JP2003335552A - Substrate coated with ito film and its manufacturing method, and organic el element having it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate coated with an ITO film that has less rugged and flat surface and is free from complicated manufacturing steps such as a heat treatment after coating or polishing a surface of the transparent ITO film, and its manufacturing method, as well as an organic EL element of an unlikely possibility of generating dark spots that a current is low to drive. <P>SOLUTION: A substrate coated with tin-doped indium oxide comprising a base film of which the main component is zirconium oxide and the tin-doped indium oxide film formed next to said base film, and characterized by having said base film of 1 to 15 nm film thickness and said ITO film of 1.2 nm or less mean surface roughness R<SB>a</SB>, and the organic EL element having said substrate coated with tin-doped indium oxide, are provided. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a substrate with an ITO film and an organic EL device having the substrate with an ITO film.

[0002]

2. Description of the Related Art In recent years, research on organic EL (electroluminescence) elements has been actively conducted. This organic EL element is usually composed of an anode having a transparent conductive film formed on a substrate such as glass, a hole transporting layer, a light emitting layer, and a cathode. 1
Because of the extremely high brightness of 0000 cd / m ² , it is drawing attention as a next-generation display element.

The anode is formed by forming a conductive film on a substrate such as glass. As the conductive film, IT is used.
O (tin-doped indium oxide) film, IZO (zinc-doped indium oxide) film, and the like are known. In particular, the ITO film has excellent conductivity, high visible light transmittance, and excellent chemical resistance, but has an excellent feature that it can be easily patterned because it is soluble in a certain acid.

From the viewpoint of conductivity and chemical resistance, ITO
The membrane is preferably crystalline. However, the crystalline film tends to have irregularities on the surface. When the ITO film is used as a conductive film of an organic EL device, if the unevenness of the ITO film surface is large, problems such as leak current and dark spots may occur.

In Japanese Patent Laid-Open No. 11-87068, 10
After forming the ITO film at a relatively low temperature of ~ 150 ° C, 10
An invention is disclosed in which the crystal orientation of the ITO film is changed to the (111) orientation by heat treatment at 0 to 450 ° C. to suppress the leak current and the dark spot of the organic EL element. But,
The heat treatment after film formation complicates the manufacturing process and is not preferable in terms of productivity. Attempts have also been made to reduce the irregularities on the surface of the ITO film by polishing the surface of the ITO film, acid treatment, etc., but all of these methods complicate the manufacturing process and also result in poor productivity.

In Japanese Laid-Open Patent Publication No. 11-126689, reverse sputtering is performed on a substrate in advance, and then I is deposited on the substrate.
An invention of a method for manufacturing an organic EL element for forming a TO film is disclosed. In this reverse sputtering process, abnormal growth of the crystal of the ITO film occurs during the formation of the ITO film, and the generated product causes unevenness on the ITO film, so that defects such as dark spots easily occur. In addition, since flying objects to the ITO film cause unevenness on the ITO film, defects such as dark spots are likely to occur.

Japanese Unexamined Patent Publication No. 10-10557 discloses that a transparent conductive film is subjected to reverse sputtering in an atmosphere containing hydrogen gas as a main component. Since this method uses explosive hydrogen, it is not preferable from the viewpoint of safety.

Further, the driving voltage of the organic EL element is preferably low from the viewpoint of life and reduction of driver load, and an organic EL element having a low driving voltage has been desired.

[0009]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention According to the present invention, ITO having small unevenness on the film surface and excellent in flatness, and which does not require a complicated manufacturing process such as heat treatment after film formation and polishing of the surface of the transparent conductive film
It is an object of the present invention to provide a substrate with a conductive film having a film, a method for manufacturing the same, and an organic EL element in which a driving current is low and a dark spot hardly occurs.

[0010]

According to the present invention, an undercoating film containing zirconium oxide as a main component and having a thickness of 1 to 15 nm is formed on a substrate, and then a tin-doped indium oxide film is contacted with the undercoating film. There is provided a method for producing a substrate with a tin-doped indium oxide film, which comprises forming the tin-doped indium oxide film and subjecting the tin-doped indium oxide film to reverse sputtering in an atmosphere of a sputtering gas containing oxygen gas.

