Abstract:
In order to enable a highly-sensitive certifying test by detecting a signal with a high S/N ratio while controlling the glide height of a magnetic head to be optimized at the time of the certifying test, a method for inspecting a magnetic disk by conducting the certifying test for the magnetic disk using the magnetic head incorporating a heater includes: writing data into the magnetic disk using the magnetic head; and reading the data written into the magnetic disk using the magnetic head. Electric power applied to the heater incorporated in the magnetic head is switched between when writing the data and when reading the data.

Description:
BACKGROUND 
       [0001]    The present invention relates to a method and an apparatus for inspecting a magnetic disk by conducting a certifying test for the magnetic disk. 
         [0002]    Along with increasing recording density of a magnetic disk, the glide height of a magnetic head gliding above a surface of the disk that is rotated at a high speed becomes a level of 1.5 to 1.8 nm, and is further reduced to a level of 1 nm or smaller as the density is further increased. Fine protrusions on the surface are strictly controlled for a magnetic disk for which a minute glide height is required, and it is confirmed by a glide height test that there are no protrusions on the surface of the magnetic disk that collide with the head when the head is gliding. 
         [0003]    A certifying test that is the final inspection process for a magnetic disk includes a test (read/write test) in which data are written into the disk that has passed the glide height test using a head for a test, and the written data are read. 
         [0004]    The main items of the certifying test include a parametric test in which electric characteristics are examined at plural points on the magnetic disk, and a defect test on the whole surface of the disk. 
         [0005]    Japanese Patent Application Laid-Open Publication No. H9-259401 describes that the glide height test and the certifying test are simultaneously conducted using an output from one test head. 
         [0006]    Further, Japanese Patent Application Laid-Open Publication No. 2001-143201 describes that the certifying test is conducted, at small track pitches, for a magnetic disk with the small number of minute surface defects, and the certifying test is conducted, at large inspection track pitches, for a magnetic disk with the large number of minute surface defects in accordance with the result of the glide height test. 
         [0007]    Furthermore, Japanese Patent Application Laid-Open Publication No. 2009-199660 describes that a magnetic head having a heating element that controls the protrusion amount of the head is allowed to glide at a low height while controlling the glide height at a set height to improve the quality of a signal, and defects are inspected using a signal read by the head while controlling the glide height to be different from that set by heating the heating element. 
         [0008]    Along with increasing recording density of a magnetic disk, there has been increasing demand of a highly-sensitive certifying test. 
         [0009]    In the technique described in Japanese Patent Application Laid-Open Publication No. H9-259401, it can be expected that the throughput of the inspection can be improved by simultaneously conducting the glide height test and the certifying test using an output from one test head. However, there is no consideration of suppressing variations in inspection sensitivity caused by variations in characteristics of test heads among plural inspection apparatuses. 
         [0010]    Further, in the technique described in Japanese Patent Application Laid-Open Publication No. 2001-143201, the efficiency of the inspection can be improved by conducting the certifying test in accordance with the result of the glide height test. However, there is no consideration of suppressing variations in inspection sensitivity caused by variations in characteristics of test heads among plural inspection apparatuses at the time of conducting the certifying test. 
         [0011]    Furthermore, in Japanese Patent Application Laid-Open Publication No. 2009-199660, the inspection is conducted while shifting the glide height by heating the magnetic head from the optimum head glide height at which a signal with a high S/N ratio can be detected while suppressing generation of reduction in thermal asperity that is generated by the magnetic head colliding with protrusions of the surface of the magnetic disk, so that defects can be detected under the same environment as the operation. However, there is no description about implementation of a highly-sensitive certifying test. 
       SUMMARY 
       [0012]    The present invention provides a method and an apparatus for conducting a certifying test which enable a highly-sensitive certifying test by detecting a signal with a high S/N ratio while controlling the glide height of a magnetic head to be optimized at the time of conducting the certifying test. 
