Trench-gate LDMOS structures
AssigneeFairchild Semiconductor Corporation
InventorsPeter H. Wilson, Steven Sapp
Life of this patent
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Abstract
MOSFET devices for RF applications that use a trench-gate in place of the lateral gate conventionally used in lateral MOSFET devices. A trench-gate provides devices with a single, short channel for high frequency gain. Embodiments of the present invention provide devices with an asymmetric oxide in the trench gate, as well as LDD regions that lower the gate-drain capacitance for improved RF performance. Refinements to these TG-LDMOS devices include placing a source-shield conductor below the gate and placing two gates in a trench-gate region. These improve device high-frequency performance by decreasing gate-to-drain capacitance. Further refinements include adding a charge balance region to the LDD region and adding source-to-substrate or drain-to-substrate vias.
Claims12
A field effect transistor comprising:
- a first silicon region comprising a body region having a first conductivity type, the first silicon region having a top surface;
- a gate-trench region extending from the top surface of the first silicon region into the first silicon region, wherein the gate-trench region has a first sidewall, a bottom, and a second sidewall, the gate-trench region comprising:
- a source-shield region comprising a first conductive region;
- a gate region comprising a second conductive region, the gate region located between the top surface of the first silicon region and the source-shield region;
- a first insulating layer between the gate region and the first sidewall;
- and
- a second insulating layer between the gate region and the second sidewall, the second insulating layer being thicker than the first insulating layer;
- a highly-doped drain region of a second conductivity type at the top surface of the first silicon region and contacting a drain electrode, the highly-doped drain region being laterally spaced from the gate-trench region, the second conductivity type being opposite to the first conductivity type;
- a lightly-doped drain region of the second conductivity type in the first silicon region, the lightly-doped drain region laterally extending along the top surface of the first silicon region between the second sidewall of the gate-trench region and the highly-doped drain region, and further extending under the bottom of the gate-trench region;
- wherein a portion of the lightly-doped drain region laterally extending along the top surface of the first silicon region extends to a depth shallower than a bottom of the gate-trench region;
- and
- a source region at the top surface of the first silicon region, the source region comprising a dopant region of the second conductivity type extending along the first sidewall of the gate-trench region.
Dependencies are inferred from the claim text.