JPH11329085A - Low electrical resistant transparent conductive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film having electrical conductivity, low electrical resistivity and high visible light permeability even under a low film-forming temperature condition by using the In oxide as a main component, and including a specified quantity of Ge or Ge oxide so as to obtain a specified carrier density and carrier mobility. SOLUTION: In a spattering device, a target made of In2 O3 or the like doped with Sn according to need is spattered in the O2 included inert gas atmosphere so as to form a transparent conductive film mainly composed of In2 O3 on a board at 250 deg.C or below. At this stage, a metal Ge chip is placed on the In2 O3 target at the predetermined area ratio so as to form a compound target, and this compound target is spattered, and content percentage of Ge in the formed conductive film is regulated at 2-10 atom.% in relation to Ge+In, desirably at 5-7 atom.%. A film having carrier density at 9×10<20> /cm<3> or more, desirably at 15×10<20> /cm<3> or more, carrier mobility at 20 cm<3> /Vs or more, desirably 25 cm<3> /Vs, electrical resistivity at 10×10<-4> Ωcm or less, and visible light permeability at 80% or more 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 having a low electric resistance, and more particularly, to a transparent conductive film having a low electric resistance and a high visible light transmittance, and more particularly to a liquid crystal display and an electroluminescent display. The present invention relates to a transparent conductive film which can be suitably used as a transparent electrode of a flat panel display such as a plasma display or a transparent electrode of a solar cell. It belongs to the technical field of conductive films.

[0002]

2. Description of the Related Art A transparent conductive film having electric conductivity, low electric resistance and high visible light transmittance is used for a liquid crystal display; a liquid crystal display (hereinafter, referred to as an LCD), an electroluminescent display device, and a solar cell. It is applied to transparent electrodes, touch panels, antistatic films, gas sensors and the like.

[0003] Among these, LCDs have been used in recent years because of their thinness, light weight, small power consumption, and high resolution as compared with conventional cathode-ray tubes.

[0004] Such an LCD screen display is made by changing the arrangement of liquid crystal molecules by controlling the applied voltage.
This is performed by adjusting the amount of projection light from a backlight that can pass through the pixel liquid crystal and reach the screen. Therefore, the electrodes used to drive the liquid crystal are required to have a low electrical resistivity in order to apply a stable voltage to the liquid crystal molecules, and are required to be visible in order to efficiently use the projected light for screen display. It is required to have high transmittance in the light region.

[0005] SnO ₂ , ZnO, and In ₂ O ₃ can be cited as transparent conductive materials having high transmittance in the visible light region and exhibiting electrical conductivity. The transparent electrode of an LCD is a thin film having a thickness of 500 to 5000 mm. To be used as these SnO ₂ , ZnO, In ₂ O
₃ cannot be used due to high electrical resistance. For use as a transparent electrode of LCD, the electrical resistivity is 10 × 10 ^-4 Ωcm
And the transmittance must be 80% or more in the visible light region. At present, a transparent conductive film that satisfies this requirement and is used as a transparent electrode of an LCD is an Sn-added In conductive film.
₂ O ₃ (; Indium Tin Oxide) (hereinafter referred to as ITO)
Such an ITO thin film for an LCD transparent electrode is mainly formed by a magnetron sputtering method.

[0006] With the recent trend toward larger LCDs, larger colors, and higher definition LCDs, lower specific resistance and higher transmittance of the transparent electrodes of LCDs are becoming the most important required characteristics. In other words, when aiming for a larger LCD,
As the size of the display screen increases, a transparent electrode having a longer length is required. Therefore, a transparent conductive film having a lower specific resistance than that of the conventional one is required. The electrical resistivity of the film greatly depends on the film forming temperature during sputtering, and the higher the film forming temperature, the lower the electrical resistivity of the obtained film becomes. When the film forming temperature is 400 ° C. or higher, the electric resistivity is 1.2. A film of about × 10 ⁻⁴ Ωcm is obtained.

