JP2015038847A - Transparent conductive zinc oxide thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent conductive zinc oxide thin film having a film thickness of 50 nm or less, which has excellent wet-heat resistance and surface characteristics, and a low absorption coefficient, and in which the wavelength dependency of the light transmissivity is reduced.SOLUTION: The transparent conductive zinc oxide thin film is obtained by adding a first element composed of Ga and/or Al and a second element composed of at least one selected from the group comprising In, Sn, Si, Bi, Se, Ce, Cu, Mn, Er and Eu to zinc oxide, and has characteristics (1) to (3) mentioned below, and a film thickness of 50 nm or less. (1) When an environmental test is performed under conditions of a temperature of 60°C and 95% relative humidity for 500 h, the relative change rate of the specific resistance after the environmental test to the specific resistance before the environmental test is 15% or less. (2) The relation between crystallite size L and a-axis lattice constant La is as follows: L≥100×La. (3) The arithmetic average roughness Ra of the surface satisfies 0.2nm<Ra<1nm.

Description

  The present invention relates to a transparent conductive zinc oxide thin film having a thickness of 50 nm or less, which is excellent in moisture and heat resistance and surface characteristics, and has a low light absorption rate and a reduced wavelength dependency of light transmittance.

  As a conductive film for a transparent electrode used in a liquid crystal display device or the like, an ITO (indium tin oxide) film having low specific resistance and high transparency is widely used. However, since indium is expensive and there are concerns about resource limitations, a zinc oxide-based transparent conductive film containing zinc oxide (ZnO) as a main component is being developed as a conductive film that replaces the ITO film.

  As a typical method for producing a zinc oxide-based transparent conductive film at a mass production level, a direct current magnetron sputtering method and an ion plating method are known. In particular, if the ion plating method is used, a zinc oxide-based transparent conductive film having a low surface resistance is produced at a high film formation rate (3-5 of the direct current magnetron sputtering method described above) without producing a large specific resistance distribution as in the sputtering method. It is possible to form a large film forming area.

  The ion plating method uses a plasma gun or an electron gun to irradiate a target (evaporation material) with a plasma beam or an electron beam to evaporate (eject) the evaporation material (in the form of a sintered body or powder), and the evaporated particles In this method, ionization is performed before reaching the substrate, and the energy of evaporated particles is controlled using a potential gradient, and then vapor deposition (incident) is performed on the substrate.

  As a manufacturing method of the zinc oxide type electrically conductive film by an ion plating method, the method of patent documents 1-3 is mentioned, for example.

  Patent Document 1 relates to a manufacturing method capable of forming a zinc oxide-based conductive film having a small specific resistance at a high film-forming speed and a large film-forming area. Zinc oxide added with gallium (Ga) or a gallium compound is an evaporation material. A method is described in which the film is formed as a (target) and the oxygen partial pressure in the film forming chamber is 0.012 Pa or less.

  Patent Document 2 and Patent Document 3 are both filed by the applicant of the present application, and ion plating for producing a zinc oxide-based conductive film capable of preventing or suppressing a splash phenomenon that occurs when a target is heated. Is related to the target. In the column of Examples, an example using a sintered body containing gallium as a conductivity-imparting component is disclosed as a zinc oxide-based sintered body used as a target.

  By the way, in general, the zinc oxide-based transparent conductive film is inferior in durability as described in Non-Patent Document 1, etc., and has poor resistance stability in a moist heat resistance environment test (specific resistance before and after the moist heat resistance environment test). Have a high rate of change). The above problem becomes remarkable in a zinc oxide based transparent conductive film formed by sputtering. On the other hand, in the ion plating method, oxygen gas is supplied into the ion plating film forming apparatus while being freely controlled for film formation for the purpose of supplementing oxygen deficient in the film. Therefore, it is possible to optimize the electrical characteristics of the zinc oxide-based transparent conductive film required for application as compared with the sputtering method, and as a result, the electrical characteristics that are lower have been realized so far. However, at present, resistance stability in a heat and humidity resistance test required for application is poor as in the case of a zinc oxide-based transparent conductive film formed by sputtering. In particular, instability of resistance becomes significant when the film thickness of the transparent conductive film is 200 nm or less.

  Therefore, there is a demand for a transparent conductive zinc oxide thin film that has a low rate of change in specific resistance before and after heating even when heated in an air atmosphere such as an oxygen atmosphere and is excellent in moisture and heat resistance. In Patent Documents 1 to 3 described above, no consideration is given to improvement in heat and moisture resistance.

In view of the above circumstances, the applicant of the present application discloses a transparent conductive film with improved moisture and heat resistance in Patent Document 4 and Patent Document 5.
In general, the thinner the film, the more advantageous in terms of light transmittance, but the specific resistance and heat-and-moisture resistance decrease.
Patent Document 4 discloses a part of a thin film having an extremely thin film thickness of 100 nm or less. However, when the film thickness is thin, the content of indium is large, and conversely, when the indium content is small, the film thickness is large. However, there is no disclosure of a transparent conductive film having an excellent specific resistance and heat-and-moisture resistance when the indium content is small and the film thickness is thin, which is expensive and has resource constraints.
The transparent conductive film of Patent Document 5 has a film thickness of about 150 nm, and the film thickness is less than that, so that the moisture and heat resistance is not improved.

