Abstract:
A method and system for providing a magnetic element are described. The method and system include providing a pinned layer, fabricating a metallic spacer layer and oxidizing a portion of the spacer layer in an environment including at least oxygen and a gas inert with respect to the spacer layer to provide an oxide layer. The method and system also include creating a free layer. The oxide layer is between a remaining metallic portion of the spacer layer and the free layer. In one aspect, the system includes a chamber and a gas diffusion apparatus within the chamber. The gas diffusion apparatus includes a plurality of nozzles and defines a plane. The gas exits each of the plurality of nozzles in a cone having an apex angle. The nozzles are directed at a nozzle tilt angle of at least half of the apex angle from the plane and the spacer layer.

Description:
FIELD OF THE INVENTION 
     The present invention relates to magnetic recording technology, and more particularly to a method and system for providing a spin valve sensor that has improved magnetostriction. 
     BACKGROUND OF THE INVENTION 
       FIG. 1  depicts a conventional magnetic element  10 , typically termed a spin valve, that exhibits giant magnetoresistance. The conventional magnetic element  10  includes a seed layer  12 , an antiferromagnetic (AFM) layer  14 , a pinned layer  16 , a conventional spacer layer  24 , a conventional oxide layer  26 , a pinned layer  28 , and a capping layer  34 . The pinned layer  16  is a synthetic pinned layer including two ferromagnetic layers  18  and  22  separated by a nonmagnetic conductive spacer layer  20  that is typically Ru. The conventional oxide layer  26  is an oxide of Cu, formed as described below. The conventional free layer  28  includes a bilayer having a CoFe layer  30  and a NiFe layer  32 . 
       FIG. 2  depicts a conventional method  50  for providing the conventional magnetoresistive element  10 .  FIG. 3  depicts a conventional system  80  for performing at least a portion of the method  50 . The system  80  includes a chamber  82 , a gas inlet  84  and a pump  86 . Also depicted is a wafer  81  on which multiple conventional magnetic elements  10  are fabricated. Referring to  FIGS. 2 and 3 , the seed layer  12  and AFM layer  14  are provided on the wafer  81 , via step  52  and  54 , respectively. The pinned layer  16  is formed, via step  56 . Step  56  typically includes depositing the ferromagnetic layers  18  and  22  as well as the conductive spacer layer  20 . The Cu spacer layer  24  and the conventional oxide layer  26  are fabricated by depositing Cu in step  58  and oxidizing a portion of the Cu in an oxygen atmosphere, via step  60 . During the oxidation step  60 , oxygen gas is let into the chamber  82  via the gas inlet  84 . The flow rate of oxygen gas into the chamber  82  in step  60  is not closely controlled. As a result of the oxidation in step  60 , the conventional oxide layer  26  is formed. The free layer  28  is fabricated in step  62 . The capping layer  34  is provided, via step  64 . 
     Use of the conventional free layer  28  including a CoFe layer  30  and a NiFe layer  32  allows the conventional magnetic element  10  to have a soft magnetic response and improved signal amplitude, which are desirable for magnetic recording applications. This conventional oxide layer  26  is used also to improve the output amplitude for the conventional magnetic element  10 . As a result, the conventional magnetic element  10  may be used in device applications. 
     Although the method  50  and system  80  are used to configure the magnetic element  10  to have certain properties that are desirable for devices, the magnetic element  10  is subject to serious drawbacks. In particular, the magnetic element  10  may be subject to magnetostriction. Use of the conventional oxidation in step  60  may result in an unstable Fe-oxide phase in the free layer  28 . This phase has a large magnetostriction, for example on the order of 3 to 5×10 −7 . A high magnetostriction adversely affect the stability of a read head (not shown) incorporating the conventional magnetic element  10 . Moreover, this magnetostriction is not repeatable over different runs in the apparatus  80 . Consequently, the magnetostriction in the free layer  28  may vary widely between conventional magnetic elements  10 . Thus, two conventional magnetic elements  10  that are formed using the same method may have significantly different properties. Thus, conventional magnetic elements  10  manufactured using the conventional method  50  and the conventional system  80  may have undesirable magnetostriction that can vary from element to element. 