Further, the present invention is a substrate with a tin-doped indium oxide film, comprising a base film containing zirconium oxide as a main component on the base and a tin-doped indium oxide film formed in contact with the base film. , The thickness of the base film is 1
The tin-doped indium oxide film-provided substrate has _a mean surface roughness _Ra of 1.2 nm or less.

Further, the present invention provides an organic EL element having an anode, a hole transport layer, a light emitting layer and a cathode, wherein the tin-doped indium oxide film-coated substrate is used as the anode.

In the present invention, the average surface roughness of the ITO film surface means the average surface roughness of the surface of the ITO film-attached substrate (ITO film surface).

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The substrate in the present invention includes a transparent substrate, and examples thereof include an inorganic substrate such as a glass substrate and an organic substrate such as a plastic substrate. Examples of the glass substrate include alkali-containing glass substrates such as soda lime silicate glass substrates and non-alkali glass substrates such as borosilicate glass substrates. The average surface roughness _{R a} of the alkali-free glass substrate is 0.1
It is about 5 nm. The average surface roughness _{R a} of the alkali-containing glass substrate is about 0.1 to 10 nm. In the present invention, the average surface roughness _Ra is JIS B0601.
The cutoff value is 0.8 μm and the evaluation length is 2.4 μm.

When an alkali-containing glass substrate is used as the substrate, in order to prevent the alkali ions contained in the glass substrate from diffusing into the ITO film and affecting the resistance value of the ITO film, silicon oxide is used as the alkali barrier layer. It is preferable to form a (SiO ₂ ) film or the like on the substrate.

The alkali with the alkali barrier layer formed
Re-containing glass substrate average surface roughness R _aIs 0.1-10n
It is preferably about m. In addition, the alkaline burr
The layer thickness is 10 to 500 nm (meaning geometrical thickness)
To do. same as below. ) Is preferable. Film thickness is 1
If it is less than 0 nm, the alkali barrier performance is insufficient, and 5
If it exceeds 00 nm, it is disadvantageous in terms of surface roughness and cost. film
It is particularly preferable that the thickness is 10 to 50 nm.

The method for forming the alkali barrier layer on the glass substrate is not particularly limited, and includes a thermal decomposition method (a method of applying a raw material solution and then heating to form a film), a CVD method, a sputtering method, an evaporation method, an ion plating method. Ting method and the like. For example, in the case of a SiO ₂ film, an RF (radio frequency) sputtering method using a SiO ₂ target or S
A film forming method such as an RF or DC (direct current) sputtering method using an i target can be used. When using a Si target, it is preferable to use an Ar—O ₂ mixed gas as a sputtering gas and determine the gas ratio of Ar and O ₂ so that the SiO ₂ film becomes a transparent film without absorption.

The substrate with an ITO film formed according to the present invention has a base film having zirconium oxide as a main component, which is in contact with the bottom of the ITO film. The base film affects the crystal growth of the ITO film, and as a result, the crystal orientation of the ITO film can be changed, and contributes to the improvement of the average surface roughness of the ITO film surface. The base film may contain impurities such as Hf, Fe, Cr, Y, Ca and Si in zirconium oxide as a main component, but the total amount of the impurities is the total amount of Zr and the impurity element. 10 atomic% or less, especially 1
It is preferably at most atomic%.

The thickness of the base film is 1 to 15 nm.
The thickness of the base film is within the above range, and the IT
By performing the reverse sputtering treatment in O film, the average surface roughness R _a of the surface of the ITO film-coated substrate can be easily controlled below 1.2 nm. If the thickness of the base film is less than 1 nm, ITO
The effect as a base film of reducing the average surface roughness of the film surface cannot be obtained. Further, the film thickness of the underlying film in the 15nm exceeds lowers the effect as a base film, the average surface roughness R _a of the ITO film surface be less 1.2nm difficult. The film thickness of the base film described above is the average film thickness, and the same applies when the film is not a continuous film.

