Subnanometer-precision metrology for 100-nm gate linewidth control

The 0.13 micrometer semiconductor manufacturing generation will have transistor gate structures as small as 100 nm, creating a demand for 10 nm gate linewidth control and for measurement precision on the order of 2 nm. This process control requirement is inherently long-term. Therefore, measurement equipment should be able to run days or weeks without significant excursions. The requirement for long-term precision drives both the design and use of measurement equipment. We have found that long-term measurement precision on a single tool may be divided into orthogonal components corresponding to static repeatability, short-term dynamic reproducibility, and long-term stability of the tool. The static component is limited primarily by signal-to-noise ratio, the dynamic component is limited primarily by sample positioning and focusing, and the long-term component is limited primarily by instrument drift and, in the case of monitor wafers, aging of the sample. In this work, we show that each of these components can be reduced to less than 1 nm, 3-sigma, for CD SEM measurements of etched polysilicon gate structures.