Patent Application
20090203194
The present invention relates to film deposition apparatus and a method of film formation for continuously forming a transparent conductive film having a multilayer structure by the MOCVD method.
The sputtering method and the metal-organic chemical vapor deposition (MOCVD) method are used in the step of forming a transparent conductive film among solar cell production steps. Reactions in the MOCVD method proceed at low temperatures (200° C. or lower) and it is a chemical vapor deposition method. Because of these, the MOCVD method is a mild film deposition technique which causes no mechanical damage to other thin constituent layers unlike the techniques in which the bombardment of energy particles damages underlying thin constituent layers, such as the sputtering method.
In producing a CIGS type thin-film solar cell, a transparent conductive film is formed over thin constituent layers on the light incidence side thereof. The transparent conductive film formed by the MOCVD method has the function of enhancing the effect (function) of the buffer layer. In the case of the sputtering method, however, the transparent conductive film is known to cause damage to the buffer layer, rather than enhances its effect, and to reduce the performances of the solar cell.
Techniques for forming a transparent conductive film by the MOCVD method have been disclosed (see, for example, patent documents 1 and 2). The techniques disclosed therein comprise heating a substrate on a heated support, evacuating the chamber and allowing the substrate to stand therein for about 20 minutes to make the temperature thereof even, and then conducting film deposition for about 30 minutes by the MOCVD method to thereby deposit a transparent conductive film in about 1 μm. An MOCVD-method film deposition apparatus is described in patent document 3. It has a constitution in which gases are introduced into a quartz reaction tube through a gas introduction opening and gases in the reaction tube are discharged through a gas discharge opening. This reaction tube has a susceptor made of carbon disposed therein, and a substrate is set on this susceptor. This apparatus has a structure in which the susceptor and the substrate are inductively heated with a high-frequency coil disposed outside the reaction tube. In this film deposition apparatus, an alkylaluminum is mainly used as an organometallic compound to be applied to the substrate. This MOCVD-method film deposition apparatus is not one for continuously forming a transparent conductive film having a multilayer structure, and has had a problem that it cannot form a transparent conductive film having a large area. On the other hand, an apparatus for the continuous formation of a thin semiconductor film has been disclosed in which two or more reaction chambers are disposed and film deposition is successively conducted therein (see, for example, patent document 4). However, this apparatus for continuous film deposition is not one for forming a transparent conductive film by the MOCVD method but one for forming a thin semiconductor film. There has been a problem that it is difficult to directly divert such an apparatus for continuously forming a thin semiconductor film to the continuous formation of a transparent conductive film by the MOCVD method.
Patent Document 4: Japanese patent No. 2842551
Furthermore, the related-art MOCVD-method film deposition apparatus include an MOCVD-method film deposition apparatus for an alkylzinc such as that shown in
This apparatus is an apparatus for the batch treatment of substrates. First, the chamber is opened in the air in order to introduce a substrate (hereinafter, a structure comprising a substrate and layers necessary for a CIGS type thin-film solar cell other than a transparent conductive film, which include a light absorption layer and a buffer layer, formed thereon is referred to as substrate). After a substrate is placed on the hot plate, the chamber is brought into a vacuum state. After the substrate has been heated to a set temperature, raw materials (e.g., an organometallic compound, e.g., diethylzinc Zn(C2H5)2, diborane B2H6, and pure water H2O) are introduced through raw-material introduction ports. A carrier gas is used to spray these raw materials over the substrate through nozzles respectively corresponding to the raw materials. A transparent conductive film is deposited on the substrate over a certain time period (in a certain thickness) Thereafter, the feeding of the raw materials is stopped. The chamber is then opened in the air (the internal pressure is returned to atmospheric pressure) and the substrate is taken out. Since the process is a batch treatment, a next substrate is thereafter placed on the hot plate. Subsequently, the same operation as described above is repeated to thereby form a transparent conductive film on the substrate. This apparatus has had the following features 1 to 3.
