Abstract:
Three structures, and processes for manufacturing them, that improve the performance of a TAMR feature in a magnetic write head are disclosed. This improvement is achieved by making the separation between the edge plasmon generator and the plasmon shield less than the separation between the edge plasmon generator and the optical wave-guide.

Description:
RELATED PATENT APPLICATIONS 
     U.S. Pat. No. 8,036,069 and US Patent Pub. No. 2010/0315735 are related to this application, are owned by a common Assignee, and are herein incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The disclosed structures and processes relate to ways to improve the performance of a TAMR feature by making the separation between the edge plasmon generator and the plasmon shield less than the separation between the edge plasmon generator and the optical wave-guide. 
     BACKGROUND 
     Thermally assisted magnetic recording (TAMR) is expected to be one of the future generation magnetic recording technologies that will enable recording at 1˜10 Tb/inch 2  data density. TAMR converts optical power into localized heating of the magnetic recording medium to temporarily reduce the field needed to switch the magnetizations of the medium grains. With a sharp temperature gradient alone, or together with the magnetic field gradient when both gradients are aligned correctly, data storage density can be further improved over the current state-of-the-art magnetic recording technology. 
     A TAMR head usually comprises, in addition to its conventional magnetic recording structure, an optical wave-guide (WG) and a Plasmon generator (PG). The WG serves to guide external laser light to the PG, where the optical mode is coupled to the Plasmon mode of the PG. After being converted to plasmon mode the optical energy then concentrated at the location where heating of the medium is required. When the heating spot is correctly aligned relative to the write field of the magnetic recording structure, TAMR is achieved. 
     We refer now to the prior art air bearing surface (ABS) view shown in  FIG. 1   a . This illustrates a TAMR head located at the end of main pole  10 , integrated with Edge Plasmon generator (EPG)  15  and having, in cross-section, triangular shape  16 . This shaped edge is placed in the vicinity of optical waveguide  11  where it supports the very confined Edge Plasmon (EP) mode. The optical energy in WG  11  is efficiently transformed to edge plasmon mode through evanescent coupling and its energy is directed towards the ABS. The local confinement of the edge plasmon mode is determined by the angle and radius of 16&#39;s triangular corner, by the noble metal from which the EPG is formed, as well as by the dielectric material that surrounds tip  16 . 
     Referring next to  FIG. 1   b , for a 25 nm tip radius, the size of optical spot  18  in recording medium  9  is about 100 nm across its half-maximum intensity area. By placing plasmon shield  12  a small dielectric gap distance from EPG  15 , optical spot  18  can be further reduced in size since, in the presence of plasmon shield  12 , the spot size is mainly determined by PSG which is gap distance  13  between edge plasmon generator  15  and plasmon shield  12 . For example, a 50 nm optical spot size can be achieved if this gap distance is less than 40 nm. 
     Plasmon shield  12  is placed at the front of wave-guide  11 . Using the current (prior art) process, the top surface of plasmon shield  12  is at the same level as the top surface of WG  11  or even slightly lower than the top surface of WG  11  due to different CMP rates for the Au of layer  15  and the Ta 2 O 5  used for WG  11 . 
     When PSG  13  is scaled down, WEG  19  (the gap between WG  11  and EPG  15 ) will also be reduced. One consequence of a reduced WEG is poorer optical coupling efficiency between WG  11  and EPG  15 , so some optical power will be wasted as a result. This coupling efficiency cannot be improved by fine turning the length of EPG  15  when WEG  19  is less than 25 nm. Thus, to simultaneously achieve both good optical efficiency and a small optical spot, it is important to have both a large fixed WEG as well as a small PSG. 
     SUMMARY 
     It has been an object of at least one embodiment of the present disclosure to simultaneously achieve both good optical efficiency and a small optical spot in a TAMR magnetic write head. 
     Another object of at least one embodiment of the present disclosure has been to devise a structure in which the gap between the plasmon shield and the plasmon generator is smaller than the gap between the waveguide and the plasmon generator. 
