Abstract:
There is provided a method for measuring positions of a plurality of thin film magnetic head elements formed in a line on a bar optically, efficiently, quickly and with high accuracy. The method includes the steps of: in order that the measured result is fed back to the manufacturing step to stabilize the manufacturing process of the thin film magnetic head elements, obtaining the estimated quantity of positions of samples in the bar from the elements, the amount of deviation in position of the next element, and the distance between the elements, and estimating them by a primary approximate linear or several-order approximate curve, moving the estimated amount and the distance between the elements simultaneously, and photo-converting an image formed by a lens optical system to convert it to an image signal; and computing dimensions, wherein the conversion step is carried out immediately after movement of the next element and is continuously repeated, and the computing step is processed in parallel with the step for converting to the image signal. Thereby, it is possible to measure an image with high precision, high stabilization and high resolution to enable measurement with high accuracy of a narrow track width of GMR head.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a manufacturing method for a thin film magnetic head, an inspecting method for a thin film magnetic head, and an apparatus therefor, and particularly to a manufacturing method for a thin film magnetic head, an inspecting method for a thin film magnetic head, and an apparatus therefor including an inspecting step for measuring with high accuracy dimensions of track width of a magnetic recording element in the form of a bar formed from a plurality of elements cut out of a substrate.  
           [0002]    Recently, smaller size and larger capacity magnetic recording disk drives have been developed, and at present, small magnetic recording disk drives using a disk having the sizes of 3.5 inch and 2.5 inch have occupied the mainstream. In such a small disk drive as described above, since a rotational speed of the disk is low, where a magnetic induction type magnetic head in which a read output depends on the disk speed is used, the lowering of the read output poses a problem. On the other hand, in a magneto resistive head (hereinafter called GMR head) using a magneto resistive element (hereinafter called GMR element, GMR: Giant Magento-resistive), since the read output does not depend on the disk speed, even the small magnetic recording disk drive whose rotational speed is low is able to obtain a high read output. Further, to provide the magnetic recording disk drive having higher recording density, it is necessary to have a narrower track which narrows the track width of the magnetic head. The GMR head is advantageous in that even in case of narrower track, a high read output is obtained as compared with the magnetic induction type magnetic head. It is contemplated from the foregoing that the GMR head is a magnetic head suitable for smaller size and larger capacity.  
           [0003]    So, there has been proposed a laminated thin film head using the GMR head as a read-back head, and a magnetic induction type magnetic head as a recording head, respectively.  
           [0004]    On the other hand, in order to realize higher recording density, in case of face recording density of 20 G bit/inch 2  of a magnetic disk, it is necessary that track width be about 0.7 to 0.5 micro meter (μm), and in addition, with respect to the accuracy, about ±0.07 to 0.05 micro meter (μm) is required.  
           [0005]    To exceed 60 G bit/inch 2  for higher density, it is necessary that track width be 0.3 micro meter (μm) or less, and with respect to the accuracy, about ±0.03 micro meter (μm) is expected to be required. With the narrower track as described, it is has been difficult to inspect a track width in the process of manufacturing thin film magnetic heads.  
           [0006]    First, the manufacturing method for the GMR head which is a thin film magnetic head will be described with reference to FIGS.  2 ( a ) to ( c ). FIG. 2( a ) is a top view of a wafer formed with the GMR element. The GMR element is formed by a thin film process represented by sputtering, exposure, ion milling and the like, in accordance with the method not shown. In the embodiment shown in FIG. 2, elements are patterned by a batch exposure, as one unit U. An element formed by the thin film process is cut in the rectangular shape and separated out of a wafer  1 . FIG. 2( b ) shows a group of elements in the rectangular shape (hereinafter referred to as a bar  2 ) separated out of the wafer. A single bar  2  is formed with a plurality of, for example, 30 GMR elements  101  (hereinafter referred to as an element  101 ). FIG. 2( c ) shows a slider  100  having the element  101  cut out of the bar  2 . The slider  100  is incorporated into the magnetic recording disk drive by the method not shown. The typical method for forming the GMR head is described in Japanese Patent Laid-open No. Hei 8-241504.  
           [0007]    [0007]FIG. 3 is a sectional perspective view of the GMR head. In the figure, this side of the figure is a floating surface  102  of the element  101  with respect to the disk surface (not shown). An upper magnetic shield film  103  and a lower magnetic shield film  104  perform the action for enhancing signal resolving power. A signal from a magnetic disk (not shown) close to the floating surface  102  is read by a pair of signal detecting electrodes  105 . A spacing between the signal detecting electrodes  105  is a read track  106 , whose width is a read track width T WR . A write coil  107  is formed on the upper magnetic shield film  10 , and a write head  108  is formed above the write coil  107 . An extreme end of the write head  108  is a write track  109  whose width is a write track width T WW . These track widths are observed from the floating surface  102  (the arrow in the figure).  
