JP3849698B2 - Method for producing transparent conductive film - Google Patents

Description

  The present invention relates to a transparent conductive film that can be used for a surface emitting thin film LED such as an organic thin film EL element, and more particularly to a method for producing a transparent conductive film having excellent surface smoothness and light transmittance, low resistance, and a large surface work function.

  Conventionally, ITO (a composite oxide of indium and tin) transparent conductive film has been required to have a low resistance for liquid crystal display devices. Therefore, in order to improve the crystallinity of the film, the substrate is heated to 200 ° C. or higher. I often filmed.

  The organic thin film EL element is generally formed in the order of a hole transport layer, a light emitting layer, an electron injection layer, and a metal cathode on a transparent anode made of an ITO film or a semitransparent metal vapor deposition film. A surface-emitting thin-film LED made of an inorganic semiconductor such as SiC is generally composed of a p-type semiconductor, an i-type light emitting layer, an n-type semiconductor and a metal cathode on a transparent anode. The distance between the anode and the cathode is about 100 m. The light emitting layer or the like may be formed to a thickness of about 5 nm, and in order to form the layer without disturbing the layer, the ITO transparent anode has an unevenness of 10 nm or less, preferably 5 nm or less. In addition, if the irregularities of the transparent anode are large, the electric field applied to the convex part increases, and a minute discharge occurs at that part, destroying the element, generating a non-light emitting point and reducing the life of the element. A transparent anode is desired.

  However, when the substrate is heated during film formation by sputtering, for example, even when the film is formed to have a film thickness of about 120 nm, there is a problem that unevenness of 20 to 30 nm is generated on the surface due to crystal growth and the smoothness is impaired. The same applies to other film forming methods such as electron beam evaporation.

The work function of a commercially available ITO film or an ITO film formed by heating the substrate to a thickness of about 100 to 150 nm and a low resistance of 30 Ω / □ or less is 4.6 to 4.8 eV (manufactured by Riken Keiki Co., Ltd.). : Measured with a surface analysis apparatus AC-1 at a light intensity of about 800 nW), and a work function of 4.9 eV (manufactured by Riken Keiki Co., Ltd .: “Surface analysis apparatus AC”) -1 "and measured with a light amount of 15 nW). In order to further increase the efficiency of hole injection from the transparent anode to the light-emitting layer, a material having a work function of 5 eV or more close to the value of the light-emitting layer material (about 5.8 eV for a commonly used Al oxine complex) is desired. Yes.

  In addition, similar to ITO used in a liquid crystal display, it is required to have a low resistance in order to reduce unevenness of light emission depending on the location as much as possible, and to have a high light transmittance in order to increase the efficiency of external extraction of light emission.

  In order to obtain a low-resistance ITO transparent conductive film, it is necessary to improve crystallinity, prevent scattering of electrons in the film, and increase the density of carrier electrons due to oxygen vacancies and tin. However, if the substrate is heated to improve the crystallinity or the film is formed using particles with high incident energy, the particles attached on the substrate easily move to a stable place, resulting in the growth of large crystal grains. Surface smoothness deteriorates.

  In addition, increasing the oxygen vacancies in the film and increasing the carrier density also increases the number of electron scattering centers and decreases the mobility of the electrons. Therefore, if the oxygen partial pressure during film formation is changed, an appropriate oxygen partial pressure can be obtained. The resistance of the film is maximized. Furthermore, the permeability of the membrane is worsened as oxygen vacancies increase and lower oxides increase in the membrane.

  From this, it was considered that a smooth transparent transparent conductive film with low resistance can be obtained by controlling the oxygen partial pressure during film formation and annealing and the energy of film formation particles. However, when an ITO film is formed at an oxygen partial pressure that provides the lowest resistance after annealing in air, there is a problem in that the lower oxide remains in the film even after annealing and the transparency is lowered. On the contrary, when the film is formed with an increased oxygen partial pressure, there is a problem that oxygen is excessive after annealing in the air, the carrier density is lowered, and the resistance is increased.

  Therefore, after forming the film at an oxygen partial pressure that is about 20% higher than the oxygen partial pressure in the film forming apparatus during the film forming process that has the lowest resistance by annealing after the film forming process, the inert gas, nitrogen gas, hydrogen The resistance was lowered by annealing in a non-oxidizing atmosphere such as a gas or a reduced pressure atmosphere to grow crystals. However, there remains a problem that the work function does not increase as it is.

  The present invention has been made to solve this problem, and the problem is that the surface smoothness is excellent, the surface work function is high, the surface resistivity is low, and the substrate is included. Another object of the present invention is to provide a transparent conductive film having a high visible light transmittance at 450 to 800 nm and a method for producing the same.

