Method of silicide formation by adding graded amount of impurity during metal deposition

A method is provided for forming a metal semiconductor alloy that includes providing a deposition apparatus that includes a platinum source and a nickel source, wherein the platinum source is separate from the nickel source; positioning a substrate having a semiconductor surface in the deposition apparatus; forming a metal alloy on the semiconductor surface, wherein forming the metal alloy comprises a deposition stage in which the platinum source deposits platinum to the semiconductor surface at an initial rate at an initial period that is greater than a final rate at a final period of the deposition stage, and the nickel source deposits nickel to the semiconductor surface; and annealing the metal alloy to react the nickel and platinum with the semiconductor substrate to provide a nickel platinum semiconductor alloy.