           [0008]    FIGS.  4 ( a ) to  4 ( c ) show the detail of the bar  2  after cut. FIG. 4( a ) is a view as viewed form the side for carrying out element forming by the film process, that is, from the upper surface, and FIG. 4( b ) is a view as viewed from the arrow of FIG. 4( a ), that is, from the floating surface side. Various dimensions of the element  101  are measured from this direction. In FIG. 4( b ), X-direction is the direction in which the elements  10  are continuously arranged, and Y-direction is the direction at right angle thereto. As described above, the bar  2  is in the rectangular shape; for example, in case of length: 50 mm, height: 15 mm, and thickness: 0.5 mm, the bar  2  is, generally, flexed like a bow as shown in FIG. 4( b ) although different depending on the conditions at the time of cutting, and the flexing amount S thereof is often scores of micro meters (μm) in the central part.  
           [0009]    [0009]FIG. 5 shows the procedure for measuring in accordance with the conventional measuring method. First, the bar  2  is set to observation means such as a microscope in a direction (the floating surface side) of FIG. 4( b ) to observe the element  101 . First, an image of a first element is obtained, and various element dimensions of the element  101  are computed. In case of not a final element, the bar  2  is moved by 1 pitch in the direction X to obtain an image of a next element. Where an element can be measured, element dimensions are computed. This operation is repeated to find all the element dimensions. However, since the bar  2  is flexed like a bow, it is sometimes that the element is not within the detecting range when an image is obtained merely by movement in the direction X, making it impossible to measure the element dimensions. In this case, it is necessary that to enable measurement of the element dimensions, the element is moved in a direction in which the bar  2  is flexed, that is, in the direction Y so that the element is within the detecting screen. Further, where a nanometer order is detected, an aberration of an optical system need also be taken into consideration. To this end, it is necessary accurately locate an element in the center of a field of view of an objective lens for which an optical aberration is best corrected.  
           [0010]    This will be explained in more detail with reference to FIGS.  6 ( a ) to ( c ). FIG. 6( a ) is an image in which a first element is detected. Since it is necessary for detecting of element dimensions with high accuracy to detect the element  10  in an enlarged scale, a field of detecting of an image is about 20 micro meters (μm). The height of the element  101  is approximately 10 micro meters (μm). For example, the bar  2  is set in the direction Y so as to assume a height Y 1  position within the measuring range  111 . The bar  2  is stepwise moved in the direction X in order to detect next element as previously mentioned. FIG. 6( b ) shows an image of an element in the vicinity of the center. Within the measuring range  111 , the element  101  is detected downward due to the flexure of the bar  2  to assume a height Y 2 . Since in this state, the element  101  is not within the detecting range  111 , it is impossible to measure element dimensions. Therefore, the bar  2  is moved in the direction Y, and moved so that the element  101  assumes a height Y 3  within the measuring range  111 , as shown in (c). As described above, in the conventional observing system, the element  101  is outside the detecting range due to the flexure of the bar  2  merely by the movement in the direction X, and therefore, observing means such as the bar  2  or a microscope is moved to a sensible position to compute element dimensions, thus taking two times or more for obtaining an image and for the computing time.  
           [0011]    As a method for measuring element dimensions, there is a method that uses an optical microscope or a photo electric conversion sensor, and multiplies an area obtained from brightness data of a signal obtained from the photo electric conversion sensor by a suitable coefficient to obtain a desired width, as described in Japanese Patent Laid-Open No. Hei 10-82616.  
           [0012]    [0012]FIG. 7 shows the procedure of element dimensions computing processing in the conventional apparatus. A focal position of observing means such as a microscope is adjusted to a camera, after which the camera is exposed to detect an image. The image is subjected to photo electric conversion and transferred to a memory. As described above, an element position is confirmed; and if element dimensions can be detected, various dimensions are computed. The result is displayed, after which the bar is moved in the direction X to detect a next element. This operation is shown as the measuring time of one element  500 . As described above, where element dimensions cannot be detected in the vicinity of the central part of the bar, the bar is moved in the direction Y and a focal point of an optical system is adjusted again to a camera, after which an image of an element is detected. This operation is repetitively carried out until dimensions of an element can be detected. This operating time  501  is added to the measuring time of 1 element. When this computing processing flow is applied, each processing is performed in series, and therefore the measuring time is prolonged, failing to perform efficient measurement. Further, reduction in measuring time becomes difficult, and when exposure time of a camera is changed due to the change in light quantity, the measuring time is to change, failing to perform stabilized measurement.  
           [0013]    In the method described in the prior art, where a bar formed with a plurality of elements is measured continuously, a position of an element becomes deviated vertically and is forced out of the detecting range, thus making it necessary to grasp the position of an element on all such occasions to correct it. To measure all the elements, several detectings per element are necessary, thus increasing the time required for the measurement of elements. Further, since movement of a bar, locating and the like are repeated, the detecting reproducing properties are also lowered. Further, since computing processing of elements is processed in series, the detecting time is prolonged, failing to perform efficient measurement.  
