Phase change memory device and fabrication method thereof
A phase change memory device is disclosed. A second conductive spacer is under a first conductive spacer. A phase change layer comprises a first portion substantially parallel to the first and second conductive spacers and a second portion on top of the second conductive spacer, wherein the second conductive spacer is electrically connected to the first conductive spacer through the second portion of the phase change layer.
1. A phase change memory device, comprising:
a first dielectric layer comprising a first opening and a second opening under the first opening, wherein width of first opening is greater than the width of the second opening;
a first conductive spacer on a sidewall of the first opening;
a second conductive spacer on a sidewall of the second opening;
a phase change layer at least covering sidewalls of the first and second conductive spacers and top of the second conductive spacer; and
a second dielectric layer on the phase change layer,
wherein each of the first conductive spacer and the second conductive spacer is L shaped and includes a vertical portion and a horizontal portion, the vertical portion is separated from the phase change layer by a dielectric spacer, and the horizontal portion contacts the phase change layer.
2. The phase change memory device as claimed in claim 1 , wherein the first and second openings expose a bottom electrode.
3. The phase change memory device as claimed in claim 1 , wherein the first conductive spacer and the second conductive spacer are electrically connected through a portion of the phase change layer on top of the second conductive spacer.
4. The method for forming a phase change memory device as claimed in claim 3 , wherein an active region of the phase change memory device is disposed in the portion of the phase change layer.
5. A method for forming a phase change memory device, comprising:
forming a first dielectric layer on a bottom electrode;
patterning the first dielectric layer to form a first opening;
expanding the first opening;
patterning the first dielectric layer to form a second opening under the first opening;
forming a conductive-spacer layer on the first dielectric layer and in the first and second openings;
forming a dielectric-spacer layer on the conductive-spacer layer;
anisotropically etching the conductive-spacer layer and the dielectric-spacer layer to form a first conductive spacer on a sidewall of the first opening, a second conductive spacer on a sidewall of the second opening, a first dielectric spacer adjacent to the first conductive spacer and a second dielectric spacer adjacent to the second conductive spacer;
conformally depositing a phase change layer in the first and second opening; and
forming a second dielectric layer on the phase change layer,
wherein each of the first conductive spacer and the second conductive spacer is L shaped and includes a vertical portion and a horizontal portion, the vertical portion is separated from the phase change layer by one of the first and second dielectric spacers, and the horizontal portion contacts the phase change layer.
6. The method for forming a phase change memory device as claimed in claim 5 , wherein anisotropically etching the conductive-spacer layer and anisotropically etching the dielectric-spacer layer are accomplished in the same etching step.
7. The method for forming a phase change memory device as claimed in claim 5 , wherein expanding the first opening and forming the second opening are accomplished by a single self-aligned etching process.
8. The method for forming a phase change memory device as claimed in claim 7 , wherein the single self-aligned etching process is anisotropic etching.
9. The method for forming a phase change memory device as claimed in claim 5 , further comprising in-situ deposition of a protective layer on the phase change layer before forming the second dielectric layer.
10. The method for forming a phase change memory device as claimed in claim 5 , further comprising planarizing the second dielectric layer.
11. The method for forming a phase change memory device as claimed in claim 5 , further comprising forming a top electrode on the second dielectric layer.
12. The phase change memory device as claimed in claim 1 , wherein the vertical portion of the first conductive spacer contacts a first horizontal portion of the phase change layer, the horizontal portion of the first conductive spacer contacts a first vertical portion of the phase change layer, the vertical portion of the second conductive spacer contacts a second horizontal portion of the phase change layer, and the horizontal portion of the second conductive spacer contacts a second vertical portion of the phase change layer.