KR20090112333A - Transparent conducting thin films consisting of zinc oxide and fabricating method for the same - Google Patents

Abstract

PURPOSE: A transparent conducting thin film consisting of a zinc oxide and a fabricating method for the same are provided to obtain improved electric characteristics by providing a higher free charge mobility than a doped zinc oxide transparent conductive thin film. CONSTITUTION: A method for fabricating a transparent conducting thin film consisting of a zinc oxide comprises the steps of doping a halogen anionic element and a hydrogen onto a zinc oxide or doping a halogen anionic element, a hydrogen and group III cationic metal element on a zinc oxide, wherein the doped halogen anionic element is 0.05~2.5at%.

Description

Transparent conducting thin films consisting of zinc oxide and fabricating method for the same}

The present invention relates to a zinc oxide-based transparent conductive thin film and a method for manufacturing the same, and more particularly, even when the free charge concentration is low, the free charge mobility may be reduced due to grain boundary scattering. The present invention relates to a zinc oxide-based transparent conductive thin film capable of maintaining mobility and a method of manufacturing the same.

Transparent conductive thin films are used in flat panel displays such as TFT-LCD (thin film transistor-liquid crystal display), plasma display panel (PDP), field emission display (FED), and organic light emitting diodes (OLED). Used, good light transmission and conductivity in the visible and near infrared range are required.

Currently, Sn ₂ doped In ₂ O ₃ (In ₂ O ₃ : Sn, Indium Tin Oxide, ITO) is most commonly used as a high quality transparent conductive thin film. However, In, which is a major constituent of ITO, is extremely expensive in comparison with Ag due to its extremely low reserves compared to Sn and Zn. As a substitute material for ITO, ZnO is a material doped with Group 3 cationic metal elements such as Al, Ga, In, and B. Among them, ZnO: Al doped with Al and ZnO: Ga doped with Ga Has received the most attention. Zn, the main constituent of ZnO, is a material with abundant reserves of about 1000 times more than In. It is inexpensive and has the advantage of being stable in hydrogen plasma atmosphere (SiH ₄ ). There is a movement to actively use the same purpose.

The measure of excellence of such a transparent conductive thin film depends on how well free charge can move at a given concentration of free carrier, that is, how large the carrier mobility of free charge is.

The zinc oxide transparent conductive thin film has a hexagonal wurtzite structure, and the zinc oxide transparent conductive thin film obtained by a conventional deposition method grows in a direction in which the crystal plane is parallel to the substrate, and the grain size is It is common to grow into polycrystalline of 10 to 50 nm. In such a polycrystalline zinc oxide-based transparent conductive thin film, when the concentration of free charge is low, grain boundary scattering caused by an energy barrier formed by free charge trapped at a grain boundary is applied. Therefore, the mobility of free charge is extremely low. On the other hand, if the concentration of the free charge is large, the free charge that can overcome the energy barrier formed in the grain boundary is increased, the mobility of the free charge is increased to some extent. However, if the concentration of free charge is increased above a certain level, ionized impurity in the thin film increases, causing scattering between free charge and ionized impurity and consequently reducing the mobility of free charge. do.

Meanwhile, as a method for increasing the free charge concentration in a zinc oxide transparent conductive thin film, a free charge is formed by doping the group III cationic metal element in the zinc oxide transparent conductive thin film, and the free charge concentration is controlled by controlling the doping amount. There is a way. Specifically, when the Group 3 cationic metal element such as Al or Ga is doped into the zinc oxide-based transparent conductive thin film, the Group 3 cationic metal element substitutes for Zn which is divalent, and free charge is generated by the difference in charge amount. The concentration of free charge is controlled by However, when the doping amount is above a certain level, the concentration of free charge is rather reduced. For example, when Al is doped in a predetermined amount or more, a secondary phase such as Al ₂ O ₃ is formed in the thin film to reduce the concentration of free charge. Accordingly, the doping amount of a metal element such as Al or Ga is usually 1 It is adjusted to the range of -4 at%.

On the other hand, the free charge mobility of a zinc oxide based thin film doped with a metal element such as Al or Ga using physical vapor deposition such as sputtering or pulse laser deposition is generally 30 cm ² /. It is difficult to exceed Vs and usually has a value of about 10 ~ 20cm ² / Vs. In particular, when the free charge concentration is 10 ²⁰ cm ^-3 or less, the free charge mobility is much lower than 20 cm ² / Vs due to grain boundary scattering.

