JP2011070729A - Device and method for inspecting substrate for magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid mixture in shipment in production of various types of products (board thickness and glass type) and to minimize costs in inspection and a degradation of efficiency of a production line. <P>SOLUTION: The inspection device is equipped with: an illuminating device 32 which illuminates from one end side of a glass substrate D, a housing cassette 30 of a structure in which the glass substrate D is contained and light penetrates from one end part to the other end part of the glass substrate; an imaging apparatus 31 which is arranged facing the illuminating device 32 across the housing cassette 30, and picks up the glass substrate D contained in the housing cassette 30 from the other end part side of the glass substrate D; and an inspection device 33 which carries out image processing of the picked-up image obtained by the imaging apparatus 31, and inspects a housing state of the glass substrate D contained in the housing cassette 30. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an inspection apparatus and an inspection method for a magnetic disk substrate used in a magnetic disk apparatus such as a hard disk drive apparatus (HDD apparatus).

  There is a magnetic disk as a magnetic recording medium mounted on a hard disk drive device (HDD device). A magnetic disk is manufactured by laminating a magnetic layer or a protective layer on a substrate, a glass substrate, or a ceramic substrate on which a NiP film is deposited on a metal plate made of an aluminum-magnesium alloy or the like. Conventionally, an aluminum alloy substrate has been widely used as a substrate for a magnetic disk. However, with recent downsizing, thinning, and high-density recording of magnetic disks, surface flatness and A glass substrate having excellent strength with a thin plate has been used.

  Such a magnetic disk substrate includes a shape processing step and a first lapping step (first grinding step); an end shape step (a coring step in which a circular hole (hole) is formed in the central portion; Chamfering step (chamfered surface forming step)) for forming a chamfered surface on the outer peripheral edge and the inner peripheral edge); end surface polishing step (outer peripheral edge and inner peripheral edge); second lapping step (second grinding step); Surface polishing process (first and second polishing processes); manufactured through processes such as a chemical strengthening process.

  By the way, since the glass substrate is easily damaged and the thickness is usually as thin as about 0.6 mm to 1.5 mm, the glass substrates are mutually connected in processing in each process of manufacturing and transporting the glass substrate after each process. It is necessary not to be damaged by contact and to prevent foreign matter from adhering. Therefore, a storage cassette that stores a plurality of glass substrates at a predetermined interval is used for transporting the glass substrates. As such a storage cassette, for example, the one disclosed in Patent Document 1 is known. FIG. 4 is a perspective view showing the storage cassette 21 disclosed in the document. The storage cassette 21 shown in the figure has a plurality of ribs (partition portions) 23 on the side wall 22 and stores the glass substrate D in a groove 24 formed by a gap between the ribs 23. The glass substrate D is inserted into the groove 24 from the opened upper side of the storage cassette 21. In this way, the glass substrate D is supported by the chamfer surface (chamfered surface) and stored in the storage cassette 21 in a standing state.

  Prior to the shipping process, the glass substrate D stored in the storage cassette 21 is inspected by visual observation to determine whether it is missing. At present, substrates having different thicknesses (for example, 635 microns and 800 microns) and glasses having different compositions are produced, but there is a problem that these are mixed in the process and shipped without being discovered. Therefore, it is inspected whether a glass substrate D having a different thickness is mixed in one storage cassette 21 and whether a glass substrate D having the same size but a different glass type is mixed.

JP 2007-261594 A

However, inspecting the missing glass substrate D by visual observation in a state where a plurality of glass substrates D are continuously arranged in the storage cassette 21 has a variation in inspection accuracy and completely eliminates an oversight. It is difficult.
In addition, there are current glass substrate thicknesses of 635 microns and 1270 microns, for example, and 635 microns and 800 microns are planned for the future. It is expected to become more difficult.
Furthermore, although there are glass substrates having the same outer diameter, inner diameter, and plate thickness but different glass types, since both are translucent glass substrates, it is difficult to distinguish them by visual inspection.

