CMP methods in which a polishing pad is moved relative to a wafer and a retainer
ring implement instructions for applying required pressure to the wafer for CMP
operations. Accuracy of computations of the pressures, and of conversion of the
pressure to force, is improved without use of high resolution components, such
as high resolution digital devices. Such improved accuracy is achieved using both
digital and analog operations, and by converting values of required pressure or
force from one set of units to a second set of units and then back to the first
set of units. A quantization process is performed using data processed by average
resolution digital devices. The process transfers both pressure/force scale and
pressure/force set point data between separate processors to obtain computed values
of pressure and force having acceptable accuracy, such that quantization errors
are eliminated or significantly reduced.
