Getting the measure of silicon wafers

In the last few years, semiconductor circuit features have shrunk to sub-100 nanometre (nm) dimensions, while the size of the thin silicon wafers that these circuits are constructed on has grown from 200mm to 300mm (about 12 inches). The payoff is a higher yield of finished devices from fewer wafers.

The tough part, however, is to make wafers substantially larger while simultaneously meeting higher quality control specifications. The optics and materials for "printing" nanoscale circuit lines require that the wafers used are perfectly flat and of uniform thickness.

To help the semiconductor industry meet its 2010 quality control roadmap goals, researchers at the National Institute of Standards and Technology (NIST) recently developed a new instrument that accurately measures differences in thickness across a 300mm wafer with an excellent repeatability of 5nm. The researchers hope the tool, with further refinements, will allow them to establish a new calibration service for "master wafers" used in the industry to measure wafer thickness.