  The present invention has been made in view of the above points, and in the production of a variety of products (sheet thickness, glass type), it is possible to avoid mixing at the time of shipment, minimizing the cost in the inspection and the reduction in efficiency of the production line. An object of the present invention is to provide a magnetic disk substrate inspection apparatus and inspection method that can be suppressed.

  The present inventor has found that a product is put in a shipping case with a camera, and the captured image can be image-processed to simultaneously remove the substrate, identify the thickness, and identify the glass type. I arrived.

  The inspection apparatus for a magnetic disk substrate according to the present invention is a storage cassette having a structure in which glass substrates serving as magnetic disk substrates are stored at predetermined intervals and light is transmitted from one end of the glass substrate to the other end. Illuminating means for illuminating from one end side of the glass substrate and the illuminating means with the storage cassette interposed therebetween, and the glass substrate stored in the storage cassette is placed on the other end of the glass substrate An image pickup means for picking up an image from the section side and an inspection means for inspecting the state of the glass substrate in the storage cassette by performing image processing on the picked-up image obtained by the image pickup means.

  According to this inspection apparatus, since the captured image obtained by imaging the storage cassette in which the glass substrate is stored at a predetermined interval is image-processed to inspect the status of the glass substrate in the storage cassette, the glass substrate in the storage cassette In this situation, the board can be removed, the thickness, and the glass type can be identified without the visual observation of the inspector. In the production of various types (plate thickness, glass type), mixing at the time of shipment can be avoided. It is possible to minimize the cost of the inspection and the decrease in efficiency of the production line.

  In the inspection apparatus for a magnetic disk substrate of the present invention, the inspection means is based on a glass substrate interval from a contrast image in which a region corresponding to the glass substrate is a dark portion and a region corresponding to a gap between the glass substrates is a bright portion. The presence / absence of a substrate missing is determined by comparing the threshold value determined in this way with the width of the bright portion.

  According to this configuration, when the width of the bright portion is larger than the threshold due to the substrate missing, it can be determined that the substrate is missing.

  In the inspection apparatus for a magnetic disk substrate of the present invention, the inspection means determines the number of dark portions from a contrast image in which a region corresponding to the glass substrate is a dark portion and a region corresponding to a gap between the glass substrates is a bright portion. It is characterized in that the presence or absence of a substrate is determined by counting.

  According to this configuration, since there is a missing substrate, if the number of dark portions corresponding to the glass substrate is smaller than the original number of glass substrates, it can be determined that the substrate is missing.

  In the inspection apparatus for a magnetic disk substrate according to the present invention, the inspection means determines the thickness of the glass substrate from a contrast image in which a region corresponding to the glass substrate is a dark portion and a region corresponding to a gap between the glass substrates is a bright portion. The presence or absence of mixing of glass substrates having different plate thicknesses is determined by comparing the threshold value determined based on the above and the width of the dark part.

  According to this configuration, if glass substrates having a plate thickness larger than the original plate thickness are mixed, the width of the dark portion becomes larger than the threshold value, so that it is possible to detect mixing of the glass substrate having a large plate thickness. Further, if glass substrates having a plate thickness smaller than the original plate thickness are mixed, the width of the dark portion becomes smaller than the threshold value, so that the mixing of the glass substrate having a small plate thickness can be detected.

  In the inspection apparatus for a magnetic disk substrate of the present invention, the inspection means transmits a transmission corresponding to a glass type from a contrast image in which a region corresponding to the glass substrate is a dark portion and a region corresponding to a gap between the glass substrates is a bright portion. The presence or absence of mixing of glass substrates of different glass types is determined based on the difference in rate.

  According to this configuration, since the presence or absence of a glass substrate of a different glass type is determined from the contrast image obtained by imaging the storage cassette based on the difference in transmittance according to the glass type, it is difficult to discriminate by conventional human visual observation. It is possible to detect glass substrates of different glass types.

  In the magnetic disk substrate inspection apparatus of the present invention, it is preferable that the illumination unit generates red illumination light when the inspection unit determines whether or not glass substrates of different glass types are mixed.

