Fabrication of ultrahigh-density nano-pyramid arrays (NPAs) on [100] silicon wafer using scanning probe lithography and anisotropic wet etching

Convex and concave nano-pyramid arrays (NPAs) with an areal bit density of 64.5 Gbits/in² has been demonstrated by means of scanning probe lithography (SPL) and wet etching on the [100]-orientation silicon wafer. First, we investigated the use of a contact-mode atomic force microscope (AFM) in the generation of oxide patterns on silicon [100] surfaces. Subsequently, utilizing the oxide pattern as Si etching masks, the Si substrate was dipped in aqueous KOH solution, where un-oxidized regions were selectively etched by aqueous KOH orientation-dependent etching (ODE). Using this simple process, 20 nm convex NPAs with 100 nm pitch can be fabricated successfully. Similarly, about 2 nm concave NPAs with 100 nm were obtained after the oxidized samples were dipped in aqueous HF solution, the oxide regions were selectively etched away. To demonstrate the capability of this technology, we have showed an AFM micrograph of the letters "TLS". These patterns correspond to an ultrahigh data-storage density of about 64.5 Gbits/in², more than 20 times increase in areal density compared to conventional optical recording. We also demonstrated that the minimum size of the pyramids and the minimum pitch could be easily controlled by the apex size of the pyramid, that is, the size of the oxidized region by AFM-based field-induced oxidation. The results indicated that this technique has potential to provide a pathway to the higher densities that will be needed in the decades ahead. Also, the influenced parameters of oxide pattern and the influence of wet etching on etching rate and shape of etched structure will be discussed.