# Patent

## Title
Method for making ultra-narrow read sensor and read transducer device resulting therefrom

## Abstract

Disclosed are methods for making ultra-narrow track width (TW) read sensors, and read transducers incorporating such sensors. The methods utilize side-wall line patterning techniques to prepare ultra-narrow mill masks that can be used to prepare the ultra-narrow read sensors.

## Background
RELATED CASES
This application claims the benefit of U.S. Provisional Application Ser. No. 61/835,913 filed Jun. 17, 2013, which is hereby incorporated herein by reference in the entirety.


TECHNICAL FIELD
This disclosure relates to the field of read sensors, and their methods of manufacture.
BACKGROUND
Computer hard drives store data by affecting the magnetic field of memory cells on a hard drive disk. The stored data is read by passing a read head sensor above a memory cell to respond to, and thus detect, the orientation of the magnetic field in the memory cell. The smaller the memory cells on the hard drive disk, the more densely they can be packed, increasing the density of data storage possible on a hard drive disk.
However, making smaller memory cells is not all that is required to increase data density storage capacity. Increasingly smaller memory cells require increasingly smaller read sensors, particularly read sensors with a narrow track width, in order to be responsive to the magnetic field of a single memory cell.
Currently there is no commercial lithography tool than can provide read sensors with line widths less than about 30 nm.



BRIEF DESCRIPTION OF THE DRAWINGS
The present application is illustrated by way of example, and not limitation, in the figures of the accompanying drawings in which:
FIG. 1 illustrates steps in an exemplary method for preparing an ultra-narrow mill mask using a side-wall line deposition technique.
FIG. 2 is a SEM image of a side-wall structure formed as a intermediate structure during the exemplary method shown in FIG. 1.
FIG. 3 is a SEM image of a side-wall line structure formed as a intermediate structure during the exemplary method shown in FIG. 1.
FIG. 4 is a SEM image of an ultra-narrow mill mask formed from the exemplary method shown in FIG. 1.
FIGS. 5A and 5B are SEM images of two alumina mill masks (at about 10 nm and 18 nm thick, respectively) prepared according to one exemplary method.
FIG. 6 is a contour plot showing critical dimension uniformity of line structures prepared according to an exemplary method.
FIG. 7 illustrates steps for preparing an ultra-narrow read sensor using an ultra-narrow mill mask according to one exemplary method.
FIG. 8 is a SEM image of an alumina mill mask remaining above a SiC ultra-narrow line structure prepared as an intermediate step in the exemplary method seen in FIG. 7.
FIGS. 9A and 9B are SEM images of two SiC ultra-narrow line structures (at about 10 nm and 18 nm thick, respectively) prepared as an intermediate step in the exemplary method seen in FIG. 7.
FIG. 10 is a SEM image of a ultra-narrow reader junction prepared according to the exemplary method seen in FIG. 7.
FIG. 11 illustrates steps for preparing an ultra-narrow read sensor using an ultra-narrow mill mask according to another exemplary method.
FIG. 12 is a SEM image of a ultra-narrow reader junction prepared according to the exemplary method seen in FIG. 11.



