Abstract:
A method of forming an energy assisted magnetic recording (EAMR) writer is disclosed. A structure comprising a bottom cladding layer and a near field transducer (NFT) is provided. A patterned sacrificial layer is formed over the structure. A top cladding layer is deposited over the patterned sacrificial layer and a remaining region of the structure not covered by the patterned sacrificial layer. A patterned resist is formed over the top cladding layer. A first etching operation is performed on the top cladding layer via the patterned resist, whereby a top cladding having a sloped region is formed. The patterned sacrificial layer provides an etch stop for the first etching operation.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to magnetic recording and, in particular, relates to method of forming dielectric slope for EAMR and magnetic writer. 
     BACKGROUND 
     With current perpendicular magnetic recording technology, the magnetic recording areal density has been pushed to around 500˜600 Gb/in 2 , and has almost reached the physical upper limit imposed by the superparamagnetic effect. Even with the availability of a higher coercivity magnetic material such as FePt and CoPd, a poor writability resulting from saturation of the writing head is expected to become a bottle neck. Energy Assisted Magnetic Recording (EAMR) or Heat Assisted Magnetic Recording (HAMR) technology has become the common pursuit in data storage circle, since the technology offers a way to circumvent the writability bottleneck and further push the data areal density to 1 Tbit/in 2  and beyond. The EAMR/HAMR technology can eventually merge with the patterned media. 
     Near Field Transducer (NFT) is a critical element for an EAMR or HAMR head to transfer enough energy to a tiny bit region and heat the region up to a temperature close to the Currier Temperature temporarily so as to achieve the writability within the short duration.  FIG. 1  is a diagram depicting an NFT  102  disposed adjacent to a magnetic pole  104  and having a sloped top cladding  106  comprised of a dielectric material (e.g., an aluminum oxide). 
     A traditional approach to form such a top cladding having a sloped region (hereinafter referred to as “dielectric slope”) is by a milling or RIE operation which requires a buffer or metal etch stop layer. Typically, such a buffer or metal etch stop layer remains under the dielectric slope after the etching operation. For some optical applications, such as in an EAMR writer, only an optically transparent dielectric material can be used for the buffer or metal etch stop layer, thereby severely limiting the choice of metals and buffer materials that can be used for this purpose. 
     BRIEF SUMMARY OF THE INVENTION 
     The present disclosure addresses this and other problems by providing various methods of forming a dielectric slope by the use of a sacrificial metal etch stop layer. In certain aspects, the use of a sacrificial metal etch stop layer enables formation of a dielectric slope having a slope angle in the range of 30 and 60 degrees and a thickness of up to 1 micron from AlO x  or other RIE-etchable dielectric materials. In some aspects, the sacrificial metal etch stop layer can be subsequently removed by an isotropic wet etch, and a resulting undercut can be refilled by an atomic layer deposition process (e.g., AlOx ALD). 
     In certain aspects, methods of forming an energy assisted magnetic recording (EAMR) writer are provided. The methods comprise providing a structure comprising a bottom cladding layer and a near field transducer (NFT). The methods can further comprise forming a patterned sacrificial layer over the structure. The methods can further comprise depositing a top cladding layer over the patterned sacrificial layer and a remaining region of the structure not covered by the patterned sacrificial layer. The methods can further comprise forming a patterned resist over the top cladding layer. The methods can further comprise performing a first etching operation on the top cladding layer via the patterned resist, whereby a top cladding having a sloped region is formed. The patterned sacrificial layer provides an etch stop for the first etching operation. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a diagram depicting an NFT structure having a sloped top cladding. 
         FIGS. 2A-I  represent a sequence of diagrams illustrating an exemplary fabrication process for an NFT structure with a dielectric slope such as the one depicted of  FIG. 1  according to certain aspects of the present disclosure. 
         FIG. 3  is a flowchart illustrating an exemplary process for producing an NFT structure having a dielectric slope according to certain aspects of the subject disclosure. 
         FIGS. 4A and 4B  are focused ion beam cross section images of NFT structures with dielectric slopes formed by one or more of fabrication methods of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth to provide a full understanding of the present invention. It will be apparent, however, to one ordinarily skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and techniques have not been shown in detail to avoid unnecessarily obscuring the present invention. 
