Wafer support structure for a wafer backplane with a curved surface

Abstract

The wafer support structure is used with a movable backplane having a curved upper surface which is moved between a wafer access position and a wafer process position to clamp a wafer against a clamping structure during processing. A guide ring surrounds the backplane and a floating ring is spring-mounted on the guide ring by flat, elongated lift springs. RF bias springs are positioned on top of the floating ring along with wafer support pins which support a wafer above the curved backplane surface. When the backplane is moved toward the clamping structure to clamp the wafer, the RF bias springs make electrical contact with a portion of the clamping structure, and the clamping structure acts against the floating ring to flex the lift springs and lower the floating ring such that the wafer is transferred to the backplane surface to be clamped against the clamping structure. When the wafer is clamped, the support pins are out of contact with the wafer. The wafer is stably supported by the support pins over the backplane surface during access of the wafer and is securely clamped between the backplane and clamping structure away from the wafer support during processing of the wafer. A filler ring around the backplane reduces formation of a secondary plasma.