JP3515688B2 - Low electric resistance 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 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, a liquid crystal display and an electroluminescent display. The present invention relates to a transparent conductive film that 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. Among them, a transparent conductive film that can have a low electric resistance even when formed by a sputtering method at 250 ° C. or less. It belongs to the technical field of conductive films.

[0002]

2. Description of the Related Art Transparent conductive films having electric conductivity, low electric resistance and high visible light transmittance are used for liquid crystal displays; Liquid Crystal Display (hereinafter referred to as LCD), electroluminescence display devices, and solar cells. It is applied to transparent electrodes, touch panels, antistatic films, gas sensors, etc.

Among these, the LCD has been widely used in recent years because it is thinner, lighter in weight, smaller in electric power and higher in resolution than the conventional cathode ray tube.

The screen display of such an LCD is achieved 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 the visible light is required to efficiently use the projected light for screen display. It is required to have high transmittance in the light region.

SnO ₂ , ZnO and In ₂ O ₃ are examples of transparent conductive materials having high transmittance in the visible light region and exhibiting conductivity. LCD transparent electrodes are thin films with a thickness of 500 to 5000 Å. These SnO ₂ , ZnO, In to be used as
₂ O ₃ cannot be used due to its high electrical resistance. To use as a transparent electrode of LCD, the electric resistivity is 10 × 10 ^-4 Ω
It is required to be less than or equal to cm and the transmittance to be greater than or equal to 80% in the visible light region. Currently, Sn is added to the transparent conductive film that satisfies this requirement and is used as a transparent electrode of LCD.
In ₂ O ₃ (; Indium Tin Oxide) (hereinafter referred to as ITO), and the ITO thin film for an LCD transparent electrode is mainly formed by a magnetron sputtering method.

By the way, in recent years, due to the trend toward larger size, colorization and higher definition of LCDs, it is becoming the most important required characteristics for the transparent electrodes of LCDs to have low specific resistance and high transmittance. That is, when aiming to increase the size of the LCD,
Along with the increase in size of the display screen, a long transparent electrode is required. Therefore, a transparent conductive film having a lower specific resistance than the conventional ones is required. The electrical resistivity of the film depends largely on the deposition temperature during sputtering, and the higher the deposition temperature, the lower the electrical resistivity of the film obtained. At the deposition temperature of 400 ℃ or higher, the electrical resistivity: 1.2 A film of about 10 ^-4 Ωcm is obtained.

However, in order to cope with the colorization of LCD, it is necessary to form a transparent conductive film on a color filter or a plastic substrate having poor heat resistance. Therefore, the transparent electrode is formed at a substrate temperature of 250 ° C. or less. It is necessary to do it under the condition of. The electrical resistivity is 10 × 10 ^-4 Ωcm when the film is formed at 250 ℃ or less.
The above increase contributes to the deterioration of 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 a low electric resistance and a high transmittance at the same time is required even when the film is formed at a substrate temperature of 250 ° C. or less. . Here, if the film 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 is reduced and the brightness and color tone of the liquid crystal screen (LCD display screen) are hindered. become. In order to support the further high definition of LCD in the future, 250 ℃
Also 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.

The conventional conductive mechanism of ITO, ie, Sn-doped In ₂ O ₃ as a conventional transparent electrode for LCD is as follows. That is, oxygen defects are present in the matrix In ₂ O ₃ , and carrier electrons are supplied from this defect level, and In ₂ O ₃ exhibits electrical conductivity. When the amount of oxygen defects is small, visible light is not absorbed by the defect level and the transmittance is improved. On the other hand, the supply amount of carriers from the defect level is decreased and the electric resistance is increased.

Sn in ITO combines with oxygen defects in In ₂ O ₃ to release carrier electrons. Therefore, In
_The carrier density can be increased by adding Sn to ₂ O ₃ , and the electrical resistivity of the ITO film is lower than that of the In ₂ O ₃ film.

