JP4337567B2 - Method for manufacturing organic electroluminescence element - Google Patents

Description

  The present invention relates to an organic electroluminescence element and a method for manufacturing the same.

  An organic electroluminescence element (organic EL element) is an electronic device using electroluminescence of a fluorescent organic substance, and is put into practical use for a backlight of a liquid crystal display or a small display. An organic EL device basically has an organic material layer as a light emitter disposed between two electrodes, an anode and a cathode, and holes injected from the anode and electrons injected from the cathode are recombined in the light emitting layer. It is a self-luminous type device that emits light by doing so. Since organic EL elements use organic substances in the light-emitting layer, the electrode and the exposed part of the organic substance layer are usually covered with a protective film in order to prevent the light-emitting layer from being chemically degraded by oxygen or moisture in the atmosphere. is doing. Conventionally, as this kind of protective film, a technique for forming a single layer silicon nitride film or diamond-like carbon film on an electrode surface by ECR plasma CVD is known (for example, see Patent Document 1).

JP-A-10-261487 (second page, FIG. 1)

  The protective film of the organic EL element is desirably a highly moisture-proof one. Silicon nitride has a dense structure and high moisture resistance as a protective film, but has a relatively large internal stress. Since the silicon nitride film of Patent Document 1 is a single-layer film, when the film thickness is increased in order to improve moisture resistance, the internal stress increases abruptly, and the organic EL element is always in a state in which strain is inherent. As a result, there is a problem that the performance is deteriorated, the life is shortened, and the reliability is lowered.

(1) The method of manufacturing an organic electroluminescent element according to claim 1 includes a step of forming a hole injection electrode layer on a substrate, a step of forming an organic layer on the hole injection electrode layer, and an electron injection electrode on the organic layer. A step of forming a protective layer, and a step of forming a protective film by laminating at least two silicon nitride layers and a hydrogenated silicon nitride layer in order on the exposed surfaces of the electron injection electrode layer and the organic material layer, Is formed by a film formation method using high-density plasma, and the silicon hydronitride layer is formed by applying H ₂ gas to the surface of the silicon nitride layer in a state where formation of the high-density plasma is stopped It is characterized by.

(2) The invention of claim 2 is the method of manufacturing an organic electroluminescence device according to claim 1, wherein the high-density plasma film forming method uses surface wave excitation plasma, electron cyclotron resonance plasma, or inductively coupled plasma. It is a law .

  According to the present invention, a highly moisture-proof protective film with reduced internal stress is formed by laminating at least two layers of a silicon nitride layer and a silicon hydronitride layer. Therefore, a highly reliable organic electroluminescence element Can be provided.

  Hereinafter, an organic electroluminescence element (organic EL element) according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a partial cross-sectional view of an organic EL element according to an embodiment of the present invention. The organic EL element 1 is manufactured by sequentially forming a hole injection electrode layer (anode) 12, an organic material layer 13, an electron injection electrode layer (cathode) 14, and a protective film 20 on a transparent substrate 11. The protective film 20 includes five layers including a silicon nitride layer 15, a hydrogenated silicon nitride layer 15 a, a silicon nitride layer 16, a hydrogenated silicon nitride layer 16 a, and a silicon nitride layer 17.

The transparent substrate 11 is made of an inorganic material such as glass or quartz glass, or a synthetic resin such as PET (polyethylene terephthalate), polycarbonate, or PMMA (polymethyl methacrylate). For the hole injection electrode layer 12, a transparent ITO (InO ₃ —SnO ₂ ) film having conductivity is usually used. The hole injection electrode layer 12 may be patterned as shown, or may not be formed with a pattern. The organic layer 13 is composed of a hole transport layer, a light emitting layer, and an electron transport layer in this order from the hole injection electrode layer 12 side. For example, the hole transport layer is a triphenylamine derivative (MTDATA), and the light emitting layer is 8-hydroxyquinoline. Aluminum (Alq ₃ ) and 10-benzo (h) -quinolyl-beryllium complex (BeBq ₂ ) are used for the electron transport layer. The electron injection electrode layer 14 is made of a metal or alloy having a low work function such as aluminum, magnesium, an Al—Li alloy, or an Al—Mg alloy.

