Selectivity to silicon nitride in chemical vapor deposition of titanium silicide

Abstract

A high selectivity to silicon nitride in the chemical vapor deposition of titanium silicide is needed to avoid deposition on the spacer region along the sidewalls of polysilicon structures. Deposition was performed in a rapid thermal chemical vapor deposition system using a mixture of TiCl4, SiH4, SiH2Cl2, and H2. Silicide film was found to deposit on silicon nitride film at conditions when deposition on oxide was not observed. The selectivity was found to depend on the flow rate of TiCl4. A higher flow rate reduced the silicide deposition on the silicon nitride, but also increased the consumption of substrate silicon. Good selectivity to silicon nitride at a lower TiCl4 flow was achieved at a lower wafer temperature. The Si/N ratio of the nitride film also affects silicide growth, but it is not a primary factor. The effect of SiH2Cl2 flow on selectivity was not detected. It is proposed that the growth on silicon nitride starts from the formation of a finely grained TiN film followed by the formation of TiSi2.