     Accordingly, what is needed is a method and system for improving the magnetostriction of magnetic elements. The present invention addresses such a need. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a method and system for providing a magnetic element. The method and system comprise providing a pinned layer, fabricating a metallic spacer layer and oxidizing a portion of the spacer layer in an environment including at least oxygen and a gas inert with respect to the spacer layer to provide an oxide layer. The method and system also comprise creating a free layer. The oxide layer is between a remaining metallic portion of the spacer layer and the free layer. In one aspect, the system comprises a chamber and a gas diffusion apparatus within the chamber. The gas diffusion apparatus includes a plurality of nozzles and defines a plane. The gas exits each of the plurality of nozzles in a cone having an apex angle. The nozzles are directed at a nozzle tilt angle of at least half of the apex angle from the plane and the spacer layer. In another aspect, the system comprises a gas diffusion means that defines an indirect path to the magnetic element 
     According to the method and system disclosed herein, a magnetic element can be fabricated to have repeatably reduced magnetostriction. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a diagram of a conventional magnetic element. 
         FIG. 2  is a flow chart depicting a conventional method for fabricating a conventional magnetic element. 
         FIG. 3  is a high level diagram of a conventional system for fabricating a conventional magnetic element. 
         FIG. 4  is a diagram of one embodiment of a magnetic element in accordance with an embodiment of the present invention. 
         FIG. 5  is a high-level flow chart in accordance with an embodiment of the present invention. 
         FIG. 6  depicts a top view of a system in accordance with an embodiment of the present invention. 
         FIG. 7  depicts a cross-sectional view of a system in accordance with an embodiment of the present invention. 
         FIG. 8  is a more detailed flow chart in accordance with an embodiment of the present invention. 
         FIG. 9  is a graph depicting magnetostriction versus flow rate for a magnetic element formed in accordance with one embodiment of the present invention. 
         FIG. 10  is a graph depicting magnetostriction versus oxidation time a magnetic element formed according to one embodiment of the present invention. 
         FIG. 11  is a graph depicting magnetostriction versus run number for a magnetic element formed according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 4  depicts a diagram of a magnetic element  100  in accordance with one enabling and exemplary embodiment of the present invention. The magnetic element includes at least a pinned layer  106 , a spacer layer  114 , an oxide layer  116 , and a free layer  118 . The pinned layer  106  is preferably a synthetic pinned layer including ferromagnetic layers  108  and  112  separated by a conductive, nonmagnetic spacer layer  110 . The nonmagnetic spacer layer  110  is preferably composed of Ru and has a thickness that is configured such that the magnetizations of the ferromagnetic layers  108  and  112  are antiferromagnetically aligned. The free layer  118  is preferably a bilayer including a CoFe layer  120  and a NiFe layer  122 . The spacer layer  114  is a conductor, is nonmagnetic, and preferably comprised of Cu. The oxide layer  116  is an oxide of the same conductor used in forming the spacer layer  114 . Furthermore, the oxide layer  116  is formed as described below, by oxidizing a portion of the conductor in an environment including a mixture of oxygen and a gas that is inert with respect to the conductor used in forming the spacer layer  114 . In a preferred embodiment, the oxygen and gas are premixed and are introduced through a gas diffusion apparatus, described below. The magnetic element  100  also preferably includes a seed layer  102  and an AFM layer  104  that is used in pinning the magnetization of the pinned layer  106 . The magnetic element  100  also includes a capping layer  124 . 
