Abstract:
In fabricating magnetic heads on a wafer surface, magnetoresistive sensors having two different stripe heights and the same stripe width are formed. Additionally, two different electronic lapping guides (ELGs) having different stripe heights and the same stripe width are also formed. While the design widths and heights of the sensors and ELGs are known, the actually fabricated widths and heights of the sensors and ELGs is unknown, due to the windage in the fabrication process. In the present invention, to determine the actual track width of the sensors, the change in electrical resistance of the sensors and ELGs is experimentally determined during the application of a magnetic field to the sensors and ELGs. Through a mathematical analysis, the actual track width of the fabricated sensors is determined utilizing the design widths and heights of the sensors and ELGs, together with the experimentally determined changes in electrical resistance of the sensors and ELGs.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to methods for determining the track width of magnetoresistive sensors of magnetic heads at the wafer level, and more particularly to the utilization of electrical resistance measurements of the magnetoresistive sensor while applying a magnetic field to determine the track width of the sensor. 
     2. Description of the Prior Art 
     Magnetic heads are fabricated in large quantities upon wafer substrates in an expensive fabrication process involving many steps. The magnetoresistive sensor of the read head portion of the magnetic heads is fabricated early in the overall head fabrication process, and a critical parameter to magnetic head performance is the track width of the fabricated magnetoresistive sensor. Therefore, following the fabrication of the magnetoresistive sensors on the wafer substrate, efforts are undertaken to measure the fabricated track width. Where the fabricated track width of the magnetoresistive sensors is not within product design parameters, time and expense can be saved by halting further fabrication of magnetic heads on such a wafer that has magnetoresistive sensors having an unacceptable track width. 
     Presently, optical inspection methods are utilized to determine the track width of the fabricated magnetoresistive sensors on the wafer. However, efforts to increase the areal data storage density of magnetic disks have resulted in efforts to decrease the track width of the hard disk data tracks, such that more data tracks per inch can be written onto the magnetic disk. In conjunction therewith, the track width of the magnetoresistive sensor has likewise been reduced in order to properly read data from the narrow data tracks, and current magnetoresistive sensors are fabricated with track widths of less than 0.5 microns. At this dimension, current optical scanning methods incur substantial resolution problems in accurately determining the track width of the magnetoresistive sensors upon the wafer surface, and a non-optical method for determining the track width of the magnetoresistive sensors is desirable. 
     The present invention utilizes the electrical and magnetic properties of the magnetoresistive sensors to determine the track width of the magnetoresistive sensors upon the wafer, as will be understood from the detailed description that follows. 
     SUMMARY OF THE INVENTION 
     In fabricating magnetic heads on a wafer surface, magnetoresistive sensors having two different stripe heights and the same stripe width are formed. Additionally, two different electronic lapping guides (ELGs) having different stripe heights and the same stripe width are also formed. While the design widths and heights of the sensors and ELGs are known, the actually fabricated widths and heights of the sensors and ELGs is unknown, due to the windage in the fabrication process. In the present invention, to determine the actual track width of the sensors, the change in electrical resistance of the sensors and ELGs is experimentally determined during the application of a magnetic field to the sensors and ELGs. Through a mathematical analysis, the actual track width of the fabricated sensors is determined utilizing the design widths and heights of the sensors and ELGs, together with the experimentally determined changes in electrical resistance of the sensors and ELGs. 
     It is an advantage of the method for determining the track width of magnetoresistive sensors of the present invention that a non-optical method for determining the actual track width of the magnetoresistive sensors is provided. 
     It is another advantage of the method for determining the track width of magnetoresistive sensors of the present invention that the actual track width of magnetoresistive sensors can be determined where the track width is so narrow that optical track width measuring techniques are inaccurate. 
     It is a further advantage of the method for determining the track width of magnetoresistive sensors of the present invention that electrical measurements of sensors and ELGs can be utilized to determine the actual track width of the sensors. 
     It is yet another advantage of the method for determining the track width of magnetoresistive sensors of the present invention that a rapid, accurate method for determining the actual track width of the sensors is provided. 
     It is yet a further advantage of the method for determining the track width of magnetoresistive sensors of the present invention that the actual track width of the sensors can be rapidly determined at various locations throughout the wafer surface, such that wafer process parameters can be analyzed. 
