JP2005310575A - Method of forming thin film of organic material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit an inclination of a boat-type evaporation source caused by the heating expansion and distortion thereof. <P>SOLUTION: In a method of forming a thin film of an organic material using a thin film forming apparatus having a substrate for forming a thin film and a boat-type evaporation source for vaporizing a material in a vacuum chamber, both ends of the boat-type evaporation source into which the organic material is filled are fixed to electrodes, and the source is heated by resistance-heating. One electrode of a power supply for heating is not fixed to a body of a vapor deposition machine. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming an organic material thin film for an organic EL element.

  Electroluminescent elements using electroluminescence (hereinafter referred to as EL elements) are highly visible due to self-emission and have excellent characteristics such as impact resistance because they are completely solid. Attention has been paid. There are inorganic EL elements using inorganic compounds and organic EL elements using organic compounds. Among these EL elements, organic EL elements can significantly reduce the applied voltage, so next-generation self-luminous As a device, research into practical use has been actively conducted.

  An organic EL element is composed of an organic compound layer including a light emitting layer and a pair of electrodes sandwiching the organic compound layer. Specifically, the organic EL element is basically composed of an anode / light emitting layer / cathode, and includes a hole transport layer, Known are those provided with an electron transport layer as appropriate, such as anode / hole transport layer / light-emitting layer / cathode, and anode / hole transport layer / light-emitting layer / electron transport layer / cathode. In these organic EL devices, when a DC voltage of 3 to 20 V is applied between both electrodes, holes from the anode and electrons from the cathode are injected into the organic material layer, and organic matter emits light by recombination of the holes and electrons.

  As described above, the basic structure of the organic EL element is such that an organic thin film containing a light emitting material is formed between an anode and a cathode. The organic material forming the organic EL element is roughly classified into a polymer material obtained by polymerizing monomers and a low molecular material. In general, a polymer material is manufactured by application from a solution or an inkjet method. In the case of a low molecular material, an organic thin film is formed mainly by a vacuum deposition method.

  The vacuum evaporation method is a method of forming a thin film by evaporating an evaporation source filled with a material by heating it in vacuum and attaching it to the surface of a substrate facing the evaporation source. The basic configuration of the vapor deposition apparatus includes a vacuum layer, a vacuum exhaust system, an evaporation source, a shutter, and a substrate holder. As a heating method for heating the material, a resistance heating method, an electron beam heating method, a high-frequency heating method, and the like are known. As a method for evaporating an organic material used in an organic EL element, a resistance heating method is widely used because the configuration of a film forming apparatus is simple and a high-quality thin film can be formed at a low price. The evaporation source used in the resistance heating method includes a quartz crucible, a Knudsen cell, a boat type evaporation source processed into a boat shape from a thin plate-like refractory metal (tungsten, tantalum, molybdenum, etc.) Among these, the boat-type evaporation source is widely used because it has excellent operability and can be easily applied to many target substances.

Patent Document 1 can be cited as such a technique.
JP 2002-246175 A

  The boat-type evaporation source has a material accommodating portion at the center and an electrode extraction portion in the left-right direction, and is heated by fixing both ends of the electrode extraction portion to electrodes installed in the vacuum vapor deposition apparatus body and energizing them. At that time, the temperature of the boat-type evaporation source rises due to heat generated by energization, and extends according to the linear expansion coefficient of the boat metal material and the heated temperature.

  However, since the position of the electrode member that fixes both ends of the boat-type evaporation source is fixed to the main body of the vapor deposition machine as shown in FIG. 3, the boat-type evaporation source extended by heating maintains the shape before heating. Instead, the amount of elongation causes distortion, and the material container at the center of the boat-type evaporation source is inclined. As a result, a change occurs in the evaporation direction of the material, and the variation in the film thickness in the film formation substrate surface after vapor deposition becomes large. Since the organic EL element is a current-driven element, variations in film thickness have a large effect on the light emission characteristics of the element, and a non-uniform film causes variations in in-plane light emission and device life. . The improvement in the method for forming an organic material thin film using a boat-type evaporation source is described in, for example, Japanese Patent Application Laid-Open No. 2002-246175. It can be said that the method is suitable. However, there has not yet been reported an example in which film thickness variation reduction has been improved by paying attention to the inclination of the evaporation source due to expansion during the boat-type evaporation source energization heating.

