JP3061342B2 - Method for manufacturing transparent conductive film and photoelectric conversion semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a transparent conductive film having good controllability of conductivity used for a high-efficiency solar cell or a display device, and an application thereof.

[0002]

_2. Description of the Related Art Conventionally, a Nesa film (SnO ₂ ), an ITO film and the like are known as a transparent conductive film. The movement to use a ZnO film as a transparent conductive film has recently become active. The ZnO film is less expensive than a Nesa film or an ITO film, but has a short history as a transparent conductive film, and is not necessarily higher in performance than a Nesa film or an ITO film. Currently, there is a demand for realizing high performance ZnO films. A method for producing a ZnO film with few crystal defects, which is the basis of this high performance;
Knowledge of the relationship between crystal defects and conduction due to impurity doping is not sufficient.

[0003]

It is generally said that ZnO has a non-stoichiometric composition and exhibits n-type conductivity when Zn is excessive. However, for example, a ZnO film produced by a commonly used sputtering method has a conductivity of about 10 ⁻⁸ / Ωcm and high resistance unless the substrate temperature is set to 300 ° C. or higher. There is no clear explanation for this mechanism yet, but this fact indicates that the presence or absence of excess Zn and the self-compensation effect must be examined in detail. However, until now, only Ar has been used as the sputtering gas,
Add H to r, or IIB which is the parent in ZnO crystal
It is known that when a group Zn atom is replaced with a group IIIA atom or a parent O atom in a ZnO crystal is replaced with an F atom, the electric resistance decreases. In any case, a ZnO film formed by a conventional high-frequency sputtering method has electrical conductivity based on crystal defects, and its conductivity is determined by a sputtering gas composition and a substrate temperature at the time of forming a thin film. It was not good.

[0004] Accordingly, the present invention provides a method for producing Zn with less crystal defects.
An object of the present invention is to provide a method for manufacturing an O film and a method for manufacturing a low-resistance transparent conductive film based on impurity doping with good controllability. Another object of the present invention is to provide a method for manufacturing a photoelectric conversion semiconductor device using the transparent conductive film.

[0005]

SUMMARY OF THE INVENTION The present invention provides a molecular beam of molecules or atoms necessary to provide ZnO, that is, at least a molecular beam of ZnO or a molecular beam of Zn and O;
Group IA (H) and group IIIA (B, Al, Ga,
In) or a molecular beam of any of the VIIA (F, Cl, I, Br) atoms onto a substrate on which a film is to be formed, thereby forming a Zn-doped impurity atom.
A method for producing a transparent conductive film, comprising forming a transparent conductive film made of O.

Here, ionizing a part of the molecular beam of O, Zn and impurity atoms is effective in lowering the substrate temperature at the time of film formation. Also, Zn
The use of an O molecular beam in addition to a ZnO molecular beam when forming an O film is effective in preventing the resulting ZnO film from being O-deficient.

A method for manufacturing a photoelectric conversion semiconductor device according to the present invention includes a step of forming a ZnO film on a substrate using a semiconductor film forming a heterojunction or a homojunction by the above-described method. Further, the method for manufacturing a photoelectric conversion semiconductor device of the present invention includes a step of forming a ZnO film on a transparent substrate by the above method, and a step of forming a semiconductor film for forming a heterojunction or a homojunction on the ZnO film. Have.

[0008]

According to the present invention, since ZnO is formed basically using a molecular beam, it is possible to obtain a ZnO film with few crystal defects, and also to use a molecular beam of impurity atoms in an arbitrary manner in the ZnO film. By impurity doping distributed to the position,
The electric resistance can be reduced with good controllability.

As described above, it is said that excess Zn exists in the ZnO film formed by the sputtering method, but there is no clear explanation about the mechanism of increasing the resistance. However, this fact can be interpreted as a remarkable effect of crystal defects, and if a ZnO film with few crystal defects can be produced by another film forming method, a transparent conductive film with good controllability by impurity doping described later. Can be produced with good reproducibility. It has been known that replacing the parent group IIB Zn atom with the group IIIA atom in the ZnO crystal reduces the electrical resistance, and if impurity doping that exceeds the self-compensation effect due to crystal defects can be performed. Usually, this is on the order of several atomic%.
The nO film can be doped with charge carriers. Similarly, by replacing the group VI O atom with a group VIIA atom, Z
The nO film can be doped with charge carriers. Substitution of the Zn or O atom with a Group IIIA or Group VIIA atom can be achieved by injecting an electron into the sp sigma antibonding orbit in the Zn—O bond constituting the conduction band, or
It has the meaning of injecting holes into the sp sigma bond orbital in the O bond. Doping of group IA (H) atoms depends on their mass and ionic radius.
Unlike doping of group IA atoms, doping of charge carriers by atom substitution cannot be realized, H penetrates into interstitial positions of ZnO, and sp
Conduction electrons are injected into the conduction band through orbital hybridization.

