KR100567386B1 - Composite structure of transparent conducting films and method for forming the same - Google Patents

Abstract

The present invention proposes a transparent conductive thin film having a composite thin film structure of ZnO-ITO having an inclined composition layer, thereby providing a transparent conductive thin film having a much improved surface roughness compared to the transparent conductive thin film formed of a conventional ITO composition. It is to provide. The transparent thin film structure according to an aspect of the present invention, which contains a ZnO component and an ITO component together, has a gradient composition in which the component ratio of the ZnO decreases and at the same time the component ratio of the ITO increases as it moves away from the ZnO layer. Phosphorus gradient composition layer.

Slanted Composition, Thin Film, Transparent Conductive Film, ITO, ZnO, Sputtering, Coating

Description

Transparent conductive composite thin film structure, method for forming the same, and sputtering device TECHNICAL FIELD

1 shows the effect of interfacial roughness when the ITO single thin film of the prior art is used.

2 illustrates a transparent thin film structure having a gradient composition layer in accordance with one embodiment of the present invention.

3 is a block diagram showing an example of a sputtering apparatus used to obtain a transparent conductive thin film of the present invention.

4 conceptually illustrates a thin film stack structure formed by the apparatus of FIG. 3.

FIG. 5 shows the results of SIMS (Secondary Ion Mass Spectrometry) analysis of the cross-sectional composition of the transparent conductive thin film structure to which the present invention is applied.

6 illustrates a sputtering apparatus using a bipolar pulse power supply.

7 shows alternate pulse voltages provided by a bipolar pulse power source.

8 is a result of measuring the surface roughness in the case of depositing a conventional ITO single film by AFM (Atomic Force Microscopy).

9 is a result of measuring the surface roughness when the ITO-ZnO composite film having a gradient composition of the present invention is deposited by AFM (Atomic Force Microscopy).

<Description of the symbols for the main parts of the drawings>

100: transparent conductive thin film 110: lower layer

120: ZnO thin film layer 130: ITO-ZnO composite gradient composition layer

140: ITO thin film layer

The present invention relates to a transparent conductive thin film used for a display element, a touch panel, and the like, and more particularly, in order to improve the surface roughness of the transparent conductive thin film, a composite thin film structure of ITO-ZnO having a gradient composition layer is proposed. In addition, an efficient manufacturing method for forming such a composite thin film structure using an inline sputtering method is proposed.

Transparent conducting oxide (TCO) since the first report showed that a transparent electrical conductive film could be obtained by oxidizing a cadmium (Cd) metal film deposited in a chamber of a glow discharge device in 1907. The commercial availability of the outlines has emerged.

Full-scale R & D and commercialization of TCO thin film material started in 1960s, and TCO thin film of SnO2 composition by pyrolysis spray or sputtering was developed to save energy for building windows or photovoltaic cells. It has been applied to (photovoltaic cell). Meanwhile, Sn doped In ₂ O ₃ based (ITO) high-quality TCO thin films using sol-gel, evaporation, and sputtering are mainly used for flat panel display devices. It is now the most widely used TCO.

However, in the case of SnO 2 -based TCO, the specific resistance has not been improved any more due to the limitation of 3-5 × 10 ⁻⁴ μm cm and ITO 1 × 2 × 10 ⁻⁴ μm cm for the last 20 years.

In In, the main raw material of ITO, the world's small reserves are expected to rapidly deplete In when the flat display device market increases as the current trend, and instability of supply and demand is inherent. Research on materials has been actively conducted. On the other hand, despite many studies, as mentioned above, there is a limit to the improvement of the electrical properties of ITO over the past 20 years, and thanks to the results of rapid research and development of oxide superconducting materials, a new perspective on the research of transparent conductive oxide materials is introduced. A three-membered element containing two or more of three or more multi-cations of Cd ⁺² , In ⁺³ , Ga ⁺³ , Sn ⁺⁴ as well as binary oxide materials in recent years. Research on ternary or quaternary oxides is also active.