In order to solve this problem, the present invention produces an ITO thin film that is amorphous or microcrystalline in X-ray diffraction on an insulating substrate while keeping the substrate temperature at 0 to 100 ° C. Thereafter, an ITO film annealed at 100 to 500 ° C. under reduced pressure or in a non-oxidizing atmosphere and grown in a flat plate shape is formed as an underlayer, and the work function is 5.1 eV to 6.0 eV on the ITO film. By depositing a transparent conductive layer with a film thickness of 100 nm or less, the surface height difference is 1 nm to 10 nm in the range of 1 μm square, the surface work function is 5.1 to 6.0 eV, and the surface resistivity is 3 to 50Ω. / □ provides a transparent conductive film having a visible light transmittance of 75 to 90% at 450 to 800 nm including the substrate.

  As is apparent from the above, the production method of the present invention makes it possible to obtain a transparent conductive film having high surface smoothness, low resistivity and high light transmittance. When this transparent conductive film is used as a transparent anode of a surface emitting thin film LED element such as an organic thin film EL element, it has a great effect on extending the life of the element.

  The present invention will be described in detail below.

  As a result of intensive studies, the inventor has formed fine particles which are amorphous in X-ray diffraction on the substrate without heating the substrate, and then a temperature of 100 to 500 ° C., preferably 200 to 400 ° C. When crystallizing at a temperature of 5 ° C., the fine particles sinter in the plane direction and grow into a crystal in a mosaic shape, and therefore, it was found that an extremely smooth surface having an unevenness measured by an atomic force microscope of 3 nm or less can be obtained. It was found that the work function which was 4.6 to 4.8 eV becomes 5.1 eV or more by annealing at a moderate oxidizing atmosphere of 100 ° C. to 500 ° C. or irradiating with a plasma such as oxygen or argon. It was.

Examples of the method for forming X-ray diffraction amorphous particles on the substrate in the present invention include sputtering, electron beam evaporation, and plasma CVD.
[Action]
In the present invention, after the film formation, the surface work function is increased to 5.1 eV or more by annealing in an oxidizing atmosphere such as in the air or irradiating plasma such as oxygen or argon. At this time, since the inside of the film is already crystallized and dense, oxygen hardly enters and the resistivity does not increase greatly.

  In addition, according to the method of the present invention, an ITO film having a low resistance and a high transmittance, which is not a conventional high work function of 5.1 eV or higher, is formed and used as a base. It is possible to form a transparent electrode having a multilayer structure by forming a film under conditions or materials that provide a high work function.

  For example, after the ITO film is formed amorphous at a substrate temperature of 100 ° C. or lower by a method such as vapor deposition or sputtering, the surface height difference obtained by crystal growth by annealing in a non-oxidizing atmosphere or a reduced pressure atmosphere is 1 μm square. An ITO film having a range of 10 nm or less and a surface resistivity of 40 Ω / □ or less and a visible light transmittance of 80% or more including the substrate is 80% or more, and a work function of 5.1 eV or more is formed thereon. A transparent conductive layer is laminated to form a transparent electrode having a two-layer structure.

  The transparent conductive layer having a work function of 5.1 eV or more used for the upper layer is formed by giving priority to the low resistance of the base when the high work function ITO is formed using the same film forming apparatus as the base. Oxygen partial pressure higher than the film forming conditions (in the case of the embodiment of the present invention, it is about 2 times, but it is not particularly limited because it depends on the apparatus used), and the substrate temperature is 100 nm or less, preferably 5 to 20 nm. Then, the film is formed by annealing in an oxidizing atmosphere such as air or by irradiating with a plasma such as oxygen or argon.

  When a material having a work function of 5.1 eV or more other than ITO is used for the upper layer, a thickness of about 20 nm or less of amorphous semiconductor such as amorphous silicon carbide, chalcogenite group simple substance such as selenium, etc. To form a film on the underlying ITO.

  When the obtained ITO film is patterned by wet etching, it can be performed either before or after annealing performed after film formation, but if the film is stabilized by crystallization by annealing, etching is performed faster. be able to.

  Moreover, in order to make a transparent conductive film having a lower resistance, a light-transmitting metal thin film layer can be provided so as to overlap with the ITO film layer.

  The light-transmitting metal thin film layer is formed by depositing a metal layer having a thickness of 20 nm or less, preferably about 5 to 10 nm, by a method such as vapor deposition, ion plating, sputtering, or wet plating.

  As the metal material, a simple metal or an alloy such as copper, silver, tin, nickel, platinum, palladium, and chromium can be used, but it is not particularly limited to the above example.

  Hereinafter, examples of the present invention in the case of performing by RF magnetron sputtering will be described.