         [0013]    In order to achieve the above-described object, an aspect of the present invention provides a method for inspecting a magnetic disk including: obtaining a relation between electric power applied to a heater and the number of error counts by conducting a read/write test at a predetermined area of the magnetic disk using a magnetic head while changing the glide height of the magnetic head gliding above the magnetic disk being rotated by controlling the electric power applied to the heater incorporated in the magnetic head; setting the electric power applied to the heater at the time of conducting the read/write test on the basis of the obtained relation between the electric power applied to the heater and the number of error counts; applying the set electric power to the heater; and conducting the read/write test at the predetermined area of the magnetic disk using the magnetic head in a state where the set electric power is applied to the heater. 
         [0014]    Further, in order to achieve the above-described object, another aspect of the present invention provides a method for inspecting a magnetic disk by conducting a certifying test for the magnetic disk using a magnetic head incorporating a heater, the method including: writing data into the magnetic disk using the magnetic head; and reading the data written into the magnetic disk using the magnetic head, wherein electric power applied to the heater incorporated in the magnetic head is switched between when writing the data and when reading the data. 
         [0015]    Further, in order to achieve the above-described object, another aspect of the present invention provides an apparatus for inspecting a magnetic disk by conducting a certifying test, the apparatus including: a stage on which the magnetic disk as an inspection target sample is mounted to be rotated and to be moved in one axis direction; a magnetic head in which a heater is incorporated; a heater electric power control circuit that controls electric power applied to the heater; a current driving circuit that controls a current value applied to the magnetic head; a voltage detecting circuit that detects the voltage of the magnetic head in which current is allowed to flow by the current driving circuit; a data reading/writing circuit that writes data into the magnetic disk and reads the written data through the magnetic head; and a controller that controls the certifying test for the magnetic disk, wherein the heater electric power control circuit, the current driving circuit, and the voltage detecting circuit are formed as one IC chip. 
         [0016]    According to the present invention, it is possible to conduct a highly-sensitive certifying test by detecting a signal with a high S/N ratio while controlling the glide height of a magnetic head to be optimized at the time of conducting the certifying test. 
         [0017]    These 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 
         [0018]      FIG. 1  is a block diagram for showing an outlined configuration of an inspection apparatus that conducts a certifying test; 
           [0019]      FIG. 2  is a cross-sectional view of a magnetic head gliding above a substrate; 
           [0020]      FIG. 3  is a graph for showing a relation between electric power applied to a heater incorporated in the magnetic head and the number of error counts on the substrate detected by the magnetic head; 
           [0021]      FIG. 4  is a flowchart for showing processes of the certifying test while controlling the glide height of the magnetic head according to a first embodiment of the present invention; and 
           [0022]      FIG. 5  is a flowchart for showing processes of the certifying test while controlling the glide height of the magnetic head according to a second embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    Hereinafter, embodiments of the present invention will be described using the drawings. 
       First Embodiment 
       [0024]    A configuration of an inspection apparatus that conducts a certifying test for a magnetic disk in a first embodiment is shown in  FIG. 1 . 
         [0025]    The inspection apparatus includes a mechanism  10 , a reading/writing circuit  100 , a data reading/writing circuit  110 , and a data processor/storage  120 . 
         [0026]    The mechanism  10  includes a rotational shaft (spindle shaft)  11  that allows a magnetic disk  1  for inspection to be mounted and rotated, a movable stage  12  that allows the rotational shaft  11  to be moved in a plane, a head element  13  that writes and reads data into/from the magnetic disk (substrate)  1 , and a head arm  15  that supports the head element  13 . 
         [0027]    Here, as the head element  13 , a composite magnetic head composed of an MR (magnetoresistive effect) head for reading and a thin-film inductive head for writing is used. 
         [0028]    The reading/writing circuit  100  is formed as one chip including a reading amplifier  104   a,  a writing amplifier  104   b,  a head heating control circuit  105 , a current driving circuit  106 , a voltage detecting circuit  107 , and a parallel/serial converter  108 . 
         [0029]    The head heating control circuit  105  includes a D/A converter  105   a,  a current output OP amplifier  105   b,  and a current inversion OP amplifier  105   c.    
         [0030]    The current driving circuit  106  includes a D/A converter  106   a,  a current output OP amplifier  106   b,  and a current inversion OP amplifier  106   c,  and the voltage detecting circuit  107  includes an A/D converter  107   a  and a high input impedance OP amplifier  107   b.    
