JP2015108168A - Production method of nanostructure thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a nanostructure thin film capable of forming nano-sized projections on a wide region in a high density.SOLUTION: In a production method of a nanostructure thin film for forming nano-sized projections by sputtering on a substrate, sputtering is performed in the state where a sputtering target is tilted and faced to the substrate, and an angle θ formed between a vertical axis of the substrate and a vertical axis of the sputtering target is 5-60°.

Description

The present invention relates to a method for producing a nanostructured thin film capable of forming nanosized protrusions in a wide area with high density.

In recent years, various types of solar cells such as silicon solar cells, dye-sensitized solar cells, and organic thin film solar cells have been studied. In these solar cells, as a method for obtaining high photoelectric conversion efficiency, a method of using a nanostructured thin film having a large surface area, in which a plurality of nanosize protrusions are formed on the surface, as an electrode has been studied.

Patent Document 1 describes a metal oxide film having a dense metal oxide layer (1) and a metal oxide layer (2) having a columnar structure on a substrate. A dye-sensitized solar cell having a structure in which an oxide film is used as an electrode, a dye is adsorbed on the electrode, and an electrolyte is sandwiched between the electrode and the counter electrode is also described. Patent Document 2 describes an indium tin oxide ITO solid electrode provided with a plurality of indium tin oxide ITO nanorods on the surface of a conductive layer. This indium tin oxide ITO solid electrode is used as an organic solar battery, dye sensitized. It is also described that it can be applied to organic photoelectric devices such as solar cells and organic light emitting diodes.

The nanostructure thin film described in Patent Document 1 or 2 has nano-sized protrusions formed by oblique deposition. Non-patent documents 1 to 4 also describe methods for forming nano-sized protrusions by oblique deposition. However, in the oblique deposition, the deposition direction of the deposited metal is likely to vary in the plane, the density of the nano-sized projections becomes non-uniform, and there are cases where the density of the nano-sized projections is low.

JP 2006-351355 A JP 2010-283313 A

Hoon Sik Jang et al. , “Field emission from cone-like single crystal indium tin oxide nanos”, Materials Letters, Volume 59, Issue 12, May 2005, 1526-1529. Richard Gaughan, “Low-Refractive-Index Nanolayer Layer Improved LED Extraction Efficiency”, Applied Physics Letters, Jan. 2,2006,013501. C. H. Chiu et al. , "Oblilectron-beam evolution of distinctive indium-tin-oxide nanostrands for enhanced light extraction from InGaN / GaN lightemitting." 17, Issue 23, 21250-21256 (2009). Yung-Chi Yao et al. , “Use of two-dimensional nanoarrays with slanted ITO film to enhance optical abstraction for photovoltaic applications, Optics Exp. 20, Issue 4, 3479-3489 (2012).

An object of this invention is to provide the manufacturing method of the nanostructure thin film which can form a nanosize protrusion in a high density | concentration in a wide area | region.

The present invention relates to a method for producing a nanostructured thin film that forms nano-sized protrusions on a substrate by sputtering, wherein sputtering is performed with a sputtering target inclined to the substrate, and the substrate is vertically This is a method for producing a nanostructured thin film, wherein the angle θ formed by the axis and the vertical axis of the sputtering target is 5 to 60 °.
The present invention is described in detail below.

The present inventor considered forming nano-sized protrusions on a substrate by sputtering instead of the conventional oblique deposition.
FIG. 3 schematically shows an example of a general sputtering method. As shown in FIG. 3, in a general sputtering method, sputtering is performed in a state where the sputtering target 4 attached to the target electrode 3 is opposed to the substrate 2 held by the substrate holder 1. Thereby, sputtered atoms 4 ′ made of the same material as the sputtering target 4 enter the surface of the substrate 2 and are deposited on the surface of the substrate 2. However, in such a general sputtering method, when a nanostructure thin film is manufactured instead of a flat thin film, it is difficult to form nano-sized protrusions at a high density in a wide region.
In contrast, in the method of manufacturing a nanostructured thin film in which nano-sized protrusions are formed on a substrate by sputtering, the present inventor performs sputtering in a state where the sputtering target is inclined to face the substrate at a specific angle. As a result, it was found that nano-sized protrusions can be formed in a wide area at a high density, and the present invention has been completed.