  Note that Patent Document 6 discloses a transparent conductive film having improved heat and humidity resistance by sputtering rather than ion plating. However, since this transparent conductive film is a transparent conductive film mainly composed of expensive indium, the In atomic quantity ratio In / (In + Zn) is 0.55 to 0.80, and a large amount of expensive indium is contained. Need to use. Further, in Patent Document 6, since a sputtering method is employed, a thin film having an extremely thin film thickness of 100 nm or less has a high specific resistance that is not suitable for application. The film thickness of the transparent conductive film obtained is as thick as about 200 to 350 nm.

  In addition, the conventional transparent conductive film has a problem that the light transmittance varies depending on the wavelength of light. When the wavelength dependency of the light transmittance is large, there is a problem that light control is difficult.

  The present applicant has applied for a transparent conductive zinc oxide thin film in Japanese Patent Application No. 2013-51053, which aims to achieve both improvement in heat and moisture resistance and reduction in wavelength dependency of light transmittance. The thin film previously applied has a full width at half maximum (FWHM (θ-2θ)) of 0.30 to 0 from the (002) plane obtained by X-ray diffraction (XRD) measurement. FWHM (ω), which is the half width of the (002) ω rocking curve, is 4.00 to 5.00. A thin film having these parameters in this specific numerical range can achieve improvement in heat and humidity resistance and reduction in wavelength dependency of light transmittance.

  Through further research, the present applicant has found that parameters different from the previously filed thin film are more closely related to the improvement of heat-and-moisture resistance, leading to the present invention.

JP 2004-95223 A JP 2007-56351 A JP 2007-56352 A JP 2009-114538 A JP 2011-74479 A JP-A-6-318406

APPLIED PHYSICS LETTERS 89,091904 (2006)

  The present invention has been made in order to solve the above-described problems, and has a film thickness of 50 nm or less with excellent moisture and heat resistance and surface characteristics, low light absorption, and reduced wavelength dependence of light transmittance. The transparent conductive zinc oxide thin film is provided.

The invention according to claim 1 is selected from the group consisting of zinc oxide, a first element made of Ga and / or Al, and In, Sn, Si, Bi, Se, Ce, Cu, Mn, Er and Eu. The present invention relates to a transparent conductive zinc oxide thin film having a thickness of 50 nm or less having the following characteristics (1) to (3) to which at least one second element is added.
(1) When an environmental test is performed for 500 hours at 60 ° C. and a relative humidity of 95%, the relative change rate of the specific resistance after the environmental test with respect to the specific resistance before the environmental test is 15% or less. (2) Crystallite The relationship between the size L and the a-axis lattice constant La is L ≧ 100 × La
(3) Arithmetic average roughness Ra of the surface is 0.2 nm <Ra <1 nm

  The invention according to claim 2 relates to the transparent conductive zinc oxide thin film according to claim 1, wherein the kurtosis Rku of the surface roughness curve is Rku ≦ 3.

  The invention according to claim 3 relates to the transparent conductive zinc oxide thin film according to claim 1 or 2, wherein the skewness Rsk of the surface roughness curve is Rsk <0.

  The invention according to claim 4 relates to the transparent conductive zinc oxide thin film according to any one of claims 1 to 3, wherein the light absorptance at a wavelength of 500 to 565 nm is 0.8% or less.

  The invention according to claim 5 is the transparent conductive zinc oxide according to any one of claims 1 to 4, wherein the difference between the maximum value and the minimum value of the light transmittance at a wavelength of 400-1400 nm is 15% or less. It relates to a thin film.

  The invention according to claim 6 is characterized in that a relative change rate of the average light transmittance at the wavelength 400 to 1400 nm after the environmental test with respect to the average light transmittance at the wavelength 400 to 1400 nm before the environmental test is 1% or less. The transparent conductive zinc oxide thin film according to any one of claims 1 to 5.

  The invention according to claim 7 is characterized in that the relative change rate of the specific resistance after the environmental test with respect to the specific resistance before the environmental test is 10% or less. The present invention relates to a functional zinc oxide thin film.

  The invention according to claim 8 relates to the transparent conductive zinc oxide thin film according to any one of claims 1 to 7, wherein the film thickness is 20 to 50 nm.

