JP2004214184A - Transparent conductive film and forming method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming an ITO (indium tin oxide) transparent conductive film with a low resistance rate of 10<SP>-4</SP>Ωcm order on an organic substrate made of a plastic film or the like without heating the substrate. <P>SOLUTION: Sputtering particles from a target is transported and deposited on an organic substrate by the compulsory gas flow of sputter gas, by using the target containing indium oxide and tin oxide and impressing a DC bias voltage or an RF bias on the organic substrate. At this time, the organic substrate is made to positively get close to the target so as to be influenced by a plasma. By the above, the ITO transparent conductive film with a low resistance of 10<SP>-3</SP>Ω cm or less is formed on the organic substrate. A ratio of peak intensity at (222) plane to that of (400) plane of the indium tin oxide of the ITO transparent conductive film at an X-ray diffraction is not less than 1:1 and not larger than 4:1. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a transparent conductive film made of an oxide of indium and tin (ITO) and a method for forming the same, and more particularly, to a novel film having an extremely low resistivity while being formed on an organic substrate without heating the substrate. The present invention relates to a transparent conductive film and a method for forming the same.

  Indium and tin oxide (ITO) is widely used as a transparent electrode of various display devices such as a liquid crystal display and an organic EL display, and is further used as a transparent electrode of a touch panel.

  The ITO transparent conductive film is usually formed on a glass substrate, and a film having a low resistivity is obtained by heating the substrate. For example, by using an ITO sintered body as a target by a reactive DC magnetron sputtering method and forming an ITO film while heating the substrate temperature to 300 ° C. or more, a low-resistivity ITO transparent conductive material having good crystallinity can be obtained. A membrane can be made. In addition, reactive DC magnetron sputtering is performed using an In—Sn alloy as a target to deposit InO and Sn, which are lower oxides of In, on a substrate, and then heat-treated at 170 to 180 ° C. in the air. Thus, an ITO transparent conductive film having a low resistivity can also be manufactured.

As described above, in order to produce a transparent conductive film having a low efficiency of 10 ⁻³ Ω · cm or less, for example, in the first half of 10 ⁻⁴ Ω · cm, ITO must be crystallized, and the substrate must be at least 160 Ω. Must be heated above ℃. If an ITO film is deposited without heating the substrate, the film quality is a mixture of amorphous and microcrystalline, resulting in a film having a high resistivity of the order of 10 ⁻³ Ω · cm.

  In the fields of the liquid crystal display and the organic EL display, use of an organic substrate such as a plastic substrate or a plastic film instead of a glass substrate has been studied in consideration of weight reduction, thinning, handling, and the like. Further, it is necessary to form a transparent electrode for a touch panel on a plastic film. These plastic substrates and organic substrates such as plastic films are weak to heat, and it is difficult to heat the substrates. Therefore, a major issue is how to form a low-resistance ITO film on an organic substrate that is vulnerable to heat.

  As a technique for forming an ITO transparent conductive film on a plastic film, a method of forming a film by reactive sputtering while applying a bias voltage has been proposed (for example, see Patent Document 1). In the technique described in Patent Document 1, when forming an ITO transparent conductive film on a transparent plastic film substrate by a reactive sputtering method, a bias voltage for accelerating ions in the direction of the substrate between the transparent conductive film and the ground is applied. According to this, a transparent conductive film having high transparency and adhesion and improved abrasion resistance can be stably manufactured.

As a film formation method for forming various films without damaging the substrate, a so-called gas flow sputtering method has been proposed (for example, see Patent Document 2 and Patent Document 3). The gas flow sputtering method is a transport type sputtering method in which sputter particles generated inside a cathode are transported to a substrate side by a flow of an atmospheric gas. In the technique of Patent Document 3, sputtering is performed in a direction perpendicular to a central axis of a target. An exhaust port for discharging gas is provided, and the substrate is disposed at a position on the exhaust port side, and a thin film is formed so that the substrate is not affected by plasma and high-energy particles.
JP-A-62-222518 Japanese Patent Publication No. 2-14427 and JP 2001-14066 A

However, the technique disclosed in Patent Document 1 is basically an extension of the above-described conventional technique, and the transparent conductive film to be produced is not sufficient in terms of resistivity because the substrate is not heated. For example, it is difficult to realize a transparent conductive film having a resistivity of 10 ⁻³ Ω · cm or less.

