Linewidth measurement: From fine art to science

Traditional methods of linewidth measurement on integrated circuit photomasks and wafers have employed an optical microscope with some type of measuring eyepiece. In recent years, the push to finer line geometries has revealed systematic measurement differences between instruments as large as 1.0 µm. Modeling of linewidth measurement systems has shown that these differences may be attributed to differences in edge detection criteria. New techniques have been developed at the NBS for accurate optical edge detection and calibration of other optical linewidth measurement systems.