JP2007133985A - Magnetic recording/optical recording disk inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system for inspecting a magnetic disk such as a discrete medium and a pattern medium which will be produce on a commercial basis in future, which has a groove structure on the disk surface, with high resolution and in short inspection period of time. <P>SOLUTION: The inspection apparatus is composed of: a stage setting and rotating the magnetic disk; a light source of an incident light beam being a probe; a detector detecting its reflection light beam; and a controller collecting and analyzing signals from the detector. In this way, the defect or foreign matter of the groove structure is inspected by optical scatterometry technology. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic disk inspection apparatus having grooves on its surface for separating adjacent tracks or adjacent bits.

Magnetic recording devices are incorporated in personal computers, video decks, and the like, and the production volume of magnetic disks and optical disks, which are the media, tends to increase. In the production of these discs, it is an important problem how to check the flatness of the base or how to find out defects and foreign matters attached during the production process. In particular, since the recording density is increasing, that is, the tendency of the recording unit to be miniaturized is increasing year by year, a technique for recording and reproducing minute signals is necessary. The case where it brings about is considered. That is, the size of the foreign matter to be detected is also miniaturized. However, inspection of mass-produced disks is also important for throughput. In the past, for example, as described in [Patent Document 1], the inspection was performed by observing the scattering of the laser beam while rotating the disk at a high speed.
On the other hand, in order to improve the surface recording density of magnetic recording, discrete media and patterned media having a groove structure on the surface have been studied. As the recording unit becomes smaller, it becomes difficult to magnetically control the recording bit shape, and sufficient S / N cannot be obtained. In order to solve this problem, a groove between recording tracks or bits is formed by a lithography technique, and a ferromagnetic material which is a recording layer is divided or deformed, so that a boundary portion or recording bit between adjacent recording tracks is obtained. Discrete media and patterned media are expected to improve the S / N by controlling the shape of the boundary. At present, research is underway as a future technology for magnetic recording, but its method and manufacturing method have not yet been fixed. However, when mass production is taken into consideration, it is said that an imprinting method in which a pattern is transferred to a large number of disks based on a master disk that has been subjected to lithography processing to form grooves is said to be promising. In that case, the magnetic disk produced by transferring the substrate or the pattern requires inspection of the created groove pattern or foreign matter adhering to the inside of the groove during processing or transfer. As described above, inspection of foreign matters and defects will be important.

JP-A-10-143801

  The light scattering method introduced in the above prior art has a sufficient resolution in the current magnetic disk. However, when recording density is improved and discrete media and patterned media are commercialized, it is certain that the track pitch will be 200 nm or less. In addition, the size of foreign matter and defects to be detected must be reduced with the miniaturization of recording units. By the time the above technology is commercialized, even 50 nm level foreign matter has a major problem in recording and reproduction. There is no doubt that it will come. In the detection of such minute foreign matter, the current light scattering method has a limit due to the wavelength of light (several hundreds of nanometers), so that sufficient resolution cannot be obtained.

  Thus, when the inspection method using light lacks resolution, a method using an electron beam can be considered as an alternative. However, in the case of a microscope using an electron beam, the S / N is generally worse than that of the optical system, and the photographing itself takes time. For example, with the current inspection method using light, the entire inspection can be completed in about 1 minute per disc, but when using a scanning electron microscope, it takes 10 hours or more to obtain the same resolution as the light. When inspecting a large number of magnetic disks, it is essential to shorten the inspection time per piece, and an inspection method using an ordinary electron beam is also inappropriate.

  An object of the present invention is to provide a high resolution and short inspection time inspection method for a magnetic disk having a groove structure on the disk surface, such as a discrete medium or a patterned medium that will be commercialized in the future. .

  According to the present invention, as described above, it is possible to provide a method capable of inspecting a magnetic disk that will be commercialized in the future, such as a discrete medium or a patterned medium, with high resolution and in a short time by optical scatterometry. The scatterometry method requires complicated measurements that are not available in conventional magnetic disk inspection devices, such as changing the incident angle. However, as described above, using multiple light sources and optical detectors can shorten the measurement time. Means can also be provided.

