Isolation and termination structures for semiconductor die
View Patent ↗Various integrated circuit devices, including a lateral DMOS transistor, a quasi-vertical DMOS transistor, a junction field-effect transistor (JFET), a depletion-mode MOSFET, and a diode, are formed inside an isolation structure which includes a floor isolation region and a trench extending from the surface of the substrate to the floor isolation region. The trench may be filled with a dielectric material or may have a conductive material in a central portion with a dielectric layer lining the walls of the trench. Various techniques for terminating the isolation structure by extending the floor isolation region beyond the trench, using a guard ring, and a forming a drift region are described.
1. An isolation structure formed in a semiconductor substrate of a first conductivity type, the substrate not comprising an epitaxial layer, the isolation structure comprising:
a floor isolation region of a second conductivity type opposite to the first conductivity type submerged in the substrate;
a trench extending from a surface of the substrate at least to the floor isolation region, the trench comprising a dielectric material, the trench and the floor isolation region together forming an isolated pocket of the substrate;
a guard ring of the first conductivity type at the surface of the substrate outside the isolated pocket, the guard ring having a doping concentration greater than a doping concentration of the substrate;
wherein the floor isolation region extends a predetermined distance beyond an outside edge of the trench in a direction towards the guard ring.
2. The isolation structure of claim 1 comprising a submerged region of the first conductivity type located directly below the guard ring, the submerged region being spaced apart from the guard ring and laterally surrounding the trench and having a doping concentration greater than the doping concentration of the substrate.
3. The isolation structure of claim 1 comprising a drift region of the second conductivity type adjacent the surface of the substrate and the trench outside the isolated pocket, the drift region being laterally separated from the guard ring and vertically separated from the floor isolation region by respective portions of the substrate.
4. The isolation structure of claim 3 comprising at least a second trench, the second trench comprising a dielectric material and extending from the surface of the substrate into the drift region, a floor of the second trench being located in the drift region.
5. The isolation structure of claim 1 comprising a second trench extending from the surface of the substrate, the second trench being filled with a dielectric material, the second trench being located between the first trench and the guard ring and being separated from the first trench and the guard ring by respective portions of the substrate.
6. The isolation structure of claim 1 wherein the dielectric material lines the walls of the trench and the trench comprises a conductive material at a central portion of the trench, the conductive material being in contact with the floor isolation region.
7. The isolation structure of claim 6 comprising a submerged region of the first conductivity type located directly below the guard ring, the submerged region being spaced apart from the guard ring and laterally surrounding the trench and having a doping concentration greater than the doping concentration of the substrate.
8. The isolation structure of claim 6 comprising a drift region of the second conductivity type adjacent the surface of the substrate and the trench outside the isolated pocket, the drift region being laterally separated from the guard ring and vertically separated from the floor isolation region by respective portions of the substrate.
9. The isolation structure of claim 8 comprising at least a second trench, the second trench comprising a dielectric material and extending from the surface of the substrate into the drift region, a floor of the second trench being located in the drift region.
10. The isolation structure of claim 6 comprising a second trench extending from the surface of the substrate, the second trench being filled with a dielectric material, the second trench being located between the first trench and the guard ring and being separated from the first trench and the guard ring by respective portions of the substrate.