Hybridized Oxide Capping Layer for Perpendicular Magnetic Anisotropy

• US 20150008547A1
• Filed: 07/05/2013
• Published: 01/08/2015
• Est. Priority Date: 07/05/2013
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Headway Technologies Incorporated (TDK Corporation)
• Inventors: Wang, Yu-Jen, Tong, Ru-Ying, Pi, Keyu
• Granted Patent: US 9,147,833 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: H10B 61/00 Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
• CPC Class Codes: H10N 50/01 Manufacture or treatment
• CPC Class Codes: H10N 50/10 Magnetoresistive devices
• CPC Class Codes: H10N 50/80 Constructional details
• CPC Class Codes: H10N 50/85 Magnetic active materials
• CPC Class Codes: H10N 52/00 Hall-effect devices integrated devices or assemblies of multiple devices H10N59/00
• CPC Class Codes: H10N 52/01 Manufacture or treatment
• CPC Class Codes: H10N 52/80 Constructional details

Abstract

A hybrid oxide capping layer (HOCL) is disclosed and used in a magnetic tunnel junction to enhance thermal stability and perpendicular magnetic anisotropy in an adjoining free layer. The HOCL has a lower interface oxide layer and one or more transition metal oxide layers wherein each of the metal layers selected to form a transition metal oxide has an absolute value of free energy of oxide formation less than that of the metal used to make the interface oxide layer. One or more of the HOCL layers is under oxidized. Oxygen from one or more transition metal oxide layers preferably migrates into the interface oxide layer during an anneal to further oxidize the interface oxide. As a result, a less strenuous oxidation step is required to initially oxidize the lower HOCL layer and minimizes oxidative damage to the free layer.

Claims

1. A hybrid oxide capping layer (HOCL) that induces or enhances perpendicular magnetic anisotropy (PMA) in an adjoining ferromagnetic layer in a magnetic device, comprising:

(a) an interface oxide layer made by oxidation of a first metal or alloy layer which forms an interface with the adjoining ferromagnetic layer; and

(b) one or more transition metal oxide layers formed by oxidation of one or more transition metal layers wherein each transition metal has an absolute value of free energy of oxide formation less than that of the first metal or alloy.

2. The hybrid oxide capping layer of claim 1 wherein the interface oxide layer is comprised of one or more of MgTaOx, SrTiOx, BaTiOx, CaTiOx, LaAlOx, MgO, TaOx, MnOx, VOx and BOx.

3. The hybrid oxide capping layer of claim 1 wherein the one or more transition metal oxide layers is comprised of one or more of RuOx, PtOx, RhOx, MoOx, WOx, SnOx, or InSnOx.

4. The hybrid oxide capping layer of claim 1 wherein the ferromagnetic layer is a free layer comprised of one or more of CoFeB, CoFe, Co Fe, CoB, FeB, and CoFeNiB.

5. The hybrid oxide capping layer of claim 4 wherein the free layer has a FL1/S/FL2 configuration wherein each of the FL1 and FL2 layers is made of one or more of CoFeB, CoFe, Co, Fe, CoB, FeB, or CoFeBNi, and S is a non-magnetic spacer that is one of Ta, Mg, Zr, Hf, Mo, W, and Nb.

6. The hybrid oxide capping layer of claim 1 further comprised of a dopant that is one or more of Fe, Co, Ni, Ru, Cr, Au, Ag, and Cu.

7. A magnetic tunnel junction (MTJ), comprising:

(a) a reference layer;

(b) a tunnel barrier layer formed between the reference layer and a free layer;

(c) the free layer that forms a first interface with a surface of the tunnel barrier layer, and that forms a second interface with an adjoining interface oxide layer in a hybrid oxide capping layer structure; and

(d) the hybrid oxide capping layer structure comprised of;

(1) the interface oxide layer that forms the second interface with the free layer, the interface oxide layer is made of a first metal or first alloy;

(2) a first transition metal oxide layer formed from a second metal or second alloy that has an absolute value of free energy of oxide formation less than that of the first metal or first alloy; and

(3) a second transition metal oxide layer formed from a third metal or third alloy that has an absolute value of free energy of oxide formation less than that of the first metal or first alloy.

8. The MTJ of claim 7 wherein the MTJ has a bottom spin valve configuration wherein a seed layer, the reference layer, the tunnel barrier layer, the free layer, and the hybrid oxide capping layer are sequentially formed on a substrate, and each of the free layer and reference layer exhibit perpendicular magnetic anisotropy.

9. The MTJ of claim 7 further comprising a second hybrid oxide capping layer that is formed between the seed layer and the reference layer, the second hybrid oxide capping layer has an interface oxide layer adjoining the reference layer and a transition metal oxide layer adjoining the seed layer.

10. The MTJ of claim 7 wherein the interface oxide capping layer is comprised of one or more of MgTaOx, SrTiOx, BaTiOx, CaTiOx, LaAlOx, MgO, TaOx, MnOx, VOx, and BOx.

11. The MTJ of claim 7 wherein each of the first transition metal oxide layer and second transition metal oxide layer is comprised of RuOx, PtOx, RhOx, MoOx, WOx, SnOx, or InSnOx.

12. The MTJ of claim 7 wherein the free layer is comprised of one or more of CoFeB, CoFe, Co, Fe, CoB, FeB, and CoFeNiB.

13. The MTJ of claim 12 wherein the free layer has a FL1/S/FL2 configuration wherein each of the FL1 and FL2 layers is made of one or more of CoFeB, CoFe, Co, Fe, CoB, FeB, or CoFeNiB, and S is a non-magnetic spacer that is one of Ta, Mg, Zr, Hf, Mo, W, and Nb.

