Semiconductor device and method of fabricating the same

Abstract

A lower portion of an interlayer insulating film is formed contiguous with a semiconductor wafer. The lower portion has a high impurity concentration and a high etching rate. An upper portion of an interlayer insulating film is formed over the lower portion apart from the semiconductor wafer. The upper portion has a low impurity concentration and a low etching rate. A plurality of contact holes are formed through the interlayer insulating film by anisotropic etching. The bottom portion of each contact hole is expanded by isotropic etching, and a contact is formed in the contact hole. Thus, a satisfactory contact is formed in a hole of a large aspect ratio.

1 . A semiconductor device comprising: 
 a semiconductor base layer;    a multilayer interlayer insulating film formed on said semiconductor base layer and consisting of a plurality of layers differing from each other in etching rate; and    at least a contact formed in a hole which is in turn formed in said multilayer interlayer insulating film, the contact being in contact with said semiconductor base layer;    wherein the diameter of said contact is increased in a portion thereof contiguous with said semiconductor base layer.    
     
     
         2 . The semiconductor device according to  claim 1 , wherein at least a conductive element is formed in one of said layers having a relatively low etching rate among said layers of said interlayer insulating film, spaced a predetermined distance apart from said semiconductor base layer and in parallel to said semiconductor base layer, and said contact is formed at a position close to said conductive element.  
     
     
         3 . The semiconductor device according to  claim 2 , wherein a plurality of said conductive elements are formed, and said contact is positioned between the adjacent pair of said plurality of conductive elements.  
     
     
         4 . The semiconductor device according to  claim 1 , wherein the diameter of said contact is increased toward said semiconductor base layer in a portion contiguous with said semiconductor base layer.  
     
     
         5 . The semiconductor device according to  claim 4 , wherein said diameter of said contact is increased stepwise toward said semiconductor base layer in a portion contiguous with said semiconductor base layer.  
     
     
         6 . The semiconductor device according to  claim 4 , wherein the diameter of said contact is increased continuously toward the semiconductor base layer, in a portion contiguous with the semiconductor base layer.  
     
     
         7 . The semiconductor device according to  claim 1 , wherein a portion of said interlayer insulating film contiguous with said semiconductor base layer is formed to have a high etching rate, as compared with other portions of said interlayer insulating film.  
     
     
         8 . A semiconductor device comprising: 
 a semiconductor base layer;    a lower conductive element contiguous with said semiconductor base layer;    an interlayer insulating film formed on said semiconductor base layer so as to cover said lower conductive element;    an upper conductive element formed in said interlayer insulating film at a predetermined distance from said semiconductor base layer; and,    at least a contact formed so as to be in contact with said semiconductor base layer in a hole formed in said interlayer insulating film at a position near said upper conductive element and said lower conductive element;    wherein the diameter of said contacts is increased between portions including said upper conductive element or said lower conductive element in the interlayer insulating film.    
     
     
         9 . A semiconductor device comprising: 
 a semiconductor base layer;    a plurality of conductive elements formed on, and contiguously with, said semiconductor base layer,    an etching resistant film covering at least side surfaces of said conductive elements, respectively;    an interlayer insulating film consisting of a plurality of layers differing in etching rate from each other and formed on said semiconductor base layer so as to cover said etching resistant films formed on said plurality of conductive elements; and    at least a contact formed in a hole, formed in a portion of said interlayer insulating film between said adjacent etching resist films of the plurality of said conductive elements and extending through said adjacent etching resistant film to said semiconductor base layer;    wherein a portion of the interlayer insulating film, contiguous with said semiconductor base layer and said etching resistant film, is formed to have a high etching rate as compared with the other portion of said interlayer insulating film.    
     
     
         10 . The semiconductor device according to  claim 9 , wherein said plurality of conductive elements are covered with a silicon dioxide film.  
     
     
         11 . The semiconductor device according to  claim 9 , wherein said semiconductor base layer and said plurality of conductive elements are covered with a silicon dioxide film.  
     
     
         12 . The semiconductor device according to  claim 9 , wherein the diameter of each of the contacts is increased between said adjacent conductive elements toward said etching resistant film covering said conductive element.  
     
     
         13 . The semiconductor device according to  claim 10 , wherein the diameter of said contact is increased between said adjacent conductive elements toward said silicon dioxide film covering said conductive elements.  
     
     
         14 . A method of fabricating a semiconductor device comprising the steps of: 
 forming on a semiconductor base layer an interlayer insulating film in which the portion nearer to the semiconductor base layer has relatively higher etching rate and the portion farther from the semiconductor base layer has relatively low etching rates, respectively;    forming at least a hole through the interlayer insulating film so that the diameter of the hole increases toward the semiconductor base layer; and    forming a contact in the hole so as to be connected to the semiconductor base layer.    
     
     
         15 . The semiconductor device fabricating method according to  claim 14 , wherein the step of forming the holes in the interlayer insulating film includes: 
 forming an etching resistant film provided with at least an opening over said interlayer insulating film;    forming a hole via said opening through said interlayer insulating film by anisotropic etching; and,    expanding the diameter of a bottom portion of said hole by isotropic etching.    
     
     
         16 . A semiconductor device fabricating method comprising the steps of: 
 forming a plurality of conductive elements on a semiconductor base layer, at least the side surfaces of said conductive elements being covered with an etching resistant film, respectively;    forming an interlayer insulating film on said semiconductor base layer so as to cover said etching resistant film, a portion contiguous with said semiconductor base layer and said etching resistant film having a relatively high etching rate, and a portion apart from said semiconductor base layer and said etching resistant film having a relatively low etching rate;    forming at least a hole in said interlayer insulating film between said adjacent etching resistant film of said plurality of conductive elements; and,    forming a contact in said hole so as to be connected to said semiconductor base layer.    
     
     
         17 . The semiconductor device fabricating method according to  claim 16 , further comprising a step of forming a silicon dioxide film over said the plurality of conductive elements.  
     
     
         18 . The semiconductor device fabricating method according to  claim 16 , further comprising a step of forming a silicon dioxide film over said semiconductor base layer and said plurality of conductive elements.  
     
     
         19 . The semiconductor device fabricating method according to  claim 16 , further comprising a step of removing a portion of said interlayer insulating film having a relatively higher etching rate at the bottom of said hole by isotropic etching.  
     
     
         20 . The semiconductor device fabricating method according to  claim 16 , further comprising a step of removing a portion of said etching resistant film exposed in said hole by isotropic etching.