JP7076096B2 - Silicon-based thin film and its manufacturing method - Google Patents

Description

The present invention relates to a silicon-based thin film suitable for a thermoelectric conversion element and a method for producing the same.

A thermoelectric conversion element is known as an element capable of mutual conversion between thermal energy and electric energy. This thermoelectric conversion element is configured by using two types of thermoelectric conversion materials (thermoelectric materials), p-type and n-type, and these two types of thermoelectric materials are electrically connected in series and thermally in parallel. It is said to be arranged. In this thermoelectric conversion element, when a voltage is applied between both terminals, holes move and electrons move, and a temperature difference occurs between both sides (Perche effect). Further, in this thermoelectric conversion element, if a temperature difference is applied between both sides, holes and electrons also move, and an electromotive force is generated between both terminals (Zebeck effect).

For this reason, the thermoelectric conversion material is studied as an element for cooling the CPU, refrigerator, car air conditioner, etc. of a personal computer using the Pelche effect, and power generation using waste heat generated from a waste incinerator using the Seebeck effect. Studies are underway as an element for a device. In particular, since the amount of waste heat of an automobile engine is so large that it cannot be ignored, it is being considered to generate electricity by using the waste heat of the engine, and the temperature range is said to be several hundred degrees.

Conventionally, Bi ₂ Te ₃ has been mainly put into practical use as a thermoelectric material constituting a thermoelectric conversion element, and Se is generally added when forming, for example, an n-type thermoelectric material with a Bi-Te system material. To. However, since the elements Bi, Te and Se constituting these thermoelectric materials are highly toxic, there is a risk of environmental pollution. Therefore, a thermoelectric material having a low environmental load, that is, having no toxicity is desired. Further, the Bi-Te material is mainly used at about 100 ° C., and is not suitable for the use of waste heat of automobiles. Further, a lightweight and resource-rich material is desired for use in waste heat recovery of automobiles. Among them, silicon compounds are attracting attention as thermoelectric materials because they are abundant in resources and have low toxicity.

Among them, Mg ₂ Si is known as a high-performance n-type thermoelectric material for medium temperature (see, for example, Patent Document 1). Further, as another silicon compound, a material for a thermoelectric element using BaSi ₂ has been proposed (see, for example, Patent Document 2), but the thermoelectric characteristics such as Seebeck coefficient and thermal conductivity are clear only from the data on conductivity. As a general idea, the higher the conductivity, the smaller the Seebeck coefficient and the larger the thermal conductivity. Therefore, even if only the conductivity is simply controlled, high thermoelectric characteristics cannot be obtained. Further, a system in which silicide is used as a parent phase and silicon is added has been proposed (see, for example, Patent Document 3), but in such a structure, ZT is as low as about 0.4, which is not practical. A Ba—Si clathrate compound has also been proposed (see, for example, Patent Document 4), which is a Ba: Si = 4.6: 33.5 at% clathrate compound and is an n-type semiconductor. It has been shown to be present, but its properties are unknown and it cannot be determined whether it is useful. At present, it is not clear what kind of crystal phase, what kind of composition, and what kind of structure are useful for thermoelectric properties in Ba—Si materials.

Japanese Unexamined Patent Publication No. 2002-368291 JP-A-2015-160997 JP-A-2015-225951 Japanese Unexamined Patent Publication No. 2001-335309

An object of the present invention is to provide a novel silicon-based thin film suitable for a thermoelectric conversion element having high thermoelectric characteristics using silicon as a main raw material, and a method for efficiently producing the same.

In view of the above background, as a result of diligent studies, the present inventors have specified the composition of Ba—Si, the base crystal phase, and further made the structure a specific structure to obtain a high Seebeck coefficient. It has been found that a thermoelectric conversion element material having the above can be obtained, and the present invention has been completed.

