JP2014177663A - Transparent conductive zinc oxide thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent conductive zinc oxide thin film which has a small variation in specific resistance even if the film is exposed to a high-temperature high-humid environment, and a reduced wavelength dependence of light transmittance.SOLUTION: A transparent conductive zinc oxide thin film is zinc oxide added with a first element of Ga and/or Al, and at least one second element selected from a group consisting of In, Bi, Se, Ce, Cu, Er, and Eu. When an environmental test is performed at 60°C and a relative humidity of 95% for 500 hours, the transparent conductive zinc oxide thin film changes in specific resistance by 15% or less after the test compared to that before the test. The transparent conductive zinc oxide thin film has a half width (Full Width at Half. Maximum: FWHM(θ - 2θ)) of a (002) plane diffraction peak obtained by X ray diffraction (XRD) measurement of 0.30 to 0.38, a FWHM(ω) of 4.00 to 5.00, which is a half width of (002)ω of a rocking curve, and a film thickness is 50 nm or less.

Description

  The present invention relates to a transparent conductive zinc oxide thin film excellent in wet heat resistance and having 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.
That is, a transparent conductive film in which both improvement in wet heat resistance and reduction in wavelength dependence of light transmittance have not been developed yet.

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 to solve the above-mentioned problems, and the change rate of the specific resistance is small even when exposed to a high temperature and high humidity environment, and the wavelength dependency of the light transmittance is reduced. A transparent conductive zinc oxide thin film is provided.

  According to the first aspect of the present invention, the zinc oxide comprises a first element composed of Ga and / or Al and at least one selected from the group consisting of In, Bi, Se, Ce, Cu, Er, and Eu. A transparent conductive zinc oxide thin film to which two elements have been added. When an environmental test is conducted for 500 hours at 60 ° C. and a relative humidity of 95%, the specific resistance after the environmental test with respect to the specific resistance before the environmental test. Of the diffraction peak from the (002) plane obtained by X-ray diffraction (XRD) measurement (Full Width at Half. Maximum: FWHM (θ-2θ)) is 0. 30 to 0.38, FWHM (ω), which is the half width of the (002) ω rocking curve, is 4.00 to 5.00, and the film thickness is 50 nm or less. In To.

  The invention according to claim 2 relates to the transparent conductive zinc oxide thin film according to claim 1, wherein the difference between the maximum value and the minimum value of light transmittance in the wavelength range of 400 to 1400 nm is 15% or less.

  The invention according to claim 3 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 claim 1 or 2.

  The invention according to claim 4 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. Relates to a thin zinc oxide film.

  The invention according to claim 5 relates to the transparent conductive zinc oxide thin film according to any one of claims 1 to 4, wherein the film thickness is 20 to 50 nm.

According to the first aspect of the present invention, the zinc oxide includes at least one selected from the group consisting of a first element made of Ga and / or Al, and In, Bi, Se, Ce, Cu, Er and Eu. And a specific resistance of the transparent conductive zinc oxide thin film with FWHM (θ-2θ) of 0.30 to 0.38 and FWHM (ω) of 4.00 to 5.00. Can be made into a transparent conductive zinc oxide thin film that is small and excellent in electrical conductivity and excellent in heat and moisture resistance.
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 invention which concerns on Claim 2, 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 of claim 3, the relative change rate of the average light transmittance at the wavelength 400-1400 nm after the environmental test with respect to the average light transmittance at the wavelength 400-1400 nm before the 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 4, 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 invention which concerns on Claim 5, when it is 20-50 nm in film thickness, it is excellent in wet heat resistance and light transmittance, and the transparent electroconductivity which has sufficient intensity | strength by which the wavelength dependence of light transmittance was reduced. 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 2 before the wet heat resistance test, and the IGZnO thin film of Example 2. It is a graph which shows the relationship between the wavelength of the GNZnO thin film of the comparative example 2 and the IGZnO thin film of Example 2 after a heat-and-moisture resistance test. 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 2, and light transmittance. It is a graph which shows the relationship between the wavelength before the wet heat resistance test of the IGZnO thin film of Example 2 and Comparative Example 3, and light transmittance. It is a figure for demonstrating the parallel arrangement degree (FWHM ((omega))) of the pillars (crystallite) in a GZnO thin film and the transparent conductive zinc oxide thin film (IGZnO thin film) of this invention.

  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 includes a first element composed of Ga and / or Al, and a first element composed of at least one selected from the group consisting of In, Bi, Se, Ce, Cu, Er, and Eu. It is a transparent conductive zinc oxide thin film to which two elements are 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 made of at least one selected from the group consisting of In, Bi, Se, Ce, Cu, 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.

