Patent Application
20150171257
1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor film.
2. Description of the Related Art
A solar cell has advantages that the volume of carbon dioxide emissions per electric generation amount is small and it is not necessary to use fuel for electric generation. Therefore, the solar cell has been expected as an energy source to inhibit global warming. Among solar cells practically used, a mono-junction solar cell having a pair of p-n junction and employing a single crystal silicon or a polycrystalline silicon has become mainstream. However, the light absorption rate of the mono-junction solar cell is low, whereby the theoretical limit of the photoelectric conversion efficiency thereof is low. Therefore, studies related to solar cells capable of improving the light absorption rate and the theoretical limit of the photoelectric conversion efficiency have been actively conducted.
A compound thin film solar cell is one of the solar cells capable of improving the light absorption rate and the theoretical limit of the photoelectric conversion efficiency. The compound thin film solar cell saves resources, is easy to be mass produced, and has a possibility of largely improving the conversion efficiency. Recently, as a material for a buffer layer and a light emitting device for the compound thin film solar cell, Zn(1-x)MgxO (0<x<1. Hereinafter Zn(1-x)MgxO is sometimes referred to as “ZnMgO”.) has been focused on. ZnMgO is conventionally manufactured by means of a vapor phase deposition method employing a sputtering method and the like, and the band gap of ZnMgO has been increased by increasing adding amount of Mg. However, apparatuses for the vapor phase deposition method are expensive, and it is difficult to fully cover a substrate having concavity and convexity by means of the vapor phase deposition method, since raw materials flow to one direction. A liquid phase deposition method can solve these problems, thus it is considered that ZnMgO is desirably manufactured by the liquid phase deposition method.
As a technique related to a solar cell prepared with ZnMgO, for example Patent Document 1 discloses a manufacturing method of a solar cell including a step of forming a layer containing Zn, Mg, and O, by means of a sputtering method. Also, for example Non-Patent Document 1 discloses that ZnMgo thin film is manufactured by means of a sol-gel method.
In a case where ZnMgO is used for the compound thin film solar cell such as a CIGS solar cell, in order to have a configuration in which electrons can transfer to a p layer side in forming a p-n junction interface and a configuration in which electrons generated due to light absorption can transfer to an electrode, it is required to make the adding amount of Mg to Zn more than 20 mol % (make x as x>0.2). According to the technique disclosed in Patent Document 1, it can be considered that a ZnMgO film in which the adding amount of Mg to Zn is more than 20 mol % can be formed. However, since this technique employs a vapor phase disposition method to form the ZnMgO film, apparatuses to use are expensive and it is difficult to form a ZnMgO film which fully covers a substrate having concavity and convexity. These problems can be solved by the technique disclosed in Non-Patent Document 1 in which a ZnMgO film is formed by means of a liquid phase disposition method. However, if the ZnMgO film in which the adding amount of Mg to Zn is increased is tried to be formed by means of the conventional liquid phase disposition method as disclosed in Non-Patent Document 1, a phase-isolated MgO phase is easy to be formed together with a ZnMgO phase. Therefore, with the technique disclosed in Non-Patent Document 1, it is difficult to manufacture the ZnMgO film in which the adding amount of Mg to Zn is more than 20 mol %.
Accordingly, an object of the present invention is to provide a method for manufacturing a semiconductor film capable of manufacturing a ZnMgO film in which the adding amount of Mg to Zn is more than 20 mol %, by means of a liquid phase deposition method.
The inventors of the present invention have found out the following points as a result of an intensive study. The present invention has been made based on these findings.
(1) When the ZnMgO film is formed by means of the liquid phase disposition method, by making the ratio of Mg included in the raw materials (more specifically, when the amount of Zn in the raw materials is defined as X [mol] and the amount of Mg in the raw materials is defined as Y [mol], the value of Y/(X+Y). The same is applied hereinafter) large, the adding amount of Mg to Zn (hereinafter sometimes referred to as “Mg solid solution amount”) becomes easy to be increased.
(2) In an equilibrium state, the Mg solid solution amount to ZnO is kept around 4 mol %. Since the liquid phase disposition method is a process closer to the equilibrium state than the vapor phase disposition method, when the ZnMgO film is formed by means of the same method as the conventional liquid phase disposition method except that the ratio of Mg in the raw materials is increased, the maximum value of the adding amount of Mg to Zn is easy to be kept at 20 mol % or less.
(3) If the ZnMgO film is produced by means of the same method as the conventional method except that the ratio of Mg in the raw materials is increased, in order to make the adding amount of Mg to Zn more than 20 mol %, an MgO phase is easy to be formed together with a ZnMgO phase.
(4) In order to manufacture the ZnMgO film in which the adding amount of Mg to Zn is increased by means of the liquid phase disposition method, it is effective to introduce a non-equilibrium process.