The emission of carrier electrons in ITO occurs due to the combined effect of Sn and oxygen defects. Therefore, when the amount of oxygen defects decreases, the effect of Sn addition does not appear. Therefore, it is necessary to form the ITO film with oxygen defects left to some extent. Also, if there are too many oxygen defects, the composite structure with Sn is disturbed and the amount of carrier electrons emitted is reduced. Furthermore, when the amount of oxygen defects is large, the carrier mobility also decreases.

Specifically, the 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.

Further, as the number of oxygen defects increases, the light absorption by the defect level increases, so that the visible light transmittance of the film decreases. Therefore, it is desirable that the number of oxygen defects is small in order to increase the transparency of the film. Also, the transmittance decreases even if the amount of Sn added increases.

As described above, the main film formation parameters that control the oxygen defects in the film, which have an important influence, are the oxygen partial pressure in the film formation gas and the film formation rate.

The amount of oxygen (that is, the oxygen partial pressure) which makes the amount of oxygen defects in ITO appropriate is 0.0001 to 0.002 mTorr. When film formation is performed under this oxygen partial pressure, an appropriate amount of oxygen defects remain, so that the electrical resistivity becomes minimum. When film formation is performed in an atmosphere containing more oxygen than this, the amount of oxygen defects decreases, so that the transmittance increases but the electrical resistivity increases. Therefore, it is not possible to form a film under a high oxygen partial pressure.

Next, the relationship between the film formation rate and the amount of oxygen defects will be described. In the film formation under the condition that the film formation speed is high, defects are likely to occur 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 deposition rate can be controlled by controlling the distance between the electrodes and the film deposition power. When the film deposition rate is 20 Å / second (Å / s) or less, the electrical resistivity is 2 × at 250 ℃. 10 ^-4 Ωcm
Thus, a film having a transmittance of 80% can be formed at a film thickness of 1000Å or more. However, when the film-forming rate is 20 Å / s or more, the transmittance drops sharply. Therefore, with ITO, it is not possible to unnecessarily increase the film formation speed 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 even in film formation at 250 ° C. or less, and the transmittance is visible light. It is indispensable to have a transparent conductive film capable of forming a film at a high film forming rate from the viewpoint of productivity, which is 80% or more in the area.
It is desired to develop a new transparent conductive film that replaces the conventional ITO.

[0017]

The present invention has been made in view of such circumstances, and its purpose is to form a film at a film forming temperature (substrate temperature) of 250 ° C. or less. The resulting film has a low electric resistivity even at 10 × 10 ^-4
It is intended to provide a transparent conductive film having an Ωcm or less and a high visible light transmittance of 80% or more.

[0018]

In order to achieve the above object, the transparent conductive film according to the present invention is the transparent conductive film according to claims 1 to 3, and it has the following constitution. 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, and the content of Ge with respect to the total of the amount of Ge and the amount of In. 2 to 10 atom%, and the film formation rate is 45 to 100 Å / s
And an oxygen-containing gas is used as the atmosphere gas during film formation.
And manufacturing conditions that the oxygen partial pressure during film formation is 0.002 mTorr or more
And the carrier density is 9
× 10 ²⁰ / cm ³ or more, carrier mobility is 20 cm ³ / Vs or more, electrical resistivity is 10 × 10 ^-4 Ωcm or less , visible light transmittance is 80% or more, low electrical resistance transparent conductivity It is a film (first invention).

The transparent conductive film according to claim 2 has a Ge content of 5 to 7 atomic% with respect to the total amount of Ge and In, a carrier density of 15 × 10 ²⁰ / cm ³ or more, and a carrier mobility of 25 cm ³ / Vs or more, the electrical resistivity is low electric resistant transparent conductive film according to claim 1, wherein the visible light transmittance of 80% or more with it 1.6 × 10 ^-4 Ωcm or less (second invention). The transparent conductive film according to claim 3 is the low-electric-resistance transparent conductive film according to claim 1 or 2 used as a transparent electrode of a liquid crystal display (third invention).

