Reduction of Capping Layer Resistance Area Product for Magnetic Device Applications

• US 20130264665A1
• Filed: 04/06/2012
• Published: 10/10/2013
• Est. Priority Date: 04/06/2012
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Headway Technologies Incorporated (TDK Corporation)
• Inventors: Jan, Guenole, Tong, Ru-Ying
• Granted Patent: US 10,312,433 B2
• Time in Patent Office: Days
• US Class Current: 257/421
• CPC Class Codes: G11C 11/161 details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
• CPC Class Codes: H01F 10/3286 Spin-exchange coupled multilayers having at least one layer with perpendicular magnetic anisotropy
• CPC Class Codes: H01F 10/329 Spin-exchange coupled multilayers wherein the magnetisation of the free layer is switched by a spin-polarised current, e.g. spin torque effect
• CPC Class Codes: H01F 41/308 lift-off processes, e.g. ion milling, for trimming or patterning
• CPC Class Codes: H10N 50/01 Manufacture or treatment
• CPC Class Codes: H10N 50/10 Magnetoresistive devices

Abstract

A ferromagnetic layer is capped with a metallic oxide (or nitride) layer that provides a perpendicular-to-plane magnetic anisotropy to the layer. The surface of the ferromagnetic layer is treated with a plasma to prevent diffusion of oxygen (or nitrogen) into the layer interior. An exemplary metallic oxide layer is formed as a layer of metallic Mg that is plasma treated to reduce its grain size and enhance the diffusivity of oxygen into its interior. Then the plasma treated Mg layer is naturally oxidized and, optionally, is again plasma treated to reduce its thickness and remove the oxygen rich upper surface.

Claims

1. A capped ferromagnetic layer having perpendicular-to-plane magnetic anisotropy, comprising:

a ferromagnetic layer having an upper surface in a plane of its deposition;

wherein

a first plasma treatment has been applied to said upper surface; and

wherein

an oxide layer or a nitride layer is formed as a cap on said plasma-treated upper surface to promote a perpendicular-to-plane magnetic anisotropy in said ferromagnetic layer; and

wherein

a region between said upper surface of said oxide layer or said nitride layer and said ferromagnetic layer is characterized by an oxygen concentration profile or a nitrogen concentration profile; and

wherein

an annealing process has been applied to said capped ferromagnetic layer to provide an enhanced Hk and Hc and an improved value of a resistance and surface area product, RA.

2. The capped ferromagnetic layer of claim 1 wherein said cap is an oxide layer that is a native oxide layer of the ferromagnetic material.

3. The capped ferromagnetic layer of claim 1 wherein said cap is an oxide layer that is a deposited metallic layer that is subsequently oxidized.

4. The capped ferromagnetic layer of claim 1 wherein said first plasma treatment produces a smoother upper surface of said free layer.

5. The capped ferromagnetic layer of claim 3 wherein said first plasma treatment produces an upper surface of said free layer that is resistant to oxygen diffusion.

6. The capped ferromagnetic layer of claim 3 including a second plasma treatment applied to an upper surface of said deposited metal layer prior to said oxidation process.

7. The capped ferromagnetic layer of claim 6 wherein said deposited metal layer is a layer of Mg.

8. The capped ferromagnetic layer of claim 6 wherein said deposited metal layer is a layer of Si, Ba, Ca, La, Mn, Zn, Hf, Ta, Ti, B, Cu, Cr, V or Al.

9. The capped ferromagnetic layer of claim 6 wherein said second plasma treatment produces a smooth upper surface of said metal layer.

10. The capped ferromagnetic layer of claim 6 wherein said second plasma treatment reduces a metallic grain size of said metal layer.

11. The capped ferromagnetic layer of claim 10 wherein said reduced metallic grain size promotes a more uniform oxygen diffusion through said metal layer and thereby produces a more uniform oxide layer.

12. The capped ferromagnetic layer of claim 1 wherein an upper surface of said oxide layer or said nitride layer has been made smooth by a third plasma treatment.

13. The capped ferromagnetic layer of claim 1 wherein said oxide layer or said nitride layer has been thinned by a third plasma treatment.

14. The capped ferromagnetic layer of claim 1 wherein said oxygen concentration profile or said nitrogen concentration profile is smoothly reduced from its maximum value at an upper surface of said oxide layer to an approximately zero value at an interface between said oxide layer and said ferromagnetic layer.