  In order to achieve the above object, an inspection apparatus according to the present invention collects a stage that sets and rotates a magnetic disk, a light source of incident light as a probe, a detector that detects the reflected light, and a signal from the detector. It consists of a control device to analyze. In this state, the groove structure is inspected for defects or foreign matter by optical scatterometry. Regarding optical scatterometry, for example, Proceedings of SPIE, Vol. 4344, pages 716 to 725 (2001) (Proceedings of SPIE, Vol. 4344, pp. 716-725 (2001)) The details are described in Applied Optics Vol. 37, pages 5112 to 5115 (1998) (Applied Optics Vol. 37, pp. 5112-5115 (1998)), so only a brief description will be given here. Irradiate a structure with a one-dimensional periodic structure, and investigate the dependence of the intensity distribution of the reflected light on the incident angle, wavelength, polarization direction, and reflection order. This is a method for obtaining information such as period, cross-sectional shape and material. There are many methods in which the number of periodic structures of a certain material is assumed and the intensity distribution of reflected light is calculated from that to determine which pattern the experimental data is close to. The greatest feature of this method is that it can detect minute differences in the periodic structure below the wavelength of light, or foreign matter and defects. There is also a report that the resolution is 2 nm (Applied Optics Vol. 37, pp. 5112-5115 (1998)) (Applied Optics Vol. 37, pages 5112 to 5115 (1998)).

  The principle of this inspection method using scatterometry will be described below. First, fix the disc on the stage and rotate it. In this state, light is irradiated to the inner peripheral edge or the outer peripheral edge of the magnetic disk. Then, a detector is set at a position where the 0th-order reflected light can be detected, and the reflected light intensity is sequentially measured. The entire surface is scanned by rotating the disk and moving the irradiation light in the radial direction. At that time, the reflected light intensity of each obtained point of the disk is stored in a circumferential coordinate system. Thereafter, the same experiment is performed by changing the incident angle, the polarization direction, the position of the detector, and the like. By repeating such an experiment as many times as necessary, the reflected light intensity can be examined as a function of the incident angle and the polarization direction, and the period of the groove structure, defects, foreign matter, etc. can be examined based on the scatterometry principle. Alternatively, it is possible to end the measurement in a shorter time by entering multiple lights with different incident angles (irradiation points may or may not be the same) and installing as many detectors as necessary. it can.

  As described above, by using the magnetic disk inspection apparatus obtained by the present invention, the groove structure of a magnetic disk that will be commercialized in the future, such as a discrete medium or a patterned medium, or those groove structures are imprinted. Thus, it is possible to provide a method capable of inspecting the master in a high resolution and in a short time.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic view of an embodiment of a magnetic disk inspection apparatus according to the present invention. A magnetic disk or magnetic disk master 1 to be inspected is attached to a rotary stage 2, and one point thereof is irradiated with light 4 from a light source 3. The intensity of the 0th-order reflected light from that point is measured by the photodetector 5. When the disk set on the stage is rotated, the light irradiation point on the disk changes in the circumferential direction even when the light source 3 is fixed. After measuring one round, the light irradiation point is shifted in the disk radial direction by moving the light source in parallel or rotating. In the case of rotational movement, the angle of incidence of light changes, but it is calibrated after data collection. In this manner, the data on the entire surface of the disk is obtained by shifting the irradiation point in the radial direction for each rotation of the disk. Alternatively, the light source is gradually rotated or translated while rotating the disk, and data on the entire surface of the disk is acquired while moving the irradiation point on the disk in a spiral shape. The obtained data is stored in the storage unit 12 in the control device 6 according to, for example, circumferential coordinates (r, θ). When the data on the entire surface of the disk has been collected, the light source is translated or rotated to change the incident angle when irradiating the same point, and the same data is collected. In this way, data obtained by changing the incident angle with respect to each (r, θ) point is acquired and stored in the storage unit 12. Based on the data, the calculation unit 13 determines the groove structure at each irradiation point and the presence or absence of foreign matter by a scatterometry method. In the scatterometry method, the reflected light intensity in several types of groove patterns is calculated in advance and stored in the storage unit 12 in the control device 6. Which pattern the obtained data is close to or does not resemble any one is compared and determined by the calculation unit 13 in the control device. In this way, the presence or absence of foreign matter or the presence or absence of disturbance of the groove pattern at each point displayed by (r, θ) is determined, and the result is displayed on the display unit 11 or stored in the storage unit 12. Also, if servo information has already been written in the groove structure of the magnetic disk 1, the servo information section is irradiated with light at a certain angle as the disk is rotated, and the light detector 5 detects the reflected light therefrom. Will do. In such a case, it is necessary to divide the data mapped by the (r, θ) coordinates by a certain range of θ and separately analyze the servo information portion and the other portions.