However, it is necessary to form a transparent conductive film on a color filter or a plastic substrate having inferior heat resistance in order to cope with the colorization of the LCD. Therefore, the transparent electrode is formed at a substrate temperature of 250 ° C. or less. Must be performed under the following conditions. When the film is formed at 250 ° C or less, the electric resistivity is 10 × 10 ^-4 Ωcm
This increases the accuracy of the color display screen of the LCD. Therefore, in order to improve the accuracy of the display screen of such a color LCD, a transparent conductive film having low electric resistivity and high transmittance at the same time is required even when the film is formed at a substrate temperature of 250 ° C. or lower. . Here, if the thickness of the transparent conductive film is increased in order to avoid an increase in the electrical resistivity, the transmittance of the transparent conductive film decreases, and the brightness and color tone of the liquid crystal screen (LCD display screen) are hindered. become. In order to cope with higher definition of LCDs in the future, 250 ℃
Even in the following film formation, development of a transparent conductive film having an electric resistivity of 10 × 10 ⁻⁴ Ωcm or less and a transmittance of 85% or more in a visible light region is strongly desired.

By the way, the conductive mechanism of the general ITO, ie, Sn-doped In ₂ O ₃ , as a conventional transparent electrode for LCD is as follows. That is, the base In ₂ O ₃ has oxygen vacancies, carrier electrons are supplied from the defect levels, and the In ₂ O ₃ exhibits electric conductivity. When the amount of oxygen vacancies is small, the absorption of visible light by the defect levels is small and the transmittance is improved. On the other hand, the supply amount of carriers from the defect levels is small, so that the electric resistance increases.

[0009] Sn in ITO has a function of emitting carrier electrons in combination with oxygen vacancies in In ₂ O ₃ . Therefore, In
By adding Sn to ₂ O ₃ , the carrier density can be increased, and the electrical resistivity of the ITO film is lower than that of the In ₂ O ₃ film.

The release of carrier electrons in ITO is caused by the combined effect of Sn and oxygen vacancies. Therefore, when the amount of oxygen vacancies decreases, the effect of Sn addition does not appear. Therefore, it is necessary to form the ITO film while leaving some oxygen defects. Also, if the number of oxygen vacancies is too large, the composite structure with Sn is disturbed and the amount of emitted carrier electrons is reduced. Furthermore, when the amount of oxygen vacancies is large, the carrier mobility also decreases.

Specifically, an ITO film formed at room temperature has a carrier density of 7 × 10 ²⁰ / cm ³ and a carrier mobility of 13 cm ³ / Vs
The electrical resistivity is about 11 × 10 ⁻⁴ Ωcm.

Furthermore, when the number of oxygen vacancies increases, light absorption due to defect levels increases, so that the visible light transmittance of the film decreases. Therefore, it is desirable that the number of oxygen vacancies be small in order to increase the transparency of the film. Further, even if the amount of Sn added increases, the transmittance decreases.

As described above, the main film forming parameters that govern oxygen defects in the film that have an important effect are the oxygen partial pressure in the film forming gas and the film forming speed.

The amount of oxygen (that is, oxygen partial pressure) for making the amount of oxygen vacancies in ITO an appropriate amount is 0.0001 to 0.002 mTorr.
When a film is formed under this oxygen partial pressure, an appropriate amount of oxygen vacancies remains, so that the electrical resistivity is minimized. When the film is formed in an atmosphere containing oxygen more than this, the amount of oxygen vacancies is reduced, so that the transmittance increases but the electrical resistivity increases. Therefore, a film cannot be formed under a high oxygen partial pressure.

Next, the relationship between the film forming rate and the amount of oxygen defects will be described. In the film formation under a condition where the film formation speed is high, defects are easily generated in the film due to collision of recoil Ar or the like in the sputtering gas, and the defects are reduced when the film formation speed is low. The film formation rate can be controlled by controlling the distance between the electrodes and the film formation power. When the film is formed at a film formation rate of 20Å / second (Å / s) or less, the electrical resistivity becomes 2 × at 250 ° C. 10 ^-4 Ωcm
Thus, a film having a transmittance of 80% at a film thickness of 1000 ° or more can be formed. However, when the film formation rate is set to 20 ° / s or more, the transmittance is rapidly reduced. Therefore, it is not possible to increase the film formation rate in ITO in order to increase productivity.

