Method for forming a hard bias structure in a magnetoresistive sensor

1. A method for forming a hard bias structure in a magnetoresistive sensor, comprising

providing a substrate comprising a gap layer having a top surface;

forming a magnetoresistive sensor structure over the substrate, the magnetoresistive sensor structure comprising at least a soft magnetic bias layer, a spacer layer over the soft magnetic bias layer, and a magnetoresistive layer over the spacer layer;

forming a mask over a portion of the magnetoresistive sensor structure to define a central region of the magnetoresistive sensor;

ion milling the masked magnetoresistive structure to remove portions of the magnetoresistive sensor structure not shielded by the mask, to form a central region of the magnetoresistive sensor having sloped sides, and to expose a region of the gap layer laterally adjacent the sloped sides of the central region;

forming a first underlayer onto at least the sloped sides of the central region by depositing a first underlayer material at a high deposition angle;

forming a second underlayer at least partially overlapping the first underlayer by depositing a second underlayer material at a first lower deposition angle;

and forming a hard bias layer over at least a portion of the second underlayer by depositing a hard bias material at a second lower deposition angle, wherein the first lower deposition angle is approximately equal to the second lower deposition angle.

2. The method of claim 1 wherein forming the first underlayer comprises depositing Cr.

3. The method of claim 1 wherein forming the first underlayer comprises depositing CrY, wherein Y is selected from the group consisting of V, Ti, Mo and W.

4. The method of claim 1 wherein forming the first underlayer comprises depositing CrW.

5. The method of claim 1 wherein forming the second underlayer comprises depositing Cr.

6. The method of claim 1 wherein forming the second underlayer comprises depositing CrY, wherein Y is selected from the group consisting of V, Ti, Mo, and W.

7. The method of claim 1 wherein forming the hard bias layer comprises depositing CoPt.

8. The method of claim 1 wherein forming the hard bias layer comprises depositing CoCrPt.

9. The method of claim 1 wherein forming the hard bias layer comprises depositing CoCrTa.

10. The method of claim 1 wherein forming the hard bias layer comprises depositing CoCrPtTa.

11. The method of claim 1 wherein depositing the first underlayer comprises depositing the underlayer material to a thickness at least about 20 Å at the sloped sides of the central region.

12. The method of claim 11 wherein depositing the first underlayer comprises depositing the underlayer material to a thickness at least about 30 Å at the sloped sides of the central region.

13. The method of claim 1 wherein depositing the first underlayer comprises depositing the underlayer material to a thickness in a range from about 20 Å to about 80 Å at the sloped sides of the central region.

14. The method of claim 1 wherein depositing the first underlayer comprises depositing the underlayer material to a thickness at least about 20 Å at the exposed region of the gap layer.

15. The method of claim 14 wherein depositing the first underlayer comprises depositing the underlayer material to a thickness at least about 50 Å at the exposed region of the gap layer.

16. The method of claim 1 wherein depositing the first underlayer comprises depositing the underlayer material to a thickness in a range from about 20 Å to about 80 Å at the exposed region of the gap layer.

17. The method of claim 1 wherein depositing the first underlayer comprises depositing the underlayer material to a thickness in a range from about 50 Å to about 70 Å at the exposed region of the gap layer.

18. The method of claim 1 wherein forming a first underlayer onto the sloped sides of the central region and onto the exposed substrate comprises depositing the underlayer material at a deposition angle in a range from about 20° to about 60° from perpendicular to an upper surface of the substrate.

19. The method of claim 1 wherein forming a second underlayer on a portion of the first underlayer comprises depositing the underlayer material to a thickness sufficient to make the first and second underlayers have a combined thickness over the region of the gap layer laterally adjacent the central region at least about 60 Å.

20. The method of claim 19 wherein forming a second underlayer on a portion of the first underlayer comprises depositing the underlayer material to a thickness sufficient to make the first and second underlayers have a combined thickness over the region of the gap layer laterally adjacent the central region in a range from about 60 Å to about 250 Å.