1. A feature of the nozzles resides in the structure which evenly sprays the organometallic compound, diborane, and pure water in a vacuum, as shown in
2. Because a substrate is directly placed on a metallic hot plate in growing a transparent conductive film, the heat distribution of the hot plate directly leads to the distribution of the transparent conductive film. There has hence been a problem that in case where the hot plate has an uneven heat distribution, a transparent conductive film which is uneven in sheet resistance, etc. is formed.
3. The apparatus has only one chamber. There has hence been a problem that the rate of substrate treatment is low and the rate of film deposition is low.
A first object of the invention, which is for eliminating the problems described above, is to improve the efficiency of utilization of raw materials and to reduce the necessity of maintenance. A second object is to form a transparent conductive film having an even sheet resistance. A third object is to improve the rate of film deposition while maintaining high film quality.
(1) The invention, which is for eliminating the problems described above, provides a transparent-conductive-film deposition apparatus having a film deposition chamber, wherein after the chamber is evacuated, an organometallic compound (alkylzinc Zn(CnH2n+1; n is an integer)2; preferably diethylzinc Zn(C2H5)2), diborane (B2H6), and water (water vapor) are reacted in a vapor phase while heating a substrate to form a transparent conductive film comprising an n-type semiconductor on the substrate by the metal-organic chemical vapor deposition (MOCVD) method, wherein
diborane and an inert gas are used as a dopant for conductivity regulation and a carrier gas, respectively, and the organometallic compound and pure water are used as raw materials for film deposition, and the apparatus is equipped inside with a group of nozzles of a planar structure comprising pipe-form nozzles which have ejection holes formed on the ejection side thereof for simultaneously or separately spraying the three raw materials consisting of the organometallic compound, diborane, and pure water and are arranged adjacently to each other in the same plane without leaving a space between these, and is further equipped with a nozzle-cooling mechanism which cools the group of nozzles.
(2) The invention provides a in-line type film deposition apparatus for the continuous formation of a multilayered transparent conductive film, which comprises a substrate attachment part where a substrate is attached to a setter in the air, a charging part where evacuation is conducted, a multilayer deposition treatment part comprising two or more deposition treatment parts for forming a multilayered transparent conductive film comprising an n-type semiconductor on the substrate by the metal-organic chemical vapor deposition (MOCVD) method by reacting an organometallic compound (alkylzinc Zn(CnH2+1; n is an integer)2; preferably diethylzinc Zn(C2H5)2), diborane (B2H6), and water (water vapor) in a vapor phase while heating the substrate, a takeout part where the substrate having the multilayered transparent conductive film in a vacuum is returned to the atmospheric pressure, a substrate detachment part where the substrate having the multilayered transparent conductive film is detached from the setter, and a setter return part where the setter from which the substrate having the multilayered transparent conductive film was detached in the substrate detachment part is returned to the substrate attachment part, and in which film deposition is successively conducted while moving the substrate sequentially through the parts to form the multilayered transparent conductive film comprising a multilayered n-type semiconductor on the substrate, wherein
in each deposition treatment part in the multilayer deposition treatment part, diborane and an inert gas are used as a dopant for conductivity regulation and a carrier gas, respectively, and the organometallic compound and pure water are used as raw materials for film deposition, and the deposition treatment part is equipped inside with a group of nozzles of a planar structure comprising pipe-form nozzles which have ejection holes formed on the ejection side thereof for simultaneously or separately spraying the three raw materials consisting of the organometallic compound, diborane, and pure water and are arranged adjacently to each other in the same plane without leaving a space between these, and is further equipped with a nozzle-cooling mechanism which cools the group of nozzles.
(3) The invention provides the film deposition apparatus for the continuous formation of a multilayered transparent conductive film as described under (2) above, wherein the charging part and the takeout part are equipped with a preheating mechanism and a substrate-cooling mechanism, respectively, whereby a multilayered film having a necessary thickness is formed by two or more deposition treatment parts at an improved film deposition rate.
