The present invention relates to a method for producing a metal oxide film and a metal oxide film and is applicable to a method for producing a metal oxide film for use in, for example, solar cells and electronic devices.
Techniques such as metal organic chemical vapor deposition (MOCVD) and sputtering that use a vacuum are employed as the method for depositing a metal oxide film for use in, for example, solar cells and electronic devices. The metal oxide films produced by those methods for producing a metal oxide film have excellent film properties.
For example, a transparent conductive film produced by the above-mentioned method for producing a metal oxide film has a low resistance and, if the produced transparent conductive film is heated, its resistance does not increase.
Patent Literature 1 is an example of the prior literatures regarding the deposition of a zinc oxide film by the MOCVD technique. Patent Literature 2 is an example of the prior literatures regarding the deposition of a zinc oxide film by the sputtering technique.
Unfortunately, the MODVD technique requires a high cost in addition to requiring the use of materials that are unstable in the air, which makes it less convenient. Also, a plurality of apparatuses are required in producing a metal oxide film having a laminated structure by sputtering, which unfortunately increases an apparatus cost. Therefore, a method for producing a metal oxide film, which is capable of producing a low-resistance metal oxide film at low cost, is desired.
The present invention therefore has an object to provide a method for producing a metal oxide film, which is capable of producing a low-resistance metal oxide film at low cost. The present invention has another object to provide a metal oxide film deposited by the method for producing a metal oxide film.
To achieve the above-mentioned objects, a method for producing metal oxide film according to the present invention includes the steps of: (A) spraying a solution containing an alkyl metal onto a substrate placed under non-vacuum; and (B) spraying a dopant solution containing a dopant including an inorganic compound onto the substrate in the step (A).
The method for producing metal oxide film according to the present invention includes the steps of: (A) spraying a solution containing an alkyl metal onto a substrate placed under non-vacuum; and (B) spraying a dopant solution containing a dopant including an inorganic compound onto the substrate in the step (A).
As described above, the method for producing metal oxide film according to the present invention performs the deposition process for a metal oxide film on a substrate under non-vacuum. This reduces the cost for the deposition process (deposition apparatus cost), which also improves convenience.
The method for producing a metal oxide film according to the present invention sprays a solution containing an alkyl metal onto the substrate, to thereby deposit a metal oxide film. Owing to high reactivity of the alkyl metal, the substrate merely needs a heat treatment at low temperature (not higher than 200° C.) and does not need a heat treatment at high temperature.
The method for producing a metal oxide film according to the present invention sprays, onto the substrate, a solution containing an alkyl metal and a dopant solution containing a dopant including an inorganic compound, to thereby deposit a metal oxide film on the substrate. Therefore, a supply of a dopant solution to the substrate can prevent the inclusion of an organic material in the metal oxide film due to the supply of the dopant solution, which allows reducing a resistance of the metal oxide film to be deposited.
The object, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the attached drawings.
A method for producing a metal oxide film according to the present invention performs a deposition process under non-vacuum (at atmospheric pressure). Herein, a metal oxide film deposited under non-vacuum (at atmospheric pressure) can have high resistance. The present invention therefore provides a method for producing a metal oxide film, which is capable of suppressing an increase in the resistance of a metal oxide film deposited under non-vacuum (at atmospheric pressure).
The inventors carried out the method for producing a metal oxide film as described below.
The inventors prepared a solution containing an alkyl metal and also prepared a doping solution containing an organic compound including indium (In). Additionally, they prepared water as an oxidation source. They used zinc (Zn) as a metal element constituting the alkyl metal. Then, the inventors formed the solution, doping solution, and water into mist, and sprayed the misted solutions onto a heated substrate.