As described above, in order to support future high-definition color LCDs, the electrical resistivity is 10 × 10 ⁻⁴ Ωcm or less and the transmittance is visible light even at 250 ° C. or less. A transparent conductive film that is 80% or more in the area and that can be deposited at a high deposition rate is indispensable from the viewpoint of productivity.
There is a demand for the development of a new transparent conductive film that replaces the conventional ITO.

[0017]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to form a film under a film forming temperature (substrate temperature): 250 ° C. or less. even low electrical resistivity of the resulting film when that, 10 × 10 ^-4
It is an object of the present invention to provide a transparent conductive film having a Ωcm or less and a high visible light transmittance of 80% or more.

[0018]

In order to achieve the above object, a transparent conductive film according to the present invention is a transparent conductive film according to claims 1 to 5, which has the following structure. is there. That is, the transparent conductive film according to claim 1 is a transparent conductive film containing an oxide of In as a main component and containing Ge or a Ge oxide, wherein the Ge content is relative to the sum of the Ge amount and the In amount. A low electric resistance transparent conductive film characterized by having a carrier density of 9 × 10 ²⁰ / cm ³ or more and a carrier mobility of 20 cm ³ / Vs or more (first invention).

The transparent conductive film according to claim 2 has an electric resistivity of 10 × 10 ⁻⁴ Ωcm or less and a visible light transmittance of 80%.
The low electric resistance transparent conductive film according to claim 1, which is the above (second invention). The transparent conductive film according to claim 3, wherein the content of Ge is 5 to 7 atomic% with respect to the total of the Ge amount and the In amount, the carrier density is 15 × 10 ²⁰ / cm ³ or more, and the carrier mobility is 25 cm ³ / The low electric resistance transparent conductive film according to claim 1, which is not lower than Vs (third invention). The transparent conductive film according to claim 4 has an electric resistivity of 1.6 × 10 ⁻⁴ Ωcm or less and a visible light transmittance.
The low electric resistance transparent conductive film according to claim 3, which is 80% or more (fourth invention). The transparent conductive film according to claim 5 is used as a transparent electrode of a liquid crystal display.
A transparent conductive film according to 2, 3, or 4 (fifth invention).

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The transparent conductive film according to the present invention can be formed, for example, by a sputtering method as follows. That is, a substrate is placed in a sputtering apparatus, while a sputtering target such as In ₂
A composite target having a Ge chip placed thereon is placed on an O ₃ target, and the substrate is heated in an inert gas atmosphere containing oxygen gas, and then an electric field is applied between the substrate and the composite target. By applying
Formation (film formation) of a transparent conductive film made of In ₂ O ₃ containing Ge
can do. In this case, In ₂
The Ge content can be changed by changing the surface area ratio between the O ₃ target and the Ge chip. By adjusting the Ge content and the film formation conditions, the transparent conductive film according to the present invention can be obtained.

The present inventors formed transparent conductive films of various compositions by a sputtering method, and examined the compositions and characteristics of the transparent conductive films. As a result, a transparent conductive film containing an oxide of In as a main component and containing Ge or a Ge oxide, wherein the content of Ge is 2 to 10 with respect to the total of the Ge amount and the In amount.
Atomic% means that the film has a low electric resistivity even at a film forming temperature (substrate temperature) of 250 ° C. or less, that is, 10 × 10 ⁻⁴ Ωcm or less. The inventors have found that the transmittance is high and is 80% or more, and have completed the present invention.

The details will be described below.

In the In ₂ O ₃ film to which Ge is added, such as the transparent conductive film according to the present invention, Ge has a function of emitting carrier electrons by itself independently of oxygen defects of In ₂ O ₃ . Therefore,
In the In ₂ O ₃ film to which Ge is added, unlike the conventional ITO, which requires a proper amount of oxygen deficiency because Sn in ITO is combined with oxygen vacancy, the oxygen deficiency in the film is different. Has no effect on the carrier electron emission from Ge. As a result, oxygen vacancies can be reduced by film formation under a high oxygen partial pressure, scattering caused by oxygen vacancies can be reduced, and electric resistivity can be reduced as compared with ITO. In addition, even when there are many oxygen defects, the carrier density emitted from Ge does not change much, so that under a condition that a few defects are generated, for example, under a high power or a high film formation rate, Under the conditions described above, a low electric resistance film can be formed.

