Abstract:
Methods of fabricating perpendicular magnetic recording media are disclosed. The multilayer structures of the perpendicular magnetic recording media are fabricated by varying the sputtering conditions (i.e., pressure, sputtering gas, etc) in a single sputtering module so that multiple sputtering modules are not needed to form the multilayer structures. These fabrication methods allow sputtering tools with a limited number of chambers, which were designed for the manufacture of longitudinal media, to be used to efficiently produce perpendicular media architectures which heretofore required a large number of sputtering modules. It is further shown that media structures involving a geometric weak-link architecture are suited for these fabrication techniques.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is related to the field of fabrication of perpendicular magnetic recording media and, in particular, to the growth of certain multilayer structures of a recording media structure in a single sputtering process module of a multi-station manufacturing tool. 
     2. Statement of the Problem 
     Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives have typically been longitudinal magnetic recording systems, where magnetic data is recorded as magnetic transitions formed with their magnetization aligned parallel to the disk surface. The surface of the disk is magnetized in a direction along a track of data and then switched to the opposite direction, both directions being parallel with the surface of the disk and parallel with the direction of the data track. 
     Unfortunately, data density requirements are fast approaching the physical limits. Overall data density (or areal density) may be improved by improving linear density and/or track density. To improve linear density, bit sizes on a track need to be reduced which in turn requires decreasing the grain size of the magnetic medium. As this grain size shrinks, the thermal stability of the written domains decreases. Therefore, materials with higher magnetic anisotropy are utilized thereby requiring higher magnetic fields to be reversed. 
     One way to achieve higher density recordings is with perpendicular recording. In perpendicular recording systems, bits of data are recorded with their magnetization perpendicular to the plane of the surface of the disk. A perpendicular magnetic recording disk is generally formed by depositing on a suitable substrate an adhesion layer, a soft magnetic underlayer (SUL) stack, a seed layer(s), an intermediate non-magnetic layer(s), a magnetic recording layer(s), a capping layer(s), and an overcoat structure. The adhesion layer is formed on the substrate to improve adhesion of subsequently deposited layers to the substrate. The soft magnetic underlayer (SUL) stack serves to concentrate a magnetic flux emitted from a main pole of a write element and to act as a flux return path back to a return pole of the write element during recording on the magnetic recording layer. The seed layer(s) provide a transition for the growth of crystalline thin films on the amorphous SUL layers. The intermediate layer(s) controls the crystallographic texture, grain size, and the segregation of the magnetic recording layer. The intermediate layer also serves to magnetically de-couple the SUL stack and the magnetic recording layer. The magnetic recording layer(s) act as a storage layer for the data encoded as bit transitions. The capping layer(s) are employed to improve the recording media writeability and noise performance. 
     The layers of perpendicular magnetic recording media are formed by sequentially sputtering the layers on the substrate. Each individual layer of the perpendicular magnetic recording media is sputtered in a separate sputtering processing module (station) of a multi-station thin film deposition tool. The following paragraphs describe a typical fabrication process for perpendicular magnetic recording media. 
     A substrate is loaded onto a carrier mechanism in a loading chamber of the fabrication tool. The carrier mechanism then transports the substrate to a first sputtering process module. The desired sputtering conditions are set for the first sputtering module, and an adhesion layer, such as AlTi, NiTa, etc, is sputtered onto the substrate. The carrier mechanism then transports the substrate to a second sputtering module. 
     The next three sputtering modules form an antiparallel (AP) SUL stack. To form the AP SUL stack, the desired sputtering conditions are set for the second sputtering module, and a first layer of the SUL stack, such as a CoTaZr-based alloy, is sputtered onto the adhesion layer. The carrier mechanism then transports the substrate to a third sputtering module. The desired sputtering conditions are set for the third sputtering module, and a second layer of the SUL stack, such as Ru, is sputtered onto the first SUL layer. The carrier mechanism then transports the substrate to a fourth sputtering module. The desired sputtering conditions are set for the fourth sputtering module, and a third layer of the SUL stack, such as a CoTaZr-based alloy, is sputtered onto the second SUL layer. The carrier mechanism then transports the substrate to a fifth sputtering module. 
