Plasma processing chamber with dual axial gas injection and exhaust

A method for semiconductor wafer processing, comprising:

• positioning an outer peripheral structure on a top surface of a chuck so as to form an uninterrupted fluid seal between a bottom surface of the outer peripheral structure and the top surface of the chuck, the outer peripheral structure extending in a solid form from a top surface of the outer peripheral structure to the bottom surface of the outer peripheral structure, the outer peripheral structure surrounding and enclosing a perimeter of a plasma generation volume above the chuck;
• positioning a gas distribution unit above the plasma generation volume so as to extend across the plasma generation volume in a substantially parallel orientation with respect to the chuck, and so as to form an uninterrupted fluid seal between the top surface of the outer peripheral structure and the gas distribution unit around the perimeter of the plasma generation volume, the gas distribution unit separating the plasma generation volume from an exhaust region, the gas distribution unit including an arrangement of gas supply ports configured to direct an input flow of a plasma process gas into the plasma generation volume, the gas distribution unit including an arrangement of through-holes that each extend through the gas distribution unit to fluidly connect the plasma generation volume to the exhaust region;
• and
• controlling a subset of through-holes of the arrangement of through-holes to be open to the exhaust region and others of the arrangement of through-holes to be closed to the exhaust region.