         [0031]    The data reading/writing circuit  110  includes a data reading circuit  111 , a data writing circuit  112 , and a test data generating circuit  113 . 
         [0032]    The data processor/storage  120  includes an MPU  121 , a memory  122 , a display  123 , an interface  124 , a keyboard  125 , and a bus  126  that couples these units to each other. A magnetic disk inspection program  122   a,  an MR head resistance value measuring program  122   b,  a head deterioration determination program  122   c,  an MR head initial resistance value measuring program  122   d,  an accumulated inspection time calculating program  122   e,  and the like are stored in the memory  122 . Further, a work area  122   f  and a parameter area  122   g  for measurement are set. 
         [0033]    In the above-described configuration, the head heating control circuit  105  controls electric power applied to a heater inside the head element  14  on the basis of head heating data stored in the work area  122   f  of the data processor/storage  120 . 
         [0034]    In the current driving circuit  106 , the D/A converter  106   a  inputs a command from the parallel/serial converter  108 , and converts the input signal from digital to analog to be output to the current output OP amplifier  106   b.  The current output OP amplifier  106   b  outputs current amplified in response to the output from the D/A converter  106   a.  The output current is applied to the head element  14  located at a tip end of the head arm  15  through a reading signal line  16   a,  and the current flowing into the head element  14  is sunk at the current inversion OP amplifier  106   c  of the current driving circuit  106  through a reading signal line  16   b.    
         [0035]    In the voltage detecting circuit  107 , the A/D converter  107   b  inputs signals from the reading signal lines  16   a  and  16   b,  and outputs a voltage signal, as a measurement signal, in accordance with a potential difference (voltage) between the lines to the A/D converter  107   a.  The A/D converter  107   a  receives and converts the measurement signal from analog to digital, and outputs the digital signal to the parallel/serial converting circuit  108 . 
         [0036]    The parallel/serial converting circuit  108  calculates the resistance value of the head element  14  on the basis of the current value set by the current driving circuit  106  and the voltage value detected by the voltage detecting circuit  107 , and transmits a signal to the data processor/storage  120 . 
         [0037]    Next, as a configuration of the head element  14 , an example of a partial cross-section of the MR head is shown in  FIG. 2 . 
         [0038]    The partial cross-section of the head element  14  shown in  FIG. 2  includes a write element  141 , a read element  142 , a heater  143 , and a resin  144 . Further, the write element  141  includes an upper electrode  1411 , a lower electrode  1412 , a coil  1413 , and an insulating material  1414 .  FIG. 2  shows a state in which the substrate  1  mounted at the rotational shaft (spindle shaft)  11  is rotated at a high speed and the head element  14  is allowed to glide above the substrate  1 . 
         [0039]    In this configuration, the heater  143  is coupled to wirings  17   a  and  17   b  for the heater shown in  FIG. 1  (not shown in  FIG. 2 ), and the electric power to be applied is controlled on the basis of the head heating data stored in the work area  122   f  of the data processor/storage  120 . 
         [0040]    In  FIG. 2 , an area represented by the dotted line on the lower side of the head element  14  shows a state in which when the electric power applied to the heater  143  is increased, the head element  14  is thermally expanded. The head element  14  is expanded by heating the head element  14  using the heater  143 , and a tip end of the head element protrudes towards the substrate by a head protrusion amount of Δh. Accordingly, an interval (head glide height) between the head element  14  and the substrate  1  is reduced. 
         [0041]    On the other hand, there is a proper range for the interval between the head element  14  and the substrate  1 . Specifically, if the interval between the head element  14  and the substrate  1  becomes too large, noise components are increased, resulting in deterioration in an S/N ratio. In addition, false detection in the read/write test is increased, resulting in an increase in the number of error counts. Further, if the interval between the head element  14  and the substrate  1  becomes too small, the head element  14  comes closer to the substrate  1  to collide with protrusions on a surface of the substrate  1 , and the interval between the head element  14  and the substrate  1  is changed to generate a noise signal. This case also causes false detection. 
