Patent Publication Number: US-2010116645-A1

Title: Surface processing method and manufacturing method of recording medium

Description:
TECHNICAL FIELD 
     The present invention relates to a surface processing method of processing a surface of a substrate and a manufacturing method of a recording medium. 
     BACKGROUND ART 
     As the information-oriented society develops, the amount of information continues to increase steadily. To cope with this increase in the amount of information, the development of an information recording scheme and information storage device for achieving a remarkably high recording density has been eagerly awaited. In particular, magnetic disks in which information access is performed in a magnetic field have gained much attention as a high-density recording medium capable of rewriting information, and active research and development efforts are being made to achieve still higher recording densities, etc. 
     A magnetic disk, in general, has a structure in which a under layer to be a base layer, and a magnetic layer for recording information are successively laminated on a substrate and, further on top of the magnetic layer, a protection layer made up of, for example, DLC (Diamond Like Carbon) is formed. As a magnetic disk device which may access information at a high recording density to and from a magnetic disk, magnetic disk devices of a floating-head type, in which a magnetic head for generating a magnetic field is floated by an air flow produced by the rotation of the magnetic disk, are widely used. There is a risk with a floating-head type magnetic disk device that, in order to efficiently apply a magnetic field to the magnetic disk device, the distance between the magnetic disk and the magnetic head is very small and, for example, when the magnetic disk device is subjected to an impact while the magnetic head is floated, the magnetic head may collide with the magnetic disk to cause the protection layer to peel off thereby destroying the information recorded in the magnetic layer of the magnetic disk. In order to solve such a problem, an attempt is made to laminate a lubricant layer further on top of the protection layer of the magnetic disk to reduce the friction of the surface of the magnetic disk so that upon collision, the magnetic head slides on the surface of the magnetic disk. This lubricant layer also serves to prevent the adherence of moisture and a foreign matter, etc. onto the surface of the magnetic disk, as well as to improve the wear resistance of the magnetic disk and the magnetic head. 
     However, while the magnetic disk is in operation, the interior of the magnetic disk device is generally in a state of high temperature, and thereby a problem may arise in that a lubricant layer applied to the surface of the magnetic disk is moved toward a circumferential side because of a centrifugal force resulted from a high-speed revolution and a high temperature, and the lubricant layer eventually peels off from the magnetic disk during repeated uses. 
     In this respect, Japanese Laid-Open Patent Publication Nos. H06-325357 and 2003-223710 describe a technique to improve the adherence strength of a lubricant layer, by applying a sputtering using an oxygen or nitrogen plasma, etc. on the surface of the protection layer to add a surface functional group onto the protection layer surface and thereafter applying the lubricant layer. Hereafter, an example of the processing method of the protection layer will be described. 
     First, a magnetic disc with a protection layer being applied thereto is held by a metallic holder, and the magnetic disk is disposed in a metallic chamber in vacuum. Introducing a source gas such as oxygen and nitrogen into the chamber to increase the pressure thereinside, and further applying a high-frequency voltage between the chamber and the magnetic disk, will result in a generation of a plasma of the source gas in the chamber. At this moment, there is generated on the surface of the magnetic disk, a cathode drop potential of a magnitude responsive to the high-frequency voltage applied to the magnetic disk, and ions in the plasma are accelerated by the cathode drop potential to collide with the magnetic disk surface. As a result, a sputtering by ions and a chemical change of the source gas simultaneously take place, and the protection layer of the magnetic disc surface is oxidized and nitrided resulting in a surface functional group being added to the protection layer. 
     In this occasion, although it is ideal that the cathode drop potential generated on the surface of the magnetic disk is entirely utilized for the sputtering treatment, in reality, the cathode drop potential is partly returned as a reflected wave. Since the magnitude of the reflected wave will change depending on the contact area between the holder and the magnetic disk, stains in the metallic chamber, the impedance of the holder, and the like, when processing the surface of the magnetic disk, it is practiced to measure the cathode drop potential and the reflected wave thereby determining the processed state of the surface of the magnetic disk. 
       FIG. 1  is a graph to illustrate an example of cathode drop potential and reflected wave. 
