JP2013020846A - Transparent conductive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent conductive film including carriers stably existing at high concentration therein and low in infrared light transmittance, while reducing high-cost indium content.SOLUTION: The transparent conductive film contains at least indium, tin and zinc. In the transparent conductive film, an atomic ratio represented as In/(In+Sn+Zn) is 0.25-0.6, an atomic ratio represented as Sn/(In+Sn+Zn) is 0.15-0.3, an atomic ratio represented as Zn/(In+Sn+Zn) is 0.15-0.5, a light transmittance in a visible range is 70% or more, and a light transmittance in an infrared range is 65% or less.

Description

  The present invention relates to a transparent conductive film and a method for producing the same.

  Transparent conductive substrates are used as transparent electrode substrates, electromagnetic wave shielding sheets, transparent film substrates and the like in inorganic / organic electroluminescent elements, liquid crystal elements and the like. The transparent conductive film is an indium tin oxide film formed on the surface of an inorganic transparent substrate such as glass or quartz, or a substrate film made of PET, PES, PC, or the like by sputtering, ion plating, or vapor deposition. Objects (ITO) dominate.

  However, representative transparent conductive oxides such as ITO and indium zinc oxide are representative, and both contain 90 mol% or more of indium oxide, which causes a problem of high raw material costs. As transparent conductive oxides that do not use indium oxide, there are AZO and GZO in which Al or Ga is added to ZnO, but these are inferior in weather resistance and chemical resistance, and their uses are extremely limited.

As a material in which the content of indium oxide is reduced, a transparent conductive material containing In, Sn, and Zn at the same time is disclosed (Patent Document 1).
In Patent Document 1, the atomic ratio In / (In + Sn + Zn) is 0.25 to 0.6, the atomic ratio Sn / (In + Sn + Zn) is 0.15 to 0.3, and the atomic ratio Zn / (In + Sn + Zn) is 0.15 to 0. An indium tin zinc oxide (ITZO) transparent electrode having a specific resistance of 400 μΩcm to 900 μΩcm is obtained by a sputtering method using a sputtering target of 0.5.
However, when this ITZO is used as a transparent electrode or a heat ray reflective film, there are problems that the carrier concentration is lowered and the resistance is increased or the heat ray reflectivity is low.

JP 2007-63649 A

  An object of the present invention is to provide a transparent conductive film in which the carrier is present stably at a high concentration and the infrared light transmittance is low while suppressing the high-cost indium content.

According to the present invention, the following transparent conductive film and the like are provided.
1. Contains at least indium, tin and zinc,
The atomic ratio represented by In / (In + Sn + Zn) is 0.25-0.6, the atomic ratio represented by Sn / (In + Sn + Zn) is 0.15-0.3, and is represented by Zn / (In + Sn + Zn). The atomic ratio is 0.15 to 0.5,
A transparent conductive film having a light transmittance in a visible region of 70% or more and a light transmittance in an infrared region of 65% or less.
2. 2. The transparent conductive film according to 1, which has been subjected to an annealing treatment.
3. 3. The transparent conductive film according to 1 or 2, wherein the light transmittance in the infrared region after the heat resistance test is 65% or less.
4). The transparent conductive film in any one of 1-3 whose activation energy is 1 meV or more and 15 meV or less.
5. It contains at least indium, tin and zinc, the atomic ratio represented by In / (In + Sn + Zn) is 0.25 to 0.6, and the atomic ratio represented by Sn / (In + Sn + Zn) is 0.15 to 0.3. Yes, using a sputtering target having an atomic ratio represented by Zn / (In + Sn + Zn) of 0.15 to 0.5, a film is formed on the substrate by a sputtering method, and the film is formed at a substrate temperature of 700 ° C. A method for producing a transparent conductive film, comprising annealing.
6). 6. The method for producing a transparent conductive film according to 5, wherein the annealing is performed in an atmosphere having an oxygen partial pressure of 50 to 200 hPa.

