Semiconductor device formed on insulating layer and method of manufacturing the same

Abstract

In a semiconductor device having an SOI structure and a method of manufacturing the same, influence by a parasitic transistor can be prevented, and no disadvantage is caused in connection with a manufacturing process. In this semiconductor device, an upper side portion of a semiconductor layer is rounded. Thereby, concentration of an electric field at the upper side portion of the semiconductor layer can be prevented. As a result, lowering of a threshold voltage of a parasitic transistor can be prevented, so that the parasitic transistor does not adversely affect subthreshold characteristics of a regular transistor. Owing to provision of a concavity of a U-shaped section, generation of etching residue can be prevented when etching a gate electrode for patterning the same. Thereby, a disadvantage is not caused in connection with the manufacturing process.

1 . A semiconductor device comprising: 
 a semiconductor layer formed at a predetermined region of an insulating layer and having a main surface; and    a field-effect transistor formed on the main surface of said semiconductor layer, wherein    said semiconductor layer has a round section at an upper portion of its side surface, and said insulating layer has a U-shaped concavity at a region located near a lower end of the side surface of said semiconductor layer.    
   
   
       2 . The semiconductor device according to  claim 1 , wherein 
 said lower end of the side surface of said semiconductor layer extends substantially perpendicularly to the main surface of said insulating layer; and    an open end of said concavity of said insulating layer extends continuously to said lower end of the side surface of said semiconductor layer.    
   
   
       3 . The semiconductor device according to  claim 1 , further comprising: 
 a first side wall insulating film formed in contact with the side surface of said semiconductor layer; and    a second side wall insulating film formed in contact with a side surface of said first side wall insulating film.    
   
   
       4 . A semiconductor device comprising: 
 an insulating layer patterned into an isolated form and having a main surface;    a semiconductor layer formed on the main surface of said insulating layer;    an oxide film formed in contact with at least a side surface of said semiconductor layer;    a first field-effect transistor formed on the main surface of said semiconductor layer; and    a nitride film formed in contact with a side surface of said insulating layer and a lower portion of said oxide film located at the side surface of said semiconductor layer.    
   
   
       5 . The semiconductor device according to  claim 4 , wherein 
 said insulating layer includes first and second insulating layers spaced by a predetermined distance,    said semiconductor layer includes first and second semiconductor layers formed on main surfaces of said first and second insulating layers, respectively,    said nitride film includes a first nitride film formed in contact with a side surface of said first insulating layer and a lower portion of a side surface of said first semiconductor layer, and a second nitride film formed in contact with a side surface of said second insulating layer and a lower portion of a side surface of said second semiconductor layer, and    an oxide film is buried between said first and second nitride films.    
   
   
       6 . The semiconductor device according to  claim 4 , wherein 
 said nitride film has a portion being in contact with the lower portion of the side surface of said oxide film over a length substantially equal to a thickness of said oxide film located at the side surface of said semiconductor layer.    
   
   
       7 . The semiconductor device according to  claim 4 , wherein 
 said insulating layer includes first and second insulating layers spaced by a predetermined distance,    said semiconductor layer includes first and second semiconductor layers formed on main surfaces of said first and second insulating layers, respectively,    said nitride film is buried such that said first insulating layer and said first semiconductor layer are opposed to said second insulating layer and said second semiconductor layer with said nitride film therebetween.    
   
   
       8 . The semiconductor device according to  claim 4 , wherein 
 the side surface of said semiconductor layer may have a round section at its upper end.    
   
   
       9 . The semiconductor device according to  claim 4 , wherein 
 said patterned insulating layer is formed on a main surface of a semiconductor substrate, and    a second field-effect transistor neighboring to said insulating layer is formed at the main surface of said semiconductor substrate.    
   
   
       10 . The semiconductor device according to  claim 9 , wherein 
 each of said first and second field-effect transistors has a different conductivity type.    
   
   
       11 . A semiconductor device comprising: 
 a semiconductor layer of a trapezoidal section formed at a predetermined region on said insulating layer, having a main surface, and having a round section at an upper portion of its side surface; and    a field-effect transistor formed at the main surface of said semiconductor layer.    
   
   
       12 - 50 . (canceled)