Semiconductor device having a ferroelectric capacitor and a fabrication process thereof

Abstract

A method of fabricating a semiconductor device having a ferroelectric capacitor includes the steps of forming a lower electrode layer of the ferroelectric capacitor on an insulation film covering an active device element, forming a ferroelectric film on the lower electrode layer as a capacitor insulation film, crystallizing the ferroelectric film by applying a thermal annealing process in an atmosphere containing a non-oxidizing gas and an oxidizing gas, and forming an upper electrode layer on the ferroelectric film.

What is claimed is:  
     
         1 . A method of fabricating a semiconductor device having a ferroelectric capacitor, comprising the steps of: 
 forming an active device element on a substrate;    forming an insulation film over said substrate to cover said active device element;    forming a lower electrode layer of said ferroelectric capacitor over said insulation film;    forming a ferroelectric film on said lower electrode layer as a capacitor insulation film of said ferroelectric capacitor;    crystallizing said ferroelectric film by applying a thermal annealing process in an atmosphere containing a non-oxidizing gas and an oxidizing gas; and    forming an upper electrode layer on said ferroelectric film.    
     
     
         2 . A method as claimed in  claim 1 , wherein said step of forming said lower electrode layer includes a step of depositing a Ti layer and a Pt layer consecutively.  
     
     
         3 . A method as claimed in  claim 1 , wherein said step of crystallizing said ferroelectric film is conducted by setting the composition of said atmosphere such that said atmosphere contains said oxidizing gas with a fraction of 1-50% in volume.  
     
     
         4 . A method as claimed in  claim 1 , wherein said non-oxidizing gas is selected from a group consisting of Ar, He, Ne, Xe and N 2 .  
     
     
         5 . A method as claimed in  claim 1 , wherein said oxidizing gas is selected from a group consisting of O 2 , N 2 O, NO and NO 2 .  
     
     
         6 . A method as claimed in  claim 1 , wherein said step of crystallizing said ferroelectric film is conducted by a rapid thermal annealing process.  
     
     
         7 . A method as claimed in  claim 1 , wherein said step of forming said step of forming said ferroelectric film comprises the step of forming said ferroelectric film by a sputtering process.  
     
     
         8 . A method as claimed in  claim 7 , wherein said ferroelectric film has a perovskite structure.  
     
     
         9 . A method as claimed in  claim 8 , wherein said ferroelectric film is a film of zirconate titanate of Pb.  
     
     
         10 . A method as claimed in  claim 1 , further comprising the step, after said step of crystallizing said ferroelectric film, of oxidizing said ferroelectric film in an oxidizing atmosphere.  
     
     
         11 . A method as claimed in  claim 1 , wherein said step of crystallizing said ferroelectric film is conducted under a reduced total pressure.  
     
     
         12 . A method of fabricating a semiconductor device having a ferroelectric capacitor, comprising the steps of: 
 forming an active device element on a substrate;    forming an insulation film over said substrate to cover said active device element;    forming a lower electrode layer of said ferroelectric capacitor over said insulation film;    forming a ferroelectric film on said lower electrode layer as a capacitor insulation film of said ferroelectric capacitor;    crystallizing said ferroelectric film by applying a thermal annealing process in an atmosphere of an oxidizing gas under a reduced total pressure smaller than an atmospheric pressure; and    forming an upper electrode layer on said ferroelectric film.    
     
     
         13 . A method as claimed in  claim 1  wherein said oxidizing gas is O 2  and wherein said total pressure is set in the range between 1 Torr and 40 Torr.  
     
     
         14 . A method of fabricating a semiconductor device having a ferroelectric capacitor, comprising the steps of: 
 forming an active device element on a substrate;    forming an insulation film over said substrate to cover said active device element;    forming a lower electrode layer of said ferroelectric capacitor over said insulation film, said lower electrode layer including a layer part containing Ti atoms;    forming a ferroelectric film on said lower electrode layer as a capacitor insulation film of said ferroelectric capacitor;    crystallizing said ferroelectric film by applying a thermal annealing process in an atmosphere of an oxidizing gas; and    forming an upper electrode layer on said ferroelectric film,    wherein said step of crystallizing said ferroelectric film is conducted by supplying O 2  controlled to cause an oxidation in said Ti atoms reached a surface of said lower electrode from said layer part containing Ti atoms.    
     
     
         15 . A semiconductor device, comprising: 
 a substrate;    an active device element formed on said substrate;    an insulation film provided over said substrate to cover said active device element;    a lower electrode provided over said insulation film;    a ferroelectric film provided on said lower electrode, said ferroelectric film having a columnar microstructure extending from an interface between said lower electrode and said ferroelectric film in a direction substantially perpendicular to a principal surface of said lower electrode, said ferroelectric film essentially consisting of crystal grains having a generally uniform grain diameter of less than about 200 nm; and    an upper electrode provided on said ferroelectric film.    
     
     
         16 . A semiconductor device as claimed in  claim 15 , wherein said crystal grains constituting said ferroelectric film have an average diameter of about 150 nm.  
     
     
         17 . A semiconductor device as claimed in  claim 15 , wherein said lower electrode comprises a Ti layer and a conductor layer provided further on said Ti layer.  
     
     
         18 . A semiconductor device as claimed in  claim 17 , wherein said conductor layer is formed of Pt.  
     
     
         19 . A semiconductor device as claimed in  claim 17 , wherein said ferroelectric film has a perovskite structure.  
     
     
         20 . A semiconductor device as claimed in  claim 19 , wherein said ferroelectric film comprises a zirconate titanate of Pb.