  In order to solve the above problems, the means provided by the present invention can be achieved by the following invention.

  According to claim 1, in a method for forming an organic material thin film using a substrate for forming a thin film in a vacuum layer and a thin film forming apparatus having a boat type evaporation source for evaporating the material, boat type evaporation filled with an organic material is used. A method for forming an organic material thin film in which both ends of a source are fixed to an electrode and heated by resistance heating, wherein one of the electrodes is fixed to a vapor deposition machine main body, and the other electrode is not fixed to the vapor deposition machine main body It is characterized in that it is a method for forming an organic material thin film that is vacuum-deposited using a resistance heating electrode.

  According to the present invention, in the vapor deposition of an organic material by a resistance heating method using a boat-type evaporation source, it is possible to suppress the inclination of the boat-type evaporation source due to thermal expansion / distortion of the boat-type evaporation source, and a desired film thickness. An organic thin film having a distribution can be formed.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing the structure of a vacuum film forming apparatus for forming an organic material thin film of the present invention. In FIG. 1, a substrate 2 is disposed in the upper part of the vacuum layer 1 to form a film formation region. In addition, an evaporation source 7 is installed at the bottom of the vacuum layer, and the material can be evaporated by being energized and heated by the power source 6.

  Next, a detailed configuration around the evaporation source will be described. FIG. 2 is a schematic cross-sectional view showing a specific configuration example of the evaporation source peripheral member of the present invention. In FIG. 2, an electric power supply wiring 10 as an evaporation source peripheral member, an electrode 11 installed and fixed on the vapor deposition machine body, a movable electrode 12 not installed and fixed on the vapor deposition machine main body, a boat type evaporation source 13 and a boat type evaporation source support A jig 14 and a roller 15 are provided.

  A boat-type evaporation source 13 is arranged between an electrode 11 installed and fixed on the main body of the vapor deposition machine and a movable electrode 12 which is not installed and fixed on the main body of the vapor deposition machine, and both ends of the boat-type evaporation source 13 are connected to the both electrodes. And fix the connection. An electrode take-out part of the boat-type evaporation source 13 is provided in the electrode take-out part 17 of the boat-type evaporation source between the material storage part 16 of the boat-type evaporation source and the movable electrode 12 that is not installed and fixed to the vapor deposition machine body. The boat-type evaporation source support jig 14 that enables the horizontal movement of 17 and the roller 15 enable support. When the boat-type evaporation source 13 is heated by supplying a desired current to both electrodes, the boat-type evaporation source 13 is installed and fixed to the boat-type evaporation source 13 and the main body of the vapor deposition device according to the amount of elongation in the longitudinal direction due to the thermal expansion of the boat-type evaporation source 13. There is no movable electrode 12 to move horizontally. For this reason, the boat-type evaporation source 13 is only slid in the parallel direction due to the extension in the longitudinal direction, and is not distorted or tilted. As a result, the evaporation angle of the material is constant, and a stable organic thin film can be formed.

  The boat-type evaporation source support jig 14 is fixed to the vapor deposition machine body so that the vertical distortion can be suppressed and the height of the boat-type evaporation source can be kept constant. The boat-type evaporation source support jig 14 is made of an insulator so as not to affect the current flowing through the boat-type evaporation source 13. In addition, the installation surface with the boat-type evaporation source 13 is smooth, and has a function of promoting sliding in the parallel direction due to expansion of the boat-type evaporation source. Further, a roller 15 is disposed above the boat-type evaporation source support jig 14, and has a function of keeping the height of the boat-type evaporation source 13 constant and smoothing the slide in the horizontal direction.

  The boat-type evaporation source 13 needs to be electrically conductive, and is preferably made of a metal such as tungsten, tantalum, or molybdenum having a high melting point. In the schematic view of the present embodiment, as a type of boat-type evaporation source, as a boat for vapor deposition of a sublimable organic material, a partition plate is provided on the material container 16 and a communication hole is provided in the partition plate, and further a small hole is provided. Although the provided lid is used, there is no particular limitation on the presence and shape of the partition plate and lid, and a known metal boat evaporation source can be used. However, it is necessary to select those that chemically react with the evaporation material.

