Multi-step etching of three-dimensional sub-millimeter curved silicon microstructures with in-plane principal axis

We report a micromachining method for batch fabrication of three-dimensional curved microstructures exhibiting in-plane principal axis with respect to the wafer substrate. The target profile in the out-of-plane direction is controlled by a multi-step technique involving etching and protection alternatively with pre-designed timing of each step. The versatility of the method is studied theoretically and found to be suitable for curved microstructure realization with height-to-radius-of-curvature ratios in the order of 0.25 to 1. The method is applied experimentally on silicon substrates and an inductively coupled plasma reactor is used to carry out the multiple steps of etching and protection without human interruption. Three-dimensional curved microstructures with sub-millimeter radii of curvature are successfully demonstrated.