Vertical power devices fabricated using implanted methods
A precursor for a vertical semiconductor device is provided with a substrate, a drift region over the substrate, and an upper precursor region over the drift region. The top surface of the precursor is substantially planar, and the substrate and the drift region are doped with a first dopant of a first polarity. In a first embodiment, a series of implants with a second dopant is provided in the upper precursor region via the top surface to form each of at least two gate regions such that each implant of the series of implants is provided at a different depth below the top surface. In a second embodiment, a series of implants with the first dopant is provided in the upper precursor region via the top surface to form a channel region that has at least a portion between two gate regions.
1. A method for forming a vertical semiconductor device comprising:
providing a precursor comprising a substrate, a drift region over the substrate, and an upper precursor region, wherein a top surface of the precursor is substantially planar, and the substrate and the drift region are doped with a first dopant of a first polarity;
providing a series of implants with a second dopant in the upper precursor region via the top surface to form each of at least two gate regions, such that each implant of the series of implants is provided at a different depth below the top surface, wherein:
the second dopant has a second polarity opposite that of the first polarity;
at least a portion of a channel region is provided between the at least two gate regions; and
a conducting gap is defined within the channel region and between opposing sidewalls of the at least two gate regions.
2. The method of claim 1 further comprising: prior to providing the series of implants, providing a mask on the top surface over an area below which a central portion of the channel region will be formed, wherein areas on the top surface over which the at least two gate regions will be formed are exposed for the series of implants.
3. The method of claim 1 wherein each successive one of the series of implants is below and has an inner sidewall that straggles further inward toward the channel region than a preceding one of the series of implants.
4. The method of claim 3 further comprising, prior to providing the series of implants, providing a mask on the top surface over an area below which a central portion of the channel region will be formed wherein areas on the top surface over which the at least two gate regions will be formed are exposed for the series of implants.
5. The method of claim 4 wherein the mask is the only mask used for the series of implants.
6. The method of claim 3 further comprising providing an implant of the first dopant in the channel region to form a deep implant, wherein the deep implant is horizontally aligned with and overlaps opposing sidewalls of at least one of the series of implants to effectively move the opposing sidewalls of the at least one of the series of implants laterally outward from the channel region.
7. The method of claim 6 wherein the deep implant is horizontally aligned with a second or greater of the series of implants.
8. The method of claim 7 wherein the deep implant is not horizontally aligned with a first of the series of implants.
9. The method of claim 6 wherein the deep implant is not horizontally aligned with a first of the series of implants.
10. The method of claim 1 wherein each successive one of the series of implants is below and has an inner sidewall that is substantially aligned with a preceding one of the series of implants.
11. The method of claim 10 further comprising:
prior to a first implant of the series of implants, providing a mask on the top surface over an area below which a central portion of the channel region will be formed wherein areas on the top surface over which the at least two gate regions will be formed are exposed for the series of implants; and
prior to each successive implant of the series of implants after the first implant, providing a lateral extension of the mask on a side opposite that of the channel region by a desired thickness sufficient to keep the inner sidewall of each successive implant of the series of implants substantially aligned with the inner sidewall the preceding one of the series of implants.
12. The method of claim 11 wherein providing each lateral extension of the mask comprises:
depositing an etchable layer over the mask and exposed portions of the top surface; and etching the etchable layer such that a residual portion of the etchable layer remains on a sidewall of the mask to provide the lateral extension.
13. The method of claim 1 further comprising, prior to a first implant of the series of implants, providing a mask on the top surface over an area below which a central portion of the channel region will be formed, wherein sidewalls of the mask are angled such that a bottom surface of the mask and each of the sidewalls of the mask form an acute angle.
14. The method of claim 13 wherein the acute angle is in a range of 30 to 90 degrees.
15. The method of claim 13 wherein each successive one of the series of implants is below a preceding one of the series of implants and wraps around a sidewall of a preceding one of the series of implants.
16. The method of claim 13 wherein each successive one of the series of implants is below a preceding one of the series of implants and wraps around a sidewall of a preceding one of the series of implants up to a top surface of the precursor.
17. The method of claim 1 further comprising providing an implant of the first dopant along a bottom of the upper precursor region to form a spreading layer.
18. The method of claim 1 further comprising providing an implant of the second dopant in each of the at least two gate regions adjacent the top surface of the precursor to form at least two gate ohmic regions.
19. The method of claim 18 further comprising forming a gate contact over each of the at least two gate ohmic regions.
20. The method of claim 1 wherein there are at least three implants in the series of implants.
21. The method of claim 1 wherein each successive one of the series of implants is below a preceding one of the series of implants.
22. The method of claim 1 wherein each successive one of the series of implants is above a preceding one of the series of implants.
23. The method of claim 1 further comprising providing an implant of the second dopant beneath a top surface of the channel region to form a source ohmic region and forming a source contact on the top surface of the channel region over the source ohmic region.
24. The method of claim 1 wherein the vertical semiconductor device is a junction field-effect transistor.
25. The method of claim 1 wherein the vertical semiconductor device is a diode.
26. The method of claim 6 further comprising: prior to providing the series of implants, providing a mask on the top surface over an area below which a central portion of the channel region will be formed, wherein areas on the top surface over which the at least two gate regions will be formed are exposed for the series of implants.
27. The method of claim 26 wherein the mask is the only mask used for the series of implants.
28. The method of claim 1 further comprising providing a series of channel implants of dopants having the first polarity within the channel region, such that each channel implant of the series of channel implants is provided at a different depth below the top surface.
29. The method of claim 28 wherein each successive one of the series of channel implants is below and has an inner sidewall that straggles further outward toward the gate region than a preceding one of the series of channel implants.
30. The method of claim 29 further comprising providing an implant of a dopant of the second polarity in the gate region to form a deep gate implant, wherein the deep gate implant is horizontally aligned with and overlaps opposing sidewalls of at least one of the series of channel implants to effectively move the opposing sidewalls of the at least one of the series of channel implants laterally outward from the gate region.
31. The method of claim 30 wherein the deep gate implant is horizontally aligned with a second or greater of the series of channel implants.