According to the first aspect of the present invention, the zinc oxide is selected from the group consisting of the first element made of Ga and / or Al, and In, Sn, Si, Bi, Se, Ce, Cu, Mn, Er and Eu. The transparent conductive zinc oxide thin film having the above-mentioned characteristics (1)-(3) is added with at least one second element, and thus has low specific resistance, excellent conductivity, and resistance to moist heat. A transparent conductive zinc oxide thin film having excellent surface properties and low light absorption can be obtained.
When an environmental test is performed for 500 hours at 60 ° C. and a relative humidity of 95%, the relative change rate of the specific resistance after the environmental test with respect to the specific resistance before the environmental test is 15% or less. A transparent conductive zinc oxide thin film having excellent conductivity that can be used even under such conditions can be obtained.
When the film thickness is 50 nm or less, the light transmittance is excellent and the wavelength dependency of the light transmittance can be reduced, so that a transparent conductive zinc oxide thin film that can be used for various applications can be obtained. . Moreover, when storing with a roll, lamination | stacking is easy and it becomes possible to laminate | stack more thin films.
In general, when the film thickness is 50 nm or less, the heat-and-moisture resistance decreases, but as described above, the transparent conductive zinc oxide thin film according to claim 1 has a very small relative change rate of specific resistance of 15% or less before and after the environmental test. Further, the wavelength dependency of the light transmittance is further reduced.

  According to the second aspect of the invention, when the kurtosis Rku of the surface roughness curve is Rku ≦ 3, it is possible to obtain a transparent conductive zinc oxide thin film with more excellent heat and moisture resistance and surface characteristics.

  According to the third aspect of the invention, when the skewness Rsk of the surface roughness curve is Rsk <0, a transparent conductive zinc oxide thin film having more excellent heat and moisture resistance and surface characteristics can be obtained.

  According to the invention of claim 4, the transparent conductive oxidation excellent in transmittance regardless of the human visibility depending on the brightness because the light absorptivity at a wavelength of 500 to 565 nm is 0.8% or less. It can be a zinc thin film.

  According to the invention which concerns on Claim 5, light control can be easily performed because the difference of the maximum value of light transmittance in wavelength 400-1400nm and the minimum value is 15% or less.

  According to the invention which concerns on Claim 6, the relative change rate of the average light transmittance in the wavelength 400-1400 nm after the said environmental test with respect to the average light transmittance in the wavelength 400-1400 nm before the said environmental test is 1% or less Thus, a transparent conductive zinc oxide thin film having excellent light transmittance that can be used under conditions of high temperature and high humidity can be obtained.

  According to the invention which concerns on Claim 7, when the relative change rate of the specific resistance after the said environmental test with respect to the specific resistance before the said environmental test is 10% or less, the electroconductivity which can be used also on the conditions used as high temperature high humidity It can be set as the transparent conductive zinc oxide thin film excellent in the rate.

  According to the eighth aspect of the invention, since the film thickness is 20 to 50 nm, it has excellent moisture resistance and light transmittance, and has a sufficient strength with reduced wavelength dependency of light transmittance. It can be a zinc oxide thin film.

It is the schematic of the ion plating apparatus used for manufacture of the transparent conductive zinc oxide thin film of this invention. It is a graph which shows the relationship between the wavelength and the light transmittance of the GNZnO thin film of the comparative example 3 before the wet heat resistance test, and the IGZnO thin film of Example 1. It is a graph which shows the relationship between the wavelength and the light transmittance of the GNZnO thin film of the comparative example 3 after the wet heat resistance test, and the IGZnO thin film of Example 1. It is a graph which shows the relationship between the wavelength before and behind the wet heat resistance test of the IGZnO thin film of Example 1, and light transmittance. It is a graph which shows the light absorptivity in wavelength 500-565nm of Example 1 and Comparative Examples 1-3.

  Hereinafter, the transparent conductive zinc oxide thin film according to the present invention will be described.

The transparent conductive zinc oxide thin film according to the present invention is a group consisting of zinc oxide, a first element made of Ga and / or Al, and In, Sn, Si, Bi, Se, Ce, Cu, Mn, Er, and Eu. A transparent conductive zinc oxide thin film to which a second element consisting of at least one selected from the above is added.
The 1st element which consists of Ga and / or Al is added as an electroconductivity provision component, and can also improve the light transmittance.
The ratio of the first element contained in the transparent conductive zinc oxide thin film is preferably 0.1 to 6% by weight.
If the ratio of the first element is less than 0.1% by weight, the conductivity of the zinc oxide thin film cannot be sufficiently improved, which is not preferable.
When the ratio of the first element exceeds 6% by weight, the improvement of the wet heat resistance of the zinc oxide thin film is realized, but the conductivity is rapidly decreased, which is not preferable.

In the transparent conductive zinc oxide thin film of the present invention, a second element composed of at least one selected from the group consisting of In, Sn, Si, Bi, Se, Ce, Cu, Mn, Er, and Eu is added. .
By adding the second element, the wet heat resistance of the zinc oxide thin film can be improved.
The ratio of the second element contained in the transparent conductive zinc oxide thin film is such that the atomic quantity ratio of Zn to the second element: (second element / (second element + Zn)) ≈ (second element / Zn) is 0 at the maximum. It is preferably .46% (0.0046).
The present invention is not a conventional ITO (indium tin oxide) film but a conductive film mainly composed of zinc oxide. Indium is expensive and there are concerns about resource constraints. The atomic quantity ratio In / (In + Zn) in Patent Document 6 is 55 to 80% (0.55 to 0.80), and the ratio of In element of the present invention is remarkably small.

