Apparatus for reducing entrapment of foreign matter along a moveable shaft of a substrate support

A semiconductor processing chamber comprising:

• a chamber body having an aperture formed in a bottom of the chamber body;
• a substrate support disposed in the chamber body;
• a moveable shaft coupled to the substrate support, the movable shaft extending through the aperture;
• a step formed in an inner surface of the aperture;
• and
• a substantially annular guard ring positioned within the step, wherein the guard ring further comprises:
• a first flange disposed against the shaft;
• a second flange disposed against the step formed in the inner surface;
• a channel separating the first flange from the second flange;
• a base portion coupling the first and second flanges, the base portion having an outer circumference and an inner perimeter, wherein the outer circumference contacts the step and the inner perimeter is adapted for substantially sealing a gap between the shaft and the aperture;
• wherein the inner perimeter is formed substantially as a wedge portion, that slopes radially inwards and upwards into sealing contact with the shaft;
• and
• an insert positioned within a portion of the inner perimeter, the insert further comprising:
• an arced surface conforming to the inner perimeter of the ring;
• and
• a flat surface positioned substantially parallel to a diameter of the ring.