       FIGS. 2A-H  represent a sequence of diagrams illustrating an exemplary fabrication process for an NFT structure with a dielectric slope such as the one depicted of  FIG. 1  according to certain aspects of the present disclosure.  FIG. 2A  is a diagram depicting a structure  200 A comprising a bottom cladding layer  210  and an NFT  220 . The bottom cladding layer  210  is comprised of a dielectric material such as aluminum oxide (AIOx), silicon dioxide (SiO 2 ), gallium nitride (GaN), and silicon oxi-nitride (SiON). In the illustrated example, the NFT  220  is disposed in a groove formed in the bottom cladding layer  210 , and a top surface of the NFT  220  is coplanar with the top surface of the bottom cladding layer  210 . 
       FIG. 2B  is a diagram illustrating a step for forming an intermediate structure  200 B having a set of patterned sacrificial layers  242 ,  244  over the structure  200 A of  FIG. 2A . This step includes but is not limited to: forming a first patterned photoresist (PR 1 )  230  on a first region  212  of the structure  200 A and depositing a set of first patterned sacrificial layers  242 ,  244  on the PR 1   230  and a second region  214  of the structure  200 A, respectively. The set of first patterned sacrificial layers  242 ,  244  have a thickness in the range of about 10 and 40 nm and are comprised of a sacrificial material that can act as an etch stop layer in a first RIE etching operation to be described below. In certain embodiments, the sacrificial material includes a metal selected from the group consisting of Cr, NeFe, and Ru. The metal sacrificial material can be deposited using a known deposition process such as a sputter deposition. 
       FIG. 2C  is a diagram illustrating a step for forming an intermediate structure  200 C having a top cladding layer  250 . This step includes but is not limited to: removing the PR 1   230  and the first patterned sacrificial layer  242  deposited thereon by a lift-off process and depositing a dielectric material comprising the top cladding layer  250  on the exposed first region  212  of the structure  200 A and the remaining first patterned sacrificial layer  244 . In certain embodiments, the dielectric material comprising the top cladding layer  250  is the same as the dielectric material comprising the bottom cladding layer  210 . In other embodiments, the dielectric material comprising the top cladding layer  250  is different from the dielectric material comprising the bottom cladding layer  210 . The dielectric material comprising the top cladding layer  250  is typically deposited using any suitable deposition process such as ion beam deposition, sputter deposition, or chemical vapor deposition. 
       FIG. 2D  is a diagram illustrating a step for forming an intermediate structure  200 D having a second patterned photoresist (PR 2 )  260  over the top cladding layer  250 . This step includes but is not limited to: depositing a photoresist layer over the top cladding layer  250 ; patterning the photoresist layer to obtain a patterned photoresist having a relatively sharp edge (not shown); and reflowing the patterned photoresist at an elevated temperature (e.g., slightly below the glass transition temperature of the photoresist material) for a specific duration to form a sloped resist region  262  in the PR 2   260 . As will be described below with respect to  FIG. 2E , a profile (e.g., thickness and contour of the sloped resist region  262 ) of the PR 2   260  determines a profile (e.g., thickness and slope angle) of a sloped region  254  of a patterned top cladding layer  252  to be formed via the PR 2   260 . 
       FIG. 2E  is a diagram illustrating a step for forming an intermediate structure  200 E having the patterned top cladding layer  252 . The patterned top cladding layer  252  includes the sloped region  254  that has a thickness  257  and makes a slope angle θ  259  with respect to the top surface of the first patterned sacrificial layer  242 . This step includes but is not limited to: performing a first RIE etching operation on the top cladding layer  250  of the structure  200 D ( FIG. 2D ) via the PR 2   260  having the sloped resist region  262 . During the first RIE etching operation, the first patterned sacrificial layer  242  functions as an etch stop layer that protects the underlying NFT  220  and the lower cladding layer  210  from the RIE etching. 
     As indicated above, the profile (e.g., the thickness  257  and the slope angle θ  259 ) of the slopped cladding region  254  is controlled at least in part by the profile (e.g., thickness and contour of the sloped resist region  262 ) of the PR 2   260 . Also as indicated above, the profile of the PR 2  is controlled by a reflow process in which the photoresist having a relatively sharp-angled edge is baked at an elevated temperature for a specified duration. By varying the temperature and the duration of the reflow process, the thickness  257  of the patterned top cladding layer  252  can be controlled between about 0.1 to 1 μm, and the slope angle θ  259  of the patterned top cladding layer  252  can be controlled between about 15 to 90 degrees. 
