Trench MOSFET with multi-resistivity drain to provide low on-resistance
First Claim
1. A MOSFET comprising:
- a semiconductor member having a trench formed therein and a gate positioned in said trench;
a source region of a first conductivity type located in said semiconductor member adjacent said trench;
a body region of a second conductivity type located in said semiconductor member adjacent said source region;
a drain region of said first conductivity type located in said semiconductor member adjacent said body region, said drain region comprising;
a heavily doped region;
a drift region overlying and adjoining said heavily-doped region and having a concentration of dopant of said first conductivity type lower than a concentration of dopant of said first conductivity type in said heavily-doped region; and
a region of high resistivity adjacent a bottom of said trench, said region of high resistivity having a concentration of dopant of said first conductivity type lower than a concentration of dopant of said first conductivity type in said drift region; and
wherein said MOSFET includes a cell bounded on at least two sides by said gate, said MOSFET further comprising a delta doped layer separated laterally from said trench and located below said body region in a central region of said cell, said delta doped layer having a concentration of dopant of said first conductivity type greater than said concentration of dopant of said first conductivity type in said region of high resistivity.
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Accused Products
Abstract
A MOSFET switch with a gate formed in a trench has a drain which includes a region of relatively high resistivity adjacent the trench and a region of relatively low resistivity further away from the trench. The drain may also include a "delta" layer having even lower resistivity in a central region of the MOSFET cell. The high resistivity region limits the strength of the electric field at the edge of the trench (particularly where there are any sharp corners) and thereby avoids damage to the gate oxide layer. The central "delta" layer helps to insure that any breakdown will occur near the center of the MOSFET cell, away from the gate oxide, and to lower the resistance of the MOSFET when it is in an on condition.
155 Citations
36 Claims
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1. A MOSFET comprising:
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a semiconductor member having a trench formed therein and a gate positioned in said trench; a source region of a first conductivity type located in said semiconductor member adjacent said trench; a body region of a second conductivity type located in said semiconductor member adjacent said source region; a drain region of said first conductivity type located in said semiconductor member adjacent said body region, said drain region comprising;
a heavily doped region;
a drift region overlying and adjoining said heavily-doped region and having a concentration of dopant of said first conductivity type lower than a concentration of dopant of said first conductivity type in said heavily-doped region; and
a region of high resistivity adjacent a bottom of said trench, said region of high resistivity having a concentration of dopant of said first conductivity type lower than a concentration of dopant of said first conductivity type in said drift region; andwherein said MOSFET includes a cell bounded on at least two sides by said gate, said MOSFET further comprising a delta doped layer separated laterally from said trench and located below said body region in a central region of said cell, said delta doped layer having a concentration of dopant of said first conductivity type greater than said concentration of dopant of said first conductivity type in said region of high resistivity. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A MOSFET comprising:
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a semiconductor member having a trench formed therein and a gate positioned in said trench, said gate defining a MOSFET cell which is bounded on at least two sides by said gate; a source region of a first conductivity type located in said semiconductor member adjacent said trench; a body region of a second conductivity type located in said semiconductor member adjacent said source region; and a drain region of said first conductivity type located in said semiconductor member adjacent said body region, said drain region comprising;
a heavily doped region;
a drift region overlying and adjoining said heavily-doped region and having a concentration of dopant of said first conductivity type lower than a concentration of dopant of said first conductivity type in said heavily-doped region; and
a region of high resistivity adjacent a bottom of said trench, said region of high resistivity having a concentration of dopant of said first conductivity type lower than a concentration of dopant of said first conductivity type in said drift region, said MOSFET further comprising;a delta doped layer separated laterally from said trench and located below said body region in a central region of said cell, said delta doped layer having a resistivity lower than a resistivity in said region of high resistivity.
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19. A trench MOSFET having a multi-resistivity drain, said MOSFET comprising:
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a substrate; a trench formed in said substrate, a gate insulated from said substrate being positioned in said trench; a source region of a first conductivity type located adjacent a top surface of said substrate and a side wall of said trench; a body region of a second conductivity type located adjacent said source region and said side wall; and a multi-resistivity drain region of said first conductivity type located adjacent a bottom of said trench and below said body region, said multi-resistivity drain region comprising; a first region of a relatively low resistivity; a second region having a resistivity greater than the resistivity of said first region, said second region being located adjacent to and generally above said first region; and a third region having a resistivity greater than the resistivity of said second region, said third region being located generally above said second region and abutting a bottom of said trench, and a fourth region having a resistivity less than the resistivity of the second region; wherein said MOSFET includes a cell bounded on at least two sides by said gate, said fourth region being located generally at a central region of said cell and being laterally spaced apart from said trench. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27)
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28. A trench MOSFET having a multi-resistivity drain, said MOSFET comprising:
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a substrate; a trench formed in said substrate, a gate insulated from said substrate being positioned in said trench; a source region of a first conductivity type located adjacent a top surface of said substrate and a side wall of said trench; a body region of a second conductivity type located adjacent said source region and said side wall; and a multi-resistivity drain region of said first conductivity type located adjacent a bottom of said trench and below said body region, said multi-resistivity drain region comprising; a first region of a relatively low resistivity; a second region having a resistivity greater than the resistivity of said first region, said second region being located adjacent to and generally above said first region; and a third region having a resistivity greater than the resistivity of said second region, said third region being located generally above said second region and abutting a bottom of said trench and said body region, said MOSFET comprising a cell bounded on at least two sides by said trench, said drain region further comprising a fourth region which intersects a midpoint of said cell and which is at least partially bounded by said third region, said fourth region having a resistivity less than the resistivity of one of said second and third regions, a lower boundary of said fourth region abutting an upper boundary of said second region. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36)
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Specification