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US 5,688,725 AGranted
Method of making a trench mosfet with heavily doped delta layer to provide low on-resistance
AssigneeSiliconix Incorporated
InventorsMohamed N. Darwish, Richard K. Williams
Life of this patent
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Abstract
In a vertical trench MOSFET, a layer of increased dopant concentration is formed in a lightly-doped or "drift" region which separates the body region from the drain region of the MOSFET. The layer of increased dopant concentration denominated a "delta" layer, operates to spread out the current as it emerges from the channel of the MOSFET and thereby reduces the resistance of the MOSFET when it is turned on.
Claims16
A method of fabricating a vertical trench MOSFET, said method comprising the steps of:
- providing a substrate of a first conductivity type;
- forming an epitaxial layer of said first conductivity type on a surface of said substrate;
- performing a first implant of dopant of said first conductivity type through a top surface of said epitaxial layer so as to form a delta implant region having a dopant concentration greater than a dopant concentration of a remaining portion of said epitaxial layer;
- performing a second implant of dopant of a second conductivity type that is opposite to said first conductivity type through said top surface of said epitaxial layer to form a deep diffusion;
- after said step of performing a first implant, forming a first trench and a second trench at said top surface, said first and second trenches defining a cell of said MOSFET, said deep diffusion being located in a central region between said first and second trenches, said deep diffusion not being in contact with either said first trench or said second trench;
- performing a third implant of dopant of said second conductivity type into said epitaxial layer to form a body implant region;
- performing a fourth implant of dopant of said first conductivity type into said epitaxial layer to form a source region;
- and
- depositing metal so as to form a contact with said source and body implant regions.
6 more elements
A method of fabricating a vertical trench MOSFET, said method comprising the steps of:
- providing a substrate of a first conductivity type;
- forming an epitaxial layer of said first conductivity type on a surface of said substrate;
- providing a mask at a top surface of said epitaxial layer;
- performing a first implant of dopant of said first conductivity type through said mask so as to form a delta implant region having a dopant concentration greater than a dopant concentration of a remaining portion of said epitaxial layer;
- performing a second implant of dopant of a second conductivity type that is opposite to said first conductivity type through said top surface of said epitaxial layer to form a deep diffusion;
- after said step of performing a first implant, forming a first trench and a second trench at said top surface, said first and second trenches defining a cell of said MOSFET, said deep diffusion being located in a central region between said first and second trenches, said deep diffusion not being in contact with either said first trench or said second trench;
- performing a third implant of dopant of said second conductivity type into said epitaxial layer to form a body implant region;
- performing a fourth implant of dopant of said first conductivity type into said epitaxial layer to form a source region;
- and
- depositing metal so as to form a contact with said source and body implant regions.
7 more elements
A method of fabricating a vertical trench MOSFET, said method comprising the steps of:
- providing a substrate of a first conductivity type;
- forming an epitaxial layer of said first conductivity type on a surface of said substrate;
- providing a mask at a top surface of said epitaxial layer;
- performing an implant of dopant of said first conductivity type through said mask so as to form a delta implant region having a dopant concentration greater than a dopant concentration of a remaining portion of said epitaxial layer;
- performing a second implant of dopant of a second conductivity type that is opposite to said first conductivity type through said top surface of said epitaxial layer to form a deep diffusion;
- defining an active region at said top surface of said epitaxial layer;
- forming a trench at said top surface adjacent said active region wherein said mask is configured such that said delta implant region is separated from said trench;
- performing a third implant of dopant of said second conductivity type into said epitaxial layer to form a body implant region;
- performing a fourth implant of dopant of said first conductivity type into said epitaxial layer to form a source region;
- and
- depositing metal so as to form a contact with said source and body implant regions.
8 more elements
Dependencies are inferred from the claim text.