When a ZnO film is formed by a high-frequency sputtering method, both the ZnO target and the ZnO film on the substrate alternately repeat etching and deposition by the number of times corresponding to the frequency. This results in a film having many defects. In contrast, Z
When a film is formed using a molecular beam of nO or a molecular beam of Zn and O, a ZnO film having extremely few crystal defects is obtained because there are no high-speed charged particles and the molecular beam has only energy of heat of aggregation. Can be. In the process of fabricating a ZnO film having few crystal defects, a group IA (H), a group IIIA (B,
Al, Ga, In) or VIIA (F, Cl, I, B)
r) together with a molecular beam of any atom, Z
An impurity atom can be doped at an arbitrary position in the nO film with good controllability, and the electric resistance can be more effectively reduced with a smaller doping amount.

It is also effective to ionize a part of the molecular beam of O in order to lower the substrate temperature at the time of forming the ZnO film, and to ionize some of the atoms of the IA group, IIIA group or VIIA group. It is also effective to do so. This is because more complete networking energy of the Zn—O bond can be supplied partly by the thermal energy from the substrate and partly by the potential of the ions. Therefore, if a ZnO thin film using a molecular beam or a partially ionized ion beam that can be produced at a low substrate temperature is used as a transparent conductive film, a solar cell or a display device that is concerned about stability and temperature deterioration during long-term use. And other device characteristics are improved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

Example 1 A ZnO powder sintered body, Zn and Al were put in a crucible in a vacuum of about 1 × 10 ^-6 Torr, and each was heated and evaporated using an electron beam to obtain Zn.
Create molecular beams of O, Zn and Al. On the other hand, a substrate is prepared in which a metal electrode and a semiconductor film are sequentially formed on a glass substrate. The substrate is held by the substrate holder 300 ° C. in the same vacuum as above, the semiconductor film to O fed through ₂ gas supply line O ₂ gas continuously to maintain the vacuum degree of about 1 × 10 ^-5 Torr I do. Next, the shutter of the ZnO crucible facing the semiconductor film of the base is opened, and an undoped ZnO film is deposited on the semiconductor film. When a desired film thickness of the undoped ZnO film is obtained by the film thickness monitor, the shutter of the Al crucible is opened and a ZnO film doped with Al is deposited on the undoped ZnO film. Desired Zn by film thickness monitor
When the O: Al film thickness is obtained, the shutter of the crucible of ZnO and Al is closed. The intensity ratio between the molecular beams of ZnO and Al is
It only needs to be necessary to obtain the desired conductivity, 1: 1
~ 2: 1 is appropriate. The temperature of the substrate holder is Z
It is sufficient that the crystal structure of nO is about normal temperature or more,
Usually, 200 to 400 ° C. is used. Undoped ZnO
Needless to say, the thickness of the film may be about 0.01 to 0.1 μm which can prevent a short circuit between the transparent electrode and the semiconductor film / metal electrode.

Under the above-mentioned conditions in which the substrate holder is set at 300 ° C., the conductivity of the undoped ZnO film having a thickness of 0.2 μm is 10
^-8 / Ωcm, which is very small, and ZnO and Al
The conductivity of the Al-doped ZnO film having a thickness of 1 to 2 μm when the intensity ratio of the molecular beam is 1: 1 is very large, on the order of 10 ³ / Ωcm. This is because, when a film is formed by using a molecular beam, the number of crystal defects in the obtained ZnO film is reduced as described from the viewpoint of the deposition mechanism as compared with the case of using the high frequency sputtering method, and This is because the contribution to electric conduction is reduced and the undoped film has a high resistance, and the doped film exhibits the effect of impurities to the maximum and has a low resistance.

