KR20090035908A - Method for preparing zinc oxide based transparent conductive thin film - Google Patents

Abstract

A manufacturing method of a zinc oxide transparent conductive thin film is provided to improve the uniformity of the resistivity according to the location on a thin file surface. a manufacturing method of the zinc oxide transparent conductive thin film forms the zinc oxide transparent conductive thin film on materials by using a sputtering method. The size of the magnetic flux density applied at a sputtering target is 1.5 KG-4.5 KG range. The difference of the resistivity according to the location on the thin film surface is 10-50 % range of the maximum resistivity. The zinc oxide transparent conductive thin film has the resistivity of 2.00 x 10^4cm-5.00 x10^4Фcm range. The method is performed in the H2 mixed gas atmosphere of Ar or Ar and 0.1-10 vol%. The formed thickness of the thin film is 10-300nm range. The element furnace minor Al or Ga is added to the zinc oxide.

Description

METHODS FOR PREPARING ZINC OXIDE BASED TRANSPARENT CONDUCTIVE THIN FILM}

The present invention relates to a method for producing a zinc oxide transparent conductive thin film on a substrate by a sputtering method.

Transparent electrodes are used in various types of electrodes of various displays, photoelectric conversion elements such as solar cells, touch panels, and the like, and are manufactured by forming transparent conductive thin films on transparent substrates such as glass and transparent films. Currently, the transparent conductive material mainly used is indium tin oxide (ITO) doped with tin, and has excellent transparency and low specific resistance (1 × 10 ⁻⁴ to 2 × 10 ⁻⁴ Ωcm). Known.

The method of manufacturing a transparent conductive thin film includes vacuum deposition methods such as sputtering, chemical vapor deposition (CVD), ion beam deposition, and pulsed laser deposition, and spray coating. There are various methods, such as coating, spin coating, and wet methods such as dip coating. Among these methods, a vacuum deposition method such as sputtering is more preferred, and since the vacuum deposition method uses plasma, it is possible to grow a film having high particle energy, thereby obtaining a high quality film having a higher density than other methods. . In addition, there is an advantage that the thin film of good quality can be grown at low temperature without additional heat treatment.

Recently, the demand for ITO is increasing rapidly as the flat display market grows. However, due to supply and demand instability due to high price of indium and harmfulness to human body, development of low-cost transparent conductive material that can replace ITO is required. to be.

Such substitutes include tin oxide (SnO ₂ ), zinc oxide (ZnO), and the like. In this regard, attempts have been made to produce a conductive thin film having a low specific resistance (2 × 10 ⁻⁴ to 3 × 10 ⁻⁴ Ωcm) by doping aluminum (Al) to zinc oxide. It is known that zinc oxide (ZnO) is a semiconductor material having a wide bandgap (~ 3.3ev), and can have excellent transmittance (more than 85%) and low resistivity through doping, and is relatively inexpensive for doped zinc oxide. And, since it is a material harmless to the human body, it is receiving great attention as a material that can replace ITO. Currently, research is mainly focused on materials for transparent electrodes made of zinc oxide (ZnO) containing aluminum (Al), gallium (Ga), silicon (Si) and / or indium (In). In terms of ITO, it still has to meet the needs of ITO.

In the case of depositing a zinc oxide transparent conductive thin film on various substrates by the sputtering method, since the resistance of the center portion of the specimen generally tends to be larger than that of other portions, it is necessary to improve the uniformity of the electrical properties.

The present inventors can change the strength of the magnet used in the sputtering device to solve the above problems, it is possible to improve the uniformity of the resistivity, zinc oxide system having a lower resistivity than other methods for improving the uniformity It has been found that a transparent conductive thin film can be prepared. The present invention is based on the above.

