JP2013004368A - Manufacturing method of organic el element - Google Patents

Abstract

An organic EL device manufacturing method that improves carrier mobility (electron injection) while improving the crystallinity of an ITO film by non-heating treatment.
A method of manufacturing a top emission type organic EL element includes a reflective anode 7 as a first electrode on a substrate 4, an organic thin film 12 including an organic light emitting layer 12, an electron injecting protective film 13 including an n-type dopant, And the transparent electrode 14 made of ITO as the second electrode in this order, and the sealing layer 30 so as to cover the first electrode 7, the organic thin film 12, the electron injecting protective film 13, and the second electrode 14. The XRD diffraction peak intensity in the plane orientation 222 of the ITO film formed on the electron injecting protective film 13 is larger than that of the amorphous ITO film.
[Selection] Figure 6

Description

  The present invention relates to an organic EL display (Organic Light Emitting Display, hereinafter referred to as “OLED”) in which an organic light emitting material is filled in a region partitioned by a partition, particularly an organic EL element or a region partitioned by a partition). The present invention relates to a method for forming a transparent conductive film constituting a plasma display panel (PDP) filled with a material.

  The OLED has a structure in which an organic layer including an organic light emitting layer is sandwiched between two electrodes, and causes the organic light emitting layer to emit light by passing a current between the electrodes. The organic layer is formed by laminating one or more thin films made of a predetermined organic material. In order to make the organic light emitting layer emit light efficiently, the thickness of the thin film layer is very important, and it is necessary to suppress the thickness of the whole organic layer to 1 μm or less.

  In a general OLED, a transparent electrode, an organic thin film, and a metal electrode are sequentially formed on a glass substrate. On the other hand, a top emission type OLED is formed on a glass substrate in the order of a metal electrode, an organic thin film, and a transparent electrode. With these structures, a color filter can be manufactured on the sealing substrate side and bonded to the light-emitting element substrate. Further, when the OLED is applied as an active matrix drive display, the top emission type in which light is extracted from the upper part of the element on the side opposite to the substrate is not blocked by the drive circuit on the substrate, and an increase in aperture ratio can be expected.

  For the practical application of OLED, the performance items that are most strongly demanded for improvement at present are life and durability. One of the degradation modes of OLED is drive degradation. In drive deterioration, the brightness of the OLED when it is continuously driven with a constant DC current gradually decreases, and further the drive voltage increases. In general, the term “lifetime” refers to the time until the luminance with respect to a constant current becomes half of the initial value, and strongly depends on the initial luminance, the environmental temperature, and the driving method.

  There are various influencing factors regarding the driving life, but the carrier injection electrode part is considered to have an extreme influence on the life characteristics. Traditionally, single films of low work function alkali metals, alkaline earth metals, or alloys thereof have been used as cathode materials. However, since these metals are not stable when used alone, a method of inserting a relatively stable alkali metal compound in the atmosphere between the organic layer and the cathode is currently used.

  Alkali metal compounds are highly stable in film formation, but are generally insulative, which may hinder electron injection. However, an alkali metal compound does not exhibit insulation at a very small amount, forms an extremely efficient electrode, and has an advantage that the formed electrode has high heat resistance. LiF + Al (lithium fluoride + aluminum) electrodes, etc., not only significantly improve current-voltage characteristics (electron injection properties) and current-luminance efficiency characteristics, but also dramatically increase drive life compared to Al single electrodes. It is known to be.

  In the top emission type OLED, the upper electrode is a transparent conductive film made of a material such as ITO (Indium Tin Oxide) and is formed so as to be in contact with the electron injecting organic film. Therefore, the physical properties of the transparent conductive film serving as the carrier injection electrode have a great influence on the driving life of the OLED.

ITO is an n-type degenerate semiconductor and has a high carrier density of 10 ²⁰ cm ⁻³ to 10 ²¹ cm ⁻³ , but Sn (tin) which is one of the constituent elements (addition donor) is a mother crystal. Some In ₂ O ₃ (indium oxide) does not completely dissolve in a substitutional form but exists as interstitial atoms in crystal grains. This forms a scattering center for neutral or ionized impurities and causes a decrease in carrier mobility.

  On the other hand, promoting electron injection is synonymous with increasing the conductivity of the ITO film itself. The conductivity (σ) is the product (σ = n × e × μ) of the carrier density (n), the elementary charge (e) and the carrier mobility (μ), and increases the carrier mobility (μ). Efficient electron injection is possible. The mobility (μ) corresponds to the ease of movement of carriers (electrons or holes) and is also an amount that depends mainly on the ITO crystallinity. That is, if the crystallinity is good and the impurity is small, the carrier mobility (μ) increases. On the other hand, if the crystallinity is poor and there are many lattice defects, dislocations, crystal grain boundaries, etc., the carrier is trapped and the mobility (μ) Causes a drop. Therefore, impurities are a major factor that hinders carrier movement. Usually, since a small amount of doping has a great influence on mobility, it is very important to improve the crystallinity and control the doping concentration.

