6 452 231

6,452,231 Title:

Semiconductor device

According to the present invention, there are proposed semiconductor devices each constituted in such a manner that the ON resistance thereof is lowered without increasing the area of the element. More specifically, as the insulated gate structure, there is used a trench gate structure constituted in such a manner that a gate electrode is formed in a state buried, through a gate insulation film, in trenches formed in the surface of an n-type high-resistance layer. Further, an n-type RESURF (Reduced Surface Field) diffused-layer extending as far as the trenches in a state contacted with the n-type drain layer is formed in the surface of the n-type high-resistance layer. As a result, the channel width can be increased with the area of the element remaining unvaried corresponding to the depth of the trenches to thereby reduce the channel resistance.

What is claimed is:

1. A lateral semiconductor device comprising: an active region; a base region of a first conductivity type formed in said active region; a source region of a secondconductivity type formed in said base region; a drain region formed in said active region and formed substantially deeper than said source region; a buried electrode connected to said drain region; a plurality of trenches formed between said sourceand drain regions, said trenches having sidewalls; an insulation layer formed on a surface region of said active region including said plurality of trenches; and a gate electrode formed in said trenches and over a portion of said active region disposedbetween said trenches through said insulation layer; said gate electrode having a portion formed over said active region and extended toward said drain region; wherein a thickness of said insulation layer under said portion of said gate electrode isgreater than a thickness of said insulation layer formed on said sidewalls of said trenches.

2. A lateral semiconductor device comprising: an active region; a base region of a first conductivity type formed in said active region; a source region of a second conductivity type formed in said base region; a drain region formed in saidactive region; a plurality of trenches formed between said source and drain regions, said trenches having sidewalls; an insulation layer formed on a surface region of said active region including said plurality of trenches; a gate electrode formed insaid trenches and over a portion of said active region disposed between said trenches through said insulation layer; said gate electrode having a portion formed over said active region and extended toward said drain region; and a buried region of saidsecond conductivity type formed in contact with said drain region and extending toward said base region; wherein a thickness of said insulation layer under said portion of said gate electrode is greater than a thickness of said insulation layer formedon said sidewalls of said trenches.

3. A device as recited in claim 2, comprising: said buried region having a higher conductivity than said active region.

4. A lateral semiconductor device comprising: an active region; a base region of a first conductivity type formed in said active region; a source region of a second conductivity type formed in said base region; a drain region formed in saidactive region; a plurality of trenches formed between said source and drain regions, said trenches having sidewalls; an insulation layer formed on a surface region of said active region including said plurality of trenches; a gate electrode formed insaid trenches and over a portion of said active region disposed between said trenches through said insulation layer; said gate electrode having a portion formed over said active region and extended toward said drain region; and a doped region of saidsecond conductivity type formed in a surface region of said active region and connected to said drain region and extending between said base region and said drain region, said doped region having a conductivity higher than said active region and lowerthan said drain region; wherein a thickness of said insulation layer under said portion of said gate electrode is greater than a thickness of said insulation layer formed on said sidewalls of said trenches.

5. A lateral semiconductor device comprising: an active region; a base region of a first conductivity type formed in said active region; a source region of a second conductivity type formed in said base region; a drain region formed in saidactive region; a plurality of trenches formed between said source and drain regions; a gate electrode formed in said trenches and over portions of said active region disposed between said trenches; and a buried region of said second conductivity typeformed in contact with said drain region and extending toward said base region.

6. A device as recited in claim 5, comprising: said buried region having a higher conductivity than said active region.

7. A device as recited in claim 5, comprising: a doped region of said second conductivity type formed in a surface region of said active region and connected to said drain region and extending between said base region and said drain region.

8. A device as recited in claim 7, comprising: said doped region having a conductivity higher than said active region and lower than said drain region.

9. A semiconductor device comprising a lateral MOSFET and bipolar transistor, said lateral MOSFET comprising: a first active region; a first base region of a first conductivity type formed in said first active region; a source region of asecond conductivity type formed in said first base region; a drain region formed in said first active region; a plurality of trenches formed between said source and drain regions; a gate electrode formed in said trenches and over portions of saidfirst active region disposed between said trenches; and a first buried region of said second conductivity type formed in contact with said drain region and extending toward said first base region; said bipolar transistor comprising; a second activeregion; a collector region of a second conductivity type formed in said second active region; a second base region of a first conductivity type formed on said collector region; an emitter region of a second conductivity type formed on said second baseregion; and a second buried region of said second conductivity type formed in said second active region under said collector region; wherein said first and second buried region are formed substantially with the same thickness and the same depth and thesame concentration of a conductive impurity.