Bulk Micromachining of Si by Annealing-Driven Magnetically Guided Metal-Assisted Chemical Etching

Herein, the bulk micromachining of Si by a magnetically guided metal-assisted chemical etching (MACE) process is demonstrated. To improve the etching performance of Si, a trilayer metal catalyst (Au/Fe/Au) is deposited on Si to obtain faster etching speed by a magnetic pulling force. An annealing process is performed on the catalyst to obtain rougher surface morphologies due to agglomeration and improve ferromagnetic properties, which increase the etching rate for magnetically guided MACE. By the bulk micromachining of Si through the introduced direction-controlled MACE technique with the annealing process, Si microsheet arrays are fabricated. We show that vertically aligned Si microsheet arrays are produced within 17 h of etching, even at an etching thickness of over 500 pm, by magnetically guided MACE under a fixed vertical magnetic pulling force. Moreover, introducing magnetically guided MACE can fabricate Si microhole arrays in various dimensions by adjusting pattern size and etching time. Curved Si microhole arrays are fabricated by altering the direction of the magnetic pulling force by changing the position of the hard magnet, which shows that the etching direction is effectively adjusted during the bulk micromachining of Si. The etching method developed here can be applied to cost-effective bulk Si slicing processes.