Fabrication of a perpendicular magnetic tunnel junction (PMTJ) using block copolymers

1. A method, comprising:

forming an etch-stop layer above a substrate in a film thickness direction;

forming a matrix layer above the etch-stop layer in the film thickness direction;

forming a set of pillars above the matrix layer in the film thickness direction, the set of pillars having a predefined spacing therebetween along a plane in an element width direction and an element depth direction, the plane being normal to the film thickness direction;

forming a functionalization layer above the pillars, along sides of the pillars, and above the matrix layer in the film thickness direction;

forming first diblock copolymer layers above the functionalization layer in the film thickness direction, the first diblock copolymer layers self-segregating into a first polymer and a second polymer in a first pattern;

removing the first polymer from the first diblock copolymer layers to create a first mask layer; and

removing portions of the matrix layer that are not covered by the first mask layer in the film thickness direction to expose portions of the etch-stop layer positioned therebelow and create a second pattern in the matrix layer that forms a second mask layer.

2. The method as recited in claim 1 , further comprising:

forming second diblock copolymer layers on sides of the second mask layer and above the second mask layer in the film thickness direction, the second diblock copolymer layers self-segregating into a third polymer that is formed on the sides of the second mask layer and above the second mask layer and a fourth polymer that is formed in holes of the second mask layer above the etch-stop layer; and

removing the fourth polymer and portions of the etch-stop layer positioned therebelow in the film thickness direction that are not covered by the second mask layer and a portion of the third polymer that is formed on the sides of the second mask layer to form a plurality of contact holes through the etch-stop layer in a third pattern.

3. The method as recited in claim 2 , wherein each of the contact holes have a substantially cylindrical shape with a circular cross-section along the plane in the element width direction and the element depth direction.

4. The method as recited in claim 3 , wherein a diameter of each of the plurality of contact holes formed through the etch-stop layer is controlled by a thickness of the third polymer formed on sides of the second mask layer, and wherein the second diblock copolymer layers comprise poly(styrene-b-polymethyl methacrylate) (PS-b-PMMA).

5. The method as recited in claim 4 , wherein the first polymer is PDMS, wherein the third polymer is PS, wherein the matrix layer has a thickness in a range from about 35 nm to about 65 nm, and wherein the functionalization layer has a thickness in a range from about 1 nm to about 3 nm.

6. The method as recited in claim 2 , further comprising:

removing the pillars prior to creating the first mask layer;

annealing the first diblock copolymer layers prior to creating the first mask layer;

oxidizing a surface of the second polymer prior to creating the first mask layer; and

forming a plurality of perpendicular magnetic tunnel junction (pMTJ) stacks in the plurality of contact holes according to the third pattern.

7. The method as recited in claim 1 ,

wherein the substrate comprises Si,

wherein the etch-stop layer comprises a nitride material,

wherein the matrix layer comprises amorphous silicon (α-Si),

wherein the functionalization layer comprises hydroxyl-terminated polystyrene (PS),

wherein each of the set of pillars comprises hydrogen silsesquioxane (HSQ), and

wherein the first diblock copolymer layers comprise poly(styrene-b-dimethylsiloxane) (PS-b-PDMS).

8. The method as recited in claim 1 , wherein each pillar of the set of pillars has a diameter of about 21 nm and a height of about 33 nm, and wherein the predefined spacing of the set of pillars comprises a first spacing in the element depth direction of about 36 nm and a second spacing in the element width direction of about 100 nm or about 300 nm.

9. The method as recited in claim 1 , wherein forming each of the pMTJs comprises:

forming a seed layer above a corresponding electrode in the film thickness direction;

forming an underlayer above the seed layer in the film thickness direction;

forming a synthetic antiferromagnetic (SAF) seed layer above the underlayer in the film thickness direction;

forming a first SAF layer above the SAF seed layer in the film thickness direction;

forming a spacer layer above the first SAF layer in the film thickness direction;

forming an antiferromagnetic (AFM) coupling layer above the spacer layer in the film thickness direction;

forming a second SAF layer above the AFM coupling layer in the film thickness direction;

forming a ferromagnetic (FM) coupling layer above the second SAF layer in the film thickness direction;

forming a reference layer above the FM coupling layer in the film thickness direction;

forming a barrier layer above the reference layer in the film thickness direction;

forming a free layer above the barrier layer in the film thickness direction; and

forming at least one cap layer above the free layer in the film thickness direction.

10. A method, comprising:

forming an etch-stop layer above a substrate in a film thickness direction;

forming a matrix layer above the etch-stop layer in the film thickness direction;

forming a set of pillars above the matrix layer in the film thickness direction, the set of pillars having a predefined spacing therebetween along a plane in an element width direction and an element depth direction, the plane being normal to the film thickness direction;

forming a functionalization layer above the pillars, along sides of the pillars, and above the matrix layer in the film thickness direction;

forming first diblock copolymer layers above the functionalization layer in the film thickness direction, the first diblock copolymer layers self-segregating into a first polymer and a second polymer in a first pattern;

annealing the first diblock copolymer layers;

removing the first polymer from the first diblock copolymer layers to create a first mask layer;

removing the pillars;

removing portions of the matrix layer that are not covered by the first mask layer in the film thickness direction to expose portions of the etch-stop layer positioned therebelow and create a second pattern in the matrix layer that forms a second mask layer;

forming second diblock copolymer layers on sides of the second mask layer and above the second mask layer in the film thickness direction, the second diblock copolymer layers self-segregating into a third polymer that is formed on the sides of the second mask layer and above the second mask layer and a fourth polymer that is formed in holes of the second mask layer above the etch-stop layer; and

removing the fourth polymer and portions of the etch-stop layer positioned therebelow in the film thickness direction that are not covered by the second mask layer and a portion of the third polymer that is formed on the sides of the second mask layer to form a plurality of contact holes through the etch-stop layer in a third pattern.

