A typical example of the flexible display includes a film which is made of a synthetic resin such as polyimide (hereinafter, referred to as “plastic film”), and elements supported by the plastic film, such as TFTs (Thin Film Transistors) and OLEDs (Organic Light Emitting Diodes). The plastic film functions as a flexible substrate. The flexible display is encapsulated with a gas barrier film (encapsulation film) because an organic semiconductor layer and an electrode layer which are constituents of the OLED are likely to deteriorate due to water vapor.
Production of the above-described flexible display is carried out using a glass base on which a plastic film is formed over the upper surface (flexible display supporting substrate). The glass base functions as a support for keeping the shape of the plastic film flat during the production process. Elements such as TFTs and OLEDs, a gas barrier film, and the other constituents are formed on the plastic film, whereby the structure of a flexible device is realized while it is supported by the glass base. Thereafter, the flexible device is separated from the glass base and gains flexibility. The entirety of a portion in which elements such as TFTs and OLEDs are arrayed is also referred to as “functional layer”.
A foreign substance such as particles (hereinafter, also referred to as “contamination”) is likely to adhere to the surface of a plastic film supported by a glass base. The contamination can deteriorate the device characteristics and the gas barrier film. A particle whose diameter is greater than, for example, 0.5 μm (typically, a particle which has a height of 1 μm to 5 μm) can be a cause of defects in TFTs, a cause of short-circuit or breakage of wires in the functional layer, or a cause of formation of a leak path for water vapor in the gas barrier film.
Patent Document No. 1 discloses a minute protrusion polishing apparatus for polishing away minute protruding portions on a flat plate by bringing a polishing tape into contact with the minute protruding portions. When such a protrusion polishing apparatus is used, particles can be removed by polishing.
Patent Document No. 2 discloses the technique of applying a mixture prepared by dissolving an insulative material in a solvent from the tip of a needle to defective portions such as a foreign substance on a pixel electrode and raised and recessed portions so as to cover these defective portions. The mixture is in the form of a liquid when it is applied. By subsequent heating, the mixture changes into a solidified insulating film. The insulating film that covers the defective portions suppresses occurrence of an abnormal electric current which is attributed to the defective portions.