     Still another object of at least one embodiment of the present disclosure has been to provide a process for manufacturing said structure 
     These objects have been achieved in three different ways: 
     In the first structure that is disclosed, a triangular indentation is formed in the top surface of the wave-guide so WEG becomes the distance between the floor of this indentation and the edge of the plasmon generator. Since the top surface of the plasmon shield is coplanar with the top surface of the wave-guide, it follows that PSG is smaller than WEG. 
     In the second structure that is disclosed, the sharp lower edge of the plasmon generator comprises two seamlessly connected parts. The first part is directly above the plasmon shield and is also closer to the plane of the plasmon shield&#39;s top surface than the second part is. 
     In the third structure that is disclosed, there is a ‘dummy’ a layer of dielectric material on the optical wave-guide&#39;s top surface with the plasmon shield located between the dummy layer and the ABS whereby any plasmon radiation propagating towards the ABS through the dummy layer will be blocked; 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a  and  1   b  show two views of a TAMR feature of the prior art. 
         FIGS. 2   a - 2   c  illustrate a first embodiment of the disclosed structure 
         FIGS. 3   a - 8   c  describe a process for manufacturing this first embodiment of the disclosed structure 
         FIG. 9  shows a second embodiment of the disclosed structure 
         FIGS. 10   a - 13   b  describe a process for manufacturing this second embodiment of the disclosed structure 
         FIGS. 14   a - 14   c  show a third embodiment of the disclosed structure 
         FIGS. 15-17  describe a process for manufacturing this third embodiment of the disclosed structure 
     
    
    
     DETAILED DESCRIPTION 
     A first embodiment of the disclosed methodology is shown in  FIG. 2   a  that is a cross-sectional view along a plane (see  FIG. 2   b ) formed parallel to the ABS and located behind plasmon shield  12 . A first novel feature is how to increase WEG  21 . This is achieved by forming indentation  22  which is a trench of triangular cross-section that extends downwards from the top surface of optical wave-guide  11 , starting at plasma plasmon shield (PS)  12 , and, as seen in the cross-section in  FIG. 2   b , extending away therefrom for a sufficient distance to a back end  11   b  to no longer be directly below edge plasmon generator  15 . EPG  15  may be made of Au, Ag, Cu, Ru, Ta, Co or alloys thereof. The thickness of PS  12  is 50-200 nm, and its top surface is aligned with the top surface of WG  11 . The indentation can also be in other shapes, for example, rectangular or half circular. According to one embodiment, WG  11  has a refractive index from 1.9 to 3.9 and is made of tantalum oxide, SiON, TaSiOx, or Si. 
     The second novel feature is how to simultaneously decrease PSG  13 . This is achieved by allowing PS  12  to extend above the floor of indentation  22 , as shown in  FIG. 2   b . Also apparent from the view given in  FIG. 2   b  is that WEG  21 , the physical gap between WG  11  and EPG  15 , is larger than PSG  13  (the gap between PS  12  and EPG  15 ). WEG  21  is kept in the 20-30 nm range to ensure efficient WG to EPG coupling. 
     It can be seen in the ABS view in  FIG. 2   c  that plasmon shield  12  is slightly wider than wave-guide  11 . If so desired, PS  12  could even be made wide enough to connect with a suitably located heat sink. 
     The process to manufacture the first embodiment is as follows: 
     The process starts, as shown in  FIGS. 3   a  and  3   b , with the provision of optical wave-guide  11  onto whose top surface is deposited layer  31  of a low dielectric constant material such as alumina. Photoresist mask  32  is then formed on layer  31 , following which, as shown in  FIGS. 4   a  and  4   b , triangular indentation  22  is etched all the way through layer  31  as well as an additional short distance (between about 5 and 40 nm) into wave-guide  11 . 
     Control of the latter depth is achieved through over-etching layer  31  using an angled Ion Beam Etching (IBE) for which tantala has a faster etch rate than alumina. Note that  FIG. 4   a  represents a cross-section made through the floor (i.e. apex) of indentation  22  so dielectric layer  31  and photoresist mask  32  do not appear in  FIG. 4   a  even though they are still present in the structure at this point. 
     Following the removal of mask  32  and dielectric layer  31 , the structure has the appearance shown in  FIGS. 5   a  and  5   b.    
