SiC power vertical DMOS with increased safe operating area
View Patent ↗A SiC Power Semiconductor device of the Field Effect Type (MOSFET, IGBT or the like) with “muted” channel conduction, negative temperature coefficient of channel mobility, in situ “ballasted” source resistors and optimized thermal management of the cells for increased Safe Operating Area is described. Controlling the location of the Zero Temperature Crossover Point (ZTCP) in relationship to the drain current is achieved by the partition between the “active” and “inactive” channels and by adjusting the mobility of the carriers in the channel for the temperature range of interest. The “Thermal management” is realized by surrounding the “active” cells/fingers with “inactive” ones and the “negative” feedback of the drain/collector current due to local increase of the gate bias is achieved by implementing in-situ “ballast” resistors inside of each source contact.
1. A silicon carbide (SiC) vertical power MOSFET structure, comprising:
a SiC substrate including an upper layer of a first dopant type defining a drift region extending from an upper surface of the substrate depthwise into the substrate;
first and second body regions in the upper layer and adjoining the upper surface of the substrate and spaced apart about the drift region, the body regions being of a second dopant type opposite the first dopant type and having opposed lateral peripheries each forming a first PN junction with the drift region;
first and second source regions positioned respectively in the first and second body regions across the upper surface of the substrate to define first and second source contact regions and located with respect to the opposed lateral peripheries of the body region to form a second PN junction spaced laterally from the first PN junction and to define first and second channel regions along the upper surface between the first and second PN junctions;
a gate oxide layer on the upper surface extending over each of the channel regions;
a gate conductor contacting the gate oxide; and
a source conductor contacting the source regions and the body region therebetween;
a portion of the first channel region being muted with respect to the second channel region so that the second channel region becomes conductive before the muted portion of the first channel region becomes conductive.
2. A silicon carbide (SiC) vertical power MOSFET structure according to claim 1 , having transconductance characteristics Id-Vgs for various temperatures which have one or more crossover points in the drain current range specified by the maximum current rating of the part.
3. A silicon carbide (SiC) vertical power MOSFET structure according to claim 1 in which mobility of an inversion layer forming the channel regions has a negative temperature coefficient.
4. A silicon carbide (SiC) vertical power MOSFET structure according to claim 1 in which a portion of the first source region is offset at a first distance from the lateral periphery of first body region greater than a second distance of the second source region from the lateral periphery of the second body region so that a portion of the first channel region has a longer channel than the second channel region.
5. A silicon carbide (SiC) vertical power MOSFET structure according to claim 1 in which a portion of the first channel region is implanted with a higher doping concentration than the doping concentration of the second channel region.
6. A silicon carbide (SiC) vertical power MOSFET structure according to claim 5 in which the second body region is implanted with a retrograde doping profile.
7. A silicon carbide (SiC) vertical power MOSFET structure according to claim 1 in which a portion of the gate conductor overlying a portion of the first channel region is notched so that said portion of the first channel region is muted relative to the second channel region.
8. A silicon carbide (SiC) vertical power MOSFET structure according to claim 7 in which a portion of the first source region is notched.
9. A silicon carbide (SiC) vertical power MOSFET structure according to claim 1 in which a portion of the first source region is notched.
10. A silicon carbide (SiC) vertical power MOSFET structure according to claim 1 in which the source includes an in-situ ballast resistor.
11. A silicon carbide (SiC) vertical power MOSFET structure according to claim 10 in which a portion of the source region adjoining the second PN junction has a lower doping concentration than the remainder of the source region.
12. A silicon carbide (SiC) vertical power MOSFET structure according to claim 10 in which the source is coupled to a source conductor through a resistive barrier metal layer.
13. The SiC power MOSFET structure of claim 1 , in which the gate oxide layer has a first thickness, the structure further including a terraced dielectric layer on the upper surface extending laterally from the gate oxide layer over the drift region, the terraced dielectric layer having a second thickness greater than the first thickness of the gate oxide layer.
14. The SiC power MOSFET structure of claim 1 , including a JFET region of the first dopant type in an upper portion of the upper layer, enhancing a doping concentration of the drift region around the body region.
15. The SiC power MOSFET structure of claim 1 , including a JFET implant region of the first dopant type in an upper portion of the upper layer, forming a disrupted lattice structure in the channel regions to provide the negative mobility characteristic.
16. The SiC power MOSFET structure of claim 1 , including a UIS region of the second dopant type in the upper layer spaced laterally inward from the channel regions beneath the source regions, enhancing a doping concentration of the body region beneath the source regions.
17. The SiC power MOSFET structure of claim 1 , including a pair of counterdoped regions extending along the opposite lateral peripheries of the body regions, the counterdoped regions spaced below the channel regions and away from the source regions and having a doping concentration less than a doping concentration of the body region at the upper surface.
18. The SiC power MOSFET structure of claim 1 in which the first and second channel regions each have a threshold voltage, the threshold voltage of the portion of the first channel being greater than the threshold voltage of the second channel region.
19. The SiC power MOSFET structure of claim 1 in which the gate oxide layer over the portion of the first channel region is thicker than the gate oxide layer over the second channel region.