= Solution
\b[A real <positive photoresist> pattern usually has finite edge slope and rounding rather than mathematically sharp vertical steps.] The optical aerial image and finite resist contrast give a graded exposure boundary. Absorption through the film, focus, reflections from <silicon> and development kinetics can make the opening narrower or wider at different heights.
Incomplete development can leave residual material at the floor; standing-wave exposure can cause sidewall ripples, and substrate-related chemistry can produce footing. Bake history and developer transport can modify corners and line width. An undercut can be engineered with a suitable resist stack, but it is not an automatic consequence of ordinary positive-tone processing. The final profile must therefore be measured rather than inferred solely from the mask artwork.
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