Method of making a trench mosfet with heavily doped delta layer to provide low on-resistance
First Claim
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1. 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.
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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.
42 Citations
16 Claims
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1. A method of fabricating a vertical trench MOSFET, said method comprising the steps of:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of fabricating a vertical trench MOSFET, said method comprising the steps of:
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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.
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16. A method of fabricating a vertical trench MOSFET, said method comprising the steps of:
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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.
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Specification