Hybrid lithography based fabrication of 3D patterns by deep reactive ion etching

Abstract Electron-beam lithography (EBL) possesses tremendous capabilities in terms of patterning ultra-small features, with very low line edge roughness and high overlay accuracy. In order to reduce write times and processing steps, hybrid lithography is an interesting alternative. Here, an approach combining EBL and ultraviolet lithography (UVL) was pursued in order to pattern multi-level 3D-structures by inductively coupled plasma deep reactive ion etching (ICP-DRIE). The substrate etched hereby consisted of a silicon nitride thin film and the underlying silicon. The correlation of UVL under- and overexposures with the resist layer height and sidewall taper after development, in combination with the optimization of the ICP-DRIE selectivity in dependence of the biasing conditions and the aspect ratio dependent etch lag for small features, allowed for the accurate prediction and therefore programming of the desired structures. Further, the selectivity was tailored by introducing an oxygen pulse after the breakthrough step. This facilitated the simultaneous etching of structures with an in-plane resolution of down to 250 nm (aspect ratio 1:22) and trench depths ranging from 200 nm to 25 μm.