Siliconix Incorporated

Christiana Yue

Kyle Terrill

Deva N Pattanayak

Kuo-In Chen

Kam Hong Lui

Robert Xu

Mohamed N Darwish

Frederick Perry Giles

Sharon Shi

Yuming Bai

Ronald Wong

Karl Lichtenberger

David Chang

Ben Chan

Robert Q Xu

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.

Method of fabricating super trench MOSFET including buried source electrode

Super trench MOSFET including buried source electrode

Super trench MOSFET including buried source electrode and method of fabricating the same

In accordance with the present invention, a trench MOSFET is formed by creating a trench in a semiconductor substrate. A portion of either a side wall of the trench or the bottom of the trench is implanted with an implant species. An insulating layer is then grown overlying the bottom and side wall of the trench. The implant species is selected such that the insulating layer grows more quickly on the bottom of the trench than on the side wall of the trench, resulting in a thicker insulating layer in the bottom of the trench than on the trench side walls.

Self-aligned differential oxidation in trenches by ion implantation

The gate oxide layer of a trench MIS device includes a graduated transition region, where the thickness of the gate oxide layer decreases gradually from a thick section adjacent the bottom of the trench to a thin section adjacent the sidewall of the trench. The PN junction between the body and drain regions intersects the trench in the transition region. This structure allows for a greater margin of error in the placement of the PN junction during the manufacture of the device, since the intersection between the PN junction can be located anywhere in the transition region. The MIS device also has improved breakdown characteristics.

Trench MIS device with graduated gate oxide layer

A process for manufacturing a trench MIS device includes depositing a conformal nitride layer in the trench; etching the nitride layer to create an exposed area at the bottom of the trench; and heating the substrate and thereby growing an oxide layer in the exposed area. This process causes the mask layer to 'lift off', creating a 'bird's beak' structure. This becomes a &#x201c;transition region&#x201d;, where the thickness of the oxide layer decreases gradually in a direction away from the exposed area. The method further includes diffusing a dopant into the substrate, the dopant forming a PN junction with a remaining portion of said substrate, and controlling the diffusion such that the PN junction intersects the trench in the transition region. Because the thickness of the oxide layer decreases gradually, the PN junction does not need to be located at a particular point, i.e., there is a margin of error. This improves the manufacturability of the device and enhances its breakdown characteristics.

Method of fabricating trench MIS device with graduated gate oxide layer

A trench MOSFET is formed by creating a trench in a semiconductor substrate, then forming a barrier layer over a portion of the side wall of the trench. A thick insulating layer is deposited in the bottom of the trench. The barrier layer is selected such that the thick insulating layer deposits in the bottom of the trench at a faster rate than the thick insulating layer deposits on the barrier layer. Embodiments of the present invention avoid stress and reliability problems associated with thermal growth of insulating layers, and avoid problems with control of the shape and thickness of the thick insulating layer encountered when a thick insulating layer is deposited, then etched to the proper shape and thickness.

Thicker oxide formation at the trench bottom by selective oxide deposition

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Milpitas, CA, United States of America

Christiana Yue