WO2006068427A1

WO2006068427A1 - Multi-layered ito for transparent electrode and method of and apparatus for vapor-depositing the same

Info

Publication number: WO2006068427A1
Application number: PCT/KR2005/004449
Authority: WO
Inventors: Ji Pyoung Choi; Byung Chang Park; Suk Hyun Choi; Choon Sig Kim; Young Sun Yun
Original assignee: Plaworks Co., Ltd
Priority date: 2004-12-23
Filing date: 2005-12-22
Publication date: 2006-06-29
Also published as: KR100546632B1

Abstract

Disclosed is a multi-layered ITO for a transparent electrode. The multi-layered ITO comprises a first ITO layer having a first thickness, and a second ITO layer having a second thickness. The first ITO layer is deposited on a glass substrate through an ion beam sputtering using a sputtering gas supplied from an ion source under oxygen atmosphere maintained around the glass substrate. The second ITO layer is deposited on the first ITO layer through a DC sputtering. A method of and an apparatus for fabricating the multi-layered ITO are also disclosed.

Description

MULTI-LAYERED ITO FOR TRANSPARENT ELECTRODE AND METHOD OF AND APPARATUS FOR VAPOR- DEPOSITING THE SAME

Technical Field

[1] The present invention relates to a multi-layered ITO used for manufacturing a transparent conductive film of display devices and a method of vapor-depositing the same. More specifically, the invention relates to a multi-layered ITO including a first ITO layer of a first thickness deposited on a glass substrate through an ion sputtering process and a second ITO layer of a second thickness deposited on the first ITO layer through a DC vapor-deposition process, and a method of and an apparatus for vapor- depositing such a multi-layered ITO.

[2]

Background Art

[3] In recent years, flat panel display (FPD) devices such as a liquid crystal display device (LCD) and an organic light emitting diode (OLED) having a lightweight and slim form, with compared to a cathode ray tube (CRT), have been increasingly used as screen display devices. Simultaneously, a transparent electrode used for a pixel electrode has been increasing demanded. The transparent electrode should be formed of a material having a low specific electrical resistance, and a high transmissivity for a visible light.

[4] Currently, transparent electrodes are formed typically of oxide semiconductors.

Among them, Indium-Tin-Oxide (ITO) thin film is widely employed in the flat panel displays such as liquid crystal displays (LCDs), plasma display panels (PDPs) or organic light emitting diodes (OLEDs). This is because ITO has several advantages that it has a low specific electrical resistance, can be vapor-deposited at a relatively low substrate temperature (lower than 200°C), has a high transmissivity for a visible light, and also it can be easily wet-etched.

[5] In particular, OLED draws many attractions as a flat panel display of next generation, due to its self-emitting characteristic, low power driven characteristic, fast response speed, low power consumption, wide viewing angle, or the like. However, since OLED is current-driven, a charge is accumulated at the tip of an electrode surface and leads to a spark. Therefore, the device can be degraded or damaged by an electrical shock.

[6] Thus, the flat surface characteristic of an ITO thin film, which is used as an anode of the OLED, is considered as an important face, along with its electrical (low resistance) and optical characteristics.

[7] The flat surface characteristic of an ITO thin film is significantly affected by the crystal structure thereof. The crystal structures of an ITO thin film are categorized into domain structure and grain structure. The domain structure is composed of numerous domains (each sub-domain having the same orientation and plane) and interfaces between them. The grain structure is constituted of plural grain boundaries without domain boundary. In the grain structure, each grain has the same plane and orientation.

[8] Each crystal structure of the ITO thin film has its own characteristics. First, in the domain structure, the respective sub-domains have different planes and crystal orientations and are delineated by domain boundaries, and thus a difference occurs in their heights along the domain boundary, thereby resulting in an increased surface roughness.

[9] Next, in the case of a grain structure, its whole structure has the same crystal plane and orientation, so that a (222) plane in a stable energy state is generated over the whole surface thereof, thereby providing substantially no surface roughness. Thus, a most suitable crystal structure to OLED requirement is a crystal structure is the grain structure having the same crystal plane and orientation resulting in a low surface roughness.

