A novel self-aligned double patterning integrated with Ga+ focused ion beam milling for silicon nanowire definition

Abstract

Self-aligned double (SADP) or quadruple (SAQP) patternings have been used to obtain sub-resolution lithographies (sub-10 nm). For this purpose, usually, these patternings are integrated with 193 nm immersion (193iL), extreme ultra-violet (EUVL) and electron beam (EBL) lithographies. In this work, SADPs are integrated with Ga+ Focused Ion Beam (FIB) milling, which is a novel alternative to traditional 193iL, EUVL and EBL, mainly for prototyping of nanodevices. Furthermore, the FIB milling is a maskless process, thus being more flexible than EBL and cheaper than EUVL. The FIB milling was carried out on the a-Si:H/Al (deposited on Si substrate) to pattern the parallel Al nanowires (AlNWs), which are used as mandrel in our SADP. The a-Si:H layer, used as spacer in our SADP, also is an effective barrier against the Ga+ ion bombardment directly on Al surface, avoiding damages on the AlNW mandrel. Thus, after FIB milling, SADP and plasma etch steps, Silicon Nano-Wires (SiNWs), with dimensions (extracted by Scaning Electron Microscopy (SEM)) of fin width and pitch of 35 nm and 170 nm, respectively, were obtained. This is an excellent result, similar to obtained by SADP methods integrated with traditional lithographies. Therefore, our SADP with FIB milling is a flexible alternative to obtain SiNWs for 3D nanostructure technologies prototypes. Furthermore, a last important result, extracted from energy dispersive x-ray spectroscopy (EDS) spectrum, is the Ga peak absence, indicating that no trace of gallium (for an EDS detection limit of 1%) could be detected into SiNWs. This result agrees the TRIM (Transport and Range of Ions in Matter) simulation of gallium ion implantation in a-Si:H/Al structure.