In the above, when the shutter of the ZnO crucible is opened when the shutter of the ZnO crucible is opened, the ZnO crucible is opened.
An Al-doped ZnO film can be obtained using O, Zn, Al, and O ₂ molecular beams. In this case, ZnO, Z
The intensity ratio between the molecular beams of n and Al is, for example, 1: 0.1:
Let it be 1. Also, if you close the shutter of the ZnO crucible,
Al-doped Zn using molecular beams of Zn, Al and O ₂
An O film can be obtained. Note that if a ZnO film is formed using only ZnO molecular beams, the resulting ZnO film tends to be O-deficient. Therefore, it is preferable to use O ₂ molecular beams as described above.

Further, instead of Al, B, Ga,
By using H ₂ and F ₂ molecular beams, a ZnO film doped with these impurity atoms can be obtained. Table 1 shows an example of the characteristics of a ZnO film doped with these impurity atoms.

[0017]

[Table 1]

[Embodiment 2] Next, it is also effective to ionize a part of the molecular beam of O _{2 and} the molecular beam of impurity atoms such as Al and use those ion beams. That is, O ₂
An O ₂ ion gun connected to a gas supply line is provided, O ₂ is ionized using thermionic electron bombardment, and O ₂ ions are irradiated on the semiconductor film of the opposing base. The degree of vacuum at this time is 2
At about × 10 ^-5 Torr, ion acceleration voltage is 400V-
About 500V is appropriate. This degree of vacuum should be determined in correlation with the film forming speed, and it goes without saying that the acceleration voltage of ions should be determined in consideration of the threshold energy of sputtering. Film formation speed is 2nm /
At about s, the flux of O ₂ ions is 10 ¹⁶ / cm ² s
About.

In order to obtain an Al ion beam, 1
Sputtering is performed using Ar ¹⁺ ions accelerated to about 000 eV. The sputtered Al atoms are partially ionized under the influence of the potential barrier at the interface when released from the solid surface into a vacuum. The ionization probability is estimated to be about 0.001-0.1%. This Ar1 ⁺
An Al-doped ZnO film can be obtained by using Al particles ionized by ion sputtering together with the above-described O ₂ ions and the molecular beams of ZnO, Al, and O ₂ . The degree of vacuum at this time is about 1 × 10 ⁻⁴ Torr. This is to minimize the mean free path of high energy particles reaching about 1000 eV at the maximum and to reduce the adverse effect on the ZnO film, that is, the generation of crystal defects as much as possible. By compensating for the decrease in thermal energy given by the substrate holder with the potential energy of the ions, the temperature of the ZnO film can be reduced, which is a great advantage in application to solar cells and display devices.

[Embodiment 3] The above-described semiconductor film / metal electrode /
In the case where a compound semiconductor CuInSe ₂ thin film having a chalcopyrite structure is used for a light absorbing layer on a glass substrate, a compound semiconductor CdS thin film having a wurtzite structure is further formed thereon, and a pn heterojunction is formed and displayed as a semiconductor film. I have. Normally, a solar cell was configured by mounting a ZnO film as a transparent electrode on this semiconductor film. This uses Cd, a toxic and polluting substance, from the viewpoint of global environmental problems, and also from the viewpoint of energy problems such as lattice mismatching at the heterojunction interface and the restriction on characteristics due to the recombination center. Was not a preferred structure.

In order to solve these problems, the above-described process of forming an impurity-doped ZnO film is applied to obtain a homojunction CZ.
The production of the uInSe ₂ semiconductor layer and the production of the ZnO transparent electrode are performed simultaneously. First, by irradiating chalcopyrite structure compound semiconductor CuInSe2 thin ion beam of the aforementioned Al showing a p-type conductivity, and then cancel the Al ion beam irradiation irradiation aforementioned O ₂ ions, the molecular beam of ZnO and O ₂ An undoped ZnO film is deposited. When the desired thickness of the undoped ZnO film is obtained by the film thickness monitor, the Al ion beam irradiation is restarted and the irradiation of the Al molecular beam is started, and a ZnO film doped with Al is deposited on the undoped ZnO film. By the first Al ion beam irradiation, p-type CuInSe
₂ near the interface with ZnO, p-type CuInSe ₂
To form a n-type conduction CuInSe ₂ layer, thereby realizing a pn homojunction. According to the present invention, Cu
Simultaneously with or immediately after the production of the InSe ₂ homojunction, the formation of a ZnO film is started, the Al doping is interrupted simultaneously with the start of the ZnO film formation, and the Zn
It is possible to make the O thin film intrinsic, n-type, and low in resistance.