In addition, increasing the free charge concentration by increasing the doping amount of Al, Ga, etc. is the absorption phenomenon in the visible region due to the ionized impurities and free carrier absorption in the long wavelength region and near infrared region of the visible ray There is a problem that the light absorption is increased to increase the free charge concentration in applications where high light transmittance of the transparent conductive thin film is required, such as in a solar cell.

On the other hand, in addition to the Group 3 cationic metal elements, F, a halogen group anionic element, has been proposed as a doping element for zinc oxide thin films, and is oxidized using CVD, Sol-Gel, or spray pyrolysis. A study of doping zinc with F has been reported. However, the concentration of free charges generated in the thin film by the F doping was low, which did not attract much attention. In particular, there have been few reports of physical vapor deposition such as sputtering, which is most commonly used in the production of zinc oxide transparent conductive thin films. This is because the concentration of free charges generated in the thin film by doping is lower than that of metal dopants such as Al.

As described above, in the zinc oxide transparent conductive thin film, it is difficult to secure a characteristic of having high free charge mobility while having an appropriate free charge concentration.

The present invention has been made to solve the above problems, and even if the free charge concentration is low can improve the free charge mobility by grain boundary scattering, high free charge mobility can be maintained even at an appropriate free charge concentration. An object of the present invention is to provide a zinc oxide transparent conductive thin film and a method for manufacturing the same.

Zinc oxide-based transparent conductive thin film according to the present invention for achieving the above object is a zinc oxide doped with a halogen anionic element and hydrogen or zinc oxide doped with a halogen anionic element, hydrogen and a Group 3 cationic metal element. It features.

When zinc oxide is doped with a halogen-based anionic element and hydrogen, the decrease in free charge mobility due to grain boundary scattering is minimized even at low free charge concentrations. When doping, the free charge concentration of the titration is secured and high free charge mobility is maintained.

The halogenated anionic element doped with zinc oxide may be any one of F, Cl, Br, and I, of which F most similar in oxygen and atomic radius may be most likely used. In addition, the doping amount of the halogen anionic element is preferably 0.05 to 2.5 at%. If the doping amount of the halogen anionic element is less than 0.05at%, the doping amount is too small to effect the doping effect. If the doping amount exceeds 2.5at%, it not only prevents grain growth during thin film growth but also ZnF ₂ and The same secondary phase is formed so that the free charge mobility is lowered.

On the other hand, the Group 3 cationic metal element is doped with zinc oxide for the purpose of increasing the free charge concentration, wherein the doping amount of the Group 3 cationic metal element is preferably 1 at% or less. In the prior art, when doping a group 3 cationic metal element to zinc oxide, it is generally applied in the range of 1 to 4 at%. In the present invention, AlF ₃ produced by reacting a halogen anionic element with a group 3 cationic metal element In order to minimize the formation of secondary phases, such as doping amount of the Group 3 cationic metal element is adjusted to 1 at% or less. Here, any one of Al, Ga, B, In, Sc, Fe, Cr may be used as the Group 3 cationic metal element.

Hydrogen is doped into the zinc oxide-based transparent conductive thin film of the present invention, and the hydrogen is characterized in that the hydrogen in the process gas is contained in the thin film using a gas containing hydrogen as the process gas.

Hydrogen or a gas containing hydrogen is an ubiquitous gas, and since the trace amount is present inside the vacuum apparatus for thin film deposition, it is very small in the synthesis of the thin film, but it is incorporated in the thin film. However, in the present invention, to improve the characteristics of the zinc oxide-based transparent conductive thin film, it is suggested that the hydrogen is actively doped into the thin film, rather than containing hydrogen as an inevitable phenomenon as described above.

To this end, the present invention forms a zinc oxide-based transparent conductive thin film by physical vapor deposition or chemical vapor deposition, such as a sputtering method or a pulsed laser deposition method. In this case, the hydrogen is doped in the thin film using hydrogen or a gas containing hydrogen as a process gas.

Specifically, when the zinc oxide-based transparent conductive thin film is formed by using physical vapor deposition, hydrogen may be doped in three forms.