  By illuminating the glass substrate with red illumination light, the contrast becomes clear according to the difference in the glass type of the glass substrate, and the determination accuracy can be improved.

  In the inspection apparatus for a magnetic disk substrate according to the present invention, the glass substrate has an annular shape and has an inner hole at the center of the substrate, and the inspection of the storage state of the glass substrate by the inspection means is performed on the glass substrate. It is preferably performed after the end surface polishing step of the outer diameter end portion and the inner diameter end portion.

  By polishing the end surfaces of the outer and inner diameter ends of the glass substrate, illumination light enters from the end surface of the glass substrate, and the contrast of the glass substrate stored in the storage cassette becomes clearer and high accuracy. The state of the glass substrate in the storage cassette can be inspected.

  The method for inspecting a magnetic disk substrate according to the present invention includes a storage cassette having a structure in which glass substrates serving as magnetic disk substrates are stored at predetermined intervals and light is transmitted from one end of the glass substrate to the other end. Illuminating from one end side of the glass substrate, capturing the glass substrate stored in the storage cassette from the other end side of the glass substrate, obtaining a captured image, And a step of performing image processing on the captured image and inspecting the storage state of the glass substrate stored in the storage cassette.

  According to the present invention, in the production of a variety of products (plate thickness, glass type), mixing at the time of shipment can be avoided, and the cost in the inspection and the decrease in efficiency of the production line can be minimized.

It is a schematic diagram of an inspection device concerning an embodiment of the invention. It is the schematic diagram which changed the camera arrangement | positioning in the inspection apparatus shown in FIG. (A) The figure which shows the picked-up image with the board | substrate omission obtained with the inspection apparatus shown in FIG. 1, (b) The figure which shows the picked-up image with plate | board thickness mistake obtained with the inspection apparatus shown in FIG. It is a perspective view of a conveyance holder. It is a figure which shows the camera specification and number of apparatuses which are calculated | required by an inspection apparatus. It is a figure which shows the plate | board thickness measurement result about two types of glass substrates whose plate | board thickness is 635 microns and 800 microns. It is a figure which shows the camera resolution required for the detection of a plate | board thickness difference. These are figures which show the plate | board thickness difference detection result of 2 types of glass substrates with plate | board thickness of 635 microns and 800 microns.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present embodiment, the case where the magnetic disk substrate is a glass substrate will be described.

  Here, as the material for the magnetic disk substrate, aluminosilicate glass, soda lime glass, borosilicate glass, aluminum-magnesium alloy, or the like can be used. In particular, aluminosilicate glass can be preferably used in that it can be chemically strengthened and can provide a magnetic disk substrate excellent in flatness of the main surface and substrate strength.

  The manufacturing process of the magnetic disk substrate includes a shape processing step and a first lapping step; an end shape step (a coring step for forming a hole, a chamfered surface at an end (outer peripheral end and / or inner peripheral end)) Chamfering step to be formed (chamfered surface forming step)); end surface polishing step (outer peripheral end and inner peripheral end); second lapping step; main surface polishing step (first and second polishing step); chemical strengthening step, etc. These steps are included.

Below, each process of the manufacturing process of the board | substrate for magnetic discs is demonstrated.
(1) Shape processing step and first lapping step First, in the shape processing step, the surface of the sheet glass is lapped (ground) to form a glass base material, and the glass base material is cut to cut out a glass disk. Various plate glasses can be used as the plate glass. This plate-like glass can be manufactured by using a known manufacturing method such as a press method, a float method, a downdraw method, a redraw method, or a fusion method using a molten glass as a material. Of these methods, if a press method is used, a sheet glass can be produced at a low cost.

  In the first lapping step, both main surfaces of the sheet glass are lapped to form a disk-shaped glass substrate. This lapping process can be performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed on both sides of the plate glass from above and below, the grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relative to each other for lapping. Do. By this lapping process, a glass substrate having a flat main surface can be obtained.

