US Patent 7435638 Dual poly deposition and through gate oxide implants

Dopants are implanted at relatively high energies into an unmasked first region of a semiconductor substrate through a thin layer of gate electrode material and a gate dielectric layer. Lower energy dopants are then implanted into the thin layer of gate electrode material. The first region is then masked off, and the process is repeated in a previously masked, but now unmasked, second region of the semiconductor substrate. A second (and usually thicker) layer of gate electrode material is then formed over the thin layer of gate electrode material. The layer of thick gate electrode material, the layer of thin gate electrode material and the layer of gate dielectric material are patterned to form one or more gate structures over the doped regions of the substrate. Source and drain regions are formed in the substrate regions adjacent to the gate structures to establish one or more MOS transistors.