# Patent

## Title
Systems and methods for using double mask techniques to achieve very small features

## Abstract

System and methods are provided for the manufacture of a magnetic write head including a pole and yoke region, and a nose shape transition region connecting the yoke to the pole having very small minimum radius of curvature, providing for a sharp transition. A double mask technique is used providing for the adjustment of an offset and illumination conditions between the first and second mask, which provides the capability of tuning the shape of the transition region, and achieving features that would otherwise not be achievable due to distortions caused by optical proximity effect.

## Background
CROSS-REFERENCE TO RELATED APPLICATION(S)
This application claims priority to provisional U.S. Patent Application Ser. No. 61/894,540 filed on Oct. 23, 2013 and entitled “SYSTEMS AND METHODS TO OPTIMIZE THE WRITER POLE NOSE SHAPE USING A DOUBLE MASK TECHNIQUE,” which is incorporated herein by reference.


BACKGROUND
The description that follows includes illustrative systems, methods, techniques, instruction sequences, and computing machine program products that embody the aspects of the present invention. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide an understanding of various embodiments of the inventive subject matter. It will be evident, however, to those skilled in the art that embodiments of the inventive subject matter may be practiced without these specific details. In general, well-known instruction instances, protocols, structures and techniques have not been shown in detail.
As used herein, the term “or” may be construed in either an inclusive or exclusive sense. Similarly, the term “exemplary” is construed merely to mean an example of something or an exemplar and not necessarily a preferred or ideal means of accomplishing a goal. Additionally, although various exemplary embodiments discussed below focus on quality control of professionals, the embodiments are given merely for clarity and disclosure. Alternative embodiments may employ other systems and methods and are considered as being within the scope of aspects of the present invention. Additionally, for simplicity, some steps may be omitted, interleaved, and/or combined. Also, for simplicity, only single components are shown. However, multiples of each component and/or their sub-components, might be used.



BRIEF DESCRIPTION OF THE DRAWINGS
Various ones of the appended drawings merely illustrate exemplary embodiments of the present invention and cannot be considered as limiting its scope.
FIG. 1 shows a current mask and simulated resist pattern.
FIG. 2 shows resist pattern and a transition curve from pole to yoke.
FIGS. 3A-3E show an exemplary two mask embodiments.
FIG. 4 shows the actual resist image using an embodiment of the double mask technique.
FIG. 5 illustrates experimental results achieved using an embodiment of the double mask technique.
FIG. 6 illustrates method of manufacturing a magnetic pole according to an exemplary embodiment.



