JP2005339828A - Organic electroluminescent element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element with high reliability free from deterioration due to moisture or oxygen in the atmosphere. <P>SOLUTION: The organic electroluminescent element 1 is provided with a hole injection electrode layer 12, an electron injection electrode layer 14, an organic material layer 13 pinched between the hole injection electrode layer 12 and the electron injection electrode layer 14, and a protective film 20 coating an exposed face each of the electron injection electrode layer 14 and the organic material layer 13. A silicon nitride film is used for the protective film. The silicon nitride film is made by using film-forming gas of SiH<SB>4</SB>, NH<SB>3</SB>, and Ar in a high-density plasma CVD method. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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. doing. Conventionally, as this kind of protective film, a silicon nitride film (SiNx) formed by using a deposition gas of SiH ₄ , N ₂ , and H ₂ by a high-density plasma CVD method is known (Patent Document 1). In addition, it is known that a silicon nitride film is formed as a protective film using a deposition gas of SiH ₄ , NH ₃ , and N ₂ by a CVD method (Patent Document 2).

JP 2004-63304 A JP-A-6-267941

When a silicon nitride film is formed by using a high-density plasma CVD method described in Patent Document 1 and using a deposition gas of SiH ₄ , N ₂ , and H ₂ , the content of H in the silicon nitride film is small. There is a problem that it is difficult to adjust the stress of the silicon nitride film and the film hardness by controlling the H content in the silicon nitride film. On the other hand, when a silicon nitride film is formed by a high-density CVD method using SiH ₄ , NH ₃ , and N ₂ film forming gases described in Patent Document 2 instead of SiH ₄ , N ₂ , and H ₂ film forming gases, Since the ionization rate of the film forming gas is high, the film forming speed is too high, and it is difficult to control the silicon nitride film forming speed and the grain growth.

According to a first aspect of the present invention, there is provided a method of manufacturing an organic electroluminescence device comprising: forming a hole injection electrode layer on a substrate; forming an organic layer on the hole injection electrode layer; and forming an electron on the organic layer. In the method of manufacturing an organic electroluminescent element, comprising the step of forming an injection electrode layer, and the step of forming a protective layer on the exposed surface of the electron injection electrode layer and the organic material layer, the protective layer is a silicon nitride layer, The silicon nitride layer is formed by a high density plasma CVD method, and SiH ₄ gas, NH ₃ gas, and Ar gas are used as a film forming gas for forming the silicon nitride layer.
According to a second aspect of the present invention, in the method of manufacturing an organic electroluminescence element according to the first aspect, the silicon nitride layer is formed by a surface wave excitation plasma CVD apparatus.
The organic electroluminescence device according to the invention of claim 3 is manufactured by the manufacturing method of claim 1 or 2.

  According to the present invention, the film growth rate and grain growth rate of a silicon nitride film can be controlled, so that a protective film with low gas permeability and low internal stress can be produced, and highly reliable organic electroluminescence. An 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 is silicon nitride.

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 organic layer 13 includes a hole transport layer 13a, a light emitting layer 13b, and an electron transport layer 13c. For example, the hole transport layer 13a has a triphenylamine derivative (MTDATA) and the light emitting layer 13b has 8-hydroxyquinoline aluminum (Alq). ₃ ) 10-benzo (h) -quinolyl-beryllium complex (BeBq ₂ ) is used for the electron transport layer 13c. 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 by forming a 1.0 μm thick silicon nitride layer on the electron injection electrode layer 14. As shown in FIG. 1, the protective film 20 is formed not only to cover the surface of the electron injection electrode layer 14 but also to cover the end face A where the organic material layer 13 and the electron injection electrode layer 14 are exposed. Is done. 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.

Next, functions of the layers constituting the protective film 20 will be described. In general, silicon nitride is a hard ceramic represented by the chemical formula SiNx, and Si ₃ N ₄ is a representative one. The silicon nitride layer itself is a very dense film and has excellent moisture resistance due to low gas permeability.