14. The MTJ of claim 7 wherein the MTJ has a top spin valve configuration with a seed layer, the second transition metal oxide layer, the first transition metal oxide layer, the interface oxide layer, the free layer, the tunnel barrier layer, and the reference layer sequentially formed on a substrate, the free layer and reference layer each exhibit perpendicular magnetic anisotropy.

15. The MTJ of claim 7 wherein the hybrid oxide capping layer has a resistance×

area (RA) value that is reduced by decreasing a thickness of the hybrid oxide capping layer or reducing an oxidation state in one or more of the interface oxide layer, first transition metal oxide layer, and second transition metal oxide layer.

16. The MTJ of claim 7 wherein one or more of the interface oxide layer, first transition metal oxide layer, and second transition metal oxide layer comprise less than a stoichiometric amount of oxygen such that there is unoxidized metal or unoxidized alloy remaining in the hybrid oxide capping layer.

17. The MTJ of claim 7 wherein the hybrid oxide capping layer is doped with one or more of Fe, Co, Ni, Ru, Cr, Au, Ag, and Cu to increase conductivity therein.

18. The MTJ of claim 10 wherein the interface oxide layer is MgO/TaOx and is formed by oxidation of a Mg/Ta stack wherein Ta has an α

-Ta phase, or is MgTaOx and is formed by oxidation of a Mg;

Ta alloy wherein Ta has an α

-phase.

19. The MTJ of claim 7 wherein the interface oxide layer is a composite with a lower oxide layer that contacts the free layer and an upper oxide layer, the lower oxide layer has a greater absolute value of free energy of oxide formation than the upper oxide layer.

20. A magnetic tunnel junction (MTJ), comprising:

(a) a reference layer;

(b) a tunnel barrier layer; and

(c) a laminated structure represented by (free layer/HOCL)_m where m is ≧

2 and HOCL is a hybrid oxide capping layer comprised of a lower interface oxide layer and at least an upper transition metal oxide layer having an absolute value of free energy of oxide formation less than that of the interface oxide layer.

21. The MTJ of claim 20 wherein the free layer is comprised of one or more of CoFeB, CoFe, Co, Fe, CoB, FeB, and CoFeNiB.

22. The MTJ of claim 20 wherein each of the lower interface oxide layers is comprised of one or more of MgTaOx, SrTiOx, BaTiOx, CaTiOx, LaAlOx, MgO, TaOx, MnOx, VOx, and BOx.

23. The MTJ of claim 20 wherein each of the upper transition metal oxide layers is comprised of one or more of RuOx, PtOx, RhOx, MoOx, WOx, SnOx, or InSnOx.

24. The MTJ of claim 20 wherein one or both of the lower interface oxide layer and upper transition metal oxide layer in each HOCL comprises less than a stoichiometric amount of oxygen such that there is unoxidized metal or unoxidized alloy remaining in each of the HOCL layers.

25. The MTJ of claim 20 wherein one or more of the HOCL layers in the laminated (free layer/HOCL)_m structure is comprised of a dopant that is one or more of Fe, Co, Ni, Ru, Cr, Au, Ag, and Cu.

26. A method of forming a hybrid oxide capping layer in a magnetic device, comprising:

(a) providing a substrate;

(b) depositing a first metal or first alloy layer on the substrate and performing a first oxidation step that at least partially oxidizes the first metal or first alloy layer to form an interface oxide layer;

(c) depositing a second metal or second alloy layer on the interface oxide layer and performing a second oxidation step that at least partially oxidizes the second metal or second alloy layer to form a first transition metal oxide layer, the second metal or second alloy has an absolute value of free energy of oxide formation that is less than that of the first metal or first alloy;

(d) depositing a third metal or third alloy layer on the first transition metal oxide layer and performing a third oxidation step that at least partially oxidizes the third metal or third alloy layer to form a second transition metal oxide layer, the third metal or third alloy has an absolute value of free energy of oxide formation that is less than that of the first metal or first alloy; and

(e) performing an anneal process that increases an oxidation state of the interface oxide layer to form a hybrid oxide capping layer (HOCL) comprised of a lower interface oxide layer, a first transition metal oxide layer, and a second transition metal oxide layer.

27. The method of claim 26 wherein the substrate is a free layer in a magnetic tunnel junction (MTJ), the free layer is comprised of one or more of CoFeB, CoFe, Co, Fe, CoB, FeB, and CoFeNiB, and exhibits perpendicular magnetic anisotropy.

28. The method of claim 26 wherein the HOCL has a resistance×

area (RA) value that is reduced by decreasing a thickness of the HOCL or by reducing an oxidation state in one or more of the interface oxide layer, first transition metal oxide layer, and second transition metal oxide layer.

29. The method of claim 26 wherein the interface oxide layer is comprised of one or more of MgTaOx, SrTiOx, BaTiOx, CaTiOx, LaAlOx, MgO, TaOx, MnOx, VOx, and BOx.

30. The method of claim 26 wherein each of the first transition metal oxide layer and second transition metal oxide layer is comprised of RuOx, PtOx, RhOx, MoOx, WOx, SnOx, or InSnOx, and the second metal or second alloy is different from the third metal or third alloy.

31. The method of claim 26 further comprised of doping the HOCL with one or more of Fe, Co, Ni, Ru, Cr, Au, Ag, and Cu to increase conductivity therein.

32. The method of claim 26 wherein the anneal process is performed for a period of about 10 minutes to 2 hours at a temperature between about 250°

C. and 500°

C.

33. The method of claim 29 wherein the interface oxide layer is MgO/TaOx and is formed by oxidation of a Mg/Ta stack wherein Ta has an α

-Ta phase, or is MgTaOx and is formed by oxidation of a Mg;

Ta alloy wherein Ta has an α

-phase.