Brim and gas escape for non-contact wafer holder

Abstract

The present invention comprises a brim surrounding a wafer or wafer-like object during plasma etching in a non-contact wafer holder, such brim facilitating uniform flow of the plasma discharge around the edge of the wafer during plasma etching. The brim of the present invention avoids plasma instability and non-uniform flow typical of conventional plasma etching near the edges of the wafer being etched. The brim of the present invention, by facilitating uniform and stable plasma flows, decreases non-uniform etching. One embodiment of the present invention permits the brim to move in the axial direction from a position substantially. This permits the etching process to be controlled for more uniform and precise wafer etching as lowering the brim tends to shadow the edge region of the wafer from the plasma, reducing etching in the edge region while not significantly affecting etching in the central regions of the wafer. Another embodiment of the wafer includes a barrier on the upper side of the brim directed upward from the brim at an oblique angle away from the wafer. This barrier contacts the upper surface of the brim so as to leave a protrusion or debris-collecting shelf on the upper interior portion of the brim. This shelf in combination with the upward oblique barrier deflects the plasma and debris from plasma etching away from the wafer. Another embodiment of the invention includes a gas-controlling baffle in which gas flow around the edge of the wafer may be controlled to compensate for mechanical imprecision in the gap between the brim and the wafer and/or to provide an additional means of controlling etching in the vicinity of the edge of the wafer.