In the method for producing a nanostructured thin film of the present invention, nanosize protrusions are formed on a substrate by sputtering.
Although the said board | substrate is not specifically limited, It is preferable that it is transparent, for example, inorganic substrates, such as a glass substrate and a metal substrate, a plastic film, etc. are mentioned. As the plastic film, a PET film, a polyethylene naphthoate film, a polycarbonate film, a polyimide film, a cycloolefin resin film and the like are preferable.
The thickness of the substrate is not particularly limited, but the thickness of the inorganic substrate such as the glass substrate is preferably 50 μm to 10 mm, and the thickness of the plastic film is preferably 8 to 200 μm.

The sputtering apparatus used for the sputtering is not particularly limited, and may be a batch type sputtering apparatus or a roll-to-roll type sputtering apparatus.

By adjusting the sputtering conditions, a target nano-sized protrusion can be formed on the substrate.
Among these, it is preferable to perform sputtering without introducing oxygen gas, and it is more preferable to perform sputtering in an argon gas atmosphere. Note that sputtering without introducing oxygen gas may include at least a step of performing sputtering without introducing oxygen gas, and even if sputtering is performed by introducing oxygen gas before that step. Good. In the case of introducing oxygen gas, it is preferable to perform sputtering in a mixed gas atmosphere of argon gas and oxygen gas, and then perform sputtering in an argon gas atmosphere not containing oxygen gas.

In the sputtering, the temperature at which the substrate is heated (film formation temperature) is not particularly limited, but a preferable lower limit is 130 ° C. and a preferable upper limit is 500 ° C. By setting it as such film forming temperature, a nanosize protrusion can fully be formed.
Especially, when the said board | substrate is inorganic board | substrates, such as the said glass substrate, the minimum with preferable film forming temperature is 150 degreeC, and a more preferable minimum is 175 degreeC. By setting the film forming temperature to 175 ° C. or higher, it becomes easy to form nanosized protrusions having a target shape.
Further, since the plastic film is generally thin and has high thermal conductivity, when the substrate is the plastic film, a preferable lower limit of the film forming temperature is 130 ° C. By setting it as such film forming temperature, the said plastic film can be used as said board | substrate, and the obtained nanostructure thin film is suitably utilized also for a flexible thing among the electrodes of photoelectric devices, such as a solar cell. It will become a thing.

Sputtering target used in the sputtering is not particularly limited, for _example, SnO 2 3.0 to 50 wt% of the ITO target, and the like. With such a SnO ₂ content, it is possible to sufficiently form the nano-sized protrusions. Also, as the SnO ₂ content increases, the nano-sized protrusions become longer and the density increases, and the diameter of the sphere present at the tip of the cone tends to decrease. A more preferred lower limit of the SnO ₂ content is 5% by weight, a more preferred upper limit is 45% by weight, a still more preferred lower limit is 7% by weight, and a still more preferred upper limit is 35% by weight.

The sputtering method is not particularly limited, and may be DC sputtering or RF sputtering, or may be superimposed sputtering of DC sputtering and RF sputtering. The sputtering pressure, input power, and the like are not particularly limited. For example, a pressure of 0.666 Pa, input power of 300 W, or the like can be used.

In the method for producing a nanostructured thin film of the present invention, sputtering is performed with the sputtering target inclined and facing the substrate. Thereby, nanosize protrusions can be formed at a high density in a wide region.
The reason for this is not clear, but by tilting the sputtering target with respect to the substrate, 1) the energy of the target material reaching the substrate can be controlled, and 2) the substrate and the generated film are damaged by the argon plasma (reversely) This is presumed to be because the sputtering can be controlled. The energy reached to the substrate of the target material in 1) is considered to be involved in the formation of nano-sized protrusions, and the damage due to argon plasma in 2) is caused by the selective disappearance of the generated nano-sized protrusions by reverse sputtering. It is thought that it contributes to.

