Plasma-processing apparatus with upper electrode plate and method for performing plasma treatment process

A plasma-processing apparatus, comprising:

• a processing chamber having an upper portion and a lower portion, wherein the upper portion has a gas inlet;
• an upper electrode plate disposed in the upper portion, wherein the upper electrode plate has a central portion and a peripheral portion surrounding the central portion, the upper electrode plate has a plurality of first gas holes passing through the central portion and a plurality of second gas holes passing through the peripheral portion, and a first diameter of the first gas hole is greater than a second diameter of the second gas hole;
• a protective layer disposed over inner walls of the first gas holes;
• and
• a lower electrode pedestal disposed in the lower portion for supporting a substrate.