As described above, the atomic quantity ratio (second element / Zn) between Zn and the second element contained in the transparent conductive zinc oxide thin film of the present invention is preferably 0.15 to 0.46%.
If the atomic quantity ratio of Zn to the second element (second element / Zn) is less than 0.15%, the wet heat resistance of the zinc oxide thin film cannot be sufficiently improved, which is not preferable.
When the atomic quantity ratio of Zn to the second element (second element / Zn) exceeds 0.46%, the specific resistance of the zinc oxide thin film increases and the light transmittance decreases, which is not preferable.

In the transparent conductive zinc oxide thin film of the present invention, the crystallite size L parallel to the substrate surface is 100 times or more the a-axis lattice constant La, that is, L ≧ 100 × La.
The average surface diffusion distance on the surface of adsorbed water molecules is approximately several tens to 100 times the a-axis lattice constant La. In the transparent conductive zinc oxide thin film of the present invention, the relationship between the crystallite size L parallel to the substrate surface and the a-axis lattice constant La is L ≧ 100 × La. As a result, the transparent conductive zinc oxide thin film of the present invention becomes a thin film excellent in wet heat resistance. When the crystallite size L is less than 100 times the a-axis lattice constant La, it is not preferable because sufficient heat and heat resistance cannot be obtained.

The transparent conductive zinc oxide thin film of the present invention has a surface arithmetic average roughness Ra of 0.2 nm <Ra <1 nm.
In the vicinity of the surface of the thin film having a high crystallinity and a flat surface in the crystallite, it is considered that the fluctuation of the spatial distribution of atomic density is small.
One of the main factors that determine the diffusion characteristics of water molecules into a thin film is considered to be a density gradient (a diffusion phenomenon occurs from a high density space region to a low density space region). In order to suppress diffusion of water molecules into the thin film, a thin film having a flat surface is more desirable.
Since the transparent conductive zinc oxide thin film of the present invention has an arithmetic average roughness Ra of the surface of 0.2 nm <Ra <1 nm, diffusion of water molecules into the thin film can be suppressed, so that the heat and heat resistance is excellent. A transparent conductive zinc oxide thin film can be obtained. The plane spacing of the (002) plane of the zinc oxide thin film is half the c-axis lattice constant, and is about 0.26 nm. When the crystallinity is high and there is no large disturbance in the arrangement of crystallites, Ra does not have a value smaller than the interplanar spacing. That is, when Ra is less than 0.2 nm, the crystallinity of the zinc oxide thin film is poor, which is not preferable. When Ra is 1 nm or more, the surface spacing is about 3.8 times or more, and the steps in the crystallites and grain boundaries are large, resulting in a thin film having a large density gradient. For this reason, the diffusion of water molecules into the thin film cannot be suppressed, and as a result, sufficient moisture and heat resistance cannot be obtained.

  In the transparent conductive zinc oxide thin film of the present invention, the kurtosis Rku of the surface roughness curve is preferably Rku ≦ 3. The kurtosis Rku represents the degree of sharpness of the surface shape, and is 3 if it is a normal distribution. The kurtosis Rku is obtained by dividing the fourth power average of the curve Z (x) at the reference length lr by the fourth power of the root mean square Rq, and is expressed by the following formula 1.

  The transparent conductive zinc oxide thin film of the present invention has a kurtosis Rku of the surface roughness curve of Rku ≦ 3. That is, a thin film surface having a small cross-sectional curve sharpness and a small atomic density gradient is formed. Thereby, it becomes difficult for water molecules to penetrate into the thin film, and as a result, a transparent conductive zinc oxide thin film excellent in moisture and heat resistance can be obtained. On the other hand, when Rku is 3 or more, it is determined that there are many broken chemical bonds near the surface, and a thin film surface with a large atomic density gradient is formed in the vicinity. As a result, water molecules are not preferable because they easily diffuse and penetrate into the thin film.

  In the transparent conductive zinc oxide thin film of the present invention, the skewness Rsk of the surface roughness curve is preferably Rsk <0. The skewness Rsk is obtained by dividing the cube mean of the curve Z (x) at the reference length lr by the cube of the root mean square Rq, and is expressed by the following equation (2).

  In the transparent conductive zinc oxide thin film of the present invention, the skewness Rsk of the surface roughness curve is preferably Rsk <0, that is, the distribution of the surface shape curve is in a gentle state on the upper side. Thereby, on the outermost surface, there are few broken chemical bonds, and the atomic density gradient near the surface is small. Therefore, it becomes difficult for water molecules to diffuse and penetrate into the thin film, and as a result, a transparent conductive zinc oxide thin film having excellent moisture and heat resistance can be obtained. When Rsk is greater than or equal to 0, the distribution of the surface shape curve is steeply upward. As a result, the chemical bond is often broken at the outermost surface, and the atomic density gradient near the surface is increased. Therefore, water molecules are likely to enter the thin film, and as a result, sufficient moisture and heat resistance cannot be obtained.