     The next two sputtering modules form a multilayer seed layer. To form the multilayer seed layer, the desired sputtering conditions are set for the fifth sputtering module, and a first seed layer, such as a CrTi, is sputtered onto the third SUL layer. The carrier mechanism then transports the substrate to a sixth sputtering module. The desired sputtering conditions are set for the sixth sputtering module, and a second seed layer, such as NiW or NiWCr, is sputtered onto the first seed layer. The carrier mechanism then transports the substrate to a seventh sputtering module. 
     The next two sputtering modules form a multilayer intermediate layer. This intermediate layer is typically non-magnetic and serves to decouple the magnetic recording layer from the SUL. This layer also serves as a growth template for the magnetic layers that will be deposited in the next sputtering modules. To form the multilayer intermediate layer, the desired sputtering conditions are set for the seventh sputtering module, and a first intermediate layer, such as a Ru (low pressure), is sputtered onto the second seed layer. The carrier mechanism then transports the substrate to an eighth sputtering module. The desired sputtering conditions are set for the eighth sputtering module, and a second intermediate layer, such as Ru (high pressure), is sputtered onto the first intermediate layer. The carrier mechanism then transports the substrate to a ninth sputtering module. 
     The desired sputtering conditions are set for the ninth sputtering module, and a magnetic recording layer(s), such as a CoPtCr-based alloy, is sputtered onto the second intermediate layer. It has been found that improved recording properties can be derived if a plurality of magnetic layers (two or more) is employed as the storage medium. For example, the stack may include magnetic layers differing in composition and magnetic properties to generate a magnetically modulated recording structure across the thickness of the recording layer. This permits improvements in writeability, jitter, and signal-to-noise. Therefore, it is common in current-art media fabrication to employ a plurality of sputtering modules housing magnetic targets with different compositions to fabricate a compositionally modulated storage layer. The carrier mechanism then transports the substrate to a tenth sputtering module. The desired sputtering conditions are set for the tenth sputtering module, and a capping layer(s), such as CoPtCrB, is sputtered onto the magnetic recording layer. As in the case of the storage layer, it is also advantageous to employ a plurality of layers for achieving the functionality of the capping layer (improved writeability through exchange coupling of the recording layer with a softer overlayer, such as the cap layer, whose magnetization orientation is more easily altered by the writing field). At least two layers are employed in some designs with one of the layers mediating the exchange coupling between the storage layer and the cap. The carrier mechanism then transports the substrate to an eleventh sputtering module. The desired sputtering conditions are set for the eleventh sputtering module, and a first overcoat layer, such as IBD, is sputtered onto the capping layer. The carrier mechanism then transports the substrate to a twelfth sputtering module. The desired sputtering conditions are set for the twelfth sputtering module, and a second overcoat layer, such as CNx, is sputtered onto the first overcoat layer. The carrier mechanism then transports the substrate to an unloading chamber. 
     As is evident from the above fabrication process, twelve or more individual sputtering modules are used to form the perpendicular magnetic recording media. The number of different sputtering steps used for fabricating longitudinal recording media is usually less than twelve. Thus, many existing fabrication tools have less than twelve sputtering modules. Therefore, it was widely accepted in the industry that current-art fabrication tools developed for fabricating longitudinal magnetic recording media are inadequate for the manufacturing of perpendicular recording media. In order to fabricate the perpendicular magnetic recording media described above, disk drive manufacturers may have to update their fabrication tools, which comes at a very high investment. It would therefore be desirable to find ways to use existing fabrication tools to fabricate perpendicular magnetic recording media. 
     SUMMARY 
     Embodiments of the invention solve the above and other related problems by fabricating multiple layers of perpendicular magnetic recording media in single sputtering modules by sputtering using a common composition target under varying sputtering conditions. By changing the sputtering conditions, multilayer structures of perpendicular magnetic recording media may be formed in single sputtering modules. As a result, the total number of sputtering modules used to fabricate perpendicular magnetic recording media may be reduced so that current-art longitudinal media fabrication tools may be used. Disk drive manufacturers thus do not need to invest large amounts of capital into updating their fabrication tools in order to manufacture perpendicular magnetic recording media. In addition, these techniques may also be applied to sputtering tools where multiple cathodes are present in a single chamber. Thus, one can further increase the ability of these tools to rapidly produce flexible, multilayer media structures in a minimum number of sputtering modules. 
