KR20050030403A - High flatness indium tin oxide thin film and its manufacturing method - Google Patents

Abstract

An ITO(Indium Tin Oxide) thin film having high flatness and a fabricating method thereof are provided to form the ITO having an excellent surface roughness property by controlling the deposition temperature and the sputtering power to set a condition having optimum uniaxial alignment. A method for fabricating an ITO thin film having high flatness includes a process for sputtering a target onto a glass substrate(10) on which a diffusion barrier layer(11) is formed. The temperature of the glass substrate(10) is more than 350 degrees centigrade. In the method for fabricating the ITO thin film, the density of the sputtering power is maintained below 2W/cm^2.

Description

Indium tin oxide thin film having a high flatness and a manufacturing method thereof {HIGH FLATNESS INDIUM TIN OXIDE THIN FILM AND ITS MANUFACTURING METHOD}

The present invention relates to a laminate in which a transparent conductive film of indium tin oxide (ITO) is formed, and more particularly, to induce crystal growth direction in one direction by appropriately adjusting sputtering power and substrate temperature when forming a transparent conductive film. The present invention relates to a method for obtaining a transparent conductive film having improved surface roughness and a structure thereof.

As is well known, an electroluminescent display device is a display device using a principle that a fluorescent material emits light by a recombination energy between a hole injected from an anode and an electron injected from a cathode by applying an electric field, and an inorganic electric field according to the material used. It can be classified into a light emitting display device and an organic electroluminescent display device. Until now, inorganic electroluminescent display devices using inorganic materials have become mainstream, and such inorganic electroluminescent display devices are mainly used in LCD backlights, light emitting diodes (LEDs), CD players, mobile phones, and personal digital assistants (PDAs). However, inorganic electroluminescent display devices have relatively high driving voltage, difficulty in full color, and high manufacturing cost of peripheral driving circuits.

On the other hand, in recent years, as a generation display device for overcoming the limitation of the inorganic electroluminescent display device, development of an organic electroluminescent display device using an organic material has been actively progressed.

The organic electroluminescent display device has a two-layer structure consisting of a hole transport layer and an electron transport / light emitting layer, or a three-layer structure consisting of a hole transport layer, a light emitting layer, and an electron transport layer.

1 is a cross-sectional view illustrating a structure of a conventional organic electroluminescent display device, and includes an organic material layer having a three-layer structure. As shown in FIG. 1, a conventional organic electroluminescent display device includes a cathode electrode 11, a hole transport layer 12, an emission layer 13, an electron transport layer 14, and a cathode electrode 15 on a glass substrate 10. ) The anode electrode 11 is generally an ITO thin film, the light emitting layer 13 is an organic material in the form of a thin film, and the cathode electrode 15 is a metal layer.

In the conventional organic electroluminescent display device configured as described above, when positive voltage is applied to the positive electrode 11 and negative voltage is applied to the negative electrode 15, holes are injected into the positive electrode 11 and the negative electrode At 15, electrons are injected. The injected holes and electrons recombine in the emission layer 13 through the hole transport layer 12 and the electron transport layer 14, respectively, thereby generating light.

The anode 11 is used not only as an electrode for driving the organic electroluminescent display, but also serves as a hole injection. The transparent conductive film used as the anode electrode 11 is a metal thin film such as gold (Au), silver (Ag), or palladium (Pd), an oxide semiconductor thin film such as indium oxide, tin oxide, or zinc oxide, and a stack of metal oxides and metals. Multilayer thin film and the like. The characteristics of the transparent conductive film are evaluated through reliability evaluations such as electrical conductivity, transmittance, surface roughness, acid resistance, and moisture resistance. The metal thin film has excellent electrical conductivity but poor optical properties such as transmittance. Although the conductivity is inferior, there is an advantage in that optical characteristics such as transmittance are good.