The transparent conductive zinc oxide thin film of the present invention has an optical absorptance of 0.8% or less at a wavelength of 500 to 565 nm.
There are two types of human photoreceptors: rod cells and cone cells. The wavelength of the light that provides the maximum luminous efficiency is different between the cone and the rod. In the bright place where the cone is working, the long wavelength range, red appears bright and vivid, but when it becomes darker and the rod starts working, the sensitivity to light in the short wavelength range becomes relatively high. , Blue will appear bright and vivid. Therefore, the sensitivity curve of the photoreceptor cell depending on the brightness has the maximum sensitivity at a wavelength of about 510 nm, whereas that of the cone is about 555 nm. This phenomenon is called “Purkinje phenomenon” after the name of the discoverer. As one factor for improving the transmittance of the transparent conductive film, considering the light absorption rate, the light absorption rate (A, unit%) is desirably lower in the wavelength region of 500 nm to 565 nm, 0.8 % Or less is desirable. Here, the light absorptance is obtained by A = 100−TR from the transmittance (T, unit%) and the reflectance (R, unit%) obtained by the spectrophotometer.

The film thickness of the transparent conductive zinc oxide thin film of the present invention is 50 nm or less, preferably 20 to 50 nm.
In general, the thinner the zinc oxide thin film, the greater the ratio of the contact area with the atmosphere to the volume of the entire thin film, as compared to the case where the film thickness is large. In addition, the thinner the zinc oxide thin film, the more often it does not crystallize, and the orientation is disturbed even in rare cases. Therefore, when the film thickness is thin, the relative contact area with the atmosphere increases, and water is easily absorbed from the gap formed by the disorder of orientation, so that the moisture and heat resistance is lowered.
However, the present inventors have succeeded in maintaining the structural characteristics of the film even when thinned to an ultrathin level of 50 nm or less, thereby reducing the wavelength dependence of light transmittance and minimizing the degradation of moisture and heat resistance. The inventors have invented a transparent conductive zinc oxide thin film that is limited to the limit.
When the film thickness is 50 nm or less, a transparent conductive zinc oxide thin film having high light transmittance and reduced wavelength dependency of light transmittance can be obtained. Further, it is advantageous because the total cost including the raw material cost and the production cost during the film formation becomes lower.
From the viewpoint of strength, the film thickness is preferably 20 nm or more.

When the transparent conductive zinc oxide thin film of the present invention was subjected to an environmental test for 500 hours at 60 ° C. and a relative humidity of 95%, the relative change rate of the specific resistance after the environmental test with respect to the specific resistance before the environmental test was 15% or less, preferably 10% or less.
The relative change rate Δρ of the specific resistance is expressed by the following equation.
Δρ = {(ρ−ρ ₀ ) / ρ ₀ } × 100
ρ: Specific resistance of thin film after environmental test ρ ₀ : Specific resistance of thin film before environmental test

  As described above, in general, the thinner the zinc oxide thin film is, the lower the moisture and heat resistance is. In the present invention, even when the film thickness is 50 nm or less, when the environmental test is performed for 500 hours under the conditions of 60 ° C. and 95% relative humidity, the relative change rate of the specific resistance after the environmental test with respect to the specific resistance before the environmental test is 15%. In the following, it is preferably 10% or less, and has very excellent wet heat resistance.

  In the transparent conductive zinc oxide thin film of the present invention, the difference between the maximum value and the minimum value of the light transmittance at a wavelength of 400 to 1400 nm is 15% or less, and the wavelength dependency of the light transmittance is very small. Since the wavelength dependency of the light transmittance is very small, there is an advantage that the light control becomes easy.

  The transparent conductive zinc oxide thin film of the present invention preferably has an average visible light transmittance of 80% or more at a wavelength of 400 to 780 nm, and an average light transmittance from a visible light region to a near infrared region at a wavelength of 400 to 1400 nm. It is more preferable if it is 85% or more. Due to the excellent transparency realized in this wide wavelength range, it is possible to use a transparent electrode in a wide range such as a liquid crystal display, a touch screen (touch panel), an organic EL, a light emitting diode electrode, a (thin film) solar cell and the like. In addition, because of its high resistance to moist heat, it can be applied to chemical sensors for flammable gases (eg, hydrogen sensors, carbon monoxide sensors, etc.).

  Subsequently, the manufacturing method of the transparent conductive zinc oxide thin film of this invention is demonstrated below with reference to figures.

  First, an ion plating apparatus suitable for carrying out the method for producing a transparent conductive zinc oxide thin film of the present invention will be described with reference to FIG.

FIG. 1 is a schematic view of an ion plating apparatus used in the method for producing a transparent conductive zinc oxide thin film of the present invention.
The ion plating apparatus (10) includes a vacuum vessel (12) as a film forming chamber, a plasma gun (plasma beam generator) (14) as a plasma source for supplying a plasma beam PB into the vacuum vessel (12), and An anode member (16) that is disposed at the bottom of the vacuum vessel (12) and receives the plasma beam PB and a substrate holding member WH that holds the substrate W to be deposited are disposed above the anode member (16). And a transport mechanism (18) to be moved appropriately.