       FIG. 5  is a high-level flow chart  150  for fabricating at least a portion of magnetic element  100 , according to one embodiment of the present invention. Referring to  FIGS. 4 and 5 , the pinned layer  106  is provided, via step  152 . In one embodiment, step  152  includes providing the first ferromagnetic layer  108 , the conductive nonmagnetic spacer layer  110 , and the second ferromagnetic layer  112 . The conductive material for the spacer layer  114  is deposited, via step  154 . A portion of the conductive material is oxidized in an environment including oxygen and at least one gas inert with respect to the conductive material used in the spacer layer  114 , via step  156 . Thus, the oxide layer  116  is formed. In a preferred embodiment, only one gas, preferably argon, is mixed with the oxygen. In one embodiment, less than three percent of oxygen is mixed with the gas. In a preferred embodiment, between one half and one and a half percent oxygen is mixed with the gas. In a preferred embodiment, step  156  includes premixing the gas and the oxygen before it is introduced the region surrounding the conductive material. The oxygen and gas can be introduced via an indirect path to the magnetic element  100  being formed. In such an embodiment, the oxygen and gas may be introduced using the gas diffusion apparatus described below. In one embodiment, the flow of the gas and oxygen are also controlled so that any artifacts in the magnetic element  100  of the flow of gas coming from a particular direction are reduced or eliminated. Moreover, the flow rate of oxygen and gas is preferably controlled to have a desired value. The free layer  118  is created, via step  158 . Step  158  preferably includes forming the CoFe layer  120  and the NiFe layer  122 . 
     Exemplary magnetic element  100  can exhibit reduced magnetostriction. In particular, magnetostriction of near zero, or slightly negative can be achieved by controlling the flow rate of the premixture of oxygen and the gas and the oxidation time for the oxide layer  116 . Furthermore, the higher output signal and the soft magnetic properties of the magnetic element  100  can be maintained through the use of the oxide layer  116  and the free layer  118  including a CoFe layer  120  and a NiFe layer  122 . 
       FIGS. 6 and 7  depict top and side, sectional views of a system  200  in accordance with an exemplary embodiment of the present invention for performing at least a portion of the method  150 . The system  200  includes a chamber  210  that is preferably a vacuum chamber, a gas inlet  212 , a pump  214 , and a gas diffusion apparatus  220 . The gas diffusion apparatus  220  has a number of nozzles  222  that are preferably simple holes. Also depicted is a wafer  201  on which multiple magnetic elements  100  are fabricated. The gas diffusion apparatus  220  is depicted in this exemplary embodiment as a ring. However, the gas diffusion apparatus  220  might have another shape depending on various factors including the shape of the chamber  210  and the placement of the substrate  201  with respect to the gas diffusion apparatus  220 . 
     In the embodiment of  FIGS. 6 and 7 , the diffusion apparatus  220  is located around the wafer  201 . The nozzles  222  are preferably configured to define an indirect path for the gas and oxygen from the gas diffusion apparatus  220  to the spacer layer  116  on the wafer  201 . Molecules of oxygen and the gas leaving the gas diffusion apparatus  220  are generally ballistic in nature, traveling in a substantially straight path until undergoing a collision with other molecules, the chamber  210  or another solid body. In one embodiment, the nozzles are angled such that the gas and oxygen exiting the gas diffusion apparatus are directed in a line that is not towards the wafer  201 . Stated differently, the nozzles are configured such that gas exiting the apparatus is directed along an indirect path to the wafer. In such an embodiment, the gas leaving the nozzles  222  is generally confined to the cone  223  depicted in  FIG. 7 . The apex angle of the cone is Φ. For the embodiment depicted in  FIGS. 6 and 7 , the gas diffusion apparatus  220  generally defines a plane  221 . According to one embodiment, the nozzles  222  are directed away from this plane by a nozzle tilt angle, Θ. This nozzle tilt angle has a minimum value of one half of the apex angle of the cone (Φ/2). Such a nozzle tilt angle ensures that the gas molecules are not directed towards the wafer  201 . If the gas diffusion apparatus  220  embodies a ring having simple holes  222  that are located around the ring, the normal  224  to the surface of the hole  222  may be directed at the nozzle tilt angle of at least Φ/2 from the plane of the ring, as shown in  FIG. 7 . Also in such an embodiment, the ring can have a diameter of approximately ten millimeters, while the holes  222  can have a diameter of less than one millimeter. Thus, in this embodiment the gas exiting the holes  222  travels in a direction that is not directly toward the spacer layer  116  on the wafer  201 . 