As described above, a metal oxide film was deposited on a substrate using the doping solution containing an organic compound, and resultantly, metal oxide films (zinc oxide films) having physical properties as shown in the experimental results of
To reduce the resistance of the metal oxide film, a dopant (indium) was introduced into the metal oxide film. As shown in
To be more specific, for the metal oxide film deposited by the above-mentioned production method, the resistivity of the metal oxide film containing a dopant tends to be larger than the resistivity of an undoped metal oxide film (In/Zn=0%). Also, as shown in
In other words,
The inventors have considered various aspects, for example, an aspect that the film thickness of a metal oxide film to be deposited increases largely as the dopant concentration increases a little as shown in
The inventors have found that the resistance of a metal oxide film to be disposed increases even if the dopant concentration is increased by adopting a dopant solution containing an organic compound. The inventors have also found that when they adopt a dopant solution containing an inorganic compound, the dopant concentration is increased, which reduces the resistance of a metal oxide film to be deposited.
The present invention will be specifically described below with reference to the drawings showing an embodiment thereof
The method for producing a metal oxide film according to this embodiment will be specifically described with the use of a production apparatus (deposition apparatus) shown in
First, a solution 7 containing at least an alkyl metal is produced. Herein, zinc is used as a metal element contained in the solution 7. Also, an organic solvent such as ether or alcohol is used as a solvent of the solution 7. The produced solution 7 is filled into a container 3A as shown in
Water (H2O) is used as an oxidation source 6 and, as shown in
Also, a dopant solution 5 containing a dopant composed of an inorganic compound is produced. For example, a boric acid (H3BO3) solution is usable as the dopant solution 5 containing a dopant composed of an inorganic compound. The produced dopant solution 5 is filled into a container 3C as shown in
Next, the solution 5, the oxidation source 6, and the solution 7 are individually formed into mist. The container 3A is provided with an atomizer 4A on the bottom thereof, the container 3B is provided with an atomizer 4B on the bottom thereof, and the container 3C is provided with an atomizer 4C on the bottom thereof. The atomizer 4A forms the solution 7 in the container 3A into mist, the atomizer 4B forms the oxidation source 6 in the container 3B into mist, and the atomizer 4C forms the dopant solution 5 in the container 3C into mist.
The misted solution 7 passes through a path L1 to be supplied to a nozzle 8, the misted oxidation source 6 passes through a path L2 to be supplied to the nozzle 8, and the misted dopant solution 5 passes through a path L3 to be supplied to the nozzle 8. As shown in
As shown in
In this spraying, the substrate 1 is heated to, for example, about 200° C. by the heating unit 2.
The above-mentioned process deposits a metal oxide film (zinc oxide film being a transparent conductive film) having a predetermined film thickness on the substrate 1 placed under non-vacuum (at atmospheric pressure). As apparent from the above-mentioned process, in the present invention, the deposited metal oxide film not only contains zinc or the like but also contains a predetermined amount of dopant.
The above-mentioned method for producing a metal oxide film is used to form a plurality of metal oxide films by changing a molar concentration of a dopant (dopant contained in the dopant solution 5, which is boron in the description above) to be supplied to the substrate 1 as an inorganic compound with respect to a molar concentration of a metal element (metal element in the solution 7, which is zinc in the description above) to be supplied to the substrate 1 as an alkyl metal (hereinafter, a (dopant molar concentration)/(metal element molar concentration) is referred to as a molar concentration ratio). Then, the resistivity, film thickness, carrier concentration, and mobility of each metal oxide film were measured.
In the present invention, the molar concentration ratio is changeable by adjusting the carrier gas amount (liter/min) of the solution 7 to be supplied to the nozzle 8 (or the substrate 1), the molar concentration of zinc in the solution 7, the carrier gas amount (liter/min) of the dopant solution 5 to be supplied to the nozzle 8 (or the substrate 1), and the molar concentration of a dopant in the dopant solution 5.
The metal oxide films deposited and measured include a metal oxide film containing zinc that is undoped and a plurality of metal oxide films containing a dopant and zinc. Herein, the dopant is boron.
The plurality of metal oxide films containing a dopant and zinc include a metal oxide film having a B/Zn molar concentration of 0.16% when zinc and boron were supplied to the substrate 1, a metal oxide film having a B/Zn molar concentration of 0.32% when zinc and boron were supplied to the substrate 1, a metal oxide film having a B/Zn molar concentration of 0.4% when zinc and boron were supplied to the substrate 1, a metal oxide film having a B/Zn molar concentration of 1.0% when zinc and boron were supplied to the substrate 1, and a metal oxide film having a B/Zn molar concentration of 1.8% when zinc and boron were supplied to the substrate 1.