  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 on the transparent substrate 11 having a thickness of 0.5 mm as a hole injection electrode layer 12 by vacuum deposition.

On the ITO film, 50 nm thick MTDATA as the hole transport layer 13a, 60 nm thick Alq ₃ as the light emitting layer 13b, and 50 nm thick BeBq ₂ as the electron transport layer 13c are sequentially formed by resistance heating vapor deposition, An organic layer 13 is formed. 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 transported into the surface wave excitation plasma CVD apparatus 100 shown in FIG. 2 to form a protective film. FIG. 2 is a cross-sectional view showing a schematic configuration of the surface wave excitation plasma CVD apparatus. A surface wave excited 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 excited plasma (SWP: It is called “Surface Wave Plasma”.

  In FIG. 2, the SWP-CVD apparatus 100 includes a chamber 101, a microwave waveguide 102, a termination matching unit 103, a slot antenna 104, a dielectric plate 105, a side reflector 106, a process gas introduction pipe 107, and a material gas introduction pipe 108. The vacuum exhaust pipe 109 and the substrate holder 110 are provided. The chamber 101 is a sealed container for forming a film on the surface of the substrate 10 held by the substrate holder 110 using the surface wave excitation plasma P generated in the internal space. The substrate holder 110 can be moved and rotated in the vertical direction, and is configured to be able to heat, cool, apply an electric field, etc., as necessary, to the substrate 10 to be deposited.

  A dielectric plate 105 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 105. A plurality of slot antennas 104 having long rectangular openings are provided on the bottom plate of the microwave waveguide 102 in contact with the dielectric plate 105.

Of the deposition gas, NH ₃ gas and Ar gas are introduced into the chamber 101 from the process gas introduction pipe 107. Of the film forming gas, SiH ₄ gas is introduced into the chamber 101 as a material gas from the material gas introduction pipe 108.

  A vacuum exhaust pipe 109 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 107 and the material gas introduction pipe 108, 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 from the microwave generation source into the microwave waveguide 102, and the TE10 mode electromagnetic wave standing wave is transmitted by the termination matching unit 103. T is generated. The standing wave T is radiated to the dielectric plate 105 from the slot antenna 104 installed at the wavelength interval of the standing wave T. The electromagnetic wave radiated from the slot antenna 104 propagates inside the dielectric plate 105 and generates a unique standing wave in a range surrounded by the side reflector 106. Then, a surface wave SW is generated on the surface of the dielectric plate 105. The surface wave SW ionizes and dissociates the film forming gas immediately below the dielectric plate 105 to generate surface wave excited plasma P.

The surface-wave-excited plasma P has an electron density equal to or higher than the cut-off density of the microwave, totally reflects the electromagnetic wave at the plasma interface, and does not absorb the electromagnetic wave into the plasma. The ion energy maintains a low temperature of 10 eV or less. In the surface wave excitation plasma P, energy is transferred between the surface of the dielectric plate 105 and the plasma boundary surface, and high-energy plasma is distributed only in the vicinity of the surface of the dielectric plate 105, and the index increases as the distance from the dielectric surface increases. The energy level decreases functionally. At a distance of about 200 mm from the dielectric plate 105, the ion energy is 20 ev or less. As described above, since the high-energy region and the low-energy region are generated in the surface wave-excited plasma P, radicals are generated in the high-energy region and a material gas such as SiH ₄ is introduced into the low-energy region. Generation and low-damage high-speed film formation are possible.

  Since the surface wave SW spreads over the entire inner surface of the dielectric plate 105, the surface wave plasma P also spreads in the corresponding region in the chamber 101. Therefore, it is possible to cope with a large area by expanding the dielectric plate 105. The protective film 20 is formed on the organic EL element substrate 10 using the surface wave excitation plasma P.

