Exploring the relationship between doping and Ti-silicidation for advanced FDSOI applications

High phosphorus dopant concentrations are todays required in Si:P sources and drains to improve device performances. However, their impact on Ti thin film silicidation phase sequence remains unclear. This study focused on Ti silicide formation on in-situ phosphorus doped Si (100) layers for two doping concentrations and on phosphorus redistribution during solid-state reactions. The impact of the amount of phosphorus dopant and the Ti silicidation phase sequence were explored in the TiN/Ti/Si:P system through sheet resistance and X-Ray diffraction measurements. Meanwhile, dopant redistribution was analyzed by time-of-flight secondary ion mass spectrometry. Silicidation was achieved with a 10 nm Ti thin film using rapid thermal annealing. The overall phase sequence was as follows: (1) intermixing by Si diffusion into Ti, (2) formation of an intermediate crystalline phase and, (3) formation of metastable C49-TiSi 2 phase. It was found that increasing dopant concentration led to the formation of a less resistive crystalline phase with a still unclear nature. On the other hand, increasing phosphorus concentration favored dopant segregation at surfaces/interfaces, that could be explained by phosphorus supersaturation into the layers. The phosphorus concentration in silicide layers was found to increase with the annealing temperature. In the highly-doped sample, after annealing at 950 °C, phosphorus segregation at the TiN/C49-TiSi 2 disappeared, while phosphorus concentration into the silicide layer rose. This could be correlated to the formation of a crystalline phase. We thus demonstrated that higher phosphorus concentration had an impact on the silicide phase sequence and on the redistribution of P during Ti silicidation in the TiN/Ti/Si:P system.