The deposition temperature for all the metal oxide films is 200° C. The metal oxide films were deposited in the deposition apparatus shown in
As shown in
As shown in
A dopant composed of an organic compound is dissolved in a dopant solution, an alkyl metal is dissolved in a solution, and the dopant solution and the solution are sprayed onto the substrate 1, to thereby deposit a metal oxide film on the substrate 1.
In this case, as shown in
Meanwhile, by employing the method for producing a metal oxide film according to the present invention, a dopant composed of an inorganic compound is dissolved in the dopant solution 5, an alkyl metal is dissolved in the solution 7, and the dopant solution 5 and the solution 7 are sprayed onto the substrate 1, to thereby deposit a metal oxide film on the substrate 1.
In this case, as shown in
To be specific, as shown in
The measurement results shown in
As shown in
Herein,
For the metal oxide film deposited by using a dopant composed of an organic compound, as shown in
The deposition conditions of the metal oxide films being measurement targets of
As described above, the method for producing a metal oxide film according to this embodiment performs the process of depositing a metal oxide film on the substrate 1 under non-vacuum. This reduces a cost for the deposition process (deposition apparatus cost) and also improves convenience.
The inventors have deposited metal oxide films using a solution containing a complex metal rather than an alkyl metal. In this case, the resistivity of the metal oxide film can be reduced even if a dopant composed of an organic compound is supplied to the substrate. However, due to high reactivity of the complex metal, the substrate 1 needs to be heated to a considerably high temperature in deposition.
Meanwhile, the method for producing a metal oxide film according to this embodiment sprays the solution 7 containing an alkyl metal onto the substrate 1, to thereby deposit a metal oxide film. The alkyl metal has high reactivity. Therefore, it suffices to perform a heat treatment at low temperature (not higher than 200° C.) on the substrate 1 in deposition, eliminating the need to perform a high-temperature heat treatment on the substrate 1.
The resistances of the metal oxide films, deposited by spraying a solution containing an alkyl metal and a dopant solution containing a dopant composed of an organic compound onto the substrate 1 placed under non-vacuum, tend to become higher as shown in the data of
The method for producing a metal oxide film according to this embodiment therefore sprays, onto the substrate 1 placed under non-vacuum, the solution 7 containing an alkyl metal and the dopant solution 5 containing a dopant composed of an inorganic compound, to thereby deposit a metal oxide film on the substrate 1.
The supply of the dopant solution 5 to the substrate 1 can prevent the inclusion of an organic matter in a metal oxide film due to the supply of the dopant solution 5, which allows reducing the resistance of a metal oxide film to be deposited. As described above, the method for producing a metal oxide film according to this embodiment can deposit a low-resistance metal oxide film through the low-temperature deposition process.
Differently from the deposition process under vacuum, the deposition process under non-vacuum (at atmospheric pressure) allows easy inclusion of an organic matter in a metal oxide film. The present invention including the step of spraying, onto the substrate 1, the dopant solution 5 containing a dopant composed of an inorganic compound is therefore more effective in the deposition process under non-vacuum (at atmospheric pressure).
Zinc has been illustrated as an alkyl metal to be dissolved in the solution 7. Alternatively, other metal elements may be used as long as they are alkyl metals, and cadmium (Cd) and magnesium (Mg) can be used.
The method for producing a metal oxide film according to this embodiment may use, as a dopant composed of an inorganic compound, boron phosphate (BPO4), boron tribromide (BBr3), gallium bromide (GaBr3), gallium chloride (GaCl3), gallium fluoride (GaF3), gallium iodide (GaI3), indium bromide (InBr3), indium chloride (InCl3), indium fluoride (InF3), indium hydroxide (In(OH)3), indium iodide (InI3), aluminum bromide (AlBr3), aluminum chloride (AlCl3), aluminum fluoride (AlF3), aluminum hydroxide (Al(OH)3), aluminum iodide (AlI3), and the like, in addition to boron described above.
