TREA

Process for the fabrication of multilayer thin film magnetoresistive sensors

Follow

Information

  • Patent Application
  • 20070266549
  • Publication Number
    20070266549
  • Date Filed
    May 16, 2006
    18 years ago
  • Date Published
    November 22, 2007
    16 years ago
Information
Abstract
An improved method for the manufacture of magnetoresistive multilayer sensors is disclosed. The method is particularly advantageous for the production of magnetic tunnel junction (MTJ) sensors, which can be damaged at the air bearing surface by conventional lapping and ion milling. The disclosed process protects the ABS of the magnetoresistive sensor by depositing a diamond like carbon layer which remains in place through ion milling. The DLC layer is removed by oxidation subsequent to the formation of the ABS.
Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:



FIG. 1 (Prior Art) is a partial cross sectional view of a thin film read/write head combination;



FIG. 2 (Prior Art) is a schematic block diagram of a simplified process for making a MTJ sensor;



FIG. 3 is a partial cross sectional view of a sensor structure subsequent to the blanket deposition of the film stack layers in a magnetoresistive (MR) sensor in accordance with an embodiment of the present invention;



FIG. 4 is a partial cross sectional view of a sensor structure subsequent to the defining of the magnetoresistive (MR) sensor in accordance with an embodiment of the present invention;



FIG. 5 is a partial cross sectional view of a sensor structure subsequent to the deposition of the DLC layer in accordance with an embodiment of the present invention;



FIG. 6 is a partial cross sectional view of a sensor structure subsequent to the deposition of a filler oxide layer and planarization in accordance with an embodiment of the present invention;



FIG. 7 is a partial cross sectional view of a sensor structure subsequent to the deposition of the second shield layer 110 in accordance with an embodiment of the present invention;



FIG. 8 is a partial cross sectional view of a sensor structure subsequent to the mechanical lapping step in accordance with an embodiment of the present invention;



FIG. 9 is a partial cross sectional view of a sensor structure subsequent to the ion milling step in accordance with an embodiment of the present invention;



FIG. 10 is a partial cross sectional view of a sensor structure subsequent to the oxidizing etch step in accordance with an embodiment of the present invention;



FIG. 11 is a partial cross sectional view of a combined read/write head structure prior to the mechanical lapping step in accordance with an embodiment of the present invention;



FIG. 12 is a partial cross sectional view of a combined read/write head structure subsequent to the mechanical lapping step in accordance with an embodiment of the present invention;



FIG. 13 is a partial cross sectional view of a combined read/write head structure subsequent to the ion milling step in accordance with an embodiment of the present invention;



FIG. 14 is a partial cross sectional view of a combined read/write head structure subsequent to the oxidizing etch step in accordance with an embodiment of the present invention; and,



FIG. 15 is a schematic block diagram of a simplified process for making a MTJ sensor in accordance with an embodiment of the present invention.





DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention discloses an improved method for making multilayer magnetoresistive (MR) sensors. The method eliminates damage caused during the formation of the air bearing surface by mechanical lapping and/or ion milling. The method is particularly suited for the production of magnetic tunnel junction (MTJ) sensors or tunneling magnetoresistive (TMR) sensors, since damage to the barrier oxide layer is to be avoided in these sensors. However, the methods of the present invention are suitable for the production of other types of MR sensors as well.



FIGS. 1 and 2 (Prior Art) have been discussed above in the Background section.



FIGS. 3-10 illustrate the embodiments of the present invention as applied to the MR sensor solely. FIGS. 11-14 illustrate the embodiments of the present invention as applied to a combined read/write head structure.



FIG. 3 is a partial cross sectional view of a sensor structure 300 subsequent to the blanket deposition of the film stack layers 302 in a magnetoresistive (MR) sensor in accordance with an embodiment of the present invention. Layers 302 comprise the complete stack of materials in a typical MR sensor, preferably a MTJ or TMR sensor. The composition, thickness, number of layers, etc., are well known to those skilled in the art. The layers 302 are deposited on the first shield layer 108, which may or may not be deposited on another substrate.



FIG. 4 is a partial cross sectional view of a sensor structure 400 subsequent to the defining of the magnetoresistive (MR) sensor stack 160 in accordance with an embodiment of the present invention. The lateral dimensions of sensor 160 is defined by lithographic and etching processes well known in the art, as is the projected position of the air bearing surface (ABS) ref 402.



FIG. 5 is a partial cross sectional view of a sensor structure 500 subsequent to the deposition of the DLC layer 502 in accordance with an embodiment of the present invention. Following the defining of MR sensor stack 160 as shown in FIG. 4, a diamond like carbon layer (DLC) is deposited conformally over all exposed surfaces, particularly the vertical surfaces of sensor 160 that define the ABS. The DLC film is deposited to a thickness between 2 and 10 nm.