  The plasma gun (14) is a pressure gradient type, and its main body is provided on the side wall of the vacuum vessel (12). By supplying power to the cathode (14a), intermediate electrode (14b), (14c), electromagnet coil (14d) and steering coil (14e) of the plasma gun (14), it is supplied into the vacuum vessel (12). The intensity and distribution state of the plasma beam PB is controlled. Reference numeral (20a) indicates a carrier gas introduction path made of an inert gas such as Ar, which is the source of the plasma beam PB.

  The anode member (16) includes a hearth (16a) which is a main anode for guiding the plasma beam PB downward, and an annular auxiliary anode (16b) arranged around the hearth.

  The hearth (16a) is controlled to an appropriate positive potential and sucks the plasma beam PB emitted from the plasma gun (14) downward. In the hearth (16a), a through hole TH is formed at a central portion where the plasma beam PB is incident, and a target (22) is loaded in the through hole TH. The target (22) is a tablet formed into a columnar shape or a rod shape, and is heated by current from the plasma beam PB and sublimates to generate a vapor deposition material. The hearth (16a) has a structure for gradually raising the target (22), and the upper end of the target (22) always protrudes from the through hole TH of the hearth (16a) by a certain amount.

  The auxiliary anode (16b) is composed of an annular container disposed concentrically around the hearth (16a), and a permanent magnet (24a) and a coil (24b) are accommodated in the container. The permanent magnet (24a) and the coil (24b) are magnetic field control members that form a cusp-like magnetic field directly above the hearth (16a), thereby controlling the direction of the plasma beam PB incident on the hearth (16a). And amended.

  The transport mechanism (18) has a large number of rollers (18b) arranged in the transport path (18a) at equal intervals in the horizontal direction to support the substrate holding member WH, and rotates the rollers (18b) to rotate the substrate holding member WH. And a drive device (not shown) that moves the motor in the horizontal direction at a predetermined speed. The substrate W is held by the substrate holding member WH. In this case, the substrate W may be fixedly disposed above the inside of the vacuum vessel (12) without providing the transport mechanism (18) for transporting the substrate W.

  The oxygen gas in the oxygen gas container (19) is supplied to the vacuum container (12) while the flow rate is adjusted to a predetermined amount by the mass flow meter (21). Reference numeral (20b) indicates a supply path for supplying an atmospheric gas other than oxygen, and reference numeral (20c) indicates a supply path for supplying an inert gas such as Ar to the hearth (16a). Reference numeral (20d) denotes an exhaust system.

  An ion plating method using the ion plating apparatus (10) configured as described above will be described.

First, the target (22) is mounted in the through hole TH of the hearth (16a) disposed at the lower part of the vacuum vessel (12).
The method for producing a transparent conductive zinc oxide thin film of the present invention comprises, as a target (22), a first element composed of Ga and / or Al or a compound thereof, and In, Bi, Se, Ce, Cu, Er, and Eu. A sintered body of zinc oxide to which a second element selected from the group or a compound thereof is added is used.
By using the target, in addition to the first element composed of Ga and / or Al, the second element composed of at least one selected from the group consisting of In, Bi, Se, Ce, Cu, Er, and Eu. A transparent conductive zinc oxide thin film can be produced, and this thin film is excellent in heat and moisture resistance, light transmittance, and conductivity.

In the method for producing a transparent conductive zinc oxide thin film of the present invention, the atomic quantity ratio of Zn to the second element (second element / Zn) contained in the ion plating target (22) is 0.15 to 0.46%. It is preferable that
If the atomic quantity ratio of Zn to the second element (second element / Zn) is less than 0.15%, the wet heat resistance of the manufactured zinc oxide thin film cannot be sufficiently improved, which is not preferable.
If the atomic quantity ratio of Zn to the second element (second element / Zn) exceeds 0.46%, the specific resistance of the zinc oxide thin film to be produced increases and the light transmittance decreases. Absent.

The content of the first element contained in the ion plating target is preferably 0.1 to 6% by weight.
If the content of the first element is less than 0.1% by weight, the conductivity of the manufactured zinc oxide thin film cannot be sufficiently improved, which is not preferable.
When the content of the first element exceeds 6% by weight, the conductivity of the manufactured zinc oxide thin film is rapidly decreased, which is not preferable.

  Next, the substrate W is placed at an opposing position above the hearth (16a).

Next, a process gas corresponding to the film forming conditions is introduced into the vacuum vessel (12).
Oxygen is supplied from the oxygen gas container (19) into the vacuum container (12). The oxygen flow rate is not particularly limited, but is preferably 5 to 30 sccm, and more preferably 5 to 20 sccm. When the oxygen flow rate is less than 5 sccm, the heat-and-moisture resistance of the transparent conductive zinc oxide thin film deteriorates, and the relative change rate of the specific resistance increases before and after the environmental test for 500 hours under the conditions of 60 ° C. and 95% relative humidity. Therefore, it is not preferable.
When the oxygen flow rate exceeds 30 sccm, the specific resistance of the obtained transparent conductive zinc oxide thin film becomes large, and the specific resistance of the thin film after an environmental test for 500 hours at 60 ° C. and a relative humidity of 95% is also obtained. Since it will become large and will become a film | membrane unsuitable as a electrically conductive film, it is unpreferable.