         SUMMARY OF THE INVENTION  
         [0014]    According to the embodiments of the present invention described below, there can be provided a manufacturing method for a thin film magnetic head, an inspecting method for a thin film magnetic head, and an apparatus therefor including an inspecting step for measuring, efficiently, stably, and with high accuracy, dimensions of a track width of a magnetic recording element in the form of a bar formed by a plurality of elements cut out of a substrate.  
           [0015]    That is, according to the present invention, the manufacturing method for a thin film magnetic head as described hereinafter is provided.  
           [0016]    First, the invention disclosed in the embodiment is characterized by a manufacturing method for a thin film magnetic head comprising the steps of: forming a plurality of thin film patterns corresponding to a plurality of thin film magnetic head elements on a substrate; cutting the substrate formed with the plurality of thin film patterns to cut out a group of thin film magnetic head elements; measuring dimensions of a predetermined part of the thin film patterns for the group of thin film magnetic head elements separated; selecting a group of good thin film magnetic head elements on the basis of the result of measurement; and feeding the group of good thin film magnetic head elements selected to the next step wherein in the step of measuring dimensions, the thin film patterns are image-picked up, and the dimensions are measured from images of the thin film patterns obtained by image-picking up.  
           [0017]    Preferably, in the inspecting step, dimensions corresponding to a track width of the thin film magnetic head are measured, the measurement of dimensions corresponding to the track width is carried out for all the thin film magnetic head elements constituting the group of thin film magnetic head elements, and the group of thin film magnetic head elements in which the dimensions corresponding to the track width are within the predetermined range is fed as the good product to the next step.  
           [0018]    Preferably, in the inspecting step, dimensions corresponding to a track width of the thin film magnetic head are measured, and the measurement of dimensions corresponding to the track width is sequentially carried out for all the thin film magnetic elements constituting the group of thin film magnetic head elements.  
           [0019]    Preferably, when the measurement of dimensions corresponding to the track width is sequentially carried out for all the thin film magnetic head elements constituting the group of thin film magnetic head elements, a position of a thin film magnetic head element to be measured next is estimated from positional information of the thin film magnetic head element measured previously.  
           [0020]    The present invention further is characterized by a manufacturing method for a thin film magnetic head comprising the steps of: forming a plurality of thin film patterns corresponding to a plurality of thin film magnetic head elements on a substrate; cutting the substrate formed with the plurality of thin film patterns; image-picking up a section of the substrate cut to obtain an image of the section of the substrate including the plurality of thin film patterns; and measuring dimensions of a predetermined part of the thin film patterns from the image of a section of the substrate including the plurality of thin film patterns.  
           [0021]    Preferably, in the step of measuring dimensions of a predetermined part of the thin film patterns, dimensions corresponding to a track width of the thin film magnetic head are measured, and the measurement of dimensions corresponding to the track width is sequentially carried out for all the thin film patterns on the substrate cut.  
           [0022]    Preferably, when the measurement of dimensions corresponding to the track width is sequentially carried out for all the thin film patterns on the substrate cut, a position of a thin film pattern to be measured next is estimated from positional information of the thin film pattern measured previously.  
           [0023]    Preferably, the result of the measurement of dimensions of a predetermined part of the thin film patterns is recorded on a schematic diagram for the thin film patterns on the substrate.  
           [0024]    Furthermore, the present invention is characterized by an inspecting apparatus for a thin film magnetic head comprising: an illumination optical system for irradiating with illumination light a group of thin film magnetic head elements separated by cutting a substrate formed with a plurality of thin film patterns corresponding to a plurality of thin film magnetic head elements; image obtaining means for image-picking up the group of thin film magnetic head elements irradiated with illumination light by the illumination optical system to obtain an image of the group of thin film magnetic head elements; dimensions measuring means for processing the image of the group of thin film magnetic head elements obtained by the image obtaining means to sequentially measure dimensions of a predetermined part of the plurality of thin film patterns of the group of thin film magnetic head elements; and selection means for selecting a group of good thin film magnetic head elements on the basis of the dimensions of the predetermined part of the thin film patterns measured by the dimensions measuring means.  
           [0025]    Preferably, the image obtaining means includes an objective lens for forming an image of the group of thin film magnetic head elements, and further includes a focusing optical system for focusing the objective lens into the thin film magnetic head.  
           [0026]    Preferably, the illumination optical system irradiates the group of thin film magnetic head elements with either visible light, ultraviolet light or deep ultraviolet light, as illumination light.  
           [0027]    Since the present invention is constituted as described above, in the production line in the GMR head forming process, high accuracy and short time measurement of a track width in the state formed to be bar-like become enabled, and it is possible to monitor the circumstances of the element forming steps in the in-process. Further, mapping in the wafer state is possible, and inconvenience of the process in the element step is found early to improve a process parameter whereby occurrence of inferior goods can be reduced, and high yield can be maintained.  