(5) It is possible to inhibit the formation of an MgO phase (phase isolation of MgO) by: producing a precursor film including zinc hydroxide and magnesium hydroxide; thereafter rapidly heating to fire the precursor film so that the precursor goes through in a short time the temperature range in which the precursor film is cyristallized. Whereby, it is possible to manufacture the ZnMgO film in which the adding amount of Mg to Zn is increased more than 20 mol %.
In order to solve the above problems, the present invention takes the following means. That is, a first aspect of the present invention is a method for manufacturing a semiconductor film, the method including: a first step of preparing a mixed liquid including zinc hydroxide, magnesium hydroxide, and a liquid; a second step of applying the mixed liquid to a member to be film-deposited; and a third step of heating the member to be film-deposited to which the mixed liquid is applied, having a temperature range from 300° C. to 400° C. for 100/30 minutes or less.
In the first aspect of the present invention and other aspects of the present invention shown below, the precursor film including zinc hydroxide and magnesium hydroxide is applied to the member to be film-deposited which is to be heated in the third step after the second step. A producing method of the precursor film is not particularly limited as long as zinc hydroxide and magnesium hydroxide are dispersed in the precursor film. The precursor film can be produced by means of a liquid phase deposition method such as Chemical Bath Deposition (CBD) method and a sol-gel method for example. It is possible to inhibit a phase isolation of MgO by heating the precursor film having a temperature range from 300° C. to 400° C. which includes the temperature range in which the precursor film is crystallized for 100/30 minutes or less. As a result, it is possible to manufacture the ZnMgO film in which the adding amount of Mg to Zn is more than 20 mold.
Also, in the first aspect of the present invention, in the third step, it is preferable to heat the member to be film-deposited having a temperature range from 300° C. to 400° C. for 100/36 minutes or less. This configuration makes it possible to manufacture the ZnMgO film in which the adding amount of Mg to Zn is 30 mol % or more.
A second aspect of the preset invention is a method for manufacturing a semiconductor film, the method including: a first step of preparing a mixed liquid including zinc hydroxide, magnesium hydroxide, and a liquid; a second step of applying the mixed liquid to a member to be film-deposited; and a third step of heating the member to be film-deposited to which the mixed liquid is applied so that an average temperature rising rate from 300° C. to 400° C. is 30° C./min or more.
Here, “an average temperature rising rate from 300° C. to 400° C. is 30° C./min or more” means that, defining the time when the temperature of the precursor film is 300° C. as T1 and the time when the temperature of the precursor film is 400° C. as T2, the temperature rising rate from the time T1 to the time T2 is 30° C./min or more. For example, in a case where the required time for the temperature to reach from 300° C. to 400° C. is 10/3 minutes, the average temperature rising rate from 300° C. to 400° C. is 30° C./min. By heating the precursor film so that the average temperature rising rate from 300° C. to 400° C. including the temperature range in which the precursor film is crystallized is 30° C./min or more, it becomes possible to inhibit a phase isolation of MgO. As a result, it becomes possible to manufacture the ZnMgO film in which the adding amount of Mg to Zn is more than 20 mol %.
Also, in the second aspect of the present invention, in the third step, it is preferable to heat the member to be film-deposited to which the mixed liquid is applied so that the average temperature rising rate from 300° C. to 400° C. is 36° C./min or more. This configuration makes it possible to manufacture the ZnMgO film in which the adding amount of Mg to Zn is 30 mol % or more.
Also, in the first aspect or the second aspect of the present invention, it is preferable that the boiling temperature of the liquid is less than 300° C. This configuration makes it easy to manufacture the ZnMgO film in which the adding amount of Mg to Zn is more than 20 mol %.
Also, in the first aspect or the second aspect of the present invention, in the first step, determining the amount of Zn included in the raw material as X [mol] and the amount of Mg included in the raw material as Y [mol], it is preferable to produce the mixed liquid with a raw material satisfying Y/(X+Y)>0.4. This configuration makes it easy to manufacture the ZnMgO film in which the adding amount of Mg to Zn is more than 20 mol %.
According to the present invention, it is possible to provide a method for manufacturing a semiconductor film, capable of manufacturing a ZnMgO film in which the adding amount of Mg to Zn is more than 20 mol % by means of a liquid phase disposition method.