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The transparent conductive film according to the present invention can be formed as follows by, for example, a sputtering method. That is, the substrate is placed in a sputtering apparatus, while a sputtering target such as In _{2 is used.}
A composite target in which a Ge chip is placed on an O ₃ target is placed, and in an inert gas atmosphere containing oxygen gas, the substrate is heated, and then an electric field is applied between the substrate and the composite target. On the substrate by applying
Forming a transparent conductive film made of In ₂ O ₃ containing Ge (deposition)
can do. At this time, In ₂
The Ge content can be changed by changing the surface area ratio between the O ₃ target and the Ge chip. The transparent conductive film according to the present invention can be obtained by adjusting the Ge content and adjusting the film forming conditions.

The present inventors formed transparent conductive films of various compositions by the sputtering method, and investigated the composition and characteristics of the transparent conductive film. As a result, it is a transparent conductive film containing an oxide of In as a main component and Ge or a Ge oxide, and the content of Ge is 2 to 10 with respect to the total amount of Ge and In.
Atomic% has a low electric resistivity of 10 × 10 ⁻⁴ Ωcm or less even when the film is formed under a film forming temperature (substrate temperature): 250 ° C. or less, and a visible light The inventors have found that the transmittance is high and 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 as in the transparent conductive film according to the present invention, Ge has a function of emitting carrier electrons independently of oxygen defects of In ₂ O ₃ . Therefore,
In the In ₂ O ₃ film containing such Ge, unlike the conventional ITO in which Sn in ITO is compounded with oxygen defects, an appropriate amount of oxygen defects are required. The carrier electron emission from Ge is not affected even if the amount of is reduced. As a result, it is possible to reduce oxygen defects by film formation under a high oxygen partial pressure, reduce scattering due to oxygen defects, and reduce electrical resistivity as compared with ITO. In addition, even when there are many oxygen defects, the carrier density released from Ge does not change so much, so under the condition that some defects are generated, for example, under the condition of high power film formation or high film formation rate. It is possible to form a low electric resistance film under the above film forming conditions.

Further, since Ge has a smaller atomic radius than Sn, the strain of the crystal itself generated in In ₂ O ₃ becomes large. At this time, when the strain of the crystal is increased, the carrier mobility is reduced and the electrical resistivity is increased. If the film formation is performed at a slower film formation rate, the strain generated in the crystal remains, so it is necessary to form the film in a high energy state to some extent. That is, when the film is formed at a high film formation speed, 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 it in order to fully exhibit its performance. The film forming method and film forming conditions will be described below.

First, in order to reduce the strain remaining in the In ₂ O ₃ film itself, film formation is performed in a high energy state.
Specifically, the film forming rate is set to 45 to 100 Å / s. On this occasion,
If the deposition rate exceeds 100 Å / s, the decrease in transmittance due to crystal defects due to recoil Ar collision becomes unavoidable, and the film thickness 1000 Å
The transmittance is less than 80% for the above films. If it is less than 45Å / s, the carrier mobility will be increased due to the disorder of the crystal structure.
Since it is less than 20 cm ³ / Vs, the electrical resistivity exceeds 10 × 10 ^-4 Ωcm.

Next, in order to reduce the amount of oxygen defects in Ge and improve the transmittance without increasing the electrical resistivity,
The oxygen partial pressure in the film forming gas is set to 0.002 mTorr or more. Under this condition, a transmittance of 80% or more can be obtained for a film having a film thickness of 1000Å or more.

Under the above film forming conditions, the Ge content is equal to the Ge amount.
When the content of In is 2 to 10 atom%, it is difficult to form a low electric resistance film. At a film forming temperature of 250 ℃ or less, the carrier density is 9 × 10 ²⁰ / cm ³ or more and the carrier mobility is 20 cm. 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.
A transparent conductive film containing In ₂ O ₃ is obtained.

