Methods and apparatuses for controlling gas flow conductance in a capacitively-coupled plasma processing chamber

A method of controlling gas flow conductance in a plasma processing chamber including an upper electrode disposed opposite a lower electrode with a gap therebetween, the lower electrode adapted to support a substrate, the apparatus comprising a ground ring configured to concentrically surround the lower electrode, the ground ring including a first set of slots formed therein, a bypass choke ring, a cover ring disposed over the ground ring and bypass choke ring, the cover ring including a second set of slots formed therein, and an actuation mechanism adapted to move the bypass choke ring relative to the ground ring to control gas flow conductance through the first and second sets of slots between (i) an ON state in which the first set of slots is in fluid communication with the second set of slots such that gas can flow through the first and second sets of slots and (ii) an OFF state in which the first set of slots is blocked by the bypass choke ring such that gas cannot flow through the first and second sets of slots, the method comprising:

• supporting a semiconductor substrate in the plasma processing chamber;
• providing process gas into the gap between the upper and lower electrodes;
• exciting the process gas into plasma;
• and
• moving the bypass choke ring between the ON state and the OFF state with the actuation mechanism to control a gas flow rate through the first set of slots;
• wherein the gas passes through the first and second set of slots and is removed from the plasma processing chamber by a vacuum pump;
• wherein moving the bypass choke ring comprises moving, in an axial direction, the bypass choke between the ON state and OFF state with the actuation mechanism to control gas flow conductance;
• and
• the bypass choke ring comprises multiple protrusions;
• the actuation mechanism further comprises:
• a plasma confinement ring assembly and an actuation rod coupled to the plasma confinement ring assembly;
• and
• wherein moving the bypass choke ring further comprises:
• moving the actuation rod in an axial direction of the ground ring;
• and
• controlling a spacing between the protrusions and inner surfaces of the slots.