  FIG. 7 shows a cross-sectional structure of an organic EL element used in an OLED (for example, Patent Document 1) that employs a DLC (Diamond Like Carbon) film as an anode as a measure for improving the efficiency and extending the life of the OLED. The organic EL element 110 includes an auxiliary electrode 112 on a transparent substrate 111 made of glass. An opening 112A for light emission extraction is provided on the auxiliary electrode 112, and a cathode 113 made of an ITO layer is formed in the opening 112A and on the auxiliary electrode 112.

  An electron injection layer 114 is formed on the cathode 113, an electron transport layer 115 is formed on the electron injection layer 114, an organic light emitting layer 116 is formed on the electron transport layer 115, and the organic light emitting layer 116 is formed. A hole transport layer 117 is formed on the anode, an anode 118 is formed on the hole transport layer 117, an auxiliary electrode 119 is formed on the anode 118, and a single nitride is formed on the auxiliary electrode 119. A protective layer 120 made of silicon (SiN) is formed. The cathode 113 is made of an ITO layer, and the anode 118 is made of a DLC film to which nitrogen is added as an impurity.

  As described above, the hole injection efficiency is improved by forming a p-type DLC film in which a small amount of nitrogen is added to the anode 118, while light emission from the organic light emitting layer 116 is achieved by forming a transparent conductive film on the cathode 113. , And taken out from the opening 112A provided in the auxiliary electrode 112. By adopting such a laminated structure, the organic EL element is characterized in that the gas barrier property is improved and the device life is extended.

  The DLC film is an amorphous carbon film that is flat and can be synthesized at a low temperature of about 200 ° C., in which both the sp3 bond of diamond and the sp2 bond of graphite have a skeleton structure. The DLC film has characteristics such as high hardness, high wear resistance, low friction coefficient, high insulation, high chemical stability, high gas barrier properties, high seizure resistance, and high infrared transmittance.

JP 2002-343579 A

  In the production of OLEDs, the biggest issue is how to improve the device lifetime regardless of whether it is a low molecule or a polymer. However, the factors governing life are not well understood. One of the reasons is that the OLED itself consists of a thin film multilayer element of several hundreds of nanometers, and the laminated layers are organic layers that are difficult to distinguish from the constituent elements except for the electrodes. Sometimes.

  In the above-mentioned OLED (Patent Document 1), a DLC film in which a small amount of a trivalent or pentavalent impurity having high chemical stability is added to the uppermost layer opposite to the substrate is used for the anode. This makes up for the low hole injection efficiency due to the n-type degenerate semiconductor, which is a problem when ITO is used as a transparent anode, and improves the device durability by enhancing the gas barrier property.

  However, in the case of a top emission type layer structure, it is difficult to employ a DLC film having excellent near-infrared transmittance but low visible-light transmittance as the upper electrode. In addition, since the film quality is amorphous, carrier mobility is low, and when one of the electrodes is a transparent anode made of ITO, it is still difficult to adopt a p-type DLC film in which injected carriers become electrons as a cathode.

  In a top emission type OLED in which the light extraction efficiency of the device is increased in order to maximize the light emission potential, the film quality of ITO formed so as to be in contact with the electron injecting protective film greatly affects the driving life. Therefore, how to increase the carrier mobility of ITO, which is one of the lifetime controlling factors, is a problem for improving the lifetime.

  Sputtering, which is widely used as a means for forming an ITO film, provides a dense and smooth thin film by a relatively low-temperature process, as compared with film-forming means such as vacuum deposition and CVD (Chemical Vapor Deposition). There is an advantage of being able to. However, a thin film formed by sputtering is often amorphous, and in order to obtain a crystalline film, it is necessary to perform sputtering while heating the substrate to 200 ° C. or higher.

  The DC pulse sputtering method is a sputtering method developed for the purpose of maintaining the discharge more stably for a long time in accordance with such a requirement. The DC pulse sputtering method turns on / off the power applied to the target at a constant cycle, and is often used at a duty ratio of 70% or more, which is the ratio of the ON time in one cycle. In this case, discharge stability such as avoiding arcing is increased and the generation of pinholes during film formation is reduced. However, other thin film physical properties are not significantly different from those formed by DC sputtering. Even in the DC pulse sputtering method, a thin film with high crystallinity cannot be obtained particularly when a film is formed on a low-temperature or non-heated substrate.

  On the other hand, when an ITO film is formed by sputtering on an organic thin film having a thickness of several tens of nanometers, the function is ensured when the organic thin film is a functional thin film made of a phosphor or an n-type or p-type semiconductor. Accordingly, the process (firing) temperature needs to be lower than the glass transition point (Tg). Furthermore, the substrate incidence frequency and energy of sputtered particles, which are high energy particles, must be controlled.

  However, at present, it is difficult to form a crystalline ITO film on an organic thin film at a process temperature below the glass transition point Tg. Further, although the incident frequency and energy of sputtered particles can be controlled by process parameters (film formation pressure, etc.), it is still difficult to ensure film properties and crystallinity.