That is, the aspects of the present invention are as follows.
(1) A polycrystalline thin film containing barium and silicon as constituent elements, which are composed of crystalline silicon particles and particles having a phase different from the crystalline silicon particles, and is characterized in that the crystal phase having the highest peak in X-ray diffraction is silicon. Silicon-based thin film.
(2) The thin film of (1) above, wherein the average crystal particle diameter of crystalline silicon particles is 3 nm or more and 1 μm or less.
(3) The thin film of (1) or (2) above, wherein the average particle diameter of particles having a phase different from that of crystalline silicon particles is 1 nm or more and 10 nm or less.
(4) The thin film according to any one of (1) to (3) above, wherein the particles having a phase different from that of crystalline silicon particles are amorphous.
(5) The thin film according to any one of (1) to (4) above, wherein the atomic ratios of barium and silicon constituting the thin film satisfy the following relationship when the respective contents are Ba and Si, respectively.
0.1 at% ≤ Ba / (Ba + Si) ≤ 12 at%
(6) The thin film according to any one of (1) to (5) above, wherein the amount of oxygen contained as a constituent element is 20 at% or less.
(7) The thin film according to any one of (1) to (6) above, wherein the oxygen concentration ratio of the particles having a different phase to the crystalline silicon particles satisfies the following relationship.
1 <oxygen (particles of different phases) / oxygen (crystalline silicon particles) ≤ 5
(8) In the method for producing a thin film according to any one of (1) to (7) above, a sputtering target having BaSi ₂ as a main crystal phase is used, the distance between the target and the substrate is 100 mm or more, and the temperature is 400 ° C. A manufacturing method characterized by forming a film at 700 ° C. or higher.
(9) The method for producing a thin film according to (8) above, wherein the heat treatment is performed at 350 ° C. or higher and 800 ° C. or lower in an inert gas atmosphere after the film is formed. (10) Any of the above (1) to (7). A thermoelectric conversion element that uses a thin film.

INDUSTRIAL APPLICABILITY According to the present invention, a thin film of a silicon-based material suitable for a thermoelectric conversion element having high thermoelectric characteristics using silicon as a main raw material, and a manufacturing method for efficiently manufacturing the thin film are provided.

It is a plot of the figure of merit-measurement temperature for the thin film obtained in Example 6. 6 is a TEM image of a surface cut in a direction parallel to the thin film substrate obtained in Example 3.

Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments.
The present invention is a polycrystalline thin film containing barium and silicon as constituent elements, in which crystalline silicon phase (hereinafter, also referred to as “main phase”) particles and a phase different from the particles (hereinafter, referred to as different phases) are used. It is in a thin film material composed of particles and characterized in that the highest peak crystal phase in X-ray diffraction is silicon.

The thin film here refers to a thin film having a thickness of 0.1 mm or less and having a self-supporting property, or a film formed on a substrate or a substrate without being self-supporting, and the thickness thereof is preferably uniform.
The highest peak here refers to the highest peak among the peaks caused by the thin film, excluding the peaks caused by the substrate or the substrate.

In considering a material having high thermoelectric conversion performance, it is extremely important to achieve both electric conductivity and low thermal conductivity while maintaining a high Seebeck coefficient. In order to realize this, the thin film of the present invention has barium and silicon in particular, but barium is a heavy element having an atomic weight of about 137, and the larger the atomic weight, the lower the transfer of phonon, which controls heat conduction, so that the thermal conductivity increases. Decrease. On the other hand, silicon is an element most often used in semiconductors, and it is relatively easy to impart conductivity by adding an element.

Silicon must be crystallized in order to exhibit high electrical conductivity. By crystallizing, it becomes possible to realize higher electric conductivity. Further, it is preferable that a dopant is contained in order to exhibit the electric conductivity, but it is preferable that barium is present in a specific amount in the silicon crystal in order to suppress the transmission of phonons and increase the electric conductivity. .. Further, the thin film is characterized by being a polycrystalline thin film. In a single crystal, it is difficult to intersperse different phases, and it is difficult to realize the characteristics required for a thermoelectric element.