  FIG. 2 is an enlarged schematic view of the light irradiation point on the disk in the present invention, as viewed from the direction perpendicular to the disk surface. The magnetic disk or magnetic disk master 1 has a groove structure 7 for tracking at a pitch of 400 nm or less. Usually, when a fine groove structure is optically evaluated, the resolution is limited by the wavelength. Even in a currently used apparatus for evaluation using visible light, a structure of 400 nm or more can be evaluated, but a structure of less than that cannot be evaluated sufficiently. The angle φ8 formed by the in-disk component of the incident direction vector of the light 4 and the groove direction may be, for example, 90 degrees, but may be other angles. It is only necessary to be able to calculate the reflected light intensity according to the angle and to analyze the data while referring to it. Further, during the measurement, the irradiation point may be displaced in the radial direction of the disk due to the eccentricity of the disk or the like (the horizontal direction in FIG. 2). In this case, the reflected light intensity is analyzed, or if the servo signal is written on the disk, it is read to adjust the irradiation position of the light 4, or the acquired data is shifted in the r direction for analysis. Etc.

  FIG. 3 is an enlarged schematic view of the light irradiation point on the disk in the present invention, as viewed from the direction perpendicular to the disk surface. A groove structure 7 for tracking and a groove structure 7 for forming a bit boundary portion are formed at a pitch of 400 nm or less in a master disk 1 used for manufacturing a magnetic disk or a magnetic disk. Even in this case, both the groove structures 7 can be inspected using the incident angle, polarization angle, and the like of the light 4 as parameters.

  FIG. 4 is an enlarged schematic view of a light irradiation point on the disk in the present invention, as viewed from the disk cross-section track direction. The magnetic disk or magnetic disk master 1 has a groove structure 7 for tracking at a pitch of 400 nm or less. The angle θ9 formed by the incident direction of the light 4 and the disk surface is changed, and the relationship between the plural θ and the reflected light intensity is measured. The measurement data is compared with the simulation results that have been performed in advance to inspect foreign matter and defects on the groove structure.

  FIG. 5 is a schematic view of an embodiment of a magnetic disk inspection apparatus according to the present invention. Here, the control device is omitted. After the light 4 emitted from the light source 3 enters the polarizer 10, the magnetic disk or the magnetic disk master 1 is irradiated. By providing the light 4 with linearly polarized light or circularly polarized light at an arbitrary angle, it is possible to adjust the scatterometry characteristics and realize a simple and accurate measurement system. In the case of linearly polarized light, there is a method in which a plurality of sets of data are taken by changing the polarization angle, and the groove structure and foreign matter are estimated from the dependency of the reflected light intensity on the polarization angle.

  FIG. 6 is a schematic view of an embodiment of a magnetic disk inspection apparatus according to the present invention. Here, the control device is omitted. After the light 4 emitted from the light source 3 is irradiated onto the magnetic disk or the magnetic disk master 1, the reflected light is put into the spectroscope 11 and the intensity distribution is subjected to energy analysis. Thus, by analyzing the energy of the reflected light and measuring the intensity distribution, the experimental value of the reflected light intensity and the simulation result can be compared more finely, and the presence of the groove structure and foreign matter can be accurately estimated.

