Si nanowires by a single-step metal-assisted chemical etching process on lithographically defined areas: formation kinetics

Abstract

In this paper, we investigate the formation kinetics of Si nanowires [SiNWs] on lithographically defined areas using a single-step metal-assisted chemical etching process in an aqueous HF/AgNO3 solution. We show that the etch rate of Si, and consequently, the SiNW length, is much higher on the lithographically defined areas compared with that on the non-patterned areas. A comparative study of the etch rate in the two cases under the same experimental conditions showed that this effect is much more pronounced at the beginning of the etching process. Moreover, it was found that in both cases, the nanowire formation rate is linear with temperature in the range from 20°C to 50°C, with almost the same activation energy, as obtained from an Arrhenius plot (0.37 eV in the case of non-patterned areas, while 0.38 eV in the case of lithographically patterned areas). The higher etch rate on lithographically defined areas is mainly attributed to Si surface modification during the photolithographic process.PACS: 68; 68.65-k.

Metal-assisted chemical etching of silicon and the behavior of nanoscale silicon materials as Li-ion battery anodes

“…Additionally, the NW crystal orientation and doping density mimic the underlying substrate, while VLS NWs preferentially grown in the [111] and [112] directions can vary with NW dimension and synthetic growth conditions [71,72]. Moreover, doping of VLS Si NWs uses harsh chemicals such as phosphine that are not ideal [73].…”

“…MAC etching of a Si (100) substrate using a gold mesh as a catalyst was used to fabricate Si NWs with varying orientations and morphologies, including zigzag Si NWs [111], Si NWs, and curved Si NWs [116]. It was found that the crystal orientation and morphology of Si NWs are controlled by the injection of holes (h + ) into the valence band and removal of oxidized Si by HF.…”

“…Variation of the etching direction in (111) n-type Si has also been illustrated through changes in the HF:AgNO 3 ratio and the etching temperature and time. The etching directions of the Ag particles were shown to be (111), (110), (211), (311), and zigzag depending on the etching conditions as shown in Figs. 8(g)-8(l) [122].…”

“…This was due to hexamethyldisilazane (HMDS), which is used in the deposition of the photoresist. The HMDS removed -OH groups from the Si surface and formed a hydrophobic surface that improved the etch rate [111].…”

“…Initially, it was shown that etching in (100) and (111) Si occurred in the vertical direction only [59,118]. However, more recently, contradictory reports have shown the formation of slanted NWs from substrates with these orientations [59,80,[118][119][120].…”