Next, the manufacturing process of the silicon nitride layer which is the protective film 20 of the organic EL element 1 of this Embodiment is explained in full detail.
The organic EL element substrate 10 is set on the substrate holder 110 and the chamber 101 is evacuated to a high vacuum of about 0.01 Pa. NH ₃ gas and Ar gas are respectively introduced into the chamber 101 through the process gas introduction pipe 107, SiH ₄ gas is introduced into the chamber 101 through the material gas introduction pipe 108, and the pressure inside the chamber 101 is maintained at 4.5 Pa. To do. A film formation is performed for 4 minutes by the surface wave plasma P generated by the microwave power of 2.8 kW to form the silicon nitride layer 20 having a thickness of 1.0 μm. The gas flow rates in this case were SiH ₄ gas, 50-80 sccm, NH ₃ gas, 80-100 sccm, and Ar gas, 300 sccm. The substrate temperature is 80 ° C. or lower.

Next, FIG. 3 shows the characteristics of the silicon nitride layer manufactured by the above manufacturing process. Sample numbers 1 to 4 are silicon nitride layers produced using the deposition gas of SiH ₄ , NH ₃ , and Ar according to the present invention. For comparison, Sample Nos. 5 and 6 also show the characteristics of a silicon nitride layer manufactured using SiH ₄ , NH ₃ , and N ₂ film forming gases. The gas permeability was measured by the Mocon method.

The internal stress of the silicon nitride layers of Sample Nos. 1 to 4 manufactured using SiH ₄ , NH ₃ , and Ar film forming gases is as small as 30 to 78 MPa. On the other hand, the internal stress of the silicon nitride layers of Sample Nos. 5 and 6 produced using SiH ₄ , NH ₃ and N ₂ film forming gases is as large as 90 to 178 MPa. From this, it can be understood that the protective film 20 of the organic EL element 1 having a small internal stress can be manufactured by forming a silicon nitride layer using a film forming gas of SiH ₄ , NH ₃ , and Ar. Therefore, as described in Patent Document 1, it is not necessary to alternately stack a silicon nitride layer having a compressive stress and a silicon nitride layer having a tensile stress, and even if it is a single layer, the organic EL element 1 is distorted. Don't make it happen.

The gas permeability of the silicon nitride layers of Sample Nos. 1 to 4 manufactured using SiH ₄ , NH ₃ , and Ar film forming gases is as low as 0.03 to 0.20 g / cm ² · day. On the other hand, the gas permeability of the silicon nitride layers of Sample Nos. 5 and 6 produced using SiH ₄ , NH ₃ and N ₂ film forming gases is as large as 0.26 to 0.39 g / cm ² · day. From this, it can be seen that the protective film 20 of the organic EL element 1 having a low gas permeability can be manufactured by forming a silicon nitride layer using a film forming gas of SiH ₄ , NH ₃ , and Ar.

The internal stress and gas permeability of the silicon nitride layer produced by using the high-density plasma CVD method using the SiH ₄ , NH ₃ , and Ar film forming gases are SiH ₄ , NH ₃ , and N ₂ film forming gases. The reason why it is smaller than the silicon nitride layer manufactured in this way is as follows.
If a film forming gas of SiH ₄ , NH ₃ , or N ₂ is used in the high-density plasma CVD method, the N ₂ gas reacts with Si even during the formation of the silicon nitride film, so that the film forming speed becomes too high and the internal stress is increased. It becomes difficult to set conditions for producing a small protective film having a low gas permeability.

On the other hand, when Ar gas is used instead of N ₂ , Ar gas is involved only in the dissociation of SiH ₄ and NH ₃ and not in the reaction during the formation of the silicon nitride film. Even if it is fabricated, the film growth rate and grain growth rate of the silicon nitride film are not so fast that they cannot be controlled. For example, by controlling the introduction rate of the material gas, the film growth rate can be controlled in the range of 500 Å to 1500 ガ ス / min. Therefore, by using Ar gas, the film growth rate and grain growth rate of the silicon nitride film can be controlled. That is, by adjusting the film growth rate and the grain growth rate, the silicon nitride film has a dense structure with a small crystal grain size, and at the same time, by adjusting the flow rates of SiH ₄ and NH ₃ , the silicon nitride film Si The number of —H groups can be increased. Therefore, the protective film 20 with low internal stress and low gas permeability can be produced.