The method of forming the base film is not particularly limited, and includes a thermal decomposition method, a CVD method, a sputtering method, a vapor deposition method,
Ion plating method and the like can be mentioned, for example, RF or DC sputtering method using a metal Zr target, or R using a stabilized zirconia target.
The F sputtering method and the like can be mentioned. Since the stabilized zirconia target has many impurities such as Y and Ca, it is more preferable to use the metal Zr target. Further, the sputtering method is preferably the DC sputtering method from the viewpoint of the film formation rate. It is preferable to use an Ar—O ₂ mixed gas as the sputtering gas and determine the gas ratio of Ar and O ₂ so that the base film becomes a transparent film without absorption.

The ITO film in the present invention is a film composed of In ₂ O ₃ and SnO _2, and its composition is (I
1 to ₂ of SnO ₂ with respect to the total amount of n ₂ O ₃ + SnO ₂ ).
It is preferably contained in an amount of 0 mass%. The film thickness of the ITO film is preferably 50 to 350 nm, and particularly preferably 100 to 200 n, from the viewpoint of resistance, transmittance, and the like.
m. From the viewpoint of the conductivity of the film, the specific resistance value is 4 × 10.
It is preferably ⁻⁴ Ω · cm or less, and the sheet resistance value is preferably 20 Ω / □ or less.

The method of forming the ITO film is not particularly limited, and includes a thermal decomposition method, a CVD method, a sputtering method, a vapor deposition method,
Ion plating method and the like can be mentioned, for example, IT
An RF or DC sputtering method using an O target may be used. Ar-O ₂ mixed gas is used as the sputtering gas, and Ar is used to minimize the specific resistance of the ITO film.
It is preferable to determine the gas ratio of O ₂ and O ₂ .

When a film is formed by using the sputtering method,
The substrate temperature during sputtering is preferably 100 to 500 ° C. If the temperature is lower than 100 ° C, the ITO film is likely to be amorphous and the chemical resistance of the film is lowered. When it is higher than 500 ° C., the crystallinity is promoted and the unevenness of the film surface becomes large.

The reverse sputtering process in the present invention is a process different from the ordinary sputtering process in which plasma is generated by applying an electric field to the substrate side and the ITO film surface is subjected to sputter etching with ions. The reason for including oxygen gas in the sputtering gas is as follows.
Oxygen negative ions formed in plasma are highly reactive,
Since the ability to repel atoms in the film (sputtering) is small, it is considered that the energy of oxygen negative ion particles is mainly converted to heat. In—O or Sn—O bonds are present as irregularities on the surface of the ITO film, and the I
It is considered that the n—O or Sn—O bond strength is weaker than the In—O or Sn—O bond strength of the concave portion. Therefore, when the surface of the ITO film is heated by the oxygen negative ions, In—O or Sn—O bond of the convex portion can be selectively evaporated, and as a result, the surface roughness of the ITO film surface can be improved.

Further, in the present invention, the film thickness of the underlayer film is set to 1 to 15 nm, and the ITO film is subjected to reverse sputtering in an atmosphere of a sputtering gas containing oxygen gas to obtain an average surface roughness of the ITO film surface. 1.2 nm
The following can be easily controlled. The reason is that the main orientation plane of the ITO film is (400) and the ratio of the diffraction intensity of the (400) plane to the diffraction intensity of the (222) plane is (400) / (22).
2) It is considered that since the diffraction intensity ratio is 1.0 or more, oxygen negative ions generated by the reverse sputtering process are likely to be selectively etched on the convex portions on the surface of the ITO film.

The film thickness of the ITO film after the reverse sputtering process is preferably 50 to 350 nm, which is equivalent to the film thickness of the ITO film before the reverse sputtering process.

[0027] in that it can reduce the average surface roughness _{R a,} the concentration of oxygen gas in the sputtering gas in the reverse sputtering treatment is preferably 10 to 100 vol%, more preferably from 50 to 100% by volume And particularly preferably 80 to 100% by volume.

