Technique for Eliminating Notching in Through-wafer Etching

 In through-wafer silicon etching using highdensity low-pressure inductively coupled plasma, a notching (or footing) effect occurs at the silicon-insulator interface. The insulator layer is common, as the silicon wafer has either an oxide layer to avoid break through of the plasma or is bonded to a handle wafer using either photoresist or other adhesives. Notching at the foot of micro-structures can lead to a significant degradation of the mechanical performance and is unacceptable when an optically flat surface is needed. A novel method to avoid notching by eliminating charge buildup through the use of a thin metal coating is presented.