The first is a zinc oxide target containing a Group 3 cationic metal element, a zinc oxide target containing a halogen anionic element, or a zinc oxide target containing both a Group 3 cationic metal element and a halogen anionic element. When a zinc oxide transparent conductive thin film is formed using hydrogen, a gas containing hydrogen or hydrogen as a process gas, for example, H ₂ , H ₂ O or the like, is used to hydrogen-dope the zinc oxide transparent conductive thin film. . In this case, when using a zinc oxide target containing a Group 3 cationic metal element, it is preferable to use a gas containing hydrogen and a halogen anionic element together as a process gas, for example, using HF, CHF _3, or the like. It is also possible.

Second, zinc oxide transparent conductive thin film doped with a group 3 cationic metal element, zinc oxide transparent conductive thin film doped with a halogen anionic element, oxidation doped with both a group 3 cationic metal element and a halogen anionic element In the state in which one of the zinc-based transparent conductive thin film is prepared, the zinc oxide-based transparent conductive thin film is subjected to heat treatment under a gas atmosphere containing hydrogen or hydrogen to dope the hydrogen oxide-based transparent conductive thin film. In this case, when the heat treatment is performed on the zinc oxide-based transparent conductive thin film doped with a Group 3 cationic metal element, it is preferable to use a gas including hydrogen and a halogen anionic element as a process gas, for example, HF , CHF ₃ and the like can also be used.

Third, zinc oxide transparent conductive thin film doped with Group 3 cationic metal element, zinc oxide transparent conductive thin film doped with halogen anionic element, oxidation doped with both Group 3 cationic metal element and halogen anionic element In the state in which one of the zinc-based transparent conductive thin film is prepared, hydrogen is doped into the zinc oxide-based transparent conductive thin film by using hydrogen or a plasma containing hydrogen with respect to the zinc oxide-based transparent conductive thin film. In this case, when the plasma treatment is performed on the zinc oxide-based transparent conductive thin film doped with a group 3 cationic metal element, it is preferable to use those in which plasma and hydrogen anionic anionic element are included together.

The second and third methods, that is, the heat treatment or plasma treatment method for the thin film may be equally applied to the thin film manufactured by chemical vapor deposition.

In the case of forming a zinc oxide-based transparent conductive thin film by chemical vapor deposition, a precursor containing a halogen anionic element or a precursor containing both a group 3 cationic metal element and a halogen anionic element is used as a precursor. At this time, hydrogen or a gas containing hydrogen may be used as the process gas, and a gas containing both hydrogen and a halogen anionic element may be used. Here, hydrogen may be included in the precursor.

Heat treatment may be applied to the finished zinc oxide-based transparent conductive thin film to improve free charge mobility and free charge concentration characteristics. Here, the heat treatment may be performed at a temperature of 200 to 500 ℃ in a vacuum or gas atmosphere containing hydrogen, the heat treatment time may be applied to 20 to 200 minutes.

Such a zinc oxide-based transparent conductive thin film of the present invention can be formed on a glass substrate or a plastic substrate.

The zinc oxide-based transparent conductive thin film and the method of manufacturing the same according to the present invention have the following effects.

When the zinc oxide transparent conductive thin film according to the present invention is applied to a transparent electrode material of a flat panel display, a transparent electrode of a solar cell, or a glass for shielding electromagnetic waves, a zinc oxide based transparent conductive thin film doped only with a conventional Group 3 cationic metal element Or, compared with the zinc oxide-based transparent conductive film doped with only halogen anionic elements, it provides higher free charge mobility and ultimately improves electrical characteristics.

<Example 1>

Example 1 shows a zinc oxide-based transparent conductive thin film (hereinafter referred to as specimen A) in which fluorine (F), which is one of the halogenated anionic elements on the periodic table, is doped with zinc (H) together with hydrogen (H), and hydrogen is not doped. The resistivity characteristics, free charge concentration and free charge mobility of zinc oxide transparent conductive thin films (hereinafter referred to as specimen B) were compared.

Specimen A and Specimen B were prepared under the following process conditions.