  As a means for improving film crystallinity, it is known that promotion of surface migration (migration) by increasing substrate incident energy is effective. However, there is a concern that an increase in substrate incident energy may cause film function deterioration such as a fluorescence quantum yield or a Stokes shift change of an organic film as a base. Note that the Stoke shift is a difference in transition energy between absorption and fluorescence, and the amount of shift increases as the nuclear arrangement in the excited state of the organic molecule increases from that in the ground state.

  In view of the above-described problems, an object of the present invention is to provide a method for manufacturing an organic EL element that improves carrier mobility (electron injection) while improving the crystallinity of an ITO film by non-heating treatment.

  In order to solve the above problems, the present invention provides a reflective anode as a first electrode, an organic thin film including an organic light emitting layer, an electron injecting protective film including an n-type dopant, and an ITO as a second electrode on the substrate. And a step of forming a sealing layer so as to cover the first electrode, the organic thin film, the electron injecting protective film, and the second electrode. A method for manufacturing an organic EL device, characterized in that an XRD diffraction peak intensity in a plane orientation of an ITO film formed on the electron injecting protective film is larger than that of an amorphous ITO film.

  According to the present invention, a crystalline ITO film having a controlled particle size is formed as an upper electrode by DC magnetron sputtering without causing heating on the electron-injecting protective film and degrading the film function due to destruction of the molecular structure. As a result, electron injection is promoted, and the device has a long life.

It is a figure which respectively shows the lifetime of the top emission type green organic EL element which formed the ITO (indium tin oxide) film | membrane in the upper electrode by the formation method of the transparent conductive film which concerns on this invention, and another method. It is a figure which respectively shows the (electron) current-voltage characteristic of the electronic single charge device which formed the ITO film | membrane in the upper electrode by the formation method of the transparent conductive film which concerns on this invention, and another method. It is a figure which respectively shows the crystallinity of the ITO film | membrane formed so that it may contact on the electron injectable protective film by the formation method of the transparent conductive film which concerns on this invention, and another method. It is an energy diagram (conceptual diagram) of an organic layer and a cathode interface in an ITO non-degenerate state and a degenerate state. It is sectional drawing which shows typically the structure of the element for evaluation for confirming the correlation of ITO film | membrane physical property and device lifetime. It is a figure which shows the structure of the magnetron sputtering apparatus used for ITO film formation which concerns on embodiment of this invention. It is sectional drawing showing schematic structure of the conventional organic EL element.

Hereinafter, embodiments of the present invention will be described in detail. Specifically, the improvement in crystallinity of the ITO film which is one of the objects of the present invention is that the diffraction intensity in the plane orientation (222) which is the main peak of In ₂ O ₃ is larger than that of the amorphous ITO film and This is realized by controlling the average crystal grain size so that the carrier mobility is maximized. The most important parameters for film structure control in sputter deposition are the deposition temperature (substrate temperature) and gas pressure.

  When forming an ITO film on a functional organic thin film having poor heat resistance, an excessive substrate temperature rise must be suppressed. Therefore, the existence of sputtered particle kinetic energy is important as driving energy for structural control instead of thermal energy. The sputter particle kinetic energy greatly depends on the ion fraction in the plasma and the plasma potential. Among the sputtered particles, ions have energy about 10 to 100 times that of neutral particles, and the ion fraction is 10% or more, so controlling the kinetic energy (incident energy) of ions is effective for controlling the film structure. It is.

  When film formation is performed by controlling the average incident ion energy to 50 eV to 100 eV and the ratio of the Ar (argon) ion incident amount to the sputter particle incident amount within a range of 0.01 to 0.1, it is suitable for film structure control. . On the other hand, when the film is formed outside the same control range, the film formation surface is re-sputtered, resulting in a decrease in film formation rate, an increase in film formation surface temperature, and a decrease in film function due to ion incident damage to the underlying organic layer. Concerned. That is, suppressing the increase in film defect density due to resputtering and the accompanying Ar trap promotion leads to the formation of a dense film with high crystallinity and orientation.

  Based on the above, the average crystal grain size and the maximum crystal grain size of the non-heat-treated ITO film according to the example of the present invention were observed with a scanning electron microscope (SEM), respectively, and the carrier mobility and As a result of investigating the correlation, the carrier mobility is maximized within the range of 20 nm to 50 nm for the former and 60 nm to 100 nm for the latter, and the ITO film is formed so as to be in contact with the electron injecting protective film As shown in FIG. 3, it was confirmed that the film showed strong diffraction intensity in the plane orientation (222). In FIG. 3, the vertical axis represents diffraction intensity [cps: count per second], and the horizontal axis represents diffraction angle 2θ [°].

  Further, in the top emission type OLED having the layer configuration of FIG. 5, when the embodiment of the present invention was applied, it was confirmed that the highest lifetime characteristic was exhibited as shown in FIG. These events suggest that crystal grain size control, that is, structure control contributes to improvement in crystallinity and, in turn, device drive life.