     In  FIG. 1 , the lateral axis indicates time, the longitudinal axis of the upper graph g 1 _ 1  indicates the magnitude of cathode drop potential, and the longitudinal axis of the lower graph g 2 _ 1  indicates the magnitude of reflected wave. 
     Upon determination of the processed state of the surface of the magnetic disk, the magnitudes of a cathode drop potential V_t 0  and a reflected wave R_t 0  at a time when a time period t 0  in which the cathode drop potential is empirically considered to be sufficiently stabilized has elapsed since a high-frequency voltage is applied between the holder and the chamber are respectively measured. If the cathode drop potential V_t 0  is not less than a predetermined threshold V 0  and the reflected wave R_t 0  is less than a predetermined threshold R 0 , it is inferred that the cathode drop potential has been sufficiently generated and further, sputtering processing is performed with a small amount of reflected wave, leading to a determination that the processed state of the surface of the magnetic disk is good. Further, if the cathode drop potential V_t 0  is less than the threshold V 0  or the reflected wave R_t 0  is not less than the threshold R 0 , it is considered that the cathode drop potential is not sufficiently generated or the reflected wave is large so that the cathode drop potential has not been sufficiently utilized for sputtering treatment, leading to a determination that the processed state of the surface of the magnetic disk is not good. In the example illustrated in  FIG. 1 , since at a time when a time period t 0  has elapsed, the cathode drop potential V_t 0  exceeds the threshold V 0  and further the reflected wave R_t 0  is less than the threshold R 0 , it is determined that the processed state of the surface of the magnetic disk is good. 
     DISCLOSURE OF INVENTION 
     Here, in general, a reflected wave is likely to be generated in the interval before cathode drop potential is stabilized; however, when abnormal discharge takes place because of the stains of the chamber, poor contact between the magnetic disk and the holder, and the like, the reflected wave is likely to continue to be generated even after the cathode drop potential is stabilized. For this reason, even if the reflected wave temporarily subsides at a time t 0 , a large reflected wave may be generated thereafter leading to a risk that the surface of the magnetic disk may not be sufficiently processed. 
       FIG. 2  is a graph to illustrate an example of cathode drop potential and reflected wave. 
     In  FIG. 2  as well, the lateral axis indicates time, and the longitudinal axis of the upper graph g 1 _ 2  indicates the magnitude of the cathode drop potential and the longitudinal axis of the lower graph g 2 _ 2  indicates the magnitude of the reflected wave. 
     In the example illustrated in  FIG. 2 , since the cathode drop potential V_t 0  exceeds the threshold V 0  at a time when a time period t 0  has elapsed, and further the reflected wave R_t 0  is less than the threshold R 0 , according to the above described determination, the processed state of the surface of the magnetic disk will be good; however, in reality, a large reflected wave takes place after the time t 0 , and part of the cathode drop potential is not utilized for sputtering treatment and the surface processing is insufficient. Thus, conventional techniques have a problem that the determination accuracy of the processed state is low. 
     Further, such problem is not limited to magnetic disks, but may arise in general in the fields where a surface processing method of applying a high-frequency voltage to a substrate and sputtering the surface of the substrate is utilized. 
     In view of the foregoing, it is an object in one aspect of the invention to provide a method of surface processing and a method of manufacturing a recording medium, in which it is possible to accurately determine a processed state of a substrate. 
     According to an aspect of the invention, a surface processing method of processing a surface of a substrate, includes: 
     disposing the substrate in a vacuum chamber; 
     processing by applying a high-frequency voltage to the substrate and by sputtering the surface of the substrate; 
     measuring a cathode drop potential generated at the substrate in the processing and obtaining a time integration value of the cathode drop potential, and 
     determining whether or not a processed state of the surface of the substrate is good based on the time integration value obtained in the measuring. 
     It is noted that while a cathode drop potential has a negative value since it indicates a fall from a reference potential, and the time integration value of the cathode drop potential also has a negative value, “the time integration value of cathode drop potential” referred to in the present invention indicates the absolute value with the sign removed. 
