SYMMETRIC TARGET DESIGN IN SCATTEROMETRY OVERLAY METROLOGY

摘要

Metrology methods, systems and targets are provided, which implement a side by side paradigm. Adjacent cells with periodic structures are used to extract the overlay error, e.g., by introducing controllable phase shifts or image shifts which enable algorithmic computation of the overlay. The periodic structures are designed to exhibit a rotational symmetry to support the computation and reduce errors.

主权项

1. A method of estimating an overlay error between at least two layers, the method comprising:
illuminating a metrology target that comprises at least two periodic structures which are at different layers, are along a common measurement direction and have a same pitch, wherein the metrology target is symmetric with respect to a 180° rotation about an axis that is perpendicular to the target, and wherein the illumination is carried out simultaneously with respect to the at least two periodic structures; measuring interference of at least one diffraction order from the at least two periodic structures; and extracting the overlay error from the measured interference.