Patterned wafer containing logic dies and 3D NAND memory dies, (f) X-ray ptychography, (g) THz wave-based defect inspection system, and (h) Coherent Fourier scatterometry techniques using ...

Photolithography uses light to transfer a pattern of features from a mask to a light-sensitive chemical photoresist on a semiconductor wafer. As the pattern is transferred, it is reduced in scale ...

and inspection of patterned masks is satisfactorily addressed today using a combination of DUV mask inspection and broadband plasma optical patterned wafer inspection focused on repeating defects on ...

The same Redditor pointed out later under the post that this appears to be what's known as a "test wafer" used to calibrate the lithography machines that pattern the circuitry onto production wafers.