(4) The invention provides the film deposition apparatus for the continuous formation of a multilayered transparent conductive film as described under (1), (2), or (3) above, wherein the nozzle-cooling mechanism comprises cooling pipes each disposed between nozzles of the group of nozzles without leaving a space between these.
(5) The invention provides the film deposition apparatus for the continuous formation of a multilayered transparent conductive film as described under (1), (2), or (3) above, wherein the nozzle-cooling mechanism comprises either a group of cooling pipes arranged adjacently to each other or a platy cooler, wherein the group of cooling pipes or the platy cooler is disposed on the group of nozzles of a planar structure on the side (back side) opposite to the ejection side.
(6) The invention provides the film deposition apparatus for the continuous formation of a multilayered transparent conductive film as described under (2) above, wherein the setter is a production jig for fixing the substrate and conveying it through each part in the film deposition apparatus and is made of a member having high thermal conductivity (e.g., carbon composite) whose surface is coated with a metallic coating having high thermal conductivity and high mechanical strength (e.g., nickel deposit), wherein the setter has a pin for substrate fixing.
(7) The invention provides an in-line type film deposition method for the continuous formation of a multilayered transparent conducting film comprising a multilayered n-type semiconductor on a substrate, the method comprising: a step in which a substrate is attached to a setter in the air; a step in which the substrate attached to the setter is evacuated; a step in which film deposition by the metal-organic chemical vapor deposition (MOCVD) method comprising reacting an organometallic compound (alkylzinc Zn(CnH2n+1; n is an integer)2; preferably diethylzinc Zn(C2H5)2), diborane (B2H6), and water (water vapor) in a vapor phase while heating the substrate is repeatedly conducted two or more times to form a multilayered transparent conductive film comprising an n-type semiconductor on the substrate; a step in which the substrate having the multilayered transparent conductive film in a vacuum is returned to the atmospheric pressure; a step in which the substrate having the multilayered transparent conductive film is detached from the setter; and a step in which the setter from which the substrate having the multilayered transparent conductive film was detached is returned to the substrate attachment part.
(8) The invention provides the film deposition method for the continuous formation of a multilayered transparent conductive film as described under (7) above, wherein in the step in which a multilayered transparent conductive film is formed, diborane and an inert gas are used as a dopant for conductivity regulation and a carrier gas, respectively, and the organometallic compound and pure water are used as raw materials for film deposition, and the apparatus is equipped inside with a group of nozzles of a planar structure comprising pipe-form nozzles which have ejection holes formed on the ejection side thereof for simultaneously or separately spraying the three raw materials consisting of the organometallic compound, diborane, and pure water and are arranged adjacently to each other in the same plane without leaving a space between these, and is further equipped with a nozzle-cooling mechanism which cools the group of nozzles.
In the invention, each deposition treatment part in the multilayer deposition treatment part is equipped inside with a group of nozzles of a planar structure comprising pipe-form nozzles which have ejection holes formed on the ejection side thereof for simultaneously or separately spraying the three raw materials consisting of the organometallic compound, diborane, and pure water and are arranged adjacently to each other in the same plane without leaving a space between these, and is further equipped with a nozzle-cooling mechanism which cools the group of nozzles. Because of this constitution, the group of nozzles have a one-plate structure having no space between the nozzles. As a result, a reaction product can be prevented from accumulating on the nozzles and the efficiency of utilization of raw materials can be improved. Furthermore, the prevention of reaction product accumulation on the nozzles can further reduce the necessity of maintenance.
In the invention, the setter may be made of a member having high thermal conductivity (carbon composite) whose surface is coated with a metallic coating having high thermal conductivity and high mechanical strength (e.g., nickel deposit) This constitution enables an even transparent conductive film to be formed. Furthermore, by disposing pins for substrate fixing on the setter, a substrate having any desired size can be treated.
In the invention, the charging part and the takeout part may be equipped with a preheating mechanism and a substrate-cooling mechanism, respectively. These mechanisms, in combination with the two or more deposition treatment parts, enable a multilayered film to be formed at an improved film deposition rate without deteriorating film quality.