           [0028]    These and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]    [0029]FIG. 1 is a front view showing the schematic constitution of a GMR head narrow track width measuring device (hereinafter abbreviated as a track width measuring device) according to a first embodiment of the present invention;  
         [0030]    [0030]FIG. 2( a ) is a plan view of a wafer showing the forming state of a bar on the wafer,  
         [0031]    [0031]FIG. 2( b ) is a plan view of a bar-like head, and  
         [0032]    [0032]FIG. 2( c ) is a plan view of the head;  
         [0033]    [0033]FIG. 3 is a perspective view of a typical GMR head.  
         [0034]    [0034]FIG. 4( a ) is a plan view of a bar-like head, and  
         [0035]    [0035]FIG. 4( b ) is a side view of the bar-like head;  
         [0036]    [0036]FIG. 5 is a sequence view showing an inspecting method according to a conventional system;  
         [0037]    [0037]FIG. 6 is a view showing one embodiment of a detected image of a head front according to a conventional system.  
         [0038]    [0038]FIG. 7 is a view showing one embodiment of inspecting time according to a conventional system;  
         [0039]    FIGS.  8 ( a ) to ( c ) are respectively schematic front views of an optical system showing a focusing method of the present invention, and  
         [0040]    [0040]FIG. 8( d ) is a graph showing a relationship between a bar position and an output of an optical system;  
         [0041]    [0041]FIG. 9 is a graph showing the spectral transmittance characteristics of a dichroic mirror according to the present invention;  
         [0042]    [0042]FIG. 10( a ) is a side view of a bar showing one embodiment of a flexed shape of a bar after cut, and  
         [0043]    [0043]FIG. 10( b ) is a view showing a relationship between a position of an element on the bar and a position in a direction Y;  
         [0044]    FIGS.  11 ( a ) to  11 ( c ) are respectively detected images of a bar side according to the system of the present invention, and  
         [0045]    [0045]FIG. 11( d ) is a view showing a method for presuming an amount of flexure of a bar;  
         [0046]    [0046]FIG. 12( a ) is a detected image of a bar side, and FIG. 12( b ) is a view showing a differential waveform taken on A-A section;  
         [0047]    [0047]FIG. 13 is a view showing one embodiment of the measuring procedure according to the present invention;  
         [0048]    [0048]FIG. 14 is a view showing a further embodiment of the measuring procedure according to the present invention;  
         [0049]    [0049]FIG. 15 is a front view showing the schematic constitution of a track width measuring device according to a first embodiment of the present invention;  
         [0050]    [0050]FIG. 16( a ) is a side view of a bar showing a second method for presuming an amount of flexure according to the present invention, and  
         [0051]    [0051]FIG. 16( b ) shows a relationship between a position of an element on a bar and a position in a direction Y of each element;  
         [0052]    [0052]FIG. 17( a ) is a side view of a bar showing a third method for presuming an amount of flexure according to the present invention, and  
         [0053]    [0053]FIG. 17( b ) shows a relationship between a position of an element on a bar and a position in a direction Y of each element;  
         [0054]    [0054]FIG. 18 is a side view of a bar showing a fourth method for presuming an amount of flexure according to the present invention;  
         [0055]    [0055]FIG. 19 is a flow chart of the manufacturing step showing one embodiment applied to the manufacturing step of the present invention;  
         [0056]    [0056]FIG. 20 is a plan view of a wafer showing one embodiment in which a change in dimensions of track width is subjected to mapping on the wafer on the basis of the result measured according to the present invention; and  
         [0057]    [0057]FIG. 21 is a plan view of a wafer. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0058]    The embodiments of the present invention will be described in detail hereinafter with reference to the drawings.  
         [0059]    For performing manufacturing by which the performance of a thin film magnetic head is stabilized and high yield is obtain, it is naturally necessary, in the manufacturing step for a thin film magnetic head, to stabilize the manufacturing process for a magnetoresistive layer and the like. However it is particularly necessary to measure track width in a short time and accurately, in the state of a bar cut from a wafer, to apply feedback to the manufacturing process quickly. In the present invention, therefore, a description will be made of a manufacturing method for a thin film magnetic head including the inspecting step capable of accurately measuring dimensions of elements such as track width in a short time and positively.  
         [0060]    In the conventional measuring apparatus, since the bar is flexed in a direction at right angles to that elements are continuously arranged, the elements become deviated in position as the elements are measured by way of the step and repeat operation. So, detection is to be carried out while correcting the deviation, thus making it difficult to perform measurement in a short time and with high accuracy.  
         [0061]    The present invention has been accomplished in view of such a restriction as mentioned above with respect to measured objects. First, a first embodiment will be described with reference to FIG. 1 and FIGS.  8  to  14 .  
         [0062]    [0062]FIG. 1 shows a GMR head narrow track width measuring apparatus (hereinafter abbreviated as a track width measuring apparatus) in the first embodiment according to the present invention. The present track width measuring apparatus comprises a measurement optical system  200 , an automatic focusing system  201 , an image signal processing and control system  202 , and a stage system  203 .  
