JPH06283746A - Manufacture of transparent conductive film and manufacture of photoelectric-conversion semiconductor device using it - Google Patents

Abstract

PURPOSE:To provide a low-resistance ZnO transparent conductive film whose controllability is good and which has been doped with impurities, to provide its manufacturing method and to provide the manufacturing method of a photoelectric-conversion semiconductor device using it. CONSTITUTION:An element which is provided with a CuInSe2 thin film and with a ZnO thin film is manufactured on an Mo lower-part electrode, the element is irradiated with an accelerated Ca atomic ion beam, the resistance of the ZnO thin film is lowered, a homojunction is formed in the CuInSe2 thin film, and a photoelectric-conversion semiconductor device is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent conductive film which can be used in a high-efficiency solar cell or a display device and has a good controllability of conductivity, a method for producing the same, and its application.

[0002]

_2. Description of the Related Art Hitherto, a Nesa film (SnO ₂ ) or an ITO film has been known as a transparent conductive film. The movement of using a ZnO film as a transparent conductive film has recently become vigorous. Although the ZnO film is cheaper than the Nesa film or the ITO film, it cannot be said that the ZnO film is necessarily high in performance as compared with the Nesa film or the ITO film since it has a short history as a transparent conductive film. At present, it is required to realize a high performance ZnO film. It cannot be said that the knowledge about the conduction mechanism by the impurity doping, which is the basis of this high performance, is sufficient.

[0003]

It is generally said that ZnO has a non-stoichiometric composition and exhibits n-type conduction when Zn is in excess. However, for example, a ZnO film produced by a sputtering method, which is often used, has a conductivity of about 10 ⁻⁸ / Ωcm and a high resistance unless the substrate temperature is set to 300 ° C. or higher. Although there is no clear explanation for this mechanism yet, this fact indicates that the presence or absence of excess Zn and the self-compensation effect must be investigated in detail. However, the group IIB Zn that has become the host in ZnO crystals so far.
It is known that replacing atoms with Group IIIA atoms reduces electrical resistance.

The present invention is not based on the non-stoichiometric composition, which has poor controllability, which is determined by the thin film forming temperature, and not electric conduction.
An object of the present invention is to provide a method for manufacturing a low resistance transparent conductive film based on impurity control with good controllability and a method for manufacturing a semiconductor device using the same.

[0005]

[Means for solving the problem] Accelerated IA, IIIA,
Alternatively, an ion beam of any atom of group VIIA is used alone or in combination to form a heterojunction or homojunction with a transparent conductive film in which this atom is present at a desired concentration in ZnO at a desired position. Using a semiconductor film as a base, and using an accelerated ion beam of any one of IA, IIIA, or VIIA atoms in a ZnO film formed on the base, alone or in combination.
A method for manufacturing a photoelectric conversion semiconductor device in which ZnO is present at a desired position at a desired concentration to reduce electric resistance, and a method for manufacturing a photoelectric conversion semiconductor device in which ZnO is present at a desired concentration in ZnO to reduce electric resistance At the same time, a method for manufacturing a photoelectric conversion semiconductor device in which the velocity of the ion beam is controlled to dope charge carriers to an arbitrary depth of the substrate, or a group IA, IIIA, or VIIA accelerated to a ZnO film formed on a transparent substrate is used.
Using an ion beam of any atom of the group alone or in combination, the atom is present at a desired position in ZnO at a desired concentration to reduce electric resistance, and a heterojunction is formed on the ZnO film,
Alternatively, a conventional method has been solved by a method for manufacturing a photoelectric conversion semiconductor device in which a semiconductor film forming a homojunction is formed.

[0006]

For example, the ZnO film formed by the sputtering method has a conductivity of about 10 ⁻⁸ / Ωcm. It is said that excess Zn exists in the ZnO film, but there is no clear explanation for the mechanism of this increase in resistance. This fact can be interpreted that the self-compensation effect is prominent. However, it has been known that replacing the host IIB group Zn atom in the ZnO crystal with the group IIIA atom reduces the electrical resistance, and the impurity doping should exceed the self-compensation effect. If possible, Z made at low temperature
The nO film can be doped with charge carriers. As well
It is also possible to dope the ZnO film with charge carriers by substituting Group VI O atoms with Group VIIA atoms. The substitution of the Zn or O atom with the IIIA group atom or the VIIA group atom injects an electron into the Zn-Os-p sigma antibonding orbital or a hole into the Zn-Os-p sigma bond orbital, which forms the conduction band, respectively. It has the meaning to say.