In FIG. 1, an example of the manufacturing method of the nano structure thin film of this invention is shown typically. As shown in FIG. 1, in the method for producing a nanostructured thin film of the present invention, sputtering is performed in a state where a sputtering target 4 attached to a target electrode 3 is inclined and opposed to a substrate 2 held by a substrate holder 1. Do. As a result, sputtered atoms 4 ′ made of the same material as the sputtering target 4 are incident on the surface of the substrate 2 and deposited on the surface of the substrate 2 to form nano-sized protrusions. Usually, sputtering is performed while rotating the substrate holder 1.
Although the substrate 2 is shown horizontally in FIG. 1, as long as the sputtering target 4 is inclined and opposed to the substrate 2, both the substrate 2 and the sputtering target 4 may be horizontal. It does not have to be horizontal.

In the method for producing a nanostructured thin film of the present invention, the lower limit of the angle θ (see FIG. 1) formed by the vertical axis of the substrate and the vertical axis of the sputtering target is 5 °, and the upper limit is 60 °. When the angle θ is less than 5 °, it becomes difficult to form nano-sized protrusions at a high density in a wide region. When the angle θ exceeds 60 °, a decrease in crystallinity during film formation and a delay in film formation rate are observed. In particular, when an ITO target is used, when the angle θ exceeds 60 °, the surface resistance tends to increase due to deterioration of the film quality. The preferable lower limit of the angle θ is 10 °, the preferable upper limit is 55 °, the more preferable lower limit is 15 °, and the more preferable upper limit is 45 °. By forming the film at an angle in such a preferable range, the density of the nano-sized protrusions can be increased.

In the method for producing a nanostructured thin film of the present invention, the obtained nanostructured thin film may be subjected to heating, plasma treatment or the like in order to enhance crystallinity.

According to the method for producing a nanostructured thin film of the present invention, nanosized protrusions can be formed in a wide area with a high density.
The nanosized protrusions are, 1 mm ² or more areas, preferably preferably formed 100 mm ² to 1 m ² things a large area in 1 mm ² per 1 × ¹⁰ 2 ~3 × ^{10 9} pieces of density. If density is less than 1 × 10 ² per 1 mm ^2, no difference between the thin film having no nanostructures, the effect of the nanostructure can not be obtained. When the density exceeds 3 × 10 ⁹ , there are too many nano-sized protrusions, and the density may become non-uniform. The more preferable lower limit of the density is 1 × 10 ⁴ per 1 mm ² , the more preferable upper limit is 5 × 10 ⁸ per 1 mm ² , the more preferable lower limit is 1 × 10 ⁵ per 1 mm ^{2, and the} more preferable upper limit is 1 mm ^2. 1 × 10 ⁸ pieces.

“The nano-sized protrusions are formed at a density of 1 × 10 ^{2 to} 3 × 10 ⁹ per 1 mm ^{2 in} a region of 1 mm ² or more” means an electron micrograph of the surface of the nanostructured thin film ( The average value of the density of the nano-sized protrusions calculated for any five or more locations over a region of 1 mm ² or more using a SEM image) is 1 × 10 ^{2 to} 3 × 10 ⁹ per 1 mm ^2. means.

In the nano-sized protrusion, a ratio H / W between a height H in a direction perpendicular to the substrate and a width W in a cross section in the horizontal direction with respect to the substrate is preferably 1 to 1000. It is preferable that nano-sized protrusions having substantially the same ratio H / W are formed at the same density at any location of the obtained nanostructured thin film. When the ratio H / W is less than 1, nanosized protrusions are not sufficiently formed, and the conduction performance of the obtained nanostructured thin film may be deteriorated. When the ratio H / W exceeds 1000, the nano-sized protrusions may be easily broken by physical force.

