Anisotropic And High Selective Multi-step Polycide Etching
Original Publication Date: 1985-Dec-01
Included in the Prior Art Database: 2005-Feb-19
The formation of an interfacial oxide between polysilicon and silicide during the deposition of tungsten silicide prohibits a single highly selective polysilicon-to-gate oxide etching process. Residue after plasma etching silicide also requires a clean process for silicide etching. A multi-step process to etch composite structures of silicide/poly- siliconin a planar parallel reactor, which produces an acceptable structure, is disclosed. In the first step, CCl2F2 with oxygen added is used to etch tungsten silicide anisotropically and residue-free down to the polysilicon. In the second step, CCl2F2 at low pressure is used to carry the silicide etching down to polysilicon anisotropically and with low selectivity. The third step uses CCl2F2/NH3 to etch doped polysilicon anisotropically and with high selectively to the gate oxide.