DETAILED DESCRIPTION
Exemplary embodiments provide techniques to manufacture writer pole nose shape having very small minimum radius allowing for a much shaper transition from pole to yoke. The small radius writer pole nose shape and other similar small design features present significant and difficult challenges when using photolithography to pattern the desired shape. In the exemplary embodiment of patterning the main pole, optical proximity effect yields rounded nose shapes. Various exemplary embodiments use innovative double mask techniques that significantly reduce optical proximity effect and achieve a wide range of desired shapes. It further provides maximum design flexibility and tuning capability.
Hard Disk Drives (HDD) remain one of the most cost effective means for storage of electronic data. The demand for ever increasing storage capacity is forcing engineers to design and manufacture devices with more strict requirements.
In general, an HDD includes a media (magnetic disk) where magnetic bits on the media are used to store digital data, a magnetic writer writing data onto the media, and a read sensor reading data from the media. The shape and size of the writer pole defines how closely magnetic bits can be written on the media.
FIG. 1 shows a current mask and simulated resist pattern. An exemplary writer pole fabricated using a single mask technique is shown in FIGS. 1 and 2. This exemplary pole shape has been in production for several generations of perpendicular recording media (PMR) products. However, increasing recording density is forcing engineers to reduce the size of the magnetic writer element. In exemplary embodiments, a magnetic write head mask 100 includes a yoke region 102, a main pole region 104, and a transition region 106. The single mask 100 may further include one or more optical proximity effect correction features 108, developed to reduce the effect of optical diffraction and related process limitations that, in the case of the structure shown in FIG. 1 would result in a rounded and less sharply defined transition from the yoke region 102 to the pole region 104. Optical proximity correction (OPC) is a photolithography enhancement technique commonly used to compensate for image errors due to diffraction or process effects. OPC corrects some of the optical diffraction and certain process limitation errors by moving edges of features, or adding extra polygons to the patterns drawn on a photomask. However, OPC has drawbacks and limitations. These drawbacks include issues related to cost, as well as limitations of the corrective effects of OPC technique.
Optical proximity correction (OPC) features may be created using specially designed OPC software or tables. Although the use of OPC features reduce the undesirable effects caused by diffraction and process limitations, for each new shape design, a new mask must be created that includes new OPC features customized to the new structure design. Therefore the use of a single mask technique includes inherent limitations and drawbacks. As seen in the FIG. 1, the shape of the photoresist 110 covering the transition region 106 connecting the yoke region 102 to the main pole region 104 may not exactly match the shape of the mask, and during photo processing the resulting shape of the writer structure may deviate from the desired geometry. This deviation due to optical proximity effect may be more extreme for certain features such as the radius of curvature shown in FIG. 2.
FIG. 2 shows resist pattern and a transition curve from pole to yoke. As shown in FIG. 2, the minimum radius (min Rc) at the nose corner of the yoke is used to characterize the transition curvature from the pole region to the yoke region. A smaller min Rc means sharper transition which corresponds to improved writer characteristics including. New design specifications for future generation devices require much shaper transition curvatures and smaller min Rc. These types of design requirements are very challenging to achieve with the traditional photolithography processes, due to optical proximity effects that yield rounded nose curvature with large min Rc.
FIGS. 3A-3E show an exemplary two mask embodiment. Exemplary embodiments describe innovative double mask techniques. By separating into two masks the area that covers the nose shaped transition 106, connecting the yoke region 102 to the pole region 104, the interference between the yoke and pole patterns caused by optical proximity effect is largely avoided, resulting in much sharper nose transition and small min Rc. As shown in FIG. 3A, an exemplary rectangular shaped first mask 302 is used to expose the photoresist covering the yoke-pole transition region of the writer 100. FIG. 3B shows an exemplary second mask 304 used to define the yoke to pole region transition shape. The exposure of the photoresist covering the yoke region 102 and pole region 104 through the first mask 302 and then the second mask 304 results in the double exposure of the transition region 306 shown in FIG. 3C. However, the use of two separate masks to achieve the shape and the radius of curvature of the yoke to pole transition region 106 results in lower interference between the competing shapes at the transition region 306, making the formation of a smaller radius of curvature with a sharp transition more feasible. In alternative embodiments, the second mask 304 may be shifted or offset in a vertical direction with respect to the first mask 302 as shown in FIG. 3D, or shifted down with respect to the second mask 302, as shown in FIG. 3E. In yet another alternative embodiment, the second mask 304 may be shifted or offset in a horizontal direction with respect to the first mask 302.