The shape of the nano-sized protrusion is not particularly limited, and examples thereof include a rod shape (conical shape, cylindrical shape), a hump shape, a quadrangular prism shape, a quadrangular pyramid shape, etc., but a rod shape is preferable, and a conical shape is more preferable. . As for these shapes, only a single shape may be present, or two or more shapes may be mixed.
The conical shape is preferably a conical shape having a height of 10 nm to 150 μm and a bottom surface diameter of 1 to 500 nm. In this case, it is more preferably a shape having a sphere having a diameter of 1 to 500 nm at the tip of the cone. As the quadrangular prism shape and / or the quadrangular pyramid shape, a quadrangular prism shape and / or a quadrangular pyramid shape having a height of 10 nm to 100 μm and a bottom side of 1 to 500 nm are preferable.
Moreover, the said nanosize protrusion may contain what has a branched structure. The branch structure may be a random structure, but a structure having branches branched in a direction of approximately 90 ° from a main trunk projecting portion extending from the substrate is preferable, and a tree-like structure having a large number of such branches ( A tree-like structure is more preferable. In the above-mentioned dendritic structure, it is more preferable that the main trunk protrusion and each branch form a cross shape.

The ratio H / W and shape of the nano-sized protrusion can be obtained from an electron micrograph (SEM image) obtained by observing the cross section or surface of the nanostructure thin film. The ratio H / W of nano-sized protrusions means an average value of 30 or more nano-sized protrusions.

The nanostructure thin film obtained by the method for producing a nanostructure thin film of the present invention may have an underlying conductive layer made of the same material as the nanosize protrusion between the substrate and the nanosize protrusion. Good. The thickness of such a base conductive layer is not particularly limited, but is preferably 5 nm to 100 μm.
In the conventional method for producing a nanostructured thin film, a base conductive layer is formed on a substrate by various conventional film forming methods, and then nano-sized protrusions are formed on the base conductive layer by oblique deposition (that is, The underlying conductive layer and the nano-sized protrusion were formed by different means). Therefore, it takes time to manufacture the nanostructured thin film, and in addition, protrusions that cannot be electrically connected to the underlying conductive layer may be formed, which causes a decrease in the conductive performance.
On the other hand, in the method for producing a nanostructured thin film of the present invention, since the base conductive layer and the nanosize protrusions made of the same material can be formed on the substrate in one step, the obtained nano The conduction performance of the structural thin film is improved. Note that “consisting of the same material” means that the constituent elements are the same. If the constituent elements are the same, the composition ratios of the constituent elements are not necessarily the same.

The material of the base conductive layer and the nanosize protrusion is not particularly limited as long as it has conductivity, but the base conductive layer and the nanosize protrusion preferably include at least indium, tin, and oxygen. Furthermore, it is preferable to contain nitrogen. Specific examples of the material for the base conductive layer and the nano-sized protrusion include tin oxide containing indium, tin oxide containing aluminum, tin oxide containing zinc, tin oxide containing gallium, and nitrogen. Examples thereof include tin oxide.

In the nanostructure thin film obtained by the method for producing a nanostructure thin film of the present invention, the base conductive layer may be directly formed on the substrate, but the surface of the substrate is subjected to surface treatment, A thin film layer may be formed between the substrate and the base conductive layer.
As said thin film layer, when the said board | substrate is the said plastic film, the thin film layer etc. which can improve the gas barrier property of this plastic film are mentioned, for example. The thin film layer is preferably transparent when the obtained nanostructure thin film is used as an electrode of a photoelectric device such as a solar cell. Specific examples of the thin film layer include metal oxide layers such as SiO ₂ and Al ₂ O ₃ , transparent resin layers made of acrylic, silicone, and the like.

In FIG. 2, an example of the nanostructure thin film obtained by the manufacturing method of the nanostructure thin film of this invention is shown typically. A nanostructure thin film 5 shown in FIG. 2 has a base conductive layer 7 formed on a substrate 6 and a nanosize protrusion 8 made of the same material as the base conductive layer 7 in contact with the base conductive layer 7.