         [0042]    As described above, by applying electric power to the heater  143  of the head element  14 , the head element  14  is expanded and the interval between the substrate  1  and the head element  14  is changed.  FIG. 3  shown an example of a result obtained by examining a relation between the electric power applied to the heater  143  and the number of error counts detected by the head element  14  at the time of conducting the read/write test.  FIG. 3  is a diagram obtained by plotting the number of defects detected when the same area (predetermined track range) on the substrate  1  is inspected by the head element  14  while changing the electric power applied to the heater  143 . 
         [0043]    In a state where the electric power applied to the heater  143  is low, noise is increased and the possibility of false detection by the head element  14  becomes high due to the large interval between the head element  14  and the substrate  1 . If the electric power applied to the heater  143  is gradually increased, the number of defects that are wrongly detected by the head element  14  is reduced, and the number becomes closer to the real number of defects. In addition, if the electric power applied is increased beyond a certain value, the number of detected defects is increased again. The dotted line in the drawing shows a moving average (an average with the previous (left side) value). 
         [0044]    As being apparent from the graph of  FIG. 3 , by properly setting the interval between the head element  14  and the substrate  1 , the number of defects that are wrongly detected by the head element  14  can be being reduced, and highly accurate and reliable inspection of defects can be conducted. 
         [0045]    In the embodiment, head characteristics as shown in  FIG. 3  are obtained and the electric power applied to the heater  143  is stored in the work area  122   f  of the data processor/storage  120  before conducting the certifying test. In the case where the certifying test is conducted, the data processor/storage  120  controls the head heating control circuit  105 , so that the electric power applied to the heater  143  is set to be equal to that stored in the work area  122   f.    
         [0046]    Next,  FIG. 4  shows a processing flow of sequentially conducting the certifying test for the substrate  1  in a state where the data as shown in  FIG. 3  are obtained in advance to determine the electric power applied to the heater  143  and the value of the electric power is stored in the work area  122   f  of the data processor/storage  120 . 
         [0047]    First, the MPU  121  reads the magnetic disk inspection program  122   a  stored in the memory of the data processor/storage  120  before conducting the certifying test. Next, a predetermined area (predetermined track area) of the substrate  1  is inspected to detect defects using the head element  14  while changing the electric power applied to the heater  143 , and the relation between the electric power applied to the heater and the number of detected defects as shown  FIG. 3  is obtained. In addition, the electric power applied to the heater at which the number of detected defects becomes smallest is obtained using information of the moving average on the basis of the obtained relation between the electric power applied to the heater and the number of detected defects, and is stored in the work area  122   f  of the data processor/storage  120  (S 401 ). 
         [0048]    Next, the MPU  121  controls the head heating control circuit  105  through the interface  124  to control the electric power applied to the heater  143  on the basis of the information of the electric power applied to the heater stored in the work area  122   f  of the data processor/storage  120  (S 402 ). 
         [0049]    Next, the MPU  121  reads the MR head initial resistance value measuring program  122   d  stored in the memory area  122  of the data processor/storage  120 , and controls the current driving circuit  106  and the voltage detecting circuit  107  through the interface  124  to measure the initial resistance value of the MR head (S 403 ). The measured initial resistance value is stored in the work area  122   f  of the data processor/storage  120 . 
         [0050]    After measuring the initial resistance value of the MR head, writing data are transmitted from the test data generating circuit  113  and the data writing circuit  112  of the data reading/writing circuit  110  to the head element  14  through the writing amplifier  104   b  by a command from the MPU  121  on the basis of the magnetic disk inspection program  122   a  which is read beforehand, and the data are written into the substrate  1  by the write element  141 . Next, the written data are read by the read element  142  of the head element  14 , and the signal thereof is input to the data reading circuit  111  through the reading amplifier  104   a . The MPU  121  receives and processes the signal output from the data reading circuit  111 , so that the certifying test for the substrate  1  is conducted (S 404 ). 
