Narrow Line Effect of Nickel Silicide on p+ Active Lines and Its Suppression by Fluorine Ion Implantation

The narrow line effect of nickel silicide, which is the increase in sheet resistance (Rs) at narrow active lines, is first reported. The Rs of nickel silicide on p+ active lines gradually increases at a linewidth of less than 200 nm. From detailed analyses, it is revealed that the Rs at the borders of the active lines, which are in the region ranging from 50 to 60 nm from shallow trench isolation (STI) edges, is higher than that at the center of an active line, and as a result, the Rs at the narrow lines increases. The high Rs of nickel silicide at the narrow lines might be caused by both nickel monosilicide (NiSi) agglomeration and nickel disilicide (NiSi2) nucleation due to the poor thermal stability of NiSi. In order to suppress this degradation, we examined fluorine ion (F+) implantation just before Ni film deposition. The poor thermal stability of NiSi is effectively improved by F+ implantation, and the Rs increase at the borders of p+ active lines is successfully suppressed. As a result, the narrow line effect of nickel silicide on p+ active lines is completely suppressed.