     Applying a high-frequency voltage to a substrate causes a cathode drop potential to be generated on the surface of the substrate, and by the cathode drop potential, the surface of the substrate is processed by sputtering. However, in general, the generated cathode drop potential is not entirely utilized for sputtering, but is partly returned as a reflected wave. Conventionally, in a surface processing treatment for processing the surface of a substrate, when the cathode drop potential is sufficiently generated and the reflected wave is small at a time when a predetermined time has elapsed since a high-frequency voltage is applied, it is determined that the processed state of the surface of the substrate is good. As a result of this, when a large reflected wave is generated or the generation amount of cathode drop potential has decreased after a further time has elapsed, a problem arises in that defective products in which the substrate is not sufficiently processed are mixed in normal products. 
     As a result of analyzing such a problem, it is confirmed that there is a good correlation between the time integration value of the cathode drop potential and the processing amount of the surface of the substrate. In the surface processing method of the present invention, utilizing such analysis result, a time integration value of a cathode drop potential, which is generated by the application of a high-frequency voltage to the substrate, is measured and based on the time integration value thereof, the processed state of the surface of the substrate is determined. For this reason, even when a large reflected wave is generated or the generation amount of the cathode drop potential has decreased while the surface of the substrate is processed, it is possible to accurately determine the processed state of the surface of the substrate. 
     In addition, in the surface processing method according the one aspect of the invention, it is preferable that the surface processing method according to claim  1 , further includes: 
     instructing a stop of the applying of the high-frequency voltage to the substrate, wherein 
     the processing is stopping the applying of the high-frequency voltage to the substrate upon receipt of the instruction of the stop the applying of the high-frequency voltage to the instructing, and 
     the measuring is obtaining a time integration value of the cathode drop potential generated in an interval from when the high-frequency voltage is applied to the substrate to when the applying of the high-frequency voltage is stopped. 
     According to this preferred surface processing method, by instructing the stop of the application of high-frequency voltage, it is possible to control the amount of high-frequency voltage applied to the substrate, and to adjust the processing amount of the surface of the substrate. 
     In addition, in the surface processing method, it is preferable that the determining is determining that the processed state of the surface of the substrate is good if the time integration value is not less than a predetermined first threshold value. 
     It is confirmed that there is a good correlation between the time integration value of cathode drop potential and the processing amount of the surface of a substrate, and by using whether or not the time integration value is not less than a first threshold value determination criterion, it is possible to accurately determine the processed state of the surface of the substrate. 
     In addition, in the surface processing method according to the invention, it is preferable that the surface processing method further includes introducing a gas into the chamber, wherein the processing is forming a plasma of the gas on the substrate by applying the high-frequency voltage to the substrate, and sputtering the surface of the substrate with an ion in the plasma. 
     By using a plasma, it is possible to efficiently process the surface of the substrate. 
     In addition, in the surface processing method according to the invention, it is preferable that the processing is sputtering the surface of the substrate by using a nitrogen plasma or an oxygen plasma. 
     By utilizing a nitrogen plasma or an oxygen plasma, it is possible to concurrently generate a sputtering by means of ions in the plasma and an oxidation or nitriding treatment. 
     Further, according to an aspect of the invention, a manufacturing method of a recording medium to record information, includes: 
     forming, on a substrate, a recording layer to record information, and a protection layer to protect the recording layer; 
     disposing the substrate in a vacuum chamber; 
     processing by applying a high-frequency voltage to the substrate and by sputtering the surface of the substrate; 
     measuring a cathode drop potential generated in the substrate in the processing to acquire a time integration value of the cathode drop potential; 
     determining whether or not a processed state of the surface of the substrate is good based on the time integration value obtained in the measuring; and 
     forming a lubricant layer on the protection layer if it is determined that the processed state of the protection layer is good in the determining. 
     According to the manufacturing method of the recording medium of the one aspect of the present invention, it is possible to accurately determine the processed state of the surface of the substrate on which a recoding layer and a protection layer are formed, and to form a lubricant layer only on a substrate which is in good processed state. 
     Furthermore, the manufacturing method according to the invention, it is desirable the processing is producing a surface functional group in the protection layer, by sputtering the protection layer. 
