Semiconductor device and method for manufacturing the same

Abstract

A semiconductor device includes an insulating film provided over a semiconductor substrate, a conductive plug buried in the insulating film, an underlying conductive film which is provided on the conductive plug and on the insulating film and which has a flat upper surface, and a ferroelectric capacitor provided on the underlying conductive film. At least in a region on the conductive plug, the concentration of nitrogen in the underlying conductive film gradually decreases from the upper surface to the inside.

1 . A method for manufacturing a semiconductor device comprising:
 forming an insulating film over a semiconductor substrate;   burying a conductive plug in the insulating film;   forming a high melting point metal film on the conductive plug and the insulating film;   planarizing the upper surface of the high melting point metal film by polishing the upper surface thereof;   nitriding the high melting point metal film to form an underlying conductive film by performing a heat treatment in an atmosphere containing nitrogen; and   forming a ferroelectric capacitor on the underlying conductive film.   
     
     
         2 . The method for manufacturing a semiconductor device according to  claim 1 , wherein, in a region on the conductive plug, only an upper layer portion of the underlying conductive film is nitrided. 
     
     
         3 . The method for manufacturing a semiconductor device according to  claim 1 , wherein, when planarizing the upper surface of the high melting point metal film, the high melting metal film is polished until the insulating film is exposed. 
     
     
         4 . The method for manufacturing a semiconductor device according to  claim 1 , further comprising:
 diffusing nitrogen in the insulating film after burying a conductive plug in the insulating film and before forming a high melting point metal film,   wherein, when nitriding the high melting point metal film to form an underlying conductive film, the high melting point metal film is further nitrided at a lower layer portion thereof by the nitrogen diffused in the insulating film.   
     
     
         5 . The method for manufacturing a semiconductor device according to  claim 4 , wherein, when diffusing nitrogen in the insulating film, the upper surface of the insulating film is exposed to a plasma containing nitrogen to diffuse nitrogen in the insulating film. 
     
     
         6 . The method for manufacturing a semiconductor device according to  claim 5 ,
 wherein the plasma containing nitrogen includes NH 3  plasma or N 2  plasma.   
     
     
         7 . The method for manufacturing a semiconductor device according to  claim 4 , further comprising:
 sputtering the plasma on the upper surface of the insulating film after burying a conductive plug in the insulating film and before diffusing nitrogen in the insulating film.   
     
     
         8 . The method for manufacturing a semiconductor device according to  claim 1 , wherein the underlying conductive film includes titanium or tantalum. 
     
     
         9 . The method for manufacturing a semiconductor device according to  claim 1 , further comprising:
 after nitriding the high melting point metal film to form an underlying conductive film and before forming a ferroelectric capacitor, forming another high melting point metal film on the underlying conductive film and nitriding an upper layer portion of the another high melting point metal film to form another underlying conductive film by performing a heat treatment in an atmosphere containing nitrogen.   
     
     
         10 . The method for manufacturing a semiconductor device according to  claim 9 , further comprising:
 after nitriding the high melting point metal film to form an underlying conductive film and before forming another high melting point metal film, exposing the upper surface of the underlying conductive film to a plasma including NH 3  plasma.