Fig. 4: Uniform 4-inch wafer-scale patterning using IL-GPSE.

a Schematic of uniform nanopatterning using secondary exposure to compensate the linewidth variation due to the non-uniform laser beam intensity during IL. b Photograph of IL-exposed 400-nm-period gratings over a 4-inch wafer with the diffracted blue light intensity gradually decreasing from the center to the edge. c SEM images taken in the labeled positions in b, showing a poor control of linewidth and roughness. d Photograph of 400-nm-period gratings over a 4-inch wafer using secondary exposure with a designed projected grayscale pattern after IL exposure, diffracting uniform blue light. e SEM images recorded in the labeled positions in g, showing the uniform linewidth and linewidth roughness. f The 4-inch (i) intensity distribution for linewidth tailoring and (ii) devised grayscale image transformed by the characterized relation between the digital grayscale value and projected light intensity via the UV projector. The comparisons of g linewidth and h linewidth roughness distributions over the radius of 4-inch wafers w/o the secondary exposure, respectively. Scale bars: 500 nm