As shown in
The first step (hereinafter sometimes referred to as “S1”) is a step of preparing a mixed liquid including zinc hydroxide (Zn(OH)2)2), magnesium hydroxide (Mg(OH)2), and a liquid. The configuration of S1 is not particularly limited as long as the mixed liquid including Zn(OH)2, Mg(OH)2, and a liquid can be prepared. In a case where the precursor film to be heated in the third step which is described later is produced by means of a CBD method, S1 may be, for example, a step of: putting a Zn source and an Mg source in a container in which an ammonia aqueous solution is contained; thereafter increasing the temperature of the ammonia aqueous solution to a temperature at which Zn(OH)2 and Mg(OH)2 precipitate. By increasing the temperature of the ammonia aqueous solution, it becomes possible to lower the pH of the ammonia aqueous solution by vaporizing ammonia, whereby it becomes possible to change the state of the ammonia aqueous solution in which Zn(OH)2 precipitates. Also, by increasing the temperature of the ammonia aqueous solution, it becomes possible to change the state of the ammonia aqueous solution in which Mg(OH)2 precipitates.
The second step (hereinafter sometimes referred to as “S2”) is a step of applying the mixed liquid produced in S1 to the member to be film-deposited. S2 can be a step of putting the member to be film-deposited (hereinafter sometimes referred to as “substrate”) in a container which contains the mixed liquid produced in S1 and holding the substrate for a predetermined time, to thereby apply the mixed liquid to the substrate. After applying the mixed liquid to the substrate in S2, taking out the substrate (the substrate with precipitated Zn(OH)2 and precipitated Mg(OH)2 on the surface thereof) from the container containing the mixed liquid, followed by drying, a precursor film including dispersed Zn(OH)2 and Mg(OH)2 can be produced on the surface of the substrate.
The third step (hereinafter sometimes referred to as “S3”) is a step of heating the precursor film having a temperature range from 300° C. to 400° C. which includes the temperature range in which Zn(OH)2 and Mg(OH)2 included in the precursor film produced by going through the above steps are crystallized, for 100/30 minutes or less. In other words, S3 is a step of heating the precursor film so that the average temperature rising rate from 300° C. to 400° C. is 30° C./min or more. By heating the precursor film with this configuration, as shown in
The firing step (hereinafter sometimes referred to as “S4”) is a step of firing the precursor film rapidly heated in S3 at a predetermined temperature. The firing temperature in S4 is not particularly limited as long as the temperature is higher than the maximum temperature of the temperature range in which Zn(OH)2 and Mg(OH)2 are crystallized. The firing time in S4 is not particularly limited as long as a crystallized ZnMgO film can be produced. For example, S4 can be a step of firing the precursor film at 500° C. for 1 hour.
According to the manufacturing method of the present invention including S1 to S3, since it is possible to inhibit a phase isolation of MgO by introducing a non-equilibrium process in S3, it is possible to manufacture the ZnMgO film in which the adding amount of Mg to Zn is more than 20 mol %.
In the manufacturing method of the present invention, the configuration of Zn source and Mg source contained in the raw material employed for producing the precursor film is not particularly limited. As the Zn source and Mg source, for example, acetates thereof, chlorides, nitrates, hydrosulfates and the like can be adequately employed.
Also, in the manufacturing method of the present invention, the liquid to be employed for producing the mixed liquid is not particularly limited as long as the ZnMgO film in which the adding amount of Mg to Zn is more than 20 mol % can be manufactured. However, in view of having a configuration in which the ZnMgO film as above is easy to be manufactured, preferably the liquid has a boiling temperature of less than 300° C.
Also, in the manufacturing method of the present invention, the compounding ratio of the Zn source and the Mg source contained in the raw material employed for producing the mixed liquid in S1 is not particularly limited. However, in view of having a configuration in which the ZnMgO in which the adding amount of Mg to Zn is more than 20 mol % is easy to be manufactured, defining Zn contained in the raw material as X [mol] and Mg contained in the raw material as Y [mol], preferably Y/(X+Y)>0.4.
Also, in the manufacturing method of the present invention, S3 is not limited as long as S3 is a step of heating the precursor film having a temperature range from 300° C. to 400° C. for 100/30 minutes or less (heating the film so that the average temperature rising rate is 30° C./min or more). However, in view of having a configuration in which the ZnMgO film in which the adding amount of Mg to Zn is 30 mol % or more is easy to be manufactured, it is preferable that S3 is a step of heating the precursor film having a temperature range from 300° C. to 400° C. for 100/36 minutes or less (heating the film so that the average temperature rising rate is 36° C./min or more).
Also, in the manufacturing method of the present invention, the substrate employed in S2 is not particularly limited as long as the substrate is capable of bearing the firing temperature in S4 and capable of forming a ZnMgO film on the surface thereof. As the substance which can configure the substrate, a quarts glass, stainless steel substrate, soda lime glass substrate and the like can be exemplified.
