Phase-change memory device and method

1. A device comprising:

a first metallization layer over a substrate, the substrate comprising active devices;

a first bit line over the first metallization layer, the first bit line connected to first interconnects of the first metallization layer, the first bit line extending in a first direction, the first direction parallel to gates of the active devices;

a first phase-change random access memory cell over the first bit line;

a first dielectric layer having a first portion and a second portion, the first portion surrounding the first bit line, the second portion surrounding the first phase-change random access memory cell, the first portion having a first height, the second portion having a second height, the second height being greater than the first height;

a word line over the first phase-change random access memory cell and the second portion of the first dielectric layer, the word line extending in a second direction, the second direction perpendicular to the gates of the active devices; and

a second metallization layer over the word line, the word line connected to second interconnects of the second metallization layer.

2. The device of claim 1 further comprising:

a second bit line over the first metallization layer, the second bit line extending in the first direction; and

a second phase-change random access memory cell over the second bit line, the word line disposed over the second phase-change random access memory cell, the first phase-change random access memory cell being separated from the second phase-change random access memory cell by a distance in a range of 20 nm to 50 nm.

3. The device of claim 2 , wherein the first phase-change random access memory cell and the second phase-change random access memory cell each have a width in a range of 15 nm to 30 nm.

4. The device of claim 1 further comprising:

a bit line pad over the first metallization layer, the bit line pad and the first bit line being a first continuous conductive feature;

a first conductive via connecting the bit line pad to the first interconnects of the first metallization layer; and

a first inter-metal dielectric around the first conductive via, the first continuous conductive feature disposed over the first inter-metal dielectric.

5. The device of claim 4 further comprising:

a word line pad over the bit line pad, the word line pad and the word line being a second continuous conductive feature;

a second conductive via connecting the word line pad to the second interconnects of the second metallization layer; and

a second inter-metal dielectric around the second conductive via, the second inter-metal dielectric disposed over the second continuous conductive feature.

6. The device of claim 5 further comprising:

a third conductive via extending through the first inter-metal dielectric and the second inter-metal dielectric, the third conductive via connecting the first interconnects of the first metallization layer to the second interconnects of the second metallization layer.

7. The device of claim 1 further comprising:

a second dielectric layer over the first bit line and the first portion of the first dielectric layer, the second dielectric layer surrounding the word line and the second portion of the first dielectric layer.

8. The device of claim 1 , wherein the first phase-change random access memory cell comprises:

a bottom electrode connected to the first bit line;

a top electrode connected to the word line; and

a phase change material element between the top electrode and the bottom electrode.

9. The device of claim 8 further comprising:

an ovonic threshold switching layer between the bottom electrode and the first bit line.

10. A device comprising:

a first inter-metal dielectric;

a first conductive via extending through the first inter-metal dielectric;

a first conductive feature having a bit line pad portion and a bit line portion, the bit line pad portion disposed on the first conductive via, the bit line portion disposed on the first inter-metal dielectric;

a phase-change random access memory cell on the bit line portion of the first conductive feature;

a second inter-metal dielectric surrounding the phase-change random access memory cell and the first conductive feature; and

a second conductive feature having a word line pad portion and a word line portion, the word line pad portion disposed on the second inter-metal dielectric, the word line portion disposed on the phase-change random access memory cell.

11. The device of claim 10 further comprising:

a second conductive via on the word line pad portion of the second conductive feature; and

a third inter-metal dielectric surrounding the second conductive via.

12. The device of claim 10 , wherein the second inter-metal dielectric has a first portion and a second portion, the first portion surrounding the bit line pad portion, the second portion surrounding the phase-change random access memory cell and the bit line portion, the first portion having a first height, the second portion having a second height, the second height being greater than the first height, the device further comprising:

a third inter-metal dielectric over the first portion of the second inter-metal dielectric, the third inter-metal dielectric surrounding the second portion of the second inter-metal dielectric.

13. The device of claim 10 further comprising:

an ovonic threshold switching layer between the phase-change random access memory cell and the bit line portion.

14. A device comprising:

a first inter-metal dielectric over a semiconductor substrate;

a first conductive feature on the first inter-metal dielectric, the first conductive feature having a bit line pad portion and a bit line portion, the bit line portion extending in a first direction in a top-down view;

a memory cell on the bit line portion;

a second inter-metal dielectric around the memory cell and the first conductive feature; and

a second conductive feature on the second inter-metal dielectric, the second conductive feature having a word line pad portion and a word line portion, the word line portion extending in a second direction in the top-down view, the second direction perpendicular to the first direction, the memory cell disposed at an intersection of the word line portion and the bit line portion in the top-down view.

15. The device of claim 14 further comprising:

a third inter-metal dielectric around the second conductive feature.

16. The device of claim 14 further comprising:

a first conductive via extending through the first inter-metal dielectric, the bit line pad portion disposed on the first conductive via.

17. The device of claim 16 further comprising:

a third inter-metal dielectric over the second conductive feature; and

a second conductive via extending through the third inter-metal dielectric, the second conductive via disposed on the word line pad portion.

18. The device of claim 14 , wherein the memory cell is a phase-change random access memory cell.

19. The device of claim 14 , wherein the second inter-metal dielectric has a first portion adjacent the memory cell and has a second portion adjacent the bit line pad portion, the first portion having a first height, the second portion having a second height, the second height being different than the first height.

20. The device of claim 14 further comprising:

an ovonic threshold switching layer between the memory cell and the bit line portion.