On the other hand, research on transparent conductive films having a multi-layered structure of TCO / metal layer / TCO, which reduces ITO usage and has excellent permeability and electrical conductivity, is being actively conducted. Ag or Ag alloys are mainly used for the metal layer because Ag has a very low absorption in the visible region compared to other metals. However, the Ag thin film, like the general metal thin film, when the thickness of the film becomes thick, the light transmittance rapidly decreases. Therefore, the thickness of the Ag thin film used in the three-layer structure transparent conductive film should be a thin film of about 10nm. Even if an Ag thin film of about 10 nm is inserted into the TCO layer, it is reported that a sheet resistance reduced by about 50% can be obtained as compared with a single TCO thin film having the same thickness.

Also, in 1998, in a multilayer film in which Ag and dielectric films were alternately stacked in four or more layers, a resonance tunneling effect was obtained even if the total thickness of the Ag thin film was a single layer of metal film, even though the thickness of the Ag thin film was not transmitted. There is a theoretical and experimental report that can form a one-dimensional photonic band-gap (PBG) due to the increase in transmittance in a specific wavelength band. By using this phenomenon, TCO thin film and Ag thin film are alternately stacked in order to use for low-emissivity coating for building glass and filter for PDP. Research into using low surface resistance by Ag thin film included in a multilayer structure is actively conducted.

However, in such a transparent conductive film having a multilayer structure, since the thickness of each metal film included in the multilayer structure is about 10 nm and very thin, the interface state between the thin film layers, that is, the interfacial roughness at the time of lamination, has the electrical and optical characteristics of the multilayer structure. Has a big impact on If the surface roughness of the transparent film deposited on the substrate is large, the surface roughness of the thin metal film layer stacked on the transparent film is also worsened, and the thin film layer of the transparent film stacked thereon also has a large surface roughness. Since the specific resistance of the metal is about 100 times smaller than that of the transparent conductive oxide, even in a multilayer structure using the transparent conductive oxide, the electrical conductivity is determined by the metal film layer interposed between the transparent film layers. However, when the roughness of the interface between the thin film layers becomes bad, the mean free path of electrons moving through the metal layer is reduced, thereby increasing the electrical resistance.

In FIG. 1, the effect of this interface roughness of the prior art is shown in schematic diagram. When a thin film having a multi-layer structure of the ITO transparent conductive film 20 for forming the optical band gap and the metal film 30 such as Ag is formed on the substrate 10, the transparent conductive film under the metal film 30 ( 20) The roughness of the surface IS is reflected in the metal film 30 as it is shown in FIG. Accordingly, the path of the movement of electrons 40 in the metal film 20 is limited by the interface as shown in FIG. 1, and the resistance increases as the mobility of the electrons decreases.

ITO, the most widely used transparent conductive film at present, has a surface roughness of about 2 to 3 nm, which is not very good, and the surface roughness may be partially improved by a method of surface treatment through plasma processing. It is difficult to achieve good surface roughness of less than 1 nm. In order to obtain excellent permeability and stable electrical properties during ITO film formation, ITO thin film with crystalline structure should be made. For this purpose, film formation is usually performed at 200 ℃ or higher. Although ITO can be manufactured at room temperature without using such a high temperature, ITO having an amorphous phase structure can be manufactured, but since amorphous ITO is unstable, crystallization proceeds later and its characteristics change with time. Therefore, in order to obtain stable electrical properties, the ITO film is generally formed to have a crystal structure at a high temperature as described above, and a film having such a crystal structure generally has a problem in that surface roughness is not as good as that of an amorphous film.

The present invention has been made to solve such a problem, and proposes a transparent conductive thin film having a composite thin film structure of ZnO-ITO having a gradient composition to reduce the amount of In used compared to the case of the transparent conductive thin film formed of ITO alone in the prior art. It is to provide a transparent conductive thin film to improve the electrical conductivity and light transmittance with excellent surface roughness while reducing the cost by reducing.

In addition, the present invention is to provide a high productivity and reliable manufacturing method applying in-line sputtering to form a thin film laminate having the structure described above.

Transparent thin film structure according to an aspect of the present invention for achieving the above object, the substrate; And a ZnO component and an ITO component formed on the substrate and having an inclined composition in which the component ratio of ZnO decreases from the bottom of the film to the top of the film, and at the same time, the component ratio of the ITO increases. It contains a composition layer.
Preferably, the Zn0 thin film layer formed between the substrate and the ITO-ZnO composite gradient composition layer; And an ITO thin film layer formed on the ITO-ZnO composite gradient composition layer.
Preferably, the ITO-ZnO composite gradient composition layer is characterized in that the amorphous.
Preferably, the RMS roughness at the surface of the ITO-ZnO composite gradient composition layer is 1 nm or less.
Preferably, the thickness of the ITO-ZnO composite gradient composition layer is characterized in that more than 10Å 5um.