[10] Conventionally, this ITO thin film has been deposited on a substrate through a physical vapor deposition method, such as an ion beam sputtering, a DC sputtering, an RF sputtering, an electron beam evaporation, or a reactive evaporation, and a chemical vapor deposition method, such as a sol-gel or a spray pyrolysis.

[11] The ITO electrode deposition through the conventional ion beam sputtering has problems in that its deposition rate is very low, although it provides the satisfactory surface roughness. Due to its low deposition rate, it is practically impossible that only the ion beam sputtering is used for vapor deposition of an ITO electrode in the mass production of devices.

[12] On the other hand, the conventional DC sputtering method has a high deposition rate to thereby provide a favorable productivity. However, in the conventional DC sputtering, the crystal structure of the formed ITO layer constitutes a domain structure to thereby provide a degraded surface evenness. Thus, subsequent to the ITO deposition, a separate polishing process must be performed in order to improve its surface evenness. Disclosure of Invention Technical Problem

[13] Therefore, the present invention has been made in order to solve the above problems in the art, and it is an object of the invention to provide a multi-layered ITO for transparent electrodes having an improved surface evenness, and a method of and an apparatus for vapor-depositing such a multi-layered ITO at an increased deposition rate.

Technical Solution

[14] In order to accomplish the above object, according to one aspect of the invention, there is provided a multi-layered ITO for a transparent electrode. The multi-layered ITO comprises: a first ITO layer having a first thickness, the first ITO layer being deposited on a glass substrate through an ion beam sputtering using a sputtering gas supplied from an ion source under oxygen atmosphere maintained above the glass substrate; and a second ITO layer having a second thickness, the second ITO layer being deposited on the first ITO layer through a DC sputtering.

[15] The thickness of the first ITO layer is thinner than that of the second ITO layer.

[16] Argon gas is employed as the sputtering gas in the deposition of the first ITO layer and the second ITO layer.

[17] In a case where the whole thickness of the multi-layered ITO is 150OA preferably, the first thickness is 50-300A and the second thickness is 1200-1450A

[18] The whole thickness of the multi-layered ITO may vary as long as the ratio of the first thickness to the second thickness is maintained.

[19] The first ITO layer and the second ITO layer have a grain structure with (222) planes of [111] orientation, where the growth plane and orientation of the first ITO layer affects those of the second ITO layer.

[20] According to another aspect of the invention, there is provided a method of vapor- depositing a multi-layered ITO for a transparent electrode. The method comprises the steps of: depositing a first ITO layer having a first thickness at a first deposition rate on a glass substrate through an ion beam sputtering using a sputtering gas supplied from an ion source under oxygen atmosphere maintained around the glass substrate; and depositing a second ITO layer having a second thickness on the first ITO layer at a second deposition rate through a DC sputtering.

[21] The sputtering gas used in the first and second steps is argon gas.

[22] The first ITO layer has a grain structure with (222) planes of [111] orientation.

Preferably, the second ITO layer has a grain structure with (222) planes of [111] orientation.

[23] The first deposition rate is 2.5~4.5A/sec and the second deposition rate is

2OO~4OθA/sec.

[24] In a case where the whole thickness of the multi-layered ITO is 150OA preferably, the first thickness is 50-300A and the second thickness is 1200-1450A.

[25] But the ratio of the first thickness to the second thickness for the whole thickness may be varied. The first thickness is defined by a preferred thickness to provide a grain structure to the substrate and the thickness of the second ITO layer may vary with other characteristic such as use, electrical resistance and visible light transmissivity of the substrate.

[26] According to another aspect of the invention, there is provided an apparatus for vapor-depositing a multi-layered ITO for a transparent electrode. The apparatus comprises: a first ITO layer depositing section for depositing a first ITO layer having a first thickness at a first deposition rate on a glass substrate through an ion beam sputtering using a sputtering gas supplied from an ion source under oxygen atmosphere maintained around the glass substrate; a second ITO layer deposition section for depositing a second ITO layer having a second thickness on the first ITO layer at a second deposition rate through a DC sputtering; and a buffer section for guiding the substrate from the first ITO layer deposition section to the second ITO layer deposition section.