  The protective film 20 is formed on the electron injection electrode layer 14 with a silicon nitride layer 15 having a thickness of 0.2 μm, a hydrogenated silicon nitride layer 15 a having a thickness of 0.02 μm, a silicon nitride layer 16 having a thickness of 0.2 μm, and a thickness. This is a multilayer film in which five layers of a hydrogenated silicon nitride layer 16a having a thickness of 0.02 μm and a silicon nitride layer 170c having a thickness of 0.2 μm are sequentially formed. The silicon nitride layers 15, 16, and 17 are all the same material formed under the same film formation conditions. The silicon hydronitride layers 15a and 16a are also the same material formed under the same film formation conditions.

  As shown in FIG. 1, such a five-layer protective film 20 not only covers the surface of the electron injection electrode layer 14 but also the end surface A from which the organic material layer 13 and the electron injection electrode layer 14 are exposed. It is formed so that it may also coat. Thus, since the protective film 20 is formed so as to cover all the exposed surfaces of the organic material layer 13 and the electron injection electrode layer 14, the organic material layer 13 and the electron injection electrode layer 14 are free from moisture and oxygen in the atmosphere. Not affected at all.

  Next, the function of each layer constituting the protective film 20 will be described. The silicon nitride constituting the silicon nitride layers 15, 16, and 17 is generally a hard ceramic represented by the chemical formula SiNx, and the bonds between Si atoms and the bonds between Si atoms and N atoms are covalent bonds having a high bonding force. . The silicon hydronitride that forms the hydrogenated silicon nitride layers 15a and 16a is also a hard ceramic, has Si-H bonds in addition to Si-Si bonds and Si-N bonds, and has a denser structure than silicon nitride. . That is, the silicon nitride layers 15, 16, and 17 and the hydrogenated silicon nitride layers 15a and 16a are all structurally dense, have low gas permeability, and optically have a refractive index of 1.7 to 2.1. It has a rate and is almost transparent to visible light.

  Since the hydrogenated silicon nitride layers 15a and 16a contain a large number of Si—H groups, the silicon hydrogen nitride layers 15a and 16a alleviate internal stress of the silicon nitride layers 15 and 16, respectively. The protective film 20 of the organic EL element 1 according to the present embodiment has a hydrogenated silicon nitride layer 15 a interposed between the silicon nitride layer 15 and the silicon nitride layer 16, and between the silicon nitride layer 16 and the silicon nitride layer 17. Since the silicon hydronitride layer 16a is interposed between the protective film 20 and the entire protective film 20, the internal stress is relaxed. In addition, the protective film 20 has a sufficient moisture-proof property because each layer constituting the protective film 20 is dense and has low gas permeability, although the total thickness is comparatively thin at approximately 0.6 μm. Therefore, the organic EL element 1 has excellent reliability because it has reduced internal strain and is not affected by moisture or oxygen in the atmosphere.

  Further, the refractive index of each layer constituting the protective film 20 can be adjusted by the film forming conditions or the forming conditions, and the silicon nitride layers 15, 16, 17 and the hydrogenated silicon nitride layers 15a, 16a are 1.7-2. A range of 1 can be taken. In general, the greater the number of Si—H groups, the greater the refractive index of the SiNx crystal. For example, if the refractive index of each layer is the same, reflection at the interface of each layer is eliminated, so that light from the light emitting layer is radiated to the outside with almost no loss. Further, if the refractive index difference between the silicon nitride layers 15, 16, 17 and the hydrogenated silicon nitride layers 15a, 16a is reduced, the reflection at the interface of each layer is also small, equivalent to a single layer film, and the light from the light emitting layer is Radiated to the outside with almost no loss. As described above, when the light emission (top emission) transmitted through the protective film 20 is used, the emitted light is not shielded by the electric circuit in the active matrix system, so that it is possible to display without any light loss. When top emission is used, an opaque substrate can be used instead of the transparent substrate 11.

  Hereinafter, the manufacturing method of the organic EL element of this Embodiment is demonstrated. First, an ITO film having a thickness of 150 nm is formed as a hole injection electrode layer 12 on a transparent substrate 11 having a thickness of 0.5 mm by vacuum deposition, a resist layer is applied on the ITO film by spin coating, and then a mask is used. The hole injection electrode layer 12 is formed from an ITO film having a predetermined pattern.