The present invention provides a method for producing a zinc oxide-based transparent conductive thin film on a substrate by a sputtering method, characterized in that the magnetic flux density applied to the sputtering target is in the range of 1.5KG to 4.5KG and the method described above. The zinc oxide system is characterized in that the difference in specific resistance according to the position on the thin film surface is in the range of 10 to 50% of the maximum specific resistance, and has a specific resistance in the range of 2.00 × 10 ^-4 Ωcm to 5.00 × 10 ^-4 Ωcm Provided is a transparent conductive thin film.

In the present invention, in manufacturing a zinc oxide-based transparent conductive thin film by the sputtering method, by adjusting the strength of the magnet used in the sputtering device, it is possible to greatly improve the uniformity of the specific resistance according to the position on the thin film surface, the lower specific resistance Zinc oxide-based transparent conductive thin film can be prepared. In addition, by simply changing the magnet in the sputtering apparatus without changing other deposition conditions that may affect the properties of the thin film, the uniformity of the specific resistance can be simply improved, and the deposition rate of the thin film can also be increased.

In forming a thin film, a sputtering method injects a sputtering gas such as argon into a vacuum chamber, collides with a target material to be formed, generates a plasma, and then coats it on a substrate. As a method of coating, magnetron sputtering is a method in which the generated plasma is collected by flux generated from a permanent magnet and deposited on a substrate. Magnetron (magnetron) is mainly located on the back of the target, the magnetron sputtering (magnetron sputtering) method is widely used in the field of thin film deposition because the higher film formation rate than the conventional sputtering method is obtained.

In the early days of sputtering methods, magnets were not used, but in recent years, sputtering methods use magnets in almost all aspects of efficiency, and are used regardless of RF or DC methods. Thus, the method of the present invention can be used for all zinc oxide thin film deposition methods using a sputtering apparatus with a magnet.

Sputtering apparatus used in the present invention is a target for generating a target material therein; A vacuum chamber in which a base seating portion is formed on which the base is seated at a predetermined distance from the target; A gas injection unit for injecting gas into the vacuum chamber; A vacuum pump for removing gas or impurities in the vacuum chamber; A magnet formed outside the vacuum chamber to form a magnetic field on a target; And it may include a power supply for supplying power to the target and the wafer.

In the present invention, in producing a zinc oxide-based transparent conductive thin film on a substrate using the sputtering method as described above, by adjusting the strength of the magnet attached to the sputtering device, it is possible to uniformize the resistivity at each position on the thin film surface. . That is, when adjusting the strength of the magnet in the range of 1.5 KG to 4.5 KG, it is possible to greatly improve the uniformity of the specific resistance at each position on the thin film surface.

For example, a magnetron sputtering device that coats a 70 mm by 70 mm substrate using about 70 L of chamber and 75 W of power, for example, a 5 KG magnet is typically used attached to the target backside. In the case of sputtering by replacing it with a magnet of 2.5 KG, it is possible to deposit a zinc oxide-based transparent conductive thin film having a significantly improved uniformity of specific resistance without changing other conditions.

In general, it is known that the strength of the magnet attached to the sputter and the DC bias formed on the target tend to be opposite to each other, and as the strength of the magnet decreases, the magnitude of the DC bias does not increase linearly but increases rapidly. It is known. Therefore, considering only the DC bias, it can be expected that the specific resistance of the center portion of the thin film surface is greatly increased due to the impact caused by the particles having high energy, and thus the uniformity of the specific resistance becomes worse.

However, the present invention shows a phenomenon in which the uniformity of the specific resistance is significantly improved even when the strength of the magnet attached to the sputtering device is reduced, which does not seem to be simply an effect of DC bias alone, and the magnetic field formed on the target ( It is judged that the effect of the change of the magnetic field) is a result of the combined action.

In the present invention, the magnitude of the magnetic flux density applied to the sputtering target may range from 1.5 KG to 4.5 KG. If the magnetic flux density is larger than the above range, the variation of the specific resistance at each position on the thin film surface is too large, so it is difficult to expect desirable physical properties as the transparent conductive film. If the magnetic flux density is smaller than the above range, the DC bias is large, so the thin film There is a problem that the electrical properties are degraded due to the physical damage of.