[27] The sputtering gas used in the first ITO layer deposition section and the second ITO layer deposition section is argon gas.

[28] In a case where the whole thickness of the multi-layered ITO is 150OA preferably, the first thickness is 50-300A and the second thickness is 1200-1450A.

[29] But the ratio of the first thickness to the second thickness for the whole thickness may be varied. The first thickness is defined by a preferred thickness to provide a grain structure to the substrate and the thickness of the second ITO layer may vary with other characteristic such as use, electrical resistance and visible light transmissivity of the substrate.

[30] The first ITO layer exhibits a preferred growth with (222) planes of [ 111 ] orientation.

[31] The buffer section connects the first ITO layer deposition section and the second

ITO layer deposition section with each other in series. The buffer section includes an independent buffer chamber, through which the degree of vacuum of the first ITO layer deposition section is sequentially converted into that of the second ITO layer deposition section.

Advantageous Effects

[32] As described above, the first ITO layer grown in the [111] orientation through the ion beam sputtering deposition affects the second ITO layer, which is also grown in the same plane and orientation, thereby obtaining a good surface evenness. In addition, the deposition rate of the second ITO layer is significantly higher than that of the conventional ion beam sputtering deposition, thereby improving production efficiency.

Brief Description of the Drawings [33] Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[34] Fig. 1 schematically illustrates a general configuration of an apparatus for vapor- depositing a multi-layered ITO for transparent electrodes according to an embodiment of the invention;

[35] Fig. 2 is a schematic view of the ion gun deposition section in Fig. 1 ;

[36] Fig. 3 is a schematic view of the DC sputtering deposition section in Fig. 1 ;

[37] Fig. 4 is a vertical sectional view of a multi-layered ITO for a transparent electrode according to the present invention;

[38] Fig. 5 is a photograph showing the surface of a grain structure in a multi-layered

ITO for transparent electrodes according to the present invention;

[39] Fig. 6 is a photograph showing the surface of a domain structure in an ITO layer according to a conventional DC-sputtering process;

[40] Fig. 7 shows an XRD analysis result for crystallographic structure of a multi- layered ITO according to the invention and an ITO layer according to the conventional DC-sputtering deposition process;

[41] Fig. 8 is a photograph showing an AFM analysis for the domain structure of an ITO layer according to the conventional DC-sputtering deposition process;

[42] Fig. 9 is a photograph showing an AFM analysis for the grain structure of a multi- layered ITO according to the present invention; and

[43] Fig. 10 is a graph showing transmissivity for a multi-layered ITO according to the invention and an ITO layer according to the conventional DC-sputtering deposition process. Best Mode for Carrying Out the Invention

[44] Hereafter, the preferred embodiments of the present invention will be explained, with reference to the accompanying drawings.

[45] Fig. 1 schematically illustrates a general configuration of an apparatus for vapor- depositing a multi-layered ITO for transparent electrodes according to an embodiment of the invention. As shown in Fig. 1, the apparatus includes a loader section 10 for loading a substrate, an ion gun deposition section 20 for vapor-depositing a first ITO layer on the surface of the loaded substrate using an ion gun, a buffer section 30 for temporarily holding the substrate passed through the ion gun deposition section 20 in order to load into a DC sputtering deposition section 40, the DC sputtering deposition section 40 for receiving the substrate coated with the first ITO layer from the buffer section 30 and vapor-depositing a second ITO layer on the first ITO layer, and an unloader section 50 for receiving the substrate coated with the second ITO layer from the DC sputtering deposition section 40.

[46] In Fig. 1, the ion gun deposition section 10 forms a first ITO layer having a first thickness on a glass substrate received from the loader section 10. The first ITO layer is deposited through an ion beam sputtering deposition using an electron cyclotron resonance (ERC) ion beam sputtering deposition equipment.

[47] The substrate passes through the buffer section 30. On the surface of the first ITO layer formed on the glass substrate is formed a second ITO layer having a second thickness through a DC sputtering deposition in the DC sputtering section 40, which employs a DC magnetron sputtering deposition equipment.