On the other hand, in the gas flow sputtering methods disclosed in Patent Literature 2 and Patent Literature 3, emphasis is placed on avoiding damage to the substrate, and studies on the characteristics of a film to be formed are not always sufficient. In particular, there is no report on the application of the gas flow sputtering method to the formation of the ITO transparent conductive film, nor on the film characteristics of the formed ITO transparent conductive film. In fact, the present inventors tried to form an ITO transparent conductive film by the method described in Patent Document 1 or Patent Document 2, but formed an ITO transparent conductive film of the order of 10 ⁻⁴ Ω · cm. I couldn't.

  The present invention has been proposed in view of such conventional circumstances, and provides a transparent conductive film having a low resistivity that has never been realized while forming a film on an organic substrate without heating the substrate. It is another object of the present invention to provide a film forming method.

  The present inventors have conducted various studies over a long period of time in order to achieve the above object. As a result, it has been found that in a gas flow sputtering method, a bias voltage is applied to a substrate to form a low-resistivity ITO conductive film without damaging the substrate.

The present invention has been completed based on the above findings, and the invention according to claim 1 is mainly composed of an oxide containing indium and tin, and is formed on an organic substrate by a sputtering method, and has a resistivity. Is not more than 10 ⁻³ Ω · cm.
The invention according to claim 2 is the transparent conductive film according to claim 1, wherein the transparent conductive film has a peak intensity of (222) plane and a peak intensity of (400) plane of indium tin oxide in X-ray diffraction. Is 1: 1 or more and 4: 1 or less.
The invention according to claim 3 is the transparent conductive film according to claim 1, wherein the organic substrate is a plastic film.
The invention according to claim 4 uses a target containing indium and tin and transports and deposits sputtered particles from the target on the organic substrate by a sputter gas flow while applying a bias voltage to the organic substrate. This is a characteristic method for forming a transparent conductive film.
According to a fifth aspect of the present invention, there is provided the method for forming a transparent conductive film according to the fourth aspect, wherein the target is a hollow target, and a sputtering gas is caused to flow in a central axis direction of the target. Wherein the organic substrate is disposed so as to face a flow of a sputtering gas.
The invention according to claim 6 is the method for forming a transparent conductive film according to claim 5, wherein a voltage is applied to the target to generate plasma, and the plasma generates sputter particles. This is a method for forming a transparent conductive film.
The invention according to claim 7 is the method for forming a transparent conductive film according to claim 6, wherein the organic substrate is brought close to a target so as to be affected by the plastic. It is a membrane method.
The invention according to claim 8 is the method for forming a transparent conductive film according to claim 7, wherein the distance between the organic substrate and the target is 2 cm or more and 10 cm or less. It is.
The invention according to claim 9 is the method for forming a transparent conductive film according to claim 7, wherein the organic substrate is cooled from the back side as necessary. is there.
The invention according to claim 10 is the method for forming a transparent conductive film according to claim 4, wherein a plastic film is used as the organic substrate, and the transparent conductive film is continuously formed while running the plastic film. This is a method for forming a transparent conductive film.
The invention according to claim 11 is the method for forming a transparent conductive film according to claim 4, wherein a DC bias voltage is applied to the organic substrate as the bias voltage. It is.
According to a twelfth aspect of the present invention, there is provided the method for forming a transparent conductive film according to the eleventh aspect, wherein the DC bias voltage is -80 V or more and -10 V or less with respect to a discharge plasma potential. This is a film formation method.
The invention according to claim 13 is the method for forming a transparent conductive film according to claim 4, wherein a high frequency bias voltage is applied to the organic substrate as the bias voltage. It is.
The invention according to claim 14 is the method for forming a transparent conductive film according to claim 13, wherein the high-frequency bias voltage is applied by a high-frequency electrode provided on the back side of the organic substrate, and the organic substance to which the transparent conductive film adheres is applied. A method for forming a transparent conductive film, characterized in that the average value (DC component) of the high-frequency voltage on the front surface of the substrate is -80 V or more and -10 V or less with respect to the discharge plasma potential.