  A DC voltage is applied between the cathode (14a) and the hearth (16a) of the plasma gun (14).

  Then, a discharge is generated between the cathode (14a) and the hearth (16a) of the plasma gun (14), thereby generating a plasma beam PB. The plasma beam PB is guided by a magnetic field determined by the steering coil (14) and the permanent magnet (24a) in the auxiliary anode (16b) and reaches the hearth (16a). At this time, since argon gas is supplied around the target (22), the plasma beam PB is easily attracted to the hearth (16a).

  The target (22) exposed to the plasma is gradually heated. When the target (22) is sufficiently heated, the target (22) sublimates and the vapor deposition material evaporates (emits). The vapor deposition material is ionized by the plasma beam PB, adheres (incides) to the substrate W, and is formed into a film.

  In addition, since the flight direction of the vapor deposition material can be controlled by controlling the magnetic field above the hearth (16a) by the permanent magnet (24a) and the coil (24b), the plasma activity above the hearth (16a) The film formation rate distribution on the substrate W can be adjusted in accordance with the degree distribution and the reactivity distribution of the substrate W, and a thin film with uniform film quality can be obtained over a wide area.

  Although it demonstrates still in detail based on the following examples, the transparent conductive zinc oxide thin film concerning the present invention is not limited to these.

Example 1
As a target, ZnO (purity 99.99%) to which 3% by weight of Ga ₂ O ₃ (purity 99.9%) and 0.75% by weight of In ₂ O ₃ (purity 99.9%) were added (manufactured by Hux Itec Corp.) ) Was used to form an indium gallium-doped zinc oxide thin film (IGZnO thin film) having a thickness of 50 nm by an ion plating method. The film forming conditions are shown below.
(Film forming conditions)
Substrate: Alkali-free glass with a thickness of 0.7 mm Film thickness: 50 nm
Substrate temperature: 200 ° C
Pre-heating of substrate before film formation: None Pressure during film formation: 0.2 Pa
Atmospheric gas conditions during film formation: argon = 140 sccm, oxygen = 15 sccm
Discharge current during film formation: 140 A
Film forming time: 18 seconds Oxygen flow rate: 15 sccm
Ion plating device: “RPD (Reactive Plasma Deposition) device” manufactured by Sumitomo Heavy Industries, Ltd.

Comparative Example 1
An IGZnO thin film having a thickness of 50 nm was formed under the same conditions as in Example 1 except that the oxygen flow rate was 5 sccm.

Comparative Example 2
As a target, a sintered body of ZnO (purity 99.99%) (manufactured by Hakusui Tech Co., Ltd.) added with 3% by weight of Ga ₂ O ₃ (purity 99.9%) was used, and gallium having a film thickness of 50 nm was formed by ion plating. An additive zinc oxide thin film (GZnO thin film) was formed. The film forming conditions are shown below.
(Film forming conditions)
Substrate: Alkali-free glass with a thickness of 0.7 mm Film thickness: 50 nm
Substrate temperature: 200 ° C
Pre-heating of substrate before film formation: None Pressure during film formation: 0.2 Pa
Atmospheric gas conditions during film formation: argon = 140 sccm, oxygen = 5 sccm
Discharge current during film formation: 140 A
Film formation time: 18 seconds Oxygen flow rate: 5 sccm
Ion plating device: “RPD (Reactive Plasma Deposition) device” manufactured by Sumitomo Heavy Industries, Ltd.

Comparative Example 3
A 50 nm-thick GZnO thin film was formed under the same conditions as in Comparative Example 2 except that the oxygen flow rate was 15 sccm.

  The parameters described in Table 1 below were measured for the thin films of Example 1 and Comparative Example 1-3. In addition, since the thin films of Comparative Examples 1 and 2 had a large arithmetic average roughness Ra, reliable data on the kurtosis Rku and the skewness Rsk could not be measured.

(Characteristic evaluation of transparent conductive zinc oxide thin film)
For the transparent conductive zinc oxide thin film of Example 1 and Comparative Example 3, the specific resistance, carrier density, hole mobility, and light transmittance before and after the wet heat resistance test were measured. In the heat and humidity resistance test, an environmental test was conducted for 500 hours in a constant temperature and humidity chamber set at 60 ° C. and a relative humidity of 95%. The specific resistance, carrier density, hole mobility, light transmittance, and light absorption rate before and after the wet heat resistance test were measured by the following methods to evaluate the relative rate of change of each parameter.

(1) Specific Resistance, Mobility, and Carrier Density Specific resistance, mobility, and carrier density were measured at room temperature by the Van der Pauw method using an ACCENT HL5500PC HALL effect device.

(2) Light transmittance The light transmittance with a wavelength of 350-2000 nm was measured using a U-4100 type spectrophotometer manufactured by Hitachi High-Technologies Corporation.

(3) Light Absorption Rate The light absorption rate at a wavelength of 500 to 565 nm was measured using a U-4100 type spectrophotometer manufactured by Hitachi High-Technologies Corporation.

  The results are shown in Table 2 below.

