Electronic properties of silicon nanoneedle structure obtained by RIE for nonvolatile memory applications

Nanotechnology is one of the newly rising technological fields and acquiring the research priorities in these days. Nanostructures found to have high optical gain, and found to be a key element in the nonvolatile memory devices. The major drawback in the formation of nanocrystalline silicon (nc-Si) is the lack of uniformity and low density. Uniform and packed needle like silicon surface with a size of 50 nm and with a depth of 300 nm was established in the present study using a reactive ion etching (RIE) system. SF₆ and O₂ gases were used for the reactive ion etching process. The ratio of gas flow rates during etching was optimized for the anisotropic etching of silicon to generate nanostructures. Surface morphology was investigated after etching using scanning electron microscope (SEM). The sample etched at an SF₆ flow rate of 13 sccm was found to be smooth, but as the SF₆ flow rate increases, we can see the formation of columnar microstructures. For a typical flow of SF₆ with the flow rate of 22 sccm, we found the silicon surface covered by columnar structures with diameters ～ 50 nm and depth of about 300 nm. Radio Frequency (RF) power, etching time and oxygen flow rate were fixed to 100 W, 15 min and 12 sccm, respectively, during the experiment for all the samples. In order to observe the effect of RF power on the formation of nanoneedle silicon surface, experiments were carried out at different powers (60 W, 80 W and 100 W) and at a constant SF₆ and oxygen flow rates of 22 sccm and 13 sccm. From this study, we formed a deep nanoneedle structured silicon surface at a power of 100 W. Photoluminescence (PL) and capacitance–voltage (C–V) characteristics were recorded on metal-oxide-semiconductor (MOS) capacitors with nanoneedle surface structure of silicon.