity are improved and thermal conductivity is decreased can be obtained.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art The thermoelectric performance of a thermoelectric material is represented by a figure of merit Z using a Seebeck coefficient S, an electrical conductivity σ, and a thermal conductivity λ.

Z = S ² σ / λ 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 a 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 forming a preferential bond between Si and oxygen over Fe and oxygen [Matsubara. Kakuei: Energy Conversion Technology, 1984, p12
3 to p133].

Further, in the structure of the thin film material prepared by the IAD (ion assisted deposition) method at the atomic level, Fe fine particles having an average particle size of about 100 Å are present in the form of islands in the Si--O system amorphous. It is reported to be in a state [K.Nagao et al.:Proc. 13th Symp. O
n Ion Source and Ion assisted Tech.'90 (1990) 24
Five.].

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 material, the IAD method will be described below with reference to FIG.

FIG. 5 is a schematic vertical sectional view showing the construction of a conventional thermoelectric material manufacturing apparatus. In the vacuum device 1, a crucible 2 and an electron gun 3 are installed. The ion gun 4 is obliquely installed in the central portion of the vacuum device 1. A substrate 5 is held near the upper portion of the vacuum device 1. The vacuum device 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 in the crucible 2 are irradiated with an electron beam from the electron gun 3 to generate Fe particles 6
To 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 such a method is
1000-1200 in nitrogen gas or argon gas
By performing the heat treatment at a temperature of about ° C, it is possible to obtain a stable structure in which fine Si particles having an average particle size of about 100Å are present in an island shape in the Si-O system amorphous.

[0010]

However, in the case of such a thermoelectric material, spherical fine particles are scattered, and when performing electron and hole conduction such as tunnel conduction or hopping conduction between the particles, the Since the portion having the shortest distance is a point, the electric conduction path is narrowed, the amount of electric charge passing cannot be increased, and it is difficult to increase the electric conductivity.

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

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

[0013]

In order to achieve the above-mentioned object, the present invention provides a step of producing microscopic projections on the surface of an organic film substrate in a vacuum device, and a metal on the microscopic projections of the organic film substrate. Alternatively, a step of producing columnar metal ultrafine particles of a metal-silicon alloy, a step of forming a Si-based thin film containing oxygen or hydrogen on the columnar metal ultrafine particles, a step of removing the organic film substrate, Oxygen or hydrogen is produced by a production method comprising a step of etching the surface of the thin film on the side where the organic film substrate is removed and a step of forming a Si-based thin film containing oxygen or hydrogen again on the etched surface. A thermoelectric material having a structure in which ultrafine columnar metal particles are independently present in the Si-based thin film containing the so that their long axis directions are aligned and do not contact each other.

[0014]

According to the above-described manufacturing method, the thermoelectric particles having a structure in which the ultrafine columnar metal particles are independently present in the Si-based thin film containing oxygen or hydrogen so that their longitudinal axes are aligned and do not contact each other. The material can be made. Among such columnar metal ultrafine particles, when conducting electron and hole conduction by tunnel conduction or hopping conduction between the particles,
Since the portion having the shortest distance between the particles becomes linear and the electric conduction path becomes wide, the amount of electric charge passing becomes large and the electric conductivity can be increased.

Further, since all the steps can be performed in a vacuum without performing a high temperature heat treatment at 1000 ° C. or higher, reactions such as association between ultrafine particles, particle growth, oxidation and nitriding are avoided, and Si and oxygen or hydrogen are removed. The bond is strongly achieved, and the particle size and amount of the ultrafine particles can be easily controlled.

[0016]

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

(Embodiment 1) FIGS. 1 (a) to 1 (d) and 2 (a) to 2 (c) show steps of a manufacturing method according to an embodiment of the present invention.
Shown in. That is, the series of steps of this embodiment are described separately in FIG. 1 and FIG. 2 in relation to the drawing paper size.

FIG. 1A shows the organic film substrate 7. In this case, the organic film substrate 7 uses a polyvinyl resin. In addition, ethylene-based and phenol-based resins can be used.

