Preparation and etching of porous silicon as a sacrificial layer used in RF-MEMS devices

A process using porous silicon (PS) as a sacrificial layer to RF-MEMS devices is developed. In a special receptacle, PS was fabricated in different concentrations of HF solutions, and their qualities were compared. Formed in high concentration of HF solution by electrochemical dissolution, the PS is suitable to be used as sacrificial layers in RF-MEMS devices. The recommendatory condition is anodized in a 20% HF solution at a current density J=40mA/cm². It was found PS would be removed when boiling in pure H₃PO₄, a standard solution for removal of the Si₃N₄ layer. To remove the Si₃N₄ on the substrate, a long time of immersing in HF solution is recommended. With the use of TMAH solution instead of KOH to remove the PS, the surface after etching will be more lubricous, and the process is compatible with CMOS technology.