Complementary metal-oxide-semiconductor (CMOS) devices comprise source regions, drain regions, and gate electrodes, which are often formed of silicon-containing materials. To reduce the contact resistance between the silicon-containing source/drain regions and the silicon-containing gate electrodes, metal silicides may be formed atop the source/drain regions and the gate electrodes prior to the formation of various metal layers comprising conductive interconnect lines and vias. The most commonly used metal silicides are nickel silicide and cobalt silicide, typically formed by a self-aligned silicide (salicide) process.
In a salicide process, a thin layer of metal is blanket deposited by physical vapor deposition (PVD) over a semiconductor wafer, specifically over exposed source/drain regions and gate electrodes. The wafer is then subjected to one or more annealing steps, for example, at a temperature of 250° C. or higher. The annealing process causes the metal to selectively react with the exposed silicon of the source/drain regions and the gate electrodes, thereby forming metal silicide regions. The process is referred to as a self-aligned silicidation process because the silicide layer is formed where the metal material directly contacts the silicon source/drain regions and the gate electrode. Following the formation of the silicide regions, the un-reacted metal is removed. An interconnect process is then performed to provide conductive paths, such as by forming via holes through a deposited interlayer dielectric and filling the via holes with a conductive material, e.g., tungsten or copper.
For sub-65 nm technologies, nickel is widely used to form silicides. A problem of the nickel silicide is its poor thermal stability, and the tendency of forming agglomeration. The resistivity of the resulting silicide is increased as a result of the agglomeration. To improve the thermal stability of nickel silicides, platinum may be added to the nickel silicide. To add platinum, the target that is used in the PVD is added with platinum, which may have a percentage between about 5 percent and about 10 percent. The improvement in the thermal stability of the silicides as a result of adding platinum, however, is still not satisfactory, and the thermal stability of the silicides needs to be improved further.