By M. David Levenson
WaferNews Technical Editor
Nanometrics, a company with a long history in film metrology, has introduced an optical CD metrology tool for the sub-130nm market that has made libraries of templates superfluous.
The Nanometrics 9300ocd uses normal incidence polarized light reflectometry to extract the spectroscopic signatures of line-space pattern dimensions, pretty much as do spectroscopic and angle-dependent scatterometry tools. However, the use of normal incidence significantly simplifies the calculations, making libraries of templates unnecessary.
Nanometrics also uses an R-theta stage to position the wafer, rather than the more familiar x-y stage, resulting in a dramatic footprint reduction. Because the orientation of the line-space pattern will vary with theta, they also employ patented polarization and image rotating technology, according to Senior Marketing Manager Peter Gise. The CDs measured optically on the Nanometrics system correlate well with the ensemble average of 20 SEM measurements made within the 50-micron diameter target, but less well with individual SEM measurements, which suffer from noise. While the system has sub-nanometer precision, it is insensitive to line edge roughness, a current metrology concern. According to Prasana Chitturi, senior director of marketing, Nanometrics is developing integrated metrology applications of their OCD technology first, but will also offer the same instrument as a stand-alone system.