Nonvolatile memory cell comprising a reduced height vertical diode
View Patent ↗A nonvolatile memory cell according to the present invention comprises a bottom conductor, a semiconductor pillar, and a top conductor. The semiconductor pillar comprises a junction diode, including a bottom heavily doped region, a middle intrinsic or lightly doped region, and a top heavily doped region, wherein the conductivity types of the top and bottom heavily doped region are opposite. The junction diode is vertically oriented and is of reduced height, between about 500 angstroms and about 3500 angstroms. A monolithic three dimensional memory array of such cells can be formed comprising multiple memory levels, the levels monolithically formed above one another.
1. A method for forming a monolithic three dimensional memory array, the method comprising:
i) forming a first memory level, the steps for forming the first memory level comprising:
a) forming a plurality of substantially parallel, substantially coplanar first conductors above a substrate;
b) forming a plurality of substantially parallel, substantially coplanar second conductors above the first conductors;
c) forming a plurality of first vertically oriented pillars, each first pillar comprising a first junction diode and disposed between one of the first conductors and one of the second conductors,
wherein the first junction diodes have a first height between about 500 angstroms and about 3000 angstroms; and
ii) monolithically forming a second memory level on the first memory level.
2. The method of claim 1 wherein the height of the first junction diodes is between about 800 angstroms and about 3000 angstroms.
3. The method of claim 2 wherein the height of the first junction diodes is between about 1300 angstroms and about 2500 angstroms.
4. The method of claim 1 wherein the step of forming the first conductors comprises:
depositing a first conductive layer;
patterning and etching the first conductive layer into the first conductors;
depositing a first dielectric material on and between the first conductors; and
planarizing to expose the first conductors separated by the first dielectric material.
5. The method of claim 4 wherein the step of forming the first pillars comprises:
depositing a semiconductor layer stack on the first conductors and the first dielectric material; and
patterning and etching the semiconductor layer stack to form the first pillars.
6. The method of claim 5 wherein the step of forming the first pillars further comprises forming a top heavily doped region in each of the first pillars wherein the top heavily doped region is not doped by in situ doping.
7. The method of claim 6 wherein the top heavily doped region is doped by ion implantation, plasma immersion, gas source diffusion, or solid source diffusion.
8. The method of claim 7 wherein the top heavily doped region is doped by ion implantation.
9. The method of claim 8 wherein, during ion implantation, BF 2 ions are implanted.
10. The method of claim 5 wherein the step of forming the first pillars further comprises forming a bottom heavily doped region in each of the first pillars wherein the bottom heavily doped region is not doped by in situ doping.
11. The method of claim 10 wherein the bottom heavily doped region is doped by ion implantation, plasma immersion, gas source diffusion, or solid source diffusion.
12. The method of claim 11 wherein the bottom heavily doped region is doped by ion implantation.
13. The method of claim 12 wherein, during ion implantation, arsenic ions are implanted.
14. The method of claim 5 wherein the step of forming the first pillars further comprises forming a bottom heavily doped region in each of the first pillars by in situ doping.
15. The method of claim 1 wherein the step of forming a second memory level comprises:
forming a plurality of substantially parallel, substantially coplanar third conductors above the second conductors; and
forming a plurality of second vertically oriented pillars above the first pillars.
16. The method of claim 15 wherein each of the second pillars is disposed between one of the second conductors and one of the third conductors.
17. The method of claim 15 further comprising forming a plurality of substantially parallel, substantially coplanar fourth conductors above the third conductors, wherein each of the second pillars is disposed between one of the third conductors and one of the fourth conductors.
18. The method of claim 1 wherein the step of forming the first pillars comprises:
forming first bottom heavily doped regions doped by ion implantation having a first conductivity type;
forming first middle intrinsic or lightly doped regions immediately above the first bottom heavily doped regions; and
forming first top heavily doped regions immediately above the first middle intrinsic or lightly doped regions, the first top heavily doped regions doped by ion implantation and having a second conductivity type opposite the first conductivity type.
19. The method of claim 18 wherein the first bottom heavily doped regions are doped with arsenic ions.
20. The method of claim 18 wherein the first top heavily doped regions are doped with BF 2 ions.
21. The method of claim 18 wherein the first top heavily doped regions are doped with arsenic ions.
22. The method of claim 18 wherein the first bottom heavily doped regions are doped with BF 2 or boron ions.