Selective oxide deposition in the bottom of a trench
AssigneeFairchild Semiconductor Corporation
InventorJames J. Murphy
Life of this patent
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Abstract
A gate isolation structure of a semiconductor device and method of making the same provides a trench in a silicon substrate, wherein a dielectric layer is formed on sidewalls and bottom of the trench, the dielectric layer having a first thickness on the sidewalls and a second thickness at the bottom that is greater than the first thickness. The thicker dielectric layer at the bottom substantially reduces gate charge to reduce the Miller Capacitance effect, thereby increasing the efficiency of the semiconductor device and prolonging its life.
Claims21
A method of forming a gate dielectric layer of a trench field effect transistor, the method comprising the steps of:
- forming a trench in a silicon substrate;
- growing a thermal oxide layer on the sidewalls and bottom of the trench;
- etching away the thermal oxide layer from the bottom of the trench to expose the silicon substrate;
- depositing a selective oxide layer at the bottom of the trench over the silicon substrate to a desired thickness, wherein the desired thickness is greater than a thickness of the thermal oxide layer on the sidewalls of the trench;
- removing the thermal oxide layer from the sidewalls of the trench;
- and
- forming a gate oxide layer on the sidewalls of the trench, to a thickness that is less than the desired thickness of the selective oxide layer.
A method of forming a gate dielectric layer for a trench semiconductor device, the method comprising the steps of:
- forming a first trench in a silicon substrate;
- growing a thermal oxide layer on the sidewalls and bottom of the first trench;
- depositing a layer of nitride over the thermal oxide layer;
- etching away the thermal oxide layer and the nitride layer from the bottom of the first trench;
- forming a second trench at the bottom of the first trench to expose the silicon substrate on the sidewalls and bottom of the second trench;
- and
- depositing a selective oxide layer into the second trench over the silicon substrate to a desired thickness, wherein the desired thickness corresponds to a depth of the second trench and is greater than a thickness of the thermal oxide layer on the sidewalls of the trench.
A method of manufacturing a trench MOSFET, comprising the steps of:
- forming a plurality of trenches in a semiconductor substrate having a first conductivity type, each trench defined by sidewalls and a bottom;
- growing a thermal oxide on the sidewalls and the bottom of the trenches;
- etching away the thermal oxide layer on the sidewalls and the bottom of the trenches to expose portions of a surface of the semiconductor substrate;
- depositing a selective oxide layer on the bottom of the trenches over the exposed portions of the surface of the semiconductor substrate to a predetermined thickness, wherein the predetermined thickness is greater than a thickness of the thermal oxide layer on the sidewalls of the trenches;
- lining the oxide layer and selective oxide layer and filling the trenches with polysilicon;
- doping the polysilicon with a dopant having a first conductivity type;
- patterning the substrate and implanting a dopant having a second conductivity type to form a well into which the trenches are positioned;
- patterning the substrate and implanting a dopant having the second conductivity type to form a plurality of heavy bodies positioned within the well and between trenches;
- and
- patterning the substrate and implanting a dopant having the first conductivity type to form source regions within the well, the source regions positioned adjacent to and on opposite sides of each trench.
A method of forming a trench MOSFET comprising the steps of:
- forming a plurality of primary trenches in a semiconductor substrate, each primary trench having sidewalls and a bottom;
- forming a first dielectric layer on the sidewalls and the bottom of the primary trenches;
- forming a second dielectric layer over the first dielectric layer;
- etching through the first and second dielectric layers at the bottom of the primary trenches and into the semiconductor substrate to form a plurality of secondary trenches;
- filling the secondary trenches with an oxide to a predetermined depth;
- removing the first and second dielectric layers from the primary trench sidewalls;
- and
- forming a gate oxide layer on the primary trench sidewalls.
Dependencies are inferred from the claim text.