(2) End shape process (coring process for forming a hole, chamfering process for forming a chamfered surface at the end (outer peripheral end and inner peripheral end) (chamfered surface forming process))
In the coring step, for example, an inner hole is formed at the center of the glass substrate using a cylindrical diamond drill to obtain an annular glass substrate. In the chamfering step, the inner peripheral end surface and the outer peripheral end surface are ground with a diamond grindstone, and a predetermined chamfering process is performed.

(3) Second Lapping Step In the second lapping step, the second lapping process is performed on both main surfaces of the obtained glass substrate in the same manner as in the first lapping step. By performing this second lapping step, it is possible to remove in advance the fine unevenness formed on the main surface in the cutting step and end surface polishing step, which are the previous steps, and shorten the subsequent polishing step on the main surface. Will be able to be completed in time.

(4) End surface polishing step In the end surface polishing step, the outer peripheral end surface and the inner peripheral end surface of the glass substrate are mirror-polished by a brush polishing method. At this time, as the abrasive grains, for example, a slurry containing cerium oxide abrasive grains (free abrasive grains) can be used. By this end face polishing step, the end face of the glass substrate is in a mirror state that can prevent the precipitation of sodium and potassium.

(5) Main surface polishing step (first polishing step)
As the main surface polishing step, first, a first polishing step is performed. The first polishing process is a process whose main purpose is to remove scratches and distortions remaining on the main surface in the lapping process described above. In the first polishing step, the main surface is polished using a hard resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains can be used.

(6) Chemical strengthening step In the chemical strengthening step, the glass substrate that has been subjected to the lapping step and the polishing step described above is chemically strengthened. As a chemical strengthening solution used for chemical strengthening, for example, a mixed solution of potassium nitrate (60%) and sodium nitrate (40%) can be used. In the chemical strengthening, the chemical strengthening solution is heated to 300 ° C. to 400 ° C., the cleaned glass substrate is preheated to 200 ° C. to 300 ° C., and immersed in the chemical strengthening solution for 3 hours to 4 hours. In soaking, in order to chemically strengthen the entire surface of the glass substrate, the immersion is preferably performed in a state of being accommodated in a holder so that the plurality of glass substrates are held at the end surfaces.

  Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions in the surface layer of the glass substrate are respectively replaced with sodium ions and potassium ions having a relatively large ion radius in the chemical strengthening solution. Will be strengthened.

(7) Main surface polishing process (final polishing process)
Next, a second polishing process is performed as a final polishing process. The second polishing step is a step aimed at finishing the main surface into a mirror surface. In the second polishing step, both main surfaces are mirror-polished using a soft foam resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the slurry, cerium oxide abrasive grains or colloidal silica finer than the cerium oxide abrasive grains used in the first polishing step can be used.

(8) Cleaning process Since abrasives and impurities adhere to the surface of the glass substrate, cleaning is performed to remove them. Cleaning methods include physical cleaning and chemical cleaning. Physical cleaning includes scrub cleaning and ultrasonic cleaning. As the chemical cleaning, there are cleaning by etching the glass substrate, cleaning using a chemical that dissolves impurities and abrasives adhering to the glass substrate, and cleaning by controlling the potential using a surfactant. In the cleaning process between each process from the grinding process to the first polishing and the second polishing, chemical cleaning + ultrasonic cleaning is used.

(9) Defect inspection process Defect inspection includes total inspection and sampling inspection. All items that can be inspected are inspected, but those that cannot be inspected are sampled. As defect types to be inspected, there are scratches, dirt (particles), material factors, and shape changes. In a clean room, an AFM (Atomic Force Microscope) is used to check the condition of the surface of the glass substrate, measure chamfer angles of ID and OD, measure roundness, and concentricity. After the cleaning after the second polishing, the glass substrate is carried into a clean room and a visual inspection is performed. At this time, the glass substrate is inspected for cracks, adhesion of dust, chipping, cracks, abrasives, and the like. The same visual inspection is performed after cleaning after chemical strengthening. By such a defect inspection process, it is determined whether or not the specifications for forming the recording surface are satisfied for both main surfaces of the glass substrate. If the specification is satisfied, it is determined as “OK”, and if the specification is not satisfied, it is determined as “NG”. Glass substrates determined as “NG” are excluded from the final product.