The crystal phase of the thin film of the present invention can be confirmed by X-ray diffraction measurement. For example, collating the diffraction peak detected in the X-ray diffraction measurement using Cu as the radiation source (hereinafter referred to as XRD) with the card data of JCPDS (Joint Committee for Powder Diffraction Standards) corresponding to each crystal phase. It can be confirmed at.

Here, the fact that silicon is crystallized means that the diffraction peak caused by the silicon phase can be confirmed in the XRD pattern of the thin film, and the diffraction peak showing the maximum intensity in the diffraction peak group is the peak caused by the silicon phase. Indicates that there is. For example, when the crystal phase is identified by using the JCPDS card in the XRD measurement, for example, the card No. The diffraction peak at the (220) plane and the diffraction angle 47.313 ° in Si: 01-0772-2110 is defined as the diffraction peak of silicon.

Further, the present invention is characterized in that particles having a phase different from that of crystalline silicon are present. The separate phase is mainly required to inhibit heat conduction and needs to be a separate phase from silicon. In the present invention, as another phase, an amorphous body in which a halo is observed by XRD measurement, or a BaSi-based alloy such as BaSi ₂ or BaSi ₆ can be exemplified. The amorphous body may contain at least one of silicon and barium.

The average particle size of the silicon crystal is preferably 3 nm or more, and more preferably 5 nm or more. If it is smaller than 3 nm, the grain boundary portion is relatively large, the overall crystallinity is lowered, and as a result, the electrical conductivity is lowered. Further, the average particle diameter is preferably 1 μm or less, more preferably 100 nm or less, further preferably 50 nm or less, and most preferably 20 nm or less. By setting the average particle size as described above, it is possible to effectively show the effect of lowering the heat conduction by another phase, which is the second component, and it is possible to show a high value of the thermoelectromotive force.

The average particle size of the different phase is preferably 1 nm or more and 10 nm or less, more preferably 1 nm or more and 5 nm or less, and further preferably 2 nm or more and 4 nm or less. Within the above range, it is possible to suppress heat conduction low without inhibiting electrical conduction and to exhibit a high Seebeck coefficient.
Here, the average particle diameters of both the silicon crystal and the different phase represent the median, the so-called median diameter (D50). The particle size can be calculated by measurement in an image obtained by observation with an electron microscope.

The above-mentioned separate phase may be various phases other than the silicon crystalline phase, but is preferably amorphous. By making it amorphous, it is possible to suppress the thermal conductivity and maintain a high Seebeck coefficient.

The thin film of the present invention preferably has a Ba / (Ba + Si) of 0.1 at% or more when the atomic ratios of barium and silicon constituting the thin film are Ba and Si, respectively. 0.3 at% or more is more preferable, and 0.5 at% or more is more preferable.

By setting Ba / (Ba + Si) to 0.1 at% or more, barium can be solidified in crystalline silicon while another phase can be precipitated, which improves electrical conductivity and reduces thermal conductivity. It enables the improvement of the Seebeck coefficient. On the other hand, when Ba / (Ba + Si) is smaller than 0.1 at%, their effects are reduced.

On the other hand, Ba / (Ba + Si) is preferably 12 at% or less, more preferably 8 at% or less, further preferably 6 at% or less, and most preferably 4 at% or less.

When the Ba / (Ba + Si) is 12 at% or more, the ratio of another phase increases, the electrical conductivity decreases, and another crystal phase other than silicon is formed, so that a desired film structure cannot be obtained.

The thin film preferably has an oxygen content of 20 at% or less as a constituent element, and more preferably 15 at% or less. By doing so, highly crystalline silicon crystals can be maintained. The oxygen content is preferably 5 at% or more, more preferably 8 at% or more. By containing that much oxygen, it is possible to maintain crystallinity even if it becomes a microcrystal, and even in another phase, by containing a large amount of oxygen, the crystal collapses and becomes amorphous. It becomes possible to further inhibit heat conduction.