In alternative embodiments, exposure of the photoresist through the first mask 302 may use illumination conditions that have a different intensity as compared to illumination conditions used to expose the photoresist 110 through the second mask 304. In alternative embodiments, a different aperture may be used to expose the photoresist through the first mask 302 than through the second mask 304. In exemplary embodiments, a first aperture in the shape of an annular, a quasar, dipole or a circular (aka conventional) aperture may be used to expose the photoresist 110 through the first mask 302, and a different shaped aperture may be used with the second mask 304. In yet other embodiments, different exposure times may be used with the first mask 302 and the second mask 304. So as shown in FIGS. 3D and 3E, the shifting of the first mask 302 in the vertical or horizontal direction with respect to the second mask 304, in addition to the variation of exposure time, aperture and light intensity between the first and second mask provides the possibility of adjusting multiple parameters to achieve a great deal of flexibility, allowing the designer to fabricate a structure that is closest to the desired shape. It should be apparent to one of skill in the art that newer photolithography tools may provide automatic adjustments for variables such as exposure intensity, exposure time and any degradation or variation in the output of the photolithography illumination source. Therefore, an operator may only need to select the desired exposure dose and aperture type, and the photolithography tool will automatically calculate the proper light intensity and exposure time to provide the desired exposure dose.
Thus, the various embodiments of the double mask techniques taught allow for greater engineering and design flexibility as compared to the traditional single mask techniques. Changing the overlay or offset between the two masks in two exposures, nose shape and curvature can be varied in a wide range. The two exposures can also be optimized separately with different illumination conditions that provide additional shape tuning capability. In summary, various exemplary embodiments provide new double mask techniques to not only achieve shapes requiring smaller min Rc writer nose shape, but also wide range of curvatures and shapes, providing maximum design and shape tuning capabilities by simply changing overlay/offset and illumination conditions.
FIG. 4 shows the actual resist image using an embodiment of the double mask technique. As seen in FIG. 4, the minimum Rc achieved using exemplary embodiments disclosed herein is smaller as compared to the minimum Rc possible with traditional techniques. FIG. 5 will further illustrate the range of minimum feature sizes that may be achieved using various exemplary embodiments of the double or multi-mask technique.
FIG. 5 illustrates experimental results achieved using an embodiment of the double mask technique. As shown in FIG. 5, by the changing the overlay between the two masks 302 and 304, transition region radius of curvatures Rc with different minimum curvatures may be achieved. FIG. 5 illustrates the changes in the minimum radius Rc, while the offset is varied in the vertical direction from negative to positive values. The data lines 502, 504 and 506 each correspond to a fixed intensity and aperture settings, while the offset is varied in the vertical direction. For example, the data tracing curve 502 is generated with a quasar shaped aperture, and a 0.8 millijoule/sq cm illumination condition (also referred to as the exposure dose). The offset between the first mask 302 and second mask 304 was varied by moving the second mask 304 with respect to the first mask 302, in the vertical direction from negative fifty nanometer (−50 nm) to positive one hundred nanometer (+100 nm). As seen illustrated by curve 502, the lowest minimum radius of curvature Rc of seventy nanometer (70 nm) was reached. Similarly, curve 504 illustrates that using a quasar aperture and an illumination condition set at 0.8 millijoule/sq cm, a minimum Rc of about 75 nm was achieved at the negative offset of −50 nm. Curve 506 illustrates Rc ranges of about 100 nm to 165 nm, using an annular aperture and an illumination condition or exposure dose set at 0.8 millijoule/sq cm. The ability of using the same two masks and varying the offset between the two masks to achieve a wide range of geometries gives great flexibility to the designers, as well as allowing for great time and cost savings, by avoiding the need for having to manufacture a different mask for each desired shape design. The various embodiments of the two masks offset design provide savings in time, effort and cost of having to create a set of masks for each experimental shape design. In summary, exemplary embodiments provide new double mask techniques to not only achieve shapes requiring smaller min Rc writer nose shape, but also wide range of curvatures and shapes, providing maximum design and shape tuning capabilities by simply changing offset and illumination conditions.
FIG. 6 illustrates a method of manufacturing a magnetic pole according to an exemplary embodiment. In operation 602, two photomasks are designed to form the features of the main pole. In order to achieve the transition from the yoke region 102 to the main pole region 104 with a small radius of curvature, a first mask 302 defining the main pole wide is formed. The second mask 304 roughly defines the shape of the transition region. The shape of the transition region is actually defined by the combination the two masks 302 and 304, the adjustment of the offset between the first and second mask, as well as other exposure parameters or illumination conditions.
In operation 604, the photoresist 110 covering the yoke 102 and pole region 104 is exposed using the first mask 302. In operation 606, the photoresist 110 is exposed using the second mask 304. The offset of the second mask 304 with respect to the first mask 302 is adjusted to achieve the optimum transition shape and lowest radius of curvature for the yoke 102 and main pole region 104.
In operation 608, the photoresist is exposed through the second mask with the proper vertical or horizontal offset to best achieve the desired yoke to pole transition region. As previously described, exposure parameters such the aperture and, the illumination or light intensity may also vary when exposing the photoresist layer using the first and second mask. For example the first exposure may use an annular quasar aperture shape with the first mask and a different aperture shape may be used with the second mask. Similarly, the illumination conditions may be varied between the exposure through the first and second mask. In summary, exemplary embodiments provide for new double mask techniques to not only achieve shapes requiring smaller min Rc writer nose shape, but also wide range of curvatures and shapes, providing maximum design and shape tuning capabilities by simply changing offset and illumination conditions.
The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and sub-combinations are intended to fall within the scope of this disclosure. In addition, certain method, event, state or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other suitable manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.