Since Ge has a smaller atomic radius than Sn, the strain of the crystal itself generated in In ₂ O ₃ increases. At this time, when the strain of the crystal increases, the carrier mobility decreases and the electric resistivity increases. If the film is formed at a low film formation rate, the strain generated in the crystal remains, so that it is necessary to form the film in a high energy state to some extent. In other words, when a film is formed at a high film formation rate, a good film having high crystallinity and high carrier mobility can be obtained.

Since Ge-added In ₂ O ₃ has the above-mentioned properties, it is important to apply a film forming method suitable for this in order to sufficiently exhibit its performance. The film forming method and the film forming conditions will be described below.

First, in order to reduce the distortion remaining in the In ₂ O ₃ film itself, the film is formed in a high energy state.
Specifically, the film forming speed is set to 45 to 100 Å / s. On this occasion,
When the film formation rate exceeds 100 mm / s, a decrease in transmittance due to crystal defects due to recoil Ar collision becomes inevitable, and the film thickness becomes 1000 mm / s.
The transmittance of the above film is less than 80%. If it is less than 45Å / s, carrier mobility may be reduced due to disorder of the crystal structure.
Since it is less than 20 cm ³ / Vs, the electric resistivity exceeds 10 × 10 ⁻⁴ Ωcm.

Next, in order to reduce the amount of oxygen vacancies in Ge and improve the transmittance without increasing the electrical resistivity,
The oxygen partial pressure in the deposition gas is set to 0.002 mTorr or more. Under these conditions, a transmittance of 80% or more is obtained for a film having a thickness of 1000 mm or more.

Under the above film forming conditions, the content of Ge is
When the In content is 2 to 10 atomic% with respect to the total amount, the carrier density is 9 × 10 ²⁰ / cm ³ or more and the carrier mobility is 20 cm at a deposition temperature of 250 ° C. or less where it is difficult to form a low electric resistance film. ³ / Vs
As a result, crystalline Ge having an electric resistivity of 10 × 10 ⁻⁴ Ωcm or less and a visible light transmittance of 80% or more is obtained.
A transparent conductive film comprising In ₂ O ₃ is obtained.

At this time, if the content of Ge with respect to the sum of the amount of Ge and the amount of In (hereinafter referred to as Ge content) is 5 to 7 atomic%, the carrier density becomes 15 × at a film formation temperature of 250 ° C. or less.
10 ²⁰ / cm ³ or more, carrier mobility 25 cm ³ / Vs or more,
A crystalline film having an electric resistivity of 1.6 × 10 ⁻⁴ Ωcm or less and a visible light transmittance of 80% or more is obtained.

When the film formation temperature is higher than 250 ° C., the above carrier density and carrier mobility can be easily achieved, and a film having an electric resistivity of 1.6 × 10 ⁻⁴ Ωcm or less can be easily obtained.

Here, when the Ge content is less than 2 atomic%, the carrier density becomes less than 9 × 10 ²⁰ / cm ³ , so that the film has an electric resistivity of more than 10 × 10 ⁻⁴ Ωcm, and , Ge content is 10
When the content is more than atomic%, the carrier mobility becomes less than 20 cm ³ / Vs, so that the film has an electric resistivity of more than 10 × 10 ⁻⁴ Ωcm, and does not become a low electric resistance transparent conductive film.

The present invention has been completed on the basis of the above findings, and the transparent conductive film according to the present invention is formed when the film is formed under a film forming temperature (substrate temperature): 250 ° C. or less. The electrical resistivity of the obtained film is low, 10 × 10 ^-4 Ω
cm or less, and has a high visible light transmittance of 80% or more.

Incidentally, Japanese Patent Application Laid-Open No. 62-202415 discloses that
Sn content is 0.01 to 3 moles per mole of In, Ge content is In1
0.0001 to 0.6 mol per mol of In ₂ O ₃ film (ITO
Film) at a film formation temperature of 400 ° C. with an electric resistivity of 2 × 10 ⁻⁴ Ω
An example in which a film having a size of not more than cm is formed is disclosed. However, as described above, the film formation conditions required for lowering the resistance of Ge-added In ₂ O ₃ are significantly different from the film formation conditions required for lowering the resistance of ITO. Ge-added In ₂ O ₃ is formed using a different Ge
A unique film forming method for lowering the resistance of the added In ₂ O ₃ film is required.