DETAILED DESCRIPTION
Disclosed are methods for making ultra-narrow track width (TW) read sensors and read transducers incorporating such sensors. The methods utilize side-wall line patterning techniques to prepare ultra-narrow mill masks that can be used to prepare the read sensors.
In the following description, numerous specific details are set forth to provide a thorough understanding of various embodiment of the present invention. It will be apparent however, to one skilled in the art that these specific details need not be employed to practice various embodiments of the present invention. In other instances, well known components or methods have not been described in detail to avoid unnecessarily obscuring various embodiments of the present invention.
As used herein, the phrase “ultra-narrow” refers to a dimension on the order of less than about 35 nm; such as between about 3 and 35 nm; such as between about 5 and 30 nm; such as between about 5 and 25 nm; such as between about 5 and 20 nm; such as between about 7 and 18 nm; or between about 5 and 10 nm; such as between about 5 and 7 nm; or between about 10 and 18 nm.
Currently there is no commercial lithography tool than can provide 10-20 nm linewidth structures. Described herein are side-wall line patterning techniques that are capable of delivering ultra-narrow linewidth structures. In particular, the side-wall line patterning techniques described herein are capable of delivering well defined linewidths controlled by thickness of a conformally deposited material. In particular, the conformally deposited material may be applied via an atomic layer deposition technique or the like, which allows for controlled deposition across a wide range of thicknesses as needed for desired reader design and fabrication requirements. Further, in some embodiments, the conformally deposited material is deposited under such conditions as to provide a high degree of CD uniformity. When deposited so as to provide a coating on a side-wall of a layered structure, the resulting coated structure can be further processed according to appropriate etching chemistries known in the art to provide an ultra-narrow mill mask on a substrate, which allows for further patterning so as to prepare an ultra-narrow reader junction for use in a read sensor.
An exemplary embodiment of a side-wall patterning technique usable to deliver linewidth structures is shown in FIG. 1. As seen in FIG. 1, the side-wall line patterning techniques may comprise deposition of one or more sacrificial layers above a substrate, where each sacrificial layer comprises a material that is susceptible to an etching chemistry, such as a reactive ion etching chemistry.
As will be understood by one of skill in the art, any suitable deposition technique, including vapor deposition, may be used depending on the desired composition of the one or more sacrificial layers. In some embodiments, the one or more sacrificial layers comprises a layer of amorphous carbon. In such embodiments, the amorphous carbon may be deposited by vapor deposition. Various thicknesses of the amorphous carbon layer may be used. In some embodiments, the thickness is less than or equal to about 100 nm thick. In addition, or in the alternative, the one or more sacrificial layers comprises a layer of tantalum. Like amorphous carbon, tantalum may also be deposited by vapor deposition. Again, various thicknesses may be used, such as less than or equal to about 40 nm. In some embodiments, the one or more sacrificial layers may comprise a plurality of sacrificial layers. In one particular exemplary embodiment, the one or more sacrificial layers comprise a tantalum layer on top of an amorphous carbon layer.
In some embodiments, a masking layer is applied to at least a portion of the uppermost sacrificial layer after the one or more sacrificial layers are in place. The masking layer may comprise a material that is not susceptible to the same reactive ion etching chemistry as the uppermost sacrificial layer. In some embodiments, the masking layer is applied as a photoresist pattern leaving at a portion of the uppermost sacrificial layer exposed. The masking layer may be applied such that an edge of the masking layer defines a straight line along an exposed portion of the uppermost sacrificial layer.
An intermediate structure prepared according to such a method is shown as the starting point of sequence in FIG. 1. The initial structure comprises a substrate 1, two sacrificial layers 2 and 3, and a masking layer 4.
Once the masking layer 4 is in place, the layered structure is subjected to reactive ion etching chemistries selected to etch the exposed portion of the sacrificial layers. The masking layer protects the covered portion of the sacrificial layers, thereby creating a vertical side-wall structure defined by the sacrificial layer materials. In the exemplary method shown in FIG. 1, the masking layer 4 is then removed, exposing a horizontal surface of the uppermost sacrificial layer, and leading to the layered structure seen between steps A and B. A SEM image of such an exemplary intermediate layered structure is also seen in FIG. 2.
A material capable of conformal deposition is then applied to layered structure, coating the horizontal and vertical surfaces. As used herein, a material capable of “conformal” deposition is a material that is deposited as a coating with substantially even thickness, regardless of the orientation of the surfaces it is being deposited on. In this regard, substantially even thickness means that the variation between surface thickness is less than or equal to about 10%, such as less than or equal to about 5%, such as less than or equal to about 2%, regardless of surface orientation. In some embodiments, this conformally deposited material is not susceptible to the same reactive ion etching chemistry as at least one of the sacrificial layers. In the exemplary method shown in FIG. 1, the conformally deposited layer 5 applied in step B.
In some embodiments, the conformally deposited material is applied via atomic layer deposition. In some embodiments, the conformally deposited material comprises alumina (i.e. aluminum oxide). However, it is not intended that the methods described herein are limited to any particular conformally deposited material being applied by any particular fashion. As described above, it is sufficient that the material is capable of being conformally deposited at a desired thickness, and that the material is not susceptible to the same reactive ion etching chemistry as at least one of the sacrificial layers.
Once the material has been conformally deposited, the deposited material covering a horizontal surface of the uppermost sacrificial layer is removed in a way that leaves at least a portion of the material covering a vertical surface intact. This removal may be accomplished by any method known in the art, including a reactive ion etching specifically targeted to the conformally deposited material. Removal of the conformally deposited material from a horizontal surface of the uppermost sacrificial layer, and subsequent removal of the uppermost sacrificial layer, is seen as step C in FIG. 1. A SEM image of such an exemplary intermediate structure with a side-wall coating is seen in FIG. 3.