First, the organic film substrate 7 is etched to form a large number of minute projections 8 on the surface as shown in FIG. 1 (b). That is, since the organic film substrate 7 has a structure in which carbon chains are entangled everywhere, the bonding strength for cutting the carbon chains in the minute portion is different, and the etching proceeds from the weak bonding strength portion. , Where strong bond strength remains, and is formed as a minute projection.

The protrusions 8 in this case have a diameter of 100 to 150Å and a height of 15 depending on the type of the organic film substrate 7.
It is desirable that the distance is 0 to 300Å and the interval is about 1000 to 1500Å. When etching is performed by reverse sputtering, it is easy to obtain a projection having a desired shape.

Next, as shown in FIG. 1 (c), metal atoms 9 are deposited on the organic film substrate 7 in a high vacuum (10 ⁻³ to 10 ⁻⁶ Torr) by PVD (physical vapor deposition). To fly. Then,
Since the interval between the minute protrusions 8 is sufficiently smaller than the mean free path of the metal atoms 9, the minute protrusions 8 are
By the VD method, it becomes an obstacle to Fe metal atoms 9 flying from all directions. Therefore, the shadowing effect occurs,
As shown in FIG.
The spherical ultrafine particles having a diameter of 0Å are connected to each other and grow into a columnar shape, whereby the columnar metal ultrafine particles 10 can be manufactured.

The PVD method is preferably a sputtering method of a single metal or alloy target, and this phenomenon is
[S. Ohnuma, Y. Nakanouchi and T. Matsumoto: Amorp
housUltrafine Metallic Particles Prepared by Sputt
ering Method, Proc. 5th Intern. Conf. on Rapid Que
nched Metals, Elsevier, pp.1117-1124 (1985).].

It is desirable to control the sputtering time to produce columnar ultrafine metal particles having a diameter of 400 to 500Å and a length of 800 to 1000Å.

Subsequently, a Si-based thin film 11 containing oxygen or hydrogen is vapor-deposited thereon by a CVD (Chemical Vapor Deposition) method as shown in FIG. 1 (d). In this case, the CVD is performed in order to wrap around between the columnar metal ultrafine particles 10 without causing a shadowing effect and deposit a thin film without a gap.
Vapor deposition by the method is desirable. Further, this thin film is an amorphous thin film unless heat treatment is performed.

Then, after depositing the Si-based thin film 11 until all of the columnar metal ultrafine particles 10 are completely covered, FIG.
As shown in (a), the organic film substrate 7 is removed by being decomposed by heating or melting. Next, FIG. 2 (b)
As shown in, the residual organic matter is removed, and etching is performed until the columnar metal ultrafine particles 10 are separated from each other. Finally, as shown in FIG. 2C, the Si-based thin film 12 containing oxygen or hydrogen is vapor-deposited by the CVD method on the surface where the organic film substrate 7 is removed and the etching is performed.

By using the manufacturing method as described above, a columnar metal super-particle having a diameter of 400 to 500 Å and a length of 800 to 1000 Å is contained in an amorphous thin film having a preferential bond between Si and oxygen or hydrogen. It is possible to fabricate a structure in which the long axis directions are aligned so that the fine particles do not come into contact with each other and exist independently.

FIGS. 3 (a) and 3 (b) are schematic sectional views showing the structure of the thin film thermoelectric material 13 produced by the above manufacturing method. A cross-sectional view parallel to the film surface of the thin film thermoelectric material 13 is
As shown in FIG. 3A, Si containing oxygen or hydrogen
The columnar metal ultrafine particles 15 are scattered in the amorphous system 14 independently of each other. As shown in FIG. 3B, a cross-sectional view of the thin-film thermoelectric material 13 in a direction perpendicular to the film surface shows that the columnar metal ultrafine particles 15 are in the axial direction in the Si-based amorphous material 14 containing oxygen or hydrogen. They are aligned and stand independent of each other.

In the structure of the thin film thermoelectric material 13, since the metal or alloy having a large electric conductivity and a small Seebeck coefficient is a columnar metal ultrafine particle, scattering due to lattice defects and phonons is a problem within the particle. Since it does not become (that is, it is in the same state as in the single crystal), the electric conductivity is higher and the electrons and holes are in the activated state at the interface.

