Method of fabricating super trench MOSFET including buried source electrode
First Claim
1. A method of fabricating a MOSFET comprising:
- forming a trench at a first surface of a semiconductor substrate, said substrate comprising dopant of a first conductivity type;
depositing a mask layer over said first surface, said mask layer lining the walls and floor of said trench;
removing a portion of said mask layer adjacent the floor of said trench, remaining portions of said mask layer remaining attached to sidewalls of said trench;
etching said substrate through said bottom of said trench with said remaining portions of said mask layer remaining attached to sidewalls of said trench so as to form a cavity in said substrate;
heating said substrate with said remaining portions of said mask layer remaining attached to sidewalls of said trench so as to form a first dielectric layer in said cavity;
removing said remaining portions of said mask layer;
introducing a first layer of a conductive material into said cavity, said first layer of conductive material being electrically isolated from said substrate by said first dielectric layer;
heating said substrate so as form a second dielectric layer at an exposed surface of said conductive material and a gate dielectric layer along walls of said trench;
introducing a second layer of conductive material into said trench;
forming a body region of a second conductivity type opposite to said first conductivity type in said substrate, said body region abutting said gate dielectric layer;
forming a source region of said first conductivity type abutting said gate oxide layer and forming a junction with said body region;
covering said second layer of conductive material in said trench with a third dielectric layer;
depositing a metal layer over said substrate, said metal layer being in electrical contact with said source region andforming an electrical connection between said first layer of conductive material and said source region.
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Abstract
In a trench MOSFET, the lower portion of the trench contains a buried source electrode, which is insulated from the epitaxial layer and semiconductor substrate but in electrical contact with the source region. When the MOSFET is in an “off” condition, the bias of the buried source electrode causes the “drift” region of the mesa to become depleted, enhancing the ability of the MOSFET to block current. The doping concentration of the drift region can therefore be increased, reducing the on-resistance of the MOSFET. The buried source electrode also reduces the gate-to-drain capacitance of the MOSFET, improving the ability of the MOSFET to operate at high frequencies. The substrate may advantageously include a plurality of annular trenches separated by annular mesas and a gate metal layer that extends outward from a central region in a plurality of gate metal legs separated by source metal regions.
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Citations
13 Claims
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1. A method of fabricating a MOSFET comprising:
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forming a trench at a first surface of a semiconductor substrate, said substrate comprising dopant of a first conductivity type; depositing a mask layer over said first surface, said mask layer lining the walls and floor of said trench; removing a portion of said mask layer adjacent the floor of said trench, remaining portions of said mask layer remaining attached to sidewalls of said trench; etching said substrate through said bottom of said trench with said remaining portions of said mask layer remaining attached to sidewalls of said trench so as to form a cavity in said substrate; heating said substrate with said remaining portions of said mask layer remaining attached to sidewalls of said trench so as to form a first dielectric layer in said cavity; removing said remaining portions of said mask layer; introducing a first layer of a conductive material into said cavity, said first layer of conductive material being electrically isolated from said substrate by said first dielectric layer; heating said substrate so as form a second dielectric layer at an exposed surface of said conductive material and a gate dielectric layer along walls of said trench; introducing a second layer of conductive material into said trench; forming a body region of a second conductivity type opposite to said first conductivity type in said substrate, said body region abutting said gate dielectric layer; forming a source region of said first conductivity type abutting said gate oxide layer and forming a junction with said body region; covering said second layer of conductive material in said trench with a third dielectric layer; depositing a metal layer over said substrate, said metal layer being in electrical contact with said source region and forming an electrical connection between said first layer of conductive material and said source region. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of fabricating a MOSFET comprising:
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forming a trench at a first surface of a semiconductor substrate, said substrate comprising dopant of a first conductivity type; forming a first dielectric layer on the walls and bottom of said trench; depositing a first layer of a conductive material in a lower portion of said trench, leaving an exposed portion of said first dielectric layer on the walls of an upper portion of said trench, said first layer of conductive material being electrically isolated from said substrate by said first dielectric layer; removing said exposed portion of said first dielectric layer and a portion of said first dielectric layer that is laterally adjacent an upper portion of said first layer of conductive material, thereby exposing portions of lateral surfaces of said first conductive layer; forming a second dielectric layer on the walls of said upper portion of said trench and on a top surface and said exposed portions of lateral surfaces of said first conductive layer; depositing a second conductive layer in said upper portion of said trench, said first and second conductive layers vertically overlapping; forming a body region of a second conductivity type opposite to said first conductivity type in said substrate, said body region abutting said second dielectric layer; forming a source region of said first conductivity type abutting said second dielectric layer and forming a junction with said body region; covering said second conductive layer with a third dielectric layer; depositing a metal layer over said substrate, said metal layer being in electrical contact with said source region; and forming an electrical connection between said first conductive layer and said source region. - View Dependent Claims (9, 10, 11, 12)
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13. A method of fabricating a MOSFET comprising:
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forming a trench at a first surface of a semiconductor substrate, said substrate comprising dopant of a first conductivity type; forming a thick dielectric layer on the walls and bottom of said trench; depositing a first layer of a conductive material in said trench, said first layer of conductive material being electrically isolated from said substrate by said first dielectric layer; removing an upper portion of said thick dielectric layer, said upper portion being located between said source electrode and said substrate, thereby forming a cavity between said substrate and said source electrode; forming a thin dielectric layer in said cavity, a first section of said thin dielectric layer abutting a wall of said trench, a second section of said thin dielectric layer abutting a wall of said source electrode; depositing a second conductive layer in a space between said first and second thin dielectric layers; forming a body region of a second conductivity type opposite to said first conductivity type in said substrate, said body region abutting said first section of said thin dielectric layer; forming a source region of said first conductivity type abutting said first section of said thin dielectric layer and forming a junction with said body region; covering said second conductive layer with a third dielectric layer; and depositing a metal layer over said substrate, said metal layer being in electrical contact with said source region and said source electrode.
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Specification