(10) Substrate condition inspection step An image pickup device that satisfies the necessary resolution is used to identify the removal of the substrate in the storage cassette and the plate thickness. In order to identify the glass type, it is desirable to select an illumination color (wavelength) that is likely to cause a difference in brightness of light transmitted through the substrate. Place the storage cassettes containing the substrates one by one between the imaging device and the illumination device so that the substrates are observed from the side (in the direction from one end of the glass substrate toward the other end). As a result, it is possible to simultaneously remove the substrate, inspect the plate thickness, and identify the glass type.

Substrate status inspection process is an inspection process without sacrificing inspection accuracy and sacrificing production efficiency by providing the inspection process after the end face polishing process of the inner and outer diameter ends of the glass substrate, preferably immediately before packing in the shipping process. Costs can be minimized and the above problems can be solved.
The glass substrate determined to be “OK” on at least one side in the defect inspection process is stored in the storage cassette. However, the glass substrate is removed, the thickness of the glass substrate generated in the operation process of storing the glass substrate in the storage cassette, or Inspect for glass substrates of different glass types.

FIG. 1 is a schematic view of an inspection apparatus used in a substrate status inspection process.
The storage cassette 30 has a structure for storing a plurality of glass substrates D at a predetermined interval in the same manner as the storage cassette 21 shown in FIG. 4, and further, from one end of the glass substrate D to the other. It has a structure that allows light to pass through the end of the. In this example, the storage cassette 30 is formed of a translucent material through which at least the bottom lid 21a and the top lid 21b transmit illumination light.

  In the inspection apparatus shown in the figure, an imaging device 31 is disposed above the storage cassette 30, and an illumination device 32 is disposed below the storage cassette 30. The storage cassette 30 is arranged so that the glass substrate D stored therein is in an upright state, and the imaging device 31 captures an image from the edge side of the glass substrate D. The imaging range of the imaging device 31 is set so as to cover the entire storage cassette 30. The illumination device 32 generates illumination light that uniformly illuminates the storage cassette 30 from below. The illumination device 32 includes a power source 32a, an LED backlight 32b, and a color filter 32c that can switch illumination light to blue, white, and red.

  The imaging device 31 can be configured with, for example, a 5 million pixel CCD camera, but may be configured with two 2 million pixel CCD cameras, for example, as shown in FIG. In the case of two CCD cameras, it is preferable to set the field of view to partially overlap as shown in FIG. Since it is not necessary to use the edge of the camera visual field in image processing to be described later, high recognition accuracy can be realized over the entire storage cassette case.

  FIG. 5 shows the camera specifications and the number required for the inspection apparatus. Two types of 5 million pixels and 2 million pixels were examined. If the field of view is wide and the resolution is high, the entire measurement can be covered with one unit, but the camera price is expensive. When using a CCD camera, the use of two 2 million pixel cameras is recommended for cost effectiveness.

  The inspection apparatus 33 constructs an information processing organization that realizes a predetermined inspection function by organically cooperating hardware resources such as a CPU, ROM, and RAM and an image processing program for inspection described later. The inspection device 33 is connected to a display device 34 that can display the captured image and the inspection result. An instructor's instruction input to the inspection device 33 is performed from the input device 35. Here, an inspection function for inspecting glass substrate removal, mixing of glass substrates having different thicknesses or glass types performed in the inspection apparatus 33 will be described.

First, the processing content for detecting missing of the glass substrate by image processing will be described.
The entire length of the storage cassette 30 is illuminated substantially uniformly from below with illumination light of a predetermined wavelength (for example, white light) from the illumination device 32. The imaging device 31 images the upper surface of the storage cassette 30 and outputs image data to the inspection device 33. As schematically shown in FIG. 1, the glass substrate D stored in the storage cassette 30 stands upright from the bottom lid 21a to the upper lid 21b with a certain gap between the adjacent glass substrates D. It is arranged. Accordingly, a contrast image is formed with different amounts of transmitted light between the illumination light passing between the glass substrates D and the illumination light passing through the glass substrate D from one end to the other end.

