Self-centering wafer support system

Abstract

Improvements in the design of a low mass wafer holder are disclosed. The improvements include the use of peripherally located, integral lips to space a wafer or other substrate above the base plate of the wafer holder. A uniform gap is thus provided between the wafer and the base plate, such as will temper rapid heat exchanges, allow gas to flow between the wafer and wafer holder during wafer pick-up, and keep the wafer holder thermally coupled with the wafer. At the same time, thermal disturbance from lip contact with the wafer is reduced. Gas flow during pick-up can be provided through radial channels in a wafer holder upper surface, or through backside gas passages. A thicker ring is provided at the wafer holder perimeter, and is provided in some embodiments as an independent piece to accommodate stresses accompanying thermal gradients. Self-centering mechanisms are provided to keep the wafer holder centered relative to a spider which is subject to differential thermal expansion.