Differential metrology of very large scale integration, oxide isolation structures using a confocal scanning laser microscope

A confocal scanning laser microscope (CSLM) has been used to study a variety of oxide isolation structures, including LOCOS and SLOCOS, by means of a confocal differential Fizeau metrology (CDFM) technique recently developed at Philips Research Laboratories Sunnyvale (PRLS). This technique permits measurement between Fizeau fringes less than 200 nm in width (FWHM), with less than 50 nm of optical offset, greater than 50% contrast, and mean standard errors in the nanometer range. Comparisons are made between measurement tools (CSLM and SEM), between processes (LOCOS and SLOCOS), between process steps (nitride mask definition and local thermal oxidation), between individual wafers (levels of nitride mask thickness), and between individual features on a wafer (levels of nitride mask linewidth). Unique metrological evidence is presented for a stress‐related deformation mechanism in both LOCOS and SLOCOS structures at nitride mask thicknesses greater than about 250 nm.