  As shown in FIG. 1, a substrate holder 3 is provided in the upper part of the vacuum layer 1, and the substrate 2 is placed in a desired position on the substrate holder 3 with the surface to be deposited facing downward. It comes to arrange. A mechanism (not shown) that can set the vapor deposition mask 4 can be appropriately provided thereunder. A shutter 9 supported by the support shaft 8 is disposed below the substrate 2 and the vapor deposition mask 4. In the above apparatus, the vapor deposition mask 4 is for pixels, and the shutter 9 is for vapor deposition material. The shutter 9 rotates about the support shaft 8 to block the vapor flow caused by heating of the evaporation material.

  However, there is no particular limitation on the vacuum deposition apparatus in which the configuration of the evaporation source peripheral member of this embodiment can be used. As a degree of vacuum for forming an organic material thin film necessary for manufacturing an organic EL element, a level of 10 −3 Pa or higher is usually used. What is necessary is just to use what can energize about 30-100A with respect to the boat-type evaporation source 13 as a power supply. The distance between the boat-type evaporation source 13 and the substrate 2 may be determined as appropriate according to the area of the deposition target substrate. It is preferable to provide a shutter mechanism between the boat-type evaporation source 13 and the substrate 2 so that impurities that evaporate before reaching the temperature necessary to obtain a predetermined evaporation rate do not adhere to the deposition target substrate. Further, it is preferable to dispose a film thickness monitor such as a crystal oscillator type for monitoring the evaporation rate.

  When depositing, first, the boat-type evaporation source 13 is filled with an organic material to be evaporated, and after the substrate 2 is mounted at a predetermined position, exhaustion in the vacuum layer 1 is started, and the vacuum in the vacuum layer of the vacuum deposition apparatus is started. The temperature is monitored with an ionization vacuum gauge, and after entering the 10-3 Pa range, the heating power source of the evaporation source is operated. The current value of the power source 6 is gradually increased while monitoring the evaporation rate with the film thickness monitor. Thereafter, when the desired evaporation rate (usually 0.5 to 5 liters / s) is reached, the shutter 9 is opened and vapor deposition is performed. In the case of this embodiment, it is preferable to perform vapor deposition with a constant evaporation rate on the film thickness monitor. When the predetermined film thickness is reached, the shutter 9 is closed, the power source 6 is turned off, and the deposition is finished.

  As described above, according to the present embodiment, in the formation of the organic thin film, both ends of the electrode take-out part of the boat-type evaporation source 13 are installed and fixed on the vapor deposition machine main body, and are not installed and fixed on the vapor deposition machine main body. Each of the movable electrodes 12 is connected and fixed, and the boat-type evaporation source supporting treatment is provided between the material storage portion 16 of the boat-type evaporation source 13 and the electrode extraction portion 17 between the movable electrode 12 that is not installed and fixed to the vapor deposition machine body. It is performed by a method using a configuration in which it is supported by the tool 14 and the roller 15, and both of the conventional ones as shown in FIG. 3 are installed and fixed on the vapor deposition machine main body whose position is fixed on the vapor deposition machine main body. This is different from the method using the configuration in which the boat-type evaporation source 13 is connected to the electrode 11. Therefore, the boat-type evaporation source 13 is only moved in the parallel direction due to extension in the longitudinal direction during energization heating, and distortion and inclination are greatly reduced. The evaporation angle is stable, and an organic thin film can be formed with little in-plane film thickness variation.

  A glass substrate 2 having a size of 76 mm × 76 mm × 1.1 mm was set on the substrate holder 3 disposed on the boat-type evaporation source 13 in the vacuum layer 1. As the vapor deposition mask 4, a plurality of metal masks having a unit opening of 3.0 mm × 3.0 mm were arranged close to the substrate. The boat-type evaporation source 7 was disposed directly under the substrate 2, and the distance between the boat-type evaporation source 13 and the substrate 2 was 270 mm. Tris (8-hydroxyquinoline) aluminum complex (Alq3) was used as the organic material 18 to be deposited.