The transparent conductive zinc oxide thin film of the present invention has a full width at half maximum (FWHM (θ-2θ)) of 0 from the (002) plane obtained by X-ray diffraction (XRD) measurement. 30 to 0.38, FWHM (ω), which is the half width of the (002) ω rocking curve, is 4.00 to 5.00.
FWHM (θ-2θ) represents good or bad crystallinity in the column in the thin film, and the larger the value, the worse the crystallinity.
FWHM (ω) represents the degree of parallel arrangement of columns (crystallites) arranged in the vertical direction in the thin film, and the larger the value, the worse the parallelism.
The transparent conductive zinc oxide thin film of the present invention has a good crystallinity of FWHM (θ-2θ) of 0.30 to 0.38, so that the transparent conductive zinc oxide thin film excellent in low resistance conductivity and can do.
On the other hand, the FWHM (ω) of the transparent conductive zinc oxide thin film of the present invention is 4.00 to 5.00, which is larger than that of a normal gallium-doped zinc oxide thin film (GZnO thin film).
FIG. 6 is a diagram for explaining the degree of parallel alignment (FWHM (ω)) between columns (crystallites) in the GNZnO thin film and the indium / gallium-doped zinc oxide thin film (IGZnO thin film) of the present invention.
As shown in FIG. 6, the IGZnO thin film of the present invention has a FWHM (ω) value larger than that of a normal gallium-doped zinc oxide thin film (GSZnO thin film). The gap between the boundaries (grain boundaries) between the crystallites is large. Therefore, flying atoms such as oxygen atoms and zinc atoms are likely to be mixed into the grain boundaries during the growth of the thin film. Then, after the thin film growth, a dense grain boundary having a high atomic density is formed. Since the density is high, there is no water infiltration and diffusion path, and as a result, the water resistance is improved.
On the other hand, if the density of the grain boundaries is too high, such grain boundaries will play the role of a wall that reflects current, resulting in an increase in the resistance of the entire thin film.
When the FWHM (ω) of the transparent conductive zinc oxide thin film of the present invention is 4.00 to 5.00, a transparent conductive zinc oxide thin film having excellent water resistance and excellent conductivity can be obtained. .

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 (eg, hydrogen sensors).

  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 = 5 sccm
Discharge current during film formation: 140 A
Film formation time: 18 seconds Ion plating device: “RPD (Reactive Plasma Deposition) device” manufactured by Sumitomo Heavy Industries, Ltd.

Example 2
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 15 sccm.

Comparative Example 1
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 Ion plating device: “RPD (Reactive Plasma Deposition) device” manufactured by Sumitomo Heavy Industries, Ltd.

Comparative Example 2
A 50 nm-thick GZnO thin film was formed under the same conditions as in Comparative Example 1 except that the oxygen flow rate was 15 sccm.

Comparative Example 3
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 IGZnO thin film having a thickness of 100 nm by ion plating. The film forming conditions are shown below.
(Film forming conditions)
Substrate: Alkali-free glass with a thickness of 0.7 mm Film thickness: 100 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: 35 seconds Ion plating device: “RPD (Reactive Plasma Deposition) device” manufactured by Sumitomo Heavy Industries, Ltd.

(Characteristic evaluation of transparent conductive zinc oxide thin film)
With respect to the transparent conductive zinc oxide thin film of Example 1 and Comparative Example 1, 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%. Specific resistance, carrier density, hole mobility, and light transmittance before and after the wet heat resistance test were measured by the following methods, and the relative change rate of each parameter was evaluated.

(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.

  The results are shown in Table 1 below.

As shown in Table 1, the relative change rate of the specific resistance after the heat resistance test of Comparative Example 2 is a very large value of 66.25%, whereas the specific resistance of the specific resistance after the heat resistance test of Example 2 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 2 is much smaller than that of Comparative Example 2.
From this result, it can be seen that the transparent conductive zinc oxide thin film of Example 2 has very excellent moisture and heat resistance even at an extremely thin level of 50 nm.