         [0063]    It is estimated that the lateral direction of paper surface is the direction X, the direction at right angles to the paper surface is the direction Y, and the vertical direction of the paper surface is the direction Z. The stage system  203  comprises a Y stage  3 , an X stage  6 , a Z stage  9 , and a jig (not shown) for holding a bar  2 . The Y stage  3  can be moved in the direction Y by a Y stage control system  5  in a method not shown by a drive part  4 . The X stage  6  can be moved in the direction X by an X stage control system  8  in a method not shown by a drive part  7 . The Z stage  9  can be moved in the direction Z by a Z stage control system  11  in a method not shown by a drive part  10 . A bar  2  is held by a jig (not shown) for holding the bar  2  on the Z stage  9 .  
         [0064]    The measurement optical system  200  comprises a light source  12 , an objective lens  15 , an image-forming lens  23 , and a CCD camera  24 . Light from the light source  12  is formed at the pupil  15   a  of the objective lens  15  by a relay lens  13  and a beam splitter  14  to Keller-illuminate an element part of the bar  2  by K hler illumination. The beam splitter  14  is provided for illumination and detected light separation. Reflecting light from the element part on the bar  2  is formed on the CCD camera  24  by the objective lens  15  and the image-forming lens  23 .  
         [0065]    The measurement optical system  200  is controlled by a microscope control system  16 . The wavelength of the light source  12  used to illuminate the bar  2  includes deep ultraviolet light such as wavelength 248 nm, or ultraviolet light such as wavelength 365 nm, or visible light such as wavelength 500 nm or so. Of course, the objective lens  15 , the image-forming lens  23  and the CCD camera  24 , which have the efficiency according to the wavelength.  
         [0066]    The automatic focusing system  201  comprises an illuminating sensor  19  and a division sensor  20 . Light from the illuminating laser  19  within an automatic focal unit  17  obliquely illuminates the element part on the bar  2  in the objective lens  15  by a dichroic mirror  18 . The reflecting light from the element part reflects the dichroic mirror  18 , and is received by the division sensor  20  within the automatic focusing unit  17 . Output of the division sensor  20  computes a position in the direction Z of the bar  2  by a computing circuit  21 . The result of computation is controlled by the automatic focal control system  22 . The dichroic mirror  18  is provided to separate the wavelength of the illuminating laser  19  different from the light source  12 , for example, 780 nm.  
         [0067]    The image signal processing and control system  202  comprises a computer  27 , an interface circuit  32 , a CPU  33 , and a display  34 . An image signal from the CCD camera  24  is converted into a digital signal by an AD converter  26 , and afterwards is input into an image input circuit  28  of the computer  27 . The CCD camera  24  controls the image pick-up timing, the exposure time and the like by a camera control system  25 . In the computer  17 , a plurality (two in the present embodiment) of operation circuits  29 ,  30  are provided to switch input of an image signal from the image input circuit  28  to enable the computing processing of track width of elements in parallel. Further, a position of an element within the detected image can be computed by an image position operation circuit  31 .  
         [0068]    The stage system  203 , the optical system  200 , the automatic focal system  201 , and the image signal processing and control system  202  are controlled by the CPU  33  through the interface circuit  32 . The result or the like is displayed on the display  34 .  
         [0069]    The operation of the above constitution will be described hereinafter. The objective lens  15  of the measurement optical system  200  is indispensable to the focusing with high accuracy when an image is input. In the present embodiment, the focusing is carried out by the automatic focal system  201 . A parallel beam of, for example, wavelength 780 nm, emitted from a semiconductor laser  19  is reflected by the dichroic mirror  18  and is incident on the circumferential part of the pupil  15   a  of the objective lens  15 , the beam being condensed obliquely on the bar  2  and irradiated. The reflecting light is incident on the objective lens  15  obliquely, and incident on the division sensor  20  as a parallel beam.  
         [0070]    FIGS.  8 ( a ) to  8 ( d ) show the operation of the automatic focal system  201  with respect to the vertical change of the bar  2 . FIG. 8( a ) shows the state that a focal position of the objective lens  15  is adjusted to the surface of the bar  2 . The division sensor  20  comprises two light receiving parts  20   a  and  20   b . An output signal from each light receiving part is input into a differential circuit  17   a , and a differential signal (for example, output of the light receiving part  20   a —output of the light receiving part  20   b ) sensor is fed to the operation circuit  21 . When the bar  2  is in the focused state, the reflecting light from the bar  2  impinges on the center part of the division sensor  20 . Then, outputs of the light receiving parts  20   a  and  20   b  are the same level, and when a difference therebetween is obtained, the differential signal is 0. FIG. 8( b ) shows the case where the bar  2  is moved to the vicinity of the objective lens  15 , and FIG. 8( c ) shows the case where the bar  2  is moved far from the objective lens  15 .  