What remains is at least one sacrificial layer defining a vertical side-wall that is coated with the conformally deposited material. As will be appreciated, the thickness of the side-wall coating is determined by the thickness of the initial conformal deposition. In this regard, atomic layer deposition is particularly useful, as the thickness of the deposited layer can by finely controlled, allowing for deposition of a layer of virtually any desired thickness, such as a thickness less than about 35 nm; such as between about 3 and 35 nm; such as between about 5 and 30 nm; such as between about 5 and 25 nm; such as between about 5 and 20 nm; such as between about 7 and 18 nm; or between about 5 and 10 nm; such as between about 5 and 7 nm; or between about 10 and 18 nm.
The remaining structure may then be subjected to reactive ion etching specifically directed to remove all remaining sacrificial layer material, leaving a ultra-narrow line structure that can be used to serve as a mill mask for further processing of the underlying substrate. This removal step is shown in FIG. 1 as step D, with the resulting ultra-narrow mill mask 6 atop substrate 1. A SEM image of such an exemplary ultra-narrow mill mask atop a substrate is seen in FIG. 4.
Given the fact that the thickness of the conformal coating ultimately determines the thickness of the mill mask, various embodiments of the methods described herein may be used to provide mill masks with ultra-narrow critical dimension. For instance, SEM images of two exemplary ultra-narrow mill masks produced by methods described herein are shown in FIG. 5. The thicknesses of the shown ultra-narrow mill masks were measured to be about 10 nm (FIG. 5A) and 18 nm (FIG. 5B), although thinner mill masks have been produced.
An additional feature of some of the ultra-narrow mill masks produced by some of the embodiments presented herein results from the consistent thickness that a conformal coating may be applied. That is, ultra-narrow mill masks produced by various embodiments of the methods described herein may exhibit high critical dimension uniformity. For instance, a side-wall patterned mill mask may have a critical dimension uniformity (expressed as within wafer variation) of less than about 1 nm; such as less than about 0.75 nm; such as less than about 0.6 nm. An contour plot demonstrating such critical dimension uniformity for a mill mask produced according to one embodiment is seen in FIG. 6. Observed within wafer variation (WIW sigma) for this example was about 0.58 nm.
Further, it is intended that a substrate may be any suitable material or structure. In particular, a substrate may be a read sensor stack comprising a plurality of layers. In such embodiments, a side-wall patterned mill mask may be used to further process the substrate to make a read sensor with an ultra-narrow track width.
In some embodiments, a substrate comprises an uppermost layer comprising a material that is susceptible to a reactive ion etching chemistry that is different from any of the one or more sacrificial layers. This uppermost layer may be of any suitable thickness, which may be selected based on the chemical identity of the uppermost substrate layer. In some embodiments, the uppermost substrate layer comprises silicon carbide (SiC). If present as the uppermost substrate layer, silicon carbide may be at any desired thickness, including a thickness of about 50 nm or less.
The substrate may further comprise an etch stop layer found directly beneath the uppermost substrate layer. In such embodiments, the etch stop layer comprises a material that is not susceptible to the same reactive ion etching chemistry as the uppermost substrate layer. Again, this uppermost layer may be of any suitable thickness, which may be selected based on the chemical identity of the etch stop layer. In some embodiments, the etch stop layer may comprise a chromium layer; such as a chromium layer that is about 25 Å thick.
One exemplary method of processing a multilayered substrate into a reader junction is seen in FIG. 7. The initial structure comprises a multi-layered substrate 1 comprising a base layer 7, an etch stop layer 8, and an uppermost substrate layer 9. In the method shown in FIG. 7, the uppermost substrate layer 9 is subjected to a reactive ion etch so as to remove portions of the substrate layer 9 not protected by the mill mask 6. The resulting line structure is a layered line structure comprising the original mill mask above the protected portion of the substrate layer 9 (shown in FIG. 7 as the structure following step A). A SEM image of an exemplary layered line structure prepared according to this method is shown in FIG. 8.
The original mill mask may then be removed, leaving a line structure 10 formed of the uppermost substrate material, and with about the same thickness of the original mill mask. SEM images of two exemplary line structures are seen in FIGS. 8A (about 10 nm thick) and 8B (about 18 nm thick). The remaining substrate and line structure may then be processed by techniques known in the art to form a reader junction with a track width equal to about the thickness of the line structure 10. A SEM image of an example of a reader junction prepared by this method is seen in FIG. 10.
Another exemplary method for further processing a reader stack substrate into a reader junction is seen in FIG. 11. This exemplary method is simpler than that seen in FIG. 7 in that the side-wall line patterned mill mask 6 is used directly to pattern a reader junction 11. In these embodiments, the substrate may comprise a tunneling magnetoresistive (TMR) surface. A SEM image of an example of a reader junction prepared by this method is seen in FIG. 12.
As such, methods described herein may be used to prepare read sensors comprising a read junction track width of less than about 35 nm; such as between about 3 and 35 nm; such as between about 5 and 30 nm; such as between about 5 and 25 nm; such as between about 5 and 20 nm; such as between about 7 and 18 nm; or between about 5 and 10 nm; such as between about 5 and 7 nm; or between about 10 and 18 nm. Similarly, these read sensors may be used to prepare transducers comprising read sensors with a read junction track width of less than about 35 nm; such as between about 3 and 35 nm; such as between about 5 and 30 nm; such as between about 5 and 25 nm; such as between about 5 and 20 nm; such as between about 7 and 18 nm; or between about 5 and 10 nm; such as between about 5 and 7 nm; or between about 10 and 18 nm.
In the foregoing specification, embodiments of the disclosure have been described with reference to specific exemplary features thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the disclosure. The specification and figures are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

