1. Field of the Invention
The present invention relates to a plasma processing method and a plasma processing apparatus.
2. Description of the Related Art
A plasma processing apparatus is known which includes a high frequency power source for providing high frequency electric power for plasma generation and a high frequency power source for providing high frequency electric power for bias, and performs a plasma process on a substrate by forming plasma from gas by these high frequency electric powers (see Patent Document 1, for example). According to Patent Document 1, high frequency electric power for plasma generation and high frequency electric power for bias are applied to a mounting table.
When performing a plasma process, the above described two high frequency electric powers are superimposed and a standing wave is generated by a high harmonics wave component of each of the high frequency electric powers. Due to generation of the standing wave, electric field at a center portion of a substrate may become higher than electric field at an edge portion or an area between the center portion and the edge portion (hereinafter referred to as a “middle portion” as well) of the substrate.
In such a case, an etching rate (hereinafter simply referred to as “ER” as well) becomes higher at the center portion of the substrate compared with the middle portion or the edge portion of the substrate. When the etching rate becomes uneven as such, process sizes of Critical Dimension (CD) or etching depths at the center portion and areas other than the center portion vary, and it becomes difficult to perform a uniform plasma process on the substrate.