Through Focus Signature Analysis for Nano Features

Semiconductor device fabrication process is the most sophisticated and complex manufacturing process. Advances in the manufacturing processes has brought down the feature size of gate to as low as 22 nm. Hence there is a great demand for process control of feature dimension below the resolution limit of visible wavelength microscopy. Lot of research has been focused on increasing the resolution of the metrology tools. We have adopted a novel optical technique that shows nanoscale measurement sensitivity using conventional optical microscopes. Here through-focus images are acquired at different focus positions. These focused and defocused images are used to build an intensity map whose signature reflects the target pattern. This technique is used to identify relative nanoscale change in dimension between two targets by finding the change in the signature of the intensity map.