When manufacturing a zinc oxide-based transparent conductive thin film on a substrate by the sputtering method, by adjusting the magnitude of the magnetic flux density applied to the sputtering target as described above, the uniformity of the specific resistance at each position on the thin film surface is greatly improved. Preferably, the difference in specific resistance according to the position on the thin film surface may be to be in the range of 10 to 50% of the maximum specific resistance.

In the case of manufacturing the zinc oxide-based transparent conductive thin film by the method of the present invention, not only the resistivity uniformity can be improved, but also the resistivity of the thin film can be lowered as compared with the conventional uniform thin film.

Conventionally, a method of moving a specimen or a magnet attached to a sputter is used to improve uniformity of resistivity on a thin film surface. However, in the case of using such a method, the uniformity may be improved, but there is a problem in that the average specific resistance value is increased. However, the method of the present invention not only improves the uniformity, but also has the advantage of lowering the average specific resistance value. (See Fig. 3)

Therefore, the zinc oxide-based transparent conductive thin film manufactured by the method of the present invention may have a specific resistance in the range of 2.00 × 10 ⁻⁴ cm 3 to 5.00 × 10 ⁻⁴ cm 3.

The zinc oxide-based transparent conductive thin film manufactured by the method of the present invention may be composed of only zinc oxide (ZnO), but may include one or more doping materials to improve electrical conductivity, and non-limiting examples of such doping materials. May be Al, Ga, Si, In, Ge, or Ti, and the doping amount may range from 0.1 wt% to 10 wt%. When the doping amount is smaller than the above range, it is difficult to expect the effect of improving the electrical conductivity by doping. When the doping amount is larger than the above range, the structure of the zinc oxide crystal is hard to be maintained, and the electrical conductivity of the thin film may be impaired by the decrease of electron mobility. Can be.

On the other hand, the thickness of the zinc oxide-based transparent conductive thin film manufactured by the manufacturing method of the present invention may be in the range of 10 ~ 300nm. In general, a doped zinc oxide thin film manufactured by a sputtering method is a relatively thick film of 500 nm or more in order to have a similar resistivity (2x10 ^-4 Ωcm ~ 3x10 ^-4 Ωcm) to ITO. The specific resistivity means the unit area and the resistance per unit length. Therefore, even if the film thickness changes, the same resistivity is the same even if the material is the same.However, in the case of the zinc oxide thin film manufactured by sputtering, the thicker the crystallite, ), The electrical resistance is also proportional to the size of the grains, so the exceptional resistance tends to depend on the thickness of the thin film.

Of course, if the thickness of the thin film may cause a problem in the transmittance, the thickness of the thin film may be limited when used as a transparent electrode material, but in the case of zinc oxide thin film is increased due to the excellent transmittance (85% or more) Even if the decrease in the transmittance does not appear much.

However, if the film thickness is high, the deposition time may be long when the thin film is manufactured, which may cause a problem that productivity is reduced. Therefore, in terms of the production process, having a low specific resistance even at a thinner thickness (about 300 nm or less) may shorten the production time and may be advantageous.

When sputtering by the method of the present invention, the gas injected into the chamber may be argon (Ar) alone or a mixed gas of argon (Ar) and hydrogen (H ₂ ) 0.1-10 vol%. When hydrogen gas is included, oxygen vacancy is formed in the zinc oxide thin film, and this oxygen deficiency may act as an electron donor to increase the electron concentration, thereby reducing the resistivity. You can expect.

The zinc oxide-based transparent conductive thin film produced by the method of the present invention is formed on a transparent substrate, non-limiting examples of the substrate is a glass substrate or a plastic substrate, non-limiting examples of the glass substrate is TFT glass, Soda-lime glass, and the like, and non-limiting examples of plastic substrates include polyethylene terephthalate (PET), polyethylene 2,6-naphthalate (PEN), polyether sulfone (PES), polyether imide (PEI), and PMMA (polymethylmethacrylate), PC (polycarbonate), and the like.