  FIG. 3A is a schematic diagram of a top image taken from the upper lid 21b side of the storage cassette 30 by the imaging device 31. FIG. This figure shows a captured image when the glass substrate is removed from between the ribs at an arbitrary position S1 formed in the storage cassette 30. As shown in the figure, contrast is formed at the same pitch as the interval between the glass substrates D stored in the storage cassette 30. And only the pitch of the position which pulled the glass substrate becomes a different pitch from another area | region. The inspection apparatus 33 inspects by image processing whether there is a place where the pitch interval is larger than the threshold from one of the input images (contrast image having a predetermined pitch) shown in FIG. The threshold value for the pitch interval can be determined based on the interval between the glass substrates in the storage cassette 30 and the imaging magnification of the imaging device 31.

  In addition to the method of comparing the pitch interval of the contrast image with the threshold value, the number of glass substrates may be counted from the contrast image by image processing. Since the area corresponding to the glass substrate is a vertically long dark portion, the number of the vertically long dark portions is counted by image processing and compared with the planned number of glass substrate stored in the storage cassette 30. If the number of vertically long dark portions <the planned number of glass substrate storage, it can be determined that the glass substrate is missing.

Next, processing contents for detecting whether or not glass substrates having different thicknesses are mixed by image processing will be described.
As described above, since the contrast image obtained from the imaging device 31 has a vertically long dark portion in an area corresponding to the glass substrate, the width W of the vertically long dark portion is measured by image processing, so that the glass substrates having different plate thicknesses are obtained. Can be detected.

  FIG. 3B is a schematic diagram of a top image taken from the upper lid 21 b side of the storage cassette 30 by the imaging device 31. The figure shows a captured image when a glass substrate having a thicker plate width than any other glass substrate D stored in the storage cassette 30 is mixed. As shown in the figure, a vertically long dark portion having the same width as the thickness of the glass substrate D stored in the storage cassette 30 is formed. The width of the vertically long dark portion of the glass substrate D having the original plate thickness is W1, while the width of the vertically dark portion corresponding to the glass substrate having a large plate width is W2 (> W1). The inspection apparatus 33 inspects by image processing whether or not there is a dark part in which the width W of the vertically long dark part is larger than the threshold from one of the input images (contrast image in which dark parts corresponding to the plate thickness are continuous) shown in FIG. . The threshold for the width W of the vertically long dark portion can be determined based on the original plate thickness W1 of the glass substrate D stored in the storage cassette 30 and the imaging magnification of the imaging device 31. Further, the threshold value may be determined by including another plate thickness W2 that may be mixed as a reference.

  In some cases, the storage cassette 30 has a glass plate with an original plate thickness of W2 and a thin plate thickness of W1. In this case, the threshold value and the inspection algorithm are configured so that a glass substrate having a thin plate thickness W1 can be detected.

  FIG. 6 shows the measurement results of measuring the plate thickness of two types of glass substrates having a plate thickness of 635 microns and 800 microns using the system shown in FIG. A CCD camera with 5 million pixels and 2 million pixels is used as an imaging device. In the figure, the average indicates the average of the number of pixels (unit: pixels) corresponding to the thickness of the substrate obtained by 10 measurements, and δ indicates the repeated measurement error (standard deviation).

  FIG. 7 shows the camera resolution necessary for detecting the plate thickness difference. The vertical axis indicates the number of pixels corresponding to the difference in plate thickness between two types of glass substrates having a plate thickness of 635 microns and 800 microns. FIG. 8 shows the results of detecting the difference in thickness between two types of glass substrates having a thickness of 635 microns and 800 microns. A difference in thickness between two glass substrates having a thickness of 635 microns and 800 microns is detected as a difference of 3 pixels or more. Therefore, when detecting the difference in thickness between two types of glass substrates of 635 microns and 800 microns, a value from 2 pixels to 3 pixels may be set as the threshold value.