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According to another aspect of the present invention, a sputtering apparatus includes a vacuum chamber; A substrate support traveling through the vacuum chamber by a predetermined controlled mechanical drive; One or more substrates mounted on the substrate support; At least one ITO target disposed in the vacuum chamber and providing ITO flux to the substrate surface by sputtering; And at least one ZnO target disposed adjacent to the ITO target in the vacuum chamber and providing a ZnO flux to the substrate surface, wherein the relative placement of the ZnO target and the ITO target is caused by movement of the substrate support. The substrate is disposed so as to have a section that passes the front of the ZnO target before the front of the ITO target, and the ITO flux and the ZnO flux spatially overlap each other.

Preferably, further comprising a bipolar pulse power supply for applying a bipolar pulse voltage of relatively polarity with the ZnO target and the ITO target as a positive electrode, the relative of the positive and negative pulses of the bidirectional pulse voltage By controlling the period, the density of the ITO flux and the density of the ZnO flux can be controlled respectively.

According to still another aspect of the present invention, there is provided a method of forming a transparent conductive thin film, comprising: a sputtering apparatus including a vacuum chamber, a substrate support traveling through the vacuum chamber by controlled mechanical driving, and one or more substrates mounted on the substrate support. A method of forming a transparent conductive thin film, the method comprising: depositing a ZnO film on a substrate by moving the substrate support so that the substrate passes the front of a ZnO target; Moving the substrate support to deposit an ITO-ZnO composite film on the substrate by passing the ZnO flux and the ITO flux formed by the ZnO target and the ITO target spatially overlap each other in the chamber; ; And depositing an ITO film on the substrate by moving the substrate support such that the substrate passes the front of the ITO target.
The step of depositing the ITO-ZnO composite film includes a ZnO component and an ITO component together on the substrate, and the component ratio of the ZnO decreases with increasing distance from the ZnO layer and at the same time the component ratio of the ITO increases. It is characterized by forming a ZnO composite gradient composition layer.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to preferred embodiments of the present invention.

2 shows a transparent thin film structure according to a preferred embodiment of the present invention. The transparent thin film structure 100 is formed on the lower layer 110. The lower layer 110 may be a glass or plastic substrate, or may be another thin film such as a metal film.

The transparent thin film structure 100 of FIG. 2 is characterized in that the ITO-ZnO composite gradient composition layer 130 has. The ITO-ZnO composite gradient composition layer 130 contains both a ZnO component and an ITO component, and the component ratio of ZnO decreases toward the top thereof, and at the same time, the component ratio of ITO increases. A thin film layer 120 containing ZnO as a main component may be deposited under the ITO-ZnO composite gradient composition layer 130. At this time, the lowest ZnO density of the ITO-ZnO composite gradient composition layer 130 has a continuous relationship with the ZnO density of the lower ZnO thin film layer 120. Thus, the boundaries of each layer are not physically distinct.

In addition, a thin film layer 140 containing ITO as a main component may be formed on the ITO-ZnO composite gradient composition layer 130. Similarly, the ITO density at the top of the ITO-ZnO composite gradient composition layer 130 has a continuous relationship with the ITO density of the ITO thin film layer 140 thereon. Thus, the boundaries of each layer are not physically distinct.

Here, the ITO thin film layer 140 and the ZnO thin film layer 120 are not essential. However, by the addition of the ITO thin film layer 140, a transparent conductive film having better electrical characteristics can be obtained, and by the addition of the ZnO thin film layer 120, the surface roughness and stable amorphous film can be obtained.

FIG. 3 is a block diagram showing an example of a sputtering apparatus used to obtain a transparent conductive thin film of the present invention, and FIG. 4 conceptually illustrates a thin film stack structure formed by the apparatus of FIG. In the chamber 51 of the sputtering apparatus, a ZnO sputter source S1 and an ITO sputter source S2 are positioned, and regions in which fluxes Z1 and Z2 of the coating material reached from the two sources overlap each other ( Z12) is arranged to form.