Furthermore, since the columnar metal ultrafine particles are aligned in the long axis direction in the Si-based amorphous material having a large Seebeck coefficient and a small electric conductivity, electrons and holes in tunnel conduction or hopping conduction are generated between the particles. It is possible to increase conduction.

In this case, if it is too small, it becomes difficult to secure a conduction path between the particles, and if it is too large, the columnar metal ultrafine particles are associated with each other during the production of the ultrafine particles by sputtering, thereby making them independent. As it cannot be done, the diameter is 400 to 5
Those having a length of 00Å and an axial length of 800 to 1000Å are suitable for exhibiting this performance.

That is, since such a structure is achieved, this thermoelectric material has a large Seebeck coefficient and a large electric conductivity. Furthermore, the state in which the ultrafine columnar metal particles independently exist in this manner is advantageous for the movement of minute carriers such as electron and hole conduction, but scattering occurs everywhere in collective phonon diffusion such as heat. Occurs and the thermal conductivity is reduced. That is, it is possible to obtain a thermoelectric material having excellent thermoelectric properties, in which the Seebeck coefficient and the electric conductivity are improved and the thermal conductivity is reduced. In addition, the Seebeck coefficient and the electrical conductivity can be easily controlled by changing the etching conditions of the organic film substrate and the production conditions of the ultrafine particles to control the particle size and amount of the ultrafine particles to be produced.

(Embodiment 2) FIG. 4 is a schematic sectional view of an embodiment of a thermoelectric material manufacturing apparatus of the present invention.

The sputtering vacuum device 16, the Si-based thin film forming vacuum device 17, and the vacuum device 18 for rotating the front and back of the substrate and for heating the substrate are provided by the preliminary evacuation chambers 19 and 20 with a shutter having a substrate transfer mechanism. , Are connected. Further, the vacuum devices 16, 17, 18 and the preliminary exhaust chambers 19, 20 are each independently a vacuum pump (not shown).
It is connected to the.

A sputtering gas introduction valve 21 is provided in the sputtering vacuum device 16, and source gas introduction valves 22 and 23 are provided in the Si-based thin film forming vacuum device 17 for heating the substrate and rotating the front and back surfaces of the substrate. A valve 24 for introducing oxygen gas is attached to the device 18.

First, the vacuum devices 16 and 17 are set to 10 ⁻⁶ To.
Evacuate to the rr stage. Next, the organic film substrate 25 is set in the movable substrate holder 26 in the vacuum device 18. Then, the vacuum device 18 and the preliminary evacuation chamber 19 are evacuated, and the substrate transport mechanism 27 in the preliminary evacuation chamber 19 moves the substrate holder 26 to move the organic film substrate 25 to the substrate installation inside the vacuum device 16. Move to electrode 28.

In the vacuum device 16, an electrode 29 and a target 30 are installed facing the electrode 28. In this case, Fe alone is used as the target. The electrodes 28 and 29 are connected to RF power sources 33 and 34 through circuit switching units 31 and 32. The circuit switching units 31 and 32 are interlocked with each other, and when one electrode is connected to the RF power source, the other electrode is grounded. By switching this circuit, the positive sputtering to the target 30 and the organic film substrate 25 can be performed.
The reverse sputtering for etching is switched.

The organic film substrate 25 is placed on the electrode 28 for placing the substrate, and the valve for the preliminary exhaust chamber 19 is closed,
When the gas is sufficiently evacuated, Ar gas is introduced as a sputtering gas from the valve 21 to generate plasma discharge, and the organic film substrate 25 is formed by reverse sputtering.
Etching the surface of. Then, the surface of the organic film substrate 25 has a diameter of 100 to 150Å and a height of 150 to 30.
A large number of minute protrusions with 0Å and an interval of 100 to 400Å are produced.

Next, after temporarily stopping the plasma discharge and switching the power supply circuit by the circuit switching units 31 and 32,
Plasma discharge is caused again to perform positive sputtering on the Fe target 30 to knock out Fe atoms. This positive sputtering causes a shadowing effect due to the fine protrusions, and Fe ultrafine particles are generated with the fine protrusions as nuclei. Sputtering is stopped and gas introduction is stopped before the ultrafine particles grow and associate with each other.