As shown in Table 2, the relative change rate of the specific resistance after the heat resistance test of Comparative Example 3 is a very large value of 66.25%, whereas the specific resistance of the specific resistance after the heat resistance test of Example 1 is The relative rate of change is a very small value of 7.37%. As for the carrier density and the hole mobility, the relative change rate of Example 1 is very small as compared with Comparative Example 3.
From this result, it can be seen that the transparent conductive zinc oxide thin film of Example 1 is very excellent in moisture and heat resistance even at an extremely thin level of 50 nm.

  Then, the light transmittance of wavelength 350-2000 nm in the transparent conductive zinc oxide thin film of Example 1 and Comparative Example 3, and the light of wavelength 500-565 nm in the transparent conductive zinc oxide thin film of Example 1 and Comparative Examples 1-3. The absorptance was measured using a U-4100 type spectrophotometer manufactured by Hitachi High-Technologies Corporation.

2 and 3 are graphs showing the relationship between the wavelength and the light transmittance of the GNZnO thin film of Comparative Example 3 and the IGZnO thin film of Example 1, FIG. 2 is before the wet heat resistance test, and FIG. 3 is the wavelength after the wet heat resistance test. It is a graph which shows the relationship between light transmittance.
4 is a graph showing the relationship between the wavelength and light transmittance before and after the wet heat resistance test of the IGZnO thin film of Example 1. FIG.
2 and 3, the GZnO thin film of Comparative Example 3 and the IGZnO thin film of Example 1 have substantially the same curves before and after the wet heat resistance test. Therefore, it can be seen that simultaneous addition of In does not affect the relationship between wavelength and light transmittance.
FIG. 4 shows that the light transmittance of the IGZnO thin film of Example 1 is almost unchanged before and after the wet heat resistance test.

FIG. 5 is a graph showing the light absorptance of Example 1 and Comparative Examples 1 to 3. Here, the light absorptance is a value obtained by A = 100−TR from the transmittance (T, unit%) and the reflectance (R, unit%) obtained by the spectrophotometer. The light absorptance of the thin film of Example 1 at a wavelength of 500 to 565 nm is 0.6% <A <0.7% before the moisture and heat resistance test, A = 0.64% at a wavelength of 510 nm, and A = at a wavelength of 555 nm. 0.62%. Even after the wet heat resistance test, the light absorption is 0.8 or less at a wavelength of 500 to 565 nm, which is a very low value.
On the other hand, the light absorptance of the thin films of Comparative Examples 1 and 2 at a wavelength of 500 to 565 nm is higher than that of the thin film of Example 1. The light absorption rate of the thin film of Comparative Example 3 is lower than that of Comparative Examples 1 and 2, but is higher than that of Example 1. Further, the thin film of Comparative Example 3 is an unfavorable thin film in terms of moisture and heat resistance as shown in Table 2.

  From the above, the transparent conductive zinc oxide thin film of the present invention has excellent moisture and heat resistance, low light absorption, and reduced wavelength dependence of light transmittance, even at an ultra-thin level of 50 nm or less. It is very useful because it is a thin film. Furthermore, since it has excellent surface characteristics, it can be suitably used for organic EL displays and the like.

  The present invention is suitably used for an organic EL display or the like.

Claims (8)

A first element composed of Ga and / or Al and a second element composed of at least one selected from the group consisting of In, Sn, Si, Bi, Se, Ce, Cu, Mn, Er, and Eu. A transparent conductive zinc oxide thin film having a thickness of 50 nm or less and having the following characteristics (1) to (3):
(1) When an environmental test is performed for 500 hours at 60 ° C. and a relative humidity of 95%, the relative change rate of the specific resistance after the environmental test with respect to the specific resistance before the environmental test is 15% or less. (2) Crystallite The relationship between the size L and the a-axis lattice constant La is L ≧ 100 × La
(3) Arithmetic average roughness Ra of the surface is 0.2 nm <Ra <1 nm   The transparent conductive zinc oxide thin film according to claim 1, wherein the kurtosis Rku of the surface roughness curve is Rku ≦ 3.   The transparent conductive zinc oxide thin film according to claim 1 or 2, wherein the skewness Rsk of the surface roughness curve is Rsk <0.   4. The transparent conductive zinc oxide thin film according to claim 1, wherein the light absorptance at a wavelength of 500 to 565 nm is 0.8% or less.   The transparent conductive zinc oxide thin film according to any one of claims 1 to 4, wherein a difference between a maximum value and a minimum value of light transmittance at a wavelength of 400 to 1400 nm is 15% or less.   The relative change rate of the average light transmittance at a wavelength of 400 to 1400 nm after the environmental test with respect to the average light transmittance at a wavelength of 400 to 1400 nm before the environmental test is 1% or less. The transparent conductive zinc oxide thin film according to claim 1.   The transparent conductive zinc oxide thin film according to any one of claims 1 to 6, wherein a relative change rate of a specific resistance after the environmental test with respect to a specific resistance before the environmental test is 10% or less.   The transparent conductive zinc oxide thin film according to any one of claims 1 to 7, wherein the film thickness is 20 to 50 nm.