As a method of forming a transparent conductive film used as an anode electrode of such a conventional organic electroluminescent display device, there are sputtering, ion plating, and electron beam evaporation. Although the general characteristics and the optical characteristics differ greatly from each method, the surface roughness, that is, the surface roughness is generally 3 nm or more based on the root mean square (RMS). Therefore, spikes are easily formed on the surface during the subsequent process for forming the hole transport layer 12.

The characteristics of an organic electroluminescent display are greatly influenced by the surface roughness of the transparent conductive film used as the anode electrode. If the surface roughness is bad, there is a problem of deterioration of the device characteristics such as protrusions are formed in the subsequent process to generate a leakage current, non-uniform emission luminance and deterioration of light emission characteristics. Obtaining a conductive film is a very important problem. In particular, since the uniformity and surface roughness of the transparent conductive film manufactured by the conventional method are not constant, there is a problem in that the luminance of each part is different from each other, and in severe cases, a part of the pixel does not emit dark spots (Dark Spot) This happens too.

The most widely used manufacturing method for solving the surface roughness problem of the transparent conductive film of the conventional organic electroluminescent display device is disclosed in "Organic electroluminescent display device and its manufacturing method" described in Japanese Patent Laid-Open No. 9-120890. It is. In this patent, after forming a conductive metal oxide thin film, a separate polishing process is performed to improve surface roughness, and then the residue is washed with an acidic solution such as nitric acid (HNO 3), sulfuric acid (H 2 SO 4), and hydrochloric acid (HCl). How to remove it.

However, when the transparent conductive film is formed by the above manufacturing method and applied to the organic electroluminescent display device, the residue generated during the polishing process deteriorates the characteristics of the organic electroluminescent display device, thereby deteriorating the emission luminance. That is, the residue generated in the above-described polishing process remains without being completely removed even through the cleaning process.

Accordingly, recently, many techniques for improving the surface roughness of the transparent conductive film by a method of not using a polishing process have been developed, and an ion-plating method is one of them. The ion plating method is known to be excellent in surface roughness because it is deposited in a state of high energy as a method of vaporizing a metal by directly hitting a source target by making a plasma in a beam state. However, ion plating equipment is expensive and there is a problem in cost in depositing a transparent conductive film with such equipment.

In addition, there is a method of using indium zinc oxide (IZO), but the surface roughness characteristics are excellent, but there is a problem of low electrical conductivity.

On the other hand, when the ITO thin film is deposited by a conventional DC power magnetron sputtering method, the ITO thin film is formed to be polycrystalline. In this case, the crystals of the polycrystalline ITO thin film are not grown in one direction, but crystal growth is induced in various directions depending on adsorption mobility due to surface energy and external thermal energy. As a result, the growth rate varies depending on the crystal growth direction. Therefore, the crystal grains having different growth directions are present in the polycrystalline ITO thin film, and the height difference occurs on the surface thereof to roughen the surface of the ITO thin film.

Therefore, if the crystal growth direction is induced in one direction at the beginning of crystal growth of the ITO thin film, the thin film grown on the upper layer grows along the crystal orientation of the lower layer, and thus crystal growth is possible in one direction. In the uniaxially grown crystals, the difference in height at the surface of the thin film caused by the growth direction can be eliminated, thereby obtaining an ITO thin film having excellent surface roughness.

Conventionally, there was a method of inducing a crystal growth direction by inserting a seed layer into a lower layer before forming an ITO thin film. However, this has a problem of having to go through two steps and a problem that affects the upper layer according to the crystal state of the lower layer. have.

The present invention is to solve the above problems, to provide an ITO thin film excellent in surface roughness and a method of manufacturing the same by adjusting the sputtering power, substrate temperature, etc. at the time of forming the ITO transparent conductive film to have a uniaxial orientation. The purpose.

In addition, an object of the present invention is to provide an organic electroluminescent display device having improved surface roughness of an ITO transparent conductive film to solve the nonuniformity of light emission, and a liquid crystal display device having excellent characteristics.

In the method of forming the indium tin oxide thin film according to the present invention for achieving the above object, in the method for producing an indium tin oxide thin film by sputtering a target on a glass substrate with a diffusion barrier layer, the temperature of the glass substrate is 350 ℃ or more. It features.