  FWHM (θ-2θ) and FWHM (ω) of the IGZnO thin films of Example 1-2 and Comparative Example 1-2 were measured. The measuring device is ATX-G manufactured by Rigaku Corporation. The results are shown in Table 2 below. In both the examples and comparative examples, the value of FWHM (θ-2θ) was low, indicating that the crystallinity in the column (crystallite) was high. On the other hand, FWHM (ω) showed a higher value for the FWHM (ω) of the example, and in particular, the IGZnO thin film of the example 2 showed a higher value. This indicates that the gap between the boundaries (grain boundaries) between columns (crystallites) arranged in the vertical direction in the thin film is large. As shown in Table 1, Example 2 with larger intergranular gaps was superior in water resistance to Comparative Example 2, so that during the growth of the thin film, flying atoms such as oxygen atoms and zinc atoms entered the intergranular gaps. It is thought that the atomic density at the grain boundary became higher after the thin film growth due to the contamination of the film, and this led to a drastic decrease in the water intrusion route, making it difficult for intrusion and diffusion.

  Next, the light transmittance at a wavelength of 350 to 2000 nm in the transparent conductive zinc oxide thin films of Example 2, Comparative Example 2 and Comparative Example 3 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 light transmittance of the GNZnO thin film of Comparative Example 2 and the IGZnO thin film of Example 2. FIG. 2 shows the wavelength before the wet heat resistance test and FIG. 3 shows the wavelength after the heat resistance test. It is a graph which shows the relationship between light transmittance.
FIG. 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 2.
2 and 3, the GZnO thin film of Comparative Example 2 and the IGZnO thin film of Example 2 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 2 is not substantially changed before and after the wet heat resistance test.

FIG. 5 is a graph showing the relationship between the wavelength of the IGZnO thin film of Example 2 and Comparative Example 3 before the wet heat resistance test and the light transmittance.
As can be seen from this graph, for example, at a wavelength of 2000 nm, the light transmittance of Example 2 (film thickness 50 nm) is about 76%, whereas the light transmittance of Comparative Example 3 (film thickness 100 nm) is about 56%. In Example 2 (film thickness 50 nm), the wavelength dependency of light transmittance is smaller than that in Comparative Example 3 (film thickness 100 nm). This difference in wavelength dependency of the light transmittance is considered to be due to the difference in film thickness.

Moreover, the light transmittance of the IGZnO thin film (film thickness 50 nm) of Example 2 exceeds 80% at a wavelength of about 470 to 1770 nm, which is much higher than that of the IGZnO thin film (film thickness 100 nm) of Comparative Example 3. It can be seen that the transmittance can be achieved. It can be seen that at a wavelength of about 550 nm or more, the light transmittance of Example 2 with a film thickness of 50 nm is overwhelmingly higher than that of Comparative Example 3 with a film thickness of 100 nm.
This is because light is not absorbed in the thin film because the film thickness of the thin film of Example 2 is thinner, thereby increasing the light transmittance. It is on the long wavelength side that it appears straight away. Since light on the long wavelength side has small light energy, the light energy on the long wavelength is absorbed in the thin film and the light is not transmitted. As a result, the light transmittance is drastically reduced. However, it can be seen that the reduction width of the transparent conductive zinc oxide thin film of Example 2 can be reduced.
In addition, the peak in the vicinity of the wavelength of 400 nm in Comparative Example 3 is a peak due to the light interference effect, that is, the effect that the light reflected on the glass substrate surface and the light reflected on the transparent conductive zinc oxide thin film surface strengthen each other. The strength of the effect depends on the material (refractive index and surface flatness) of the substrate.

  From the above, the transparent conductive zinc oxide thin film of the present invention is a thin film that has excellent heat and moisture resistance and reduced wavelength dependency of light transmittance even at a very thin level of 50 nm or less. Very useful.

  The present invention is suitably used for flat display panels, thin film solar cells, and chemical sensors (eg, reducing gas sensors such as hydrogen sensors and carbon monoxide sensors).

Claims (5)

Transparent conductivity in which 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, Bi, Se, Ce, Cu, Er and Eu are added to zinc oxide Zinc oxide thin film,
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,
Full width at half maximum (FWHM (θ-2θ)) from 0.30 to 0.38, (002) ω rocking, obtained from X-ray diffraction (XRD) measurement. FWHM (ω) which is the half width of the curve is 4.00 to 5.00,
A transparent conductive zinc oxide thin film having a film thickness of 50 nm or less.   The transparent conductive zinc oxide thin film according to claim 1, 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 400-1400 nm after the environmental test with respect to the average light transmittance at a wavelength of 400-1400 nm before the environmental test is 1% or less. Transparent conductive zinc oxide thin film.   The transparent conductive zinc oxide thin film according to any one of claims 1 to 3, 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 4, wherein the film thickness is 20 to 50 nm.