Microfluidic Neural Probes with Buried Channels Fabricated Using Continuous Flow XeF2 Etching of Silicon

This paper reports on the fabrication and characterization of thin silicon (Si) probes with integrated channels for minimally invasive drug delivery into the brain. Buried channels are realized in Si using plasma-free, vapor-phase, continuous-flow (cf) xenon difluoride (XeF
₂
) etching, with the microfluidic probes subsequently thinned down to 70 μm using the etching-before-grinding approach. While plenty of data are available in literature on pulsed XeF
₂
etching, the characteristics of cf-XeF
₂
processing, which provides a more controlled etch process, have to date not been widely discussed. To the best of our knowledge, this is the first study that reports on the detailed characterization of cf-XeF
₂
etching for the fabrication of micro-channels in single-crystal Si. By using etch openings of different dimensions and varying the process parameters, process characteristics such as etch rate, aperture effect, etch anisotropy, and surface roughness are investigated. Flow and mechanical fracture tests demonstrate the suitability of the fabricated probes for in vivo applications.