The thin film of the present invention has a structure in which Ba is segregated from the particles having a different phase with respect to the particles having a polycrystalline phase of silicon, and the Ba concentration ratio between the polycrystalline phase (main phase) of silicon and the different phase (Ba (different phase)). ) / Ba (main phase)) is more than 1, preferably 30 or less, more preferably 5 or more and 20 or less, and even more preferably 7 or more and 15 or less.

As described above, by allowing the minimum required amount of Ba to exist in the silicon polycrystalline layer and segregating Ba into another phase, it is possible to form a structure in which the other phase is easily oxidized. By intentionally using the other phase as an unstable Ba—Si—O phase as a crystal, it is possible to amorphize the phase and improve the crystallinity of the silicon crystal layer.

Further, in the thin film of the present invention, the oxygen concentration ratio (oxygen (different phase) / oxygen (main phase)) of the particles of another phase to the polycrystal phase particles of silicon is larger than 1 and 5 or less. It is preferably greater than 1 and more preferably 3 or less, and even more preferably greater than 1 and less than or equal to 2.

By differentiating the oxygen concentration as described above, it is possible to make the other phase amorphous and improve the thermoelectric characteristics while maintaining the crystallinity of silicon.

It is preferable that the intensity ratio of the highest peak to the second highest peak among the peaks of the polycrystalline phase of silicon is 5 or more. It is more preferably 10 or more, and even more preferably 20 or more. By doing so, it is possible to obtain a thin film having the same crystal orientation, and it is possible to improve the electrical conductivity. The peak intensity here was calculated by the following formula.
Peak intensity = (maximum peak value- (background mean value in the measurement range))

In the thin film of the present invention, it is preferable that the highest peak among the peaks of the polycrystalline phase of silicon is the (220) plane. In particular, by orienting the surface (220), it is possible to further improve the conductivity.

The thin film of the present invention is preferably formed on a substrate. The substrate may be a plate-shaped substrate or another complicated shape. The material of the substrate is not particularly limited, but a glass substrate, a sapphire substrate, a quartz substrate, a silicon substrate and the like are preferable.

The thickness of the thin film of the present invention is preferably 10 nm or more, more preferably 100 nm or more, still more preferably 500 nm or more. By doing so, the thermoelectric characteristics can be exhibited more. The thickness is preferably 500 μm or less, more preferably 10 μm or less, still more preferably 5 μm or less.

By satisfying the above structure, the thin film of the present invention exhibits an electric conductivity of 1 × 100 S / cm or more and ^{2 × 10 2 S} / cm or less, and exhibits high thermoelectric characteristics.
The output factor (power factor, PF) is expressed by the following formula, and shows a maximum of 0.05 × 10 ^-3 W / mK ² or more when changed from room temperature to 700 ° C. In the equation, S is the Seebeck coefficient and σ: is the electrical conductivity ((W / mK ² ).
PF = S ² × σ
Further, the figure of merit (ZT) is expressed by the following formula, and when the temperature is changed from room temperature to 700 ° C., a thin film showing good thermoelectric characteristics showing a maximum of 0.02 or more can be obtained. In the equation, S is the Seebeck coefficient, σ is the electrical conductivity ((W / mK ² )), and κ is the thermal conductivity (dimensionless).
ZT = S ² × σ / κ

Next, the method for producing the thin film of the present invention will be described. An example is shown here, but it is not always necessary to use that method.

There are various methods for producing the thin film of the present invention, such as a vapor deposition method and a coating method, and among them, it is preferable to form a film by using a sputtering method.
In order to obtain the thin film of the present invention, the film formation temperature is preferably 400 ° C. or higher and 700 ° C. or lower, more preferably 500 ° C. or higher and 650 ° C. or lower. By doing so, although crystallization occurs, since the crystal growth is small, it becomes possible to generate microcrystals of silicon. Further, by growing crystals at the time of film formation, it is possible to obtain a film having high orientation. By forming a film at a high temperature, the crystallinity of individual crystallites is improved and the electrical conductivity is improved. Furthermore, barium, which is an additive, tends to be stably present.

