Thin film transistor and method of manufacturing the same

Abstract

A thin film transistor of this invention has a structure obtained by sequentially stacking, on an insulating substrate, a silicon nitride film, a silicon oxide film, a polysilicon thin film with a channel region and source and drain regions facing each other via the channel region, an insulating film, and a gate electrode. The boron concentration decreases from the channel region toward the silicon nitride film in the silicon oxide film region between the channel region and the silicon nitride film. The silicon oxide film region between the channel region and the silicon nitride film is made up of a first region which is in contact with the channel region and has a boron concentration of 1×10 16 atoms/cm 3 or more, and a second region between the first region and the silicon nitride film, which has a boron concentration of less than 1×10 16 atoms/cm 3 . The first region has a thickness of 200 Å or less.

1 . A thin film transistor comprising: 
 an insulating substrate;    a silicon nitride film formed on said insulating substrate;    a silicon oxide film formed on said silicon nitride film;    a polysilicon thin film formed on said silicon oxide film, said polysilicon thin film having a channel region containing boron as an impurity at a concentration of 5×10 16  to 1.5×10 18  atoms/cm 3 , and source and drain regions facing each other via the channel region;    an insulating film formed on said polysilicon thin film; and    a gate electrode formed on said insulating film,    wherein the boron concentration decreases from the channel region toward said silicon nitride film in a region of said silicon oxide film between the channel region and said silicon nitride film, and    the region of said silicon oxide film between the channel region and said silicon nitride film is made up of 
 a first region in contact with the channel region, which has a boron concentration of not less than 1×10 16  atoms/cm 3 , and  
 a second region between the first region and said silicon nitride film, which has a boron concentration of less than 1×10 16  atoms/cm 3 ,  
 the first region having a thickness of not more than 200 Å.  
   
     
     
         2 . A transistor according to    claim 1   , wherein an interface region between said silicon nitride film and said silicon oxide film that is positioned between the channel region and said silicon nitride film has a boron concentration of less than 1×10 16  atoms/cm 3 .  
     
     
         3 . A transistor according to    claim 1   , wherein said insulating substrate is a glass substrate.  
     
     
         4 . A method of manufacturing a thin film transistor, comprising the steps of: 
 sequentially stacking a silicon nitride film and a silicon oxide film on an insulating substrate;    stacking a non-singlecrystal silicon thin film on said silicon oxide film;    depositing boron on an upper surface of at least one of said silicon oxide film and said non-singlecrystal silicon thin film; and    irradiating light onto said non-singlecrystal silicon thin film to fuse and crystallize said non-singlecrystal silicon thin film, and to diffuse the deposited boron into said fused non-singlecrystal silicon thin film, there by forming a boron-doped polysilicon thin film.    
     
     
         5 . A method according to    claim 4   , wherein the step of depositing boron comprises depositing boron on the upper surface of at least one of said silicon oxide film and said non-singlecrystal silicon thin film at a dose of not less than 4×10 10  atoms/cm 2 .  
     
     
         6 . A method according to    claim 4   , wherein the step of depositing boron comprises depositing boron on the upper surface of at least one of said silicon oxide film and said non-singlecrystal silicon thin film at a dose of 4×10 10  to 5×10 12  atoms/cm 2 .  
     
     
         7 . A method according to    claim 4   , wherein the step of depositing boron comprises exposing said insulating substrate to a boron-containing atmosphere.  
     
     
         8 . A method according to    claim 7   , wherein the atmosphere has a boron concentration of not less than 5×10 12  atoms/L.  
     
     
         9 . A method according to    claim 7   , wherein the atmosphere has a boron concentration of 5×10 12  to 5×10 15  atoms/L.  
     
     
         10 . A method according to    claim 4   , wherein the step of depositing boron is performed to deposit boron on the upper surface of said non-singlecrystal silicon thin film after the step of stacking said non-singlecrystal silicon thin film.  
     
     
         11 . A method according to    claim 4   , wherein the step of depositing boron is performed to deposit boron on the upper surface of said silicon oxide film before the step of stacking said non-singlecrystal silicon thin film.  
     
     
         12 . A method according to    claim 4   , wherein said insulating substrate is a glass substrate.