Semiconductor devices employing poly-filled trenches
View Patent ↗Structure and method are provided for semiconductor devices. The devices include trenches filled with highly doped polycrystalline semiconductor, extending from the surface into the body of the device for, among other things: (i) reducing substrate current injection, (ii) reducing ON-resistance and/or (iii) reducing thermal impedance to the substrate. For isolated LDMOS devices, the resistance between the lateral isolation wall (tied to the source) and the buried layer is reduced, thereby reducing substrate injection current. When placed in the drain of a lateral device or in the collector of a vertical device, the poly-filled trench effectively enlarges the drain or collector region, thereby lowering the ON-resistance. For devices formed on an oxide isolation layer, the poly-filled trench desirably penetrates this isolation layer thereby improving thermal conduction from the active regions to the substrate. The poly filled trenches are conveniently formed by etch and refill. Significant area savings are also achieved.
1. A semiconductor device, comprising:
a substrate of a first conductivity type and having a substrate surface;
a source region, a drain region and a gate region operatively coupled to form a transistor;
a buried layer over the substrate surface and underlying at least a portion of the transistor, wherein the buried layer is of a same conductivity type as the source region;
an epitaxial layer located above the buried layer and of an opposite conductivity type as the source region, wherein the epitaxial layer has an epitaxial layer surface;
an enclosing isolation region within the epitaxial layer, overlying a portion of the buried layer and separated from the source region, wherein the enclosing isolation region is of the same conductivity type as the source region; and
a poly-filled trench surrounded by the enclosing isolation region, the poly-filled trench extending from the substrate through the buried layer and through the enclosing isolation region.
2. The device of claim 1 , wherein the poly-filled trench has the same conductivity type as the source region.
3. The device of claim 1 , wherein the poly-filled trench extends to the epitaxial layer surface.
4. The device of claim 1 , wherein the poly-filled trench extends to the drain region.
5. The device of claim 1 , wherein the enclosing isolation region is separated from the source region by at least a portion of the epitaxial layer.
6. The device of claim 1 , further comprising:
an insulating dielectric isolation layer between the substrate surface and the buried layer, wherein the poly-filled trench also extends through the insulating dielectric isolation layer.
7. The device of claim 2 , wherein the source region, the drain region and the gate region form a lateral transistor.
8. The device of claim 7 , wherein the source region, the drain region and the gate region form an LDMOS transistor.
9. The device of claim 8 , wherein the source region, the drain region and the gate region form an ILDMOS transistor.
10. A semiconductor device, comprising:
a drain region of a first conductivity type formed in an epitaxial layer of the device;
the epitaxial layer of a second opposite conductivity type;
a substrate of the second opposite conductivity type underlying and spaced apart from the drain region by the epitaxial layer;
a poly-filled trench of the first conductivity type extending from the drain region to or into the substrate; and a buried layer of the first conductivity type located between the drain region and the substrate, and electrically coupled to the poly-filled trench.
an enclosing isolation region surrounding the poly-filled trench and of the first conductivity type.
11. The device of claim 10 , further comprising an oxide isolation layer penetrated by the poly-filled trench and formed between the drain region and the substrate.
12. The device of claim 10 , further comprising:
a buried layer of the first conductivity type overlying the substrate and underlying the drain region and separated therefrom; and
a region of the second conductivity type laterally separated from the drain region and the poly-filled trench and extending substantially from an outer surface of the device to the substrate.
13. The device of claim 11 , further comprising a buried layer of the first conductivity type located between the drain region and the oxide isolation layer, and electrically coupled to the poly-filled trench.
14. A semiconductor device, comprising:
a substrate of a first conductivity type and having a first surface;
a semiconductor layer of the first or a second opposite conductivity type on the first surface and having a second surface opposite the first surface;
a trench filled with polycrystalline semiconductor of a conductivity type opposite the conductivity type of the semiconductor layer and extending through the semiconductor layer from the second surface to the first surface or into the substrate;
an oxide isolation layer between the first surface and the semiconductor layer and a buried layer of conductivity type opposite the conductivity type of the semiconductor layer between the first surface and the semiconductor layer.
15. The device of claim 14 , wherein the trench extends substantially through the buried layer and the oxide isolation layer.