Methods and apparatus for forming word line stacks comprise one, or a combination of the following: a silicon diffusion barrier layer, doped with oxygen or nitrogen, coupled between a bottom silicon layer and a conductor layer; an amorphous silicon diffusion barrier coupled between a polysilicon layer and a conductor layer; a thin nitride layer coupled between a bottom silicon layer and a titanium silicide conductor layer, and a bottom silicon layer coupled to a conductor layer, which comprises C54-titanium silicide. Word line stacks formed by the methods of the invention are used in sub-0.25 micron line width applications and have a lower resistivity and improved thermal stability.