Phase-change memory device and method

1. A method comprising:

forming a dielectric layer over a substrate, the dielectric layer having a top surface;

etching an opening in the dielectric layer;

forming a bottom electrode within the opening, the bottom electrode comprising a barrier layer;

forming a phase-change material (PCM) layer within the opening and on the bottom electrode, wherein a top surface of the PCM layer is level with or below the top surface of the dielectric layer, wherein sidewalls of the PCM layer are free of the barrier layer; and

forming a top electrode on the PCM layer.

2. The method of claim 1 , wherein forming the bottom electrode comprises:

depositing the barrier layer in the opening;

depositing a conductive material on the barrier layer; and

etching the barrier layer and the conductive material, wherein the etching exposes sidewalls of the opening.

3. The method of claim 2 , wherein, after etching the barrier layer and the conductive material, the top surface of the conductive material is convex.

4. The method of claim 2 , wherein, after etching the barrier layer and the conductive material, the top surface of the barrier layer is level with the top surface of the conductive material.

5. The method of claim 1 , wherein forming the PCM layer comprises:

depositing a phase-change material over the bottom electrode and the dielectric layer; and

etching the phase-change material to remove the phase-change material from the top surface of the dielectric layer.

6. The method of claim 1 , wherein the bottom electrode has a thickness that is between 25% and 50% of the thickness of the dielectric layer.

7. The method of claim 1 , wherein the PCM layer has a thickness that is between 30% and 70% of the thickness of the dielectric layer.

8. The method of claim 1 , wherein the PCM layer physically contacts the dielectric layer.

9. A method comprising:

depositing an inter-metal dielectric (IMD) layer over a first conductive feature;

forming an opening in the IMD layer that exposes the first conductive feature;

forming a second conductive feature in the opening, comprising filling the opening with a conductive material;

performing a first etch back process to recess the second conductive feature in the opening;

depositing a phase-change material (PCM) in the opening and over the second conductive feature;

performing a second etch back process to remove upper portions of the PCM; and

depositing a conductive material on the PCM.

10. The method of claim 9 , wherein forming the second conductive feature comprises depositing a layer of tantalum nitride and depositing the conductive material on the layer of tantalum nitride, wherein the conductive material comprises titanium nitride.

11. The method of claim 9 , wherein the first etch back process is an atomic layer etching (ALE) process.

12. The method of claim 9 , wherein the first etch back process comprises:

flowing first process gases into a process chamber; and

performing a plurality of etching cycles, wherein each etching cycle comprises:

flowing second process gases into the process chamber;

igniting the second process gases into a plasma while using a first voltage bias; and

igniting the second process gases into a plasma while using a second voltage bias that is less than the first voltage bias.

13. The method of claim 12 , wherein the second process gases comprises Cl 2 , BCl 3 , Ar, and He.

14. The method of claim 12 , wherein the first etch back process further comprises:

prior to performing the plurality of etching cycles, flowing third process gases into the process chamber; and

igniting the third process gases into a plasma.

15. The method of claim 9 , wherein the second etch back process comprises:

flowing fourth process gases into a process chamber; and

igniting the fourth process gases into a plasma.

16. A method comprising:

forming a metallization layer over a semiconductor substrate;

forming an inter-metal dielectric (IMD) layer over the metallization layer; and

forming a phase-change random access memory (PCRAM) cell, comprising:

forming a bottom electrode in the IMD layer, wherein the bottom electrode is electrically connected to the metallization layer, wherein a top surface of the bottom electrode is below a top surface of the IMD layer;

forming a phase-change material (PCM) layer on the bottom electrode and within the IMD layer, wherein a top surface of the PCM layer is below the top surface of the IMD layer; and

forming a top electrode on the PCM layer and extending on the top surface of the IMD layer, wherein the top electrode is electrically connected to the PCM layer.

17. The method of claim 16 , wherein the top surface of the IMD layer is free of the PCM layer.

18. The method of claim 16 , wherein the sidewalls of the PCM layer physically contact the IMD layer.

19. The method of claim 16 , wherein the PCM layer comprises GeSbTe (GST).

20. The method of claim 16 , wherein the PCM layer has a uniform thickness.