  When depositing Alq3, a boat-type evaporation source 13 made of molybdenum was used. The overall size of the boat is 100mm x 12mm. This boat-type evaporation source 13 has a material container 16 filled with Alq3 powder as a recess, has a partition plate provided with a communication hole on it, and further has a lid provided with a small hole. Is. The length of the concave portion in the longitudinal direction of the material accommodating portion is 30 mm, the depth of the concave portion is 2 mm, and the length of the electrode extraction portions 17 on both sides thereof is 35 mm. The thickness of all members is 0.1mm.

  The boat-type evaporation source 13 was filled with 80 mg of Alq3 powder, and one end of each of the boat-type evaporation sources 13 was fixed to the electrode 11 that was installed and fixed to the vapor deposition machine body, and the other was fixed to the movable electrode 12 that was not installed and fixed to the vapor deposition machine body. It should be noted that the electrode extraction part 17 of the previous boat type evaporation source between the material container 16 of the previous boat type evaporation source 13 and the movable electrode 12 that is not installed and fixed to the main body of the previous vapor deposition machine has a 20 mm × A fluororesin boat-type evaporation source support jig 14 with a surface area of 20 mm is arranged, and a fluororesin roller 15 is arranged on the upper part of the previous electrode connection part to keep the height constant. The horizontal movement is now possible. After completing the installation of the boat-type evaporation source 13, evacuation was performed to 3.0 × 10 −4 Pa.

  In order to heat the material, the boat-type evaporation source 13 was gradually energized to increase the current value to 55A. Thereafter, the energization current value was adjusted so that the deposition rate was 5 Å / s. When the deposition rate reached 5 mm / s, the shutter 9 was opened, and Alq3 was deposited to a thickness of 600 mm.

  In order to examine the in-plane film thickness distribution of the Alq3 thin film produced, the film thickness distribution of the substrate after film formation was measured using a stylus-type film thickness meter. The film thickness of the thickest part was 603 mm. Thus, the thickness of the thinnest part was 574 mm. From the above results, the film thickness variation between the thickest part and the thinnest part was 4.8%. Further, when the boat-type evaporation source 13 after the vapor deposition was observed, the shape distortion and the inclination of the material container 16 were not observed.

(Comparative example)
For comparison, a vapor deposition machine having two electrodes 11 installed and fixed on the vapor deposition machine main body to which the boat type evaporation source 13 is connected as shown in FIG. 600 mm of film was formed on 2. In this comparative example, the method is the same as that of the example except that the state of the electrode of the vapor deposition machine main body to which the boat-type evaporation source 13 is connected is different.

  When the thickness distribution in the substrate surface of the prepared Alq3 thin film was measured, the film thickness of the thickest part was 592 mm, and the film thickness of the thinnest part was 538 mm. From the above results, the film thickness variation between the thickest part and the thinnest part was 9.1%. Further, when the boat-type evaporation source 13 after the vapor deposition was observed, the longitudinal direction thereof was slightly curved in a convex shape, and a slight inclination was observed in the material accommodating portion 16.

Schematic configuration sectional view showing a configuration of a vacuum film forming apparatus for forming an organic material thin film of the present invention Schematic configuration sectional view showing a specific configuration example of the evaporation source peripheral member of the present invention Schematic configuration sectional view showing a specific configuration example of a conventional evaporation source peripheral member Schematic configuration sectional view showing a specific configuration example of a boat-type evaporation source

Explanation of symbols

1 Vacuum layer
2 Board
3 Substrate holder
4 Deposition mask
5 Vacuum pump
6 Power supply
7 Evaporation source
8 Spindle
9 Shutter
10 Power supply wiring
11 Electrodes installed and fixed on the main body of the vapor deposition machine
12 Movable electrodes that are not fixed to the evaporator body
13 Boat-type evaporation source
14 Boat type evaporation source support jig
15 rollers
16 Material compartment
17 Electrode outlet
18 Organic materials

Claims (1)

  In a method for forming an organic material thin film using a substrate for forming a thin film in a vacuum layer and a thin film forming apparatus having a boat type evaporation source for evaporating the material, both ends of the boat type evaporation source filled with the organic material are electrodes A method of forming an organic material thin film that is fixed to the substrate and heated by resistance heating, wherein one of the electrodes is fixed to the vapor deposition machine main body, and the other electrode is not fixed to the vapor deposition machine main body. A method of forming an organic material thin film by vacuum deposition using a resistance heating electrode.

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