WSi2/Polysilicon Gate Etching Using TiN Hard Mask in Conjunction with Photoresist

Abstract

We found that the selectivity between TiN and poly-Si film was high enough in Cl2/O2 plasma to use TiN as an etching mask for poly-Si gate etching. We also discovered that the oxidation of the TiN surface is the reason why TiN serves as an etching mask in poly-Si etching using Cl2/O2 plasma. By using a TiN hard mask in conjunction with a thin photoresist, we were able to reduce electron shading damage. The low aspect ratio of the space of a line-and-space (L&S) pattern is the major reason for the reduction in electron shading damage in this TiN mask process. A portion of the TiN surface on which no charge up occurs is exposed to the plasma during the overetch step because photoresist is eroded by ion bombardment. This is an another reason for the reduced electron shading damage.