  FIG. 7 is a schematic view of an embodiment of a magnetic disk inspection apparatus according to the present invention. A plurality of pairs of the light source 3 and the optical detector 5 are mounted, and measurement is performed simultaneously under different conditions of the incident angle θ and the irradiation point to the magnetic disk master 1. If the area to be measured by each pair is divided by the disk radius r, the incident angle θ of each pair may be the same. Since the inspection apparatus according to the present invention measures the reflected light intensity as a function of the incident angle of the light 4, for example, it takes time compared to a conventional method for inspecting a smooth disk with light. Therefore, if a plurality of light source 3 and light detector 5 pairs are mounted and measured simultaneously, the time can be shortened. In addition, when the same measurement time as when only one set of the light source 3 and the light detector 5 is used, data with good S / N can be acquired, and accurate inspection can be performed. Further, when measuring a plurality of pairs of light sources 3 and optical detectors 5 at different incident angles, there is an advantage that the movable range of each light source 3 and optical detector 5 can be reduced.

  FIG. 8 is a schematic view of an embodiment of a magnetic disk inspection apparatus according to the present invention. A plurality of pairs of the light source 3 and the optical detector 5 are mounted, and the incident angle θ to the magnetic disk master 1 is different and the irradiation point is simultaneously measured under the same conditions. As described in the embodiment of FIG. 7, the inspection apparatus according to the present invention takes time compared to the conventional inspection method. Therefore, if a plurality of light source 3 and light detector 5 pairs are mounted and measured simultaneously, the time can be shortened and the movable range of each light source 3 and light detector 5 can be reduced. Further, since the irradiation points are the same, a plurality of light sources 3 and a plurality of light detectors 5 can be arranged together, and there is an advantage that the apparatus configuration can be made compact.

  FIG. 9 is a schematic view of an embodiment of a magnetic disk inspection apparatus according to the present invention. A plurality of pairs of the light source 3 and the optical detector 5 are mounted, and measurement is performed simultaneously under the condition that the incident angle θ to the magnetic disk master 1 is the same and the irradiation point is different. Even if the irradiation points are different, if a plurality of light sources 3 and a plurality of photodetectors 5 are arranged together as in the present embodiment, there is an advantage that the apparatus configuration can be made compact compared to the case of FIG.

  FIG. 10 is a schematic view of an embodiment of a magnetic disk inspection apparatus according to the present invention. A plurality of optical detectors 5 are arranged for one light source 3 to detect not only the reflected light but also several orders of diffracted light, and the scatterometry method is applied.

  FIG. 11 is a schematic view of an embodiment of a magnetic disk inspection apparatus according to the present invention. For one light source 3, a plurality of photodetectors 5 are arranged, and a plurality of sets are arranged. Similar to the embodiment shown in FIG. 10, it detects not only the reflected light but also the diffracted light. However, in order to increase the amount of data to be measured, the measurement time is shorter than that of FIG. 10, or the measurement accuracy can be improved. There are advantages such as.

FIG. 12 shows an example of a data storage format in the storage unit 12 in FIG. Each data is mapped using polar coordinates (r, θ). Inspection area of the disc inner periphery r _i, and an outer peripheral r _o, is the step size of r direction [Delta] r, the step size θ direction [Delta] [theta]. Since data is acquired using a rotary stage, first, data on θ is taken in increments of Δθ while rotating the disk with respect to a certain value of r. After completing one rotation (from Δθ to 2π), the rotation stage or incident light is shifted by Δr, and θ data is again acquired in increments of Δθ. Alternatively, there is a method of gradually rotating or translating the light source while rotating the disk, and shifting the radial position of the irradiation point by Δr while the disk makes one round. In this case, data on the entire surface of the disk is acquired while moving the irradiation point on the disk in a spiral shape. It is desirable that Δr and Δθ, which are step sizes, be approximately the same as or smaller than the beam diameter of incident light. In this way, in FIG. 12, data is first acquired in the horizontal direction, and when the disc has completed one rotation, the data is acquired so that the next column is filled by moving one in the vertical direction. This makes it easy to collect data and makes it easy to perform an analysis of taking a difference or viewing an average amount. Even in the case where the groove structure is changed in a certain θ range for the servo information section or the like, such polar coordinate display is easy to distinguish. Further, if Δθ is the same between the inner periphery and the outer periphery, the step width as seen from the distance in the circumferential direction of the disk becomes rougher on the outer periphery side. Since it creates the possibility that the resolution of inspection differs between the inner and outer circumferences, there is also a method of changing Δθ between the inner and outer circumferences.

