The primary charged-particle-based metrology system used today is the CD-SEM. It accelerates electrons across the measurement structure and looks at the electron yield for imaging. For the last 15 or so years, ion based imaging systems have been explored, but no production-worthy tools are available as of 2015, and no production-grade ion beam tools will be commercially available in the foreseeable future.
The CD-SEM is the primary CD metrology tool for IC manufacturing. It has the resolution, precision, and accuracy to measure small-scale dimensions in nanometers. In addition, after 20þ years of development and improvements, it has the automation and throughput to be the sole production-proven CD metrology tool. CD metrologies are used in two critical image-transfer process steps: lithography and etch. CDs in different layers refer to different feature dimensions, such as linewidths, spacewidths, contact, via hole diameters, etc. Different measurement algorithms have been developed to measure different CDs.
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