Development of nanopillars on mm² area of quantum-grade diamond membranes
Résumé
Recently, progress in diamond synthesis through plasma-assisted microwave chemical vapor deposition (CVD), along with post-treatments, has enabled the production of quantum-grade single-crystal diamond films with highly controlled densities of NV centers, ranging from a few parts per billion (ppb) to several parts per million (ppm) [1]. The excellent spin properties of this type of diamond allow the development of sensors that operate at room temperature, initialize, and optically read their quantum spin. However, beyond the perfect control of the quantum material, many challenges still lie in the insufficient development of micro- and nanometric diamond shaping processes. This work aims to process and handle diamond membranes with thicknesses of several tens of micrometers, featuring a forest of NV-doped nanopillars with a high aspect ratios, on their surface. These nanostructured membranes will be used for developing quantum technologies applications such as bio-sensing or to investigate solutions for sensing neuronal activity at the sub-micrometer scale. For this application, the NV-doped nanopillars array will serve as a scaffold for the growth of neuron branches that extend across the adjacent pillars [2]. It implies a millimeter-sized array on a diamond substrate, with 1 µm height, 2 µm periodicity, and around 400 nm diameters. To pattern materials, optical lithography is well-known but limited to micrometer-scale resolution. Electron-beam lithography offers higher resolution (nanometer-scale) but encounters long processing time on large areas (mm2) and charge effects on diamond. In this paper, we will present an original interferometric lithography that offers higher resolution (few hundred nanometers across several mm²) and short processing time. Results of selective resist insolation, followed by etching using ICP-RIE etching process, leading to a forest of nanopillars dimensionally adapted to neuronal culture will be presented and characterized. [1] Achard, J. et al., J. Phys. D: Appl. Phys. 2020. [2] Losero, E. et al., arXiv:2207.09903, 2022.