Method of soft-landing gate etching to prevent gate oxide damage

Abstract

Abstract A soft-landing etch process is provided to form an oxide layer with uniform thickness on an open area between flash memory transistors on a substrate. A dielectric oxide layer, such as silicon dioxide, is formed on a semiconductor substrate. A polysilicon layer used to form gates of flash memory transistors is then formed on the oxide layer. The polysilicon layer is covered with a layer of conductive material, such as tungsten silicide (WSi). A cap polysilicon layer is deposited on the conductive layer. An anti-reflecting coating, such as SiON, is formed on the cap polysilicon layer. A photo-resist mask comprising a pattern defining a gate is formed on the surface of the anti-reflecting coating. The softlanding etch process performed to expose oxide layer on the substrate area between flash memory transistors includes three etch steps. The first etch step is carried out to remove materials covering the gate polysilicon layer on the area between flash memory transistors. Then, the second etch step having high polysilicon-to-oxide selectivity is performed to remove polysilicon covering the oxide layer on the open area. The third etch step is conducted to clean polysilicon residues from the oxide layer surface on the open area.

Inventors

• 👤 Lewis Shen
• 👤 Wenge Yang

Bibliographic Details