  The sputtering equipment uses Tokuda Seisakusho Co., Ltd .: “TOKUDA CFS-10 EP-70”, and the substrate is Dow Corning Co., Ltd .: “Corning 7059 (thickness 1.1 mm, 5 inch square)”. The distance between the ITO target (tin oxide 10 wt%) having a diameter of 5 inches and the jig surface was set to 17.5 cm.

  Sputtering was performed at a flow rate ratio of argon / oxygen = 340/1 (pressure 0.31 Pa), an RF output of 300 W, and a substrate temperature of 30 minutes at room temperature.

  As a result, an ITO film having a light transmittance of 71% at 500 nm, a surface resistance of 75Ω / □, a work function of 4.6 eV, and a film thickness of 150 nm was obtained. An SEM photograph of the surface of the film is shown in FIG. 1, and an X-ray diffraction diagram is shown in FIG. 2, and it can be seen that the film is almost amorphous, consisting of smooth fine crystals.

  Next, when this ITO film is annealed at 300 ° C. under a reduced pressure of 27 Pa for 10 minutes, the light transmittance at 500 nm is 85%, and the visible light transmittance at 450 to 800 nm including the substrate is 80% or more. The ITO film had a rate of 27Ω / □ and a work function of 4.6 eV.

  The SEM photograph is shown in FIG. 3, and the X-ray diffraction diagram is shown in FIG.

  Further, when this ITO film is annealed in air at 300 ° C. for 10 minutes, the light transmittance at 500 nm is 86%, the visible light transmittance at 450 to 800 nm including the substrate is 80% or more, and the surface resistivity is 32Ω / □, ITO film with high light transmittance and low resistance of work function 5.2 eV.

  When the irregularities on the surface of 1 μm square were measured with an “SPM3700” atomic force microscope manufactured by Seiko Denshi Kogyo Co., Ltd., the surface was highly smooth with a maximum of 3 nm or less. The SEM photograph is shown in FIG. 5, and it can be seen that the crystal grows in a flat plate shape.

  The ITO film before annealing at 300 ° C. for 10 minutes in the air in Example 1 was exposed to argon plasma with an output of RF 100 W at a pressure of 27 Pa for 15 minutes. The work function of the surface was 5.2 eV.

The ITO film before annealing for 10 minutes in air at 300 ° C. in Example 1 was exposed to oxygen plasma of RF 100 W output at a pressure of 27 Pa for 15 minutes. The work function of the surface was 5.2 eV.
<Comparative Example 1>
When the ITO film before annealing for 10 minutes at 300 ° C. under a reduced pressure of 27 Pa in Example 1 was annealed in air at 300 ° C. for 10 minutes, the light transmittance at 500 nm was 85%, and 450 to 800 nm including the substrate was observed. Visible light transmittance is 80% or more, work function is 5.2 eV, SEM photograph As shown in FIG. 6, a flat crystal was grown and a smooth surface was obtained, but a high resistivity with a surface resistivity of 100Ω / □ was obtained. ITO film was obtained.
<Comparative example 2>
Using the same apparatus as in Example 1, sputtering was performed on the same substrate with an argon / oxygen flow ratio of 425/1 (pressure 0.31 Pa). As a result, an amorphous ITO film having a light transmittance of 49% at 500 nm, a surface resistivity of 214Ω / □, and a work function of 4.7 eV and a low light transmittance was obtained.

  Further, this ITO film was annealed in air at 250 ° C. for 1 hour. However, the light transmittance at 500 nm is 68%, the surface resistivity is 16Ω / □, and the work function is 5.0 eV. It became a film.

  In Example 1, instead of annealing in air at 300 ° C. for 10 minutes to increase the work function of the surface, ITO having a high work function is laminated with a thickness of several tens of nm or less as shown below.

  On the ITO film annealed for 10 minutes at 300 ° C. under a reduced pressure of 27 Pa in Example 1, using the same apparatus as in Example 1, the argon / oxygen flow rate ratio was 170/1 (pressure 0.31 Pa), RF output 300 W. Then, sputtering is performed at a substrate temperature of room temperature for 3 minutes to deposit an amorphous ITO film having a thickness of 15 nm.

Furthermore, when this ITO film is crystallized by annealing at 250 ° C. for 1 hour in the air, the light transmittance at 500 nm is 85%, and the visible light transmittance at 450 to 800 nm including the substrate is 80% or more. A smooth ITO film having a high light transmittance of 33 Ω / □, a work function of 5.5 eV, a high work function, and a surface height difference of 1 μm square measured by an atomic force microscope is 10 nm or less.
<Comparative Example 3>
Using the same apparatus as in Example 1, ITO was deposited by sputtering for 30 minutes at a substrate temperature of 200 ° C., a flow rate ratio of argon / oxygen = 340/1 (pressure 0.31 Pa), and RF output of 300 W. As a result, the light transmittance at 500 nm is 88%, the visible light transmittance at 450 to 800 nm including the substrate is 75% or more, an ITO film having a surface resistance of 16Ω / □, a work function of 4.7 eV, and a film thickness of 150 nm. Obtained. An SEM photograph of the film surface is shown in FIG. Low resistance and high light transmittance, but crystal growth and surface irregularities are severe.

