Electrochemical etching of porous silicon sacrificial layers for micromachining applications

Using porous silicon (PS) as a thick sacrificial layer, free-standing structures at a large distance from the bulk can be obtained. The very high specific surface of PS makes its removal using dilute alkaline solutions possible. In this work different technological conditions, such as adding ethanol or ultrasonic stirring, are studied in order to optimize the removal of PS using a one-step process with 0.1% KOH solution. Finally, cathodic polarization of the sample during the removal process is proposed as a method to enhance and improve the etching of PS whilst avoiding possible oxide formation. This electrochemical etching of a PS sacrificial layer allows good quality free-standing polysilicon structures featuring a smooth substrate to be obtained.