N⁺/P junction leakage characteristics of Co salicide process for 0.15 μm CMOS devices

We have proposed that As dopants in the n⁺/p active region are redistributed during Co salicidation process, especially in the active edge area in contact with the field oxide. The dopant redistribution has been verified through a novel two-dimensional (2-D) dopant profiling method, i.e., the transmission electron microscope (TEM) combined with selective chemical etching. It was shown that As dopants move down from the silicide layer into the junction area, which results in the deeper junction compared with nonsilicided junction. On the contrary, the junction profile behavior at the active edge area is completely opposite to that inside active region. That is, the junction profile is bent upward at the active edge, which results in the increase or even fail of junction leakage current of perimeter intensive diodes due to the decreased distance from the silicide bottom to the junction depth. Therefore, the dopant redistribution at the n⁺/p active edge should be reduced or suppressed for reliable shallow silicided junction formation.