Selectivity to silicon nitride in chemical vapor deposition of titanium silicide

A high selectivity to silicon nitride in the chemical vapor deposition of t itanium silicide is needed to avoid deposition on the spacer region along t he sidewalls of polysilicon structures. Deposition was performed in a rapid thermal chemical vapor deposition system using a mixture of TiCl4, SiH4, S iH2Cl2, and H-2 Silicide film was found to deposit on silicon nitride film at conditions when deposition on oxide was not observed. The selectivity wa s 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 consump tion of substrate silicon. Good selectivity to silicon nitride at a lower T iCl4 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 gr ained TIN film followed by the formation of TiSi2. (C) 1999 American Vacuum Society. [S0734-211X(99)06705-0].