Fast and Robust Overlay Metrology from Visible to Infrared Wavelengths Using Dark-field Digital Holographic Microscopy

The aggressive reduction of semiconductor device dimensions drives many improvements in optical wafer metrology. Currently, chips with device feature sizes below 10 nm are in production which requires robust overlay metrology with sub-nm precision. We will present a compact dark-field Digital Holographic Microscope (df-DHM) that is able to measure overlay on small metrology targets from visible to infrared wavelengths. The coherent amplification and the aberration correction capabilities that is offered by df-DHM allow robust overlay metrology even on weak targets that are covered by absorbing layers. Measured data will be shown that demonstrate the capabilities of this metrology concept