By using this manufacturing method, there is no need for a toxic substance or a pollutant, Cd, and a new non-conductivity that reduces the lattice mismatch at the bonding interface and the characteristic restriction due to the recombination center. Pollution and high performance solar cells can be configured. In the present embodiment, the impurity has been described as an example of Al, but Ga, In, and B can also be used. As described above, the method for manufacturing a photoelectric conversion semiconductor device of the present invention forms a homojunction after the basic structure of the photoelectric conversion semiconductor device is manufactured, so that the manufacturing process can be simplified,
Since the present invention can be applied to fine adjustment of the conversion efficiency of the photoelectric conversion semiconductor device, there is also an effect that the yield can be improved.

[0023]

According to the present invention, a ZnO film is formed using ZnO and a molecular beam of Zn or O. According to the method using these molecular beams, unlike high-frequency sputtering, there are no high-speed charged particles, and the molecular beams have energy of only about the heat of aggregation. Obtainable. In the process of producing a ZnO film with few crystal defects, the IA group (H) and I
Group IIA (B, Al, Ga, In) or Group VIIA (F,
Cl, I, Br) is combined with a molecular beam of any atom to dope an impurity atom at an arbitrary position in the ZnO film with good controllability and to reduce the electric resistance more effectively with a smaller doping amount. Can be done. It is also effective to ionize a part of the molecular beam of O in order to lower the substrate temperature at the time of fabrication, and it is also effective to ionize a part of any atom of the IA group, the IIIA group, or the VIIA group. This is because more complete energy for networking Zn-O bonds can be supplied partly by thermal energy from the substrate and partly by the potential energy of ions.

According to the method of the present invention, the doping of the impurity atoms for reducing the electric resistance can be carried out with good controllability from the viewpoint of the conductivity and the spatial distribution thereof. Compared with the conventional method of mixing objects, the present invention is more applicable to the manufacture of a semiconductor device having a complicated structure, and can provide a new photoelectric conversion semiconductor device manufacturing process. In the manufacture of the photoelectric conversion semiconductor device, not only the reduction of the electrical resistance of the ZnO transparent conductive film but also the control of the speed of the ion beam of the accelerated atoms allows the charge carrier to reach an arbitrary depth of the semiconductor film as the base. It is also possible to form a homojunction by doping, so that the manufacturing process of the photoelectric conversion semiconductor device can be simplified. By using this technology to form a homojunction in a chalcopyrite structured thin film, the problem of lattice mismatch due to the formation of a heterojunction and the deterioration of characteristics due to the recombination center, which has been conventionally used, is solved. A pollution-free solar cell that does not use Cd, which is a substance, is realized, and has the effect of contributing to solving problems such as energy and the global environment.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-110125 (JP, A) JP-A-5-90620 (JP, A) JP-A-3-268335 (JP, A) JP-A-2- 202068 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078 C01G 9/02-9/03 H01B 5/00-5/16 H01B 13/00 -13/32

Claims (8)

(57) [Claims] 1. A method for irradiating a molecular beam of ZnO and a molecular beam of an atom belonging to any one of Group IA, IIIA, or VIIA onto a substrate on which a film is to be formed. A method for producing a transparent conductive film, comprising forming a transparent conductive film made of: 2. A Zn and O molecular beam, a group IA, IIIA
A transparent conductive film made of ZnO doped with the atoms by irradiating a molecular beam of any one of the atoms of Group IV or VIIA onto a substrate on which a film is to be formed. Manufacturing method of membrane. 3. A substrate on which a film is to be formed is irradiated with a molecular beam of ZnO, a molecular beam of Zn and O, and a molecular beam of any one of atoms of Group IA, IIIA, or VIIA on a substrate on which a film is to be formed. A method for manufacturing a transparent conductive film, comprising forming a transparent conductive film made of ZnO doped with atoms. 4. The method according to claim 1, further comprising a step of irradiating the atomic ion beam. 5. The method for producing a transparent conductive film according to claim 2, further comprising a step of irradiating an O ion beam. 6. The method for producing a transparent conductive film according to claim 2, comprising a step of irradiating a Zn ion beam. 7. A photoelectric device comprising: a semiconductor film forming a heterojunction or a homojunction as a base; and a step of forming a ZnO film on the base by the method according to claim 1. Description: A method for manufacturing a conversion semiconductor device. 8. A step of forming a ZnO film on a transparent substrate by the method according to claim 1;
A method for manufacturing a photoelectric conversion semiconductor device, comprising a step of forming a semiconductor film that forms a heterojunction or a homojunction on an O film.