A new Ti salicide technology that uses nitrogen diffusion from a TiN cap layer by RTA in an argon ambient is demonstrated. The key point for achieving a fine-line Ti salicide iscontrolling the two competing reaction processes in thin Ti (<30 nm): nitridation at the Ti surface, and silicidation at the interface between Ti and Si. In the conventional Ti silicidation process using atmospheric nitrogen RTA, however, control of nitridation is difficult due to a high concentration of nitrogen at the Ti surface. Therefore, the remaining TiSi2 film is very thin and contains larger amount of nitrogen . The new technology provides good controllability of Ti nitridation for thin Ti by using an argon atmospheric RTA.
A major advantage of nitrogen diffusion from a TiN cap layer is controllability of the nitrogen concentration at the interface between TiN and Ti. After TiN and Ti sputtering, silicidation was performed by two-step annealing in argon (RTA1: 680°C, 30 s; RTA2: 800°C, 10 s). When the thickness ratio (TiN/Ti) was 1, Ti2N formed on the field oxide. The Ti2N layer suppresses excessive silicidation over the field oxide in the same way that TiN does. Sheet resistance results show that silicidation is suppressed by the impurity effect in the case of thinner Ti (<20 nm). Furthermore, when TiN is thick (>20 nm), large metal strength retards silicidation . Optimization of TiN/Ti thickness (20/20 nm) is essential for achieving low sheet resistance of 10 Ω for p+ and n+ quarter micron lines.