Semiconductor storage device and method of fabricating thereof

Abstract

In a semiconductor storage device, an access transistor, which has a gate electrode and a pair of impurity diffusion layers, is formed at a device activation region defined by a device isolation structure of a semiconductor substrate. A first insulating film, which has a first contact hole for exposing a portion of the surface of one of the pair of impurity diffusion layers, is formed over the access transistor. A protective film, which has a second contact hole formed on the first contact hole, is formed on the first insulating film. A second insulating film is formed on the side wall faces of the first and second contact holes. A memory capacitor has a lower electrode and an upper part electrode which are opposed each other and are capacitive-coupled through a dielectric film. The lower electrode is filled inside the first and second contact holes to be formed in an island-like shape on the first insulating film through the protective film so as to be electrically connected with the one of the pair of impurity diffusion layers. Each of the first and second contact holes has a diameter which is made smaller by an existence of the second insulating film than a minimum dimension determined by an exposure limit in a photolithography.

What is claimed is:  
     
         1 . A semiconductor storage device, comprising: 
 a semiconductor substrate having a device activation region defined by a device isolation structure;    an access transistor formed at said device activation region in said semiconductor substrate, and having a gate electrode and a pair of impurity diffusion layers;    a first insulating film formed over said access transistor, and having a first contact hole for exposing a portion of a surface of one of said pair of impurity diffusion layers;    a protective film formed on said first insulating film, and having a second contact hole formed on said first contact hole;    a second insulating film formed on a side wall face of said first contact hole in said first insulating film and on a side wall face of said second contact hole in said protective film; and    a memory capacitor in which a lower electrode and an upper electrode are opposed to each other and capacitive-coupled through a dielectric film, wherein    said lower electrode of said memory capacitor is filled inside said first and second contact holes to be formed in an island-like shape on said first insulating film through said protective film so as to be electrically connected with the one of said pair of impurity diffusion layers.    
     
     
         2 . A semiconductor storage device as claimed in  claim 1 , wherein each of said first and second contact holes has a diameter of a minimum dimension determined by an exposure limit in a photolithography.  
     
     
         3 . A semiconductor storage device as claimed in  claim 1 , wherein each of said lower and upper electrodes of said memory capacitor is made of a polycrystal silicon film.  
     
     
         4 . A semiconductor storage device as claimed in  claim 1 , wherein said protective film is a silicon nitride film.  
     
     
         5 . A semiconductor storage device as claimed in  claim 1 , wherein said protective film is a polycrystal silicon film, and is formed only between said island-like shaped lower electrode and said first insulating film.  
     
     
         6 . A semiconductor storage device as claimed in  claim 1 , further comprising a bit line formed under said lower electrode of said memory capacitor and in proximity to the side wall face of said first contact hole, wherein 
 said lower electrode is insulated from said bit line by said second insulating film.    
     
     
         7 . A semiconductor storage device as claimed in  claim 1 , wherein 
 said gate electrode of said access transistor is formed under said lower electrode of said memory capacitor and in proximity to the side wall face of said first contact hole; and    said lower electrode is insulated from said gate electrode by said second insulating film.    
     
     
         8 . A semiconductor storage device as claimed in  claim 1 , wherein said device isolation structure is a field oxide film which is formed by LOCOS method.  
     
     
         9 . A semiconductor storage device as claimed in  claim 1 , wherein said device isolation structure is a trench type device isolation structure in which an insulating film is formed in a groove which is formed in said semiconductor substrate.  
     
     
         10 . A semiconductor storage device, comprising: 
 a semiconductor substrate having a device activation region defined by a device isolation structure;    an access transistor formed at said device activation region in said semiconductor substrate, and having a gate electrode and a pair of impurity diffusion layers;    a first insulating film formed over said access transistor, and having a contact hole for exposing a portion of a surface of one of said pair of impurity diffusion layers;    a second insulating film formed on a side wall face of said contact hole in said first insulating film in such a manner as to protrude from said contact hole; and    a memory capacitor in which a lower electrode and an upper electrode are opposed to each other and capacitive-coupled through a dielectric film, wherein    said lower electrode of said memory capacitor is filled inside said contact hole through said second    a memory capacitor in which a lower electrode and an upper electrode are opposed to each other and capacitive-coupled through a dielectric film, wherein    said lower electrode of said memory capacitor is filled inside said first and second contact holes to be formed in an island-like shape on said insulating film through said protective film so as to be electrically connected with the one of said pair of impurity diffusion layers.    
     
     
         14 . A semiconductor storage device as claimed in claim  13 , wherein an existence of said conducting film allows said first and second contact holes to have diameters each of which is smaller than a minimum dimension determined by an exposure limit in a photolithography.  
     
     
         15 . A semiconductor storage device as claimed in claim  13 , wherein each of said lower and upper electrodes of said memory capacitor is made of a polycrystal silicon film.  
     
     
         16 . A semiconductor storage device as claimed in claim  13 , wherein said conducting film is a polycrystal silicon film.  
     
     
         17 . A semiconductor storage device as claimed in claim  13 , wherein said protective film is a silicon nitride film.  
     
     
         18 . A semiconductor storage device as claimed in claim  13 , further comprising a bit line which is formed under said lower electrode of said memory capacitor and in proximity to a side wall face of said first contact hole.  
     
     
         19 . A semiconductor storage device as claimed in claim  13 , wherein said device isolation structure is a field oxide film which is formed by LOCOS method.  
     
     
         20 . A semiconductor storage device as claimed in claim  13 , wherein said device isolation structure is a trench type device isolation structure in which an insulating film is formed in a groove which is formed in said semiconductor substrate.  
     
