Forming tapered lower electrode phase-change memories
View Patent ↗A phase-change memory may have a tapered lower electrode coated with an insulator. The coated, tapered electrode acts as a mask for a self-aligned trench etch to electrically separate adjacent wordlines. In some embodiments, the tapered lower electrode may be formed over a plurality of doped regions, and isotropic etching may be used to taper the electrode as well as part of the underlying doped regions.
1. A phase-change memory cell comprising: a substrate; a plurality of layers of different doping levels in the substrate; a tapered lower electrode for the phase-change memory cell over the substrate; and a trench in said layers, on either side of said tapered electrode.
2. The memory of claim 1 including an insulator over said electrode.
3. The memory of claim 1 including a substrate under said tapered electrode, said substrate including a lower portion and a tapered upper portion.
4. The memory of claim 3 wherein said insulator covers said tapered substrate portion.
5. The memory of claim 4 wherein said lower substrate portion is free of said insulator.
6. The memory of claim 2 wherein said trenches are self-aligned to said tapered electrode.
7. The memory of claim 2 wherein said tapered electrode is conical.
8. The memory of claim 3 wherein said tapered substrate portion includes a first region of a first conductivity type over a second region of a second conductivity type.
9. The memory of claim 8 wherein said first type is P type and said first region is sandwiched between said second region and said electrode.
10. The memory of claim 9 including a buried wordline formed in said upper portion.