     These and other features and advantages of the present invention will no doubt become apparent to those skilled in the art upon reviewing the following detailed description which makes references to the several figures of the drawings. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a top plan view of a wafer surface during a magnetic head fabrication process, depicting a plurality of magnetoresistive sensors and electronic lapping guides (ELGs) on the wafer surface; 
     FIG. 2 is an enlarged top plan view of a portion of the wafer surface depicted in FIG. 1; 
     FIG. 3 is a graph depicting the change in electrical resistance of ELGs in relationship to an applied magnetic field; and 
     FIG. 4 is a graph depicting the change in resistance of magnetoresistive sensors in relationship to an applied magnetic field. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Magnetic heads are fabricated in large quantities upon the surface of wafer substrates, and FIG. 1 is a top plan view of a typical prior art wafer depicting a stage in the fabrication of such magnetic heads. As depicted in FIG. 1, the devices that are being fabricated upon the surface  12  of the wafer  10  include a first magnetic head  16 , a second magnetic head  20 , an electronic lapping guide  24  disposed between the heads  16  and  20 , a third magnetic head  28 , a fourth magnetic head  32  and a second ELG  36 . These devices  16 ,  20 ,  24 ,  28 ,  32 ,  36 , form a basic cell  40  that is repeatedly fabricated across the wafer surface  12 . Each of the devices  16 - 36  are next described with the aid of FIG. 2, which is an enlarged view of a single cell  40 . 
     As depicted in FIG. 2, a cell  40  includes the four magnetic head devices  16 ,  20 ,  28  and  32  as well as the two ELG devices  24  and  36 . In the magnetic head fabrication step depicted in FIGS. 1 and 2 a read head sensor element  50  has been fabricated within each magnetic head  16 ,  20 ,  28  and  32 . Significantly, the ELG elements  56  are also composed of magnetoresistive material, and are fabricated in the same fabrication steps in which the magnetoresistive sensor elements  50  are fabricated. Thus the ELG elements  56  have the same layers and layer thicknesses as the sensors  50 , although they have different width and stripe height dimensions as is discussed below. In a subsequent fabrication step electrical leads  60  are fabricated in electrical connection with the magnetoresistive sensor elements  50  of the read heads, and in the same fabrication step, electrical leads  64  are fabricated in electrical connection with the ELG magnetoresistive elements  56 . 
     There are several significant design characteristics of the magnetoresistive elements of the heads and ELGs, including that the track width of all of the magnetoresistive sensors  50  is designed to be identical; the stripe height of the magnetoresistive sensors of magnetic heads  16  and  28  is designed to be identical, whereas the stripe height of the magnetoresistive sensors of heads  20  and  32  is designed to be identical but longer than the stripe height of the magnetoresistive sensor of heads  16  and  28 . Similarly, the width of the ELG magnetoresistive elements  56  of the ELGs  24  and  36  is designed to be identical, whereas the stripe height of the magnetoresistive element of ELG  24  is designed to be larger than the stripe height of the magnetoresistive element of ELG  36 . It is therefore the case that each cell  40  contains two types of heads, such as  16  and  20 , that have sensors  50  having different stripe heights but the same stripe width. In the analysis that follows, the designation S 1  will refer to the sensor that is formed in heads  16  and  28 , and the designation S 2  will refer to the sensor that is formed in heads  20  and  32 . The designation H S1  will refer to the stripe height of sensor S 1 , H S2  will refer to the stripe height of sensor S 2 , and W S  will refer to the width of the sensors S 1  and S 2 , which width is designed to be identical. The cell  40  also contains two types of ELGs  24  and  36 , and in the following analysis ELG  24  shall be referred to as E 1  and ELG  36  shall be referred to as E 2 . The stripe height of the magnetoresistive element of E 1  is designated as H E1 , the stripe height of the MR element of E 2  is designated as H E2  and the width of the MR element of both ELGs E 1  and E 2  is designated as W E , which width is designed to be identical. 
     It is significant to note that all of the structures and features described hereabove with regard to FIGS. 1 and 2 are practiced in prior art wafer fabrication, and are therefore well known to those skilled in the art. A typical stripe height H S1  for the magnetoresistive sensors of heads  16  and  28  is approximately 3 microns, a typical stripe height H S2  for the magnetoresistive sensors of heads  20  and  32  is approximately 5 microns, the stripe height H E1  of the magnetoresistive element  56  of ELG  24  is approximately 10.5 microns and the stripe height H E2  of the magnetoresistive element of ELG  36  is approximately 6.5 microns. The stripe width W E  of the magnetoresistive elements  56  of ELGs  24  and  36  is designed to be equal and approximately 8 microns and the track width W S  of the magnetoresistive sensors  50  of the magnetic heads  16 ,  20 ,  28  and  32  is designed to be equal and approximately 0.5 microns. 
     As indicated hereabove, the present invention is a method for determining the fabricated track width of the magnetoresistive sensor elements  50  subsequent to their fabrication on the wafer surface utilizing the electrical resistance and magnetoresistive properties of the sensor elements. Generally, the electrical resistance R of a fabricated device, such as E 1  (that is, ELG  24 ), can be stated as: 
     
