Shaped electrodes for improved plasma exposure from vertical plasma source

A processing chamber comprising:

• a susceptor assembly within the processing chamber, the susceptor assembly having a top surface to support and rotate a plurality of substrates around a central axis;
• and
• a gas distribution assembly having a front surface facing the top surface of the susceptor assembly to direct a flow of gases toward the top surface of the susceptor assembly, the gas distribution assembly including a plasma source assembly comprising
• a housing having an inner peripheral edge, an outer peripheral edge and a front face, the housing including a gas inlet to form a flow path from the gas inlet to allow a flow of gas to pass through the housing and out an opening in the front face,
• an RF hot electrode within the housing, the RF hot electrode having an elongate body with a first surface and a second surface, an inner peripheral end adjacent the inner peripheral edge of the housing and an outer peripheral end adjacent the outer peripheral edge of the housing and defining a length of the RF hot electrode, the RF hot electrode including a leg extending at an angle to the elongate body,
• a first return electrode within the housing, the return electrode having an elongate body extending between the inner peripheral edge and the outer peripheral edge of the housing, the first return electrode spaced from the first surface of the RF hot electrode to provide a first gap in which a plasma can form,
• a second return electrode within the housing, the second return electrode having an elongate body extending between the inner peripheral edge and the outer peripheral edge of the housing, the second return electrode spaced from the second surface of the RF hot electrode to provide a second gap in which a plasma can form, and
• an RF feed connected to the RF hot electrode at a distance from the inner peripheral end of the RF hot electrode that is less than or equal to 25% of the length of the RF hot electrode,
• wherein the front face of the housing of the plasma source assembly is positioned a distance from the top surface of the susceptor assembly in the range of 1 mm to 5 mm, and an ion flux generated at the inner peripheral end of the RF hot electrode is less than an ion flux generated at the outer peripheral end of the RF hot electrode
• a RF hot electrode cladding positioned so that the RF hot electrode is not exposed directly to the susceptor assembly;
• a return electrode cladding positioned so that the first return electrode and second return electrode are not exposed directly to the susceptor assembly;
• one or more of an RF hot electrode gap between the RF hot electrode and the RF hot electrode cladding or a return electrode gap between the return electrode cladding and the return electrode, the RF hot electrode gap and/or the return electrode gap having a dimension that changes along the length of the gap between the RF hot electrode and the return electrode.

A plasma source assembly comprising:

• a housing having an inner peripheral edge, an outer peripheral edge and a front face, the housing including a gas inlet to form a flow path from the gas inlet to allow a flow of gas to pass through the housing and out an opening in the front face;
• an RF hot electrode within the housing, the RF hot electrode having an elongate body with an inner peripheral end adjacent the inner peripheral edge of the housing and an outer peripheral end adjacent the outer peripheral edge of the housing and defining a length of the RF hot electrode, the RF hot electrode including a leg extending at an angle to the elongate body;
• a return electrode having an elongate body extending between the inner peripheral edge and the outer peripheral edge of the housing, the return electrode spaced from the RF hot electrode to provide a gap in which a plasma can form;
• an RF feed connected to the RF hot electrode at a distance from the inner peripheral end of the RF hot electrode that is less or equal to 25% of the length of the RF hot electrode;
• a RF hot electrode cladding positioned so that the RF hot electrode is not exposed;
• and
• a return electrode cladding positioned so that the return electrode is not exposed, wherein one or more of the RF hot electrode cladding has a dimension that changes along the length of the gap between the RF hot electrode and the return electrode, or the return electrode cladding has a dimension that changes along the length of the gap between the RF hot electrode and the return electrode.