Work function adjustment with the implant of lanthanides

Abstract

Semiconductor devices and fabrication methods are provided, in which fully silicided gates are provided. A lanthanide series metal is implanted into the gate electrode layer prior to silicidation and diffuses into the gate dielectric during an activation anneal. This process and resultant structure provides adjustment of the gate electrode work function, thereby tuning the threshold voltage of the resulting transistor.

What is claimed is: 
     
         1 . A method of forming a transistor, comprising:
 forming a gate dielectric over a semiconductor body, wherein the gate dielectric comprises a material in a top portion thereof that does not extend to an interface between the gate dielectric and the semiconductor body, wherein the material is selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium; and   forming a silicon gate electrode over the gate dielectric.   
     
     
         2 . The method of  claim 1 , further comprising fully siliciding the gate electrode. 
     
     
         3 . The method of  claim 2 , wherein fully siliciding the gate electrode comprises:
 forming a nickel layer over the gate electrode; and   performing one or more thermal processes so as to fully react the silicon of the gate electrode with the nickel layer, thereby causing substantially the entire gate electrode to comprise a nickel silicide.