Seminconductor device with spreading layer
A vertical field-effect transistor (FET) device includes a monolithically integrated bypass diode connected between a source contact and a drain contact of the vertical FET device. According to one embodiment, the vertical FET device includes a pair of junction implants separated by a junction field-effect transistor (JFET) region. At least one of the junction implants of the vertical FET device includes a deep well region that is shared with the integrated bypass diode, such that the shared deep well region functions as both a source junction in the vertical FET device and a junction barrier region in the integrated bypass diode. The vertical FET device and the integrated bypass diode may include a substrate, a drift layer over the substrate, and a spreading layer over the drift layer, such that the junction implants of the vertical FET device are formed in the spreading layer.
1. A semiconductor device comprising:
a substrate;
a drift layer over the substrate;
a spreading layer over the drift layer, wherein the substrate, the drift layer, and the spreading layer have a first doping type, and a doping concentration of the spreading layer is greater than a doping concentration of the drift layer;
a metal-oxide semiconductor field-effect transistor (MOSFET) comprising:
a first implant region and a second implant region in the spreading layer opposite the drift layer, wherein the first implant region and the second implant region are separated by a portion of the spreading layer and have a second doping type that is opposite the first doping type;
a first trench in the spreading layer opposite the drift layer between the first implant region and the second implant region;
a first oxide layer on the spreading layer in the first trench;
a channel re-growth layer between the first oxide layer and the spreading layer in the first trench and between the first oxide layer and a top surface of the first implant region, wherein the channel re-growth layer has the first doping type;
a gate contact on the first oxide layer;
a source contact on the spreading layer over the first implant region and the second implant region; and
a drain contact on the substrate opposite the drift layer; and
a junction barrier Schottky (JBS) diode adjacent to the MOSFET and comprising:
a third implant region in the spreading layer opposite the drift layer, wherein the third implant region is separated from the second implant region by a portion of the spreading layer and has the second doping type;
an anode contact on a surface of the spreading layer between the second implant region and the third implant region, wherein the channel re-growth layer is between the anode contact and the spreading layer; and
a cathode contact on a surface of the substrate opposite the drift layer.
2. The semiconductor device of claim 1 wherein a doping concentration of the substrate is greater than the doping concentration of the drift layer.
3. The semiconductor device of claim 2 wherein:
the doping concentration of the drift layer is between about 6×10 15 cm −3 and 1.5×10 16 cm −3 ; and
the doping concentration of the spreading layer is between about 5×10 16 cm −3 and 2×10 17 cm −3 .
4. The semiconductor device of claim 3 wherein each one of the first implant region, the second implant region, and the third implant region has a doping concentration between about 5×10 17 cm −3 and 1×10 20 cm −3 .
5. The semiconductor device of claim 2 wherein the spreading layer comprises multiple layers.
6. The semiconductor device of claim 5 wherein each layer of the spreading layer has a different doping concentration.
7. The semiconductor device of claim 6 wherein:
a first layer of the spreading layer opposite the drift layer has a doping concentration of about 2×10 17 cm −3 ;
a second layer of the spreading layer adjacent to the drift layer has a doping concentration of about 5×10 16 cm −3 ; and
a doping concentration of each additional layer of the spreading layer between the first layer and the second layer decreases in proportion to a distance of the additional layer from the first layer, starting at the doping concentration of the first layer, and ending at the doping concentration of the second layer.
8. The semiconductor device of claim 1 wherein a portion of the spreading layer closest to the drift layer has a doping concentration of about 5×10 16 cm −3 that is graduated as the spreading layer extends away from the drift layer to a doping concentration of about 2×10 17 cm −3 .
9. The semiconductor device of claim 1 wherein the semiconductor device is a silicon carbide (SiC) device.
10. The semiconductor device of claim 1 wherein the anode contact comprises a low barrier height Schottky metal.
11. The semiconductor device of claim 10 wherein the anode contact comprises Tantalum.
12. The semiconductor device of claim 1 wherein the first implant region and the second implant region have a depth that is greater than a depth of the first trench.
13. The semiconductor device of claim 12 wherein the first implant region and the second implant region are in contact with a sidewall of the first trench at least to a depth that is greater than a depth of the gate contact.
14. A method of manufacturing a semiconductor device comprising:
growing a drift layer on a substrate;
growing a spreading layer on the drift layer such that the substrate, the drift layer, and the spreading layer have a first doping type, and the spreading layer has a doping concentration that is higher than a doping concentration of the drift layer;
providing a metal-oxide semiconductor field-effect transistor (MOSFET) comprising:
implanting a first implant region and a second implant region in the spreading layer opposite the drift layer such that the first implant region and the second implant region are separated by a portion of the spreading layer and have a second doping type that is opposite the first doping type;
etching a first trench in the spreading layer opposite the drift layer between the first implant region and the second implant region;
depositing a first oxide layer on the spreading layer in the first trench;
providing a channel re-growth layer between the first oxide layer and the spreading layer in the first trench and between the first oxide layer and a top surface of the first implant region, wherein the channel re-growth layer has the first doping type;
providing a gate contact on the first oxide layer;
providing a source contact on the spreading layer over the first implant region and the second implant region; and
providing a drain contact on the substrate opposite the drift layer; and
providing a junction barrier Schottky (JBS) diode adjacent to the MOSFET and comprising:
providing a third implant region in the spreading layer opposite the drift layer such that the third implant region is laterally separated from the second implant region by a portion of the spreading layer and has the second doping type;
providing an anode contact on a surface of the spreading layer between the second implant region and the third implant region such that the channel re-growth layer is between the anode contact and the spreading layer; and
providing a cathode contact over a surface of the substrate opposite the drift layer.
15. The method of claim 14 wherein a doping concentration of the substrate is greater than the doping concentration of the drift layer.
16. The method of claim 14 wherein:
the doping concentration of the drift layer is between about 6×10 15 cm −3 and 1.5×10 16 cm −3 ; and
the doping concentration of the spreading layer is between about 5×10 16 cm −3 and 2×10 17 cm −3 .
17. The method of claim 15 wherein each one of the first implant region, the second implant region, and the third implant region has a doping concentration between about 5×10 17 cm −3 and 1×10 20 cm −3 .
18. The method of claim 15 wherein the spreading layer comprises multiple layers.
19. The method of claim 18 wherein each layer of the spreading layer has a different doping concentration.
20. The method of claim 19 wherein:
a first layer of the spreading layer opposite the drift layer has a doping concentration of about 2×10 17 cm −3 ;
a second layer of the spreading layer adjacent to the drift layer has a doping concentration of about 5×10 16 cm −3 ; and
a doping concentration of each additional layer of the spreading layer between the first layer and the second layer decreases in proportion to a distance of the additional layer from the first layer, starting at the doping concentration of the first layer, and ending at the doping concentration of the second layer.
21. The method of claim 14 wherein a portion of the spreading layer closest to the drift layer has a doping concentration of about 5×10 16 cm −3 that is graduated as the spreading layer extends away from the drift layer to a doping concentration of about 2×10 17 cm −3 .
22. The method of claim 14 wherein the semiconductor device is a silicon carbide (SiC) device.
23. The method of claim 14 wherein the anode contact comprises a low barrier height Schottky metal.
24. The method of claim 23 wherein the anode contact comprises Tantalum.
25. The method of claim 14 wherein the first implant region and the second implant region are implanted to a depth that is greater than a depth of the first trench.
26. The method of claim 14 wherein the first implant region and the second implant region are provided such that they are in contact with a sidewall of the first trench at least to a depth that is greater than a depth of the gate contact.