Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2017 / Paper 1 / Section B / 9 / iii

For a positive-tone opening, place small clear serifs beyond convex outer corners and extend the ends of the L arms to compensate for line-end shortening. Adjust the concave inner corner with a local inward boundary correction or opaque notch where excess exposure would otherwise round/fill it. The diagram exaggerates these additions and the inner correction for visibility; their dimensions are subresolution corrections, not intended printed protrusions. In an opposite mask/resist polarity the clear/opaque roles reverse. An L with corrected ends, outer-corner serifs and an independently corrected inner corner is the appropriate mask concept. The particular bias must be fitted to the aerial image plus resist threshold over the required focus/exposure window. A printed test L, measured at the inner and outer corners, is more informative than assuming any decorative serif produces an exact L.