JP2928016B2 - Method for forming transparent conductive film - 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 forming a transparent conductive film used for a solar cell, a thin film display device and the like.

[0002]

2. Description of the Related Art SnO ₂ and ITO have been put into practical use as transparent conductive film materials used for electrodes on the light incident side of solar cells. Above all, SnO ₂ is inexpensive, and its resistance can be reduced by hydrogen treatment. It is widely used as a current-collecting electrode for thin-film solar cells because it is possible to expect effective light confinement by controlling unevenness on the film surface according to the film manufacturing conditions, that is, by so-called texturing. However, since the film formation method by CVD is mainly used, the substrate temperature must be set to about 400 ° C., and it has not been possible to deposit later on a material such as amorphous silicon.

[0003] On the other hand, ITO has a film characteristic of low resistance and high transmittance obtained by sputtering at a substrate temperature as low as about 150 ° C. in an atmosphere containing moisture. A large area such as a solar cell for electric power is limited in terms of cost because it is used. For this reason, ZnO-based materials have been reviewed again. ZnO has been practically used as a piezoelectric material and a gas sensor material, and products such as surface acoustic wave devices, gas leak alarms, and varistors are commercially available.

[0004] ZnO and SnO ₂ have an oxygen-deficient conduction mechanism, and the resistivity thereof easily changes due to the exchange (oxidation-reduction reaction) with the electrons of the defective lattice. That is, the resistivity increases in the oxidation reaction and decreases in the reduction reaction. Therefore, A
Impurities such as l and B are added to reduce resistance and stabilize characteristics. The resistivity of the N-type semiconductor ZnO is represented by a mobility of μ _N ,
When the carrier density is N _N , it is given by the following equation (1).

Ρ = 1 / (μ _N N _N ) ────── (1) Accordingly, the resistivity can be reduced by increasing μ _N and increasing N _N. High mu _N of the to improve the crystallinity, high N _N
Can be realized by increasing the concentration of the impurity added. On the other hand, another important characteristic, light transmittance, is: transmitted light intensity I, incident light intensity I _O , absorption coefficient α, film thickness t, electron charge e, wavelength λ, refractive index n, the speed of light C, and the effective mass of the electron m ^*, when the relaxation time was tau, the following two formulas
(2) and (3).

[0006] _{I = I O exp (-αt)} ────── (2) α = N N e 2 λ a / (πnC 3 m * τ) ────── (3) (3) formula From this, it is understood that it is important to reduce N _{N in order} to reduce the absorption coefficient α and increase the transmittance. This is inconsistent with increasing the N _N in order to reduce the ρ by (1). Therefore, adding a suitable amount of impurities, and without deteriorating the crystallinity, the condition of high mu _N low film formation resistivity by transmitting good light coercive a.

[0007]

For example, considering application to a solar cell, ρ <1 × 10 ⁻³ Ω ·
cm is required. In addition, since the light output current is proportional to the transmittance, if a current as high as SnO ₂ is to be obtained, the transmittance becomes 90%.
It is necessary to raise to the extent. However, Al ₂ as an impurity
O ₃ is used, and ZnO to which about 2% by weight is added is 2 ×
A resistivity of 10 ⁻⁴ Ω · cm was obtained, and thermal stability was good, so that it was conventionally used as a transparent conductive film, but the transmittance was as low as about 70%.

An object of the present invention is to provide a method for forming a transparent conductive film having high transmittance and low resistivity, which is made of ZnO to which Al ₂ O ₃ is added as an impurity.

[0009]

According to the present invention, there is provided, according to the present invention, a zinc oxide containing aluminum oxide at a concentration of 0.5 to 1 weight percent. A method for forming a transparent conductive film by sputtering in an inert gas atmosphere containing hydrogen, using a get, a step of forming a thin film by sputtering in an inert gas atmosphere containing hydrogen, and forming the formed thin film. The step of exposing to an inert gas atmosphere containing hydrogen is alternately repeated. Here, it is preferable that the inert gas is an argon gas. In addition, sputtering is preferably performed using an RF magnetron sputtering device.

[0010]

[Action] 0.5% by weight or more of Al_TwoO_ThreeCan be added to ZnO
And higher N_NAl can be removed_TwoO_Three1 weight concentration
% And hydrogen into the sputtering atmosphere
Low μ by adding_NIs being measured. High transparency with this
The rate is realized. Where Al _TwoO_ThreeIs more than 1% by weight
Resistivity, but film deposition and inertness including hydrogen
Reduction reaction by exposure to an inert gas atmosphere.
By repeating the process, water can be reduced without lowering the oxygen concentration in the film.
Element can be added. This hydrogen is the acid at the lattice defect.
Since the element is compensated and contributes to conduction, the resistance of the film is reduced.

