Vertical type power mosfet having trenched gate structure

A power MOSFET comprising:

• a drain layer of a first conductivity type;
• a drift layer of the first conductivity type provided on said drain layer;
• a base layer of the first conductivity type provided on said drift layer;
• a source region of the first conductivity type provided on said base layer;
• a gate insulating film formed on an inner wall surface of a trench penetrating the base layer and reaching at said drift layer to have a bottom portion formed in the drift layer;
• and
• a gate electrode provided on said gate insulating film inside said trench, wherein
• said gate insulating film is formed such that a portion thereof adjacent to said drift layer is thicker than a portion thereof adjacent to said base layer, and said drift layer has a step shaped impurity concentration gradient higher in the vicinity of said drain layer and lower in the vicinity of said source region along a depth direction of the trench.

A power MOSFET comprising:

• a drain layer of a first conductivity type;
• a drift layer of the first conductivity type provided on the drain layer;
• a base layer of second conductivity type provided on said drift layer;
• a source region of the first conductivity type provided on said base layer;
• a gate insulating film formed on an inner wall surface of a trench penetrating the base layer and reaching the drift layer to have a bottom portion formed within the drift layer;
• and
• a gate electrode provided on said gate insulating film inside said trench, wherein
• said gate insulating film is formed such that a portion thereof adjacent to the drift layer is thicker than a portion thereof adjacent to the base layer, and said drift layer has a V-shaped impurity concentration gradient distribution having a peak point near the base layer and another peak point near the drain layer and having a portion in which the impurity concentration of the first conductivity type along a depth direction of the trench is at a minimum value between the peak points.

A power MOSFET comprising:

• a drain layer of a first conductivity type;
• a drift layer of the first conductivity type provided on the drain layer;
• a base layer of second conductivity type provided on said drift layer;
• a source region of the first conductivity type provided on said base layer;
• a gate insulating film formed on an inner wall surface of a trench penetrating the base layer and reaching the drift layer to have a bottom portion formed in the drift layer;
• and
• a gate electrode provided on said gate insulating film inside said trench, wherein
• said gate insulating film is formed such that a portion thereof adjacent to the drift layer is thicker than a portion thereof adjacent to the base layer, and said drift layer has a step shaped impurity concentration distribution having a gradient higher in the vicinity of said drain layer and lower in the vicinity of said source region along a depth direction of the trench.