Semiconductor device and method for fabricating the same

Abstract

The semiconductor device comprises a pair of impurity diffused regions formed in a silicon substrate 10, spaced from each other, and a gate electrode 26 formed above the silicon substrate 10 between the pair of impurity diffused regions 38 intervening a gate insulation film 12 therebetween. The gate electrode 26 is formed of a polycrystalline silicon film 16 formed on the gate insulation film 12, a polycrystalline silicon film 30 formed on the polycrystalline silicon film 16 and having crystal grain boundaries discontinuous to the polycrystalline silicon film 16, a metal nitride film 20 formed on the polycrystalline silicon film 30, and a metal film 22 formed on the barrier metal film 20. Whereby diffusion of the boron from the first polycrystalline silicon film 16 toward the metal nitride film 20 can be decreased. Thus, depletion of the gate electrode 26 can be suppressed.

What is claimed is:  
     
         1 . A semiconductor device comprising: 
 a pair of impurity diffused regions formed in a silicon substrate, spaced from each other; and    a gate electrode formed above the silicon substrate between the pair of impurity diffused regions intervening a gate insulation film therebetween, the gate electrode being formed of a first polycrystalline silicon film formed on the gate insulation film, a second polycrystalline silicon film formed on the first polycrystalline silicon film and having crystal grain boundaries which are discontinuous to the first polycrystalline silicon film, and a metal nitride film formed on the second polycrystalline silicon film.    
     
     
         2 . A semiconductor device comprising: 
 a pair of impurity diffused regions formed in a silicon substrate, spaced from each other; and    a gate electrode formed above the silicon substrate between the pair of impurity diffused regions intervening a gate insulation film therebetween, the gate electrode being formed of a first polycrystalline silicon film formed on the gate insulation film, a second polycrystalline silicon film formed on the first polycrystalline silicon film and having crystal grain boundaries which are discontinuous to the first polycrystalline silicon film, a metal nitride film formed on the second polycrystalline silicon film, and a metal film form on the metal nitride film.    
     
     
         3 . A semiconductor device according to  claim 1 , wherein 
 a native oxide film is formed between the first polycrystalline silicon film and the second polycrystalline silicon film.    
     
     
         4 . A semiconductor device according to  claim 2 , wherein 
 a native oxide film is formed between the first polycrystalline silicon film and the second polycrystalline silicon film.    
     
     
         5 . A semiconductor device according to  claim 1 , wherein 
 the first polycrystalline silicon film is doped with boron.    
     
     
         6 . A semiconductor device according to  claim 2 , wherein 
 the first polycrystalline silicon film is doped with boron.    
     
     
         7 . A semiconductor device according to  claim 1 , wherein 
 the first polycrystalline silicon film and the second polycrystalline silicon film are doped with boron, a boron concentration in the first polycrystalline silicon film near an interface between the first polycrystalline silicon    
     
     
         11 . A method for fabricating a semiconductor device comprising the steps of: 
 forming a gate insulation film on a silicon substrate;    forming a first silicon film doped with boron on the gate insulation film;    forming a second silicon film on the first silicon film;    forming a metal nitride film on the second silicon film;    forming a metal film on the metal nitride film; and    patterning a layered structure of the first silicon film, the second silicon film, the metal nitride film and the metal film to form a gate electrode of the layered structure.    
     
     
         12 . A method for fabricating a semiconductor device according to  claim 11 , wherein 
 the step of forming the first silicon film includes the step of forming a polycrystalline silicon film on the gate insulation film and the step of doping boron in the polycrystalline silicon film.    
     
     
         13 . A method for fabricating a semiconductor device according to  claim 12 , further comprising between the step of forming the polycrystalline silicon film and the step of doping boron, 
 the step of amorphizing the surface of the polycrystalline silicon film.    
     
     
         14 . A method for fabricating a semiconductor device according to  claim 11 , wherein 
 the step of forming the first silicon film includes the step of forming an amorphous silicon film on the gate insulation film and the step of doping boron in the amorphous silicon film.    
     
     
         15 . A method for fabricating a semiconductor device according to  claim 11 , wherein 
 in the step of forming the second silicon film, the second silicon film is formed on the first silicon film intervening a native oxide film therebetween.    
     
     
         16 . A method for fabricating a semiconductor device according to  claim 11 , further comprising between the step of forming the first silicon film and the step of forming the second silicon film, 
 the step of thermal processing to activate the boron doped in the first silicon film.    
     
     
         17 . A method for fabricating a semiconductor device according to  claim 11 , wherein 
 in the step of forming the second silicon film, the second silicon film is formed in a 2-20 nm-thick.