         [0071]    When deviated from the focal position of the objective lens  15 , the opposition of the reflecting beam from the bar  2  is changed. Therefore, the outputs of the light receiving parts  20   a  and  20   b  are changed, and the output from the differential circuit  17   a  is changed. FIG. 8( d ) shows the output change of the differential circuit  17   a . The axis of abscissa indicates the amount of vertical change of the bar  2 , and the axis of ordinates indicates the output of the differential circuit  17   a . The position of 0 of the differential output is the focal position of the objective lens  15 . The right hand in which signal is large is the case where the bar is deviated far shown in FIG. 8( c ), and the left hand in which signal is small is the case where the bar is deviated near shown in FIG. 8( b ). As described above, when the focal position changes, the differential signal  17   b  changes, and the change direction of the focal position can be grasped by the symbols of the change.  
         [0072]    [0072]FIG. 9 shows the spectral transmittance characteristics of the dichroic mirror  18 . Light of wavelength (for example, 248 nm) used for the image measurement transmits by about 90%, and wavelength (for example, 780 nm) of laser beam used for automatic focus reflects by about 95%. The present measurement optical system  200  is composed of a double telecentric optical system, which is less error in magnification relative to slight deviation of the focal position. The automatic focusing may be done by a system for calculating contrast of a pattern of a detected image itself, and finely adjusting the Z stage  9  so that the contract is maximum. The spectral characteristics may be changed according to the wavelength used for the image measurement and the wavelength used for automatic focusing.  
         [0073]    FIGS.  10 ( a ) to  10 ( b ) show one example of deviations resulting from the flexure of the bar  2 . FIG. 10( a ) is a view in which the bar  2  is viewed from the detecting direction. As described above, the bar  2  is arranged continuously from the first element  101   a  to  101   b ,  101   c , . . . final  101   e  by pitch P.  
         [0074]    An element in the central part is  101   n . FIG. 10( b ) shows the results in which the position in the direction Y of elements  101 . It is understood that the change in the direction Y is small in amount of change near the center, and large in periphery. When an approximate equation is obtained from the position in the direction Y and the pitch P, the present embodiment is applied to a secondary approximate equation  201 .  
         [0075]    FIGS.  11 ( a ) to  11 ( d ) show one example of prediction of a position of the bar  2 . FIG. 11( a ) shows an image in which the element  101   a  is detected. The bar  2  is positioned by the X stage  6  and the Y stage  3  so that measurement items of the element  101   a  can be detected within the field of detecting  202 . The focal position of the objective lens  15  is adjusted to the surface of the element  101   a  by the automatic focal system  201 .  
         [0076]    In this state, the position in the direction Y within the field of detecting of the element  101   a , for example, the distance Y 1  from the lower part of the screen is calculated. The bar  2  is moved in the direction X by the distance of the pitch P by the X stage  6 . FIG. 11( b ) shows a detected image of next element  101   b . The element  101   b  is detected within the field of detecting  202 . As described above, the element  101   b  is detected downward of the element  101   a  due to the flexure of the bar  2 . Similarly, the distance Y 2  from the lower part of the screen is calculated. FIG. 11( d ) shows the distance in the direction Y and the approximate curve. A secondary approximate equation is derived using the change amount in the direction Y and the pitch P.  
         [0077]    Since the next element  101   c  can be estimated from the approximate equation, the position after moved by the pitch P of the element  101   c  is estimated to be Y 3 , and a difference between the position of Y 3  and the position Y 1  of the element  101   a  is obtained to obtain a corrected amount Yh 3 .  
         [0078]    As shown in FIG. 11( c ), the Y stage  3  is moved by the distance of the corrected value Yh 3  whereby the detected image of the element  101   c  can be detected at the same position as the element  101   a  irrespective of the flexure of the bar  2 . The position in the direction Y and the estimated position are stored.  
         [0079]    A secondary approximate equation is likewise further derived from the next element on the basis of the position stored to estimate positions in the direction Y after the next element, obtain the corrected value in the direction Y, and perform correction in the Y stage. The approximate equation is prepared using the previous positions of elements sequentially, which is used as a standard to enhance the accuracy of the corrected amount. Correction is performed in the Y stage simultaneously with the movement of the X stage. This operation is repetitively carried out till the final element.  
         [0080]    While in the present embodiment, the secondary approximate equation is used, it is contemplated that a linear approximate or a high-order approximate equation is used depending on the tendency of the flexure of the bar  2 . Thereby, all the elements can be detected in the center part of the objective lens  15 , enabling the measurement in a nanometer order.  