The transparent conductive film of the present invention is mainly composed of an oxide containing indium and tin, is formed on an organic substrate by a sputtering method, and has a resistivity of 10 ⁻³ Ω · cm or less.
No transparent conductive film formed on an organic substrate and having a resistivity of 10 ⁻³ Ω · cm or less has been reported so far. Such a transparent conductive film having a low resistivity is provided by the present invention. This was realized for the first time.

  It is considered that the low resistivity of the transparent conductive film of the present invention is closely related to the film formation method, but the detailed mechanism and the reason are unknown. However, for example, analysis results of X-ray diffraction show that the film structure is significantly different from that of a film formed by a normal sputtering method. The ITO transparent conductive film formed by a normal sputtering method has a dominant peak derived from the (400) plane of indium tin oxide, and is a (100) oriented film. In a film having such a crystal orientation, if the crystallinity is not good, the resistivity of the transparent conductive film does not decrease. On the other hand, in the transparent conductive film of the present invention, a peak derived from the indium tin oxide (222) plane was observed and shifted to the (111) orientation, and was clearly a film formed by a normal sputtering method. Differs greatly from the film structure. The ratio of the peak intensity derived from the (222) plane to the peak intensity derived from the (400) plane varies depending on sputtering conditions and the like. As a result of examination, the peak intensity of the (222) plane of indium tin oxide and ( It was found that a low resistivity was realized when the ratio of the peak intensity of the (400) plane was 1: 1 or more and 3: 1 or less.

  On the other hand, the method for forming a transparent conductive film of the present invention uses a target containing indium oxide and tin oxide, and applies a bias voltage to an organic substrate while sputtering particles from the target by the sputter gas flow. It is characterized by being transported and deposited on a substrate.

  Although the film forming method of the present invention is based on so-called gas flow sputtering, the most characteristic feature is that a bias voltage such as a DC bias voltage or a high frequency (RF) bias voltage is applied. The ITO transparent conductive film formed by ordinary gas flow sputtering is a porous film, and the film becomes dense by applying a bias voltage, that is, by applying ion bombardment. When a bias is applied, the carrier density becomes higher and the hole mobility becomes 10 times or more as compared with a sample without a bias. Therefore, it is considered that the resistivity decreases.

  In the film forming method of the present invention, the ITO transparent conductive film having good characteristics is obtained by bringing the organic substrate close to the target so as to be positively affected by the plasma. This is also different from the conventional technique of forming a thin film without being affected by high energy particles.

As is clear from the above description, according to the present invention, a film having a low level of 10 ⁻⁴ Ω · cm, which has never been realized, is formed on an organic substrate such as a plastic film without heating the substrate. It is possible to provide an ITO transparent conductive film having resistivity.

Hereinafter, a transparent conductive film to which the present invention is applied and a method for forming the same will be described.
The basic idea of the present invention is to form an ITO transparent conductive film on an organic substrate while applying a bias voltage by a gas flow sputtering method. explain.

  In the present invention, as a technique for forming the ITO transparent conductive film, a gas flow sputtering method having a higher operating pressure than a normal sputtering method is used. In the gas flow sputtering method, atoms sputtered by a target are carried on a forced gas flow of a sputtering gas (Ar gas) from behind the target and transported to a substrate. Since the pressure in this transport process is higher than that of normal sputtering, the sputtered particles repeatedly undergo collision and scattering, become thermalized, and release energy. Therefore, low energy particles are deposited on the substrate, and the substrate is not damaged.

Here, since the substrate is not damaged, an organic substrate such as a plastic substrate or a plastic film can be used as the film formation substrate. As a target material of the target, an oxide, a metal, an alloy, or the like which is a raw material of the ITO transparent conductive film can be used. For example, a mixture of In ₂ O ₃ which is an oxide of indium and SnO ₂ which is an oxide of tin Etc. can be used. Alternatively, an alloy of indium and tin can be used.

  The shape of the target may be a cylindrical shape, a flat plate shape, or the like, but is not limited thereto, and may be any shape as long as a forced gas flow can be supplied from one end side along the target surface. During sputtering, a voltage is applied to the target to generate plasma, and the plasma generates sputtered particles. In this target, a large sputter current can be obtained by utilizing a hollow cathode discharge.