  Next, processing contents for detecting whether or not glass substrates of different glass types are mixed by image processing will be described.

  In the present invention, glass substrates of glass types having different transmittances are targeted.

  The first glass type and the second glass type have different wavelength characteristics, and by selecting the color (wavelength) of the LED backlight 32b, the difference in transmittance becomes remarkable and the detection accuracy can be improved.

  The inventor verified the transmittance of each of blue, white, and red illumination light using each of the first glass substrate and the second glass substrate that had been subjected to end surface polishing of both inner and outer diameters. When the first glass substrate and the second glass substrate are respectively illuminated with blue, white, and red LED backlights, and the substrates are observed from the side, in the case of red illumination, the first glass substrate and the second glass substrate are more than the first glass substrate. It was found that the glass substrate No. 2 was darker and the contrast with the surroundings became clear.

  Next, using a red backlight and observing a glass substrate on which either or both of the inner and outer diameters were not polished, it became darker, but there was no difference between the glass types.

  From this, it was found that both the inner and outer diameters of the glass substrate must be polished so that the illumination light can be transmitted. In addition, when a substrate with both surfaces polished was used, illumination was arranged on one side of the substrate and a CCD camera was arranged on the other side, and there was no difference in brightness due to the glass type. It has been found that it is necessary to increase the distance through which light passes (from the lower end to the upper end of the substrate) like the former.

  Therefore, when shifting to the inspection of whether or not glass substrates of different glass types are mixed, the color filter 32c of the illumination device 32 is switched from white to red illumination. A contrast image of the glass substrate illuminated by the red illumination light is captured by the imaging device 31 and output to the inspection device 33. At this time, since the illumination is performed from the lower end of the glass substrate D, the distance through which light is transmitted (from the lower end to the upper end of the substrate) is increased, and the brightness and darkness between the glass types becomes clear.

  In the inspection apparatus 33, since the brightness is different between the first glass type and the second glass type, if there is a dark glass substrate lower than a predetermined threshold value from the storage cassette 30 storing the first glass type, the second glass type. Is determined to be mixed. Conversely, if there is a glass substrate brighter than a predetermined threshold from the storage cassette 30 that stores the second glass type, it is determined that the first glass type is mixed.

  Note that the input image captured by the imaging device 31 may be displayed on the display device 34 at the same time. It is preferable to display the inspection result together with the image on the display device 34. The inspector automatically displays the inspection result obtained by image processing of the input image by the inspection device 33 on the display device 34. Therefore, the inspector performs the inspection without the visual observation by the human system or with the visual observation. Can be completed.

  In addition, when the same experiment as described above was performed with the glass substrate placed in the storage cassette 30 and packed in a transparent packaging bag, when the wrinkle of the packaging bag looks wrong on the glass substrate, the image is blurred and contrast of light and dark is added. I found it difficult. In addition, when an opaque packing bag was used, no light was transmitted. Therefore, it was found that it was necessary to inspect before packing.

  In addition, when comparing the case where the upper and lower lids of the cassette were removed and attached, it was found that the former was more sensitive to substrate removal, plate thickness measurement, and glass type identification, but the latter is also possible without error. It turns out that. However, in the former case, dust may adhere to the substrate during the inspection. The inspection proved better with the top and bottom lids.

  Further, when the above inspection was carried out immediately after the final cleaning step, the substrate could be removed intentionally, and the inspection could be performed accurately even if a plate thickness or a different glass type was mixed. However, in the subsequent final inspection, packing, and shipping process, the missing substrate was detected, but when the missing substrate was replenished or batch mixing was performed, a mixture of plate thicknesses and a mixture of different glass types occurred. From this, it was found that it was necessary to carry out an inspection immediately before shipping packaging.

