US Patent 9952518 Inspection method and apparatus and lithographic apparatus

Disclosed are an inspection method and apparatus and an associated lithographic apparatus. The inspection method comprises illuminating a structure with inspection radiation of a selected wavelength, the structure being of a type comprising a plurality of layers (for example a 3D memory structure). The resultant diffraction signal is detected a physical property of a subset of said layers is determined from said diffraction signal. The subset of layers for which said physical property is determined is dependent upon the selected wavelength of the inspection radiation.