       FIG. 2F  is a diagram illustrating a step for forming an intermediate structure  200 F arrived after removing the first patterned sacrificial layer  244  from the structure  200 E ( FIG. 2E ). This step includes but is not limited to performing a metal etching operation on the first patterned sacrificial layer  244 . The metal etching operation can include an RIE operation or a wet etching operation suitable for the particular metal (e.g., Cr) used to form the first patterned sacrificial layer  244 . The removal of the first patterned sacrificial layer  242  creates an undercut  260  in a distal end of the patterned top cladding layer  252  as shown in  FIG. 2F . In certain embodiments, the undercut  260  is refilled with a refilling dielectric material by steps illustrated in  FIGS. 2G-H  and described below. 
       FIG. 2G  is a diagram illustrating a step for forming an intermediate structure  200 G having a set of second patterned sacrificial layers  272 ,  274  deposited on the patterned top cladding layer  252  and the second region  214  of the structure  200 A, respectively. This step includes but is not limited to depositing a thin sacrificial material to a thickness in the range of about 1 and 5 nm by an ion beam deposition (IBD) process, for example. The sacrificial material is selected so that it can function as an etch stop layer for a second RIE etching operation to be described below with respect to  FIG. 2I . In certain embodiments, the sacrificial material includes a metal selected from the group consisting of Cr, NeFe, and Ru. 
       FIG. 2H  is a diagram illustrating a step for forming an intermediate structure  200 H having a set of dielectric layers  282 ,  284 ,  286  deposited over and in the structure  200 G ( FIG. 2G ). This step includes but is not limited to depositing a refilling dielectric material to a thickness in the range of about 10 and 40 nm by an atomic layer deposition (ALD) process, for example. The refilling dielectric material is preferably the same dielectric material comprising the patterned top cladding layer  252 . During the ALD deposition process, the undercut  260  ( FIG. 2F ), formed in the patterned top cladding layer  252  by the removal of the first patterned sacrificial layer  244 , is refilled with the refilling dielectric material. 
       FIG. 2I  is a diagram illustrating a step for forming a final NFT structure  2001  including the patterned top cladding layer  252  with undercut  260  refilled with the refilling dielectric material  286 . This step includes but is not limited to removing the refilling dielectric material  282 ,  284  that are not used for refilling the undercut  260 . The removal can be achieved, for example, by an RIE operation suitable for the particular refilling dielectric material (e.g., AlOx) used. The final NFT structure  2001  includes the sloped region  254  having the thickness  257 , the slope angle θ  259 , and a slope pole position offset  205 . During the RIE etching operation, the second sacrificial layer  272 ,  274  functions as an etch stop layer. At least a portion of the second sacrificial layer  272 ,  274  can be removed during the RIE etching operation (“over etch”). The amount of the over etch can determine the slope pole position offset  205  shown in  FIG. 2I . The remaining portion of the second sacrificial layer  272 ,  274  can be subsequently removed by a wet etching operation, for example. 
       FIG. 3  is a flowchart illustrating an exemplary process  300  for fabricating an NFT structure having a dielectric slope according to certain aspects of the subject disclosure. For the sake of clarity only without the intention to limit the scope of the subject disclosure in any way, the process  300  will be described below with references to  FIGS. 2A-I . The process  300  begins at start state  301  and proceeds to operation  310  in which the structure  200 A ( FIG. 2A ) comprising the bottom cladding layer  210  and the NFT  220  is provided. The bottom cladding layer  210  can be a dielectric material selected from the group consisting of aluminum oxide (AlOx), silicon dioxide (SiO 2 ), gallium nitride (GaN), and silicon oxi-nitride (SiON). The NFT  220  can be any metal that can support surface plasmon resonance (SPR) including but limited to Au, Ag, Al and a combination thereof. 
     The process  300  proceeds to operation  320  in which the set of first patterned sacrificial layers  242 ,  244  are formed over the structure  200 A to obtain the intermediate structure  200 B of  FIG. 2B . The operation  320  can include forming the first patterned photoresist (PR 1 )  230  on the first region  212  of the structure  200 A by a known photolithography process and depositing the set of first patterned sacrificial layers  242 ,  244  on the PR 1   230  and the second region  214  of the structure  200 A, respectively. The sacrificial material can be a metal selected from the group consisting of Cr, NeFe, and Ru. The metal sacrificial material is deposited using a known metal deposition process such as sputter deposition. The PR 1   230  and the first patterned sacrificial layer  242  formed thereon are removed by a lift-off process. 
