Diffused junction termination structures for silicon carbide devices and methods of fabricating silicon carbide devices incorporating same
View Patent ↗An electronic device includes a silicon carbide layer having a first conductivity type and a main junction adjacent a surface of the silicon carbide layer, and a junction termination region at the surface of the silicon carbide layer adjacent the main junction. Charge in the junction termination region decreases with lateral distance from the main junction, and a maximum charge in the junction termination region may be less than about 2×10 14 cm −2 .
1. A method of forming a junction termination extension for an electronic device, the method comprising:
forming a mask on a semiconductor layer adjacent a main junction region, the semiconductor layer having a first conductivity type and the mask including a plurality of openings;
providing a source of second conductivity type dopants within the semiconductor layer;
diffusing the second conductivity type dopants into the semiconductor layer to form doped regions in the semiconductor layer corresponding to respective one of the mask openings that coalesce while leaving dopant peaks in the semiconductor layer corresponding to respective one of the mask openings near a surface of the semiconductor layer; and
removing a near-surface region of the semiconductor layer, wherein the removed portion of the near surface region of the semiconductor layer includes the dopant peaks.
2. The method of claim 1 , wherein the mask openings have respective areas that expose areas of a surface of the semiconductor layer that become smaller with lateral distance from the main junction region.
3. The method of claim 1 , wherein the doped regions provide a diffused junction termination region in the semiconductor layer having a lateral doping gradient that decreases with distance from the main junction region.
4. The method of claim 1 , wherein the semiconductor layer comprises a silicon carbide layer.
5. The method of claim 4 , wherein removing the near-surface region of the silicon carbide layer comprises removing material from the silicon carbide layer including the dopant peaks.
6. The method of claim 4 , wherein diffusing the second conductivity type dopants comprises annealing the silicon carbide layer including the second conductivity type dopants at a temperature in excess of 1800° C.
7. The method of claim 6 , further comprising forming a graphite cap layer on the silicon carbide layer, wherein annealing the silicon carbide layer comprises annealing the silicon carbide layer and the graphite cap layer.
8. The method of claim 4 , wherein a peak charge of second conductivity type dopants in the silicon carbide layer after removal of the dopant diffusion peak is about 1×10 14 cm −2 or less.
9. The method of claim 4 , wherein the junction termination region has a peak dopant concentration that decreases in a lateral direction away from the main junction region.
10. The method of claim 4 , wherein the source of second conductivity dopants provides peak dopant concentrations in the silicon carbide layer at locations corresponding to the plurality of openings.
11. The method of claim 4 , wherein the plurality of openings have a lateral width Ld and a spacing between adjacent openings of Lnd, and wherein Ld decreases with distance from the main junction region and/or Lnd increases with width from the main junction region.
12. The method of claim 11 , wherein Ld varies from about 2.5 μm to about 1 μm.
13. The method of claim 11 , wherein Lnd is about 2 μm.
14. The method of claim 11 , wherein the mask comprises a plurality of zones, including a first zone closest to the main junction region and a second zone that is farther from the main junction region from the first zone, wherein in the first zone, the spacing Lnd between adjacent openings remains constant with distance from the main junction region and the lateral width Ld of the openings decreases with distance from the main junction region, and wherein in the second zone, the spacing Lnd between adjacent openings increases with distance from the main junction region and the lateral width Ld of the openings remains constant with distance from the main junction region.
15. The method of claim 14 , wherein the mask comprises a third zone that is farther from the main junction region than the second zone, and wherein in the third zone, the lateral width Ld of the openings remains constant with distance from the main junction, and the spacing Lnd between adjacent openings increases by an increasing amount with distance from the main junction region.
16. The method of claim 1 , wherein providing the source of second conductivity type dopants comprises implanting second conductivity type dopants into the semiconductor layer.
17. The method of claim 1 , wherein providing the source of second conductivity type dopants comprises providing a diffusion source of second conductivity dopants adjacent the semiconductor layer to cause second conductivity dopants in the diffusion source to diffuse into the semiconductor layer.
18. The method of claim 1 , wherein the junction termination region has a peak dopant concentration that decreases smoothly in a lateral dimension.
19. A method of forming a junction termination extension for an electronic device, the method comprising:
providing a semiconductor layer including a main junction;
diffusing second conductivity type dopants into the semiconductor layer adjacent the main junction to form at least one doped region in the semiconductor layer while leaving at least one dopant peak in the semiconductor layer near a surface of the semiconductor layer; and
removing a near-surface region of the semiconductor layer, wherein the removed portion of the near surface region of the semiconductor layer includes the at least one dopant peak to form a junction termination region adjacent the main junction.