Semiconductor device and fabrication process therefor

Abstract

A surface of a substrate is oxidized at a temperature equal to or higher than 1050° C., or at a oxidation speed equal to or higher than 7.5 nm/min to form an oxide film with a thickness equal to or more than 1500 nm. When the oxide film is removed, a density of pits existent at the surface of a substrate is equal to or less than that prior to the oxidation treatment and a depth of a pit existent there is equal to or less than 50 nm. An element isolation withstand voltage can be prevented from lowering and a fabrication yield of a miniaturized, highly integrated semiconductor device can be improved.

What is claimed is:  
     
         1 . A semiconductor device, in which a surface of a substrate is subjected to an oxidation treatment at a temperature equal to or higher than 1050° C. to form an oxide film with a thickness equal to or more than 1500 nm and thereafter, the oxide film is removed, thereby decreasing a density of pits existing at the surface of said substrate to a value thereof equal to or less than a density of pits prior to the oxidation treatment.  
     
     
         2 . A semiconductor device, in which a surface of a substrate is subjected to an oxidation treatment at an oxidation speed equal to or higher than 7.5 nm/min to form an oxide film of a thickness equal to or more than 1500 nm and thereafter, the oxide film is removed, thereby decreasing a density of pits existing at the surface of a substrate to a value thereof equal to or less than a density of pits prior to the oxidation treatment.  
     
     
         3 . A semiconductor device, in which a surface of a substrate is subjected to an oxidation treatment at a temperature equal to or higher than 1050° C. to form an oxide film of a thickness equal to or more than 1500 nm and thereafter, the oxide film is removed, thereby decreasing a depth of a pit existing at the surface of a substrate to a value equal to or less than 50 nm.  
     
     
         4 . A semiconductor device, in which a surface of a semiconductor substrate is subjected to an oxidation treatment to form an oxide film and thereafter, the oxide film is removed, thereby decreasing a depth of a pit existing at the surface of a semiconductor substrate to a value equal to or less than 50 nm.  
     
     
         5 . A semiconductor device according to any one of  claims 1  to  4 , wherein a gettering film is formed on a back surface of the semiconductor substrate.  
     
     
         6 . A semiconductor device according to  claim 5 , wherein the gettering film is a polysilicon film.  
     
     
         7 . A fabrication process for a semiconductor device, comprising the steps of: 
 oxidizing surfaces of a substrate at a temperature equal to or higher than 1050° C. to form oxide films each of a thickness equal to or more than 1500 nm; and    thereafter, effecting element isolation on the surface of a substrate.    
     
     
         8 . A fabrication process for a semiconductor device, comprising the steps of: 
 oxidizing surfaces of a substrate at an oxidation speed equal to or higher than 7.5 nm/min to form oxide films each of a thickness equal to or more than 1500 nm; and    thereafter, effecting element isolation on the surface of a substrate.    
     
     
         9 . A fabrication process for a semiconductor device according to  claim 7  or a, wherein an oxide film is removed by etching after formation of the oxide films.  
     
     
         10 . A fabrication process for a semiconductor device according to  claim 7  or  8 , comprising the steps of: after said step of forming the oxide films, 
 removing only an oxide film formed on a back surface of the substrate by etching;  
 depositing polysilicon films on both surfaces of the substrate;  
 etching the substrate so as to remove the polysilicon film and the oxide film formed on the surface of the substrate while at least one portion of the oxide film on the surface of the substrate is preserved; and  
 further etching the substrate using an etching liquid with which substantially no etching of silicon occurs so as to remove the preserved oxide film on the surface of the substrate.  
 
     
     
         11 . A fabrication process for a semiconductor device according to  claim 10 , wherein the etching liquid with which substantially no etching of silicon occurs is hydrofluoric acid.  
     
     
         12 . A fabrication process for a semiconductor device according to any one of  claims 9  to  11 , wherein a density of pits existing at the surface of a substrate after the etching is equal to or less than a density of pits prior to the oxidation treatment.  
     
     
         13 . A fabrication process for a semiconductor device according to any one of  claims 9  to  11 , wherein the depth of a pit existing at the surface of a substrate after the etching is of a value equal to or less than 50 nm.  
     
     
         14 . A fabrication process for a semiconductor device, wherein the process comprises the step of giving a substrate a hydrogen treatment at a temperature ranging from 1000° C. to 1300° C. prior to a step of effecting element isolation of a surface of the substrate.  
     
     
         15 . A fabrication process for a semiconductor device according to  claim 14 , comprising the steps of: 
 forming oxide films on both surfaces of a substrate after the hydrogen treatment;    depositing polysilicon films on both surfaces of the substrate; etching the substrate so as to remove the polysilicon film and the oxide film formed on the surface of a substrate while at least one portion of the oxide film on the surface of a substrate is preserved; and    further etching the substrate using an etching liquid with which substantially no etching of silicon occurs so as to remove the preserved oxide film on the surface of a substrate.    
     
     
         16 . A fabrication process for a semiconductor device according to  claim 15 , wherein a density of pits existing at the surface of a substrate after etching off the preserved oxide film on the surface of a substrate is equal to or less than a density of pits prior to the hydrogen treatment.  
     
     
         17 . A fabrication process for a semiconductor device according to  claim 15 , wherein a depth of a pit existing at the surface of a substrate after etching off the preserved oxide film on the surface of a substrate is of a value equal to or less than 50 nm.  
     
     
         18 . A fabrication process, comprising the steps of: 
 forming a silicon oxide film on a surface of a substrate or silicon oxide films on both surfaces of the substrate;    giving the substrate a nitrogen treatment at a temperature ranging from 1000° C. to 1200° C.; and    thereafter, effecting element isolation of the surface of a substrate.    
     
     
         19 . A fabrication process for a semiconductor device according to  claim 18 , comprising the steps of: 
 removing only an oxide film formed on a back surface of a substrate by etching after the nitrogen treatment step;    depositing polysilicon films on both surfaces of the substrate;    etching the substrate so as to remove the polysilicon film and the oxide film formed on the surface of a substrate while at least one portion of the oxide film on the surface of a substrate is preserved; and    further etching the substrate using an etching liquid with which substantially no etching of silicon occurs so as to remove the preserved oxide film on the surface of a substrate.    
     
     
         20 . A fabrication process for a semiconductor device according to  claim 19 , wherein a density of pits existing at the surface of a substrate after etching off the preserved oxide film on the surface of a substrate is equal to or less than a density of pits prior to the nitrogen treatment.  
     
     
         21 . A fabrication process for a semiconductor device according to  claim 19 , wherein a depth of a pit existing at the surface of a substrate after etching off the preserved oxide film on the surface of a substrate is of a value equal to or less than 50 nm.