Vertical-type metal insulator semiconductor field effect transistor device, and production method for manufacturing such transistor device

1. A vertical-type metal insulator field effect transistor device comprising:

a first conductivity type drain region layer;

a plurality of second conductivity type base regions produced and arranged in said first conductivity type drain region layer;

a first conductivity type source region produced in each of said second conductivity type base regions;

both a flat gate insulating layer and a flat gate electrode layer formed on said first conductivity type drain region layer such that a plurality of unit transistor cells are produced in conjunction with said second conductivity type base regions and said first conductivity type source regions, each of said unit transistor cells including respective span portions of said gate insulating layer and said gate electrode layer, which bridge a space between the first conductivity type source regions formed in two adjacent second conductivity base regions; and

a buried-insulator region produced in said first conductivity type drain region layer beneath each of the portions of said gate electrode layer.

2. The vertical-type metal insulator field effect transistor device as set forth in claim 1 , wherein said first conductivity type drain layer includes a first conductivity type semiconductor substrate, and a first conductivity type drift layer formed thereon and having a first conductivity type impurity concentration smaller than that of said first conductivity type semiconductor substrate, the production and arrangement of said second conductivity type base regions being carried out in said first conductivity type drift layer.

3. The vertical-type metal insulator field effect transistor device as set forth in claim 1 , wherein each of said buried-insulator regions is integrated with a corresponding span portion of said gate insulating layer.

4. The vertical-type metal insulator field effect transistor device as set forth in claim 1 , wherein each of the second conductivity type base regions has a depth which is equal to or more than that of each of said buried-insulator regions.

5. The vertical-type metal insulator field effect transistor device as set forth in claim 1 , wherein each of said buried-insulator regions has more than ten times a thickness of said gate insulating layer.

6. The vertical-type metal insulator field effect transistor device as set forth in claim 1 , wherein a space, which is defined between each of said buried-insulator regions and the adjacent second conductivity type base regions is set such that depletion regions, which are created along P-N junctions between the first conductivity type drain region layer and the second conductivity type base regions, are integrated with each other to thereby produce a single depletion region when a gate-drain is reversely biased.

7. The vertical-type metal insulator field effect transistor device as set forth in claim 1 , wherein a frame-like isolation layer is formed on said first conductivity type drain region layer along peripheral sides thereof, such that a portion of said frame-like isolation layer is buried in said first conductivity type drain region layer.

8. The vertical-type metal insulator field effect transistor device as set forth in claim 1 , wherein each of said buried-insulator regions is defined by vertical side wall faces.

9. The vertical-type metal insulator field effect transistor device as set forth in claim 1 , wherein each of said buried-insulator regions is spaced apart from an adjacent one of said second conductivity type base regions by a constant distance.