Dual poly deposition and through gate oxide implants

Abstract

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.

1 . A MOS transistor comprising:
 a gate structure, comprising:
 a gate dielectric formed over a semiconductor substrate; 
 a first gate electrode formed over the gate dielectric; and 
 a second gate electrode formed over the first gate electrode; 
   a source region formed in the semiconductor substrate adjacent to one side of the gate structure; and   a drain region formed in the semiconductor substrate adjacent to the other side of the gate structure.   
   
   
       2 . The transistor of  claim 1 , where the first gate electrode comprises a dopant of Arsenic at a concentration of between about 1e15/cm 2  and about 4e15/cm 2 . 
   
   
       3 . The transistor of  claim 2 , where the first gate electrode is formed to a thickness of between about 80 Angstroms and about 300 Angstroms and the second gate electrode is formed to a thickness of between about 800 Angstroms and about 1000 Angstroms. 
   
   
       4 . The transistor of  claim 3 , where the source and drain regions are formed in a well region in the semiconductor substrate, where the well region has a retrograde profile of a dopant of Boron at a concentration of between about 1e18/cm 3  and about 2e18/cm 3  at a depth of between about 200 Angstroms and about 400 Angstroms and a concentration of between about 3e17/cm 3  and about 1e18/cm 3  at a depth of between about 0 Angstroms and about 100 Angstroms.