  Regarding the average incident ion energy, the ion acceleration potential difference (Vp-Vf) is measured by plasma diagnosis using the Langmuir probe method, and the target potential (VT) is measured by observing the pulse discharge waveform using an oscilloscope. Made. The Langmuir probe method is also called an electrostatic short needle method, and various plasma quantities that can be measured include an electron temperature (Te), an electron energy distribution function (EEDF: Electron Energy Distribution Function), an electron density (Ne), an ion density ( Ni), floating potential (Vf), plasma potential (Vp), and the like. The measurement is simple and can be obtained by measuring the voltage-current characteristics at the probe tip at the tip of the probe unit inserted in the plasma. At this time, it is assumed that the EEDF has a Maxwell-Bolzmann distribution.

  Further, the film forming pressure is controlled to a pressure 0.1 Pa higher than the plasma discharge threshold. The reason for this is to improve crystallinity by suppressing abnormal discharge under low gas pressure, increasing the ion incident energy and frequency, and activating migration of sputtered particles on the substrate. In addition, abnormal discharge is caused by the generation of nodules (black spatter residue: oxygen deficient ITO), positive and negative charges are accumulated on the nodule formation surface like capacitors, and the charges that continue to accumulate during sputtering exceed a certain limit value. Local dielectric breakdown is caused, and particles generated by arc discharge generated at that time also cause problems such as deterioration of film quality and damage to the power source.

  Sputter film formation for forming a transparent electrode is an initial film formation on the surface layer of an electron-injecting protective film containing an n-type dopant, and the process gas is not doped with oxygen and forms 1/4 of the total film thickness. In the secondary film formation, the remaining film is formed by setting the ratio of the oxygen flow rate to Ar to 0.01 to 0.05, thereby preventing the highly active alkali metal or alkaline earth metal as the n-type dopant from being oxidized. In addition, by forming a thin initial film, it is possible to suppress a decrease in film transmittance due to oxygen non-doping. Further, regarding the increase in film resistance, carriers (electrons) are tunnel-injected by setting the film thickness to be extremely thin. As a result, a decrease in electron injectability is suppressed, and a decrease in lifetime due to higher device drive is also suppressed.

  Here, the correlation between the crystallinity of the ITO film and the EL element characteristics and the mechanism in the method for manufacturing the organic EL element according to the embodiment of the present invention will be described. FIG. 1 shows the lifetime characteristics of G (green) elements in which ITO films are formed by different methods in a top emission type OLED. Specifically, the point P is a magnetron sputtering method according to an embodiment of the present invention, the point Pc1 is a counter target sputtering method as a comparative example 1, and the point Pc2 is a lifetime of a device formed by a plasma deposition method as a comparative example (Life time). / H). From this figure, it can be confirmed that the luminance half-life of the element formed with the ITO film according to the embodiment of the present invention is more than twice as long as the life of the element formed with the ITO film by other methods. This is because the crystallinity of the ITO film is improved according to the embodiment of the present invention, so that electron injection is efficiently performed from this film, and the injection balance of both hole and electron carriers is improved. This is thought to be due to the improvement.

FIG. 2 shows (electron) current-voltage characteristics of an EOD (Electron Only Device) having an ITO film. In the figure, the horizontal axis represents the applied voltage (V), and the vertical axis represents the electron current (mA). A dotted line La1 indicates the current-voltage characteristics of the conventional aluminum deposited film. Solid lines L, Lc1, and Lc2 indicate the current-voltage characteristics of the ITO films in the embodiment of the present invention, Comparative Example 1, and Comparative Example 2 described with reference to FIG. From this figure, although the electron current of the element in which the ITO film is formed according to the embodiment of the present invention is inferior to that of the Al vapor deposition film, the opposed target sputtering method (Comparative Example 1) and the plasma vapor deposition method (Comparative Example 2) It can be confirmed that the current flows well (electron injection property is high) compared to the current of the element on which the ITO film is formed. This is also because the crystallinity of the ITO film formed according to the example of the present invention was improved and electrons were efficiently injected from this film.

  FIG. 3 shows an X-ray diffraction (XRD) result of the ITO film formed so as to be in contact with the electron injecting protective film. In the figure, the horizontal axis represents the diffraction angle 2θ [°], and the vertical axis represents the diffraction intensity [cps: counts per second]. Lines C, Cc1, and Cc2 indicate the crystallinity of the ITO films according to the embodiment of the present invention, Comparative Example 1, and Comparative Example 2 described with reference to FIG. From this figure, the ITO film according to the embodiment of the present invention can confirm a clear diffraction peak intensity at 2θ = 30.6 °, that is, the plane orientation (222), and an ITO film formed by another method (Comparative Example 1). It can be confirmed that the crystallinity is higher than that of Comparative Example 2). This is because, in the ITO film according to the embodiment of the present invention, Ar ions are incident on the film deposition surface while controlling the ion energy to 50 to 100 eV, thereby improving the film density. That is, it is considered that ion energy is a driving force to promote stress migration and improve crystal orientation.