The thin film of the present invention is preferably heat-treated after film formation. By performing such a heat treatment, it becomes possible to segregate barium, which is an additive element, without changing the crystal particle size. The temperature of the heat treatment is preferably 350 ° C. or higher and 800 ° C. or lower, more preferably 450 ° C. or higher and 800 ° C. or lower, and further preferably 600 ° C. or higher and 800 ° C. or lower. By setting the temperature in the above range, it is possible to promote barium segregation and improve the crystallinity of silicon while keeping the particle size in a preferable range.
Since the heat treatment atmosphere does not allow excessive oxygen to be introduced, it is preferable to perform the heat treatment in an inert atmosphere, for example, in an inert gas (He, Ar, N ₂ , etc.) atmosphere containing 1 vol% or less of oxygen.

The target used in sputtering is not particularly limited, but a barium-silicon compound is preferable. By doing so, it becomes possible to obtain a film having a uniform composition. Although various barium-silicon compounds can be considered, it is preferable to use BaSi ₂ which is relatively stable.

Further, in sputtering, it is preferable to intentionally introduce oxygen. Therefore, oxygen may be used as the sputtering gas, but it is preferable that the sputtering target contains a certain amount of oxygen. The amount of oxygen is preferably 1 at% or more and 20 at% or less, more preferably 3 at% or more and 15 at% or less, and further preferably 10 at% or more and 14 at% or less.

Further, it is preferable that the angle between the target and the substrate is 50 ° to 70 °. By doing so, in the barium-silicon system, a film having a fine structure is likely to grow.
In the sputtering apparatus, the substrate may be installed at either the center of the pedestal or the end of the pedestal. Depending on the mounting position of the substrate with respect to the pedestal, the element scattering state at the time of spattering of BaSi changes, causing a difference in the Ba / Si ratio. Therefore, the substrate is preferably installed in the center of the pedestal.

The sputter gas pressure is preferably a low gas pressure, preferably 1.5 Pa or less, more preferably 0.5 Pa or less, still more preferably 0.3 Pa or less. By lowering the gas pressure, the energy of the sputtered particles can easily reach the substrate, and a film having higher crystallinity and orientation can be obtained. The gas pressure is preferably 0.05 Pa or more, more preferably 0.1 Pa or more. Within that range, stable discharge is possible.

The gas used in the sputtering is not particularly specified if it is an inert gas, but Ar, Ne, nitrogen and the like are preferable, and Ar is more preferable.
The discharge power is preferably 1 W / cm ² or more, more preferably 2 W / cm ² or more. By doing so, barium and silicon are stably sputtered, and a uniform film is formed. The upper limit is preferably 20 W / cm ² or less. By doing so, even if the strength of the target is low, it is possible to discharge without cracking.

The target used in sputtering is not particularly limited as long as it contains barium and silicon, but barium has unstable properties such as being easily oxidized in the atmosphere, so that it is preferably uniformly alloyed. Among them, Si / Ba preferably has an alloy phase of 2 or more, and particularly preferably has a BaSi ₂ peak in order to have a relatively strong oxidation resistance and a stable structure. At that time, the Si / Ba atomic weight ratio is preferably 1.9 or more and 2.1 or less.

When a BaSi ₂ target is used, the amount of Ba in the film increases with respect to the preferable content, and it becomes difficult to obtain a film having a desired structure. Therefore, a method of reducing Ba is required. Therefore, from the difference in atomic weight between Ba and Si (Ba: 137.33, Si: 28.09), the difference in energy at the time of atom emission by sputtering is used to prepare the thin film of the present invention in which the amount of Ba is adjusted. Is now possible.
For that purpose, it is necessary to adjust the distance between the target and the substrate. The distance is preferably 100 mm or more, more preferably 120 mm, still more preferably 150 mm or more. By increasing the distance between the target and the substrate, it becomes difficult for Ba to reach the substrate, and the amount of Ba can be adjusted.