     
         21 . A method of fabricating a semiconductor storage device, said semiconductor storage device comprising: a semiconductor substrate having a device activation region defined by a device isolation structure; an access transistor formed at said device activation region in said semiconductor substrate, and having a gate electrode and a pair of impurity diffusion layers; and a memory capacitor in which a lower electrode and an upper electrode are opposed to each other and capacitive-coupled through a dielectric film, comprising: 
 a first step of forming a first insulating film over said access transistor;    a second step of forming a protective film on said first insulating film;    a third step of patterning said first insulating film and said protective film by means of a photolithography so as to form first and second contact holes for exposing a portion of a surface of one of said pair of impurity diffusion layers in said first insulating film and said protective film, respectively;    a fourth step of forming a second insulating film in a uniform film thickness or a homogeneous film thickness on side wall faces of said first and second contact holes and on a surface of said protective film;    a fifth step of etching said second insulating film with said protective film as a stopper so as to leave said second insulating film only on the side wall faces of said first and second contact holes;    a sixth step of forming a conducting film on said protective film so as to fill said first and second contact holes; and    a seventh step of patterning said conducting film so as to form said lower electrode of said memory capacitor in an island-like shape on said protective film.    
     
     
         22 . A method of fabricating a semiconductor storage device as claimed in  claim 21 , wherein each of said first and second contact holes has a diameter of the minimum dimension determined by the exposure limit in the photolithography.  
     
     
         23 . A method of fabricating a semiconductor storage device as claimed in  claim 21 , wherein each of said lower and upper electrodes is made of a polycrystal silicon film.  
     
     
         24 . A method of fabricating a semiconductor storage device as claimed in  claim 21 , wherein said protective film is made of a silicon nitride film.  
     
     
         25 . A method of fabricating a semiconductor storage device as claimed in  claim 21 , wherein 
 said protective film is made of a polycrystal silicon film; and    in said seventh step, said protective film is patterned together with said conducting film so as to form said protective film only between said island-like shaped lower electrode and said first insulating film.    
     
     
         26 . A method of fabricating a semiconductor storage device as claimed in  claim 21  further comprising, before said first step, a step of forming a bit line after forming said access transistor, wherein 
 in said third step, said first contact hole is formed so that said bit line is positioned in proximity to said first contact hole formed in said first insulating film, or so that a side face of said bit line is exposed on the side wall face of said first contact hole; and  
 in said fifth step, said lower electrode of said memory capacitor is insulated from said bit line by covering the side wall face of said first contact hole with said second insulating film.  
 
     
     
         27 . A method of fabricating a semiconductor storage device as claimed in  claim 21 , wherein said device isolation structure is a field oxide film which is formed by LOCOS method.  
     
     
         28 . A method of fabricating a semiconductor storage device as claimed in  claim 21 , wherein said device isolation structure is a trench type device isolation structure in which an insulating film is formed in a groove which is formed in said semiconductor substrate.  
     
     
         29 . A method of fabricating a semiconductor storage device as claimed in  claim 21 , wherein 
 in said third step, said first contact hole is formed so that said gate electrode of said access transistor is positioned in proximity to said first contact hole formed in said first insulating film, or so that the side face of said gate electrode is exposed on the side wall face of said first contact hole; and    in said fifth step, said lower electrode of said memory capacitor is insulated from said gate electrode by covering the side wall face of said first contact hole with said second insulating film.    
     
     
         30 . A method of fabricating a semiconductor storage device as claimed in  claim 21 , wherein in said fourth step, said second insulating film is formed in a film thickness not greater than one-half of the diameter of said first or second contact hole.  
     
     
         31 . A method of fabricating a semiconductor storage device, said semiconductor storage device comprising: a semiconductor substrate having a device activation region defined by a device isolation structure; an access transistor formed at said device activation region in said semiconductor substrate, and having a gate electrode and a pair of impurity diffusion layers; and a memory capacitor in which a lower electrode and an upper electrode are opposed to each other and capacitive-coupled through a dielectric film, comprising: 
 a first step of forming an insulating film over said access transistor;    a second step of forming a protective film on said insulating film;    a third step of patterning said protective film by means of a photolithography so as to form a first contact hole in said protective film;    a fourth step of forming a first conducting film inside said first contact hole and on a surface of said protective film;    a fifth step of etching said first conducting film with said protective film as a stopper so as to leave said first conducting film only on a side wall face of said first contact hole;    a sixth step of etching said insulating film with said protective film as a mask so as to form a second contact hole for exposing a portion of a surface of one of said pair of impurity diffusion layers, said first conducting film being left on the side wall face of said first contact hole in said protective film;    a seventh step of forming a second conducting film on said protective film so as to fill said first and second contact holes; and    an eighth step of patterning said second conducting film so as to form said lower electrode of said memory capacitor in an island-like shape on said protective film.    
     
     
         32 . A method of fabricating a semiconductor storage device as claimed in  claim 31 , wherein an existence of said first conducting film allows said first and second contact holes to have diameters each of which is smaller than a minimum dimension determined by an exposure limit in a photolithography.  
     
     
         33 . A method of fabricating a semiconductor storage device as claimed in  claim 31 , wherein said first conducting film is made of a polycrystal silicon film.  
     
     
         34 . A method of fabricating a semiconductor storage device as claimed in  claim 31 , wherein each of said lower and upper electrodes is made of a polycrystal silicon film.  
     
     
         35 . A method of fabricating a semiconductor storage device as claimed in  claim 31 , wherein said protective film is made of a silicon nitride film.  
     
     
         36 . A method of fabricating a semiconductor storage device as claimed in  claim 31 , wherein said device isolation structure is a field oxide film which is formed by LOCOS method.  
     
     
         37 . A method of fabricating a semiconductor storage device as claimed in  claim 31 , wherein said device isolation structure is a trench type device isolation structure in which an insulating film is formed in a groove which is formed in said semiconductor substrate.