1. Field of the Invention
The present invention belongs to a technical field related to a display device in which a semiconductor device (typically, a transistor) is used as a device, in particular, a light emitting device represented by an electroluminescence display device, and to a technical field related to an electronic apparatus equipped with the display device in an image display portion.
2. Description of the Related Art
In recent years, development of liquid crystal display devices and electroluminescence display devices in which transistors (particularly, thin film transistors) are integrated on a substrate have progressed. Such display devices are respectively characterized in that the transistors are formed on a glass substrate by using a thin film formation technique, and the transistors thus formed are disposed in pixels each arranged in matrix and made to function as a display device for image display.
A variety of specifications are conceivable, which are required for areas (hereinafter, referred to as pixel portions), in which the image display is performed in the display device. However, the following are given as examples thereof: a large number of dots and high definition are ensured; an area of an effective display region in each pixel is large and bright image display is possible; and the pixel portion involves no defects that may induce point defects or line defects in its entirety. In order to achieve those specifications, not only the performance of the transistors arranged in each pixel should be satisfactory but also a technique of forming the transistors while increasing yield through a stable process is necessary.
Further, in an organic electroluminescence display device among the electroluminescence display devices, an organic compound is used for a light emitting element serving as a light emitting source. Accordingly, a measure for suppressing deterioration of the organic compound is most highly required in ensuring its reliability. In other words, in order to achieve a highly reliable display device, attention must be paid not only to an influence of an accumulated damage in the process during manufacturing the device but also to the subsequent deterioration with time, which results from the accumulated damage.
In the above-mentioned circumstances of development, the applicants of the present invention are most concerned, in the present conditions, with problems such as variation and shift of a threshold voltage in the transistors, which arise due to the accumulation of plasma damages on an insulating film etc. in an etching process.