Also, in the manufacturing method of the present invention, the temperature of the ammonia aqueous solution to be increased in S1 is not particularly limited as long as Zn(OH)2 and Mg(OH)2 can be precipitated at the temperature. In order to precipitate Zn(OH)2 and Mg(OH)2, the temperature of the ammonia aqueous solution is preferably 30° C. or more for example. Also, in view of having a configuration in which a large variation in ion concentration and depletion of the solution can be prevented, the temperature of the ammonia aqueous solution is preferably 80° C. or less for example. The temperature of the ammonia aqueous solution is more preferably 40° C. or more and 60° C. or less.
Also, the configuration of S1 is not particularly limited as long as the mixed liquid containing Zn(OH)2, Mg(OH)2, and a liquid can be prepared. However, in view of having a configuration in which Zn(OH)2 and Mg(OH)2 are easy to be precipitated and the like, it is preferable to have a configuration in which the temperature of the stirred ammonia aqueous solution is increased so that Zn(OH)2 and Mg(OH)2 precipitate.
Water in an amount of 175 ml and 25 ml of 10% ammonia aqueous solution were put in a beaker. On the other hand, a Zn source (zinc acetate) and an Mg source (magnesium acetate) were weighed so that the molar ratio of zinc acetate and magnesium acetate was 1:1, and put in the beaker. Thereafter, a rotor was put in the beaker and the contents of the beaker were stirred well on a stirrer, whereby zinc acetate and magnesium acetate were dissolved. After zinc acetate and magnesium acetated were dissolved, a quarts glass substrate was put in the beaker. Then, while stirring the ammonia aqueous solution, the beaker was bathed in a water bath heated at 60° C. and allowed to left for 30 minutes. Thereafter, the quarts glass substrate was taken out and dried at 200° C. for 1 hour, whereby a precursor film was produced by means of a CBD method. Next, the produced precursor film was rapidly heated so that the average temperature rising rate from 300° C. to 400° C. was 4° C./min, 16° C./min, 30° C./min, 36° C./min, 50° C./min, or 60° C./min, thereafter fired at 500° C. for 1 hour. Controlling of the average temperature rising rate was carried out by controlling the temperature of the substrate. More specifically, setting the substrate temperature at the start of the heating up as 200° C. and the substrate temperature at the end of the heating up as 500° C., and by changing the required time for the substrate temperature to reach 500° C. from 200° C., the average temperature rising rate from 300° C. to 400° C. was controlled to be 4° C./min, 16° C./min, 30° C./min, 36° C./min, 50° C./min, or 60° C./min. By going through the above steps, a ZnMgO film was manufactured. The manufactured ZnMgO film was thereafter cooled in a furnace and taken out for evaluation.
<Film Evaluation>
The band gap of the produced film was identified by measuring light absorption coefficient by means of an ultraviolet visible light spectrophotometer (V-570, manufactured by JASCO Corporation). Results are shown in
Mg solid solution amount[mol %]=(band gap−3.2)/0.024 (1)
Also, X-diffraction measurement was carried out by means of an X-ray diffraction apparatus (Smart-Lab, manufactured by Rigaku Corporation). Results are shown in
<Results>
As shown in
Also, as shown in
[Effect Evaluation of Raw Material Compounding Ratio]
Water in an amount of 175 ml and 25 ml of 10% ammonia aqueous solution were put in a beaker. On the other hand, a Zn source (zinc acetate) and an Mg source (magnesium acetate) were weighed so that molar ratios of zinc acetate and magnesium acetate were 9:1, 8:2, 7:3, 6:4, and 1:1. They were put in separate beakers. Then, a rotator was put in each beaker and the contents of the beaker was stirred well on a stirrer to dissolve zinc acetate and magnesium acetate. After dissolving zinc acetate and magnesium acetate, a quarts glass substrate was put in the beaker. Then, while stirring the ammonia aqueous solution, the beaker was bathed in a water bath heated at 60° C. and allowed to left for 30 minutes. Thereafter, the quarts glass substrate was taken out and dried at 200° C. for 1 hour, whereby a precursor film was produced by means of a CBD method. Next, to the produced precursor film, a conventional heating or a rapid heating was carried out, thereafter the film was fired at 500° C. for 1 hour whereby a ZnMgO film was produced. The conventional heating was a heating in which the average temperature rising rate in the temperature range from 300° C. to 400° C. was 4° C./min and the rapid heating was a heating in which the average temperature rising rate in the temperature range from 300° C. to 400° C. was 30° C./min, 36° C./min, 50° C./min, or 60° C./min. The ZnMgO film produced by going through the above steps was cooled in a furnace and taken out for evaluation.
<Film Evaluation>
The band gap of the produced film was identified by measuring light absorption coefficient by means of an ultraviolet visible light spectrophotometer (V-570, manufactured by JASCO Corporation). The solid solution amount of Mg was obtained by the following Formula (1). Results are shown in
As shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-147030 | Jun 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/060905 | 4/11/2013 | WO | 00 |