  The X-ray diffraction method used for the crystallinity evaluation described above has an atomic X-ray spectrum of about 0.1 nm, which is smaller than the typical atomic spacing (0.2 to 0.3 nm) of a solid, and the crystal lattice is X-ray. It is a kind of crystal structure analysis method that uses a phenomenon that becomes a diffraction grating and interferes with incident X-rays with the same degree of secondary X-rays emitted from the electrons outside the shell of each atom.

  Specifically, a specific direction due to this interference (when X-rays are incident on a crystal having a lattice spacing d, θ having a relationship of 2 d sin θ = nλ, that is, a Bragg angle, where n is an arbitrary integer) As a result, the X-ray intensity increases, and a diffraction pattern reflecting the crystal structure is obtained.

  FIG. 4 shows an energy diagram (conceptual diagram) between the organic layer and the cathode interface in the ITO non-degenerate state (FIG. 4A) and the degenerate state (FIG. 4B). From this figure, in the ITO degenerated state (FIG. 4 (b)), the double carrier density of the electric double layer formed at the interface is higher than that in the ITO non-degenerated state (FIG. 4 (a)). (The Fermi level of ITO is closer to the vacuum level than the bottom level of the conduction band).

This model shows that the electron injection property in the ITO degenerate state is improved with respect to the non-degenerate state, and the mechanism is that when In ₂ O ₃ which is the mother crystal of ITO is doped with Sn. Tetravalent Sn is dissolved in substitution at the trivalent In site, and the substituted Sn emits one carrier per atom, and a carrier density of 10 ²⁰ to 10 ²¹ cm ⁻³ is stably obtained. It is expressed by.

  When the Fermi level of the n-type semiconductor is higher than the work function of the metal at the contact between the metal and the organic semiconductor, the free electrons of the n-type semiconductor flow to the metal side. Even if electrons move to the metal side, the charge can only exist on the surface of the metal. In other words, all the electrons that have entered the metal exist only on the metal surface and cannot go to the back. As a result, an electric double layer is formed at the interface between the n-type semiconductor and the metal.

  When a vacuum level shift occurs due to the formation of the interfacial electric double layer, the shift amount becomes 1 eV depending on the combination of the n-type semiconductor and the metal, which is not negligible compared to the magnitude of the band gap energy Eg. In many cases, the polarity of the interface electric double layer is positive for an n-type semiconductor and negative for a metal.

  This is due to the characteristics of the n-type semiconductor. That is, the n-type semiconductor originally generates a free electron by dissociating the donor, so that the state where the free electron exists is electrically neutral. When the electrons disappear, the non-movable donor ions that form part of the semiconductor lattice remain in their original locations, and the n-type semiconductor is positive and the metal is negative. The portion where the electrons disappear is called a depletion layer. The space charge density of the depletion layer is the product of donor ion density and elementary charge.

FIG. 5 schematically shows the structure of an evaluation element for confirming the correlation between the ITO film physical properties, which is the main object of the present invention, and the device lifetime. A planarizing film 6 and a reflective anode 7 as a first electrode are formed on the glass substrate 4 and the TFT substrate 5, respectively, and a partition wall 9 is formed by a photolithography method as a pixel partition member. The pixel region partitioned by the partition wall 9 includes a hole injection layer 10, an interlayer (electron blocking layer) 11, an organic light emitting layer (RGB) 12 that is an organic thin film, an n-type doped electron injection layer 13, and a second electrode. A certain transparent electrode 14 is provided in order. The reflective anode 7, the organic light emitting layer 12, and the transparent electrode 14 provided on the substrate are sealed mainly for the purpose of protecting both the electrodes 7 and 14 and the organic light emitting layer 12 from moisture in the environment. Stopped. For sealing, a thin film sealing layer (SiNx + Al ₂ O ₃ ) 30 composed of two layers of a first sealing layer 15 (SiNx) and a second sealing layer 16 (Al ₂ O ₃ ), and a resin sealing layer 17 Is formed on the transparent electrode 14, and the color correction color filter 20 is attached to the color filter glass substrate. As described above, the evaluation element having the configuration shown in FIG. 5 can perform the life evaluation without being influenced by the influence of the external atmosphere.

In the conventional top emission type OLED shown in FIG. 5, sealing is performed by forming only the first sealing layer 15 (SiNx) on the transparent electrode 14. However, the coverage of the device end is insufficient. Furthermore, when a foreign substance is present on the transparent electrode 14, a sealing layer defect path is generated mainly due to the directivity of the film-forming particles, and moisture, oxygen, etc. in the atmosphere diffuse and invade from here to easily oxidize. The n-type doped electron injection layer 13 and the organic light-emitting layer 19 which are properties are modified. As described above, the sealing layer 120 is conventionally formed of only one layer of SiNx, whereas in the present invention, the sealing layer 30 is formed of two layers of SiNx + Al ₂ O ₃ .