Further, by adjusting the spatter gas pressure, the Ba amount can be further adjusted. This is because the lower the gas pressure, the less Ar is in the space, and the easier it is for Si to reach the substrate.

The ultimate vacuum in sputtering is preferably 1 × 10 ^-3 Pa or more and 1 × 10 ^-4 Pa or less. Within this range, oxygen appropriately remaining in the apparatus is introduced into the film, and it becomes possible to obtain a film having high thermoelectric characteristics.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

(Each metal composition and purity)
After cutting the thin film using FIB (focused ion beam processing observation device), the composition ratio is the total of barium and silicon using TEM (transmission electron microscope) -EDS (energy dispersion type X-ray spectroscope) from the cross-sectional direction. Calculated as the ratio of each element to the amount. The purity was defined as the ratio (at%) of the total amount of barium and silicon in the detected total metal elements.

For the local composition, after cutting the thin film in the direction parallel to the surface using FIB, the central part of the thin film is stripped by the ion milling method, and the crystalline silicon phase and another phase are separated by TEM using TEM-EDS. The particles were specified, and the composition ratio (at%) for each particle was calculated.
Barium amount = Ba / (Ba + Si)

(Oxygen content)
The amount of oxygen in the entire thin film was determined by RBS (Rutherford Backscattering Spectroscopy) measurement as a ratio (at%) to the total amount of oxygen, barium, and silicon in the alloy.
Oxygen amount = O / (O + Ba + Si)
The local oxygen content was measured by EDS as in the measurement of the metal composition.

The amount of oxygen in the sintered body was obtained by thermally decomposing the measured object, and the amount of oxygen was measured by the thermal conductivity method using an oxygen / nitrogen / hydrogen analyzer (manufactured by Leco), and the total of barium and silicon in the alloy was added. The ratio to the amount (at%) was used.

(Seebeck coefficient)
The object to be measured was processed into a required shape, and the Seebeck coefficient from room temperature to 700 ° C. was measured according to JIS R1650-1 using a thermoelectric characterization device (manufactured by ULVAC, Inc .: ZEM-3). The measurement atmosphere was carried out under reduced pressure He.

(Measurement of thermal conductivity)
Using a thermal conductivity measuring device for thin films manufactured by Pico Thermo (a thin film thermophysical property measuring device (PicoTR) by the picosecond thermoreflectance method), molybdenum of about 100 nm is formed on the surface layer as a reflective film, and then pulsed light heating thermoreflectance. The heat penetration in the cross-sectional direction of the thin film was measured by the surface heating / surface temperature measurement (FF) of the method. The obtained temperature history curve (phase signal) was fitted by simulation calculation, and the thermal conductivity of the target thin film and the interfacial thermal resistance between the layers were calculated. The specific heat capacity was assumed to be crystalline silicon, and the literature values were used.

(X-ray diffraction measurement)
A general powder X-ray diffractometer (device name: UltimaIII, manufactured by Rigaku Co., Ltd.) was used. The conditions for XRD measurement are as follows.

Radioactive source: CuKα ray (λ = 0.15418 nm)
Measurement mode: 2θ / θ scan Measurement interval: 0.01 °
Divergence slit: 0.5 deg
Scattering slit: 0.5 deg
Light receiving slit: 0.3 mm
Measurement time: 1.0 second Measurement range: 2θ = 20 ° to 80 °
The crystal phase to be identified was identified with reference to the JCPDS card below.
Si: 01-0772-2110
BaSi ₂ : 01-071-2327
BaSi ₆ : 01-079-5227

