Simulation of optical lithography in the presence of topography and spin-coated films

Experimental results on etched silicon wafers show that after two consecutive spin-coat processes the upper material surface achieves near planar flatness. This was observed for three separate dual layer BARC systems and the case of photoresist over a single layer BARC. The wafer topography step height (60 nm) and the thicknesses of the organic films (20 nm - 100 nm) were typical for state-of-the-art IC manufacturing lithography processes. A lithographic proximity effect driven by wafer topography pitch was experimentally observed for a single layer BARC system. The response was reproduced with good quantitative accuracy using rigorous wafer plane EMF simulations incorporating ideal etched wafer topography, a planarizing resist film and a simple spin-coat approximation of the BARC coverage, as observed by x-section SEM. In contrast, simulations assuming the limiting cases of a perfectly conformal BARC and a perfectly planarizing BARC failed to predict any meaningful proximity effect.