1. Field of the Invention
The present invention relates to a manufacturing apparatus used for film formation of a material that can be formed into a film by evaporation (hereinafter referred to as evaporation material) and a manufacturing method of a light emitting device typified by an EL element. In particular, the present invention relates to a technique using an organic material as the evaporation material and being effective when manufacturing a light emitting device. Note that the term “light emitting device” in this specification refers to an image display device, a light emitting device, or a light source (including illuminating devices). Also included in the definition of the light emitting device are: a module in which a connector such as an FPC (flexible printed circuit), a TAB (tape automated bonding) tape, or a TCP (tape carrier package) is attached to a light emitting device; a module in which a printed wiring board is provided on the tip of a TAB tape or a TCP; and a module in which an IC (integrated circuit) is mounted directly to a light emitting element by a COG (chip on glass) method.
2. Description of the Related Art
In recent years, the research of light emitting devices using an EL element as a self-luminous element has become active. In particular, light emitting devices using an organic material as an EL material are attracting more attention. The light emitting devices are called organic EL displays (OELD) or organic light emitting diodes (OLED).
Note that an EL element has a layer (hereinafter referred to as EL layer) containing an organic compound in which luminescence developed by applying an electric field (electroluminescence) is obtained, an anode, and a cathode. The types of the organic compound luminescence includes light emission when returning from a singlet excitation state to a ground state (fluorescence) and light emission when returning from a triplet excitation state to a ground state (phosphorescence). Both types of light emission can be applied to a light emitting device produced by a film forming apparatus and a film formation method according to the present invention.
Unlike liquid crystal display devices, light emitting devices are of a self-luminous type, thereby causing no problem of a view angle. More specifically, the light emitting devices are more suitable as a display used outside than the liquid crystal displays. Thus, the use of the light emitting devices in various forms has been proposed.
An EL element has a structure in which an EL layer is sandwiched between a pair of electrodes, and the EL layer normally has a laminate structure. A typical example of the laminate structure is one composed of “a hole transporting layer/a light emitting layer/and an electron transporting layer”. Most of the light emitting devices currently under research and development adopt the structure due to its extremely high light emitting efficiency.
Alternatively, another laminate structure may be used in which: a hole injecting layer, a hole transporting layer, a light emitting layer, and an electron transporting layer are laminated onto an anode in the stated order; or a hole injecting layer, a hole transporting layer, a light emitting layer, an electron transporting layer, and an electron injecting layer are laminated onto an anode in the stated order. Fluorescent pigments and the like may also be doped into the light emitting layers. Further, all of the above layers may be formed using only low-molecular weight materials, or may be formed using only high-molecular weight materials.
Further, EL materials used to form an EL layer are broadly divided into low-molecular weight (monomer-based) materials and high-molecular weight (polymer-based) materials, while the low-molecular weight materials are formed into films mainly by evaporation.
The EL material is extremely likely to deteriorate, because the EL material is easily oxidized due to presence of oxygen or moisture. Thus, a photolithography step cannot be performed after film formation. In order to form a pattern, it is necessary to use a mask (hereinafter referred to as evaporation mask) having an opening portion to separate out the pattern region at the same time of the film formation. Therefore, most of the sublimated organic EL materials are adhered to an inner wall of a film forming chamber or an adhesion proof shield (protective plate for preventing an evaporation material from adhering to the inner wall of the film forming chamber). As a result, an evaporation apparatus needs regular maintenance such as a cleaning process for removing adhered substances from the inner wall of the film forming chamber and the adhesion proof shield, thereby making it inevitable to temporarily stop a manufacturing line for mass production during the maintenance.
In order to improve uniformity of a film thickness, conventional evaporation apparatuses have a larger interval between a substrate and an evaporation source, so that the apparatuses per se have a larger size. Also, the conventional evaporation apparatuses have a structure, as shown in FIG. 22, in which the interval between a substrate and an evaporation source is set to 1 m or more and the substrate is rotated to obtain a film having a uniform thickness. Further, the evaporation apparatuses have such a structure as to rotate the substrate, so that there is a limitation on an evaporation apparatus for attaining a large-area substrate. Also, the interval between a substrate and an evaporation source is large, so that a speed of film formation is reduced and a longer time is necessary to exhaust a film forming chamber, thereby reducing the throughput.
In addition, in the conventional evaporation apparatuses, the utilization efficiency of an expensive EL material is as extremely low as approximately 1% or low. Thus, the manufacturing costs of a light emitting device are extremely high.
An EL material is extremely expensive and costs higher per gram than gold costs per gram. Therefore it is desired to use an EL material as efficiently as possible. However, in the conventional evaporation apparatuses, the utilization efficiency of the expensive EL material is low.