     As a result of a surface functional group being formed on the protection layer, it is possible to improve the adhesive strength between the lubricant layer and the protection layer. 
     As so far described, according to the present invention, it is possible to provide a surface processing method which enable to accurately determine the processed state of the substrate surface, and a manufacturing method of a recording medium. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a graph to illustrate an example of a cathode drop potential and a reflected wave. 
         FIG. 2  is a graph to illustrate an example of cathode drop potential and reflected wave. 
         FIG. 3  illustrates a manufacturing method of a magnetic disk to which an embodiment of the present invention is applied. 
         FIG. 4  illustrates a surface processing apparatus for processing the surface of a magnetic disk. 
         FIG. 5  illustrates a state of a surface of a magnetic disk when a high-frequency voltage is applied. 
         FIG. 6  is a graph illustrating a relationship between a time integration value of a cathode drop potential Vdc and a nitriding amount. 
         FIG. 7  is a graph illustrating examples of the cathode drop potential and the reflected wave. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereafter, embodiments of the present invention will be described with reference to the drawings. 
       FIG. 3  illustrates a manufacturing method of a magnetic disk to which an embodiment of the present invention is applied. 
     The present embodiment is a manufacturing method of a magnetic disk for manufacturing magnetic disks which record information using a magnetic field, and  FIG. 3  illustrates the layer structure of the magnetic disk in each process. 
     First, a substrate  10  of a magnetic disk is prepared (step S 1  of  FIG. 3 ). As the substrate  10 , a nonmagnetic metal material and glass etc. may be applied, and an aluminum substrate is applied in the present embodiment. 
     Next, a under layer  20  is formed on the substrate  10  (step S 2  of  FIG. 3 ). As the under layer  20 , a nonmagnetic metal material etc. may be applied, and chromium is formed by sputter deposition in the present embodiment. 
     When the under layer  20  is formed, a magnetic layer  30  is laminated further thereon (step S 3  of  FIG. 3 ). The magnetic layer  30 , in the present embodiment, which provides a recording layer for recording information, is formed by sputter deposition of Co—Ni. The magnetic layer  30  corresponds to an example of the recording layer referred to in the present invention. 
     Further, a protection layer  40  is formed on the magnetic layer  30  (step S 4  of  FIG. 3 ). As the protection layer  40 , which is for protecting the magnetic layer  30  etc., carbon is laminated by a plasma CVD (Chemical Vaporing Deposition) method. Since the plasma CVD method is a layer deposition method which has been widely used heretofore, detailed description thereof will be omitted herein. The protection layer  40  corresponds to an example of the protection layer referred to in the present invention. 
     The above described series of treatments from step S 1  to step S 4  correspond to an example of the forming layers in the manufacturing method of a recording medium of the present invention. Although the magnetic disk  1 A, as it is in the present state, may read and write information at this time point, a lubricant layer  50  is further formed on the protection layer  40  of the magnetic disk  1 A in order to prevent the adherence of moisture or a foreign matter to the surface of the magnetic disk and to improve the wear resistance of the magnetic disk. In the present embodiment, before the lubricant layer  50  is formed, the protection layer  40  is subjected to a surface processing treatment to add a surface functional group  41  thereby increasing the bonding strength of the lubricant layer  50  (step S 5  of  FIG. 3 ). 
     Now, temporarily, description of  FIG. 3  will be interrupted and the surface processing treatment in step S 5  of  FIG. 3  will be described in detail. 
       FIG. 4  illustrates a surface processing apparatus for processing the surface of a magnetic disk. 
     A surface processing apparatus  100  includes a metallic chamber  110 , a gas inlet tube  130  for introducing a gas from a gas inlet port  131 , a gas outlet tube  140  for discharging a gas from a gas outlet port  141 , a metallic holder  120  that holds the magnetic disk, a high-frequency power supply  180  that applies a high-frequency voltage, a matching box  150  that adjusts the impedance of the high-frequency voltage, a CPU  160  that controls the entire surface processing apparatus  100 , an operation member  170  for inputting various instructions, and the like. The chamber  110  and the holder  120  are made up of a metal having conductivity and also serve as electrodes. 
