MOS semiconductor device

Abstract

The semiconductor device according to an aspect of the present invention includes: a semiconductor substrate of a first conductive type; a first semiconductor layer of the first conductive type formed on the main surface of the semiconductor substrate, the impurity concentration of the first semiconductor layer being lower than that of the semiconductor substrate; a second and third semiconductor layers of a second conductive type formed on the first semiconductor layer, the second and third semiconductor layers being isolated from each other; a first and second MOS transistors MOS 1 and MOS 2 of the first conductive type formed in the second and third semiconductor layers, the first semiconductor layer and the semiconductor substrate serving as drains of the first and second MOS transistors; and a conductive layer.

What is claimed is: 
     
       1. A semiconductor device comprising:
 a semiconductor substrate of a first conductive type; 
 a first semiconductor layer of the first conductive type formed on a main surface of said semiconductor substrate, an impurity concentration of said first semiconductor layer being lower than that of said semiconductor substrate; 
 second and third semiconductor layers of a second conductive type formed on said first semiconductor layer; 
 a first MOS transistor of the first conductive type including first source regions formed in said second semiconductor layer, said first semiconductor layer and said semiconductor substrate serving as drains of said first MOS transistor; 
 a first metal layer electrically connected to said first source regions 
 a second MOS transistor of the first conductive type including second source regions; formed in said third semiconductor layer, said first semiconductor layer and said semiconductor substrate serving as drains of said second MOS transistor; 
 a second metal layer electrically connected to said second source regions, said second metal layer being isolated from said first metal layer; and 
 a conductive layer formed on a reverse surface of said semiconductor substrate; 
 wherein the conductive layer forms a current flow path from the first MOS transistor to the second MOS transistor. 
 
     
     
       2. The semiconductor device according to  claim 1 , wherein:
 said first MOS transistor includes a gate electrode formed, via a gate insulating film, in a trench formed in said second semiconductor layer so as to reach said first semiconductor layer, and said first source regions provided near a surface of said second semiconductor layer at both sides of said trench, said first source regions contacting said trench; and 
 said second MOS transistor includes a gate electrode formed, via a gate insulating film, in a trench formed in said third semiconductor layer so as to reach said first semiconductor layer, and said second source regions provided near a surface of said third semiconductor layer at both sides of said trench, said second source regions contacting said trench. 
 
     
     
       3. The semiconductor device according to  claim 2 , wherein:
 each of said first and second MOS transistors includes a plurality of said gate electrodes and a respective plurality of said first and second source regions; 
 said first and second source regions of said first and second MOS transistors are covered by respective first and second metal layers; and 
 solder balls for drawing source electrodes are formed on each of the common metal layers. 
 
     
     
       4. The semiconductor device according to  claim 3 , wherein said gate electrodes of each of said first and second MOS transistors transistor are commonly connected to each other and said gate electrodes of said second MOS transistor are commonly connected to each other. 
     
     
       5. The semiconductor device according to  claim 3 , further comprising:
 a fourth semiconductor layer of the second conductive type, provided near a surface of said second semiconductor layer between adjacent gate electrodes of said first MOS transistor and between said first source regions corresponding to the adjacent gate electrodes, an impurity concentration of said fourth semiconductor layer being higher than that of said second semiconductor layer; and 
 a fifth semiconductor layer of the second conductive type, provided near a surface of said third semiconductor layer between adjacent gate electrodes of said second MOS transistor and between said second source regions corresponding to the adjacent gate electrodes, impurity concentration of said fifth semiconductor layer being higher than that of said third semiconductor layer. 
 
     
     
       6. The semiconductor device according to  claim 5 , wherein said fourth and fifth semiconductor layers are covered by said respective first and second metal layers. 
     
     
       7. The semiconductor device according to  claim 1 , wherein said first semiconductor layer is an epitaxial layer. 
     
     
       8. The semiconductor device according to  claim 1 , wherein said conductive layer is formed of a vanadium-nickel-gold alloy or aluminum. 
     
     
       9. The semiconductor device according to  claim 2 , wherein the gate electrode of the first MOS transistor is electrically isolated from the gate electrode of the second MOS transistor. 
     
     
       10. The semiconductor device according to claim 1, wherein said first metal layer is over a gate electrode of the first MOS transistor and spaced from the gate electrode of the first MOS transistor by an insulating film. 
     
     
       11. The semiconductor device according to claim 2, wherein the gate electrode of said first MOS transistor extends inwardly of said second semiconductor layer, and the gate electrode of said second MOS transistor extends inwardly of the said third semiconductor layer. 
     
     
       12. The semiconductor device according to claim 11, wherein the gate electrode of said first MOS transistor extends through said second semiconductor layer, and the gate electrode of said second MOS transistor extends through the third semiconductor layer. 
     
     
       13. The semiconductor device according to claim 1, wherein the first conductive type is n type. 
     
     
       14. The semiconductor device according to claim 10, further comprising a first insulating layer overlying the gate electrode of the first MOS transistor and a portion of the first source regions, wherein said first conductive metal layer is isolated from the gate electrode of the first MOS transistor by the first insulating layer, and contacts the first source regions in a location adjacent to the first insulating layer. 
     
     
       15. The semiconductor device according to claim 14, further comprising a second insulating layer located over the second semiconductor layer and the third semiconductor layer, wherein the first conductive metal layer and the second conductive metal layers are separated from one another by the second insulating layer. 
     
     
       16. The semiconductor device according to claim 1, wherein said second semiconductor layer extends from the first MOS transistor to the second MOS transistor. 
     
     
       17. A semiconductor device comprising:
 a semiconductor substrate of a first conductive type having a main surface and a reverse surface;   a first semiconductor layer of the first conductive type formed on the main surface of said semiconductor substrate, an impurity concentration of said first semiconductor layer being lower than that of said semiconductor substrate;   second and third semiconductor layers of a second conductive type formed on said first semiconductor layer;   a first MOS transistor of the first conductive type including first source regions formed in said second semiconductor layer, said first semiconductor layer and said semiconductor substrate serving as drains of said first MOS transistor;   a first metal layer electrically connected to said first source regions   a second MOS transistor of the first conductive type including second source regions formed in said third semiconductor layer, said first semiconductor layer and said semiconductor substrate serving as drains of said second MOS transistor, said second and third semiconductor layers being adjacent to each other on the first semiconductor layer;   a second metal layer electrically connected to said second source regions, said second metal layer being isolated from said first metal layer; and   a conductive layer formed on the reverse surface of said semiconductor substrate.   
     
     
       18. The semiconductor device of claim 17, wherein the conductive layer forms a current flow path from the first MOS transistor to the second MOS transistor. 
     
     
       19. The semiconductor device of claim 18, said first MOS transistor includes a gate electrode formed, via a gate insulating film, in a trench formed in said second semiconductor layer so as to reach said first semiconductor layer, and said first source regions are provided near a surface of said second semiconductor layer at both sides of said trench, said first source regions contacting said trench; and
 said second MOS transistor includes a gate electrode formed, via a gate insulating film, in a trench formed in said third semiconductor layer so as to reach said first semiconductor layer, and said second source regions are provided near a surface of said third semiconductor layer at both sides of said trench, said second source regions contacting said trench.   
     
     
       20. The semiconductor device of claim 19, wherein the first metal layer overlies the gate electrode of the first MOS transistor and is separated from the gate electrode of the first MOS transistor by an insulating film.