JPH03273141A - Defect detecting method for magnetic disk magnetic film and detection optical system - Google Patents

Abstract

PURPOSE:To detect a defect in the size of the magnetic film of the coating type magnetic disk by detecting a photodetection signal which varies to above or below the reference composite signal of scattered light beams from respective magnetic particulates in a normal magnetic film. CONSTITUTION:The magnetic film 1a of the coating type magnetic disk 1 is scanned spirally with a spot Sp'. The outer shape of the spot Sp' is made elliptic so that the minor axis is at an angle DELTATHETA to the direction of an angle theta of rotation and the direction of a radius R perpendicular t the scanning is the major axis and DELTAR. The DELTAthetais the angle, but set tens of the size of magnetic particulates in terms of length and DELTAR is is further several times the as large as DELTAtheta. This elliptic spot Sp' is put in spiral scanning at intervals nearly equal to the DELTAR of the major axis. The phtodetection signal Km corresponding to scattered light from the normal magnetic film (m) is regarded as a reference level Vo and an upper threshold value VSU and a lower threshold value VSL are set above and below the reference level. Waveforms Kn, Kt, and Ku corresponding to a projection (n), a spot (t), and a foreign matter (u) are detected with the threshold value VSU and waveforms Kp and Kq corresponding to a groove (p) and a recessed surface (q) are detected with the threshold value VSL respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting defects in a magnetic film coated on a magnetic disk and a detection optical system therefor.

[Prior Art] Hard magnetic disks used as information recording media are coated type disks in which the surface of an aluminum disk is coated with epoxy resin mixed with magnetic fine particles such as iron oxide. The size of the particles and the thickness of the magnetic film have been gradually reduced from the original size to about 1 μm, and the recording density has increased. Although there are plating disks and sputtering disks that are further improved, coated disks are still mass-produced as the mainstream product due to their superior productivity and reliability.

Now, when the magnetic film of a magnetic disk has protrusions or grooves, or when foreign matter or stains are attached, the recording performance is impaired and the quality is degraded.

Therefore, a method for detecting these defects is needed. Conventionally, surface defect inspection devices have been developed for 7-recon wafers, glass plates, or aluminum disks with smooth mirror surfaces, and it is thought that this device can be applied to coating-type magnetic disks.

FIGS. 3(a) and 3(b) are explanatory diagrams outlining the basic optical system of a conventional surface defect inspection apparatus and a method of processing detected data. However, scanning of the laser spot on the surface is performed using a rotation method. In Figure (a), for example, the object 1 to be inspected is an aluminum disk that rotates, and the light projection system 2
A laser beam from a light source 2a is focused to a small diameter spot Sp by a focusing lens 2b, and the surface of the disk 1 is rotated and scanned in a spiral manner. When there is a defect on the surface, the scattered light is transmitted to the condensing lens 3 of the light receiving system 3.
The light is focused by a, and is received by the charging converter 3c through the pinhole of the pinhole plate 3b, and is output as a defect signal. There are systems that have improved the detection performance by improving the basic optical system described above, but all of them target defects on the micron order due to the small spot diameter.

Since the spot diameter described above is minute on the order of microns, if the defect is larger than this, a plurality of defect signals will be detected for the same single defect, resulting in an error in the number of defects. On the other hand, a method is used to eliminate this error through signal processing. This will be explained using Figure (b). The surface of the disk 1 is divided into unit cells Q having Δθ in the direction of the rotation angle θ and Δr in the direction of the radius r. A plurality of scanning lines run within the unit cell Q, and multiple defect signals detected for one defect are aggregated into one signal through signal processing and stored in the memory address corresponding to the unit cell Q. . The stored defect data is displayed as a map (not shown) at a position corresponding to the unit cell Q by the output display section.

[Problem to be solved] The surface defect inspection device described above has a spot diameter of the aforementioned micron order in order to detect even the smallest defects of the submicron order, but this is applied to magnetic films. In this case, magnetic fine particles -r of the magnetic film are detected and cannot be distinguished from defects. Here, defects in the magnetic film can be tolerated to a much smaller extent than in the case of magnetic fine particles, and in practical use,
It is considered a defect if it has a size of F several μm or more -L. Therefore, it is necessary to ignore the detection signal of the magnetic fine particles and distinguish the defect signal of the problematic size.

The present invention has been made in view of the above, and it is an object of the present invention to provide a method and a detection optical system for detecting defects of the above-mentioned size in a magnetic film of a coated magnetic disk.

[Means for Solving the Problems] The present invention focuses a laser beam from a light source onto a spot to scan the surface of an object to be inspected, and focuses scattered light from the spot to identify defects existing on the surface. A method for detecting defects in a magnetic disk magnetic film and a detection optical system in a surface defect inspection apparatus.

The object to be inspected in this invention is limited to a coated magnetic disk in which a magnetic film containing magnetic particles is coated on the surface of an aluminum disk.

