Self-aligned implants for silicon carbide (SiC) technologies and fabrication method
A method for fabricating a silicon carbide semiconductor device includes providing a SiC epitaxial layer disposed over a surface of a SiC substrate, forming an implant aperture in a hardmask layer on a surface of the expitaxial SiC layer, implanting contact and well regions in the SiC epitaxial layer through the hardmask layer, the contact region lying completely within and recessed from edges of the well region by performing one of implanting the well region through the implant aperture, reducing the area of the implant aperture forming a reduced-area contact implant aperture and implanting the contact region through the reduced-area implant aperture to form a contact region, and implanting the contact region through the implant aperture, increasing the area of the implant aperture to form a increased-area well implant aperture and implanting the well region through the increased-area implant aperture to form a well region completely surrounding the contact region.
1. A method for fabricating a silicon carbide semiconductor device comprising:
providing a silicon carbide (SiC) substrate having a SiC epitaxial layer disposed over a surface of the SiC substrate, the SiC substrate having a first conductivity and the SiC epitaxial layer having the first conductivity;
forming an implant aperture in a hardmask layer on a surface of the SiC epitaxial layer;
implanting a contact region and a well region in the SiC epitaxial layer through the hardmask layer, the contact region and the well region having a doping level of a second conductivity opposite the first conductivity, wherein the contact region lies completely within the well region, is not in contact with a region having the first conductivity and has edges recessed from edges of the well region by performing one of:
implanting the well region through the implant aperture, reducing the area of the implant aperture to form a reduced-area contact implant aperture and then implanting the contact region through the smaller-area implant aperture to form a contact region lying completely within the well region; and
implanting the contact region through the implant aperture, increasing the area of the implant aperture to form an increased-area well implant aperture and then implanting the well region through the increased-area well implant aperture to form a well region completely surrounding the contact region.
2. The method of claim 1 wherein:
implanting the well region comprises forming a p-well region; and
implanting the contact region comprises forming a p-type contact region.
3. The method of claim 1 wherein forming the hardmask layer over the top surface of the SiC epitaxial layer comprises forming a hardmask layer from one of SiO 2 , SiN, SiON, PSG, BPSG, and polysilicon.
4. The method of claim 1 wherein forming the implant aperture in the hardmask layer comprises masking and etching the hardmask layer.
5. The method of claim 4 wherein etching the hardmask layer comprises etching the hardmask layer using one of reactive ion etching and wet etching.
6. The method of claim 1 wherein implanting the well region through the implant aperture in the SiC epitaxial layer comprises implanting Al through the implant aperture.
7. The method of claim 6 wherein implanting Al through the implant aperture comprises implanting Al with an implant dose of from 5E13 to 1E15 atoms/cm 2 , at an implant energy from 200 to 600 KeV.
8. The method of claim 1 wherein reducing the area of the implant aperture to form the reduced-area contact implant aperture comprises forming sidewall spacers on the hardmask layer in the implant aperture.
9. The method of claim 8 wherein forming sidewall spacers on the hardmask layer in the implant aperture comprises depositing SiO 2 using plasma enhanced chemical vapor deposition.
10. The method of claim 1 wherein implanting the contact region comprises implanting Al through the contact aperture with an implant dose of from 1E14 to 1E16 atoms/cm 2 at an energy of from 20 to 150 KeV.
11. The method of claim 10 wherein implanting the p-type contact comprises performing a sequence of implants.
12. The method of claim 1 wherein:
forming the implant aperture in a hardmask layer comprises forming the implant aperture in a polysilicon hardmask layer; and
increasing the area of the implant aperture to form the increased-area well implant aperture comprises oxidizing the surface of the polysilicon hardmask layer and removing the oxide from the surface of the polysilicon hardmask layer to enlarge the contact implant aperture to form the increased-area well implant aperture in the polysilicon hardmask layer.
13. The method of claim 12 wherein forming the implant aperture in the hardmask layer comprises masking and etching the polysilicon hardmask layer.
14. The method of claim 13 wherein etching the polysilicon hardmask layer comprises etching the polysilicon hardmask layer using one of reactive ion etching and wet etching.
15. The method of claim 12 wherein oxidizing the surface of the polysilicon hardmask layer comprises thermally growing SiO 2 on the surface of the polysilicon hardmask layer.