In the present invention, when a thin film sealing layer (SiNx + Al ₂ O ₃ ) 30 composed of two layers is formed on the transparent electrode 16 and sealing is performed, the end coverage is improved. Further, by improving the film density of the second sealing layer (Al ₂ O ₃ ) 18, the occurrence of a sealing layer defect path (leakage path) can also be suppressed. The second sealing layer 18 also has a function as an optical adjustment layer, and an organic compound such as parylene may be used in addition to the inorganic compound.

  With reference to FIG. 6, a magnetron sputtering apparatus used for forming an ITO film according to an embodiment of the present invention will be described. The magnetron sputtering apparatus 100 includes a sputtering target unit 32 including an earth shield 32a, a target 32b, a backing plate 32c, and a cathode magnet 32d therein, and a substrate rotation holding mechanism for holding the translucent substrate 28 at a position facing the sputtering target unit 32. 22 is provided. Note that a substrate cooling plate 22b is provided on the back side of the substrate in order to suppress an excessive increase in substrate temperature due to ion bombardment during sputtering film formation.

Outside the magnetron sputtering apparatus 100, a pipe 41 for introducing a sputtering gas (Ar, N ₂ ), a gas flow controller MFC (Mass Flow Controller) 42, a ground 43, and a DC pulse as a plasma discharge power source A power source 37 and an exhaust unit 38 including a rotary pump and a cryopump are provided. The magnetron sputtering apparatus 100 uses various transparent materials by using ITO, IZO (indium zinc oxide), GZO (gallium doped zinc oxide), AZO (aluminum doped zinc oxide), ZnO (zinc oxide) or the like as the material of the target 32b. Conductive film formation is possible.

  The magnetron sputtering method is a method in which electrons are constrained by a magnetic field formed on the front surface of a target and gas ionization by electron collision is promoted to increase the plasma density near the target. However, restraining charged particles by a magnetic field also reduces the number of ions that reach the substrate. Therefore, in the magnetron sputtering method, most of the sputtered particles that reach the substrate are neutral particles that are not affected by the magnetic field. In this case, since the acceleration of the charged particles due to the potential difference of the plasma sheath cannot be expected, the kinetic energy is low.

  On the other hand, in the sputtering method using only DC bipolar or high frequency, the substrate temperature rises remarkably due to the incident of secondary electrons on the substrate, but in magnetron sputtering, many electrons are wound around the magnetic field and collide with gas molecules while performing cyclotron motion. Since the energy is repeatedly deactivated to reach and enter the substrate, the substrate temperature rises little.

  In order to control the kinetic energy of the substrate incident particles, it is most effective to use ions, and the potential difference (Vp−Vf) between the plasma potential (Vp) and the substrate potential (Vf), that is, the ion acceleration potential difference is set. By changing, the kinetic energy of ions can be changed greatly. As a result, high energy particles can collide (apply energy) to the formed film, and the collision frequency can also be increased by increasing the number of ions themselves.

  An increase in ion collision frequency leads to an improvement in the crystallinity of the film and an increase in carrier mobility, and also promotes the substitution and ionization of Sn with In atoms, thereby increasing the electron density. As a result, electron injection is promoted.

  On the other hand, in the pulse sputtering method, the negative bias applied to the target is reversed for a short time, and the positive charges on the surface of the insulating film accumulated during the sputtering are neutralized by electrons. Since the mobility of electrons in the plasma is larger than that of ions, the positive bias application time (duty ratio) necessary for neutralization is short. Therefore, it can be expected that the film forming speed is inferior to that of DC sputtering.

Further, in the pulse sputtering method, the substrate incidence of high energy particles can be easily realized simply by replacing the normal DC power source with the pulse power source. However,
1. The particle energy in pulse sputtering greatly depends on the behavior of the target applied voltage;
2. Since the electron density of pulse sputtering is similar to that of normal DC sputtering, high ion fraction cannot be expected; and
3. When the substrate is not grounded, the floating potential of the substrate follows the plasma potential, so that the ion acceleration potential difference (Vp−Vf) does not increase, and as a result, the particles reaching the substrate may not necessarily have high energy. It is necessary to keep this in mind.

  Ion bombardment to the substrate by rare gas ions such as Ar ions has the effect of improving the adhesion of the formed film (stress migration control) and increasing the film density. If the ion energy is appropriately controlled, the residual stress of the formed film It is possible to control the preferential orientation plane such as a polycrystalline film. By utilizing such features of ion bombardment, it becomes possible to change the chemical bonding state of the film and activate the chemical reaction on the surface.

  On the other hand, excessive ion bombardment causes compositional deviation (change in optical constant) due to elimination of constituent elements when the underlying film is an inorganic compound, and molecular bond breakage (change in conjugate length → change in fluorescence quantum yield) when the base film is an organic compound. , There are concerns that each cause. As the plasma density in the vicinity of the substrate increases, the substrate temperature also increases.

  The particles sputtered from the target surface reach the substrate while colliding with surrounding gas particles. The collision frequency depends on the mean free path determined by the gas pressure. Since the mean free path of particles becomes long under low gas pressure, sputtered particles reach the substrate without being affected by scattering due to collision with gas particles and without activating kinetic energy. Kinetic energy serves as a driving force for migration of sputtered particles on the substrate, and a part thereof is converted into thermal energy. This thermal energy contributes directly to the substrate temperature rise.

