Metrology target design method, substrate having metrology target, overlay measurement method, and device manufacturing method

摘要

A design method for overlay targets and metrology recipes, in which accuracy is well defined and controlled, and robust to process-induced variations. Metrology targets are formed by a lithographic process, each target comprising a lower grating and an upper grating. The overlay performance of the lithographic process is measured by illuminating each target with radiation and observing the asymmetry of the diffracted radiation. Metrology recipe and target design parameters are selected to maximize the accuracy of the overlay measurement, rather than repeatability. The method comprises at least from between (i) a first radiant component representing radiation diffracted by the upper grating and (ii) a second radiant component representing radiation diffracted by the lower grating after passing through the upper grating and intervening layers. Calculating one relative amplitude and relative phase. The design of the top grating may be modified so that the relative amplitude approaches one. The wavelength of the illumination radiation of the metrology recipe can be adjusted so that the relative phase approaches π / 2 or 3π / 2. [Selection] Figure 8