Si micro-turbine by proton beam writing and porous silicon micromachining

A 3D Si micro-turbine characterized by high aspect ratio vertical walls was formed by the combination of proton beam writing (PBW) and subsequent selective porous Si (PS) etching. Crystal damages generated by the implanted protons result in increased resistivity, thereby limit or even prevent the current to flow through the implanted area during electrochemical etching. Characteristic feature of the proposed process is that the shape of the micro electro-mechanical (MEMS) components is defined by two implantation energies. A higher energy is applied for defining the housing of the device while the lower energy is used to write the moving components. The implantation energies were selected such as to result appropriate difference between the two projected ranges, thereby providing structures with different height after development. The thickness of the walls of the moving component and the isotropic etching profile of the electrochemical PS formation was also taken into consideration. The electrochemical etching is driven until the sacrificial PS layer completely underetches the moving components, but the etch-front does not reach the bottom of the housing. Therefore, the dissolution of PS results in a ready-to-operate device with a released moving component embedded in the cavity of the housing. This work is the first demonstration of a silicon device containing a moving part made by proton beam writing.