     First, a magnetic disk  1 A, which is formed with a protection layer  40  in step S 4  of  FIG. 3 , is disposed in the chamber  110  in vacuum. This process of disposing the magnetic disk  1 A corresponds to an example of the disposing referred to in the present invention. 
     Next, a source gas which provides the raw material for plasma is introduced into the chamber  110  from the gas inlet tube  130  and part of the source gas is discharged from the gas outlet tube  140  so that the interior of the chamber  110  becomes a predetermined pressure. In the present embodiment, nitrogen gas is applied as the source gas. This process of introducing nitrogen gas corresponds to an example of the introducing gas referred to in the present invention. 
     Next, a high-frequency voltage is applied to the magnetic disk  1 A with the chamber  110  and the holder  120  as the electrodes. 
       FIG. 5  illustrates the state of the surface of the magnetic disk  1 A when a high-frequency voltage is applied. 
     The high-frequency voltage supplied from the high-frequency power supply  180  is applied to the chamber  110  and the holder  120 , which work as the electrodes, after the impedance is matched by the matching box  150 . Since, in the present embodiment, the magnetic disk  1 A held by the holder  120  is formed on its surface with a carbon-based protection layer  40  having conductivity, the high-frequency voltage applied to the holder  120  is directly conducted to the surface of the magnetic disk  1 A. As a result, the chamber  110  works as an anode and the magnetic disk  1 A works as a cathode, causing a cathode drop potential Vdc to be generated at the surface of the magnetic disk  1 A. 
     Further, as a result of the high-frequency voltage being applied to the magnetic disk  1 A, with the nitrogen gas in the chamber  110  provided as the raw material, a nitrogen plasma, in which nitrogen ions  201  and electrons  202  coexist, is generated. Further, nitrogen ions  210  are attracted by the cathode drop potential Vdc generated at the surface of the magnetic disk  1 A to collide with the protection layer  40  of the magnetic disk  1 A thereby being partly replaced with carbon ions  301  that form the protection layer  40 . 
     In this way, the carbon making up the protection layer  40  at the surface of the magnetic disk  1 A is replaced with nitrogen, and the protection layer  40  is subjected to a nitriding treatment to be added with a surface functional group  41 . When the user instructs the end of treatment using the operation member  170 , the application of high-frequency voltage from the high-frequency power supply  180  is stopped thereby terminating the nitriding treatment. This process of sputtering the surface of the magnetic disc  1 A corresponds to an example of the processing referred to in the present invention. 
     Here, the amount of the surface functional group  41  that is added through the nitriding treatment of the protection layer  40  of the magnetic disk  1 A is controlled by the amount of the source gas and the cathode drop potential Vdc, and the generation amount of cathode drop potential Vdc may be adjusted by the high-frequency voltage applied to the magnetic disk  1 A and the application time of the high-frequency voltage. However, the generated cathode drop potential Vdc is not entirely utilized for the nitriding treatment of the magnetic disk  1 A, but is partly returned as a reflected wave. Since the amount of such reflected wave will change depending on a dirt level of the chamber  101 , the impedance of the holder  120 , the contact area between the magnetic disk  1 A and the holder  120 , and the like, the surface of the magnetic disk may not be sufficiently processed even when a cathode drop potential Vdc is generated by sufficiently applying high-frequency voltage to the magnetic disk  1 A. In the present embodiment, determination of whether or not the processed state is good is made for the magnetic disk  1 B after being subjected to the nitriding treatment. 
     In the matching box  150  illustrated in  FIG. 4 , while the high-frequency voltage is applied from the high-frequency power supply  180 , a cathode drop potential Vdc being generated at the surface of the magnetic disk  1 A is measured. In the present embodiment, the cathode drop potential Vdc is calculated according to the high-frequency voltage which is applied to the magnetic disk  1 A from the high-frequency power supply  180 , and the Langmuir-Child equation. The calculated cathode drop potential Vdc is notified to the CPU  160 . 
     In the CPU  160 , the time integration value of the cathode drop potential Vdc, which is notified from the matching box  150 , is calculated. The process of measuring the cathode drop potential and calculating the time integration value of the cathode drop potential corresponds to an example of the measuring referred to in the present invention. 
