3D out-of-plane rotational etching with pinned catalysts in metal-assisted chemical etching of silicon

Pinned structures in conjunction with shaped catalysts are used in metal-assisted chemical etching (MACE) of silicon to induce out-of-plane rotational etching. Sub-micro- and nanostructures are fabricated in silicon, which include scooped-out channels and curved subsurface horns, along with vertically oriented thin metal structures. Five different etching modes induced by catalyst and pinning geometry are identified: 1) fully pinned-no etching, 2) rotation via twist, 3) rotation via delamination, 4) in-plane bending, and 5) swinging. The rotation angle is roughly controlled through catalyst geometry. The force and pressure experienced by the catalyst are calculated from the deformation of the catalyst and range between 0.5-3.5 μN and 0.5-3.9 MPa, respectively. This is a new, simple method to fabricate 3D, heterogeneous sub-micro- and nanostructures in silicon with high feature fidelity on the order of tens of nanometers while providing a method to measure the forces responsible for catalyst motion during MACE.