It is the schematic of the magnetic disc by the optical scatterometry method of one Example of this invention, or a magnetic disc original disc inspection system. It is the figure which looked at the relationship between the magnetic disk or magnetic disk original disc in which the circumferential-shaped or circular arc-shaped groove structure is inspected by this invention, and incident light from the disk surface perpendicular | vertical direction. FIG. 5 is a diagram showing the relationship between incident light and a magnetic disk or a magnetic disk master in which circumferential or arc-shaped grooves and radial grooves are inspected according to the present invention, as viewed from a direction perpendicular to the disk surface. is there. It is the figure which looked at the relationship between the magnetic disk or magnetic disk original disk in which the circumferential or circular-arc-shaped groove structure was inspected by this invention, and incident light from the cross-sectional direction of the disk. It is the schematic of the magnetic disc by the optical scatterometry method of the other Example of this invention, or a magnetic disc original disc inspection system. It is the schematic of the magnetic disc by the optical scatterometry method of the other Example of this invention, or a magnetic disc original disc inspection system. It is the schematic of the magnetic disc by the optical scatterometry method of the other Example of this invention, or a magnetic disc original disc inspection system. It is the schematic of the magnetic disc by the optical scatterometry method of the other Example of this invention, or a magnetic disc original disc inspection system. It is the schematic of the magnetic disc by the optical scatterometry method of the other Example of this invention, or a magnetic disc original disc inspection system. It is the schematic of the magnetic disc by the optical scatterometry method of the other Example of this invention, or a magnetic disc original disc inspection system. It is the schematic of the magnetic disc by the optical scatterometry method of the other Example of this invention, or a magnetic disc original disc inspection system. It is one Example of the data acquisition format in the magnetic disc by the optical scatterometry method of this invention or a magnetic disc original disc inspection system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Magnetic disk or magnetic disk original disk, 2 ... Rotary stage, 3 ... Light source, 4 ... Light, 5 ... Optical detector, 6 ... Control device, 7 ... Groove structure, 8 ... In-plane direction of incident vector of light 4 Angle formed by the component and the groove direction, 9 ... An angle formed by the in-disk component of the incident direction vector of the light 4 and the disk surface, 10 ... Polarizer, 11 ... Display unit, 12 ... Storage unit,
13 ... arithmetic unit, 14 ... control unit.

Claims (6)

  In an inspection apparatus for inspecting a magnetic recording disk having a groove structure on the disk surface or a master for manufacturing the magnetic recording disk, the inspection apparatus has a stage for rotating the disk, and has a different incident angle with respect to the groove structure on the disk surface. It comprises means for irradiating a plurality of lights or changing the incident angle of one light, measuring the reflected light, and measuring or / and evaluating the disk surface based on the measurement result. Inspection device.   In an inspection apparatus for inspecting a magnetic recording disk having a groove structure on the disk surface or a master disk for manufacturing the magnetic recording disk, a linearly polarized light having a stage for rotating the disk and different from the groove structure on the disk Characterized in that it comprises means for irradiating a plurality of lights having a surface and means for measuring the light reflected by irradiating the light, and means for measuring or / and evaluating the disk based on the measurement result. Inspection device to do.   In an inspection apparatus for inspecting a magnetic recording disk having a groove structure on a disk surface or a master for manufacturing the magnetic recording disk, the disk surface has a stage for rotating the disk, and the groove surface on the disk A means for irradiating light from the vertical direction; a means for measuring a plurality of orders of diffracted light from the disk surface; and a means for measuring or / and evaluating the disk surface based on the measurement result. Characteristic inspection device.   4. The magnetic recording disk inspection apparatus according to claim 1, wherein the obtained data is analyzed by mapping the obtained data to circumferential coordinates.   4. The inspection apparatus according to claim 1, wherein the inspection area is adjusted by shifting the light irradiation area according to the servo signal recorded on the disk or the reflected light intensity data being acquired. Inspection device characterized by having a function. The inspection apparatus according to any one of claims 1 to 3,
The means for measuring or / and evaluating the disk surface is a control device having at least a storage unit in which a groove structure is stored in advance and a calculation unit that compares the stored groove structure with the measurement result. Inspection equipment.

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