On the ITO film, by resistance heating vapor deposition, an MTDATA having a thickness of 50nm as the hole transport layer, the thickness of 60NmAlq ₃ as a light-emitting layer, the BeBq ₂ thick 50nm are sequentially formed as an electron transport layer, an organic layer 13 formed Film. Further, an Al—Li alloy layer having a thickness of 0.2 μm is formed on the BeBq ₂ as the electron injection electrode layer 14 by vacuum deposition. Hereinafter, the organic EL element 1 manufactured through the steps up to here is referred to as an organic EL element substrate 10. The organic EL element substrate 10 itself is a known one.

  The organic EL element substrate 10 formed up to the electron injection electrode layer 14 is transferred into the surface wave excitation plasma CVD apparatus 100 shown in FIG. 2 to form a protective film. FIG. 2 is a sectional view showing a schematic configuration of the surface wave excitation plasma CVD apparatus. A surface wave excitation plasma CVD apparatus (hereinafter referred to as SWP-CVD apparatus) can easily generate a high-density plasma with a large area using surface waves, and this plasma is a surface wave excitation plasma (SWP: It is called “Surface Wave Plasma”.

  2, the SWP-CVD apparatus 100 includes a chamber 101, a microwave waveguide 102, a slot antenna 103, a dielectric plate 104, a process gas introduction pipe 105, a material gas introduction pipe 106, a vacuum exhaust pipe 107, and a substrate holder 108. Prepare. The chamber 101 is a sealed container for forming a film on the surface of the substrate held by the substrate holder 108 using the plasma P generated in the internal space. The substrate holder 108 can move and rotate in the vertical direction indicated by arrows in the figure, and is configured to be able to heat, cool, apply an electric field, etc., as necessary, to the substrate that is the film formation target.

  A dielectric plate 104 made of quartz, alumina, zirconia or the like is provided on the upper portion of the chamber 101. A microwave waveguide 102 is placed in contact with the upper surface of the dielectric plate 104. A plurality of slot antennas 103 having long rectangular openings are provided on the bottom plate of the microwave waveguide 102 in contact with the dielectric plate 104.

The process gas introduced into the chamber 101 from the process gas introduction pipe 105 is a gas that is a raw material for reactive active species such as N ₂ gas, O ₂ gas, H ₂ gas, NO ₂ gas, NO gas, NH ₃ gas, and the like. A rare gas such as Ar gas, He gas, Ne gas, Kr gas, or Xe gas. The material gas introduced into the chamber 101 from the material gas introduction pipe 106 is a gas containing Si element which is a component of a silicon thin film or a silicon compound thin film such as SiH ₄ gas or Si ₂ H ₆ gas.

  A vacuum exhaust pipe 107 connected to a vacuum exhaust pump (not shown) is disposed on the bottom plate of the chamber 101. By exhausting while introducing a predetermined gas into the chamber 101 at a predetermined flow rate through the process gas introduction pipe 105 and the material gas introduction pipe 106, the inside of the chamber 101 can be maintained at a predetermined pressure.

  In the SWP-CVD apparatus 100 configured as described above, a microwave having a frequency of 2.45 GHz is propagated into a microwave waveguide 102 from a microwave generation source (not shown), and is radiated to the dielectric plate 104 through the slot antenna 103. Let The microwave becomes the surface wave SW, and the process gas in the chamber 101 is ionized and dissociated by the surface wave energy, and the plasma P is generated. Since the surface wave SW spreads over the entire inner surface of the dielectric plate 104, the plasma P also spreads in the corresponding region in the chamber 101. Using this plasma P, a protective film 20 is formed on the organic EL element substrate 10.

Hereinafter, the manufacturing process of the protective film 20 of the organic EL element 1 of this Embodiment is explained in full detail.
(1) Formation of silicon nitride layer 15 The organic EL element substrate 10 is set on the substrate holder 108, and the inside of the chamber 101 is evacuated to a high vacuum of about 0.01 Pa. H ₂ gas, N ₂ gas, and Ar gas are respectively introduced into the chamber 101 through the process gas introduction pipe 105 at a predetermined flow rate, and SiH ₄ gas is introduced into the chamber 101 through the material gas introduction pipe 106 at a flow rate of 85% of the H ₂ gas. The pressure inside the chamber 101 is maintained at 4 Pa. Film formation is performed for 2 minutes with plasma P generated by microwave power of 3.0 kW to form a silicon nitride layer 15 having a thickness of 0.2 μm.

