| 摘要 |
A patterning device, including alignment targets having alignment features formed from a plurality of diffractive elements, each diffractive element including an absorber stack and a multi-layered reflector stack is provided. The diffractive elements are configured to enhance a pre-determined diffraction order used for pre-alignment and to diffract light in a pre-determined direction of a pre-alignment system when illuminated with light of a wavelength used for the pre-alignment. The diffractive elements may occupy at least half of an area of each alignment feature. The diffractive elements may be configured to enhance first or higher order diffractions, while substantially reducing zeroth diffraction orders and specular reflection when illuminated with a wavelength used for reticle prealignment. The dimensions of each diffractive element may be a function of a diffraction grating period of each alignment feature.
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