  On the ITO film before annealing at 300 ° C. for 10 minutes in air in Example 1, silane, ethane, diborane, and hydrogen gas are used as raw materials, and the gas atomic ratio is Si: C: B: H = 10: 20: The mixture is mixed to 0.8: 442, plasma CVD is performed under the conditions of a substrate temperature of 160 ° C., a pressure of 0.15 Torr, and an RF output of 20 W to deposit 15 nm of p-type amorphous silicon carbide. A membrane was prepared.

  As a result, the light transmittance at 500 nm is 85%, the visible light transmittance at 450 to 800 nm including the substrate is 75% or more, the surface resistivity is 27Ω / □, and the work function is 5.2 eV (measured light amount 1 nW). A smooth transparent conductive film having a transmittance and a high work function, and having a surface height difference of 1 μm square measured by an atomic force microscope of 10 nm or less was obtained.

  The ITO film prepared in Example 2 was used as a transparent anode, and copper phthalocyanine was deposited as a first hole transporting layer in an order of about 15 nm on top of that as a second hole transporting layer.

を４８ｎｍスピンコートし、さらに第３正孔輸送層としてＮ，Ｎ’−ジフェニル−Ｎ，Ｎ’−パラ−トリル−ベンジジンを５ｎｍ蒸着し、発光層としてキナクリドンを約０．５％添加したＡｌオキシン錯体を５ｎｍ蒸着し、電子輸送層としてＡｌオキシン錯体のみを４５ｎｍ蒸着し、陰極としてＡｌＬｉ合金を２７ｎｍ共蒸着した後、Ａｌのみを１８０ｎｍ積層（発光部面積８ｍｍ^２）し、封止層としてＧｅＯを素子上全面に蒸着した後カバーガラスを感光性樹脂で接着した。

Oxine having a thickness of 48 nm spin-coated, 5 nm of N, N′-diphenyl-N, N′-para-tolyl-benzidine as a third hole transporting layer, and about 0.5% of quinacridone added as a light emitting layer After depositing 5 nm of the complex, depositing only 45 nm of the Al oxine complex as the electron transporting layer, co-depositing 27 nm of the AlLi alloy as the cathode, and laminating only 180 nm of Al (light emitting part area 8 mm ² ), and using GeO as the sealing layer After vapor deposition on the entire surface of the device, the cover glass was adhered with a photosensitive resin.

Driving this element in 10 mA / cm ^2, the initial luminance 587cd ^/ m 2 (8.6V), maintaining the high luminance than ever and 184cd ^/ m 2 (11.2V) even after thousands of hours, the non-emission by visual observation Stable light emission without generation of spots.

2 is a surface SEM photograph of an amorphous ITO film formed at a substrate temperature of room temperature in Example 1. It is a figure of the X-ray diffraction of the same sample as FIG. It is a SEM photograph of the sample surface of Example 2 which annealed the sample of FIG. 1 under pressure reduction. It is a figure of the X-ray diffraction of the same sample as FIG. It is a SEM photograph of the surface of the sample of Example 3 which annealed the sample of FIG. 3 in the air. It is the SEM photograph of the surface of the sample of Example 2 which annealed the sample of FIG. 1 in the air. 4 is a SEM photograph of the sample surface of Comparative Example 3.

Claims (3)

On the insulating substrate, the substrate temperature is kept at 0 to 100 ° C., and an amorphous ITO film that is amorphous or microcrystalline in X-ray diffraction is produced, and thereafter, under reduced pressure or in a non-oxidizing atmosphere Annealing at 100-500 ° C. to grow a crystal in a plate shape to form an underlayer;
A transparent conductive layer having a work function of 5.1 eV to 6.0 eV is formed with a film thickness of 100 nm or less on the ITO film, and the surface height difference of the transparent conductive layer is set to 1 nm to 10 nm within a range of 1 μm square. The manufacturing method of the transparent conductive film characterized by including a process. The transparent conductive layer is made of an ITO film, and the step of forming the transparent conductive layer is formed with an oxygen partial pressure higher than the ITO film forming condition of the underlayer, and after the film formation, annealed in an oxidizing atmosphere, The method for producing a transparent conductive film according to claim 1, wherein the transparent conductive film is a step of plasma irradiation . The method for producing a transparent conductive film according to claim 1, wherein the transparent conductive layer is made of an amorphous semiconductor having a thickness of 20 nm or less .

Images