     One embodiment of the invention comprises a method of fabricating perpendicular magnetic recording media. The method includes sputtering an adhesion layer on a substrate, sputtering an SUL stack on the adhesion layer, and sputtering a seed layer on the SUL stack. The method further includes sputtering an intermediate layer on the seed layer, sputtering a magnetic recording layer on the intermediate layer, sputtering a capping layer on the magnetic recording layer, and sputtering an overcoat layer on the capping layer. One or more of the layers of the perpendicular magnetic recording media may comprise multilayer structures formed from the same material, such as one or more of the seed layer, the intermediate layer, the magnetic recording layer, and the capping layer. The multilayer structures of the perpendicular magnetic recording media are fabricated (from a common sputtering target) by varying (or altering) the sputtering conditions in the same sputtering module. By varying the sputtering conditions, such as the pressure, the sputtering gas composition, the growth rate, bias, etc, thin films deposited from a common sputtering target will exhibit different microstructural properties. and therefore, variations of such parameters during the deposition of said target material may be employed to fabricate a multilayer structure with optimized microstructural properties in a single sputtering module. 
     The invention may include other exemplary embodiments described below. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The same reference number represents the same element or same type of element on all drawings. 
         FIG. 1  is a cross-sectional view of perpendicular magnetic recording media in an exemplary embodiment of the invention. 
         FIG. 2  is a flow chart illustrating a method of fabricating perpendicular magnetic recording media in an exemplary embodiment of the invention. 
         FIG. 3  illustrates a fabrication process for fabricating perpendicular magnetic recording media in a multi-station sputtering tool in an exemplary embodiment of the invention. 
         FIG. 4  illustrates sputtering conditions for fabricating a multilayer seed layer in an exemplary embodiment of the invention. 
         FIG. 5  illustrates sputtering conditions for fabricating a multilayer intermediate layer in an exemplary embodiment of the invention. 
         FIG. 6  illustrates sputtering conditions for fabricating a multilayer magnetic recording layer in an exemplary embodiment of the invention. 
         FIG. 7  illustrates grain boundaries in a magnetic recording layer in an exemplary embodiment of the invention. 
         FIG. 8  illustrates grain boundaries in a magnetic recording layer in another exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1-8  and the following description depict specific exemplary embodiments of the invention to teach those skilled in the art how to make and use the invention. For the purpose of teaching inventive principles, some conventional aspects of the invention have been simplified or omitted. Those skilled in the art will appreciate variations from these embodiments that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described below, but only by the claims and their equivalents. 
       FIG. 1  is a cross-sectional view of perpendicular magnetic recording media  100  in an exemplary embodiment of the invention. The illustration of perpendicular magnetic recording media  100  is of the basic building blocks of the media. Perpendicular magnetic recording media  100  is fabricated by depositing multiple thin films on a substrate  102  (e.g., a glass or AlMg substrates). Perpendicular magnetic recording media  100  may or may not include an adhesion layer  104  formed on the substrate  102 . Perpendicular magnetic recording media  100  further includes a SUL stack  106  formed on adhesion layer  104 . SUL stack  106  has an antiparallel (AP) structure comprising a first ferromagnetic SUL layer  108 , an AP coupling layer  109 , and a second ferromagnetic SUL layer  110 . Perpendicular magnetic recording media  100  further includes a seed layer  112  formed on the SUL stack  106 . Although the term “layer” is used in singular form, seed layer  112  and other layers in perpendicular magnetic recording media  100  may be comprised of multiple layers. Perpendicular magnetic recording media  100  further includes an intermediate layer  114  formed on the seed layer  112 , and a magnetic recording layer  116  formed on the intermediate layer  114 . Perpendicular magnetic recording media  100  further includes a capping layer  118  formed on the magnetic recording layer  116 , and an overcoat layer  120  formed on the capping layer  118 . 
       FIG. 1  illustrates just one embodiment of the layers of perpendicular magnetic recording media  100 . In other embodiments, the layers of perpendicular magnetic recording media  100  may be rearranged or may be substituted with other layers. 