The substrate with an ITO film of the present invention is suitably used as an electrode of a display device such as an organic EL element, an LCD or an inorganic EL element, or an electrode of a solar cell in view of transparency and conductivity.

The organic EL device comprises an anode, a hole transport layer,
It has a light emitting layer and a cathode, and if necessary, an electron transporting layer and an electron injecting layer can be provided between the light emitting layer and the cathode.
The ITO film-coated substrate of the present invention is particularly preferably used as an anode of the organic EL device. Further, the ITO film-coated substrate of the present invention is also suitably used as a cathode of the organic EL element.

By using the substrate with the ITO film as the anode of the organic EL element, the number of dark spots generated can be reduced and the yield can be improved. The dark spot means a black spot generated on the surface of the electrode when the current stops flowing through a part of the organic EL element, which is a major cause of lowering the yield of products. The main cause of dark spots is that pinholes are formed on the cathode by the protrusions present on the surface of the anode, moisture contained in the outside air penetrates through the pinholes, and the cathode interface and the light emitting layer are centered around the pinholes. It is thought to be due to deterioration. In the present invention, since the convex portion of the ITO film can be eliminated by the reverse sputtering treatment, the number of dark spots generated can be reduced. Incidentally, in order to suppress the infiltration of water, it is usually practiced to cover the periphery of the organic EL element with a protective glass substrate and seal it with a sealing adhesive or the like. However, in the present invention, in order to clearly determine the presence or absence of the effect, the number of dark spots was measured under the condition that sealing is not performed, that is, the condition that water easily enters from the outside and dark spots easily occur.

Further, the substrate with the ITO film of the present invention is prepared by using organic E
By using it as the anode of the L element, the driving voltage can be lowered and the yield can be improved. The drive voltage is
It means the voltage when the light emitted from the organic EL element has a constant brightness, and when a current (leakage current) in the opposite direction is generated,
Since the luminous efficiency is lowered and the driving voltage is increased, it is important to lower the driving voltage as much as possible in order to improve the yield. The generation of the leak current is closely related to the unevenness of the ITO film, and by eliminating the unevenness, the driving voltage can be lowered and the yield can be improved.

The material of the hole transport layer is not particularly limited as long as it has a property of injecting holes or blocking electrons, and is, for example, N, N′-diphenyl- (3-methylphenyl) -1. , 1'-biphenyl-4,4 'diamine,
One or more selected from the group consisting of 4,4′-bis (N- (1-naphthyl) -N-phenylamino) biphenyl (α-NPD), triphenyldiamine and the like can be mentioned. As a method of forming the hole transport layer, a known method such as a vacuum deposition method or a spin coating method can be used, and the hole transport layer has a thickness of 5 to 200 nm in terms of electro-optical characteristics of the device. It is more preferably 20 to 100 nm.

The material of the light emitting layer is not particularly limited as long as it has a light emitting ability. For example, tris (8-quinolinol) aluminum (Alq) and the like can be mentioned.
As a method for forming the light emitting layer, a known method such as a vacuum deposition method or a spin coating method can be used, and the thickness of the light emitting layer is 5 to 2
From the viewpoint of the electrical and optical characteristics of the device, the thickness is preferably 00 nm, and particularly preferably 20 to 100 nm.

As the material of the cathode, metals and alloys having a small work function are preferably used, and Al, LiF, Li
₂ O, Na ₂ O, etc. are exemplified, and a film is formed by a vacuum deposition method or the like.

An interface layer may be provided between the anode and the hole transport layer for the purpose of preventing leak current, reducing the hole injection barrier, and improving adhesion. As the material of the interface layer, 4,4 ′, 4 ″ -tris (N- (3-methylphenyl) -N-phenylamino) triphenylamine,
4,4 ′, 4 ″ -tris (N, N-diphenylamino) triphenylamine and copper phthalocyanine can be used. As a method for forming the interface layer, a known method such as a vacuum vapor deposition method or a spin coating method can be used, and it is preferable that the thickness of the interface layer is 5 to 100 nm from the viewpoint of electro-optical characteristics of the device.

[0036]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited thereto.

