Novel isotropic and anisotropic etching of MEMS structures by controlling the dynamics of the etchant

In MEMS technology there is an increasing interest in developing high aspect ratio silicon columns having rounded corners, slightly positive tapered shaft, sharp tips, and smooth surface. A precise control of the profile can be used for different applications, such as for molds used in polymer hot embossing processes, micro needles used for drug delivery and blood sampling, and neural probes used for controlling motor or sensory prosthetic devices. The mixture of hydrofluoric acid (HF) and nitric acid (HNO₃) is an isotropic etchant and is used in MEMS technology to etch silicon. We present a novel way of isotropically and anisotropically etch MEMS structures using the HF-HNO₃ etchant. The shape and size of the structure is controlled by the dynamics of reactants.