Subsequently, the organic film substrate 25 having Fe ultrafine particles attached thereto is transferred into the vacuum device 18 via the preliminary evacuation chamber 19 using the substrate transfer mechanism 27 without opening to the atmosphere. Subsequently, the substrate is transferred into the vacuum device 17 via the preliminary exhaust chamber 20 by using the substrate transfer mechanism 35, and is moved to above the electrode 36 for setting the substrate. In this case, since the ultrafine particles are in the activated state, there is a possibility that reactions such as association of the ultrafine particles, particle growth, oxidation and nitriding may proceed when opening to the atmosphere. Carry with the condition maintained.

In the vacuum device 17, an electrode 37 is installed so as to face the electrode 36. The electrode 37 is an RF power source 38.
Is connected to. When the organic film substrate 25 is placed on the electrode 36 for placing the substrate, the valve with the preliminary exhaust chamber 20 is closed, and the vacuum exhaust is sufficiently performed, SiH ₄ gas is supplied from the valve 22 and N ₂ O is supplied from the valve 23. Introduce gas,
Glow discharge is generated between the electrodes 36 and 37, and SiH ₄ , N ₂
O gas is decomposed, and a Si—O-based amorphous thin film is deposited on the organic film substrate 25 from above Fe columnar metal ultrafine particles by C.
Deposit by VD evaporation. This CVD deposition is performed until the Fe ultrafine particles are hidden. After that, the glow discharge is stopped and the gas introduction is stopped. In this case, the reason why the CVD deposition is performed without PVD deposition is that it does not cause the shadowing effect and easily wraps around the Si ultra fine particles even between the Fe ultrafine particles.
This is for depositing a system amorphous thin film.

Then, using the substrate transfer mechanism 35, the Fe ultrafine particles and Si are transferred from the vacuum device 17 to the vacuum device 18 again.
The organic film substrate 25 to which the -O-based amorphous thin film is attached is transported. In the vacuum device 18, there are a substrate holder 39 and a substrate exchanger 40 at positions facing the substrate holder 26. Then, with this substrate exchanger 40,
The organic film substrate 25 is removed from the substrate holder 26, and the organic film substrate 25 is placed on the substrate holder 39 so that the portion where the Si—O based amorphous thin film is deposited is in contact with the substrate holder 39.

Next, the substrate holder 26 and the substrate holder 3
Rotate and replace the position of 9 while swapping the top and bottom. That is, in this state, on the substrate holder 39, the back side of the organic film substrate 25, which has been hidden up to that point, is exposed and becomes a surface, and the portion that was the surface until then is hidden on the back side. Then, while introducing oxygen gas through the valve 24, the substrate heating device 41 heats it to 200 to 300 ° C. to decompose and remove the organic film substrate 25 into carbon dioxide and water. That is, after that, the Si-O-based thin film has F
The substance to which the e-based ultrafine particles are attached becomes a substrate and remains on the substrate holder 39.

Next, the substrate in which the Fe-based ultrafine particles are adhered to the Si-O-based thin film is conveyed to the vacuum device 16 and is etched by reverse sputtering to remove residual organic substances and eliminate the connection between the ultrafine particles. Then, it is conveyed to the vacuum device 17 via the vacuum device 18, and Si
Introducing H ₄ and N ₂ O gas to cause glow discharge and Si-
CVD deposition of an O-based amorphous thin film is performed.

By performing the above procedure on the above apparatus, a Si--O system amorphous thin film having a preferential bond between Si and oxygen has a diameter of 400 to 500Å and a length of 8
Columnar Fe with a very small particle size distribution of 00 to 1000Å
It becomes possible to fabricate a structure in which the ultrafine particles are aligned independently in the major axis direction so that they do not contact each other.

The form of the columnar metal ultrafine particles produced by the production apparatus and the production method as described above can be controlled by the substrate type, the substrate etching conditions and the sputtering deposition conditions. Furthermore, the ultrafine particles produced by such a manufacturing method include 1) an arbitrary shape,
It is characterized in that the size can be selected, 2) any metal or alloy composition can be selected, and 3) it can be easily compounded with different materials.

According to this embodiment, the thermoelectric material having high thermoelectric performance described in Embodiment 1 can be efficiently produced.