       FIG. 6  is a graph to illustrate the relationship between the time integration value of the cathode drop potential Vdc and the nitriding amount at the surface of the magnetic disk  1 A. 
     The lateral axis of  FIG. 6  indicates the time integration value (Vs) of the cathode drop potential Vdc, and the longitudinal axis of  FIG. 6  indicates the nitriding amount of the surface of the magnetic disk  1 A. It is noted that in order to confirm the composition of the protection layer  40  of the magnetic disk  1 A, an electron spectroscopy spectrum is measured to obtain a peak strength at the binding energy level of carbon (C — 1s: 284 eV) and a peak strength at the binding energy level of nitrogen (N — 1s: 399 eV) in the spectrum, and the ratio of the peak levels is calculated as the nitriding amount of the magnetic disk  1 A. As illustrated in  FIG. 6 , there is a good correlation between the time integration of the cathode drop potential Vdc and the nitriding amount of the magnetic disk  1 A. 
     In the CPU  160  illustrated in  FIG. 4 , the time integration value of the cathode drop potential Vdc in the interval from when a high-frequency voltage is applied to the magnetic disk  1 A to when the application of the high-frequency voltage is stopped is calculated; and if the calculated time integration value is not less than a predetermined reference value V 0 , it is determined that the processed state of the surface of the magnetic disk  1 A is good, and if the absolute value of the time integration value is less than the reference value V 0 , it is determined that the processed state of the surface of the magnetic disk  1 A is not good. It is noted that although since the cathode drop potential Vdc has a negative value, the time integration value of the cathode drop potential Vdc also has a negative value, in the present embodiment, the determination is made based on the absolute value of the time integration value of the cathode drop potential Vdc. That is, in the CPU  160 , determination is made on whether or not the absolute value of the calculated time integration value of the cathode drop potential Vdc is not less than the absolute value of the reference value V 0  (in the present embodiment, V 0 =−34.0 Vs). This process of determining the processed state of the surface of the magnetic disk  1 A corresponds to an example of the determining referred to in the present invention. 
       FIG. 7  is a graph to illustrate an example of the cathode drop potential and the reflected wave. 
     In the four graphs in the upper side of  FIG. 7 , the lateral axis indicates time and the longitudinal axis indicates cathode drop potential, and in the four graphs in the lower side, the lateral axis indicates time and the longitudinal axis indicates reflected wave. 
     In the graph V 1  of the cathode drop potential illustrated in the left side of  FIG. 7 , it is seen that between a time t 1  when a high-frequency voltage is applied, and a time t 2  when the high-frequency voltage is stopped, a stable and sufficient cathode drop potential is generated, and in the graph R 1  of reflected wave, it is seen that the reflected wave is small. In this case, since the time integration value of the generated cathode drop potential is −39.2 Vs, and the absolute value thereof is larger than the absolute value of the reference value V 0 =−34.0 Vs, it is determined that the processed state of the surface of the magnetic disk  1 A is good. 
     In the graph V 2  of the cathode drop potential illustrated in the second from left in  FIG. 7 , it is seen that it takes some time from when a high-frequency voltage is applied to when the cathode drop potential is stabilized, and in the graph R 2  of the reflected wave, it is seen that the reflected wave is large. Since the time integration value of the generated cathode drop potential in graph V 2  is −31.2 Vs and thus the absolute value thereof is smaller than the absolute value of the reference value V 0 =−34.0 Vs, it is determined that the processed state of the surface of the magnetic disk  1 A is not good. In this case, since the reflected wave is large, it is considered that nitriding treatment has not been sufficiently performed. 
     In the graph v 3  of the cathode drop potential illustrated in the second from right in  FIG. 7 , it is seen that the time period between a time t 5  when a high-frequency voltage is applied and a time t 6  when the high-frequency voltage is stopped is small, and the generation time of the cathode drop potential is small; and in the graph R 3  of the reflected wave, it is seen that the reflected wave is small. Since the time integration value of the generated cathode drop potential in graph V 3  is −30.2 Vs and thus the absolute value thereof is smaller than the absolute value of the reference value V 0 =−34.0 Vs, it is determined that the processed state of the surface of the magnetic disk  1 A is not good. In this case, since the generation time of the cathode drop potential is too short, it is considered that the nitriding treatment has not been sufficiently performed. 