[48] Fig. 2 is a schematic view showing a configuration of the ion gun deposition section

20 for vapor-depositing a first ITO layer in Fig. 1.

[49] The ion gun deposition section 20 for deposition of a first ITO layer includes a vacuum chamber 22 for providing a closed space for deposition of the first ITO layer near the underneath of the glass substrate linearly moving in horizontal direction, a heater 23 installed above the glass substrate in parallel thereto and spaced apart therefrom, an ECR ion source 24 installed in a vacuum chamber wall perpendicular to the glass substrate for generating ion beam, a vacuum pump 25 installed another vacuum chamber 22 wall facing the ECR ion source 24, a target holder 27 installed in the lower side of the inside of the vacuum chamber for pivotably holding a target 26 within certain degrees, and the target 26 supported by the target holder 27 and having the same chemical composition as an ITO layer to be deposited.

[50] As the ion gun used in the ion gun deposition section, an ECR ion gun is employed, in which the ion beam generating area is relatively linear, the profile of ion beam can be easily controlled, the ion source has a linear form, and a two-step grid having a rectangular shape is installed in the ion beam generator to thereby be able to accelerate ions.

[51] As to process conditions, the process vacuum of the ion gun deposition section is maintained at about 10 Torr, and the working gas and the reactive gas employ argon and oxygen respectively. The working temperature is maintained around 200~350°C.

[52] Hereafter, the operation of the ion gun deposition section for deposition of the first

ITO layer will be explained. Argon gas is ionized due to ECR effect and the ionized positive argon ion is advanced towards the target 16. The ionized positive argon ions are bombarded on the surface of the target 16 with an energy of 500~900eV. The bombardment of argon ions exerts a physical force on the target 16 and atoms of the target 16 are ejected from the target due to the physical force. The atoms ejected from the target 16 are deposited on the glass substrate 21 loaded through the loader section 10 and rested on the glass substrate 21 to thereby carry out a sequential deposition, which is grown on the plane (222) in a preferred [111] orientation. Consequently, the first ITO layer having a thickness of 50-300 is formed at a deposition rate of 2.5-4.5 A/sec. At this time, the target atoms having an energy of several hundreds eV are deposited on the glass substrate 21 having a sufficient thermal energy under oxygen atmosphere, which is formed by oxygen flown near the glass substrate 21. During the above continuous process, the injected oxygen is chemically reacted with the target atom being deposited on the glass substrate 21 and simultaneously part of oxygen atoms are negatively ionized to exert a physical force on the surface of the substrate, thereby contributing the formation of crystal structure of the substrate. The above conditions are inter-acted to one another to develop desired electrical and crys- tallographic properties.

[53] Thereafter, the buffer section 30 includes a buffer chamber 31 and gates 32a and

32b installed in both ends of the butter chamber 31. The front gate 32a is opened, then the substrate advanced from the ion gun deposition section 20 is moved into the buffer section 30, and the gate 32a is closed. An inert gas such as argon gas is injected in the buffer section 30 to adjust the vacuum thereof to the same as the working vacuum of the DC sputtering deposition section 40 for a second ITO layer. Thereafter, the rear gate 32b is opened, the substrate is moved into the DC sputtering deposition section 40, and then the rear gate 32b is closed. Then, in order to receive a further substrate from the ion gun deposition section 20, the vacuum of the buffer chamber 31 is changed back into the same as that of the ion gun deposition section 20 in the same manner as above. According to the above-described continuous process, the glass substrate formed with a first ITO layer is transferred into the DC sputtering deposition section 40 for deposition of a second ITO layer.

[54] Fig. 3 is a schematic view showing the configuration of the DC sputtering deposition section 40 for vapor-depositing a second ITO layer.