In the implantation of a Group IA (H) ZnO film, due to the difference in mass and ionic radius, the doping of charge carriers by atomic substitution cannot be realized, unlike the implantation of Group IIIA or Group VIIA atoms. H invades into the interstitial position of H, and conduction electrons are injected into the conduction band through local H-Os-p orbital hybridization.

In the ion implantation technique using an accelerated ion beam, the depthwise distribution of the doped impurity atoms is controlled by controlling the acceleration energy of the ions, and the impurity amount of the doped impurity atoms is controlled by controlling the dose amount of the ions. The concentration can be controlled.

Therefore, by combining various kinds of ion species, acceleration energy, and dose amount, it is possible to realize an arbitrary conductivity at an arbitrary place. If a ZnO thin film using an accelerated ion beam is used as a transparent conductive film, a solar cell is obtained. Alternatively, the device characteristics of the display device or the like are improved.

[0010]

EXAMPLES Group IA (H), Group IIIA (B, Al, Ga, I
n) or VIIA (F, Cl, I, Br) atom ion beam is accelerated to collide with the ZnO film formed on the substrate to distribute the atom in the film, thereby doping the ZnO with impurities. I do. The impurity distribution in the film can be controlled by the degree of acceleration of the ion beam of the atoms, and the electric resistance can be reduced while controlling by the degree of ion beam irradiation.

A semiconductor film forming a heterojunction or a homojunction is used as a substrate, and a ZnO film formed on the substrate is subjected to a transparent conductivity using an accelerated ion beam of any one of the atoms of group IA, group IIIA, or group VIIA. It is possible to reduce the electric resistance of the film and at the same time dope the charge carriers to an arbitrary depth of the semiconductor film which is the base by controlling the velocity of the ion beam, which simplifies the manufacturing process of the photoelectric conversion semiconductor device. Can also be realized.

Example 1 A ZnO powder sintered body was vacuumed.
Ar target 80% + O₂20% composition
High-frequency sputtering at 1 kW using the gas that it has, at room temperature
ZnO thin film 2.5 μm thick on the glass substrate
Only deposit. On the other hand, H ₂Gas as raw material
Ionization using thermoelectrons as an ion accelerator
H accelerated to a predetermined speed⁺This ion that keeps the ions at room temperature
Implant into ZnO film. Injection volume is measured by a micro ammeter
When the predetermined implantation amount is reached, the ion implantation is stopped.

In FIG. 1, H ⁺ ions are accelerated with an acceleration energy of 100.
Zn implanted at a dose of 1 × 10 ¹⁶ pieces / cm ^{2 at} keV
The conductivity of the O thin film is shown. FIG. 2 shows the distribution of H implantation and the density distribution of crystal defects due to ion implantation.

Even in the state immediately after the implantation of ions containing high-density crystal defects, the conductivity is improved by about 8 digits as compared with that before the implantation. Conducting heat treatment in N ₂ gas for the purpose of recovery of crystal defects and diffusion of impurities (H) further improves the conductivity.

This heat treatment, as shown in FIG.
200 ° C N is more effective than that of 0 ° C N. This is because the diffusion of H at 400 ° C N is larger than that at 200 ° C, and in the case of H which becomes an interstitial impurity, a low temperature of about 200 ° C is sufficient to recover crystal defects. Is shown. This means that a low temperature process is possible, which is a great advantage in application to solar cells, display devices, and the like.

(Example 2) In a vacuum, a ZnO powder sintered body was used as a counter target and a high frequency sputtering was performed at 1 kW using a gas having a composition of Ar 80% + O ₂ 20%, and a ZnO thin film was formed on a glass substrate kept at room temperature. Is deposited to a thickness of 2.5 μm. On the other hand, in a vacuum, B ⁺ , Al ⁺ , and Ga ⁺ ions, which are atomized by sputtering using solid as a raw material and further ionized by using thermoelectrons and accelerated to a predetermined speed by an ion accelerator, are kept at room temperature. Implant into ZnO film. The implantation amount is measured by a minute ammeter, and when the prescribed implantation amount is reached, the ion implantation is stopped.