     As described in the Background, conventional methods of fabricating perpendicular magnetic recording media use a fabrication tool comprising a plurality of independent sputtering processing modules or often referred as process stations, which are housed within the same deposition tool vacuum assembly. A substrate is placed in the fabrication tool and the layers of the perpendicular magnetic recording media are sputtered onto the substrate. The fabrication tool includes a plurality of sputtering modules, where each sputtering module is adapted to sputter a layer of material from a sputtering target based on a particular set of sputtering conditions. Thus, when a multilayer structure is fabricated, a different sputtering module is needed to form each layer of the multilayer structure. According to embodiments provided herein, multilayer structures of perpendicular magnetic recording media  100  as illustrated in  FIG. 1  do not need to be fabricated in different sputtering modules. 
       FIG. 2  is a flow chart illustrating a method  200  of fabricating perpendicular magnetic recording media  100  in an exemplary embodiment of the invention. Method  200  illustrates just one embodiment, and there may be many variations from this embodiment that are within the scope of the invention. The steps of method  200  will be described in reference to  FIG. 1 . 
     Step  202  comprises sputtering an adhesion layer  104  on substrate  102 . For the specification and claims “on” means “above”, but not necessarily “in contact with”. Step  204  comprises sputtering an SUL stack  106  on the adhesion layer  104 . To sputter the SUL stack  106 , step  204  may comprise the further steps of sputtering a first ferromagnetic SUL layer  108 , sputtering an AP coupling layer  109 , and sputtering a second ferromagnetic SUL layer  110 . Present SUL stacks employ AP coupled high permeability amorphous films to minimize magnetic noise interference with the layer where the encoded information is stored. Applying the teachings of this invention, it is possible to overcome the noise contributions of a single layer SUL by employing the multi-step processing to control its magnetic domain structure, thereby dispensing with the need to employ a separate sputtering module to deposit the AP coupling layer, such as Ru. 
     Step  206  comprises sputtering a seed layer  112  on the SUL stack  106 . Step  208  comprises sputtering an intermediate layer  114  on the seed layer  112 . Step  210  comprises sputtering a magnetic recording layer  116  on the intermediate layer  114 . Step  212  comprises sputtering a capping layer  118  on the magnetic recording layer  116 . Step  214  comprises sputtering an overcoat layer  120  on the capping layer  118 . 
     One or more of the layers of perpendicular magnetic recording media  100  may comprise multilayer structures formed from the same material. For instance, one or more of seed layer  112 , intermediate layer  114 , magnetic recording layer  116 , and capping layer  118  may be comprised of a multilayer structure. Instead of fabricating the multilayer structures in separate sputtering modules as is presently performed, the multilayer structures of perpendicular magnetic recording media  100  are fabricated (from a common sputtering target) by varying the sputtering conditions in the same sputtering module. By varying the sputtering conditions, such as the pressure, the sputtering gas, bias voltage, etc, a multilayer structure with a desired microstructure may be fabricated in a single sputtering module. As a result, conventional fabrication tools having a limited number of sputtering modules may be used to fabricate perpendicular magnetic recording media  100 . 
     As one example, assume that seed layer  112  comprises a multilayer structure formed from the same material. To sputter seed layer  112  in step  206 , substrate  102  is introduced into a sputtering module with a seed material target. The seed material target may comprise a NiWCr-based alloy or another type of material. A first seed layer is then sputtered at a first pressure to achieve a desired thickness of the first seed layer. A second seed layer is then sputtered at a second pressure (which is different than the first pressure) to achieve a desired thickness of the second seed layer. By varying the sputtering conditions (i.e., pressure) in this example, a multilayer seed layer  112  may be formed in a single sputtering module to have a desired structure. Although seed layer  112  includes two layers in this example, those skilled in the art will appreciate that seed layer  112  may include more layers in other examples. 