FIG. 6 is a partial cross sectional view of a sensor structure 600 subsequent to the deposition of a filler oxide layer 602 and planarization in accordance with an embodiment of the present invention. Following the deposition of the DLC layer as shown in FIG. 5, an oxide layer 602 is deposited over the DLC layer. Typically, the oxide layer 109 between the first 108 and second 110 shield layers is alumina (Al2O3). In the present invention, alumina is replaced with oxides of tantalum, preferably Ta2O5. The purpose is to provide more uniform etching during a subsequent ion milling step and will be discussed in further detail below. Following the oxide deposition, the structure is planarized to expose the top layer of MR sensor 106, by methods well known in the art.



FIG. 7 is a partial cross sectional view of a sensor structure subsequent to the deposition of the second shield layer 110 in accordance with an embodiment of the present invention. At this point, the process for forming the air bearing surface (ABS) will be described. For more detail on forming the ABS in a combined read/write head structure, please see FIGS. 11-14. To form the ABS, all material to the right of the plane indicated by the dashed line in FIG. 7 must be removed. As previously discussed in the Background section, this is typically done in the prior art by mechanical lapping followed by ion milling. The combination of these two processes produces damage to the MR sensor stack 160. In the present invention, DLC layer 502 effectively protects sensor stack 160 and allows formation of the ABS without damage to the sensor layers.



FIG. 8 is a partial cross sectional view of a sensor structure 800 subsequent to the mechanical lapping step in accordance with an embodiment of the present invention. Mechanical lapping is used to remove the bulk of material to the right of the ABS in FIG. 7, because it is the fastest and most efficient method to remove large amounts of material. The process is stopped short of the anticipated ABS position, by a distance 802, to prevent any smearing or mechanical damage from affecting layers at the ABS. In the present invention, it is also desirable to avoid mechanical lapping of the DLC layer 502 due to the mechanical hardness of this layer. Distance 802 is not critical, and should be between zero and about 10 nm. Subsequent to the mechanical lapping process, ion milling will be carried out to remove additional material. Conditions of the ion milling process are well known to those skilled in the art.



FIG. 9 is a partial cross sectional view of a sensor structure 900 subsequent to the ion milling step in accordance with an embodiment of the present invention. In accordance with the present invention, tantalum oxide was chosen to provide a faster etch rate than alumina during the ion milling process, to ensure that the outer surfaces of the protective DLC component 902 would be cleared of all oxide material while simultaneously defining the ABS in the layers above and below the MR sensor stack 160. This requires balancing the etch rate of the oxide 602 with that of shield layers 108 and 110. It is imperative that the protective DLC artifact 902 be devoid of oxides covering its surface so that it can easily be removed in a oxidation step. However, once exposed, the surfaces of DLC have a much lower etch rate in the ion milling process, protecting the MR sensor stack 160 from the ion milling damage.



FIG. 10 is a partial cross sectional view of a sensor structure 1000 subsequent to the oxidizing etch step in accordance with an embodiment of the present invention. The final step in forming the ABS is the removal of the protective DLC artifact 902. This is accomplished in a oxidizing etch step following the ion milling. The oxidation step has little or no impact on the materials comprising the MR sensor stack or the shield layers 108 and 110. DLC layers are easily removed by such an oxidation step due to their carbon content, as is well known to those skilled in the art. In accordance with the present invention, the forgoing processes result in a damage free MR sensor stack at the ABS.



FIGS. 11-14 illustrate the forgoing process steps in the manufacture of a combined read/write head structure. Write coil and backgap details are omitted for clarity. FIG. 11 is a partial cross sectional view of a combined read/write head structure 1100 prior to the mechanical lapping step in accordance with an embodiment of the present invention. FIG. 12 is a partial cross sectional view of a combined read/write head structure 1200 subsequent to the mechanical lapping step in accordance with an embodiment of the present invention. FIG. 13 is a partial cross sectional view of a combined read/write head structure 1300 subsequent to the ion milling step in accordance with an embodiment of the present invention. FIG. 14 is a partial cross sectional view of a combined read/write head structure 1400 subsequent to the oxidizing etch step in accordance with an embodiment of the present invention.



FIG. 15 is a schematic block diagram 1500 of a simplified process for making a MTJ sensor in accordance with an embodiment of the present invention. In step 1502, the MTJ sensor stack is formed. This step includes the deposition of the stack layers and the subsequent defining of the sensor stack, corresponding to the steps illustrated in FIGS. 3 and 4. In step 1504, the DLC layer is deposited on the MTJ sensor stack surfaces, corresponding to FIG. 5 above. In step 1506, the oxide filler layer is deposited, corresponding to FIG. 6. In step 1508, the sensor structure is mechanically lapped, corresponding to FIGS. 8 and 12. In step 1510, the structure is ion milled, corresponding to FIGS. 9 and 13. In step 1512, the DLC protective artifact is removed from the ABS of the MTJ sensor, corresponding to FIGS. 10 and 14.


The present invention is not limited by the previous embodiments heretofore described. Rather, the scope of the present invention is to be defined by these descriptions taken together with the attached claims and their equivalents.