       
           R   E1   =R   L +ρ M ( W   E +δ)/( H   E1   +ΔH   E )  EQ. 1 
       
     
     wherein R L  is the resistance of the leads  64 , ρ M  is the resistivity of the magnetoresistive material, W E  is the designed width of the magnetoresistive element  56 , δ is the windage in the width, H E1  is the stripe height of element E 1  and ΔH E  is the windage in the stripe height. As is understood by those skilled in the art, windage is the term used to describe the difference between the actual dimension of a fabricated device and the design dimension of that device. Thus, for instance, W E  is the design width of the magnetoresistive element  56  while W E +δ is the actual width of the fabricated magnetoresistive element  56 . Similarly, H E1  is the design stripe height of magnetoresistive element  56  of ELG  24  and H E1 +ΔH E  is the fabricated stripe height of the element  56  of ELG  24 . 
     Significantly, if a magnetic field is applied to the ELG  24  and its electrical resistance is simultaneously determined, that resistance is stated as: 
     
       
           R   E1M   =R   L +ρ MM ( W   E +δ)/( H   E1   +ΔH   E )  EQ. 2 
       
     
     wherein R E1M  is the resistance of the element during the application of the magnetic field, R L  is the resistance of the leads (which does not change during the application of the magnetic field) and ρ MM  is the resistivity of the magnetoresistive element  56  which does change upon the application of the magnetic field; the dimensions and windages of the element  56  do not change. 
     Significantly, where the difference in the electrical resistance due to the application of the magnetic field is determined, the resistance of the leads is removed from the analysis according to equation 3, as follows: 
     
       
           ΔR   E1 =Δρ M ( W   E +δ)/( H   E1   +ΔH   E )  EQ. 3 
       
     
     where ΔAR E1  is the change in electrical resistance due to the application of the magnetic field and Δρ M  is the change in the resistivity of the magnetoresistive element due to the application of the magnetic field; that is, Δρ m =ρ m −ρ mm . 
     Utilizing a similar analysis for E 2 , it can be stated that: 
     
       
           ΔR   E2 =Δρ M ( W   E +δ)/( H   E2   +ΔH   E )  EQ. 4 
       
     
     Utilizing equations 3 and 4, the ELG element stripe height windage is determined as: 
     
       
           ΔH   E =( H   E2   ΔR   E2   −H   E1   ΔR   E1 )/(Δ R   E1   −ΔR   E2 )  EQ. 5 
       
     
     and the ELG stripe width windage is reflected in the equation: 
      Δρ M ( W   E +δ)=Δ R   E1 ( H   E1   +ΔH   E ).  EQ. 6 
     Similar equations for the sensors S 1  and S 2  are similarly derived; that is, 
     
       
           ΔR   S1 =Δρ M ( W   S +δ)/( H   S1   ΔH   S )  EQ. 7 
       
     
     
       
           ΔR   S2 =Δρ M ( W   S +δ)/( H   S2   ΔH   S )  EQ. 8 
       
     
     wherein ΔR S1  is the change in resistance of sensor S 1  upon the application of a magnetic field, Δρ M  is the change in the resistivity of the magnetoresistive material upon the application of the magnetic field (which is identical to Δρ M  of the ELGs E 1  and E 2 ), δ is the windage of the track width of the sensors S 1  and S 2 , ΔH S  is the windage in the stripe height of the sensors S 1  and S 2  and ΔR S2  is the change in resistance of sensor S 2  upon the application of a magnetic field thereto. The windage ΔH S  can be determined from equations 7 and 8, as is set forth in equation 9 below: 
     
       
           ΔH   S =( H   S2   ΔR   S2   −H   S1   ΔR   S1 )/( ΔR   S1   −ΔR   S2 )  EQ. 9 
       
     
     and the track width windage δ can be reflected in equation 10, which is derived from equations 7 and 8 as shown below: 
     