First, Specimen A was sputtered with a pure zinc oxide (ZnO) target under a gas atmosphere in which argon (Ar), CF ₄ and H ₂ were mixed with a glass substrate (Corning Eagle2000) mounted in a process chamber. It was formed to a thickness of 300nm on the phase. At this time, the process pressure is 1mTorr, the process temperature is 150 ℃, RF power was 50W, the F content of the prepared specimen A is 1.7at%. On the other hand, Specimen B was manufactured under the same process conditions as the process of Specimen A, except that H ₂ was removed from the process gas.

Looking at the characteristics of the prepared specimen A and specimen B is shown in Table 1 below.

TABLE 1

target CF ₄ (vol%) H ₂ (vol%) Resistivity (Ωcm) Free charge mobility (cm ² / Vs) Free charge concentration (cm ^-3 ) Psalm A pure ZnO 0.8 2 1.85 × 10 ^-3 40.69 8.30 × 10 ¹⁹ Psalm B pure ZnO 0.8 0 5.12 × 10 ^-2 7.66 1.59 × 10 ¹⁹

As shown in Table 1, specimen A with hydrogen has better resistivity than specimen B without hydrogen, and specimen A has 40.69 cm ² / Vs for free charge mobility and free charge concentration, respectively. , as opposed to indicating the 8.30 × 10 ¹⁹ cm ^-3 specimen B is a free charge carrier mobility is 7.66cm ² / Vs, both free charge concentration of 1.59 × 10 ¹⁹ cm ^-3 in the bar, the free charge carrier mobility and free arc concentrations We can see that specimen A is far superior to specimen B.

<Example 2>

Example 2 shows a zinc oxide transparent conductive thin film doped with aluminum (Al), fluorine (F) and hydrogen (H) (hereinafter referred to as specimen C), and an oxide doped with only aluminum (Al) and fluorine (F). The resistivity characteristics, free charge concentration and free charge mobility of zinc-based transparent conductive thin films (hereinafter referred to as specimen D) were compared.

Specimen C and Specimen D were prepared under the following process conditions.

First, Specimen C RF-zinc targets a zinc oxide (ZnO) target containing 1wt% Al ₂ O ₃ under a gas atmosphere in which Ar, CF ₄ and H ₂ are mixed with a glass substrate (Corning Eagle2000) mounted in the process chamber. It was sputtered to form a thickness of 300nm on the glass substrate. At this time, the process pressure, the process temperature and the RF power applied to the target are the same as the process conditions of Example 1, the Al content of the prepared specimen C is 0.8at%, F content is 0.7at%. On the other hand, the specimen D was manufactured under the same process conditions as the process of the specimen C, but was manufactured in a state in which H ₂ is excluded from the process gas.

Looking at the characteristics of the prepared specimen C and specimen D is shown in Table 2 below.

TABLE 2

target CF ₄ (vol%) H ₂ (vol%) Resistivity (Ωcm) Free charge mobility (cm ² / Vs) Free charge concentration (cm ^-3 ) Psalm C ZnO-1wt% Al ₂ O ₃ 0.4 4 3.93 × 10 ^-4 25.34 6.26 × 10 ²⁰ Psalm D ZnO-1wt% Al ₂ O ₃ 0.4 0 1.04 × 10 ^-2 7.47 8.06 × 10 ¹⁹

As shown in Table 2, it can be seen that specimen C containing hydrogen has superior resistivity, free charge mobility, and free charge concentration characteristics compared to specimen D without hydrogen. It can be seen that the free charge concentration increases compared to specimen A and specimen B.

<Example 3>

Example 3 shows the resistivity, free charge concentration and freeness of Al, F and hydrogen (H) doped zinc oxide transparent conductive thin films (hereinafter referred to as specimen E) which increased the doping amount of Al relative to specimen C. It shows the charge mobility characteristics.

Specimen E was prepared under the same process conditions as in Example 2 except that a zinc oxide (ZnO) target containing 1 wt% Al ₂ O ₃ was used as the sputtering target. The Al content of the prepared specimen E was 1.56 at%, which is higher than the 0.8 at% Al content of the specimen C.