     Referring next to  FIGS. 6   a  and  6   b , photoresist mask  62  is laid down to define the future location of trench  61  as extending inwards away from the ABS, following which trench  61  is formed by etching wave-guide  11  to a depth of 20 to 500 nm and then leaving photoresist layer in place. 
     Then, as shown in  FIG. 7   a , trench  61  is just filled with gold (or other suitable metal (such as Ag, Cu, Ru, Zr, Cr, Ta, Ni, Co, and their alloys), thereby forming plasmon shield  12 , and photoresist  62  is lifted off to give the structure the appearance shown in  FIGS. 7   a  and  7   b . Finally, as illustrated in  FIGS. 8   a - 8   c , layer  24  of alumina is deposited to a thickness that exceeds the height of PS  12  above wave-guide  11 &#39;s top surface, thereby determining values for both WEG and PSG (designated as gaps  21  and  13 , respectively, in earlier figures).  FIG. 8   c  is an ABS view of the completed structure before processing the EPG. 
     In a second embodiment, in the region directly over the plasmon shield, the EPG lower edge is selectively brought closer to the plasmon shield, as shown in  FIG. 9  while the remainder of the EPG&#39;s bottom surface is left at its normal level of higher than the tip portion, whereby WEG  21  becomes larger than PSG  13 . The top surface of PS  12  is at the same level as the top surface of the WG in this case. 
     Referring now to  FIGS. 10   a  and  10   b  the process for the second embodiment begins with the provision of optical wave-guide  11  Then, at wave-guide  11 &#39;s ABS end, plasmon shield  12  is formed, as described earlier for the first embodiment (see  FIGS. 6   a  to  8   b ) but with the CMP step continued until the top surface of PS  12  is coplanar with the top surface of WG  11 . 
     Following the deposition of alumina layer  118  on the top surface of wave-guide  11 , photoresist mask  116  is formed on layer  118  and cavity  112  is formed by under-etching layer  118  with mask  116  so that the floor of cavity  112  is located a distance above the top surface of wave-guide  11 , as shown in  FIG. 11   b.    
     Referring next to  FIGS. 12   a  and  12   b , after protecting the area immediately above PS  12  with photoresist mask  126 , first gold layer  121  is laid down to a thickness in the range of from 20 to 80 nm Following the removal of photoresist  126 , second gold layer  123  is laid down to a thickness in the range of from 5 to 50 nm, giving the structure the appearance shown in  FIGS. 9 ,  13   a , and  13   b.    
     In a third embodiment, a blocked layer is used to reduce PSG while leaving WEG unchanged. This is illustrated in  FIGS. 14   a - c .  FIG. 14   a  shows dielectric layer  141  inside which plasmon radiation will have been induced by edge plasmon generator  15  (see  FIG. 1 ) but which is unable to reach the recording medium since it is blocked by PS  12 .  FIG. 14   b  is a cross-section through WG  11  made some distance away from PS  12  while  FIG. 14   c  is a cross-section through WG  11  made at the intersection of PS  12  with blocked layer  141 . Note that blocked layer  141  is made of a low dielectric constant material such as silica or alumina, and its refractive index should be lower than that of WG  11 . 
     As illustrated in  FIG. 15 , the process for manufacturing the blocked layer begins with the deposition of layer  141  on the top surface of WG  11 . Layer  141  should have a thickness in a range of 5 to 25 nm with a thickness in a range of 10 to 20 nm being preferred. Next, as shown in  FIG. 16 , trench  161  is formed at the ABS end of WG  11 . Finally, following the deposition of sufficient gold to fill trench  161 , the structure is planarized to remove all gold outside trench  161 , giving the completed structure illustrated in  FIG. 17  which shows the top surface of PS  12  to be at the same level as the top surface of blocked layer  141 . 
     The advantages of the reduced Plasmon shield gap structures and processes include:
         1. The ability to reduce and shape the optical spot, thereby reducing the size of the thermal spot in the recording medium, resulting in a higher thermal gradient which achieves narrower track, higher BPI and greater areal density;   2. A larger wave-guide to Plasmon Generator gap together with a smaller Plasmon Shield to Plasmon Generator gap whereby there is minimal loss in optical efficiency;   3. The processes that have been disclosed for the manufacture these structures are simple to achieve as well as being suitable for mass production.