(2) Formation of hydrogenated silicon nitride layer 15a First, the introduction of SiH ₄ gas into the chamber 101 is stopped, and the microwave power is also cut off. H ₂ gas and He gas are introduced into the chamber 101 through the process gas introduction pipe 105 at a flow ratio of 100: 5, and the inside of the chamber 101 is held at a pressure of 5 Pa for 30 seconds. That is, H ₂ gas and He gas are supplied to the surface of the silicon nitride layer 15 in a state where the plasma P is not generated. Since the silicon nitride layer 15 is heated to a maximum of about 90 ° C. during film formation, H ₂ molecules adhere to the surface of the silicon nitride layer 15 and hydrogenation occurs on the outermost surface, resulting in a hydrogen having a thickness of 0.02 μm. A silicon oxynitride layer 15a is formed. H ₂ gas and He gas have a thermal conductivity at 0 ° C. of 16.82 × 10 ⁻² W · m ⁻¹ · K ⁻¹ , 14.22 × 10 ⁻² W · m ⁻¹ · K ⁻¹ , respectively. It is high in gas, and the surface temperature of the silicon nitride layer 15 decreases due to the cooling effect of both. When the substrate holder 108 is cooled, an inert He gas is interposed between the substrate holder 108 and the organic EL element substrate 10 to efficiently cool the organic EL element substrate 10.

(3) Formation of silicon nitride layer 16 After the chamber 101 is evacuated to a high vacuum of about 0.01 Pa, a thickness of 0 is formed on the silicon hydronitride layer 15a under the same film formation conditions as the silicon nitride layer 15 described above. A silicon nitride layer 16 having a thickness of 2 μm is formed.
(4) Formation of Hydrogenated Silicon Nitride Layer 16a A silicon hydrogenated nitride layer 16a having a thickness of 0.02 μm is formed on the silicon nitride layer 16 under the same formation conditions as the silicon hydrogenated nitride layer 15a described above.
(5) Formation of silicon nitride layer 17 After the chamber 101 is evacuated to a high vacuum of about 0.01 Pa, the silicon nitride layer 17 is formed on the hydrogenated silicon nitride layer 16a under the same film formation conditions as the silicon nitride layers 15 and 16 described above. A silicon nitride layer 17 having a thickness of 0.2 μm is formed.

  Under the film formation conditions of the silicon nitride layers 15, 16, and 17, Si—H bonds are usually present in the SiNx crystal, and the larger the number of Si—H groups, the smaller the crystal grain size and the denser the structure. Thus, the gas permeability is lowered. When the hydrogenated silicon nitride layers 15a and 16a are formed on the outermost surfaces of the silicon nitride layers 15 and 16, respectively, so-called dangling bonds are covered with H atoms, so that the silicon hydrogenated nitride layers 15a and 16a are made of materials. Gas permeability is lower than that of the silicon nitride layers 15 and 16. Further, since the formation of the silicon hydronitride layers 15a and 16a suppresses the growth of SiNx crystals in the silicon nitride layers 15 and 16, the silicon nitride layers 15 and 16 are compared with the case where the silicon hydronitride layer is not formed. Gas permeability is low.

  In the present embodiment, since the pressure in the chamber 101 at the time of forming the silicon nitride layers 15, 16, and 17 is relatively high at 4 Pa, the mean free path of various molecules is short and the step coverage is excellent. Due to this effect, when a protective film 20 having a thickness of 0.6 μm is formed on the surface of the organic EL element substrate 10, the thickness of the protective film 20 on the side surface (end surface A in FIG. 1) is about 0.3 μm. Since the protective film 20 is composed of a dense layer as described above even in a thin portion having a thickness of about 0.3 μm, the moisture resistance is sufficient. Thus, the protective film 20 completely covers the organic material layer 13 and the electron injection electrode layer 14 and sufficiently exhibits moisture resistance.

When the protective film 20 is formed, the organic material layer 13 is inevitably heated, but in this embodiment, the protective film having a thickness of 0.6 μm is not continuously formed, and the silicon hydronitride layer 15a, Since the forming process 16a is included, the organic EL element substrate 10 is not exposed to a high temperature of 90 ° C. or higher. Further, in the formation process of the silicon hydronitride layers 15a and 16a, the organic EL element substrate 10 is cooled by H ₂ gas and He gas, so that the organic layer 13 is not deteriorated by heating. This effect is particularly prominent when a low molecular weight organic material having low heat resistance is used as the organic material layer 13.