21. The method of claim 1 wherein forming a second underlayer on a portion of the first underlayer comprises depositing underlayer material to a thickness great enough so that a midplane of the hard bias layer passes through the free layer.

22. A method for forming a hard bias structure in a magnetoresistive sensor, comprising

providing a substrate comprising a clap layer having a top surface;

forming a magnetoresistive sensor structure over the substrate, the magnetoresistive sensor structure comprising at least a soft magnetic bias layer, a spacer layer over the soft magnetic bias layer, and a magnetoresistive layer over the spacer layer;

forming a mask over a portion of the magnetoresistive sensor structure to define a central region of the magnetoresistive sensor;

ion milling the masked magnetoresistive structure to remove portions of the magnetoresistive sensor structure not shielded by the mask, to form a central region of the magnetoresistive sensor having sloped sides, and to expose a region of the clap layer laterally adjacent the sloped sides of the central region;

forming a first underlayer onto at least the sloped sides of the central region by depositing a first underlayer material at a high deposition angle;

forming a second underlayer at least partially overlapping the first underlayer by depositing a second underlayer material at a first lower deposition angle;

and forming a hard bias layer over at least a portion of the second underlayer by depositing a hard bias material at a second lower deposition angle, wherein forming the first underlayer onto the sloped sides of the central region and onto the exposed substrate comprises depositing the underlayer material at a deposition angle at least about 20° from perpendicular to an upper surface of the substrate.

23. The method of claim 22 wherein forming the first underlayer onto the sloped sides of the central region and onto the exposed substrate comprises depositing the underlayer material at a deposition angle at least about 23° from perpendicular to an upper surface of the substrate.

24. A method for forming a hard bias structure in a magnetoresistive sensor, comprising

providing a substrate comprising a clap layer having a top surface;

forming a magnetoresistive sensor structure over the substrate, the magnetoresistive sensor structure comprising at least a soft magnetic bias layer, a spacer layer over the soft magnetic bias layer, and a magnetoresistive layer over the spacer layer;

forming a mask over a portion of the magnetoresistive sensor structure to define a central region of the magnetoresistive sensor;

ion milling the masked magnetoresistive structure to remove portions of the magnetoresistive sensor structure not shielded by the mask, to form a central region of the magnetoresistive sensor having sloped sides, and to expose a region of the clap layer laterally adjacent the sloped sides of the central region;

forming a first underlayer onto at least the sloped sides of the central region by depositing a first underlayer material at a high deposition angle;

forming a second underlayer at least partially overlapping the first underlayer by depositing a second underlayer material at a first lower deposition angle;

and forming a hard bias layer over at least a portion of the second underlayer by depositing a hard bias material at a second lower deposition angle, wherein forming the first underlayer onto the sloped sides of the central region and onto the exposed substrate comprises depositing the underlayer material at a deposition angle generally normal to the slope of the sides of the central region at the junction.

25. The method of claim 24 wherein forming the first underlayer onto the sloped sides of the central region and onto the exposed substrate comprises depositing the underlayer material at a deposition angle in a range about 85° to about 95° with respect to the slope of the sides of the central region at the junction.

26. The method of claim 24 wherein forming the first underlayer onto the sloped sides of the central region and onto the exposed substrate comprises depositing the underlayer material at a deposition angle about 90° with respect to the slope of the sides of the central region at the junction.

27. A method for forming a hard bias structure in a magnetoresistive sensor, comprising

providing a substrate comprising a clap layer having a top surface;

forming a magnetoresistive sensor structure over the substrate, the magnetoresistive sensor structure comprising at least a soft magnetic bias layer, a spacer layer over the soft magnetic bias layer, and a magnetoresistive layer over the spacer layer;

forming a mask over a portion of the magnetoresistive sensor structure to define a central region of the magnetoresistive sensor;

ion milling the masked magnetoresistive structure to remove portions of the magnetoresistive sensor structure not shielded by the mask, to form a central region of the magnetoresistive sensor having sloped sides and to expose a region of the clap layer laterally adjacent the sloped sides of the central region;

forming a first underlayer onto at least the sloped sides of the central region by depositing a first underlayer material at a high deposition angle;

forming a second underlayer at least partially overlapping the first underlayer by depositing a second underlayer material at a first lower deposition angle;

and forming a hard bias layer over at least a portion of the second underlayer by depositing a hard bias material at a second lower deposition angle, wherein forming a second underlayer on a portion of the first underlayer comprises depositing the underlayer material at a deposition angle generally normal to an upper surface of the substrate.