  The substrate is, for example, a target having a hollow shape and, when a sputtering gas is flowed as a forced gas flow in the central axis direction, the substrate is disposed orthogonal to the central axis, and the substrate is disposed so as to face the forced gas flow. . As a result, the forced gas flow is sprayed directly on the surface of the substrate, and sputter particles riding on the forced gas flow are efficiently deposited on the substrate surface.

  At this time, it is preferable that the distance between the substrate and the target is set as small as possible, and the substrate is brought close to the target so as to be affected by the plasma. The optimum distance varies depending on the device configuration, the magnitude of a bias voltage described later, the plasma conditions, and the like. If the distance between the substrate and the target is too large, the effect of applying the substrate bias will be insufficient, and it will be difficult to form a low resistivity film. However, if the distance is too close, when a plastic film or the like is used as a substrate, there is a possibility that damage or the like may become a problem, so care must be taken. In order to avoid such damage to the substrate, it is effective to provide a cooling mechanism such as circulating cooling water through the substrate holder. By providing a cooling mechanism in the substrate holder and cooling the substrate from the back side of the substrate, the substrate is not damaged even when the substrate is arranged so as to be affected by the plasma.

  The ITO transparent conductive film is formed on the organic substrate by the above-described gas flow sputtering method, and what is important here is to apply a bias voltage to the organic substrate. By applying a direct current (DC) bias voltage or an alternating current (high frequency: RF) bias voltage and performing so-called bias sputtering, an impurity (nitrogen or the like) in the ITO transparent conductive film to be formed is knocked out to improve the crystallinity. And a low-resistance ITO transparent conductive film can be obtained. Further, it becomes harder and denser than an ITO transparent conductive film obtained by a normal gas flow sputtering method, and the adhesion to an organic substrate is also improved.

FIG. 1 is a schematic view showing a state of DC bias sputtering in gas flow sputtering. At least a part of the surface of a substrate 3 having an insulating surface is provided with electrodes 4 and 5.
The electrodes 4 and 5 are formed by patterning a metal thin film (a thin film of a metal such as aluminum) formed by an evaporation method or a sputtering method, and are in close contact with the surface of the substrate 3.

  Here, the substrate 3 is rectangular as shown in FIG. 1, and the electrodes 4 and 5 are arranged near two longitudinal sides of the substrate 3, respectively. The surface of the substrate 3 is exposed between the electrodes 4 and 5. These electrodes 4 and 5 are connected to a DC power source 6 so that the same voltage is applied to the two electrodes 4 and 5.

  The target 1 has a cylindrical shape such as a cylinder, one end of which is directed to the surface of the substrate 3 on which the electrodes 4 and 5 are formed. When a sputtering gas (for example, Ar gas) is introduced into the internal space of the cylinder from the other end of the target 1 and a voltage is applied to the target 1 to sputter the surface exposed in the internal space of the cylinder of the target 1, the target 1 generates The sputtered particles 2 get on the sputtering gas flowing through the internal space of the cylinder, reach the surface of the substrate 3 and the surfaces of the electrodes 4 and 5, and adhere to the sputtered particles, whereby the ITO transparent conductive film grows.

The growing ITO transparent conductive film is in contact with the electrodes 4 and 5, and the portion located on the surface of the substrate 3 is also electrically connected to the electrodes 4 and 5.
Accordingly, the ITO transparent conductive film is grown in a state where a negative voltage is applied from the DC power supply 6, and as a result, the positive ions of the sputtering gas in the plasma enter the surface of the ITO transparent conductive film while being incident on the surface of the ITO transparent conductive film. A conductive film grows, resulting in improved crystallinity.

  FIG. 2 is a schematic diagram showing a state of RF bias sputtering in gas flow sputtering. In the case of RF bias sputtering, an earth plate 7 is arranged on the front surface of the substrate 3 and an RF electrode 8 is installed on the rear surface side of the substrate 3, and an RF power source 11 is connected thereto via a matching box 9 and an amplifier 10. I do. The applied RF bias voltage is monitored by the oscilloscope 12. In the case of the RF bias, a bias voltage can be applied to the insulator substrate.

