Electron beam lithography using SiO2 as a sensitive layer

In this paper, we study the capabilities and some features of direct electron-beam lithography using a layer of silicon dioxide SiO2 (grown by thermal oxidation) as a resist sensitive to the action of the electron beam and a developing composition based on an aqueous solution of dilute buffered hydrofluoric acid. Additional factors influencing the lithography result (the existence of an initial period of exposure effect enhancement) are found. To explain this feature, a hypothesis about the mechanism of the influence of the electric charge introduced into the SiO2 layer (during exposure) on the process of further development of the latent image is proposed. As a measure eliminating the manifestations of contamination phenomena, an approach using a sacrificial copper layer applied during the exposure period is proposed. A rationale for choosing the metal of the sacrificial layer is given based on experimental observations and a hypothesis about the possible chemical composition of contamination spots in the exposed areas. The parameters of the direct lithography process on SiO2 known from the literature are clarified. The nonlinear nature of the effect of the electron beam on the silicon dioxide layer is found and simple empirical dependencies that allow a quantitative description of the result of the lithography process for the case of large-scale structures are proposed. It is shown that even when using a sacrificial copper layer, it is possible to achieve a lithographic process resolution of no worse than 30 nm.