In addition, the method for producing an indium tin oxide thin film according to the present invention is characterized in that the sputtering power density is performed by maintaining 2 W / cm ² or less.

The ITO thin film prepared according to the present invention has much better surface roughness, specific resistance and transmittance characteristics than the ITO thin film prepared by the conventional sputtering method, and has a dense crystal structure to increase the electron carrier concentration in the film and increase the electron mobility. Voltage drop between wirings can be prevented.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. This embodiment is not intended to limit the scope of the invention, but is presented by way of example only.

The ITO thin film of the present invention is manufactured by the following method. First, a diffusion barrier layer is formed on a substrate such as soda-lime glass or alkali-free glass. As the diffusion barrier layer, inorganic oxides such as SiO ₂ , Nb ₂ 0 ₅ , Ti0 ₂ , and inorganic nitrides such as Si ₃ N ₄ are used. Preferably, SiO ₂ having a fast thin film formation rate is the most suitable material, and in one embodiment of the present invention, a thickness of about 20 nm is formed. The diffusion barrier layer suppresses the phenomenon that Na ions implanted during soda lime glass formation are activated in a high temperature process during ITO thin film formation.

Sputtering, E-Beam Evaporation, Chemical Vapor Deposition, Ion-Plating, etc. are used as a method of forming an ITO thin film used as an anode electrode. Among these, sputtering is most preferable. In the sputtering method, an inert gas such as argon is used as a discharge gas for forming plasma, and oxygen is used as a reaction gas. The amount of argon may be 150 sccm to 1000 sccm, but preferably 200 to 500 sccm, and the amount of oxygen is preferably 0 sccm to 20 sccm, but preferably 0.1 sccm to 5 sccm. The power can be from 1KW to 30KW, but preferably 1KW to 10KW. In addition, either the AC power source or the DC power source can be used as the power supply method of magnetron sputtering in the present invention, but in one embodiment of the present invention, the DC power source method is used.

Since the deposition of the ITO thin film after forming the diffusion barrier layer should have a uniaxial orientation, the thin film formation conditions are very important. In general, when the seed layer is not applied as a lower layer, X-ray diffraction analysis results when the ITO thin film is formed by the DC power magnetron sputtering method are described as (222), (400), (211), (622), etc. Crystal growth in the direction is achieved at the same time. The crystals having different growth directions have different magnitudes of surface energy at which crystals grow on the surface, and different speeds of crystal growth. In general, it is reported that the crystal growth rate in the (222) direction is fast, and that the (400) direction is slow.

Input values in DC power magnetron sputtering are power, substrate temperature, argon flow rate, oxygen flow rate, combination ratio of indium oxide and tin oxide of ITO target, and by adjusting these values, it is possible to secure optimum thin film formation conditions. do.

ITO thin film formation conditions according to an embodiment of the present invention are as follows. DC power was changed from 5KW to 0.5KW and temperature was changed from 230 ℃ to 370 ℃. The argon flow rate and oxygen flow rate were changed to 300 to 500 sccm and 1.9 to 3 sccm, respectively, and the film thickness was maintained at 150 nm. In sputtering, a rotary pump and a turbomolecular pump were used to evacuate the chamber until the initial vacuum degree was 1 × 10 −3 Pa to make the chamber into a vacuum. Pre-sputtering was performed for 5 minutes to remove surface oxidation of the target.

X-ray diffraction analysis was performed to examine the crystal state inside the ITO thin film manufactured by the above method, and atomic force microscopy was used to measure the surface roughness. In addition, scanning electron microcopy (SEM) was used to observe the surface structure of the ITO thin film.

Table 1 shows the thin film formation conditions for the embodiment of the method.