The nanostructured thin film obtained by the method for producing a nanostructured thin film of the present invention has nanosized protrusions formed at a high density in a wide area, and therefore can be suitably used as an electrode of a photoelectric device such as a solar cell. It is. That is, for example, by using the nanostructure thin film obtained by the method for producing a nanostructure thin film of the present invention as an electrode, the photoelectric conversion efficiency of the solar cell can be increased. This is presumably because charge carriers are efficiently collected by increasing the electrode area and bringing the electrode closer to the charge generation portion.
As the photoelectric device, in addition to the solar battery, an LED, an organic EL, and the like can be given.
Furthermore, the nanostructured thin film obtained by the method for producing a nanostructured thin film of the present invention can be suitably used as a sensor electrode.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the nanostructure thin film which can form a nanosize protrusion in a wide area | region with high density can be provided.

It is the figure which showed typically an example of the manufacturing method of the nano structure thin film of this invention. It is sectional drawing which showed typically an example of the nanostructure thin film obtained by the manufacturing method of the nanostructure thin film of this invention. It is the figure which showed typically an example of the general sputtering method.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
A sputtering target SnO ₂ 7.0 wt% ITO target was attached to the target electrode of a DC magnetron sputtering apparatus, and a substrate (Corning glass # 1737 substrate, thickness 0.7 mm) was heated in an argon gas atmosphere to perform sputtering on the substrate. The nanostructure thin film which has a base conductive layer and a nanosize protrusion on a substrate was obtained.
At this time, the angle θ formed by the vertical axis of the substrate and the vertical axis of the sputtering target was 5 °. The argon pressure was 0.666 Pa, the film forming temperature was 300 ° C., the input power was 300 W, and the film forming time was 10 minutes.

(Examples 2 to 5)
A nanostructured thin film having a base conductive layer and a nanosize protrusion on the substrate was obtained in the same manner as in Example 1 except that the angle θ was changed as shown in Table 1.

(Comparative Example 1)
A thin film was obtained in the same manner as in Example 1 except that sputtering was performed with the sputtering target facing the substrate in parallel.

(Comparative Examples 2 and 3)
A thin film was obtained in the same manner as in Example 1 except that the angle θ was changed as shown in Table 1.

<Evaluation>
The following evaluation was performed about the nanostructure thin film obtained by the Example and the comparative example. The results are shown in Table 1.

(1) Observation of nano-sized protrusions Using the electron micrograph (SEM image) obtained by observing the surface of the nanostructured thin film, the density of the nano-sized protrusions calculated for any five or more locations over a region of 1 mm ² or more. The average value was obtained. Moreover, the ratio H / W and the shape of the nano-sized protrusion were obtained from an electron micrograph (SEM image). The thin films obtained in Comparative Examples 1 to 3 were flat thin films in which nano-sized protrusions were not sufficiently formed, and nano-sized protrusions having a ratio H / W of 1 or more were not obtained. all right.

(2) Conductivity performance The surface resistance (Ω / sq) of the nanostructure thin film obtained in the example was measured by a four-probe method using a resistivity meter (Loresta AX MCP-T370, manufactured by Mitsubishi Chemical Analytech). did. In addition, although the nanosize protrusion was not obtained, the surface resistance was measured also about the thin film obtained by Comparative Examples 1-3 for reference. In addition, if surface resistance is 100 ohm / sq or less, it can be considered that it can utilize suitably as an electrode of photoelectric devices, such as a solar cell.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the nanostructure thin film which can form a nanosize protrusion in a wide area | region with high density can be provided.

DESCRIPTION OF SYMBOLS 1 Substrate holder 2 Substrate 3 Target electrode 4 Sputtering target 4 'Sputtering atom 5 Nanostructure thin film 6 Substrate 7 Underlying conductive layer 8 Nanosize protrusion

Claims (3)

A method for producing a nanostructured thin film that forms nanosize protrusions on a substrate by sputtering,
Sputtering is performed with the sputtering target inclined and opposed to the substrate,
The method for producing a nanostructured thin film, wherein an angle θ formed by a vertical axis of the substrate and a vertical axis of the sputtering target is 5 to 60 °. 2. The method for producing a nanostructured thin film according to claim 1, wherein sputtering is performed without introducing oxygen gas. The method for producing a nanostructured thin film according to claim 1 or 2, wherein the sputtering target is an ITO target.

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