At this time, if the Ge content (hereinafter referred to as Ge content) with respect to the total Ge content and In content is 5 to 7 atomic%, the carrier density is 15 × at a film forming temperature of 250 ° C. or less.
10 ²⁰ / cm ³ or more, carrier mobility is 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 can be obtained.

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

When the Ge content is less than 2 atomic%, the carrier density is less than 9 × 10 ²⁰ / cm ³ , so that the film has an electric resistivity of more than 10 × 10 ⁻⁴ Ωcm. , Ge content is 10
If it is more than atomic%, the carrier mobility will be less than 20 cm ³ / Vs, resulting in a film having an electric resistivity of more than 10 × 10 ⁻⁴ Ωcm, which is not a low electric resistance transparent conductive film.

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

By the way, JP-A-62-202415 discloses that
0.01 to 3 moles of Sn content and 1 mole of In, Ge content of In1
An In ₂ O ₃ film (ITO having a molar ratio of 0.0001 to 0.6 mol)
Film) with an electrical resistivity of 2 × 10 ^-4 Ω at a deposition temperature of 400 ° C
An example in which a film having a thickness of cm or less is formed is disclosed. However, as mentioned above, the film formation conditions required to reduce the resistance of Ge-doped In ₂ O ₃ are significantly different from the film formation conditions required to reduce the resistance of ITO. In order to form a Ge-doped In ₂ O ₃ film, the Ge film formation conditions differ from those of ITO.
A unique film formation method is required to reduce the resistance of the added In ₂ O ₃ film.

Further, since the film forming conditions for exerting the Ge ability are greatly different from the film forming conditions for exerting the Sn ability, when Ge and Sn are simultaneously added, Ge addition I
It is difficult to select the film formation conditions that sufficiently bring out the ability of the n ₂ O ₃ film to lower the resistance, and the electrical resistivity of the simultaneous addition is Ge or Sn.
Is higher than the electrical resistivity when added alone.

Therefore, in order to realize a transparent conductive film having a high transmittance and a low electrical resistivity at a film forming temperature of 250 ° C. or less, Ge alone is added, or Ge is added and there is no adverse effect. It is unavoidable to add Sn in an amount (Sn addition amount: 2 atomic% or less with respect to the total of Sn amount and In amount) and to satisfy the above-mentioned film forming conditions and the Ge addition amount.

Since the transparent conductive film according to the present invention has excellent properties as described above, it can be suitably used as a transparent electrode for display devices such as LCDs and solar cells.

[0037]

Example 1 As a sputtering target, a composite target in which a 5 mm square Ge chip (purity 99.9%) was placed on an In ₂ O ₃ target (purity 99.95%, relative density 95%) in a predetermined amount,
Alternatively, using an In ₂ O ₃ target containing a specified amount of Ge, a film-forming rate of a Ge-added In ₂ O ₃ film with a thickness of 1500Å and a Ge content of 7 atom% is controlled by a magnetron sputtering method on a glass substrate. While forming (deposition). The film forming conditions at this time are as follows.

Film forming temperature (substrate temperature) ---- 200 ° C. Atmosphere gas -------------- O ₂ -containing Ar oxygen partial pressure ----------- ----- 0.002mTorr Electricity -------------------- 4.5 W / cm ²

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

Example 2 Ge-added In ₂ O ₃ obtained by forming a film under the same conditions as in Example 1
The electrical resistivity of the film was measured by the same method as in Example 1, and the carrier density and carrier mobility were measured by the van der Pauw method. The result is shown in FIG. Deposition rate: 45 Å / s or less, carrier mobility is
20 cm ³ / Vs or less, so the electrical resistivity is 10 ^-4 Ωcm
More than that.

Example 3 As a sputtering target, a composite target in which a 5 mm square Ge chip (purity 99.9%) was placed on an In ₂ O ₃ target (purity 99.95%, relative density 95%) in a predetermined amount,
Alternatively, an In ₂ O ₃ target containing a predetermined amount of Ge was used to form a Ge-added In ₂ O ₃ film having a thickness of 1500 Å on the glass substrate by magnetron sputtering. The film forming conditions at this time are as follows.