No. Temperature (℃) Power (KW) Power Density (W / cm ² ) Argon (sccm) Oxygen (sccm) Example 1 230 3 1.29 410 1.9 Example 2 230 5 2.15 410 1.9 Example 3 280 3 1.29 410 1.9 Example 4 280 1.5 0.65 410 1.9 Example 5 300 1.5 0.65 410 1.9 Example 6 320 1.5 0.65 410 1.9 Example 7 335 1.5 0.65 410 1.9 Example 8 350 1.5 0.65 410 1.9 Example 9 370 1.5 0.65 410 1.9 Example 10 350 1.5 0.65 410 3 Example 11 350 1.5 0.65 300 1.9 Example 12 350 1.5 0.65 500 1.9 Example 13 350 2 0.86 410 1.9 Example 14 350 3 1.29 410 1.9 Example 15 370 1.2 0.52 410 1.9 Example 16 370 One 0.43 410 1.9 Example 17 370 0.5 0.22 410 1.9

Examples 1-9 are for observing the influence of power and temperature, and Examples 10-12 are for observing the influence of the argon gas and oxygen gas which are injected. In addition, Examples 13 to 17 are for observing the influence of the power.

Table 2 summarizes the electrical conductivity, optical transmittance, surface roughness, crystal orientation by X-ray diffraction analysis and the like according to each example.

No. Specific resistance (μΩcm) Transmittance (%) Surface roughness X-ray diffraction analysis R _RMS R _A R _PV (222) (400) (222) / (400) Example 1 183 86.3 13.2 10.2 132 458 237 1.93 Example 2 202 86.8 37.6 30.5 322 557 404 1.38 Example 3 147 88.7 21.9 16.9 196 437 346 1.26 Example 4 165 87.9 11.9 9.2 110 369 256 1.44 Example 5 155 89.1 20.0 15.3 172 354 296 1.20 Example 6 154 90.3 19.1 14.6 181 342 316 1.08 Example 7 145 90.6 16.3 12.7 141 314 323 0.97 Example 8 188 90.7 7.41 5.75 65.9 286 428 0.67 Example 9 135 90.7 9.7 8.5 92 324 999 0.32 Example 10 142 90.6 11.2 9.2 122 292 1102 0.26 Example 11 139 90.5 12.1 11.3 128 310 1011 0.31 Example 12 129 90.5 14.3 11.8 146 324 1014 0.32 Example 13 130 90.7 13.2 10.2 132 361 954 0.38 Example 14 174 90.2 16.1 12.7 146 339 630 0.54 Example 15 158 90.9 13.2 10.2 132 388 534 0.73 Example 16 162 90.1 14.1 10.7 112 412 502 0.82 Example 17 167 90.2 15.5 11.9 139 323 408 0.79

As shown in Table 2, it can be seen that one of the most important factors in the thin film formation condition is the power density. The power density is a value obtained by dividing the power supplied to the target by the area of the target, and means the injection amount of power per unit area. Since the density of the target is different when the size of the target is different, it is accurate and effective to express the power injection amount by the power density rather than by the power value applied directly from the DC power source.

Table 3 and Table 4 summarize the thin film formation conditions of the conventional example and the resulting electrical conductivity, optical transmittance, surface roughness, X-ray diffraction crystal orientation, etc. for comparison with the above examples. Conventional examples are based on thin film formation conditions commonly used.

No. Temperature (℃) Power (KW) Power Density (W / cm ² ) Argon (sccm) Oxygen (sccm) Conventional Example 1 300 5 2.15 410 1.9 Conventional Example 2 350 5 2.15 410 1.9 Conventional Example 3 350 3 1.29 410 1.9 Conventional Example 4 370 8 3.44 410 1.9 Conventional Example 5 350 8 3.44 410 1.9

No. Specific resistance (μΩcm) Transmittance (%) Surface roughness () X-ray diffraction analysis R _RMS R _A R _PV (222) (400) (222) / (400) Conventional Example 1 170 89.5 43.1 35.4 351 697 209 3.32 Conventional Example 2 163 90.4 34.6 28.1 265 595 223 2.67 Conventional Example 3 160 90.4 27.7 20.9 257 666 347 1.92 Conventional Example 4 163 90.4 31.2 26.7 354 758 241 3.14 Conventional Example 5 166 90.1 30.2 28.6 324 729 238 3.06

Comparing the conventional example and the embodiment according to the present invention, it can be seen that the factor that most influences the surface roughness is also power. In the case of the conventional example, since the crystal is formed with a relatively high power, a large amount of crystal growth occurs not only in the (400) direction but also in the (222) direction as a result of the X-ray analysis, but when the power is moderately low, only the (400) direction is grown.

