Low compliance seal for gas-enhanced wafer cooling in vacuum

Apparatus for thermal transfer with a semiconductor wafer in a vacuum processing chamber includes a platen with a surface for supporting the wafer, a clamping ring for clamping the wafer to the platen, and passages for supplying a low pressure gas into a thermal transfer region between the wafer and the platen surface. A low compliance seal surrounds the thermal transfer region and inhibits the gas from reaching the processing chamber without overstressing the wafer. The seal includes an elastomer ring having an elongated cross-section, and a sealing groove having a first groove portion for gripping one edge of the ring and a second groove portion which receives the other edge of the ring by bending deformation thereof when a wafer is clamped to the platen. In a preferred embodiment, the ring has a parallelogram-shaped cross-section and is oriented at an acute angle to the platen surface.