Sensitivity of SEM width measurements to model assumptions
John S. Villarrubia, Zejun Ding
The most accurate width measurements in a scanning electron microscope (SEM) require raw images to be corrected for instrumental artifacts. Corrections are based upon a physical model that describes the sample-instrument interaction. Models differ in their approaches or approximations in the treatment of scattering cross sections, secondary electron (SE) generation, material properties, scattering at the surface potential barrier, etc. Corrections that use different models produce different width estimates. We have implemented eight models in the JMONSEL SEM simulator. Two are phenomenological models based upon fitting measured yield vs. energy curves. Two are based upon a binary scattering model. Four are variants of a dielectric function approach. These models are compared to each other in pairwise simulations in which the output of one model is fit to the other using adjustable parameters similar to those used to fit measured data. The differences in their edge position parameters is then a measure of how much these models differ with respect to a width measurement. With electron landing energy, beam width, and other parameters typical of those used in industrial critical dimension measurements, the models agreed with one another to within ±2 nm on silicon and ±2.6 nm on copper 95 % of the time.
Proceedings of SPIE Advanced Lithography, Vol 7272
February 23-27, 2009
San Jose, CA
to within ±2 nm on silicon and ±2.6 nm on copper 95 % of the time. critical dimension (CD), model-based metrology, Scanning Electron Microscopy (SEM), secondary electron generation, uncertainty