  As described above, in the manufacturing method of the present embodiment, the same SWP-CVD apparatus 100 can be used to manufacture the multi-layered protective film 20 having excellent moisture resistance simply by changing the process conditions. Since the organic EL element substrate 10 is not exposed to the atmosphere during the production of the protective film 20, the protective film 20 is a clean film that does not adsorb moisture or oxygen.

  The organic EL device 1 manufactured by the above method was subjected to an environmental test under conditions of 60 ° C.-90% RH and 500 hours, and then the positive terminal was used for the hole injection electrode layer 12 and the negative terminal was used for the electron injection electrode layer 14. And a DC voltage was applied. As a result, no non-light emitting portion (dark spot) was observed in the light emitting layer in the organic material layer 13, and the luminance was not lowered as compared with that before the environmental test. Further, the electron injecting electrode layer 14 is not oxidized or rusted, and the moisture resistance of the protective film 20 is sufficiently high.

In this embodiment, the SWP-CVD apparatus has been described as the film forming apparatus for the protective film 20, but a CVD apparatus using electron cyclotron resonance (ECR) plasma or inductively coupled plasma (ICP) can also be used. The SWP-CVD apparatus, the ECR-CVD apparatus, and the ICP-CVD apparatus can obtain high-density plasma with an electron density of about 10 ¹² cm ⁻³ and have an ion energy as small as about 10 to 20 eV. Therefore, compared with other plasma CVD apparatuses, there is an advantage that decomposition of the material gas, chemical reaction with the reactive gas, and the like are performed efficiently, and damage and heating due to ion bombardment on the substrate are very small.

  Hereinafter, modifications of the present embodiment will be described. In the present embodiment, the protective film 20 of the organic EL element 1 is composed of five layers including a silicon nitride layer 15, a hydrogenated silicon nitride layer 15 a, a silicon nitride layer 16, a hydrogenated silicon nitride layer 16 a, and a silicon nitride layer 17. However, as long as the silicon nitride layer and the hydrogenated silicon nitride layer are stacked, the protective film may be formed of two or more layers. The outermost layer in the protective film may be either a silicon nitride layer or a hydrogenated silicon nitride layer.

  As described above, the protective film 20 is formed as a plurality of layers composed of a silicon nitride layer and a silicon hydronitride layer, and the protective film 20 is highly moisture-proof and has reduced internal stress. The organic EL element 1 of the present embodiment has improved moisture resistance and reliability as a device. Further, the protective film 20 is highly transparent and can sufficiently cope with top emission. Moreover, since the formation process of the silicon hydronitride layers 15a and 16a is included when forming the protective film 20, the organic EL element substrate 10 is not exposed to high temperature, and the organic layer 13 is deteriorated by heating. Nor. The present invention is not limited to the embodiments described above as long as the characteristics are not impaired.

It is a fragmentary sectional view of the organic EL element concerning an embodiment of the invention. It is sectional drawing which shows schematic structure of the surface wave excitation plasma CVD apparatus used for the manufacturing method of the organic EL element which concerns on embodiment of this invention.

Explanation of symbols

1: Organic EL device (organic electroluminescence device)
10: Organic EL element substrate 11: Transparent substrate 12: Hole injection electrode layer (anode)
13: Organic layer 14: Electron injection electrode layer (cathode)
15, 16, 17: Silicon nitride layer 15a, 16a: Hydrogenated silicon nitride layer 20: Protective film 100: SWP-CVD apparatus (surface wave excitation plasma CVD apparatus)
A: End face

Claims (2)

Forming a hole injection electrode layer on the substrate;
  Forming an organic layer on the hole injection electrode layer;
  Forming an electron injection electrode layer on the organic layer;
  Forming a protective film by laminating at least two silicon nitride layers and one hydrogenated silicon nitride layer in order on the exposed surfaces of the electron injection electrode layer and the organic material layer;
  The protective film is formed by a film forming method using high-density plasma,
  The hydrogenated silicon nitride layer is formed on the surface of the silicon nitride layer with the formation of the high density plasma stopped. ₂ A method for producing an organic electroluminescence element, wherein the organic electroluminescence element is formed by applying a gas. In the manufacturing method of the organic electroluminescent element of Claim 1,
The method of manufacturing an organic electroluminescence element, wherein the high-density plasma film forming method is a film forming method using surface wave excitation plasma, electron cyclotron resonance plasma, or inductively coupled plasma.

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