The chamber 51 is vacuumed by the vacuum valve 54 and the vacuum pump 55. Inside the device, the substrate 57 moves 58 in front of two sources S1 and S2. The ZnO target is installed in the front source S1, and the ITO target is installed in the rear source S2. An inert gas such as Ar is introduced into the chamber 51 by a gas injection device not shown, and a sputter power source is operated.

As a result of the coating using such an apparatus, a thin film of a laminated structure having different compositions is formed on the substrate 57 according to the position from the substrate surface as shown in FIG.

Here, by adjusting the installation angles of the two targets S1 and S2 or the distance between the targets, it is possible to control the range of the region Z12 in which the fluxes Z1 and Z2 provided from the two targets to the substrate overlap. In some cases, the flux (Z1, Z2) provided from each target may be completely overlapped, and by such adjustment, the relative thicknesses of the ZnO layer, the ITO-ZnO composite gradient composition layer, and the ITO layer of the thin film may be adjusted. do.

In order to form a region Z12 in which the fluxes Z1 and Z2 of the coating material provided from the two sources S1 and S2 overlap each other, it is possible without necessarily adjusting the angle of the target. It is also possible to use a configuration such as not providing a partition wall between S1 and S2, minimizing the mutual separation distance from each other, or sufficiently separating the distance from the substrate. Also in this manner, an intermediate layer having an inclined composition is formed on the substrate 57 as shown in FIG.

In FIG. 6, the case where a bipolar pulse power supply is used for such a sputter apparatus is shown. Bipolar pulse power supply refers to a power supply that is connected to two sputter targets S1 and S2, each of which is a positive electrode, and provides an alternating pulse voltage having a waveform shown in FIG. .

Since the voltage is alternated as shown in FIG. 7, sputtering is performed only for a target that takes a negative voltage during a period where a relatively negative voltage is applied. Therefore, if the duty ratio of the positive period and the negative period is respectively controlled or the magnitudes of the positive and negative pulses are controlled independently with respect to the pulse of FIG. 7, the concentration of the sputtered flux is relatively controlled. It is possible to control the composition ratio of ZnO and ITO in water.

Hereinafter, the characteristics of one transparent conductive thin film formed by applying the embodiment of the present invention will be exemplarily described.

An ITO-ZnO composite thin film specimen having a gradient composition was fabricated using an in-line sputtering apparatus as shown in FIG. 3 in which an ITO (In 2 O 3 (90 wt%): SnO 2 (10 wt%)) target and a ZnO target were installed. The size of the target used for fabrication of the specimen was 5 "× 20" × 0.25 ". The initial vacuum of the system for thin film fabrication was 2 × 10 ^-6 Torr, and when the thin film was fabricated, Ar 59sccm and O ₂ 1sccm were injected. The internal pressure was maintained at 2 mTorr The substrate was set to pass under the ZnO target and below the ITO target at a feed rate of 0.6 cm / sec.

The output of the bipolar pulse power supply was 3kW, and the output waveform was set to (-) pulse: (+) pulse = 45:45 as shown in FIG. 7, so that the pulse width applied to the ITO target and the ZnO target was the same. It was.

5 shows the result of analyzing the cross-sectional composition of the transparent conductive thin film structure according to the application example of the present invention by the Secondary Ion Mass Spectrometry (SIMS) analysis method. As shown in FIG. 5, it can be seen that the concentration of In decreases and the concentration of Zn increases closer to the lower substrate from the film surface. In this application example, the concentration of In and the concentration of Zn have an inverse relationship with each other.

8 and 9 are results of surface roughness measured by AFM (Atomic Force Microscopy) when the ITO single layer of the prior art is deposited and the ITO-ZnO composite layer having the gradient composition of the present invention is deposited, respectively. In the prior art of FIG. 8, the root mean square (RMS) roughness of the surface has a very high value of 10.1 μs, but the ITO-ZnO composite film having the gradient composition of the present invention has a very good surface roughness of about 1.3 μs. In comparison with the conventional ITO thin film, it can be confirmed that the surface roughness of the ITO-ZnO composite thin film to which the present invention is applied is about 7.8 times better.