## Claims

1. A method of taking advantage of the optical proximity effects in the fabrication of thin film heads (TFH) including small features, the method comprising:
providing at least a first and second photolithography masks (mask) corresponding to a desired shape, wherein each of the first and the second masks includes one critical feature of the desired shape; and
sequentially exposing a photoresist layer covering an area corresponding to the desired shape using the at least first and second masks.

2. The method of claim 1 further comprising:
adjusting an offset between the at least first and second masks to modify features of the desired shape.

3. The method of claim 1 wherein a decrease in the offset increases the sharpness of the desired shape.

4. The method of claim 1 further comprising:
exposing the photoresist layer through the first mask with a first set of illumination conditions and exposing the photoresist layer through the second mask with a second set of illumination conditions.

5. The method of claim 4 wherein the first and the second set of illumination conditions are the same.

6. The method of claim 4 wherein the first and the second set of illumination conditions are different.

7. The method of claim 1, wherein the desired shape forms a transition from a yoke region to a main pole region in a magnetic writer.

8. The method of claim 7, wherein the desired shape is a partial circular shape with a minimum radius of less than 100 nm.

9. The method of claim 7, wherein the desired shape is a partial circular shape with a minimum radius of less than 80 nm.

10. The method of claim 1 wherein the first mask has a T shape.

11. The method of claim 10 wherein the width of an upper rectangle of the T shape is between 1 micron to 0.5 microns and the width of the lower rectangle is between 200 nm to 500 nm.

12. The method of claim 1, wherein the second mask has a funnel shape.

13. The method of claim 1, wherein the width of the upper part of the funnel is between 2.5 microns to 1 micron and the width of the lower part of the funnel is between 400 nm to 700 nm.

14. The method of claim 1 wherein the illumination conditions parameters include the light shape, intensity, exposure time and aperture.

15. The method of claim 14, wherein the aperture includes quasar aperture, annular aperture and circular aperture.

16. A method of using a double mask technique for optimizing a shaped transition having a shape and curvature, and connecting a main pole to a yoke region in a magnetic write head, the method comprising:
providing a first photo mask (mask) including a first set of features corresponding to a shaped transition region, wherein the transition connects a main pole region to a yoke region;
providing at least a second mask including a second set of features corresponding to the shaped transition region;
exposing the transition region sequentially through the first mask and the at least second mask, wherein the sequential exposure through the first mask and the second mask utilizes optical proximity effects to minimize distortions of the shaped transition region.

17. The method of claim 16, further comprising:
exposing the shaped transition region through the first mask using a first set of illumination conditions; and
exposing the shaped transition region through the second mask using a second set of illumination conditions.

18. The method of claim 16, further comprising:
adjusting an offset between the first mask and the second mask, in order to tune the shape and the curvature of the shaped transition region.

19. The method of claim 18 wherein the first set of illumination conditions are different from the second set of illumination conditions.