Further, since the film forming conditions for exhibiting the ability of Ge and the film forming conditions for exhibiting the ability of Sn are greatly different, when Ge and Sn are simultaneously added, the Ge added I
It is difficult to select film-forming conditions for sufficiently exhibiting the capability of lowering the resistance of the n ₂ O ₃ film.
Is increased more than the electrical resistivity in the case of adding singly.

Accordingly, in order to realize a transparent conductive film having a high transmittance and a low electric resistivity at a film formation temperature of 250 ° C. or less, it is necessary to add Ge alone or add Ge so as not to adversely affect the conductive film. It is inevitable that the amount of Sn added (Sn addition amount: 2 atomic% or less based on the total of Sn amount and In amount) and that the above-described film forming conditions and Ge addition amount are satisfied.

As described above, since the transparent conductive film according to the present invention has excellent characteristics, it can be suitably used as a transparent electrode for a display device such as an LCD or a solar cell.

[0037]

EXAMPLES Example 1 In ₂ O ₃ target (purity 99.95%, relative density 95%) as a sputtering target
A composite target in which a predetermined amount of a 5 mm square Ge chip (purity 99.9%) is provided, or In ₂ O ₃ containing a predetermined amount of Ge
Using a target, a Ge-added In ₂ O ₃ film having a thickness of 1500 ° and a Ge content of 7 atomic% was formed (deposited) on a glass substrate while controlling the deposition rate by a magnetron sputtering method. The film forming conditions at this time are as follows.

The film forming temperature (substrate temperature) ---- 200 ° C. ambient gas -------------- O ₂ containing Ar partial pressure of oxygen ----------- ----- 0.002mTorr Electric power -------------------- 4.5 W / cm ²

The electrical resistivity (resistivity) of the transparent conductive film (Ge-added In ₂ O ₃ film) obtained by the above film formation was measured by a four-terminal (probe) method, and was measured by a self-recording spectrophotometer. The visible light transmittance (550 nm) was measured. The result is shown in FIG.
When the deposition rate is 45Å / s or less, the electrical resistivity is 10 ^-4 Ωcm
When the film formation rate is 100 mm / s or more, the transmittance decreases to 80% or less.

Example 2 An electric resistivity of a Ge-added In ₂ O ₃ film obtained by forming a film under the same conditions as in Example 1 was measured in the same manner as in Example 1, and Carrier density and carrier mobility were measured by the van der Pauw method. The result is shown in FIG. When the film forming rate is 45 ° / s or less, the carrier mobility decreases to 20 cm ³ / Vs or less, and the electric resistivity increases to 10 ⁻⁴ Ωcm or more.

Example 3 An In ₂ O ₃ target (purity: 99.95%, relative density: 95) was used as a sputtering target.
%) On which a 5 mm square Ge chip (purity 99.9%) is installed in a predetermined amount, or an In containing a predetermined amount of Ge
_{Using a 2} O ₃ target, a thickness of 1500 mm on a glass substrate
A Ge-added In ₂ O ₃ film was formed by a magnetron sputtering method. The film forming conditions at this time are as follows.

The film forming temperature (substrate temperature) ---- 200 ° C. ambient gas -------------- O ₂ containing Ar partial pressure of oxygen ----------- ----- 0.04mTorr Electric power -------------------- 4.5 W / cm ²

With respect to the transparent conductive film (Ge-added In ₂ O ₃ film) obtained by the above film formation, the electric resistivity and the visible light transmittance (550 nm) were measured in the same manner as in Examples 1 and 2. It was measured. The result is shown in FIG. A transparent conductive film having an electric resistivity of 1.0 × 10 ⁻³ Ωcm or less can be obtained when the Ge content is between 2 and 10 at%. A transparent conductive film having an electric resistivity of 1.5 × 10 ⁻⁴ Ωcm or less can be obtained when the Ge content is between 5 and 7 at%. In the case of Ge content: 6 atomic%, electric resistivity: 1.2 × 10 ^-4 Ωcm
It is. Ge content: High visible light transmittance of 80% or more between 0 and 10 atomic%. If the Ge content exceeds 10 atomic%, the transmittance becomes 80% or less.

