Single-step resistless hardmask fabrication using selective surface oxidation

Electrolithography (ELG) is a unique case of local anodic oxidation (LAO) based lithography. ELG is performed by electrically stressing chromium (Cr) thin films, resulting in the formation of an oxide material which is a liquid material and spreads to over 100 μm within a few seconds. The rate of spread of the oxide domain is proportional to the oxidation current flowing through the circuit. The liquid chromium oxide creates an additional resistance affecting the magnitude of the oxidation current, which in turn affects the repeatability of the formed patterns if the process is not meticulously planned. In an aim to reduce such reliability concerns governing the ELG technique, we propose to alter the electrical nature of the sample underneath the Cr layer, against the conventionally used insulating layers. Despite incorporating non-insulating layers underneath the Cr layer, the results presented in this study indicate that the said oxidation process remains as aggressive as has been reported before and thereby possibly opens up a plethora of direct write applications of the ELG technique. We have proposed and successfully demonstrated one such application of ELG, where it can be used to pattern and electro-etch Cr films to act as hard masks for dry etching. • Conventionally, in the SPL-based ELG technique in-plane electric field is applied. • The effect of the through-plane electric field is explored in great detail. • The change in electric field direction has no significant effect on ELG process. • This enables us to perform ELG on non-insulating substrates. • ELG can be used for resistless hardmask patterning for RIE of Si substrates.