For example, in the case of the DC bias shown in FIG. 1, it is preferable that the bias voltage be −80 V or more and −10 V or less with respect to the discharge plasma potential. If the DC bias voltage is less than −10 V with respect to the discharge plasma potential, the resistivity of the obtained ITO transparent conductive film cannot be sufficiently reduced, and a resistivity of 10 ⁻³ Ω · cm or less can be realized. difficult. Conversely, if the DC bias voltage exceeds -80 V with respect to the discharge plasma potential, discharge on the film surface is confirmed during deposition, and the film may be damaged.

In the case of the RF bias shown in FIG. 2, the RF bias voltage for self-biasing the organic substrate surface is preferably -100 V or less (DC component), and the electrode voltage of the bias electrode provided on the back surface of the substrate is adjusted. There is a need to. In particular, a high-frequency bias voltage is applied by a high-frequency electrode provided on the back side of the organic substrate, and the average value (DC component) of the high-frequency voltage on the front surface of the organic substrate to which the transparent conductive film adheres is -80 V or more with respect to the discharge plasma potential. It is more preferable to adjust the voltage to 10 V or less. This results in a resistivity on the order of 10 ⁻⁴ Ω · cm. Further, the frequency of the RF bias voltage is preferably 300 kHz or more.

The other sputtering conditions in the gas flow sputtering method are, for example, the sputtering pressure is preferably 13 Pa or more and 133 Pa or less. It is preferable that the sputtering power be 1.6 W / cm ² or more and 11 W / cm ² or less. Although it depends on the size of the target, for example, when the opening area is 80 cm ² , the Ar gas flow rate is preferably 1000 scm or more (+1000 sccm). At that time, the flow rate of the O ₂ gas is preferably set to 10 sccm or less.

  The above is the outline of gas flow sputtering in the present invention.In the present invention, as described above, by combining gas flow sputtering and bias sputtering, film formation on an organic substrate such as a plastic substrate has been achieved so far. It is possible to realize the formation of an ITO transparent conductive film having a low resistivity, which has never been achieved.

The gas flow sputtering method is advantageous for forming a film on an organic substrate such as a plastic film in that the substrate is not damaged, but when applied to the formation of an ITO transparent conductive film, for example, a low-resistance film is obtained. I can't. When the electrical characteristics of the ITO transparent conductive film formed by the gas flow sputtering method are measured, it is as high as 1 × 10 ⁻² Ω · cm. The reason is that the carrier density is small and the hole mobility is very small. In the ITO transparent conductive film formed by the gas flow sputtering method, In and Sn are not substituted well, and the carrier density is small. Further, as a result of the composition analysis, it is considered that nitrogen was contained in the film, and this became a neutral scattering center, which reduced the mobility.

  When the bias was applied, the mobility was 10 times or more as compared with the sample without the bias, and it is considered that the resistivity was reduced because of this. In particular, by bringing the substrate closer to the target under the influence of the plasma, sputtered particles of relatively high energy are deposited on the substrate, and a synergistic effect with the effect of the bias application is used to form an ITO transparent conductive film having extremely low resistivity. A film can be formed.

The transparent conductive film of the present invention formed by the above-described method is an ITO transparent conductive film mainly composed of an oxide containing indium and tin, and has a resistivity of 10 ⁻³ Ω · while being formed on an organic substrate. cm and extremely low resistivity. Specifically, a low-resistance film having a resistivity of 2.5 × 10 ⁻⁴ Ω · cm at a DC bias of −50 V and a voltage of 3.3 × 10 ⁻⁴ Ω · cm at an RF electrode voltage of 160 V could be produced.

  The ITO transparent conductive film of the present invention has an amorphous-like microcrystalline structure, and is significantly different from a normal sputtered film having a clear crystal structure. This difference in the crystal structure is also notable in the results of X-ray diffraction. The ITO transparent conductive film of the present invention has a component in which a (222) plane peak is observed by X-ray diffraction and is oriented in 111 directions. In a normal sputtered film, the peak of the (400) plane is dominant and oriented in 100 directions. Although the detailed mechanism of how this difference in crystal structure is related to the electric resistance is unknown, in the ITO transparent conductive film of the present invention, the peak intensity of the (222) plane of indium tin oxide and It is known that the resistivity becomes low when the ratio of the peak intensities of the (400) plane is 1: 1 or more and 4: 1 or less.