In forming the silicon nitride film, the following advantages can be obtained as another effect of using Ar gas instead of N ₂ .
When N ₂ gas is used, since Si and N ₂ gas react, energy for dissociating the film forming gas is consumed by the reaction. On the other hand, since Ar gas does not react with Si, energy for dissociating the film forming gas is not consumed. Therefore, when Ar gas is used, the microwave output of the SWP-CVD apparatus 100 can be reduced as compared with the case where N ₂ gas is used.

  In this embodiment, the pressure in the chamber 101 is relatively low at 4.5 Pa, which is excellent in step coverage. Thereby, if the protective film 20 having a thickness of 1.0 to 2.0 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 0.5 to 1. 0.0 μm. Since the protective film 20 completely covers the organic material layer 13 and the electron injection electrode layer 14, the moisture resistance is sufficiently exhibited.

  When the protective film 20 is formed, the organic material layer 13 is inevitably heated, but in this embodiment, the time for forming the protective film having a thickness of 1.0 μm is as short as 4 minutes and the film is continuously formed. Even in this case, the maximum temperature of the silicon nitride film is 80 ° C. or less (FIG. 3). Therefore, there is no thermal effect on the structure and structure of the organic material layer 13, and the stability of light emission and the light emission lifetime can be ensured. Further, it is not necessary to cool the protective film 20 when it is formed. 3 reaches 85 ° C., and sample number 6 reaches 100 ° C.

According to such a method of manufacturing an organic electroluminescence element, the following effects can be obtained.
(1) Since the film growth rate and grain growth rate of the silicon nitride film can be controlled, a protective film with low gas permeability and low internal stress can be produced.
(2) Since the protective film completely covers the organic material layer and the electron injection electrode layer, the moisture-proof property is sufficiently exhibited.
(3) Since the temperature at the time of forming the silicon nitride film is low, the organic matter in the organic matter layer is not deteriorated by heat, and the light emission stability and the light emission lifetime can be ensured.

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.

  In the present embodiment, the silicon nitride film of the present invention is used as a protective film for an organic electroluminescence element (organic EL element), but is used as a moisture-proof film for a film substrate when a film substrate is used as a transparent substrate for the organic EL element. May be. Moreover, you may use as a moisture-proof film | membrane of the color conversion filter used for full color realization of an organic EL element.

As described above, a silicon nitride film is produced by using SiH ₄ , NH ₃ , and Ar as a deposition gas by a high-density plasma CVD method, so that the film quality can be controlled, the moisture resistance is high, and the internal stress is high. The reduced protective film 20 can be manufactured. And the organic EL element by this Embodiment improves the moisture resistance and reliability as a device. 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. It is a figure which shows the characteristic of the silicon nitride film concerning 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)
20: Protective film 100: SWP-CVD apparatus (surface wave excitation plasma CVD apparatus)
A: End face

Claims (3)

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;
In the method for manufacturing an organic electroluminescent element, comprising the step of forming a protective layer on the exposed surface of the electron injection electrode layer and the organic material layer,
The protective layer is a silicon nitride layer;
The silicon nitride layer is formed by a high density plasma CVD method,
A method of manufacturing an organic electroluminescence element, wherein SiH ₄ gas, NH ₃ gas, and Ar gas are used as a film forming gas for forming the silicon nitride layer. In the manufacturing method of the organic electroluminescent element of Claim 1,
The method of manufacturing an organic electroluminescence element, wherein the silicon nitride layer is formed by a surface wave excitation plasma CVD apparatus.   The organic electroluminescent element manufactured by the manufacturing method of Claim 1 or 2.

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