     As another example, assume that intermediate layer  114  comprises a multilayer structure formed from the same material. To sputter intermediate layer  114  in step  208 , substrate  102  is introduced into a sputtering module with an intermediate material target. The intermediate material target may comprise Ru, RuCr alloys (with the Cr content ranging from 0 to 20%), or another type of material. A first intermediate layer is then sputtered at a first pressure to achieve a desired thickness of the first intermediate layer. A second intermediate layer is then sputtered at a second pressure (which is different than the first pressure) to achieve a desired thickness of the second intermediate layer. By varying the sputtering conditions (i.e., pressure) in this example, a multilayer intermediate layer  114  may be formed in a single sputtering module to have a desired structure. 
     As another example, assume that magnetic recording layer  116  comprises a multilayer structure formed from the same material. To sputter magnetic recording layer  116  in step  210 , substrate  102  is introduced into a sputtering module with a recording material target. The recording material target may comprise a CoPtCr-based alloy or another type of material. A first magnetic recording layer is then sputtered at a first pressure using a first sputtering gas to achieve a desired thickness of the first magnetic recording layer. The first sputtering gas may comprise an inert gas, such as Ar, and Oxygen. A second magnetic recording layer is then sputtered at the first pressure using the first sputtering gas to achieve a desired thickness of the second magnetic recording layer. A third magnetic recording layer is then sputtered at a second pressure using a second sputtering gas to achieve a desired thickness of the third magnetic recording layer. The second sputtering gas may comprise just an inert gas, such as Ar. By varying the sputtering conditions (i.e., pressure and sputtering gas) in this example, a multilayer magnetic recording layer  116  may be formed in a single sputtering module to have a desired structure. 
       FIG. 3  illustrates a fabrication process for fabricating perpendicular magnetic recording media  100  in a fabrication tool  300  in an exemplary embodiment of the invention. Fabrication tool  300  includes nine sputtering modules in this embodiment, although those skilled in the art will appreciate that fabrication tools may include more or less sputtering modules in other embodiments. 
     To start the fabrication process, a substrate  102  is loaded onto a carrier mechanism in a loading chamber  302 . The carrier mechanism then transports the substrate  102  to a first sputtering module  304 . Sputtering module  304  sputters adhesion layer  104  on substrate  102 . Adhesion layer  104  may be formed from AlTi, NiTa, or another target that is sputtered to a thickness of about 1-10 nanometers. The carrier mechanism then transports the substrate  102  to a second sputtering module  306 . Sputtering module  306  sputters a first SUL layer  108  on adhesion layer  104 . The first SUL layer  108  may be formed from a CoTaZr-based alloy or another target that is sputtered to a thickness of about 5 to 50 nanometers. The carrier mechanism then transports the substrate  102  to a third sputtering module  308 . Sputtering module  308  sputters an AP coupling layer  109  on the first SUL layer  108 . The AP coupling layer  109  may be formed from Ru or another target that is sputtered to a thickness of about 0.4 to 1.0 nanometers. The carrier mechanism then transports the substrate  102  to a fourth sputtering module  310 . Sputtering module  310  sputters a second SUL layer  110  on AP coupling layer  109 . The second SUL layer  110  may be formed from a CoTaZr-based alloy or another target that is sputtered to a thickness of about 5 to 50 nanometers. 
     The carrier mechanism then transports the substrate  102  to a fifth sputtering module  312 . Sputtering module  312  is adapted to fabricate a multilayer seed layer  112  on the second SUL layer  110 . To fabricate the multilayer seed layer  112  in sputtering module  312 , the sputtering conditions are varied.  FIG. 4  illustrates sputtering conditions for fabricating the multilayer seed layer  112  in an exemplary embodiment of the invention. Assume for this embodiment that the seed material target is NiWCr, although other seed material targets may be used. Sputtering module  312  sputters a first seed layer at 7.5 mTorr for about 2 seconds to achieve a thickness of about 5 nanometers. After a 2.8 second delay (such as by turning off the plasma voltage), sputtering module  312  sputters a second seed layer at 15 mTorr for about 1 second to achieve a thickness of about 2.6 nanometers. Those skilled in the art will appreciate that numerous permutations of time duration, deposition rates, sputter pressures, delay times, etc, may be used to form seed layer  112 . 