The invention provides a film deposition apparatus for continuously forming a multilayered transparent conductive film comprising a multilayered n-type semiconductor on a substrate and a method of the formation thereof. As shown in
In each of the deposition treatment parts 41 . . . 4n in the multilayer deposition treatment part 4 shown in
The main reactions are the following 1 and 2.
Zn(C2H5)2+2H2O→Zn(OH)2+2C2H6 1
Zn(OH)2→ZnO+H2O 2
Diborane (B2H6) is incorporated into the ZnO in a slight amount.
Specifically, the following reaction occurs:
Zn(C2H5)2+H2O+nB2H6→ZnO:B+2C2H6+nB2O3
provided that n is considerably small.
Each of the deposition treatment parts 41 . . . 4n in the multilayer deposition treatment part 4 shown in
The cooling pipes 4c cool the nozzles 4a and 4b to inhibit an organometallic compound, diborane, and pure water, which are raw materials for film deposition, from reacting around the nozzles. Since the nozzles 4a and 4b and the cooling pipes 4c have a flat-plate (one-plate) structure in which they are closely disposed without leaving a space therebetween, the raw materials do not accumulate on the back side of the nozzles or an upper part of the chamber (the structure functions as an adhesion-preventive plate). Consequently, the amount of the raw materials to be used is reduced. The embodiment described above is one in which ZnO is deposited as a transparent conductive film. In the case of depositing aluminum oxide Al2O3, however, the organometallic compound to be used as a raw material is Al(CnH2+1)3, preferably Al(CH3)3 or Al(C2H5)3.
The setter 7a is a production jig for fixing a substrate and conveying it through each part in the film deposition apparatus, and is made of a member having high thermal conductivity (carbon composite). For the purpose of enhancing the mechanical strength of the carbon material, which has low mechanical strength, a metallic coating having high thermal conductivity and high mechanical strength (e.g., nickel deposit) is applied to the surface thereof. Moreover, pins for substrate fixing are disposed in order to enable the setter to accept a substrate of any size.
The charging part 3 is equipped with a preheating mechanism 3A for heating the substrate from above with a heater, and the takeout part 5 is equipped with a substrate-cooling mechanism 5A for cooling the substrate from below with a cooling plate.
Table 1 given below shows a comparison in the efficiency of utilization of raw materials for a transparent conductive film between the case where a transparent conductive film was formed with the composite nozzles 4A shown in
As shown in Table 1, it was found that the composite nozzles 4A according to the invention are superior in the efficiency of raw-material utilization to the nozzles in a related-art film deposition apparatus.
Table 2 given below shows a comparison in substrate treatment rate between the case where a transparent conductive film was formed with the film deposition apparatus for the continuous formation of a multilayered transparent conductive film of the invention in which the charging part 3 and the takeout part 5 were equipped with a preheating mechanism 3A and a substrate-cooling mechanism 5A, respectively, and the case where a transparent conductive film was formed with a related-art film deposition apparatus.
As shown in Table 2, it was found that the film deposition apparatus for the continuous formation of a multilayered transparent conductive film of the invention attains a shorter film deposition time than the related-art film deposition apparatus.
Table 3 given below shows a comparison in solar cell characteristics between a CIS type thin-film solar cell employing a transparent conductive film formed with the film deposition apparatus for the continuous formation of a multilayered transparent conductive film of the invention and a CIS type thin-film solar cell employing a transparent conductive film formed with the related-art film deposition apparatus.
As shown in Table 3, it was found that the film deposition apparatus for the continuous formation of a multilayered transparent conductive film of the invention attains better solar cell characteristics than the related-art film deposition apparatus.
Furthermore,
A comparison between the sheet resistances of the transparent conductive films in the case where film deposition was repeatedly conducted batchwise using the related-art nozzles (see
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-013682 | Jan 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/300888 | 1/20/2006 | WO | 00 | 7/23/2007 |