  In addition, when the above inspection was performed immediately before shipment packaging, even if the board was intentionally removed, even if a plate thickness or different glass type was mixed, the inspection could be performed accurately, and the above problems would not occur during shipment. I understood.

(11) Magnetic disk manufacturing process After the above-described pre-shipment inspection process, the glass substrate stored in the storage cassette is carried into a magnetic disk manufacturing facility through a transport process. In a magnetic disk manufacturing facility, an adhesion layer made of Cr alloy, a soft magnetic layer made of FeCoCrB alloy, an underlayer made of Ru, a perpendicular magnetic recording layer made of CoCrPt-TiO2 alloy, and a protection made of hydrogenated carbon on both surfaces of a glass substrate. A perpendicular magnetic recording disk is manufactured by sequentially forming a lubricating layer composed of layers and perfluoropolyether.

  The present invention is not limited to the above embodiment, and can be implemented with appropriate modifications. The material, the number, the size, the processing procedure, and the like in the above embodiment are merely examples, and various modifications can be made within the range where the effects of the present invention are exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

21 Storage Cassette 31 Imaging Device 32 Illumination Device 32a Power Supply 32b LED Backlight 32c Color Filter 33 Inspection Device 34 Display Device 35 Input Device

Claims (8)

A storage cassette having a structure in which a glass substrate serving as a magnetic disk substrate is stored at a predetermined interval and light is transmitted from one end of the glass substrate to the other end is provided from one end of the glass substrate. Illumination means for illuminating;
An imaging means that is disposed opposite to the illumination means across the storage cassette and images the glass substrate stored in the storage cassette from the other end side of the glass substrate;
Inspection means for inspecting the state of the glass substrate in the storage cassette by performing image processing on the captured image obtained by the imaging means;
An inspection apparatus for a magnetic disk substrate, comprising:   The inspection means includes a contrast image in which a region corresponding to the glass substrate is a dark portion, and a region corresponding to a gap between the glass substrates is a bright portion, and a threshold value determined based on a glass substrate interval and the width of the bright portion. 2. The apparatus for inspecting a magnetic disk substrate according to claim 1, wherein the presence or absence of the substrate is determined by comparison.   The inspection means counts the number of the dark portions from a contrast image in which a region corresponding to the glass substrate is a dark portion and a region corresponding to a gap between the glass substrates is a bright portion, and determines whether or not the substrate is missing. 2. The magnetic disk substrate inspection apparatus according to claim 1, wherein   From the contrast image in which the area corresponding to the glass substrate is a dark part and the area corresponding to the gap between the glass substrates is a bright part, the inspection means has a threshold value determined based on the thickness of the glass substrate and the width of the dark part. 4. The magnetic disk substrate inspection apparatus according to claim 1, wherein the presence / absence of mixing of glass substrates having different plate thicknesses is determined.   From the contrast image in which the region corresponding to the glass substrate is a dark portion and the region corresponding to the gap between the glass substrates is a bright portion, the inspection means is based on a difference in transmittance according to the glass type. 5. The magnetic disk substrate inspection apparatus according to claim 1, wherein presence or absence of contamination is determined.   6. The magnetic disk substrate inspection apparatus according to claim 5, wherein the illumination unit generates red illumination light when the inspection unit determines whether or not glass substrates of different glass types are mixed. The glass substrate has a ring shape and an inner hole at the center of the substrate,
The inspection of the storage state of the glass substrate by the inspection means is performed after the end surface polishing step of the outer diameter end portion and the inner diameter end portion of the glass substrate. The inspection apparatus for a magnetic disk substrate as described. A storage cassette having a structure in which a glass substrate serving as a magnetic disk substrate is stored at a predetermined interval and light is transmitted from one end of the glass substrate to the other end is provided from one end of the glass substrate. Illuminating step;
Imaging the glass substrate stored in the storage cassette from the other end side of the glass substrate to obtain a captured image;
Inspecting the storage status of the glass substrate stored in the storage cassette by performing image processing on the captured image;
A method for inspecting a magnetic disk substrate, comprising:

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