In FIG. 1, the acceleration energies of B ⁺ , Al ⁺ and Ga ⁺ ions are 500, 1000 and 2000 keV, respectively.
Shows the conductivity of the ZnO thin film implanted with a dose of 1 × 10 ¹⁶ atoms / cm ² . B, A in FIGS. 3, 4, and 5, respectively.
The distributions of 1 and Ga implantation and the density distribution of crystal defects accompanying ion implantation are shown. Even in the state immediately after the ion implantation including the high-density crystal defects, the conductivity is about 2 to 3 orders of magnitude higher than that before the implantation, and the conductivity of the substitutional type is higher than that of H which is an interstitial impurity. With B, Al, and Ga that are impurities, the effect immediately after implantation is not great. Conducting heat treatment in N ₂ gas for the purpose of recovering crystal defects and replacing the lattice Zn of the implanted impurities (B, Al, Ga) improves the conductivity.

This heat treatment, as shown in FIG.
0 ° C N is significantly more effective than that at 200 ° C. This indicates that a temperature of about 400 ° C. N is required to replace atoms at lattice positions. By this heat treatment at 400 ° C. N, the conductivity is improved by about 8 orders of magnitude as compared with that before the injection. Zn is used for semiconductor devices that may become hot during use.
When the O transparent conductive film is applied, it can be seen that doping of substitutional impurities such as B, Al and Ga is effective from the viewpoint of stability.

(Example 3) A ZnO powder sintered body was prepared in a vacuum.
Ar target 80% + O₂20% composition
High-frequency sputtering at 1 kW using the gas that it has, at room temperature
ZnO thin film with a thickness of 2.5 μm on the glass substrate
Only deposit. On the other hand, H ₂Gas as raw material
Ionization using thermoelectrons as
H accelerated to a predetermined speed⁺Z with ions kept at room temperature
Implant into the nO film. The injection volume is measured with a micro ammeter.
When the predetermined implantation amount is reached, the ion implantation is stopped.

Acceleration energy of H ⁺ ions is 10, 30, 6
In 0,100,150,200KeV, each dose of 1 × 10 ¹⁵ / cm ² implanted conductivity of the ZnO thin film shown in FIG. 6, showing implantation distribution of H respectively in Fig.

Since the dose amount is smaller than that in the case of FIG. 1 by one digit, the conductivity is smaller than that in the case of FIG. 1 even after the heat treatment in N ₂ gas. However, using H ⁺ ions
As shown in the H measurement results of SIMS,
2.5 that can be put to practical use with a low acceleration energy of keV or less
Since it can cover μm thickness, the dose amount is 1 × 1
If it is set to 0 ¹⁶ pieces / cm ² , the resistance can be reduced by the low temperature process over the entire ZnO film thickness.

(Example 4) As shown in FIG. 9, a Mo electrode was formed on a glass substrate in a vacuum, a chalcopyrite structure compound semiconductor CuInSe ₂ thin film was formed thereon, and a wurtzite structure compound semiconductor CdS thin film was formed thereon. Fabricate and form a pn heterojunction.

On this semiconductor film, a ZnO powder sintered body was used as a counter target, a gas having a composition of Ar 80% + O ₂ 20% was used, high frequency sputtering was performed at 1 kW, and a ZnO thin film was formed on a glass substrate kept at room temperature. Is deposited to a thickness of 2.5 μm.

H ₂ gas is used as a raw material, ionized by using thermoelectrons, and accelerated to a predetermined speed by an ion accelerator.
⁺ Ions are implanted into the ZnO film kept at room temperature. The implantation amount is measured by a minute ammeter, and when the prescribed implantation amount is reached, the ion implantation is stopped.

Accelerating energy of H ⁺ ions to 10, 30, 6
A solar cell is formed by injecting a dose of 1 × 10 ¹⁶ cells / cm ² at 0, 100, 150, and ²⁰⁰ keV to form a low-resistance transparent conductive film.