The kinetic energy of the sputtered atoms has a great influence when adsorbed on the glass substrate. Crystal growth in the same direction is possible only if the sputtered atoms move with the same energy and with the same adsorption mobility.

As the power increases, crystals grow in two directions as the sputtered atoms reach a glass substrate with high energy at high speed and rapidly crystallize to form a thin film. In addition, the higher the power, the greater the energy of the sputtered atoms, so that the time to reach the glass substrate is much shorter, so that one layer is accumulated, and then the next layer is accumulated before stabilization, so that the thin film is not dense. Therefore, the ITO thin film grown at high power has the greatest difference in surface height and poor surface roughness because the (222) and (400) planes coexist and are not dense.

On the other hand, if the power is properly lowered, the kinetic energy of the sputtered atoms is reduced and the force induced by the electric field when adsorbed on the glass substrate is reduced. do. Accumulated sputtered atoms at such a slow rate allows formation of an ITO thin film with good flatness.

According to an embodiment of the present invention, a result having an appropriate surface roughness at about 2 W / cm ² or less, preferably about 0.65 W / cm ² .

On the other hand, the results of Examples 1 to 9 can be seen that as the temperature of the glass substrate at the time of thin film formation increases, the crystal growth in the center of the (222) direction gradually shifts to the crystal growth in the (400) direction. When the temperature of the glass substrate at the time of forming the thin film is low, crystal growth occurs in the (222) direction, and weakly crystal growth occurs in the (400) direction. On the contrary, when the temperature of the glass substrate becomes high, the crystal growth in the (222) direction gradually weakens, and the crystal growth in the (400) direction begins to become strong. At 350 ° C or higher, almost no crystal growth occurs in the (222) direction, and crystals are uniaxially formed only in the (400) direction. This is because the adsorption mobility of the (222) plane is higher than that of the (400) plane, so that crystal growth works well even with low energy. For losing.

FIG. 2A is an X-ray diffraction analysis result of the ITO thin film manufactured by the conventional method, and FIG. 2B is an X-ray diffraction analysis result of the ITO thin film manufactured according to Example 10 of the present invention. As can be seen in Figure 2b, the ITO thin film grown at high temperature, low power is mainly doped with crystal growth in the (400) direction. On the other hand, as shown in FIG. 2A, the ITO thin film grown at low temperature or high power co-exists in 222 and 400 directions to generate crystal growth.

Based on the results of X-ray diffraction analysis, the correlation with the surface roughness shows that in low temperature conditions, the crystals grow appropriately in the directions of (222) and (400), so that the surface roughness due to the difference in crystal growth direction is obtained. The results are bad. On the other hand, at high temperatures, crystal growth occurs uniaxially in the (400) direction, indicating that the surface roughness of the ITO thin film is excellent.

In summary, the reason why the ITO thin film formed under the condition of high temperature and low power crystallizes in one direction is as follows. When the sputtered atoms in the low energy state reach the hot glass substrate with high energy, the rate of formation of the thin film is relatively slow, but the adsorption energy of the glass substrate and the sputtered atoms increases due to the high energy state at the surface. The crystal grows with a more compact structure.

For this reason, as the power is lowered, the thin films are densely stacked and crystal growth in one direction is achieved. However, if the power is too low, the average running distance of the sputtered atoms during thin film formation will be shorter, and the thin film will not be dense. In addition, if the energy of the atom is too high, the average running distance is too long, so that the thin film is not dense.