     The carrier mechanism then transports the substrate  102  to a sixth sputtering module  314 . Sputtering module  314  is adapted to fabricate a multilayer intermediate layer  114  on the seed layer  112 . To fabricate the multilayer intermediate layer  114  in sputtering module  314 , the sputtering conditions are varied.  FIG. 5  illustrates sputtering conditions for fabricating the multilayer intermediate layer  114  in an exemplary embodiment of the invention. Assume for this embodiment that the intermediate material target is Ru, although other intermediate material targets may be used. Sputtering module  314  delays for 0.2 seconds before the cathodes are ignited, and then sputters a first intermediate layer at 7.5 mTorr for about 0.7 seconds to achieve a thickness of about 5.3 nanometers. At the end of the 0.7 second deposition cycle, the sputter pressure is incremented in sputtering module  314  to about 48 mTorr. The second intermediate layer is then sputtered at this pressure for about 4.4 seconds to achieve a thickness of about 12.7 nanometers. Those skilled in the art will appreciate that numerous permutations of time duration, deposition rates, sputter pressures, delay times, etc, may be used to form intermediate layer  114 . 
     The carrier mechanism then transports the substrate  102  to a seventh sputtering module  316 . Sputtering module  316  is adapted to fabricate a multilayer magnetic recording layer  116  on the intermediate layer  114 . To fabricate the multilayer magnetic recording layer  116  in sputtering module  316 , the sputtering conditions are varied.  FIG. 6  illustrates sputtering conditions for fabricating the multilayer magnetic recording layer  116  in an exemplary embodiment of the invention. Assume for this embodiment that the recording material target is a CoPtCr-based alloy, although other recording material targets may be used. Sputtering module  316  is then programmed to wait for about 0.4 seconds before cathode ignition, and follows with a high pressure burst (about 35 mTorr) of a sputtering gas. Sputtering module  316  then sputters a first magnetic recording layer at a total pressure of about 17 mTorr (pressure for Ar and Oxygen) for a duration of approximately 0.5 seconds to achieve a thickness of about 1.5 nanometers. At the end of the 0.5 second deposition cycle, sputtering module  316  sputters a second magnetic recording layer at the same sputter pressure for about 2.5 seconds with a −250 volt bias voltage applied to achieve a thickness of about 7.6 nanometers. At the end of the 2.5 second deposition cycle, sputtering module  316  sputters a third magnetic recording layer in pure Ar at a pressure of about 11 mTorr with the same bias voltage to achieve a thickness of about 3.9 nanometers. Those skilled in the art will appreciate that numerous permutations of time duration, deposition rates, sputter pressures, delay times, etc, may be used to form magnetic recording layer  116 . 
     The carrier mechanism then transports the substrate  102  to an eighth sputtering module  318 . Sputtering module  318  sputters the capping layer  118  on magnetic recording layer  116 . Capping layer  118  may be formed from CoPtCrB or another target. The carrier mechanism then transports the substrate  102  to a ninth sputtering module  320 . Sputtering module  320  sputters an overcoat layer  120  on capping layer  118 . Overcoat layer  120  may be formed from IBD, CNx, or another target. The carrier mechanism then transports the substrate  102  to an unloading chamber  322 . 
     By changing the sputtering conditions, multilayer structures of perpendicular magnetic recording media  100  may be formed in a single sputtering module. As a result, the total number of sputtering modules used to fabricate perpendicular magnetic recording media  100  may be reduced so that existing fabrication tools may be used. For instance, only nine sputtering modules are needed in the embodiment of  FIG. 3 . In present fabrication processes, twelve or more sputtering modules are needed. Thus, the embodiments provided herein allow for fewer sputtering modules to be used. As a result, disk drive manufacturers thus do not need to invest large amounts of capital into updating their fabrication tools in order to fabricate perpendicular magnetic recording media. 
     In addition to the embodiments provided above for fabricating a multilayer magnetic recording layer  116 , the following provides some alternative embodiments for fabricating magnetic recording layer  116 . When CoCrPt-based alloys are used for the magnetic recording layer, non-magnetic Cr segregates to the grain boundaries that magnetically isolate the magnetic crystal grains. However, the size of the Cr boundaries is small, which results in a high amount of exchange coupling between magnetic crystal grains that contributes to unwanted noise. To reduce the exchange coupling, segregation of the magnetic crystal grains may be promoted with oxides and nitrides (referred to herein as segregants) to form a granular medium. With the magnetic crystal grains segregated by sufficient grain boundaries, the media noise may be reduced. 