(Embodiment 5) As shown in FIG. 10, a Mo electrode is formed on a glass substrate in vacuum, and a chalcopyrite structure compound semiconductor CuInSe ₂ showing p-type conduction is formed on the Mo electrode.
Make a thin film. On this semiconductor film, a ZnO powder sintered body was used as a facing target, a gas having a composition of Ar 80% + O ₂ 20% was used, high frequency sputtering was performed at 1 kW, and a ZnO thin film was formed on a glass substrate kept at room temperature. 5 μm
Deposited at a thickness of.

Ga ⁺ ions, which are atomized by sputtering using a solid as a raw material and further ionized by using hot electrons and accelerated to a predetermined speed by an ion accelerator, are injected from above the ZnO film kept at room temperature to the semiconductor film. . The implantation amount is measured by a minute ammeter, and when the prescribed implantation amount is reached, the ion implantation is stopped.

The acceleration energy of each Ga ⁺ ion is 10
0, 250, 500, 750, 1000, 1250, 1
500, 1750, 2000, 2250, 2500, 2
750, 3000, 3250 keV, dose 1 × 1
Inject ¹⁶ cells / cm ² .

When a heat treatment of 400 N is performed in N ₂ gas for 10 minutes, a low resistance ZnO transparent conductive film is realized. Along with this, ZnO of p-type CuInSe ₂ under the ZnO transparent conductive film
In the vicinity of the interface with CuInSe ₂ Ga,
An n-type conductive CuInSe ₂ layer is formed to realize a pn homojunction.

As already described in the fourth embodiment, the conventional method is C
A solar cell was composed of a heterojunction of uInSe ₂ and CdS. This uses Cd, which is a toxic substance and a pollutant, from the viewpoint of the global environment, and also from the viewpoint of the lattice mismatch at the heterojunction interface and the energy problem of the characteristic restriction due to the recombination center. Is also not a preferred structure.

On the other hand, in the method of manufacturing the photoelectric conversion semiconductor device of the present invention, the resistance of the ZnO thin film is lowered and at the same time CuInSe is formed.
₂ Homozygotes are produced. By using this manufacturing method, Cd, which is a toxic substance and a pollutant, is not used, and further, a lattice-mismatch at the bonding interface and a new pollution-free property which reduces the restriction on the characteristics due to the recombination center. A high performance solar cell is constructed.

Typical examples thereof have been shown above. A low resistance ZnO transparent conductive film and a low resistance ZnO transparent conductive film are prepared by using an accelerated ion beam of any one of atoms of group IA, group IIIA or group VIIA. The acceleration energy of the ion beam used to realize the homojunction formation of the semiconductor film passes through the ZnO film at the maximum,
It suffices that the energy is necessary to form a homojunction at a desired depth in the semiconductor film, and the dose of ions obtains the desired conductivity of ZnO, so that the conductivity type is surely changed in the semiconductor film. It is sufficient if the amount is sufficient to cause Therefore, it is obvious that this dose amount varies depending on whether the crystallinity of the ZnO film or the semiconductor film in the element in which the structure is first formed is good or bad.

It is obvious that an annealing step after ion implantation is included as part of the doping step, and the conditions of this annealing are acceleration energy at ion implantation, dose amount, initial ZnO film, and crystallinity of semiconductor film. It is also obvious that various changes can be made under various conditions.

In this embodiment, the case of substituting with Ga has been described, but Al, In, B can also be used. Thus, the method for manufacturing a photoelectric conversion semiconductor device of the present invention, after the basic structure of the photoelectric conversion semiconductor device is produced,
Since a homojunction is formed by ion implantation, the manufacturing process can be simplified, and since it can be applied to fine adjustment of conversion efficiency of a photoelectric conversion semiconductor device, the yield can be improved.

[0035]

INDUSTRIAL APPLICABILITY The present invention relates to group IA (H) and group IIIA (B, A).
l, Ga, In), or VIIA group (F, Cl, I, B)
The ion beam of any of the atoms of r) is accelerated so as to collide with the ZnO film formed on the substrate to distribute the atom in the film and reduce the electric resistance. The distribution of impurities in the film can be controlled by the type and the degree of acceleration, and the electric resistance can be controlled by the degree of ion beam irradiation.