Example 4 The electrical resistivity, carrier density, and carrier mobility of a Ge-added In ₂ O ₃ film obtained under the same conditions as in Example 3 were measured. The result is shown in FIG. Ge content: between 2 and 10 at% electric resistivity:
A transparent conductive film of 1.0 × 10 ⁻³ Ωcm or less is obtained. If the Ge content is 2 to 10 atomic%, the carrier density is 9 × 10 ²⁰ / c
m ³ or more, carrier mobility: 20 cm ³ / Vs or more, and electric resistivity: 10 × 10 ⁻⁴ Ωcm or less.

Example 5 An In ₂ O ₃ target (purity: 99.95%, relative density: 95) was used as a sputtering target.
%) On which a 5 mm square Ge chip (purity 99.9%) is installed in a predetermined amount, or an In containing a predetermined amount of Ge
_{Using a 2} O ₃ target, a Ge-added In ₂ O ₃ film having a thickness of 1500 ° was formed on a glass substrate having a thickness of 0.5 mm by a magnetron sputtering method. The film forming conditions at this time are as follows.

The film forming temperature (substrate temperature) ---- 20 ° C. ambient gas -------------- O ₂ containing Ar partial pressure of oxygen ----------- ----- 0.06mTorr Electric power -------------------- 4.5 W / cm ²

The electrical resistivity of the transparent conductive film (Ge-added In ₂ O ₃ film) obtained by the above film formation was measured. As a result, the Ge content was 3.8 atomic%, and the electrical resistivity was 3.6 ×
A transparent conductive film of 10 ^-4 Ωcm was obtained. The visible light transmittance at 550 nm was 91%.

[0048]

The transparent conductive film according to the present invention has the above-mentioned structure and functions, and is used when the film is formed under a film forming temperature (substrate temperature): 250 ° C. or less. Also, the obtained film has a low electric resistivity of 10 × 10 ⁻⁴ Ωcm or less, and a high visible light transmittance of 80% or more, so that it can be suitably used as a transparent electrode of a display device. In particular, it is possible to obtain a remarkable effect that it is possible to improve the functions and quality of the display, such as enlargement, colorization, and definition of the display, in the future.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a film formation rate, a resistivity, and a transmittance of a transparent conductive film according to Example 1.

FIG. 2 is a diagram showing a relationship among a film formation rate, a resistivity, a carrier density, and a carrier mobility for a transparent conductive film according to Example 2.

FIG. 3 is a diagram showing the relationship between the amount of Ge added (Ge / Ge + In) and the resistivity and transmittance of a transparent conductive film according to Example 3.

FIG. 4 is a diagram showing the relationship between the amount of Ge added (Ge / Ge + In) and the resistivity, carrier density, and carrier mobility of a transparent conductive film according to Example 4.

Claims (5)

[Claims] An oxide of In as a main component, Ge or Ge
A transparent conductive film containing an oxide, wherein the Ge content is Ge
A low electric resistance transparent conductive film, characterized in that the content is 2 to 10 atomic%, the carrier density is 9 × 10 ²⁰ / cm ³ or more, and the carrier mobility is 20 cm ³ / Vs or more based on the total of the amount of In and the amount of In. 2. The low electric resistance transparent conductive film according to claim 1, wherein the electric resistance is 10 × 10 ⁻⁴ Ωcm or less and the visible light transmittance is 80% or more. 3. The method according to claim 1, wherein the content of Ge is 5 to 7 atomic% with respect to the sum of the amount of Ge and the amount of In, the carrier density is 15 × 10 ²⁰ / cm ³ or more, and the carrier mobility is 25 cm ³ / Vs or more. Item 4. A low electric resistance transparent conductive film according to Item 1. 4. The low electric resistance transparent conductive film according to claim 3, wherein the electric resistivity is 1.6 × 10 ⁻⁴ Ωcm or less and the visible light transmittance is 80% or more. 5. The transparent conductive film according to claim 1, which is used as a transparent electrode of a liquid crystal display.