(Electrical conductivity)
The object to be measured was processed into a required shape, and the resistivity was measured from room temperature to 700 ° C. using a thermoelectric characterization device (manufactured by ULVAC, ZEM-3). The measurement atmosphere was carried out under reduced pressure He.
(Output factor, figure of merit)
The output factor and figure of merit are the output factor (PF) = S ² × σ (W / mK ² ) obtained by the following calculation.
(S: Seebeck coefficient (V / K) σ: electrical conductivity (S / cm))
Figure of merit (ZT) = S ² x σ x T / κ
(T: temperature (K) κ: thermal conductivity (W / mK))

(Average particle size)
For the local composition, after cutting the thin film in the direction parallel to the surface using FIB, the central part of the thin film is stripped by the ion milling method, and the properties are observed by TEM (transmission electron microscope), and the silicon polycrystalline phase. At least 50 or more particle diameters of different phases were measured, and the median value (D50) was calculated.

Examples 1-7
As the sputtering target, a 50 mmφBaSi ₂ target was used. The Ba / Si atomic weight ratio in the target was 1: 2.0. The amount of oxygen contained was 5 at%, and the purity was 98%.
The spatter conditions are as shown in Table 1. The substrate was not rotated. As a result, the physical characteristics of the thin film are as shown in Table 2, and a thin film showing desired characteristics was obtained. Table 3 shows the thermophysical properties of the obtained thin film.
The temperature dependence of ZT for the thin film obtained in Example 6 is shown in FIG. Further, FIG. 2 shows a TEM image in the direction parallel to the thin film substrate obtained in Example 3.

Comparative Examples 1-2
As the sputtering target, a 75 mmφBaSi ₂ target was used. The Ba / Si atomic weight ratio in the target was 1: 2.0. The amount of oxygen contained was 5 at%, and the purity was 98%.
The spatter conditions are as shown in Table 1. The substrate was not rotated.
As a result, the physical characteristics of the thin film are as shown in Table 2, and a thin film having desired characteristics could not be obtained.

Comparative Example 3
As the sputtering target, 50 mmφ polycrystalline silicon was used. The purity of silicon was 99,999%.
The spatter conditions are as shown in Table 1. The substrate was not rotated. As a result, the physical characteristics of the thin film are as shown in Table 2, and a thin film having desired characteristics could not be obtained.

The silicon-based thin film of the present invention can be suitably used as a thermoelectric conversion element.

Claims (9)

It is a polycrystalline thin film containing barium and silicon as constituent elements, and is composed of crystalline silicon particles and particles with a phase different from that. The crystal phase with the highest peak in X-ray diffraction is silicon , and crystalline silicon. A silicon-based thin film characterized in that the oxygen concentration ratio of the particles having different phases to the particles (oxygen (particles having different phases) / oxygen (crystalline silicon particles)) satisfies the following relationship .
1 <oxygen (particles of different phases) / oxygen (crystalline silicon particles) ≤ 5 The thin film according to claim 1, wherein the average particle size of the crystalline silicon particles is 3 nm or more and 1 μm or less. The thin film according to claim 1 or 2, wherein the average particle diameter of particles having a phase different from that of crystalline silicon particles is 1 nm or more and 10 nm or less. The thin film according to any one of claims 1 to 3, wherein the particles having a phase different from that of crystalline silicon particles are amorphous phases. The thin film according to any one of claims 1 to 4, wherein the atomic ratios of barium and silicon constituting the thin film satisfy the following relationship when the respective contents are Ba and Si, respectively.
0.1 at% ≤ Ba / (Ba + Si) ≤ 12 at% The thin film according to any one of claims 1 to 5, wherein the oxygen content contained as a constituent element is 20 at% or less. The method for producing a thin film according to any one of claims 1 to 6 .
A manufacturing method characterized by using a sputtering target having BaSi ₂ as a main crystal phase, setting the distance between the target and the substrate to 100 mm or more, and forming a film at 400 ° C. or higher and 700 ° C. or lower. The method for producing a thin film according to claim 7 , wherein the film is heat-treated at 350 ° C. or higher and 800 ° C. or lower in an inert gas atmosphere. A thermoelectric conversion element using the thin film according to any one of claims 1 to 6 .

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