  When the distance between the substrate and the target is sufficiently larger than the dimensions of the target and the substrate (surface to be sputtered), the incident direction of the sputtered particles substantially coincides with the normal direction of the substrate surface. Since the mean free path is shortened under high gas pressure, the sputtered particles repeatedly collide with the gas particles until reaching the substrate, and the kinetic energy is largely deactivated. In addition, the movement direction of the sputtered particles greatly changes due to scattering due to the collision, and the number of particles obliquely incident at an angle with respect to the normal direction of the substrate surface increases. These obliquely incident particles are greatly involved in the denseness and crystallinity of the thin film.

  From the above, the method for producing an organic EL device of the present invention is such that the transparent electrode is formed by magnetron sputtering, the sputtering film formation parameters are adjusted, the average incident ion energy, and the neutral particles (sputtered particles) and ions are incident on the underlying film. This is performed while controlling the frequency ratio (effective film thickness). Specifically, the gas pressure is set lower than in the prior art to activate migration and increase the incidence of ions on the deposition surface, thereby increasing the film density. This makes it possible to increase the crystallinity (plane orientation, diffraction peak intensity, half-value width, crystal grain size) of the ITO film. That is, by applying the manufacturing method of the present invention to the formation of a transparent electrode in OLED fabrication, injection of electrons as injection carriers can be promoted, and the device life can be extended.

In the evaluation element shown in FIG. 5, an aluminum alloy film having a thickness of 200 nm as a reflective anode 7 is formed directly on the reflective anode 7 on the glass substrate 4 having a thickness of 0.7 mm as an IZO interface layer. (In ₂ O ₃ —ZnO) each having a thickness of 35 nm are stacked by DC magnetron sputtering, and then the two layers of the reflective anode 7 and the anode interface layer are collectively patterned by photolithography to form a stripe pattern did.

Next, a tungsten oxide film having a thickness of 12 nm is formed as the hole injection layer 10 by the sputtering method in the same manner as the reflective anode 7 in which the anode interface layer is directly laminated. And the hole injection layer 10 is deposited) at 230 ° C. for 45 minutes, and the partition wall 9 is formed by photolithography using a polyimide material so as to cover the end of the stripe-shaped reflective anode 7. did. An organic electron blocking material (interlayer 11) between the partition walls 9 is dissolved in a mixed solvent composed of cyclohexylbenzene (CHB) and methylanisole (MA), coated and formed as an ink, and then after firing. Vacuum baking was performed at 200 ° C. for 60 minutes so that the dry film thickness was 10 nm. Further, on the interlayer 11, a green organic light emitting material (Light Emitting Polymer: LEP) made of polyfluorene (PF) is dissolved in a mixed solvent made of CHB and MA as in the case of the interlayer 11, and formed as an ink. so that dry film thickness after firing becomes 80 nm, between 60min at 170 ° C., and calcined under _{N 2} atmosphere.

  Next, Ba (barium) as an n-type dopant and an electron injecting organic substance are co-evaporated on the LEP film (organic light emitting layer 12) at a thickness of 80 nm, and an anode interface layer is formed on the reflective anode 7 described above. A mask was formed so as to be orthogonal to the stripe pattern of the directly laminated anode layer. Note that as the electron-injecting organic material, oxadiazole or an oxadiazole derivative having a high glass transition temperature (Tg), in which a branched or twisted structure is introduced into the main structure, may be used.

  Here, using the transparent conductive film forming method of the present invention, ITO was formed as a cathode by 35 nm magnetron (pulse) sputtering on the electron injecting organic film containing the n-type dopant. The ITO film forming conditions are as follows: gas pressure is 0.6 Pa, Ar flow rate is 200 sccm, oxygen flow rate is 10 sccm, discharge power is 5.4 kW, frequency is 250 kHz, duty ratio is 75%, and transport speed in passing film formation is 41. It was 2 mm / s. The substrate temperature during sputter deposition was 50 ° C. or less, the average incident ion energy was 70 eV, the visible light transmittance of ITO 35 nm formed as a single film under these conditions was 90% or more, and the sheet resistance was 160Ω / □ or less. It was. From the above, it is preferable to perform sputtering film formation for forming the transparent electrode 14 by setting the frequency of the applied power to 150 kHz to 300 kHz and the duty ratio to 60% to 80% using a DC pulse power source.

Finally, the first sealing layer 15 (SiNx film) is formed to a thickness of 620 nm by the CVD method on the entire light emitting region of the device, and the second sealing layer 16 (Al ₂ layer) by the ALD (Atomic Layer Deposition) method. O ₃ film) was formed to a thickness of 20 nm, respectively, and further sealed with a glass substrate 4 through a thermosetting epoxy resin to obtain a top emission type OLED. The film thickness in each of the above-described layers is calculated by optical simulation of the film thickness at which the light extraction efficiency is maximized.

