Vertical power MOSFET having reduced sensitivity to variations in thickness of epitaxial layer
First Claim
1. A vertical trench-gated power MOSFET comprising:
- a semiconductor substrate of a first conductivity type;
an epitaxial layer formed on said substrate;
a gate formed in a trench extending downward from a surface of said epitaxial layer;
a source region of said first conductivity type formed in said epitaxial layer adjacent said surface thereof;
a body region of a second conductivity type opposite to said first conductivity type formed in said epitaxial layer adjacent said source region and a wall of said trench, said source and body regions being formed in a cell of said MOSFET bordered on at least two sides by said trench;
a drain which comprises said substrate and a portion of said epitaxial layer located adjacent said body region, said portion of said epitaxial layer being doped with ions of said first conductivity type to a first concentration level; and
a buried layer formed within said epitaxial layer and extending continuously across said cell, said buried layer having an upper edge that is located at a level above an interface between said substrate and said epitaxial layer and a lower edge that is located at a level below said interface, a portion of said buried layer within said epitaxial layer being doped with ions of said first conductivity type to a second concentration level which is greater than said first concentration level.
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Accused Products
Abstract
A vertical power MOSFET, which could be a trench-gated or planar double-diffused device, includes an N+ substrate and an overlying N-epitaxial layer. An N-type buried layer is formed in the epitaxial layer and overlaps the substrate, the buried layer having a dopant concentration which is greater than the dopant concentration of the epitaxial layer but less than the dopant concentration of the substrate. The ion implant which is used to create the buried layer is preferably performed after most of the high temperature operations in the fabrication process in order to minimize the diffusion of the buried layer. This controls the distance between the top edge of the buried layer and the drain-body junction of the MOSFET and allows the breakdown voltage and on-resistance of the MOSFET to be determined substantially without regard to the thickness of the epitaxial layer.
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Citations
25 Claims
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1. A vertical trench-gated power MOSFET comprising:
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a semiconductor substrate of a first conductivity type; an epitaxial layer formed on said substrate; a gate formed in a trench extending downward from a surface of said epitaxial layer; a source region of said first conductivity type formed in said epitaxial layer adjacent said surface thereof; a body region of a second conductivity type opposite to said first conductivity type formed in said epitaxial layer adjacent said source region and a wall of said trench, said source and body regions being formed in a cell of said MOSFET bordered on at least two sides by said trench; a drain which comprises said substrate and a portion of said epitaxial layer located adjacent said body region, said portion of said epitaxial layer being doped with ions of said first conductivity type to a first concentration level; and a buried layer formed within said epitaxial layer and extending continuously across said cell, said buried layer having an upper edge that is located at a level above an interface between said substrate and said epitaxial layer and a lower edge that is located at a level below said interface, a portion of said buried layer within said epitaxial layer being doped with ions of said first conductivity type to a second concentration level which is greater than said first concentration level. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A process of fabricating a MOSFET comprising the steps of:
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forming an epitaxial layer on a surface of a semiconductor substrate, said epitaxial layer having a substantially planar top surface, both of said substrate and said epitaxial layer being doped with ions of a first conductivity type, said substrate being doped to a greater concentration level than said epitaxial layer; implanting ions of said first conductivity type through said top surface of said epitaxial layer so as to form a buried layer of said first conductivity type; forming a trench extending downward from said surface of said epitaxial layer; forming a dielectric layer on a wall of said trench; filling said trench with a conductive gate material, said gate material being electrically insulated from said epitaxial layer by said dielectric layer; forming a body region of a second conductivity type opposite to said first conductivity type in said epitaxial layer; and forming a source region of said first conductivity type in said epitaxial layer; wherein at the completion of said process an upper edge of said buried layer is at a level that is located above an interface between said substrate and said epitaxial layer and a lower edge of said buried layer is at a level that is located below said interface. - View Dependent Claims (15, 16, 17, 18, 19, 23)
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20. A process of fabricating a MOSFET comprising the steps of:
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forming an epitaxial layer on a surface of a semiconductor substrate, said epitaxial layer having a substantially planar top surface, both of said substrate and said epitaxial layer being doped with ions of a first conductivity type, said substrate being doped to a greater concentration level than said epitaxial layer; implanting ions of said first conductivity type through said top surface of said epitaxial layer so as to form a buried layer of said first conductivity type; forming a dielectric layer on said surface of said epitaxial layer; forming a gate over said dielectric layer; forming a body region of a second conductivity type opposite to said first conductivity type in said epitaxial layer; and forming a source region of said first conductivity type in said epitaxial layer; wherein at the completion of said process an upper edge of said buried layer is at a level that is located above an interface between said substrate and said epitaxial layer and a lower edge of said buried layer is at a level that is located below said interface. - View Dependent Claims (21, 24)
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22. A process of fabricating a MOSFET comprising the steps of:
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providing a semiconductor substrate doped with ions of first conductivity type; implanting ions of said first conductivity type into said substrate so as to form a layer of said first conductivity type within said substrate; forming an epitaxial layer on a surface of said semiconductor substrate, said epitaxial layer being doped with ions of said first conductivity type; allowing ions within said layer of said first conductivity type to diffuse across an interface between said substrate and said epitaxial layer; forming a trench extending downward from said surface of said epitaxial layer; forming a dielectric layer on a wall of said trench; filling said trench with a conductive gate material, said gate material being electrically insulated from said epitaxial layer by said dielectric layer; forming a body region of a second conductivity type opposite to said first conductivity type in said epitaxial layer; and forming a source region of said first conductivity type in said epitaxial layer; wherein at the completion of said process said layer of ions of said first conductivity type extends across an interface between said substrate and said epitaxial layer downward to a level below said interface and upward to a level above a bottom of said trench. - View Dependent Claims (25)
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Specification