     The process  300  proceeds to operation  330  in which the top cladding layer  250  is deposited over the first region of the structure  200 A and the first patterned sacrificial layer  244  as shown in  FIG. 2C . In certain embodiments, the dielectric material comprising the top cladding layer  250  is the same as the dielectric material comprising the bottom cladding layer  210  such as aluminum oxide (AlOx), silicon dioxide (SiO 2 ), gallium nitride (GaN), and silicon oxi-nitride (SiON). In other embodiments, the dielectric material comprising the top cladding layer is different from the dielectric material comprising the bottom cladding layer. The dielectric material comprising the top cladding layer  250  is typically deposited using sputter deposition process, although any other suitable deposition process such as ion beam deposition and chemical vapor deposition may be used. 
     The process  300  proceeds to operation  340  in which the second patterned photoresist (PR 2 )  260  is formed over the top cladding layer  250  to arrive at the intermediate structure  200 D of  FIG. 2D . As described above with respect to  FIG. 2D , the operation  340  involves depositing a photoresist layer over the top cladding layer  250 ; patterning the photoresist layer to obtain a patterned photoresist having a relatively sharp edge; and reflowing (e.g., baking) the patterned photoresist at an elevated temperature (e.g., slightly below the glass transition temperature of the photoresist material) for a specific duration to form the sloped resist region  262  of the second patterned photoresist (PR 2 )  260 . 
     The process  300  proceeds to operation  350  in which a first etching operation is performed on the top cladding layer  250  via the PR 2   260  to form the patterned top cladding layer  252  that includes the sloped region  254  having the thickness  257  and the slope angle θ  259 . The operation  350  includes performing a first RIE etching operation on the top cladding layer  250  via the PR 2   260  having the sloped resist region  262 . During the first RIE etching operation, the first patterned sacrificial layer  242  functions as an etch stop layer that protects the underlying NFT  220  and the lower cladding layer  210  from the RIE etching. 
     The process  300  proceeds to operation  360  in which a second etching operation is performed to remove the first patterned sacrificial layer  242  as shown in  FIG. 2F . The operation  360  can include performing a metal etching operation. As described above with respect to  FIG. 2F , the metal etching operation can include an RIE operation or a wet etching operation such as Cr RIE or CR wet etching operation. The removal of the first patterned sacrificial layer  242  leaves behind the undercut  260  in a distal end of the patterned top cladding layer  252  as shown in  FIG. 2F . 
     The process  300  proceeds to operation  370  in which the undercut  260  is refilled with a refilling dielectric material by steps described above with to respect to  FIGS. 2G-I  which are not repeated here for the sake of brevity. 
       FIGS. 4A and 4B  are focused ion beam cross section images of NFT structures with dielectric slopes formed by fabrication methods described above. The images demonstrate that the profile (e.g., the thickness and the slope angle) of dielectric slope may be controllably varied by the methods described herein while maintaining a specific slope pole position offset (80 nm in the experimental embodiments). The EL 1  position offset is determined mainly from the etching operation (e.g., AlOx RIE etching) performed to remove residual refilling dielectric materials  282 ,  284  described above with respect to  FIG. 2I . The slope pole position offset can be controlled accurately by the end point provided by the second sacrificial layer  272 . The 80 nm slope pole position offset in the experimental embodiments of  FIGS. 4A and 4B  were achieved with a 10% over etch. Different resist reflow processes (e.g., different baking temperature and duration) can affect the profile of the dielectric slope, but not the slope pole position offset. 
     Various dielectric slope fabrication methods described herein provide distinct advantages over prior art methods. The advantages include but are not limited to: 1) no residue or any contamination left behind; 2) the slope angle being tunable, e.g., from 25 to 50 degrees, to meet design requirements; 3) achieving superior WIW and WTW sigmas; 4) easy integration with other components of EAMR head such as mode converter and NFT heat sink; and 5) adaptability of the approach to fabrication of a single writer which requires a VP 3  pole angle of greater than 35 degrees. 
     The description of the invention is provided to enable any person skilled in the art to practice the various embodiments described herein. While the present invention has been particularly described with reference to the various figures and embodiments, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the invention. 
     There may be many other ways to implement the invention. Various functions and elements described herein may be partitioned differently from those shown without departing from the spirit and scope of the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and generic principles defined herein may be applied to other embodiments. Thus, many changes and modifications may be made to the invention, by one having ordinary skill in the art, without departing from the spirit and scope of the invention. 
     A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Underlined and/or italicized headings and subheadings are used for convenience only, do not limit the invention, and are not referred to in connection with the interpretation of the description of the invention. All structural and functional equivalents to the elements of the various embodiments of the invention described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the invention. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description.