Power semiconductor devices and methods
First Claim
1. A power semiconductor device, comprising:
- a first-conductivity-type semiconductor substrate, and at least one second-conductivity-type epitaxial layer overlying and forming a junction with said substrate;
at least one trench, extending downwardly into said epitaxial layer, which has dielectric material therein, and also includes vertically graded spatially fixed net electrostatic charge which tends to deplete adjacent second-conductivity-type semiconductor material;
a semiconductor drift region, in said epitaxial layer, which extends down to said junction, and which has a dopant concentration which generally decreases with depth, EXCEPT that an additional concentration of said second-conductivity type dopants is present in said drift region at said junction;
a semiconductor source region, which has said first conductivity type, and a semiconductor body region which has said second conductivity type and which separates said source region from said drift region; and
at least one gate electrode which controls accumulation or depletion of a portion of said body region to thereby define a channel region therein;
wherein, under at least some conditions, majority carriers pass from said source, through said channel and through said drift region to said substrate.
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Abstract
The present inventors have realized that manufacturability plays into optimization of power semiconductor devices in some surprising new ways. If the process window is too narrow, the maximum breakdown voltage will not be achieved due to doping variations and the like normally seen in device fabrication. Thus, among other teachings, the present application describes some ways to improve the process margin, for a given breakdown voltage specification, by actually reducing the maximum breakdown voltage. In one class of embodiments, this is done by introducing a vertical gradation in the density of fixed electrostatic charge, or in the background doping of the drift region, or both. Several techniques are disclosed for achieving this.
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Citations
8 Claims
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1. A power semiconductor device, comprising:
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a first-conductivity-type semiconductor substrate, and at least one second-conductivity-type epitaxial layer overlying and forming a junction with said substrate; at least one trench, extending downwardly into said epitaxial layer, which has dielectric material therein, and also includes vertically graded spatially fixed net electrostatic charge which tends to deplete adjacent second-conductivity-type semiconductor material; a semiconductor drift region, in said epitaxial layer, which extends down to said junction, and which has a dopant concentration which generally decreases with depth, EXCEPT that an additional concentration of said second-conductivity type dopants is present in said drift region at said junction; a semiconductor source region, which has said first conductivity type, and a semiconductor body region which has said second conductivity type and which separates said source region from said drift region; and at least one gate electrode which controls accumulation or depletion of a portion of said body region to thereby define a channel region therein; wherein, under at least some conditions, majority carriers pass from said source, through said channel and through said drift region to said substrate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification