Method of making a trench MOSFET with multi-resistivity drain to provide low on-resistance by varying dopant concentration in epitaxial layer
First Claim
1. A method of fabricating a MOSFET in a semiconductor material, said method comprising the steps of:
- providing a substrate;
growing an epitaxial layer;
introducing a dopant of a first conductivity type into said epitaxial layer while said epitaxial layer is being grown;
reducing the concentration of said dopant of said first conductivity type being introduced into said epitaxial layer while said epitaxial layer is being grown so as to form a region of high resistivity, said region of high resistivity having a resistivity which is higher than a resistivity of other portions of said epitaxial layer;
etching a trench in said semiconductor material;
forming an insulated gate in said trench;
introducing a dopant of a second conductivity type into said semiconductor material so as to form a body region; and
introducing a dopant of said first conductivity type into said semiconductor material so as to form a source region.
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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.
98 Citations
21 Claims
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1. A method of fabricating a MOSFET in a semiconductor material, said method comprising the steps of:
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providing a substrate; growing an epitaxial layer; introducing a dopant of a first conductivity type into said epitaxial layer while said epitaxial layer is being grown; reducing the concentration of said dopant of said first conductivity type being introduced into said epitaxial layer while said epitaxial layer is being grown so as to form a region of high resistivity, said region of high resistivity having a resistivity which is higher than a resistivity of other portions of said epitaxial layer; etching a trench in said semiconductor material; forming an insulated gate in said trench; introducing a dopant of a second conductivity type into said semiconductor material so as to form a body region; and introducing a dopant of said first conductivity type into said semiconductor material so as to form a source region. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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Specification