28. The method of claim 27 wherein forming a second underlayer on a portion of the first underlayer comprises depositing the underlayer material at a deposition angle in a range about 0° to about 5° from perpendicular to an upper surface of the substrate.

29. The method of claim 27 wherein forming a second underlayer on a portion of the first underlayer comprises depositing the underlayer material at a deposition angle less than about 5° from perpendicular to an upper surface of the substrate.

30. A method for forming a hard bias structure in a magnetoresistive sensor, comprising

providing a substrate comprising a clap layer having a top surface;

forming a magnetoresistive sensor structure over the substrate, the magnetoresistive sensor structure comprising at least a soft magnetic bias layer, a spacer layer over the soft magnetic bias layer, and a magnetoresistive layer over the spacer layer;

forming a mask over a portion of the magnetoresistive sensor structure to define a central region of the magnetoresistive sensor;

ion milling the masked magnetoresistive structure to remove portions of the magnetoresistive sensor structure not shielded by the mask, to form a central region of the magnetoresistive sensor having sloped sides and to expose a region of the clap layer laterally adjacent the sloped sides of the central region;

forming a first underlayer onto at least the sloped sides of the central region by depositing a first underlayer material at a high deposition angle;

forming a second underlayer at least partially overlapping the first underlayer by depositing a second underlayer material at a first lower deposition angle;

and forming a hard bias layer over at least a portion of the second underlayer by depositing a hard bias material at a second lower deposition angle, wherein ion milling to remove portions of the magnetoresistive sensor structure not shielded by the mask further comprises overmilling, to remove a portion of the gap layer.

31. The method of claim 30 wherein the overmilling comprises removing a portion of the gap layer to a depth in the gap layer in a range up to about 30 Å.

32. The method of claim 30 wherein the overmilling comprises removing a portion of the gap layer to a depth in the gap layer in a range up to about 20 Å.

33. The method of claim 32 wherein the overmilling comprises removing a portion of the gap layer to a depth in the gap layer in a range up to about 10 Å.

34. The method of claim 30 wherein forming the first underlayer comprises depositing the first underlayer material to a first thickness and forming the second underlayer comprises depositing the second underlayer material to a second thickness, and the sum of the first thickness and the second thickness is at least equal to the quantity FL+T−HS/2−FT,

and is at most equal to the quantity

FL+T−HS/2+FT,

where FL is an elevation of a midplane of the free layer above the top surface of the gap layer, T is the overmill depth, HS is the thickness of the hard bias layer, and FT is the thickness of the free layer.

35. The method of claim 30 wherein forming the first underlayer comprises depositing the first underlayer material to a first thickness and forming the second underlayer comprises depositing the second underlayer material to a second thickness, and the sum of the first thickness and the second thickness is at least equal to the quantity

FL+T−HS/2−FT/2,

and is at most equal to the quantity

FL+T−HS/2+FT/2,

where FL is an elevation of a midplane of the free layer above the top surface of the gap layer, T is the overmill depth, HS is the thickness of the hard bias layer, and FT is the thickness of the free layer.

36. The method of claim 30 wherein forming the first underlayer comprises depositing the first underlayer material to a first thickness and forming the second underlayer comprises depositing the second underlayer material to a second thickness, and the sum of the first thickness and the second thickness is approximately equal to the quantity

FL+T−HS/2,

where FL is an elevation of a midplane of the free layer above the top surface of the gap layer, T is the overmill depth, and HS is the thickness of the hard bias layer.