In the embodiment according to the present invention, the optimum condition showed the optimum condition when a power of 0.65W / cm ² was applied, and the lower the power, the worse the crystal structure or surface roughness characteristics. .

3A is an image of an atomic force microscope of an ITO thin film manufactured by a conventional method, and FIG. 3B is an image of an atomic force microscope of an ITO thin film manufactured according to the present invention. As shown in FIG. 3B, the ITO thin film according to the exemplary embodiment of the present invention generally shows the form of a uniform crystal structure. However, in FIG. 3A, which is an image of the ITO thin film according to the conventional method, the crystal structure having a different crystal form is present in the middle. Is observed.

4A is an SEM image of an ITO thin film manufactured by a conventional method, and FIG. 4B is an SEM image of an ITO thin film manufactured according to the present invention. In the case of FIG. 4A, various types of crystal grains and domains are observed according to the crystal formation direction, but in FIG. 4B, the surface in which crystals are grown in one direction and uniform grains can be confirmed.

On the other hand, the argon flow rate can control the high and low amount of sputtering atoms, and the injection of oxygen may make carriers and oxygen vacancies in the indium tin oxide thin film to affect the electrical mobility and optical transmittance characteristics. As the amount of oxygen used as the reactant gas increased, the surface roughness characteristics deteriorated a little, but the specific resistance and transmittance characteristics were improved. According to the flow rate of argon gas, the grain shape of the ITO thin film was slightly increased as the flow rate of argon increased, but it was confirmed that it did not significantly affect the physical properties.

As described above, the deposition temperature and power are the most important variables, and as the deposition temperature is higher, the lower the power, the stronger the uniaxial orientation characteristic toward the (400) direction and the better the surface roughness characteristics are.

Embodiments of the present invention described above and illustrated in the drawings should not be construed as limiting the technical idea of the present invention. The protection scope of the present invention is limited only by the matters described in the claims, and those skilled in the art can change and change the technical idea of the present invention in various forms. Therefore, such improvements and modifications will fall within the protection scope of the present invention as long as it will be apparent to those skilled in the art.

According to the method for forming an indium tin oxide (ITO) thin film of the present invention, by controlling the deposition temperature and the sputtering power by setting the conditions having an optimal uniaxial orientation by optimizing the crystal growth in one direction (400), An ITO thin film with excellent roughness characteristics can be obtained. Meanwhile, the ITO thin film manufactured according to the present invention is very suitable for use as an anode electrode of an organic light emitting display device and a transparent electrode of a liquid crystal display device.

1 is a schematic view of an organic light emitting display device according to the prior art.

Figure 2a is an X-ray diffraction analysis of the ITO thin film according to the prior art.

Figure 2b is an X-ray diffraction analysis of the ITO thin film according to the present invention.

3A is an image of an atomic force microscope of an ITO thin film according to the prior art.

3B is an image of an atomic force microscope of an ITO thin film according to the present invention.

4A is an SEM image of an ITO thin film according to the prior art.

4b is an SEM image of an ITO thin film according to the present invention.

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

10 Glass substrate 11 Diffusion barrier layer

12 Indium Tin Oxide Electrode 13 Hole Transport Layer

14 Light Emitting Layer 15 Electron Transport Layer

16 Cathode Electrode

Claims (6)

In the method for producing an indium tin oxide thin film by sputtering a target on a glass substrate having a diffusion barrier layer, The temperature of a glass substrate is 350 degreeC or more, The indium tin oxide thin film manufacturing method characterized by the above-mentioned. The method of claim 1, The sputtering power density is carried out by maintaining 2 W / cm ² or less indium tin oxide thin film manufacturing method. An indium tin oxide thin film prepared by the method of any one of claims 1 to 2. The method of claim 3, wherein The indium tin oxide thin film having a more crystalline of the indium tin oxide thin film in the (400) direction than the portion in the (200) direction. A liquid crystal display device using the indium tin oxide thin film of claim 4 as a transparent electrode. An organic light emitting display device using the indium tin oxide thin film of claim 4 as an anode electrode