  According to the present invention, it is possible to provide a transparent conductive film in which carriers are stably present at a high concentration and the infrared light transmittance is low while suppressing the content of high-cost indium.

It is a figure which shows the light transmittance of the transparent conductive film obtained in Example 1 and Comparative Example 2. It is a figure which shows the carrier mobility of the transparent conductive film obtained in Example 1 and Comparative Example 2, temperature dependence, and activation energy.

The transparent conductive film of the present invention contains at least indium, tin, and zinc and satisfies the following atomic ratio.
In / (In + Sn + Zn) = 0.25-0.6
Sn / (In + Sn + Zn) = 0.15-0.3
Zn / (In + Sn + Zn) = 0.15 to 0.5
The transparent conductive film has a light transmittance in the visible region of 70% or more and a light transmittance in the infrared region of 65% or less.
The atomic ratio can be measured by inductively coupled plasma (ICP) emission analysis.

If the atomic ratio In / (In + Sn + Zn) is smaller than 0.25, the resistance of the transparent conductive film obtained by sputtering may increase. If it exceeds 0.6, the indium reduction effect may not be obtained.
The atomic ratio In / (In + Sn + Zn) is preferably 0.44 to 0.55.

If the atomic ratio Sn / (In + Sn + Zn) is smaller than 0.15, the heat resistance of the transparent conductive film in the atmosphere may be reduced. If it exceeds 0.3, the transparency may be impaired. The atomic ratio Sn / (In + Sn + Zn) is preferably 0.20 to 0.25.

If the atomic ratio Zn / (In + Sn + Zn) is smaller than 0.15, wet etching may be difficult in processing the transparent conductive film into a desired shape for a product. If it is larger than 0.5, the heat resistance and conductivity of the transparent conductive film obtained by sputtering may be lowered.
The atomic ratio Zn / (In + Sn + Zn) is preferably 0.20 to 0.40.

The light transmittance in the visible region is an average value of the light transmittance of electromagnetic waves having a wavelength of 380 to 780 nm, and the light transmittance in the infrared region is an average value of light transmittance of electromagnetic waves having a wavelength of 1200 to 2600 nm.
The light transmittance can be measured with a spectrophotometer.

When the average transmittance in the visible region is less than 70%, the transparency is poor and it is unsuitable for use as a transparent electrode for a display element or a transparent heat ray reflective film.
Further, if the transmittance in the infrared region exceeds 65%, the heat ray reflectance is lowered, and there is a risk that the heat insulation effect is lowered in the building material and the heat generation is insufficient in the anti-fogging glass.
The average transmittance in the visible region is preferably 80% or more, and the light transmittance in the infrared region is preferably 60% or less.

  The transparent conductive film of the present invention preferably has a light transmittance of 65% or less in the infrared region even after a heat resistance test. The heat resistance test is performed by the method described in the examples.

The transparent conductive film of the present invention preferably has an activation energy of 1 to 15 meV.
The activation energy is calculated by measuring the temperature dependence of the Hall effect. Specifically, the measurement is performed as follows.
The values of the hole mobility obtained by the Hall effect are μ1 at the temperature T1 and μ2 at the temperature T2. Here, T1 is preferably about 270 to 330 K around room temperature. T2 is preferably about 100K lower than T1.
μ1 and μ2 can be expressed as follows.
μ1 = Aexp (−E / kT1), μ2 = Aexp (−E / kT2)
(In the formula, A is a constant, E is an activation energy, and k is a Boltzmann constant.)
The activation energy E can be obtained from μ1 and μ2 as follows.
E = − {k × log (μ1 / μ2)} / {(1 / T1) − (1 / T2)}

The activation energy indicates the temperature dependence of the mobility of electrons.
When the activation energy exceeds 15 meV, the speed of electrons decreases particularly at low temperatures, and the heat ray reflectivity may be lost. The smaller the activation energy, the better. However, if the activation energy is less than 1 meV, it means that the metal is in a semi-metallic state, and the transparency may be lost.
The activation energy is preferably 2 to 10 meV.