15. The capped ferromagnetic layer of claim 1 wherein said ferromagnetic layer is a tri-layer comprising two layers of CoFeB of approximately 10 angstroms thickness separated by a layer of Ta of approximately 1.5 angstroms thickness.

16. The capped ferromagnetic layer of claim 15 wherein said capping layer is an oxide layer that is a first metallic layer of Mg of thickness approximately 6 angstroms that is oxidized and plasma treated and over which a second layer of metallic Mg of thickness 3 angstroms is formed.

17. The capped ferromagnetic layer of claim 1 wherein said ferromagnetic layer is a free magnetic layer.

18. The capped ferromagnetic layer of claim 2 wherein an upper surface of said oxide layer has been made smooth by a third plasma treatment.

19. The capped ferromagnetic layer of claim 2 wherein said oxide layer has been thinned by a third plasma treatment.

20. The capped ferromagnetic layer of claim 19 where a metal layer of Mg is formed over said thinned oxide layer.

21. A method of forming a capped ferromagnetic layer having a perpendicular-to-plane magnetic anisotropy, comprising:

providing a ferromagnetic layer having an upper surface in a plane of its deposition;

applying a first plasma treatment to said upper surface to smooth said surface and provide a barrier to oxygen diffusion;

then

forming an oxide layer, as a cap, on said plasma-treated upper surface to promote a perpendicular-to-plane magnetic anisotropy in said ferromagnetic layer;

wherein

a region between said upper surface of said oxide layer and said ferromagnetic layer is characterized by an oxygen concentration profile that approaches zero at the upper surface of said ferromagnetic layer; and

then

annealing said capped ferromagnetic layer to provide an enhanced Hk and Hc.

22. The method of claim 21 wherein said oxide capping layer is formed within a temperature range between room temperature and 400°

C.

23. The method of claim 21 wherein said annealing process is carried out at a temperature of up to 400°

C.

24. The method of claim 21 wherein the annealing process is carried out at approximately 300°

C.

25. The method of claim 21 wherein said oxide layer is formed by a process comprising:

forming a metallic layer on said plasma treated upper surface;

oxidizing said metallic layer using an oxidation process.

26. The method of claim 21 wherein said oxide layer is formed as a native oxide by natural oxidation of said ferromagnetic layer.

27. The method of claim 26 wherein a second plasma treatment, using a radio frequency inert gas plasma is applied to said metallic layer prior to said oxidation process.

28. The method of claim 26 wherein said oxidation process is a natural oxidation process.

29. The method of claim 27 wherein said second plasma treatment reduces a grain size of said metallic layer thereby improving the diffusion of oxygen within said layer, reducing the thickness of said layer and rendering the interior of said layer more uniform and continuous.

30. The method of claim 21 including a third plasma treatment of an upper surface of said oxidized layer, thereby reducing the thickness of said oxide.

31. The method of claim 21 wherein said oxide layer is a layer of the native oxide of the ferromagnetic layer.

32. The method of claim 21 wherein said ferromagnetic layer is formed as a tri-layer comprising two layers of CoFeB of approximately 10 angstroms thickness separated by a layer of Ta of approximately 1.5 angstroms thickness.

33. The method of claim 32 wherein said ferromagnetic layer is treated by an inert gas, radio frequency plasma applied at a power of 10 watts for a time of 30 seconds.

34. The method of claim 21 wherein said oxide layer is formed by a process comprising:

forming a first metallic layer of Mg of thickness approximately 6 angstroms;

applying a second plasma treatment to said first metallic layer;

then

oxidizing said first metallic layer;

then

forming a second layer of metallic Mg of thickness 3 angstroms on said oxidized first metallic layer.

35. The method of claim 34 wherein said second plasma treatment is applied by a radio frequency inert gas plasma at a power of 15 watts for a time of 30 seconds.

36. The method of claim 35 wherein said oxidizing of said first metallic layer is carried out by natural oxidation using oxygen supplied at a rate of 1 sccm for a time of 60 seconds.

37. A TMJ spin torque transfer cell comprising:

a reference layer having a perpendicular-to-plane component of magnetic anisotropy;

a tunneling bather layer formed on the reference layer;

a free layer having a perpendicular-to-plane component of magnetic anisotropy a capping layer formed as a metallic oxide layer on said free layer, wherein said capping layer maintains a perpendicular-to-plane component of magnetic anisotropy of said free layer by means of a combined plasma treatment and oxidation process during its formation that produces an oxygen concentration profile in said capping layer that goes to zero at the interface of said free layer.