         [0081]    Next, the measuring method for track width which is an object of measurement will be described below. FIGS.  12 ( a ) to  12 ( b ) are an example of an image detected by the track width measuring apparatus in which the GMR head as an example of the object of measurement is shown in the present embodiment. FIG. 12( a ) shows the entirety of the detected image. In the detected image  112  are detected a read track  106 , a right track  109 , an upper shield  102 , and a lower shield  103 . The focal point is adjusted to the surface layer of the bar  2  by the automatic focal system. FIG. 12( b ) shows a signal taken on section A-A of an image. An image signal  113  in which edge in the direction of track width is detected is obtained. Points of intersection h1 and h2 when set to a certain level are obtained relative to the signal, and track widths (TWR, TWW) are obtained. Further, a difference between the center position of the read track  106  and the center position of the right track  109  is obtained to enable obtaining an offset amount between both the tracks.  
         [0082]    By the above-described operation, movement-stop-image input-computing processing is repeated by step-and-repeat scanning control of the X stage  6  and the Y stage  3 . When the image input is terminated with respect to all the elements of the bar  2 , the bar is moved to a removing position by the X stage  6  and the Y stage  3 . The next bar  2  is set, and moved again to a detecting position by the X stage  6  and the Y stage  3  to repeat measuring. Respective dimensions and variations are displayed on the display  34  as measured results for track width and the like.  
         [0083]    [0083]FIG. 13 shows one example of the measuring procedure in the present embodiment. First, the whole sequence will be described. The bar  2  is adjusted to the focusing position by the automatic focal system  201 . The element  101  is image-picked up by the camera  24 , and a signal thereof is transferred to the memory  28  within the computer  27 . The X stage  6  and the Y stage  3  are simultaneously moved to the movement of the pitch P to the next element and the distance for correcting the flexure amount of the bar  2 . The bar  2  is again adjusted to the focus point by the automatic focal system at that position (next element) to effect the camera exposure. This operation is repeated. When the camera exposure is finished, the memory transfer within the operation circuit  29 , the dimensions operation, and the result display are carried out in a separate sequence. A plurality of operation circuits  29  are provided. The operation circuit  30  sets up a sequence similar to the operation circuit  29 .  
         [0084]    As described above, in the computation of element A, computation of dimensions of element A can be carried out by the operation circuit  29 , and computation of dimensions of element B can be carried out by the operation circuit  30 . In the computation of element C, since the computation of element A is terminated before memory transfer in element C, the memory transfer can be carried out promptly. The exposure of elements and movement of stages are enabled continuously irrespective of the computation time of element dimensions. The detecting time  301  per element is substantially the time from the focusing to the termination of stage movement. The last element will receive serial operation since no next element exists, but this computation is carried out during operation for taking out elements, and the time is not substantially extended.  
         [0085]    While in the present embodiment, a description has been made of an example in which a plurality of operation circuits are provided, it is noted that where the operation circuit is terminated till detection of the next element due to higher speed of operation circuit, it is not necessary to provide a plurality of operation circuits. FIG. 14 shows one example. A signal is transferred to the memory of the operation circuit  29  after termination of camera exposure, similarly to FIG. 13. Computation of dimensions of elements and display of results are terminated by the memory transfer of camera exposure of the next element. Thereby, the operation circuit  29  can be realized by one circuit. Detecting time  301  per element is similar to FIG. 13.  
         [0086]    A second embodiment is shown in the drawing. FIG. 15 is a view of the entirety of the second embodiment. An automatic focal system  201 , a computing system  202 , and a stage system  203  are similar in constitution to FIG. 1. An optical system  200  has a low magnification objective lens  15   b  and a high magnification objective lens  15 . The detecting field of the low magnification objective lens  15   b  is 10 times of that of the high magnification objective lens  15 . Further, it has the detecting range capable of sufficiently detecting the flexure amount of the bar  2 . The high magnification objective lens  15  and the low magnification objective lens  15   b  can be switched by the microscope control system  16  as occasion demands. Other constitutions are similar to FIG. 1.  
         [0087]    The operation will be described with reference to FIGS.  16 ( a ) to  16 ( b ). FIG. 16( a ) is a view in which the bar  2  is viewed from the detecting direction. First, the lens is switched to the low magnification objective lens  15   b . As shown in FIG. 16( a ), all elements are detected by the low magnification objective lens  15   b  to obtain an amount of deviation in the direction Y of element. An element  101   a  is detected by a detecting range  300   a  to detect a position in the direction Y of the element  101   a . The X stage is moved by pitch P, and an element  101   b  is detected by a detecting range  300   b  to detect a position in the direction Y of the element  101   b . This operation is repetitively carried out with respect to all elements to store positions in the direction Y of all elements.  
         [0088]    At that time, the detecting field of the objective lens  15   b  is wider than the flexure S of the bar  2 . That is, the stage is not caused to be moved in the direction Y. FIG. 16( b ) shows a positional relationship in the direction Y of all elements detected. Next, switching is made from the low magnification objective lens  15   b  to the high magnification objective lens  15 . Since the amount of deviation in position in the direction Y of each element can be calculated, all elements are detected while correcting the amount of movement of each element and while simultaneously moving the distance of pitch P in the X stage  6 .  