The transparent conductive film of the present invention may contain a metal element other than In, Sn, and Zn described above as long as the effects of the present invention are not impaired, or substantially only from In, Sn, and Zn. It may be.
In the present invention, “substantially” means that the effect as a transparent conductive film is attributed to the above In, Sn, and Zn, or 98 wt% to 100 wt% (preferably 99 wt%) of the metal element of the transparent conductive film. % Or more and 100% by weight or less) means In, Sn and Zn.
As described above, the metal element contained in the transparent conductive film is substantially composed of In, Sn, and Zn, and may contain other inevitable impurities as long as the effects of the present invention are not impaired.

The manufacturing method of the transparent conductive film of this invention includes forming into a film by sputtering method on a board | substrate using a sputtering target, and annealing in the range of substrate temperature -700 degreeC.
A sputtering target used for film formation contains at least indium, tin, and zinc, an atomic ratio In / (In + Sn + Zn) is 0.25 to 0.6, and an atomic ratio Sn / (In + Sn + Zn) is 0.15 to 0.00. 3 and the atomic ratio Zn / (In + Sn + Zn) is 0.15 to 0.5.
The sputtering target can be manufactured by a known method.

If the annealing temperature is lower than the substrate temperature at the time of film formation, the effect of annealing cannot be obtained, and there is a possibility that a transparent conductive film lacking the stability of the carrier concentration is obtained. When the annealing temperature exceeds 700 ° C., the carrier concentration decreases, and the function as a conductive film may not be achieved.
The annealing temperature is usually 100 to 500 ° C, preferably 300 to 500 ° C.

The annealing is preferably performed in an atmosphere having an oxygen partial pressure of 50 to 200 hPa.
When the oxygen partial pressure is 50 hPa or more, the resistance to coloring due to reduction is excellent. When the oxygen partial pressure is 200 hPa or less, the conductivity is excellent.
The oxygen partial pressure is preferably 100 to 190 hPa.

When the annealing treatment is not performed, the carrier concentration decreases and the resistance increases or the heat ray reflectivity decreases during the use process as the transparent electrode. This is due to the fact that the transparent electrode obtained by sputtering is thermodynamically non-equilibrium and oxygen vacancies that carry carriers do not exist stably.
Although the oxygen deficiency can be stabilized by performing the annealing treatment, the carrier concentration may be decreased or the transmittance may be decreased simply by annealing.
The annealing treatment at the specific temperature can prevent the carrier concentration and the heat ray reflectivity from being lowered.

  The sputtering method and sputtering conditions used are not particularly limited, but a direct current (DC) magnetron method, an alternating current (AC) magnetron method, and a radio frequency (RF) magnetron method are preferable. For liquid crystal display (LCD) panel applications, the DC magnetron method and the AC magnetron method are preferable because the apparatus becomes large, and the AC magnetron method capable of stable film formation is particularly preferable.

The sputtering pressure is usually 0.05 to 2 Pa, and the ultimate pressure is usually 10 ⁻³ to 10 ⁻⁷ Pa. The substrate temperature is usually 25 to 500 ° C, preferably 50 to 300 ° C, more preferably 100 to 250 ° C.

  As the introduction gas, an inert gas such as Ne, Ar, Kr, or Xe can be used. Of these, Ar is preferable in that the film forming speed is high. Moreover, when oxygen is included in the introduced gas in an amount of 0.01 to 5%, the specific resistance is preferably lowered. In addition, it is preferable that 0.01 to 5% of hydrogen is included in the introduced gas because the resistance of the obtained transparent conductive film tends to decrease.

  The transparent conductive film of the present invention is preferably amorphous or microcrystalline, and particularly preferably amorphous. Whether or not the transparent conductive film of the present invention is amorphous can be determined by an X-ray diffraction method. Since the transparent conductive film is amorphous, etching can be easily performed, etching residues are hardly generated, and a uniform film can be obtained even in a large area.