In addition, as described above, when the amorphous film is formed at a low temperature in the conventional ITO membrane, there is a problem in that a thin film having stable characteristics cannot be obtained as the crystallization progresses, but the ITO-ZnO composite thin film having a gradient composition as in the present invention In the case of the amorphous formed at a low temperature was able to obtain a consistently stable characteristics. This is interpreted to be because the gradient composition structure of the present invention, in which the concentration of ZnO gradually decreases toward the top, serves to prevent crystallization of ITO.

In addition, when the ZnO layer is used at the bottom of the thin film, it acts as a buffer layer to further improve the surface roughness of the entire thin film. It makes it conductive. In addition, as described above, when the bipolar pulse power is used, there is an additional advantage of controlling the relative amounts of ITO and ZnO included in the thin film by adjusting the widths of the positive and negative pulses.

As described above, in the detailed description of the present invention, specific embodiments have been described, but it should be taken as exemplary, and various modifications may be made without departing from the technical spirit of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims.

By applying the ZnO-ITO composite film structure having a gradient composition proposed by the present invention, compared to the case of the transparent conductive thin film formed of ITO alone composition of the prior art, the surface roughness is significantly improved while reducing the amount of In used, It is possible to provide a transparent conductive thin film having stable electrical and optical properties.

In addition, it is possible to produce a thin film having good characteristics with high productivity by a gradient composition by the transparent conductive thin film forming apparatus and method using the sputtering method provided by the present invention.

Claims (8)

Board; And The ITO-ZnO composite gradient composition is formed on the substrate and contains a ZnO component and an ITO component, and has a gradient composition in which the component ratio of ZnO decreases from the bottom of the film to the top of the film and at the same time, the component ratio of the ITO increases. A transparent conductive thin film structure comprising a layer. The method of claim 1, A Zn0 thin film layer formed between the substrate and the ITO-ZnO composite gradient composition layer; And The transparent conductive thin film structure further comprising an ITO thin film layer formed on the ITO-ZnO composite gradient composition layer. The method according to claim 1 or 2, The ITO-ZnO composite gradient composition layer is a transparent conductive thin film structure, characterized in that the amorphous. The method according to claim 1 or 2, RMS roughness on the surface of the ITO-ZnO composite gradient composition layer is less than 1nm. The method according to claim 1 or 2, The ITO-ZnO composite gradient composition layer is a transparent conductive thin film structure, characterized in that the thickness of more than 10Å 5um. A vacuum chamber; A substrate support traveling through the vacuum chamber by a predetermined controlled mechanical drive; One or more substrates mounted on the substrate support; At least one ITO target disposed in the vacuum chamber and providing ITO flux to the substrate surface by sputtering; And At least one ZnO target disposed adjacent to the ITO target in the vacuum chamber and providing a ZnO flux to the substrate surface, The relative arrangement of the ZnO target and the ITO target, The substrate passes the front of the ZnO target before the front of the ITO target by the movement of the substrate support, And a sputtering apparatus arranged such that the ITO flux and the ZnO flux have a spatial overlap with each other. The method of claim 6, A bipolar pulse power supply for applying a bidirectional pulse voltage having relatively polarity alternately using the ZnO target and the ITO target as positive electrodes; It is possible to control the density of the ITO flux and the density of the ZnO flux by controlling the relative periods of the positive and negative pulses of the bidirectional pulse voltage, respectively. Sputtering device. A transparent conductive thin film forming method using a sputtering apparatus having a vacuum chamber, a substrate support traveling through the vacuum chamber by a controlled mechanical drive, and at least one substrate mounted on the substrate support. Depositing a ZnO film on the substrate by moving the substrate support such that the substrate passes the front of the ZnO target; Moving the substrate support to deposit an ITO-ZnO composite film on the substrate by passing the ZnO flux and the ITO flux formed by the ZnO target and the ITO target spatially overlap each other in the chamber; ; And Moving the substrate support such that the substrate passes the front of the ITO target, depositing an ITO film on the substrate, The step of depositing the ITO-ZnO composite film includes a ZnO component and an ITO component together on the substrate, and the component ratio of the ZnO decreases with increasing distance from the ZnO layer and at the same time the component ratio of the ITO increases. A method for forming a transparent conductive thin film, comprising forming a ZnO composite gradient composition layer.

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