Fig. 3: Spatial modulation of nanostructure feature sizes using grayscale-patterned SE.

a Schematic of spatial modulation of linewidth using patterned secondary exposure. b A 3-inch wafer carrying the HKU logo consisting of 600-nm-period photoresist gratings with the linewidths in different regions modulated by projected grayscale pattern. c SEM images taken on background, “H”, “K”, and “U” letters on the wafer, showing corresponding linewidths of 250, 190, 140, and 110 nm. d SEM image of a 600-nm-period hole array modulated by DLW secondary exposure. e Plot of the filling ratio of nanostructures in the green box in d versus the horizontal position, showing a resolution of 1.7 µm. f Optical microscope image of a 12-point-star pattern, consisting of 600-nm-period gratings with linewidths modulated by contact photolithography using a photomask. SEM images taken inside and outside the secondary exposure pattern, showing the 245-nm and 170-nm linewidths, respectively. g Green box and h yellow-box regions in f, characterized by (i) SEM images and (ii) linewidth distributions. i The linewidth variation measured every 200 nm along a grating line (white, Fig. 3h), showing the grating linewidth gradient of 35 nm/µm. Scale bars, 500 nm (c, f), 1 µm (g, h), and 2 µm (d)