  The transparent conductive film of the present invention can be used as a transparent electrode of a thin film transistor by performing a treatment such as etching.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples at all.

Example 1
(1) Production and evaluation of sputtering target (i) Production of target As raw materials for production of target, indium oxide having an average particle diameter of 3.4 μm, purity 4N, average particle diameter 0.6 μm, zinc oxide having purity 4N, and average grain Tin oxide having a diameter of 0.5 μm and a purity of 4N has an atomic ratio [In / (In + Sn + Zn)] of 0.53, an atomic ratio [Sn / (In + Sn + Zn)] of 0.17, and an atomic ratio [Zn / (In + Sn + Zn)]. It mixed so that it might become 0.30, this was supplied to the wet ball mill, and it mixed and ground for 72 hours, and obtained the raw material fine powder.

  After granulating the obtained raw material fine powder, it is press-molded to a size of 10 cm in diameter and 5 mm in thickness, inserted into a firing furnace, fired at 1400 ° C. for 48 hours under oxygen gas pressure, and sintered (target ) The temperature rising rate during firing was 3 ° C./min.

(Ii) Evaluation of target The theoretical relative density of the obtained target was 97%, and the bulk resistance value measured by the four-probe method was 1.3 mΩ · cm.
When elemental analysis was performed by ICP emission analysis, In / (In + Sn + Zn) = 0.53, Sn / (In + Sn + Zn) = 0.17, and Zn / (In + Sn + Zn) = 0.30.

(2) Film formation and evaluation of transparent conductive film (i) Film formation of transparent conductive film The obtained sputtering target was mounted on a DC magnetron sputtering apparatus and sputtered at room temperature (RT), and the transparent conductive film was formed on the glass substrate. Was deposited.
The sputtering conditions at this time were a sputtering pressure of 1 × 10 ⁻¹ Pa, an ultimate pressure of 5 × 10 ⁻⁴ Pa, a substrate temperature RT, an input power of 120 W, a film formation time of 45 minutes, and the introduced gas was 100% argon gas.
The transparent conductive glass obtained by annealing the transparent conductive substrate thus obtained under atmospheric pressure, oxygen partial pressure of 50 hPa, 300 ° C., and 1 hour to form a transparent conductive oxide having a film thickness of about 300 nm was gotten.

(Ii) Evaluation of physical properties of transparent conductive film The physical properties of the transparent conductive film obtained in (i) were evaluated as follows. The results are shown in Table 1.
When the specific resistance was measured by a four-point probe method, it was 5 × 10 ⁻⁴ Ω · cm. Further, the carrier concentration was measured by the Hall effect and found to be 2.0 × 10 ²⁰ cm ⁻³ .
Further, this transparent conductive oxide had an average visible region (wavelength of 380 to 780 nm) light transmittance of 72%, and was excellent in transparency. Moreover, the average transmittance | permeability of the near-infrared area | region (wavelength 1200-2600nm) was 63%, and was excellent also in the heat ray reflective effect. The light transmittance was measured using UV3600 manufactured by Shimadzu Corporation.

When this transparent conductive film was etched at 45 ° C. of oxalic acid, the etching rate was 150 nm / min.
Moreover, the etching rate by PAN (phosphoric acid-acetic acid-nitric acid type etching agent) was 20 nm / min or less at 50 ° C., and the PAN resistance was good.

The transparent conductive film was subjected to a durability test (heat resistance test) in air at 120 ° C. for 1000 hours to confirm changes in resistance and carrier concentration.
As a result, it was confirmed that the resistance was 5.1 × 10 ⁻⁴ Ω · cm, the carrier concentration was 1.9 × 10 ²⁰ cm ⁻³ , and the durability was high.
The light transmittances in the visible region and the near infrared region were 83% and 56%, respectively.
The heat ray (infrared light) reflectivity after the heat resistance test is ○ when the average transmittance in the visible region (380 to 780 nm) is 70% or more and the transmittance in the infrared region (1200 to 2600 nm) is 65% or less at the same time. Other than that, it was set as x.