     In the graph V 4  of the cathode drop potential illustrated in the right side in  FIG. 7 , it is seen that the cathode drop potential is not stabilized; and in the graph R 4  of the reflected wave, it is seen that the reflected wave is large. Since the time integration value of the generated cathode drop potential in the graph v 4  is −23.2 Vs, and the absolute value thereof is smaller than the absolute value of the reference value V 0 =−34.0 Vs, it is determined that the processed state of the surface of the magnetic disk  1 A is not good. In this case, since the reflected wave is large and the generation time of the cathode drop potential is too small, it is considered that nitriding treatment has not been sufficiently performed. 
     In this way, according to the present embodiment, it is possible to accurately determine the processed state of the surface of the magnetic disk  1 A. 
     Now, description will be made returning to  FIG. 3 . 
     When nitriding treatment is applied to the protection layer  40  of the magnetic disk  1 A, the surface functional group  41  is formed on the surface of the magnetic disk  1 A (step S 5  of  FIG. 3 ). In the CPU  160  illustrated in  FIG. 4 , the processed state of the surface functional group  41  of the magnetic disk  1 A is determined, and only the magnetic disks  1 B which are determined that the surface functional group  41  is sufficiently formed (the processed state is good) are passed to the next lubricant application process. 
     The magnetic disk  1 B which has been passed over to the lubricant application process is applied with a lubricant on the surface functional group  41  formed on the surface of the magnetic disk  1 B and is formed with a lubricant layer  50  (step S 5  in  FIG. 3 ). In the present embodiment, a fluorine-containing organic compound is applied as the lubricant layer  50 . The process of forming the lubricant layer  50  corresponds to an example of the forming a lubricant layer referred to in the present invention. 
     Since in the magnetic disk  1 , which has been fabricated through the processes as described above, the lubricant layer  50  is strongly adhered to the protection layer  40  by the surface functional group  41 , the peeling off of the lubricant layer  50  is prevented, and it is possible to mitigate the adherence of unwanted matters to the surface of the magnetic disk  1  and the wear of the magnetic disk  1  for a long period of time. 
     So far, the description of the first embodiment of the present invention has been completed and a second embodiment of the present invention will be described. Since the second embodiment of the present invention is subjected to generally similar treatments as in the first embodiment excepting that the surface processing treatment is performed by using an oxygen plasma, only the differences from the first embodiment will be described. 
     In the manufacturing method of the magnetic disk of the present embodiment, by introducing an oxygen gas into the chamber  110  illustrated in  FIG. 4  from the gas inlet tube  130  to generate an oxygen plasma, oxidation treatment is applied to the protection layer  40  of the magnetic disk  1 A. Oxidizing a carbon-based protection layer  40  by using an oxygen plasma will result in the formation of surface functional group  41  such as ether (C—O—C), carbonyl (C═O), peroxide (C—O—OH), and the like on the surface of the protection layer  40 , making it possible to improve the adsorptivity of the lubricant layer  50  particularly made up of a fluorine-containing organic compound etc. 
     Although, so far in the above description, an example of determining the processed state of the surface of the magnetic disk by using the time integration value of cathode drop potential has been described, the determining referred to in the present invention may determine the processed state by using the time integration value of reflected wave in addition to the time integration value of cathode drop potential. 
     Further, although in the above description, an example of processing the surface of a magnetic disk has been described, the surface processing method of the present invention may be applied to the surface processing of, for example, CD-ROM, etc. 
     Furthermore, although in the above description, an example of performing sputtering treatment by using a plasma has been described, the processing referred to in the present invention may perform sputtering treatment by using a target. 
     Further, although in the above description, an example of applying a high-frequency voltage to the magnetic disk until the user give the instructions to stop the application of the high-frequency voltage has been described, the processing referred to in the present invention may apply a high-frequency voltage to the substrate for a predetermined time period.