Image-Based Overlay

Overlay registration refers to the relative alignment of two layers in the thin film photolithographic process. The microscope-based, aerial imaging measurement technology utilizes a high magnification, low distortion imaging system combined with proprietary software algorithms to numerically quantify the alignment.

 

Diffraction-Based Overlay

Nanometrics introduced diffraction-based overlay metrology at the prestigious SPIE Conference on Microlithography in February 2003, as an alternative solution for overlay technology nodes below 90 nm. This novel technique extracts overlay alignment error from our broadband OCD technology using specially designed diffraction targets in real-time. The technique is based on spectroscopy rather than imaging, is much more robust than aerial imaging methods, and the total measurement uncertainty is about six times smaller than traditional techniques. This new technology is capable of meeting the advanced design requirements of the ITRS roadmap for semiconductors. A major advantage of the diffraction technique is that the measurement targets can be produced that match the dimensions of the circuits being manufactured, thus providing the immediate benefit of looking at the overlay performance of features that closely resemble the circuit features.