The exposure and development of PMMA sublayers used in multilayer resist processing schemes have been simulated. For thick planarization sublayers (>2 μm) diffraction of the deep-UV radiation produces significant exposure variations across the resist mask apertures. This effect leads to an edge-sharpening phenomena. The Fresnel diffraction approximation is used to calculate exposure variations within the sublayer and a modified SAMPLE program to obtain the sublayer image. Estimates of the wall profiles and dimensional deviations have been obtained for various isolated space feature sizes.
L. K. White,
"Image Formation In The Sublayer Of A Multilayer Resist Structure", Proc. SPIE 0469, Advances in Resist Technology I, (21 May 1984); doi: 10.1117/12.941771; https://doi.org/10.1117/12.941771