Method for manufacturing semiconductor device, and semiconductor device

Abstract

The present invention provides a technique for efficiently forming a high-breakdown voltage transistor and a low-breakdown voltage transistor on the same substrate while reducing the deterioration of each transistors' characteristics. At first, an insulating film is formed. The insulating film protions above the drain and source formation regions fo rhte high-breakdown voltage transistor are thicker than those for the low-breakdown voltage transistor. Next, gates are formed on the insulating film. Then sidewalls are formed on the sides of the low-breakdown voltage transistor gate, and apertures are made in the insulating film portions above the drain and source formation regions for each transistor. When apertures are made in the relatively thick insulating film portions above the drain and source formation regions for the high-breakdown voltage transistor, etching is performed not to narrow widths of the sidewalls formed on the sides of the gate for the low-breakdown voltage transistor. Then drain and source regions are formed for each transistor by introduction of impure elements through the apertures.

What is claimed is:  
     
         1 . A semiconductor device comprising: 
 a semiconductor substrate; and    a high-breakdown voltage transistor and a low-breakdown voltage transistor of insulated-gate type, having different drain-source breakdown voltages, formed on the semiconductor substrate;    wherein the low-breakdown voltage transistor comprises:    a first gate insulating film;    a first gate formed over the first gate insulating film; and    first sidewalls formed on the sides of the first gate and composed of different material from the first gate insulating film.    
     
     
         2 . The semiconductor device according to  claim 1 , wherein the semiconductor substrate is a silicon substrate; 
 the first gate insulating film is a silicon oxide film; and    the first sidewalls are composed of silicon nitride.    
     
     
         3 . The semiconductor device according to  claim 2 , wherein the first gate is formed on polysilicon into which impure elements have been introduced.  
     
     
         4 . The semiconductor device according to  claim 3 , wherein a silicon oxide film is formed between the first gate and the first sidewalls.  
     
     
         5 . The semiconductor device according to  claim 1 , wherein the high-breakdown voltage transistor comprises: 
 a second gate insulating film;    a second gate formed over a center portion of the second gate insulating film; and    a protective layer covering at least a peripheral portion of the second gate insulating film.    
     
     
         6 . The semiconductor device according to  claim 1 , wherein the high-breakdown voltage transistor comprises: 
 a second gate insulating film; and    a second gate formed over a center portion of the second gate insulating film,    wherein the second gate is formed of polysilicon into which impure elements have been introduced, and a silicide is formed on the upper surface of the second gate except for a peripheral edge portion.