First, in the defect detection method, the above-mentioned spot has a short axis with a length P several times as long as the diameter of the magnetic particle in the scanning direction, and a short axis in the direction perpendicular to the scanning. The magnetic film is shaped like an ellipse with a long axis several times as long as , and the interval between adjacent spots during scanning is approximately equal to the length of the long axis, so that the surface of the magnetic film is completely scanned without overlapping spots. . A composite signal of scattered light from each magnetic fine particle of a normal magnetic film obtained by scanning is used as a reference level, and defects in the magnetic film are detected from a received light signal that changes above or below the reference level.

Next, the detection optical system is composed of a light projecting system and a light receiving system.

The projection system consists of a projection lens group that collimates the projection laser beam from the light source and focuses it on an elliptical spot, and a projection lens group that reflects the projection laser beam emitted from the projection lens group in a perpendicular direction and rotates it. It consists of a plane mirror that projects a spot perpendicularly to the magnetic film surface of a magnetic disk, and the spot is scanned in a spiral manner. The light receiving system is provided close to the magnetic film, has a central hole that transmits the projected laser beam from the plane mirror, and includes a condensing lens with a hole that collects the scattered light from defects in the magnetic film, and A hole mirror has a central hole that transmits the laser beam, and reflects the scattered light that is collected by the holed condensing lens and reflected by the plane mirror in the right angle direction, and a condenser that condenses the scattered light reflected by the aperture mirror. It consists of an optical lens.

[Operation] In the defect detection method according to the present invention, the short axis is a decimal number, and the short axis is several times the short axis, compared to the outer shape of the laser spot or the size of the magnetic particles in the magnetic film of the coated magnetic disk. Since it has an elliptical shape with a long axis, a large number of magnetic particles enter the spot at the same time, and the scattered light from each particle is combined, so that individual particles are not detected. In a normal magnetic film other than the defective part, the distribution of particles is fairly uniform, so the detection signal is at a constant level corresponding to the combined scattered light, and this is taken as the reference level. Since the size of the defect to be detected is larger than that of magnetic fine particles, the scattered light is either larger or smaller, and therefore the defect signal has a peak value that changes below the above reference level and is easily detected. be done. Furthermore, the long axis of the oval shape of Japanese cedar and tortoise is very long,
Moreover, since the scanning interval is approximately equal to this, the scanning time for the entire surface is shortened in inverse proportion to the scanning interval. For example, when the conventional spot diameter is 5 μm and the long axis of the spot in this case is 200 μm, the diameter is shortened to 1/40. Furthermore, since adjacent spots are scanned without blurring or omitted scans, there is no need to detect a single defect twice as in the conventional method. It is displayed directly on the map without the need to aggregate it into a map.

Next, the defect detection optical system according to the present invention is for a rotary scanning method, in which a rotating magnetic disk to be inspected is scanned in a spiral manner with an elliptical spot focused by a light projecting system, and a light receiving system is used to scatter defects. Light is received. In the light receiving system, scattered light is efficiently focused over a wide angular range by a condensing lens with holes provided close to the magnetic film, reflected by a mirror with holes, and further condensed by a condensing lens. The light is received by the charging converter. In this case, the aperture mirror and the apertured condensing lens allow the projected laser beam to pass through and prevent it from entering the light receiving system, thereby improving the S/N ratio. Further, the plane mirror is shared by the light projecting system and the light receiving system.

[Example] FIG. 1(a) shows an elliptical spot and a scanning interval in an example in which the method for detecting defects in a magnetic disk magnetic film according to the present invention is applied to a rotation scanning type surface defect inspection apparatus. The object to be inspected is a coated magnetic disk 1, and a spot Sp is spirally scanned with respect to the magnetic film 1a. Spot S
The outer shape of p' is an ellipse, its minor axis is an angle Δe in the direction of the rotation angle θ, and its major axis is ΔR in the direction of the radius R perpendicular to the scanning direction. Δe is an angle, which is converted into a length, which is a decimal value of the size of the magnetic fine particles, and ΔR is several times larger than Δθ. For example, when the diameter of the fine particles is ~1 μm, Δe is 10-20 μm, ΔR is 100-200 μm.
Let it be m. Such an elliptical spot sp' is spirally scanned at intervals approximately equal to the major axis ΔR. The traversing scanning method is not a spiral method, but may be a concentric circle method with constant intervals or an XY method.

FIGS. 1(b) and 1(c) show various examples of defects existing in the magnetic film and the waveforms of the light reception signals corresponding to the defects. The light reception signal km in Figure (C) with respect to the light scattered by the normal magnetic film m in Figure (B) is at a substantially constant level. This is the reference level V
o, and an upper threshold vsU and a lower threshold vsL are set at appropriate positions above and below it. The waveforms kn, kt, kU for the protrusion n1 stain t1 foreign object U pair are detected by the threshold value VSU, and the waveforms kp, kq for the groove p1 concave surface q are detected by the threshold value vSL. Note that a specific detection circuit will be omitted.

