High voltage SOI semiconductor device

Abstract

In an SOI (Silicon On Insulator) semiconductor device, a first semiconductor layer overlies a semiconductor substrate so as to sandwich an insulating layer, and second and third semiconductor layers with a different conductivity type from the second semiconductor layer are formed on the surface of the first semiconductor layer. At the interface between the first semiconductor layer and the insulating layer, a fourth semiconductor layer with a different conductivity type from the first semiconductor layer is formed. The fourth semiconductor layer includes an impurity of larger than 3×10 12 /cm 2 so as not to be completely depleted even though a reverse bias voltage is applied between the second and third semiconductor layers.

1. An SOI semiconductor device comprising:
 a first semiconductor layer;  
 a second semiconductor layer that is formed on a first part of a first main surface of the first semiconductor layer;  
 a third semiconductor layer with a conductivity type different from a conductivity type of the second semiconductor layer, the third semiconductor layer being formed on a second part of the first main surface of the first semiconductor layer, the second part being separated from the first part;  
 a fourth semiconductor layer with a conductivity type different from a conductivity type of the first semiconductor layer, the fourth semiconductor layer being formed on a second main surface of the first semiconductor layer; and  
 a first insulating layer that is formed on a main surface of the fourth semiconductor layer opposite to the first semiconductor layer,  
 wherein the fourth semiconductor layer includes an impurity of an amount greater than 3×10 12 /cm 2  which is not completely depleted even when a reverse bias voltage is applied between the second and third semiconductor layers, the reverse bias voltage making a potential of a drain lower than a potential of a source  a potential of a source lower than a potential of a drain.  
 
     
     
       2. The SOI semiconductor device according to  claim 1 , wherein the amount of the impurity per unit area in the fourth semiconductor layer is larger than 1.5 times an amount of an impurity per unit area in the first semiconductor layer. 
     
     
       3. The SOI semiconductor device according to  claim 1 , wherein the first semiconductor layer includes 5×10 14 /cm 3  to 1×10 15 /cm 3  of an impurity. 
     
     
       4. The SOI semiconductor device according to  claim 1 , wherein
 an isolation trench is formed in an outer region of the first semiconductor layer so as to surround the second and third semiconductor layers and be deep enough to reach the first insulating layer, and  
 a second insulating layer is formed on an side wall of the isolation trench.  
 
     
     
       5. The SOI semiconductor device according to  claim 4 , wherein a fifth semiconductor layer with the same conductivity type as the conductivity type of the fourth semiconductor layer is formed at an interface between the first semiconductor layer and the second insulating layer. 
     
     
       6. The SOI semiconductor device according to  claim 5 , wherein the fifth semiconductor layer includes more than 3×10 12 /cm 2  of an impurity. 
     
     
       7. The SOI semiconductor device according to  claim 5 , wherein an amount of the impurity per unit area in the fifth semiconductor layer is larger than 1.5 times an amount of an impurity per unit area in the first semiconductor layer. 
     
     
       8. The SOI semiconductor device according to  claim 4 , wherein an interior space of the isolation trench is filled with an electrically conductive material. 
     
     
       9. The SOI semiconductor device according to  claim 8 , wherein the electrically conductive material is provided with an electrode. 
     
     
       10. The SOI semiconductor device according to  claim 9 , wherein the electrically conductive material is polysilicon, and
 the electrode is ohmically connected to the polysilicon via a conductive semiconductor layer.  
 
     
     
       11. The SOI semiconductor device according to  claim 1 , wherein
 a semiconductor substrate is joined to the fourth semiconductor layer at the main surface of the fourth semiconductor layer opposite to the first semiconductor layer, and  
 the first insulating layer is an oxide film that has been formed on at least one of (1) the main surface of the fourth semiconductor layer opposite to the first semiconductor layer and (2) a surface of the semiconductor substrate at which the semiconductor substrate is joined to the fourth semiconductor layer.  
 
     
     
       12. The SOI semiconductor device according to  claim 1 , wherein
 the first insulating layer is an insulating substrate, and  
 a metal film is formed on a main surface of the insulating substrate opposite to the fourth semiconductor layer.  
 
     
     
       13. The SOI semiconductor device according to  claim 1 , wherein the SOI semiconductor device is a MOS transistor. 
     
     
       14. The SOI semiconductor device according to  claim 1 , wherein the SOI semiconductor device is a pn diode. 
     
     
       15. The SOI semiconductor device according to  claim 1 , wherein the SOI semiconductor device is a lateral insulated gate bipolar transistor. 
     
     
       16. The SOI semiconductor device according to  claim 1 , wherein the SOI semiconductor device is a lateral thyristor. 
     
     
       17. An SOI semiconductor device comprising:
 a first semiconductor layer;  
 a second semiconductor layer that is formed on a first part of a first main surface of the first semiconductor layer;  
 a third semiconductor layer with a conductivity type different from a conductivity type of the second semiconductor layer, the third semiconductor layer being formed on a second part of the first main surface of the first semiconductor layer, the second part being separated from the first part;  
 a fourth semiconductor layer with a conductivity type different from a conductivity type of the first semiconductor layer, the fourth semiconductor layer being formed on a second main surface of the first semiconductor layer;  
 a first insulating layer that is formed on a main surface of the fourth semiconductor layer opposite to the first semiconductor layer;  
 a source electrode, and  
 a drain electrode wherein the fourth semiconductor layer includes an impurity of an amount that is large enough so as not to be completely depleted even when a reverse bias voltage is applied between the second and the third semiconductor layers, and the drain electrode is set at a potential lower  higher than a potential of a source, the impurity amount is greater than 3×10 12 /cm 2  and equal to or less than 1.0×10 17 /cm 2 .  
 
     
     
       18. The SOI semiconductor device according to  claim 17  wherein the first semiconductor layer includes 5×10 14 /cm 3  to 1×10 15 /cm 3  of an impurity. 
     
     
       19. The SOI semiconductor device according to  claim 18  wherein the amount of the impurity per unit area in the fourth semiconductor layer is larger than 1.5 times an amount of an impurity per unit area in the first semiconductor layer. 
     
     
       20. In a system for improving the operating voltage of a semiconductor device having means for applying voltages to the semiconductor device, the improvement of an SOI semiconductor device comprising:
 a first semiconductor layer;  
 a second semiconductor layer that is formed on a first part of a first main surface of the first semiconductor layer;  
 a third semiconductor layer with a conductivity type different from a conductivity type of the second semiconductor layer, the third semiconductor layer being formed on a second part of the first main surface of the first semiconductor layer, the second part being separated from the first part;  
 a fourth semiconductor layer with a conductivity type different from a conductivity type of the first semiconductor layer, the fourth semiconductor layer being formed on a second main surface of the first semiconductor layer; and  
 a first insulating layer that is formed on a main surface of the fourth semiconductor layer opposite to the first semiconductor layer,  
 wherein the fourth semiconductor layer includes an impurity of an amount greater than 3×10 12 /cm 2  which is not completely depleted even when a reverse-bias voltage is applied between the second and third semiconductor layers, the reverse bias voltage making a potential of a drain lower than a potential of a source  a potential of a source lower than a potential of a drain.