The use of the zinc oxide thin film is not limited to a specific one, but may be used as, for example, a transparent conductive thin film, which may be used in various applications such as transparent electrodes of various display devices, photoelectric conversion elements such as solar cells, and touch panels. have.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited thereto.

Example 1

A gallium oxide (Ga) -doped zinc oxide-based transparent conductive thin film was deposited on a glass substrate using an RF magnetron sputtering device. At this time, a zinc oxide (ZnO) target containing 5.5 wt% of gallium (Ga) was used as the sputtering target. As a magnet mounted on the sputter, a magnet having a magnetic flux density of 2.5 KG was used.

At this time, the bias voltage applied to the target was about −100 V, the pressure in the sputtering chamber was 3 × 10 ⁻³ torr, and the flow rate of argon (Ar) gas was 50 sccm.

The thickness of the prepared zinc oxide transparent conductive thin film was about 150 nm.

Comparative Example 1

A zinc oxide transparent conductive thin film was manufactured in the same manner as in Example 1, except that a magnet mounted on a sputter had a magnetic flux density of 5 KG.

Figure 1 shows the schematic shape and strength of the magnet used in Example 1 and Comparative Example 1. The poles of the center and surrounding magnets are arranged oppositely and a magnetic field is formed between the two magnets so that the area between the two magnets becomes an effective erosion area.

2, in the case of Comparative Example 1 using a magnet having a high magnetic flux density, the uniformity of the specific resistance according to the position on the surface of the conductive thin film was very bad. It can be seen that the specific resistance increases sharply in the center (position 0), which is thought to be due to defect formation due to collision of energetic particles.

In the case of Example 1 using a magnet having a low magnetic flux density, it was found that the distribution of the specific resistance was significantly improved compared to that of Comparative Example 1.

Meanwhile, in Comparative Example 1, the DC bias formed on the target during sputtering was about -70 V, and the deposition rate of the thin film was 7.3 nm / min, but in Example 1 where the magnet strength of the sputtering device was reduced- DC bias of about 100 V was formed and thin film deposition rate also increased to 9.5 nm / min.

1 is a diagram showing the schematic shape of the magnet inside the gun mounted on the sputter and the strength of the magnet used in Example 1 and Comparative Example 1. FIG.

2 is a graph showing the results of measuring the specific resistance of the zinc oxide transparent conductive thin films prepared in Example 1 and Comparative Example 1 for each position on the surface of the conductive film.

Figure 3 is a schematic diagram showing the specific resistance distribution according to the position of the zinc oxide-based transparent conductive thin film prepared by a general method and the thin film prepared by the embodiment of the present invention.

Claims (7)

A method for producing a zinc oxide-based transparent conductive thin film on a substrate by a sputtering method, wherein the magnitude of magnetic flux density applied to the sputtering target is in the range of 1.5 KG to 4.5 KG. The method according to claim 1, wherein the difference in specific resistance according to the position on the thin film surface is in the range of 10 to 50% of the maximum specific resistance. The method of claim 1, wherein the zinc oxide-based transparent conductive thin film has a specific resistance in a range of 2.00 × 10 ⁻⁴ cm 3 to 5.00 × 10 ⁻⁴ cm 3. The compound of claim 1, further comprising Ar; Or Ar and sputtered in a H ₂ mixed gas atmosphere of 0.1 ~ 10 vol%. The method according to claim 1, wherein the thickness of the formed thin film is in the range of 10 to 300 nm. The method according to claim 1, wherein the dopant element contained in zinc oxide is Al or Ga. Manufactured by the method according to any one of claims 1 to 6, the difference in specific resistance depending on the position on the thin film surface is in the range of 10 to 50% of the maximum specific resistance, 2.00 × 10 ^-4 Ωcm ~ 5.00 × 10 Zinc oxide-based transparent conductive thin film characterized by having a specific resistance in the range of ^-4 Ω㎝.

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