Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2023 / Paper 1 / Section A(ii) / 3 / iii

Depth of focus is the axial tolerance over which the projected pattern remains acceptable. Wafer topography, resist thickness, wafer tilt and focus-setting errors can move part of the film outside that range, reducing contrast and changing printed linewidth. Increasing numerical aperture can improve lateral resolution while reducing this axial process window.

Using the supplied coefficient in the conventional expression,This is the range assigned to DOF by that convention. Whether an instrument reports a full allowable interval or a one-sided defocus tolerance must be stated separately; an additional factor of two cannot be inferred from the numerical coefficient alone.