The boron described above is used a dopant composed of an inorganic compound, leading to various effects described below.
Boron is a substance used stably and safely in the air, leading to more improved convenience. Boron is an inexpensive material, leading to a reduction in the producing cost for a metal oxide film. While the metal oxide film (in particular, a zinc oxide film or other film) is easily etched in a strong acid and a strong base, boron is a weak acid. Thus, even when boron is sprayed onto the substrate 1 as a dopant during deposition, a metal oxide film can be prevented from being etched during the deposition. The use of boron as a dopant composed of an inorganic compound prevents a situation in which the deposition of a metal oxide film on the substrate 1 is inhibited.
The resistivity of a metal oxide film can be reduced even when a solution containing a complex metal and a dopant solution containing boron are supplied to the substrate. However, as described above, the reactivity of the complex metal is low, and thus, the substrate needs to be heated to a sufficiently high temperature in deposition, which is contrary to a demand for a low-temperature process.
In the method for producing a metal oxide film according to this embodiment, during deposition, a molar concentration of a dopant (boron) composed of an inorganic compound to be supplied to the substrate 1 with respect to a molar concentration of an alkyl metal to be supplied to the substrate 1 is set to be smaller than 1.8%.
The molar concentration ratio is set to be smaller than 1.8% in a case where boron is used as a dopant composed of an inorganic compound, allowing for deposition of a metal oxide film that is doped and has a resistivity lower than the resistivity of the undoped metal oxide film as shown in
In a case where an organic solvent is used as the solvent of the solution 5, a dopant composed of an inorganic compound may be insoluble in the solution 5. Therefore, as shown in
In the present invention, the deposition process is performed under non-vacuum (at atmospheric pressure), allowing for the use of atmospheric oxygen as an oxidation source. Adoption of the configuration in which the oxidation source 6 is actively supplied to the substrate 1, as illustrated in
As shown in
Ozone, oxygen, and the like can be used as the oxidizing agent 6. However, ozone has strong reactivity and oxygen has weak reactivity. Therefore, water is adopted as the oxidizing source 6. This allows the oxidizing agent 6 having appropriate reactivity to be sprayed onto the substrate 1 at low cost.
The deposition apparatus illustrated in
For example, the following configurations are adoptable: the solution 7 and the oxidation source 6 are put in the same one of the containers and the dopant solution 5 is put in the other container; the dopant solution 5 and the oxidation source 6 are put in the same one of the containers and the solution 7 is put in the other container; and the solution 7 and the dopant solution 5 are put in the same one of the containers and the oxidation source 6 is put in the other container.
Whether a container is provided for each of the solutions 5, 6, and 7 or a container is used in common for two solutions can be selected depending on the types of the dopant solution 7, the oxidation source 6, and the solution 5 (as an example, depending on the dopant solubility and the reactivity of each of the solutions 5, 6, and 7). For example, boric acid is soluble in water, and thus, boric acid being the dopant solution 5 and water being the oxidation source 6 can be put in the same container. It is difficult to put the solution 5 containing an organic solvent and the dopant solution 5 containing a dopant composed of an inorganic compound in the same container. To prevent the reaction between the solution 7 and the oxidation source 6 at the place other than the substrate 1, it is not preferable to put the solution 7 and the oxidation source 6 in the same container.
If the molar concentration ratio needs to be adjusted, it is preferable to adopt the configuration in which the containers 3A, 3B, and 3C are provided for the solutions 5, 6, and 7, respectively, and the solutions 5, 6, and 7 are supplied to the substrate 1 through the different systems L1, L2, and L3. This is because the above-mentioned configuration can adjust the molar concentration most easily.
The present invention has been described in detail, but the above-mentioned description is illustrative in all aspects and the present invention is not intended to be limited thereto. Various modifications not exemplified are construed to be made without departing from the scope of the present invention.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2012/058156 | 3/28/2012 | WO | 00 | 9/4/2014 |