Consideration of local shadowing and ion beam voltage effects in the prediction of a surface evolving under ion milling

Ion milling applications in the micro-electronics industry are becoming mor e challenging due to decreasing feature sizes and increasing aspect ratios. A simulation of the milling problem which is capable of predicting surface evolution in the presence of high aspect ratios where local shadowing of t he substrate surface becomes an important issue is described. A method of c haracteristics solution based on surface inclination angles is derived for a three-dimensional surface evolution model. An algorithm is developed to a ccount for local shadowing effects, where raised areas of the substrate sur face (i.e.. the photomask) prevent the ion beam from reaching hidden or sha dowed portions of the surface. The yield (sputtering) function is modified to account for beam voltage as well as the angle of beam incidence. Yield f unction parameters are determined experimentally for Al2O3, Ti, permalloy ( 83/17 wt % Ni-Fe) and postbaked AZ P4400 photoresist. Model predictions are in good agreement with experimental results for the surface evolution of a photopatterned Al2O3 substrate. (C) 2000 American Vacuum Society. [S0734-2 101(00)02801-3].