       
         Δρ M ( W   S +δ)= ΔR   S1 ( H   S1   +ΔH   S ).  EQ. 10 
       
     
     A reasonable assumption reflected in the analysis set forth above is that the windage δ in the width of the ELG (W E ) is identical to the windage δ in the width W S  of the sensors S 1  and S 2 . 
     As stated above, it is the goal of the present invention to determine the actual track width of the sensors S 1  and S 2 , that is, to determine the value W S +δ, where W S  is the design track width. Thus, it is necessary to determine δ, which may be accomplished by determining the ratio β, where: 
      β=Δρ M ( W   S +δ)/Δρ M ( W   E +δ).  EQ. 11 
     Therefore, utilizing equations 6 and 10 it is derived that: 
     
       
         β=Δ R   S1 ( H   S1   +ΔH   S )/Δ R   E1 ( H   E1   +ΔH   E )  EQ. 12 
       
     
     Additionally, equation 11 can be solved for δ which yields: 
     
       
         δ=( W   S   −βW   E )/(β−1)  EQ. 13 
       
     
     And, as indicated above, the actual track width TW S  of the magnetoresistive sensors S 1  and S 2  of the heads  16 ,  20 ,  28  and  32  is determined as: 
     
       
           TW   S   =W   S +δ  EQ. 14 
       
     
     From the preceding equations it is seen that δ is determined from equation 13 by determining the value of β because W S  and W E  are known design values. The value of β is determined from equation 12 by determining ΔR S1  and ΔR E1  which are experimentally determined values, wherein H S1  and H E1  are known design parameters, and wherein ΔH S  and ΔH E  are determined from equations 9 and 5. Referring to equation 9, it is seen that ΔH S  is a function of the experimental values of ΔR S2  and ΔR S1 , wherein H S2  and H S1  are known design parameters. Likewise, from equation 5, ΔH E  is determined from the experimental values of ΔR E2  and ΔR E1 , wherein H E2  and H E1  are known design parameters. 
     Therefore, where the design parameters of the sensors S 1  and S 2  and the ELGs E 1  and E 2  are known, the value of δ is experimentally determinable by measuring the change in resistance of the elements S 1 , S 2 , E 1  and E 2  upon the application of a magnetic field; that is, by the values ΔR S1 , ΔR S2 , ΔR E1  and ΔR E2 . 
     Therefore, with reference to FIG. 2, electrical probe tips of a testing device are applied to electrical leads, such as leads  64  of the ELG E 1 , and a magnetic field is swept across the magnetoresistive element  56 , and the change in resistance of the element E 1  is determined experimentally. In a similar manner, the change in resistance of ELG element E 2  and the sensors S 1  and S 2  is determined. By way of example, FIG. 3 is a graphical depiction of the change in resistance of the ELG elements E 1  and E 2  as a magnetic field is applied. Curve  74  is associated with the shorter stripe ELG E 2 , and curve  70  is associated with the longer stripe ELG E 1 . Similarly, FIG. 4 is a graphical representation of the change in resistance of the magnetoresistive sensors of the four heads  16 ,  20 ,  28  and  32  within a cell  40 . Curves  84  and  86  reflect the change in resistance of sensor S 1 , which is the shorter stripe magnetoresistive sensor of heads  16  and  28  within cell  40 , and curves  80  and  82  represent the change in resistance of the longer stripe sensor S 2  as included in heads  20  and  32  of cell  40 . 
     It is therefore to be understood that the actual track width TW S  of the sensors S 1  and S 2  is determined from equation  13  as the design track width W S  plus the windage δ, where δ is determined from known design parameters and the experimentally measured change in resistance of the sensor elements S 1 , S 2 , E 1  and E 2  of a cell  40  as described above. Furthermore, the actual track width TW S  can be determined for the various cells  40  from differing portions of the surface of the wafer. These results can be utilized to determine whether magnetic heads that are being fabricated upon the wafer surface are within design guidelines, as well as to provide information regarding variations in process parameters across the surface of the wafer. 
     While the present invention has been shown and described with regard to certain preferred embodiments, it is to be understood that those skilled in the art will no doubt devise certain alterations and modifications in form and detail that nevertheless include the true spirit and scope of the invention. It is therefore intended that the following claims cover all such alterations and modifications, in form and detail, that nevertheless include the true spirit and scope of the invention.