The effect of the degree of asymmetry in the arrangement of metal masks on the matching of the lower electrode with a high-frequency displacement generator during selective reactive-ion etching of massive substrates in plasma-forming gas mixtures based on freon-14 is studied theoretically and experimentally. Theoretically, the absence of the influence of the asymmetry of the mask location on the specific reactive power is shown. It is shown that at the edge of the substrate, especially with a mask, there is a sharp increase in the RF current density, which proves mainly the surface (end) nature of its flow. The influence of the mask location on the behavior of the electric charge density, which correlates with the distribution of the RF current density in the near-surface layer of the substrate, is established. No redistribution of the charge density of the chemically active plasma particles at the edge of the mask was detected. In accordance with the theoretical results obtained, it is experimentally shown that metal masks with a side length ratio of 36/0 mm reduce the power reflection coefficient within 5%. Keywords: diffractive optical element, reactive ion etching, inductively coupled plasma, contact mask, lower electrode, simulation Multiphysics.