The resistivity, free charge mobility and free charge concentration characteristics of the fabricated specimen E are compared to specimen C as shown in Table 3 below. As shown in Table 3, it can be seen that the specimen E having a relatively high Al content has a lower resistivity characteristic and a lower free charge mobility and free charge concentration than the specimen C having a relatively low Al content. Specimen E with high Al content has lower free charge mobility and free charge concentration than specimen C with low Al content for the following reasons. When the doping amount of Al is increased, Al reacts with F, which is a halogen element, to form a secondary phase such as AlF _3, and the free charge concentration is lowered due to the secondary phase to lower the free charge mobility.

Therefore, the Al content in zinc oxide and the characteristics of <free charge mobility and free charge concentration> do not have a linear proportional relationship. It can be seen that not preferred.

TABLE 3

target CF ₄ (vol%) H ₂ (vol%) Resistivity (Ωcm) Free charge mobility (cm ² / Vs) Free charge concentration (cm ^-3 ) Psalm E ZnO-2wt% Al ₂ O ₃ 0.4 4 9.06 × 10 ^-4 13.37 5.15 × 10 ²⁰ Psalm C ZnO-1wt% Al ₂ O ₃ 0.4 4 3.93 × 10 ^-4 25.34 6.26 × 10 ²⁰

<Example 4>

In Example 4, specimens C, D, and E were each heat-treated at 300 ° C. for 1 hour in a vacuum to prepare specimens (hereinafter referred to as specimen C-ann, specimen D-ann, and specimen E-ann), and their resistivity characteristics, Free charge mobility and free charge concentration characteristics are compared with specimens C, D, and E.

In general, when the heat treatment is performed on the thin film, stress and defects remaining in the thin film are removed to improve the characteristics of the thin film. In this embodiment, the specimens C, D, and E are each heat treated at 300 ° C. for 1 hour in a vacuum. As a result, as shown in Table 4, specimen C-ann and specimen D-ann having a relatively low Al content can be confirmed that the free charge mobility is improved by heat treatment. Particularly, specimen C- containing hydrogen ann can be seen to be superior to the hydrogen-free specimen D-ann, with free charge mobility reaching 36 cm ² / Vs. On the other hand, specimen E-ann with a relatively high Al content shows little change in free charge mobility compared to specimen E, rather, it can be seen that the characteristics of the free charge concentration is reduced.

TABLE 4

target CF ₄ (vol%) H ₂ (vol%) Resistivity (Ωcm) Free charge mobility (cm ² / Vs) Free charge concentration (cm ^-3 ) Psalm C-ann ZnO-1wt% Al ₂ O ₃ 0.4 4 2.90 × 10 ^-4 36.24 5.94 × 10 ²⁰ Psalm C ZnO-1wt% Al ₂ O ₃ 0.4 4 3.93 × 10 ^-4 25.34 6.26 × 10 ²⁰ Psalm D-ann ZnO-1wt% Al ₂ O ₃ 0.4 0 1.07 × 10 ^-3 15.37 3.80 × 10 ²⁰ Psalm D ZnO-1wt% Al ₂ O ₃ 0.4 0 1.04 × 10 ^-2 7.47 8.06 × 10 ¹⁹ Psalm E-ann ZnO-2wt% Al ₂ O ₃ 0.4 4 1.15 × 10 ^-3 13.21 4.11 × 10 ²⁰ Psalm E ZnO-2wt% Al ₂ O ₃ 0.4 4 9.06 × 10 ^-4 13.37 5.15 × 10 ²⁰

Claims (26)

