Workpiece support platen for semiconductor process chamber

Abstract

Apparatus and method for mounting a workpiece support platform or platen within a semiconductor process vacuum chamber to provide electrical or thermal insulation and mechanical stability, but yet minimize mechanical stresses due to differential thermal expansion between the platen and the dielectric spacer. Specifically, the invention includes a workpiece support platen having a rear surface abutting a front surface of a platen-support shelf. The shelf preferably provides electrical or thermal insulation between the platen and the wall of the vacuum chamber. The shelf is attached to the enclosure of the vacuum chamber, but the platen is not rigidly attached to the shelf. Instead, a pressure actuator, such as a spring or pneumatic piston, presses the platen against the shelf. In one embodiment, the pressure actuator can be turned off to allow the platen to expand or contract during periods of heating or cooling, such as when the chamber is turned off or on before or after maintenance. When the temperature of the platen is stable during processing of semiconductor workpieces, the pressure actuator can be turned on to hold the platen firmly in position against the shelf. In a second embodiment, the pressure actuator is adjusted to apply a pressure high enough to inhibit inadvertent movement of the platen, yet low enough to accommodate differential thermal expansion between the platen and the shelf by the platen sliding across the front surface of the shelf, thereby minimizing mechanical stresses between the platen and the shelf.