METROMEET - 5th International Conference on Industrial Dimensional Metrology

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Programme

Modeling for Industrial Nanometer-Scale Size Metrology

Dr. John Villarrubia
NIST - USA

Presentation abstract

Measuring instruments sense sample topography using probes (mechanical tips, electron beams, pho¬tons…) that interact with the sample within a finite-sized interaction volume. If measurement data are interpreted naively, assigned positions of features may have errors comparable to the characteris¬tic size of this interaction volume: typically several nanometers up to micrometers. Usually we are interested in position differences. In a favorable case, e.g., when the difference is between the centers (as in a pitch measurement) or tops (height measurement) of similar features, such errors may to a good approximation cancel. Width is not one of these favorable cases because opposite edges are nec¬essarily dissimilar. In semiconductor manufacturing and nanotechnology, where the needed measure¬ment uncertainty is measured in nanometers (or fractions thereof) this source of uncertainty is often the limiting one. Such errors and their associated uncertainties can be reduced if we develop and make proper use of accurate models for the probe-sample interaction. I will describe examples of two such models, one for AFM (atomic force microscopy, but also applicable to coordinate measuring machines), the other for SEM (scanning electron microscopy). The challenges in the two cases are different. For AFM the probe shape correction can be expressed in a mathematically concise form, but knowing the actual AFM probe shape can be a challenge. For SEM the available models are for the forward problem, determining the image given a sample and beam conditions; they are involved and time-consuming. The challenge is to solve the inverse problem (determining the sample given the image and beam conditions) in reasonable time.

Information about the speaker

John Villarrubia has been a physicist at the U.S. National Institute of Standards and Technology (NIST) since 1989. His work focuses on aspects of nanometer-scale dimensional metrology, including modeling the instrument function for atomic force and scanning electron microscopes. He received his Ph.D. from Cornell University in 1987. Afterwards, he was a visiting scientist for two years at IBM, where he did scanning tunneling microscopy of silicon sur¬faces.