FIG. 2 shows a block configuration of an embodiment of the detection optical system according to the present invention. Note that parts having the same purpose as the optical system of the surface defect inspection device shown in FIG. 3(b) are given the same numbers,
Assign a sign. A laser beam from a light source 2a is made parallel by a collimator 2C, reflected in the horizontal direction by a mirror 2d, and transformed into an elliptical beam by a cylindrical lens 2e. The elliptical beam passes through the center hole of the aperture mirror 3e, is reflected at right angles from the plane mirror 2f, and passes through 16 holes in the apertured condenser lens 3d.
A spot Sp' is projected perpendicularly to the magnetic film 1a to be inspected, and the magnetic disk l rotates in response to the spot Sp'.
Soto Sp' is scanned smoothly. When there is a defect in the magnetic film 1a, the scattered light is transmitted to the holed condensing lens 3.
Excluding the center hole of d< Jff, the light is focused on the plane mirror 2
f and the periphery of the aperture mirror 3e, respectively, to the condenser lens 3a! The light is focused from this, passes through the pinhole of the pinhole plate 3b, and is received by the charging converter 3C, as shown in FIG. 1(c).
The light reception signal illustrated in is output.

[Effects of the Invention] As is clear from the above explanation, in the optical system for detecting defects in the magnetic film of a magnetic disk according to the present invention), the outer shape of the spot is set so that the minor axis is more than ten times larger than that of the magnetic fine particles. By making a specific elliptical shape with the long axis several times the length of the short axis and scanning at intervals approximately equal to the length of the long axis, a large number of magnetic particles are simultaneously placed in this spot. The scattered lights are combined, and various defects in the magnetic film are detected by detecting a signal waveform that exceeds or differs from the level of the received light signal. In addition, inspection efficiency is improved because the scanning time for the entire surface is significantly shortened compared to a mirror defect inspection device, and defect data processing is simple. The defect detection optical system is simply configured with a hole mirror, a condensing lens with a hole, a plane mirror, etc., and can efficiently collect scattered light and detect defects reliably. There are significant effects that contribute to the inspection of magnetic films on disks.

[Brief explanation of drawings]

FIGS. 1(a), (b), and (C) show an embodiment of the method for detecting defects in a magnetic disk magnetic film according to the present invention.
Figure 2 shows an elliptical spot, its scanning method, an example of a defect existing in a magnetic film, and a waveform of the received light signal, respectively.
The figure is a configuration diagram of an optical system for detecting defects in a magnetic disk magnetic film according to the present invention, and FIGS. 3(a) and 3(b) are explanatory diagrams of the basic optical system and defect data processing method of a conventional surface defect inspection apparatus. . DESCRIPTION OF SYMBOLS 1... Object to be inspected or magnetic disk, 1a... Magnetic film, 2... Light projection system 2a... Light source,
2b...Focusing lens, 2C...Collimator,
2d... Mirror 2e... Cylindrical lens. 2f...Flat mirror 3...Light receiving system, 3a...
・Condensing lens, 3b...Pinhole plate, 3c・
...Photoelectric converter, 3d...Condensing lens with hole, 3e
... Hole mirror Sp ... Laser spot, S
p′...Oval spot.

Claims (2)

[Claims] (1) In a surface defect inspection device that scans the surface of an object to be inspected by focusing a laser beam from a light source onto a spot, and detects defects existing on the surface by focusing the scattered light of the spot, aluminum The object to be inspected is a coated magnetic disk in which a magnetic film containing magnetic fine particles is coated on the surface of the disk, and the outer shape of the spot is about 10 or more compared to the diameter of the magnetic fine particles in the scanning direction. The shape is an ellipse having a short axis twice the length and a long axis several times the short axis in the direction perpendicular to the scanning, and the interval between adjacent spots in the scanning is set to the above length. The spot is made approximately equal to the length of the axis, and the surface of the magnetic film is thoroughly scanned without overlapping, and the composite signal of the scattered light of each magnetic fine particle of the normal magnetic film obtained by the scanning is used as a reference. 1. A method for detecting defects in a magnetic film of a magnetic disk, characterized in that defects in the magnetic film are detected from a received light signal that changes upward or downward relative to a reference level. (2) In the above, a projection lens group collimates the projection laser beam from the light source and focuses it on the elliptical spot, and reflects the projection laser beam emitted from the projection lens group in a right angle direction. a light projection system, which is provided close to the magnetic film surface, and includes a flat mirror that projects a spot perpendicularly to the magnetic film surface of the rotating magnetic disk, and spirally scans the spot; a condenser lens with a hole that transmits the projected laser beam from the plane mirror and that collects the scattered light of the defects in the magnetic film; and a central hole that transmits the projected laser beam;
A hole mirror that reflects the scattered light collected by the holed condensing lens and reflected by the plane mirror in a perpendicular direction, and a condenser lens that collects the scattered light reflected by the hole mirror. An optical system for detecting defects in a magnetic film of a magnetic disk, which includes a light receiving system.