Patent ID: 8394231

Claim:
A plasma process system comprising: a chamber; an electrode plate having a projection in a center portion and being connected to a high-frequency power supply and provided with first gas holes for supplying a process gas into said chamber; a shield ring which is provided with second gas holes, having an opening formed to cover a periphery of said projection at a lower portion of said projection in the center portion of said electrode plate and placed in such a way that said projection of said electrode plate is fitted in said opening and exposed to the inside of said opening, wherein said electrode plate exposed to the inside of said opening comprises an exposed surface, said exposed surface is a major surface and forms a substantially flat surface together with said shield ring; and a hollow diffusion portion defined by surfaces of the electrode plate and shield ring, such that the same gas is supplied from the hollow diffusion portion to the first and second gas holes, wherein a blowoff diameter is delimited by a combination of the first gas holes and the second gas holes and a ratio of the blowoff diameter to a diameter of the exposed surface is equal to or greater than 1.1 and said shield ring is formed of an insulating material.