         [0089]    The similar effect can be obtained even by the method shown in FIGS.  17 ( a ) to  17 ( b ). FIG. 17( a ) is a view in which the bar  2  is viewed from a detecting direction. The low magnification objective lens  15   b  is used for detection similar to FIG. 16. In the present embodiment, elements in both ends  101   a ,  101   e , and a central part  101   n  are detected, and an amount of deviation in position in the direction Y is obtained by the element. FIG. 17( b ) shows a positional relationship between each element and a position in the direction Y. A secondary approximate curve  303  is obtained using the amounts of deviation in position at three points and the distance between the elements. Since the pitch P of each element is constant, a portion from the position at the first element  101   a  to the position in the direction Y of the next element  101   b  can be estimated by the secondary approximate curve. This estimated amount is used as the corrected amount. Next, switching is made from the low magnification objective lens  15   b  to the high magnification objective lens  15 . All elements are detected while correcting the Y stage  3 , in accordance with the above-described corrected amount, and while simultaneously moving the distance of pitch P in the X stage  6 .  
         [0090]    While in the above-described embodiment, a description has been made of a case of a single bar  2 , it is noted that this can be also applied to a case where a plurality of bars  2  are arranged. FIG. 18 shows an embodiment of a case where a plurality of bars  2  are arranged, which is a view in which the bars are viewed from a detecting direction. A plurality of bar  2  is loaded on a jig  402 . Detecting is made by the low magnification objective lens  15   b , similar to FIG. 17. In the present embodiment, elements in both ends  101   a ,  101   e , and a central part  101   n  are detected, and an amount of deviation in position in the direction Y is obtained by the element. A secondary approximate curve in the bar  2  is obtained.  
         [0091]    Next, elements in both ends  305   a ,  305   e , and a central part  305   n  are detected, and an amount of deviation in position in the direction Y is obtained by the element. A secondary approximate curve in the bar  2   b  is obtained. All elements are detected using the secondary approximate curve according to the bars, while making correction in the Y stage  3 , and further while simultaneously moving the distance of pitch P in the X stage  6 , in accordance with the aforementioned corrected amount by the method explained in FIG. 17.  
         [0092]    [0092]FIG. 19 shows one embodiment of the step for processing a head. When the track width dimensions, the variations, and the amount of displacement of center of the track measured in the track width measuring apparatus explained above exceed a fixed value, the corresponding bars  2  and the element numbers within the bars  2  are displayed, and the inferior products are removed so as not to be moved to the next processing step and only the good products are moved thereto. Further, mapping in the wafer state is reconstructed from the result of measurement of dimensions in the bar state, and the dominant cause of inferior dimensions is estimated to specify the step that need be improved. Instructions for improvement are given to the specified step.  
         [0093]    [0093]FIG. 20 shows one embodiment in which the change in dimensions of track width is mapped on the wafer. In the figure, dimensions of track width are classified by dimensions. Mapping is applied to the wafer on the basis of the value of the classification so as to correspond to the bars prior to cutting shown in FIGS.  2 ( a ) to  2 ( c ) to form an image  500 .  
         [0094]    The dominant cause of inferior dimensions is estimated from values of variations in dimensions on the basis of the mapping result. On the basis of the dominant cause of inferior dimensions, an exposure device, a resist coating device, a film forming device and the like in the element forming step are improved to find inconvenient early and minimize uneven illuminance, as shown in FIG. 19. There is carried out the feedback such as correction of a process parameter such as fine adjustment of membrane pressure, which is applied to process management and control. For example, variation in dimensions caused by variation in film thickness, local variation in focus of an exposure device (adhesion of foreign matter on the chuck), and variation in illuminance can be estimated from data subjected to mapping.  
         [0095]    Further, accumulated data obtained by the apparatus can be used for monitoring and analyzing variation in dimensions and unevenness for a long period. Thereby, it is possible to enhance the yield and maintain the high yield.  
         [0096]    While in the present embodiment, a description has been made taking the GMR head as an example, it is note of course that the embodiment can be also applied to the MR head.  
         [0097]    Also in the production process for semiconductors, there can be obtained similar effects in the aforementioned method. That is, as shown in FIG. 21, measurement of line width of a chip  501  is continuously carried out in the state of wafer  1  to enable measurement of regular variations. On the basis of this result, mapping as shown in FIG. 20 is carried out whereby the cause of inferiority resulting from variations in process can be estimated to apply it to management and control of the semiconductor process such as exposure and development. With respect to the method of measurement of line width, calculation can be made by the method as described above.  
         [0098]    As described above, according to the embodiments of the present invention, in the production line in the GMR head forming process, measurement with high precision and in a short time of track width in the state formed to be bar-like becomes enabled to obtain the effect that the state of the element forming step can be monitored in the in-process. Further, mapping in the wafer state becomes enabled, and inconvenience of process in the element step is found early and a process parameter is improved to thereby obtain the effect of making it possible to reduce occurrence of inferior products and maintain high yield.  
         [0099]    The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.