US Patent 7467990 Back pressure control system for CMP and wafer polishing

A wafer carrier with a back pressure applicator system adapted to provide high resolution back pressure control. A plurality of millimeter scale distensible elements are disposed between the wafer carrier pressure plate and a process wafer, and selectively distended to provide excess backpressure to select small areas of a wafer known to exhibit resistance to removal vis-à-vis the surrounding wafer surface. Distensible elements may be in the form of expandable pneumatic chambers or electro-mechanical elements such as solenoids, shape memory elements, electrostatic plates, etc.