Low voltage high density trench-gated power device with uniformly doped channel and its edge termination technique
First Claim
1. A method for manufacturing a power mosfet comprising the steps of:
- forming a gate trench mask with open and closed regions on the surface of a semiconductor substrate;
removing semiconductor material from areas exposed by the open regions of the trench mask to form a plurality of gate trenches;
forming a sacrificial gate oxide layer on the sidewalls of the trenches;
implanting the substrate with a drift region implant that penetrates the oxide on the floors of the trenches and is stopped on the surface of the substrate by the residual trench mask;
annealing the substrate to diffuse the drift implant to form a continuous drift layer and define the length of the gate;
removing the trench mask and the sacrificial oxide and forming a gate oxide on the surface of the trench;
depositing a layer of polysilicon on the surface of the substrate and in the trenches;
removing the polysilicon from the surface of the semiconductor substrate and leaving enough polysilicon in the gate trenches to form gates in the trenches;
implanting the substrate with a source dopant to form source regions in the surface of the semiconductor substrate and to increase the conductivity of the polysilicon in the trenches to form gate regions in the trenches;
depositing a layer of BPSG on the substrate;
removing at least apart of the BPSG layer to expose portions of the surface having the source implant;
depositing and patterning a conductive layer over the surface of the substrate to form electrical contacts to the source regions.
6 Assignments
0 Petitions
Accused Products
Abstract
Merging together the drift regions in a low-power trench MOSFET device via a dopant implant through the bottom of the trench permits use of a very small cell pitch, resulting in a very high channel density and a uniformly doped channel and a consequent significant reduction in the channel resistance. By properly choosing the implant dose and the annealing parameters of the drift region, the channel length of the device can be closely controlled, and the channel doping may be made highly uniform. In comparison with a conventional device, the threshold voltage is reduced, the channel resistance is lowered, and the drift region on-resistance is also lowered. Implementing the merged drift regions requires incorporation of a new edge termination design, so that the PN junction formed by the P epi-layer and the N+ substrate can be terminated at the edge of the die.
-
Citations
6 Claims
-
1. A method for manufacturing a power mosfet comprising the steps of:
-
forming a gate trench mask with open and closed regions on the surface of a semiconductor substrate;
removing semiconductor material from areas exposed by the open regions of the trench mask to form a plurality of gate trenches;
forming a sacrificial gate oxide layer on the sidewalls of the trenches;
implanting the substrate with a drift region implant that penetrates the oxide on the floors of the trenches and is stopped on the surface of the substrate by the residual trench mask;
annealing the substrate to diffuse the drift implant to form a continuous drift layer and define the length of the gate;
removing the trench mask and the sacrificial oxide and forming a gate oxide on the surface of the trench;
depositing a layer of polysilicon on the surface of the substrate and in the trenches;
removing the polysilicon from the surface of the semiconductor substrate and leaving enough polysilicon in the gate trenches to form gates in the trenches;
implanting the substrate with a source dopant to form source regions in the surface of the semiconductor substrate and to increase the conductivity of the polysilicon in the trenches to form gate regions in the trenches;
depositing a layer of BPSG on the substrate;
removing at least apart of the BPSG layer to expose portions of the surface having the source implant;
depositing and patterning a conductive layer over the surface of the substrate to form electrical contacts to the source regions. - View Dependent Claims (2)
-
-
3. A power mosfet with trench gates comprising:
-
a semiconductor substrate;
a drain layer on one surface of the substrate doped with a high concentration of a dopant of one polarity;
an epitaxial layer above the drain layer and lightly doped with a dopant of opposite polarity;
a source layer at the other surface of the substrate and doped with a high concentration of the same dopant and the drain layer;
a plurality of trenches penetrating the source layer, said trenches substantially filled with conductive gate polycrystalline material doped with the same dopant type as the source layer; and
a drift layer in the substrate forming a continuous lightly doped drift region extending between sidewalls of the trenches and from the drain layer toward the source region and along a lower portion of the trench sidewalls to provide a variable, lightly doped concentration that gradually decreases in density from the sidewalls of the trenches toward a plane about midway between the trenches. - View Dependent Claims (4)
-
-
5. A power mosfet with trench gates comprising:
-
a semiconductor substrate having a drain layer heavily doped with dopants of one polarity;
an epitaxial layer on the substrate and comprising dopants of an opposite polarity;
a plurailty of source regions on the surface of the epitaxial layer and heavily doped with dopants of the same polarity as the drain;
a plurality of trenches penetrating the source regions, separated from the epitaxial layer by a gate insulating layer and comprising conductive material;
channel regions in the epitaxial layer adjacent the gate insulating layer of the trenches; and
a continuous drift layer comprising dopants of the same polarity as the source and drain and disposed in the epitaxial layer adjacent the substrate and extending toward the floors of the trenches and between the trenches, said continuous drift layer having a variable and lightly doped concentration of dopants between the trenches with a maximum concentration at the trench sidewall and gradually decreasing in concentration toward a plane midway between the trenches. - View Dependent Claims (6)
-
Specification