Abstract: The present invention provides a method for controlling dopant density of a plug-shaped doped polysilicon layer formed within a plug-shaped recess to prevent the dopant contained in the plug-shaped doped polysilicon layer from diffusing into a conductive layer under the plug-shaped recess through a bottom side of the plug-shaped recess, the plug-shaped recess being formed within a dielectric layer which is positioned above the conductive layer, the method comprising: (1) forming an undoped silicon layer on the surface of the plug-shaped recess; (2) forming a doped polysilicon layer on top of the undoped silicon layer to fill the plug-shaped recess; and (3) performing a thermal treatment to the semiconductor wafer so as to make the doped poly-silicon layer interact with the undoped silicon layer inside the plug-shaped recess which forms a completely doped polysilicon layer within the plug-shaped recess.