## Claims

1. A method for making a read sensor, the method comprising:
depositing a read sensor stack on a substrate, wherein the read sensor stack comprises a plurality of layers;
providing a mill mask above the read sensor stack, wherein the mill mask is a line structure comprising alumina deposited via a side-wall line patterning technique, wherein the mill mask has critical dimension uniformity of less than about 1 nm; and
patterning the read sensor stack.

2. The method of claim 1, wherein the mill mask comprises a material forming a conformal deposition.

3. The method of claim 1, wherein the mill mask comprises a line structure with a thickness within the range of about 3 to 35 nm.

4. The method of claim 1, wherein the mill mask comprises a line structure with a thickness within the range of about 5 to 20 nm.

5. The method of claim 1, wherein prior to providing the mill mask above the read sensor stack, the method further comprises depositing above the read sensor stack a first layer susceptible to a first reactive ion etching chemistry.

6. The method of claim 5, wherein after the mill mask is provided but before patterning the read sensor stack, the method further comprises performing a first reactive ion etch to remove at least a portion of the first layer not covered by the mill mask; and removing the mill mask from the remaining first layer material.

7. The method of claim 5, further comprising depositing a second layer above the read sensor stack prior to depositing the first layer; wherein the second layer comprises a material not susceptible the first reactive ion etching chemistry.

8. The method of claim 5, wherein the second layer comprises a chromium (Cr) layer.

9. The method of claim 5, wherein the layer susceptible a first reactive ion etching chemistry is a silicon carbide (SiC) layer.

10. A method for making an side-wall patterned mill mask, the method comprising:
depositing one or more sacrificial layers above a substrate, wherein each of said one or more layers comprises a material susceptible to a reactive ion etching chemistry;
applying a masking layer to at least a portion of the uppermost sacrificial layer; wherein said masking layer comprises a material not susceptible to the same reactive ion etching chemistry as the uppermost sacrificial layer;
removing a portion of at least the uppermost sacrificial layer via reactive ion etching, thereby exposing a vertical surface of at least the uppermost sacrificial layer;
removing the masking layer, thereby exposing a horizontal surface of at least the uppermost sacrificial layer;
applying a coating of alumina forming a conformal deposition to said horizontal and vertical surfaces of the uppermost sacrificial layer, wherein said material is not susceptible to the same reactive ion etching chemistry as at least one of the sacrificial layers;
removing the deposited material from the horizontal surface of the uppermost sacrificial layer so as to leave at least a portion of the coating on the vertical layer intact;
removing the remaining one or more sacrificial layers via reactive ion etching, thereby leaving a side-wall patterned mill mask comprising the material forming a conformal deposition, wherein the mill mask has critical dimension uniformity of less than about 1 nm.

11. The method of claim 10, wherein the substrate comprises a read sensor stack comprising a plurality of layers.

12. The method of claim 10, wherein the coating of material forming a conformal deposition is applied via atomic layer deposition.

13. The method of claim 10, wherein the width of the side-wall patterned line structure is determined by the thickness of the coating of material forming a conformal deposition.

14. The method of claim 10, wherein the width of the side-wall patterned mill mask is within the range of 3 to 35 nm thick.

15. The method of claim 10, wherein the width of the side-wall patterned mill mask is within the range of 5 to 20 nm thick.

16. The method of claim 10, wherein the one or more sacrificial layers comprise a layer of amorphous carbon.

17. The method of claim 10, wherein the one or more sacrificial layers comprise a layer of tantalum.

18. The method of claim 10, wherein at least one of the one or more sacrificial layers is deposited via vapor deposition.

19. The method of claim 10, wherein the masking layer is applied as a photoresist pattern.

20. The method of claim 10, wherein the substrate comprises an uppermost layer comprising a material susceptible to a reactive ion etching chemistry different from any of the one or more sacrificial layers.

21. The method of claim 17, wherein the uppermost substrate layer comprises silicon carbide (SiC).

22. The method of claim 17, wherein the substrate further comprises an etch stop layer directly beneath the uppermost substrate layer, wherein the etch stop layer is not susceptible to the same reactive ion etching chemistry as the uppermost substrate layer.

23. The method of claim 19, wherein the etch stop layer comprises a chromium (Cr) layer.