[55] The DC sputtering deposition section 40 includes a vacuum chamber 41 as a chamber for forming a second ITO layer, a vacuum control means (not shown) for controlling vacuum inside the vacuum chamber 41, a sputtering cathode 42 connected to a DC high- voltage power supply for plasma discharge through an electrical connection line, a palette placed facing the sputtering cathode 42 and spaced apart therefrom, and a sputter-gas supply (not shown) for supplying working gas such as argon gas into the vacuum chamber. The sputtering cathode 42 includes an ITO target plate 42a, a backing plate 42b and a permanent magnet 42c. The target plate 42a is fixed to the backing plate 42b and the permanent magnet 42c is disposed rearwards of the backing plate 42b.

[56] As to process conditions, the process vacuum of the DC sputtering deposition section is maintained at about 10^"3 Torr, and the working gas and the reactive gas employ argon and oxygen respectively. The working temperature is maintained around 200~350°C.

[57] Hereafter, the operation of the DC sputtering deposition section for deposition of the second ITO layer will be explained. The permanent magnet 42c forms an electromagnetic field above the ITO target plate 42a and a negative voltage is applied to the cathode 42 from a DC power supply. The injected argon gas is ionized near the formed electromagnetic field. The ionized positive argon ion is accelerated at the cathode of negative voltage. The accelerated positive argon ion is bombarded on the surface of the ITO target plate 42a fixed to the cathode. At this time, due to the impact energy, the atoms of the target is ejected towards the first ITO layer in the opposite direction to the impact. According to the above continuous actions, a deposition is continuously carried out on the (222) plane of the first ITO layer in preferred [111] orientation. Consequently, the second ITO layer having a thickness of 1200-1450A is formed at a deposition rate of 200~400A/sec. Here, it can be seen that the deposition rate of the second ITO layer is about one hundred times that of the first ITO layer.

[58] The target used for the deposition of the first and second ITO layers is formed of an

ITO (purity: 99.99% or above) containing In O and Sn O at the ratio 9: 1 of weight percent. The ratio may vary with equipment characteristics and thin film functions.

[59] Fig. 6 shows the structure of a multi-layered ITO for transparent electrodes according to the invention. Fig. 5 shows the structure of an ITO layer deposited according to a conventional DC-sputtering deposition process. Referring Figs. 5 and 6, the ITO layer according to the conventional DC-sputtering deposition process has a domain structure having a high surface roughness. In contrast, the multi-layered ITO according to the present invention exhibits a grain structure having a good surface evenness.

[60] In addition, Fig. 7 shows an XRD analysis result for crystallographic structure of a multi-layered ITO according to the invention and an ITO layer according to the conventional DC-sputtering deposition process. In Fig. 7, according to the XRD analysis, the multi-layered ITO of the present invention exhibits a distinguished peak value of [111] orientation and no substantial peaks. Thus, it can be seen that the multi-layered ITO of the present invention has a grain structure with [111] orientation. In contrast, the ITO layer according to the conventional DC deposition process shows peaks at (222), (400), (440) planes and the like, which means that the conventional ITO layer was not grown in any preferred orientation. Therefore, it can be seen that the deposition layer through the conventional DC-sputtering deposition process constitutes a domain structure to thereby exhibit a degraded surface roughness.

[61] In view of the fact that the first ITO layer and the second ITO layer are mostly grown in the preferred [111] orientation, it can be seen that the growth plane and orientation of the first ITO layer determined those of the second ITO layer. In addition, it has been found that the deposition rate for the second ITO layer is about one hundred times that of the first ITO layer through the ion beam deposition. Therefore, according to the present invention, the grains having the preferred [111] orientation, which are stabilized in terms of its energy and have a good roughness, can be grown, thereby enabling a high deposition rate.

[62] In addition, Fig. 8 is a photograph showing an AFM (Atomic force microscope) analysis for the domain structure of an ITO layer according to the conventional DC- sputtering deposition process. Fig. 9 is a photograph showing an AFM analysis for the grain structure of a multi-layered ITO according to the present invention. Referring to Figs. 8 and 9, it can be seen that the multi-layered ITO of the present invention exhibits an improved surface roughness.