  The luminance half-life (initial luminance 4,000 cd / A: LT50) of the top emission type OLED manufactured by the manufacturing method described above is about 17 times longer than that of a device in which ITO is formed as a cathode by a conventional method. Furthermore, the drive voltage (light emission start voltage) decreased by 0.7 V, and the light emission efficiency (current efficiency) increased by 1.7 cd / A. This is because electrons are efficiently injected from the ITO formed according to the present invention, and the carrier balance with respect to holes is improved (hole accumulation at the interface is suppressed). This suggests that the lifetime which is a characteristic and long-term reliability is improved.

  Further, in contrast to the above-mentioned top emission type OLED, an EOD having a layer structure excluding a hole injection layer and an interlayer is an element specialized for confirming the behavior of electrons as injection carriers. The current-voltage characteristics of the EOD in which ITO was formed on the electron injection layer containing the n-type dopant by the transparent conductive film forming method of the present invention showed the greatest inclination. This also suggests that electron injection was efficiently performed from the ITO formed according to the present invention.

Further, on the substrate where the electron injection protective film is formed, the crystallinity of ITO was 100nm deposited by the sputtering conditions, compared to ITO formed on the same substrate in a conventional method, Lord In ₂ O ₃ The diffraction peak intensity was detected with high sensitivity at the plane orientation (222), and no sub-peak was detected at other plane orientations.

As described above, the transparent conductive film forming method of the present invention belongs to a cubic system and has a crystal structure called “bixbyte” and has a lattice constant of Sn ⁴⁺ in substitutional solid solution at the In ³⁺ position of In ₂ O ₃ . This suggests that an ITO film with high orientation can be formed without a large change (lattice strain).

  The present invention is not limited to the manufacture of organic EL elements, but can be used for display devices such as PDPs, and can also be used for semiconductor processes, solar cells, and the like, including thin film transistors (drive elements).

4 Glass substrate 5 TFT substrate 6 Flattened film 7 Reflective anode 9 Partition 10 Hole injection layer 11 Interlayer (electron blocking layer)
12 Organic light emitting layer (RGB)
13 (n-type doped) electron injection layer 14 Transparent electrode (sputtered ITO)
15 First sealing layer (CVD: SiNx)
16 Second sealing layer (ALD: Al ₂ O ₃ )
17 Resin sealing layer 22 Substrate rotation holding mechanism 22b Substrate cooling plate 28 Translucent substrate 32 Sputter target unit 32a Earth shield 32b Target (ITO)
32c Backing plate 32d Cathode magnet 37 DC pulse power supply 38 Exhaust unit 41 Piping 42 Gas flow controller 43 Earth 100 Magnetron sputtering device 110 Organic EL element 111 Transparent substrate 112 Auxiliary electrode 112A Opening 113 Cathode 114 Electron injection layer 115 Electron transport layer 116 Organic light emitting layer 117 Hole transport layer 118 Anode 119 Auxiliary electrode 120 Protective layer

Claims (7)

Forming a reflective anode as a first electrode on the substrate, an organic thin film including an organic light emitting layer, an electron injecting protective film including an n-type dopant, and a transparent electrode made of ITO as a second electrode in this order;
In the manufacturing method of a top emission type organic EL device comprising the step of forming a sealing layer so as to cover the first electrode, the organic thin film, the electron injecting protective film, and the second electrode,
A method for producing an organic EL element, wherein an XRD diffraction peak intensity in a plane orientation of an ITO film formed on the electron injecting protective film is larger than that of an amorphous ITO film.   The ITO film formed as the transparent electrode has an average crystal grain size of 20 nm to 50 nm and a maximum microcrystal grain size of 60 nm to 100 nm in a non-heat treatment. The manufacturing method of the organic EL element of description.   In the transparent electrode formation, the average incident ion energy is controlled to 50 eV to 100 eV by a sputtering method, and the ratio of the Ar ion incident amount to the sputtered particle incident amount is controlled to 0.01 to 0.1. The manufacturing method of the organic EL element of Claim 1 or 2.   Sputter film formation for forming the transparent electrode, in the initial film formation on the surface of the electron-injection protective film containing n-type dopant, forming a quarter of the total film thickness without doping the process gas oxygen, The organic EL device according to any one of claims 1, 2, and 3, wherein in the secondary film formation, the remaining film is formed with a ratio of an oxygen flow rate to Ar of 0.01 to 0.05. Manufacturing method.   The sputter film formation for forming the transparent electrode uses any one of ITO, IZO, GZO, AZO, and ZnO as a target material. The manufacturing method of the organic EL element of description.   The sputter film formation for forming the transparent electrode is performed at a film formation pressure that is 0.1 Pa higher than a plasma discharge threshold value, according to any one of claims 1, 2, 3, 4, and 5. The manufacturing method of organic EL element.   The sputter film formation for forming the transparent electrode is performed by using a DC pulse power source and setting the frequency of applied power to 150 kHz to 300 kHz and the duty ratio to 60% to 80%. The manufacturing method of the organic EL element of any one of 3, 4, 5, and 6.