[0011]

[Embodiment] Using an RF magnetron sputtering apparatus, Zn
The ZnO thin film was formed on a glass substrate by changing the concentration of Al ₂ O ₃ in the O target within the range of 0 to 2% by weight and the concentration of H ₂ in the atmosphere gas, Ar gas, within the range of 0 to 10%. Substrate temperature is 15
The temperature was set to 0 ° C., and the film thickness was adjusted so that the sheet resistivity became 10Ω. FIGS. 1 and 2 show the results of measuring the resistivity and the white light transmittance of the formed transparent conductive film using a tungsten lamp.
Shown in

FIG. 1 shows Al ₂ O in a ZnO target of resistivity.
_{3 The} concentration dependency is shown as a parameter and the concentration of H ₂ contained in the Ar atmosphere. The solid line 11 is 100% Ar and the chain line 12 is H ₂ 2
% Containing Ar, dotted line 13 is the case where sputtering is performed in H ₂ containing 10% Ar. FIG. 2 shows the dependence of the white light transmittance on the Al ₂ O ₃ concentration in the ZnO target in the presence of H ₂ in the Ar atmosphere.
The conditions shown as the density and the parameters, and the symbols attached to each line correspond to the case of the same symbol in FIG.

As shown in FIGS. 1 and 2, the conventional Al ₂ O
_{(3) When} sputtering is performed in a hydrogen-free atmosphere using a target having a concentration of 2% by weight, the resistivity ρ = 2 × 10 ⁻⁴ Ω
-Although cm was obtained, the transmittance showed a low value of 73%. On the other hand, when sputtering is performed in an atmosphere of hydrogen addition at an Al ₂ O ₃ concentration of 0.5% by weight or 0.8% by weight according to the embodiment of the present invention, the transmittance becomes 90%, and characteristics similar to SnO ₂ are obtained. Obtained. Furthermore, by repeating the operation of depositing a thin film of about one molecule by sputtering for about several seconds and exposing it to the atmosphere in the sputtering chamber, the resistivity could be reduced to 2 × 10 ⁻⁴ Ω · cm.

In another embodiment, the substrate is changed to a plastic film, the H ₂ concentration is set to 2%, and ZnO containing Al ₂ O _{3 is used.}
When a transparent conductive film was formed using the target, film characteristics with the same resistivity and transmittance on a glass substrate were obtained.
Conventionally, formation of a ZnO thin film on a substrate that is vulnerable to thermal damage, such as a plastic film, has conventionally required a D
Although it was possible only by the C magnetron sputtering method,
R with good controllability by lowering plasma temperature by adding hydrogen
Film formation on a film by F magnetron sputtering has become possible.

[0015]

According to the present invention, ZnO for lowering the resistance is used.
By adding H ₂ to a sputtering atmosphere that suppresses the concentration of Al added to the target, a transparent conductive film having a transmittance similar to that of SnO ₂ can be formed. The addition of hydrogen to the atmosphere during sputtering lowers the plasma temperature, and alternately repeats film formation and exposure to the atmosphere, thereby compensating for the increase in resistivity due to the decrease in Al ₂ O ₃ concentration. It can be applied to a low-cost ZnO film not only as a transparent conductive film for a solar cell but also as a transparent conductive film for a display and the like, and can be put into practical use as a thin film for preventing dew condensation.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the Al ₂ O ₃ concentration in a ZnO solar cell and the resistivity of a ZnO thin film using the H ₂ concentration in Ar as a parameter.

FIG. 2 is a diagram showing the relationship between the Al ₂ O ₃ concentration in a ZnO solar cell and the transmittance of white light from a ZnO thin film using the H ₂ concentration in Ar as a parameter.

[Explanation of symbols]

11 Ar 100% 12 H ₂ 2% content Ar 13 H ₂ 10% content Ar

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 31/04 C23C 14/08 H01B 13/00 H01L 21/285

Claims (3)

(57) [Claims] 1. A tar comprising zinc oxide containing aluminum oxide at a concentration of 0.5 to 1% by weight.
A method for forming a transparent conductive film by sputtering in an inert gas atmosphere containing hydrogen, using a get, a step of forming a thin film by sputtering in an inert gas atmosphere containing hydrogen, and forming the formed thin film. A method of alternately repeating the step of exposing to a hydrogen-containing inert gas atmosphere. 2. The method according to claim 1, wherein the inert gas is argon gas.
The method for forming a transparent conductive film according to the above. 3. The method according to claim 1, wherein the sputtering is performed using an RF magnetron sputtering apparatus.