Stable work function for narrow-pitch devices

Abstract

A work function setting metal stack includes a configuration of layers including a high dielectric constant layer and a diffusion prevention layer formed on the high dielectric constant layer. An aluminum doped TiC layer has a thickness greater than 5 nm wherein the configuration of layers is employed between two regions as a diffusion barrier to prevent mass diffusion between the two regions.

1 - 12 . (canceled) 
     
     
         13 . A method of forming a gate structure between a plurality of nanosheets of nanosheet fin, the plurality of nanosheets comprising a first nanosheet and an adjacent second nanosheet below the first nanosheet, the method comprising:
 forming a high-k dielectric layer on the first and second nanosheets;   after forming the high-k dielectric layer, forming a work function metal stack comprising a common metal layer disposed between the first and second nanosheets, wherein the common metal layer has a thickness of about 5 nm, and forming the work function metal stack comprises:
 forming a diffusion barrier layer on the high-k dielectric layer; and 
 forming a metal layer on the diffusion barrier layer, wherein the metal layer merges with itself to form the common metal layer. 
   
     
     
         14 . The method of  claim 13 , wherein the metal layer comprises titanium and aluminum. 
     
     
         15 . The method of  claim 14 , wherein the concentration of aluminum in the metal layer is between about 20% and about 40%. 
     
     
         16 . The method of  claim 14 , wherein the metal layer further comprises carbon. 
     
     
         17 . The method of  claim 16 , wherein the metal layer further comprises oxygen. 
     
     
         18 . The method of  claim 16 , wherein forming the common metal layer comprises depositing the metal layer to a thickness greater than 2.5 nm. 
     
     
         19 . The method of  claim 13 , wherein the gate structure is formed between adjacent fins of a plurality of nanosheet fins, and the metal layer merges with itself in regions between the adjacent nanosheet fins. 
     
     
         20 . The method of  claim 13 , wherein the diffusion barrier layer comprises titanium and nitrogen. 
     
     
         21 . The method of  claim 20 , wherein the diffusion barrier layer has a thickness of about 1 nm. 
     
     
         22 . The method of  claim 13 , wherein the high-k dielectric layer comprises hafnium and oxygen. 
     
     
         23 . The method of  claim 22 , wherein the high-k dielectric layer has a thickness between about 1 nm and about 2 nm. 
     
     
         24 . The method of  claim 13 , wherein the gate structure has a gate length equal to the sum of 2 times the thickness of the high-k dielectric layer, 2 times the thickness of the diffusion barrier layer, and the thickness of the common metal layer. 
     
     
         25 . The method of  claim 13 , further comprising:
 before forming the high-k dielectric layer, forming an interfacial oxide layer on each of the plurality of nanosheets, the interfacial oxide layer comprising silicon.   
     
     
         26 . The method of  claim 25 , wherein the interfacial oxide layer has a thickness between about 0.5 nm and about 5 nm. 
     
     
         27 . The method of  claim 25 , wherein the interfacial oxide layer has a thickness between about 0.5 and about 1 nm. 
     
     
         28 . The method of  claim 25 , wherein the interfacial oxide layer has a thickness between about 1 nm and about 5 nm. 
     
     
         29 . The method of  claim 25 , wherein:
 the high-k dielectric layer is formed directly on the interfacial oxide layer;   the diffusion barrier layer comprises titanium and nitrogen;   the diffusion barrier layer is formed directly on the high-k dielectric layer;   the metal layer is formed directly on the diffusion barrier layer; and   the metal layer comprises titanium, aluminum and carbon.   
     
     
         30 . The method of  claim 29 , wherein the metal layer further comprises oxygen. 
     
     
         31 . The method of  claim 29 , wherein the gate structure has a gate length equal to the sum of 2x the thickness of the high-k dielectric layer, 2x the thickness of the diffusion barrier layer, and the thickness of the common metal layer.