A zinc oxide-based transparent conductive thin film, wherein zinc oxide is doped with a halogen anionic element and hydrogen. A zinc oxide-based transparent conductive thin film, wherein zinc oxide is doped with a halogen anionic element, hydrogen, and a group 3 cationic metal element. The zinc oxide-based transparent conductive thin film according to claim 1 or 2, wherein the halogenated anionic element is doped with 0.05 to 2.5 at%. 3. The zinc oxide-based transparent conductive thin film according to claim 2, wherein the Group 3 cationic metal element is larger than 0 and doped at 1 at% or less. The zinc oxide-based transparent conductive thin film according to claim 1 or 2, wherein the halogen anionic element is any one of F, Cl, Br, and I. The zinc oxide-based transparent conductive thin film according to claim 2, wherein the Group 3 cationic metal element is any one of Al, Ga, B, In, Sc, Fe, and Cr. A method for producing a zinc oxide-based transparent conductive thin film, comprising: producing a thin film doped with zinc oxide with an halogen-based anionic element. A method for producing a zinc oxide-based transparent conductive thin film, characterized in that a zinc oxide is doped with a halogen anionic element, hydrogen, and a group 3 cationic metal element. The method of manufacturing a zinc oxide-based transparent conductive thin film according to claim 7 or 8, wherein the thin film is manufactured by physical vapor deposition or chemical vapor deposition. 9. The method of claim 7 or 8, wherein the halogen anionic element is doped with 0.05 to 2.5 at%. 9. The method of claim 8, wherein the Group 3 cationic metal element is larger than 0 and doped to 1 at% or less. The method of claim 9, wherein the physical vapor deposition method is used. Using either a zinc oxide target containing a Group 3 cationic metal element, a zinc oxide target containing a halogen anionic element, or a zinc oxide target containing both a Group 3 cationic metal element and a halogen anionic element, and A process for producing a zinc oxide-based transparent conductive thin film, comprising using hydrogen or a gas containing hydrogen as a process gas. The method of claim 9, wherein the physical vapor deposition method or the chemical vapor deposition method is used. Zinc oxide transparent conductive thin film doped with Group 3 cationic metal element, Zinc oxide transparent conductive thin film doped with halogen anionic element, Zinc oxide transparent conductive doped with both Group 3 cationic metal element and halogen anionic element Process for producing a zinc oxide-based transparent conductive thin film, characterized in that the heat treatment for any one of the thin film in the gas atmosphere containing hydrogen or hydrogen. The method of claim 9, wherein the physical vapor deposition method or the chemical vapor deposition method is used. Zinc oxide transparent conductive thin film doped with Group 3 cationic metal element, Zinc oxide transparent conductive thin film doped with halogen anionic element, Zinc oxide transparent conductive doped with both Group 3 cationic metal element and halogen anionic element Process for producing a zinc oxide-based transparent conductive thin film, characterized in that for plasma treatment using any one of the thin film or a plasma containing hydrogen. The zinc oxide-based transparent conductive thin film manufacturing method according to claim 12, wherein when using a zinc oxide target containing the Group 3 cationic metal element, a gas containing both hydrogen and a halogen anionic element is used as a process gas. Way. The method of claim 13, wherein when the heat treatment is performed on the zinc oxide-based transparent conductive thin film doped with the Group 3 cationic metal element, a gas including hydrogen and a halogen anionic element is used as the process gas. Zinc oxide transparent conductive thin film manufacturing method. 15. The zinc oxide system according to claim 14, wherein when the plasma treatment is performed on the zinc oxide-based transparent conductive thin film doped with a Group 3 cationic metal element, the plasma includes hydrogen and a halogen anionic element. Transparent conductive thin film manufacturing method. The method of claim 9, wherein the chemical vapor deposition method is used. When forming a zinc oxide transparent conductive thin film, a precursor containing a halogen anionic element or a precursor containing both a group 3 cationic metal element and a halogen anionic element is used as a precursor, and hydrogen or hydrogen is included. A method for producing a zinc oxide transparent conductive thin film, comprising using the prepared gas as a process gas. 19. The method of claim 18, wherein the precursor further comprises hydrogen. 19. The method of claim 18, wherein a gas containing hydrogen and a halogen anionic element together is used as the process gas. The method of manufacturing a zinc oxide-based transparent conductive thin film according to claim 9, wherein a sputtering method or a pulse laser deposition method is used as the physical vapor deposition method. The method of claim 7 or 8, wherein the halogenated anionic element is any one of F, Cl, Br, and I. A method for producing a zinc oxide-based transparent conductive thin film. 9. The method of claim 8, wherein the Group 3 cationic metal element is any one of Al, Ga, B, In, Sc, Fe, and Cr. The method of claim 7 or 8, wherein the thin film is formed on a glass or plastic substrate. The method for manufacturing a zinc oxide-based transparent conductive thin film according to claim 7 or 8, wherein a heat treatment process is applied to the produced zinc oxide transparent conductive thin film. The zinc oxide-based transparent conductive thin film according to claim 25, wherein the heat treatment is performed for 20 to 200 minutes at a temperature of 200 to 500 ° C under vacuum.