Hereinafter, specific examples of the present invention will be described based on experimental results.
Gas Flow Sputtering + DC Bias In this experiment, a DC bias voltage was applied to the substrate in gas flow sputtering, and the effect was examined.

  FIG. 3 shows the configuration of the sputtering apparatus used in this experiment. This gas flow sputtering apparatus includes a target 22 having a vacuum chamber 21 and a cooling mechanism 23, a substrate holder 25 for supporting a substrate 24 on which an ITO transparent conductive film is formed, and the like. A target 22 is disposed, and a substrate 24 is disposed in a vacuum chamber 21 by being attached to a substrate holder 25. Then, by supplying a forced gas flow of Ar gas and oxygen gas from behind the target 22, the sputtered particles generated from the target 22 are transported and deposited on the substrate 24 with the forced gas flow. An exhaust port 26 is provided on the side of the vacuum chamber 21 at right angles to the central axis of the target 22, and the supplied Ar gas and oxygen gas are quickly exhausted from the exhaust port 26.

  In the sputtering apparatus of this embodiment, a discharge prevention plate 28 made of a metal plate such as aluminum is provided at the forced gas flow inlet 21a of the vacuum chamber 21 to prevent unnecessary arc discharge generated at this portion. Like that.

  In the vicinity of the substrate 24 on which the ITO transparent conductive film is formed, a shutter 29 for blocking unnecessary sputtered particles and forced gas flow is provided. The shutter 29 is opened as necessary, and ITO by gas flow sputtering is provided. A film of the transparent conductive film is formed on the substrate 24.

An electrode 30 is arranged on the surface of the substrate 24 along the edge thereof.
The electrode 30 has a ring shape in plan view. Except for the difference in the planar shape, it has the same material and the same structure as the electrodes 4 and 5 in FIG. 1. When the DC bias power supply 31 is started and a DC voltage is applied to the electrode 30, the voltage becomes It is configured to be applied to the film.

The ITO transparent conductive film was formed using the above-described sputtering apparatus. The DC bias sputtering conditions at this time are as follows.
DC bias sputtering conditions Sputtering pressure: 15 Pa
Sputtering power: 500W
Ar gas flow rate ... 1000 sccm (+1000 sccm)
O ₂ gas flow rate ···· 0 sccm or more and 5 sccm or less Preliminary evacuation ····· 8 × 10 ⁻³ Pa or less Substrate ···· Polyethylene terephthalate DC bias voltage (relative to discharge plasma potential) 80 V or more and 0 V or less Target: In ₂ O ₃ : SnO ₂ = 95: 5 (% by weight)
Substrate temperature ..... room temperature (without substrate heating)

  FIG. 4 shows the relationship between the DC bias voltage at an oxygen flow rate of 1.2 sccm and the resistivity of the formed ITO transparent conductive film. As is clear from FIG. 4, the resistivity is minimum when the DC bias voltage is -50 V. When the DC bias voltage was set to -80 V or higher, discharge was confirmed on the film surface during deposition.

  FIG. 5 shows the relationship between the deposition time and the resistivity at a DC bias voltage of -50V. With a deposition time of 4 minutes or more, an ITO transparent conductive film having a small resistivity is obtained. When the deposition time is 4 minutes or less, it is considered that there is an influence of the initial layer to which no bias voltage is applied.

  FIG. 6 shows the relationship between the oxygen flow rate and the resistivity at each DC bias voltage, and FIG. 7 shows the oxygen flow rate dependence of carrier density and hole mobility at a DC bias of -30 V. In any case, the smaller the oxygen flow rate, the better the results.

  FIG. 8 is an X-ray diffraction chart showing the crystallinity at each DC bias voltage when the oxygen flow rate is 1.2 sccm. The orientation changes from the (111) orientation to the (100) orientation as the bias voltage increases. At a DC bias voltage of -70 V, the number of diffraction peaks is smaller than in the case of a voltage lower than -70 V.

  FIG. 9 is a scanning electron microscope (SEM) photograph (magnification: 60,000) showing the surface morphology of the obtained ITO transparent conductive film. 9A shows the surface of the ITO transparent conductive film at a DC bias voltage of −30 V, FIG. 9B shows the surface of the ITO transparent conductive film at a DC bias voltage of −50 V, and FIG. As the DC bias voltage increases, the crystal becomes finer.