       FIG. 7  illustrates grain boundaries  704  in magnetic recording layer  116  in an exemplary embodiment of the invention. Magnetic recording layer  116  in this embodiment is formed from a first magnetic recording layer  711  and a second magnetic recording layer  712 . Magnetic recording layers  711 - 712  are formed from a recording material target such as CoCrPt with a segregant such as SiO 2 . The magnetic recording layers  711 - 712  are sputtered in a single sputtering module much as described above. Due to the formation of magnetic recording layers  711 - 712 , the SiO 2  segregates to surround the CoCrPt which forms magnetic crystal grains  702  that are separated by grain boundaries  704 . 
     According to embodiments provided herein, the area of grain boundaries  704  are increased at the interface  714  between the first magnetic recording layer  711  (the hard magnetic layer) and the second magnetic recording layer  712  (the soft magnetic layer). For example, the area of grain boundaries  704  at location  721  is larger than at locations  722  and  723 . The area of grain boundaries  704  may be increased or decreased by varying sputtering conditions. For example, a change the oxygen content in the plasma gas mixture from zero to 2% results in a reduction of the magnetic grain size of 12%. This may be attributed to an increase in the amount of segregant at the grain boundaries  704 . Controlling the area of the grain boundaries  704  allows for optimization the interlayer coupling between the first magnetic recording layer  711  and the second magnetic recording layer  712 . 
     Interlayer coupling (J) is generally defined by the local exchange coupling strength density (j el ) multiplied by the grain interface area (A), which is J=j el *A. The grain interface area is defined by the area of contact between the first magnetic recording layer  711  and the second magnetic recording layer  712  at interface  714 . Thus, by increasing the area (or size) of the grain boundaries  704  at the interface  714  between the first magnetic recording layer  711  and the second magnetic recording layer  712 , the area of contact between the first magnetic recording layer  711  and the second magnetic recording layer  712  is reduced. And consequently, the interlayer coupling between the first magnetic recording layer  711  and the second magnetic recording layer  712  is reduced. This media architecture thus controls the inter-layer exchange interactions by means of a “geometric weak-link” at the boundary between the hard and the soft magnetic layers. 
     Intergranular exchange plays a leading role in determining the recording performance of magnetic media. In perpendicular media, exchange counteracts the deleterious effects of demagnetization interactions. Modest exchange leads to an optimum switching field distribution resulting in low noise and excellent resolution. However, increasing exchange improves the writeability of the media and can result in larger than desired write-widths. In addition, excessive exchange gives rise to clusters of grains at the transition between magnetically-defined bits. These grain clusters result in increased noise and thus, reduce the performance of a recording system. In a dual layer perpendicular media with a soft capping layer and a hard base layer, exchange is optimally controlled in the system by varying the physical and magnetic properties of the capping layer. However, this soft magnetic capping layer serves several, often contradictory functions. The capping layer controls both the inter-granular exchange in the system, which is the dominant contribution to noise and resolution, as well as vertical exchange which is the dominant contribution to the writeability of the media. As a result of the multiple roles played by the capping layer in present perpendicular recording, techniques to segregate and control these functions, such as the methods disclosed herein, lead to improved recording performance. 
     In addition to increasing the area of the grain boundaries  704  at the interface  714  between the first magnetic recording layer  711  and the second magnetic recording layer  712 , the area of the grain boundaries  704  may additionally be increased in other locations in the first magnetic recording layer  711  and the second magnetic recording layer  712 .  FIG. 8  illustrates grain boundaries  704  in magnetic recording layer  116  in another exemplary embodiment of the invention. In this embodiment, the area of grain boundaries  704  are increased at the interface  714  between the first magnetic recording layer  711  and the second magnetic recording layer  712 , and one or more other locations. For example, the area of grain boundaries  704  at location  721  and location  722  are larger than at location  723 . There may be multiple other locations where the areas of the grain boundaries are increased to provide desired media performance. 
     Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents thereof.