Shower head electrode assembly and plasma processing apparatus

A shower head electrode assembly of a plasma processing apparatus, comprising:

• an electrode having a plurality of first gas flow paths and having a surface exposed to plasma;
• and a backing member attached to the electrode and having a plurality of second gas flow paths which communicate with the plurality of first gas flow paths, wherein each of the plurality of second gas flow paths is a slit-shaped elongated hole, each slit-shaped elongated hole has a traversed width D3 less than the circumference of the backing member, and is configured such that a length of the elongated hole in radial direction is longer than a length of the elongated hole in circumferential direction with respect to a central axis of the shower head electrode assembly, the backing member includes a support surface that contacts a back surface of the electrode and an opposite surface that is opposite to the support surface, the elongated hole is chamfered at an opening on the opposite surface of the backing member, the traversed width D3 of the slit-shaped elongated hole of each of the plurality of second gas flow paths is greater than a sum of diameters of at least two of the plurality of first gas flow paths, and the at least two of the plurality of first gas flow paths are located within the traversed width D3 of the slit-shaped elongated hole of each of the plurality of second gas flow paths.