In recent years, flat panel displays are used in various commodity products and fields, and thus flat panel displays are required to have a large size, high image quality and low power consumption.
Under the circumstances, organic EL display devices, which include an organic EL element that utilizes electro luminescence of an organic material, are attracting great attention as all-solid state flat panel displays that are excellent as having capability of low voltage operation, quick responsivity and light emission.
Active matrix type organic EL display devices, for example, are provided with a thin film-like organic EL element on a substrate having a TFT (thin film transistor). In the organic EL element, organic EL layers including a light emitting layer are laminated between a pair of electrodes. The TFT is connected to one of the pair of electrodes. Then, voltage is applied across the pair of electrodes so as to cause the light emitting layer to emit light, whereby an image is displayed.
In a full-color organic EL display device, generally, organic EL elements including light emitting layers of respective colors of red (R), green (G) and blue (B) are formed and arranged on a substrate as sub-pixels. By causing these organic EL elements to selectively emit light at the desired brightness by using the TFT, a color image is displayed.
In order to manufacture an organic EL display device, it is necessary to form a light emitting layer made of organic light emitting materials that emit respective colors in a predetermined pattern for each organic EL element.
Known methods for forming light emitting layers in a predetermined pattern are vacuum vapor deposition method, inkjet method and laser transfer method. For example, the vacuum vapor deposition method is often used for low molecular organic EL display devices (OLEDs).
In the vacuum vapor deposition method, a mask (also called a “shadow mask”) having a predetermined pattern of openings is used. The deposition surface of a substrate having the mask closely fixed thereto is disposed so as to oppose a vapor deposition source. Then, vapor deposition particles (film forming material) from the vapor deposition source are deposited onto the deposition surface through the openings of the mask, whereby a predetermined pattern of a coating film is formed. Vapor deposition is performed for each color of the light emitting layer, which is referred to as “vapor deposition by color”.
Patent Document 1 describes a vapor deposition device in which a plurality of line vapor deposition sources that respectively include slot-shaped discharge openings are disposed such that the longitudinal directions of the discharge openings are parallel to each other and a limiting plate is provided between the neighboring line vapor deposition sources in order to prevent a vapor deposition material from mixing. A substrate to which a vapor deposition mask is closely fixed is moved relative to the plurality of line vapor deposition sources in a direction orthogonal to the longitudinal directions of the discharge openings. The plurality of line vapor deposition sources include three line vapor deposition sources that respectively discharge, for example, an organic hole injection material, an organic hole transport material, and an organic light emitting material. Accordingly, a hole injection layer, a hole transport layer and a light emitting layer can be formed on a substrate in this order via mask openings of the vapor deposition mask.
Meanwhile, it is known that in an organic EL element, a light emitting layer is formed by using a doping method with which an additive called a “dopant” is added to a parent material called a “host” in order to obtain a desired luminescent color, to improve the light-emission efficiency, or the like.