[Substrate with ITO film] (Example 1) A cleaned soda lime silicate glass substrate (average surface roughness _Ra is 0.5 nm) is set in a sputtering apparatus, and the substrate is heated to 250 ° C. to form a film by sputtering. Also in this case, the substrate temperature was kept at 250 ° C. A SiO ₂ film was formed as an alkali barrier layer on this substrate by RF sputtering. At this time, the target is
A disk-shaped SiO ₂ target having a diameter of 150 mm was used. The sputtering gas was used Ar-O ₂ mixed gas.
The gas ratio of Ar to O ₂ was Ar: O ₂ = 90: 10 (volume ratio), and the total pressure was 0.6 Pa. A film was formed by discharging at 0.5 kW. The film thickness was 20 nm. The average surface roughness R of the formed SiO ₂ film-coated substrate of the SiO ₂ film surface
_a was 0.5 nm.

Next, on the SiO ₂ film, Zr as a base film is formed.
The O ₂ film was formed by the RF sputtering method. At this time, a disk-shaped metal Zr target having a diameter of 150 mm was used as the target. The sputtering gas was used _{Ar-O 2} mixed gas. The gas ratio of Ar to O ₂ is Ar: O ₂ = 9.
It was 0:10 (volume ratio) and the total pressure was 0.6 Pa.
A film was formed by discharging at 0.3 kW. The film thickness was 8 nm.

Then, an ITO film was formed on the base film by the RF sputtering method. The target is 150m in diameter
A m-shaped ITO target was used. The composition of the ITO target was such that SnO ₂ was 10 mass% with respect to the total amount of (In ₂ O ₃ + SnO ₂ ). The sputtering gas was used _{Ar-O 2} mixed gas. The gas ratio of Ar to O ₂ is Ar: O ₂ = 99.5: 0.5 (volume ratio),
The total pressure was 0.6 Pa. A film was formed by discharging at 0.3 kW. The film thickness was 150 nm. The composition of the obtained ITO film was the same as the composition of the target.

Then, using an RF power source, the ITO film thus formed was subjected to reverse sputtering treatment in a floating bias to obtain a substrate with an ITO film. At this time, oxygen gas was used as the sputtering gas, and the total pressure of the oxygen gas was 2 Pa.
And the power density per unit area was 0.4 W / cm ² .

Example 2 (Comparative Example) A substrate with an ITO film was obtained in the same manner as in Example 1 except that the reverse sputtering treatment was not performed.

Example 3 (Comparative Example) An ITO film-coated substrate was obtained in the same manner as in Example 1 except that the ZrO ₂ film was not formed.

[Characteristic Evaluation of Substrate with ITO Film] The obtained substrate with an ITO film was evaluated by the following method. 1) Average surface roughness _Ra : JIS B0601 (1994)
(FY), the unevenness of the surface was measured with an AFM (atomic force microscope). The cutoff value is 0.8μ
m, and the evaluation length was 2.4 μm. 2) Specific resistance value: Measured by the four-ended needle method. 3) Sheet resistance value: It was determined by measuring the film thickness with a stylus type film thickness meter and dividing the specific resistance value by the film thickness. 4) Crystal orientation: The crystal state of the surface was measured by X-ray diffraction measurement by the θ / 2θ method. The measurement conditions were a Cu target radiation source, a tube voltage of 40 kV, a tube current of 20 mA, a sampling width of 0.02 degrees, a scanning speed of 4 degrees / minute, a divergence slit of 1.0 degree, a scattering slit of 1.0 degree, and a light receiving slit. It was set to 0.15 mm. In the diffraction intensity obtained from the peak height after subtracting the background, the (400) / (222) diffraction intensity ratio, which is the ratio of the diffraction intensity of the (400) plane and the diffraction intensity of the (222) plane obtained, It was calculated.

Table 1 shows the evaluation results of the characteristics of the obtained substrate with an ITO film.

[0045]

[Table 1]

The thickness of the ITO film of the ITO film-provided substrates obtained in Examples 1 to 3 was measured using a stylus type film thickness measuring device. 3 150nm each, IT even if reverse sputtering process
It was confirmed that the thickness of the O film did not change.