11. The method as recited in claim 10 , wherein each of the contact holes have a substantially cylindrical shape with a circular cross-section along the plane in the element width direction and the element depth direction.

12. The method as recited in claim 11 , wherein a diameter of each of the plurality of contact holes formed through the etch-stop layer is controlled by a thickness of the third polymer formed on sides of the second mask layer.

13. The method as recited in claim 10 , further comprising:

oxidizing a surface of the second polymer prior to creating the first mask layer; and

forming a plurality of perpendicular magnetic tunnel junction (pMTJ) stacks in the plurality of contact holes.

14. The method as recited in claim 10 ,

wherein the substrate comprises Si,

wherein the etch-stop layer comprises a nitride material,

wherein the matrix layer comprises amorphous silicon (α-Si),

wherein the functionalization layer comprises hydroxyl-terminated polystyrene (PS),

wherein each of the set of pillars comprises hydrogen silsesquioxane (HSQ),

wherein the first diblock copolymer layers comprise poly(styrene-b-dimethylsiloxane) (PS-b-PDMS), and

wherein the second diblock copolymer layers comprise poly(styrene-b-polymethyl methacrylate) (PS-b-PMMA).

15. The method as recited in claim 14 , wherein the first polymer is PDMS, wherein the third polymer is PS, wherein the matrix layer has a thickness in a range from about 35 nm to about 65 nm, and wherein the functionalization layer has a thickness in a range from about 1 nm to about 3 nm.

16. The method as recited in claim 10 , wherein each pillar of the set of pillars has a diameter of about 21 nm and a height of about 33 nm, and wherein the predefined spacing of the set of pillars comprises a first spacing in the element depth direction of about 36 nm and a second spacing in the element width direction of about 100 nm or about 300 nm.

17. A method, comprising:

forming an etch-stop layer above a substrate in a film thickness direction;

forming a matrix layer above the etch-stop layer in the film thickness direction;

forming a set of pillars above the matrix layer in the film thickness direction, the set of pillars having a predefined spacing therebetween along a plane in an element width direction and an element depth direction, the plane being normal to the film thickness direction;

forming a functionalization layer above the pillars, along sides of the pillars, and above the matrix layer in the film thickness direction;

forming first diblock copolymer layers above the functionalization layer in the film thickness direction, the first diblock copolymer layers self-segregating into a first polymer and a second polymer in a first pattern, wherein the first diblock copolymer layers comprise poly(styrene-b-dimethylsiloxane) (PS-b-PDMS), the first polymer being PDMS;

removing the first polymer from the first diblock copolymer layers to create a first mask layer;

removing portions of the matrix layer that are not covered by the first mask layer in the film thickness direction to expose portions of the etch-stop layer positioned therebelow and create a second pattern in the matrix layer that forms a second mask layer;

forming second diblock copolymer layers on sides of the second mask layer and above the second mask layer in the film thickness direction, the second diblock copolymer layers self-segregating into a third polymer that is formed on the sides of the second mask layer and above the second mask layer and a fourth polymer that is formed in holes of the second mask layer above the etch-stop layer, wherein the second diblock copolymer layers comprise poly(styrene-b-polymethyl methacrylate) (PS-b-PMMA), the third polymer being PS; and

removing the fourth polymer and portions of the etch-stop layer positioned therebelow in the film thickness direction that are not covered by the second mask layer and a portion of the third polymer that is formed on the sides of the second mask layer to form a plurality of contact holes through the etch-stop layer in a third pattern.

18. The method as recited in claim 17 , wherein each of the contact holes have a substantially cylindrical shape with a circular cross-section along the plane in the element width direction and the element depth direction, wherein a diameter of each of the plurality of contact holes formed through the etch-stop layer is controlled by a thickness of the third polymer formed on sides of the second mask layer, and wherein the matrix layer has a thickness in a range from about 35 nm to about 65 nm, and wherein the functionalization layer has a thickness in a range from about 1 nm to about 3 nm.

19. The method as recited in claim 17 , further comprising:

removing the pillars prior to creating the first mask layer;

annealing the first diblock copolymer layers prior to creating the first mask layer;

oxidizing a surface of the second polymer prior to creating the first mask layer; and

forming a plurality of perpendicular magnetic tunnel junction (pMTJ) stacks in the plurality of contact holes according to the third pattern.

20. The method as recited in claim 17 ,

wherein the substrate comprises Si,

wherein the etch-stop layer comprises a nitride material,

wherein the matrix layer comprises amorphous silicon (α-Si),

wherein the functionalization layer comprises hydroxyl-terminated polystyrene (PS),

wherein each of the set of pillars comprises hydrogen silsesquioxane (HSQ), and

wherein each pillar of the set of pillars has a diameter of about 21 nm and a height of about 33 nm, and

wherein the predefined spacing of the set of pillars comprises a first spacing in the element depth direction of about 36 nm and a second spacing in the element width direction of about 100 nm or about 300 nm.