Scanning probe-based nanolithography: nondestructive structures fabricated on silicon surface via distinctive anisotropic etching in HF/HNO3 mixtures

HF/HNO3 mixtures were typical isotropic etching systems for processing silicon (Si) surface, and still suffer from difficulties in controllably fabricating nanostructures. Here, fast and anisotropic etching approach with HF/HNO3 mixtures was developed to overcome this challenge. An atomic force microscope diamond tip was used for the preparation of friction-induced hillocks, mainly consisting of amorphous Si, through reciprocating sliding of Si surfaces below critical contact pressure. The hillock acted as a mask against HF/HNO3 mixtures etching, forming nanostructures through subsequent distinctive anisotropic etching. The effects of volume ratio of HF/HNO3 mixtures, sliding cycle, normal load, and etching time on anisotropic etching were systematically investigated to optimize fabrication parameters. Further analysis suggested that lower average dangling bond density in scanned regions may retard the breakup of Si–H bonds and polarized Si–Si backbonds, leading to lower dissolution rates compared to original Si surface. Cross-sectional high-resolution transmission electron microscope observations revealed defect-free nanostructures fabricated by the anisotropic etching. Also, several nondestructive nanostructures with different patterns were realized on Si surfaces by programming tip scanning traces. In sum, the proposed method is promising for the fabrication of controllable nano-sized functional devices by HF/HNO3 mixtures. Nanofabrication of nondestructive structures on silicon surface via distinctive anisotropic etching in HF/HNO3 mixtures