| abstract |
A method of etching a trench in a silicon layer is disclosed. The silicon layer being disposed below an oxide layer. The oxide layer being disposed below a nitride layer. The nitride layer being disposed below a photoresist mask. The etching taking place in a plasma processing chamber. The method includes flowing a first etchant source gas into the plasma processing chamber, forming a first plasma from the first etchant source gas and etching substantially through the nitride layer with the first plasma. The method further includes flowing a second etchant source gas into the plasma processing chamber, forming a second plasma from the second etchant source gas and etching through the oxide layer and a portion of the silicon layer with the second plasma wherein the etching with the second plasma is extended for a period of time after the pad oxide layer is etched through. The period of time being sufficiently long to form an effective top-rounded feature on a portion of the trench. |