Field of the Invention
The present invention relates to a metal plate for use in manufacturing a deposition mask with a plurality of through-holes formed therein.  In addition, the present invention relates to a method of manufacturing the metal plate.  In addition, the present invention relates to a method of manufacturing a deposition mask with a plurality of through-holes formed therein, by using the metal plate. 
Background Art
A display device used in a portable device such as a smart phone and a tablet PC is required to have high fineness, e.g., a pixel density of 300 ppi or more.  In addition, there is increasing demand that the portable device is applicable in the full high-definitions standard.  In this case, the pixel density of the display device needs to be 450 ppi or more, for example. 
An organic EL display device draws attention because of its excellent responsibility and low power consumption.  A known method of forming pixels of an organic EL display device is a method which uses a deposition mask including through-holes that are arranged in a desired pattern, and forms pixels in the desired pattern.  To be specific, a deposition mask is firstly brought into tight contact with a substrate for organic EL display device, and then the substrate and the deposition mask in tight contact therewith are put into a deposition apparatus so as to deposit an organic material and so on.  In general, a deposition mask can be manufactured by forming through-holes in a metal plate by means of an etching process using photolithographic technique (for example, Patent Document 1).  For example, a resist film is firstly formed on the metal plate.  Then, the resist film, with which an exposure mask is in tight contact, is exposed to form a resist pattern.  Thereafter, through-holes are formed by etching areas of the metal plate, which are not covered with the resist pattern. 
Patent Document 1: JP2004-039319A