High-speed AFM for 1x node metrology and inspection: Does it damage the features?

Abstract

This paper aims at unraveling the mystery of damage in high speed AFMs for 1X node and below. With the device dimensions moving towards the 1X node and below, the semiconductor industry is rapidly approaching the point where existing metrology, inspection and review tools face huge challenges in terms of resolution, the ability to resolve 3D, and throughput.In this paper, we critically asses the important issue of damage in high speed AFM for metrology and inspection of semiconductor wafers. The issues of damage in four major scanning modes (contact mode, tapping mode, non-contact mode, and peak force tapping mode) are described to show which modes are suitable for which applications and which conditions are damaging. The effects of all important scanning parameters on resulting damage are taken into account for materials such as silicon, photoresists and low K materials.Finally, we recommend appropriate scanning parameters and conditions for several use cases (FinFET, patterned photoresist, HAR structures) that avoid exceeding a critical contact stress such that sample damage is minimized.In conclusion, we show using our theoretical analysis that selecting parameters that exceed the target contact stress, indeed leads to significant damage. This method provides AFM users for metrology with a better understanding of contact stresses and enables selection of AFM cantilevers and experimental parameters that prevent sample damage.

Chaos: The speed limiting phenomenon in dynamic atomic force microscopy

“…The latter also determines the maximum speed allowed for the raster scanning i.e., scanning too fast without performing an accurate Z measurement can cause crash or surface loss. 6,14,21 Fortunately, linear (or weakly nonlinear) parts such as actuators, sensors, filters, and the Proportional-Integral (PI) controller do have a cut-off frequency or relaxation time which determines their speed. However, for the strongly nonlinear dynamics of the cantilever interacting with the surface, determining such a limit-frequency is an elusive problem.…”