Gravitation toward a dry silicon etch process for electron projection lithography (EPL) mask fabrication is beneficial because of the concomitant increase in the available membrane area. In order to help understand the complex Bosch etch process and its dependence upon hardware design and process parameters for scattering with angular limitation in projection election beam lithography (SCALPEL) mask fabrication, a combined equipment and feature scale model has been employed. For case studies such as varying the deposition cycle time or ramping the bias power, computed sidewall profiles from the model deviate from experimental data by only about 5.5%. Given the extreme complexity of the Bosch process, this correlation is considered excellent. The best experimental Bosch etch conditions produce SCALPEL substrates with an effective silicon etch rate of 2.7 mum/min, 6.1% etch uniformity, selectivity to tetraethyl orthosilicate >240:1, and average strut sidewall angles of 87.4degrees. Introduction of hardware into the chamber results in partially blocking the transport of important etch and polymer deposition species to the wafer, thereby altering the etch and passivation rates. The provided learning is applicable to projection reduction exposure with variable axis immersion lenses format EPL masks as well.