       FIG. 8  is a more detailed flow chart of a method  160  that accords with one embodiment of the present invention. The method  160  is described in the context of the system  200  and the magnetic element  100  depicted in  FIGS. 5 ,  6 , and  7 . Referring to  FIGS. 5 ,  6 ,  7 , and  8 , the seed layer  102  and AFM layer  104  are provided on the wafer  201 , via step  162  and  164 , respectively. The pinned layer  106  is formed via step  166 . Step  166  preferably includes depositing the ferromagnetic layers  108  and  112  as well as the conductive, nonmagnetic spacer layer  110 . The spacer layer  114  and the conventional oxide layer  116  are fabricated by first depositing a conductor, preferably Cu, via step  168 . The Cu is oxidized in an environment containing oxygen and at least one gas that is inert with respect to the conductor, via step  170 . Preferably, argon gas is used. In addition, the argon and oxygen are preferably premixed. In one embodiment, the mixture includes not more than three percent of oxygen. In a preferred embodiment, not less than one-half and not more than one and one half percent oxygen is used with the gas. Moreover, the gas and the oxygen are preferably introduced using a gas diffusion apparatus such as the gas diffusion apparatus  220 . In a preferred embodiment, the flow rate of oxygen and the gas into the chamber  210  as well as well as the oxidation time are controlled so that the magnetostriction of the magnetic element  100  is close to zero and slightly negative. As a result of the oxidation in step  170 , the oxide layer  116  is formed. The free layer  118  is fabricated via step  172 . In a preferred embodiment, the step  172  includes providing both the CoFe layer  120  and the NiFe layer  122 . The capping layer  124  is provided via step  174 . 
     Magnetostriction of near zero, or slightly negative can be achieved by controlling the flow rate of the premixture of oxygen and the gas and the oxidation time for the oxide layer  116 . At the same time, the higher output signal and the soft magnetic properties of the magnetic element  100  can be maintained through the use of the oxide layer  116  and the free layer  118  including a CoFe layer  120  and a NiFe layer  122 . 
     Examples of the improvements achieved using the method  150  or  160  and system  200  in accordance with an embodiment of the present invention can be seen in  FIGS. 9-11 .  FIGS. 9-11  are graphs depicting the improved magnetostrictive properties of one embodiment of the magnetic element  100 .  FIG. 9  is a graph  250  depicting the magnetostriction vs. flow for one embodiment of a magnetic element  100  having an oxide layer  116  formed using a mixture of argon gas with one percent of oxygen gas. As can be seen, for a flow of between about forty and sixty sccm, the magnetic element  100  has a very low magnetostriction.  FIG. 10  is a graph  252  depicts the magnetostriction versus oxidation time for two flows, twenty sccm and forty sccm, used in forming one embodiment of a magnetic element  100  in accordance with the present invention. As can be determined from the graph  252 , the magnetostriction can be controlled by controlling a combination of the oxidation time and the flow rate of the oxygen and argon gas premixture.  FIG. 11  is a graph  264  depicting the magnetostriction versus the run number for both conventional magnetic elements  10  formed using the conventional method  50  and for the magnetic elements  100  made in accordance with an embodiment of the present invention formed using the method  150  or  160  and the system  200 . As can be seen from the graph  264 , the low magnetostriction is consistently repeated for multiple runs. This is in contrast to magnetic elements  10  formed using the conventional method  50 , for which the magnetostriction varies widely. Thus, using the novel methods  150  and  160  and the novel system  200 , the magnetostriction can be lowered in a repeatable fashion.