[63] Fig. 10 is a graph showing visible light transmissivity for a multi-layered ITO according to the invention and an ITO layer according to the conventional DC- sputtering deposition process. From Fig. 10, it can be seen that the multi-layered ITO of the present invention and the conventional ITO layer have almost the same high visible light transmissivity. That is, the multi-layered ITO of the invention has an improved productivity and surface property, while maintaining substantially the same electrical and optical characteristics as the conventional ITO layer, which is formed through a single deposition process, i.e., the conventional DC deposition or ion beam deposition.

[64]

Industrial Applicability

[65] As described above, in the present invention, the first ITO layer grown in the preferred [111] orientation through the ion beam sputtering deposition affects the second ITO layer, which also has the same orientation, thereby obtaining a good surface evenness. In addition, the deposition rate of the second ITO layer is significantly higher than that of the conventional ion beam sputtering deposition, thereby improving production efficiency. The present invention provides a multi-layered ITO of high quality, and a method of and an apparatus for fabricating such a multi-layered ITO.

[66] While the present invention has been described with reference to several preferred embodiments, the description is illustrative of the invention and is not construed as limiting the invention. Various modifications and variations may occur to those skilled in the art, without departing from the scope and spirit of the invention, as defined by the appended claims.

Claims

[I] A multi-layered ITO for a transparent electrode, the multi-layered ITO comprising: a first ITO layer having a first thickness, the first ITO layer being deposited on a glass substrate through an ion beam sputtering using a sputtering gas supplied from an ion source under oxygen atmosphere maintained around the glass substrate; and a second ITO layer having a second thickness, the second ITO layer being deposited on the first ITO layer through a DC sputtering. [2] The multi-layered ITO as claimed in claim 1, wherein argon gas is employed as the sputtering gas in the deposition of the first ITO layer and the second ITO layer. [3] The multi-layered ITO as claimed in claim 1, wherein the second ITO layer has a grain structure. [4] The multi-layered ITO as claimed in claim 1, wherein the first ITO layer and the second ITO layer have a grain structure grown in [111] orientation. [5] The multi-layered ITO as claimed in claim 1, wherein the first thickness is

50-300A and the second thickness is 1200-1450A. [6] A method of vapor-depositing a multi-layered ITO for a transparent electrode, the method comprising the steps of: depositing a first ITO layer having a first thickness at a first deposition rate on a glass substrate through an ion beam sputtering using a sputtering gas supplied from an ion source under oxygen atmosphere maintained around the glass substrate; and depositing a second ITO layer having a second thickness on the first ITO layer at a second deposition rate through a DC sputtering. [7] The method as claimed in claim 6, wherein the sputtering gas used in the first and second steps is argon gas. [8] The method as claimed in claim 6, wherein the first ITO layer has a grain structure grown in [111] orientation. [9] The method as claimed in claim 6, wherein the second ITO layer has a grain structure grown in [111] orientation. [10] The method as claimed in claim 6, wherein the first deposition rate is

2.5~4.5A/sec and the second deposition rate is 2OO~4OθA/sec.

[II] The method as claimed in claim 6, wherein the first thickness is 50-300A and the second thickness is 1200-1450A.

[12] An apparatus for vapor-depositing a multi-layered ITO for a transparent electrode, the apparatus comprising: a first ITO layer depositing section for depositing a first ITO layer having a first thickness at a first deposition rate on a glass substrate through an ion beam sputtering using a sputtering gas supplied from an ion source under oxygen atmosphere maintained around the glass substrate; a second ITO layer deposition section for depositing a second ITO layer having a second thickness on the first ITO layer at a second deposition rate through a DC sputtering; and a buffer section for guiding the substrate from the first ITO layer deposition section to the second ITO layer deposition section.

[13] The apparatus as claimed in claim 12, wherein the sputtering gas used in the first

ITO layer deposition section and the second ITO layer deposition section is argon gas.

[14] The apparatus as claimed in claim 12, wherein the buffer section connects the first ITO layer deposition section and the second ITO layer deposition section with each other in series.

[15] The apparatus as claimed in claim 12, wherein the buffer section includes an independent buffer chamber, through which the glass substrate deposited by the ion beam sputtering is guided into the second ITO layer deposition section.

[16] The apparatus as claimed in claim 12, wherein the first thickness is 50-300A and the second thickness is 1200-1450A.