Silicon selective etching by gold implantation: Feasibility and nanofabrication capabilities

Silicon nanofabrication plays a crucial role in the development of advanced electronic, photonic, and quantum devices. Focused ion beam (FIB) milling is widely used for direct patterning at the nanoscale, but it requires high ion fluences, leading to long processing times, material redeposition, and increased contamination. In this work, we demonstrate an alternative FIB-based approach that relies on gold ion implantation at significantly lower fluences, enabling selective silicon etching while minimizing these drawbacks.

Gold ions (Au⁺) were implanted into silicon substrates with a kinetic energy of 35 keV, followed by wet etching in tetramethylammonium hydroxide (TMAH). We identified the process window of Au fluences between 1 × 10¹⁵ and 1 × 10¹⁷ ions/cm², with secondary ion mass spectrometry (SIMS) confirming an Au concentration threshold of 3.5 × 10²⁰ atoms/cm³ necessary to sustain etching resistance, value predicted also by Monte Carlo simulations (TRIDYN). This approach enables the fabrication of suspended silicon nanowires with a minimum width of 36 nm, a thickness of 20 nm, and lengths up to 8 μm, achieving aspect ratios exceeding 400, as well as more complex suspended structures likes nets which can be targeted for applications in nanoelectromechanical systems (NEMS) reaching nanowire width over pitch down to 2 %.

The proposed method presents a promising alternative to conventional silicon patterning, significantly reducing processing complexity while enhancing nanostructure resolution. The results provide new insights into ion-implantation-assisted etching mechanisms and expand the possibilities for silicon nanostructure fabrication.