[Organic EL Element] (Example 4) I of the substrate with ITO film formed in Example 1
The TO film was patterned to form a light emitting portion (2 mm square) and a wiring portion. Patterned ITO
A mask for patterning was set on the film such that the light emitting portion of the ITO film overlaps but the wiring portion does not overlap. Then, an interface layer was formed using copper phthalocyanine as a material by a vacuum deposition method, and 4,4'-bis (N-
A hole transport layer is formed using (1-naphthyl) -N-phenylamino) biphenyl (α-NPD) as a material, a light emitting layer is formed using tris (8-quinolinol) aluminum (Alq) as a material, and aluminum is used as a material. A cathode was formed as to obtain an organic EL device. The thicknesses of the interface layer, the hole transport layer, the light emitting layer, and the cathode are 10 nm, 80 nm, and 60 n, respectively.
m and 80 nm.

(Example 5) The same procedure as in Example 4 was carried out except that the substrate with an ITO film formed in Example 2 was used in place of the substrate with an ITO film formed in Example 1, and the organic E film was treated.
An L element was obtained.

[Evaluation of Light Emitting Properties of Organic EL Element] The organic EL elements formed in Examples 4 and 5 were evaluated by the following method. 1) Driving voltage: Anode of organic EL device under nitrogen atmosphere
When a voltage is applied between the cathodes, the emission brightness from the organic EL element is 1
The voltage value when reaching 000 cd / m ² was measured. The brightness was measured by a brightness meter (BM-7 Topcon). 2) Number of dark spots: 50 times to 100 within a range of 2 mm square of the light emitting surface, which occurs when light is emitted at a brightness of 400 cd / m ² by applying a voltage between the anode and the cathode in the atmosphere without sealing. The number measured by observing with an optical microscope at a magnification of about twice was measured as the number of dark spots.

Table 2 shows the evaluation results of the emission characteristics of the obtained organic EL device.

[0051]

[Table 2]

[0052]

EFFECTS OF THE INVENTION According to the present invention, an ITO film having a base film containing zirconium oxide as a main component and having a limited film thickness,
By performing the reverse sputtering treatment in the atmosphere of the sputtering gas containing oxygen gas, the unevenness of the surface can be reduced without the complicated manufacturing steps such as the heat treatment after the ITO film formation, the polishing of the ITO film surface and the acid treatment. It is possible to obtain a substrate with an ITO film having excellent flatness and high conductivity.

Further, since the ITO film-coated substrate of the present invention has the excellent characteristics as described above, it is suitably used as an anode of an organic EL device, and it is possible to suppress the generation of leak current and dark spots and improve the yield. Can be made.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3K007 AB03 AB06 AB08 CB01 DB03                 4G059 AA08 AB09 AB11 AC03 AC14                       EA01 EA03 EB02 EB04 GA01                       GA04 GA12                 5G307 FA01 FB01 FC10                 5G323 BA02 BB05 BC03

Claims (4)

[Claims] 1. A base film having zirconium oxide as a main component and having a thickness of 1 to 15 nm is formed on a substrate, then a tin-doped indium oxide film is formed in contact with the base film, and then an oxygen gas is contained. A method for producing a substrate with a tin-doped indium oxide film, which comprises subjecting the tin-doped indium oxide film to reverse sputtering in an atmosphere of a sputtering gas. 2. The concentration of the oxygen gas in the sputtering gas is 1
The method for producing a substrate with a tin-doped indium oxide film according to claim 1, which is 0 to 100% by volume. 3. A substrate with a tin-doped indium oxide film, comprising: a base film containing zirconium oxide as a main component on a base; and a tin-doped indium oxide film formed in contact with the base film. thickness is 1-15 nm, tin-doped indium oxide film-substrate, wherein an average surface roughness R _a of the tin-doped indium oxide film surface is not more than 1.2 nm. 4. An organic EL element having an anode, a hole transport layer, a light emitting layer and a cathode, wherein the anode is the substrate with a tin-doped indium oxide film according to claim 3.