According to this method, the doping of the impurity atom which brings about the reduction of the electric resistance can be carried out with good controllability from the viewpoint of the electric conductivity and the spatial distribution thereof, and the oxide of the impurity element is preliminarily used as a component for the sputtering film formation target. The present invention has a greater applicability in manufacturing a semiconductor device having a more complicated structure than the conventional method of mixing, and can provide a novel photoelectric conversion semiconductor device manufacturing process.

In manufacturing a photoelectric conversion semiconductor device, Z
In addition to reducing the electric resistance of the nO transparent conductive film, by controlling the speed of the accelerated ion beam of atoms, the charge carriers are doped to an arbitrary depth of the semiconductor film as the base to form a homojunction. It is also possible to simplify the manufacturing process of the photoelectric conversion semiconductor device.

By using this technique of forming a homojunction in a chalcopyrite structure thin film, the problem of the lattice mismatch due to the formation of a heterojunction and the characteristic deterioration due to the recombination center accompanied therewith, which has been conventionally used, is solved. There is also an effect that a pollution-free solar cell that does not use Cd, which is a harmful substance or a pollutant, can be realized and can contribute to solving problems such as energy and the global environment.

[Brief description of drawings]

1] ZnO: H, B, Al, Ga of the present invention (implantation amount 1
x10 ¹⁶ pieces / cm ² ) conductivity of the film

FIG. 2 Distribution of atoms and crystal defects when H is injected into ZnO at 100 keV

FIG. 3 Distribution of atoms and crystal defects when B is injected into ZnO at 500 keV.

FIG. 4 Distribution of atoms and crystal defects when Al is injected into ZnO at 1000 keV.

FIG. 5: Distribution of atoms and crystal defects when Ga is injected into ZnO at 2000 keV

FIG. 6 ZnO: H of the present invention (implantation amount 1 × 10 ¹⁵ pieces / cm 3
² ) Membrane conductivity

FIG. 7: H is 10, 30, 60, 100, 150, 20
Distribution of atoms when injected into ZnO at 0 keV

FIG. 8 is a graph of ZnO of 10,3 by secondary ion mass spectrometry.
Distribution of H in samples injected with H at 0, 60, 100, 150 and 200 keV

FIG. 9: Manufacturing process of heterojunction solar cell using H ion implantation of the present invention

FIG. 10: Manufacturing process of homojunction solar cell using Ga ion implantation of the present invention

Claims (4)

[Claims] 1. An accelerated ion beam of an atom of any one of Group IA, Group IIIA, and Group VIIA, either alone or in combination, to form ZnO.
A method for producing a transparent conductive film, characterized in that the atoms are made to exist at a desired position in a desired concentration therein. 2. A semiconductor film that forms a heterojunction or a homojunction is used as a substrate, and an accelerated ion beam of any one of IA, IIIA, or VIIA atoms is independently applied to a ZnO film formed on the substrate. Alternatively, a method of manufacturing a photoelectric conversion semiconductor device, characterized in that the atoms are present at a desired concentration in ZnO at a desired concentration to reduce electric resistance, when used in combination. 3. A semiconductor film forming a heterojunction or a homojunction is used as a substrate, and an ion beam of any one of IA, IIIA, or VIIA atoms accelerated by a ZnO film formed on the substrate is used alone. Alternatively, they are used in combination to reduce the electric resistance by allowing the atoms to exist at a desired concentration in a desired position in ZnO and, at the same time, to control the ion beam speed to reach an arbitrary depth of the semiconductor film which is the substrate. A method for manufacturing a photoelectric conversion semiconductor device, which comprises doping charge carriers. 4. A ZnO film formed on a transparent substrate is accelerated.
Using an ion beam of any atom of group IA, group IIIA, or group VIIA, alone or in combination, the atom is present at a desired position in ZnO at a desired concentration to reduce the electric resistance, and Z
A method of manufacturing a photoelectric conversion semiconductor device, comprising forming a semiconductor film forming a heterojunction or a homojunction on an nO film.