Gas Flow Sputtering + RF Bias In this experiment, an RF bias voltage was applied to the substrate in gas flow sputtering, and the effect was examined.

  FIG. 10 shows the configuration of the sputtering apparatus used in this experiment. This gas flow sputtering apparatus has the same basic structure as the sputtering apparatus shown in FIG. 3, but is modified to apply an RF bias voltage. Specifically, in this example, the film is formed while the organic substrate 34 in the form of a film is running between the pair of rolls 32 and 33. A bias applying unit 35 having an RF bias electrode 36 is disposed on the back side of the traveling organic substrate 34. The RF bias electrode 36 is connected to a high frequency power supply 39 via a matching box 37 and an amplifier 38. I have. In the bias applying unit 35, an earth shield 41 is provided on an outer peripheral surface via an insulator 40, and a cooling water circulation mechanism 42 for supplying cooling water to the inside is provided. Further, an earth shield 43 is provided between the organic substrate 34 and the shutter 29.

The ITO transparent conductive film was formed using the above-described sputtering apparatus. The RF bias sputtering conditions at this time are as follows.
RF bias sputtering conditions Sputter pressure: 15 Pa
Sputtering power: 500W
Ar gas flow rate ... 1000 sccm (+1000 sccm)
O ₂ gas flow rate ····· 0 sccm or more and 5 sccm or less Preliminary evacuation ····· 8 × 10 ^-3 Pa or less Substrate ···· Polyethylene terephthalate (125 μm thickness)
RF bias voltage: -75V or more and 0V or less (DC component)
RF electrode voltage ・ ・ ・ 0V _PP or more and 200V _PP or less Frequency ・ ・ ・ ・ ・ ・ ・ 10MHz
Target: In ₂ O ₃ : SnO ₂ = 95: 5 (% by weight)
Substrate temperature ..... room temperature (without substrate heating)
In the above conditions, the RF bias voltage is a peak voltage (peak to peak voltage) V _PP in the RF electrode voltage waveform. Further, under the above conditions, the RF bias voltage (DC component) on the front surface of the substrate was about 0.28 times the RF electrode voltage.

FIG. 11 shows the relationship between the RF electrode voltage at an oxygen flow rate of 1.2 sccm and the resistivity of the formed ITO transparent conductive film. When the RF electrode voltage is 100 V _PP or more, the resistivity is on the order of 10 ⁻⁴ Ω · cm. A minimum resistivity of 3.33 × 10 ⁻⁴ Ω · cm was obtained at an RF electrode voltage of 160 V _PP .

FIG. 12 is an X-ray diffraction chart showing the crystallinity at each RF electrode voltage when the oxygen flow rate is 1.2 sccm. When the RF electrode voltage is 80 V _PP or more, peaks on the (222) and (400) planes are observed, and improvement in crystallinity is recognized. At a voltage of 160 V _PP or higher, the peak of the (222) plane is broad, and at 200 V _PP , the peak of the (400) plane is large. Under these conditions, a sample with an RF electrode voltage of 120 V _PP gives the best results.

FIG. 13 is a scanning electron microscope (SEM) photograph (magnification: 60,000) showing the surface morphology of the obtained ITO transparent conductive film. 13A shows an RF electrode voltage of 0 V _PP , FIG. 13B shows an RF electrode voltage of 40 V _PP , FIG. 13C shows an RF electrode voltage of 80 V _PP , and FIG. 13D shows an RF electrode voltage of 120 V _PP . (E) shows the surface of the ITO transparent conductive film when the RF electrode voltage is 160 V _PP , and FIG. 13 (F) shows the surface of the ITO transparent conductive film when the RF electrode voltage is 200 V _PP . It was observed that the crystallinity was improved up to an RF electrode voltage of 120 V _PP, and that the grain size was reduced above that.

  As described above, in the present invention, a DC voltage is applied to the substrate by applying a DC voltage to the electrode on the front surface of the insulating substrate, or by applying an AC voltage to the electrode disposed on the back surface of the substrate. Not only an AC voltage is applied, but also a DC voltage or an AC voltage is applied to the growing transparent conductive film.

