Magnetic tunneling junction (MTJ) element with an amorphous buffer layer and its fabrication process

1. A method for manufacturing a memory device, comprising:

forming a bottom electrode layer over a substrate;

performing a first etch process, thereby defining one or more holes in the bottom electrode layer and defining a bottom electrode;

forming a pair of insulators within the one or more holes such that the insulators are disposed on opposing sides of the bottom electrode;

forming a buffer layer, a seed layer, a magnetic tunnel junction (MTJ) stack, and a top electrode over the bottom electrode; and

performing a second etch process to remove a portion of the buffer layer, the seed layer, the MTJ stack, and the top electrode, thereby defining a memory cell.

2. The method of claim 1 , wherein the first etch process is different from the second etch process.

3. The method of claim 1 , wherein the pair of insulators is formed after the first etch process and before the second etch process.

4. The method of claim 1 , wherein the buffer layer comprises a Co—Hf film with a Hf content ranging from 18 atomic percentage (at %) to 40 at %.

5. The method of claim 4 , wherein the buffer layer is disposed between the seed layer and the bottom electrode.

6. The method of claim 1 , wherein the pair of insulators continuously extend from a top surface of the bottom electrode to a point vertically below a bottom surface of the bottom electrode.

7. The method of claim 1 , wherein the buffer layer is disposed on a top surface of the bottom electrode and a top surface of the pair of insulators during the second etch process.

8. The method of claim 1 , wherein the pair of insulators laterally encloses an outer perimeter of the bottom electrode.

9. A method for manufacturing a memory device, comprising:

forming a bottom electrode over a substrate, wherein forming the bottom electrode comprises forming a bottom electrode layer over the substrate and performing a first etch process on the bottom electrode layer;

forming a buffer layer over the bottom electrode;

forming a seed layer over the buffer layer;

forming a magnetic tunnel junction (MTJ) stack over the seed layer; and

wherein the buffer layer comprises a material with a form X—Z, where X is iron (Fe) or cobalt (Co) and Z is hafnium (Hf), yttrium (Y), or Zirconium (Zr) with a Z content ranging from 18 atomic percentage (at %) to 40 at %, wherein forming the buffer layer includes depositing the buffer layer along a top surface of the bottom electrode and performing a second etch process on the buffer layer, and wherein the first etch process is different from the second etch process.

10. The method of claim 9 , wherein the material is an amorphous nonmagnetic alloy.

11. The method of claim 9 , wherein the buffer layer directly contacts a bottom surface of the seed layer.

12. The method of claim 9 , wherein the first etch process is performed on the bottom electrode layer according to a first masking layer and the second etch process is performed on the buffer layer according to a second masking layer different from the first masking layer.

13. The method of claim 9 , further comprising:

forming an insulator structure along outer sidewalls of the bottom electrode before forming the buffer layer.

14. The method of claim 13 , wherein the insulator structure has an outer perimeter that fully surrounds and is larger than an outer perimeter of the MTJ stack.

15. The method of claim 9 , further comprising:

performing a planarization process on the bottom electrode before the second etch process.

16. A method for manufacturing a memory device, comprising:

forming a diffusion barrier layer over a substrate;

forming a bottom electrode layer over the diffusion barrier layer;

performing a first etch process, defining one or more holes in the bottom electrode layer and the diffusion barrier layer, defining a bottom electrode and a diffusion barrier;

forming an insulator layer over the bottom electrode, filling the one or more holes;

performing a planarization process to remove a portion of the insulator layer, defining a pair of insulators;

forming a buffer layer, a seed layer, a hard bias stack, a magnetic tunnel junction (MTJ) stack, a capping layer, a top electrode, a hard mask, and a photoresist over the bottom electrode; and

performing a second etch process to remove the hard mask, the photoresist, and a portion of the buffer layer, the seed layer, the hard bias stack, the MTJ stack, the capping layer, and the top electrode.

17. The method of claim 16 , further comprising:

forming a sidewall spacer over the top electrode and the bottom electrode;

forming an inter-level dielectric (ILD) layer over the sidewall spacer; and

forming a top electrode via over the top electrode.

18. The method of claim 16 , wherein the buffer layer is made from an amorphous nonmagnetic binary alloy of form X—Y, where X is Fe or Co and Y is Hf, Y, or Zr.

19. The method of claim 16 , wherein the buffer layer prevents diffusion of a diffusive species from the bottom electrode to the seed layer, as well as to aid a planarization of a top surface of the bottom electrode.

20. The method of claim 16 , wherein the buffer layer has a substantially flat upper surface and the bottom electrode has a substantially rough upper surface.