Nondestructive Submicron Dimensional Metrology Using the Scanning Electron Microscope

The evolution of integrated circuit dimensions into the submicron region for the Very Large Scale Integration (VLSI) and Very High Speed Integrated Circuits (VHSIC) programs necessitates inspection techniques with a resolution exceeding that of the optical microscope. Inspection using scanning electron microscopes (SEM), operated in the low accelerating voltage mode, is becoming common place in the on-line fabrication of these submicron devices due to the high spatial resolution and greater depth of field afforded by these instruments. Use of the SEM is necessitated by the desire of many processing facilities which presently work at a 10% process control level to implement process control of 5% or better. This means that the process precision goal is now (or soon will be) in the nanometer range. Even though optical microscopes can be useful for critical linewidth measurement and inspection to about 0.5μm, many fabrication lines presently are integrating low-voltage scanning electron microscopes into the production sequence at chip levels of 1.25-μm geometry and below. This enables the training of operators and the acquisition and development of expertise and experience with control charts for this type of instrumentation. Advanced scanning e-beam instruments are presently being developed to facilitate this work and to do automated inspection