Film forming temperature (substrate temperature) ---- 200 ° C. Atmosphere gas -------------- O ₂ -containing Ar oxygen partial pressure ----------- ----- 0.04mTorr Electricity -------------------- 4.5 W / cm ²

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

Example 4 Ge-doped In ₂ O ₃ obtained by forming a film under the same conditions as in Example ₃
The electrical resistivity, carrier density, and carrier mobility of the film were measured. The result is shown in FIG. Ge content: 2
A transparent conductive film having an electric resistivity of 1.0 × 10 ⁻³ Ωcm or less can be obtained at 10 atom%. Ge content: 2 to 10 atom%
Carrier density: 9 × 10 ²⁰ / cm ³ or more, carrier mobility: 20
cm ³ / Vs or more and electrical resistivity: 10 × 10 ^-4 Ωcm or less.

(Example 5) As a sputtering target, a composite target in which a 5 mm square Ge chip (purity 99.9%) was placed on an In ₂ O ₃ target (purity 99.95%, relative density 95%) in a predetermined amount,
Or, using In ₂ O ₃ target containing a predetermined amount of Ge, thickness on a glass substrate having a thickness of 0.5mm is: 1500 Å of Ge added In ₂ O ₃
The film was formed by the magnetron sputtering method.
The film forming conditions at this time are as follows.

Film forming temperature (substrate temperature) ---- 20 ° C Atmosphere gas -------------- O ₂ -containing Ar oxygen partial pressure ----------- ----- 0.06mTorr Electricity -------------------- 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]

EFFECTS OF THE INVENTION The transparent conductive film according to the present invention has the above-described constitution and functions, and is formed under the film forming conditions of film forming temperature (substrate temperature): 250 ° C. or less. 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. Therefore, it can be suitably used as a transparent electrode of a display device. In particular, it is possible to achieve a remarkable effect that the display can be improved in function and quality such as upsizing, colorization, and high definition in the future.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between a film forming rate, a resistivity, a carrier density, and a carrier mobility of a transparent conductive film according to Example 2.

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

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

─────────────────────────────────────────────────── ─── of the front page continued (56) references Toshiro Maruyama, Teruoki Tago, Germ anium- and silicon -doped indium-oxid e thin films prepa red by radio-frequ ency magnetron spu tterin, Appl. Phys. Lett. , USA, American Institute of Physics, March 14, 1994, Vol. 64, No. 11, 1935-1937 (58) Fields investigated (Int.Cl. ⁷ , DB name) H01B 5/14 H01B 13/00 501 H01B 13/00 503 C23C 14/08 G02F 1/1343

Claims (3)

(57) [Claims] 1. Ge or Ge containing In oxide as a main component.
A transparent conductive film containing an oxide, wherein the content of Ge is Ge
2 to 10 atom% with respect to the total amount of In and In , and
The film speed is 45 to 100 Å / s, and the atmospheric gas during film formation
Then, the oxygen partial pressure during film formation was adjusted to 0.002 mTo using an oxygen-containing gas.
It is a transparent conductive film obtained under the manufacturing conditions of rr or more, and
The carrier density is 9 × 10 ²⁰ / cm ³ or more, the carrier mobility is 20 cm ³ / Vs or more, the electric resistivity is 10 × 10 ⁻⁴ Ωcm or less , and the visible light transmittance is 80% or more. Low electric resistance transparent conductive film. 2. The Ge content is 5 to 7 atomic% with respect to the total of Ge content and In content, the carrier density is 15 × 10 ²⁰ / cm ³ or more, the carrier mobility is 25 cm ³ / Vs or more, and the electrical resistance is Rate 1.6 × 10 ^-4 Ω
The transparent conductive film having a low electric resistance according to claim 1, wherein the transparent conductive film has a visible light transmittance of 80% or more and is not more than cm. 3. The low electric resistance transparent conductive film according to claim 1, which is used as a transparent electrode of a liquid crystal display.