Power semiconductor device and method therefor
A power transistor includes a plurality of transistor cells. Each transistor cell has a first electrode coupled to a first electrode interconnection region overlying a first major surface, a control electrode coupled to a control electrode interconnection region overlying the first major surface, and a second electrode coupled to a second electrode interconnection region overlying a second major surface. Each transistor cell has an approximately constant doping concentration in the channel region. A dielectric platform is used as an edge termination of an epitaxial layer to maintain substantially planar equipotential lines therein. The power transistor finds particular utility in radio frequency applications operating at a frequency greater than 500 megahertz and dissipating more than 5 watts of power. The semiconductor die and package are designed so that the power transistor can efficiently operate under such severe conditions.
1. A semiconductor device comprising:
a semiconductor material including a die;
a mesh structure including a plurality of transistors, wherein each transistor of the plurality of transistors comprises a gate positioned over the semiconductor material, a drain region, and a source region wherein the gates of the plurality of transistors are coupled to each other and are disposed in closed shapes around respective source regions, and wherein the source regions and the drain regions are disposed on opposite sides of the die;
a gate contact coupled to the mesh structure, wherein the gate contact includes a gate interconnection that is disposed external to the mesh structure and that completely surrounds the mesh structure, and wherein the gate contact is coupled to the gates of the plurality of transistors of the mesh structure via one or more gate pathways; and
a dielectric structure extending from a first surface of the semiconductor material into the semiconductor material, wherein the gate contact is disposed over the dielectric structure.
2. The semiconductor device of claim 1 , wherein:
the dielectric structure surrounds the source regions of the plurality of transistors;
at least a portion of the dielectric structure is positioned between at least a portion of the mesh structure and at least a portion of the drain regions to reduce gate to drain capacitance;
the semiconductor material is an epitaxial layer;
the source regions of the plurality of transistors and at least a portion of the drain regions of the plurality of transistors are formed in the epitaxial layer; and
the dielectric structure extends from the first surface of the semiconductor material through the epitaxial layer.
3. The semiconductor device of claim 1 , wherein the area of the dielectric structure is approximately equal to at least ten percent of the total area of the semiconductor material and wherein a dielectric constant of the dielectric structure is approximately equal to or less than the dielectric constant of silicon dioxide.
4. The semiconductor device of claim 1 , wherein the dielectric structure is a solid structure substantially devoid of any air gaps.
5. The semiconductor device of claim 1 , wherein the dielectric structure comprises an air gap.
6. The semiconductor device of claim 1 , wherein the gate contact comprises an electrically-conductive material, wherein the gate contact is positioned over the dielectric structure, wherein the dielectric structure is positioned between the gate contact and the drain regions to reduce gate to drain capacitance, wherein the mesh structure comprises the electrically-conductive material, and wherein the mesh structure has openings.
7. The semiconductor device of claim 6 , wherein the electrically-conductive material comprises polysilicon, and wherein the gate contact comprises metal.
8. The semiconductor device of claim 6 , further comprising a plurality of source interconnects coupled to each of the source regions, wherein for each source interconnect, at least a portion of each source interconnect is positioned in an opening of the mesh structure and is electrically isolated from the mesh structure.
9. The semiconductor device of claim 8 , further comprising a conductive source contact coupled to each of the plurality of source interconnects.
10. The semiconductor device of claim 8 , wherein each of the plurality of source interconnects is square-shaped.
11. The semiconductor device of claim 8 , wherein each of the plurality of source interconnects is rectangular-shaped.
12. The semiconductor device of claim 8 , wherein each of the plurality of source interconnects is non-square-shaped.
13. The semiconductor device of claim 1 , wherein the plurality of transistors are vertical transistors.
14. The semiconductor device of claim 1 , further comprising an active area, wherein the source regions of the plurality of transistors are formed in the active area.
15. The semiconductor device of claim 14 , wherein the semiconductor material comprises an epitaxial layer, and wherein the dielectric structure is adjacent to a periphery of the active area such that the dielectric structure surrounds the active area to provide edge termination that induces planar breakdown by reducing curvature of an electric field in the epitaxial layer.
16. The semiconductor device of claim 1 , wherein each gate of the plurality of transistors comprises a layer of conductive material positioned over the semiconductor material, and wherein a length of each gate is approximately equal to a deposition thickness of a layer of electrically-conductive material of the mesh structure.
17. The semiconductor device of claim 16 , wherein the layer of electrically-conductive material comprises polysilicon, and wherein the length of each gate is determined by a deposition thickness of the polysilicon.
18. The semiconductor device of claim 16 , wherein the plurality of transistors are vertical transistors, and wherein the gates of the plurality of transistors each have a gate length of less than about 0.35 microns.
19. The semiconductor device of claim 1 , wherein one or more of the plurality of transistors comprises a channel region that is disposed circumferentially around the source regions such that current is capable of being conducted 360 degrees around the source regions, and wherein the drain regions of the plurality of transistors are coupled in common to each other.
20. The semiconductor device of claim 1 , wherein the dielectric structure completely surrounds the mesh structure around a periphery of and external to the mesh structure.
21. The semiconductor device of claim 1 , wherein the dielectric structure comprises a plurality of vertically-extending dielectric structures separated by one or more cavities.
22. The semiconductor device of claim 21 , wherein a dielectric material is deposited within the one or more cavities.
23. The semiconductor device of claim 21 , wherein each vertically-extending dielectric structure of the plurality of vertically-extending dielectric structures comprises:
a first portion of dielectric material; and
a second portion of dielectric material having a different composition than the first portion of dielectric material.