Moreover, when the temperature dependence of the hole mobility of this transparent conductive glass was measured and the activation energy was calculated | required, it was 10.3 meV. The results are shown in FIG.
This means that the change in the infrared light transmittance is small because a decrease in mobility is suppressed even when measured at a low temperature.

Examples 2-6
A thin film was prepared and evaluated in the same manner as in Example 1 except that the composition of the target, the substrate temperature during film formation, the annealing oxygen partial pressure, and the annealing temperature were changed as shown in Table 1. The results are shown in Table 1.

Comparative Example 1
A thin film was prepared and evaluated in the same manner as in Example 1 except that the composition of the target, the substrate temperature during film formation, the annealing oxygen partial pressure, and the annealing temperature were changed as shown in Table 1. The results are shown in Table 1.
The thin film produced in Comparative Example 1 was inferior in infrared light blocking ability because of too little In.

Comparative Example 2
The target composition was changed to indium / gallium / zinc oxide (IGZO), and the substrate temperature, annealing oxygen partial pressure, and annealing temperature during film formation were changed as shown in Table 1, and the same as in Example 1. A thin film was prepared and evaluated. The results are shown in Table 1 and FIGS.
Since the IGZO film is inferior in the infrared light shielding ability and has higher activation energy, the infrared light shielding ability at a low temperature is further greatly reduced.

Comparative Example 3
A thin film was prepared and evaluated in the same manner as in Example 1 except that the composition of the target, the substrate temperature during film formation, the annealing oxygen partial pressure, and the annealing temperature were changed as shown in Table 1. The results are shown in Table 1.
Since the activation energy is large, the carrier mobility at a low temperature is greatly lowered, and the infrared light absorption rate is lowered.

Comparative Example 4
A thin film was prepared and evaluated in the same manner as in Example 1 except that the film formation time was 15 minutes and the annealing treatment was not performed. The results are shown in Table 1.
As a result, a transparent conductive glass in which a transparent conductive oxide having a film thickness of about 100 nm was formed on the glass substrate was obtained.

Reference example 1
A thin film was prepared and evaluated in the same manner as in Example 1 except that ITO was used as a target and the substrate temperature during film formation and the annealing oxygen partial pressure were changed as shown in Table 1. The results are shown in Table 1.
ITO has excellent performance, but the problem of the raw material cost remains because the In content is 90% or more.

  The transparent conductive film of the present invention can be used for a transparent electrode of a thin film transistor.

Claims (6)

Contains at least indium, tin and zinc,
The atomic ratio represented by In / (In + Sn + Zn) is 0.25-0.6, the atomic ratio represented by Sn / (In + Sn + Zn) is 0.15-0.3, and is represented by Zn / (In + Sn + Zn). The atomic ratio is 0.15 to 0.5,
A transparent conductive film having a light transmittance in a visible region of 70% or more and a light transmittance in an infrared region of 65% or less.   The transparent conductive film according to claim 1, which has been annealed.   The transparent conductive film according to claim 1 or 2, wherein the light transmittance in the infrared region after the heat resistance test is 65% or less.   The transparent conductive film according to claim 1, wherein the activation energy is 1 meV or more and 15 meV or less.   It contains at least indium, tin and zinc, the atomic ratio represented by In / (In + Sn + Zn) is 0.25 to 0.6, and the atomic ratio represented by Sn / (In + Sn + Zn) is 0.15 to 0.3. Yes, using a sputtering target having an atomic ratio represented by Zn / (In + Sn + Zn) of 0.15 to 0.5, a film is formed on the substrate by a sputtering method, and the film is formed at a substrate temperature of 700 ° C. A method for producing a transparent conductive film, comprising annealing.   The method for producing a transparent conductive film according to claim 5, wherein the annealing is performed in an atmosphere having an oxygen partial pressure of 50 to 200 hPa.