It is a schematic diagram of DC bias sputtering. It is a schematic diagram of RF bias sputtering. FIG. 2 is a diagram illustrating a schematic configuration of a DC bias gas flow sputtering apparatus used in an experiment. FIG. 4 is a characteristic diagram showing a relationship between a DC bias voltage and a resistivity of a formed ITO transparent conductive film. FIG. 4 is a characteristic diagram showing a relationship between a deposition time and a resistivity at a DC bias voltage of −50 V. FIG. 4 is a characteristic diagram showing a relationship between an oxygen flow rate and a resistivity at each DC bias voltage. FIG. 4 is a characteristic diagram illustrating the oxygen flow rate dependence of carrier density and hole mobility at a DC bias of −30 V. 5 is an X-ray diffraction chart showing crystallinity at each DC bias voltage. It is a scanning electron micrograph which shows the surface morphology of the ITO transparent conductive film obtained by DC bias gas flow sputtering, (A) is DC bias voltage -30V, (B) is DC bias -50V, (C) is DC The surface of the ITO transparent conductive film at a bias voltage of -70 V is shown. FIG. 2 is a diagram illustrating a schematic configuration of an RF bias gas flow sputtering apparatus used in an experiment. FIG. 4 is a characteristic diagram showing a relationship between an RF electrode voltage and a resistivity of a formed ITO transparent conductive film. 5 is an X-ray diffraction chart showing crystallinity at each RF electrode voltage. A scanning electron microscope photograph showing the surface morphology of the obtained ITO transparent conductive film by the RF bias gas flow sputtering, (A) is RF electrode voltage 0V _PP, (B) the RF electrode voltage 40V _PP, (C) is The RF electrode voltage is 80 V _PP , (D) is the RF electrode voltage 120 V _PP , (E) is the RF electrode voltage 160 V _PP , and (F) is the surface of the ITO transparent conductive film when the RF electrode voltage is 200 V _PP .

Explanation of reference numerals

1 Target 2 Sputtered particles 3 Substrate 4 5 Al electrode (DC bias electrode) 8 RF electrode

Claims (14)

A transparent conductive film mainly composed of an oxide containing indium and tin, formed on an organic substrate by a sputtering method, and having a resistivity of 10 ⁻³ Ω · cm or less.   The transparent conductive film is characterized in that, in X-ray diffraction, the ratio of the peak intensity of the (222) plane of indium tin oxide to the peak intensity of the (400) plane is 1: 1 or more and 4: 1 or less. Item 4. The transparent conductive film according to Item 1.   The transparent conductive film according to claim 1, wherein the organic substrate is a plastic film.   A target containing indium and tin is used, and a bias voltage is applied to the organic substrate while a sputtered particle from the target is transported and deposited on the organic substrate by a sputter gas flow while forming a transparent conductive film. Membrane method.   5. The method according to claim 4, wherein the target is a hollow target, and a sputter gas is caused to flow in a central axis direction of the target, and the organic substrate is arranged so as to be opposed to the flow of the sputter gas at right angles to the central axis. The method for forming a transparent conductive film according to the above.   6. The method according to claim 5, wherein a voltage is applied to the target to generate plasma, and the plasma generates sputter particles.   7. The method according to claim 6, wherein the organic substrate is brought close to a target so as to be affected by the plastic.   8. The method according to claim 7, wherein a distance between the organic substrate and the target is 2 cm or more and 10 cm or less.   8. The method according to claim 7, wherein the organic substrate is cooled from the back side as needed.   5. The method for forming a transparent conductive film according to claim 4, wherein a plastic film is used as the organic substrate, and the transparent conductive film is continuously formed while running the plastic film.   The method according to claim 4, wherein a DC bias voltage is applied to the organic substrate as the bias voltage.   12. The method according to claim 11, wherein the DC bias voltage is -80 V or more and -10 V or less with respect to a discharge plasma potential.   The method according to claim 4, wherein a high frequency bias voltage is applied to the organic substrate as the bias voltage.   The high-frequency bias voltage is applied by a high-frequency electrode provided on the back side of the organic substrate, and the average value (DC component) of the high-frequency voltage on the front surface of the organic substrate to which the transparent conductive film adheres is −80 V to −10 V with respect to the discharge plasma potential. 14. The method for forming a transparent conductive film according to claim 13, wherein:

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