         [0051]    When the certifying test for the substrate  1  is completed, the substrate  1  is removed from the rotational shaft (spindle shaft)  11  using a handling unit (not shown). Then, check whether or not there is another substrate to be inspected for the next time (S 405 ). If there is no substrate for inspection, the inspection is completed. On the other hand, if there is another substrate for inspection, the substrate for inspection is mounted at the rotational shaft (spindle shaft)  11  using the handling unit (not shown) and check whether or not the accumulated inspection time so far over a predetermined period of time (S 406 ). If the accumulated inspection time is not over the predetermined period of time, the certifying test of S 404  is conducted. 
         [0052]    On the other hand, if the accumulated inspection time is over the predetermined period of time, the MPU  121  reads the MR head resistance value measuring program  122   b  stored in the memory area  122  of the data processor/storage  120 , and controls the current driving circuit  106  and the voltage detecting circuit  107  through the interface  124  to measure the resistance value of the MR head that has conducted the inspection for the predetermined period of time (S 407 ). Next, the measured resistance value is compared with the initial resistance value that was measured in the step of S 403  and stored in the work area  122   f  of the data processor/storage  120  (S 408 ) to determine whether or not a change ratio of the resistance value measured at this time to the initial resistance value falls within a predetermined range (S 409 ). If the change ratio falls within the predetermined range, the certifying test of S 404  is conducted. 
         [0053]    On the other hand, the change ratio of the resistance value measured at this time to the initial resistance value is out of the predetermined range (out of allowable range), it is determined as deterioration of the head. Then, an alert to notify that the head should be replaced is displayed on the display of the data processor/storage  120  (S 410 ), and the inspection is completed. 
         [0054]    As described above, the inspection can be conducted while the glide height of the magnetic disk gliding above the substrate that is rotated at a high speed at the time of the inspection is set to conditions under which the number of error counts becomes smallest. In addition, the glide height of the magnetic head can be kept constant until the head is deteriorated due to temporal change. Thus, a highly reliable certifying test can be conducted. 
       Second Embodiment 
       [0055]    In the first embodiment, the electric power applied to the head heating heater  143  is constant at the time of conducting the read/write test. 
         [0056]    However, there is a possibility in the read/write test that the optimum glide height of the head element  14  when writing data generated by the test data generating circuit  113  into a predetermined track area of the magnetic disk  1  by the write element  141  is different from that when reading the data from the magnetic disk  1  by the read element  142 . 
         [0057]    Accordingly, in the second embodiment, the relation between the electric power applied to the heater  143  and the number of error counts at the time of data writing and the relation between the electric power applied to the heater  143  and the number of error counts at the time of data reading in the steps of S 401  and S 402  of the processing flow in the first embodiment shown in  FIG. 4  are separately obtained, and are stored in the work area  122   f  of the data processor/storage  120 . 
         [0058]    A configuration of an inspection apparatus in the second embodiment is the same as that of the inspection apparatus in the first embodiment explained using  FIG. 1 . 
         [0059]    A processing flow of the second embodiment is shown in  FIG. 5 . 
         [0060]    First, the MPU  121  reads the magnetic disk inspection program  122   a  stored in the memory of the data processor/storage  120  before conducting the certifying test. Next, inspection data generated by the test data generating circuit  113  are written into a predetermined area (predetermined track area) of the substrate  1  using the write element  141  of the head element  14  while changing the electric power applied to the heater  143  (S 501 ). Next, the data written into the substrate  1  are read by the read element  142  in a state where the electric power applied to the heater  143  is kept constant (S 502 ), and the electric power applied to the heater at which the number of detected defects becomes smallest at the time of data writing is obtained using the information of the moving average on the basis of the relation between the electric power applied to the heater and the number of error counts at the time of inspection data writing as shown in  FIG. 3 . The obtained electric power is stored in the work area  122   f  of the data processor/storage  120  as electric power Pw applied to the heater at the time of data writing (S 503 ). 