The target used for sputtering is not limited to Fe, but Cr, Mn, C may be used.
3d transition metals such as o and Ni, Fe-Si, Cr-Si,
It goes without saying that alloy materials such as Mn-Si and Co-Si can be used.

Further, in the source gas for CVD deposition, N ₂ O is used.
NO, CO or CO ₂ gas may be used instead of gas. Furthermore, without using oxygen-based gas, SiH
Similar effects can be obtained even if the amorphous Si: H thin film is prepared while diluting the ₄ gases alone with Ar gas or H ₂ gas.

[0049]

As described above, the thermoelectric material according to the present invention is
It has a structure in which ultrafine columnar metal particles exist independently in a thin film containing oxygen or hydrogen in Si so that their long axis directions are aligned and do not contact each other, so the Seebeck coefficient and electrical conductivity increase, and thermal conductivity increases. High thermoelectric performance with a reduced rate can be obtained.

Further, according to the method for producing a thermoelectric material of the present invention, all the steps can be performed in a vacuum without passing through a high temperature heat treatment step at 1000 ° C. or higher, so that association among ultrafine particles, particle growth, oxidation and A reaction such as nitriding can be avoided, moreover, a bond between Si and oxygen or hydrogen can be achieved more strongly, a bond between a metal or a metal-silicon alloy and oxygen or hydrogen can be avoided, and the particle size and amount of ultrafine particles can be improved. Can be controlled.

[Brief description of drawings]

FIG. 1 is a process drawing showing a part of the process of an embodiment of a method for producing a thermoelectric material of the present invention.

FIG. 2 is a process diagram of the embodiment, which is carried out subsequent to the process of FIG. 1 in the embodiment.

FIG. 3 is a sectional view of a thermoelectric material obtained in the same example.

FIG. 4 is a cross-sectional view showing the configuration of an embodiment of a thermoelectric material manufacturing apparatus of the present invention.

FIG. 5 is a vertical cross-sectional view showing the structure of a conventional thermoelectric material manufacturing apparatus.

[Explanation of Codes] 7,25 Organic Film Substrate 8 Minute Protrusions 10 Columnar Metal Ultrafine Particles 11, 12 Si-based Thin Film Containing Oxygen or Hydrogen 16, 17, 18 Vacuum Device 19, 20 Pre-evacuation Chamber 21, 22, 23, 24 valve 26, 39 substrate holder 27, 35 substrate transfer mechanism 28, 29, 36, 37 electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kuro Gyoten 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. A thermoelectric material having a structure in which ultrafine columnar metal particles are independently present in a Si-based thin film containing oxygen or hydrogen so that their long axis directions are aligned and do not contact each other. 2. A diameter of 400 to 500Å and a length of 800 to
The thermoelectric material according to claim 1, wherein the thermoelectric material is columnar metal ultrafine particles of 1000Å. 3. The thermoelectric material according to claim 1, wherein the Si-based thin film containing oxygen or hydrogen is amorphous. 4. The columnar metal ultrafine particles are Fe, Cr or M.
The thermoelectric material according to claim 1, which is a transition metal such as n or a transition metal-silicon alloy. 5. A step of producing fine projections on the surface of an organic film substrate in a vacuum apparatus, and a step of producing columnar metal ultrafine particles of metal or metal-silicon alloy on the fine projections of the organic film substrate. A step of forming a Si-based thin film containing oxygen or hydrogen on the columnar metal ultrafine particles, a step of removing the organic film substrate, and an etching on the surface of the thin film on the side where the organic film substrate is removed. A method of manufacturing a thermoelectric material, which comprises the steps of: performing, and a step of forming a Si-based thin film containing oxygen or hydrogen again on the etched surface. 6. A vacuum apparatus for etching and producing ultrafine particles capable of sputtering and reverse sputtering, and a vacuum apparatus for producing a Si-based thin film having a mechanism for producing Si molecules, ions or radicals having a bond with oxygen or hydrogen. And a vacuum device having a heating part and a mechanism part for switching the front and back of the substrate are connected, and the substrate transfer mechanism can move the substrate to the substrate holding part in each vacuum device without breaking the vacuum. Manufacturing equipment.