Claims
  • 1. A method for forming a magnetoresistive sensor comprising: forming a magnetoresistive sensor stack, comprising a plurality of sequentially deposited, parallel layers;forming a surface on said magnetoresistive sensor stack, said surface oriented approximately perpendicular to said plurality of sequentially deposited parallel layers;depositing a diamond like carbon layer on said surface on said magnetoresistive sensor stack, said diamond like carbon layer having an exposed surface subsequent to deposition of said diamond like carbon layer; and,removing said diamond like carbon layer from said surface of said magnetoresistive sensor stack to form an air bearing surface, said air bearing surface being approximately co-planar with said surface of said magnetoresistive sensor stack.
  • 2. The method as recited in claim 1, further comprising: depositing an oxide layer on said exposed surface of said diamond like carbon layer; and,removing a first portion of said oxide layer from at least a portion of said exposed surface of said diamond like carbon layer prior to removing said diamond like carbon layer.
  • 3. The method as recited in claim 2, wherein said oxide layer comprises tantalum oxide.
  • 4. The method as recited in claim 2, further comprising removing a second portion of said oxide layer by mechanical lapping prior to removing said first portion of said oxide layer.
  • 5. The method as recited in claim 2, wherein said first portion of said oxide layer is removed by ion milling.
  • 6. The method as recited in claim 1 wherein said diamond like carbon film is removed by oxidation.
  • 7. The method as recited in claim 1, wherein said magnetoresistive sensor is a magnetic tunnel junction (MTJ) sensor.
  • 8. The method as recited in claim 1, wherein said diamond like carbon layer is greater than or equal to 2 nm thick, and less than or equal to 10 nm thick.
  • 9. A method for forming a magnetoresistive sensor comprising: forming a magnetoresistive sensor stack, comprising a plurality of sequentially deposited, parallel layers;forming a surface on said magnetoresistive sensor stack, said surface oriented approximately perpendicular to said plurality of sequentially deposited parallel layers;depositing a diamond like carbon layer on said surface of said magnetoresistive sensor stack, said diamond like carbon layer having an exposed surface subsequent to deposition of said diamond like carbon layer;depositing an oxide layer on said exposed surface of said diamond like carbon layer;removing a first portion of said oxide layer by mechanical lapping;removing a second portion of said oxide layer by ion milling subsequent to removing said first portion, said second portion of said oxide layer being removed from at least a portion of said exposed surface of said diamond like carbon layer; and,removing said diamond like carbon layer from said surface of said magnetoresistive sensor stack to form an air bearing surface, said air bearing surface being approximately co-planar with said surface of said magnetoresistive sensor stack.
  • 10. The method as recited in claim 9, wherein said oxide layer comprises tantalum oxide.
  • 11. The method as recited in claim 9, wherein said magnetoresistive sensor is a magnetic tunnel junction (MTJ) sensor.
  • 12. The method as recited in claim 9 wherein said diamond like carbon film is removed by oxidation.
  • 13. The method as recited in claim 9, wherein said magnetoresistive sensor is a giant magnetoresistive (GMR) sensor.
  • 14. The method as recited in claim 9, wherein said diamond like carbon layer is greater than or equal to 2 nm thick, and less than or equal to 10 nm thick.
  • 15. The method as recited in claim 9, wherein removing said first portion of said oxide layer by mechanical lapping further comprises lapping to within a distance of said surface of said magnetoresistive sensor stack, said distance being greater than 10 nm.
  • 16. The method as recited in claim 15, wherein said distance is less than or equal to 20 nm.
  • 17. A method for forming a magnetoresistive sensor comprising: forming a magnetoresistive sensor stack, comprising a plurality of parallel layers deposited on a first shield layer;forming a surface on said magnetoresistive sensor stack, said surface oriented approximately perpendicular to said plurality of parallel layers;depositing a diamond like carbon layer on said surface of said magnetoresistive sensor stack, said diamond like carbon layer having an exposed surface subsequent to deposition of said diamond like carbon film;depositing a second shield layer subsequent to depositing said diamond like carbon layer, such that said magnetorestrictive sensor stack is disposed between said first and second shield layers; and,removing said diamond like carbon layer from said surface of said magnetoresistive sensor stack to form an air bearing surface, said air bearing surface being approximately co-planar with said surface of said magnetoresistive sensor stack.
  • 18. The method as recited in claim 17, further comprising: depositing an oxide layer on said exposed surface of said diamond like carbon layer prior to depositing said second shield layer; and,removing a first portion of said oxide layer from at least a portion of said exposed surface of said diamond like carbon layer prior to removing said diamond like carbon layer.
  • 19. The method as recited in claim 18, wherein said oxide layer comprises tantalum oxide.
  • 20. The method as recited in claim 18, further comprising simultaneously removing by mechanical lapping a second portion of said oxide layer, a portion of said first shield layer, and a portion of said second shield layer, prior to removing said first portion of said oxide layer.
  • 21. The method as recited in claim 18, wherein said first portion of said oxide layer is removed by ion milling.
  • 22. The method as recited in claim 17 wherein said diamond like carbon film is removed by oxidation.
  • 23. The method as recited in claim 17, wherein said magnetoresistive sensor is a magnetic tunnel junction (MTJ) sensor.
  • 24. The method as recited in claim 17, wherein said diamond like carbon layer is greater than or equal to 2 nm thick, and less than or equal to 10 nm thick.