         [0061]    Next, the inspection data generated by the test data generating circuit  113  are written into the predetermined area (predetermined track area) of the substrate  1  using the write element  141  of the head element  14  (S 504 ), and the data written into the predetermined area of the substrate  1  are read by the read element  142  while changing the electric power applied to the heater  143  (S 505 ). Then, obtaining the electric power applied to the heater  143  to minimize the number of error counts at the time of data reading by using the information of the moving average on the basis of the relation between the electric power applied to the heater and the number of error counts at the time of inspection data writing as shown in  FIG. 3 . The obtained electric power is stored in the work area  122   f  of the data processor/storage  120  as electric power Pr applied to the heater at the time of data reading (S 506 ). 
         [0062]    Next, the MPU  121  reads the MR head initial resistance value measuring program  122   d  stored in the memory area of the data processor/storage  120 , and controls the current driving circuit  106  and the voltage detecting circuit  107  through interface  124  to measure the initial resistance value of the MR head (S 507 ). The initial resistance value is stored in the work area  122   f  of the data processor/storage  120 . 
         [0063]    After measuring the initial resistance value of the MR head, writing data are transmitted from the test data generating circuit  113  and the data writing circuit  112  of the data reading/writing circuit  110  to the head element  14  through the writing amplifier  104   b  by a command from the MPU  121  on the basis of the magnetic disk inspection program  122   a  which is read beforehand, and the data are written into the substrate  1  by the write element  141 . At this time, the electric power Pw for data writing is applied to the heater  143  which was obtained in the step of S 503  and stored in the work area  122   f  of the data processor/storage  120 . Next, the data written into the substrate  1  are read by the read element  142  of the head element  14 . At this time, the electric power applied to the heater  143  is switched from Pw to Pr for reading data from the substrate  1  that was obtained in the step of S 506  and stored in the work area  122   f  of the data processor/storage  120 . The signal read by the read element  142  is input to the data reading circuit  111  through the reading amplifier  104   a,  and the MPU  121  receives and processes the signal output from the data reading circuit  111 , so that the certifying test for the substrate  1  is conducted (S 508 ). 
         [0064]    When the certifying test for the substrate  1  is completed, the substrate  1  is removed from the rotational shaft (spindle shaft)  11  using a handling unit (not shown). Then, check whether or not there is another substrate to be inspected for the next time (S 509 ). If there is no substrate for inspection, the inspection is completed. On the other hand, if there is another substrate for inspection, the substrate for inspection is mounted at the rotational shaft (spindle shaft)  11  using the handling unit (not shown) and check whether or not the accumulated inspection time so far over a predetermined period of time (S 510 ). If the accumulated inspection time is not over the predetermined period of time, the certifying test of S 508  is conducted. 
         [0065]    On the other hand, if the accumulated inspection time is over the predetermined period of time, the MPU  121  reads the MR head resistance value measuring program  122   b  stored in the memory area  122  of the data processor/storage  120 , and controls the current driving circuit  106  and the voltage detecting circuit  107  through the interface  124  to measure the resistance value of the MR head that has conducted the inspection for the predetermined period of time (S 511 ). Next, the measured resistance value is compared with the initial resistance value that was measured in the step of S 507  and stored in the work area  122   f  of the data processor/storage  120  (S 512 ) to determine whether or not a change ratio of the resistance value measured at this time to the initial resistance value falls within a predetermined range (S 513 ). If the change ratio falls within the predetermined range, the certifying test of S 508  is conducted. 
         [0066]    On the other hand, the change ratio of the resistance value measured at this time to the initial resistance value is out of the predetermined range (out of allowable range), it is determined as deterioration of the head. Then, an alert to notify that the head should be replaced is displayed on the display of the data processor/storage  120  (S 514 ), and the inspection is completed. 
         [0067]    According to the embodiment, the inspection can be conducted while the glide height of the magnetic head gliding above the substrate that is rotated at a high speed at the time of the read/write test is switched between when writing the inspection data into the substrate and when reading the data written into the substrate. By switching the glide height in writing and in reading, the read/write test is conducted under the condition in which the number of error counts becomes smallest. In addition, the glide height of the magnetic head can be kept constant until the head is deteriorated due to temporal change. Thus, a highly reliable certifying test can be conducted. 
         [0068]    The present invention achieved by the inventors has been concretely described above on the basis of the embodiments. However, it is obvious that the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the scope of the present invention. 
         [0069]    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.